WO2025228764A1

WO2025228764A1 - Waste incineration plant and method for operating the same

Info

Publication number: WO2025228764A1
Application number: PCT/EP2025/061143
Authority: WO
Inventors: Maurice Henri Waldner; Markus Mayrhofer
Original assignee: Kanadevia Inova AG
Current assignee: Kanadevia Inova AG
Priority date: 2024-04-29
Filing date: 2025-04-24
Publication date: 2025-11-06
Anticipated expiration: 2026-10-29

Abstract

The invention relates to a nozzle arrangement (92) forming vortex sections (100, 102, 104, 106) in a combustion gas duct of a waste incineration plant. Each region (100, 102, 104, 106) comprises on a wall side first and second nozzle (110, 120) arranged in a first and second wall portion (112, 122), and on an opposite wall side first and a second opposite nozzle (210, 220) arranged in a first and second opposite wall portion (212, 222) facing the second and first wall portion (122, 112), respectively. In a first region (106), first and second nozzle (110, 120) and first and second opposite nozzle (210, 220) have a total jet momentum in a ratio in one of the two ranges smaller than 0.5 or greater than 2.0. In the second region (104), the nozzles have a total jet momentum in a ratio in the other one of the two ranges.

Description

Waste incineration plant and method for operating the same The invention relates to a waste incineration plant for recovering energy from waste and a method for operating the same. Waste incineration plants for combusting solid fuels, such as municipal waste, substitute fuels, biomass and other materials, have long been used to recover energy from waste for example in the form of steam powering a turbine, which in turn can generate electricity. Some waste incineration plants are also able to provide direct heating for local communities. In general, these waste incineration plants are also referred to as energy-from-waste plants. Recently, larger and larger plants are being built to profit from the economy of scale for megacities and urban locations. Combustion lines usually grow in width, while the other aspect ratios remain largely unchanged. Historically, typical maximum width of the combustion line has been around 12 to 13 meters. However, larger combustion lines become more and more demanded to respond to the increasing need of recycling and energy recovery. A waste incineration plant usually comprises a combustion chamber for combusting waste, the combustion chamber comprising an inlet for introducing waste to be combusted from a bunker side into a primary combustion space; a combustion grate for combusting waste in the form of a combustion bed conveyed over the combustion grate under admission of primary gas by primary gas inlets, combustion gas being generated by combusting waste, and an outlet for discharge of the combusted waste residues such as ash from the primary combustion space. A24021WO/23.04.2025/ A peripheral wall encloses the primary combustion space and a secondary combustion space, the secondary combustion space being arranged downstream of the primary combustion space, as seen in a flow direction of combustion gas. The secondary combustion space is designed for the post combustion of combustion gas under injection of post combustion gas in the secondary combustion space. The peripheral wall further extends in the form of a duct up to a discharge of combustion gas and comprises a heat recovery boiler to recover heat from the combustion gas. The duct forms a first pass extending downstream up to a first pass discharge region, the first pass discharge region being preferably limited in the longitudinal direction by a first pass top wall. From the first pass discharge region the combustion gas flows into a second pass in fluid communication with the first pass. The first pass extends preferably downstream of the primary combustion space in a longitudinal direction up to the first pass discharge region. Heat exchange takes place in the first pass, the second pass and further downstream depending on the characteristics of the plant. There are distinct zones in the primary combustion space for the waste combustion: the main combustion zone formed in the upstream region of the waste bed where the combustion gas leaving the waste bed is fuel-rich (mostly CO, H₂O, CH₄, CO₂, N2), and a solid burn-out zone where the gas is fuel-lean (mostly O₂, N₂, some CO₂) and cooler in a downstream region of the waste bed. The combustion gas is then further oxidized (H2 -> H2O, CH4 -> CO₂, CO -> CO₂) in a post combustion step by injection of post combustion gas, for example air and/or recirculated flue gas, usually through nozzles that are arranged to create a swirl- like movement of the combustion gas. The swirl is usually ^{A24021WO/23.04.2025} designed as a double swirl with counter-rotational direction. EP1081434B2 discloses such an arrangement of nozzles to create a rotating combustion gas flow. In a rectangular duct, nozzles are positioned on two opposite facing walls defining the flow- duct in a plane. At least one wall section of the two facing walls has first nozzles in a row and form an angle between the wall and jet. Nozzles used for this purpose are heavy, sometimes up to 50 kg, and require a supporting structure for their installation which must be in addition designed to allow positioning of nozzles at an angle to the walls. Further, the arrangement of the nozzles requires engineering efforts to ensure that the fluid provided to each nozzle flows along approximately the same path length in the nozzle to experience the same pressure drop before exiting the nozzle, thereby forming post combustion gas jets of equal momentum. Additionally, if the nozzles have different angles, the boiler bending to accommodate the nozzles requires individual designs for each nozzle. There is still a need to simplify the conception of nozzle arrangements designed to create rotating combustion gas flow in a waste incineration plant. The fuel-rich combustion gas from the bunker side of the primary combustion space produces higher temperatures upon complete combustion and contains tars and fine ash particles, and as such is typically directed to the center of the chamber, while the cooler gases from the solid burn-out zone are directed towards the walls. Post-combustion of combustion gas can generate temperatures of more than 1250°C so that ash particles can melt and resolidify upon impact with cooler boiler walls. This can trigger undesired clinker formation on boiler walls. Therefore, the swirls are typically arranged in a way that the hotter combustion gas is directed to the center of the chamber, and the cooler combustion gas directed to the ^{A24021WO/23.04.2025} walls. Hot gas exhibits a lower density than cool gas. Because the boiler comprises water-cooled walls at an approximately constant temperature, the combustion gas is cooled in the boiler from the post-combustion zone in the direction to the first pass discharge region. As a result, the combustion gas in the upper part of the boiler is generally cooler and thus denser than the hotter gas below. This creates buoyancy forces. The larger the local density differences, the stronger the buoyancy forces. The wider the combustion chamber is, the larger is the temperature difference between combustion gas in the middle and on the sides due to the dependency of radiative heat exchange with the distance to the sides. This leads to large buoyancy forces in the middle of the boiler, which themselves then can trigger more instability phenomena towards the sides of the chamber. For example, the upwards flow of combustion gas can split at a certain height in the boiler and form two downwards directed and cooler flows on the sides. It is also possible that the whole upwards flow tilts to one side so that combustion gas flows upwards on a side of the chamber, and downwards on an opposed side, before exiting the first pass. This leads to a very wide temperature and residence time distribution of the combustion gas, which can render the experimental proof of compliance with environmental regulations (e.g. requirement of a residence time of 2 seconds at temperatures above 850°C) difficult if not impossible. Further, heat exchange between combustion gas and the boiler walls become suboptimal, especially when downwards directed and cooler proportions of combustion gas flow on the sides of the boiler, i.e. along the boiler walls, thereby reducing heat exchange. ^{A24021WO/23.04.2025} Experiments and numerical simulations show that such a tilted flow becomes very probable for a width of the combustion line larger than approximately 12 meters. Consequently, there is still a need to improve the conception of combustion lines in waste incineration plants to cover a market requiring wider combustion lines. Description of the invention The object of the present invention is to provide a waste incineration plant and a method for operating the same in which combustion gas flows from a primary combustion space through a duct comprising a boiler and forming a first pass, to a first pass discharge region from which combustion gas flows into a second pass in fluid communication with the first pass to a combustion gas discharge in such a way that the stability of the combustion gas flow remains stable to allow compliance with environmental regulations like residence time, and to limit backflows of combustion gas to the primary combustion space. The solution must be suitable for waste incineration plants of the present generation having combustion lines of typically up to approximately 12 meters, as well as of the new generation comprising wider combustion lines, while avoiding or reducing known difficulties like engineering load for their development. The object of the present invention is achieved by the waste incineration plant and the method for operating the same according to claims 1 and 14, respectively. Preferred embodiments are disclosed in the dependent claims. In a first aspect of the invention, a waste incineration plant for recovering energy from waste is disclosed. The waste ^{A24021WO/23.04.2025} incineration plant comprises a combustion chamber for combusting waste, said combustion chamber comprising a primary combustion space in which a combustion grate is arranged for combusting waste under admission of primary gas by primary gas inlets, combustion gas being generated by combusting waste. In a known manner, the combustion chamber comprises an inlet for introducing waste to be combusted into the primary combustion space, for example through a waste feeding chute, and an outlet for discharge of the combusted waste, e.g. ashes, from the primary combustion space, wherein the combusting waste is conveyed over the combustion grate in the form of a combustion bed. The combustion chamber forms a combustion line of the waste incineration plant. Primary gas can be air, recirculated combustion gas, oxygen, or mixture thereof. Post combustion gas can be air, recirculated combustion gas, oxygen, or mixture thereof. Sometimes humid fumes from the bottom ash extractor can also be added. The waste incineration plant further comprises a secondary combustion space arranged downstream of the primary combustion space, as seen in a flow direction of combustion gas, and designed for the post combustion of combustion gas under injection of post combustion gas in the secondary combustion space, a heat recovery boiler designed to recover heat from the combustion gas and a peripheral wall enclosing the primary combustion space, the secondary combustion space and the heat recovery boiler. The peripheral wall extends downstream in a longitudinal direction, usually corresponding to a vertical direction, in the form of a duct or a housing to channel combustion gas. The duct can form a first pass extending downstream up to a first ^{A24021WO/23.04.2025} pass discharge region from which the combustion gas flows into a second pass in fluid communication with the first pass. Further, combustion gas can flow into additional heat exchange and eventually to a combustion gas discharge, where for example it can be depolluted and released to the atmosphere. In a known manner, the peripheral wall or wall sections of the peripheral wall itself can form the heat recovery boiler for example by way of water-cooled tubes. The peripheral wall can also comprise wall sections arranged in the volume enclosed by the peripheral wall that are part of the heat recovery boiler. The peripheral wall comprises further a wall and an opposite wall facing the wall, as seen in a direction of waste transportation on the combustion grate. The wall and the opposite wall extend preferably approximately perpendicular, more preferably perpendicular, to the direction of waste transportation. The wall and the opposite wall can be dimensioned according to a width of the combustion line. Preferably, the wall and the opposite wall are parallel to each other. Preferably, a wall length and an opposite wall length are equal. The peripheral wall further comprises sidewalls, referred to also as first sidewall and second sidewall, wherein the wall and the opposite wall are connected on each side by a sidewall to form a casing delimiting the duct. The sidewalls extend usually along the direction of waste transportation. The length of the sidewalls can be dimensioned according to the flow characteristics desired in the combustion line, e.g. a flow having an average velocity of 4.5 m/s at a reference temperature of 1000°C. Preferably, the duct has the form of rectangular parallelepiped for the simplicity of construction. The wall or the opposite wall can be arranged on the side of a bunker in which waste is ^{A24021WO/23.04.2025} stored before being transported to the inlet of the combustion chamber. The peripheral wall comprises in addition a nozzle arrangement, the nozzle arrangement forming a plurality of vortex sections that are arranged in a transversal cross region of the duct. Nozzles are arranged in the plurality of vortex sections in the wall and in the opposite wall for injection of post combustion gas to generate each time a vortex. Each vortex section comprises on a wall side a first nozzle and a second nozzle arranged in a first wall portion and in an adjacent second wall portion of the wall, respectively, and on an opposite wall side a first opposite nozzle and a second opposite nozzle arranged in a first opposite wall portion and in an adjacent second opposite wall portion of the opposite wall, respectively. In other words, the first wall portion of the wall is adjacent to the second wall portion of the wall, and the first opposite wall portion of the opposite wall is adjacent to the second opposite wall portion of the opposite wall. The transversal cross region is defined as a region of the duct extending between two transversal cross sections of the duct. In other words, the transversal cross region forms a transversal slice of the duct. Typically, the maximum thickness of the transversal cross region for a nozzle arrangement is reached when, in operation, the interaction of the nozzles on the wall and on the opposite wall are insufficient to create a vortex. Concretely, the thickness of the transversal cross region can be less than 2 meters, more preferably less than 0.5 meters, more preferably less than 0.2 meters to allow for strong interaction between the nozzles. ^{A24021WO/23.04.2025} Further, the first wall portion faces the second opposite wall portion, and the first opposite wall portion faces the second wall portion. In other words, the arrangement of the wall portions, namely the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall, is such that the first wall portion and the first opposite wall portion are arranged at the opposed ends of a first branch of a diagonal cross in the form of a “X” that extends in the duct, and the second wall portion and the second opposite wall portion are arranged at the opposed ends of a second branch of the diagonal cross. In this arrangement, the first wall portion can be seen as facing diagonally the first opposite wall portion and the second wall portion can be seen as facing diagonally the second opposite wall portion. Preferably, the first wall portion faces the second opposite wall portion such that a projection transversely to the duct onto the opposite wall of the first wall portion and the second opposite wall portion overlap at least partially, preferably completely. Similarly, the first opposite wall portion faces the second wall portion such that a projection transversely to the duct onto the wall of the first opposite wall portion and the second wall portion overlap at least partially, preferably completely. In the region of the duct corresponding to an overlap of the wall portions and opposite wall portion, the interaction of the post combustion gas injected from the wall and the opposite wall is intensified thereby supporting the generation of vortices. The waste incineration plant comprises means to control post combustion gas injection through the nozzles. According to the invention, in a first vortex section and in a second vortex section adjacent to the first vortex section ^{A24021WO/23.04.2025} of the plurality of vortex sections, the first nozzle, the second nozzle, the first opposite nozzle and the second opposite nozzle are arranged each time in a vertical longitudinal plane at an azimuth angle of approximately 90°, preferably 90°, with respect to the wall and the opposite wall, respectively. In other words, a longitudinal axis of a nozzle remains in the vertical longitudinal plane with an azimuth angle of 90° as measured from the wall and the opposite wall, respectively, while its longitudinal axis can be oriented at different elevation angles with respect to the horizontal direction. The orientation of the nozzles are defined by the orientation of their longitudinal axis corresponding substantially to their direction of injection of post combustion gas. The feature approximately 90° must be understood in the present context as an angle of 90°, wherein small variation from this angle within the limits of manufacturing and/or assembly can be possible. Typically, such limits can be +/- 5°. Preferably, the azimuth angle lies therefore between 85° and 95° to keep the injection of post combustion gas as much as possible parallel to each other, thereby supporting an efficient creation of vortices. Jet momentum is defined as the product of post combustion gas mass flow and post combustion gas velocity at a certain time and position. In an embodiment in which there is one nozzle in a wall portion or opposite wall portion, the total jet momentum is the jet momentum of the one nozzle. In an embodiment in which a plurality of nozzles are present in a wall portion or opposite wall portion, the total jet momentum is the sum of the jet momentum of the plurality of nozzles in the wall portion or opposite wall portion, respectively. ^{A24021WO/23.04.2025} Further, in the first vortex section the first nozzle and the second nozzle on the wall side and the first opposite nozzle and the second opposite nozzle on the opposite wall side are configured to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. In other words, in the first vortex section, the total jet momentum ratio of the first nozzle to the second nozzle and the total jet momentum ratio of the first opposite nozzle to the second opposite nozzle are both in one of the two ranges “smaller than 0.5” or “greater than 2.0”. In the second vortex section the first nozzle and the second nozzle on the wall side and the first opposite nozzle and the second opposite nozzle on the opposite wall side are configured to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are extending in the longitudinal direction and rotating in opposed directions. In other words, in the second vortex section, the total jet momentum ratio of the first nozzle to the second nozzle and the total jet momentum ratio of the first opposite nozzle to the second opposite nozzle are both in the other one of the two ranges. The means to control the post combustion gas injection through the nozzles ensures that the total jet momentum is controlled within the ratio ranges defined. As a matter of example, the ratio can be “smaller than 0.5” in the first vortex section and “greater than 2.0” in the second vortex section. Two or more nozzles, here as matter of illustration the first nozzle and the second nozzle, configured to have their total jet momentum in a ratio lying in a given range, e.g. between ^{A24021WO/23.04.2025} 2.0 to 2.5, have mechanical characteristics like shape of the longitudinal cross-section and of the transversal cross- section, diameter of throat, volume of the chamber upstream of throat, that allow their operation in the given total momentum range ratio, here of 2.0 to 2.5. These mechanical characteristics and how they can be implemented to allow an operation in the range defined are well known and clear to the skilled person and are not specified individually to avoid limiting unduly the scope of the claims. Therefore, the term “configured” applied to a first and a second nozzle must be understood as defining a design and dimensioning of the nozzles that allows a given total jet momentum ratio range, for example more than 2.0. Means to control post combustion gas injection through the nozzles allows to control the first and second nozzle to deliver a specific value of total jet momentum ratio, for example 2.1, in the range for which they have been configured. Depending on the actual waste load and waste properties that is incinerated, the mechanical characteristics of the first nozzle and of the second nozzle allow a mode of operation including parameters like fluid pressure, temperature or composition that can be chosen to ensure an optimized waste combustion, for example a ratio of 2.1 in the range of 2.0 to 2.5. To make an analogy, an engine configured to work in a range of 20 hp to 50 hp as a result of its mechanical characteristics, for example the number of cylinders, the size of the combustion chamber, the size of the gas injection nozzle that are clear to the skilled person. The mode of operation in the range of 20 hp to 50 hp, i.e. the injected quantity of fuel in the engine to deliver for example 35 hp, is chosen based on the actual power of the engine required for the activity of interest. ^{A24021WO/23.04.2025} The difference between the two ranges, namely “smaller than 0.5” and “greater than 2.0”, is the arbitrary definition of what is defined as first nozzle and second nozzles in a vortex section in the nozzle arrangement. Which nozzle is defined as first nozzle and second nozzle as well as the corresponding first wall portion and second wall portion in a vortex section is determined consistently in the same manner for each vortex section of the plurality of vortex sections in the nozzle arrangement. This applies also for the first opposite nozzle and second opposite nozzle as well as the corresponding first opposite wall portion and second opposite wall portion in the same vortex section. In other words, if in a vortex section, starting from the first wall portion, one moves in the clockwise direction to the second wall portion, then to first opposite wall portion and finally to the second opposite wall portion, then the same definition of wall portions applies to all vortex sections in the nozzle arrangement. The ratio is then defined consistently for the plurality of vortex sections as first nozzle over second nozzle and first opposite nozzle over second opposite nozzle, respectively. The arrangement at an azimuth angle of approximately 90° of the second nozzle and the second opposite nozzle, i.e. at the same angle as the first nozzle and the first opposite nozzle, has the advantage that all nozzles are at the same azimuth angle with respect to the wall and the opposite wall. In contrary to arrangements known in the prior art in which a set of nozzles are at an azimuth angle different to 90° to the walls to create a vortex, the present arrangement of the nozzles is such that the fluid provided to each nozzle flows along approximately the same path length, thereby experiencing the same pressure drop before exiting the nozzle. Consequently, there is a reduced engineering effort to ensure that post combustion gas is injected with the required momentum. Further, ^{A24021WO/23.04.2025} manufacturing a supporting structure of the nozzles during the erection phase can be simplified because the nozzles can be positioned at the same azimuth angle with respect to the wall and the opposite wall. In addition, the design of the nozzles is simplified because it is not necessary to have different designs for different angles so that identical nozzles can be used. In contrary to prior art in which the nozzles are arranged at an azimuth angle different to 90° with respect to the wall or the opposite wall, the vortex is created in each vortex section by way of the total jet momentum ratio of the post combustion gas injected from each wall portion. Further downstream, the vortex continues developing in the longitudinal direction and can extend as a combustion gas vortex up to the first pass discharge region. Simulations have shown that, in a vortex section, the nozzle or, if applicable, the nozzles present in each of the two wall portions of the wall, i.e. the first wall portion and the second wall portion, must be configured such that the ratio of the total jet momentum is smaller than 0.5 or greater than 2.0 to ensure a well-developed vortex. The same applies to the nozzle or, if applicable, the nozzles present in each of the two opposite wall portions of the opposite wall, i.e. the first opposite wall portion and the second opposite wall portion, to create a vortex in the vortex section. The stability of the combustion gas flow is further increased when the vortex present in the first vortex section and in the second vortex section rotate in opposed directions. In this manner, the vortices counterbalance each other so that they remain stable, in contrary to adjacent vortices rotating in the same direction that tend to merge and destabilize the ^{A24021WO/23.04.2025} combustion gas flow. For this purpose, the ratios of the total jet momentum in the first vortex section and in the second vortex section must lie in ranges opposed to each other, namely smaller than 0.5 or greater than 2.0. The embodiment according to the invention just described can be implemented in the present generation of combustion lines of typically up to approximately 12 meters. In this case, the creation of vortices is possible without nozzles arranged at an azimuth angle different to 90° to the wall and opposite wall in contrast to the prior art EP1081434B2. For wider combustion lines, the same arrangement can be used, wherein the number of vortices can be increased to take into account a larger width of the combustion line. In a preferred embodiment, the two ranges are defined by the range between 0.05 and 0.4 and the range between 2.5 and 20.0. Such ranges increase the difference of total jet momentum between the two wall portions on the side of the wall and of the opposite wall. The effect is an increased shear of the combustion gas flow in the transversal cross region that is beneficial to the creation and the stability of the vortex in the vortex section. In a further preferred embodiment, the two ranges are defined by the range between 0.1 and 0.3 and the range between 3.3 and 10.0. These ranges show optimized vortex parameters in numerical simulations. In a preferred embodiment, in the first vortex section the total jet momentum is in a same first ratio on the wall side and on the opposite wall side, and in the second vortex section the total jet momentum is in a same second ratio on the wall side and on the opposite wall side. As a result, the vortex is created in an approximatively centered region of the vortex section. The symmetry of the arrangement is beneficial for the ^{A24021WO/23.04.2025} creation of the vortex that has approximately an elliptical or circular shape improving the stability of the combustion gas flow downstream in the duct. In a more preferred embodiment, the first ratio and the second ratio are the same to create similar vortices in the duct, thereby improving further the homogeneity of the combustion gas flow. In a preferred embodiment, the nozzle arrangement in the first vortex section and in the second vortex section is configured in a mirror symmetrical manner with respect to a longitudinal plane of symmetry extending perpendicular to the wall and the opposite wall between the two first and second vortex sections. This configuration forms a particularly simple embodiment to create a vortex in each of the plurality of vortex sections extending in the longitudinal direction and rotating in opposed directions. As a result, the total jet momentum ratio on the side of the wall is inversed between the two adjacent vortex sections when it is compared for the side of the wall and the same applies also for the side of the opposite wall. In a preferred embodiment, the plurality of vortex sections comprises multiple pairs of vortex sections comprising one first and one second vortex section. Preferably, all subsequent pairs of vortex sections of the plurality of vortex sections are configured in the same manner as the first and second vortex sections. In this manner, the vortices counterbalance each other pair by pair so that they have a better stability. However, in other embodiments the plurality of vortex sections can comprise an odd number of vortex sections, for example three vortex sections. Simulations have shown that in such embodiments, vertices can also be created. However, the central vortex section may be responsible for instability of the adjacent vortex sections as it tends to merge with either one or the other adjacent vortex sections so that a more precise ^{A24021WO/23.04.2025} adjustment of the post combustion gas injection is required. Furthermore, multiple pairs of vortex sections allow to create vortices over broader ducts, thereby ensuring an efficient combustion gas flow. Preferably, all subsequent pairs of vortex sections are arranged adjacent to each other in the transversal cross region. In a preferred embodiment, in the first and second vortex sections, the first wall portion and the second wall portion are directly adjacent and the first opposite wall portion and the second opposite wall portion are directly adjacent. In this manner, the first and second vortex sections are more compact and the stability of the vortex is improved. In a preferred embodiment, the plurality of vortex sections are arranged such that there is a vortex section directly adjacent to each sidewall. In case large buoyancy forces are present in the middle of the duct forming the heat recovery boiler, the presence of a vortex in the vicinity of the sidewalls can counterbalance the instability of the combustion gas flow created by the buoyancy forces towards the sidewalls of the duct. For example, it can be avoided that the upwards flow of combustion gas splits at a certain height in the heat recovery boiler and form two downwards directed and cooler flows on the sidewalls, which is detrimental to an optimized heat exchange with the walls, in particular with the sidewalls. The plurality of vortex sections can also comprise only one pair of vortex sections, in which case the first vortex section is adjacent to the first sidewall and the second vortex section is adjacent to the second sidewall. In a preferred embodiment, in the first and in the second vortex section, preferably in the plurality of vortex sections, the ratio of the hydraulic diameter of the first nozzle to the ^{A24021WO/23.04.2025} hydraulic diameter of the second nozzle and the ratio of the hydraulic diameter of the first opposite nozzle to the hydraulic diameter of the second opposite nozzle are both in one of the two ranges defined by smaller than 0.7 or greater than 1.4. Numerical experiments have shown that the ratio defined efficiently support the creation of a vortex and enhances the effects obtained by the ratio of total jet momentum disclosed previously when they are combined. Like in the calculation of ratios for the total jet momentum above, the difference between the two ranges, namely “smaller than 0.7” and “greater than 1.4”, is the arbitrary definition of what is defined as first and second nozzles and first and second opposite nozzles in the arrangement. Once defined for one vortex section, the definition is applied in the same manner for each vortex section, as already discussed. In a preferred embodiment, the ranges of hydraulic diameter are defined by smaller than 0.6 or greater than 1.6. More preferably the ranges of hydraulic diameter are defined by between 0.3 to 0.5 or between 2.0 to 3.4, to allow the application of stronger shear forces to the combustion gas flow, thereby improving the stability of the vortices. In a preferred embodiment, in the first vortex section and in the second vortex section, preferably in the plurality of vortex sections, the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall portion comprise a plurality of first nozzles, of second nozzles, of first opposite nozzles and of second opposite nozzles. The plurality of nozzles are distributed over the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall portion, respectively. They form a broader area from which post ^{A24021WO/23.04.2025} combustion gas is injected thereby improving the stability of the vertices in the vortex section. The plurality of first nozzles, second nozzles, first opposite nozzles and second opposite nozzles are arranged each time in a vertical longitudinal plane at an azimuth angle of approximately 90°, preferably 90°, with respect to the wall and the opposite wall, respectively. Further, in the first vortex section, on the wall side, the plurality of first nozzles and the plurality of second nozzles and, on the opposite wall side, the plurality of first opposite nozzles and the plurality of second opposite nozzles are configured to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. In the second vortex section, on the wall side, the first nozzle and the second nozzle and, on the opposite wall side, the first opposite nozzle and the second opposite nozzle are configured to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are extending in the longitudinal direction and rotating in opposed directions. Preferably, in the first vortex section and in second vortex section, preferably in the plurality of vortex sections, the number of nozzles in each plurality of nozzles is the same to simplify the control of the total jet momentum ratio. More preferably, in the first vortex section and in second vortex section, preferably in the plurality of vortex sections, in a plurality of nozzles, the nozzles are the same, in particular the nozzles have the same hydraulic diameter, to further simplify the control of the total jet momentum ratio. In a preferred embodiment, in the first and second vortex section, preferably in the plurality of vortex sections, the first nozzle and the first opposite nozzle have a same first ^{A24021WO/23.04.2025} hydraulic diameter, and the second nozzle and the second opposite nozzle have a same second hydraulic diameter. The arrangement has the advantage of a simple conception requiring a reduced engineering work and simplifies the control of the effect of the nozzles on the vortex. In addition, the effect is a symmetric shear of the combustion gas flow that is beneficial to the creation and the stability of the vortex in the vortex section. In a preferred embodiment, in the first and in the second vortex section, preferably in the plurality of vortex sections, the ratio of the hydraulic diameter of the plurality of first nozzles to the hydraulic diameter of the plurality of second nozzles and the ratio of the hydraulic diameter of the plurality of first opposite nozzles to the hydraulic diameter of the plurality of second opposite nozzles are both in one of the two ranges defined by smaller than 0.7 or greater than 1.4. Nozzles having non-circular channel cross section can be used in the nozzle arrangement disclosed. For this reason, it is referred to the hydraulic diameter of the nozzles which is usually defined as four times the open area divided by the wetted perimeter. In a preferred embodiment, the plurality of vortex sections extend over at least 80% of the transversal cross region, preferably 100% of the transversal cross region, as measured transversely to the duct. thereby ensuring that combustion air is mixed appropriately for an efficient post combustion and avoiding backflows in regions free of vortices. In a preferred embodiment, as measured transversely to the duct, the cumulated length of the first wall portion and of the second wall portion of the plurality of vortex sections ^{A24021WO/23.04.2025} equals the wall length, and the cumulated length of the first opposite wall portion and of the second opposite wall portion of the plurality of vortex sections equals the opposite wall length, to form a plurality of vortex sections covering the whole cross section of the peripheral wall. In this arrangement, the plurality of vortex sections extend over 100%, i.e. the whole cross section of the peripheral wall, thereby ensuring that the combustion gas flow is supported by vortices formed over the whole cross section of the peripheral wall. Preferably, the plurality of vortex sections have the same size, as seen transversely to the duct, to form combustion gas flows having substantially the same size that can be maintained in equilibrium with each other in the duct. In a more preferred embodiment, the first and second nozzles as well as the first and second opposite nozzles are arranged in a plane in the first vortex section and in the second vortex section, preferably in the plurality of vortex sections. In a preferred embodiment, the nozzles are distributed uniformly and equally spaced apart in their respective wall portions to further simplify the control of the total jet momentum ratio. Preferably, the first wall portion and the second opposite wall portion, and the second wall portion and the first opposite wall portion have the same size. Facing wall portions between which a vortex is created having the same size improves the stability of the vortex. However, without departing from the basic principle of this arrangement, the distribution of some of the nozzles can slightly deviate from the uniform distribution to arrange the nozzles for example between two boiler pipes extending along and within the peripheral wall. In this case, the opening of ^{A24021WO/23.04.2025} the nozzle can be slightly shifted from its position corresponding to a uniform distribution. It is also conceivable that the nozzles are distributed above and below a plane extending in the transversal cross region. For example, the nozzles can be arranged alternatively below and above the plane, wherein the openings of successive nozzles are connected by an imaginary line zigzagging along the intersection of the wall and the plane. In a preferred embodiment, the transversal cross region is a transversal cross section of the duct. The transversal cross section is formed by a transversal plane extending transversely across the duct. As a result, the arrangement of the nozzles is simplified, so that the engineering work and implementation costs of such this simple embodiment are advantageously reduced. In addition, the arrangement allows a simplified control of the vortices. Preferably, the first wall portion and the second opposite wall portion have the same length, and the second wall portion and the first opposite wall portion have the same length. More preferably the wall portions have all the same length to further increase the centrally symmetrical injection of post combustion gas. The nozzles or the plurality of nozzles can be connected in a known manner by one or more supplying wall pipes in a grouped manner, for example by vortex sections or by wall and opposite wall, or in an individual manner, wherein means to control post combustion gas injection through the nozzles is provided. It is also conceivable that the nozzles have all the same hydraulic diameter and have each means to control the post combustion gas flow rate supplied, to obtain ratios of total ^{A24021WO/23.04.2025} jet momentum of the post combustion gas injected in the range disclosed above. The means to control the post combustion gas injection or the gas flow rate can be connected to a controller system delivering orders depending for example on the waste load and waste properties being incinerated. In a preferred embodiment, the transversal cross region of the duct intersects the wall and the opposite wall each time as a horizontal line. In a preferred embodiment, the transversal cross region is oriented downwards in the same direction as combustion grate forming an angle between 0° and 20° with a horizontal plane intersecting the peripheral wall. Advantageously, this symmetrical arrangement that can be implemented with a correspondingly simplified supporting structure of the nozzles to improve the creation of vortices. The transversal cross region can be inclined in the direction to the combustion grate by 5° to 20°, preferably 10°, depending on the orientation of the combustion grate. The transversal cross region can be parallel to the direction of injection of the nozzles in some embodiments. However, in other embodiments, the transversal cross region and the direction of injection are not parallel, as will be discussed further below. In a preferred embodiment, in the first vortex section and in the second vortex section, preferably in the plurality of vortex sections, the projection of the first wall portion onto the opposite wall and the second opposite wall portion overlap and have the same size, and the projection of the first opposite wall portion onto the wall and the second wall portion overlap and have the same size. In this arrangement, it can be ensured that the post combustion gas injected in the wall portion and opposite wall portion facing each other interact ^{A24021WO/23.04.2025} to create a vortex in the vortex section. Preferably, the wall portions and the opposite wall portions have the same size to have symmetrical shear forces creating the vortex in the vortex section. In a preferred embodiment, in the first vortex section and in the second vortex section, preferably in the plurality of vortex sections, the projection of the first wall portion onto the opposite wall and the first opposite wall portion are free from overlapping, and a projection of the second wall portion onto the opposite wall transversely to the duct and the second opposite wall portion are free from overlapping. In this arrangement, it can be avoided that post combustion gas injected in a wall portion facing diagonally an opposite wall portion interacts and creates turbulences that are detrimental to the creation of a vortex in the overlapping zone. The energetical efficiency of the post combustion gas injection is thereby improved. In a preferred embodiment, the plurality of vortex sections comprises at least two pairs of first and second vortex sections, wherein vortex sections adjacent to the sidewalls connecting the wall and the opposite wall have a width of 1.0 to 1.4 times a vortex section average width, preferably 1.0 to 1.3 times, more preferably 1.0 to 1.26 and vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.6 to 1.0 times the vortex section average width, preferably 0.7 to 1.0 times, more preferably 0.74 to 1.0 times, the vortex section average width being defined as the length of the wall measured transversely to the duct divided by the number of vortex sections of the plurality of vortex sections. The larger width of the two vortex sections that are adjacent to the sidewalls plays an important role to counterbalance the instability of the combustion gas flow ^{A24021WO/23.04.2025} created by the buoyancy forces towards the sidewalls of the duct. In other words, one vortex may be more of a circular shape, while another one is more of an elliptical shape. It can be avoided that the upwards flow of combustion gas splits at a certain height in the heat recovery boiler and form two downwards directed and cooler flows on the sidewalls. In a more preferred embodiment, the vortex sections adjacent to the sidewalls have the same length, and the vortex sections arranged between the vortex sections adjacent to the sidewalls have the same length. This arrangement can be implemented more easily due to a reduced number of parameters to control, in particular the width of the vortex sections. It is also conceivable that all vortex sections have the same width. In this case, the control of the vortex sections is simplified, while the risk of a split of combustion gas can still be reduced advantageously. An auxiliary burner can also be arranged in the secondary combustion space to provide the required heat load for the start-up or, where applicable, to fulfill regulatory requirements. Preferably, the transversal cross region is arranged upstream of the auxiliary burner. In a preferred embodiment, the plurality of vortex sections are distributed over a first border region, a second border region and an inner region arranged between the first and second border region. Nozzles arranged in the first border region and in the second border region form a first group of nozzles and a second group of nozzles, respectively. The nozzles of the first group are oriented at a first elevation angle of -25° to +30° with respect to a horizontal plane and the nozzles of the second group are oriented at a second elevation angle of -25° to +30° with respect to the horizontal ^{A24021WO/23.04.2025} plane. Further, the first and the second border region extend each over up to 0.40 times, preferably 0.35 times, preferably 0.30 times, the cumulated width of the plurality of vortex sections, as measured transversely to the duct. Numerical simulations have shown that the arrangement reduces the risk of backflows and ensures a high mixing quality of the combustion gas and post combustion gas, while vortices are created efficiently in the vortex sections at the same time. The first border region and the second border region can each extend over more than one vortex section, when the plurality of vortex sections comprise more than two vortex sections. Concretely, if four vortex sections having the same width of 0.25 times the length of the wall are present, in the case of a first border region and a second border region having a width of 0.40 times the wall length, the first border region and the second border region will each overlap one vortex section completely and partially an adjacent vortex section. The first group of nozzles is formed by the first nozzles, the second nozzles, the opposite first nozzles and the opposite second nozzles that are present in the first border region. The second group of nozzles is formed identically, mutatis mutandis. The first border region and the second border region can be limited by the first sidewall and the second sidewall, respectively. In a preferred embodiment, the first elevation angle and the second elevation angle are in range of -20° to +20°, more preferably -18° to +18°, also preferably 0° to 20°, or5° to 15° to further reduce the risk of combustion gas backflow, as investigated by numerical simulation. In some embodiments, the first elevation angle and the second elevation angle can be in ^{A24021WO/23.04.2025} the ranges disclosed above and outside of the range of -3° to +3°, thereby leading also to reduced risks of backflow as investigated by numerical simulation. In a preferred embodiment, the first elevation angle and the second elevation angle are the same. The arrangement takes advantage of the symmetry of the vortices created to improve the stability of the combustion gas flow. In a more preferred embodiment, nozzles arranged in the inner region form an inner group of nozzles that are oriented at an inner elevation angle of -25° to 15° with respect to the horizontal plane. The arrangement has a positive effect on the mixing quality of the combustion gas and post combustion gas and effectively counterbalancing buoyancy of the inner, hotter gases. In a preferred embodiment, the inner elevation angle ranges from -20° to 14°, more preferably from -18° to 12°, also preferably from -15° to 5°, or from -6° to 0° to further improve the mixing quality of the combustion gas, as shown in numerical experiments. In some embodiments, the inner elevation angle can be in the ranges disclosed above and outside of the range of -3° to +3°, thereby leading also to reduced risks of backflow as investigated by numerical simulation. In an even more preferred embodiment, a difference in angle measured between the orientation of the nozzles of the first group or of the second group and the orientation of the nozzles of the inner group is between 0° and 40°, preferably between 0° to 35°, more preferably between 0° to 20°. The relative angular arrangement of the nozzles of the first and second group, i.e. the nozzles arranged in the border regions, and of the nozzles of the inner group, i.e. the nozzles arranged between the border regions, reduces the risk of backflows and ^{A24021WO/23.04.2025} ensures a high mixing quality of the combustion gas and post combustion gas, as mentioned above. In a preferred embodiment, a combination of parameters is that the vortex sections adjacent to the sidewalls connecting the wall and the opposite wall have a width of 1.0 to 1.4 times and the vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.6 to 1.0 times a vortex section average width, the first and the second border region extend each over up to 0.40 times the cumulated width of the plurality of vortex sections, the nozzles of the first group are oriented at a first elevation angle of -25° to +30°, the nozzles of the second group are oriented at a second elevation angle of -25° to +30°, the nozzles of the inner group of nozzles are oriented at an inner elevation angle of -25° to 15°, wherein the difference in angle is between 0° to 40°. In a preferred embodiment, a combination of parameters is that the vortex sections adjacent to the sidewalls connecting the wall and the opposite wall have a width of 1.0 to 1.3 times and the vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.7 to 1.0 times a vortex section average width, the first and the second border region extend each over up to 0.35 times the cumulated width of the plurality of vortex sections, the nozzles of the first group are oriented at a first elevation angle of -20° to +20°, the nozzles of the second group are oriented at a second elevation angle of -20° to +20°, the nozzles of the inner group of nozzles are oriented at an inner elevation angle of -20° to 14°, wherein the difference in angle is between 0° to 35°. In a preferred embodiment, a combination of parameters is that the vortex sections adjacent to the sidewalls connecting the wall and the opposite wall have a width of 1.00 to 1.26 times ^{A24021WO/23.04.2025} and the vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.74 to 1.0 times a vortex section average width, the first and the second border region extend each over up to 0.30 times the cumulated width of the plurality of vortex sections, the nozzles of the first group are oriented at a first elevation angle of -18° to +18°, the nozzles of the second group are oriented at a second elevation angle of -18° to +18°, the nozzles of the inner group of nozzles are oriented at an inner elevation angle of -18° to 12°, wherein the difference in angle is between 0° to 20°. In a preferred embodiment, a combination of parameters is that the vortex sections adjacent to the sidewalls connecting the wall and the opposite wall have a width of 1.00 to 1.24 times and the vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.7 to 1.0 times a vortex section average width, the first and the second border region extend each over up to 0.27 times the cumulated width of the plurality of vortex sections, the nozzles of the first group are oriented at a first elevation angle of -17° to +16°, the nozzles of the second group are oriented at a second elevation angle of -17° to +16°, the nozzles of the inner group of nozzles are oriented at an inner elevation angle of -17° to 10°, wherein the difference in angle is between 0° to 18°. Also for these combinations, the first elevation angle, the second elevation angle and the inner elevation angle can be in the ranges disclosed and outside of the range of -3° to +3° for the same reasons as discussed above. Numerical simulations have shown that these combinations of parameters provide optimized solutions to reduce the risk of backflows and ensures a high mixing quality of the combustion ^{A24021WO/23.04.2025} gas and post combustion gas, while vortices are created efficiently in the vortex sections at the same time. In a preferred embodiment, at least one further nozzle arrangement arranged in a further transversal cross region of the duct downstream of the transversal cross region is provided. Preferably, the at least one further nozzle arrangement and the nozzle arrangement are arranged in the secondary combustion space. The presence of at least one further nozzle arrangement improves the mixing behavior. The at least one further nozzle arrangement can have the same configuration as any of the embodiments disclosed above for the nozzle arrangement. In particular, it is possible that corresponding features of the nozzle arrangement and of the at least further nozzle arrangement are configured in the same manner. In other embodiments, however, corresponding features of the nozzle arrangement and of the at least further nozzle arrangement can differ as disclosed in not limiting preferred embodiments described below. In a preferred embodiment, the at least one further nozzle arrangement is limited to one further nozzle arrangement. The embodiment comprising one nozzle arrangement and one further nozzle arrangement is an economical embodiment that has proven to be effective in most simulation tests. In a more preferred embodiment, two consecutive nozzle arrangements are configured such that each vortex in one of the two consecutive nozzle arrangements rotate in a direction of rotation opposed to the corresponding vortex of the other nozzle arrangement. In each vortex section, the presence of at least two vortices rotating in opposed direction in successive transversal cross regions improves mixing of the combustion gas. ^{A24021WO/23.04.2025} In this embodiment, in the first vortex section of the one of the two consecutive nozzle arrangements, the first nozzle and the second nozzle on the wall side and the first opposite nozzle and the second opposite nozzle on the opposite wall side are configured to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. In the first vortex section of the other one of the two consecutive nozzle arrangements, the first nozzle and the second nozzle on the wall side and the first opposite nozzle and the second opposite nozzle on the opposite wall side are configured to have a respective total jet momentum in a ratio lying both in the other one of the two ranges. As a result, this creates vortices in the two consecutive first vortex sections that are extending in the longitudinal direction and rotating in opposed directions. In a preferred embodiment, the nozzle arrangement and the at least one further nozzle arrangement are configured such that the total jet momentum is different for corresponding wall portions. By corresponding wall portions, it is meant wall portions of the same wall following each other directly as seen in the flow direction or, in other words, following each other in the flow direction. In a preferred embodiment, the nozzle arrangement and the at least one further nozzle arrangement are configured such that in the nozzle arrangement, the nozzles of the first group, the nozzles of the second group and the nozzles of the inner group of nozzles are oriented at a first elevation angle, a second elevation angle and an inner elevation angle, respectively, have a same first value on the side of the wall and a same second value on the side of the opposite wall, namely in a range of -20° to +14°, preferably -18° to +12°, more preferably -17° to +10°. The same first value and the same second value ^{A24021WO/23.04.2025} can be equal. The least one further nozzle arrangement can be provided according to any one of the embodiments disclosed, preferably according to one of the combination of parameters disclosed above. An optimized mixing of gas is provided at the level of the nozzle arrangement and the provision of the at least one further nozzle arrangement ensure a limited risk of backflows. A mass flow distribution of the post combustion gas injected resulting in the transversal cross region on the side of the wall and the opposite wall can be defined as a normalized ratio between the mass flow at a position along the wall or the opposite wall and the average mass flow over the wall or the opposite wall, respectively. A wave-shaped injection gas mass flow distribution can be created by way of the nozzle arrangement described above. A similar wave-shaped mass flow distribution can be created in the further transversal cross region by way of the further nozzle arrangement, wherein the mass flow distribution can be the same or different. The same mass flow distribution corresponds to an embodiment in which maxima and minima of mass flow in the transversal cross region correspond to maxima and minima of mass flow in the further transversal cross region, respectively. A different mass flow can be an embodiment in which maxima and minima of mass flow in the transversal cross region correspond to minima and maxima of mass flow in the further transversal cross region, respectively. In the embodiment described above in which each vortex in the transversal cross region rotates in a direction of rotation opposed to the corresponding downstream vortex of the further transversal cross region, an injection mass flow maximum in the transversal cross region corresponds to a mass flow minimum in the further transversal cross region. ^{A24021WO/23.04.2025} In a preferred embodiment, the duct forms the first pass extending downstream up to the first pass discharge region from which the combustion gas flows into the second pass in fluid communication with the first pass. Further, the duct comprises at least one separation wall extending longitudinally in a plane perpendicular to the wall and the opposite wall and dividing the duct into at least two channels into which combustion gas flows to the first pass discharge region. Further, a first vortex section and a second vortex section lie on each side of the at least one separation wall. Preferably the same number of first vortex and second vortex sections lie on each side of the at least one separation wall to simplify the control of the vortex sections. The provision of the at least one separation wall allows the conception of combustion lines in which the duct has an even larger cross section, wherein the cross sections of the at least two channels can be dimensioned by an appropriate number of separation walls such that the combustion gas flow can be optimized. In particular, in each channel, an arrangement according to one of the embodiments described previously can be present. The at least one separation wall comprises a lower end facing the primary combustion space and an upper end facing the first pass discharge region. In a preferred embodiment, the at least one separation wall extends from the lower end arranged in the secondary combustion space to the upper end arranged in the first pass discharge region. In this manner, the cross section of the first pass is split over its full longitudinal extension, thereby reducing the risk of instability of the combustion gas flow in the respective channels of the first pass. The at least one separation wall can be fixed in the duct in a known manner, e.g. it can be fixed longitudinally to ^{A24021WO/23.04.2025} the peripheral wall or hung to a superstructure in the first pass discharge region. To facilitate water flow inside the tubes of the separation wall, an edge of the lower end can be advantageously arranged at an oblique angle of more than 90° with regard to the longitudinal direction of the first pass. The first pass discharge region comprises an opening connecting the first pass and the second pass, wherein the opening can extend longitudinally up to the first pass top wall. Preferably, the separation wall extends up to the first pass top wall to simplify the erection. Preferably, the at least one separation wall extends in such a way that the channels are at least approximately free from a fluidic communication between each other over the length of the first pass. This arrangement limits the interaction between the combustion gas flow in the channels. At least approximately free is to be understood such that limited passages between the at least one separation wall and the peripheral wall can be present to account for different dilatations of the peripheral wall and the at least one separation wall, thereby reducing mechanical constraints. In a preferred embodiment, the lower end of the separation wall is arranged downstream of the transversal cross region to limit high-speed vortices touching the separation wall. It has also been shown that buoyancy or a tilted flow can be prevented particularly reliably in this case. The separation wall can start 0 to 5 meters, preferably 1.5 to 3 meters, downstream the transversal cross region. Preferably, the lower end is arranged downstream of the auxiliary burner or at an equal height. More preferably, the ^{A24021WO/23.04.2025} lower end is arranged downstream of the transversal cross region and of the auxiliary burner. Preferably, the separation wall comprises water-cooled tubes to exchange heat with the combustion gas and improve the efficiency of the plant. In a preferred embodiment, the length of the wall and of the opposite wall is more than 12 meters, preferably between 13 meters and 21 meters, thereby allowing the construction of waste incineration plant generating increased economy of scale. In a further aspect of the invention, a method for optimizing the flow of combustion gas in a waste incineration plant for recovering energy from waste according to any of the previously disclosed embodiments is disclosed. The method comprises the steps of combusting waste in the combustion chamber, said combustion chamber comprising the primary combustion space in which the combustion grate is arranged for combusting waste under admission of primary gas by primary gas inlets, combustion gas being generated by combusting waste. In a known manner, the combustion chamber comprises the inlet for introducing waste and the outlet for discharge of the combusted waste from the primary combustion space. Waste to be combusted is introduced into the primary combustion space through the inlet and combusted under admission of primary gas by primary gas inlets, wherein the combusting waste is conveyed over the combustion grate in the form of a combustion bed and combusted waste is discharged through the outlet. Further, combustion gases produced by waste combustion are post combusted in the secondary combustion space arranged ^{A24021WO/23.04.2025} downstream of the primary combustion space, as seen in a flow direction of the combustion gas, under injection of post combustion gas in the secondary combustion space. In a further step, the post combustion gas injection through the nozzles is controlled by means to control the post combustion gas injection. According to the invention, the method comprises further a step in which, in the first vortex section, on the wall side, the first nozzle and the second nozzle and, on the opposite wall side, the first opposite nozzle and the second opposite nozzle are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. Further, in the second vortex section, on the wall side, the first nozzle and the second nozzle and, on the opposite wall side, the first opposite nozzle and the second opposite nozzle are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are extending in the longitudinal direction and rotating in opposed directions. Depending on the actual load and properties of waste that is incinerated, the first nozzle and the second nozzle as well as the first opposite nozzle and the opposite second nozzle are controlled to inject post combustion gas having a total jet momentum at a specified ratio lying in the total jet momentum ratio ranges resulting from the configuration, i.e. the mechanical characteristics of said nozzles. For example, a mode of operation including parameters like fluid pressure, temperature or composition that can be chosen to ensure an ^{A24021WO/23.04.2025} optimized waste combustion, for example a ratio of 2.1 in the range of 2.0 to 2.5. The advantages of the method have been discussed in relation to the corresponding features of the waste incineration plant. In a preferred embodiment, injecting post combustion gas is controlled in a manner to have the two ranges of total jet momentum defined by the range between 0.05 and 0.4 and the range between 2.5 and 20.0. In a further preferred embodiment, the two ranges are defined by the range between 0.1 and 0.3 and the range between 3.3 and 10.0. In a preferred embodiment, injecting post combustion gas is controlled in a manner to have, in the first vortex section, the total jet momentum in a same first ratio on the wall side and on the opposite wall side, and in the second vortex section, the total jet momentum in a same second ratio on the wall side and on the opposite wall side. In a more preferred embodiment, the first ratio and the second ratio are the same to create similar vortices in the duct, thereby improving further the homogeneity of the combustion gas flow. In a preferred embodiment, in the first vortex section and in the second vortex section, no post combustion gas is injected either in the first nozzle and in the first opposite nozzle or in the second nozzle and in the first second nozzle. In the former configuration, the ratio of total jet momentum equals zero in this arrangement which is a ratio smaller than 0.5 or in the latter configuration the ratio of total jet momentum can be seen as infinite, which is greater than 2.0. This embodiment at the limit of the conditions set provides a simple configuration still allowing the creation of vortices. Shear forces can be created and applied to the combustion gas flow by way of the group of nozzles injecting post combustion gas. ^{A24021WO/23.04.2025} In the preferred embodiment in which, in the first vortex section and in the second vortex section, preferably in the plurality of vortex sections, the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall portion comprise a plurality of first nozzles, of second nozzles, of first opposite nozzles and of second opposite nozzles that are distributed over the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall portion, respectively, the pluralities of nozzles are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying in the ranges as defined above for the corresponding nozzles. Description of the figures Further advantages and features of the invention are described by way of illustrative embodiments, which are explained with reference to the accompanying figures. In these figures, which are purely schematic: Fig. 1 shows a section of a first embodiment of a waste incineration plant for recovering energy from waste according to the invention that is represented in longitudinal cross section; Fig. 2 shows a perspective and transparent view of the region marked as II in fig. 1 in which a nozzle arrangement is illustrated; Fig. 3 shows a longitudinal cross section of the waste incineration plant of fig. 1 along the line III-III; ^{A24021WO/23.04.2025} Fig. 4 shows a longitudinal cross section of the waste incineration plant of fig. 1 in the plane IV-IV represented in fig. 2; Fig. 5 shows a longitudinal cross section of the waste incineration plant of fig. 1 in the plane V-V represented in fig. 2; Fig. 6 shows a mass flow distribution of post combustion gas in the plane VI of fig. 2; Fig. 7 shows a perspective and transparent view of a region similar to the region marked as II in fig. 1 for a second embodiment in which a further nozzle arrangement is present in addition to the nozzle arrangement; Fig. 8 shows a longitudinal cross section of the second embodiment along a line similar to the line III-III in fig. 1; Fig. 9 shows a longitudinal cross section of the second embodiment in the plane IX-IX represented in fig. 7; Fig. 10 shows a longitudinal cross section of the second embodiment in the plane X-X represented in fig. 7; and Fig. 11 shows the region represented in Fig. 7, wherein different total jet momentum are represented. A section of a waste incineration plant for recovering energy from waste is illustrated in fig. 1, which section covers essentially waste combustion and first steps of the combustion gas flow generated by waste combustion. Aspects related for example to waste storage and waste feeding upstream of the section and further aspects related to the combustion gas flow downstream of the section disclosed, for example for further ^{A24021WO/23.04.2025} heat exchange in economizers or discharge, are not represented and discussed. The waste incineration plant comprises a combustion chamber 10 for combusting waste, said combustion chamber comprising an inlet 20 for introducing waste to be combusted into a primary combustion space 30, and a combustion grate 40 for combusting waste in the form of a combustion bed 42 conveyed over the combustion grate under admission of primary gas by primary gas inlets 44, combustion gas 46 being generated by combusting waste, and an outlet 48 for discharge of the combusted waste from the primary combustion space 30. The combustion chamber 10 forms a combustion line of the waste incineration plant. The waste incineration plant further comprises a peripheral wall 50 enclosing the primary combustion space 30 and a secondary combustion space 60, the secondary combustion space being arranged downstream of the primary combustion space 30, as seen in a flow direction 62 of combustion gas. The secondary combustion space 60 is designed for the post combustion of combustion gas under injection of post combustion gas in the secondary combustion space. Post combustion gas can be air, recirculated combustion gas, oxygen, or mixture thereof. Primary gas can be air, recirculated combustion gas, oxygen, or mixture thereof. The peripheral wall 50 extends downstream in a longitudinal direction 52 corresponding to a vertical direction, in the form of a duct 70 or a housing in which combustion gas flows. The duct 70 comprises a first pass 72 extending downstream in a longitudinal direction up to a first pass discharge region 74 from which the combustion gas flows into a second pass 76 in fluid communication with the first pass 72 to a discharge region of combustion gas. The first pass discharge region is ^{A24021WO/23.04.2025} limited in the longitudinal direction by a first pass top wall 77. The first pass discharge region comprises an opening 78 connecting the first pass and the second pass. In the embodiment of fig. 1, the opening 78 extends longitudinally up to the first pass top wall 77. The combustion gas flows into the second pass for further heat exchange and further to a combustion gas discharge, which is not part of the section of the waste incineration plant represented in fig. 1, where for example it can be for example depolluted. The peripheral wall 50 also comprises a heat recovery boiler 79 to recover heat from the combustion gas. For this purpose, the peripheral wall can include water-cooled tubes. The peripheral wall 50 comprises further a wall 80 and an opposite wall 82 facing the wall 80, as seen in a direction 89 of waste transportation on the combustion grate. The wall 80 and the opposite wall 82 have a wall length and an opposite wall length, respectively. The wall and the opposite wall are parallel to each other as seen in a transversal cross region 84 of the duct 70. In the embodiment represented for fig. 1, the transversal cross region is a transversal cross section 84 of the duct formed by a transversal plane extending transversely across the duct. The embodiment has been chosen to allow an easier representation. However, as disclosed above the transversal cross region could also be in the form of a transversal slice of the duct, in which case the nozzles would be distributed over wall portions in the form of areas of the wall and of the opposite wall. Presently, the nozzles are distributed over wall portions essentially in the form of lines extending on the wall and on the opposite wall. The peripheral wall further comprises sidewalls, referred to as first sidewall 86 and second sidewall 88, wherein the wall ^{A24021WO/23.04.2025} and the opposite wall are connected at their end on each side by a sidewall to form a casing having a rectangular transversal cross section. In the present embodiment, the wall is arranged on the side of a bunker 90 in which waste is stored before being transported to the inlet 20 of the combustion chamber and the opposite wall is arranged on the other side facing away from the bunker. The peripheral wall comprises in addition a nozzle arrangement 92 comprising a plurality of vortex sections that are arranged in the transversal cross region 84. Nozzles are arranged in the plurality of vortex sections in the wall and in the opposite wall for injection of post combustion gas to generate each time a vortex in the transversal cross region. In the embodiment corresponding to fig. 1, the plurality of vortex sections comprises four vortex sections 100, 102, 104 and 106, corresponding to two pairs of vortex sections comprising one first vortex section and one second vortex section. One pair comprises first and adjacent second vortex section 106 and 104, respectively, and the other pair comprises first and adjacent second vortex section 102 and 100, respectively. The four vortex sections have the same width. Further, the transversal cross region 84 intersects the wall and the opposite wall each time along a horizontal line. The transversal cross region is oriented downwards in the same direction as the combustion grate forming an angle γ1 of 15° with a horizontal plane intersecting the wall 80. The angle γ1 is measured in the clockwise direction, i.e. in the direction to the combustion grate. Each vortex section comprises wall portions arranged such that a first wall portion 112 of the wall is adjacent to a second wall portion 122 of the wall, and a first opposite wall portion ^{A24021WO/23.04.2025} 212 of the opposite wall is adjacent to a second opposite wall portion 222 of the opposite wall. For the sake of clarity, the wall portions have been identified only in the vortex sections referenced as 106 and 104 in fig. 2. Further, the nozzles are represented schematically in fig. 2, fig. 7 and fig. 11 by their position identified each time by an arrow which length is proportional to the jet momentum of the post combustion gas injected. In fig. 3 and fig. 8, the nozzles are represented by their openings through which the post combustion gas is injected. As illustrated in fig. 2 and fig. 3, each vortex section comprises a plurality of first nozzles 110 having three nozzles, arranged in the first wall portion 112, and a plurality of second nozzles 120 having four nozzles, arranged in a second wall portion 122, for injection of post combustion gas each time in a direction of injection. Further, each vortex section comprises a plurality of first opposite nozzles 210 having three nozzles, arranged in the first opposite wall portion 212, and a plurality of second opposite nozzles 220 having four nozzles, arranged in a second opposite wall portion 222, for injection of post combustion gas each time in a direction of injection. In this embodiment, the plurality of first nozzles, of second nozzles, of first opposite nozzles and of second opposite nozzles are distributed uniformly and equally spaced apart over the first wall portion, the second wall portion, the first opposite wall portion and the second opposite wall portion, respectively. In the embodiment of fig. 1 as illustrated also in fig. 2 and fig. 3, in each vortex sections, the plurality of first nozzles 110 and the plurality of first opposite nozzles comprise the ^{A24021WO/23.04.2025} same number of nozzles. Similarly, the plurality of second nozzles 120 and the plurality of second opposite nozzles 220 comprise the same number of nozzles. In each vortex section, the first wall portion 112 faces the second opposite wall portion 222. A projection of the first wall portion 112 onto the opposite wall 82 in the transversal cross region 84 in the direction of injection of the first nozzle 110 overlap at least partially the second opposite wall portion 222. Further, the first opposite wall portion 212 faces the second wall portion 122. A projection of the first opposite wall portion 212 onto the wall 80 in the transversal cross region in the direction of injection of the first opposite nozzle 210 overlap at least partially the second wall portion 122. In other words, the first wall portion 112 and the first opposite wall portion 212 are arranged at the opposed ends of a first branch of a diagonal cross in the form of a “X” and the second wall portion 122 and the second opposite wall portion 222 are arranged at the opposed ends of a second branch of the diagonal cross as seen in the transversal cross region 84. In the arrangement of wall portions, the first wall portion 112 faces diagonally the first opposite wall portion 212 and the second wall portion 122 faces diagonally the second opposite wall portion 222. The first nozzle, the second nozzle, the first opposite nozzle and the second opposite nozzle are arranged each in a vertical longitudinal plane at an azimuth angle of approximately 90° with respect to the wall 80 and the opposite wall 82, respectively. Further, the waste incineration plant comprises means 230 to control post combustion gas injection through the nozzles. ^{A24021WO/23.04.2025} An auxiliary burner 232 is arranged in the secondary combustion space 60 to provide the required heat load for the start-up or, where applicable, to fulfill regulatory requirements. The transversal cross region 84 is arranged upstream of the auxiliary burner. Further, considering the pair of first and second vortex section 106 and 104, respectively, in the first vortex section 106 the first nozzles 110 and the second nozzles 120 on the wall side 80 and the first opposite nozzles 210 and the second opposite nozzles 220 on the opposite wall side 84 are configured to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. In the second vortex section 104 the first nozzles 110’ and the second nozzles 120’ on the wall side 80 and the first opposite nozzles 210’ and the second opposite nozzles 220’ on the opposite wall side 84 are configured to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section 106, 104 that are rotating in opposed directions extending downstream in the longitudinal direction. In the other pair of first and second vortex section 102 and 100, respectively, the first nozzle and the second nozzle as well as the first opposite nozzle and the second opposite nozzle are configured in the same manner as in the pair of first and second vortex section 106 and 104. In contrary to arrangements known in the prior art in which a set of nozzles are at an azimuth angle different to 90° to the walls, as it is disclosed e.g. in EP1081434B2, to create a vortex, the present arrangement of the nozzles is such that the fluid provided to each nozzle flows along approximately ^{A24021WO/23.04.2025} the same path length, thereby experiencing the same pressure drop before exiting the nozzle. Consequently, there is a reduced engineering effort to ensure that post combustion gas is injected with the required jet momentum. Further, a supporting structure of the nozzles in the peripheral wall can be simplified because the nozzles can be positioned at the same azimuth angle with respect to the wall and the opposite wall. Having arranged the nozzles at an azimuth angle of approximately 90°, the vortex is created in each vortex section by way of the total jet momentum of the post combustion gas injected from each wall portion. Further downstream the vortex continues developing and extends as a combustion gas vortex up to the first pass discharge region 74. The total jet momentum of the post combustion gas injected from a wall portion is defined as the sum of the jet momentum of the nozzles present in the wall portion. In an embodiment in which the nozzle in the wall portion is limited to one nozzle, the total jet momentum is the jet momentum of the one nozzle. In an embodiment in which the nozzle is embodied as a plurality of nozzles in the wall portion, the total jet momentum is the sum of the jet momentum of the plurality of nozzles. An exemplary calculation of the ratio of total jet momentum is given below in relation to fig. 2 for the first vortex section 106. On the side of the wall 80, assuming that each of the three first nozzles 110 of the first wall portion 112 is configured to have a jet momentum J1 and each of the four second nozzles 120 of the second wall portion 122 is configured to have a jet momentum J2, the total jet momentum is 3 x J1 and 4 x J2, ^{A24021WO/23.04.2025} respectively. For example, J1 is taken equal as 3 x J2. The ratio R of the total jet momentum can be calculated as R = (3 x J1) / (4 x J2) = 9/4 = 2.25 for a ratio calculated as “first wall portion 112 over second wall portion 122”, which is in the range “greater than 2.0”. For the inverse definition of first and second nozzles, a similar calculation would have given R = (4 x J2) / (3 x J1) = 4/9, which is smaller than 0.5. The difference between the two conditions “smaller than 0.5” and “greater than 2.0” is only the arbitrary definition of what is defined as first nozzles and second nozzles in the nozzle arrangement. On the side of the opposite wall 82 of the same first vortex section 106, assuming that each of the three first opposite nozzles 210 of the first opposite wall portion 212 is configured to have a jet momentum J1opp and each of the four second opposite nozzles 220 of the second opposite wall portion 222 is configured to have a jet momentum J2opp, the total jet momentum is 3 x J1opp and 4 x J2opp, respectively. For example, if J1_opp is also taken equal as 3 x J2_opp, the ratio R is again 9/4 like on the side of the wall and in the range “greater than 2.0”. It is also possible to configure the nozzles on the side of the opposite wall 82 such that a different ratio in the range “greater than 2.0” is obtained on the side of the opposite wall. For example, if J1_opp is taken equal as 4 x J2_opp, the ratio is R = 3, which is also in the range “greater than 2.0”. If one sticks to the initial definition in fig. 2 of first nozzles 110 and second nozzles 120 in the first vortex section 106 leading to the ratio R = 9/4 above, starting from the first wall portion 112, one moves in the clockwise direction to the ^{A24021WO/23.04.2025} second wall portion 122, then to first opposite wall portion 212 and finally to the second opposite wall portion 222. Having a ratio in the range “greater than 2.0” for the first vortex section 106, the nozzles must be configured in the second vortex section 104 such that the ratio is in the other range, i.e. “smaller than 0.5” according to the condition defined. Which nozzles are defined as first nozzles and second nozzles as well as the corresponding first wall portion and second wall portion in a vortex section is determined consistently in the same manner for each vortex section. Therefore, in the adjacent second vortex section 104, in the same manner, starting from the first wall portion 112’ one moves in the clockwise direction to the second wall portion 122’, then to first opposite wall portion 212’ and finally to the second opposite wall portion 222’. On the side of the wall 80, in the second vortex section 104, if each of the three first nozzles of the first wall portion 112’ is configured to have a jet momentum J1’ and each of the three second nozzles of the second wall portion 122’ is configured to have a jet momentum J2’, the total jet momentum is 3 x J1’ and 3 x J2’, respectively. The nozzles must be configured such that the ratio is in the range “smaller than 0.5”, which is the case for example, if J1’ is equal to 1/3 J2’. The ratio R of the total jet momentum can be calculated as R = (3 x J1’) / (3 x J2’) = 0.3. For the sake of simplicity, on the side of the opposite wall 82, the nozzles are configured to give the same ratio R = 0.3 in the range “smaller than 0.5”. For this purpose, each of the three first nozzles of the first wall portion 112’ are configured to have a jet momentum J1’ and each of the three second nozzles of the second wall portion 122’ are configured to have a jet momentum J2’. The total jet ^{A24021WO/23.04.2025} momentum is then 3 x J1’ and 3 x J2’, respectively. J1’ is again chosen to be equal to 1/3 J2’. Further, the plurality of vortex sections are arranged such that there is a vortex section, in the embodiment of fig. 2 vortex sections 106 and 100, directly adjacent to each sidewall, namely to the second sidewall 88 and to the first sidewall 86, respectively. In addition, in each vortex sections of the nozzle arrangement 92, the ratio of the hydraulic diameter of a first nozzle to the hydraulic diameter of a second nozzle is taken in the range smaller than 0.7. On the opposite wall, the ratio of the hydraulic diameter of a first opposite nozzle to the hydraulic diameter of a second opposite nozzle is therefore in the same range of smaller than 0.7. In the embodiment of fig. 1, in the first vortex section 106, the first nozzles 110 and the second nozzles 120 present in the first wall portion 112 and the second wall portion 122 are connected in series by a wall pipe 260. Further, the first opposite nozzles 210 and the second opposite nozzles 220 present in the first opposite wall portion 212 and the second opposite wall portion 222 are connected in series by an opposite wall pipe 262. Each vortex section can be supplied in the same way by a wall pipe and an opposite wall pipe, which have not been represented for each region for the sake of clarity. The duct 70 comprises at least one separation wall 270 extending longitudinally in a plane perpendicular to the wall 80 and the opposite wall 82 and dividing the duct into at least two channels 272 and 274 into which combustion gas flows up to the first pass discharge region 74. In Fig. 2 only a lower portion of the separation wall is represented in dotted lines ^{A24021WO/23.04.2025} and in Fig 3 a longitudinal cross section of the wall is represented. Further, the same number of vortex sections, in this embodiment two vortex sections, lies on each side of the at least one separation wall 270. Referring to fig. 1 and 3, the at least one separation wall 270 comprises a lower end 280 facing the primary combustion space 30 and an upper end 282 facing the first pass discharge region 74. The at least one separation wall extends from the lower end 280 arranged in the secondary combustion space 60 downstream of the burner 232 and downstream of the transversal cross region 84, up to the upper end 282 arranged in the first pass discharge region 74. The at least one separation wall 270 extends up to the first pass top wall 77. The arrangement divides the cross section of the first pass over its longitudinal extension, thereby reducing the risk of instability of the combustion gas flow in the at least two channels of the first pass. Further, the extension of at least one separation wall up to the first pass top wall avoids the creation of turbulences in the first pass discharge region caused by mixing of combustion gas coming from the at least two channels. Advantageously, the at least one separation wall can comprise water-cooled tubes to exchange heat with the combustion gas. In fig. 3, the lateral extension of the vortex sections 100, 102, 104, 106 is schematically indicated by a dotted curve to which it is referred by the corresponding reference number of the vortex section. The plurality of vortex sections are distributed in the transversal cross region 84 over a first border region 290 adjacent to the first sidewall 86 and a second border region 292 adjacent to the second sidewall 88. Further, the plurality of vortex sections are distributed in the transversal cross ^{A24021WO/23.04.2025} region over an inner region 320 extending between the first border region 290 and the second border region 292. Nozzles arranged in the first border region 290 forming a first group of nozzles are oriented at a first elevation angle of +10° with respect to a horizontal plane. Further nozzles arranged in the second border region 292 on the side of the wall 80 forming a second group of nozzles are oriented at a second elevation angle α2 of +10° with respect to the horizontal plane. The arrangement is illustrated in fig. 4 corresponding to the section along the line IV-IV represented in fig. 2. In fig. 2 and 3, the lateral extension of the first group of nozzles and the second group of nozzles are schematically indicated by a dotted curve 302 and 312, respectively, on the side of the opposite wall 82. The first and second border regions 290 and 292 extend each over approximately 0.37 (=3/8) times the wall length as measured in the transversal cross region 84. The first border region 290 and the second border region 292 each overlap with more than one vortex section, namely vortex section 100 and partially vortex section 102, and vortex section 106 and partially vortex section 104, respectively. Nozzles arranged in the inner region 320 form an inner group of nozzles that are oriented at an inner elevation angle α3 of -10° with respect to the horizontal plane. The arrangement is illustrated in fig. 5 corresponding to the section along the line V-V represented in fig. 2. In fig. 2 and 3, the lateral extension of the inner group of nozzles is schematically indicated by a dotted curve 322 on the side of the opposite wall 82 and of the wall 80. In the embodiment of fig. 1, as illustrated in fig. 4 and fig. 5, a difference in angle measured between the orientation of ^{A24021WO/23.04.2025} the nozzles of the first group and of the second group, i.e. oriented at +10° to the horizontal plane, and the orientation of the nozzles of the inner group, i.e. oriented at -10° to the horizontal plane, is consequently 20°. A resulting mass flow distribution of the post combustion gas injected in the transversal cross region 84 on the side of the wall and of the opposite wall is represented graphically in fig. 6, wherein the length of the wall is given in a X-direction of fig. 6 in relative values from 0 to 1 corresponding to 100% of the length of the wall. The position of the first nozzles and first opposite nozzles, as well as of the second nozzles and second opposite nozzles are represented schematically by a small or a large cross, respectively. In a Y-direction of fig. 6, the mass flow distribution is given on the side of the wall 80 as a normalized ratio between the mass flow at a position along the wall and the average mass flow over the wall. In the same manner, the mass flow distribution is given on the side of the opposite wall 82 on the opposite side of the graph. A wave-shaped mass flow distribution can be created by way of the nozzle arrangement described above in which maxima and minima of mass flow on the side of the wall 80 correspond to minima and maxima of mass flow on the opposite wall 82. The result is the creation of vortices rotating in opposed direction for two adjacent vortex sections. It is noted that the relative values ranging from 0 to 1.8 are given only as an example. Based on this embodiment, a method for optimizing the flow of combustion gas in a waste incineration plant for recovering energy from waste can be implemented in which waste is combusted in the combustion chamber under admission of primary gas by primary gas inlets. Combustion gases produced by waste ^{A24021WO/23.04.2025} combustion are post combusted in the secondary combustion space arranged downstream of the primary combustion space, as seen in a flow direction of the combustion gas, under injection of post combustion gas in the secondary combustion space. In a further step, the post combustion gas injection through the nozzles is controlled by means to control the post combustion gas injection. In the first vortex section, on the wall side, the first nozzle and the second nozzle and, on the opposite wall side, the first opposite nozzle and the second opposite nozzle are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0. Further, in the second vortex section, on the wall side, the first nozzle and the second nozzle and, on the opposite wall side, the first opposite nozzle and the second opposite nozzle are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are rotating in opposed directions. Referring to fig. 7, in a second embodiment, at least one further nozzle arrangement, namely a further nozzle arrangement 255 arranged in a further transversal cross region 256 downstream of the transversal cross region is provided. The further transversal cross region is also in the form of a further transversal cross section in the embodiment disclosed. In the second embodiment illustrated in fig. 7, the further nozzle arrangement 255 and the nozzle arrangement 92 are arranged in the secondary combustion space 60. The nozzle arrangement and the further nozzle arrangement of the second embodiment are substantially the same as the nozzle ^{A24021WO/23.04.2025} arrangement of the first embodiment represented in fig. 2. Same features having the same function in the nozzle arrangement are referenced by the same reference numbers. Features of the further nozzle arrangement having the same function as features of the nozzle arrangement are referenced by the same reference number followed by the letter “a”. The further transversal cross region 256 intersects the wall and the opposite wall each time along a horizontal line like it is the case for the transversal cross region and forms an angle γ2 of 20° as measured from a horizontal plane in the clockwise direction. In other words, the further transversal cross region is also oriented downwards in the same direction as the combustion grate. The further nozzle arrangement forms a plurality of vortex sections, namely four vortex sections arranged downstream of the corresponding four vortex sections of the nozzle arrangement 92. In a similar manner as for the nozzle arrangement, the four vortex sections correspond to two pairs of vortex sections comprising one first vortex section and one second vortex section. Further, each vortex section comprises wall portions arranged such that a first wall portion 112a of the wall is adjacent to a second wall portion 122a of the wall, and a first opposite wall portion 212a of the opposite wall is adjacent to a second opposite wall portion 222a of the opposite wall. Each vortex section comprises a plurality of first nozzles arranged in the first wall portion 112a, a plurality of second nozzles arranged in the second wall portion 122a, a plurality of first opposite nozzles arranged in the first opposite wall portion 212a, and a plurality of second opposite nozzles ^{A24021WO/23.04.2025} arranged in the second opposite wall portion 222a for injection of post combustion gas each time in a direction of injection. Which nozzles are defined as first nozzles and second nozzles as well as the corresponding first wall portion and second wall portion in a vortex section is determined consistently in the same manner for each vortex section. This remains true over all nozzle arrangements. As can be seen in fig. 7, one noticeable difference between the nozzle arrangement 92 and the further nozzle arrangement 255 is the direction of rotation of the vortices. More specifically, each vortex in the transversal cross region 84 rotate in a direction of rotation opposed to the corresponding downstream vortex of the further transversal cross region 256. For example, the vortex in vortex section 106 rotates counterclockwise and the vortex in the vortex section 106a downstream rotates clockwise. In the numerical example chosen above for the nozzle arrangement, for the first vortex section 106, the ratio R of the total jet momentum in the nozzle arrangement has been calculated above. The value is R = 9/4 = 2.25 on the side of the wall 80 and R = 3 on the side of the opposite wall 82, i.e. both in the range “greater than 2.0". The vortex rotates counterclockwise in the first vortex section 106. To obtain the configuration in which the vortex in the first vortex section 106a of the further nozzle arrangement 255 rotates clockwise, i.e. in the direction of rotation opposed to the vortex in the first vortex section 106, the value of the ratio R must be in the range “smaller than 0.5" on the side of the wall 80 and on the side of the opposite wall 82. ^{A24021WO/23.04.2025} Similarly, the value of the ratio R is 0.5 for the second vortex section 104 on the side of the wall 80 and on the side of the opposite wall, i.e. both in the range “smaller than 0.5”. The vortex rotates clockwise in the second vortex section 104. To obtain the configuration in which the vortex in the second vortex section 104a of the further nozzle arrangement 255 arranged downstream rotates counterclockwise, i.e. in the direction of rotation opposed to the vortex in the second vortex section 104, the value of the ratio R must be in the range “greater than 2.0" on the side of the wall 80 and on the side of the opposite wall 82. In operation, the post combustion gas injection through the nozzles is controlled by means to control the post combustion gas injection in the nozzle arrangement and in the further nozzle arrangement in a manner such that the value of the ratios R lie in the ranges defined above for the vortex sections. The stability of the combustion gas flow is further increased when the vortex present in the plurality of vortex sections rotates in opposed directions. In this manner, the vortices counterbalance each other so that they remain stable, in contrary to adjacent vortices rotating in the same direction that tend to merge and destabilize the combustion gas flow. The plurality of vortex sections extend in the further transversal cross region 256 over a first border region 290a adjacent to the first sidewall 86 and a second border region 292a adjacent to the second sidewall 88. Nozzles arranged in the first border region 290a forming a first group of nozzles are oriented at a first elevation angle of +10° with respect to a horizontal plane. Further nozzles arranged in the second border region 292a forming a second ^{A24021WO/23.04.2025} group of nozzles are oriented at a second elevation angle α4 of +10° with respect to the horizontal plane. The arrangement is illustrated in fig. 9 corresponding to the section along the line IX-IX represented in fig. 7. In fig. 7, the nozzles forming the first group of nozzles and the second group of nozzles are schematically indicated by a dotted curve 302a and 312a, respectively, on the side of the opposite wall 82. Further, the plurality of vortex sections extend in the further transversal cross region over an inner region 320a extending between the first border region 290a and the second border region 292a. Nozzles arranged in the inner region 320a form an inner group of nozzles that are oriented at an inner elevation angle α5 of -7° with respect to the horizontal plane. The arrangement is illustrated in fig. 10 corresponding to the section along the line X-X represented in fig. 7. In this embodiment, as illustrated in fig. 9 and fig. 10, a difference in angle measured between the orientation of the nozzles of the first group and of the second group, i.e. oriented at +10°, and the orientation of the nozzles of the inner group, i.e. oriented at -7°, is 17°. A similar wave-shaped mass flow distribution as the one represented in fig. 6 can be created in the further transversal cross region 256 by way of the further nozzle arrangement 255, wherein the mass flow distribution can be the same as in the nozzle arrangement or different. In the embodiment described above in which each vortex in the transversal cross region 84 rotate in a direction of rotation opposed to the corresponding downstream vortex of the further transversal cross region 256, a mass flow maximum in the transversal cross region corresponds each time to a mass flow minimum in the further transversal cross region. ^{A24021WO/23.04.2025} The embodiment represented in fig. 11 is the same as in fig. 7 except for the absence of a separation wall, wherein the nozzle arrangement is operated according to a method in which, in the nozzle arrangement, in the first vortex section 106, the plurality of second nozzles are operated such that no combustion gas is injected into them, and in the second vortex section 104, the plurality of first nozzles are operated such that no combustion gas is injected into them. In the same manner as described above, a vortex is created in the first and the second vortex section, said vortices having opposed direction of rotation. In addition, in the further nozzle arrangement, in the first vortex section 106a, the plurality of first nozzles are operated such that no combustion gas is injected into them, and in the second vortex section 104a, the plurality of second nozzles are operated such that no combustion gas is injected into them. The resulting vortex configuration is the same as the one described in relation to fig. 7. List of reference signs Combustion chamber 10 Inlet 20 Primary combustion space 30 Combustion grate 40 Combustion bed 42 Primary gas inlets 44 Combustion gas 46 Outlet 48 Peripheral wall 50 Longitudinal direction 52 Secondary combustion space 60 Flow direction of combustion gas 62 Duct 70 ^{A24021WO/23.04.2025} First, second pass 72, 76 First pass discharge region 74 First pass top wall 77 Opening 78 connecting the first pass and the second pass Heat recovery boiler 79 Wall 80 Opposite wall 82 Transversal cross region 84 First sidewall 86 Second sidewall 88 Direction of waste transportation 89 Bunker 90 Nozzle arrangement 92 Vortex sections 100, 102, 104, 104a, 106, 106a First, second wall portion 112, 122, 112’, 122’ First, second nozzle(s) 110, 120, 110’, 120’ First, second opposite nozzle(s) 210, 220, 210’, 220’ First, second opposite wall portion 212, 222, 212’, 222’ Means to control post combustion gas injection 230 Auxiliary burner 232 Further nozzle arrangement 255 Further transversal cross region 256 wall pipe 260 opposite wall pipe 262 Separation wall 270 Channels 272, 274 Lower end 280 Upper end 282 First border region 290, 290a Second border region 292, 292a First group of nozzles 302, 302a Second group of nozzles 312, 312a Inner region 320, 320a ^{A24021WO/23.04.2025} Inner group of nozzles 322 Second elevation angle(s) α2, α4 Inner elevation angle(s) α3, α5 ^{A24021WO/23.04.2025}

Claims

Claims 1. A waste incineration plant for recovering energy from waste comprising a combustion chamber (10) for combusting waste, the combustion chamber comprising a primary combustion space (30) in which a combustion grate (40) is arranged for combusting waste under admission of primary gas by primary gas inlets (44), combustion gas (46) being generated by combusting waste; a secondary combustion space (60) arranged downstream of the primary combustion space, as seen in a flow direction (62) of combustion gas, and designed for the post combustion of combustion gas under injection of post combustion gas in the secondary combustion space; a heat recovery boiler (79) designed to recover heat from the combustion gas; and a peripheral wall (50) enclosing the primary combustion space (30), the secondary combustion space (60) and the heat recovery boiler (79), the peripheral wall (50) extending downstream in a longitudinal direction in the form of a duct (70) to channel combustion gas, the peripheral wall comprising a wall (80) and an opposite wall (82) facing the wall, as seen in a direction of waste transportation (89) on the combustion grate, and a nozzle arrangement (92), the nozzle arrangement forming a plurality of vortex sections (100, 102, 104, 106) arranged in a transversal cross region (84) of the duct, wherein nozzles are arranged in the plurality of vortex sections in the wall and in the opposite wall for injection of post combustion gas to generate each time a vortex, each vortex section (100, 102, 104, 106) comprising on a wall side a first nozzle (110) arranged in a first wall portion ^{A24021WO/23.04.2025} (112) of the wall (80) and a second nozzle (120) arranged in an adjacent second wall portion (122) of the wall(80), and on an opposite wall side a first opposite nozzle (210) arranged in a first opposite wall portion (212) of the opposite wall (82) and a second opposite nozzle (220) arranged in an adjacent second opposite wall portion (222) of the opposite wall (82), the first wall portion (112) facing the second opposite wall portion (222), and the first opposite wall portion (212) facing the second wall portion (122); the waste incineration plant comprising means (230) to control post combustion gas injection through the nozzles, characterized in that, in a first vortex section (106) and a second vortex section (104) of the plurality of vortex sections, the second vortex section being adjacent to the first vortex section, the first nozzle (110, 110’), the second nozzle (120, 120’), the first opposite nozzle (210, 210’) and the second opposite nozzle (220, 220’) are arranged each time in a vertical longitudinal plane at an azimuth angle of approximately 90° with respect to the wall (80) and the opposite wall (82), respectively; in the first vortex section (106), on the wall side, the first nozzle (110) and the second nozzle (120) and, on the opposite wall side, the first opposite nozzle (210) and the second opposite nozzle (220) are configured to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0; and in the second vortex section (104), on the wall side, the first nozzle (110’) and the second nozzle (120’) and, on the opposite wall, the first opposite nozzle (210’) and the second opposite nozzle (220’) side are configured ^{A24021WO/23.04.2025} to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are extending in the longitudinal direction and rotating in opposed directions.

2. Waste incineration plant according to claim 1, characterized in that, the plurality of vortex sections comprises multiple pairs of vortex sections comprising one first and one second vortex section.

3. Waste incineration plant according to claim 1 or 2, characterized in that, in the first and second vortex section (106, 104), the hydraulic diameter ratio of the first nozzle (110) to the second nozzle (120) and the hydraulic diameter ratio of the first opposite nozzle (210) to the second opposite nozzle (220) are both in one of the two ranges defined by smaller than 0.7 or greater than 1.4.

4. Waste incineration plant according to claim 3, characterized in that, in the first and second vortex section (106, 104), the first nozzle (110) and the first opposite nozzle (210) have a same first hydraulic diameter, and the second nozzle (120) and the second opposite nozzle (220) have a same second hydraulic diameter.

5. Waste incineration plant according to any one of claims 1 to 4, characterized in that, in the first and in the second vortex sections (106, 104), the first wall portion (112), the second wall portion (122), the first opposite wall portion (212) and the second opposite wall portion (222) comprises a plurality of first nozzles (110), a plurality of second nozzles (120), a plurality of first ^{A24021WO/23.04.2025} opposite nozzles (210) and a plurality of second opposite nozzles (220), respectively.

6. Waste incineration plant according to any one of claims 1 to 5, characterized in that the plurality of vortex sections extend over at least 80%, preferably 100%, of the transversal cross region, as measured transversely to the duct (70).

7. Waste incineration plant according to any one of claims 1 to 6, characterized in that the plurality of vortex sections comprises at least two pairs of first and second vortex sections, wherein vortex sections adjacent to sidewalls connecting the wall (80) and the opposite wall (82) have a width of 1.0 to 1.4 times a vortex section average width, and vortex sections arranged between the vortex sections adjacent to the sidewalls have a width of 0.6 to 1.0 times the vortex section average width, the vortex section average width being defined as the length of the wall measured transversely to the duct divided by the number of vortex sections of the plurality of vortex sections.

8. Waste incineration plant according to any one of claims 1 to 7, characterized in that the plurality of vortex sections are distributed over a first border region (290), a second border region (292) and an inner region (320) arranged between the first and second border region, the first and the second border region (290, 292) extending each over up to 0.40 times the cumulated width of the plurality of vortex sections, as measured transversely to the duct, wherein nozzles arranged in the first border region and in the second border region form a first group of nozzles (302) and a second group of nozzles (312), ^{A24021WO/23.04.2025} respectively, the nozzles of the first group (302) being oriented at a first elevation angle of -25° to +30° with respect to a horizontal plane and the nozzles of the second group (312) being oriented at a second elevation (α2) angle of -25° to +30° with respect to the horizontal plane.

9. Waste incineration plant according to claim 8, characterized in that nozzles arranged in the inner region form an inner group of nozzles (322) that are oriented at an inner elevation angle (α3) of -25° to 15° with respect to the horizontal plane.

10. Waste incineration plant according to claim 9, characterized in that, a difference in angle measured between the orientation of the nozzles of the first group or of the second group (312) and the orientation of the nozzles of the inner group (320) is between 0° and 40°.

11. Waste incineration plant according to any one of claims 1 to 10, characterized by at least one further nozzle arrangement (255) arranged in a further transversal cross region (256) of the duct (70) downstream of the transversal cross region (84).

12. Waste incineration plant according to claim 11, characterized in that two consecutive nozzle arrangements (92, 255) are configured such that each vortex in one of the two consecutive nozzle arrangements rotate in a direction of rotation opposed to the corresponding vortex of the other nozzle arrangement.

13. Waste incineration plant according to any one of claims 1 to 12, characterized in that the duct (70) forms a first pass (72) extending downstream up to a first pass ^{A24021WO/23.04.2025} discharge region (74) from which the combustion gas flows into a second pass (76) in fluid communication with the first pass (72) and comprises at least one separation wall (270) extending longitudinally in a plane perpendicular to the wall (80) and the opposite wall (82) and dividing the duct into at least two channels (272, 274) into which combustion gas flows to the first pass discharge region, wherein a first vortex section and a second vortex section lie on each side of the at least one separation wall.

14. A method for optimizing the flow of combustion gas in a waste incineration plant for recovering energy from waste according to any of the preceding claims, in which in the first vortex section (106), on the wall side, the first nozzle (110) and the second nozzle (120) and, on the opposite wall side, the first opposite nozzle (210) and the second opposite nozzle (220) are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in one of the two ranges defined by smaller than 0.5 or greater than 2.0; and in the second vortex section (104), on the wall side, the first nozzle (110’) and the second nozzle (120’) and, on the opposite wall side, the first opposite nozzle (210’) and the second opposite nozzle (220’) are injecting post combustion gas controlled in a manner to have a respective total jet momentum in a ratio lying both in the other one of the two ranges, to create a vortex in the first and in the second vortex section that are extending in the longitudinal direction and rotating in opposed directions. ^{A24021WO/23.04.2025}

15. Method according to claim 14, characterized in that, in the first vortex section and in the second vortex section, no post combustion gas is injected either in the first nozzle and in the first opposite nozzle or in the second nozzle and in the first second nozzle. ^{A24021WO/23.04.2025}