WO2024121655A1

WO2024121655A1 - Process and plant for the conversion of tar into synthesis gas

Info

Publication number: WO2024121655A1
Application number: PCT/IB2023/061539
Authority: WO
Inventors: Maria Laura MASTELLONE
Original assignee: Bell Production SpA
Current assignee: Bell Production SpA
Priority date: 2022-12-06
Filing date: 2023-11-15
Publication date: 2024-06-13
Anticipated expiration: 2025-06-06
Also published as: IT202200025098A1; EP4630366A1

Abstract

Process for converting tar contained in a raw gasification product into synthesis gas and respective plant, the method comprising the following steps: (i) carrying out - in a first reactor - a thermal decomposition of the tar contained in the raw gasification product obtaining a decomposition product; and (ii) carrying out - in a second reactor - a catalytic decomposition of the decomposition product, obtaining a synthesis gas, wherein the synthesis gas comprises less than 1 mg/Nm³ of tar and it has a heating value greater 8 MJ/Nm³ in case of gasification with air greater than 10 MJ/Nm³ in case of gasification with oxygen at 95%.

Description

PROCESSAND PLANT FORTHECONVERSION OFTAR INTO SYNTHESIS GAS

FIELD OF THE INVENTION

The present description relates to a process and a respective plant for converting tar contained in a raw gasification product in synthesis gas and which can be directly used as fuel or feedstock.

Background of the invention

Gasification is a thermochemical process used in the petrochemical industry to convert solid fuels into synthesis gas (or syngas) and in the waste treatment industry to energetically exploit the solid waste in a more sustainable fashion with respect to direct combustion (incineration). Among the thermochemical conversion technologies, gasification is a concrete alternative to direct combustion in incinerators, given that it offers advantages in terms of minimum potential, plant cost and environmental impact.

Gasification is a well-established and widely used technology for the recovery of matter and energy from coal and biomass. The application of gasification to municipal waste treatment was initially supported by the belief that gasification it allowed lower emissions and a low environmental impact because the absence of oxygen actually blocks the formation of dioxins and furans [5]. The main advantages, however, are related to the flexibility of use of the gasification product: syngas. Syngas can be used in various applications, significantly affected by the level of purity which can be obtained by suitably selecting the operating conditions of the process and the treatments to be carried out downstream. The main alternatives are using - as an energy carrier or as a building block for the synthesis of different chemical products (from hydrogen to methanol, ammonia, liquid fuels, etc.) [2].

In recent decades, gasification of wood-cellulose biomass has also been used thanks to government incentives for small biomass plants (up to 1 MW). However, the use of solid waste containing plastics has highlighted a problem related to the production of a heavy hydrocarbon fraction called tar.

Tar consists of various substances that share the characteristic of becoming viscous and often adhesive at low temperatures. "Tar" as defined by the European Committee for Standardisation (CEN) consists of "all organic compounds present in gases produced during gasification excluding gaseous hydrocarbons Cl to C6" [1, 2].

The tar must be removed before syngas is used both in chemical industry processes and in energy conversion in turbines or internal combustion engines, given that otherwise it would cause tarry deposits and occlusions, up to the blocking of mechanical members.

Tar can be removed through primary or secondary methods; primary methods act chemically; secondary methods only remove tar with physical methods.

Conventional primary thermal or catalytic methods are applied alternatively and use external energy sources (thermal cracking) or catalysts such as nickel- based ones (catalytic cracking) to promote the cracking of high molecular weight molecules.

Conventional physical secondary methods provide for the removal of the heavy fraction through scrubbing processesresulting in the loss of high energy content material and the production of a semi-solid oily sludge that is expensive and difficult to dispose of.

Thermal cracking is generally promoted using an external energy source capable of providing enough energy to break the chemical bonds of molecules such as carbon-carbon bond and carbon-hydrogen bond, among others.

Catalytic cracking is obtained by promoting the dehydrogenation of heavy hydrocarbon molecules, that is the breaking of the C-H bond, resulting in coking on the catalyst. The loss of catalyst activity is therefore inevitable and very fast due to the high amount of coke deposited on the catalytic surface. Furthermore, a conventional catalytic cracking process needs to be supported by an external energy source in order to balance the energy demand of endothermic reactions.

A system based on primary tar reduction methods allows to increase the energy content of the synthesis gas produced, prevent the generation of waste with high disposal costs, reduce maintenance costs and downtime caused by pipe clogging and dirtying the moving parts.

The cleaning of syngas is indispensable in order to exploit the massive potential of this synthesis product, which can be used as a fuel but can above all be converted to methane or hydrogen through subsequent chemical reactions of methanation or steam reforming [6].

Gasifiers installed and supplied with wood biomass or waste produce a syngas in which the tar content may reach values that are too high, to an extent of being incompatible with use in electric energy recovery systems (Table 1).

Table 1.

Despite the fact that there are currently available various methods for removing tar from syngas, there is still a need to provide tar removal processes that are more profitable both in terms of the amount of tar removed and in terms of energy efficiency. The use of syngas as feedstock for hydrogen production requires a lot of cleaning.

SUMMARY OF THE INVENTION

The object of the present description is to provide a process and a plant for converting the tar contained in a raw gasification product into synthesis gas which overcome the disadvantages of the prior art.

A first object of the present invention is to provide a process and a plant for obtaining a gas with a high heating value and suitable for use in gas engines and turbines.

A second object is to provide a process and a plant which allow to obtain a synthesis gas suitable for use as feedstock for the production of chemicals and/or hydrogen.

A third object is to provide a process and a plant that can operate using mainly internal energy rather than energy introduced from the external.

A fourth object is to provide a process and a plant that allow to obtain a synthesis gas operating at temperatures manageable by normal thermal recovery equipment without having to resort to mechanical components made of special and very expensive materials.

According to the invention, the objects outlined above are attained thanks to the object specifically referred to in the claims below, which are deemed an integral part of the present description.

In an embodiment, the present description relates to a process for converting tar contained in a raw gasification product into synthesis gas, the process comprising the following steps:

(i) carrying out - in a first reactor - a thermal decomposition of the tar contained in the raw gasification product obtaining a decomposition product; and

(ii) carrying out - in a second reactor - a catalytic decomposition of the decomposition product, obtaining a synthesis gas, wherein the synthesis gas comprises less than 1 mg/Nm³ of tar and has a heating value greater than 8 MJ/Nm³.

In an embodiment, the present description further relates to a plant for converting tar contained in a raw gasification product into synthesis gas configured to carry out the process described above, comprising a first and a second reactor, wherein the second reactor is coupled to the outlet of the first reactor, the raw gasification product is :ntroduced into the first reactor at a top or end of the first reactor, in particular a tubular body of the first reactor, the second reactor is coupled to the first reactor in proximity of the respective opposite or lower ends, in particular tubular bodies of the reactors.

Brief description of the drawings

Now, the invention will be described in detail, solely by way of non-limiting example, with reference to the attached figures, wherein:

Figure 1: Effect of temperature on syngas composition at equilibrium.

Figure 2: Schematisation of an embodiment of a plant for converting heavy and tar hydrocarbons into syngas according to the present invention.

Detailed description of the invention

In the following description, numerous specific details are provided to provide an exhaustive understanding of the embodiments. The embodiments may be implemented with or without one or more of the specific details, or with other processes, components, materials etc. In other cases, well-known structures, materials, or operations are not described in detail so as to avoid confusing aspects of the embodiments.

Within the present application, reference to "one (numeral adjective) embodiment" or "an (indefinite article) embodiment" indicates that a particular version, structure, or characteristic described with reference to the embodiment is included in at least one embodiment. Therefore, the forms of the expressions "in one" (numeral adjective) embodiment" or "in an (indefinite article) embodiment" in various points within the present application do not all necessarily refer to the same embodiment. Furthermore, the particular versions, structures, or characteristics may be combined in any appropriate fashion in one or more embodiments.

The titles provided herein are just for the sake of convenience and they do not interpret the scope of the various embodiments.

The present invention relates to a process and a plant for the implementation of the process intended to convert the heavy hydrocarbons and the tar contained in raw gasification products into synthesis gas. The process and the plant belong to the field of primary methods given that they allow to convert the high molecular weight molecules forming the tar into small and stable molecules and with high energy content (methane, carbon and hydrogen monoxide) therefore obtaining - at the end of the process - a synthesis gas/syngas with high heating value which can be directly used as fuel or feedstock.

The process exploits a first thermal decomposition of the tar macromolecules accompanied by a chemical reaction for recomposing radical fragments with the ionised gas used and a second catalytic decomposition of the residual tar macromolecules from the first step and/or formed during thermal decomposition.

The larger fraction of tar is converted in a first High-Temperature Plasma Cracker (HTPC); the residual tar fraction, smaller than 10-15% with respect to the initial one, is instead treated in a Moderate-Temperature Catalytic Cracker (MTCC).

The conversion of tar into synthesis gas which can be obtained with the process subject of the present description is greater than 90% and the residual tar is below the threshold for the use of the synthesis gas in chemical and energy recovery processes. The adoption of the process and of the plant according to the present invention allows to maximise the production of hydrogen and paves the way to improving the performance of all gasification plants already in use.

In an embodiment, the present invention relates to a process for converting tar contained in a raw gasification product into synthesis gas, the process comprising the following steps, carried out in series:

In an embodiment, the step (i) is conducted by placing a stream of the raw gasification product in contact with a stream of an ionized steam plasma at a pressure comprised between 1000 and 1500 °C and a pressure comprised between 0 and 5000 mbarg.

In an embodiment, the ionized plasma is generated by an electric arc or by a plasma torch which uses a suitable gas to promote reactions for reforming the fragments generated by the thermal decomposition and stabilise them.

In an embodiment, the ionized plasma is generated using oxygen, air, steam and mixtures thereof.

In an embodiment, the ionized plasma is generated in the upper section of the first reactor.

In an embodiment, the raw gasification product is introduced into the first reactor at the top part of the reactor.

In an embodiment, in step (i), the stream of the raw gasification product comes into contact and mixes with the stream of the ionized plasma at an angle comprised between 70 and 110 °, preferably about 90°.

In an embodiment, the stream of the raw gasification product and the ionized plasma stream come into contact with each other at the upper end of the first reactor.

In an embodiment, the stream of raw gasification product and the ionized plasma stream flow towards the bottom (lower end) of the first reactor and come into contact with a bed of conductive particulate material having a particle size comprised between 3 and 10 mm and resistant to a temperature comprised between 2000 and 2700 °C.

In an embodiment, the bed of particulate material has a bulk density comprised between 1300 and 1700 kg/m³.

In an embodiment, the bed of particulate material is a static bed; the particle size and density may vary while ensuring that the stream of raw product, ionised gas cannot transport it.

In an embodiment, the particulate material has a spherical shape with sphericity between 0.6 and 0.9.

In an embodiment, the particulate material is silicon carbide.

In an embodiment, the decomposition product exiting from the first reactor has a temperature not lower than 1250 °C.

In an embodiment, the decomposition product is collected at the bottom (lower end) of the first reactor.

In an embodiment, the step (ii) provides for introducing the decomposition product at the bottom (lower end) of the second reactor which comprises a metal catalyst bed a metal catalyst in particle form.

In an embodiment, the particles of the catalyst have a size comprised between 0.2 and 1 mm.

In an embodiment, the metal catalyst bed has a bulk density comprised between 1300 and 1600 kg/m³.

In an embodiment, the metal catalyst bed is a fluidized bed.

In an embodiment, step (ii) is conducted at a temperature comprised between 650 and 800 °C, and at a pressure comprised between 20 and 100 mbarg.

In an embodiment, the catalyst is Pt, Sn, Fe and/or Ni-based supported on ZnO / MgO / SiO₂ or AI₂O₃, optionally doped with alkaline metals.

In an embodiment, the catalyst is Pt/Sn/A12O3 doped with alkaline metals.

In an embodiment, the synthesis gas obtained at the end of the process has a temperature comprised between 650 and 800 °C, preferably about 700 °C.

In an embodiment, the synthesis gas is extracted by the second reactor at the top part (upper end) of the reactor.

The process described herein has surprising advantages with respect to the known processes for removing tar from a raw gasification product.

In particular, the present process allows to obtain a synthesis gas which has a heating value greater than the one obtained using normal tar removal processes. Specifically, the synthesis gas obtained at the end of the process has a PCI heating value greater than 8 MJ/Nm³, where - with standard tar removal processes - the heating value of the synthesis gas is generally comprised between 5 and 7 MJ/Nm³. This fact derives from the conversion of the tar carbon into carbon monoxide and methane and from the production of molecular hydrogen thanks to the combined action of thermal decomposition with the ionized plasma radicals (O-, OH-, H-).

Should the syngas be obtained from gasification with pure oxygen and/or steam instead of air, the heating value will be greater than 40 - 50%.

Furthermore, the present process allows to obtain a synthesis gas which contains residual tar less than 1 mg/Nm3, value below the one which can be obtained with the standard removal processes which settles at values greater than 200 mg/Nm³. Using the combination of thermal decomposition combined with reforming reactions and a tar catalytic decomposition, compared to the prior art, the present process allows to significantly reduce the residual tar contained in the syngas, increase the methane, hydrogen and carbon monoxide content, surprisingly exploiting a synergistic effect between the two different decompositions and moderate the temperature level for exiting from the system so as to use - downstream - medium temperature reactors such as the shift reactor.

The process optimises the use of energy and minimises the cost for regenerating/disposing of the catalyst given that: a) it applies the thermal cracking process on the high-temperature raw gasification product, without any cooling, minimising the use of plasma generation energy for the sole enthalpy delta required to provide the cracking of the tar C-C and C-H bonds; b) it applies the thermal cracking process using an ionised carrier formed by H- and OH- capable of increasing the production of H₂, the production of CO and therefore the increase of the heating value of syngas beyond 25%, c) it applies the catalytic cracking process for a residual tar fraction, below 10-15%, minimising the cost of the catalyst and increasing the lifetime thereof and allowing to reset the residual concentration of tar in the syngas, d) it applies catalytic cracking endothermic reactions so as to reduce the temperature of the syngas to values of about 700°C allowing the use - downstream - of mechanical systems made for moderate temperatures and therefore more cost- effective and durable.

Also the emissions produced by the process described herein are lower than the ones obtained by the prior art processes. As a matter of fact, the present process uses a steam plasma generated due to the use of electric energy instead of a fossil fuel burner (methane, LPG) which releases combustion fumes into the atmosphere.

The expression gasification is used to indicate a set of chemical reactions between a carbon-based matrix and one or more reagents containing oxygen (air, water vapour, pure oxygen, carbon dioxide) at temperatures between 800 and 1400 °C, whose result is the production of a gaseous mixture (hence the expression "gasification") to be used as energy source or as basic material for the chemical industry.

There are various gasifying agents which can be used for converting the organic material into syngas:

- air;

- oxygen;

- steam;

- mixtures of the preceding gases.

Partial oxidation with air produces a diluted syngas from atmospheric nitrogen (up to the values of 60%) and it has a heating value which varies in the range from 4-8 M/Nm³. Partial oxidation with oxygen produces a nitrogen-free syngas and therefore with a greater heating value (between 8 and 14 MJ/Nm³). Gasification with steam produces a nitrogen-free syngas which has a heating value which varies in the range from 14-20 MJ/Nm³ [7].

The carbon-based matrices which can be used include: wood, carbon, plastics, rubbers, secondary solid fuel (SSF), pre-treated municipal waste.

The choice of the carbonaceous material to be gasified and the type of gasifying reagent depend on several parameters which are to be evaluated starting from the composition of the starting material (elemental composition, immediate analysis, physical status, ...) up to defining the intended use of the syngas (energy/chemical reagent); these decisions linked to the process in turn affect the design choices of the plant, such as the type of reactor, its volume, the treatment of the syngas, etc.

The reactions which occur in the gasification reactor are different and the reaction mechanism is complex. Identifying the solid material to be converted into syngas with the expression "substrate", the main reactions are reported in table 2.

Table 2. Gasification reaction

The oxidation reactions are exothermic and therefore produce thermal energy. Other reactions are instead endothermic that is they require heat supply from the external so as to occur with significant degree of conversion. In a balanced gasification process the exothermic reactions provide enough thermal energy to support the endothermic reactions and have an autothermal process as a whole.

Specifically, the reaction 1 is a partial oxidation reaction same case applying to reaction 3; the latter is however a complete oxidation reaction, therefore the extension thereof should be limited thanks to the use of an oxygen/substrate ratio that is much lower than the stoichiometric value. The introduction of steam the hydrolysis and hydrogen production reactions (reactions 6-7-8-9); these reactions are endothermic reactions hence require the administration of thermal energy or the simultaneous oxidation reaction with oxygen (reactions 1 and 3). The reactions 14-16 are high molecular weight hydrocarbon-based reactions, possibly containing cycles and aromatic rings. These molecules are tar precursors and must be converted into smaller molecules before conveying syngas to the cooling equipment (heat exchangers) and/or syngas conversion reactors. The presence of molecules such as C_xH_y con x > 12 leads to a formation of tar and oily liquids which are a major problem in the maintenance and operation of equipment.

The complexity of the reaction mechanism described above does not allow to achieve - in a single gasification reactor - the conditions for simultaneously attaining the optimal objectives of the process, namely:

A. minimising the complete oxidation and production of CO₂ resulting in maximisation of the syngas energy content;

B. minimising tar content (represented by high molecular weight and/or polycyclic aromatic structure hydrocarbons) resulting in maximisation of carbon monoxide, hydrogen and methane content.

Achieving the above objectives requires that the overall process be divided into two different stages, each optimised for the specific purpose, therefore:

- the primary gasification reactor is designed to achieve objective A;

- the system for converting the tar contained in the raw gasification product in order to achieve objective B.

The purpose of the present invention is to pursue objective B by providing a new design plant for converting the tar contained in the raw gasification product, hereinafter referred to as "HTPC-MTCC hybrid system".

The method applied for the conceptual and modeling development of the HTPC-MTCC hybrid system provides for implementing the conversion of tar through a thermal decomposition of tar macromolecules and a catalytic decomposition of residual tar macromolecules from the first step and/or formed during thermal decomposition.

The thermal decomposition of tar macromolecules occurs through the action of radicals and hydroxyl and hydroxyl ions. The bond breaking action is followed by the saturation of the fragments with the radicals/ions. Basically, an oxygen + steam mixture supplied in the form of high-energy radicals promotes decomposition reactions 15 and 16, hydrolysis reactions (reforming) 6 to 9, and partial oxidation reactions 1 to 5 (with limited extension).

The purpose of the electric arc torch or plasma torch, installed in the upper section of the plant, is therefore to produce the hydroxyl and hydroxyl radicals required for the saturation of the molecules of long- chain and/or cyclic-aromatic hydrocarbons that form the tar and react them with the molecules that form the raw gasification product promoting the thermal decomposition of the larger molecules (tar and the respective precursors such as C_nH_m where n is greater than 6).

This step is carried out in a high-efficiency first reactor where most of the tar is converted in a very short time and permanently. As observable from Figure 1, at high temperatures the conversion of carbon and hydrocarbons is totally shifted toward hydrogen and carbon monoxide.

In short, during the tar thermal decomposition step, the raw gasification product is introduced into the reactor at the temperature of approximately 850°C; the raw gasification product stream and plasma stream cross each other at about 90°, mix and then continue in a parallel flow towards the bottom of the reactor. At about 2/3 reactor height, the streams of the raw gasification product and the plasma, already under advanced reaction conditions, meet a bed of filling material capable of operating at 1400°C (silicon carbide) which promotes contact between molecules and heat exchange, promoting further thermal decomposition of tar into smaller hydrocarbon molecules. Exiting from the bed of high heat capacity material, the decomposition product has a temperature of not less than 1250°C and it is conveyed to a second reactor.

The high temperature guaranteed by the plasma stream destroys the tar molecules, but it may promote the cyclisation of a small fraction of fragments with 5- 6 or more carbon atoms in the absence of saturation of radicals. Saturation occurs with the radicals contained in the ionized plasma. The only residual fraction of cyclic and/or aromatic hydrocarbons such as those of the Benzene-Toluene-Xylene (BTX)family shall be removed in a second reactor arranged downstream and operating with a catalytic type process, more selective than the thermal one.

The decomposition product exiting the first reactor is introduced into the lower section of the second reactor.

The bottom-up flow of the decomposition product through a bed of particulate material, whose weight is exceeded by the thrust of the decomposition product while remaining in an untransported (captive) bed state, promotes fluidisation in a rough/hot/turbulent state of the bed. The fluid dynamics characteristic of the second reactor therefore lies in the fact that it is a mixed, rather than segregated, reactor but not transported.

Contact between the decomposition product and particulate material consisting of catalysts of natural or synthetic origin based on Pt/Sn, Fe/Ni/Al triggers carbonisation and dehydrogenation reactions which convert the residual heavy fraction (residual tar and/or BTX) of the decomposition product into smaller, more stable molecules.

The main effect of using a catalyst as the fluid bed material is the complete removal of BTX and residual tar. The catalyst strongly promotes the endothermic decomposition reactions of high molecular weight hydrocarbons through the following reactions: thermal cracking: C_xH_y C_nH_m + H₂ (1) carbonisation/dehydrogenation : C_nH_m nC + m/2 H₂ (2) where C_xH_y represents high molecular weight hydrocarbons (with x > 6) while C_nH_m indicates hydrocarbons with number of carbon atoms less than C_xH_y (with n < 6). The increase in H₂ concentrations is highly significant and it can reach values ranging from 8-9% up to values above 30%. The reactor temperature stabilises at lower values (around 750 °C) due to the endothermicity of the reactions.

The process subject of the present description allows to obtain synthesis gas/syngas which can be used directly as a reagent for the chemical industry and only secondarily as a fuel. In particular, the process described herein produces a syngas capable of producing chemicals and hydrogen, unlike conventional plants which produce syngas to be used exclusively as an energy carrier. The presence of tar in syngas limits the use of high-performance energy generation systems (for example gas turbine) and produces carbonaceous emissions in the exhaust systems. The process increases the recovery of electricity, if adopted in place of the production of chemicals and hydrogen, by more than 50%.

The HTPC-MTCC hybrid system is therefore a system consisting of two reactors arranged in series both containing a bed of particulate material.

The HTPC-MTCC hybrid system is described below from a technological point of view with reference to figures 2A and 2B, which respectively show the reactors of the plant in a partially cross-sectional schematic view and in a partially cross-sectional schematic perspective view.

Herein, with R01 there is indicated a first reactor, the thermal cracking reactor with ionized plasma, while with R02 there is indicated a second reactor, the catalytic cracking reactor.

The first reactor R01 is a tubular reactor, in particular comprising a tubular body 12, for example made of AISI steel that contains particulate material therein.

The second reactor R02 is a tubular reactor, with a tubular body 22, filled with a material with much smaller average size and density than the particulate material contained in the first reactor.

The first reactor R01 and the second reactor R02 are coupled using respective flanges 15, 25.

More specifically, the first reactor R01 comprises a tubular body 12, which is open, identifying an opening 17a, whose inlet section in particular is substantially orthogonal to the longitudinal main axis of tubular body 12, to a first end of the tubular body 12, upper end in the figures, and open, identifying an opening 16a, whose cross-section in particular is substantially orthogonal to the longitudinal main axis of the tubular body 12, at a second end of the tubular body 12, lower end in the figures. An inlet 10 for the incoming raw gasification product SY_in, that is an opening in the wall of the tubular body 12, whose cross-section in particular is substantially parallel to the longitudinal main axis of the tubular body 12, in proximity of the first end, to which there can be coupled a conduit for supplying the incoming raw product SY_in not shown in the figure, which therefore flows in with flow orthogonal to the longitudinal axis of the body 12. In the example, the openings 17a, 16a, 10 are probided with flanges to allow coupling with other pipes or conduits, or with other components.

With this regard, a thermal plasma generated in the proximity of the opening 10 by a torch 17, in particular a plasma torch, positioned on the top part of the reactor R01, that is on the upper end of tubular body 12, perpendicular to the stream of the incoming raw product SY_in, is indicated with 11.

The tubular body of both reactors 12, 22 is for example made of AISI steel as mentioned above, while the internal of each tubular body is covered with refractory material 13, in the example made of a double layer refractory-insulating silico-aluminous matrix, resistant to ultra-high temperatures and to reducing gas. Inside the tubular body 12 of the first reactor R01 there is, indicated with 14, non-catalytic particulate material, specifically beads of conductive material with the function of increasing the effectiveness of contact between the gaseous molecules and the transportation of radial energy. The decomposition product exiting from the first reactor R01, at the lower end of the tubular body 12, through an outlet opening 15, whose inlet crosssection in particular is substantially parallel to the longitudinal main axis of the tubular body 12, which is arranged at the lower end part thereof, is directed to the second reactor R02, which has a similar opening 25 in the lower end part of the tubular body 22. Therefore, the bed 14 of particulate material is positioned downstream with respect to the stream of raw gasification product SY_in. The opening 15 is downstream of the bed 14 and - through it - the decomposition product, indicated with Syd,d, exits from the first reactor R01.

The opening 15 and the aperture 25, which are also provided with flanges, which in the shown example are not directly coupled to each other, but through an intermediate conduit 25, which is horizontal and is coupled - at one end - to the flange of the opening 15 and - at the other - to the flange of the opening 25. Alternatively, the coupling may be direct.

In the second reactor R02 there is contained a catalytic material 28, which is fluidized by the decomposition product SY_d coming from reactor R01, and the conversion reactions promoted are carried out with energy absorption and decrease in temperature.

Therefore, the tubular body 22 comprising - therein - said bed 28 of catalytic material positioned upstream of the stream of decomposition product SY_d of an opening 20 for the outflow of the synthesis gas SY_out. The bed 28 is also positioned upstream of the opening 25.

Also the tubular body 22 of the second reactor is open, identifying an opening 27a, whose inlet section in particular is substantially orthogonal to the longitudinal main axis of tubular body 22, to a first end of the tubular body 22, upper end in the figures, and open, identifying an opening 26a, whose cross- section in particular is substantially orthogonal to the longitudinal main axis of the tubular body 22, at a second end of the tubular body 12, lower end in the figures.

The tubular body 12 and the body 22, as shown in figures 2A and 2B, are positioned with the longitudinal axes parallel and in the example they are approximately 350 cm long and measure approximately 300 mm in diameter.

Both reactors R01 and R02 are provided with an exhaust system, represented by respective actuators 16, 26 for closing/opening the lower openings 16a, 26a of the tubular body 12, 22 for the replacement of the filling/catalytic material 28 and a loading system, represented by an actuator 17 operating on the opening 27a of the upper end of the tubular body 22, for reintroduction. Clearly for loading or unloading the respective conduits - not shown - may be coupled downstream or respectively of the openings 16a, 26a, 27.

By way of example, the second reactor R02 may comprise a tubular body 22 represented by an AISI310 DN 300 steel cylinder flanged both at the base at the opening 26a, and at the top part, at the opening 27a, such tubular body 22 respectively housing a dispenser of the decomposition product SY_d flowing out from the first reactor R01, and the conduit 20 for the outflow of the synthesis gas SY_out. Such dispenser, which is not visible in figure 2, consists of a perforated plate, whose plane is horizontal, orthogonal with respect to the longitudinal axis of the body 22, with a plurality of holes, for example measuring 3 mm thick and 550 holes measuring 2 mm. The plate also serves as a support for the catalytic bed 28.

The first reactor R01 comprises a tubular body 12 comprising an AISI310 DN150 steel cylinder flanged both to the base, at the opening 16a and to the top part, at the opening 17a (to couple torch 17) and in a lateral position perpendicular to the top flange of the opening 17a at about 20 cm therefrom, corresponding to the inlet opening 10. The inflowing raw product SY_in enters from a lateral position through an opening DN80. In the top flange there is housed the 50kW 17 plasma torch through a refractory hole, for example measuring approximately 50mm. At half of the column, that is of the tubular body 12 (for example at 50cm from the top part) there is positioned an inert bed of particles 14, in particular beads of conductive material, comprising non-catalytic conductive filling material with for example measuring more than 5mm. Such bed 14 evens the temperature, ensures even contact between the molecules and promotes the recombination chemical reactions downstream of the thermal cracking. The bed 14 is housed on a horizontal plate, for example measuring 4mm made of AISI310 DN150 steel with 1000 holes measuring 2mm holes, not visible in figure 2. The catalyst in the bed 28 present in the second reactor R02 tends to become inactive due to coking; as soon as the activity decreases, the decomposition product SY_d coming from the first reactor R01 can be conveyed to a third reactor, not shown in the figure, having the same characteristics as the second reactor R02, that is in particular similar or identical, arranged parallel to the second reactor, so as to allow the intervention of operators to regenerate or change the catalyst.

Bibliographic references

[1] PAOLO DE FILIPPIS, MARCO SCARSELLA, BENEDETTA DE CAPRARIIS, GIANLUCA BELOTTI, TECHNIQUES FOR SAMPLING AND REMOVAL OF TAR AND PARTICULATES CONTAINED IN SYNGAS FROM GASIFICATION OF COAL. UNIVERSITY OF ROME "LA SAPIENZA", DEPARTMENT OF CHEMICAL ENGINEERING MATERIALS ENVIRONMENT, SEPTEMBER 2010

[2] M.L. MASTELLONE. CLEAN ENERGY FROM WASTE (LIBRO). NOVA PUBLISHERS (NEW YORK), 2015, ISBN: 9781634638272 (2015)

[3] MASTELLONE M.L., ARENA U. OLIVINE AS A TAR REMOVAL CATALYST DURING FLUIDIZED BED GASIFICATION OF PLASTIC WASTE, AMERICAN INSTITUTE OF CHEMICAL ENGINEERS J., 54:1656-1667 (2008).

[4] MASTELLONE M.L., ZACCARIELLO L. MATERIAL FLOW ANALYSIS APPLIED TO THE HYDROGEN PRODUCTION BY CATALYTIC GASIFICATION OF PLASTICS. INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, VOL. 38, P. 3621-3629, ISSN: 0360-3199, DOI: HTTP://DX.DOI.ORG/10.1016/J.IJHYDENE.2012.12.111 (2013)

[5] ZEVENHONEN R. E KILPINEN P., CONTROL OF POLLUTANTS IN FLUE GASES AND FUEL GASES, HELSINKY UNIVERSITY OF TECHNOLOGY, ISBN 951-22- 5527-8, 2002

[6] ML MASTELLONE. TECHNICAL DESCRIPTION AND PERFORMANCE EVALUATION OF DIFFERENT PACKAGING PLASTIC WASTE MANAGEMENT'S SYSTEMS IN A CIRCULAR ECONOMY PERSPECTIVE. SCIENCE OF THE TOTAL ENVIRONMENT 718, 137233 (2020)

[7] ARENA U. MASTELLONE M.L. CDR FLUID BED GASIFICATION AND POSTCONSUMPTION PACKAGING, ISBN 978-88-89972-10-6, 2009

Claims

1. A process for converting tar contained in a raw gasification product into synthesis gas, the process comprising the following steps, conducted in series:

2. The process according to claim 1, wherein step (i) is conducted by placing a stream of the raw gasification product in contact with a stream of an ionized plasma at a temperature comprised between 1250 and 1500 °C and a pressure comprised between 30 and 100 mbarg.

3. The process according to claim 1 or claim 2, wherein in step (i) a stream of the raw gasification product comes into contact and mixes with a stream of an ionized plasma at an angle comprised between 70 and 110°.

4. The process according to claim 2 or claim 3, wherein the stream of raw gasification product and the ionized plasma stream flow into the lower section of the first reactor and come into contact with a bed of conductive particulate material having a particle size comprised between 3 and 10 mm and resistant to a temperature comprised between 2000 and 2700 °C.

5. The process according to claim 4, wherein the particulate material comprises silicon carbide.

6. The process according to any one of the preceding claims, wherein step (ii) provides for introducing the decomposition product into the second reactor comprising a metal catalyst bed in particle form, wherein the size of the catalyst particles is comprised between 0.2 and 1 mm.

7. The process according to claim 6, wherein the metal catalyst bed is a fluidized bed.

8. The process according to any one of the preceding claims, wherein step (ii) is conducted at a temperature comprised between 650 and 800 °C and at a pressure comprised between 20 and 100 mbarg.

9. The process according to any one of claims 6 to 8, wherein the metal catalyst is Pt, Sn, Fe and/or Ni- based with Al/Si/Mg support.

10. The process according to any one of the preceding claims, wherein the synthesis gas obtained at the end of the process has a temperature comprised between 650 and 700 °C.

11. Plant for converting tar contained in a raw gasification product into synthesis gas configured to carry out the process according to one of claims 1 to 10, comprising a first and a second reactor, wherein said second reactor is coupled to the outlet of said first reactor, said raw gasification product being introduced into the first reactor at a top or end of the first reactor, in particular a tubular body of the first reactor, said second reactor being coupled to the first reactor in proximity of the respective opposite or lower ends, in particular tubular bodies of the reactors.

12. Plant according to claim 11, wherein said ionized plasma is generated by an electric arc or by a plasma torch, in particular configured to generate said ionized plasma at the top or end of the first reactor.

13. Plant according to claim 11, wherein said first reactor has a tubular body comprising - therein - a bed of particulate material and positioned downstream with respect to the stream of raw gasification product for the inflow of the raw gasification product and said second reactor has a tubular body comprising - therein - a bed of catalytic material positioned upstream with respect to the stream of decomposition product for the outflow of the synthesis gas.

14. Plant according to claim 11, comprising at least one third catalytic decomposition reactor of the decomposition product, in particular similar or identical to the second reactor, arranged parallel to said second reactor.