AT526670A4 - Stair grate for solid fuel counterflow gasifier - Google Patents

Abstract

A system for the thermochemical conversion of solid fuels has a stepped grate (1) with rows of grate elements (3, 4, 5). In the area above the upper end of the stepped grate (1) there is a countercurrent gasifier with a substantially vertically arranged gasifier pipe (22) which forms a gasifier chamber. In the area of the lower end the system has a device for removing ash and in the area under the stepped grate (1) there is a device (27) for supplying gaseous oxidation medium. The stepped grate (1) has rows of movable and non-movable grate elements (3, 4, 5) and two grate sections (1a, 1b) which are approximately A-shaped and particularly preferably symmetrical and are arranged in the area of their upper ends in the central area under the gasifier chamber. The grate sections (1a, 1b) have a top row of movable grate elements (3) at their upper ends and a non-movable gable (2) is arranged in the middle area above.

Description

Supplying gaseous oxidation medium is arranged.

In such gasification plants, biomass, especially wood or other solid fuels, is converted into a combustible product gas (fuel gas) using a gasification or oxidation medium (e.g. air). The gasification process can convert the solid fuel into a gaseous secondary fuel, which, if necessary after appropriate gas purification, can be used more efficiently in various ways, for example as fuel in gas engines, gas turbines or fuel cells, e.g. for power generation or as fuel, or for use as synthesis gas for chemical synthesis. The combustible product gas

can also be burned in a product gas burner.

In particular, the invention comprises a stepped grate with grate elements, which is arranged under a countercurrent gasifier. The countercurrent gasifier has a shaft-shaped reactor which contains the fuel bed and into which the fuel is fed from above by means of a fuel feed and the gasification medium is fed through the stepped grate from below. The fuel bed rests on the grate and is transported downwards by gravity and by the grate movements. The stepped grate is also coupled with a device for removing the solid combustion residues (ash). In addition to supporting the

Fuel bed and transport of the fuel as well as the

responsible.

Due to the opposite direction of movement of the fuel and the gas flow, clearly defined reaction zones are formed within the reactor, in which the respective sub-processes primarily take place. In a countercurrent gasifier shown schematically in Fig. 2a, a characteristic zone profile forms in the fuel bed 101 of the shaft-shaped reactor. The temperature profile over this profile is shown in Fig. 2b. In the uppermost bed area, into which the fuel 108 is fed, there is the drying zone 102, below that the pyrolysis zone 103, below that a gasification zone (also called reduction zone) 104, and above the grate 105 the coal combustion zone (also called oxidation zone) 106. The oxidation reactions of the coal take place in the oxidation zone 106, which forms at the lower end of the reactor where the gasification agent (oxidation medium, e.g. air) 107 is blown in from below. They provide the heat required for drying, heating and gasification of the fuel. The gas is drawn upwards above zone 102, as indicated by arrows 109, and the ash is preferably discharged downwards, as indicated by arrow 110. This typical profile is the result of the gas and fuel being fed in countercurrent. The bed height can be kept stable by measuring the height accordingly, to which the fuel supply responds. The gasifier or shaft-shaped reactor is well insulated to minimize heat losses. In the grate area, the coal is converted into ash by the supply of the oxidation medium.

which is removed at the end of the grate.

In a countercurrent carburetor, a very good combustion can be achieved

of coal. The fuel is practically

of the fuel bed.

Compared to direct current gasifiers, countercurrent gasifiers are characterized by significantly higher fuel flexibility (particularly with regard to particle size and water content), the achievable complete ash burnout, a higher cold gas utilization rate and better scalability. Countercurrent gasifiers are typically available in a power range from a few kW up to around 100 kW.

10 MW fuel heat output is used.

By appropriate control or selection of the oxidation medium, the temperature in the hot coal combustion zone can be controlled and thus ash melting or oxidation can be achieved.

Ash sintering can be prevented.

The object of the invention is to provide a plant with which fuels of different types and qualities, in particular wood, wood residues and wood-containing material, as well as other solid biogenic residues, can be reliably and continuously processed without fluctuations in performance, with high efficiency and high burnout quality of the bottom ash.

can be thermochemically converted.

According to the invention, this is achieved with a system having the features of the

Claim 1 is achieved.

A further object of the present invention is to control the ember bed temperature in the grate area by supplying oxidation medium (e.g. mixture of air and recirculated flue gas or mixture of air and water vapor) in order to prevent ash sintering, depending on the fuel used.

or to avoid ash melting on the grate.

oxidation medium.

The non-movable gable at the top of the stair grate and the top row of movable grate elements underneath enable a very even and symmetrical distribution of the fuel to be converted between the two grate sections, which results in a very

contributes to a smooth process flow.

By supplying the gaseous oxidation medium from below the stair grate through the grate sections upwards and additionally by selecting and dosing the oxidation medium, the temperature of the ember bed can be controlled very precisely in order to prevent ash sintering or ash melting at the

To avoid rust.

In a preferred development of the invention, the ash removal system is essentially gas-tight. A good seal of the ash removal system is important for operational safety and the

Controllability of the system.

In the invention, a stable stratification of the

fuel that does not mix. Below the

from the area under the grate.

It has proven advantageous to design the top element of the grate in the middle of the grate as a kind of gable to divide the fuel for further transport to the left and right. The gable forms a kind of distribution and storage wedge that supports the transport of the fuel or coal downwards with the help of the top grate element. Since the top grate level or row of grates, which is formed by the top row of movable grate elements, pushes the fuel alternately to the two grate sections, the gable arranged centrally above the top grate level acts like a barrier to actually be able to push the fuel further.

and not just move it back and forth.

Although this geometry is of course not mandatory, in a preferred embodiment of the invention the gable has an approximately A-shaped upper part, which preferably has a wedge angle of 30° to 90°, particularly preferably of about 60°. The wedge angle is advantageous because it facilitates the construction of

Prevents ash deposits.

The gable is also preferably water-cooled to protect it from

to protect against high temperatures.

A series of movable grate elements is arranged.

The stationary grate frame is preferably also used to cover all non-

connected to movable grate elements.

In a preferred embodiment of the invention, the opposing grate elements of the top row of the two grate sections are connected to each other. The top row of grates under the gable is thus designed as a kind of double element, which uses the gable to transport the fuel as

Jam wedge distributed on the left and right sides of the grate.

In a preferred development of the invention, the grate elements of the double element can be connected by a common central support part, which can also be connected to a movable grate drive and to a cooling system for the grate frame.

can be connected.

In a further preferred embodiment of the invention, the movable grate drive is formed by a grate carriage, the lifting movement of which is preferably adjustable and constant. This means that the lifting movement preferably takes place over the entire grate at a uniform feed rate. The movement of the grate can be adjusted depending on the power, with a defined movement and pause cycle for each power.

can be set.

In a further preferred embodiment of the invention, at least some of the grate elements, preferably all of the grate elements, are mounted on tubular supports through which a cooling medium flows. The tubular supports

are ideally connected to the cooling of the grate frame,

Stair grate can be cooled easily.

It is particularly preferred if all movable grate elements on one level are moved by a common drive, preferably by the grate carriage. This means that only one side is

pushing, which slows down the sliding of the bed and therefore

the carburettor bed is disturbed as little as possible.

The stair grate consists of several rows of grate elements, whereby preferably every second grate row is connected to the movable grate drive, preferably the grate carriage, and can thus be moved. This means that the top grate row, the

third from the top and so on, movable.

In a further preferred embodiment of the invention, the grate sections each have shorter grate elements in the upper

area and longer grate elements in the lower area.

In a preferred embodiment in this context, a significant advantage of the present invention is that the grate is constructed from three different grate elements, namely the double elements at the top of the grate, so-called burn-off elements, which are formed by the shorter grate elements, and so-called burn-out elements, which are formed by the longer grate elements. The shorter grate elements (burn-off elements) are arranged in the area of the cylindrical gasifier above (center of the grate), and the longer grate elements (burn-out elements) for burning out the coal and removing ash are arranged in the outer area of the grate. The burn-out grate elements are longer. They therefore form a larger support surface on which the bed of fuel or coal can rest. The ash is removed through them. Furthermore, the longer grate elements reduce the residence time of the

Coal on the outer or lower part of the grate is extended and

ensured.

If there are slots between the grate elements, the air supplied from below the grate can

oxidation medium flow.

In a further preferred embodiment of the invention, the slots can be formed in that the grate elements have side walls and that recesses are arranged in the side walls, each of which ends in front of a front and rear end of the grate elements, so that a slot of limited length is formed between two adjacent grate elements, through which the air supplied from below the grate

Oxidation medium can flow.

This creates a defined flow cross-section, while still ensuring that the grate elements can rest against each other at their front and rear ends with their side walls and thus have a defined position in the respective

Grate row is guaranteed.

The grate itself is preferably made of a thermally and chemically resistant material (typically a Cr-Ni steel)

executed.

The countercurrent gasifier has a lower edge, the distance of the lower edge from the grate sections being selected in a preferred embodiment of the invention such that the angle of repose of the fuel, starting from the lower edge, is on the lowest row of grate elements or further above the

respective grate section ends.

This can prevent a so-called “leaking” of the fuel bed

can be prevented by increasing the distance between the lower edge

extends beyond the first burnout element.

The ash that forms on the grate must be regularly removed (discharged) from the gasifier (reactor), as it would otherwise clog the reactor. The higher the ash content of the fuel, the shorter the required

Ash removal cycles.

In known solutions, the grate is opened completely or partially below the reactor at certain intervals when a sufficient amount of ash has accumulated below the ember bed in order to remove the ash. One solution for removing the ash is therefore that the grate has openings through which the ash is discharged downwards, whereby the openings are designed in such a way that the fuel (the coal) is largely retained. Depending on the properties of the fuel and the choice of oxidation medium, however, ash sintering and slag can form on or near the grate due to the high temperatures in the oxidation zone (typically between 800 and 1,100 °C). This means that stable structures are formed in the ember bed that are too large for the grate openings and therefore accumulate in the reactor and lead to problems (agglomerations) in the long term. For example, US 2018/0079978 Al discloses a rotating, circular grate for

a direct current fixed bed gasifier. The grate has slot-shaped

openings through which the ash is discharged downwards. Each opening has a direction from the top to the

The underside of the grate has a conically expanding cross-section.

In a preferred embodiment according to the invention, at the lower end or edge of each grate section there is an ash conveyor screw extending over the entire width of the grate, through which the ash is discharged. In a further, preferred development of the invention, these two screws lead into a common ash collection screw, which can be arranged laterally next to the step grate. At the end of the ash collection screw, below the screw, there is a slider which ensures the tightness of the

carburetor during operation.

In a further development of the invention, which is of course not mandatory, the slide can have an end position monitoring system to ensure tightness. The slide is preferably always arranged horizontally and not covered with ash. When the slide opens at the beginning of an ash removal cycle, the ash collection screw starts moving and conveys ash into the free slide cross-section. This ensures that the slide is not covered with ash (in order to be able to close properly after the ash removal process) and that the ash collection screw remains partially covered with ash due to the short ash removal interval. A rising screw arranged below the slide conveys the

Finally, ash is placed in an ash collection container.

During operation, the opening of the valve can take only a few seconds and can take place every three hours, for example, whereby the exact interval depends on the ash content of the fuel and can be selected. This prevents the entry of false air

during an ash removal cycle,

In a further preferred embodiment of the invention, the under-grate ash is transported away via a cross conveyor into an ash screw arranged on the side. The cross screw can then flow into an inclined screw, which subsequently throws the ash back onto an under-grate ash slider. The under-grate ash reaches one of the ash conveyor screws through this slider, from where it is transported further. The under-grate ash removal can, for example, only be activated once after ten normal ash removal cycles, since under the

Rust collects significantly less ash.

In yet another preferred embodiment of the invention, the device for supplying gaseous oxidation medium has a connection for air and recirculated flue gas. The oxidation medium is preferably supplied centrally under the grate via a mixing pipe and flows out from under the grate. This allows a reliable supply of the entire gas above the grate.

Fuel bed with oxidation medium must be ensured.

The controlled addition of recirculated flue gas to the gasification air changes the oxygen partial pressure of the mixture (the oxidation medium), which slows down the coal combustion and reduces the temperatures in the ember bed. This ensures a defined ember bed temperature. The temperature of the ember bed is

preferably between 800 °C and 1,000 °C.

This is done to control the temperature of the ember bed and thereby prevent sintering or slagging of the ash. The mixture of the oxidation medium can be varied depending on the fuel composition. The regulation of the addition of recirculated flue gas is carried out

preferably via a valve, in particular a flap, and

a defined differential pressure that corresponds to the volume flow.

Temperature monitoring is carried out, for example, by two thermocouples that are arranged above the grate in the ember bed area. If a defined temperature is exceeded there, the amount of recirculated flue gas in the

Oxidation medium increased.

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention, which does not limit the scope of protection, under

Reference to the attached drawings. It shows:

Fig. 1 is a sectional view of an exemplary embodiment of the invention,

Fig. 2a is a schematic representation of a countercurrent carburetor.

Fig. 2b a temperature profile over the zones of the carburetor,

Fig. 3 is a side view of a stair grate according to the invention,

Fig. 4 a sectional view of the uppermost part of the stair grating,

Fig. 5a, 5b and 5c external views of the invention including ash removal devices,

Fig. 6a, 6b and 6c an oblique view, a view from above and a side view of the double element at the grate tip,

Fig. 7a, 76 and 7c oblique views, a view from above and a side view of a combustion element of the stair grate,

Fig. 8a, 8b and 8cC show an oblique view, a view from below and a side view of a burn-out element of the stair grate, and

Fig. 9a and 9b a side view and a top view of the

Mixing tube for supplying the oxidation medium.

The drawings show an embodiment of a device according to the invention, which is, however, only an example and, apart from the features according to the invention as defined in the claims, can also be designed differently with regard to many components within the scope of the present invention, without this being a requirement of

requires special mention.

Fig. 1 shows a sectional view of an exemplary embodiment of the lower part of a system according to the invention with a symmetrical stair grate 1 and Fig. 3 a

Oblique view of the stair grating 1 of Fig. 1.

The stair grate 1 has two grate sections 1a, 1b, which are A-shaped and symmetrically arranged, and in the area of their upper ends in the middle area under a carburetor chamber of the

Countercurrent carburetor with a carburetor tube 22.

In the uppermost area of the stepped grate 1, in which the two grate sections 1a, 1b are brought together, a gable 2 is designed in the middle of the grate to divide the fuel to the left and right. The gable 2 is water-cooled to protect it from excessively high temperatures and has an A-shaped upper part 2', which preferably has a wedge angle x of 30° to 90°, particularly preferably of about 60°, in order to facilitate the build-up of

To prevent ash deposition.

Fig. 4 shows a sectional view of the uppermost area of the stair grating 1. The gable 2 is firmly connected to a stationary grating frame 16 and is arranged centrally above the uppermost grating level, which is formed by double grating elements 3. In the embodiment of the invention shown, the double grating elements 3 are essentially like two grating elements 3'

which are also in the underlying grate levels

used, but at their ends facing each other

are connected to each other.

The entire step grate 1 in the embodiment shown is essentially made up of three different grate elements, namely the double elements 3 at the grate tip or the upper grate end, grate elements 4 as so-called burn-off elements under the preferably essentially cylindrical gasifier tube 22, and longer grate elements 5 as so-called burn-out elements in the lower, outer area of the step grate for burning out the coal and for

Ash removal.

Fig. 6a, 6b and 6c show a sectional view, a view from below and side views of the double grate element 3, which

forms the top grate level.

Fig. 7a, 7b and 7c show a sectional view, a view from below and side views of a grate element 4, which in the context of the invention described here can also be used as a combustion element

referred to as.

Finally, Fig. 8a, 8b and 8c show a sectional view, a view from below and side views of a grate element 5, which in the context of the invention described here can also be used as

Burnout element is called.

The double grate elements 3, which are arranged in the top row of grates under the gable 2, distribute the fuel to the left and right sides of the grate with the help of the gable 2 as a retaining wedge. The double grate elements 3 have a common, central support part 3'', via which the grate elements 3', which are assigned to the respective grate sections 1a, 1b, are connected to one another. The support part 3'' is connected to

a movable grate drive, the so-called grate carriage 7,

The support part 3'' is U-shaped in the embodiment shown in the drawings and is placed on the brackets 6 from above. The grate elements 3', like the grate elements 4 and 5, have a front, rounded end 8 with which they rest and slide on the surface 9 of the grate element 4, 5 located underneath.

The burnout grate elements 5 are longer than the grate elements 3' and the burnout elements 4, but are otherwise essentially designed in the same way. The burnout grate elements 5 therefore form a larger support surface than the burnout elements 4, so that the bed of fuel can be better supported on the burnout grate elements 5 and the ash feed is also more efficient. Furthermore, the longer grate elements 5 extend the residence time of the coal in the outer area of the grate and thus

complete burnout of the coal is ensured.

The grate elements 4 and 5 also have a support part 10 which is U-shaped. The movable grate elements 4 and 5 are

from above onto the brackets 6 of the grate carriage 7

The non-movable grate elements 4, 5 are placed on tubular brackets 11 in such a way that a good heat-conducting connection is present between the support parts 10 and the tubular brackets 11. These tubular brackets 11 are ideally connected to a cooling system of the grate frame 16 and are flowed through by a cooling medium, e.g. water. A separate supply of cooling water would, however, be

of course also possible.

As can be seen in Figs. 6, 7 and 8, all grate elements 3, 4, 5 have side walls 12 on which recesses 13 are arranged, with side walls 12 remaining at their rear end in the area of the support parts 3°, 10 on the one hand and the front ends 8 on the other hand, so that between each two

A slot of limited length is formed between adjacent grate elements

is fed from below the grate through the

Oxidation medium can flow.

In addition, the grate elements 3, 4, 5 have, at least in the region of the lateral recesses, a cross-section tapering downwards, which in the embodiment shown is arranged by a narrow web 14 under the plate forming the surface 9 of the grate elements 3, 4, 5, and the

Falling through of ash particles is made easier.

The two grate sections 1a, 1b of the stair grate 1 each consist of several grate rows, whereby only every second grate row is connected to the movable grate carriage 7 and can thus be moved. The top grate row is movable, the

third from the top as well and so on.

All slatted elements 3, 4, 5 on a movable level are moved by the common slatted carriage 7. This means that only one side is sliding at a time, which prevents the bed from sliding down as a whole.

slower and therefore disturbs the carburettor bed less.

The countercurrent gasifier has an insulated gasifier tube 22, which can be cylindrical or polygonal (e.g. octagonal), and which has a lower edge 15, which is preferably located above the transition area from the grate rows with the shorter combustion elements 4 to the grate rows with the longer combustion elements 5. The distance between the lower edge 15 of the gasifier tube and the grate is dimensioned such that the angle of repose of the fuel bed (usually in a range of 35-45°) is in the area of the lowest or second or penultimate row of combustion elements, thus preventing the particles from running over the lowest edge 15 of the grate.

can be.

Fig. 5a to 5c show external views of the system according to the invention with an ash removal system. At the lower end of each grate section 1a, 1b, to the left and right below the last row of grates, there is an ash screw 23, through which the ash is discharged, and which extends over the entire width of the grate. These two ash screws 23 open into a common ash collection screw 24, which is arranged laterally outside and next to the housing of the system. At the end of the ash collection screw 24, below the screw, there is an ash slide 21, which ensures the tightness of the system during

operation.

The ash slide 21 is preferably arranged horizontally and not covered with ash. When the ash slide 21 opens at the beginning of an ash removal cycle, the ash collection screw 24 starts moving and conveys ash into the free slide cross-section. This ensures that the ash slide 21 is not covered with ash (in order to be able to close properly after the ash removal process) and that the ash collection screw 24 does not remain covered with ash by a suitably short ash removal interval. A rising screw 25 arranged below the slide 21 conveys

the ash finally into an ash collection container.

Ash that can fall through the slots between the grate elements 3, 4, 5 and is referred to as under-grate ash is transported away in the embodiment of the invention shown via a cross conveyor 17 into a laterally arranged under-grate ash screw 18. The under-grate ash screw 18 then flows into a under-grate inclined screw 19, which then throws the ash back onto a under-grate ash slider 20. The under-grate ash reaches one of the ash screws 23 arranged along the grate through this slider, from where it is transported further

For example, the under-grate ash removal can only be carried out after

10 normal ash removal cycles must be activated once, as

significantly less material collects under the grate.

9a and 9b show a side view and a top view of a mixing tube 27 which serves as a device for supplying gaseous oxidation medium. The mixing tube 27 has a connection for a supply tube 28 for air and a connection for a supply tube 29 for recirculated flue gas. The oxidation medium is supplied via this mixing tube 27 centrally under the grate and flows out from there under the step grate 1. The oxidation medium normally consists of a mixture of air and recirculated flue gas. A good mixture of the air with the recirculated flue gas is ensured via the mixing tube 27, which ensures that the recirculated flue gas is very well mixed into the combustion air before the oxidation medium exits into the space under the step grate 1. The recirculated flue gas flows axially into the mixing tube via a thinner supply tube 29. The air flows into the mixing tube 27 via a wider feed pipe 28, which is offset by 90° to supply the recirculated flue gas. The inlet openings offset by 90°, the choice of the diameters of the two inlet openings and the mixing section after the inlet openings result in a very good mixing of air and recirculated flue gas. The mixture then enters the space under the stair grate 1 via downward-facing outlet openings 30 of the mixing tube. This good mixing ensures that no streaks of air or recirculated flue gas form under the grate, which could have a negative effect on the local combustion conditions of the coal on the grate, and that the oxidation medium

is well and evenly distributed in the space under the grate.

Through the controlled addition of recirculated flue gas to the

Gasification air changes the oxygen partial pressure of the

Mixture (of the oxidation medium), which slows down the combustion of the fuel and reduces the temperatures occurring in the ember bed. In this way, a defined ember bed temperature can be ensured. The temperature of the ember bed is preferably between 800 and 1,000 °C in order to avoid sintering or slagging of the ash. It can be varied depending on the fuel composition. The regulation of the admixture of recirculated flue gas takes place via a valve, in particular a flap, and a defined differential pressure that corresponds to the volume flow.

Finally, Fig. 1 shows the preferred locations for temperature measurements in the ember bed area near the grate. For example, two thermocouples 31 can be arranged there. If a critical temperature (e.g. 1,000 °C) is exceeded at these points, the proportion

of recirculated flue gas in the oxidation medium.

The casing of the grate area 26 is insulated to minimize heat loss to the outside. Preferably, a multi-layer insulation structure is used (e.g. refractory concrete,

Insulating concrete, ceramic wool, sheet metal casing).

List of reference symbols:

1 stair grate

la grate section

1b Grate section

2 gables

2) Top

3 Double grate element

3" top grate element

3' support part

4 shorter grate element 5 longer grate element 6 tubular bracket 7 grate trolley

8 front end

9 Surface

10 Support part 11 Tubular bracket 12 Side wall

13 Recess

14 Bridge

15 Edge of the counterflow carburetor

16 Grate frame with grate frame cooling 17 Cross conveyor

18 Sub-grate ash auger

19 Under grate inclined auger

20 under-grate ash scrapers

21 Ash scraper

22 Carburettor pipe of the counterflow carburettor including lining 23 Ash screw

24 Ash collection screw

25 Ascending screw

26 Coating of the grate area

27 Mixing tube

28 Air supply pipe

101 102 103 104 105 106 107 108 109 110

21

Supply pipe for recirculated flue gas Outlet openings for the oxidation medium

Thermocouples

Fuel bed

Drying zone

Pyrolysis zone

Gasification zone

Rust

Coal combustion zone, oxidation zone, oxidant supply, fuel supply

Gas removal

Ash removal

Wedge angle

Claims (1)

Patent claims: 1. Plant for the thermochemical conversion of solid fuels, with a stepped grate (1) with rows of grate elements (3, 4, 5), wherein in the area above the upper end of the stepped grate (1) a countercurrent gasifier with a substantially vertically arranged gasifier pipe (22) is arranged, which forms a gasifier chamber, wherein the plant has a device for removing ash in the area of the lower end, and wherein in the area under the stepped grate (1) a device (27) for supplying gaseous oxidation medium is arranged, characterized in that the stepped grate (1) has rows of movable and non-movable grate elements (3, 4, 5), that the stepped grate (1) has two grate sections (la, 1b) which are arranged approximately in an A-shape and particularly preferably symmetrically, and are arranged in the area of their upper ends in the middle area under the gasifier chamber, that the grate sections (la, 1b) have an uppermost row of movable grate elements (3) at their upper ends and that in the middle area above a non movable gable (2) is arranged. 2. Installation according to claim 1, characterized in that opposing grate elements (3') of the uppermost row of the both grate sections (la, 1b) are connected to each other. 3. Installation according to claim 2, characterized in that the gable (2) in the central region extends over the interconnected grate sections (la, 1b) of the top row. 4. Installation according to one of claims 1 to 3, characterized in that the gable (2) has an A-shaped upper part (2°), which preferably has a wedge angle (x) of 30° to 90°, particularly preferably 60°. 23 Installation according to one of claims 1 to 4, characterized in that the grate sections (la, 1b) each have shorter grate elements (4) in the upper region and longer Grate elements (5) in the lower area. Plant according to claim 5, characterized in that the shorter grate elements (4) are arranged in an area under the countercurrent carburetor, and that the longer grate elements (5) are arranged in an area which is not below the countercurrent carburetor. Installation according to one of claims 1 to 6, characterized in that the grate elements (3, 4, 5) have side walls (12), and in that recesses (13) are arranged in the side walls (12), each of which ends in front of a front and rear end of the grate elements (3, 4, 5), so that a slot of limited length is formed between two adjacent grate elements (3, 4, 5), through which oxidation medium supplied from below the grate can flow. can. Installation according to one of claims 1 to 7, characterized by a stationary grate frame (16) to which all non-movable grate elements (4, 5) and the gable (2) are connected are. Installation according to one of claims 1 to 8, characterized in that all movable grate elements (3, 4, 5) of a level are driven by a common drive, preferably by a grate trolley (7). Installation according to one of claims 1 to 9, characterized in that at least some of the grate elements (4, 5) are mounted on tubular supports (11) which are through which a cooling medium flows. 12. 13. 14. 15. 16. 24 Plant according to claim 10, characterized in that further Brackets (6) are arranged on the movable grate carriage. Installation according to one of claims 9 to 11, characterized in that the lifting movement of the grate carriage (7) adjustable and preferably constant. Plant according to one of claims 1 to 12, characterized in that the device (27) for supplying gaseous oxidation medium has a connection for air and recirculated flue gas. Installation according to one of claims 1 to 13, characterized by at least one thermocouple (31), preferably two thermocouples (31), above the stair grate (1), one of which is arranged above a grate section (la, 1b), the thermocouple (31) or the thermocouples (31) being connected to a control device which is provided with a valve for controlling the supply of recirculated Flue gas is connected to the device (27). Installation according to one of claims 1 to 14, characterized in that the gasification tube (22) of the countercurrent gasification has a lower edge (15), and that the distance of the lower edge (15) from the grate sections (la, 1b) is selected such that the angle of repose of the fuel, starting from the lower edge (15), on the lowest row of grate elements (5) or further above the respective grate section (la, 1b) ends. Installation according to one of claims 1 to 15, characterized marked that at the bottom of each Grate section (la, 1b) One each extending over the entire 18. 19. 20. 21. 22. 25 The ash conveyor screw (23) extending across the grate width is over which the ashes are carried out. Plant according to claim 16, characterized in that the both ash conveyor screws (23) into a common Ash collection screw (24) which is located at the side Staircase grate is arranged. Plant according to claim 17, characterized in that the end of the ash collecting screw (24) is an ash pusher which protects the system during operation Plant according to one of claims 16 to 18, characterized in that a cross conveyor (17) is arranged below the step grate, to which a sub-grate ash screw (18) is connected, that the sub-grate ash screw (18) opens into a sub-grate screw (19) which throws the ash onto a sub-grate ash (20), and that the sub-grate ash pusher feeds sub-grate ash into one of the ash screws (23). arranged along the grate. Installation according to claim 18 or 19, characterized in that a below the ash slide (21) arranged Ascending screw (25) the ash into an ash container in the that is sealed on he (21). H (1) a ägschnecke heschieber (20) the calls for the ichnet that e he promotes. Installation according to one of claims 16 to 20, that the Facility for the removal of ash in the main is gas-tight. Process according to claims 1 to 21, characterized characterized in that a coating of the grate is insulated. chen oak (26)