Stage fire grid for solid fuel fluidized gas furnace

Abstract

To provide equipment capable of thermochemical conversion of various types and qualities of fuel.SOLUTION: Equipment for thermochemical conversion of solid fuel comprises a stage grate 1 having lows of grate elements 3, 4, 5. A counter-current gasification furnace has a gasification furnace pipe 22 forming a gasification furnace chamber and arranged substantially vertically, and the counter-current gasification furnace is arranged in an area above the stage grate 1. The equipment has a device for removing ash in a lower end area, and a device 27 for supplying a gaseous oxidizing medium is arranged in a lower area of the stage grate 1. The stage grate 1 has the lows of movable and immovable grate elements 3, 4, 5, and two grate sections 1a, 1b. The grate sections are arranged in an approximately A-shape, particularly preferably symmetrically in a lower end area thereof in a central area below the gasification furnace chamber. The grate sections 1a, 1b, on their upper ends, have an upper end low of movable grate elements 3, and an immovable gable 2 is arranged in the central area thereabove.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an installation for the thermochemical conversion of solid biomass fuel or other solid fuel, having a step grate with an array of grate elements, wherein a countercurrent gasifier having a substantially vertically arranged gasifier chamber is arranged in the upper end region of the step grate, the installation has a device for removing ash in the lower end region, and a device for supplying a gaseous oxidizing medium is arranged in the lower end region of the step grate. [Background technology]

[0002] In such gasification facilities, biomass, particularly wood or other solid fuels, are converted into combustible product gas (fuel gas) with the aid of a gasification or oxidizing medium (e.g., air). Gasification converts the solid fuel into a gaseous secondary fuel, which, after appropriate gas purification if necessary, can be used more efficiently in various applications, such as as fuel for gas engines, gas turbines, and fuel cells, for example for power generation or as fuel, or as syngas for chemical synthesis. The combustible product gas can also be combusted in a product gas burner.

[0003] In particular, the present invention provides a staged grate having grate elements disposed below a counterflow gasifier. The counterflow gasifier has a funnel-shaped reactor containing a fuel bed, to which fuel is supplied from above by a fuel supply means and a gasification medium is supplied from below through the staged grate. The fuel bed rests on the grate and is carried downward by gravity and the movement of the grate. The staged grate is also connected to a device for removing solid combustion residues (ash). In addition to supporting the fuel bed and transporting the fuel and thermally indecomposable ash, the grate also serves to uniformly distribute the gasification medium throughout the cross section of the gasifier.

[0004] The opposing flow of fuel and gas creates clearly defined reaction zones within the reactor, where each subprocess primarily occurs. In a counterflow gasifier, as shown diagrammatically in Figure 2a, a distinctive zone profile is formed in the fuel bed 101 of the shaft-shaped reactor. The temperature gradient across this profile is shown in Figure 2b. The uppermost bed region, where fuel 108 is supplied, contains a drying zone 102, a pyrolysis zone 103 below it, a gasification zone (also called a reduction zone) 104 below it, and a coal combustion zone (also called an oxidation zone) 106 above a grate 105. The oxidation reaction of coal occurs in the oxidation zone 106, formed at the lower end of the reactor, where a gasifying agent (oxidizing medium, e.g., air) 107 is injected from below. The above reactions provide the heat necessary for drying, heating, and gasifying the fuel. Gas is withdrawn upward from zone 102, as indicated by arrow 109, and ash is preferably discharged downward, as indicated by arrow 110. This typical profile is due to the countercurrent gas and fuel feed. The bed height can be kept stable by measuring the corresponding height at which the fuel feed reacts. The gasifier or funnel reactor is well insulated to minimize heat losses. In the grate area, the coal is converted to ash by the oxidizing medium feed, which is removed at the grate end.

[0005] Therefore, very good combustion of coal is possible in a counterflow gasifier: the fuel is almost completely converted into combustible gases, which are discharged from the top of the fuel bed.

[0006] Compared to parallel-flow gasifiers, counter-flow gasifiers are distinguished by significantly greater fuel flexibility (especially with regard to particle size and moisture content), more complete ash combustion, higher cold gas utilization, and greater scalability. Counter-flow gasifiers typically range from a few kW to about 10 Used in the MW fuel heat output range.

[0007] The temperature of the hot coal combustion zone can be controlled and by proper control or selection of the oxidizing medium, ash melting or ash sintering can be prevented. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide an installation capable of reliably thermochemically converting fuels of various types and qualities, in particular wood, wood residues and wood-containing materials, as well as other solid biological wastes, in a continuous process without fluctuations in performance, with high efficiency and high combustion quality of the bottom ash. [Means for solving the problem]

[0009] According to the invention, this is achieved by a system with the features of claim 1.

[0010] A further object of the present invention is to control the ember bed temperature in the grate area via the supply of an oxidizing medium (e.g. a mixture of air and recirculated exhaust gas or a mixture of air and steam) in order to avoid ash sintering or ash melting on the grate, depending on the fuel used.

[0011] The present invention uses a step grate having a row of movable and a row of non-movable grate elements, the step grate elements having two grate sections arranged symmetrically, preferably in an approximately A-shape, with the sections arranged at their upper ends in a central region below the gasifier chamber. The grate sections have an upper row of movable grate elements at their upper ends, with a non-movable gable arranged above in the central region. The system also has an ash removal system in the region of the lower ends of the grate sections and a device for supplying a gaseous oxidizing medium to the region below the step grate.

[0012] The non-movable gables at the top of the step grate and the top row of movable grate elements below them allow for a very even and symmetrical distribution of the fuel being converted over the two grate sections, which contributes to a very uniform process flow.

[0013] By supplying a gaseous oxidizing medium from below the step grate and upward through the grate section, and by selecting and metering the oxidizing medium, the temperature of the ember bed can also be controlled very precisely to avoid ash sintering on the grate or ash melting.

[0014] In a preferred further development of the invention, the ash removal system is essentially gas-tight. Good gas-tightness of the ash removal system is important for the operational safety and controllability of the system.

[0015] In the system according to the invention, a stable stratification of fuel (i.e., layers do not intermix) is formed during continuous operation. Beneath the actual ember bed, a narrow layer containing non-pyrolyzable ash components forms, which will hereafter be referred to as ash for short. By moving the step grate via a suitable drive, the fuel or coal is transported towards the lower end of the grate, thereby simultaneously completing the conversion of the fuel or coal, and the remaining ash is finally discharged through the outlet at the end of the grate. Since a small amount of ash may also fall through the grate (grate opening), it is desirable to remove ash from the area below the grate as well.

[0016] It has been found to be advantageous to design the upper grate element in the middle of the grate as a kind of gable for further transporting fuel to the left and right. The gable forms a kind of distribution and accumulation wedge, which aids in the downward transport of fuel and coal with the help of the upper grate element. The uppermost grate level or grate row formed by the row of uppermost movable grate elements pushes fuel alternately into the two grate sections, so that the uppermost grate level The centrally located gable acts as a barrier that actually pushes the fuel further rather than simply moving it back and forth.

[0017] Although this shape is not essential, in a preferred embodiment of the invention the gable has a generally A-shaped upper part, preferably with a wedge angle of 30° to 90°, particularly preferably about 60°, which is advantageous in terms of preventing ash accumulation.

[0018] The gables are also preferably water-cooled to protect against excessively high temperatures.

[0019] The gable is preferably rigidly connected to the grate frame and is centrally located above the top grate level formed by the top row of movable grate elements.

[0020] Preferably, all non-movable grate elements are also connected to the stationary grate frame.

[0021] In a preferred embodiment of the invention, the opposing grate elements of the top stages of the two grate sections are connected to each other, so that the top stage of the grate below the gable is designed as a kind of double element, with the gable acting as a collecting wedge to distribute fuel to the left and right sides of the grate.

[0022] In a preferred further development of the invention, the double-element grate elements can be connected by a common central support, which can also be connected to the movable grate drive and to a cooling device for the grate frame.

[0023] In a further preferred embodiment of the invention, the movable grate drive is formed by a grate carriage, the stroke movement of which is preferably adjustable and constant, i.e. the stroke movement is preferably performed over the entire grate at a uniform feed rate. The grate movement can be adjusted depending on the power output, and for each power output, predetermined movement and rest cycles can be specifically specified.

[0024] In a further preferred embodiment of the invention, at least some of the grate elements, preferably all of them, are mounted in tubular fittings through which a cooling medium flows, which are ideally connected to the cooling system of the grate frame, as is preferred in the invention, so that the entire step grate can be cooled in a simple manner.

[0025] It is particularly preferred if all the movable grate elements on one level are driven by a common drive, preferably a grate carriage, as this method pushes only one side at a time, slowing down the hearth slide and disturbing the gasification hearth as little as possible.

[0026] The step grate is made up of a number of rows of grate elements, whereby preferably every second row of grate elements is connected to a movable grate drive, preferably a grate carriage, and thus can be moved, so that the top row, the third row from the top, etc. can be moved.

[0027] In a further preferred embodiment of the invention, the grate sections each have short grate elements in their upper region and long grate elements in their lower region.

[0028] In a preferred embodiment in this context, an important advantage of the invention is that the grate is made up of three different grate elements: a double element at the grate tip, a so-called burn-off element formed by short grate elements, and a so-called burn-out element formed by long grate elements. Located in the upper region of the cylindrical gasifier (grate center), long grate elements (burnout elements) are located in the outer regions of the grate to burn the coal and remove the ash. The burnout grate elements are longer. Therefore, these longer grate elements provide a larger support surface for the fuel and coal. The ash passes through the grate elements and is removed. Furthermore, the longer grate elements increase the residence time of the coal in the outer or lower regions of the grate, thereby ensuring more complete combustion of the fuel.

[0029] If there are slots between the grate elements, the oxidizing medium supplied from below the grate can flow through the slots.

[0030] In a further preferred embodiment of the invention, the slots can be formed in such a way that the grate elements have side walls in which are arranged a number of recesses, each terminating in front of the front and rear ends of the grate element, so that a slot of limited length is formed in each case between two adjacent grate elements, through which the oxidizing medium supplied from below the grate can flow.

[0031] This allows the grate elements to abut each other with their side walls at their front and rear ends, thus ensuring a well-defined position in each grate row while creating a well-defined flow cross section.

[0032] The grate itself is preferably made of a thermally and chemically resistant material (typically Cr-Ni steel).

[0033] The countercurrent gasifier has a lower edge, the distance of which from the grate section is selected in a preferred embodiment of the invention so that the angle of repose of the fuel starting from the lower edge ends on the bottom row of grate elements or further above the respective grate section.

[0034] This can prevent the fuel bed from "spilling over" by reducing the distance between the lower edge of the counterflow gasifier, particularly the gasifier tubes, and the grate so that the fuel bed can rest well within the angle of repose on the lowest, second, or penultimate row of burnout elements, thereby reliably preventing particles from spilling over the bottom edge of the grate. In other words, the distance between the lower end of the gasifier tubes and the grate is designed so that the angle of repose of the coal bed (usually in the range of 35 to 45 degrees) typically does not extend beyond the first burnout element.

[0035] The ash that forms on the grate must be periodically removed (drained) from the carburetor (reactor) or it will clog the reactor. The higher the ash content of the fuel, the shorter the ash removal cycle required.

[0036] In known solutions, the grate is opened completely or partially below the reactor at regular intervals to allow ash to be discharged when a sufficient amount of ash has accumulated below the ember bed. One solution for ash discharge is to provide openings in the grate through which the ash can be discharged downwards, designed to retain a large portion of the fuel. However, depending on the fuel characteristics and the choice of oxidizing medium, the high temperatures prevailing in the oxidation zone (typically 800-1100°C) can lead to ash sintering and slagging on or near the grate. This means that stable structures that are too large for the grate openings form in the ember bed, leading to accumulation of such structures within the reactor and long-term problems (agglomeration). For example, U.S. Patent Application Publication No. 2018 / 0079978A1 discloses a rotating circular grate for a co-flow fixed-bed gasifier. The grate has slot-like openings through which ash can be discharged downwards. The cross section of each opening is 1 / 2" wide, from the top of the grate to the bottom of the grate. It widens conically from the top to the bottom.

[0037] In a preferred embodiment of the present invention, the lower end or edge of each grate section has an ash conveyor screw that extends across the entire width of the grate, and ash is discharged through this screw. In a further preferred embodiment of the present invention, these two screws lead to a common ash collection screw, which can be arranged next to each other on the side of the step grate. At the end of the ash collection screw, there is a slide below the screw to ensure the gasifier is airtight during operation.

[0038] In a further development of the invention, which is clearly not mandatory, the slide can also be equipped with an end position monitor to ensure airtightness. It is desirable that the slide is always positioned horizontally and not covered with ash. When the slide opens at the start of the ash removal cycle, the ash collection screw starts moving and transports the ash to the free cross section of the slide. This ensures that the slide is not covered with ash (and therefore can be properly closed after the ash removal process) and that the ash collection screw remains partially covered with ash due to the short ash removal interval. Finally, a lifting screw arranged below the slide transports the ash to the ash collection container.

[0039] During operation, the slide only needs to be opened for a few seconds, for example every three hours, the exact interval being selectable depending, for example, on the ash content of the fuel, thereby minimizing accidental air entrainment during the ash removal cycle.

[0040] In a further preferred embodiment of the present invention, the ash at the bottom of the grate is transported via a cross conveyor to a transversely disposed ash screw. The transverse screw then leads to an inclined screw conveyor, which then discharges the ash onto an under-grate ash slide. The ash at the bottom of the grate passes through this slide and onto one of the ash conveyor screws for further transport. Because so little ash collects below the grate, the under-grate ash removal system only needs to be operated once, for example, after 10 normal ash removal cycles.

[0041] In yet another preferred embodiment of the invention, the device for supplying a gaseous oxidizing medium has respective connections for air and recirculated exhaust gas. The oxidizing medium is preferably supplied centrally below the grate through the mixing tubes and exits the mixing tubes below the grate, thereby ensuring that the oxidizing medium is supplied to the entire fuel bed above the grate.

[0042] By controlling the addition of recirculated exhaust gas to the gasification air, the oxygen partial pressure in the mixture (oxidizing medium) is changed, which slows down the burn-off of the coal and reduces the temperature that occurs in the ember bed. This ensures a defined temperature in the ember bed. The temperature of the glowing bed is preferably between 800°C and 1000°C.

[0043] This is done to control the temperature of the ember bed and to avoid ash sintering and slagging. The mixture of oxidizing media can be varied depending on the fuel composition. The mixing of the recirculated exhaust gas is preferably controlled via a valve, in particular a flap, and via a defined pressure difference corresponding to the volumetric flow rate.

[0044] The temperature is monitored, for example, via two thermocouples located above the grate in the ember bed area, where exceeding a certain temperature leads to an increase in the amount of recirculated exhaust gas in the oxidizing medium.

[0045] Further features and advantages of the invention can be seen from the following description of preferred embodiments of the invention, with reference to the attached drawings, which do not, however, limit the scope of protection of the invention. do. [Brief explanation of the drawings]

[0046] [Figure 1] 1 is a cross-sectional view of an exemplary embodiment of the present invention; [Figure 2a] FIG. 1 is a schematic diagram of a counterflow gasifier. [Figure 2b] FIG. 1 shows the temperature profile across each zone of the gasifier. [Figure 3] 1 is a side view of a step grate according to the present invention; [Figure 4] FIG. 2 is a cross-sectional view of the top region of the stage grate. [Figures 5a-5c] FIG. 1 is an external view of the present invention including an ash removal element. [Figures 6a-6c] 1A and 1B are perspective, top and side views of the dual element upper grate; [Figures 7a-7c] 1A and 1B are perspective, top, and side views of a burn-off element of a step grate; [Figures 8a-8c] 1A and 1B show a perspective view, a bottom view, and a side view of a burnout element of a step grate. [Figure 9a-9b] 1A and 1B are side and top views of a mixing tube for supplying an oxidizing medium.

[0047] The drawings show one embodiment of the device according to the invention, but this is merely exemplary, and apart from the features according to the invention defined in the claims, different designs of many components are possible within the scope of the invention and need not be mentioned specifically below. DETAILED DESCRIPTION OF THE INVENTION

[0048] Figure 1 shows a cross-section of an exemplary embodiment of the lower part of an installation according to the invention with a symmetrical step grate 1. Figure 3 shows a perspective view of the step grate 1 of figure 1.

[0049] The step grate 1 has two grate sections 1a and 1b, which are arranged symmetrically in an A-shape, and the upper end region thereof is located in the central region below the gasification furnace chamber of the counterflow gasification furnace having the gasification furnace tubes 22.

[0050] At the top of the step grate 1, where the two grate sections 1a and 1b join, a gable 2 is designed in the center of the grate to separate the fuel into left and right halves. The gable 2 is water-cooled to protect it from excessive heat and has an A-shaped upper part 2' with a wedge angle α of preferably 30° to 90°, particularly preferably about 60°, to prevent ash accumulation.

[0051] 4 shows a cross-section of the top region of the step grate 1. The gable 2 is rigidly connected to the stationary grate frame 16 and is centrally located above the top grate level formed by the double grate element 3. In the illustrated embodiment of the invention, the double grate element 3 is essentially designed as two grate elements 3' that are also used in the grate level below, connected to each other at their opposite ends.

[0052] In the illustrated embodiment, the entire step grate 1 essentially consists of three different grate elements: a double element 3 at the grate tip or upper end of the grate, a grate element 4 as a so-called burn-off element below the preferably essentially cylindrical gasifier tubes 22, and a longer grate element 5 as a so-called burn-out element in the outer region below the step grate for burning the coal and removing the ash.

[0053] Figures 6a, 6b and 6c show a cross section, a view from below and a side view of the double grate element 3 forming the top grate level.

[0054] 7a, 7b and 7c show a cross-section, a bottom view and a side view of the grate element 4. 1 shows a grate element 4, which in the context of the invention described herein is also called a burn-off element.

[0055] Finally, Figures 8a, 8b and 8c show a cross-sectional view, a bottom view and a side view of a grate element 5, which in the context of the invention described herein is also called a burnout element.

[0056] The double grate element 3 is located below the gable 2, in the top row of the grate, and distributes fuel to the left and right of the grate with the help of the gable 2 as a collecting wedge. The double grate element 3 has a common central support 3″, through which the grate elements 3′ assigned to each grate section 1a, 1b are connected to one another. The support 3″ is connected to a movable grate drive, or so-called grate carriage 7, via a tubular mounting 6. In the embodiment shown in the drawings, the support 3″ is U-shaped and attached to the mounting 6 from above. Like the grate elements 4 and 5, the grate element 3′ has a front rounded end 8 that rests and slides on the surface 9 of the underlying grate elements 4, 5.

[0057] Burnout grate element 5 is longer than grate element 3' and burnoff element 4, but otherwise has essentially the same design. Burnout grate element 5 therefore provides a larger support surface than burnout element 4, allowing the bed of fuel to be better supported on burnout grate element 5 and more efficient ash delivery. Furthermore, the longer grate element 5 increases the residence time of the coal in the outer regions of the grate, ensuring that the coal is completely burned out.

[0058] The grate elements 4 and 5 also have U-shaped supports 10. The mobile grate elements 4 and 5 are attached to mounting parts 6 of a grate carriage 7 from above.

[0059] The non-movable grate elements 4, 5 are mounted in tubular fittings 11 so that there is a good thermally conductive connection between the support part 10 and the tubular fittings 11. Ideally, these tubular fittings 11 are connected to the cooling system of the grate frame 16, and a cooling medium, for example water, flows through the tubular fittings 11. However, it is of course also possible to provide the cooling water separately.

[0060] As can be seen in Figures 6, 7 and 8, all grate elements 3, 4, 5 have side walls 12 in which recesses 13 are arranged, which side walls 12 still remain at their rear ends in the region of the supports 3", 10 on the one hand, and at their front ends 8 on the other hand, so that slots of limited length are formed between every two adjacent grate elements, through which the oxidizing medium supplied from below the grate can flow.

[0061] The grate elements 3, 4, 5 also have a downwardly tapering cross section, at least in the region of the lateral recesses, which in the illustrated embodiment are arranged below the plates forming the surfaces 9 of the grate elements 3, 4, 5 by narrow webs 14, which facilitate the fall of ash particles.

[0062] The two grate sections 1a, 1b of the step grate 1 each consist of several grate rows, with only the second grate row being connected to a movable grate carriage 7 and therefore movable. The top row of grates is movable, as is the third row from the top, and so on.

[0063] All grate elements 3, 4, 5 on the plane of movement are moved by a common grate carriage 7. In this way, only one side is pushed at a time and the entire bed slides slowly, resulting in less disturbance of the gasification bed.

[0064] The counterflow gasifier has insulated gasifier tubes 22, which can be cylindrical or polygonal (e.g., octagonal), and a lower edge 15 that is preferably located above the transition region from the grate row with short burnout elements 4 to the grate row with long burnout elements 5. The distance between the gasifier tube lower edge 15 and the grate is dimensioned so that the angle of repose of the fuel bed (typically in the range of 35-45°) is within the region of the bottom or second or penultimate row of burnout elements, which can prevent particles from spilling over the bottom edge 15 of the grate.

[0065] Figures 5a-5c show an external view of the system according to the invention, equipped with an ash removal system. At the bottom of each grate section 1a, 1b, there is an ash screw 23, one below the last row of grates, through which ash is discharged and which extends across the entire width of the grates. These two ash screws 23 lead to a common ash collection screw 24, which is located laterally outside the system housing. At the end of the ash collection screw 24, there is an ash slide 21 below the screw, which ensures that the system remains airtight during operation.

[0066] The ash slide 21 is preferably positioned horizontally and is not covered with ash. When the ash slide 21 opens at the start of the ash removal cycle, the ash collection screw 24 starts moving and transports the ash into the free slide cross section. This ensures that the ash slide 21 is not covered with ash (so that it can close properly after the ash removal process) and that the ash collection screw 24 remains covered with ash for the correspondingly short ash removal interval. A lifting screw 25 arranged below the slide 21 finally transports the ash into the ash collection container.

[0067] Ash can fall through the slots between the grate elements 3, 4, 5, referred to as under-grate ash, and in the illustrated embodiment of the invention is conveyed via a cross conveyor 17 to a transversely arranged under-grate ash screw 18. The under-grate ash screw 18 then opens into an under-grate inclined screw 19, which discharges the ash onto an under-grate ash slide 20. This slide allows the ash at the bottom of the grate to reach one of the ash screws 23 arranged along the grate for further conveyance from there. Because relatively little material collects below the grate, under-grate ash removal only needs to be operated once, for example after about 10 normal ash removal cycles.

[0068] 9a and 9b show a side view and a top view of a mixing tube 27, which serves as a device for supplying a gaseous oxidizing medium. The mixing tube 27 is equipped with a connection for an air supply tube 28 and a connection for a recirculated exhaust gas supply tube 29. The oxidizing medium is supplied centrally below the grate via the mixing tube 27 and flows out from the mixing tube 27 below the step grate 1. The oxidizing medium usually consists of a mixture of air and recirculated exhaust gas. Good mixing of the air and recirculated exhaust gas is ensured via the mixing tube 27, so that the recirculated flue gas is very well mixed with the combustion air before the oxidizing medium exits the space below the step grate 1. The recirculated exhaust gas flows axially into the mixing tube via a narrow supply tube 29. Air flows into the mixing tube 27 via a wide supply tube 28, which is offset by 90° relative to the recirculated exhaust gas supply. The 90° offset inlet openings, the choice of diameter for the two inlet openings, and the mixing section after the inlet openings result in very good mixing of the air and recirculated exhaust gases, which then enter the space below the step grate 1 through the downward outlet opening 30 of the mixing tube. This good mixing prevents strands of air or recirculated exhaust gases from forming below the grate, which could adversely affect the local combustion state of the coal on the grate, and ensures good and uniform distribution of the oxidizing agent in the space below the grate.

[0069] By controlling the addition of recirculated exhaust gas to the gasification air, the mixture (oxidizing medium) The oxygen partial pressure in the fuel changes, slowing down the combustion of the fuel and reducing the temperature generated in the glow bed. This ensures a defined temperature in the ember bed. To avoid ash sintering and slagging, the glow bed temperature is preferably between 800 and 1000 °C. This temperature can vary depending on the fuel composition. The mixing of the recirculated exhaust gas is controlled via a valve, in particular a flap, and via a defined pressure difference corresponding to the volumetric flow rate.

[0070] Finally, Figure 1 shows preferred locations for temperature measurements in the ember bed area near the grate. For example, two thermocouples 31 can be placed at these locations. If a critical temperature (e.g., 1000°C) is exceeded at these points, the proportion of recirculated exhaust gas in the oxidizing medium can be increased.

[0071] The casing 26 in the grate area is insulated to minimize heat loss to the outside. Preferably, a multi-layer insulation structure is used (refractory concrete, insulating concrete, ceramic wool, sheet metal jacket, etc.). [Explanation of symbols]

[0072] 1 tier grate 1a Grate section 1b Grate section 2 Gable 2' upper part 3 Double grate elements 3 Upper grate element 3″ support part 4 short grate elements 5 long grate elements 6 Tubular fittings 7 Grate Carriage 8 Front end 9 surface 10 Support part 11 Tubular fitting 12 Side wall 13 Recess 14. Web 15 Edge of counterflow gasifier 16 Grate frame with cooling system 17 Cross conveyor 18 Screw conveyor below the grate 19 Inclined screw conveyor below the grate 20 Slide under the grate 21 Ash Slide 22 Gasification furnace tubes of counterflow gasification furnaces, including linings 23 Gray Screw 24 Ash collection screw 25 ascending screw 26 Casing of the grate area 27 Mixing tube 28 Air supply pipe 29 Recirculating exhaust gas supply pipe 30 Outflow opening for oxidizing medium 31 Thermocouple 101 Fuel bed 102 Dry Zone 103 Pyrolysis Zone 104 Gasification Zone 105 Grate 106 Coal combustion zone, oxidation zone 107 Oxidant Supply 108 Fuel supply 109 Gas Exhaust 110 Ash removal α wedge angle

Claims

1. An installation for the thermochemical conversion of solid fuels, comprising a step grate (1) having a row of grate elements (3, 4, 5), a countercurrent gasifier having substantially vertically arranged gasifier tubes (22) forming a gasifier chamber, and arranged in a region above the upper end of the step grate (1), the installation comprising a device for removing ash in the region of the lower end, a device (27) for supplying a gaseous oxidizing medium in the region below the step grate (1), and the step grate (1) is provided with movable and non-movable 1. An installation comprising a row of grate elements (3, 4, 5), the step grate (1) being particularly preferably arranged symmetrically in an approximately A-shape and having two grate sections (1a, 1b) arranged in the region of their upper ends in a central region below the gasification furnace chamber, the grate sections (1a, 1b) having at their upper ends a top row of movable grate elements (3), and non-movable gables (2) arranged above them in the central region.

2. 2. The installation according to claim 1, characterized in that the opposing grate elements (3') of the top rows of the two grate sections (1a, 1b) are connected to each other.

3. 3. The installation according to claim 2, characterized in that the gable (2) is arranged in the central region above the interconnected grate sections (1a, 1b) of the top row.

4. 4. The installation according to claim 1, wherein the gable (2) has an A-shaped upper part (2'), the upper part (2') having a wedge angle (α) preferably between 30° and 90°, particularly preferably 60°.

5. 2. The installation according to claim 1, characterized in that the grate sections (1a, 1b) each have short grate elements (4) in their upper region and long grate elements (5) in their lower region.

6. 6. The installation according to claim 5, characterized in that the short grate elements (4) are arranged in a region below the countercurrent gasification furnace and the long grate elements (5) are arranged in a region not below the countercurrent gasification furnace.

7. 2. The installation according to claim 1, characterized in that the grate elements (3, 4, 5) have side walls (12) in which recesses (13) are arranged, which recesses terminate respectively in front of the front and rear ends of the grate elements (3, 4, 5), so that in each case between two adjacent grate elements (3, 4, 5) a slot of limited length is formed, through which the oxidizing medium fed from below the grates can flow.

8. 2. The installation according to claim 1, characterized in that it comprises a fixed grate frame (16) to which all non-movable grate elements (4, 5) and the gable (2) are connected.

9. 2. Installation according to claim 1, characterized in that all the movable grate elements (3, 4, 5) of a plane are moved by a common drive, preferably a grate carriage (7).

10. 2. Installation according to claim 1, characterized in that at least some of the grate elements (4, 5) are mounted in tubular fittings (11) through which a cooling medium flows.

11. 11. Installation according to claims 9 and 10, characterized in that the common drive is a grate carriage (7) and that on the mobile grate carriage (7) a further mounting (6) is arranged.

12. 10. Installation according to claim 9, characterized in that the common drive is a grate carriage (7) and that the stroke movement of the grate carriage (7) is adjustable, preferably constant.

13. 2. Installation according to claim 1, characterized in that the device (27) for supplying a gaseous oxidizing medium has a connection for air and a connection for recirculated exhaust gas.

14. 2. The installation according to claim 1, characterized in that above the step grate (1) there is arranged at least one thermocouple (31), preferably two thermocouples (31), one above each grate section (1 a, 1 b), the thermocouple(s) (31) being connected to a control device connected to a valve for controlling the supply of the recirculated exhaust gas to the device (27).

15. 2. The installation according to claim 1, characterized in that the gasifier tubes (22) of the countercurrent gasifier have a lower edge (15), and the distance of the lower edge (15) from the grate sections (1 a, 1 b) is selected so that the angle of repose of the fuel, starting from the lower edge (15), ends on the bottom row of the grate elements (5) or further above each of the grate sections (1 a, 1 b).

16. 2. The installation according to claim 1, characterized in that at the lower end of each grate section (1a, 1b) there is an ash conveyor screw (23) extending over the entire width of the grate, through which ash is discharged.

17. 17. The installation according to claim 16, characterized in that the two ash conveyor screws (23) lead to a common ash collecting screw (24), which is arranged adjacent to the side of the step grate.

18. 18. The installation according to claim 17, characterized in that an ash slide (21) is arranged at the end of the ash collecting screw (24), the ash slide (21) sealing the installation during operation.

19. 17. The installation according to claim 16, characterized in that a cross conveyor (17) is arranged below the step grate (1), a grate bottom ash screw conveyor (18) is connected to the cross conveyor, the grate bottom ash screw conveyor (18) opens into a grate bottom inclined screw conveyor (19), the grate bottom inclined screw conveyor (19) discharges ash onto a grate bottom ash slide (20), and the grate bottom ash slide (20) transports the ash at the grate bottom to one of the ash screws (23) arranged along the grate.

20. 19. The installation according to claim 18, characterized in that a lifting screw (25) arranged below the ash slide (21) conveys the ash into an ash container.

21. 17. Installation according to claim 16, characterized in that the device for removing ash is essentially airtight.

22. 2. Installation according to claim 1, characterized in that the casing (26) of the grate area is insulated.

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