EP3230412B1 - Co-current fixed bed gasifier for producing a product gas from biomass particulates - Google Patents

Description

The invention relates to a direct current fixed bed gasifier for producing a product gas from pourable biomass particles according to claim 1, a method for operating such a direct current fixed bed gasifier according to claim 14, a method for starting up such a direct current fixed bed gasifier according to claim 18 and a method for shutting it down DC fixed bed gasifier according to claim 19.

Fixed bed gasifiers for generating a combustible product gas from biomass pellets, in particular from wood chips or wood pellets, are characterized by a comparatively simple structure. A distinction is made between countercurrent and cocurrent carburettors. In the case of the countercurrent gasifier, the flow direction of the combustion air and the product gas on the one hand and the feed direction of the biomass particles are opposite, and in the case of the co-current gasifier the feed direction of the biomass particles corresponds to the flow direction of the combustion air and product gas. Different reaction zones, namely drying, pyrolysis, oxidation and reduction zones, in which different thermochemical reactions take place, are distinguished in fixed bed gasifiers.

An overview of fixed bed gasification of biomass particles can be found in the lecture "Fixed bed gasification - state of the art (overview)" by Lettner, Haselbacher and Timmerer at the conference " Thermochemical biomass gasification for efficient electricity / fuel supply - state of knowledge 2007 "in February 2007 in Leipzig (http://www.holzgasjournal.de/download/2_Stufen_vergaser_1.pdf ) known. In this overview, a DC shaft gasifier is explained, in which the biomass particles are gravity fed to the gasifier tank. The combustion air is fed through nozzles in the central area and the product gas is drawn off from the lower area of the carburettor tank. In this known fixed bed gasifier the drying, pyrolysis, oxidation and reduction zone is formed from top to bottom. The oxidation zone forms in the area of the air supply and should remain limited to this zone, the reduction zone below, directly above the grate. The product gas is extracted from the area of the carburettor tank under the grate, in which the small-part ash falling through the grate also collects.

In order to maintain stable process control, the aim is that these different zones are almost stationary in the carburettor tank. In the case of direct current gasifiers, the position of the oxidation zone is determined by the position of the air supply by means of nozzles. The air supply by means of nozzles has the disadvantage that there is no homogeneous air distribution in the area of the oxidation zone and temperature differences of up to 400 degrees can occur locally. This can lead to deposits of combustion residues (slag) at undesirable locations in the gasification chamber, this affects the movement of the biomass particles and causes an inhomogeneous gas flow which leads to increased tar values in the product gas.

WO 2010/114400 A2 describes a carburetor for solid fuels with a tubular component through which the fuels are filled. This is not a direct current gasifier, since on the one hand the air is supplied from below or in the central area of the tubular component and on the other hand the product gas is removed at the top. US 2007/01694411 A1 describes a carburetor with a tubular carburetor component which is open at the top and in which the product gas is also removed above the grate.

WO 2008/006049 A2 describes a gasifier in which the product gas is discharged below under the grate as in the present invention. However, the carburetor is constructed differently: in the inner chamber of the carburetor there is an agitator that stirs or swirls the biomass. Air is supplied through an air inlet on the outer carburetor component.

Starting from the DC fixed bed gasifier according to the lecture "Fixed bed gasification - state of the art (overview)", it is an object of the present invention to provide a DC fixed bed gasifier and a method for operating such a DC fixed bed gasifier, in which harmful temperature gradients in the range the oxidation zone can be avoided. It is a further object of the invention to provide a method for starting up and shutting down such a fixed bed reactor.

This object is achieved by the features of claims 1, 14, 18 and 19 respectively.

The fact that the air is supplied through the biomass particle bed in the tubular gasifier component results in a uniform distribution of the air. This uniform distribution means that there are hardly any temperature differences in the oxidation zone. As a result, pyrolysis gases, which are generated above the oxidation zone, flow evenly through the oxidation zone. This uniformity of the gas and air flows enables a product gas to be produced with small amounts of tar.

Due to the air supply from above and the extraction of the product gas below the grate, the fixed bed gasifier is only flowed through from top to bottom. Here, the drying zone and the pyrolysis zone form in the carburetor component that protrudes into the carburetor tank, the oxidation zone forms under the open end of the carburetor component, followed by the reduction zone above the grate. The oxidation zone is bound locally by the gas flow from top to bottom and by means of a cross-sectional jump between the carburetor component and the carburettor container at the open end of the carburetor component, which results in different flow velocities. In contrast to conventional fixed-bed gasifiers, the flow rate is slowed down by expanding the cross-section. Conventional fixed bed carburettors have a constriction under the oxidation zone, which increases the gas flow rate. Due to the different flow velocities inside and outside the tubular carburetor component, the oxidation zone is virtually fixed in front of the open end of the tubular carburetor component.

Another advantage of expanding the cross-section is that the pyrolysis gases are not limited by any tube walls when flowing through the oxidation zone. There are no uniform flow conditions on the pipe walls and therefore no uniformly high temperatures. If pyrolysis gas flows through the oxidation zone at the edge of a tube wall, as is the case in the prior art, the long-chain hydrocarbons are not broken up completely. Because the pipe wall is not present, additional long-chain hydrocarbon compounds are broken up, which leads to an improvement in the motor capability of the product gas.

The advantageous embodiment of the invention according to claims 2 to 4 simplifies the structure of the direct current grease bed gasifier and enables a uniform air and product gas flow with a temperature-homogeneous oxidation zone Most of the long-chain hydrocarbon compounds break up and thus produce a high-quality product gas.

The advantageous embodiment according to claim 5 prevents clogging of the grate and a reduction in residual agglomeration, which enables ash to be drawn off through the grate as particle loading of the product gas.

According to the advantageous embodiment of the invention according to claim 6, the distance h of the open end of the carburetor component approximately corresponds to the diameter d of the carburetor component. This optimum was found empirically. If the distance h becomes smaller than this optimum, the reduction zone becomes smaller, which has a negative effect on the product gas quality. If the distance h is greater than this optimum, the reduction zone increases, which also has an unfavorable effect on the product gas quality. The DC fixed-bed carburettor still works with a 40% deviation (h = d ± 40%) from the optimum, but the product gas quality and yield deteriorate.

The smaller the inner diameter d of the carburetor component compared to the inner diameter D of the carburetor container, the greater the difference in the gas flow velocity inside and outside the tubular carburetor component. If the speed difference is too large, the fuel and material efficiency is reduced, if the speed difference is too small, the flow speed outside the carburetor component is too high. In addition, the inner diameter d of the tubular gasifier component must be large enough that a bed of the biomass particles can form in the gasifier component. The empirically found ratio interval of inner diameter D of the carburettor container to inner diameter d of the carburetor component, as found in claim 7, results in a functional direct current fixed bed carburetor.

Due to the advantageous embodiment of the invention according to claim 10, the biomass particle conveying device is used as a lock for feeding the biomass particles into the tubular carburetor component used. This configuration can also be used in other fixed bed gasifiers, independently of the present invention.

The product gas or wood gas generated in the direct current fixed bed gasifier is preferably used in a block-type thermal power station with an internal combustion engine or a fuel cell to provide electrical and thermal energy. The product gas generated in the direct current fixed bed gasifier is cooled and cleaned in a downstream gas treatment device. In the gas mixing section of the internal combustion engine, this cooled and cleaned product gas is mixed with combustion air which is cold in comparison to the product gas from the gas processing device, as a result of which further cooling takes place. This further cooling can lead to undesired precipitation of solids or liquids and in particular tar. By providing a condensate separator after the combustion air has been added to the product gas or wood gas, that is to say immediately before the combustion in the gas engine, these solid and / or liquid precipitates are separated off and can therefore not cause any damage in the gas engine - claim 11. This configuration can can also be used independently of the present invention in other fixed bed gasifiers.

Due to the advantageous embodiment of the invention according to claim 12, the product gas is cooled to temperatures, so that it z. b. can be used as fuel in a CHP.

The advantageous embodiment of the invention according to claim 13 ensures that the biomass particle bed in the gasifier component is high enough to distribute the amount of air flowing through the biomass particle bed sufficiently and uniformly in front of the first reaction zone over the entire cross section. Due to the continuous supply of combustion air via the biomass particle bed and the continuous removal of the product gas, the various reaction zones of the direct current fixed bed gasifier remain stationary and defined conditions are formed.

The use of biomass pellets as biomass particles is advantageous - claim 16.

The addition of kaolin to the biomass pellets during their production increases the melting point of the ash produced in the biomass gasification, so that clogging of the grate is less likely or avoided - claim 17. Such pellets can also be used in others independently of the present invention Wood gasifiers can be used advantageously.

The method for starting a direct current fixed bed gasifier according to claim 18 relates to a simple and preferred way of starting the direct current fixed bed gasifier filled with biomass particles. The biomass particles are advantageously ignited by blowing hot air into the area under the open end of the tubular gasifier component. The temperature of the hot air is selected so that the biomass particles are ignited safely.

As a result of the fact that in the method for shutting down a direct current fixed bed gasifier according to claim 19, the biomass gasification is continued after the end of the supply of biomass particles, the level of the biomass particle bed in the tubular gasifier component drops and as little as possible unused biomass particles remain. If a large part of unused biomass particles would remain in the tubular gasifier component after the air supply had ended, these would outgas and the moist gas would lead to the swelling of the biomass particles above. This swelling can then lead to a blockage of the tubular carburetor component when restarting.

The remaining subclaims relate to further advantageous embodiments of the invention.

• Fig. 1 eine schematische Schnittdarstellung einer beispielhaften Ausgestaltung der Erfindung mit den wesentlichen Komponenten;
• Fig. 2 eine schematische Darstellung der Kombination des Gleichstrom-Festbettvergasers nach Fig. 1 mit Gasaufbereitung und BHKW; und
• Fig. 3 zeigt die Biomasseteilchenschüttung im Vergaser und die verschiedenen Reaktionszonen.

Further details, features and advantages of the invention result from the following description of advantageous embodiments with reference to the drawing.

• Fig. 1 is a schematic sectional view of an exemplary embodiment of the invention with the essential components;
• Fig. 2 is a schematic representation of the combination of the DC fixed bed gasifier Fig. 1 with gas conditioning and CHP; and
• Fig. 3 shows the biomass particle bed in the gasifier and the different reaction zones.

Fig. 1 shows a schematic representation of an exemplary embodiment of the invention. The DC fixed bed gasifier according to the present invention comprises a tubular gasifier tank 2, the ends of which are closed by an upper cover 4 and a lower cover 5. A tubular carburetor component 6 with an open end 8 and a closed end 9 projects with the open end 8 into the carburetor tank 2. The closed end 9 of the carburetor component 6 protrudes from the carburetor tank 2 through the upper cover 4. The open end 8 of the carburetor component 6 comes to lie approximately in the middle of the carburetor container 2. At a distance h below the open end 8 of the carburetor component 6 there is a rotatable grate 10 which can be moved periodically by a motor drive 12 which passes through the lower cover 5. A supply for biomass particles 14, an air supply 16 for supplying combustion air L into the carburetor container 2 and a fill level sensor 18, with which the fill level of biomass particles in the tubular carburetor component 6 are determined, open into the protruding end 9 of the carburetor component 6 can be monitored. In the area of the open end 8 of the carburetor component 6, an ignition device 20 and a closed inspection shaft 22 are provided, which penetrate the outer wall of the carburetor container 2. The ignition device 20 is used to generate hot air in a temperature range between 300 ° C. and 600 ° C. in order to ignite the biomass particles in the region under the open end 8 of the carburetor component, ie in the region of the oxidation zone, when the DC fixed-bed gasifier starts up. The ignition device 20 comprises an air nozzle 21 for hot air, which passes through the carburetor tank 2. Through the air nozzle 21 made of ceramic, the parts of the ignition device 20, which are arranged inside the carburetor container 2, are thermally decoupled from the parts outside the carburetor container 2. When the reactor is at a standstill, maintenance work and cleaning work can be carried out above the inspection shaft 22 in the interior of the reactor vessel. In the area under the grate 10, product gas PG is withdrawn from the carburetor container 2 via a product gas discharge 24. The ash falling through the grate 10 is discharged from the fixed bed gasifier through the product gas flow PG via the product gas discharge 24.

Both the tubular carburetor container 2 and the tubular carburetor component 6 have an annular cross section and are arranged concentrically to one another. The tubular carburetor component 6 has an inner diameter d that is smaller than the inner diameter D of the tubular carburetor tank 2.

The feed for biomass particles 14 is connected via a first lock valve 28 to a biomass particle conveyor device 30 in the form of a screw conveyor. The screw conveyor 30 is gas-tightly connected to a biomass particle storage container 32, which is sealed gas-tight to the outside via a second lock valve 34. Due to the direct gas-tight connection of the biomass particle storage container 32 to the screw conveyor 30, these two components act between the two lock valves 28, 34 as a lock for the supply of biomass particles into the fixed bed gasifier.

Fig. 2 illustrates the combination of the fixed bed gasifier Fig. 1 with a downstream gas treatment unit and a CHP. The product gas PG emerging from the product gas outlet 24 is fed to a gas processing device 36. In the gas processing device 36, the product gas is cooled in a heat exchanger and solid and liquid impurities are separated out as far as possible.

The cooled and conditioned product gas from the product gas treatment device 36 is fed to a gas mixing section 40 of a gas engine 42 via a product gas line 38. The gas mixing section 40 also includes a supply for combustion air 44. By mixing comparatively cold outside air and comparatively hot product gas from the product gas processing device 36 in In a mixed gas line 46, the resulting gas mixture is cooled further, so that further liquid contaminants can fail. These liquid contaminants settle in a condensate separator 48 at the end of the mixed gas line 46 immediately before the gas mixture is fed to the gas engine 42 and can be discharged. This increases the mixed gas quality and prevents harmful impurities in the gas engine.

Fig. 3 shows the direct current fixed bed gasifier in the stationary operating state with the biomass particle bed 50 in the gasifier tank 2 and in the gasifier component 6 and the position of the different reaction zones. The oxidation zone OZ is formed directly below the open end 8 of the carburetor component 6. The reduction zone RZ, which extends to the grate 10, lies below the oxidation zone OZ. The pyrolysis zone PZ extends over the oxidation zone OZ and the drying zone TZ forms the end.

To start up the DC fixed-bed gasifier, the gasifier tank 2 is first filled with biomass particles via the feed 14 up to a desired level SP, so that the biomass bed 50 results. By blowing in hot air by means of the ignition device 20, the biomass particles are ignited immediately below the open end 8 of the carburetor component 6, so that the oxidation zone OZ can form. As soon as the combustion of the biomass particles in the oxidation zone OZ is self-sustaining, the ignition device 20 is switched off and combustion air L is now supplied via the air supply 16. As a result of the heat of combustion released in the oxidation zone OZ, the remaining reaction zones gradually form. The product gas stream from the product gas outlet 24 is fed to the gas processing device 36. The product gas quality is monitored in the gas processing device 36. During the start-up, the product gas stream from the product gas discharge 24 is flared due to its poor quality in an exhaust gas torch (not shown). As soon as a sufficient product gas quality has been established, the product gas is cooled in the gas processing device 36 and freed from solid and liquid impurities as far as possible. During stationary operation, the target level SP of the biomass particles in the carburetor component is monitored by the fill level sensor 18 and, if necessary, by the biomass particle conveyor 30, refilled 14 biomass particles via the first lock valve 28 and the feed.

When the fixed bed gasifier is shut down, the supply of biomass particles is first stopped, so that the level of the biomass particles in the gasifier component 6 drops below the desired level SP. If a large part of unused biomass particles would remain in the tubular gasifier component after the air supply had ended, these would outgas and the moist gas would lead to the swelling of the biomass particles above. This swelling can then lead to a blockage of the tubular carburetor component when restarting. When a minimum biomass particle level MP is reached, the air supply and gas production are stopped. This minimum level MP corresponds approximately to the upper limit of the pyrolysis zone PZ in the stationary operating state. In this way, as few unused biomass particles as possible remain in the gasifier container 2 and in the gasifier component 6.

Wood pellets or biomass pellets are particularly suitable for the fixed bed gasifier according to the present invention. Kaolin is added to the biomass pellets during production, so that the finished pellets contain a kaolin fraction of 1% by mass to 5% by mass and preferably 1.5% by mass to 3% by mass. The addition of kaolin increases the melting point of the ash obtained in the biomass gasification, so that clogging of the grate 10 or undesired accumulation of the ash on other components of the fixed bed gasifier is less likely or avoided.

Reference symbol list:

L

air

PG

Product gas

SP

Biomass particle target level

MP

minimum biomass particle level on shutdown

d

Inner diameter of carburetor component 6

D

Inner diameter of carburetor tank 2

TZ

Drying zone

PZ

Pyrolysis zone

OZ

Oxidation zone

RZ

Reduction zone

2nd

Carburettor tank

4th

upper lid

5

lower lid

6

Carburetor component

8th

open end of 6

9

closed end of 6

10th

rust

12

motorized grate drive

14

Feeder for biomass particles

16

Air supply

18th

Level sensor

20th

Igniter

21st

Ceramic air nozzle

22

Inspection shaft

24th

Product gas discharge

28

first lock valve

30th

Biomass particle conveyor, screw conveyor

32

Biomass particle storage container

34

second lock valve

36

Gas processing facility

38

Product gas line

40

Gas mixing section

42

Gas engine

44

Combustion air supply

46

Mixed gas line

48

Condensate separator

50

Biomass particle filling

Claims (19)

1. Cocurrent fixed-bed gasifier for producing a product gas from pourable biomass particles (50), comprising
   a gasifier vessel (2),
   a feed conduit (14) for the biomass particles in the upper region of the gasifier vessel (2),
   a grating (10) located in the lower region of the gasifier vessel (2) for supporting the biomass particles (50),
   an air feed conduit (16) for introducing combustion air into the gasifier vessel (2),
   a product gas offtake (24) leading out from the region under the grating (10) of the gasifier vessel (2) for discharging the product gas from the gasifier vessel, and
   a tubular gasifier component (6) which projects into the gasifier vessel (2),
   where the tubular gasifier component (6) has an open end (8) which is arranged in the gasifier vessel (2),
   where the tubular gasifier component (6) has a closed end (9) which projects out of the gasifier vessel (2) or ends flush with the upper side of the gasifier vessel (2),
   where the internal diameter (d) of the tubular gasifier component (6) is smaller than the internal diameter (D) of the gasifier vessel (2), where the tubular gasifier component (6) is arranged in the gasifier vessel (2) in such a way that a spacing (h) remains between the open end (2) of the tubular gasifier component (6) and the grating (10), and
   where the feed conduit (14) for the biomass particles opens into the closed end (9) of the tubular gasifier component (6),
   characterized in that the air feed conduit (16) opens into the closed end (9) of the tubular gasifier component (6).
2. Cocurrent fixed-bed gasifier according to Claim 1, characterized in that the gasifier vessel (2) and/or the tubular gasifier component (6) has a circular cross section.
3. Cocurrent fixed-bed gasifier according to Claim 2, characterized in that the tubular gasifier component (6) has its circular cross section arranged coaxially with the gasifier vessel (2) having a circular cross section.
4. Cocurrent fixed-bed gasifier according to either of the preceding Claims 2 and 3, characterized in that the tubular gasifier component (6) and/or the gasifier vessel (2) have a constant diameter.
5. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized in that the grating (10) is movable and in particular rotatable.
6. Fixed-bed gasifier according to any of the preceding claims, characterized in that the spacing (h) between the open end (8) of the tubular gasifier component (6) and the grating (10) and the internal diameter (d) of the tubular gasifier component (6) obey the following relationship: $$\mathrm{h}=\mathrm{d}\pm 10\%.$$

   
7. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized in that the internal diameter (d) of the tubular gasifier component is from 80% to 50% of the internal diameter (D) of the gasifier vessel.
8. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized in that an ignition device (20) penetrates the gasifier vessel (2) in the region of the open end (8) of the tubular gasifier component (6).
9. Cocurrent fixed-bed gasifier according to Claim 8, characterized in that the ignition device (20) comprises an injection device for hot air.
10. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized by a biomass particle store (32) which is coupled to a biomass particle transport device (30), where the biomass particle transport device (30) is connected via a gastight shutoff device (28) to the feed conduit (14) for biomass particles and the biomass particle store (32) comprises a gastight charging opening (34).
11. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized in that a gas treatment device (36) is located downstream of the product gas offtake (24), in that the gas treatment device (36) is connected via a product gas conduit (38) to a gas mixing section (40) of an internal combustion engine (42), in that the gas mixing section (40) comprises a combustion air feed conduit (44) and in that a condensate precipitate (48) is arranged in a mixed gas conduit (46) for combustion air (L) and product gas (PG).
12. Cocurrent fixed-bed gasifier according to Claim 11, characterized in that the gas treatment device (36) comprises a heat exchanger for cooling the product gas (PG).
13. Cocurrent fixed-bed gasifier according to any of the preceding claims, characterized in that a control device which controls the biomass particle transport device (30) and has a fill level sensor (18) for measuring the fill level (SP) of the biomass particles (50) in the tubular gasifier component (6) is provided.
14. Method for operating a cocurrent fixed-bed gasifier according to any of the preceding claims, comprising the process steps:

    - setting and maintaining a particular fill level (SP) of biomass particles in the tubular gasifier component (6),

    - continuously introducing air (L) via the air feed conduit (16) and

    - continuously taking off product gas (PG) via the product gas offtake (24).
15. Method according to Claim 14, characterized in that the grating (10) is moved at time intervals.
16. Method according to Claim 14 or 15, characterized in that biomass pellets are used as biomass particles.
17. Method according to Claim 16, characterized in that the biomass particles have a kaolin content of from 1% by mass to 5% by mass and preferably from 1.5% by mass to 3% by mass.
18. Method for starting up a cocurrent fixed-bed gasifier according to any of Claims 1 to 13, comprising the process steps:

    - charging the gasifier component (6) with biomass particles up to a predetermined height (SP); and

    - igniting the biomass particles by blowing hot air having a temperature of greater than 300°C into the region of the biomass particle bed (50) underneath the open end (8) of the tubular gasifier component (6).
19. Method for running down a cocurrent fixed-bed gasifier according to any of Claims 1 to 13, comprising the process steps:

    - stopping the introduction of biomass particles,

    - continuing the introduction of combustion air (L) for a predetermined period or until the fill level of biomass particles has dropped to a prescribed minimum level, and

    - stopping the introduction of combustion air (L).

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