EP3230412A1

EP3230412A1 - Downdraft fixed-bed gasifier for generating a product gas from pourable biomass particles

Info

Publication number: EP3230412A1
Application number: EP15808371.7A
Authority: EP
Inventors: Marco Senger; Michael Hofmeister; Horst Dressler; Julien UHLIG
Original assignee: Entrade Energiesysteme AG
Current assignee: Rosmarin Holdings Ltd
Priority date: 2014-12-08
Filing date: 2015-12-07
Publication date: 2017-10-18
Anticipated expiration: 2035-12-07
Also published as: DE102014225166A1; US20170275543A1; EP3230412B1; WO2016091835A1; EA201791272A1; EA034879B1

Abstract

The invention relates to a downdraft fixed-bed gasifier for generating a product gas from pourable biomass particles, to a method for operating such a downdraft fixed-bed gasifier, to a method for starting such a downdraft fixed-bed gasifier, and to a method for shutting down such a downdraft fixed-bed gasifier. By supplying air through the bed of biomass particles in the tubular gasifier component, a uniform distribution of the air is produced. Hardly any temperature differences occur in the oxidation zone by virtue of the uniform distribution. As a result, even pyrloysis gases produced over the oxidation zone flow through the oxidation zone in a uniform manner. The uniformity of the gas and the air flows allows a product gas to be generated with low tar quantities. The oxidation zone is locally connected by means of a cross-sectional jump between the gasifier component and the gasifier container at the open end of the gasifier component, different flow speeds resulting from said cross-sectional jump. By expanding the cross-section, the flow speed is slowed compared to conventional fixed-bed gasifiers. The different flow speeds within and outside the tubular gasifier component virtually fix the oxidation zone in front of the open end of the tubular gasifier component. Another advantage of the expanded cross-section is that the pyrolysis gases are not delimited by a tube wall while flowing through the oxidation zone. The flow conditions on tube walls are not uniform, and thus the temperatures there are not uniformly high. When pyrolysis gas flows on the edge of a tube wall through the oxidation zone, as is the case in the prior art, the long-chain hydrocarbons are not completely broken down. Additional long-chain hydrocarbon compounds are broken down by virtue of the absence of the tube wall, thus leading to an improvement of the motor efficiency when using the product gas.

Description

description

DC fixed-bed gasifier for producing a product gas from pourable biomass particles

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

Fixed bed gasifier for producing a combustible product gas from biomass pellets, in particular from wood chips or wood pellets, are characterized by a comparatively simple structure. A distinction between countercurrent and Gleichstromvergaser. In the case of a 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 direct current gasifier, the feed direction of the biomass particles coincides with the flow direction of combustion air and product gas. In fixed-bed gasifiers, a distinction is made between different reaction zones, namely drying, pyrolysis, oxidation and reduction zones, in which different thermochemical reactions take place.

An overview on the topic of fixed bed gasification of biomass particles is from the lecture "fixed bed gasification state of the art (overview)" of Lettner, Haselbacher and Timmerer at the conference "Thermo-chemical biomass gasification for an efficient power / fuel supply - state of knowledge 2007" February 2007 in Leipzig (http://www.holzgasjournal.de/download/2_Stufen_vergaser_1.pdf) known. In this review, a Gleichstromschachtvergaser is explained in which the biomass particles are fed from above with gravity to the carburetor. The combustion air is supplied in the middle region via nozzles and the product gas is withdrawn from the lower region of the carburetor tank. In this known Fixed-bed gasifier forms the drying pyrolysis, oxidation and reduction zone from top to bottom. The oxidation zone is formed in the area of the air supply and should remain limited to this zone, the reduction zone below, just above the grid. The product gas is withdrawn from the area of the carburetor tank under the grate in which the small ash falling through the grate also accumulates.

In order to obtain a stable process management is sought that these different zones are almost stationary in the carburetor. For DC 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 in the area of the oxidation zone no homogeneous air distribution takes place and temperature differences of up to 400 degrees can occur locally. This can lead to deposits of incineration residues (slag) at undesirable locations in the gasifier compartment, this impairs the movement of the biomass particles and causes an inhomogeneous gas flow which leads to increased tar values in the product gas.

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, wherein the harmful temperature gradients in the It is a further object of the invention to specify a method for starting up and shutting down such a fixed bed reactor.

The solution of this object is achieved by the features of claim 1, 14, 18 and 19, respectively.

The fact that the air is supplied through the biomass particle bed in the tubular carburetor component, results in a uniform distribution of the air. Due to this uniform distribution, there are hardly any temperature differences in the oxidation zone. This has the consequence that also pyrolysis gases, which arise over the oxidation zone, flow evenly through the oxidation zone. By this uniformity of the gas and air flows can produce a product gas with low tar amounts.

Due to the air supply from above and the withdrawal of the product gas below the grate, the fixed bed gasifier only flows through from top to bottom. Here, the drying zone and the pyrolysis zone forms in the carburetor component, which protrudes into the carburetor tank, the oxidation zone is formed below the open end of the carburetor component followed by the reduction zone above the grate. The local binding of the oxidation zone is effected by the gas flow from top to bottom and by means of a cross-sectional jump between carburetor component and carburetor at the open end of the carburetor component, resulting in different flow velocities. By expanding the cross section, the flow rate is slowed down in contrast to conventional fixed bed gasifiers. Conventional fixed-bed gasifiers have a constriction below the oxidation zone, which increases the flow rate of the gas. 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 the cross-sectional widening is that the pyrolysis gases are limited by no pipe wall when flowing through the oxidation zone. On pipe walls, there are no uniform flow conditions and therefore no evenly high temperatures. If pyrolysis gas flows through the oxidation zone at the edge of a pipe wall, as is the case in the prior art, the long-chain hydrocarbons are not completely broken up. Due to the absence of the pipe wall, additional long-chain hydrocarbon compounds are broken up, which leads to an improvement in the engine capability of the product gas.

The advantageous embodiment of the invention according to claim 2 to 4 simplifies the construction of the DC Fettbettvergasers and allows a uniform air and product gas flow with a temperature-homogeneous oxidation zone a Most of the long-chain hydrocarbon compounds breaks up and thus produces a high quality product gas.

Due to the advantageous embodiment according to claim 5 clogging of the grate is prevented, as well as a reduction of the residual agglomeration made, which allows an ash discharge through the grate as a 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 corresponds approximately to the diameter d of the carburetor component. This optimum was found empirically. If the distance h is smaller than this optimum, the reduction zone decreases, which has a negative effect on the product gas quality. If the distance h is greater than this optimum, the reduction zone increases, which likewise has an unfavorable effect on the product gas quality. The DC fixed-bed gasifier also works at a 40% deviation (h = d ± 40%) from the optimum, but 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 tank, the greater the difference in the gas flow velocity inside and outside the tubular carburetor component. If the speed difference becomes too large, the fuel and material efficiency will be reduced, if the speed difference becomes too small, the flow velocity outside the carburetor component will be too high. In addition, the inner diameter d of the tubular carburetor component must be so large that a bed of biomass particles can form in the carburetor component. The empirically found ratio interval of inner diameter D of the carburetor tank to inner diameter d of the carburetor component given in claim 7 results in a functional DC fixed-bed carburettor.

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

The product or wood gas produced in the DC fixed bed gasifier is preferably used in a CHP with an internal combustion engine or a fuel cell to provide electrical and thermal energy. The product gas generated in the DC fixed-bed gasifier is cooled and cleaned in a downstream gas treatment facility. In the gas mixing section of the internal combustion engine, this cooled and purified product gas is mixed with cold combustion air compared to the product gas from the gas processing device, whereby further cooling takes place. This further cooling can lead to unwanted precipitation of solids or liquids and in particular of tar. By providing a condensate separator after the admixing of combustion air to the product gas or wood gas, ie immediately before combustion in the gas engine, these solid and / or liquid precipitates are separated and thus can cause no damage in the gas engine - claim 11. This embodiment 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 is z. b. can be used as fuel in a CHP.

The advantageous embodiment of the invention according to claim 13 ensures that the Biomasszwechenschüttung in the carburetor component is high enough to distribute the amount of air flowing through the Biomasszwechenschüttung sufficiently and evenly before 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 DC 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 ashes obtained in the biomass gasification, so that clogging of the grate is less likely or avoided - claim 17. Such pellets can also independently of the present invention in others Wood gasifiers are used advantageously.

The method of starting up a DC fixed bed gasifier according to claim 18 relates to a simple and preferred way of starting the biomass particle filled DC fixed bed gasifier. The ignition of the Biomasseteilchen takes place in an advantageous manner by the blowing of hot air in the area under the open end of the tubular Vergaserbauteils. The temperature of the hot air is chosen so that the biomass particles are safely ignited.

By continuing the biomass gasification after the completion of the biomass particle supply in the method for shutting down a DC fixed-bed gasifier according to claim 19, the level of biomass particle discharge in the tubular gasifier component decreases and as few as possible unused biomass particles remain. If a large proportion of unused biomass particles remained in the tubular carburetor component after the end of the air supply, this outgassing and the moist gas would lead to swelling of the overlying biomass particles. This swelling can then lead to a clogging of the tubular carburetor component when restarting.

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

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

It shows Figure 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 Gleichstrom- fixed bed gasifier of Figure 1 with gas treatment and CHP. and

Fig. 3 shows the biomass particle bed in the gasifier and the various 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 carburettor tank 2 whose ends are closed with an upper lid 4 and a lower lid 5. A tubular carburetor component 6 with an open end 8 and a closed end 9 protrudes into the carburetor tank 2 with the open end 8. The closed end 9 of the carburetor component 6 projects through the upper lid 4 out of the carburetor tank 2. The open end 8 of the carburetor 6 comes to lie approximately in the middle of the carburetor tank 2. At a distance h below the open end 8 of the carburetor component 6, a rotatable grate 10 is arranged, which can be moved periodically by a motor drive 12 which passes through the lower lid 5. In the protruding from the carburetor tank 2 closed end 9 of the carburetor 6 open a feed for Biomasseteilchen 14, an air supply 16 for supplying combustion air L in the carburetor tank 2 and a level sensor 18, with which determine the level of biomass particles in the tubular Vergaserbauteil 6 and monitor. In the region 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 tank 2. The ignition device 20 is used to generate hot air in a temperature range between 300 ° C and 600 ° C to ignite when starting the DC fixed bed gasifier, the biomass particles in the area below the open end 8 of the carburetor, ie in the region of the oxidation zone. The ignition device 20 includes 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 within the carburetor tank 2 are thermally decoupled from the parts outside of the carburetor tank 2. About the inspection shaft 22 can be made at standstill of the reactor, maintenance, cleaning in the reactor tank interior. In the area under the grate 10 product gas PG 24 is withdrawn from the carburetor tank 2 via a product gas take-off. The ash falling through the grate 10 is discharged from the fixed-bed gasifier through the product gas stream PG via the product gas outlet 24.

Both the tubular carburetor tank 2 and the tubular carburetor component 6 have an annular cross-section and are arranged concentrically to each other. The tubular carburetor component 6 has an inner diameter d which 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 30 in the form of a screw conveyor. The screw conveyor 30 is connected in a gas-tight manner to a biomass particle reservoir 32, which is closed to the outside via a second lock valve 34 in a gastight manner with respect to the surroundings. As a result of the direct, gas-tight connection of the biomass particle storage container 32 with the screw conveyor 30, these two components act as sluice for feeding biomass particles into the fixed-bed gasifier between the two lock valves 28, 34.

FIG. 2 illustrates the combination of the fixed-bed gasifier according to FIG. 1 with a downstream gas conditioning device and a CHP. The product gas PG leaving the product gas outlet 24 is supplied to a gas treatment device 36. In the gas treatment device 36, the product gas is cooled in a heat exchanger and solid and liquid impurities are separated as far as possible.

The cooled and treated 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 of combustion air 44. By the mixture of relatively cold outside air and comparatively hot product gas from the product gas processing device 36 in a mixed gas line 46, the resulting gas mixture is further cooled, so that further liquid impurities can fail. These liquid impurities settle in a condensate separator 48 at the end of the mixed gas line 46 immediately before feeding the gas mixture to the gas engine 42 and can be discharged. This increases the quality of the mixed gas and prevents harmful impurities in the gas engine.

FIG. 3 shows the DC fixed-bed gasifier in the stationary operating state with the biomass particle bed 50 in the carburettor tank 2 and in the carburetor component 6 and the position of the various reaction zones. Immediately below the open end 8 of the carburetor component 6, the oxidation zone OZ is formed. Under the oxidation zone OZ is the reduction zone RZ, which extends to the grate 10. The pyrolysis zone PZ extends over the oxidation zone OZ and the completion zone forms the drying zone TZ.

To start up the DC fixed bed gasifier, the carburetor tank 2 is initially filled via the feed 14 to a desired level SP with biomass particles, so that the biomass bed 50 results. By injecting 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 already now combustion air L is 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 vent 24 is supplied to the gas treatment device 36. In the gas treatment device 36, the product gas quality is monitored. During startup, the product gas stream from the product gas vent 24 is flared due to its poor quality in an exhaust flare (not shown). Once sufficient product gas quality has been established, the product gas in the gas processor 36 is cooled and as far as possible freed of solid and liquid contaminants. During steady-state operation, the target level SP of the biomass particles in the gasifier component is monitored by the level sensor 18 and, if necessary, monitored via the biomass particle feeders. means 30, via the first gate valve 28 and the feed 14 biomass particles refilled.

When shutting down the fixed bed gasifier, 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 proportion of unused biomass particles remained in the tubular carburetor component after the end of the air supply, this outgassing and the moist gas would lead to swelling of the overlying biomass particles. This swelling can then lead to a clogging of the tubular carburetor component when restarting. When a minimum biomass particle level MP is reached, the air supply and the 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 little unconsumed biomass particles remain in the carburettor tank 2 and in the carburetor component 6.

Particularly suitable for the fixed bed gasifier according to the present invention are wood pellets or biomass pellets. Kaolin is added to the biomass pellets during production, so that the finished pellets contain a kaolin content of 1 mass% to 5 mass% and preferably of 1.5 mass% to 3 mass%. The addition of kaolin increases the melting point of the ashes obtained in the biomass gasification, so that clogging of the grate 0 or undesired attachment of the ash to other components of the fixed bed gasifier is less likely or avoided.

LIST OF REFERENCE NUMBERS

L air

PG product gas

SP Biomass particle target level

MP minimal biomass particle level at shutdown

d Inner diameter of carburettor component 6

D Inner diameter carburettor tank 2 TZ drying zone

PZ pyrolysis zone

OZ oxidation zone

RZ reduction zone

2 carburettor tanks

4 upper lid

5 lower lid

6 carburettor component

8 open end of 6

9 closed end of 6

10 rust

12 motor rust drive

14 Feed for biomass particles

16 air supply

18 level sensor

20 ignition device

21 Ceramic air nozzle

22 inspection shaft

24 product gas vent

28 first lock valve

30 biomass particle conveyor, screw conveyor

32 biomass particle storage tanks

34 second lock valve

36 gas conditioning device

38 product gas line

40 gas mixing section

42 gas engine

4 combustion air supply

46 mixed gas line

8 condensate separators

50 biomass particle bed

Claims

Claims . DC fixed-bed gasifier for producing a product gas from pourable biomass particles (50) with

a carburettor tank (2),

a feed (14) for the biomass particles in the upper region of the carburetor tank (2),

a grate (10) arranged in the lower region of the carburetor tank (2) for supporting the biomass particles (50),

an air supply (16) for supplying combustion air into the carburettor tank (2), and

a product gas outlet (24) leading out of the carburettor tank (2) out of the area below the grate (10) for discharging the product gas from the carburettor tank, characterized

in that a tubular carburettor component (6) projects into the carburettor tank (2), in that the tubular carburettor component (6) has an open end (8) which is arranged in the carburettor tank (2),

the tubular carburettor component (6) has a closed end (9) which protrudes from the carburettor tank (2) or terminates with the upper side of the carburettor tank (6),

the inner diameter (d) of the tubular carburettor component (6) is smaller than the inner diameter (D) of the carburetor tank (2),

the tubular carburettor component (6) is arranged in the carburetor tank (2) such that a distance (h) remains between the open end (8) of the tubular carburettor component (6) and the grate (10),

that the feed (14) for the biomass particles opens into the closed end (9) of the tubular carburettor component (6), and

in that the air feed (16) opens into the closed end (9) of the tubular carburettor component (6).

2. DC fixed bed gasifier according to claim 1, characterized in that the carburetor tank (2) and / or the tubular carburetor component (6) has a circular cross-section.

3. DC fixed bed gasifier according to claim 2, characterized in that the tubular Vergaserbauteil (6) is arranged with a circular cross section coaxial with the carburetor tank (2) with a circular cross section.

4. DC fixed bed gasifier according to one of the preceding claims 2 or 3, characterized in that the tubular Vergaserbauteil (6) and / or the carburetor tank (2) have a constant diameter.

5. DC fixed-bed gasifier according to one of the preceding claims,

characterized in that the grate (10) is designed to be movable and in particular rotatable.

6. fixed bed gasifier according to one of the preceding claims, characterized in that for the distance (h) between the open end (8) of the rohrförmi- gen Vergaserbauteils (6) and the grate (0) and the inner diameter (d) of the tubular Vergaserbauteils ( 6) the following relationship applies: h = d ± 10%.

7. DC fixed-bed gasifier according to one of the preceding claims,

characterized in that the inner diameter (d) of the tubular carburetor component is 80% to 50% of the inner diameter (D) of the carburetor tank.

8. DC fixed-bed gasifier according to one of the preceding claims,

characterized in that the carburetor tank (2) in the region of the open end (8) of the tubular carburetor component (6) passes through an ignition device (20).

9. DC fixed bed gasifier according to claim 8, characterized in that the ignition device (20) comprises a hot air injection device.

10. DC fixed bed gasifier according to one of the preceding claims, characterized by a Biomasseteilchenspeicher (32) which is coupled to a biomass particle conveyor (30), wherein the biomass particle conveyor (30) via a gas-tight locking means (28) with the feed ( 14) for biomass particles, and wherein the biomass particle store (32) comprises a gas-tight loading opening (34).

1 1. DC fixed-bed gasifier according to one of the preceding claims,

characterized in that a gas treatment device (36) is connected downstream of the product gas outlet (24), that the gas treatment device (36) via a product gas line (38) with a gas mixing section (40) of an internal combustion engine (42) is connected, that the gas mixing section (40) Combustion air supply (44), and in a mixed gas line (46) for combustion air (L) and product gas (PG) a condensate separator (48) is arranged.

12. DC fixed bed gasifier according to claim 1 1, characterized in that the gas conditioning device (36) for cooling the product gas (PG) comprises a heat exchanger.

13. DC fixed-bed gasifier according to one of the preceding claims,

characterized in that a control device is provided, which controls the biomass particle conveyor (30) and a level sensor (18) for detecting the filling level (SP) of the biomass particles (50) in the tubular carburetor component (6).

14. A method for operating a DC fixed bed gasifier according to one of the preceding claims with the method steps:

Setting and maintaining a certain level (SP) of biomass particles in the tubular carburetor component (6),

- Continuous supply of air (L) via the air supply (16), and

- Continuous decrease of product gas (PG) via the product gas vent (24).

15. The method according to claim 14, characterized in that the grate (10) is moved at intervals.

16. The method according to claim 14 or 15, characterized in that biomass pellets are used as biomass particles.

17. The method according to claim 16, characterized in that the biomass particles contain a kaolin content of 1 Ma% to 5 Ma% and preferably from 1, 5 Ma% to 3 Ma%. 8. A method for starting up a DC fixed bed gasifier according to one of the preceding claims 1 to 13 with the method steps:

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

Ignition of the biomass particles by blowing hot air with a temperature greater than 300 ° C in the area of biomass particle bed (50) under the open end (8) of the tubular carburetor component (6).

19. A method for shutting down a DC fixed bed gasifier according to one of the preceding claims 1 to 13 with the method steps:

Stopping the supply of biomass particles,

- Continuing the supply of combustion air (L) for a predetermined period of time or until the level of biomass particles has dropped to a predetermined minimum level, and

- Stop the supply of combustion air (L).