EP2356200B1 - Method for thermochemically gasifying solid fuels - Google Patents

Description

The present invention relates to a one-step process for the thermochemical gasification of solid fuels according to the principle of an ascending DC gasification. In this method, the fuel is supplied to a gasification chamber against the force of gravity and flows through in the same direction by a gasification medium and an emerging product gas. A corresponding gasifier for the thermochemical gasification of solid fuels has a gasification chamber and a fuel supply, which supplies the fuel against gravity to the gasification chamber and a supply for a gasification medium in the gasification chamber. Furthermore, the carburetor has a top side arranged on the gasification chamber outlet for a product gas.

Methods of thermochemical gasification have been known for a long time in the prior art, and in connection with regenerative energy generation and waste and waste disposal, a great potential has been seen in gasification for a long time. Nevertheless, no such method has been able to establish itself on the market in large numbers until now.

State-of-the-art fluidized bed gasifiers require relatively complex plant technology, and the tar content of the gases produced necessitates a further, complicated gas purification for most applications. They are therefore usually used electrically only for plant sizes greater than 1 MW.

From the DE 1 017 314 B is known a fluidized bed gasifier, which allows the withdrawal of slag and ash as a melt and thus without mechanical installations. For this he has a very hot at the bottom, weakly moving and in the upper part a cooler, strongly moving fluidized bed. However, this process is uneconomical for low power plants because it requires two types of gasification: pure oxygen for the lower zone and water vapor for the upper zone. By supplying the oxygen in the lower, weakly moving zone, an oxidation zone is formed there. The fuel is supplied essentially above the oxidation zone, partly also in the area of the fluidized bed, and is thereby distributed and moved by the strongly moving fluidized bed. The pyrolysis and the reduction thus take place simultaneously in the entire upper bed. The tar content of the gases produced is therefore relatively high here as well. Due to the high temperatures of up to 1500 ° C, an elaborate refractory lining is required.

Fixed bed gasifiers are usually subdivided into countercurrent and direct current gasifiers, cross flow gasifiers and double fire gasifiers are the most common mixing and special forms, but essentially have the same problems as the two basic forms. Although the countercurrent carburetors have a very good efficiency, but are due to the extreme Teerbeladung the product gas for small and medium-sized systems completely unsuitable.

A mixed form of a fixed bed gasifier is in the WO 97/01617 A1 shown. The gasification takes place there in a mixed flow composed of countercurrent, direct current and crossflow. The ash discharge takes place at the bottom of a grate. To control the process, a temperature profile is recorded via the height of the carburettor and, based on this, the position of the oxidation zone is set by moving the grate. Due to the moving grate and the process control in the mixed stream of the carburetor is structurally relatively expensive.

Descending DC gasifiers are operated in large numbers in the form of Imbert carburetor and similar devices during World War II and are used in this or slightly modified form for most of the smaller carburetor plants, as they deliver a low-tar gas. They are characterized in that the fuel sinks by gravity down and the carburetor from the gasification agent and product gas is also flowed through in this direction. They require coarse-grained fuel with a relatively narrow particle size distribution, since otherwise the underlying reduction zone is "blocked" by fines and thus is no longer permeable enough for the product gas. In addition, bridges and gas channels can form in oxidation and reduction zones, so that a fuel gas loaded with a high tar content is produced.

To overcome these problems, numerous inventions use agitators or vibrators, such as DE 197 55 700 C2 , where by means of a stirrer, the channel formation is to be prevented. The EP 0 955 350 B1 suggests, however, by means of a swirl formation with the aid of the supplied air to prevent the passage of uncooked tar from the pyrolysis gas. Below the oxidation zone in this case a diaphragm is used, on which solid particles are to accumulate.

Furthermore, ascending direct current gasifiers are known in which the fuel is supplied from below. Again, it may lead to channel and bridge formation and problems due to the Teerbeladung of the product gas.

The DE 44 17 082 C1 describes an ascending DC gasifier with an air-cooled agitator to avoid channel and bridge formation. The agitator simultaneously carries the ash out of the reaction vessel through a lateral opening by means of a rotary vane. Furthermore, an afterburner chamber with secondary air supply above the pyrolysis zone is provided in order to crack the tar-charged pyrolysis gases and to deposit dust-like pyrolysis coke.

The DE 35 09 263 A1 also shows a fixed bed gasifier operating on the ascending DC method. The fuel and the gasification agent are supplied to the carburetor from below. In order to achieve a uniform combustion and gasification of the fuel and to avoid caking and channeling, a mixing device is provided in the gasification chamber in this carburetor. Both the oxidation zone and the reduction zone are formed in this gasifier layered in a fixed bed. Each zone is assigned its own mixer.

The EP 0 531 778 A1 shows another design of a DC gasifier, in which the fresh fuel is added from above and transported through an inner tube of a screw conveyor inside the carburetor down towards the carburetor bottom. At the same time, the inner tube also forms the pyrolysis zone. At the lower end of the inner tube, the fuel exits and enters the lower outer region of the screw conveyor, where it passes through an oxidation process due to the gasification agent supplied there. By the screw conveyor, the material is transported to the upper end of the screw, where it mixes with freshly supplied from above fuel. The reduction takes place during transport of the fuel from bottom to top. The withdrawal of the product gas takes place in a central region of the screw.

Components in the area of the oxidation zone are exposed to high thermal loads and heavy wear. In addition, internals are expensive at temperatures well above 1,000 ° C and have a low life expectancy.

The object of the present invention is to provide a gasification process and a device which, with simple plant technology, enable the production of a low-tarry product gas.

The object is solved by the features of independent claim 1. Advantageous embodiments of the invention are described in the respective subclaims.

In a one-step process for the thermochemical gasification of solid fuels according to the principle of ascending DC gasification, a fuel is supplied to a gasification chamber contrary to gravity and flows through a gasification medium and a resulting product gas in the same direction. Suitable fuels here are all carbonaceous solids such as biomass, sewage sludge, plastics and the like. In question. In a single-stage gasifier, a gasification space is provided, a fuel supply, which supplies the fuel against gravity to the gasification space and a supply for a gasification medium. On the upper side of the gasification chamber, an outlet for a product gas is furthermore arranged. According to the invention, it is now provided that the fuel is supplied to the gasification chamber continuously or at least quasi-continuously via a fuel feed in the gasifier bottom, that the gasification medium via a feed, which is arranged below in the gasification layer layer forming reaction zones, through the supplied fuel through a layer-forming Oxidation zone is supplied and in this case the amount of the supplied gasification medium is adjusted by a control unit such that in a reduction zone above the oxidation zone without additional fluidizing a stationary fluidized bed is formed. The discharge of ash takes place only through the outlet for the product gas.

The fuel supply is in this case arranged in the carburetor bottom and preferably formed adjustable for continuous or quasi-continuous fuel supply. In the case of the gasifier, the feed for the gasification medium is layered below itself in the gasification space Reaction zones arranged in order to achieve a uniform flow through the pyrolysis, oxidation and reduction zone, which forms substantially homogeneously. A supply for another fluidizing means is not provided, and an ash discharging device is formed only through the outlet for the product gas and the exiting product gas. As a result of the continuous supply of the fuel, the fuel in the gasification chamber is conveyed substantially homogeneously from bottom to top through the gasification space and flows through the gasification medium from below. As a result, the fuel itself forms a distributor plate for producing a stationary fluidized bed. The supplied amount of the gasification medium is in this case controllable by a control unit such that in the lower regions of the carburetor in the fuel supply and the pyrolysis zone is a fixed bed, in the overhead reduction zone, however, can form a fluidized bed. This is made possible by the increase in volume of the gasification medium flowing through as a result of the strong rise in temperature in the oxidation zone and by the pyrolysis and combustion gases which form. Thus, it is possible to carry out simultaneously without pyrolysis in a fixed bed and a coke gasification by reduction in a fluidized bed without using a mechanical Anströmbodens and without further fluidizing in the same reactor vessel, without mechanical separation. By using the fuel as a distributor plate or the corresponding supply of the gasification medium, a stable over a wide range of air volume fluidized bed can be generated. As a result, a substantially improved implementation of the pyrolysis coke formed in the oxidation zone in gas and fly ash is possible. By the uniform flow through the pyrolysis, oxidation and reduction zone in this case a comparatively tarerarmes gas can be generated, which can be achieved by the continuous fuel supply and the almost complete implementation of the pyrolysis coke a very uniform quality of the gas. The inventive method thus operates on the basic principle of an ascending DC gasification, which is combined with an integrated fluidized bed. The resulting Ash is completely discharged by the exiting product gas. Due to the upper burnup and the almost complete material conversion, no further discharge devices for the ash are required.

According to an advantageous embodiment of the invention, the reduction zone above the oxidation zone is completely formed as a stationary fluidized bed. The implementation of the fuel or the pyrolysis coke can be done in a favorable manner and in a short time.

Advantageously, the fuel in the gasification space is loosened contactless and mixed. The loosening and mixing of the fuel is not actively mixing, but only passively, by continuously sufficient free-flowing, fresh fuel is supplied. Due to the uniform flow through the reaction zones and the introduction of the gasification medium from below through the fuel through the mixing and loosening is further supported.

The fuel is thereby kept constantly in motion, whereby a channel and bridging in the fuel can be avoided. By means of the method according to the invention it is therefore possible, without mechanical parts in the gasification space, which are always exposed to high loads, to achieve a tarerarmes gas uniform quality at a high efficiency.

Devices for conveying and / or mixing the fuel are in this case arranged exclusively outside the gasification space, so that there are no components in the temperature-loaded zones of the gasification space. The carburetor can thus be operated with little interference and is exposed to little wear. In addition, the structural complexity of such a carburetor is low. Depending on the type of fuel used, however, additional mixing devices can also be used.

The method is preferably carried out in such a way that the fuel in the oxidation zone is burned from top to bottom at a substantially constant speed. This can be achieved by a corresponding continuous supply of the gasification medium, so that forms a layered oxidation zone at a constant ratio of the supply of the gasification medium and the fuel.

Furthermore, it is advantageous if a pellet-shaped fuel is used as fuel, preferably wood pellets are used. Especially with wood pellets is a standardized fuel with defined properties available, which is available in large quantities on the market. The homogeneity and flowability of pelletized fuels enables a relatively simple carburetor design using simple conveyor technology and thus leads to cost-effective overall systems. The extra cost over non-pelleted fuels is more than offset. However, chips of small grain size are equally conceivable and suitable.

Preferably, the gasification medium is supplied together with the fuel and flows successively through a pyrolysis zone, the oxidation zone and the reduction zone. In a device for gasifying solid fuels, the feed for the gasification medium is preferably formed together with the fuel supply.

An embodiment with a separate feed for the gasification medium is also possible. Preferably, however, the supply of the gasification medium from the bottom takes place here as well, since this the mixing of the fuel is supported. Furthermore, the formation of channels and the trickling back of fines is prevented. In principle, however, it is also possible to feed the gasification medium below the pyrolysis zone laterally, for example via an annular nozzle.

It is also advantageous if the gasifier is operable with different power. For this purpose, it is advantageous if the fuel is conveyed through the gasification space with the speed decreasing towards the top. As a result of the burnup of the fuel in the oxidation zone at a substantially constant rate downwards, only the position of the oxidation zone within the gasification chamber shifts, whereby, however, a stable operating point always sets itself in a self-regulating manner.

In order to operate the carburetor with different power, it is advantageous if the gasification chamber has an upwardly widening cross-section. This ensures that the fuel is passed through the carburetor with the speed decreasing at the top. As a result, adaptation to the processes taking place at different speeds in the individual reaction zones is possible in a favorable manner. The position of the oxidation zone in the gasification chamber always adjusts itself at the point where the combustion rate and the feed rate coincide.

According to another advantageous embodiment of the invention, the gasification chamber is surrounded by an insulation, preferably of ceramic fibers. The thermal load of the carburetor outer wall can be reduced thereby.

Furthermore, it is advantageous if the gasification medium and / or the fuel are preheated. Part of the required process heat can thus be introduced into the process from the outside. Likewise, however, the required process heat can also be completely autothermal by substoichiometric combustion of a portion of the fuel.

It is furthermore advantageous if at least one temperature sensor is arranged in the gasification space, which monitors the fill level of the gasification space. It is also advantageous if in the gasification room a plurality of sensors is arranged, which detect the position of the forming reaction zones, in particular the oxidation zone. Since in the method according to the invention, the individual reaction zones form very homogeneous and layered, they have significant temperature differences. The location of the reaction zones as well as the level in the gasification space can thereby be detected simply, inexpensively and without the arrangement of moving parts by temperature sensors.

Furthermore, it is advantageous if a wall of the gasification chamber is made of a conventional steel. Due to the uniform flow through the reaction zones as well as the high material conversion in the fluidized bed, a low-tarry product gas can be produced in the device at comparatively low temperatures of approximately 850 ° C. There is a reducing atmosphere in the area of high temperatures. The structural complexity of the carburetor can thus be kept low by using a conventional steel. Special refractory lining, high temperature resistant steels or ceramics are not required.

It is furthermore advantageous if the ash discharged with the product gas is separated from the product gas by means of a separation device. This can be accomplished by simple means, such as a cyclone separator.

Figur 1

ein Ausführungsbeispiel eines Vergasers in einem schematischen Vertikalschnitt sowie eine schematische Darstellung des erfindungsgemäßen Verfahrens und

Figur 2

eine schematische Darstellung des erfindungsgemäßen Verfahrens, wobei die Reduktionszone in Form einer Wirbelschicht ausgebildet ist.

Further advantages of the invention will be described with reference to the embodiments illustrated below. Show it:

FIG. 1

an embodiment of a carburetor in a schematic vertical section and a schematic representation of the method according to the invention and

FIG. 2

a schematic representation of the method according to the invention, wherein the reduction zone is formed in the form of a fluidized bed.

In both figures, the carburetor 1 has a fuel supply 2 in the carburetor bottom with a delivery unit 5 for the fuel. In the interior of the carburetor 1, a gasification chamber 3 is arranged, which has a variable cross-section in the example shown. In the present case, the gasification chamber 3 is frusto-conical and separated from the outer Vergaserwandung by an insulation 4.

In the upper region of the gasification chamber 3, a gas collecting chamber 12 is formed, in which the resulting gases 14 are collected and withdrawn through the outlet 7 arranged on the top side of the gasification chamber 3. Furthermore, the carburettor 1 has a feed 6 for a gasification medium 16, which is in operative connection with a control unit 15. By means of the control unit 15, according to the invention, the amount of the gasification medium 16 fed in can be controlled in such a way that a fluidized bed 17 is formed automatically without mechanical distributor bottoms in the gasification space and without additional fluidizing means.

FIG. 1 in this case shows a carburetor 1, in which the feed 6 for the gasification medium 16 is formed together with the feed 2 for the fuel 8. As a result, the fuel 8 flows through from below from the gasification medium 16, so that the mixing of the fuel 8 is supported and a uniform distribution of the gasification medium 16 over the entire cross section is ensured.

However, the supply of the gasification medium 16 may also, as in FIG. 2 shown below the pyrolysis zone 9 laterally by an annular nozzle. Again, however, the supply of the gasification medium 16 through the fuel 8 passes through, thereby mixing the fuel. 8 and uniform distribution of the gasification medium 16 to achieve. Additional mechanical mixing devices are therefore not required. In addition, this can prevent fines from the overhead reaction zones 9, 10, 11 from entering the fuel 8.

In the method according to the invention, the fuel 8 is continuously or quasi-continuous against gravity, i. the same amount of fuel per unit time, pressed by the fuel supply 2 into the gasification chamber 3 and promoted by the carburetor 1. The fuel 8 in this case flows through the gasification medium 16 and product gas 14 in the same direction. It is therefore in this respect an ascending DC gasification. As a gasification medium 16 is advantageously used preheated air. However, the process can also be completely autothermic.

The combustion of the fuel 8 takes place from top to bottom, with a layer-shaped oxidation zone 10 is formed at a suitable constant ratio of air supply to fuel. By prevailing in the oxidation zone 10 temperatures of about 800 ° C is formed below the same also a layered pyrolysis zone 9, in which decomposes the fuel 8 at temperatures around 500 ° C in pyrolysis and gaseous compounds. The gas-air mixture formed in the pyrolysis zone 9 by the air 16 flowing through the fuel 8 from below through the fuel 8 maintains the energy production in the oxidation zone 10, where a part of these gases and the pyrolysis coke burns. The remaining pyrolysis coke formed in the pyrolysis zone 9 gradually migrates upwards through the oxidation zone 10 and forms a reduction zone 11 above it. The presentation of the FIG. 2 shows a process in which the reduction zone 11 is formed substantially completely in the form of a fluidized bed 17. In this way, a particularly good and rapid implementation of the pyrolysis coke can be achieved. Depending on the process control and possibly also structural conditions of the carburetor 1, however, a method according to FIG. 1 possible, wherein the reduction zone 11 above the oxidation zone 10 is first formed in layers. In the upper region of the gasification space, however, the reduction zone 11 is present as a fluidized bed 17. In each case, the gasification is carried out according to the principle of an ascending DC gasification, which, however, according to the invention is combined with an integrated fluidized bed 17 in the reduction zone 11.

In the reduction zone 11, 17, the pyrolysis coke is flowed through, inter alia, by CO ₂ and H ₂ O from the pyrolysis zone 9 and the oxidation zone 10, these being reduced endothermically to the combustible gases CO and H ₂ , whereby the pyrolysis coke is gasified.

If, in the reduction zone 11, the intermediate spaces in the pyrolysis coke become clogged by fines, the resulting gas pressure causes the pyrolysis coke to be raised and thereby loosened. It forms according to the invention by the appropriate adjustment of the supplied amount of the gasification medium 16 and the flow of the fuel 8 from below an equilibrium between the gas pressure and the weight of the pyrolysis coke up to the fluidized bed.

The supplied from below gasification medium 16, preferably air, experiences in the oxidation zone 10, a sudden increase in temperature and, associated therewith, an increase in volume. Together with the resulting pyrolysis and combustion gases, this leads in particular to the preferred use of commercially available wood pellets as fuel for permanent formation of a fluidized bed 17 in the reduction zone 11. Thus, the known from fixed bed gasifiers critical channel formation is completely suppressed in this area.

In the gasification process of the invention, the fuel 8 forms by its continuous För-tion with appropriate control of the supply of the gasification medium 16 a distributor plate for fluidized bed production. The fluidized bed 17 can be produced without further fluidizing agent. This makes it possible to almost completely convert the pyrolysis coke formed in the oxidation zone 10 to gas and fly ash and thus to achieve a high degree of efficiency of the overall process. It has been shown that the fluidized bed 17 is stable in the carburetor 1 over a relatively wide range of air volumes and thus the regulation of the amount of air through the control unit 15 is easily possible to the necessary for the thermochemical gasification air rates.

The resulting ash is preferably discharged as fly ash without additional discharge devices with the process gas 14 and then separated from the product gas 14 by simple means, for example by a cyclone separator. Due to the upper burnup in the method according to the invention and the guidance of the gasification medium 16 and the product gas 14 through the carburetor 1 and the good implementation of the fuel 8, the product gas 14 with the outlet 7 as discharge devices for the ash is completely sufficient. If, however, excess pyrolysis coke is produced or intentionally generated, this can likewise be taken off together with the resulting dusty ash with the product gas 14.

In the gasification process according to the invention, the uniform flow through the very homogeneously forming pyrolysis, oxidation and reduction zones 9, 10, 11 leads to the production of a tarry gas of very uniform quality at comparatively low temperatures of about 850 ° C. in the oxidation zone 10 possible to carry out a carburetor 1 without the use of special high-temperature resistant steels or ceramics. Even conventional structural steel can be used, since there is no appreciable oxidation due to the reducing atmosphere of the substoichiometric combustion. The avoidance of the usual in the prior art ceramic components also leads due to low heat capacity advantageously too short heating and cooling times when starting and stopping the carburetor. 1

A preferred embodiment of a carburetor 1 has, as shown in the example, an upwardly widening cross-section of the gasification chamber 3. This allows operation with different power, because it causes the fuel 8 to move upwards through the carburetor 1 with decreasing speed. The burning down to be carried out in the oxidation zone 10 at a substantially constant speed now leads to a self-regulating setting of a stable operating point at which the oxidation zone 10 remains at the point where the burning rate and feed rate of the fuel 8 coincide.

Furthermore, the continuous or quasi-continuous supply of new fuel 8, in particular in conjunction with the changing cross-section of the gasification chamber 3, ensures constant movement and thorough mixing of the material and thus prevents channeling and bridge formation in the oxidation and reduction zones 10, 11 without further mechanical devices.

In the gasification chamber a plurality of superimposed temperature sensors 13 is further arranged, which cooperate with the control unit 15 and the level of the gasification chamber 3 and the position of the reaction zones (9, 10, 11) detect by measurement. The boundaries between the fuel 8 and the pyrolysis and oxidation zone (9, 10) and between the reduction zone (11) and the overlying gas collection chamber (12) are characterized by significant temperature differences due to the very homogeneous formation in the inventive method and the carburetor , The control technology important location of the reaction zones 9, 10, 11, in particular the oxidation zone 10, and the filling level can thus be detected in a simple manner cost and without moving parts.

The advantages achieved by the invention are in particular that a carburetor 1 manages without moving parts in the hot area and has no mechanically loaded hot parts, which often constitute a source of interference in the prior art. The carburetor 1 according to the invention finds by self-regulating properties with low mechanical and / or electronic control effort a stable operating point and thus provides a durable tarerarmes product gas with only slightly fluctuating quality. Channel and bridge formation as well as tar slippage can be avoided. The carburetor 1 is therefore particularly suitable for small and medium sized systems up to about 1 MW electrically, since no complex gas aftertreatment is required. It is also possible to directly produce a motorable product gas. Furthermore, the production of charcoal is possible by means of the device with appropriate process control.

The fuel used 8 need not be coarse and may contain high amounts of fines, since the process control a tendency to clog is avoided. Thus, fuels 8 which are available in sufficient quantity on the market can be used.

Due to the simple structural design and a simple control technology by means of the control unit 15, the carburetor 1 can also be manufactured and operated inexpensively.

The invention is not limited to the illustrated embodiment. Variations and combinations within the scope of the claims also fall under the invention.

Claims (6)

1. A single-stage method for thermochemically gasifying solid fuels (8) according to the principle of rising downdraft gasification, a fuel (8) being fed into a gasifying chamber (3) against gravity, a gasifying medium (16) being mixed into the fuel in a downdraft, and a resulting product gas (14) being discharged in a downdraft, characterized in that, the fuel (8) is continuously fed into the gasifying chamber (3) via a fuel inlet (2) in the gasifier floor, and that the gasifying medium (16) is fed from below through the infed fuel (8) into a forming stratified oxidation zone (10), wherein the gasifying medium (16) is fed via an inlet (6) below a stratified pyrolysis zone (9) forming in the gasifying chamber (3) and present as a solid bed into the stratified oxidation zone (10) and into a reduction zone (11), wherein the fuel forms an impinging flow floor for generating a stationary fluidized bed and wherein the amount of the gasifying medium (16) fed in is adjusted by a controller unit (15), such that a solid bed is present in the lower regions of the gasifier in the fuel inlet and in the pyrolysis zone, and the stationary fluidized bed (17) is implemented in the reduction zone (11) above the oxidation zone (10) without a mechanical flow impingement floor, and without feeding in additional fluidizing medium, and the ash produced is carried away solely by the exiting product gas.
2. The method according to the preceding claim, characterized in that the reduction zone (11) above the oxidation zone (10) is entirely implemented as a stationary fluidized bed (17).
3. The method according to any one of the preceding claims, characterized in that the fuel (8) is broken up and mixed without contact in the gasifying chamber.
4. The method according to any one of the preceding claims, characterized in that the gasifying medium (16) is fed in together with the fuel (8) and flows through a pyrolysis zone (9), the oxidation zone (10), and the reduction zone (11) in sequence.
5. The method according to any one of the preceding claims, characterized in that the fuel (8) is transported through the gasifying chamber (3) at a velocity decreasing with upward progression.
6. The method according to any one of the preceding claims, characterized in that the fill level of the gasifying chamber (3) and/or the location of the forming reaction zones (9, 10, 11), particularly the pyrolysis zone (9), the oxidation zone (10), and the reduction zone (11) is captured by one or a plurality of temperature sensors (13).

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