EP0971017A2 - Process and apparatus for gasifying a solid fuel in lump form - Google Patents

Abstract

The low calorific gas arising from carbonization is heated in a cracker reactor (II) to T2 such that long chain and/or (poly)cyclic hydrocarbon compounds are thermally-cracked. An Independent claim is included for the corresponding gasification plant. Preferred Features: Heating is indirect and no oxidant is supplied. The char is oxidized in a combustion reactor, releasing energy to heat the fuel. Water is supplied to the gasifier. T2 is 600 degrees C or more, preferably 800 degrees C-1000 degrees C. Fuel in the gasifier is heated by a heat exchanger surface. Fuel is oxidized in a separate reactor from the gasifier. The cracker is inside the combustor, which is inside the gasifier reactor. The cracker has the form of a tubular spiral. Gasifier and combustor form a unit, with the fuel moving under gravity. Gas leaving the combustor rises into the adjacent cracker which shares a common wall with the combustor, near a combustion zone. The combustor has a conveying unit below, taking fuel in to the side, beneath the cracker. Heat exchanger surfaces in the cracker are provided with catalytic substances.

Description

The invention relates to a process for the gasification of a solid fuel in particulate form to a combustible lean gas, the fuel being heated in a degassing reactor to a temperature T ₁ such that gasification associated with its pyrolysis takes place. The invention further relates to a device for performing such a method.

Processes of the aforementioned type have been around since the 1940s generally known, with the lean gas initially generated mainly used to drive motor vehicles and unavailable fuels Should replace mineral oil base. In the course of increased environmental awareness, in particular with regard to demands for an increased use of regenerative Energy carriers, the interest in such processes has grown again. Wood comes in the form of small wood or wood waste in question, which usually rot or - without doing so to generate energy to be used - to be burned in the great outdoors.

A particularly interesting way of gasifying wood is with the lean gas generated the internal combustion engines or gas turbines of a combined heat and power plant to operate. Combined heat and power plants stand out due to the combined heat and power by their very high efficiency.

The problem of burning the lean gas in internal combustion engines exists in that its dust and long-chain and / or (poly) cyclic content Hydrocarbon compounds is very high. When the weak gas is supplied to the engine or the gas turbine there is thus condensation of tar-like Substances and for sticking the dust, what an engine operation on longer duration impossible. A variety of attempts at these substances filtering or separating has so far not led to a practical solution.

In principle, two different processes for wood gasification are known:

aufsteigende Gegenstromvergaser" verwendet, bei denen sich oberhalb eines Rostes eine Oxidationszone des Brennstoffs ausbildet. Darüber befindet sich eine Reduktionszone, die wiederum von der Pyrolysezone überlagert wird, in der die Brennstoffvergasung stattfindet. Das nach oben aus dem Brennstoff aufsteigende Schwachgas wird am oberen Ende des Gegenstromvergasers abgezogen, wo auch die Zufuhr neuen Brennstoffs erfolgt. Unterhalb des Rostes, durch den auch die zur Oxidation des Brennstoffs erforderliche Luft zugeführt wird, befindet sich ein Auffangbehälter für Asche.In a first method, the flow of the fuel is conducted in the opposite direction to the flow of the lean gas. So-called

ascending countercurrent gasifier ", in which an oxidation zone of the fuel forms above a grate. Above it is a reduction zone, which in turn is overlaid by the pyrolysis zone in which the fuel gasification takes place The counterflow gasifier is removed, where new fuel is also fed in. Below the grate, through which the air required for the oxidation of the fuel is also supplied, is a collecting container for ash.

The disadvantage of this method is that the tar and dust content of the resulting weak gas is very high.

A second known method for gasification provides that the flow of the fuel and the flow of the lean gas run in the same direction. Devices for performing this method are called descending direct current gasifier "and are provided with a cross-sectional constriction in the area of the oxidation zone in order to ensure that the glow bed is supplied with air or the oxidizing agent as evenly as possible. As a result, the most uniform possible oxidation zone is to be formed over the entire cross section.

A disadvantage of the DC gasifiers is that they are very are sensitive to differences in the fuel size. Furthermore is the controllability very poor, especially if the oxidation zone is even should extend over the entire cross section of the carburetor. Furthermore, Such types of carburettors are very difficult to design for outputs above 1 MW.

From Fraunhofer magazine 1.1998 is on page 50 ff. Under the title A wood gasifier for cogeneration plants has become known as a gasifier which uses the fluidized bed technology known from large power plants. The core of the gasifier is a reactor, into which air is blown from the underside, which whirls up a bed of sand mixed with wood chips. While the particles go up whirled, the wood burns up, producing a flammable lean gas.

Unfortunately, the lean gas must be fed to a cyclone separator be used to separate sand and ashes that enter the swirl chamber via a siphon to be led back. In a next document the lean gas must be one Gas cooler and then fed to a secondary cyclone in which a deposition from fly ash. Finally, with the help of a gas filter the separation of filter ash before the lean gas finally becomes a gas engine can be supplied.

Understandably, the known system is very complex in its structure and therefore very expensive. It is therefore not suitable for low-power carburetors.

The invention has for its object a method for the gasification of a solid To propose fuel, in which a flammable lean gas in a simple manner is generated that an internal combustion engine without further cleaning measures can be supplied.

Starting from a method of the type described in the introduction, this object is achieved according to the invention in that the lean gas formed is heated in a post-treatment reactor to a temperature T ₂ such that long-chain and / or cyclic hydrocarbon compounds contained in the lean gas are thermally split.

The thermal breakdown of the long-chain and / or (poly) cyclic hydrocarbon compounds by realizing a sufficiently long dwell time of the Gases in a hot environment is a very elegant way to get around Process end product after the aftertreatment reactor to obtain a lean gas, fed directly to an internal combustion engine without further treatment can be. The weak gas thus obtained contains almost no tar compounds and no more dust and burns almost soot-free with a bluish flame. Even in continuous operation with a lean gas, that with the invention Process was produced, there were no faults in test engines or failures.

When heating the fuel indirectly without adding an oxidizer takes place, the weak gas obtained has a particularly high Calorific value. A dilution, such as when using Air as an oxidizing agent due to the nitrogen it contains can affect this Way can be prevented.

The degassed fuel is advantageously oxidized in a combustion reactor, the heat released for heating the fuel in the degassing reactor is used.

The supply of the oxidizing agent to the combustion reactor is thus decoupled from the degassing of the fuel in the degassing reactor. The invention Processes can be controlled or regulated particularly well in this way.

To obtain a weak gas with a particularly high hydrogen content, it is proposed that that water is supplied to the degassing reactor.

In order to guarantee a complete thermal breakdown of the tar compounds, it is provided that the temperature T _{2 is} at least 600 ° C, preferably 800 ° C to 1000 ° C.

A device for the gasification of a piece of fuel into a combustible lean gas has a degassing reactor in which the fuel can be heated to a temperature such that gasification associated with its pyrolysis occurs and is characterized according to the invention by an aftertreatment reactor for the lean gas, in which it can be heated to a temperature T ₂ such that long-chain and / or (poly) cyclic hydrocarbon compounds contained in the lean gas can be thermally split.

With the device according to the invention, a high quality can be easily obtained Generate tar and dust-free lean gas, which without further cleaning or Separation processes can be used directly in an internal combustion engine.

Further developing the device according to the invention, it is proposed that the fuel in the degassing reactor can be heated indirectly via at least one heat exchanger surface. This can prevent the lean gas from being diluted with air, nitrogen or CO _2, for example, as would be the case with heating by combustion gases. The entry of ash from the oxidation of the degassed fuel is also avoided.

A particularly simple controllability of the device results when the fuel oxidizable in a combustion reactor separate from the degassing reactor is.

This is advantageous when the fuel is oxidized in the combustion reactor heat released to the degassing reactor and / or the aftertreatment reactor feedable.

From an energy point of view, an embodiment of the device offers particular advantages in which the aftertreatment reactor is arranged inside the combustion reactor and this is arranged inside the degassing reactor. The zones of highest temperatures are in this arrangement in a central area of the device, the as Isolation "acting edge areas (degassing reactor) can cover their energy needs in the form of waste heat from the combustion reactor.

With such a configuration, it is particularly advantageous if the aftertreatment reactor is in the form of a tube spiral. This will create a large heat transfer area and a sufficiently long residence time of the Low gas guaranteed in the aftertreatment reactor.

A further development of the invention is that the degassing reactor and Combustion reactor form a fuel reactor unit through which the fuel following the force of gravity, which is counter to gravity from the Fuel reactor unit flowing lean gas in the arranged next to this Aftertreatment reactor can be conducted with the fuel reactor unit in the area has a common wall in a combustion zone.

With such a device, the fuel is transported in a simple manner by the action of gravity, and the lean gas is the appropriate channels Area of the combustion zone. There is no direct connection between the aftertreatment reactor and the combustion reactor so that it there is no dilution effect of the weak gas.

Furthermore, it is provided that the fuel reactor unit on its underside is provided with a conveyor with which the fuel in the area of a combustion zone in the lateral direction below a section of the aftertreatment reactor is eligible.

In this way, the contact zone between the aftertreatment reactor and the combustion reactor increases and therefore the heat transfer to the aftertreatment reactor and the dwell time of the lean gas in it increased become.

Finally, an embodiment of the device according to the invention also provides that heat exchanger surfaces of the aftertreatment reactor with catalytically active Fabrics are provided, reducing the degree of implementation of the long chain and / or (Poly) cyclic hydrocarbon compounds further increased or the required Dwell time can be reduced.

Fig. 1

ein prinzipielles Verfahrensschaubild;

Fig. 2

eine Vergaservorrichtung mit koaxial zueinander angeordnetem Nachbehandlungsreaktor, Verbrennungsreaktor und Entgasungsreaktor;

Fig-. 3

eine alternative Ausführung mit einer Brennstoftreaktor-Einheit und

Fig. 4

wie Fig. 3, jedoch mit beweglichem Rost.

The method according to the invention is explained in more detail below on the basis of several exemplary embodiments of devices which are suitable for carrying it out. It shows:

Fig. 1

a basic process diagram;

Fig. 2

a gasification device with coaxially arranged aftertreatment reactor, combustion reactor and degassing reactor;

Fig. 3rd

an alternative version with a fuel reactor unit and

Fig. 4

3, but with a movable grate.

The process diagram shown in FIG. 1 illustrates that wood and water are fed to a degassing reactor 1. A heat exchanger surface 2 of the degassing reactor 1 transfers the heat of flue gas, which comes from a combustion reactor 3, to the wood in the degassing reactor 1, whereby this is gasified to a lean gas, leaving only coal. The coal is conveyed to the combustion reactor 3 by means of suitable conveying means - indicated by the dash-dotted line 4 - where it is burned to ashes with the supply of air. The energy released during coal combustion is transferred via a heat exchanger surface 5 into an aftertreatment reactor 6, in which the lean gas coming from the degassing reactor 1 is heated to a temperature such that tar-like substances are thermally split. In this way, a high-quality tar- and dust-free wood gas with a high H ₂ content is generated from the tar-containing lean gas. The flue gas from the combustion reactor 3 used to heat the degassing reactor 1 is cooled and released as exhaust gas.

2 shows the basic structure of a discontinuously operating gasifier, in which three reactors are arranged coaxially to one another:

The spiral-shaped aftertreatment reactor is located inside the device 11 12 through which the initially tar-containing lean gas is passed. The aftertreatment reactor 12 is located inside the tubular combustion reactor 13, in which the degassed glowing charcoal is located Ash burns. In its lower section, the combustion reactor 13 has one Grate 14, through which the resulting ash into an ash container 15 falls. Below the grate 14 is the combustion reactor 13 with a nozzle 16 provided for the supply of combustion air. The exhaust gas leaves the combustion reactor 13 at the top.

The combustion reactor 13 is surrounded on all sides by the degassing reactor 17 in where the wood to be gasified is. Because of the heat given off by the combustion reactor 13 the wood in the degassing reactor is heated to such a temperature heated that a gasification associated with the pyrolysis of the wood takes place. The tar-containing lean gas formed during the gasification is by a End connector 18 of the aftertreatment reactor 12 is introduced into and leaves the latter this as tar-free and low calorific gas.

The walls of the degassing reactor 17 are provided with insulation 19 on all sides, to keep the heat loss of the device 11 low. The feed of the Wood in the degassing reactor 17 and the transport of the degassed charcoal from the degassing reactor 17 into the combustion reactor 13 is in the drawing not shown, but can be done using known conveyor technology, so that the method can also be operated continuously. Through a nozzle 20 can Degassing reactor 17 water are supplied.

In the device shown in Fig. 3, the degassing reactor and the Combustion reactor a fuel reactor unit 22. Within this fuel reactor unit 22 is the degassing zone 23 of the upper area wood fed from above, while in a lower area the combustion zone 24 for the charcoal.

The ashes fall through a grate 25 into an ash collecting container 26 through a nozzle 27 the supply of the combustion zone 24 with combustion air possible.

The aftertreatment reactor is located to the side of the fuel reactor unit 22 28, in which the lean gas flows in from above after being in an upper one Area 29 of the fuel reactor unit 22 was deflected. A good heat conductor Wall 30 seals fuel reactor unit 22 from the aftertreatment reactor 28 from. The device described above has the advantage that a Transport of unburned and degassed fuel only through the Gravity occurs and no driving means for hot substances are required are.

The device 31 shown in FIG. 4 has a structure which is comparable in principle like the device 21 shown in FIG. 3, but is in the region of the combustion zone 32 provided with a conveyor 33, the glowing charcoal in a region to the side next to the degassing zone 34. The fuel reactor unit 35 therefore has the shape of an L. This also applies accordingly to the Post-treatment reactor arranged laterally next to the fuel reactor unit 35 36.

Due to the horizontal L-leg 37, a very large contact area 38 can be of the aftertreatment reactor 36 can be achieved with the combustion zone 32, whereby there is a particularly effective thermal decomposition in the weak gas contained tar compounds results.

An advantage of the device described above is that due to the combined Fuel reactor unit a transport of the degassed fuel from a Degassing reactor in a combustion reactor is not required.

Claims (14)

Process for the gasification of a solid fuel present in lump form to a combustible lean gas, the fuel being heated in a degassing reactor to a temperature T ₁ such that gasification associated with its pyrolysis takes place, characterized in that the lean gas formed is in a post-treatment reactor such a temperature T _{2 is} heated that the long-chain and / or (poly) cyclic hydrocarbon compounds contained in the lean gas are thermally split. A method according to claim 1, characterized in that the heating of the Fuel takes place in an indirect manner without the addition of an oxidizing agent. A method according to claim 1 or 2, characterized in that the degassed Fuel is oxidized in a combustion reactor and the fuel released in the process Heat is used to heat the fuel in the degassing reactor becomes. Method according to one of claims 1 to 3, characterized in that water is supplied to the degassing reactor. Method according to one of claims 1 to 4, characterized in that the temperature T _{2 is} at least 600 ° C, preferably 800 ° C to 1000 ° C. Device for the gasification of a fuel in piece form into a combustible lean gas, with a degassing reactor in which the fuel is heated to a temperature T ₁ such that gasification associated with its pyrolysis takes place, characterized by an aftertreatment reactor (12, 27, 36 ) for the lean gas, in which it can be heated to a temperature T ₂ such that long-chain and / or (poly) cyclic hydrocarbon compounds contained in the lean gas are thermally split. Apparatus according to claim 6, characterized in that the fuel in the degassing reactor (17) indirectly via at least one heat exchange surface is heatable. Device according to claim 6 or 7, characterized in that the fuel in a combustion reactor separate from the degassing reactor (17) (13) is oxidizable. Apparatus according to claim 8, characterized in that the oxidation the heat released in the combustion reactor (13) can be fed to the degassing reactor (17) and / or the aftertreatment reactor (12) is. Apparatus according to claim 9, characterized in that the post-treatment reactor (12) inside the combustion reactor (13) and this inside the degassing reactor (17) is arranged. Apparatus according to claim 10, characterized in that the post-treatment reactor (12) is designed in the form of a tube spiral. Apparatus according to claim 6, characterized in that the degassing reactor and the combustion reactor is a fuel reactor unit (22, 35) form, through which the fuel is movable by gravity, wherein the one that flows out of the fuel reactor unit (22, 35) against gravity Low gas in the post-treatment reactor arranged next to this (28, 36) can be conducted with the fuel reactor unit (22, 35) in the area a combustion zone (24, 32) has a common wall (30, 38). Apparatus according to claim 12, characterized in that the fuel reactor unit (35) provided on its underside with a conveyor (33) with which the fuel in the area of a combustion zone (32) in lateral Direction below a section of the aftertreatment reactor (36) can be conveyed is. Device according to one of claims 6 to 13, characterized in that Heat exchanger surfaces of the aftertreatment reactor (12, 28, 36) with catalytic acting substances are provided.

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