DE19718184C2 - Device for the energetic use of fuels, in particular biofuels - Google Patents

Description

The invention relates to a device for energetic Use of fuels, especially biofuels, preferred fuels are old and residual wood be used.

The material recycling of old and residual wood is due to the limited absorption capacity and from the emerging consumer awareness Quality requirements for these materials are limited. The Incineration in conventional waste incineration plants cannot be considered useful. The The energy content of the wood is very low in these systems used because they have the lowest possible emissions Eliminate heterogeneous waste and not on optimal use of the energy of homogeneous fuels are designed.

In various studies and surveys in recent years was the old and residual wood volume with 4 to 11 Numbered millions of tons per year. Become old and So far, residual wood mainly in waste incineration plants and landfills are disposed of, the disposal route of the Landfilling based on the specifications of the TA municipal waste no longer available in the foreseeable future. Therefore, it is necessary, immediate disposal and To create recycling alternatives.  

In the thermal recycling of old and residual wood owns the gasification technology compared to the combustion basic advantages, since the lean gas produced with a gas engine or a gas turbine directly electricity can be generated. The electrical that can be achieved Efficiency is about twice that of one Steam power process. Fixed bed gasifiers have so far been used however, difficulties in using the emerging weak gas on. The main problem is the high content of condensable components.

The gas generated during the gasification of biofuels consists essentially of hydrogen, carbon monoxide, Carbon dioxide, water vapor, methane and nitrogen. The typical composition of a primary gas in the Wood gasification is shown in Table 1. As a result incomplete gasification contains the lean gas (percent lean gas composition Table 1) proportions of condensable compounds (tar). [European Wood gasification plants, Wood gasification forum June 29, 1994 Chátel-St.-Denis].

Table 1

Typical composition of the primary gas from wood gasification

Tables 2 and 3 are examples of the raw gas values of Carburettors for particles and tar as well as the requirements presented to the clean gas for motor use.

Table 2

Gas quality of direct current gasifiers for motor applications

Table 3

Raw gas data from various carburettors

To split the condensable tar compounds high temperatures required by the addition a gasifying agent, e.g. B. air, in the carburetor can be achieved. With the increase in the nitrogen content in Low gas and the higher burnout decrease the calorific value of the gas. Carburetor according to the state of the Technology are operated with an air ratio of λ = 0.3, for an optimal yield of high quality gas to get small amounts of tar at the same time [Plant technology of wood gasification and open questions at Use of old wood Dr. Th. Nussbaumer, heating climate 9, 1990, 75-82].  

A basic distinction is made with the carburettors Fixed bed, fluidized bed and entrained flow gasifiers. In the following, only the gasification in the fixed bed is closer described.

The fixed bed carburettors are after the fuel and Gasification agent management divided. Essentially one differentiates between countercurrent, cocurrent and Cross-flow gasifiers. Of importance for the thermal So far, recycling of solid fuels is only that DC gasifier with descending gasification and the Countercurrent gasifier with ascending gasification.

The procedural principles of cocurrent and countercurrent Gasification brings different advantages and Disadvantages with it.

With a countercurrent gasifier with ascending gasification represents the high content of condensable components in the Product gas is a problem with motor use. The advantage of this type of carburetor is the simple scale up on greater achievements because of the Gasification agent addition below the fixed bed Setting even flow conditions also at an expansion of the reactor diameter is unproblematic is.

With a direct current gasifier, it is advantageous to be able to lead the gas formed through the hot oxidation zone. Here, a large part of the resulting, volatile compounds are cracked. This creates a gas that contains fewer condensable components and can be used in gas engines after cleaning. The difficulties exist when scaling up this type of gasifier to modules <1 MW _th . The gasification agent is fed to the fuel in the gasification zone from the side and must penetrate the fixed bed evenly. When the scale is enlarged, it is no longer possible to create optimal flow conditions. Hot and cold zones with quick reaction and unburned fuel are created.

The difficulties encountered with fixed bed gasifiers prevent the use in a gas engine or a gas turbine. Usually the product gas currently burned and used to produce hot water or Process steam used. The in the case of gas cooling and -Cleaning before use in the engine or turbine condensates are partly composed water-insoluble tar components and solids and others made from water mixed with a variety of soluble, organic substances is contaminated. A economical solution of water treatment exists not yet. The market does not currently offer any functional gasifier system for waste wood disposal with optimized energetic use.

DE 639 634 A describes a descending gas generator described with downward train, in the Reactor top air is supplied to sulfur fumes, such as for example, water vapor or hydrocarbons to give the carburetor to the environment. The product gas is subtracted down and a motor use fed. This means that the Sulfur vapors, although these have a relatively high latent Have energy content due to their problematic Use.  

DE 669 332 A describes a descending gas generator described, in the reactor a partial flow of added air is heated to the excess water in, Vaporizing fuel and then damaging it with others Gases are released to the environment. From one energetic use of the discarded gases is also here no speech.

Finally, DE 636 763 A shows a gas generator descending gasification, the gasification of bituminous Fuels should serve. By the provided there The long-chain hydrocarbons are turned on cracked its hot walls. This cannot insignificant deposits arise, which extend to Total failure of the carburetor. In this known Device is cracking the long chain Hydrocarbons on the glow head, only during one Additional combustion when the output increases Carburetor.

A combination is already known from DE 195 13 832 A1 a fluidized bed thermolysis and one Entrained-flow gasification known in which the gasification in Entrained current substoichiometrically using a Gasification agent is carried out.

Finally, from DE 43 16 869 C1 Gasification reactor known, in which the from Gasification reactor withdrawn gas one Combustion process fed to generate useful heat becomes. Here, both reactors are in direct current operated.

The invention is therefore based on the object known devices for the energetic use of To design and develop fuels in such a way that the content of condensable substances in the product gas minimized and the overall efficiency is optimized. The optimal use of the product gas should always be and not just during one Additional combustion phase.

This task is solved in that between the a double lock system is provided for both reactors is.

The connection according to the invention of a countercurrent reactor with a cocurrent reactor makes optimal use of the advantages of the individual reactors:

• - Good degassing of the solid to form a tar-rich gas phase in the countercurrent reactor
• - It can handle a wide range of lumpy fuel be used in the countercurrent reactor
• - Reduction in tar content and gasification of the solid, carbon-containing residue in DC reactor
• - Lead homogenized material flows in the DC reactor for even reactor operation.

To safely avoid gas exchange between Countercurrent and cocurrent reactor is now according to the invention a double lock system between the two reactors  intended. It is also expedient in each case Inlet of the countercurrent reactor and the outlet of the DC reactor with a double lock system Mistake.

Another teaching of the invention provides that Volume of the DC reactor is smaller than that of the Counterflow reactor, since the volume of the im Countercurrent reactor coke is smaller than that Volume of fuel used. In this way can be an optimal size of the whole Reach reactor unit.

To further optimize the efficiency is provided that the countercurrent reactor and / or the DC reactor a grate and a grate cone have, each grate cone at least one nozzle for Has supply of gasifying agent. Especially It is useful if the in the grate cones existing nozzles can be switched on individually.

In a further embodiment of the invention, that between the reactor unit and one Energy conversion unit for a dust collector Cleaning the weak gas and possibly a heat exchanger Cooling of the weak gas is switched. As A cyclone is the preferred dust collector Separation of coarse dust and hot gas cleaning with Ceramic candle filters used.

The countercurrent reactor and the DC reactor the same gasifying agent fed. Depending on the fuel used, however, it is also conceivable, two reactors different  Feed gasifying agent. It is also possible to Increasing the temperature in the crack zone DC reactor in addition to the lean gas further Add gasifying agents.

Air, oxygen or Steam can be used. For example, it is possible, the first gasification stage in the countercurrent reactor to operate with air and the second gasification stage in DC reactor with oxygen.

The gasification can both in the countercurrent reactor and in the DC reactor under increased pressure. Also can the gasification agent the countercurrent reactor and DC reactor in different Volume flow ratios are supplied. This is it is possible to optimize the efficiency to the respective Residual quality of various feed materials adapt.

The device according to the invention is described below one representing only one embodiment Drawing explained in more detail. In the only figure is only one reactor unit of the invention Device shown schematically in cross section.

The reactor unit according to the invention consists first and foremost of a countercurrent reactor 1 which is arranged above a cocurrent reactor 2 and is connected upstream thereof. Between the two reactors 1, 2 has a double lock system 3, an uncontrolled air exchange between countercurrent reactor 1 and reactor 2 DC to reliably prevent.

The inlet 4 and the outlet 5 of the reactor unit are also provided with double lock systems. The fuel introduced through the inlet 4 of the countercurrent reactor 1 is stacked on a grate 6 . A grate cone 7 is installed above the grate 6 . The grate cone 7 can have several, also switchable, nozzles 8 for the supply of gasification agent. Below the grate 6 there is a nozzle base 9 through which the gasification agent is fed to the countercurrent reactor 1 . The gasification agent flows through the fuel from bottom to top and the lean gas is drawn off at the top of the countercurrent reactor 1 and passed through a gas line 10 to the co-current reactor.

The partially degassed and coke-shaped fuel (not shown) which has fallen through the grate 6 is fed to the direct current reactor 2 by means of the double lock system 3 .

In the illustrated and in this respect preferred embodiment, the coke in the direct current reactor 2 is again added to a gasification medium line 11 by means of a gasification medium in order to increase the temperatures prevailing there. The gasification medium flows into the coke bed via a grate cone 14 installed on the grate 12 of the direct current reactor 2 and provided with nozzles 13 .

The lean gas supplied to the direct current reactor 2 through the gas line 10 is now passed through the hot zone prevailing in the area of the grate 12 in order to break up the long-chain hydrocarbon compounds and convert the residual carbon content of the coke into gas.

Finally, the lean gas is withdrawn behind the cracking zone by a lean gas line 15 from the DC reactor 2 and an energy conversion unit (not shown) is supplied. The ash falling through the second grate 12 is drawn off at the bottom of the direct current reactor 2 by the ash lock system present in the outlet 5 , which prevents the entry of false air.

Claims (9)

1. Device for the energetic use of fuels, in particular biofuels, with a reactor unit for gasifying the fuels and an aggregate for generating mechanical or electrical energy, the reactor unit having two reactors connected in series, of which the first reactor as a countercurrent reactor and the second as a co-current reactor are designed, characterized in that a double lock system ( 3 ) is provided between the two reactors ( 1 , 2 ). 2. Device according to claim 1, characterized in that the inlet ( 4 ) and / or the outlet ( 5 ) of the reactor unit has a double lock system. 3. Device according to claim 1 or 2, characterized in that the volume of the co-current reactor ( 2 ) is smaller than the volume of the countercurrent reactor ( 1 ). 4. Device according to one of claims 1 to 3, characterized in that the countercurrent reactor ( 1 ) and / or the cocurrent reactor ( 2 ) have a grate ( 6 , 12 ) and a grate cone ( 7 , 14 ). 5. The device according to claim 4, characterized in that each grate cone ( 7 , 14 ) has at least one nozzle ( 8 , 13 ) for supplying gasifying agent. 6. The device according to claim 5, characterized in that each nozzle ( 8 , 13 ) can be switched on. 7. The device according to claim 1 or 2, characterized in that a dust separator for cleaning the reactor Lean gas is connected downstream. 8. The device according to claim 7, characterized in that as a dust collector a cyclone for separating Coarse dust and hot gas cleaning with Ceramic candle filters is provided. 9. The device according to claim 8, characterized in that the cyclone a heat exchanger for cooling the Lean gas is connected downstream.