GB2060679A

GB2060679A - Process and Plant for the Gasification of Solid Carbonaceous Substances

Info

Publication number: GB2060679A
Application number: GB8030780A
Authority: GB
Original assignee: Rheinische Braunkohlenwerke AG
Current assignee: Rheinbraun AG
Priority date: 1979-09-25
Filing date: 1980-09-24
Publication date: 1981-05-07
Also published as: AU6254280A; FR2465776A1; DD153128A1; GB2060679B; AU537759B2; DE2938711A1

Abstract

In the process a portion of the methane of the product gas is decomposed under the action of steam, to obtain the hydrogen containing gasification agent, at least a predominant portion of the decomposition apparatus being heated by the heat of combustion of the residual coke produced during gasification. The residual coke originates from a fluidized layer reactor (14) whereby gasification and combustion are adjusted to one another. Also the use of such a reactor (14) allows for compact construction and thus lower prime costs. Further by means of a fluidized layer reactor (14) a uniform temperature is maintained over the entire fluidized layer so that there is no risk of overheating particular regions of the decomposition apparatus (26). <IMAGE>

Description

SPECIFICATION Process and Plant for the Gasification of Solid Carbonaceous Substances The present invention relates to a process and plant for the gasification of solid carbonaceous substances.

In particular, the present invention relates to the gasification of lignite, with the use of hydrogen-containing gasification agent, in which a portion of the methane contained in the product gas is decomposed in a decomposition apparatus under the action of steam in order to obtain the hydrogen-containing gasification agent, and at least the predominant portion of the decomposition apparatus is heated by the heat of combustion of the residual coke produced during gasification.

It is known from German Offenlegungsschrift 1 7 96 050.8 to burn the residual coke for the purpose of covering the heat requirement of the gasification process when gasifying coal, particularly lignite. In a plant for the hydrogasification of coal in accordance with German Offenlegungsschrift 27 04 465, this is effected by using the residual coke for heating the decomposition oven in which the hydrogen required for gasification is produced. The decomposition oven is then to be heatable either directly by the residual coke or by the gas which is produced by gasification of the residual coke. The last-mentioned possibility has the disadvantage that it requires an additional apparatus for the gasification of the residual coke.However, difficulties can arise even when the decomposition oven is directly heated by the heat of combustion of the residual coke owing to the fact that, for example, especially in the case of a high ash content, difficulties caused by ash fusions and clinker formation are to be anticipated in the combustion chamber. Furthermore, there is the risk of soiling of the contact urfaces disposed therebeyond, resulting in a corresponding reduction of output.

The aim of the present invention is to improve a process of the kind described initially such that the decomposition oven is heated in a particularly advantageous manner adapted to the nature of the residual coke, minimising the expenditure on industrial processing technique and apparatus.

This is also to be possible when the residual coke has poor combustion properties.

According to the present invention there is provided a process for the gasification of solid carbonaceous substances, by using a hydrogencontaining gasification agent, comprising the steps of decomposing a portion of the methane contained in a product gas in a decomposition apparatus under the action of steam in order to obtain the hydrogen-containing gasification agent, and heating at least the predominant portion of the decomposition apparatus by the heat of combustion of the residual coke produced during gasification, the gasification being performed in a fluidized bed and the residual coke being burnt in a fluidized bed furnace, the heat being dissipated directly in the combustion fluidized layer at least on partial regions of the heating surfaces of the decomposition apparatus.

According to a further aspect of the present invention there is provided a plant for use in the gasification of solid carbonaceous substances, comprising a fluidized-bed reactor, a decomposition oven for the decomposition of methane, apparatus for generating and/or the overheating of steam, and a fluidized layer furnace which is chargeable with the residual coke from the gasification reactor and into which extend at least partial regions of the heating surfaces of the decomposition oven.

The present invention has a number of crucial advantages. One is that the gasification on the one hand and combustion of the residual coke on the other hand, are adjusted to one another. Since the residual coke originates from a fluidized layer reactor, it provides from the outset the prerequisites necessary for maintaining the heating of the fluidized layer, such as granular size and distribution of granular size. Also the fluidized layer furnace permits an extremely compact construction which compared with other furnaces, involves lower prime costs and smaller heat losses. The compact construction results particularly from the fact that the pipes of the pipe decomposition oven directly enters the fluidized layer, thus obtaining very high heat-transfer coefficients compared with conventional flue gas furnaces.It is readily possible to perform the combustion in the fluidized layer at temperatures between 800 and 950or. and preferably between 850 and 9500C. These temperatures are particularly advantageous for the steamreforming process taking place in the decomposition oven. The satisfactory heat transfer within the fluidized layer also means that substantially uniform temperatures prevail in the entire fluidized layer, so that there is no risk of overheating particular regions of the pipe decomposition oven. A further advantage resides in the fact that the fluidized layer furnace does not place high demands on the combustion properties of the residual coke.This also applies especially to the ash content of the residual coke which can exhibit perceptible differences as a result of changes with respect to the degree of gasification of the coal which is used. Owing to the compact construction, the plant also involves lower prime costs than a conventional plant.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which a circuit diagram of one embodiment a plant according to the present invention, for the hydrogasification of lignite is illustrated.

In the plant shown in the accompanying drawing, lignite 11 is dried in a drier 12 and is introduced into a fluidized layer reactor 14. The gasification agent, predominantly comprising H2, is fed through pipe 1 6 and also serves to maintain the fluidized layer. The conversion is effected exothermically in accordance with the reaction C+H2=CH4 The gas mixture coming from the reactor 14 still contains, in particular, surplus H2 and, after cooling in a heat exchanger 18, flows through a pipe 1 7 into an apparatus 20 in which it is freed from solids. Undesired gaseous components, such as CO2, are separated in a further apparatus 22.

An apparatus 23 serves to separate CH4 and H2 and, if required, CO. A portion of the CH4 flows into a decomposition oven 26 by way of a pipe 24 after steam has previously been introduced at 28 through a pipe 29, so that the endothermic reaction CH4+H20=3H2+CO takes place in the decomposition oven 26.

The resultant gas mixture, chiefly containing H2, CO, CH4,H20 and CO2, flows through a pipe 30 and a heat exchanger 32, in which it is cooled by heat transfer to the mixture of methane and steam flowing into the decomposition oven 26 through the pipe 27, into an apparatus 33 in which the CO component of the gas mixture is converted to CO2 by the addition of steam, the CO2 being washed out in a conventional manner in an apparatus 34 disposed downstream. The mixture, predominantly comprising H2, flows from the apparatus 34 as a reaction- and fluidizing agent into the fluidized layer reactor 14 by way of the pipe 16.

The residual coke 14 produced in the reactor 14, and which still contains considerable quantities of C with a degree of gasification of, for example, 50 or 60%, is washed out of the reactor 14 operated under excess pressure, the residual coke being cooled, if required, in, for example, a cooling apparatus 36 disposed downstream of the reactor 14, to a temperature which renders it possible to handle the coke. As is indicated by the broken line 38, the residual coke enters a furnace 40 in which it is burnt within a fluidized layer whose upper boundary extends approximately at 42. The combustion air is fed through a pipe 44.

The combustion air at the same time serves as a fluidizing agent. the decomposition oven 26, generally in the form of a pipe decomposition oven, is located within the actual fluidized layer.

Furthermore, the steam generator 46 is disposed in the fluidized layer downstream of a pre-heater 48 which is heated by the exhaust gas of the fluidized layer furnace. The water feed pipe is designated 50. A superheater 52 is disposed downstream of the heat generator 46 and is heated by the flue gas of the fluidized bed furnace. The steam has a pressure of, for example, 110 bar and a temperature of, for example, 5350C and is introduced by way of a pipe 54 into a turbine 58 which drives a generator 56. Steam hdving a pressure of, for example, 40 to 50 bar and a temperature of approximately 4000C is fed to the apparatus 28 by way of the turbine and the extraction pipe 29 and is mixed with the methane before the resultant mixture is introduced into the pipe decomposition oven 26.Furthermore, an extraction pipe 60 is provided through which the steam is fed with a pressure of approximately 5 bar and a temperature of 1 700C to the drier 12 in which the lignite is dried.

The hydrogen separated in the apparatus 23 can be fed back directly into the pipe 1 6 by way of a pipe 61 and then into the fluidized bed reactor 1 4.

The exhaust gas emerging from the fluidized bed furnace 40 flows through a pipe 62 into a cleaning apparatus 63 and then, if required, into the atmosphere after separating the residual substances.

Further extraction pipes can lead from the turbine 58. With an appropriate design of the plant, the steam generated in the fluidized layer furnace 40 and the electrical energy generated in the generaor 56 are sufficient to cover the entire energy requirement of the plant. It will be appreciated that it is conceivable to provide further apparatus to supplement the plant. Thus, the CO separated in the separating device 23 might be converted to CO2 with the addition of steam, wherein the hydrogen thus released can also be introduced as a gasifying agent into the reactor 14.

If the quantity of residual coke should not be quite sufficient to cover the heat requirement of the fluidized bed furnace, it is readily possible to cover the residual requirement by other fuels, suchss raw lignite, which are to be introduced into the fluidized bed.

Claims

1. A process for the gasification of solid carbonaceous substances, by using a hydrogencontaining gasification agent, comprising the steps of decomposing a portion of the methane contained in a product gas in a decomposition apparatus under the action of steam in order to obtain the hydrogen-containing gasification agent, and heating at least the predominant portion of the decomposition apparatus by the heat of combustion of the residual coke produced during gasification, the gasification being performed in a fluidized bed and the residual coke being burnt in a fluidized bed furnace, the heat being dissipated directly in the combustion fluidized layer at least on partial regions of the heating surfaces of the decomposition apparatus.

2. A process as claimed in Claim 1, in which the gasification is performed in the fluidized bed under excess pressure.

3. A process as claimed in Claim 1 or 2, in which combustion is performed in the fluidized layer at temperatures between 800 and 9500C.

4. A process as claimed in Claim 1 or 2, in which combustion is performed in the fluidized layer at temperatures between 8500C and 9500C.

5. A plant for performing the process as claimed in any one of Claims 1 to 4, comprising a fluidized-bed reactor, a decomposition oven for the decomposition of methane, apparatus for generating and/or the overheating of steam, and a fluidized layer furnace which is chargeable with the residual coke from the gasification reactor and into which extend at least partial regions of the heating surfaces of the decomposition oven.

6. A plant as claimed in Claim 5, in which the said apparatus is disposed within the fluidized layer and/or above the same in the flue gas.

7. A plant as claimed in Claim 5 or 6, in which an evaporator forms the apparatus for generating steam and is disposed in the region of the flue gas.

8. A plant as claimed in claim 7, in which at least partial regions of the heat transfer surfaces of the evaporator are disposed within the fluidized layer.

9. A plant as claimed in any one of the preceding claims 5 to 8, in which a superheater forms the apparatus for overheating the steam, the superheater being disposed beyond the evaporator and being heatable by the flue gas.

10. A plant as claimed in any one of Claims 5 to 9, in which an ecomomizer is provided and is heatable by the exhaust gas.

11. A process for the gasification of solid carbonaceous substances, substantially as hereinbefore described with reference to the accompanying drawings.

12. A plant for performing the process of Claim 1, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.