GB2158841A

GB2158841A - Gasifier plant

Info

Publication number: GB2158841A
Application number: GB08512058A
Authority: GB
Inventors: Czeslaw Polonski
Original assignee: English Electric Co Ltd
Current assignee: English Electric Co Ltd
Priority date: 1984-05-14
Filing date: 1985-05-13
Publication date: 1985-11-20
Also published as: GB8512058D0; GB8412278D0

Abstract

In gasifier plant, the exhaust gas from a thermodynamic engine (2) (for example a diesel engine, a gas turbine or a Stirling engine) is utilised as a source of carbon dioxide and steam for a gasifier (1). In the gasifier, the carbon dioxide and steam react with carbonaceous material such as coal or domestic or industrial waste to generate a fuel gas containing carbon monoxide and hydrogen. This fuel gas may be used as feedstock for a process plant or used as fuel in the thermodynamic engine. Thus coal and other solid biomass may in effect be used as fuel in (for example) an internal combustion engine. <IMAGE>

Description

SPECIFICATION Gasifier plant The present invention relates to gas or power plant of the type comprising a gasifier in which a non-combustible gas such as steam and/or air is passed through hot solid or vapourised liquid carbonaceous material (typically coal, coke, dirty oil, charcoal, peat, wood or other biomass) to form a combustible gas containing hydrogen and/or carbon monoxide.

The combustible gas may be burnt as fuel in an engine to provide power. Additionally or alternatively it may be used as feedstock in an industrial process.

Such power plant has the advantage that a solid or dirty liquid fuel is converted to a gaseous fuel. Furthermore the carbonaceous material may comprise domestic or industrial waste which itself is too bulky and difficult to use as fuel.

However unless the power plant happens to include a source of waste steam, a steam boiler is normally provided, together with its associated combustion equipment, and this increases the capital costs.

An object of the present invention is to provide a flexible power plant of low capital cost which utilises a gasifier in an efficient and economical manner.

According to one aspect of the present invention, a combined gasifier plant comprises a thermodynamic engine and a gasifier aranged to receive exhausted gaseous combustion products from said engine and to react them with carbonaceous material to form a combustible gas.

Carbon dioxide, which is inevitably present in the exhaust gases of the engine, will react with the carbonaceous material in the gasifier to produce carbon monoxide: CO2 + Co2CO Similarly steam, which will also be present in the exhaust gases of the engine, will react with the carbonaceous material in the gasifier to produce carbon monoxide and hydrogen: H20 + CH2 + CO In order to add flexibility to the plant, provision may be made for injecting water into the hot exhaust gases or for adding water to the engine fuel. The resulting extra steam (which is generated without the need for a boiler) can be used to control the composition of the gas produced in the gasifier.

The exhaust pases from the engine will generaliy contain some oxygen, which will sustain combustion of the carbonaceous material and thereby supplement the heat balance of the overall gasification process. However air may be injected, either directly into the gasifier or into the exhaust gases from the engine, in order to supply further oxygen and add flexibility to the plant.

It will be appreciated that the high temperature of the exhaust gases (typically 500"C for diesel exhaust) will further enhance the overall energy balance of the process.

The combustible gas may be burnt as fuel or used as feedstock for a process plant.

The combustible gas may be used to power said thermodynamic engine or to power an additional thermodynamic engine whose exhaust does not feed the gasifier.

The cabonaceous material may be a solid or a liquid. A carbonaceous fuel such as oil, coal, coke, charcol, peat or wood may be used, or alternatively the carbonaceous material may be semi-combustible carbonaceous waste.

Preferably the thermodynamic engine is an internal combustion engine. The internal combustion engine may be a reciprocating engine such as a diesel, gas, petrol or dual fuel engine, or alternatively a non-reciprocating engine such as a gas turbine may be used.

Thus solid carbonaceous material may effectively be used as fuel for an internal combustion engine.

The internal combustion engine may be naturally aspirated or turbo-charged.

However the invention also includes within its scope arrangements including a thermodynamic engine powered by external combustion, for example a Stirling engine.

The gasifier may incorporate sulphur-absorbing material such as limestone in order to absorb sulphur dioxide. Other materials may be included with the carbonaceous material to absorb other pollutants. Filters may be provided for separating solid particulate material from the combustible gas produced by the gasifier.

According to another aspect of the invention, a gasifier is provided with a gas inlet adapted to be connected to the exhaust of an internal combustion engine and a fuel inlet, and is adapted in use to generate a combustible gas from the internal combustion engine exhaust gases and said fuel without any substantial heat input other than the sensible heat of said exhaust gases. Said gasifier may additionally incorporate an air inlet to provide additional oxygen for combustion in case there is not enough oxygen in the exhaust gases.

A number of embodiments of the invention will now be described by way of example with reference to Figs. 1 to 5 of the accompanying drawings, of which: Figure 1 is a schematic representation of a gasifier plant in accordance with the invention, in which the combustible gas generated is utilised externally, Figure 2 is a schematic representation of a gasifier plant in accordance with the invention in which the generated combustible gas is recycled within the plant, Figure 3 is a diagrammatic representation of a two-stage gasifier which can be used in the arrangements of Figs. 1 and 2, Figure 4 is a diagrammatic representation of a two-stage up-draught gasifier which is particularly suitable for use in the arrangement of Fig. 2, and Figure 5 is a diagrammatic representation of a devolatilisation gasifier which is also suitable for use in the arrangement of Fig. 2.

Referring to Fig. 1, the power plant shown comprises a gasifier 1 (shown diagrammatically) having one inlet connected to the exhaust 5 of a diesel engine 2. Gasifier 1 is additionally fed by a blower 3 with air at another inlet 6, and is fed with coal via a hopper 4. Air and diesel fuel are fed to diesel engine 2 as shown and solid ash is removed from gasifier 1 at an outlet 1 2. An inlet 11 is provided in the diesel exhaust 5, at which water is injected, atomised into a spray, and then vapourised into superheated steam by the hot exhaust gases (which will typically be at a temperature of 500"C).

In the gasifier 1, the only sources of heat are internal, namely the combustion of the coal with the supplementary air and the oxygen in the diesel exhaust gases and the sensible heat of the hot diesel exhaust gases. The heat thus produced liberates carbon, ash, tars, oils and moisture from the coal, pyrolyses the resulting hydrocarbons, and drives the endothermic reactions a) between carbon dioxide and carbon and b) between carbon and steam to generate carbon monoxide and hydrogen, as in a conventional gasifier.

Besides carbon dioxide and steam, the diesel exhaust will contain appreciable amounts of nitrogen and oxygen, and the combustible gas generated in the gasifier will therefore consist mainly of hydrogen, carbon monoxide and nitrogen. This gas is fed via an outlet 7 either to a process plant to be used as feedstock or to a gas engine (not shown) of higher capacity than the diesel engine 2. If necessary the shafts of the diesel engine and the gas engine may be coupled to a common output shaft.

Fig. 2 shows a similar arrangement to Fig.

1 (corresponding parts being indicated by common reference numerals), except that some of the combustible gas generated in the gasifier 1 is fed via an auxiliary outlet 1 6 to a gas cleaning system 8, comprising one or more filters and optionally an electrostatic precipitator (not shown). Engine 9 is essentially a gas engine, and is fed clean fuel gas from the cleaning system 8 via a mixer 10, where air is added. The engine is also provided with a diesel fuel inlet, and is arranged to burn a small proportion of diesel fuel (perhaps 8% in terms of calorific value) together with the fuel gas. However the system is essentially one in which coal is, in effect, used as fuel in an internal combustion engine.

It will be appreciated that carbonaceous material other than coal (for example domestic or industrial combustible waste, or dirty oil) may be used in the gasifier 1 of Figs. 1 and 2, since similar reactions will occur. Similarly it will be appreciated that a non-reciprocating engine such as a gas turbine, or an external combustion engine such as a Stirling engine, may be substituted for the engines 2 and 9 in Figs. 1 and 2.

Fig. 3 shows in more detail a two-stage gasifier 1 which is suitable for use in the arrangement of Fig. 2. The gasifier shown comprises an inner bell 1 7 which is fed with coal 1 8 from a hopper 4. The mass of coal 18 is supported on a grate 19 and supplied with exhaust gases and supplementary air at inlets 5 and 6. A relatively low temperature pyrolysis zone forms at the top of bell 17, so that the gas formed inside the bell contains tars and other hydrocarbons. This dirty "top gas" is exhausted via outlet 7 and fed as feedstock to a process plant (not shown). A relatively high temperature gasification zone near the bottom of the gasifier produces cleaner "bottom gas" which is useful as fuel and is therefore exhausted via outlet 1 6 and fed to engine 9 (Fig. 2) via a cleaning system.

Ash is removed at outlets 1 2.

The gasifier may be adapted for use in the arangement of Fig. 1 by combining outlets 7 and 1 6. Some or all of the 'top gas" can be re-circulated through the gasifier before being exhausted, in order to remove some of the tars and other hydrocarbons which it contains.

Fig. 4 shows one such system which is suitable for use in the arrangement of Fig. 2 but which can also be used to supply fuel gas to separate engine or process plant as shown in Fig. 1. The devolatalisation gasifier shown is similar to that shown in Fig. 3 except that a re-circulation loop 20 between the bell 1 7 and outer casing of the gasifier 1 is substituted for outlet 7. Exhaust gases from engine 9 (Fig. 2) are fed into the re-circulating gases via venturi mixer 21. Consequently all the gas generated in the gasifier passes through a high temperature gasification zone and the gas exhausted via outlet 1 6 is sufficiently clean to be used as fuel in engine 9 after being fed through a cleaning system. It will be appreciated that the gas from outlet 16 may alternatively be fed to a larger gas engine or a process plant as shown in Fig. 1.

Fig. 5 shows a downdraught gasifier which is single-walled but has a similar recirculation loop to that shown in Fig. 4. However the supplementary air is introduced at the bottom of the recirculation loop. The resulting downdraught forces gas through a high temperature gasification zone at the bottom of the gasifier, and the resulting cleaner gas is ex hausted at outlet 1 6 and fed to engine 9 via cleaning system 8. The gasifier may alternatively be used in the arrangement of Fig. 1.

From the foregoing, it will be apparent that many different types of gasifier other than those shown are suitable for use in arrange ments in accordance with the invention. Thus for example a fluidised bed gasifier a crossdraught gasifier or an entrained flowgasifier may be used.

Claims

1. A combined gasifier plant comprising a thermodynamic engine and a gasifier arranged to receive exhausted gaseous combustion products from said engine and to react them with carbonaceous material to form a combustible gas.

2. Plant as claimed in Claim 1 wherein said engine is an internal combustion engine.

3. Plant as claimed in Claim 2 wherein said engine is a reciprocating internal combus tion engine.

4. Plant as claimed in Claim 3 wherein said engine is a diesel or petrol engine.

5. Plant as claimed in any preceding Claim wherein means are provided for inject ing water into said exhaust in controlled amounts to control the composition of said combustible gas.

6. Plant as claimed in Claim 4 wherein water is added to the fuel of said engine.

7. Plant as claimed in any preceding Claim wherein said combustible gas is burnt as fuel in said thermodynamic engine.

8. Plant as claimed in Claim 7 wherein said carbonaceous material is in solid form.

9. Plant as claimed in any of Claims 1 to 7 wherein in use, said combustible gas is burnt as fuel in an additional thermodynamic engine whose exhaust does not feed said gasifier.

10. Plant as claimed in Claim 9 wherein the shafts of said thermodynamic engine and said further thermodynamic engine are coup led.

11. Plant as claimed in any preceding Claim wherein said gasifier is adapted to util ise domestic or industrial waste as said carbo naceous material.

1 2. Plant as claimed in any preceding Claim further comprising process plant ar ranged to utilise said combustible gas as feedstock.

1 3. Plant as claimed in any preceding Claim wherein said gasifier is a two-stage gasifier incorporating a high-temperature gasification zone and a low temperature gasification zone, first outlet means for feeding com bustible gas from said high temperature zone to a thermodynamic engine and second outlet ,means for feeding combustible gas from said low-temperature zone to process plant as feedstock.

14. Plant as claimed in any of Claims 1 to 1 2 wherein said gasifier incorporates a recirculation loop for recirculating said combustible gas within said gasifier.

15. Plant as claimed in Claim 14 wherein means are provided for injecting said gaseous combustion products from said exhaust into said recirculation loop.

1 6. A gasifier provided with a gas inlet and a fuel inlet, characterised in that said gas inlet is adapted to be connected to the exhaust of an internal combustion engine, said gasifier being adapted in use to generate a combustible gas from the internal combustion engine exhaust gases and said fuel without any substantial heat input other than the sensible heat of said exhaust gases.

1 7. Combined gasifier plant substantially as described hereinabove with reference to Figs. 1 and 3 or with reference to Figs. 2 and 3 of the accompanying drawings.

1 8. Combined gasifier plant substantially as described hereinabove with reference to Figs. 2 and 4 or with reference to Figs. 2 and 5 of the accompanying drawings.