GB2191215A

GB2191215A - Power from carbonaceous fuel

Info

Publication number: GB2191215A
Application number: GB08713007A
Authority: GB
Inventors: Trevor Williams Nurse
Original assignee: Humphreys and Glasgow Ltd
Current assignee: Humphreys and Glasgow Ltd
Priority date: 1986-06-03
Filing date: 1987-06-03
Publication date: 1987-12-09
Also published as: GB8613348D0; GB8713007D0

Abstract

A process for the production of power from a carbonaceous fuel 1 comprises partially oxidising at 3 the fuel with oxygen or an oxygen-containing gas 2 to yield a gas stream containing carbon monoxide and hydrogen at supra-atmospheric pressure, washing at 4 the gas stream with water in order to remove particulate matter therefrom and to cool the gas stream, wherein some, but not all, of the wash water is evaporated into the gas stream, expanding the steam-containing gas stream in turbine 6 to produce power, and combusting essentially all of the hydrogen and carbon monoxide of the expanded stream, with additional oxygen or oxygen-containing gas in turbine 9 to produce additional power. <IMAGE>

Description

SPECIFICATION Power from carbonaceous fuel The present invention relates to a process for the production of power from a carbonaceous fuel, such as coal.

Unlike the single stage, substantially complete combustion of such fuels, partial oxidation processes generally take place at pressures significantly higher than atmospheric pressure. The pressure energy of the partial combustion processes can then be used downstream. Although it is known to generate power by the expansion of the gaseous products of such partial oxidation processes, it is standard teaching to raise the temperature of those products as high as possible in order to extract therefrom the maximum amount of power. It has now been found to be advantageous not to expand the hot gaseous products directly but to cool them first by direct contact with water.

As a result of this direct contact, a substantial amount of the water is evaporated into the gas stream. This means that when the gas stream is expanded, not only are the gaseous products of the partial oxidation expanded, but also the steam therein is expanded. Surprisingly it has been found that the benefit of the expansion of this additional material outweighs the disadvantage of the lowering of the temperature of the stream, if, in addition to the cooling effect of the direct liquid contact, the water is used as the main means for cleaning the hot gaseous products prior to expansion.

In accordance with the present invention there is provided a process for the production of power from a carbonaceous fuel which comprises partially oxidising the fuel with oxygen or an oxygen-containing gas to yield a gas stream containing carbon monoxide and hydrogen at supra-atmospheric pressure, washing the gas stream with water in order to remove particulate matter therefrom and to cool the gas stream, wherein some, but not all, of the wash water is evaporated into the gas stream, expanding the cooled, steam-containing gas stream to produce power, and combusting essentially all of the hydrogen and carbon monoxide of the expanded stream with additional oxygen or oxygen-containing gas to produce additional power.

The carbonaceous fuel may be gasified by partial oxidation at pressure by a number of methods well known to those versed in the art. These methods normally involve gasifying the carbonaceous fuel with an oxygen-containing gas, e.g. air, or preferably with a substantially pure oxygen stream. Water or steam may be added at this stage if required. The pressure of this partial oxidation is normally in the range of 15-250 ats, but is more likely to be in the range of 40-150 ats. Examples of suitable carbonaceous fuels are coal, natural gas, naphtha, heavy fuel oil and crude oil.

Having partially oxidised the carbonaceous fuel the temperature of the resulting gas stream is usually very high, e.g. 1600 to 700"C, and furthermore almost always contains particulate matter, e.g. carbon, un-reacted coal and ash. To cool the gas stream to a more manageable temperature for handling downstream, e.g. 200 to 400"C, and also to remove essentially all of the particulate matter therefrom, the stream is washed with water.

The wash conditions are arranged so that a substantial amount of the water is evaporated.

into the hot gas stream. Not all of the wash water is evaporated so that this cooling stage also becomes a scrubbing stage and the cooled, cleaned gas stream leaving the wash stage is substantially fully saturated. Without such particulate removal the expansion of the resultant "dirty" gas stream would be detrimental to the expander.

In order to utilise the extra pressure energy residing in the evaporated wash water the hot, steam-containing gas stream is expanded, e.g. through a turbine. Desirably process conditions are arranged such that the steam-containing gas stream is, after expansion, still dry, in order to avoid erosion of the expander by the impact of liquid droplets.

Although a single washing step may be sufficient, multi-stage washing may be employed.

The steam-containing gas stream may be reheated prior to expansion in order to increase the power that can be obtained from it. Such re-heating may be effected by indirect heating, for instance by the exhaust of a downstream gas turbine. It is also possible for the gas stream to be reheated and expanded more than once. The gases leaving the expander will still be at pressure, preferably between 4 and 150 ats, but more preferably between 5 and 30 ats.

Having expanded the steam-containing gas stream it is desirable to condense the water vapour out of this mixture. In doing this its heat may be utilised in a conventional downstream sulphur removal unit, such a unit being generally needed in order to reduce the pollution of the environment.

Inasmuch as the carbonaceous fuel utilised often contains sulphur compounds the sulphur may be removed by any conventional process at this stage. For example any of the standard acid gas removal techniques may be used, noting that it is also desirable to remove carbonyl sulphide. The removal of the sulphur compounds is made easier by the fact that such removal is effected at pressure. Since such sulphur removal generally operates better on a dry stream a desaturator can be added to the flowsheet upstream of the sulphur removal unit. Preferably the desaturator is linked to a saturator unit installed at some point downstream, in order, for example, to improve the combustion characteristics of the final gas stream.

The desulphurised gases, still at pressure, are then used as a fuel in, e.g. a gas turbine to gain additional power. Both this power and the main power produced by the process of the present invention can be used either directly as shaft power or for generating electricity. One example of the utilisation of such shaft power is in storage hydroelectric schemes to pump water up to the storage reservoir.

Finally, steam may be raised at any suitable stage in the present process, for example in the exhaust of any gas turbines which are used. Such steam can itself be used to generate shaft power by expansion through one or more steam turbines.

One embodiment of the present invention will now be described by way of example with reference to the accompanying drawing in which Fig. 1 shows a schematic block diagram for a flow sheet for the generation of power from coal.

A pulverised coal feed 1 is partially oxidised with substantially pure oxygen 2 in a gasifier 3 at 40 to 150 ats, and the resultant hot gases containing carbon monoxide, hydrogen and particulate matter such as carbon are washed with water in wash unit 4. Essentially all of the particulate matter is washed out of the gases and a substantial amount, but not all, of the wash water is evaporated. The hot gases, now containing steam and having been cooled from about 1400"C to about 250 C by the evaporating water, are then heated to about 600"C in reheater 5 before being expanded down to from 1 to 30 ats in turbine 6.

The expanded gas stream leaving turbine 6 is dry, but is then made to give up a substantial proportion of the steam therein by passing it through cooler/condenser 7. The water recovered from cooler/condenser 7 is then returned with a make-up stream to wash unit 4.

The gas stream leaving cooler/condenser 7 is then desulphurised in tower 8 before being burnt as fuel in gas turbine 9.

The power from turbines 6 and 9 is used to produce electricity, whilst the hot exhaust gases from turbine 9 are utilised in reheater 5.

Claims

1. A process for the production of power from a carbonaceous fuel which comprises partially oxidising the fuel with oxygen or an oxygen-containing gas to yield a gas stream containing carbon monoxide and hydrogen at supra-atmospheric pressure, washing the gas stream with water in order to remove particulate matter therefrom and to cool the gas stream, wherein some, but not all, of the wash water is evaporated into the gas stream, expanding the cooled, steam-containing gas stream to produce power, and combusting essentially all of the hydrogen and carbon monoxide of the expanded stream with additional oxygen or oxygen-containing gas to produce additional power.

2. A process as claimed in claim 1 wherein the washed gas stream is re-heated prior to expansion.

3. A process as claimed in claim 2 wherein the washed gas stream is re-heated with heat from the said combustion stage.

4. A process as claimed in any one of the preceding claims wherein the carbonaceous fuel is coal, heavy fuel oil or crude oil.

5. A process as claimed in claim 1 substantially as hereinbefore described.

6. Power in the form of electricity when produced by a process as claimed in any one of the preceding claims.