GB2277528A

GB2277528A - The production of power from a carbonaceous fuel and methanol

Info

Publication number: GB2277528A
Application number: GB9315785A
Authority: GB
Inventors: Anthony Horton; John Griffiths
Original assignee: H & G Process Contracting
Current assignee: H & G Process Contracting
Priority date: 1993-04-29
Filing date: 1993-07-30
Publication date: 1994-11-02
Also published as: GB9315785D0; GB9308898D0

Abstract

Carbonaceous fuel is oxidised to form carbon monoxide and hydrogen, which is then catalytically shifted to produce hydrogen and carbon dioxide for combustion in the generation of power. Methanol is cracked using the heat of the shift reaction to produce more hydrogen and carbon monoxide, which optionally may be subject to a shift reaction, to provide additional fuel to meet peaks in the demand for power. The heat evolved by the shift reaction may be transferred to a methanol cracking vessel using a thermal fluid for indirect heat transfer or a methanol cracking vessel may be embedded in the shift catalyst bed. In a further alternative the methanol may be cracked over the shift catalyst bed.

Description

PEAKED CAPACITY POWER STATION This invention relates to the production of electric power from methanol and a carbonaceous fuel by the integrated gasification and combined cycle (IGCC) route; particularly to the invention described in our application number UK 8720185.

This invention is 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, adding water or steam, expanding the stream in a turbine located either upstream or downstream of a carbon monoxide shift reactor which reacts at least some of the carbon monoxide in the gas stream to produce carbon dioxide and additional hydrogen; removing sulphur compounds before combusting the hydrogen and any residual carbon monoxide with additional oxygen or an oxygen containing gas, such as air, to produce power, characterised by the cracking of methanol to carbon monoxide and hydrogen, either over the same shift catalyst concomitantly with the shift reaction, or in one or more cracking vessels using shift or other catalyst surrounded by shift catalyst or the heat evolved by the shift reaction may be transferred from the shift reactor to the methanol cracking vessel by means of indirect heat transfer such as by the use of a thermal fluid.

In said application, the invention is described as follows: 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, adding water or steam, expanding the stream in a turbine located either upstream or downstream of a carbon monoxide shift reactor which reacts at least some of the carbon monoxide in the gas stream to produce carbon dioxide and additional hydrogen; removing sulphur compounds before combusting the hydrogen and any residual carbon monoxide with additional oxygen or an oxygen containing gas, such as air, to produce power.

The reaction between carbon monoxide and water is generally known as the water gas shift reaction, or just the shift reaction. Historically it has been catalysed by two classes of catalysts - those operating above 350 C are generally known as high temperature (HT) catalysts and are more robust catalysts.

Those operating in the 250 C region are known as low temperature (LT) catalysts and can remove more carbon monoxide from given composition, but are more sensitive to impurities, and upsets in operating conditions.

Methanol may be decomposed over a catalyst to carbon monoxide and hydrogen in accordance with the following reaction: CH3OH + Co + 2H2 This cracking reaction is endothermic. In addition to shift catalysts, catalysts well known to those in the manufacture of methanol systhesis may also be used to crack the methanol.

Using this invention, the invention described in the patent application is enhanced by the cracking of methanol to carbon monoxide and hydrogen, either over the same shift catalyst concomitantly with the shift reaction, or in one or more cracking vessels surrounded by shift catalyst (see diagram); or the heat evolved by the shift reaction may be transferred from the shift reactor to the methanol cracking vessel by means of indirect heat transfer such as by the use of a thermal fluid such that the vessel in which the cracking takes place could be outside the shift reactor.

This invention does not require any additional heat but uses the exothermic heat from the carbon monoxide shift reaction, to supply the heat needed for the cracking reaction.

The methanol can be pumped into the cracking vessel as a liquid but may be pre-evaporated and could be partially saturated with water.

The methanol may be purchased and brought to the site, or it may be made on site from hydrogen and oxides of carbon particularly at times when full power is not required from the power station.

Because the evaporation and decomposition of the methanol is endothermic, the use of this invention could cause the temperature of streams to fall. In order to reduce or eliminate these falls, the main gas stream from the partial oxidation unit which passes through a boiler prior to it entering the shift reactor can be split into two streams. One of these can be bypassed around the boiler so as to raise the enthalpy of the stream immediately downstream of the boiler. In the case where the boiler condenses steam, the bypassing of said boiler ensures that the steam to reducing gas ratio is held above the minimum required.This minimum ensures that there is sufficient steam in the stream entering the shift catalyst reactor to effect the desired degree of reaction of the carbon monoxide, whilst, in the case of HT catalyst, still leaving sufficient steam to ensure that the catalyst stays oxidised.

Advantages of this invention are as follows. The generating capacity of the power station may be raise very quickly because methanol may quickly be pumped into the cracking vessel and thence into the main gas stream upstream of the shift/catalyst vessel. This for example allows time to start up an additional carbonaceous fuel gasifier. Either the generating capacity of the power station may be substantially increased, for instance to meet peak demands, alternatively the capacity of the front end of the power station (the partial oxidation system, its quench, boiler, and most importantly, its associated oxygen plant) can be significantly reduced in size. The power station could shut down some of its partial oxidation reactors for maintenance without losing generating capacity.

By utilising sensible heat in the streams to effect the cracking of the methanol instead of just burning it raises the overall efficiency of the power station. Further, it can allow additional hydrogen to be produced from an existing IGCC power station should this ever be needed, such as when the power station is associated with an oil refinery.

Claims

CLAINS

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, adding water or steam, expanding the stream in a turbine located either upstream or downstream of a carbon monoxide shift reactor which reacts at least some of the carbon monoxide in the gas stream to produce carbon dioxide and additional hydrogen; removing sulphur compounds before combusting the hydrogen and any residual carbon monoxide with additional oxygen or an oxygen containing gas, such as air, to produce power, characterised by the cracking of methanol to carbon monoxide and hydrogen, either over the same shift catalyst concomitantly with the shift reaction, or in one or more cracking vessels using shift or other catalyst surrounded by shift catalyst or the heat evolved by the shift reaction may be transferred from the shift reactor to the methanol cracking vessel by means of indirect heat transfer such as by the use of a thermal fluid.