Gas: heating and illuminating – Processes – Producer
Patent
1994-10-26
1997-12-09
McMahon, Timothy
Gas: heating and illuminating
Processes
Producer
48 76, 48 77, 48 86R, C10J 350
Patent
active
056955324
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process and apparatus for converting a particulate solid carbonaceous fuel with a high moisture content into gas for combustion. More specifically the invention provides an improved process and apparatus for the gasification of moist particulate solid carbonaceous fuel which does not involve the addition of water prior to the drying stage and in which the drying of the fuel is integrated with the cooling of the product gas. The present invention is especially suitable for converting moist coal into coal gas and for convenience the invention will be hereinafter described with reference to that application. It is to be understood however, that the present invention is also suitable for converting other types of particulate solid carbonaceous fuel into gas.
Several processes are known by which coal may be converted into coal gas. These conversion processes generally occur at elevated temperatures usually between 900.degree. C. and 1500.degree. C. depending on the process of conversion used. The processes essentially involve the partial combustion of the coal to produce carbon monoxide rather than carbon dioxide. Hydrocarbons and hydrogen chemically contained in the coal also produce some hydrogen and methane. These processes generally involve the addition of steam and result in the production of additional hydrogen through reactions between carbon and water.
Product gas must be cooled before it can be cleaned or before its flow rate can be controlled through valves. Most methods for cooling the gas use a steam generator and superheater in which the hot gases are cooled by passing over tubes in which water is boiled to produce steam.
Most of the known gasification processes require a feed coal which has a moisture content typically below 10 to 20% dependent on the process. Oxygen blown gasifiers can accept fuels with higher moisture contents. When coal with a high moisture content is to be gasified it is first necessary to dry the coal to reduce the moisture content to a suitable level.
In a known process for converting coal with a high moisture content to gas, the coal is first dried in a steam fluidised bed drying process using hot steam to dry the coal to reduce the moisture content. The process operates at atmospheric pressure with the raw coal crushed before being fed into a bed in the drying vessel. The coal bed is fluidised by bubbling hot steam injected at the bottom, keeping the particles in the bed in constant motion. Embedded within the region of the bed are numerous tubes through which hot steam is passed to heat and dry the coal. The dry coal is cooled and stored. The coal is then transferred from the storage container to the gasifier which is located elsewhere in the plant.
The gasifier has a bed which is fluidised with either air or oxygen-enriched air which also reacts chemically with the coal to produce the product gas. It operates in such a way that most of the reactions occur in the fluid bed although fine coal particles and fine ash are carried up by the gas stream into the top part of the vessel, where more air may be injected to complete the gasification process. On leaving the vessel the gas temperature is in the order of 1000.degree. C. and accordingly a high temperature, refractory-lined cyclone is required to remove the char particles which are returned to the gasifier.
The hot product gas is then cooled down to a temperature between 0.degree. C. and 450.degree. C. so that cleaning and sulphur removal can take place.
Other gasification processes are also known but these are all essentially similar to the extent that the coal is first dried and stored before being gasified in a separate process, the product gas being cooled before cleaning.
The steam fluidised bed drying process requires steam to be produced for the fluidising and drying of the coal. This can be achieved either by means of a conventional boiler or by vapour recompression of the moisture removed in the drying process. Either method requires the consumption or diversion of energy.
In a gas tur
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Anderson Bernard
Campisi Anthony
Huynh Danh Quan
Johnson Terence Richard
Pleasance Graeme Eldred
McMahon Timothy
State Electricity Commission of Victoria
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