Combustion, coal, using fluid

For central station power generation the open cycle system using electrically conducting coal combustion products as the working fluid is employed. The fuel typically is pulverized coal burned directly in the MHD combustor, although in some plant designs cleaner fuels made from coal by gasification or by beneficiation have been considered (8—10) (see Fuels, synthetic). 

On the basis of experiments carried out using a laboratory size fluid bed combustor it has been demonstrated that, provided certain precautions are taken, crushed slag and other wastes from conventional coal-burning furnaces can, in the mrgority of cases, be burnt with the recovery of worthwhile amounts of energy and with less environmental pollution from SO2 and NO emissions than could result from the combustion of an equivalent amount of coal. The ash produced has a very low carbon content and is granular in form. 

A combustion process is described using a slurry of pulverized coal in a mixture of water and air. The mixture also contains some alkali which is stated to serve as a combustion catalyst. Combustion of the coal raises the temperature to above the critical temperature of water, and the ash that is present in the coal remains suspended in the supercritical medium. This supercritical fluid combustion stream is used to boil water and superheat steam in a countercurrent superheater-boiler train. The steam that is formed in the boiler is used to generate power. 

In this type of combustion facility pulverized coal is burned with air in a reactor in the form, for example, of a horizontal cyclone. In this reactor high temperatures of ca. 1600°C are achieved and the ash components of the coal are melted to form slag. The liquid slag collects on the reactor wall as a result of the fluid-flow characteristics in the reactor. It flows out of the reactor through the tap hole and is then granulated in a water bath. The waste gas is cooled in boilers, whereby high-pressure steam is produeed, which is used to drive steam turbines for power generation. 

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