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<br />{:?'- <br />,....:.:...q <br />"x..;" <br /> <br />,~.:....~:. <br /><;"";.\ <br />(.:.~ -,", <br />",'." <br /> <br />.......:.:.. <br />';. ~.' <br /> <br />Water Requi~ements of Coal Gasification Facilities <br /> <br />r'V <br />00 <br />-J <br />C) <br /> <br />Coal gasification is the generic name of the multistep p~ocess by <br />which coal is conve~ted to burnable hydrocarbon gases. The basic <br />chemical reaction involved is hyd~ogenation. Typically, coal gasification <br />technologies are classified according to the Btu rating of the p~oduct <br />gas (i.e., high-, medium-, or low-Btu gasification), <br /> <br />High-Btu gasification technologies can be typified as those which employ <br />an oxYgen-fed gasifier, shift conve~sion, and methanation to.produce a pipe- <br />line quality gas of approximately 1,000 Btu per standard cubic foot (scf). <br />The technologies under development may be classified into three categories <br />depending on the gasifying mode (i.e., fixed-bed, fluldized-bed,or ent~ainment). <br />The fi~st two of these appear to have the highest potential for comme~cializa- <br />tion. Medi~Btu gasification consists of the same'steps as for high-Btu <br />processes, except that methanation is not employed. Finally, in 10~Btu <br />processes, air, rather than oxygen, is used in the gasifier. The use of air <br />saturates the product gas with nitrogen and results in a lower heating value. <br />In addition, the shift conversion and methanation steps are not present. <br /> <br />Fo~ the postulated high-Btu gasification developments being assessed, <br />it has been assumed that only the Lurgi process will be employed. This <br />assumption is based upon the fact that this is the most advanced of the <br />high-Btu gasification technologies, it having been tested extensively in <br />p~oducing plants in Europe and the U.S.S.R. . <br /> <br />,In general terms, the steps that consume water in the Lurgi process <br /> <br />are: <br /> <br />(I) treatment of ~aw wate~ supply to achieve process quality <br />(i.e., the waste brine is evaporated). <br /> <br />(2) gasification, <br />(3) evaporative cooling, <br />(4) ash diSposal, <br />(5) flue gas, desulfurization, and <br />(6) plant site dust control,l <br /> <br />Typical wate~ consumption estimates for a unit-sized (i,e., 250 million <br />scf/day)Lurgi plant range from about 5,000 to 7,500 ac~e-feet per year. <br />Evaporative cooling water ~equi~ements account fo~ the largest share of <br />consumption. They vary substantially depending upon the degree to which <br />dry cooling is employed. <br /> <br />1. It is frequently difficult to tell whethe~ mine site dust control and <br />~evegetation (amounting to a few hundred acre-feet pe~ yea~) a~e included <br />in literature estimates of annual water consumption. For the pu~poses of <br />this discussion, it is assumed that they are not. <br /> <br />xxix <br />