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<br />...... <br />en <br />I- <br />CD <br /> <br />2. W~STEWAT~R STRE~~S IN COAL GASIFICATION <br />2.1 Three Wastewater Streams <br />Although each individual gasification plant (i.e. each process using a <br />specific coal at a specific site) requires careful analysiS to determine the <br />water treatmen~ scheme best suited for its needs, a very large number of <br />optimum schemes will fall within the general approach depicted in Figure 2-1. <br />As shown, ~~ere are three major wastewa~er streams. First, source water is <br />treated to process quality; usually ~~is quality is boiler feed water quality. <br />This produces a wastewater stream highly concentrated in salt. Second, wastewater <br />out of the process is usually so contaminated that it cannot be directly <br />~eturned to the environment wi~hout extensive treatment. Figure 2-1 shows <br />that it is treated and delivered to the coolir.g tower where it is partially <br /> <br />consumed by evaporation. <br /> <br />~cditional makeup to the cooling towe: cernes from <br /> <br />source water. The cooling tower is blown down co prevent scale :orrnation in <br /> <br />the cooli~g system. The third principal wastewater stream is surface run-o== <br /> <br />from the plant si~e. Domestic wastes, a minor stream, will also ce ccnsicered. <br /> <br />The wastewaters are not usually retur~ed to the river. In the Colorado <br />Ri".J'er Basin the "Regulations for Implementation of the Colorado Ri'Jer Salinity <br />Standards through the NPDES Permit Program" are directed towards zero discharge. <br />However, the granting of NPDES permits is done on a case-by-case basis and <br />generalizations regarding discharge cannot be mace. Other possibil~ties, <br />shown on Figure 2-1, are to (1) mix the wastewater with coal ash or other <br />solid residues, (2) spray the wastewater to control dust on mine roads or (3) <br />~o evaporate the wastewater. We will return to the discussion of disposal for <br />each waste stream separately. First, however, we begi~ by quantifying the <br /> <br />''''aste streams. <br /> <br />2.2 Run-off <br /> <br />Run-off is not a difficult problem in the Colorado River Basin area as <br /> <br />long as it is collected and impounded properly. The quantity depends very <br /> <br />much on the site. A large quantity would, for example, be <br />falling on 0.25 square miles (~ 160 acres ~ 7 x 106 ft2). <br /> <br />15 inches of rain/year <br /> <br />Nearly <br /> <br />all or this <br />1 <br />62 x 10- <br /> <br />rainfall would be collected and would amount to 200 acre-ft/yr (~ <br /> <br />Ib/hr = 125 gal/min), which is not a large stream. As a minimum, runoff from <br /> <br />14 <br />