Figure 3.5 illustrates the generation of a net capacity of 1250 MW with an assumed capacity factor of 70%, from typical eastern high-sulfur bituminous coal. The amount of pulverized coal yielding 10.1 x 10^ kJ is required to generate one kWh of net output; this corresponds to a net plant efficiency of 35.75%. The coal characteristics assume a higher heating value of 25.6 x lO^ kJ/kg of coal on an as-received basis. At this rate, an average of 8245 metric tons (t) of coal would be needed at the site each day. Because coal storage requirements are estimated at full capacity factor, a 3-day live storage stock pile would contain 35.3 x 10^ t of coal, and a 57-day reserve storage would contain 67.2 x 10^ t of coal. A 9.1-m-high active storage and a 15.24-m-high reserve storage pile results in a site area of 56 x 10^ m2 devoted to coal storage. Other fuel in the form of natural gas is also required for reducing sulfur dioxide (SO2) from the Wellman-Lord scrubber system (Fig. 3.6) to elemental sulfur. This process requires about 148 x 10$ kJ/h of natural gas at full plant capacity or, at 70% capacity and 34 x 10^ kJ/m^ of gas, about 2.7 x 10$ m^ of natural gas per year. The design has hot electrostatic precipitators sized for the removal of 99.7% of the flyash particulates emitted from the combustion furnace boiler. Auxiliary electric power of 13.9 MW is required for effective operation of the electrostat ic prec ipitators.12,13 The combustion of 4.9 x 10$ kg/h of coal with an ash content of 10.29% by weight produces 40 x 10^ kg/h of flyash, assuming an 80% flyash/20% bottom ash proportion. (About 10^ kg/h of bottom ash would be produced.) Removal of 99.7% of this flyash leaves 120 kg/h of flyash to be sent downstream for further processing in the Wellman-Lord SO2 removal system. The sludge wastes from the electrostatic precipitators and bottom ash total 63,120 kg/h for the 1250 MW reference coal facility at 100% capacity. Downstream from the electrostatic precipitators is the Wellman-Lord flue-gas desulfurization system. This system uses a regenerable process in which SO2 is removed from flue gases with a sodium sulfite scrubbing solution. The concentrated SO2 stream that is produced can be processed into elemental sulfur or sulfuric acid, both of which are marketable industrial products. The Wellman-Lord process consists of the four basic steps shown schematically in Fig. 3.6. These steps are (1) flue gas pretreatment, (2) SO2 absorption, (3) purge treatment, and (4) sodium sulfite regeneration. A fifth step, the processing of SO2 into marketable sulfur by-products, is not part of the Wellman-Lord process, but is generally associated with Wellman-Lord installations. Tables 3.5 and 3.6 show the air pollutants and solid waste products emitted by this 1250 MW facility. The normal construction period would take a total of seven years. Two years would be taken up for site selection, design, and preparation, and five years for on-site construction. Operation of the plant would require a staff of 259.
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