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This Clean Coal Technology project will demonstrate a combination of two developed technologies to reduce both NO{sub x} and SO{sub x} emissions: gas reburning and calcium based dry sorbent injection. The demonstrations will be conducted on two pre-NSPS utility boilers representative of the US boilers which contribute significantly to the inventory of acid rain precursor emissions: tangentially and cyclone fired units. Gas reburning is a combustion modification technique that consists of firing 80--85 percent of the fuel (corresponding to the total heat release) in the lower furnace. Reduction of NO{sub x} to molecular nitrogen (N{sub 2}) is accomplished via the downstream injection of the remaining fuel requirement in the form of natural gas (which also reduces the total SO{sub x} emissions). In a third stage, burnout air is injected at lower temperatures in the upper furnace to complete the combustion process without generating significant additional NO{sub x}. Dry sorbent injection consists of injecting calcium based sorbents (such as limestone, dolomite, or hydrated lime) into the combustion products. For sulfation of the sorbent to CaSO{sub 4}, an injection temperature of about 1230{degrees}C is optimum, but calcium-sulfur reactions can also take place at lower temperatures. Thus, the sorbent may be injected at different locations, such as with the burnout air, at the exit from the superheater, or into the ducting downstream of the air heater with H{sub 2}0 added for humidification. The calcium sulfate or sulfite products are collected together with unreacted sorbent fly ash by the electrostatic precipitator. The specific goal of this project is to demonstrate NO{sub x} and SO{sub x} emission reductions of 60 percent and 50 percent, respectively, on two coal fired utility boilers having the design characteristics mentioned above.

Enhancing the use of coals by gas reburning-sorbent injection. Environmental monitoring quarterly report No. 9, July 1--September 30, 1992