Molten iron oxysulfide as a superior sulfur sorbent. Third quarter technical progress report, June 1--August 31, 1990

摘要

Slagging combustors with injected lime or limestone are being considered as replacements for conventional coal burners. They have advantages in that they can be staged to reduce NO(sub x) and SO(sub x) emissions. Iron oxide, as an alternative to lime or limestone may be effective not only as a desulfurizing agent, but under the right conditions of oxygen potential and after combination with sulfur, the reaction products of coal gases with iron oxide can act as a flux to produce a fluid phase. The thermodynamic conditions for determining the most effective operating conditions of the first stage of a combustor are calculated for several Illinois coals. These conditions include contact of the gas with the phase combinations: CaO/CaSO(sub 4), CaO/CaS, and Fe/FeO/liquid for the temperature range 950(degree) to 1300(degree)C. In the latter system, the minimum dosage of iron required at equilibrium and the calculated maximum percent sulfur removal are reported. Also given are the expected pounds of SO(sub 2) per million Btu of heat evolution calculated for complete combustion. The calculations indicate that for the Fe-O-S system, higher temperatures give better results approaching 96 percent sulfur removal from a coal containing 4.2% sulfur. For this example, the stack gas emerging from the second stage of combustion under stoichiometric conditions would contain 0.36 pounds of SO(sub 2) per million BTU's of heat generated. The temperature limits of the sulfate and sulfide forming reactions are defined.