Nonequilibrium sulfur capture and retention in an air cooled slagging coal combustor. Fifth quarterly technical progress report, October 1, 1996--December 31, 1996

Calcium oxide sorbents injected in a stagging combustor react with the sulfur released during coal combustion to form sulfur bearing particles, some of which are deposited on the liquid slag layer on the combustor wall. Since the solubility of sulfur in liquid slag is low, the slag must be drained from the combustor to limit sulfur re-evolution into the gas phase. The objective of this 24 month project is to perform a series of 16 one day tests to determine the factors that control the retention of the sulfur in the slag that is drained from the combustor. In the present quarterly reporting period, 10 days of combustor tests were performed, bringing the total number of tests performed to 15. A wide range of operating conditions were tested including injection of metal oxide powders to achieve total mineral injection rates in excess of 400 lb/hr at coal mass flow rates of around 1000 lb/hr. It was determined that efficient sulfur capture requires calcium oxide particle sizes that are too small to be effectively retained in the combustor. On the other hand, injection of coarse calcium sulfate particles into the combustor sharply increased the slag viscosity, thereby reducing the slag flow rate and causing substantial revolution of the sulfur in the slag. It is tentatively concluded that conditions necessary for sulfur capture with sorbents and its retention in the slag cannot be efficiently achieved in one step in a cyclone combustor. It is further concluded that due to the increases in slag viscosity by calcium sulfate extremely high slag mass flow rates are required for sulfur retention in slag. Further tests in that direction are planned for the next quarterly reporting period