The effect of vitiated air on the combustion of pulverized coal for applications to coal fired combined cycle steam generators

Abstract

A 15 Kg/h pulverized fuel two dimensional furnace was used to determine combustion efficiency, ignition stability, CO, C m H n , NO x profiles of experimental combustors under oxygen-lean and variable excess vitiated air conditions for applications to gas turbine-steam turbine combined engines. A domestic bituminous coal mined in Sardegna was investigated. Results show that the total vitiated air excess must be maintained above 30% and oxygen content in the primary stream cannot drop below 17% to avoid a carbon loss of over 3% wt. and unsteady flame formation. The secondary air oxygen content has a lesser influence on combustion efficiency: the tests performed show that an amount of 15% oxygen is sufficient to support a steady flame with over 0.97 combustion efficiency, if the proper swirl generator is used and the total excess of oxidizer is above the limit of 30%. The secondary vitiated air temperature and an inertial vortex generator offered a successful method of providing swirling turbulent coal flame and smoke, CO, and unburned hydrocarbons under environmental conditions.