The paper discusses three Combustion Engineering programs relating to the furnace sorbent injection process, a low-cost method for controlling sulfur dioxide (SO2) emissions from tangentially fired, coal burning boilers. The programs are: (1) pilot-scale investigations in the laboratory, (2) a prototype-scale program in a 65 MW utility boiler, and (3) a demonstration-scale program in a 180 MW utility boiler. A primary application of the technology is for retrofitting existing boilers in response to expected U.S. legislation for control of acid rain. In the process, the sorbent, usually calcium hydroxide (Ca(OH)2) or limestone (CaCO3), is injected above the flame zone where it mixes with flue gas containing SO2. The SO2 reacts chemically in the upper furnace with lime (CaO), formed from the sorbent, to make solid calcium sulfate (CaSO4). The CaSO4 is removed with fly ash in existing particulate control equipment.