Pressure-hydrators are used to produce a highly reactive sorbent with a surface area and pore size distribution which enables maximum utilization of available calcium. The hydrator vessel is operated at pressures of 90 to 150 psig with temperatures up to 300/sup 0/F. Upon expulsion of the reacted quicklime/saturated steam mix from the hydrator, water trapped inside the pore network of the hydrate particles is released explosively, yielding submicron-sized particles with a high specific surface area. The particles are flash-dried and collected for subsequent furnace injection tests. Initial tests at UNDERC were conducted to study the effect of injection-point temperature upon SO/sub 2/ removal. Optimal SO/sub 2/ removal occurred at about 1800/sup 0/-1900/sup 0/F (80%) with sorbent utilization of 40%. Progression from pilot to full-scale testing occurred in September 1984. PHLI was demonstrated at Otter Tail Power's Hoot Lake Station on a 50 MW tangentially-fired unit. Over 30 short-term tests were completed, plus one 30-hour duration of continuous injection. Fifty percent removal of SO/sub 2/ was observed with 25% sorbent utilization, and 70% removal of SO/sub 2/ occurred with sorbent utilization of 18.5%. Capture of SO/sub 2/ by the sorbent combined with inherent alkaline fly ash capture readily met compliance with the New Source Performance Standards. Compared to earlier results using limestone injection at Hoot Lake, the mass feed rate of PHL required to meet the minimum 70% removal of SO/sub 2/ decreased by a factor of 5. Emission levels were controlled at less than 10% opacity using the existing electrostatic precipitator, and boiler operation was not adversely impacted due to PHLI. An engineering and economic evaluation of PHLI has been prepared at UNDERC under DOE sponsorship.