In the process of the design study, the UAFBC system configuration has been evolved and simplified. The system combines a self-cleaning distributor/grate section (which can tolerate large coal particles) with a fluidized bed. Proper control of the distributor/grate and fluidized-bed provides high turndown capability. For maximum carbon utilization, an afterburner is provided. NO/sub x/ control is achieved by proper combustion staging and temperature control. For SO/sub x/ control, an entrained-bed sulfur scrubber, which uses small sorbent particles and long solids stay times yields efficient sulfur capture with a low calcium/sulfur ratio. The Aerojet design approach is to provide enough functional separation in the system to allow the stringent design goals to be satisfied compatibly. Various known state-of-the-art subsystems - self cleaning distributor/grate, fluidized-bed combustor, fines afterburner, entrained-bed dry scrubber - have been integrated to make this possible. The coordinated operation of the system elements is accomplished through the use of modern microprocessor controls. In this way, close control is obtained over the mechanisms of the combustion, sulfur scrubbing and particle cleanup processes without undue complexity. This high degree of process control permits development of a combustor which should exceed present environmental standards for NO/sub x/, SO/sub x/, and particulates, while allowing operation with an 8:1 turndown using a wide variety of fuels. In the design study, a number of configurations were considered and analyzed by computer simulation. Performance projections were made for various power levels and, in the case of the bench-scale system, for three different coal feeds. Greer limestone (75 wt % CaCO/sub 3/) was used as the reference sulfur sorbent. The results showed potentials for rapid commercialization of small (50,000 lb/h steam) UAFBC systems. 56 refs, 79 figs., 35 tabs.