The technology involved in coal-fired atmospheric fluidized bed (AFB) air heaters for indirect-fired gas turbine cogeneration systems differs in several respects from that already employed for AFB steam boilers. This paper presents the results to data from on ongoing research program aimed at adopting the AFB boiler firing concept to air heater service. A coal-fired air heater program has been underway since 1980 with an 18- by 18-inch AFB experimental unit. The goal is to resolve those technical issues of special importance to the indirect-fired gas turbine application which are amenable to resolution with short-term testing and small-scale hardware. The issues presently being researched include throttling to loads as low as 20 percent, safety accommodating sudden changes in load (and the interruption in cooling resulting from a turbine trip) and establishing the response characteristics of the AFB combustor/heat exchanger system as they relate to overall control system design. Other issues being evaluated include exploration of the limits of acceptable operation.
The 18- by 18-inch AFB heater test facility is located at the Rockwell Thermodynamics Laboratory in California. A series of coal-burning tests of 12 to 24 hours duration have been conducted to establish the bed operating and heat transfer characteristics at loads between 20 and 135 percent of nominal. Control transient characteristics have been evaluated through simulated load changes and interruption of cooling. Heat exchanger material specimen probes and diagnostic probes for investigation of the corrosion/erosion aspects of heat exchanger materials have been exposed. Results to date indicate that an AFB combustion system will provide a good match to the demands of an indirect-fired gas turbine system.