SummaryA model for the growth of an organism on multiple substrates was developed, assuming that. each substrate has a competitive inhibition effect, on the uptake of other substrates. The model was extended to examine mixed substrates, showing that the coexistence of several species a t steady state in continuous cultures is possible, even when all the organisms all strongly prefer the one substrate. The diversity of nutrient sources in a real system may be a key factor in supporting a heterogeneous microbial population.

A Model For Moving-Bed Coal Gasification ReactorsA steady state model of moving-bed coal gasification reactors has been developed. Model predictions are in agreement with published commercial plant data for Lurgi pressurized gasification reactors and a pilot plant slagging gasifier. The dependence of reactor performance on operating variables has been studied for Illinois and Wyoming coals. For a given coal, maximum efficiency is determined by the coal-to-oxygen feed ratio. The location of the maximum temperature, which defines the combustion zone, is an important operating variable. Efficient operation of the dry ash reactor cannot be carried out below a critical feed gas temperature because of ins&cient gasification and excessive carbon loss in the ash.

A laboratory differential reactor study was conducted at temperatures of 975-1,275 K to investigate CaO sulfation mechanisms with calcine (CaO) samples derived from pulverized limestones and dolomites, and hydrated limes. The limestones had 8-1 15 pm mean particle sizes, a range applicable for boiler sorbent injection for SO, control. Under conditions applicable for boiler sorbent injection, the sorbent performance, in terms of initial reaction rate and saturation utilization, was limited by the SO2 pore diffusion rate and by premature pore mouth plugging by CaSO, product and, thus, depended on CaO particle size and pore size. Hydrated lime and Na,CO,-promoted limestones showed performance superior to that of limestones, because they produced calcines with larger pores. Intrinsic reaction rate as reported by Borgwardt and Bruce (1986) was observed at temperatures below 1,100 K.

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The Coolside desulfurization process is a dry sorbent injection technology developed for retrofit SO2 control in coal-fired utility power stations. The process is low in capital and space requirements since, in its ideal configuration, the existing ductwork and particulate collector are used as the S02-sorbent reaction spaces. It has been developed through laboratory and 1 MW-scale field tests using hydrated lime as the primary process sorbent by Consolidation Coal Company (Consol). The field work showed promising results with observed SO2 removal ranging u p to 80%. In order to optimize the process performance through improved understanding of the process fundamentals, Consol constructed and is operating a 0.15 MW pilot test unit. This paper describes the results of a process variable test program, afirst series of tests made in the pilot unit, and the unit operability observed during the test work.