The specification of the control task resulted into a preliminary concept of the fuzzy logic controller. The operator knowledge was than used to specify the control strategy of the fuzzy logic system. Several structured audits took
place to evaluate the operator knowledge systematically. The audits focused on the operators’ manual control strategies and on the relationships between the inputs and the outputs of the process. This procedure is in accordance
with the standardized fuzzy logic design method. The audits resulted into the following concept for the fuzzy logic control: deviations of the gas throughput from its set point immediately result into a correction of the oxygen input. The coal input is adjusted accordingly to keep the ratio between coal and oxygen at a constant level. Changes of the reactor pressure predict changes of gas throughput. Therefore the pressure gradient is used as an early warning indicator for changes of the gas throughput.