Available heat
The sensible heat in POC at the critical process temperature is not available to the furnace. The higher the process critical temperature higher would be the sensible heat in POC. This sensible heat in POC is very important from the point of view of fuel utilization. We define gross available heat (GAH) as

(1)

GAH may also be considered as the heat given by POC in cooling from its flame temperature (flame temperature is AFT in the following which is T_AFT) to the process critical temperature (T_CRIT). If we assume that specific heat capacity of POC does not vary significantly with temperature and then

(2)

(3)

If for example is