Abstract: A gasifier (10) having an associated boiler (26, 32, 42, 48), for converting coal to combustible gas, and also having a desulfurizer (20) downstream of the gasifier. In order to maintain the gas leaving the gasifier and flowing to the desulfurizer above a predetermined temperature, even when operating the unit at reduced loads, a temperature sensing device (56) continuously monitors the gas temperature upstream of the desulfurizer. If the temperature drops below a predetermined value, high temperature boiler water (62) is introduced to the economizer (26) rather than feed water (24), so that less heat is absorbed by the economizer from the gases under these conditions.