A coal gasifier is retrofitted to achieve multiple advantages such as reduced oxygen consumption, reduced CO2 and NOx emissions, better H:C ratio, better carbon conversion etc. This is achieved by dividing the coal into at least two zones and modifying the gasifier and operating it as described. The coal is injected into a first zone, configured to devolatilize a substantial portion of the injected coal to produce coal char and volatiles. The operation is tuned to substantially consume the oxidant injected in the first zone. A low-calorific-value, high oxidant feedstock is injected in second zone of the gasifier. The devolatilization of the low-calorific-value, high oxidant content feedstock provides the oxygen containing compounds which gasify at least a portion of the coal char generated in the first zone.