Combustion stability, burnout and NOx emissions of the 300-MW down-fired boiler with bituminous coal: Load variation and low-load comparison with anthracite

•Industrial experiments of down-fired boiler with bituminous coal under various loads are taken.•The ignition heat of coal/air flow under different coal varieties and loads is given.•Burning bituminous coal has a large furnace flame fullness under the low-load.•Strong combustion stability is determined by the low ignition heat and high furnace temperature under the low-load.•The combustion performances of bituminous coal and anthracite under the low-load are analyzed and compared.