Experimental investigation on MILD combustion of co-firing biomass and pulverized coal fuel blend in a pilot-scale furnace

Abstract

As a widely used CO₂ zero emission renewable energy, biomass fuel has been attracting extensive attention in recent years. For the first time, the sawdust and bituminous coal fuel blend is co-fired by experiments under MILD combustion conditions. The MILD combustion is achieved with low-temperature preheating air in a 200 kW pilot-scale furnace. The pilot-experiments include the swirl low-NOx combustion, MILD combustion through symmetrical secondary air jets and MILD combustion through asymmetrical secondary air jet. The pilot-scale experiments reveal that the MILD combustion of co-firing sawdust and bituminous coal fuel blend can be realized through both the secondary air jet arrangements of symmetrical double nozzles and asymmetrical single nozzle. Compared to the swirl low-NOx combustion, the MILD combustion of the sawdust fuel blend can reduce the NO emission by 45.5% to 49% and the PM_2.5 emission by 37% to 59%. The burnout rates of the sawdust fuel blend MILD combustion are more than 95%. Considering the in-furnace distribution, low NO and PM_2.5 emissions and high burnout rate, the MILD combustion is an effective way to utilize biomass fuel blend on a large scale. The present study further widens the fuel flexibility of MILD combustion even to biomass fuel blend.