Study On Co-combustion Behavior Of Typical Biomass/Anthracite

Biomass is a promising renewable energy resource with low energy density. The co-combustion of biomass and coal can increase the energy density and reduce environmental pollution. Consequently, investigation was carried out on the co-combustion behavior. In this article combustion behaviors of spent coffee grounds, anthracite and their blends were assessed based on a thermal analysis technique and a lab-scale fixed bed furnace.The influences of heating rates, blending ratios and oxygen concentration on oxy-fuel combustion characteristics and kinetics were revealed based on thermal analysis experiment and combustion theories, which were compared with those in air. The conclusions were below:the ignition and comprehensive combustion indices increased with increasing heating rates and spent coffee grounds content in the blends. Increasing of oxygen concentration decreased the ignition temperature and increased the comprehensive combustion indice. The replacement of N2 by CO2 made a slight delay for combustion. Synergy occurred in most blended samples. The combustion kinetics were also evaluated in conjunction with volatile matter and fixed carbon burning periods based on solid kinetic theories. In air atmosphere, the activation energies of release and combustion for volatile matters in the blends ranged from 40.8 to 114.32 kJ mol-1(at pre-peak period), from 39.5 to 94.22 kJ mol-1(at post-peak period); Activation energies of char combustion in the blends varied from 25.17 to 161.45 kJ mol-1(at pre-peak period), from 39.91 to 125.08 kJ mol-1(at post-peak period). In O2/CO2 (21-40% oxygen contents) the activation energies of release and combustion for volatile matters in the blends ranged from 15.17 to 103.58 kJ mol-1(at pre-peak period), from 50.83 to 80.44 kJ mol-1(at post-peak period); Activation energies of char combustion in the blends varied from 19.06 to 193.4 kJ mol-1(at pre-peak period), from 27.34 to 111.54 kJ mol-1(at post-peak period) and increased with the blending ratios of biomass. A good linear relation between Ea and lnA of each sample was revealed.Via the isothermal and non-isothermal experiments on the lab-scale fixed bed furnace the influences of heating rates, temperatures and blending ratios on briquettes fuel combustion characteristics and kinetics and gas emissions were investigated. Analysis showed that the ignition and comprehensive combustion indices improved as spent coffee grounds increased in the blends. Under isothermal condition, combustion rate increased as temperatures and the blending ratios increased. No-isothermal activation energy for briquettes fuel ranged from 14.97 to 95.03 kJ mol"1 (at pre-peak period), from 13.14 to 116.84 kJ mol"1 (at post-peak period).The emissions of CO2 and NO increased with the increasing heating rates while NO2, SO2 were only detected at low heating rate. With the blending ratio of spent coffee grounds increased temperature CO2 and CO emission decreased. Maxima of CO2 emission increased and CO emission decreased and NO emission decreased as the blending ratio of spent coffee grounds increased. Under the isothermal condition, CO2 and NO2 emission had a slight increase while CO and NO2 emission decreased when temperature increased. CO2, NO and NO2 emission increased, SO2 emission decreased.Anthracite showed high ash fusion temperatures, all above 1518 ℃. Ash fusion temperatures for spent coffee grounds and the blend ranged from 1253 to 1518℃, from 1285 to 1518℃, respectively. The blending ratio should be less than 40% in order to prevent depositing and slagging.