Experimental investigation of co-combustion of coal and biomass using chemical looping technology

An experimental investigation into direct CLC was carried out using Yimin coal and two kinds of biomass, i.e., candlenut wood and rice hull as solid fuels and CuO as oxygen carrier. A series of tests was conducted in a thermogravimetric analyzer (TGA) to simulate the direct CLC process using coal, biomass, and their co-combustion, respectively. The synergetic effect between coal and candlenut wood was observed during the co-combustion process, but it was not found between coal and rice hull. The addition of K₂CO₃ and candlenut wood ash decreased the gasification temperature and increased the coal conversion. The theoretical coal conversion when 80 wt.% candlenut wood ash was added was similar to that when 50 wt.% K₂CO₃ was added. The high reactivity and stability of CuO was observed during cyclic operation at 800 °C. The interactions between metal oxide and ash were detected and no new phases were found after redox processes. Some changes appeared in the surface morphology of CuO-soild fuel samples after redox reactions, but no severe surface sintering was observed. Therefore, experiments and data analyses prove that CuO-based oxygen carrier was suitable for CLC of solid fuels. Some crucial considerations for the combustor operation were also given.