Experimental study on K migration, ash fouling/slagging behaviors and CO₂ emission during co-combustion of rice straw and coal gangue

Co-combustion of biomass and coal gangue (CG) is a potential technique for using both resources. The alkali migration plays a key factor for reducing ash slagging and SO₂ emission, but its mechanism unclear. Hence, the K migration in co-combustion of rice straw (RS) and CG was well studied in this work. The results indicated that the influence of CG addition on K migration is related to the CG blending ratio. For a CG blending ratio <40%, one hand the released SO₂ reacted with KCl and KOH to form relatively stable K₂SO₄; On the other hand, KCl, KOH and K₂SO₄ interacted with mullite and quartz to form KAlSi₃O₈. For a CG blending ratio >40%, K mainly reacted with mullite and quartz to form KAlSi₃O₈. Therefore, co-combustion is expected to reduce SO₂ emissions by up to 18.19% at a CG blending ratio of 30%. Furthermore, the ash fouling/slagging tendency decreased from 0.62 without CG to 0.26–0.47 with CG. Considering these reasons, we suggested a 20%–30% CG blending ratio as the optimum feedstock composition for the co-combustion of RS and CG, and the co-combustion could consume 0.17–0.23 kg/(kW·h) of CG and reduce 0.45–0.43 kg-CO₂/(kW·h).