Effect of coal ash additive on potassium fixation and melting behaviors of the mixture under simulated biomass gasification condition

In order to solve the ash related problems (such as corrosion and agglomeration) caused by potassium(K) species for efficient and clean gasification of biomass. It is feasible to add additives during the biomass gasification procedure. Coal ash has been proven to be an effective adsorbent for the gaseous K. However, the influence of coal ash on K retention in the solid phase is unclear, the interacting mechanisms and ash melting characteristics have not yet been clarified and need further explore. In this study, the effect of added coal ash on the potassium (KCl was selected as the simulated alkali model compound) retention in solid phase and the melting behaviors of the mixture during simulated gasification atmosphere is investigated by using a horizontal tube furnace and ash melting point analyzer. The results show that the higher the content of coal ash in the mixture, the greater the potassium retention in solid phase. Besides, the results of KCl release ratio and potassium retention ratio suggest that the capacity of coal ash for potassium fixation can be predicted by TG test instead of digestion experiment. It is important to provide a new research method for the subsequent similar experiments. The results of XRD and Factsge indicate that potassium was mainly fixed through the reaction of potassium with alumina/silica to form potassium aluminosilicates, which also contributes to the enhancement of the melting point. Some stable compounds with a high melting point were observed in the formed simples. The melting temperatures of the mixture were improved by different levels with the addition of NA (Ningxia coal ash) or WA (Wuming coal ash). The shrinkage analysis proves that the addition of coal ash could avoid the occurrence of agglomeration during the gasification procedure.