Transformation Of Potassium And Chlorine During Pyrolysis Of Straw And Co-pyrolysis Of Straw And Coal

Straw biomass generally contains a number of inorganic elements, such as potassium and chlorine. During biomass thermochemical conversion, potassium and chlorine can release into gas phase, causing several serious problems including corrosion, agglomeration and so on. Based on the drop tube furnace and high frequency furnace, straw and Jincheng anthracite were selected to investigate the release of potassium and chlorine and transformation of potassium in different forms during straw pyrolysis and co-pyrolysis of straw and anthracite, then a discussion of transformation pathways of potassium and chlorine was carried out.Potassium, chlorine and water soluble potassium release ratio during high frequency furnace pyrolysis were higher than those in drop tube furnace. The apparent release ratio of ion-exchangeable, acid soluble and residue potassium during high frequency furnace pyrolysis was lower than that in drop tube furnace between 800 and 900 centigrade, but the gap became smaller at higher temperatures.During the co-pyrolysis of straw and Jincheng anthracite in high frequency furnace, the anthracite restrained the release of potassium and chlorine also promoted water soluble and ion-exchangeable potassium to transfer into acid soluble and residue form. Ash free anthracite, SiO2, Al2O3 and kaolin could decrease the potassium release ratio and influence the transformation of potassium in different forms, SiO2 promoted the formation of water soluble potassium, ash free anthracite and Al2O3 promoted the formation of ion-exchangeable and residue potassium, kaolin promoted the formation of acid soluble and residue potassium. Ash free anthracite, SiO2, and kaolin contributed to the release of chlorine while Al2O3 adsorbed potassium chloride in gas phase and adhered it on the surface to reduce the release of chlorine.Simulation results from FactSage software were basically consistent with experimental results and XRD patterns. Silicon and aluminum conduced to fix potassium in pyrolysis char, and accelerated the release of hydrogen chloride simultaneously. During straw pyrolysis process, potassium and chlorine mainly existed in the form of potassium chloride, which could release into gas phase at high temperatures. When pyrolysis material was accumulated, secondary reactions that potassium chloride reacted with pyrolysis char might easily occur, causing potassium fixed in char, while hydrogen chloride released into gas phase.