Experimental investigation on the separated gasification chemical looping combustion performance of phytoremediation plant and retention of heavy metals

Abstract

Phytoremediation technology has been one of the important ways to treat soil heavy metal contaminant. However, if the harvested phytoremediation plant cannot be properly disposed, the heavy metals in phytoremediation plant may pollute the environment again. Separated gasification chemical looping combustion (SG-CLC) of phytoremediation plant is investigated in a two-stage reactor to reduce the emission of heavy metals into gas. And this technology has the superiority of traditional chemical looping combustion (CLC). The first-stage reactor temperature, bed material and steam mass flow are changed to investigate their effects on the combustion performance, retention of heavy metals in bottom residue and characteristics of oxygen carrier. Five redox experiment cycles are carried out under each condition. Results show that increasing the temperature from 450℃ to 650 ℃, the carbon conversion increases from 44.4% to 66.7%, and the retention rates of Mn, Ni, Zn and Pb decrease from 44.16%, 69.82%, 73.42% and 49.46% to 18.86%, 13.56%, 38.42% and 6.18% respectively. Increasing steam mass flow and using CaO as bed material are also beneficial to enhance the carbon conversion. This also affects the microscopic morphology of oxygen carrier in second-stage reactor. There appears obvious granular morphology on the surface of used oxygen carrier at 650 °C or using CaO as bed material. Rising the flowrate of steam from 0.36 g/min to 0.60 g/min has divergent effects on retention of heavy metals as retention rates of Mn, Ni, Zn and Pb change from 24.87%, 10.42%, 57.32% and 25.06% to 22.32%, 17.70%, 50.97% and 21.38%.