Chemical-looping combustion of plastic wastes for in situ inhibition of dioxins

摘要

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) as toxic by-products are inevitably emitted during conventional air incineration processes of chlorine containing wastes (typically, plastic wastes). The presence of O-2 in the conventional waste incineration not only participates in carbon gasification and rearrangement as an oxygen source during the de novo synthesis process of PCDD/Fs, but also promotes chlorination through generating more active Cl-2 via Deacon reaction. Chemical looping combustion (CLC), which creates an O-2-free atmosphere in the fuel reactor, was proposed to dispose plastic wastes. Comparative experiments [conventional PW incineration vs. in situ gasification-chemical looping combustion (iG-CLC) using CaO-decorated Fe2O3/Al2O3 as oxygen carrier] were conducted to measure the distribution properties of 17 toxic PCDD/Fs congeners. The total amount and toxic equivalency quantity of PCDD/Fs have been reduced by 94 % and 89 %, respectively, in iG-CLC. The absence of O-2 in fuel reactor and lower Cl-2 yield (due to the restriction of Deacon reaction and effective dechlorination by CaO) lead to the significant inhibition of the PCDD/Fs formation. Chlorine substitution modelling also demonstrated that the chlorine substitution probabilities for the formation of 7 toxic congeners of PCDDs and 10 toxic congeners of PCDFs are significantly reduced in iG-CLC. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.