Municipal waste pyrolysis (2) chlorine capture by addition of calcium and sodium-based sorbents

Abstract

Pyrolysis of municipal and industrial waste, which is currently under development, produces liquid, gaseous and solid fuels. Their utilisation as substitution fuels needs special attention environmentally and in particular a strict control of the chlorine contents is required. Indeed, chlorine can be found either in pyrolytic gases or in the char. The aim of this paper is to analyse the different ways of entrapping the chlorine in the char in a leachable form by addition of sorbents during pyrolysis. Synthetic waste mixtures containing PVC and lead oxide are pyrolysed on a laboratory scale with calcium and sodium-based sorbents. Overall mass and chlorine balances are presented using the different sorbents in various proportions. This article shows that 100% of HCl emitted in the pyrolytic gases can be captured and leaching the char can recover up to 98% of the chlorine. Pilot scale runs with mixtures of wood, PVC and calcium carbonate or lime rich sludge confirm the viability of this approach. It is demonstrated that the chlorine elimination before energy utilisation of the pyrolysis derived fuels could simplify the flue gas cleaning systems. (orig.)