Optimisation of two-stage combustion of high-PVC solid waste with HCl recovery

A process for two-stage combustion of high-PVC solid waste with HCl recovery is being optimised at Helsinki University of Technology, based on experimental evidence that PVC can be decomposed into HCl and a low-chlorine or chlorinefree residue by heating to temperatures of around 300-350°C. A theoretical analysis suggested that the process may have a thermal efficiency of ∼ 37% and nearly full recovery of the HCl, depending on pyrolysis temperature, PVC content in the solid waste and the moisture content in the solid waste. Results from these process simulations were used to construct a lab-scale test facility at our lab in Otaniemi, Espoo. The facility (approx. 40 kW fuel input) contains two fluidised-bed reactors plus heat exchangers and other side equipment. In a bubbling fluidised-bed pyrolysis reactor operated with nitrogen at ∼ 350 ° C the drying and dehydrochlorination of PVC takes place, and in a circulating fluidised-bed combustor operated at 800 ∼ 850 ° C the char from PVC plus the other fractions of the fuel are combusted. Product gases from both reactors are analysed on-line (using FT-IR) in order to evaluate process performance and especially to detect HCl from the second reactor. The first results from this experimental assessment study, which was part of the Finnish National Research Programme "Waste to REF and Energy" (1998-2001), are reported in this paper.