Enhanced dechlorination for multi-source solid wastes using gas-pressurized torrefaction and its removal mechanism

The emission of chlorinated pollutants from the thermal disposal of multi-source solid waste (MSW) incineration has posed significant hazards, garnering widespread concern. The study proposed a novel pre-dechlorination technology for MSW through gas-pressurized (GP) torrefaction without external pressurization. Typical chlorinated wastes, such as polyvinyl chloride (PVC), neoprene rubber (NR) and corn straw (CS), were selected. The study focused on two aspects: the pre-dechlorination effect of GP-torrefaction at 225-325 degrees C for each solid waste; the release of chloride during subsequent incineration utilization of semi-chars. Results showed that the GPtorrefaction had superior dechlorination efficiency than atmospheric (AP) torrefaction. For organic-Cl sources (PVC, NR), the dechlorination efficiency of GP-torrefaction for PVC reached up to 73.9-87.7 wt% at 225-275 degrees C, which was 23.79-60.17 wt% higher than AP-torrefaction. The efficiency for NR was 10.27-23.15 wt% higher than AP-torrefaction at 300-325 degrees C. Significantly, the autocatalytic reactions of HCl played an important role in dechlorination of PVC. And the C--C-Cl structure in NR were substantially converted into allyl chlorides (C-C-Cl), which were easier to dechlorination. For inorganic-Cl source (CS), GP-torrefaction enhanced the decomposition of cellulose and lignin. The abundant oxygen-containing functional groups derived from the decomposition can react with Inorg-Cl to facilitate the release of HCl/CH3Cl at 225-275 degrees C. Moreover, a portion of char-Cl (8.2-86.1 wt%) was derived from the secondary adsorption of HCl on three materials. It could be easily further removed by water-washing. In the incineration utilization, the chlorides content in the flue gas was only 1.29-2.69 % for three materials, and the HCl content being negligible for NR and CS. Overall, GP-torrefaction is a novel and effective method to reduce chlorinated pollution, providing new insights for the low consumption and efficient utilization of MSW.