Synergistic effect and chlorine migration behavior in co-pyrolysis of Pingshuo coal and polyvinyl chloride and directional chlorine enrichment using calcium oxide

Abstract

Co-pyrolysis of waste plastics and low-rank coal is an important way to realize the recycling of plastic wastes and the clean and efficient conversion of coal. However, halogens released would cause equipment corrosion and affect tar quality when halogenated plastics were co-pyrolyzed with coal. For this reason, polyvinyl chloride (PVC), as a representative of halogenated plastic, was co-pyrolyzed with Pingshuo coal (PS) in a two-stage fixed-bed reactor. The synergistic effect between PS and PVC and the migration behavior of chlorine were investigated, and the in-situ removal of chlorine during pyrolysis was explored by adding a CaO bed in the second stage of the reactor. The results showed that the addition of PVC in PS has a positive synergistic effect on tar yield with a maximum tar yield increment of 2.30 wt% at 30 wt% PVC, which is related to the negative synergistic effect on gas yield. Furthermore, the addition of PVC increases the content of 1–3 ring aromatics and decreases the content of aliphatics in the tar. The chlorine content in char and tar increases significantly with the increase of PVC addition. The addition of a CaO bed can significantly reduce the yield of HCl and the chlorine content in the tar. At 700 ℃, the dehydrochlorination efficiency of CaO can reach 78.1%. However, the CO2 produced by PS pyrolysis will reduce the dehydrochlorination efficiency of CaO, and this effect of CO2 can be reduced by increasing the temperature of the CaO bed.