MSW pyrolysis volatiles? reforming by incineration fly ash for both pyrolysis products upgrading and fly ash stabilization

The effective disposal of municipal solid wastes (MSW) and its incineration-derived fly ash (IFA), which contains large amounts of heavy metals (HMs) and chlorine (Cl), is an urgent task. In this study, IFA was used to reform MSW pyrolysis volatiles within 500-800 degrees C. The changes of reformed pyrolysis products, the migration char-acteristics of HMs and Cl between IFA and pyrolysis products were investigated. The results indicated that the O -and Cl-containing compounds in pyrolysis oil tended to decrease, light hydrocarbons and its calorific value increased accordingly after reforming; more CH4 and H2 gases were produced concurrently. The increase in reforming temperature enhanced these trends. The IFA absorbed Cl from volatiles during reforming, which reduced HCl in the gas product. The toxicity equivalent (TEQ) of PCDD/Fs in IFA decreased dramatically from 0.47 mu g/kg to 0.0055 mu g/kg after reforming at 500 degrees C, and it decreased with increasing reforming temperature. Some of the HMs' concentrations in the used IFAs increased, but their leaching capacity all decreased signifi-cantly at 800 degrees C except for Cr. The used IFA at 800 degrees C (IFA-800) corresponded to the lowest HMs leaching concentrations and could meet the landfill requirements; while the used IFA at 500 degrees C (IFA-500) corresponded to the maximum carbon deposition of 14.63 wt%, providing the energy source for its melting. Therefore 800 degrees C was recommended for harmless disposal of IFA, and 500 degrees C was better for a further melting of IFA., The contami-nation of pyrolysis liquid caused by inorganic Cl-containing compounds at 500 and 800 degrees C with much lower levels than the original. This study showed the hazardous properties of IFA can be dampened after interacting with MSW pyrolysis volatiles within the tested temperature range, and provided a good chance for the simul-taneous disposal of IFA and recovery of high-quality MSW pyrolysis products.

Automated summary

This study investigates the reformation of MSW pyrolysis volatiles using IFA, and the migration characteristics of HMs and Cl. Results show that the reformed pyrolysis oil has decreased O -and Cl-containing compounds, increased light hydrocarbons and calorific value, and produced more CH4 and H2 gases. The IFA absorbs Cl from volatiles during reforming, reducing HCl in the gas product. The toxicity of PCDD/Fs in IFA dramatically decreases with increasing reforming temperature. The used IFA at 800 degrees C has the lowest HMs leaching concentrations, meeting landfill requirements, while the used IFA at 500 degrees C has the maximum carbon deposition, providing an energy source for melting. This study demonstrates the potential for simultaneous disposal of IFA and recovery of high-quality MSW pyrolysis products, reducing the hazardous properties of IFA.