Study on As and Pb release characteristics and thermodynamics of organic solid waste combustion/gasification process

In a fixed bed reactor, the release characteristics of As and Pb and the composition of ash in the combustion/gasification process of different types of organic solid wastes at 800−1100 ℃ were studied. The effects of CaO, SiO₂ and Al₂O₃ on the migration and transformation of heavy metals As and Pb in the gasification process were explored. The results show that the release rates of As and Pb in the organic solid waste gasification process increase with the increase of temperature on the whole, and the release rates of As and Pb in the gasification process are significantly lower than those in the combustion process. The ash yield decreases with the increase of temperature, and the ash mainly contains CaO, Al₂O₃ and SiO₂. Thermodynamic studies show that at high temperature, gasification process mainly produces gaseous As and Pb, while combustion process produces a large number of As₂O₃ and PbO. The boiling points of As and Pb are higher than those of oxides, so the release rates of As and Pb in gasification process are lower than those in combustion process. Ca₃(AsO₄)₂, Ca₂PbO₄, PbSiO₃ and AlAsO₄ can be produced by CaO, SiO₂ and Al₂O₃ reacting with As and Pb below 900 ℃. As the temperature increases, the release rates of As and Pb gradually increase. Therefore, the lower the gasification temperature is, the better it is. The emission of As and Pb in the atmosphere can be reduced by appropriately increasing the contents of Ca, Si and Al in organic solid waste and reducing the contents of S and Cl.