Research On Nitrogen Transformation Characteristics During Torrefaction And Gasification Of Typical N-rich Food Waste

Food waste is an important component of municipal solid waste.The resource-based disposal of food waste is widely concerned.The disadvantages of high moisture content and low energy density of food waste restrict its transportation,storage and subsequent heat utilization.In this paper,torrefaction-gasification technology is proposed for the disposal of food waste,while high nitrogen food waste will release a large number of N-containing gases in the process of disposal,which will bring serious secondary pollution.Therefore,in this paper,pork（meat）and cabbage leaves（vegetables）were selected as two typical high nitrogen food waste representatives to study the characteristics of nitrogen transformation in the process of torrefaction gasification.In this paper,pork and cabbage leaves were selected as the research objects,respectively representing protein and lignocellulose food waste,to explore the transformation path of nitrogen to three-state products in the torrefaction process.The results showed that the N-containing structure in pork and cabbage leaves was mainly protein,and the transformation of nitrogen was mainly protein decomposition during torrefaction.Under the condition of300°C,the nitrogen remained in the pork char accounted for 64.26%of the total nitrogen,the products included protein,pyrrole,amines and quaternary nitrogen,and the nitrogen remained in the cabbage leaves char accounted for 69.08%of the total nitrogen,the products included protein,pyridine or amines,pyrrole and nitriles.The nitrogen of the liquid products in the two samples accounted for 19.10%and 25.27%of the total nitrogen,respectively,and the components were heterocyclic nitrogen,amines and nitriles.The main gaseous product of pork is NH₃,accounting for 11.10%of the total nitrogen,while the cabbage leaves almost do not produce nitrogen-containing gas,which is due to Maillard reaction between proteins and sugars.The condensation of carbonyl（-C=O）and amino（-NH₂）inhibits the release of NH₃.The effects of torrefaction temperature and gasification temperature on the release characteristics of NH₃and HCN during the gasification of pork and cabbage leaves were investigated.The results showed that during the gasification process（1000°C,H₂O/C=2）,torrefaction could significantly improve the yield of HCN from 0.75%to 24.08%after torrefaction at 280°C,but had no significant effect on NH₃;torrefaction could significantly inhibit the yield of NH₃from 7.20%to 3.12%after torrefaction at 280°C,but the change of HCN yield was not significant.This is because the cellulose,hemicellulose and lignin in the cabbage leaves can promote the deamination of protein and the formation of heterocyclic nitrogen,which indirectly promote the yield of NH₃.The Ca-containing substances in the cabbage leaves char can react with amino and inhibit the production of NH₃.