Characteristics Study On Co-pyrolysis And Co-gasification Of Sewage Sludge And Pine Sawdust

Sewage sludge contains harmful substances such as heavy metals, poorly biodegradable organic compounds, bacteria, viruses, pharmaceuticals and hormones, which make its disposal management difficult. In recent years, the traditional methods used for the disposal of sewage sludge including landfill, agricultural application and incineration are facing more and more pressure, due to the land limitations and stringent regulations. However, co-gasification of sludge and biomass, which is an innovative solution to more efficient disposal of slydge, can compensate the weakness of one fuel by another. It has great potential in sludge disposal.The pyrolytic characteristics of sewage sludge, pine sawdust, and their blends were investigated under nitrogen atmosphere by dynamic thermogravimetric analysis. It can be concluded that the interactions between the two materials in the blends are slight under the conditions used in the study. The dependence of apparent activation energy on conversion obtained by Friedman method and distributed activation energy model(DAEM) revealed that the blends can be considered as multistage process. The results indicated that the DAEM can provide reasonable fits to the experimental data.Steam fast co-gasification of biomass and sludge in ratios from 0:100% to 40:60% was studied in a small fixed-bed reactor. All gasification parameters, including producer gas composition, char yield as well as total gas yield, were measured. It can be observed that there is a substantial increase in H2, from 27.94% to 37.53%, between 700? and 800?, while much smaller increase was detected between 800? and 900?. Over the temperature range of 700-900?, the CO content was least at 800?. The hydrogen content increase from 32.17% to 37.53% with increasing biomass ratio from 0% to 40%, and the total gas yield increased gradually. The Ca impregnation was implemented during oil-frying drying can increase fuel's gasification reactivity with minimal additional cost. The produced gas from the Ca-impregnated fuel possessed higher CO2 concentrations and had lower contents of CO and CH4, especially for H2, increase from 34.08% to 50.76%. The total gas yield increased a lot. The physically mixced CaO also affected the H2, CO, CH4 and CO2 concentrations in the same tendency, but the effects were slight in comparison with that from the fuel impregnated Ca.To understand the tar evolving and cracking behavior, the main components and yields of tar were analyzed by GC/MS and gravimetric method respectively. The experiment indicates that: both elevated temperature and the addition of Ca(OH)2 could promote the tar cracking. The increase in temperature led to an obvious decrease in the formation of heterocyclic aromatics, while the relative content of both light PAHs and heavy PAHs increase. In regard to the tar yield, an increase trend were found with increasing biomass ratio from 0% to 40%. More nitrogen compounds, such as pyridine, quinolone and isoquinoline, were detected when mixed with biomass. With Ca impregnation, the content of heterocyclic aromatics increases a lot, while the content of PAHs decreases.