| Due to the ever increasing amount of sewage sludge and more stringent environmental quality standards, the treatment and disposal of sewage sludge has become an expensive and environmentally sensitive problem worldwide. Furthermore, with some traditional disposal routes coming under pressure, and others being phased out, it is necessary to seek a costeffective innovative solution to the problem caused by sewage sludge disposal. This paper presents a brief account of the current situation and developing trend of heat-decomposed treated methods of sludge of waste water plant.In this paper, the pyrolysis of sewage sludge sample was studied with thermogravimetry. The results showed that the pyrolytic reaction of sewage sludge consisted of four stages, that is, dehydration, organic compound decomposition and devolatilization,inorganic matter decomposition with remnant organic compound decomposition. By means of Coats-Redfern method, the kinetic parameters, the pre-exponential factor and the activation energy, were calculated to obtain the kinetic equation. The theoretical date fit the experimental date very well.The pyrolysis of a sewage sludge, was carried out in a laboratory furnace. Pyrolysis conditions, like heating rate and final pyrolysis temperature, were varied so that their influence on the characteristics of the resulting gases, liquids and solid residues could be studied. It was found that increasing the pyrolysis temperature decreases the solid fraction yield and increases the gas fraction yield while that of the liquid fraction remains almost constant. The pyrolysis oil of sludge was separated into three fractions: aliphatic, aromatic and polar fractions by using solvent extraction and liquid chromatography on a silicagel column. Water phase and each fraction of oil phase were analyzed and identified by GC-MS.Satisfactory results were obtained.With the help of elemental composition analysis for sewage sludge and transferred products, thermal gravimetric analysis for sewage sludge and GC/MS analysis for derived oil, it is discussed about the elements transfer, specified transfer temperature and reaction mechanism about the transfer reaction of the conversion process. The conclusion is that main conversion reactions are the evaporation of aliphatic compounds, the fission of protein peptide bond and the group transfer reaction, and that the main compositions involved in the conversion reaction are aliphatic compounds and protein, with higher reaction temperature for the former, lower for the latter and the highest for the saccharide compounds.The low-temperature pyrolysis process for sewage sludge,through which the energy can be recovered,is a developing technology. Both oils and gases produced in the pyrolysis showed relatively high overall heating values, comparable to some conventional fuels, revealing the potential application of these products as fuel.In this study,we made a bench-scale experiment with the feature of sewage sludge from a municipal wastewater plant. On the basis of the research,the optimal operation parameters have been obtained,related to the highest oil yield. It is pointed out that low temperature pyrolysis process for preparing oil from sludge has a promising future. |
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