Research On Processing Methods And Fuel Characters Of Processed Products Of The Pyrolysis Liquid From Sewage Sludge

Currently, the world is confronted with two difficult issues as energy shortage and environmental problem. Energy shortage, especially the oil shortage, has impeded the rapid development of the social economic. Sewage sludge is generated from the wastewater treatment process, the treatment and the disposal of which has become a worldwide problem. Pyrolysis is one of the promising ways of sludge resource utilization. Based on the harmless disposal of the sewage sludge, pyrolysis can also produce pyrolysis oil similar to crude oil which is receiving widespread concern. In this study, a comprehensive analysis to the characteristics of the sludge pyrolysis liquid obtained by a fixed bed was conducted. A two-step distillation method was used for processing the liquid. The componients of the processed products were then analyzed by GC-MS, and the characters of the processed products were determined according to the oil test methods. Based on the results, the processed products has the potentials to be the alternatives of the petroleum products which provided references to relieve the problem of oil shortage.After removing the water of phase separation, the water contained pyrolysis oil was obtained. Distillation method was used to dehydrate the water contained pyrolysis oil, and analyzing the fuel characteristics and non-fuel characteristics of the water-free pyrolysis oil, and the fuel characters and non-fuel characters of water-free oil were analyzed. The results indicated that water-free pyrolysis oil could basically meet the requirements of fuel oil 4#. But the sulfur content, solid particle content, and metal ion content were too high, hence further processing was needed. A two-step distillation method was employed for processing the water contained pyrolysis oil sample, the simple distillation was used to dewater and obtain the light fraction, while the reduced pressure distillation was used to obtain middle fraction and asphaltenes. During the reduced pressure distillation, decreasing the reflux ratio is an effective method to reduce the asphaltenes. At the reflux ratio of 1, four processed products were gained, which were 25% of water, 13% of light components, 31% of mid-components, 28% of asphaltenes and 3% of the volume loss during the distillation process. Through two-step distillation, the water of the water contained pyrolysis oil was removed, and some oil fractions with different characters were obtained, which indicated that the water contained pyrolysis oil had the potential as high quality oil products by two-step distillation method.By analyzing the fuel characteristics of the light fraction, mid-fraction and asphaltenes, the perspective of these three kinds of processed products were discussed. The light fraction contained large quantities of hydrocarbons with chain length between C6 and C13, and its fuel characters were similar to gasoline. The characters of light fraction were similar to motor gasoline, which indicated that light fraction had the potential to be the motor gasoline. Midlle fraction, with the carbon chain length of hydrocarbons between C10 ~ C20, included 48% organic matters containing N and O such as organic acid, alcohol, nitrile, and so on. The fuel characters of middle fraction indicated it could be used as 2# fuel oil and had similar characters with 5# diesel which showed it had the potential to be diesel. With 10% of midlle fraction contained in commercial diesel, it did not influenced the application of the mixture.This study provided a new method for solving pyrolysis kinetics model, which has the advantages of simple computation compared with conventional methods. Compared the parameters derived from the new method with those from the traditional model, little difference was found. Well data fitting results showed that the method could be used for sludge pyrolysis kinetics solution.Through the social needs analysis of the sludge pyrolysis oil and the constant calculation of the process energy consumptions and outputs, it can be concluded that with the sludge moisture content below 60%, the output value was higher than energy consumption costs, while with moisture content higher than 60%, the energy consumption costs became higher. Reducing the sludge water content and increasing the thermal efficiency of equipments can improve the economic benefits of sludge pyrolysis.