An Energy-economic Analysis Of Sewage Sludge Fast Pyrolysis

With the fast progress of urbanization and industrialization,the increasing municipal sewage sludge has posed great burden to the environment.Compared with traditional landfilling and fermentation methods,pyrolysis is reciving more and more attention as its less pollution and high energy content of pyrolysis product.Pyrolysis is a promising thermal conversion method aiming at treating sludge with clean,efficient and resoureful goal.With the support of the National High-Tech Research and Development project “Sludge Pyrolysis Utilization Technology and Engineering Demonstration”,the research is about energy and economy study of fast pyrolysis system for two kinds of municipal sludge in Wuhan.The main works are as following:For the first part,two sewage sludge samples obtained from two different sewage treatment plant in Wuhan(LWZ and TXH)were used to carry out fast pyrolysis experiment under 300,500,700 and 900℃ respectively,from which the distribution of pyrolysis products,BET and heating value of pyrolysis char,GC-MS of pyrolysis oil and GC of pyrolysis gas would be get.The outcome shows that the product of two sewage sludge varies a lot,but the highest oil yield perent at 500℃.The yield of pyrolysis char decreases with the pyrolysis temperature which corresponding to other reaserch results.Based on the experiment data,the system of self-heating sewage sludge fast pyrolysis that produce oil and the system to produce oi together with char were built by Aspen Plus.Which mainly contains the drying and crush,pyrolysis,burning and energy recovery parts.With the scale of 5t/h wet sewage sludge,the simulation results were acquired with different samples in different temperature conditions which 16 cases in total.The result lead to the exergy analysis,and the system performance would be judged via exergy loss and exergy benefit.The exergy analysis illustrates that the burning part contributes the most exergy loss,the pyrolysis part accounts the least exergy loss of the system.The exergy loss ratio of TXH is higher than LWZ,the system that produce oil lead to higher exergy loss ratio compared with the system that produce both oil and char.The exergy performance can be improved by optimizing the supply of fuel or improve the energy recovery part.In the last part,the system economic performance were studied by the Aspen Process Economic Analyser with NPV and IRR as indicators and all 16 cases had been compared.The results show that all cases are not profitable under present technology and assumptions.While the system that produce oil at 500℃ with TXH sewage shows the best opportunity to be NPV positive.Then the system profit possibility was studied as four critical factors(sewage sludge treatment subsidy,product price,coal price,and transportation distance)varied.Which turns out that when subsidy is over ￥99/t or coal price is lower than ￥177/t or transportation distance is within 9 km,the system can be profit.And the sensitivity analysis revealed that the subsidy influence the system at most,and transporation presents the least affect.