| Sludge is a by-product of urban sewage treatment plants,and how to dispose sludge with lower energy consumption and recover useful substances and energy efficiently has become a hot topic in the field.In recent years,domestic and foreign scholars have introduced microwaves into sludge pyrolysis technology to obtain effective sludge volume reduction,resource utilization,and effective fixation of heavy metals.In this paper,based on the optimization of process parameters,the composition,generation mechanism and mechanism of two kinds of energy products,namely bio-gas and bio-oil,were investigated respectively,and the migration and transformation rules of organic elements such as carbon and hydrogen were discussed,and the energy recovery efficiency of microwave pyrolysis of sludge was evaluated.By optimizing the process parameters of microwave pyrolysis sludge,microwave power was determined as a key influencing factor,and the distribution of pyrolysis products,the composition and generation rules of bio-fuel were investigated.The results showed that the heating rate of sludge accelerated with the power increasing,and the pyrolysis final temperature was also higher.At 1400 W,the simulated sludge could be rapidly heated to 901? in 10 min,and the pyrolysis final temperature was as high as 1142?.The gas production rate was as high as 48.53 wt.%,which was 1.45 times higher than the original sludge(19.80 wt.%).At this time the syngas(H2+CO)content was as high as 61.96 vol.%.The content of gasoline components with carbon number distribution of 5 to 12 in bio-oil produced by simulated sludge pyrolysis increased,which could reduce its density and viscosity.The calorific value of bio-oil and bio-gas were 28.66-35.03 MJ/kg and 4.81-12.89 MJ/Nm3,respectively,which had high energy value.At 1400 W,the energy recovery rate during the microwave pyrolysis of simulated sludge was up to 14.7%,increased by 97.2% compared to the original sludge.The effect of pyrolysis temperature on the bio-fuel was investigated.The results showed that as the temperature increased,the yields of pyrolysis residue and waterboth decreased,and bio-gas yield increased significantly.The bio-gas production rate of simulated sludge was as high as 52.93% at 1000?,and the syn-gas content was54.56 vol.%,indicating that the high temperature could promote the production of syn-gas.CO content continued to increase with increasing temperature.H2,CH4 content and H2/CO were both highest at 800?,which were 26.22 vol.%,14.81 vol.%and 0.93,respectively.Therefore,800?is more favorable for obtaining higher quality hydrogen-rich gas.The bio-oil yield first rose and then decreased with increasing temperature,and the highest yield occurred at 600?,which was due to the secondary cracking of a small amount of oil product at high temperatures.As the temperature rose,the content of oxygenated compounds and heterocyclic compounds decreased,and the content of monocyclic aromatic hydrocarbons and PAHs increased.Compared with the original sludge,the contents of aliphatic hydrocarbons and oxygenated compounds in the bio-oil produced from simulated sludge decreased,while the contents of monocyclic aromatic hydrocarbons,PAHs,and heterocyclic compounds increased,which improved the availability of components in bio-oil in chemical application,and reduced its density,viscosity,acidity,safety and stability.The carbon and hydrogen elements in the sludge showed different migration patterns with increasing temperature.Among them,the migration amounts of C and H in biochar reduced gradually,and the maximum values of carbon and hydrogen in bio-oil at 600?were 6.79% and 4.73%,respectively.With the increase of temperature,?(H,H2)and ?(C,CO)increased,and the migration of carbon and hydrogen in CH4 first increased and then decreased,and the maximum migration of carbon and hydrogen at 800 ? were 11.39% and 24.95%,respectively.These revealed the formation rules of bio-fuel produced by microwave pyrolysis of sludge deeply,laying a certain theoretical foundation for follow-up process. |
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