Influence mechanism of waste lubricating oil on slurry characteristics of municipal sludge-coal water slurry

Municipal sludge incineration can not only effectively solve some secondary pollution problems occurred in the process of sludge treatment,but also maximize the utilization of the calorific value of municipal sludge. The addition of municipal sludge would deteriorate the fluidity and calorific value of sludge-coal water slurry (SCWS),which is not conducive to the gasification or combustion of the SCWS. Due to the high calorific value and good fluidity of waste lubricating oil,the slurry ability of the SCWS could be improved by adding waste lubricating oil into the SCWS. The experimental results show that the apparent viscosity of the SCWS decreases gradually with the increase of municipal sludge content from zero to 12% under the sludge-oil ratio of 1.0. However,under the sludge-oil ratio of 1.1,the apparent viscosity of the SCWS increases first and then decreases gradually with the increase of municipal sludge content. The apparent viscosity of the SCWS reaches the maximum with the dry basis sludge content of 3%. Basically,the apparent viscosity of the SCWS increases with the increase of sludge-oil ratio. The apparent viscosity of the SCWS decreases about 52.3% from 714 mPa·s to 340 mPa·s with the increase of municipal sludge content from zero to 6% under the sludge-oil ratio of 1.0 and the SCWS calorific value of 17.42 MJ/ kg. According to the infrared spectrum analysis results,when the municipal sludge and coal powder are soaked in waste lubricating oil,the peaks of non-polar functional groups are obviously enhanced,while the peaks of polar functional groups are obviously weakened. Based on the results of X-ray energy spectrum analysis,the O/ C ratio of municipal sludge and coal powder decreases sharply from 0. 88 and 0. 23 to 0. 04 and 0. 08, respectively, and the C—H/ C—C content increases from 53. 98% and 70.44% to 93.24% and 86.83%,respectively. On the basis of wettability results,the contact angles of municipal sludge and coal powder increases from 69.5° and 63.4° to 101.3° and 94.2°,respectively,and the contact angle exhibits little change with the increase of contact time. The above analysis results show that the long-chain alkane and benzene ring of waste lubricating oil can be adsorbed on the surface of municipal sludge and coal powder and result in the decrease of the hydrophilic site on the solid surface,which is beneficial for the formation of a relatively complete hydration film around the municipal sludge and coal powder. This is the main reason behind for the enhanced slurry performance of the SCWS in the presence of waste lubricating oil. © 2022 China Coal Society. All rights reserved.