Hydrothermal Carbonization Of Petrochemical Wastewater Treatment Plant Sludge:Distribution And Evolution Of Sulfur Species And Hydrochar Pelletization

Oil sludge as a by-product from petroleum exploitation,transportation process and petrochemical wastewater treatment plant has attracted the attention of environmentalists for large output and high processing cost,which is difficult to handle.In recent years,HTC technology has been applied to municipal sludge as a solid fuel.However,studies on the distribution and transformation of sulfur in HTC products of oil sludge are relatively lacking.Therefore,according to the current research and less involved field,this paper carries out research work in the following aspects:First,four tests were set up with reaction temperatures of 180℃,220℃,260℃,and 300℃,respectively.The yield,functional groups,morphology and combustion characteristics of hydrochar were investigated.The results indicate that hydrochar yield reaches the maximum of 84.78%at 220℃.After HTC,the ash content of oil sludge increases and the volatile content decreases.The results of FTIR analysis show that the vibration of-OH functional group decreases with the increase of temperature,indicating that the process of decarboxylation and dehydration occurs in the HTC.In addition,when the HTC temperature is higher than 220℃,the surface of hydrochar is porous,which is caused by the release of volatiles in the HTC.The combustion temperature and combustion index of the four prepared samples are higher than that of the raw sample,indicating that hydrochar has better combustion performance.Second,according to the previous research,three temperature gradients of 200℃,240℃,and 280℃ is added to explore the distribution and transformation trend of sulfur in liquid phase(water phase and oil phase),solid phase and gas phase.Results indicate that the sulfur-containing components in the liquid phase are mainly sulfate ions,which reaches about 1900 mg/L at 180℃.And it shows a decreasing trend with the increase of HTC temperature.Hydrocarbons are the main components of the oil phase.The contents of Thiophene-S and Sulfate-S in hydrochar reach the maximum at 300℃,which is 37.48%and 20.96%,respectively.The poly-condensation of sulfide-S,Sulfoxide-S and Sulfone-S result in the increase of ThiopheneS content in the HTC process.In addition,Sulfate-S and Sulfoxide-S appear at 180℃.Third,after mixing oil sludge and sawdust in different proportions,HTC is carried out.And the hydrochar powder samples are pelleted in a pelletization device.Solid fuel is evaluated by element analysis,FTIR and combustion properties.The results show that the carbon and fixed carbon content increase.FTIR analysis result shows that the sample occurs aromatization during HTC.The weight loss rate of hydrochar solid fuel is 95%,indicating that the fuel efficiency is high.With the increase of oil sludge content,the hydrochar yield decreases and the calorific value increases.The calorific value of solid fuel reaches the maximum(26.74 MJ/kg)when the ratio of oil sludge to sawdust is 20%.