Research On Waster Heat Recovery And Tar Condensation Characteristics Of High Temperature Pyrolysis Gas

The hierarchical conversion polygeneration technology based on coal pyrolysis is one of the development directions of clean,efficient and high-value utilization of coal.The tar-containing high-temperature coal gas produced by coal pyrolysis has problems such as ash clogging of the heated area and low heat transfer capacity caused by tar condensation and precipitation during the waste heat recovery process.This makes the high-temperature pyrolysis gas cooling and waste heat recovery an urgent problem to be solved.In this paper,based on the high-temperature steam-cooled pyrolysis gas high temperature heat exchange-high temperature dust removal-waste heat recovery/tar condensation recovery process technology proposed by Zhejiang University,on the basis of feasibility analysis,carry out experimental research to verify the high temperature conversion of pyrolysis gas containing tar the feasibility of the thermal process and the acquisition of heat transfer characteristics at the same time provide a reference for the next step of the development and design of high-temperature pyrolysis gas waste heat recovery and tar condensation recovery devices.First,based on the composition characteristics of high-temperature pyrolysis gas,the Clausius–Clapeyron equation and the Peng Robinson equation were used to establish the tar condensation and dew point calculation models to obtain the temperature conditions for the condensation and precipitation of the major components under pyrolysis gas conditions.The results show that the main high-condensation temperature component of tar,such as asphaltene,condenses and precipitates at a temperature of about 330?under typical pyrolysis conditions.Therefore,by controlling the inlet temperature of the heating medium cooling medium and the pyrolysis gas temperature after heat exchange to ensure that the pyrolysis gas temperature remains above the condensation precipitation temperature,the condensation precipitation of tar components during heat exchange can be effectively avoided.At the same time,the analysis calculation also shows that the main components of tar,such as light oil,phenol oil,naphthalene oil,washing oil,anthracene oil,and asphalt,have condensation temperatures of 74?,109?,120?,147?,218?,and 330?,there is a clear difference,in the cooling waste heat recovery process can be carried out by staged condensation measures to achieve the recovery of different components of tar.On this basis,an 80Nm~3/h high-temperature pyrolysis gas waste heat recovery and tar condensation characteristics experimental research device was built.Using tar-containing high-temperature flue gas and high-temperature steam as the working medium,the heat exchange process was realized by controlling the heat exchange steam inlet temperature and there is no tar condensation and precipitation,which verifies the feasibility of the proposed high-temperature steam heat exchange process of tar-containing pyrolysis gas.At the same time,through the experimental study of the heat exchange characteristics under different tar contents(tar contents of 50g/Nm~3,100g/Nm~3,150g/Nm~3 respectively),the heat exchange characteristics of pyrolysis gas containing tar at high temperature were obtained.The experimental results show that due to the influence of the cracking process of the tar component on the carbon decomposition process,the heat transfer coefficient of the pyrolysis gas containing tar is reduced compared with the case without tar,but with the increase of the operating time,the heat transfer capacity is gradually stabilized.The experimental results of different tar contents show that the heat transfer coefficient of the heated surface decreases with increasing tar content.Based on the experimental results,two methods of linear fitting and nonlinear fitting were used to fit the heat transfer coefficients of convective heat transfer surfaces of different tar contents in pyrolysis gas,and the correlation of heat transfer experiment on tar-containing gas convection heating surface was obtained.In addition,by reducing the steam inlet temperature(steam inlet temperature is 290?,250?,210?),carried out tar condensation precipitation experiment.The experimental results show that as the steam inlet temperature continues to decrease,the heat transfer coefficient of the heated surface decreases accordingly.When the steam inlet temperature drops to 210°C,tar condenses and precipitates on the heat exchange wall surface,which provides a reference for the next step of the development and design of high-temperature pyrolysis gas waste heat recovery and tar condensation recovery device.