Pyrolysis analysis of large coal particle in dry distillation section of Lurgi gasifier

Coal pyrolysis is one of main ways of coal transformation and utilization.Low-rank coal is converted into tar, coke oven gas and semi-coke by means of pyrolysis, which can greatly improve its utilization value.Both large coal particle and lump coal are commonly used for pyrolysis in industry processing.The complexity of volatile components makes the relevant research more difficult.Lurgi three-stage gasifier is treated as one of the main equipment of coal pyrolysis with the wide application in industry process.Given the practical operating conditions of Lurgi gasifier and the pyrolysis mode proposed by Merrk, a comprehensive mathematical model was developed for coal pyrolysis and heat and mass transfer in the dry distillation section of Lurgi gasifier.The results were obtained based on the practical operated condition of the gasifier.It is found that the heat transfer is the main limiting step for the pyrolysis of large coal particle.For a coal particle with the diameter of 20 mm, there is a larger temperature difference up to 67 ℃ between the external layer and the core at the initial stage, then gradually de-crease to only 1.7 ℃ after an hour.The volatile yields from the coal particle reaches 29%, which accounts for 89% of the final yield.There is a big difference in the release rate of the volatile components.The release rate of the tar and H₂O is about 10 times as much as other components.As for the dry distillation section with the height of 3 m in a Lurgi gasifier, the pyrolysis mainly occurs between 0-1 m above the bottom of the section, with the corresponding temperature range is 350-550 ℃.In the region with the height range of 0.25-0.6 m, volatile yields rate is much faster and the corresponding temperature range is 430-500 ℃.