Study On The Migration And Directional Enrichment Of Chlorine In The Co-pyrolysis Of Hailaer Low Rank Coal And PVC

At present,energy shortages and environmental pollution have become the focus of global attention.The low-rank coal and PVC co-pyrolysis technology is basically the same as the coal hydro-liquefaction technology.The plastic with high H/C atom as hydrogen donors,supplying for the pyrolysis reaction process,conducived to generation liquid products.During the co-pyrolysis process,Hailaer coal(HLE)has a high ash content.The metal compound in the ash can fix the chlorine element of the PVC as a metal chloride in the solid phase product.Therefore,co-pyrolysis of chlorine-containing plastics and coal has good prospects for both resources and environment.In this paper,the pyrolysis characteristics and kinetics of HLE and PVC,were studied.The main results and conclusions include:The thermal pyrolysis and co-pyrolysis characteristics of HLE and PVC were studied by thermogravimetic(TG)analysis technology.The results show that there are three stages in the pyrolysis of HLE:the first stage is mainly dehydration stage,the second stage is the main pyrolysis stage of lignite,a large amount of volatilization is separated out,and the third stage is the coal polycondensation stage.The PVC pyrolysis is mainly divided into two stages:the first stage is mainly dechlorination,and the second stage is thecleavage of olefin chains releasing aromatic hydrocarbons.The co-pyrolysis process is divided into two stages:the first stage coincides with the PVC single thermal desorption HCl stage.Compared with the coal pyrolysis,the maximum weight loss rate corresponding to the stage gradually moves to the low temperature area;The second stage is coal devolatilization and PVC olefin chain cleavage stage.The differential method and integral method were used to analyze the main stages of the separate pyrolysis and mixed co-pyrolysis.The results show that the main pyrolysis stage of PVC belongs to D1,one-dimensional diffusion model,and the two main pyrolysis stages of Hailar lignite conform to D3,Jander three-dimensional diffusion equation;The co-pyrolysis process of the first stage conforms to D1,one Dimensional diffusion model;the second stage conforms to D3,3D diffusion model.The activation energy of the first stage is lower than the activation energy of the single pyrolysis of PVC,and the activation energy of the second stage is increased first and then decreased compared with the coal alone during pyrolysis.It shows that coal and PVC co-pyrolysis can affect each other and reduce their activation energy.The results of fixed bed pyrolysis experiments show that with the increase of pyrolysis temperature,the weight loss of HLE and PVC increases continuously,and the gas phase and liquid phase products increase with the increase of temperature.The products of HLE gas phase are mainly CO2,CO and CH4,while the PVC pyrolysis gas phase are mainly C2 and CH4,and CO2 and CO are rare.This is mainly due to the low content of O in PVC.In the process of co-pyrolysis,comparing the difference between the actual value and the theoretical value of the yield of the co-pyrolysis product,it is found that the co-pyrolysis has obvious oil-increasing effect.For gas component analysis,C2 and CH4 increase obviously;The analysis results of tar showed that PVC addition promotes the lightening of pyrolysis tar,greatly improves the quality of coal;SEM analysis of the co-pyrolysis product shows that the increase of PVC addition causes the char to be wrapped by the molten material,and the semi-coke crack is reduced,which improves the strength of coke.By analyzing the removal rate and migration law of chlorine under different temperatures and different PVC additions,it is known that the content of chlorine in the gas phase increases first and then decreases with the increase of pyrolysis temperature.The chlorine in the gas phase begins to decrease at temperature of 600?.XRF and XRD analysis result of the char showed that,the content of alkali metal compounds in coal is gradually reduced,and metal chlorides appear in the char.It is indicated that the chlorine in the PVC can react with the metal oxide in the coal to form the metal chloride,and is fixed in the solid phase product as a metal salt.