Effect Of Preoxidation On NaCl Release During Zhun Dong Coal Pyrolysis

Coal resources in Chinese energy consumption structure occupies a vital position,and it is Chinese national economy sustained and rapid development of effective support.With the rapid growth in demand for development,coal mining ratio is declining because of a large number of continuous mining.In recent years,the newly discovered Xinjiang Zhundong area is rich in coal reserves and the current proven reserves are 2136 billion tons,which will become the source of Chinese coal energy supply,But Zhundong coal has brought new challenges to Chinese coal power equipment because of its high Na content.The release of Na in the pyrolysis process leads to severe slagging and contamination of the heating surface of the boiler tail,while the most volatile in the high sodium is Na Cl,so the technology which controls the release of Na Cl to achieve the Zhundong coal reasonable application has great significance.In this paper,the following experiments were carried out on the coal using a fluidized bed/fixed bed reactor system: low temperature oxidation experiments;oxidized coal and unoxidized coal were respectively pyrolyzed at different temperatures and tested the release of Na and Cl in the process of oxidation and pyrolysis,so as to study the effect of oxygen-containing functional groups on the release of Na and Cl.The distribution of Cl and Na in coal char was detected by xps and fraction extraction,respectively,and the effects of oxygen groups on the morphological changes of Na and Cl were studied.The oxygen-containing functional groups and carbon structures in coal char were characterized by FTIR and Raman.The thermo-gravimetric analysis of different treated coal was carried out and the effect of preoxidation treatment on the chemical structure transition during coal pyrolysis was studied.The results show that coal can form some stable oxygen-containing functional groups during the preoxidation process,and the alkali metal in coal has the inhibitory effect on the oxidation process.The coal will release a large amount of Cl in the oxidation process and convert the inorganic Na to the organic Na.The oxidation process can promote the ion exchange of Na Cl with the oxygen-containing functional groups in the coal.During the pyrolysis of coal,the release of Na and Cl in Na Cl is not synchronous.Preoxidation of coal can effectively inhibit the release of Na during pyrolysis.Preoxidation can promote the release of Cl at 500 ℃,and inhibit the release of Cl at 700 ℃,800 ℃ and 900 ℃.Preoxidation can promote the conversion of inorganic Na and inorganic Cl to organic Na and organic Cl in the pyrolysis process.The inorganic Cl which is released into the gas phase at high temperature will partly convert to organic Cl,and it is one of the reasons for the preservation of Na by oxidation.The oxygen-containing functional groups formed during the pre-oxidation process will decompose and transform in the pyrolysis process,leaving more C-O,COOH and C=O in the coal char,where C=O is the most obvious.The oxygen-forming functional groups formed by the preoxidation can affect the evolution of the carbon structure during coal pyrolysis,resulting in the formation of more amorphous carbon and crosslinked structures in the coal.Preoxidation treatment can affect the law of covalent bond breakage of coal during pyrolysis,which makes the fracture process of aliphatic and aromatic more complicated and severe and makes the condensation process of aromatic ring more difficult.