The Transformation Of Alkali In Xinjiang Coal

Xinjiang has abundant coal resources and great utilization value,however,the existence of high content of alkali in coal,caused a series problems such as ash deposition,slagging,contamination and corrosion have been caused in the process of pyrolysis and gasification,which limits the utilization and prospect of high sodium coal.In that case,in order to solve those problems mentioned above,we have carried out the study of the migration alkali in,Yili,Hutubi and Naomaohu coal,the typical Xinjiang high alkali coal.This paper has a systematic analysis on Yili coal,Hutubi coal and Naomaohu coal,which belong to high sodium coal.Occurrence mode and concentration of alkali in Yili,Hutubi and Naomaohu coal were analyzed in this paper.Proximate ultimate analysis and formation analysis for the very three kinds of raw coal are carried out.Meanwhile,the XRD of three coals are got and analyzed after low temperature ashing.The results show that the sodium elements in Yili and Naomaohu coal mainly exist in water soluble sodium accounted for 80.08%and 82.10%respectively;while the Hutubi coal mainly insoluble for 27.91%.The main occurrence of potassium in three raw coals are mainly insoluble potassium.It is worth noting that the high content of sulfate anion in Yili,Hutubi and Naomaohu coals,respectively up to 2998.9?g/g,781.9?g/g,1030.7?g/g.Besides,the chlorine is in high content.The sodium release and transformation of Y and HTB were studied at different temperatures in N₂,CO₂ and H₂O atmospheres.By using sequential extraction and wet digestion separately,the occurrence mode and content of sodium in raw coal,chars were measured.The migration of sodium in two coals was studied qualitatively and quantitatively.The results show that water soluble sodium in YL coal accounts for 80.08%,while HTB,insoluble sodium accounts for61.54%.The volatilization of sodium in two coals increased with the increasing temperature;water soluble sodium in semi coke showed a decrease trend;ammonium acetate soluble sodium increase and then decrease;hydrochloric acid soluble sodium exhibits an increasing tendency.For YL coal,the volatilization of sodium is inhibited by CO₂ atmosphere while it is promoted by H₂O atmosphere compared with N₂ atmosphere;at 900?,the volatilization of sodium under CO₂atmosphere is 50.25%of N₂ atmosphere,while under H₂O atmosphere is 111.45%.For HTB coal,CO₂ atmosphere can inhibit the volatilization of sodium;at 900?,sodium under CO₂ atmosphere volatilized to 80.91%of N₂ atmosphere;in H₂O atmosphere,the volatilization of sodium is higher than N₂ before 800?and slightly lower than N₂ at 900?.The predominant form of sodium in YL coal is water soluble sodium.The water soluble sodium volatilized during increase temperature and transformed to hydrochloric acid soluble and insoluble sodium simultaneously.While HTB,insoluble sodium is the dominant occurrence mode,followed by water soluble sodium.The atmosphere of CO₂ and H₂O can promote the transformation of insoluble sodium to soluble sodium in HTB coal.The pyrolysis and gasification reaction of Naomaohu coal were studied in a laboratory fixed bed reactor,the pyrolysis and gasification reaction and corrosion experiment of Naomaohu coal in simulated moving bed reactor were also studied.During the process of pyrolysis and gasification in fixed bed,results showed that in the early stage of a fixed bed reactor,both of three atmospheres indicated volatilization and migration of sodium was mainly due to water soluble sodium in coal.The total migration of potassium is less than the sodium migration,and the main form is insoluble potassium.During the pyrolysis gasification process in simulated moving bed,the total extractable sodium have the highest enrichment percentage at low temperature reached 129.09%,119.32%and 182.13%respectively.In addition,under N₂,CO₂,80%H₂O+20%N₂ atmosphere,the total extractable sodium has a minimum value up to 57.10%,57.76%and 30.54%respectively.At N₂atmosphere,seat 3?686??gets the minimum;at CO₂ and 80%H₂O+20%N₂ atmosphere seat 4?820??reach the minimum.Corrosion under N₂,CO₂,80%H₂O+20%N₂ atmosphere was analyzed by using SEM-EDX?scanning electron microscope and X-ray energy spectrum?in the corrosion experiment.The results show that corrosion is aggravated by the increase of temperature and the most serious corrosion is under water vapor,besides,corrosion is related to alkali metals,chlorine elements,sulfur elements and so on.