| The predicted reserve of Zhundong high-alkali coal（ZDHC）was 390 billion tons.The ZDHC has huge potential for exploitation,and has an important strategic position in China’s energy structure.However,the mineral properties of ZDHC are unconventional.The content of Na and Ca is significantly higher than conventional coal.It has caused serious fouling,slagging and particulate matter release problems.These problems have restricted the application of ZDHC.In order to effectively solve these problems,this paper was based on the existence form of alkali metals and alkaline earth metals（AAEM）in ZDHC,and pretreated ZDHC with CO2-water leaching method.CO2-water leaching could provide a weakly acidic environment containing hydrogen ions,which could remove the soluble AAEM.This method may effectively solve the problems of fouling,slagging and particulate matter release during the combustion of ZDHC.Around this research idea,the effect of CO2-water leaching on the mineral composition of ZDHC,the effect of CO2-water leaching on the ash formation behavior of ZDHC and the effect of CO2-water leaching on the combustion and particulate matter release characteristics of ZDHC were investigated,independently.The specific research content is as follows:First,the Na/Ca removal efficiency by CO2-water leaching was investigated.The typical ZDHC was selected.The coal samples were leached with water and CO2-water.Based on existence form of Na/Ca,the type of Na/Ca removal from ZDHC was investigated.The study found that CO2-water leaching has a significant effect on the removal of Na/Ca from ZDHC.For part of high-alkali coal,the Na removal efficiency was close to 90%and the Ca removal efficiency was close to 30%.Except for water-soluble Na/Ca,CO2-water leaching also had significant removal efficiency on organic Na and CaCO3.By studying the effects of CO2-water leaching on low-temperature ash characteristics of ZDHC,it was found that CO2-water leaching had a significant effect on the de-ashing of ZDHC.Removal of Na,Ca,Mg,K,Cl and S from ZDHC was the important reason for the significant decrease of ash yield.Then,the effect of CO2-water leaching on the ash-forming behavior of ZDHC was researched.It was found that the Na/Ca volatility of CO2-water leached coal was less than those of the raw coal and water leached coal for different ashing temperatures.The Na volatility of CO2-water leached coal was only 25%of the Na released from the raw coal ashing at 900°C.The Ca volatility from CO2-water leached coal was 74%of the Ca released from the raw coal.With the increase of ashing temperature,the existing form of Na in coal changed from water-soluble to aluminosilicate form.Besides,the ash fusion temperature of the CO2-water leached coal ash increased obviously.The agglomeration and sintering phenomena of coal ash were inhibited significantly by CO2-water leaching.The B/A of CO2-water leached coal ash remarkable decreased.The fouling and slagging tendency of CO2-water leached coal was significantly reduced.The Na content of CO2-water leached coal was less than 1%,which achieved the standard of China’s power coal.Finally,the effect of CO2-water leaching on the combustion and particulate matter release characteristics of ZDHC was researched.The results show that the ignition and burn out temperature of CO2-water leached coal were lower than raw coal.The peak combustion rate was close to or higher than raw coal.The combustion characteristics of the CO2-water leached coal were improved compared with raw coal.CO2-water leaching can significantly reduce the generation of particulate matter during the combustion of ZDHC,especially for the submicron particulate matter.The reduction of the easily-evaporable elements in ZDHC was the main reason of the particulate matter reduction.In summary,the CO2-water leaching technology was a mild and efficient pretreatment technology before ZDHC combustion.It had a significant inhibitory effect on ZDHC fouling,slagging,and particulate matter release.This paper provides a new idea for ZDHC efficient and clean utilization.And it lays a theoretical foundation for the large-scale application of CO2-water leaching technology. |
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