Study On Desulfurization And Ash Reduction Of A High Sulfur Coal In Pu'an Of Guizhou Province

China is one of the countries with the most abundant coal resources in the world,but one third of the total coal reserves belong to high sulfur coal with high sulfur content.Guizhou is a large energy province in southern China,and its coal reserves rank fifth in China.The average content of sulfur in Guizhou coal is 2.67%,and the proportion of high sulfur coal is as high as 35.08%.The clean utilization of high sulfur coal is of great significance to the economic development and environmental protection of Guizhou Province.In this paper,a coal sample from a coal mine in Pu'an,Southwest Guizhou is taken as the research object to carry out the experimental research on impurity occurrence,quality improvement and impurity removal.The analysis of raw coal properties shows that the coal sample belongs to anthracite with high sulfur and low medium ash content,and the inorganic sulfur content is high,mainly iron sulfide sulfur,accounting for 68.62%.The analysis of pyrite dissemination characteristics by polarizing microscope shows that pyrite in coal is more complex,mainly distributed in coal as star point,berry ball or continuous distribution.In general,pyrite in raw coal has fine disseminated particle size,so gravity separation flotation combined separation process is needed for desulfurization and ash reduction.The analysis of trace elements in coal sample shows that W,Li,Cu,Co,Mo,V are enriched or even significantly enriched,followed by Nb,Zr,Ta,Y,Hf and other elements.The content of lithium in coal is between 66.6-232?g/g,which has a certain comprehensive utilization potential.The results of float and sink test show that Pu'an coal has poor washability.In order to obtain clean coal with sulfur content less than2.00%,the theoretical separation density should be lower than 1.54 g/cm³.Under the action of gravity,W,Sn,Mo,Cd are the most easily removed,followed by Cu,Th,V,U,Be,Cr,Ni,Pb,Co,Sb.The removal rate of trace elements depends on their occurrence state.The correlation between element content and ash yield can reveal the existing forms of these elements.Li,as a valuable element,can be enriched in clean coal during coal washing.The theoretical content of Li₂O in coal ash after combustion is as high as 0.26%.Therefore,gravity separation is a favorable process for subsequent lithium extraction.A shaker desulfurization and ash reduction test was carried out on the 0.25-2 mm size of raw coal.The fine coal with ash content of 8.34%,sulfur content of 1.89%and yield of 89.74%can be obtained by one roughing.The particle size of mixed coal sample of middle coal tail coal is mainly between 1-2 mm,with yield of 66.54%and sulfur content of 8.32%.75%of medium coal tail coal is ground to-0.075 mm.The coarse clean coal with a yield of 59.76%?sulfur content of 4.01%?and sulfur concentrate with sulfur grade of 18.55%can be obtained by"one roughing and one scavenging"flotation process.The flotation desulfurization test of raw coal with particle size of-0.25 mm was carried out.The results show that the collection effect of diesel oil is better than that of kerosene,and the appropriate dosage is 300 g/t.The inhibition effects of pyrogallol,mercaptoacetic acid and calcium oxide were compared under the conditions of 300 g/t diesel oil and 100 g/t secondary octanol as foaming agent.The results show that when the dosage of CaO is 100 g/t,the effect is better.The yield of clean coal is 93.65%,the sulfur content is 1.74%,and the ash content is 8.39%.The contact angle of coal and pyrite is very close before treatment with calcium oxide solution,which makes it difficult to separate by flotation;after treatment with calcium oxide solution,the wettability of coal and pyrite is obviously different,the surface contact angle of pyrite decreases from 93.3°to 68.5°while that of coal surface decreases from 94.8°to 97.3°with no obvious change,indicating that pyrite was effectively inhibited.Calcium oxide promotes the surface oxidation of pyrite and forms fine precipitates,the main elements of which are Ca,O and C.the fine precipitates formed adhere to the surface of minerals and enhance the hydrophilicity.