Study On The Effects Of Microwave Desulfurization Of Coking Coal Property

The reserves of coking coal in our country is very poor,and quite a number of coal can’t be used because of high sulfur content. As a new type of coal desulfurization method,microwave deselfurization has been widely studied,but very few reports applied this method in coking coal and investigated the property changes of coal before and after microwave desulfurization.In this paper we chose high sulfur contented clean coking coal as object,and mainly studied that what would be the microwave desulfurization impact of sulfur content and coal property.We found out relative suitable desulfurizer,optimized reaction condition and figured out the mechanism of desulfurization and property changes after desulfurization,thus providing theoretical support for industrial application of microwave desulfurization.In this paper the work of research and main conclusions are as follows:(1)Coal quality analysis shows that Xinyu(XY) and Gedui(GD) coal are both strongly caking clean coal with high sulfur content.The sulfur in samples are given priority to with organic sulfur, 91.27% and 81.63% of total sulfur content of respectively, pyrite sulfur respectively accounted for 6.18% and 17.14% of the total sulfur in samples and sulfate sulfur contents less than 3% of the total sulfur.Size analysis found that the yield of +0.074-0.125 mm grade coal was the highest. Sulfur distribution was uniform among different particle size and ash content increased with the increase of particle size and desity of samples.Both density of coal samples are mainly distributed in less than 1.4 g·cm-3.Calorific value analysis found the two coal samples are high calorific value coal, and the calorific value of samples decreased with the increase of particle size.(2)The effect of different desulfurizers on mcrowave desulfurization of coking coal in different irradiation time was studied.The results showed that HCl had little effect on sulfur removal.Alkaline assistant(Na OH) had good desulfurization only under the condition of melting.The maximum desulphurization of mixed solution(acetic acid and hydrogen peroxide) and HI was achieved in 2 min with the decrease of sulfur content by 13.16% and 24.11% for mixed solution and 20.72% and 36.76% for HI, respectively. All organic assistants do not have better effects on desulfurization in a short time and sulfur content dropped around 10% at most.The mixed additives of HAc and H2O2 shown a favorable desulfurized effect and great research value.(3) The desulphurization rate improved when the volume of two additives gets balanced and the desulfurization effect became best when the proportion achieved 1:1.The desulfurization rate improved obviously when the microwave irradiation time within 0~40 s and the microwave irradiation power had a great effect on desulfurization when the power less then 600 W,the content of each sulfur forms in coal had a different degree decreases when power increases. Neither too large nor too small can solid-liquid ratio achieved best desulfurization results and the best results appeared when the solid-liquid ratio became 1:5 and 1:3,respectively.Small dilution of additives is helpful to improve the desulfurization effect, and the strongest desulfurization effect achieved when the concentration was 83.3%.The smaller particle size of coal became the better desulfurization results would get.(4)The caking index of coal descreased when the volume of two additives gets balanced and the index became smallest when the proportion achieved 1:1,the index value is smaller in the condition of H2O2 than HAc..With the increase of irradiation time and power, the caking index decreased with different degrees.The caking index dropped most obviousl during irradiation time of 0~60 s, then it dropped slowly.When the power is between 100 to 300 W, caking index changed greatly and then became gently until 600 W when the power bigger than 600 W,the caking index decreased significantly. The caking index became smallest when solid-liquid ratio dropped to 1:5 and then increased as the volume of desulfurizers increased.As the dilution of the desulfurizer, caking index firstly decreased and then increased. The bigger particle size is,the smaller decline will achievr,and the better protection for caking index will get in the process of desulfurization.(5) The ash content of samples reduces with the increasing of desulfurization rate. Calorific value as air dried basis changed of a fluctuating,and the calorific value as air dried basis became greater after desulfurization overall.But when changed the basis to dry ash-free basis,the calorific value decreased 0.35% and 0.69%,respectively.Accord ing to the fitting results of ash content and calorific value in basis of air dry, calorific value increased when the content of ash dropped,unless the oxidation of samples became serious.(6)Sulfur form analysis found that the removel of organic sulfur took up a large proportion of total sulfur removel when achieved the maximum desulfurization rate,although the removel of inorganic sulfur is easier under different conditions.Inorganic sulfur in coal would be basicly taken off in the maximum deslfurization rate.The changing tendency of the content of oxygen containing functional groups in coal moves contrary to the caking index, the greater the content of oxygen containing functional groups is, the smaller caking index value will get.Based on the fitting results of caking index and the content of oxygen containing functional groups, we found that the carboxyl group content had the largest influence on caking index value.(7) The optimum reaction conditions obtained from the orthogonal experiment are as follows: the mixture ratio of additives is 1:5, irradiation power is 500 W, solidliquid ratio is 1:3, the concentration of additives is all additives without water, irradiation time is 40 s.The analysis of variance found the order that basised on the importance of factors for desulfurization and coal property is: ratio of fertilizer > irradiation power > solid-liquid ratio > concentration >irradiation time.Under the optimal condition,the maximum desulfurization rates for XY and GD coal were 11.31% and 24.62%,and the caking index values were 63 and 61, decreasing by 17.12% and 15.34%, respectively(8)XANES, XPS and FT-IR analysis found that mercaptan and thioether were most easily removal in organic sulur and second is thiophene.The relative content of sulfoxide and sulfone increased in desulfurization process.This explains why both of the samples had high organic sulfur content, but the desulfuization results were different.Few part of the organic sulfur forms in coal were oxidated into salts and gases, but most of the organic sulfur were not involved in the reaction, at same time,some kinds of organic sulfur form only changed into another forms(sulfoxide and sulfone), which makes it difficult to remove organic sulfur in coal.XPS analysis and FT-IR analysis shows that the contents of C-C,C-H and C-O became lower after desulfurization,and the content of C=O and O-C=O increased.The caking index of both samples also decreased with it.