Preparation Of Coal Briquettes Using Coal Solid Waste And Study On The Sulfur Retention Mechanism Of Coal Briquettes

Coal briquette is one of clean coal technology, which is an important measure to change the way of coal combustion. Slurry which is produced during the coal washing process, has high calorific value, but contains a lot of hazardous substances; coal gangue has not only the low heat value, but also contains a lot of harmful substances, it is difficult to be used. This study attempts to use the calorific value of coal slurry, add some functional additive, and prepare the coal slurry, coal gangue into clean coal briquette, to reduce the soot in the combustion process, SO2 and emissions of harmful substances. In this study, the following two aspects be carried out:on one hand develop efficient coal additives to prepare coal briquette by using the slurry, coal gangue for the civilian boiler; on the other hand, study on efficiency sulfur retention additive, in order to reduce a large number SO2 emit during the combustion of slurry and coal gangue. The results show that:(1)Through the industry analysis of slurry and coal gangue, in the full use of calorific value, coal briquette add starch, bentonite, organic silicon waterproof agent, was prepared. Experimental results show that:when the dosage of oxidized starch was 0.4%, bentonite was 2%, organic silicon waterproof agent was 2%, the compressive strength of coal can reach over 2Mpa, dropping strength can be achieved more than 95%, wet strength can be up to 95%, and coal ash, volatile matter, calorific value of coal and other indicators are in line with product standards.(2) Through the comparison of sulfur retention based calcium, magnesium respectively and sulfur retention additive, studies show that calcium based sulfur retention agent is better than magnesium based, but at the high temperature (>1000℃)a large amounts of sulfur decomposed and SO2 released; on the base of calcium, additive Fe2O3, SiO2, CuO, ZnO and other materials can promote sulfur retention rate. These results can provide a theoretical basis for using of waste coal gangue and fly ash as additives.(3) The results show that desulfurization rate is lower when MgO is as agent alone, while the desulfurization rate of coal may significantly increased when CaO and MgO were as complex reagent; through the analysis of coal gangue and fly ash components, study use coal gangue and fly ash as additive, On this basis, add a small amount of coal gangue, SiO2 and Al2O3 in it can reacts with CaSO4 and turn into the thermal stability new phase Ca5(SiO4)2(SO4)when the temperatue is higher than 900℃, thus inhibiting the decomposition of sulfur phase and improved the desulfurization rate of coal briquette; while the fly ash may be in the form of inert vitreous, SiO2, Al2O3 are difficult to react with sulfur agent into a new substances at high temperature.(4) To further enhance the activity of fly ash, fly ash was activated by calcium hydroxide in this study, which was used as sulfur retention additive. The results showed that the structure of glass beads of fly ash was destroyed by calcium hydroxide, the inert silicon, aluminum, iron substances were activated at the high temperature and could react with CaSO4 into a thermal stability Ca5(SiO4)2SO4, which can improve the sulfate decomposition temperature, and reduce the release of SO2; by adding activated fly ash, the sulfur retention rate can improve by 6.28% of coal briquette.(5) In the above conclusion, the factors influencing sulfur retention effect were studied. The results show that when the Mg/Ca mass ratio is 1:1, and (Mg+Ca)/S molar ratio is 2:1, the coal briquette has the best desulfurization; activated coal fly ash added was 3% and coal gangue was 2%, the desulfurization rate of coal increased by 5.85% and 3.72%, but with the added coal gangue continues to increase, the desulfurization rate of it declined; with the increase of combustion temperature, the sulfur retention rate of coal gangue and activated fly ash decline; the inhibit of decomposition by coal gangue and fly ash can not be the role of performance during reducing atmosphere; activated fly ash and coal gangue on sulfur inhibition will not be affected by the time.