Effects Of Calcium-based Additives On Fixed Sulfur And Change Rule Of Pyrolysis Products During High-sulfur Coal Co-pyrolysis

The relative reserves increased yearly and utilization of the limited availability of high-sulfur coal, which made clean and efficient utilization of high sulfur coal become a serious problem. One of the effective ways to use high-sulfur coal was Calcium-based additive and high-sulfur coal co-pyrolysis. The clean solid fuel was producted by calcium-based additives and high-sulfur coal copyrolysis and better fixed sulfur effect was achieved in the combustion process. The relative amounts of each component in gas products were significantly changed with CaCO₃ additive and this change was beneficial to synthesize COG（coke oven gas） downstream products（such as CH4, CH4 O, oil, etc）. In this paper, the effect of sulfur retention and distribution of gas, solid phase products were investigated during high-sulfur coal and calcium-based additives co-pyrolysis. Change rule of inorganic sulfur and organic sulfu during the coal pyrolysis were analyzed by X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）, respectively. The release of gas products were analyzed by thermogravimetric-mass spectrometry（TG-MS） and the relative contents of gas phase products were measured with gas chromatography（GC）. The study mainly included the following aspects:（1） The coke yield was decreased with calcium to sulfur ratio increasing in the case of CaCO₃ additive, while the opposite trend appeared with CaO additive. This was due to at high temperatures, decomposition of CaCO₃ to produce CO2 that reacted with C, leading to reduce coke yield.（2） Under the high feed temperature, sulfur fixation was significantly increased by calcium-based additive. In lowed Ca/S, the better sulfur fixation was showed with CaCO₃ additive. The sulfur retention efficiency was increased with Ca/S increasing. When the Ca/S reached a certain value, the different additives had a similar sulfur fixation efficiency.（3） The results indicated that calcium-based additive improved the proportion of inorganic sulfur contents and reduced the proportion of organic sulfur contents. Organic sulfur was not changed in the form of thiophene, mercaptan and thioether, during coal pyrolysis with additives, but the form of inorganic sulfur was changed. In detail, the form of FeS when there was no additive converted CaS in the presence of additive.（4） The addition of calcium-based additive was added to change the content of each component in gas-phase products. When the additive was CaCO₃, the contens of H2, CO in gas products increased, the effect on the content of CH4 was relatively small. With calcium to sulfur ratio increased, the content of CO in gas phase was gradually increased. Compared with CaCO₃, the effect of CaO on the content of gas phase was relatively small.（5） Calcium-based additive had great influence on the relative content of each component in gas products. When the additive was CaCO₃, the relative content of H2, CH4 in gas products decreased with calcium to sulfur ratio increased, on the contray, the relative content of CO was gradually increased. The change of relative content of each component in the gas phase products was unconspicuous when additive was CaO.（6） The additional of CaCO₃ changed the H2/CO and H/C ratio of gas products. H2/CO and H/C ratio were approximately linearly gradually decreased with the Ca/S increasing. In the pyrolysis process, additive CaCO₃ played a role in fill carbon to gas phase products.