Effects Of An Additive On Coal Combustion Characteristics And Its Mechanism Under Different Atmosphere

With the depletion of fossil fuels, more and more non-design coal has been used in industrial production, which will result in boiler slagging, efficiency reducing and so on, which is also the important reason for coal unefficient usage; At the samt time, fossil fuel combustion is the main source of the increasing greenhouse gases, so that the main work of the paper is to study the combustion method which can improve efficiency of the poor quality coal and reduce greenhouse gases emission.In this paper, firstly, Thermogravimetric Differential Thermal Analyzer(TG-DTA) was used to test and study the additive on single and blended coal combustion characteristics under air atmosphere; then used the horizontal tube furnace to prepare Australia coal(AO) and Australia coal added additive (AT) char under N₂ and CO₂ atmosphere, at the same time, AO and AT ash was prepared in the same horizontal tube furnace under O₂/N₂ and O₂/CO₂ atmosphere at different oxygen concentration; Infrared Gas Analyzer was used to determine NOx emission under different conditions; after that, TG-DTA was used to test the effect of the additive on AO combustion characteristics under different conditions; Finally, studied the mechanism of the additive and combustion atmosphere on coal combustion characteristics by calculating the active energy of coal combustion process under different control areas, using X-ray diffraction(XRD), Field emission scanning electron microscopy(FESEM) and Nitrogen adsorption surface area analyzer(N₂/BET).The study demonstrates that: the additive improves both single coal and blended coal's ignition and burnout under air condition, and at the same condition, the improvement of blended coal is better than single coal, and there exists the optimum range of the additive's addition. When the additive added into AO the combustion characteristics has been improved under both O₂/N₂ and O₂/CO₂ atmosphere, when the oxygen concentration increased up to 30%, the improvement of combustion characteristics under O₂/CO₂ atmosphere is better than under O₂/N₂ atmosphere and the NOx emission is lower; and the phase composition of the ash has been significantly changed when the additive has been added into AO, the level of ash particle breakage increasing, particle becoming smaller, the surface of the particle becoming brighten, the content of carbon in ash particle becoming lower, non-ash fusion aggregation phenomena occurring. When the additive has been added into AO, the char's cumulative specific surface area and the oxygen-accessibility specific surface area have been increased, at the same time, the maximum effective reactive surface area corresponding to the lower temperature and the highter burnout.Summary of previous studies and this paper obtains that the improvemental mechanisam of the additive on coal combustion is that: the additive is the mixture of Alkaline earth/Alkali metal oxide and Kaolinte by XRD testing and analyzing; at high temperature, the Alkali metal cations integrate with the unstable oxygen-containing functional groups, which results in destroying the molecular structure of the coal, producing large amounts of volatile, improving the pore structure of the coal, so the coal is easy to be ignited; after the evaporation of the volatile, the coal char's H/C atomic number ratio increased, so the char is burning more fast; at the same time, both oxidation and reduction processes of the Alkali metal cations plays a role in electron transferform, which plays the role of internal oxygen transferform during coal burnout stage, so the coal burnout rate has been improved.