Study On The Catalytic Effect And Mechanism Of Coal Ash For CO₂Gasification Of Coal Char

Based on the composition of Huainan coal ash, the factitious ash was composed of pure chemical reagent. The factitious ash and raw coal ash were respectively added into Huainan coal which was de-ashed by using HCl-HF method, and the coal chars were prepared at900℃. The gasification characteristic of the coal chars (raw coal char, ash-free coal char, coal char added with raw coal ash or factitious ash) were examined using thermogravimetric analyzer. Moreover, the effect of K2O、CaO and Fe2O3in coal ash on CO2-gasification of ash-free coal char were studied by loading the factitious ash with different composition. And the effect and mechanism of SiO2&Al2O3of coal ash on the catalysis of Fe2O3were investigated. The shrinking core mode was adopted to simulate the gasification process of coal char. The major research results were shown as follows:The de-ashing treatment could remove the ash content of Huainan coal, and increased the specific surface area in175.28%of the coal char. The reactivity of Huainan coal char after de-ashing presents was apparently improved. The existence of ash could inhibit the process of coal char graphitizing. The Huainan coal ash and factitious coal ash showed catalytic effect on coal char gasification during the low temperature range and increased the diffusion resistance of gasification agent in high temperature range resulted in decrease of the gasification rate of coal char.The research of the influence of coal ash composition on the characteristic of coal char showed that the gasification reactivity of coal char was improved by the increase of K.2O、CaO and Fe2O3amount of the ash. When there was less catalyst in coal ash, it wasn’t shown obvious influence on the gasification reactivity of coal char because of the formation of non-catalytic compounds by reacts between the catalyst and the other components of the ash. It was shown that different constituents showed different catalytic action on coal char gasification process. The K2O showed the highest catalytic effect on the coal char gasification, followed by CaO and Fe2O3. The Fe still had a catalytic role in ash with hercynite form, the SiO2in ash led to inactivated compound which restrained the formation of hercynite, resulted in weakening of the catalysis effect of Fe2O3.The experimental results of coal char gasification can be well described by shrinking core model, the gasification activation energies of Huainan coal char and Huainan ash-free coal char were155.96kJ/mol and250.91kJ/mol respectively. Added Huainan coal ash and Huainan factitious ash could reduce gasification activation energy of ash-free coal char. In general, the gasification activation energy was reduced by the increase of the amount of K2O and CaO in coal ash, but the Fe2O3in ash have no obvious regularity impact on the coal char reaction activation energy. The gasification reactivity of coal char was determined by both activation energy and reaction rate.