Study On Removal Of Na&Ca From Zhundong Coal By CO_2- Water Treatment

As power fuel, coal’s dominant position is difficult to change in quite a long period of time. Zhundong coal, which is newly found in Xinjiang autonomous region of China, enjoy some advantages, such as abundant, easy mined, low cost and high quality. So it can be used as a natural and clean power source. However, limited by it’s location and transportation conditions, the coal is difficult to be transported outwards and costly. The only solution is to make use of it in local coal power and coal chemical industry. But severely fouling and slagging occurs when local power enterprise put this fuel into use. This problem has hindered large-scale use of Zhundong coal, which definitely causes great waste of the resource.Throughout all the current measures, there isn’t a economical and practical solution can be used to completely solve the problem. The primary reason is high alkali metals and alkaline earth metals content（AAEM）. Inspired by the water-leaching pre-treatment method, we focus on a more gentle way which employ CO2 dissolved in water, to remove AAEM before burning, aiming at exploiting out a useful way to solve this problem at the beginning. Based on which, we start our research systematically.By treating some typical Zhundong coal with CO_2-water and then comparing the results with water-leaching and HCl-leaching, we confirmed the applicability and prominent economic value of this method applied to Zhundong coal. To get a clear understand of the practical effect of this technology, we have done plenty experiments on main factors such as temperature, time and solid-to-liquid ratio. In all,the optimum condition is ambient pressure, 60 ℃, 6⁹ hours. Under this condition, we can obtain a very good result with almost 80% sodium and 11% calcium removal, which has reached the standard content range of power-coals in China. Besides, taken the water shortage in Xinjiang autonomous region into account, it is worthless to minus solid-to-liquid ratio,because the decrease of solid-to-liquid ratio has limited effect on the removal of sodium and calcium content. What’s more, the results of repeat treatment is better than continuous treatment, which proves that it’s achievable to improving the technology by introduce liquid handling system.After that, we took use of ion exchange method to verify the removal efficiency of ion-exchangeable organic sodium and calcium by CO_2-water treatment. And combined the results from previous experiments, we eventually draw out the specific diagram of the removal mechanism, providing reference data for subsequent industrialized application.To sum up, it shows prominent social and economical benefit to control the formation of slagging and fouling by remove Na&Ca in the way of CO_2-water treatment under gentle conditions.