Decarbonization method of fly ash

The content of residual carbon in fly ash will seriously affect the performance indicators of fly ash products. In ceramics, if the residual carbon during sintering is not completely burned, it will lead to a decrease in the quality of the embryo and introduce impurities; In concrete, high residual carbon content increases water consumption and adsorption of air entraining agents. The level of residual carbon is related to the process of coal-fired power plants. Improving the coal burning method and process of power plants and reducing the loss on ignition can solve this problem to a certain extent. However, for the stored old fly ash, it is advisable to use decarbonization technology to separate residual carbon and improve the quality of fly ash before comprehensive utilization.
The commonly used methods for residual carbon sorting are divided into two categories: dry and wet sorting. Dry separation includes electrical separation, combustion separation, and fluidized bed separation, among others:
(1) The electric separation method involves treating fly ash with friction and electrification, so that fly ash and residual carbon carry different charges and are separated by different electric field forces in the electric field;
(2) The combustion method involves adding fly ash to coal, entering the boiler for further combustion, and is generally used in fluidized bed boilers;
(3) The fluidized bed sorting method utilizes airflow to sort by the density difference between residual carbon and fly ash. The process is simple, but fine particle fly ash is prone to entering residual carbon, affecting the purity of product carbon.
Wet flotation method is mainly used, where carbon particles have a certain hydrophobicity. During the flotation process, a certain amount of flotation agent is added to enhance the surface hydrophobicity of the particles, achieving the purpose of separation from fly ash. Ren Linzhu and others conducted flotation decarbonization experiments on a high carbon fly ash. The research showed that the carbon content of the fly ash decreased to 2.41% after flotation, and high-quality refined carbon with a calorific value of 27300kJ/kg was obtained, effectively improving the quality of the fly ash. Fan Guixia et al. found that under appropriate slurry and reagent concentrations, the segmented dosing method can improve the recovery rate of fine carbon in fly ash flotation. Research by Zhai Xue and others has shown that the use of cyclone static microbubble flotation column technology has better recovery efficiency than ordinary flotation tanks. At present, the decarbonization rate of flotation method is about 70% to 80%. The properties of residual carbon and coal are not exactly the same. Although the reagents and processes used for coal flotation can be referenced, appropriate reagents and processes should also be optimized or developed based on the physicochemical properties of fly ash to improve sorting efficiency.