Regularities of cleaning and dewatering of gas cleaning sludge from coal dust at thermal power plants

Abstract

The object of this study is the technology of cleaning and dewatering of sludges from wet gas purification systems of dust preparation department emissions in Ecomash SHS521AS-113 settling centrifuges in order to solve the problem of increasing the efficiency of treatment facilities and secondary use of purified water. Samples of gas purification sludges have been analyzed under industrial conditions, and it was found that sludges from thermal power plants contain finely dispersed dust particles less than 20 microns, which during the hydration process stick together into aggregates up to 250 microns in size. It was found that the use of settling tanks without chemical reinforcement of the process is long-term; however, they are effectively precipitated using the anionic flocculant A-19. The optimal dose of flocculant for sludges with a concentration of 20–30 g/l was selected, whichwas 130–150 g/t. In this case, flocs are formed with a sedimentation rate of 8.2–8.6 mm/s, which is sufficient for effective settling. In order to quickly determine the con centration of the solid phase in the sludge, a relationship was established between the concentration of the dispersed phase, the temperature in the range of 20–45°C, and the density of the sludge. The study of sludge purification in centrifuges without the use of reagents has made it possible to identify the rela tionship between the efficiency of solid phase retention, centrifuge productivity, and the value of the relative screw revolutions. It was found that the efficiency of solid phase retention in centrifuges increases with a decrease in work productivity, as well as a decrease in the value of the relative screw revolutions. The purification productivity of up to 15–20 m3/h was achieved with an efficiency of over 97% and a residual concentration of suspended particles of less than 0.5 g/l. The use of a modular sludge purification and dewatering unit based on a thin-layer clarifier and centrifugal units with the introduction of a flocculant before the clarifier has been proposed. It was found that the degree of sludge dehydration in Ecomash SHS521AS-113 centrifuges of wet gas treatment sludge was 32–36%.