Answers to Questions on Slag Disposal in Power Plants

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Cinder contains large amounts of porous amorphous SiO2 and Al2O3, which have a certain adsorption capacity for pollutants in wastewater, enabling color removal and the elimination of such pollutants; at the same time, Cinder also serves as a filter for pollutants. Therefore, the technology of using coal cinder to treat wastewater has been widely applied in the treatment of dyeing and printing wastewater, but its use in treating papermaking wastewater is still rare in China. Shaoxing Xinmin Paper Co., Ltd. has achieved certain results by using a power plant slag flushing system to treat the flotation effluent from paper production, and this will be introduced here. 1. Original wastewater treatment process: Shaoxing Xinmin Paper Co., Ltd. uses waste paper and commercial wood pulp to produce low-weight, high-strength Grade A kraft box board, with an annual production volume of 50,000 tons. The wastewater generated by this factory is mainly pulp-making wastewater and papermaking wastewater; the pollutant concentration in the papermaking wastewater is relatively low, and most of it is reused in the production process. Pulp-making wastewater (with a discharge volume of about 8,000 t/d) has high pollutant concentrations, with high levels of SS and CODcr in it. The production wastewater first passes through a grid to remove larger particles such as paper scraps, plastic, and wood. It then enters an inclined screen treatment unit, where longer fibers are recovered. The wastewater after this treatment flows into a regulation tank, which is equipped with perforated pipes for aeration in order to ensure uniformity in composition. The wastewater, once adjusted, is pumped to an eddy current air flotation device, where coagulants are added to combine smaller suspended particles and colloids into larger particles. The scum is discharged into the sludge tank by the screw propeller on the vortex air flotation unit, and the sludge is dewatered using a belt filter press before being sent to a boiler for incineration. The wastewater treated by air flotation, once it meets the inlet standards, is fed into the urban sewage network. II. Flotation treatment of slag-containing wastewater (I) Power generation capacity and slag disposal system: Shaoxing Xinnmin Thermal Power Co., Ltd. is equipped with 6 ultra-high pressure boilers with a capacity of 35 t/h each, as well as 3 steam-driven generator sets, giving a total installed capacity of 45 MW. The company consumes around 800 tons of coal per day and generates approximately 240 tons of coal slag per day; the boilers use hydraulic methods for slag removal. After the coal slag falls into the slag discharge outlet, high-pressure water is injected into the slag guide channel; this water combines with the wastewater containing ash from the water film dust remover and then flows into the sedimentation tank. After settling in the sedimentation tank, labyrinth tank, and clarifier, over 90% of the water is pumped back for reuse, while a small amount of wastewater has its pH adjusted to between 6 and 9; once it meets the required standards, it is discharged as overflow.