【Haichuan’s Best Practices】The technological upgrade to convert wet slag into dry slag in coal-fired boilers has achieved energy and water savings

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The successful implementation of the dry slag project in coal-fired boilers not only improved the rate of resource recovery but also brought significant economic benefits and positive environmental advantages to the company; it is necessary to summarize these experiences and improve them further in order to enhance operational efficiency. On February 28, the trial operation of the connection process from the grout tank to the high-concentration wastewater stream in Guangzhou Petrochemical’s Thermal Power Department was successful; it has been operating steadily to date, marking the successful completion of the efforts related to the dry slag treatment project for coal-fired boilers. The original design of the coal-fired furnace unit in the thermoelectric department adopted a hydraulic slag flushing operation mode; the slag had to pass through the cold ash hopper, slag skimmer, and slag crusher successively, before being sent to the slurry tank via hydraulic flushing. Thereafter, it was transported to the slurry storage area by a slurry pump for reuse. This complex transportation process involves numerous rotating devices, consumes a large amount of electricity, requires extensive maintenance of the pipelines, and carries a risk of leaks in the transmission lines. To address the problem at its root, the technical improvement project to convert wet slag to dry slag in coal-fired boilers was put on the agenda. In the second half of 2024, Guangzhou Petrochemical designated the coal powder furnace dry slag project as a key project. As it is a new technology, there is limited existing experience to draw on. Guangzhou Petrochemical established a task force to address various issues that arose during the trial operation phase by learning from experience while operating, and improving processes through continuous optimization. At the initial stage of operation of the dry slag system in the coal-fired boiler, due to an unreasonable design of the connection between the slag skimmer and the vibrating screen, the initial recovery rate of dry slag was only 70%. Through improvements and refinements, the research team independently carried out technical upgrades such as modifying the slag discharge outlet, raising the dry slag recovery rate to nearly 100%. Guangzhou Petrochemical also organized multiple departments to jointly compile a list of the problems existing in the water inflowing to the mortar pool and in the discharge processes, and addressed each issue on-site. By integrating the existing process flow and making use of waste materials from inspections and maintenance, they successfully completed the modification to recover boiler drain water into the desulfurization tank, as well as the connection between the area behind the mortar pool and the high-concentration process, thereby achieving the goal of shutting down the mortar pump. After half a year of construction, the project was put into operation on February 2 this year, successfully converting wet slag into dry slag. After switching from wet slag to dry slag operation, the main function of the slag flushing pump becomes replenishing water in the boiler’s water seal tank; as a result, the water consumption is significantly reduced, giving the pump considerable energy-saving potential. The task force took swift action; by repurposing the frequency converters from other demolition equipment and carrying out custom design and modifications, they managed to switch the slag pumping water pump from operating at line frequency to operating at a variable frequency. According to calculations, after the implementation of the measures for dealing with dry slag in coal-fired boilers, more than 1.4 million yuan in electricity and water can be saved each year. By shutting down the mortar pump and the water pump for external return, 1.71 million kWh of electricity can be saved each year, resulting in cost savings of 1.06 million yuan in electricity expenses ； By renovating existing equipment and implementing frequency conversion upgrades for the slag pumping pumps, it is expected to save 434,000 kWh of electricity per year, resulting in cost savings of 269,000 yuan ； In terms of water conservation, the successful recycling of boiler drain water has reduced the consumption of fresh water, with an estimated annual savings of 100,000 yuan in water costs.