Application of calcium hydroxide with high specific surface area in the coking industry

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Application of calcium hydroxide desulfurizer with high specific surface area. In recent years, dry flue gas desulfurization technology has been increasingly used in small- and medium-sized flue gas desulfurization systems; it is a mature technology with stable operation. Among them, the SDS desulfurization process using sodium bicarbonate as the base source has seen its market share increase rapidly, thanks to advantages such as high desulfurization efficiency, wide availability of the desulfurizing agent, and low difficulty in implementation. As the number of installations increases, the disadvantages of this technical approach have begun to become apparent, and how to deal with desulfurization ash has turned into a new environmental challenge. Sodium-based desulfurization ash is a mixture of sodium sulfate, sodium sulfite, and sodium carbonate; it has good water solubility and belongs to the category of general solid waste that is difficult to dispose of in compliance with regulations. According to official statistics, the coking industry alone generates as much as 300,000 tons of sodium-based desulfurization ash each year; when accounting for the power boilers, hot blast stoves, and heating furnaces in steel plants, as well as glass and cement kilns, the amount of sodium-based desulfurization ash increases even further. Some companies rent premises to store the waste in warehouses, while others sell it to qualified agencies for disposal; the cost per ton ranges from 300 to 500 yuan, which adds to the burden on these companies. On September 1, 2020, the revised Law of the People’s Republic of China on the Prevention and Control of Environmental Pollution by Solid Wastes came into full effect. It introduced new provisions regarding the responsibilities of enterprises that generate solid waste, stipulating strict penalties for any illegal activities. Corporate pressure is surging! Highly active calcium hydroxide with a high specific surface area features porosity, high activity, good dispersibility, and high utilization efficiency. Its specific surface area (BET) is over 40 m2/g, which is 3–4 times that of ordinary calcium hydroxide, while its desulfurization efficiency is above 95% ； The pore volume of calcium hydroxide with a high specific surface area exceeds 0.2 cm3/g, enabling rapid adsorption and absorption of HCl and SO2 in flue gas, with an utilization rate of over 85% ； High-specific-surface-area calcium hydroxide has good flowability and is unlikely to clog pipes during use. In the 1980s, Europe, the United States, and Japan began to widely use high-specific-surface-area calcium hydroxide for desulfurization in waste-to-energy plants and thermal power plants, successfully replacing baking soda. It is currently recognized internationally as an excellent dry desulfurization product. In 2010, Lhoist introduced a highly active calcium hydroxide desulfurization agent in China, which was used for treating flue gases from waste incineration plants, glass furnaces, and ceramic kilns. This marked the beginning of the use of calcium-based desulfurization agents with high specific surface area in China. The main by-products of desulfurization are calcium sulfate, calcium carbonate, calcium hydroxide, and other common solid wastes that can be recycled. However, due to the high cost of these desulfurization agents, they have not been widely adopted. After months of intensive research and the efforts of its technical staff, Tianjin HuiNeng LangTian Environmental Protection Equipment Co., Ltd. successfully developed calcium hydroxide with high activity and a high specific surface area; the BET specific surface area reached over 45 m2/g. Industrial production of this product was established, and it was introduced to the market in June 2021. The HNPS desulfurization system developed by the company has undergone pilot tests and industrial use over several months with different users; it exhibits good operational performance, low costs, and satisfies the users. Currently, it has been successfully applied in coke pusher surface stations, environmental dust control for dry quenching, and desulfurization of coke oven flue gas. Advantages of HNPS desulfurization technology: 1. It uses highly active calcium-based desulfurizing agents with a high specific surface area, which are directly injected into the flue gas and fully mixed with it, thereby enabling the adsorption and absorption of acidic substances in the flue gas; this results in high desulfurization efficiency ； 2. The HNPS dry desulfurization process is employed; there is no temperature drop during the reaction. Existing bag filters or additional bag filters are used to remove solid waste. Calcium-based solid waste does not absorb moisture, is not corrosive, and does not compact. 3. Compared to SDS, desulfurization using this method has virtually no temperature restrictions; there is no need to install a grinding system on-site, resulting in low investment and operating costs. It can directly replace baking soda in existing SDS processes ； 4. The main components of desulfurization by-products, such as calcium sulfate, calcium carbonate, and calcium hydroxide, are all general solid wastes that can be recycled and utilized ； 5. Fewer devices and equipment are required, offering flexible layout and low investment costs ； Material is delivered using tank trucks; the system is fully sealed, resulting in no dust generation at the site ； Roots blower or compressed air delivery, with low power consumption.