Application of high specific surface area calcium hydroxide desulfurizer

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In recent years, dry flue gas desulfurization technology has been increasingly applied in small- and medium-sized flue gas desulfurization systems; it is technically mature and operates stably. Among them, the SDS desulfurization process route using sodium bicarbonate as the alkali source has rapidly gained market share due to its advantages such as high desulfurization efficiency, wide availability of the desulfurizer, and low difficulty in engineering implementation. As the number of installations increases, the drawbacks of this technical approach become apparent; how to dispose of desulfurization ash has thus become 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 authoritative statistics, the coke industry alone generates as much as 300,000 tons of sodium-based desulfurization ash each year. When adding power plant boilers, hot blast stoves, reheating furnaces in steel plants, as well as glass and cement kilns, the volume of sodium-based desulfurization ash increases manifold. Some companies rent premises to build warehouses for storing such materials, while others sell them 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 severe penalties for any illegal activities. Business pressures are soaring! 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% ； Calcium hydroxide with a high specific surface area has good fluidity and is less likely to clog pipes during use. In the 1980s, Europe, the United States, and Japan began using high-specific-area calcium hydroxide extensively for desulfurization in waste-to-energy plants and thermal power plants, successfully replacing soda ash; it is currently recognized worldwide 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 ordinary solid wastes that can be recycled. However, due to the high cost of these desulfurization agents, they have not been widely used. After months of intensive research and the efforts of its technical staff, the company succeeded in developing calcium hydroxide with high activity and a high specific surface area; the BET specific surface area reached over 45 m2/g. Industrial production was established, and this product was launched on the market in June 2021. The HNPS desulfurization package developed by the company has undergone pilot tests and industrial applications by various users over several months. It demonstrates excellent operating performance, low costs, and has received high satisfaction from users. Currently, it has been successfully applied at the coke oven pusher ground station for dust removal in the dry quenching process of coke, as well as for the desulfurization of coke oven flue gases. Advantages of the HNPS desulfurization technology: 1. It utilizes a calcium-based desulfurizer with high reactivity and large specific surface area, which is directly injected into the flue gas duct and thoroughly mixed with the flue gas. This enables effective adsorption and absorption of acidic components in the flue gas, resulting in high desulfurization efficiency ； 2. The HNPS dry flue gas desulfurization process is adopted; there is no temperature drop during the reaction process. The existing bag filter or a newly installed bag filter is used to remove solid waste. The calcium-based solid waste is resistant to moisture absorption, non-corrosive, and does not cake. 3. Compared with SDS, desulfurization has almost no temperature restrictions; there is no need for a grinding system on site, and it results in low investment and operating costs. It can directly replace soda ash in existing SDS processes ； 4. The main components of desulfurization by-products, such as calcium sulfate, calcium carbonate, and calcium hydroxide, are all considered ordinary solid wastes that can be recycled ； 5. Fewer devices and equipment are required, flexible layout, and low investment ； Material is supplied 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.