Highly active calcium hydroxide

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In recent years, dry flue gas desulfurization technology has been increasingly used in small and medium-sized flue gas desulfurization systems; it is mature in technology and operates stably. 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 drawbacks of this technical approach have become apparent, and figuring out what to do 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 station boilers, hot blast stoves, and heating furnaces in steel plants, as well as glass furnace and cement kiln systems, 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 severe penalties for any illegal activities. Business pressures are soaring! Highly active calcium hydroxide with a large specific surface area features porosity, high reactivity, good dispersibility, and high utilization rate. Its specific surface area (BET) exceeds 40 m²/g, which is 3–4 times that of ordinary calcium hydroxide. It also boasts a desulfurization efficiency of over 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 to use 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, 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 by-products of desulfurization are mainly calcium sulfate, calcium carbonate, calcium hydroxide, and other 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 scientific and technical personnel, highly active calcium hydroxide with a high specific surface area was successfully developed; its specific surface area (BET) exceeded 45 m2/g. Industrial production was established, and it was launched on the market in June 2021. The HNPS desulfurization system developed by the company has undergone pilot tests over several months with various users, as well as industrial-scale use; it exhibits good operational performance, low costs, and satisfies the users. Currently, it has been successfully applied in coke pusher surface stations, environmental dust removal for dry quenching, and desulfurization of coke oven flue gas. Advantages of HNPS desulfurization technology: 1. It uses highly active calcium-based desulfurizers with a high specific surface area, which are directly injected into the flue gas and thoroughly mixed with it, thereby enabling the adsorption and absorption of acidic substances in the flue gas, resulting in high desulfurization efficiency ； 2. The HNPS dry desulfurization process is employed; there is no temperature drop during the reaction. The 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 clog. 3. Compared with SDS, desulfurization has almost no temperature limitations; there is no need for a grinding system on site, and it results 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 considered ordinary solid wastes that can be recycled ； 5. Fewer devices and equipment are required, flexible layout, and low investment ； Material is delivered using tank trucks; the system is fully sealed, resulting in no dust generation at the site ； Rotary vane blowers or compressed air delivery, with low power consumption. Zhang Guohua ①⑧③②②⑥①⑨⑧⑧⑨