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Inorganic salt industry technical transformation project highlights
**Energy-Saving Reform in Low-Temperature Pyrolysis**
Currently, the pyrolysis process is one of the most energy-intensive steps in producing light magnesium carbonate and magnesium oxide from dolomite. This year, the China Inorganic Salt Industry Association’s Calcium and Magnesium Salt Branch organized relevant companies to focus on improving the energy efficiency of this process. They proposed a shift from high-temperature to low-temperature pyrolysis, which has already been implemented in several enterprises with remarkable results.
In April, Hebei Qiuqi County Magnesium Products Co., Ltd. held several meetings to align with national energy-saving and emission-reduction goals. The company explored ways to improve its operations, focusing on reducing energy use and emissions. It decided to invest 200,000 yuan in an energy-saving pyrolysis project promoted by the Calcium and Magnesium Salt Branch. With technical support from Professor Hu Qingfu, head of the magnesium salt expert group, and Shijiazhuang Sayed Machinery Manufacturing Co., Ltd., as well as financial support from the county credit union, the project was successfully completed.
After the transformation, the pyrolysis temperature was reduced from 95–105°C to 45–60°C, and daily coal consumption for the boiler dropped from 12 tons to 6 tons. This saves approximately 1,800 tons of coal annually, reduces carbon dioxide emissions by over 600 tons, and cuts costs by 2 million yuan. Additionally, industrial waste was used to minimize pollution, and annual profits increased by 3.7 million yuan.
**Rotary Kiln Calcination Technology**
Traditionally, many Chinese inorganic salt companies have relied on box furnaces for calcination, which are highly energy-consuming. For example, magnesium oxide production typically requires about 3 tons of coal per ton of product. However, Yuncheng Yaxing Environmental Protection Technology Co., Ltd. developed and mastered rotary kiln calcination technology, reducing coal consumption to just 1.2 tons per ton of magnesium oxide.
The rotary kiln uses environmentally friendly coal with secondary combustion, significantly increasing thermal efficiency. The exhaust gas is also recycled in three stages: first to heat a waste heat steam boiler for production, then to provide hot water for domestic use and heating. As a result, all steam, hot water, and winter heating are supplied by the waste heat boiler. The thermal efficiency of the rotary kiln exceeds 80%, making it a highly efficient and eco-friendly solution.
**Titanium-Molybdenum-Nickel Tube Evaporator**
Most magnesium salt companies in China use copper tubes in their evaporators for magnesium chloride production. However, the corrosive bromine and chlorine in the waste liquid often shorten the lifespan of these tubes to just 2–3 years. Lianyungang Yinhua Magnesium Production Company replaced copper tubes with titanium-molybdenum-nickel alloy tubes, achieving excellent results.
This alloy offers high strength, corrosion resistance, and durability, especially against seawater and chloride environments. After extensive testing, Yinhua Magnesium successfully used these tubes in evaporators, extending their service life to up to 15 years—more than five times that of copper tubes. Although the initial cost is higher, the material usage is reduced by about 70%, and total costs only increase by around 75%. This innovation not only improves equipment longevity but also enhances production stability and environmental safety.
**Rotary Flash Dryer**
Nanfeng Chemical Group Co., Ltd. recently replaced its fluidized bed dryer with a rotary flash dryer in the production of magnesium sulfate monohydrate. Previously, the company tried various drying methods, including laminar air drying and tower drying, but none were successful. Fluidized bed drying eventually enabled stable production, though at a high energy cost.
By switching to a rotary flash dryer, the company improved efficiency, reduced energy consumption, and enhanced dust collection. The new system uses hot air from a hot blast stove directly for drying, minimizing heat loss. Cyclone and bag filters effectively recover materials and reduce emissions. Compared to the previous system, coal consumption dropped by 20%, and electricity use decreased by 19%.
**Production of Nano-Magnesium Hydroxide via Bubble Liquid Membrane**
The Guangdong Zhongshan Institute of Applied Chemistry developed a novel method for producing nano-magnesium hydroxide using the bubble liquid membrane technique. This process features low energy consumption and easy separation of the final product.
The key equipment, the bubble liquid film reactor, uses a unique disc stirrer to create fine bubbles, forming a thin liquid film for efficient reaction. Nanoparticles are produced through precipitation, nucleation, and growth within the bubble liquid film, all under normal temperature conditions. The resulting product is easy to filter, wash, and dry, solving traditional issues of high energy use and difficult separation.
The technology can produce 600 tons of magnesium hydroxide annually in a continuous reactor, offering scalable, cost-effective, and easy-to-maintain industrial solutions.
**Using Light Powder as Raw Material**
Traditional methods for producing light magnesium oxide and active magnesium oxide include the dolomite carbonization and ammonium bicarbonate brine processes. However, Yuncheng Yaxing Environmental Protection Technology Co., Ltd. introduced a new energy-saving process using light-fired powder as raw material.
This process involves fully hydrating the light-burned powder, removing calcium and impurities, and then producing magnesium hydroxide before calcining it into magnesium oxide. The key advantage is a significant reduction in coal and power consumption, lowering the cost per ton of magnesium oxide by approximately 3,000 yuan.