Preparation of industrial anhydrous sodium sulfate (1)

China's thenardite resources are abundant and there are many types. The process of producing industrial anhydrous sodium sulfate is also different. At present, the main domestic production methods are:
1. Full-dissolved evaporative dehydration method using natural thenardite ore as raw material Natural anhydrous sodium sulfate is used as raw material to produce industrial anhydrous sodium sulfate. The production method is full-evaporation dehydration. In the township enterprises, the natural nitrate ore is completely dissolved to produce a saturated solution of 30 ° ~ 31 ° Be, after clarification, the solid impurities are removed, and then evaporated, centrifugally dehydrated, and dried to obtain a finished product. The evaporation dehydration of this production process mainly includes a pan method and a fire tower method. The Ping Pan method is now used by about 300 township enterprises in the Xishunhe mining area of ​​Hongze County, Jiangsu Province and Sichuan Meishan, Danling, Ya'an and Xinjin. The method has the advantages of simple equipment, simple process, small investment and quick effect; the disadvantages are: high energy consumption, small output, poor product quality and serious environmental pollution.
The fire tower method is a method for direct countercurrent heat exchange between a mirabilite solution and a flue gas in a steel plate. The vaporized vapor and flue gas are withdrawn from the top of the tower by an induced draft fan, and a suspension containing anhydrous sodium sulfate crystals is taken out from the bottom of the column, and dried by a centrifuge to obtain a product containing 85% of Na ₂ SO ₄ . The advantage of this method is simple, low coal consumption. The disadvantages are serious equipment corrosion, serious environmental pollution, high labor intensity and poor product quality.
The production process of producing industrial anhydrous sodium sulfate from natural thenardite ore is shown in Figure 1 below.

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2. Using the salt lake brine as raw material to prepare industrial anhydrous sodium sulfate. Using salt lake brine as raw material, the palmite salt is obtained by beach drying and natural freezing. Because natural frozen mirabilite brings some solid impurities such as sediment, salt pond mirabilite (water nitrate) is also dehydrated by total solution to obtain anhydrous sodium sulfate. The production process is consistent with the production method using mineral nitrate as raw material.
In 1982, Shanxi Yuncheng Salinization Bureau pioneered the production method of four-effect vacuum evaporation and end-effect secondary steam waste heat treatment. This new technology still plays an important role in this bureau. Due to the continuous improvement of production technology management, the production process is mature. . The obvious advantage of the four-effect evaporation process is energy saving, which saves investment. This process is widely used in the production of anhydrous sodium sulfate with ten water mirabilite as raw material.
3. Glauberite industry as raw materials of calcium sulfate anhydrous mirabilite ore crushing, ball milling with water, made mirabilite liquid immersion (or nitrate aqueous solution obtained Chamber Method), and then purified and evaporated to dehydration, and dried to obtain the finished product may be . Although this method has many processing procedures, high energy consumption and high production cost, the product quality is high and stable (Fig. 2 below).

After 1989, Sichuan successfully applied the five-effect vacuum evaporation reverse effluent to the production of sodium sulfate, which greatly promoted the development of the Sichuan Glauberite industry. The concentration of the nitrate water obtained by the water-dissolving method of the chamber is low, so the heat exchange area of ​​the evaporator is large. In order to make full use of the heat, the counter-feed is used, and the pump is dumped. Due to the rigorous production process, the vacuum device adopts two-stage steaming, one-stage water spraying, and the vacuum can reach more than 0.09 MPa. The alkali (soda ash and caustic soda) are used to remove calcium and magnesium , and the insoluble matter is removed in the inclined plate settler. The sand filter is filtered to obtain refined nitrate water, and the tail gas dust is used for wet recovery; the fourth and fifth effect feeds, the first and second effect discharges, and the condensed water is flashed, and the secondary steam and the return water are all properly applied. This production process has a low coal consumption of around 26 kg/t and a cost of 230-300 yuan/t. Jiangsu Hongze County Chemical Group Co., Ltd. has introduced this process.
4. The sodium salt-type well brine ore as raw materials rich industrial over anhydrous sodium sulfate type salt resources Hunan, Hubei, Jiangxi, Yunnan Province, the main component is NaCl, Na ₂ SO _4. The content of sodium sulfate varies from mine to mine, generally 15 to 35 g/L. The mining method is water injection fracturing and water dissolution.
In order to ensure the smooth progress of salt production, improve the quality of refined salt, and comprehensively utilize resources, all production plants have established a nitrogen extraction workshop. At present, there are two routes for the extraction of nitrogen, one is the cold process to increase the salt and nitrate production process; the other is the thermal process to increase the salt and nitrate production process. The process flow is shown in Figures 3 and 4. The former is reliable in process and the product quality is stable, but the freezing system is seriously corroded, the one-time investment is large, and the mechanical refrigeration energy consumption is high, resulting in high production cost. The latter process is simple, the investment is small, and the energy consumption is low, but the product quality cannot be guaranteed and needs to be further improved.

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