Compared with traditional processes, the new production process for preparing sodium metabisulfite from desulfurization and regeneration gas of activated coke has the following advantages:
1) No need to purchase sulfur resources. The sulfur element required by traditional processes comes from the combustion of elemental sulfur and pyrite, etc. The cost of sulfur element accounts for a relatively high proportion of the production cost of sodium metabisulfite, and the profit margin of the target product is low. The sulfur element in the new process comes from desulfurization and regeneration gas, and sulfur resources do not need to be purchased. The profit margin of the target product is high, and it has more market advantages.
2) Energy saving. The power consumption of SO2 compressors in the production of sodium metabisulfite accounts for 50% to 60% of the total power consumption of the production system. Reducing gas phase pressure loss can significantly reduce the unit comprehensive power consumption of the target product. The traditional processes currently in operation all use a three-stage series bubble reactor, with a pressure drop loss of up to 45-56 kPa for the feed gas; The new process adopts a first stage drum bubble reactor and multi-stage tower reactor can significantly reduce the gas phase pressure drop loss, which is usually only 15 kPa. Compared to traditional processes, new processes are more energy-efficient.
3) The purity of the target product is higher. SO2 obtained by sulfur or pyrite methods generally contains φ (O2) 6% to 10% oxygen, which can oxidize SO2 to SO42-. The sulfate content in the product is high, and it is difficult to obtain a target product of sodium metabisulfite w (Na2S2O5) that exceeds 98.3%; The feed gas of the new process contains almost no oxygen, and the enrichment rate of sulfates in the circulating liquid is slow. The target product of sodium metabisulfite w (Na2S2O5) can reach 98.5% to 99.3%.
4) The target product contains fewer artificially introduced impurities. In the production of sodium metabisulfite, some additives and other impurities may be artificially introduced due to process requirements. The impurities artificially added during the production process will eventually transfer to the target product. To ensure the grain uniformity of the target product and reduce the frequency of system blockage, an appropriate amount of dispersant needs to be added to the bubbling reactor; To reduce the oxidation rate of the target product in the production process, an appropriate amount of antioxidants are usually added to the circulating liquid. The foaming path of the new process is shorter, and the amount of dispersant added is less than that of the traditional process; Meanwhile, the feed gas in the new process contains almost no oxygen and does not require the addition of antioxidants.
5) The fluctuation of international sulfur prices has a relatively weak impact on the profit margin of the target product. The main raw materials for the production of sodium metabisulfite include sulfur dioxide, caustic soda, water, steam, etc. Among them, sulfur accounts for one-third of the mass of sodium metabisulfite, with a relatively high proportion. Traditional processes require the purchase of sulfur resources from external sources, and fluctuations in international sulfur prices have a significant impact on the cost of sodium metabisulfite. The SO2 from the new process comes from desulfurization and regeneration gas, which is used for waste resource utilization, and sulfur resources require almost no cost.
6) The reaction rate is faster. The traditional process uses combustion method to prepare feed gas, which contains φ (SO2) is difficult to exceed 14%, usually only 10% to 12%; The new process uses desulfurization and regeneration gas as the feed gas, which has a high content of SO2. Dry basis in desulfurization and regeneration gas using activated coke method φ (SO2) in the range of 15% to 25%, organic amine ionic liquid desulfurization desorption gas on a wet basis φ (SO2) is above 99%. High concentration SO2 in new technology can increase the driving force of the reaction, accelerate the chemical reaction, and shorten the time to reach reaction equilibrium.
7) The storage period is longer, and the production line can produce continuously. During the inventory period, sodium metabisulfite may experience deliquescence, hardening, and oxidation. The product purity has the greatest impact on the quality of sodium metabisulfite products. Due to the lower purity of sodium metabisulfite produced by traditional processes, its value is very close to the indicator limit of industrial grade sodium metabisulfite or food grade sodium metabisulfite. To avoid a decrease in purity caused by product backlog, the vast majority of sodium metabisulfite production enterprises currently adopt an intermittent production mode. The purity of sodium metabisulfite produced by the new process can be 2-3 percentage points higher than the relevant indicators. Compared with products produced by traditional processes, the storage time of products produced by new processes can be extended by 1-3 times under the same indicator value. At the same time, the production line can produce continuously, which can effectively alleviate the situation of market supply shortage during the peak season of product demand.