A method for producing high-purity sodium sulfite and sodium sulfate by alkaline desulfurization of coal-fired flue gas

Abstract

The invention discloses a method for producing high-purity sodium sulfite and sodium sulfate by desulfurizing coal-fired flue gas through an alkaline method. A two-stage desulfurization process is adopted; first-stage desulfurization refers to coarse desulfurization in which sulfate is left in first-stage desulfurizing liquid, sodium sulfate is produced, and most of sulfur dioxide in flue gas enters second-stage desulfurization; the second-stage desulfurization refers to main desulfurization in which flue gas can be exhausted up to standard, and the desulfurizing liquid can be directly concentrated and crystalized to produce high-purity sodium sulfite. The method has the advantages of being simple in process and easy to implement; sulfur dioxide in low-concentration flue gas is recycled by adopting the two-stage desulfurization process, so that secondary pollution caused by desulfurization and zero emission are eliminated completely; 95-percent high-purity sodium sulfate and 95-percent high-purity sodium sulfite are produced by using sulfur dioxide flue gas, and sodium sulfite accounts for 90-95 percent, so that the conventional treatment way of pure resource consumption is changed, the desulfurization burdens of enterprises are relieved greatly, and even desulfurization is turned into value-added production, thus remarkable technical and economical effects are achieved.

Description

technical field [0001] The invention relates to coal-fired flue gas desulfurization technology, in particular to a method for producing high-purity sodium sulfite and sodium sulfate through alkaline desulfurization of coal-fired flue gas. Background technique [0002] Sulfur dioxide emission is one of the main reasons for the aggravation of air pollution and acid rain in my country. Since 1998, my country's SO 2 The annual emission exceeds that of the United States, ranking first in the world for many years in a row. The SO produced by burning coal 2 Emissions accounted for SO 2 More than 90% of the total emissions. [0003] Due to the different coal quality, the concentration of sulfur dioxide in coal-burning flue gas is generally 1000-3500ppm, and the oxygen content is generally 3-8%. It is: 1) The existing flue gas desulfurization process is aimed at the removal of sulfur dioxide in the flue gas to meet the emission standards; 2) After desulfurization, a large amount ...

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Problems solved by technology

[0003] Due to the different coal quality, the concentration of sulfur dioxide in coal-fired flue gas is generally 1000-3500ppm, the oxygen content is generally 3-8%, and the concentration of sulfur dioxide discharged after desulfurization is required to be 50ppm; for such a low-concentration sulfur dioxide flue gas composition, the domestic desulfurization industry processing status It is: 1) The existing flue gas desulfurization process is aimed at the removal of sulfur dioxide in the flue gas to meet the emission standards; 2) After desulfurization, a large amount of waste such as calcium sulfate, calcium sulfite, and sodium sulfite solution is accumulated, and most of the by-products of the calcium process Calcium sulfate is difficult to use, and it needs to occupy a large amount of land to store waste residues and cause secondary pollution. If it is reluctantly used, it will cost a lot and cause more burden to the enterprise. The operating cost is very high, and the recovery of sodium sulfite can lead to zero discharge, but the content of sodium sulfite is generally only about 60%, and there is no demand in the market, resulting in serious losses; 3) Existing zero-discharge processes for desulfurization wastewater involving the use of sodium hydroxide such as sodium-alkali method and double-alkali method , all of which use various new technologies or equipment to treat and reuse the wastewater of the existing desulfurization process, but still have not solved the problem of the use of by-products or are still a process of pure input cost