How are flue gas desulfurization methods classified?

Flue gas desulfurization methods can be classified into the following five types based on the type of desulfurizing agent: the calcium method using CaCO3 (limestone) as a base, the magnesium method using MgO as a base, the sodium method using Na2SO3 as a base, the ammonia method using NH3 as a base, and the organic base method using organic bases. The main technologies for industrialization include: ① Wet lime/limestone-gypsum process. In this process, a slurry of lime or limestone is used to absorb SO2 from flue gases, resulting in calcium sulfite hemihydrate or, upon reoxidation, gypsum. It features a high level of technical maturity and stable desulfurization efficiency, exceeding 90%, making it the primary method used both domestically and internationally. ②Spray drying method: In this method, lime milk is used as an absorbent and sprayed into the desulfurization tower; after desulfurization and drying, the resulting product is powdered desulfurization slag. It belongs to the semi-dry desulfurization category, with a desulfurization efficiency of around 85%. The investment required for this method is lower than that of the wet limestone-gypsum method. It is currently mainly used in the United States. ③The absorption-regeneration methods mainly include the ammonia method, magnesium oxide method, double-alkali method, and W-L method. The desulfurization efficiency can reach around 95%, and the technology is relatively mature. ④Calcium injection in the furnace – humidification-activated desulfurization method: This is a desulfurization technique that involves directly injecting powdered calcium-based desulfurizing agents (limestone) into the furnace of a burning boiler. It is suitable for boilers using medium- and low-sulfur coal, with a desulfurization efficiency of around 85%.

From the perspective of the reuse and recycling of sulfur resources, amine desulfurization is a good method.

The CO2 emissions generated by the lime-gypsum process are equal to the amount of SO2 absorbed, and with carbon taxes becoming increasingly important, the lime-gypsum process will lose its advantages.

Other metal alkali processes generate a relatively large amount of high-salt wastewater. It is the issue of sulfur resources changing from waste gas to solid and liquid waste.