Why is the concentration accuracy of drying acid and absorbing acid important?

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Non-ferrous metals generally exist in natural minerals in the form of sulfides, and the flue gas containing SO2 generated during their smelting process can be used as a raw material for producing sulfuric acid. Common non-ferrous metal smelting includes copper smelting, nickel smelting, cobalt smelting, and the smelting of other non-ferrous metals. The raw materials for these processes are mostly metal sulfide ores, and the smelting process generates flue gas containing 2%-40% SO2. The flue gas acid production process is divided into a flue gas transmission unit, a purification unit, a conversion unit, a dry absorption unit, a heating furnace unit, a fan unit, a waste heat boiler unit, an exhaust gas absorption unit, a softened water and circulating water unit, a sulfuric acid finished product storage unit, a general purpose unit, and an electrical and instrumentation unit. Among them, the units involved in chemical reaction-based acid production are the conversion unit and the dry absorption unit. The main reaction involved in the conversion unit is the conversion of sulfur dioxide gas into sulfur trioxide gas: SO2(g) + O2(g) -> SO3(g). In this unit, the conversion rate is an important indicator. Conversion rate is a key indicator that reflects the economic operating efficiency of the acid production system and measures the technological level of its process. The conversion rate can be used to assess the operating condition of the acid production system, the conditions of the flue gas, the integrity of the equipment, and the operational practices. The main reaction involved in the dry absorption unit is the absorption of sulfur trioxide gas by an acid (low-concentration sulfuric acid), resulting in the formation of high-concentration sulfuric acid: SO3(g) + H2O(l) -> H2SO4(l). In this unit, the drying rate and absorption rate are two important indicators. The control range for the concentration of the drying acid is 93.5%-94%. Generally, the concentration of this acid is determined based on the following three factors: (1) The water vapor partial pressure above the sulfuric acid solution must be low, so as to ensure that the moisture content in the flue gas after drying is less than 0.25 g/m3. (According to data (source: \"Guidelines for Modern Sulfuric Acid Production Operations and Techniques\"), the lower the water vapor partial pressure, the greater the water absorption capacity; therefore, a higher sulfuric acid concentration is preferable.) (2) Minimize the generation of acid mist, or eliminate it entirely, during the drying process. (Acid mist can cause equipment corrosion, deteriorate operating conditions, and reduce the equipment’s service life.) According to the data (source: \"Guidelines for Modern Sulfuric Acid Production Operations and Technologies\”), once stability is achieved, the higher the concentration, the greater the amount of sulfuric acid vapor present, resulting in more and finer acid mist. (3) There should be minimal dissolution of sulfur dioxide gas, in order to reduce losses of sulfur dioxide in the flue gases as much as possible. (According to data (source: \"Guidelines for Modern Sulfuric Acid Production and Operations\"), once the sulfuric acid concentration exceeds 93%, at a constant temperature, the higher the concentration, the more sulfur dioxide is dissolved; consequently, more sulfur dioxide is lost along with the acid during the drying process.) In light of this, it is best to maintain the concentration of the dried acid between 93.5% and 94%. There is a certain relationship between the concentrations of sulfur trioxide and sulfuric acid as well as temperature. When the acid temperature remains constant, the absorption rate decreases gradually as the sulfuric acid concentration exceeds or falls below 98.3%; the highest absorption rate is achieved only when the acid concentration is 98.3%. Furthermore, when the acid temperature remains constant, once the concentration of the acid being absorbed reaches 98.3%, both the water vapor pressure and the sulfur trioxide vapor pressure above the sulfuric acid solution drop to very low levels, resulting in relatively less acid mist being formed; therefore, the concentration of the acid used for absorption cannot be too low. It is thus evident that it is necessary to ensure more precise concentrations of dried sulfuric acid and absorbed sulfuric acid, in order to achieve the highest conversion rate of sulfur atoms, prevent equipment corrosion, extend the service life of the equipment, and optimize the operational procedures.