Spray drying desulfurization process

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The spray drying desulfurization process uses lime as the desulfurization absorbent. The lime is digested and mixed with water to form slaked lime slurry, which is then pumped into an atomizing device located inside the absorption tower. There, the absorbent, having been transformed into fine droplets, comes into contact with the flue gas; a chemical reaction occurs between this absorbent and the SO2 in the flue gas, resulting in the formation of CaSO3, and thus the SO2 in the flue gas is removed. At the same time, the moisture absorbed by Qi is rapidly evaporated, causing it to dry out, and as a result the temperature of the flue gas decreases. The desulfurization reaction products and the unutilized absorbent are carried out of the absorption tower with the flue gas in the form of dry particulates, and are collected in a dust collector. The flue gas after desulfurization is discharged after being filtered by a dust collector. To improve the utilization rate of desulfurization absorbents, part of the dust collector collection is generally added to the pulp production system for recycling. This process offers two different atomization methods to choose from: one is rotary spray wheel atomization, and the other is gas-liquid two-phase flow. 　　The spray drying desulfurization process features mature technology, a relatively simple process flow, and high system reliability, with a desulfurization rate of over 85%. This process has a certain degree of application in the United States and some countries in Western Europe (8%). Desulfurization ash can be used for brick manufacturing and road construction, but it is often discarded in ash dumps or used to fill old mine pits. 　　Calcium injection into the furnace combined with humidity enhancement and activation of flue gas for desulfurization. This process builds on the calcium injection technique for desulfurization by adding a humidity enhancement section at the rear of the boiler, in order to improve the efficiency of desulfurization. In this process, limestone powder is commonly used as the absorbent. It is injected into the furnace chamber at a temperature of 850–1150°C via pneumatic means; there, the limestone decomposes upon heating to form calcium oxide and carbon dioxide. Calcium oxide then reacts with sulfur dioxide in the flue gas to produce calcium sulfite. Since the reaction takes place between the gas and solid phases, it is affected by the mass transfer process, resulting in a slow reaction rate and low utilization efficiency of the absorbent. In the tail humidification activation reactor, humidified water is sprayed in mist form and comes into contact with unreacted calcium oxide to form calcium hydroxide, which then reacts with sulfur dioxide in the flue gas. When the calcium-sulfur ratio is controlled at 2.0–2.5, the desulfurization efficiency of the system can reach 65–80%. As the addition of humidifying water lowers the flue gas temperature, the outlet flue gas temperature is generally kept 10–15°C above the dew point temperature. The humidifying water evaporates rapidly due to the heating from the flue gas temperature, while the unreacted absorbent and reaction products remain in a dry state and are discharged with the flue gas, where they are collected by the dust collector. This desulfurization process is used in Finland, the United States, Canada, France, and other countries; the maximum capacity of a single unit employing this technology has reached 300,000 kilowatts. 　　Flue gas circulating fluidized bed desulfurization process The flue gas circulating fluidized bed desulfurization process consists of components such as absorbent preparation, absorption tower, desulfurization ash recycling, dust collector, and control system. This process generally uses dry slaked lime powder as the absorbent; other dry powders or slurries capable of absorbing sulfur dioxide can also be used as absorbents. 　　The untreated flue gas emitted from the boiler enters at the bottom of the absorption tower (i.e., the fluidized bed). At the bottom of the absorption tower is a Venturi device; as the flue gas passes through this venturi tube, its velocity increases, and it mixes there with very fine absorbent powder. Intense friction occurs between the particles as well as between the gas and the particles, resulting in the formation of a fluidized bed. With the addition of a uniform mist to lower the temperature of the flue gas, the absorbent reacts with sulfur dioxide present in the flue gas to produce CaSO3 and CaSO4. The flue gas, containing a large amount of solid particles after desulfurization, is discharged from the top of the absorption tower and enters the recirculation dust collector. The separated particles are returned to the absorption tower via an intermediate ash bin. Since these solid particles undergo repeated cycles of hundreds of times, the utilization efficiency of the absorbent is high. 　　The by-products generated by this process are in dry powder form, and their chemical composition is similar to that of the desulfurization process using spray drying. They mainly consist of fly ash, CaSO3, CaSO4, and unreacted absorbent Ca(OH)2, making them suitable for use in backfilling abandoned mines and as road foundations. 　　In a typical flue gas circulating fluidized bed desulfurization process, when the sulfur content in coal is around 2% and the calcium-sulfur ratio is no more than 1.3, the desulfurization efficiency can exceed 90%, with the flue gas temperature at approximately 70°C. This technology is currently used abroad in units with a capacity of 100,000 to 200,000 kilowatts. Due to its small footprint and lower investment costs, it is particularly suitable for flue gas desulfurization of existing units.