Reviewing the Old to Discover the New (Series 9)

Wet desulfurization: It features a fast absorption or chemical reaction rate, high sulfur capacity, and is suitable for feed gases with high sulfur content. The desulfurization liquid can be easily regenerated for reuse, and sulfur can also be recovered; however, the precision of desulfurization is not high. Dry desulfurization: It uses solid desulfurizing agents, offering high desulfurization accuracy – it is possible to reduce sulfides to levels of 0.1–0.5 cm3/m3. However, the desulfurization equipment is large, replacing the desulfurizing agents is cumbersome, and energy is required for their regeneration; therefore it is suitable only for removing low levels or trace amounts of sulfur.

Dry desulfurization methods include the hydroxide-iron method, activated carbon method, etc. When sulfur-containing gases pass through these solid desulfurization agents, physical and chemical changes occur, thereby removing the sulfides. Dry desulfurization is used. It has a high purification level, but the equipment is large (due to low production capacity); operation cannot be continuous and is labor-intensive. It is only suitable for gases with low levels of sulfides, which is why it is widely used for precision desulfurization. Wet desulfurization is widely used due to its large production capacity and continuous operation, as well as its relatively wide tolerance for the hydrogen sulfide content in the feed gas. The wet method can be divided into two types: the neutralization method (recycling method) and the oxidation method. Neutralization method – After hydrogen sulfide is absorbed by the desulfurizer, when the desulfurizer is regenerated, hydrogen sulfide is released again. Such as the carbonate method, ammonia neutralization method, etc. Because the production process is simple and easy to operate. Oxidation method – After hydrogen sulfide is absorbed by the desulfurization agent, the regeneration of the agent results in the release of elemental sulfur. For example, the aqueous ammonia phase-catalysis method, the modified ADA method, and the tannin method are all typical oxidation-based desulfurization methods.

Wet desulfurization: It features a fast absorption or chemical reaction rate, high sulfur capacity, and is suitable for feed gases with high sulfur content. The desulfurization liquid can be easily regenerated for reuse, and sulfur can also be recovered; however, the precision of desulfurization is not high. Dry desulfurization: It uses solid desulfurizing agents, achieving a high level of desulfurization – sulfur compounds can be reduced to levels of 0.1–0.5 cm3/m3. However, the desulfurization equipment is large in size, replacing the desulfurizing agents is a cumbersome process, and energy is required for regeneration; therefore it is suitable only for removing low levels or trace amounts of sulfur.

Wet desulfurization: It features a fast absorption or chemical reaction rate, high sulfur capacity, and is suitable for feed gases with high sulfur content. The desulfurization liquid can be easily regenerated for reuse, and sulfur can also be recovered; however, the precision of desulfurization is not high. Dry desulfurization: It uses solid desulfurizing agents, achieving a high level of desulfurization – sulfur compounds can be reduced to levels of 0.1–0.5 cm3/m3. However, the desulfurization equipment is large in size, replacing the desulfurizing agents is a cumbersome process, and energy is required for regeneration; therefore it is suitable only for removing low levels or trace amounts of sulfur.

Depending on the raw materials and processes used for desulfurization, dry and semi-dry desulfurizers mainly consist of an emulsive desulfurizing agent made from quicklime and water (calcium hydroxide), which is sprayed onto the flue gas in countercurrent or co-current fashion; gypsum is then produced, and after dust removal and solid recovery, desulfurization is achieved. Overall, the desulfurization efficiency of dry and semi-dry methods is very low, with the desulfurization efficiency generally reaching only around 70%. There are also many different types of wet flue gas desulfurization. The basic principle is that the flue gas is washed with an alkaline solution; the SO2 in the flue gas is absorbed by the solution, forming a sulfite solution. Once this solution becomes nearly saturated, it is oxidized to form sulfates, and upon crystallization, desulfurization by-products are produced. Additionally, sulfite reduction yields elemental sulfur, and sulfur, the by-product, is obtained after filtration. Wet desulfurization is highly efficient; without considering the costs associated with it, its efficiency can reach 100%. However, in methods that use absorbents such as ammonia for desulfurization, the amount of ammonia released increases, and nitrogen oxides can damage the atmosphere. It is therefore not advisable to focus solely on desulfurization! At the same time, corrosion is inevitable; this is the biggest challenge in the desulfurization industry, one that has yet to be overcome. The cause of corrosion is the complex composition of flue gas; the sulfates formed are strong acids in acidic conditions. Chloride ions present in the flue gas can corrode stainless steel, while fluoride ions can corrode glass (instrumentation). The alkaline substances added for desulfurization can also corrode steel……

Features of wet desulfurization: fast absorption or chemical reaction rate, high sulfur capacity, suitable for removing high levels of sulfur from gases; the desulfurization liquid can be easily regenerated and reused, and sulfur can also be recovered. However, due to the constraints of physical or chemical reaction equilibrium, its desulfurization accuracy is inferior to that of the dry method, which is suitable for coal and petroleum gas production. Dry desulfurization utilizes solid desulfurizing agents. The greatest advantage is high precision. Main disadvantages: The desulfurization equipment is large in size; replacing the desulfurizing agent is a cumbersome process; and energy consumption for regeneration is high. It is suitable for natural gas with low sulfur content.

Dry desulfurization involves the use of solid absorbents for desulfurization, and it offers advantages such as high desulfurization efficiency, simple operation, straightforward equipment, and easy maintenance； However, desulfurization equipment has disadvantages such as large size, discontinuous operation, high labor intensity, and significant variations in desulfurization efficiency and resistance before and after use. Features of wet desulfurization: fast absorption or chemical reaction rate, high sulfur capacity, suitable for removing high levels of sulfur from gases ； The desulfurization liquid is easy to regenerate, can be reused, and sulfur can also be recovered. However, due to the constraints of physical or chemical reaction equilibrium, its desulfurization accuracy is inferior to that of the dry method.