High-Temperature Lava Pump
Flue Gas Desulfurization Pump
1. Overview: Wet flue gas desulfurization and denitrification pumps can withstand certain levels of abrasion and corrosion. Through specialized material selection, our company has successfully deployed these pumps in flue gas desulfurization applications, aiming to introduce a new type of desulfurization circulating slurry transport equipment to the industry. China is a major coal-consuming nation, with coal dominating energy production and consumption. Coal accounts for approximately 70% of China’s energy consumption, a proportion unlikely to change significantly in the short term. Eighty percent of coal consumption involves combustion, which is the primary source of SO₂, nitrogen oxides, and particulate matter in the atmosphere—particularly PM₂.₅. This contributes significantly to widespread air pollution in China, making it the world’s largest SO₂ emitter. To meet emission standards, numerous power plants and heating enterprises have implemented measures to reduce direct SO₂ emissions. Most adopt the internationally proven limestone/gypsum wet desulfurization process. The inherent characteristics of this desulfurization and denitrification pump process demand strong corrosion and wear resistance in desulfurization components and equipment exposed to desulfurization media. This is particularly true for carbon steel components, which face electrochemical corrosion from acidic electrolytes in humid environments during desulfurization. Non-metallic materials, however, exhibit low electrolyte composition for microcell formation. Rubber, in particular, demonstrates strong corrosion and wear resistance. To manufacture slurry transfer equipment suitable for power plant desulfurization and denitrification processes, our company has accumulated successful experience in producing desulfurization and denitrification slurry pumps.
2. Specialized Material Optimization for Desulfurization and Denitrification Pumps The pump body components utilize cast iron with rubber lining. The rubber lining is semi-hard, similar to automotive tire rubber, possessing elasticity. During pump operation, particulate matter in the liquid impacts the rubber surface. The rubber’s elasticity provides cushioning, minimizing wear. If the lining material were hard, such as in plastic-lined pumps or alloy pumps, the impact would be hard-on-hard, causing severe wear.
When metal materials serve as pressure-bearing components and non-metallic materials are used as corrosion-resistant linings, the bonding strength between the non-metallic and metallic materials must be thoroughly evaluated. Concurrently, the design of the pressure-bearing components must ensure the non-metallic material maintains stable, long-term adhesion to the metallic structure. For the soft rubber lining process, our company employs a proven methodology as follows: First, the inner surfaces of the suction chamber and discharge body of the HT200 cast iron pump are cleaned to remove oil residues and sand particles. Subsequently, the rubber lining is uniformly applied to the inner surfaces using a heated, pressurized molding process. The presence of numerous micro-pits on the casting’s inner surface allows the softened non-metallic coating material to settle into these pits, forming countless micro-anchors that provide excellent mechanical bonding. Generally, different rubber formulations can be selected based on the chloride ion concentration and temperature of the desulfurization slurry, though the specific processing techniques may vary slightly.
3. Primary Corrosion Factors Affecting Pump Equipment in Wet Flue Gas Desulfurization Systems The internal operating environment of wet flue gas desulfurization systems is highly complex: solids, liquids, and gases intermingle; acids and alkalis coexist; temperatures fluctuate between hot and cold; numerous influencing factors include solid and gaseous components in flue gas, gas flow velocity, temperature, slurry pH, F⁻ and Cl⁻ ions, as well as erosion and deposition corrosion from particulate matter.
Typically, flue gas from thermal power plants contains gases such as SO₂, NO_x, HCl, and HF. Within the absorber tower, the flue gas comes into full contact with an absorbent containing substances like CaCO₃ and Ca(OH)₂, causing pollutants to be absorbed into the slurry, thereby achieving gas separation. Consequently, the desulfurization wash liquid contains H₂SO₄, HCl, HF, and Cl⁻, along with approximately 15%–20% suspended solid particles. All such scrubbing slurries are ultimately transported through the recovery system via desulfurization circulation pumps.
Due to the presence of large amounts of ions such as F⁻, Cl⁻, SO₃²⁻, and SO₄²⁻ in the limestone slurry and gypsum slurry, coupled with the recirculation of wash water within the desulfurization system, these ions gradually accumulate in the slurry, causing severe corrosion and wear on metal components. Particularly Cl⁻, the primary cause of metal pitting corrosion, crevice corrosion, stress corrosion, and selective corrosion, accelerates the corrosion damage of metal components in desulfurization wastewater pumps. Operational experience demonstrates that when Cl⁻ concentration reaches 20,000 × 10⁻⁶, conventional stainless steel becomes unsuitable, necessitating non-metallic linings. This is why our company employs rubber linings in desulfurization slurry transfer pumps.
4. Based on our company’s focus in the desulfurization industry, the selection of metal anti-corrosion materials by international manufacturers in the same sector shows that the United States currently primarily opts for high-nickel-based alloys or carbon steel cladding over high-nickel-based alloy plates in power plant desulfurization wastewater. These materials offer superior performance, including excellent temperature resistance, corrosion resistance, and resistance to medium permeation, while ensuring high construction quality. However, they are costly, require specialized manufacturing techniques and equipment, and present significant on-site installation challenges, making them unsuitable for China’s conditions. Germany, Europe, and other regions predominantly use fiberglass-reinforced plastic (FRP) and carbon steel lined with rubber plates, particularly in desulfurization slurry transport equipment, where carbon steel lined with rubber is the primary process employed.
Currently, the primary corrosion-resistant material used in China’s equipment for this field is wear-resistant and corrosion-resistant rubber lining. This non-metallic material offers excellent heat resistance and chemical stability, is easy to install, and is cost-effective. It has been in use domestically for many years and is the standard material for wet flue gas desulfurization processes widely adopted in China.
5. Pump Shaft Seal The pump shaft seal employs a K-type seal made of special materials. The slurry typically contains 20% to 40% solids such as limestone and gypsum, with particle sizes ranging from tens to hundreds of micrometers. Simultaneously, the wastewater slurry contains highly corrosive strong acids like H₂SO₄, HCl, and HF, with the slurry’s pH generally falling between 4.5 and 6.5. Given that the slurry contains both abrasive solids and acidic corrosive media, the desulfurization slurry exhibits significant corrosive properties. Therefore, careful consideration must be given to selecting the sealing material and configuration when choosing the pump shaft seal. The primary objective is to minimize pump leakage as much as possible.
6. Conclusion: In wet flue gas desulfurization (FGD) systems at power plants, corrosion of equipment caused by flue gas, slurry, and desulfurization wastewater can be categorized into three main areas: the flue duct and heat exchange system, the SO₂ absorption and oxidation system, and slurry transportation within the absorbent delivery and recovery system. Desulfurization slurry pumps are primarily used for transporting wastewater during the absorbent delivery and recovery process. Since limestone slurry in the first two stages cannot effectively absorb SO₂ from flue gas—resulting in minimal concentration reduction— SO₂ dissolves in water to form sulfuric acid mist. Combined with HCl and HF in the flue gas, this creates acidic mist. These acidic mists or liquids cause severe metal corrosion to equipment they contact. The corrosion effects of these substances manifest during desulfurization slurry transportation, demanding pumps that meet stringent process requirements. In summary, our pumps are widely applicable in desulfurization and denitrification applications.
