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**Research and Practice of Localization of Gray Sludge/Gypsum Wet Flue Gas Desulfurization Metal Slurry Circulating Pump**
**Wang Nahua¹, Lu Tianyi²**
¹Xiangfan 525 Pump Industry Co., Ltd. of China Ordnance Group, Xiangfan 441021, Hubei, China
²Hangzhou Banshan Power Generation Co., Ltd., Hangzhou 310015, Zhejiang, China
**Abstract:** This paper presents the successful development and application of a metal slurry circulating pump for wet flue gas desulfurization (FGD) systems by Xiangfan 525 Pump Industry Co., Ltd. The research covers key aspects such as hydraulic model design, structural optimization, mechanical seal technology, and material selection. The pump has achieved international advanced standards and is capable of replacing imported units in power plants ranging from 50MW to 600MW. It has been successfully implemented in several desulfurization projects in China, proving its reliability, efficiency, and cost-effectiveness.
**Keywords:** Metal slurry circulation pump; Localization; Desulfurization; Corrosion-resistant alloy; Hydraulic design
**Introduction:**
The limestone/lime–gypsum wet flue gas desulfurization process is the most mature and widely used technology globally, especially in China's thermal power plants. With over 159 FGD projects currently under construction or operational, the total installed capacity exceeds 65 million kW, with more than 130 units using the limestone/gypsum method. In these systems, the absorption tower circulation pump is a critical component often referred to as the "heart" of the plant. It must handle abrasive gypsum slurry with high chloride content, which poses significant challenges in terms of corrosion, wear, and long-term reliability.
While smaller slurry pumps have been localized, large-scale circulation pumps are still mostly imported. Xiangfan 525 Pump Company, with nearly two decades of experience in producing wear-resistant and corrosion-resistant pumps, introduced advanced French technologies in both corrosion-resistant materials and pump design. Since 2000, the company has focused on developing large-scale FGD slurry pumps, achieving notable success in material development, hydraulic design, and sealing technology.
In 2004, the company’s FGD slurry pump was recognized as a national key new product by multiple government agencies and supported by the National Science and Technology Innovation Fund. A pilot unit at Hangzhou Banshan Power Plant replaced an imported KSB pump with a domestically produced LC600/825 model, which has operated smoothly for over 4,000 hours, demonstrating the feasibility of localization.
**Technical Requirements for Flue Gas Desulfurization Slurry Pumps**
The slurry used in FGD systems contains fine particles of limestone and gypsum, with a solid concentration of around 20%. The presence of sulfuric and hydrochloric acids leads to high chloride ion concentrations (20,000–60,000 ppm) and a pH range of 3.5 to 7. These conditions demand high corrosion resistance and wear resistance in the pump components.
Pump flow rates typically range from 4,000 to 12,000 m³/h, with head between 16 and 30 meters. Given that slurry circulation pumps account for over one-third of the energy consumption in the desulfurization system, high efficiency and large flow rate are essential technical requirements. Additionally, the pumps must be reliable, safe, and easy to maintain due to their critical role in plant operations.
**Material Development and Corrosion Resistance**
To meet these demanding conditions, Xiangfan 525 Pump Company adopted advanced French corrosion-resistant and wear-resistant alloy technologies. Two main types of slurry pumps are used globally: rubber-lined pumps and alloy pumps. While rubber-lined pumps are cost-effective, they are prone to liner detachment and have limited lifespan. Alloy pumps, although more expensive upfront, offer better performance, longer life, and easier maintenance.
Based on the similarities between wet-process phosphoric acid slurry and FGD slurry, the company developed Cr30A and 2605N alloys. Cr30A, enriched with Ni and Cu, improves resistance to chloride corrosion, while 2605N, with ultra-low carbon and Mo enrichment, enhances pitting resistance and mechanical properties. These materials were tested at Xi’an Jiaotong University and showed significantly better performance compared to traditional stainless steels like 1.4539 and 1.4529.
**Efficient Hydraulic Design**
The company employed CFD (Computational Fluid Dynamics) simulations to optimize the hydraulic design of the LC series pumps. By adjusting blade thickness, flow area, and other parameters, they improved efficiency to over 82% in prototype models. Further refinement led to a 600mm diameter pump with a flow rate of 4,800 m³/h and a head of 20.6m, achieving an efficiency of 86%.
**Structural Design and Maintenance**
The pump features a simplified structure with a “back door†design for easy maintenance. Key components such as bearings and impellers can be removed without disconnecting inlet or outlet pipes. The use of imported bearings, thin oil lubrication, and a small aspect ratio (thicker shaft) reduces dynamic deflection and extends seal life.
**Performance and Industrial Evaluation**
The LC600/825 pump was installed at Hangzhou Banshan Power Plant in 2004 and has operated reliably for over 4,000 hours. Post-maintenance inspections showed minimal wear, confirming the pump’s durability and effectiveness. The pump’s performance closely matched CFD predictions, validating its design and operation.
**Conclusion**
The successful development of the metal slurry circulation pump by Xiangfan 525 Pump Company demonstrates that high-performance FGD equipment can be localized, reducing reliance on foreign imports. With its simple structure, long service life, and low maintenance needs, the pump offers a viable alternative for Chinese power plants. As the sole domestic producer of advanced corrosion-resistant pumps, the company now provides a wide range of slurry circulation pumps suitable for 50MW to 600MW power units, supporting the growth of China’s flue gas desulfurization industry.