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**Research and Practice of Localization of Gray Sludge/Gypsum Wet Flue Gas Desulfurization Metal Slurry Circulating Pump**
**Wang Nahua 1, Lu Tianyi 2**
*1 Xiangfan 525 Pump Industry Co., Ltd. of China Ordnance Group, Xiangfan 441021, Hubei, China*
*2 Hangzhou Banshan Power Generation Co., Ltd., Hangzhou 310015, Zhejiang, China*
**Abstract:** This paper presents the successful development of a metal slurry circulating pump for flue gas desulfurization (FGD) by Xiangfan 525 Pump Industry Co., Ltd. The study covers the hydraulic model, structural design, mechanical seal technology, and material research of the pump. The industrial assessment and technical evaluation have confirmed that the pump meets international advanced standards, making it fully capable of replacing imported units in thermal power plants ranging from 50MW to 600MW. The localization of this critical equipment marks a significant advancement in China’s FGD technology.
**Keywords:** Metal slurry circulation pump, Localization, Flue gas desulfurization, Corrosion-resistant alloy, Hydraulic design
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**Introduction:**
The limestone (lime)/gypsum wet flue gas desulfurization process is currently the most mature and widely used technology globally, especially in China’s thermal power plants. With over 159 FGD projects under construction or completed, the total installed capacity exceeds 65 million kW, with more than 130 units using the limestone/gypsum method. In such systems, the absorption tower circulation pump is considered the “heart†of the plant. It must handle highly corrosive and abrasive slurry containing high levels of chloride ions and solid particles, while maintaining high efficiency, reliability, and long service life.
Despite the success of localizing smaller slurry pumps, large-scale circulation pumps are still predominantly imported. Xiangfan 525 Pump Industry Co., Ltd., with nearly two decades of experience in corrosion and wear-resistant pump manufacturing, has made significant progress in developing a domestically produced solution. Through the introduction of French technologies, including corrosion-resistant alloys and advanced casting methods, the company has successfully developed a high-performance slurry pump suitable for FGD applications.
In 2004, the developed pump was recognized as a national key new product and received support from the National Science and Technology Innovation Fund for SMEs. A pilot project at Hangzhou Banshan Power Plant replaced an imported KSB pump with a locally manufactured LC600/825 unit, which has been operating smoothly for over 4,000 hours.
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**Technical Requirements of Slurry Circulation Pumps**
The slurry used in FGD systems is a complex two-phase medium, typically containing 15–20% solids (limestone and gypsum), with chloride ion concentrations ranging from 20,000 to 60,000 ppm and a pH between 3.5 and 7. These conditions pose severe challenges to pump materials and performance. The pump must also handle large flow rates (4,000–12,000 m³/h) and operate efficiently to reduce energy consumption, which accounts for over one-third of the total power used in FGD systems.
Given these demands, Xiangfan 525 focused on material development, hydraulic optimization, and structural improvements. Their efforts led to the creation of the LC series of flue gas desulfurization pumps, which were tested and validated through extensive trials and field assessments.
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**Material Development for Corrosion and Wear Resistance**
Two main approaches exist for designing corrosion-resistant slurry pumps: rubber-lined pumps and alloy-based pumps. While rubber-lined options are cost-effective, they suffer from issues like liner detachment and reduced efficiency. Alloy-based pumps, though initially more expensive, offer superior durability, reliability, and ease of maintenance.
Xiangfan 525 adopted the latter approach, introducing high-chromium corrosion-resistant alloys and ultra-low carbon nitrogen duplex stainless steels. The modified Cr30A and 2605N materials demonstrated excellent resistance to chloride-induced corrosion and abrasion, outperforming traditional stainless steels like 1.4539 and 1.4529 in laboratory tests.
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**Efficient Hydraulic Design**
To optimize performance, the company employed CFD simulations and physical testing to refine the pump’s hydraulic model. The redesigned impeller and flow channel improved efficiency significantly, reaching up to 86% in large-scale models. This level of efficiency matches international standards and ensures reliable operation under varying load conditions.
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**Structural Innovations for Reliability and Maintenance**
The pump features a simplified structure with a back-door access system, allowing for easy maintenance without disconnecting pipelines. Key components such as the impeller, bearings, and seals are designed for long-term operation and minimal downtime. The use of imported bearings and optimized shaft design further enhances reliability and reduces wear.
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**Performance Evaluation and Field Experience**
The first domestic-made metal slurry pump was installed at Hangzhou Banshan Power Plant in 2004. After three months of operation, the pump showed no signs of degradation, with all components remaining in excellent condition. To date, it has operated continuously for over 4,000 hours, proving the feasibility and effectiveness of localized production.
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**Conclusion**
The successful development and implementation of the metal slurry circulation pump by Xiangfan 525 Pump Industry Co., Ltd. represents a major breakthrough in China’s FGD industry. By combining advanced materials, efficient hydraulic design, and innovative structural solutions, the company has created a reliable, durable, and cost-effective alternative to imported pumps.
This achievement not only reduces dependency on foreign suppliers but also promotes the growth of domestic technology in critical environmental protection equipment. As the demand for cleaner power generation increases, the localization of such key components will play a vital role in supporting sustainable development.