Changsha Zhonglian Pump Industry Co., Ltd. 长沙中联泵业股份有限公司

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    Technical Analysis of High-Temperature and High-Pressure Boiler Feed Pumps

    Publication Date:

    2025-08-22

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    Boiler feedwater pump specially designed for boiler circulation make-up water, structurally classified as multistage Multistage Centrifugal Pump , compared to ordinary multistage pumps that transport normal temperature water Pump These pumps not only need to operate stably in high-temperature environments but also withstand the challenges brought by high pressure. The requirements for ordinary medium and low-pressure boiler feedwater pumps are relatively lower. However, for the high-pressure boiler feedwater pumps required by supercritical boilers, the design process is full of complex considerations. Next, the professional manufacturer of boiler feedwater pumps— Changsha Zhonglian Pump Industry —will provide an in-depth analysis of how boiler feedwater pumps are designed to adapt to high-temperature and high-pressure conditions.

     

    Boiler Feedwater Pump

     

    1. Pressure-Resistant Casing

    The pump casing is made of high-strength cast alloy steels such as ZG15Cr2Mo1 and ZG20CrMoV, and features a thick-wall design. Taking a 20MPa class boiler as an example, the pump casing wall thickness usually exceeds 80mm. Such a design is not only for pressure resistance but also based on actual working conditions. The manufacturing materials undergo normalizing and tempering treatments to ensure the stability of the metallographic structure. When operating at a high temperature of 300°C, the material's yield strength must have sufficient margin, and the allowable stress should be controlled below 60% of the material's yield strength to effectively prevent creep.

     

    2. Strength and High-Temperature Resistant Materials of Rotor Components

    The main shaft of the boiler feedwater pump is made of high-strength alloy steel such as 40CrNiMoA, which after quenching and tempering maintains a stable hardness of HB240 - 280. The impeller is made of martensitic stainless steel, such as 2Cr13, processed through precision casting, quenching, and high-temperature tempering. Among these, the thermal expansion compensation design is key: a thermal expansion gap is reserved in the shaft system, with a deliberate 0.05mm offset during cold alignment. When the temperature rises to 350°C, the expansion exactly fills the reserved gap, achieving thermal alignment.

     

    3. Ingenious Thermal Strain Design

    Thermal expansion sliding pins are installed at the pump body support position, and the foundation bolt holes are designed as elongated slots, allowing the casing to freely expand axially when heated. The inlet and outlet pipelines are equipped with Ω-shaped expansion joints that can absorb displacements over 12mm, effectively preventing flange cracking caused by thermal stress.

     

    4. Excellent Sealing Technology

    1. The shaft seal uses mechanical seals: a combination of hard alloy against graphite (or silicon carbide against silicon carbide), with the end face flatness strictly controlled within 0.0008mm.
    2. Dual cooling water protection: external condensate water is injected into the seal chamber under a pressure difference of 0.1 - 0.2MPa, which not only provides cooling but also effectively blocks steam. Meanwhile, the seal chamber itself is equipped with spiral cooling water channels similar to old-style rifling, greatly enhancing heat exchange.
    3. Balance drum pressure reduction: multi-stage pressure reduction drums are set on the high-pressure side, which can reduce axial thrust by more than 70%, allowing the thrust bearing to operate smoothly under light load.

     

    5. Key Component: Bearing High-Temperature Resistance

    The sliding bearing lining is made of Babbitt alloy, and the oil lubrication system is equipped with dual cooling sources. On one hand, the oil cooler uses circulating water for cooling; on the other hand, the bearing housing is cast with a cooling water jacket to strictly control oil temperature, ensuring it remains below 55°C. Once the oil temperature exceeds this threshold, the system immediately interlocks to shut down. This is valuable experience accumulated by the pump manufacturer through long-term practice.

    The above five points are the core designs for boiler feedwater pumps to achieve high-temperature and high-pressure resistance, mainly covering the reasonable selection of special materials, precise calculation of clearance, and reliable guarantee of the cooling system. In earlier maintenance of imported pumps, we noticed that the back of the impeller was designed with cooling ribs. Nowadays, domestic designs have caught up in this aspect. Under high-temperature conditions of 300°C, as long as the allowable stress of the material is accurately calculated, reasonable clearance is reserved, and the cooling water path is kept unobstructed, such boiler feedwater pumps can be durable and provide solid support for stable boiler operation.

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