Design of First-stage Double-suction Multi-stage Wear-resistant Centrifugal Pump

25 May , 2023

1.Foreword

In order to promote the development of coal mines, steel mills, power plants and pumping stations, various types of pumps are designed and manufactured. According to the relevant requirements of energy saving and emission reduction, combined with the design experience of existing wear-resistant centrifugal pumps for coal mines, a large-scale first-class double-suction wear-resistant centrifugal pump for coal mines is developed to solve a series of problems such as large flow demand, high cavitation demand and serious abrasion.

The first-stage double-suction multistage wear-resistant centrifugal pump developed this time, the main performance indexes of the product reach the technical level of the same type of imported pumps, and at the same time, it is superior to similar foreign products in terms of operational reliability and standardized design of product accessories, and can replace similar imported products. At the same time, technical considerations are also integrated into the supply of product accessories, which makes full technical preparations for the mass production of products. The outlet of the pump is vertical upward, and the pump inlet is located on the horizontal right side when viewed from the driving end, and the suction section, the middle section and the discharge section are connected by a bar. The static seal between the water inlet section, the middle section and the water outlet section of the pump adopts metal surface seal, and an O-shaped rubber sealing ring is added as an auxiliary seal. The shaft seal is sealed with soft packing, and a packing ring is arranged in the packing cavity. The pump is equipped with a self-circulating packing flushing pipeline, which takes water from the middle section of the first stage and rushes to the packing cavities at both ends through the flushing pipeline. The first stage impeller of the pump adopts double suction structure, which has good cavitation resistance.

2.Design Calculation

This product is located in a high-quality technical level, and it is a large horizontal first-stage multi-stage wear-resistant centrifugal pump with double suction, which mainly transports medium such as mine water, and requires high stability and wear resistance of the pump. When designing this kind of pump, according to the existing design and manufacturing experience of wear-resistant centrifugal pump for coal mine, the selection of safety factors for each part is biased towards reliability as much as possible in calculation, and the optimization design is combined with actual casting and processing technology. In the process of design, the efficiency and hydraulic model are deeply analyzed, and many experiences are summarized. The hydraulic model is newly optimized and designed, and corresponding measures are taken to improve the hydraulic efficiency to meet the design conditions. In hydraulic design, CFD flow field analysis software is integrated to assist design, and the design results can be predicted in advance and optimized according to the results of software-aided analysis, so as to improve the reliability and timeliness of design.

According to the initial parameters (such as rated flow head, efficiency, speed, etc.), the design, calculation and verification of various parts of the pump are carried out, and the calculation process and specific data are not listed here.

3.Three-dimensional Modeling

In the design process, theoretical calculation and three-dimensional modeling are carried out simultaneously, which can not only display the parts intuitively, but also check and verify the theoretical design values with the help of three-dimensional models, optimize and correct the design results, and improve the calculation efficiency and design yield.The following shows three-dimensional drawings of some parts and assemblies:

3.1.First stage Double Suction Impeller

3.2.Secondary Impeller

3.3.Guide Vane

3.4.Assembly body

4.Anti-cavitation Design and Material Selection

When designing the pump, the factors such as abrasion, easy casting, difficult deformation and cavitation resistance should be considered, and the thickness of the front and rear cover plates of the impeller and the outlet of the blade should be thickened. When pumping water containing fine particles, the effective cavitation allowance of the pump will decrease accordingly, and the greater the particle concentration, the faster the cavitation allowance will decrease. Cavitation involves chemical corrosion, electrochemical effect and thermodynamic effect, and the damage to the impeller, guide vanes and even the shell is very serious. Therefore, the model pump with good cavitation performance should be selected for conversion or the cavitation specific speed should be as large as possible in the design, and the material with high cavitation resistance should be selected, and the wall thickness of the middle section and outlet section should be thickened appropriately.

This innovation adopts the first-stage double-suction impeller structure, which is beneficial to the cavitation performance of the pump and helps to improve the flow rate at the pump inlet; The main flow parts, such as water inlet section, middle section, water outlet section, impeller, guide vanes, head and tail covers, etc., are made of wear-resistant ductile iron QT500-7, and the bushings, sealing rings and guide vane sleeves are made of wear-resistant materials such as 20Cr13, 40Cr or high alloy wear-resistant cast iron MTG-1. The balance disc device is in a dynamic balance state during operation, which can completely balance the axial force of the rotor and make the pump run more smoothly. The two ends of the pump are supported by radial bearing bush structure, which has large bearing capacity and excellent lubrication effect with thin oil. The bearing seat is made of gray iron, which is easy to cast, not easy to deform and has good shock absorption.

5.Final Thoughts

Based on the design, research and computer CFD simulation calculation of the first-stage double-suction wear-resistant multistage centrifugal pump used in coal mine, combined with the characteristics of large change of water inflow before and after siltation in mine drainage pipeline and the wear characteristics of mine water on centrifugal pump impeller, guide vane and shell, it is summarized as follows:

1) Underground drainage is related to mine safety, and the pump must be stable in operation, reliable in performance, abrasion-resistant and highly cavitation-resistant. The first stage impeller of multi-stage segmented centrifugal pump with large flow rate should adopt double suction structure, which can not only improve the inlet flow of the pump, but also effectively improve the cavitation performance of the pump.

2) When designing wear-resistant centrifugal pumps for mines, hydraulic models with excellent cavitation performance must be selected. When designing the impeller, properly increasing the blade wrap angle, reducing the outlet angle, reducing the number of blades and increasing the outlet width can reduce abrasion and increase the life of the impeller. The main parts and components of overcurrent are made of high wear-resistant materials, and smaller wear-resistant parts such as wear-resistant rings, bushings and shaft sleeves are arranged at the gaps at all levels to reduce the wear of main parts.

3) It is advisable to set packing rings and sealed flushing pipelines at the packings at both ends of the pump, and take water from the middle section of the first stage to flush the packings at both ends to prevent the packings from being overheated or even burned by particles.

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