In the chemical production process, chemical pumps are core equipment for conveying corrosive, flammable, explosive, high-temperature and high-pressure special media. Their operating stability is directly related to the safety and efficiency of the entire production line. The motor is the "power heart" of the chemical pump. Whether the power selection is reasonable not only affects the energy consumption and service life of the equipment, but may also cause safety accidents such as overload burning and medium leakage. Therefore, mastering the scientific selection method of chemical pump motor power is an important part of equipment management and safe production in chemical enterprises.

一、Clarify the core principle of motor power selection: adaptability rather than the bigger the better

Some customers mistakenly believe that a higher motor power is safer, believing it can prevent overload issues. This is not the case. In fact, this is not the case. Excessive motor power will lead to the "big horse pulling a small cart" phenomenon: on the one hand, the motor is in a low-load operating state for a long time, the power factor and efficiency are greatly reduced, resulting in energy waste; on the other hand, excessive starting current will increase the load on the power grid, and the matching degree between the motor and the pump body will be reduced, which can easily cause vibration, noise and other problems, shortening the overall life of the equipment. On the contrary, a motor with too little power will cause winding overheating, accelerated aging of the insulation layer, and even motor burnout due to long-term overload operation. At the same time, insufficient power may cause the pump flow and lift to fail to meet production requirements, affecting production progress. Therefore, the core principle of motor power selection is "precise adaptation", that is, calculating the minimum power required based on the actual working conditions of the chemical pump and reserving a reasonable safety factor.

二、Four key factors affecting motor power selection

The operating conditions of chemical pumps are complex and changeable. The selection of motor power requires comprehensive consideration of the following four core factors to ensure that the calculation results fit the actual application scenario.

1.Conveyor medium characteristics: Determines additional power loss

The types of media transported by chemical pumps vary greatly, which has a significant impact on the demand for motor power. For example, when conveying concentrated sulfuric acid with a density of 1800kg/m³, the motor power required is about 1.8 times that of clean water with a density of 1000kg/m³ at the same flow rate and head. If the medium contains solid particles (such as slurry), the wear resistance of the particles on the pump impeller needs to be additionally considered, and usually a 10%-20% increase in power margin is required. For high-viscosity media (such as crude oil and syrup), since the flow resistance of the medium in the pump cavity increases, the power calculation result needs to be corrected according to the viscosity coefficient to avoid the pump body from "stalling" due to insufficient power.

2.Operating parameters: flow rate and head are the basis

The calculation of motor power should be based on the actual operating parameters of the chemical pump. The core parameters include flow rate (Q, unit: m³/h) and head (H, unit: m). Based on the principles of fluid mechanics, the formula for calculating the pump's effective power (Peffective) is: Peffective = (ρ × g × Q × H) / 3600, where ρ is the medium density (kg/m³) and g is the acceleration due to gravity (assuming 9.81 m/s²). For example, a chemical pump transports clean water (ρ=1000kg/m³), with a flow rate of 50m³/h and a head of 30m. Its effective power is: (1000×9.81×50×30)/3600≈4087.5W, which is about 4.09kW. It should be noted that the effective power is the theoretical power required by the pump to transport the medium. The motor power needs to be further calculated based on this, combined with the pump's efficiency and safety factor.

3.Pump efficiency: avoid "ineffective power" waste

The efficiency (η) of a chemical pump is a key indicator for measuring the ability of the pump to convert motor power into effective power. It is affected by factors such as the pump's structural design, manufacturing accuracy, and operating conditions. Typically, the efficiency of a centrifugal pump is between 60% and 85%, and the efficiency of a positive displacement pump is between 70% and 90%. The input power (Pinput) of the motor must satisfy the following equation: Pinput = Peffective/η. Still taking the above case as an example, if the pump efficiency is 75%, the theoretical power required by the motor is: 4.09kW/0.75≈5.45kW. If the pump efficiency is ignored and the motor is selected directly based on the effective power, the motor power will be insufficient and unable to meet actual operating requirements.

4.Safety factor: to cope with operating condition fluctuations and emergencies

In chemical production, operating condition fluctuations (such as instantaneous increase in flow rate, change in medium viscosity) or emergencies (such as pressure increase due to pipeline blockage) often occur, so a reasonable safety factor (K) must be reserved for the motor power. According to GB/T 5656-2013 "Centrifugal, mixed-flow, axial-flow and vortex pumps - Test methods", the selection of the safety factor needs to be combined with the pump's purpose and operating risk: for scenarios where conventional media are transported and operating conditions are stable, K is 1.1-1.2; for scenarios where flammable, explosive, highly corrosive media are transported or operating conditions fluctuate greatly, K is 1.2-1.5; for high-power pumps (power > 100kW), to avoid excessive waste, K can be appropriately reduced to 1.05-1.1. Taking the above case as an example, if the safety factor is 1.2, the final motor power should be: 5.45kW×1.2≈6.54kW. At this time, a motor with a standard power of 7.5kW should be selected (the motor power must comply with the national standard series, such as 0.75kW, 1.1kW, 1.5kW, 2.2kW, 3kW, 4kW, 5.5kW, 7.5kW, 11kW, etc.).

三、Practical steps and precautions for motor power selection

1.Practical steps: complete precise matching in four steps

The first step is to collect basic data: clarify the parameters of the chemical pump's conveying medium (density, viscosity, corrosiveness, solid content), design flow rate, design head, operating temperature and pressure;

The second step is to calculate the effective power: according to the medium density, flow rate and head, substitute the formula to calculate the effective power of the pump;

The third step is to correct the theoretical power: combine the pump efficiency and safety factor to calculate the theoretical power of the required motor;

The fourth step is to match the standard motor: According to the theoretical power, select the closest standard power motor to ensure that the motor power is not less than the theoretical calculated value and avoid excessive power.

2.Note: Avoid common misunderstandings

Avoid "empiricism": The efficiency of pumps from different manufacturers varies greatly. The efficiency curve or parameter table provided by the pump manufacturer should be used as the basis, rather than relying solely on empirical estimates;

Consider starting conditions: For high-power motors (>30kW) or load-start scenarios, verify whether the motor's starting torque meets the pump's starting requirements. If necessary, configure a soft starter or frequency converter.

Pay attention to environmental factors: If the chemical pump is installed in a high temperature (>40°C) or high altitude (>1000m) environment, the output power of the motor will decrease (high temperature leads to reduced insulation performance, and high altitude leads to poor heat dissipation). The motor power needs to be adjusted according to the environmental conditions. Generally, in high altitude areas, the motor power needs to be increased by 5%-8% for every 1000m increase in altitude.

The selection of chemical pump motor power is a systematic task that requires comprehensive consideration of four core factors: medium characteristics, operating parameters, pump efficiency and safety factor. It should follow the principle of "accurate calculation, reasonable correction and standard matching" to avoid problems of excessive or insufficient power. Scientific motor power selection can not only reduce the company's energy consumption costs and extend the service life of equipment, but also provide strong guarantees for the safe and stable operation of chemical production. In actual operation, it is recommended to combine the equipment manufacturer's technical parameters with on-site operating conditions, and consult with professional engineers when necessary to ensure the scientific and practical nature of motor power selection.