How to choose a pump?

You should thoroughly study the relevant content on principles of chemical engineering.

http://bbs.hcbbs.com/viewthread.php?tid=144892&page=1#pid629247 There is a pump selection manual posted on page 3; you can go and take a look

Choosing a pump seems to require both experience and calculations

Our approach here is that the process engineers provide the relevant parameters of the pump (such as pressure, medium temperature, flow rate, NPSH, etc.), while the equipment specialists are responsible for selecting the appropriate pump. I suggest you take some time to study the textbook on principles of chemical engineering. The parameters provided by the process are also based on process calculations.

Selected based on medium conditions, flow rate, and head

Principles of Chemical Engineering – there’s a lot to read, haha

The most basic ones are flow rate and head. Then there is the cavitation problem. Another consideration is motor explosion protection, sealing types, and the requirements in standards and regulations that mandate the use of shielded pumps or magnetic drive pumps. The operating temperature ranges for different pumps, etc. Move deeper step by step.

Several factors to consider when selecting a pump include the pump type, flow rate, head, NPSH, shut-off pressure, and material. The type of pump is determined by the properties of the material; centrifugal pumps are suitable for applications requiring high flow rates and low viscosity. Gear pumps are suitable for applications with low viscosity. The head is primarily determined by the operating pressure difference between the target container and the source container, the height difference, and the frictional losses. I suggest you take a close look at the principles of chemical engineering, as it explains in detail how to calculate friction losses. How to calculate the head of a pump. NPSH is related to the stability of pump operation. It must be calculated based on the pipeline conditions and the saturated vapor pressure of the material at the operating pressure. The pump’s NPSHR must be less than the pipeline’s NPSHA. The material is related to the corrosivity and hazard of the substance. For substances that generally pose a high level of hazard, it is recommended to use magnetic drive pumps. These are some of my personal insights; I welcome any feedback.

Thank you all. I have really benefited a lot. By the way, I have a question: for the 9th floor, the NPSHR of the pump can be found in the pump’s performance table, but how is NPSHA for the piping calculated? Thank you.

Selection of pumps for the chemical industry (centrifugal pumps, screw pumps, positive displacement pumps, vacuum pumps): When choosing a pump, it is necessary to take into account the characteristics of different types of pumps. Pumps are classified into two main categories based on the principle by which they act on liquids: vane pumps and positive displacement pumps. Vane pumps draw in or discharge liquid through the centrifugal force generated by the rotating vanes inside the pump. Positive displacement pumps draw in or force out liquid by means of the compressive action generated by the reciprocating or rotating motion of the pump’s piston or rotor. Vane pumps are classified into centrifugal pumps, axial flow pumps, and vortex pumps based on the structure of the vanes inside the pump. Positive displacement pumps are further divided into piston (plunger) pumps and rotary pumps. 1 Centrifugal pumps: The viscosity of the liquid at the delivery temperature should not exceed 650 mm2/S; otherwise, the pump’s efficiency decreases significantly. (When the viscosity is greater than 650 mm2/S, the performance of centrifugal pumps declines significantly, and such pumps are generally not used. However, since centrifugal pumps deliver fluid without pulsations, do not require safety valves, and allow for easy flow regulation, they are often employed in chemical production to transport liquids with a viscosity of up to 1000 mm2/S.) The flow rate is high while the head is relatively low. The amount of gas dissolved or entrained in the liquid should not exceed 5% (by volume). When the liquid contains solid particles, special centrifugal pumps (such as slurry pumps) are recommended. When a large variation in flow rate with little change in head is required, centrifugal pumps with a flat flow-rate–head curve are suitable; whereas when a small variation in flow rate with a large change in head is needed, centrifugal pumps with a steep flow-rate–head curve are appropriate. 2 Positive-displacement pumps: When the viscosity of the liquid at the transfer temperature is greater than 650 mm2/S, and the flow rate is low while the head is relatively high, reciprocating pumps are suitable. Gases dissolved in or entrained in the liquid allow a concentration of slightly more than 5% (by volume). When accurate measurement of the liquid is required, a plunger metering pump can be used; when absolute leakage prevention is necessary, a diaphragm metering pump is suitable. Gear pumps and triple-screw pumps should not be used for liquids with poor lubricity properties, as reciprocating pumps can be an alternative. For applications with low flow rates, low temperatures, and stable pressure requirements, rotary pumps or twin-screw pumps are suitable choices. Based on the flow rate and head required by the system, the selection of pump is initially determined according to the classification and application range of pumps. Since centrifugal pumps have a simple structure, deliver fluid without pulsation, and allow for easy flow rate adjustment, they should be used whenever possible, except in situations where they are not suitable. Once the pump model has been selected, the pump series and material can be chosen based on the parameters of the process unit and the properties of the medium. Then, the specific model (specifications) of the pump is determined based on the samples and relevant technical documents provided by the pump manufacturer. For the transfer of special media, when a pump is used to transport gas-containing liquids, its flow rate, head, and efficiency all decrease. The higher the air content, the faster the efficiency declines. As the gas content increases, the pump generates additional noise and vibration; in severe cases, this can lead to increased corrosion or even flow interruption and shaft failure. To ensure the reliable operation of the pump, measures can be taken to reduce the gas content in the liquid: Type, Applicable viscosity range (mm2/s): Blade pump, Centrifugal pump – <150; Vortex pump – <37.5. Positive displacement pumps: Reciprocating pump – <850; Metering pump – <800; Rotary piston pump – 200–10,000; Single-screw pump – 10–560,000; Twin-screw pump – 0.6–100,000; Triple-screw pump – 21–600. Gear pump – <2,200. The design of the suction tank and the arrangement of the pump’s suction pipe should ensure that all pumps connected in parallel can draw in liquid in equal amounts. The suction port of the pump should have a certain depth of submersion within the suction tank, as well as a certain height above the bottom of the tank. The inlet pipe, return pipe, and waste liquid collection pipe of the liquid absorption tank should be kept away from the pump’s suction port, to prevent bubbles from being drawn into the pump before they have dissipated. At the same time, the suction tube should not be placed in the center of the tank, nor too close to the tank walls; it should generally be more than 1 unit away from the tank walls. 5D, to avoid creating vortices or vacuum. Ensure that the pipe joints are properly sealed to prevent air from leaking in. When arranging the inhalation tubing, areas where air pockets may form should be avoided. When transporting a liquid containing solid particles, the solid particles suspended in the liquid cannot absorb, store, or transfer energy like the liquid does, nor can they transfer kinetic energy to the liquid. The presence of solid particles results in lower pump head and efficiency compared to transporting clean water. When transporting volatile liquids, the main considerations are the impact of the properties of these liquids on the pump: 1. High pressure at the pump inlet; 2. The vaporization pressure changes significantly with temperature. The shaft seals of the 3 pairs of pumps require strict standards, as well as the impact of the pump’s suction pressure on the vaporization of the material. For transporting liquids that must not leak, sealless pumps (magnetic drive pumps and shielded pumps) or mechanically sealed pumps equipped with leakage collection and alarm devices should be used. Comparison between magnetically driven pumps and shielded pumps:
Item | Magnetically Driven Pump | Shielded Pump
--- | --- | ---
Thickness of isolation sleeve (or shield) | 3 times that of the shielded pump’s isolation sleeve |
Consequences of failure of the isolation sleeve (or shield) | Fluid leaks into the atmosphere | A second leak prevention layer (motor casing) prevents fluid leakage, but it can damage the motor stator
Efficiency | Slightly lower | Slightly higher
Remote operation | Not available currently | Possible; requires specific manufacturing techniques and equipment
Requirements | Lower | Higher
Driver | Standard motor or turbine | Specialized motor
Noise | Slightly higher (motor with fan) | Slightly lower (motor without fan)
Axial length | Longer | Shorter
Coupling | Coupling is present; alignment is required | No coupling
Bearing wear monitor | Still in experimental stage | Available
Price | Relatively high | Basically similar
Routine maintenance | Easy | Difficult
Application range (power in KW/temperature in °C/pressure in MPA) | Good performance | Good performance
Suitable for: Normal pressure, room temperature, clean fluids that do not vaporize easily | Generally not suitable |
Special models available | Fluids containing solid particles | Generally not suitable; especially not suitable for fluids containing iron particles. Special models exist for such fluids (external cleaning fluid required)
High-melting-point, crystalline fluids | Generally not suitable | Special models available
Highly corrosive fluids | Good performance | Not suitable (due to limitations of the shielding sleeve)
For transporting corrosive fluids, corrosion-resistant pumps should be used. These pumps have corrosion-resistant materials in their flow-through parts, while other non-corrosion-resistant components, such as brackets, need to be protected from corrosion. The clearance of the sealing ring (flange ring) is larger than that of the water pump, to prevent operation at low flow rates and thus avoid increased corrosion due to rising liquid temperature. When stopping the pump, the suction valve should be closed promptly, or a shutdown seal should be used to prevent the medium from leaking out of the pump. For commonly used metal pumps, the materials used for their flow-through components include ordinary cast iron, high-silicon cast iron, stainless steel, high-alloy steel, titanium and its alloys, etc. Different materials can be selected depending on the properties of the medium and the temperature range. High-alloy steels, titanium, and their alloys are expensive, and their use should generally be avoided unless it is absolutely necessary. Metal pumps generally have better temperature resistance, pressure resistance, and operational stability than non-metallic pumps. Materials for the flow-through components of non-metallic pumps include: polyvinyl chloride, fiberglass-reinforced plastic, polypropylene, F46, fluoropolymer alloys, PVDF, ultra-high molecular weight polyethylene, graphite, ceramics, and glass-lined materials. The material should also be selected based on the properties of the medium and the temperature range. Generally, non-metals have lower temperature and pressure resistance compared to metals. Therefore, it is commonly used in applications with low flow rates, as well as those with low temperatures and operating pressures. Selection of vacuum pumps: Vacuum pumps are devices used to achieve a vacuum level below atmospheric pressure. They are typically classified based on the degree of vacuum or the pumping speed, which determines the type of pump. They can generally be divided into vane type, positive displacement type (piston type, screw type), and water ring type. There are several indicators that can reflect the performance of a vacuum pump: A. Vacuum level: expressed in terms of absolute pressure P, with units of Kpa, Torr, and mmHg (1 atmosphere = 101.325 Kpa = 1 Torr = 760 mmHg = 1.01325 bar). B. Pumping speed: refers to the volume of gas drawn into the vacuum pump’s inlet per unit of time (i.e., the volumetric flow rate under normal temperature and pressure conditions). Per cubic unit: cubic meters per hour, liters per second. The pumping speed of a vacuum pump is related to the suction pressure; the higher the suction pressure, the greater the pumping speed. C. Ultimate vacuum: refers to the lowest stable pressure value that can be achieved by the vacuum pump during pumping, also known as the maximum degree of vacuum. D. Selection of various pumps: Mechanical pumps and piston pumps are suitable only for applications with low vacuum levels and little water vapor present; for example, W-type reciprocating vacuum pumps. Vane pumps are used in situations where a large volume of gas needs to be evacuated, and an auxiliary pump is necessary in such cases. Rotary vane vacuum pumps have a relatively low pumping speed. Molecular pumps are suitable for applications requiring high precision. Water ring pumps are appropriate for applications with low vacuum levels, such as those involving the removal of water vapor. Jet pumps, specifically water jet pumps, use water under pressure of 0.2–0.3 MPa as a driving force; they are suitable for removing water vapor and condensable gases. They function by utilizing the principle of conversion between static pressure energy and dynamic pressure energy during fluid flow. Steam jet pumps can handle various gases, and different numbers of stages can be selected according to specific requirements. Oil diffusion pumps are suitable for high vacuum levels, while molecular centrifugal pumps are also appropriate for high vacuum conditions

What was said on the 12th floor is extremely comprehensive; I’ve learned a lot from it

Agree with the view from floor 12: victory:

NPSHa = S + P – Pv – h, where S is the static head (or static suction height); if there is a static head, its value is positive, while the suction height has a negative value. P represents the absolute pressure (or atmospheric pressure) at the liquid surface in the container on the pump’s suction side. Pv is the absolute vapor pressure of the liquid at the temperature of transfer. h denotes the friction losses associated with the fittings and valves on the inlet side. All of these values are expressed in terms of liquid column height in meters. Then the calculation will be simple and easy to understand.