Pump selection and modeling calculation introduction

It is a fluid machine that uses external energy to transport liquid or liquid-solid two-phase flow. It is often used in air pollution control projects. Such as wet desulfurization project, wet dust removal project, gas-water heat exchanger cooling water circulation.

1. Classification of pumps

There are many types of pumps, such as centrifugal pumps, reciprocating pumps, rotary pumps, and jet pumps. Centrifugal pumps are mainly used in air pollution control projects. Commonly used are: clean water pump, oil pump, mud pump, sand pump, corrosion-resistant pump (acid, lye pump).

2. Performance parameters of the centrifugal pump

Flow: The volume of suction or #turbine liquid per unit time is generally proposed by the process.

Head: The energy added value of the liquid per unit volume from the inlet to the outlet of the pump. Generally expressed in m liquid column. Head calculation is an important basis for pump selection and is determined by the laying, installation and operating conditions of the pipe network system. Calculate process sketches, planes, and vertical layouts before calculation to calculate

Pipe length, pipe diameter and pipe type and quantity, and finally calculate system resistance.

3. Pump selection method and steps

1 List the basic data

a. Physical properties of the medium: the name of the medium, the specific gravity under the conveying conditions, viscosity, corrosion, and the like.

b. The medium contains the particle size and content of the solid particles.

c. Operating conditions: temperature; pressure (inlet side equipment pressure, discharge side equipment pressure, discharge side piping pressure drop); flow (normal, minimum and maximum).

d. Location of the pump: ambient temperature; altitude; pipeline level and facade requirements; inlet and discharge side equipment level to pump center distance and pipeline equivalent length.

2 determine the flow and head

a. Flow rate: When selecting the pump, it should be considered according to the maximum flow rate; if only the normal flow rate is given, the safety factor of 1.1 should be adopted according to the specific conditions of the device and the process. The above refers to the volume flow.

b. Head (or differential pressure): According to the arrangement of the pump, the head of the pump is obtained by Bernoulli's equation.

3Select the pump type and the specific model of the pump

Select the appropriate type of pump based on the characteristics of the media, the determined flow rate, the lift, and the selection criteria and the operating range of the pump. Select the specific model of the pump from the pump manufacturer's samples and instructions, and list the model and performance parameters based on clean water (flow, head or differential pressure, efficiency, critical vacuum height or critical cavitation margin) ).

4 accounting pump performance

The performance of the pump is calculated according to the actual situation. List the performance parameters after accounting, if the process requirements are met, the selected pump is available. If necessary, the calculated performance curve and piping system performance curve can be plotted to determine the operating point of the pump.

5 determine the geometric installation height of the pump

6 Calculate the shaft power of the pump

7 selected pump material and shaft seal

8 determine the cooling water (or heating steam) consumption

9 select motor

10 determine the pump backup rate and number of units

4. Parallel and series connection of centrifugal pumps

1 parallel

In the project, when the flow demand has a large change, that is, it is required to reduce or increase the flow rate within a certain period of time; or when one pump cannot meet the flow requirement, two pumps or multiple pumps can be used in parallel. When the pumps are operated in parallel, the flow rate is smaller than the sum of the flow rates when the pumps are operated separately, and the steeper the pipeline resistance curve (ie, the greater the pipeline resistance), the more the flow rate is reduced during parallel operation.

2 series

In the project, when a single pump is used, the flow can be satisfied, and the lift can not meet the predetermined requirements or the original equipment can not be used. When it is required to be used in a system with a higher lift, two or more pumps can be used. Connect in series to achieve the desired head. However, it is necessary to pay attention to whether the pump body strength can be met after each pump is connected in series to ensure safety.

In order to give full play to the efficiency of a single pump, it is advisable to use pumps of the same specification regardless of series or parallel operation.

5. Installation and operation of centrifugal pump

The pump has certain requirements in terms of installation and operation.