32 basic knowledge of chemical process pump

1. Function: chemical pump is a machine for conveying liquid and increasing its pressure

2. Special requirements for pumps in chemical production:

(1) meet the requirements of chemical process

(2) high temperature and low temperature resistance

(3) corrosion resistance

(4) wear resistance

(5) no or little leakage

(6) liquid capable of conveying a critical state

(7) reliable operation

3. Classification of pumps:

(1) according to working principle and structure: volumetric pump

(this kind of pump is divided into reciprocating pump and rotary pump), vane pump (this kind of pump can be divided into centrifugal pump, mixed flow pump, axial flow pump and vortex pump according to the structure of impeller), other types of pumps

(2) it can be divided into process pumps, utility pumps, auxiliary pumps, pipeline pumps, etc

4. Working principle of chemical centrifugal pump: before starting chemical centrifugal pump, the pump and suction pipeline should be filled with liquid. This process is called irrigation pump.

After starting the motor, the motor drives the impeller through the pump shaft and the impeller drives the liquid to rotate together. Under the action of centrifugal force, the liquid in the impeller is thrown to the impeller outlet along the impeller passage and flows through the volute to the discharge pipe.

When the liquid in the impeller is thrown towards the outlet of the impeller, a low pressure is formed at the center of the impeller inlet, and the pressure difference is generated between the liquid in the suction tank and the liquid in the center of the impeller. Under this pressure difference, the liquid in the suction tank continuously enters the impeller through the suction pipeline and the suction chamber.

In this way, the impeller in the process of rotation, while continuously inhaling the liquid, and continuously give the inhaled liquid a certain amount of energy, to discharge the liquid.

The centrifugal pump works in this way.

The centrifugal pump in the operation process, often occurs the "gas binding" phenomenon, that is, the pump into the air, so that the pump can not work properly the bottom valve is a check valve, before starting this valve closed

5. Classification of centrifugal pumps:

(1) classification by impeller suction: single suction type, double suction type

(2) classification by series: single-stage centrifugal pump, multi-stage centrifugal pump

(3) classification by lift: low pressure centrifugal pump, medium pressure centrifugal pump, high pressure centrifugal pump

6. The rotor refers to the rotating part of the centrifugal pump, which includes impeller, pump shaft, shaft sleeve, bearing and other parts

7. The impeller is the work part of the centrifugal pump, which can realize the liquid transport by rotating at high speed

8. According to the structure form, the impeller can be divided into: closed impeller, open impeller and semi-open impeller

9. When the blade curve direction is opposite to the rotation direction of the impeller, it is called the backward curved blade and vice versa (the backward curved blade has higher efficiency).

10. The main function of the pump shaft of the centrifugal pump is to transfer power, and the supporting impeller keeps normal operation at the working position

11. Common shaft seal devices include packing seal and mechanical seal

12. Packing seal is to press the packing through the packing gland to deform the packing and contact the outer circular surface of the shaft to prevent the liquid from flowing out and air from entering the pump.

The tightness of the packing seal can be controlled by adjusting the tightness of the packing gland.

A reasonable degree of tightness should allow the liquid to drip out of the stuffing box, about 15 to 20 drops per minute.

Low pressure centrifugal pump when temperature is less than 40 ℃, commonly used graphite packing or butter penetrate cotton packing;

Transfer temperature less than 250 ℃, pressure is less than 1, 8 mpa fluid, drenched in graphite asbestos packing;

Transfer temperature less than 400 ℃, and allow oil pressure is 2.5 MPa products, asbestos panels packing with metal foil bag

13. Mechanical seal structure and working principle:

The sealing device, which relies on the static ring and the end face of the moving ring to fit each other and rotate relative to each other, is called mechanical seal or end face seal.

14. The main performance parameters of the centrifugal pump include flow, head, speed, power, efficiency, allowable suction vacuum and allowable cavitation margin

15. The amount of liquid output by the pump in unit time is called flow rate

16. The energy obtained by the liquid per unit weight through the pump is called the head or pressure head of the centrifugal pump

17. The rotating speed of centrifugal pump impeller per minute is called the rotating speed, that is, the rotating speed of centrifugal pump refers to the rotating speed of pump shaft per minute

18. Power refers to the work done by the pump to the output liquid in unit time, which is called effective power

The ratio of the effective power to the shaft power transmitted by the prime engine to the pump spindle in unit time is called the pump power

19. The power of the motor selected by the manufacturer is 1.1~1.2 times of that of the shaft due to the possibility of overload during the start or operation of the pump

20. The relationship between the performance parameters of the centrifugal pump can be expressed by curve on the coordinate chart.

The curve showing the relationship between the main performance parameters of the centrifugal pump is called the performance curve of the centrifugal pump. The performance curve of the centrifugal pump is divided into flow lift curve, flow power curve and flow efficiency curve

21. The q-h curve refers to the flow lift curve, indicating the relationship between the flow rate of the centrifugal pump and the lift.

When the flow is zero, the head is a fixed value. As the flow increases, the head usually decreases

22. Q-n curve refers to flow power curve. With the increase of flow Q, the shaft power N gradually rises.

When the flow is zero, the shaft power is minimum and the outlet valve of the centrifugal pump is closed. At this time, the flow Q is zero and the starting power is minimum, which can prevent the motor from burning out due to overload

23. Q-- curve refers to flow power curve.

From the perspective of energy saving, people always want the pump to work at the highest efficiency point, but it is unrealistic in actual production. Usually, the pump should work in the area with the highest efficiency at least 90%

24. Adjustment of centrifugal pump:

1. Change the flow regulation of pipeline characteristic curve

(1) outlet pipeline throttling regulation

(2) bypass adjustment

2. Change the flow regulation of the performance curve of the centrifugal pump

(1) change the working speed of the pump

(2) cutting the outside diameter of the impeller

25. Energy saving of centrifugal pump:

(1) choose the appropriate type of pump to make the centrifugal pump work in the high efficiency area

(2) reduce pipeline resistance and reduce the required head of the pipeline

(3) improve the structure of the impeller and the work capacity of the impeller

(4) reduce the diameter or speed of the impeller

The reciprocating pump is a kind of positive displacement pump.

Features of reciprocating pump: non-uniform flow, discharge pressure can be unlimited high, flow and discharge pressure independent capacity

Diaphragm pump is a special form of volume pump.

It relies on the back-and-forth encouragement of a diaphragm to alter the volume of the chamber to inhale and expel the liquid

28. The gear pump has the ability of self-absorption, and the flow rate is independent of the discharge pressure

29. The screw pump is a volumetric rotor pump that USES one or several snacking rods to transfer liquid.

Features: the conveying medium moves along the axial direction, the liquid flow is continuous and uniform, the pulse is small, the flow rate varies little with the pressure, the operation is stable than gear pump, five vibration and noise, high efficiency, with self-absorption capacity, long life, etc.

However, the processing technology is complex, and the manufacturing cost is high. It is suitable for transporting oils with lubricating ability and free of solid impurities (such as lubricating oil, fuel oil, etc.) and liquids with high viscosity (such as banana fluid, chemical fiber adhesive liquid, etc.).

A machine that sucks gas out of a device so that the pressure inside the device is less than one atmosphere is called a vacuum pump

Classification of vacuum pumps: mechanical vacuum pumps, jet vacuum pumps and physical and chemical vacuum pumps are divided according to their working principles

31. The magnetic driving pump, like the shield pump with the same non-shaft seal structure, only has the precision seal without moving seal on the structure, which can ensure that a drop is not leaking when delivering the liquid

32, communicate magnetic application in centrifugal pump with magnetic transmission principle, all is the use of magnet can attract the ferromagnetic material in between the body and the magnetic field has the characteristics of the magnetic effect, rather than a ferromagnetic material does not affect or rarely affect the size of the magnetic force, so can not contact through the magnetic conductors for power transmission, the transmission device called a magnetic coupling.