Today, I have compiled and compiled more and more complete 14 chemical industry chain maps, and they are in high definition! Hurry up, everyone!
Content Include:
1. Schematic diagram of chemical industry chain transmission
2. Petrochemical industry chain
3. Fine chemical industry chain
4. Industrial chain of chlor-alkali chemical recycling economy
5. Coal chemical industry chain
6. Industrial chain of natural gas chemical industry
7. Organic Silicon Industry Chain
8. Industry chain of fluoride industry
9. Industrial chain of phosphorus chemical industry
10. Methanol industry chain
11. Polypropylene PP industry chain
12. PTA industry chain
13. Salt Chemical Industry Chain
14. List of the four carbon industry chains
During the flow of the fluid, part of the mechanical energy will be lost due to the flow resistance. Therefore, according to the flow rate required for production, the fluid is sent from one place to another, whether it is to send the fluid from the low specific energy to the high specific energy, or only to overcome the flow resistance, it must provide mechanical energy to the fluid . The machinery used to transport liquids is called a pump. Pumps are mainly divided into three categories according to their structural characteristics and working principles:
ⅠVane pump: This type of pump works by telling the rotating impeller to work on the fluid, so that the mechanical energy of the liquid is increased, such as various centrifugal pumps, vortex pumps, axial flow pumps, etc.
Ⅱ Positive displacement (positive displacement) pump: This type of pump uses a reciprocating piston or a rotating rotor to change the volume of the working chamber, squeeze the liquid, and do work on the liquid to increase the mechanical energy of the liquid. Such as reciprocating pumps, gear pumps, screw pumps, etc.
Ⅲ Jet pump: It is the high-speed jet generated by the working fluid to inject fluid, and then through the momentum exchange to increase the energy of the injected fluid.
Due to its simple structure, easy manufacturing, stable flow, strong adaptability, and convenient operation, it is widely used in chemical production. Xiaoqi focuses on centrifugal pumps.
Working principle of centrifugal pump
When the centrifugal pump is working, relying on the impeller rotating at high speed, the liquid obtains energy under the action of inertial centrifugal force and improves the pressure energy. Before the centrifugal pump works, the pump body and inlet pipeline must be filled with liquid medium to prevent cavitation.
When the impeller rotates rapidly, the blades cause the medium to rotate quickly, and the rotating medium flew out of the impeller under the action of centrifugal force. After the water in the pump is thrown out, the central part of the impeller forms a vacuum area. While continuously sucking in the liquid, on the other hand, it continuously gives the sucked liquid a certain amount of energy to expel the liquid. The centrifugal pump works continuously.
Structure of centrifugal pump
There are many types of centrifugal pumps. Although the structures of various types of pumps are different, the main components are basically the same.
The main components of the centrifugal pump include: impeller, pump shaft, pump casing, pump seat, packing box (shaft sealing device), leakage reduction ring, bearing seat, etc.
⒈Impeller
The impeller is the working part of the centrifugal pump. It relies on its high-speed rotation to perform work on the liquid to realize the delivery of the liquid. It is an important part of the centrifugal pump.
The impeller is generally composed of three parts: wheel blade, blade and cover. The cover plate of the impeller is divided into a front cover plate and a rear cover plate. The cover plate on the side of the impeller port is called a front cover plate, and the cover plate on the other side is called a rear cover plate.
When the centrifugal pump is started, the pump shaft drives the impeller to perform high-speed rotational movement together, forcing the liquid pre-filled between the blades to rotate. Under the action of inertial centrifugal force, the liquid moves radially from the center of the impeller to the outer periphery.
The energy gained by the liquid flowing through the impeller increases the static pressure energy and the flow velocity. When the liquid leaves the impeller and enters the pump casing, the flow path in the casing gradually expands and decelerates, part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipe tangentially.
According to the structure, the impeller can be divided into the following three types.
(1) There are covers on both sides of the closed impeller. There are 4-6 blades between the covers. The closed impeller has high efficiency and is the most widely used. It is suitable for conveying clean liquids without solid particles and fibers.
⑵The open impeller has no cover plates on both sides of the blade. It is suitable for conveying liquids containing a large amount of suspended solids. The efficiency is low and the pressure of the conveyed liquid is not high.
⑶Half-open impeller This impeller has only a back cover plate, which is suitable for conveying liquids that are easy to settle or contain solid suspended matter. Its efficiency is between open and closed impellers.
⒉Pump shaft
The main function of the pump shaft of the centrifugal pump is to transmit power and support the impeller to maintain normal operation in the working position. One end is connected to the motor shaft through a coupling, the other end supports the impeller for rotational movement, and the shaft is equipped with bearings, axial seals and other components.
Common materials for pump shafts are carbon steel and stainless steel.
The impeller and the shaft are connected by a key. Because this connection method can only transmit torque and cannot fix the axial position of the impeller, a shaft sleeve and a lock nut are also used to fix the axial position of the impeller in the water pump.
After the impeller is axially positioned with the lock nut and the sleeve, in order to prevent the lock nut from retreating, it is necessary to prevent the pump from reversing, especially for the initial installation of the pump or the pump after disassembly and maintenance. Consistent.
⒊Shaft sleeve
The role of the shaft sleeve is to protect the pump shaft, so that the friction between the packing and the pump shaft is changed into the friction between the packing and the shaft sleeve, so the shaft sleeve is an easy-wear part of the centrifugal pump.
The surface of the sleeve can also be treated by carburizing, nitriding, chrome plating, spraying and other treatment methods. The roughness of the surface generally needs to reach Ra3.2μm-Ra0.8μm. It can reduce the friction coefficient and increase the service life.
⒋ Bearing
The bearing plays the role of supporting the weight and bearing capacity of the rotor. Rolling bearings are mostly used on centrifugal pumps. The outer ring and the bearing seat holes are made of base shafts, and the inner ring and rotating shaft are made of base holes. The recommended values are in accordance with the national standards and can be selected according to specific circumstances. Bearings are generally lubricated with grease and oil.
⒌ Packing box
When the pump shaft passes through the pump casing, there is a gap between the shaft and the casing. In the single-suction centrifugal pump, if no shaft seal device is used in this part, a large amount of high-pressure water in the pump casing will leak out. Packing box is a commonly used shaft sealing device. The packing box is composed of 5 parts: shaft seal sleeve, packing, water seal tube, water seal ring and packing gland.
⒍Snail case
The volute refers to a spiral flow path with a gradually increasing cross-sectional area between the impeller outlet to the next stage impeller inlet or to the pump outlet pipe. The flow channel gradually expands, and the outlet is a diffuse tube. After the liquid flows out of the impeller, its flow rate can be gently reduced, so that a large part of the kinetic energy is converted into static pressure energy.
The advantage of the volute is that it is easy to manufacture, the high efficiency area is wide, and the efficiency change of the pump after turning the impeller is small.
The disadvantage is that the shape of the volute is asymmetric. When a single volute is used, the pressure in the radial direction of the rotor is uneven, which is easy to bend the shaft. Therefore, in the multi-stage pump, only the volute is used in the first and tail sections, and the guide wheel is used in the middle section. Device.
The material of the volute is generally cast iron. The volute of the anti-corrosion pump is stainless steel or other anti-corrosion materials, such as plastic glass steel. Due to the high pressure of the multi-stage pump, the material strength is higher, and the volute is generally made of cast steel.
⒎Guide wheel
The guide wheel is a fixed disc with a positive guide vane wrapped around the outer edge of the impeller on the front. These guide vanes form a diffuse flow channel, and a reverse guide vane on the back guides the liquid to the population of the next impeller. . After the liquid is thrown from the impeller, it smoothly enters the guide wheel and continues to flow outward along the positive guide vane. The speed gradually decreases, and most of the kinetic energy is converted into static pressure energy.
The radial unilateral gap between the impeller and guide vane is about 1mm. If the gap is too large, the efficiency will decrease; if the gap is too small, it will cause vibration and noise. Compared with the volute casing, the pump casing of the segmented multistage centrifugal pump using guide wheels is easy to manufacture and the efficiency of energy conversion is also higher. However, installation and maintenance are more difficult than the volute.
⒏Seal ring
In order to reduce internal leakage and protect the pump casing, a removable seal ring is installed on the casing corresponding to the inlet of the impeller. The radial clearance between the inner hole of the seal ring and the outer circle of the impeller is generally between 0.1-0.2mm. After the seal ring wears, the radial gap increases, the pump discharge volume decreases, and the efficiency decreases. When the seal gap exceeds the specified value, it should be replaced in time.
There are three types of seal ring structure:
Flat ring type, simple structure, easy to manufacture, but poor sealing effect;
Right-angle sealing ring, through a 90 ° channel when the liquid leaks, the sealing effect is better than the flat ring type, and it is widely used;
The labyrinth seal ring has good sealing effect, but the structure is complicated and the manufacturing is difficult. Generally, it is rarely used in centrifugal pumps.
The working process of centrifugal pump
⒈Before starting the pump, fill the pump with liquid to be transported.
⒉After starting the pump, the pump shaft drives the impeller to rotate together at high speed to generate centrifugal force. Under this action, the liquid is thrown from the center of the impeller to the outer periphery of the impeller, the pressure increases, and flows into the pump casing at a very high speed (15-25 m/s).
⒊In the volute pump casing, due to the continuous expansion of the flow channel, the flow rate of the liquid slows down, so that most of the kinetic energy is converted into pressure energy. Finally, the liquid flows into the discharge pipe from the discharge port with a higher static pressure.
⒋After the liquid in the pump is thrown out, a vacuum is formed in the center of the impeller. Under the pressure difference between the liquid surface pressure (atmospheric pressure) and the pressure in the pump (negative pressure), the liquid enters the pump through the suction line and fills up. The location of the liquid being excluded.
Classification of centrifugal pumps
Centrifugal pump products are generally divided according to their structural characteristics, and there are multiple division methods, including six classification methods according to working pressure, according to the number of working impellers, and according to the impeller water inlet method.
⒈According to working pressure:
Low-pressure pump: pressure below 100 meters of water column;
Medium pressure pump: the pressure is between 100-650 meters of water column;
High-pressure pump: pressure is higher than 650 meters of water column.
⒉According to the number of working impellers:
Single-stage pump: there is only one impeller on the pump shaft.
Multi-stage pump.: There are two or more impellers on the pump shaft. At this time, the total head of the pump is the sum of the heads generated by n impellers.
⒊According to the impeller water inlet method:
Single-side water inlet pump: also called single suction pump, that is, there is only one water inlet on the impeller.
Double-side water inlet pump: also called double suction pump, that is, there is a water inlet on both sides of the impeller. Its flow rate is double that of a single-suction pump, and it can be roughly regarded as two single-suction pump impellers placed back to back together.
⒋According to the position of the pump shaft:
Horizontal pump: The pump shaft is in a horizontal position.
Vertical pump: The pump shaft is in a vertical position.
⒌According to the joint seam form of the pump casing:
Horizontal split-open pump: there is a joint seam on the horizontal plane passing through the axis line.
Vertical joint surface pump: the joint surface is perpendicular to the axis.
⒍According to the way the water from the impeller leads to the pressure chamber:
Spiral casing pump: After the water comes out of the impeller, it directly enters the spiral casing.
Guide vane pump: After water comes out of the impeller, it enters the guide vane outside it, and then enters the next stage or flows into the outlet pipe.
⒎According to the conveying medium, it is divided into different types according to the medium conveyed by the centrifugal pump: clean water pump, oil pump, corrosion-resistant pump, etc.
Cavitation and air binding
Cavitation
According to the working principle of the centrifugal pump, when the liquid between the blades is thrown out of the impeller rotating at high speed, a low-pressure area is formed near the inlet of the impeller. When the pressure at the inlet of the impeller is equal to or lower than the saturated vapor pressure pV of the liquid being transported at the operating temperature, the liquid at that location will vaporize to generate bubbles. When the bubbles flow to the high-pressure area with the liquid, the bubbles quickly condense due to the pressure.
When the bubbles condense, a partial vacuum will be generated, and the surrounding liquid rushes to the space originally occupied by the bubbles at a high speed, causing shock and vibration, and generating a great impact force. Especially when the condensation point of the bubble is near the surface of the blade, many liquid particles impact the blade at a very high frequency and pressure; at the same time, a small amount of oxygen, etc. may also be entrained in the bubble to chemically corrode the metal material. Under the combined effect of continuous impact and chemical corrosion of the blade, the surface is damaged and there are marks and cracks, which will cause premature blade damage. This phenomenon is called the cavitation of the centrifugal pump.
Air binding
When the centrifugal pump starts, if there is air in the pump, due to the small air density and the small centrifugal force generated after rotation, the low pressure formed in the central area of the impeller is not enough to suck liquid, so even if the centrifugal pump is started, the delivery task cannot be completed. This phenomenon is called air binding.
This means that the centrifugal pump has no self-priming ability, so the centrifugal pump must be filled with the delivered liquid before starting. Of course, if the suction port of the centrifugal pump is placed below the level of the liquid being transported, the liquid will automatically flow into the pump, which is a special case. The suction line of the centrifugal pump is equipped with a bottom valve to prevent the liquid injected before starting from flowing out of the pump. The filter screen can block the solids in the liquid from inhaling and block the pipeline and the regulating valve installed in the discharge line of the pump casing is for opening. Used when pumping, stopping pumps and adjusting flow.
From the different causes of cavitation and air binding:
Air binding is the presence of air in the pump body, which generally occurs when the pump is started, mainly because the air in the pump body is not exhausted; and cavitation is due to the liquid reaching its vaporization pressure at a certain temperature, visible and conveying medium, work The situation is closely related.
There are the following methods to prevent the occurrence of air binding phenomenon:
⒈Fill the shell with liquid before starting. Do a good job in the sealing of the shell, the water filling valve and the shower head can not leak, and the sealing is better.
⒉The suction line of the centrifugal pump is equipped with a bottom valve to prevent the liquid filled before starting from flowing inside the pump. The filter screen prevents solids in the liquid from being sucked in. The discharge line is equipped with a regulating valve for starting and stopping the pump and adjusting the flow rate.
⒊Put the suction port of the centrifugal pump under the liquid surface to be transported, and the liquid will automatically flow into the pump.
Causes and solutions of cavitation
The main causes of cavitation are:
1. The resistance of the inlet pipeline is too large or the pipeline is too thin
2. The temperature of the conveying medium is too high;
3. The flow rate is too large, which means that the outlet valve is too open;
4. The installation height is too high, which affects the pump's liquid absorption;
5. Type selection issues, including pump selection, pump material selection, etc.
Solution:
1. Clean the foreign material in the inlet pipeline to make the inlet smooth, or increase the size of the pipe diameter;
2. Reduce the temperature of the conveying medium;
3. Reduce the installation height;
4. Reselect the pump, or improve some parts of the pump, such as the use of cavitation-resistant materials.
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