Some standard content:
Setting of liquid seal
HG/T 20570.17-95
Preparing unit: The Sixth Design Institute of Ministry of Chemical Industry
Approving department: Ministry of Chemical Industry
Implementation date: September 1, 1996 Preparer:
Li Xiqiao, The Sixth Design Institute of Ministry of Chemical Industry
Reviewer:
Yin Zhaorong, Wu Zhennan, The Sixth Design Institute of Ministry of Chemical Industry, Feng Shuyuan, Gong Renwei, Process System Design Technology Center Station of Ministry of Chemical Industry
1 Types of liquid seals
The following are the common types of liquid seal devices: 1.0.1 Liquid seal tank type liquid seal device
This type of liquid seal device uses the liquid level height of the liquid seal tank to maintain a certain pressure in the equipment system through an insertion tube, thereby preventing air from entering the system or the medium from leaking. In order to prevent the liquid seal liquid from flowing back into the system, an inert gas is also used to inflate the system through the liquid seal to keep the pressure in the system constant, as shown in Figure 2.0.2-1~2. Inert gas can be automatically inflated into the system through the pressure regulating system. The liquid seal liquid usually uses water or other liquids that do not react chemically with the material. This type of liquid seal is widely used in the venting system of normal and micro-pressure distillation towers and storage tanks. 1.0.2 U-shaped tube type liquid seal device
The U-shaped tube type liquid seal device uses the U-shaped tube filled with liquid, and relies on the liquid seal height of the U-shaped tube to prevent the material in the equipment system from being discharged without bringing out gas, and maintain a certain pressure in the system. The liquid seal medium is usually the material liquid of the system itself. This type of liquid seal device has many applications, as shown in Figure 2.0.2-3~4.
1.0.3Ⅱ-tube type liquid seal device
This type of liquid seal device mainly maintains a certain liquid level in the equipment through the height of the Ⅱ-tube, and prevents the gas from being carried out with the discharged liquid. It relies on the height of the Ⅱ-tube liquid seal to achieve this. The height of the Ⅱ-tube should be determined according to the liquid level required by the process, as shown in Figure 2.0.2-9~10. This type is mostly used in occasions where a certain liquid level needs to be controlled in the equipment, such as emulsification towers, etc.
1.0.4 Automatic drainer type liquid seal device
This type is mostly used in the discharge of gas-liquid separation systems with high system pressure, such as automatic discharge of condensate from compressor gas storage tanks and separation tanks. It uses the buoyancy principle of the float in the fluid to sink and float with the change of liquid level, and at the same time opens and closes the nozzle hole to achieve automatic discharge and block gas leakage, as shown in Figure 2.0.2-8. This type of device is widely used in the discharge of condensate in various compressor intercoolers, gas-liquid separators, and gas storage tanks. 467
2.0.1 Occasions where liquid seals are required
Liquid seals are required
2.0.1.1 Equipment for storing flammable liquids or flammable liquids with a flash point lower than or equal to the ambient temperature of the site, such as installing liquid seals at the drain or exhaust pipes of storage tanks. 2.0.1.2 System equipment where air may enter the system to form an explosive mixed gas with the materials during normal production or accidents, or where wet air may enter the system to affect product quality.
2.0.1.3 Liquid discharge ports of equipment where liquids need to be discharged continuously or intermittently and the gas in the system is not carried out or leaked with the liquid.
2.0.1.4 Equipment where a certain liquid level needs to be maintained, with a liquid seal pipe added to the liquid outlet. 2.0.1.5 Other occasions where liquid seals are required due to process requirements. 2.0.2 Example of liquid seal setting
2.0.2.1 Venting system of tail gas of tower
For normal and micro-pressure distillation towers, if the materials in the system do not allow water in the air to enter, or if the materials and air can form an explosive mixed gas, a liquid seal device must be set up in the venting system, as shown in Figure 2.0.2-1-2. In order to prevent the nitrogen pressure from suddenly decreasing and causing the sealing liquid to flow back into the system, the upper part of the liquid seal pipe should maintain a certain height and pipe diameter capacity. Nitrogen
Condenser
Liquid seal tank
Liquid seal tank
Figure 2.0.2-1
Schematic diagram of tower tail gas venting system (I) Tower
Condenser
Liquid seal tank
Figure 2.0.2-2
Schematic diagram of tower tail gas venting system (II) 2.0.2.2 Condenser drain pipe
In order to improve the condensation efficiency and prevent the gas from being discharged with the condensate, a U-shaped tube liquid seal device is generally provided on the condenser drain pipe, and the condensate is discharged to the middle tank through the U-shaped tube, as shown in Figure 2.0.2-3. Venting
Condenser
Figure 2.0.2-3 Condenser drainage liquid seal pipe
2.0.2.3 Tower bottom drainage pipe, tower top reflux pipe The bottom material discharge or tower top reflux of the distillation tower, absorption tower, and washing tower operated at normal pressure usually adopts gravity discharge by position difference. In order to prevent the gas in the tower from being carried out with the liquid discharge, a U-shaped pipe or liquid seal tank type liquid seal device is generally used, as shown in Figure 2:0.2-4-5. When the tower top reflux is natural reflux, its liquid seal height should be considered, as shown in Figure 2.0.2-6.
Balance pipe
Tower bottom drainage liquid seal pipe
Liquid seal tank
Condenser
Figure 2.0.2-6 Tower top reflux liquid seal pipe
2.0.2.4 Gas-liquid separation tank drainage pipe
Tower bottom drainage liquid seal tank
In order to improve the separation efficiency or prevent liquid from pouring into the compressor inlet, it is necessary to drain the separated condensed liquid in time to maintain a certain gas-liquid separation space; at the same time, to prevent gas leakage, a U-shaped tube liquid seal device should generally be set. If the pressure in the separation tank is high and the height of the U-shaped tube liquid seal is too large, it is more appropriate to use an automatic drain as a liquid seal device. See Figures 2.0.2-7~8. 470
Gas (Liquids)
Figure 2.0.2-7
Gas (Liquids)bzxZ.net
High-pressure tank
Separation tank liquid seal pipe
High-pressure tank (automatic wave remover)
Figure 2.0.28
2.0.2.5 Emulsification tower, reaction sign drain pipe
Automatic drainer liquid seal
According to the process requirements, it is necessary to maintain a certain liquid level in the equipment, and do not let the gas leak out during discharge. Usually, a II-shaped pipe liquid seal device should be installed on the discharge pipe. See Figures 2.0.29-10, where the letter NC indicates that the valve is closed under normal conditions.
Balance pipe
Emulsification tower
Emulsification tower II-shaped pipe drain
Figure 2.0.2-9
Reaction sign| |tt||Figure 2.0.2—10
Reactor II-shaped pipe drainage
2.0.2.6 Hydrogen vent pipe and airbag chlorine (or oxygen) feed pipe system Hydrogen is a flammable and explosive gas. It is easy to form explosive gas after mixing with air. In order to prevent air from entering the system and ensure safe production, a liquid seal should be installed in the hydrogen vent pipe system, as shown in Figure 2.0.2-11. The airbag storing nitrogen (or oxygen) generally has a small internal pressure resistance. In order to protect the airbag, the nitrogen (or oxygen) feed pipe system should usually be equipped with a liquid seal device, as shown in Figure 2.0.212. 472
Figure 2.0.2-11
Liquid seal tank
Liquid seal tank
Gas vent pipe liquid seal tank
Figure 2.0.2—12
2.0.2.7 Flame Inlet and outlet of fuel gas tank
Gasbag feed liquid seal
In order to maintain a certain pressure in the equipment system and ensure safe production, water seals should be set at the inlet and outlet of fuel gas tank, as shown in Figure 2.0.2-13.
Gas inlet
Water seal groove
Water seal groove
Figure 2.0.2-13
Gas tank inlet and outlet water seal
2.0.2.8 Prevent the mixing of liquids from the two systems
Gas outlet
When the tower (absorption tower) is fed with gas, in order to prevent the liquid in the tower from backwashing to the separation tank (or buffer tank) due to the pressure difference fluctuation of the previous system, the gas feed pipe should be equipped with a II-shaped pipe, and the II-shaped pipe should have sufficient height, usually its height should be 1m~2m higher than the dynamic liquid level in the tower, as shown in Figure 2.0.2-14. Gas||tt| |Finance Business Wall
Figure 2.0.2-14 Gas feed II-shaped pipe to prevent the mixing of liquids from two systems 2.0.2.9
Preventing liquid from entering the compressor
The separation tank set in front of the compressor inlet pipe may have fluctuations in liquid and pressure difference. In order to prevent the liquid in the separation tank from being sucked into the compressor under this condition, a II-shaped pipe should be installed in the pipeline from the separation tank outlet to the compressor inlet. Its height is determined according to the possible pressure difference fluctuation. Generally, its height is more than 2m, as shown in Figure 2.0.2-15. Gas
Gas (liquid)
Separation tank
Compressor
Figure 2.0.2-15 II-shaped pipe to prevent liquid from entering the compressor 2.0.2.10
When using a steam jet pump to evacuate, a liquid seal should be installed to remove the condensate, as shown in Figure 2.0.2-16. Yanqi
Vacuum system
Cooling water
Figure 2.0.216
Steam jet pump
Water seal drainage
Schematic diagram of water seal for steam jet pump
3 Precautions for setting liquid seal
3.0.1 When using II-shaped pipe as liquid seal, 1 to 2 bypass pipes can be set on the upper part of II-shaped pipe and valves can be added to facilitate liquid level adjustment.
3.0.2 When U-shaped pipe and IIII-shaped pipe are used as liquid seal, in order to prevent gas accumulation at the top of the pipe and affect liquid discharge, a vent valve should be set at the highest point or a balance pipe connected to the system should be set. 3.0.3 In order to drain the liquid in the pipe when stopping, a drain valve should be set at the lowest point of the U-shaped pipe. When it is necessary to observe the flow of liquid in the pipe, a sight glass can be set on one side of the discharge pipe. 3.0.4 The inlet and outlet of U-shaped tubes and II-shaped tubes are mainly self-flowing by position difference. The diameter of the tube is calculated according to the self-flow velocity, generally 0.1~0.3m/s, and the minimum diameter should not be less than 20mm. 3.0.5 When the U-shaped tube is used as a liquid seal, the liquid seal height is less than 3m and is widely used. When the pressure in the system is high and the liquid seal height is required to be greater than 3m, an automatic drainer or control valve should be used. The amount of liquid discharged by the control valve is adjusted according to the required liquid level in the container.
3.0.6 When the liquid seal medium is likely to freeze in winter, antifreeze measures should be taken, such as adding insulation, steam coil heating or adding antifreeze.
3.0.7 II-shaped tube liquid seals are mostly used in normal pressure or micro-pressure occasions where the medium is dissolved in the liquid seal liquid. The height is generally 10m (1 atmosphere), such as the ammonia inlet pipe in the preparation of ammonia water. 3.0.8 When the liquid seal fluid is lost due to liquid entrainment or leakage, measures should be taken in the engineering design to maintain the liquid seal height.
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