HG/T 20570.16-1995 Air seal setting HG/T20570.16-1995 standard download decompression password: www.bzxz.net

Setting of gas seal
HG/T20570.16—95
Compiled by: China Chengda Chemical Engineering Company Approved by: Ministry of Chemical Industry
Implementation date: September 1, 1996 Prepared by:
China Chengda Chemical Engineering Company
Reviewed by:
Zeng Qingxiang
Li Zhenyao of China Chengda Chemical Engineering Company
Feng Shuyuan, Process System Design Technology Center of Ministry of Chemical Industry
Gong Renwei
1.0.1 Function
1 Function and composition of gas seal device
1.0.1.1 In order to prevent the materials in the storage tank from being contaminated and deteriorated due to contact with the external gas (air) or chemical and (or) biological reactions with the external gas (air), it is often necessary to set up a gas seal system. The gas seal gas is used to maintain a certain pressure (positive pressure) in the storage tank to prevent the materials in the storage tank from contacting with the external gas. 1.0.1.2 When the material stored in the tank is pumped out and (or) the gas in the tank condenses or shrinks due to the decrease in external temperature, the system automatically replenishes the gas sealing gas to prevent the outside gas from entering. When the material is fed into the tank and (or) the liquid in the tank is gasified due to the increase in external temperature and the pressure in the tank is higher than the gas sealing pressure, the gas in the tank can be automatically discharged into the atmosphere through the pressure relief valve.
1.0.1.3 Commonly used gas sealing gases include nitrogen, fuel gas, natural gas, etc. The choice of gas sealing gas should be determined according to the nature of the stored material, whether the gas sealing gas is easy to obtain and its economy. 1.0.2 Composition of gas sealing device
The gas sealing device is shown in Figure 1.0.2-1. It consists of four parts: gas sealing valve (also known as main valve), signal valve (also known as control valve), pressure reducing valve and needle valve. Gas sealing gas
Figure 1.0.2-1
Schematic diagram of the composition of the gas sealing device
When the pressure in the storage tank is lower than the set value, the signal valve 2 opens and the gas sealing valve 1 also opens accordingly. The high-pressure gas sealing gas enters the storage tank after being reduced in pressure by the gas sealing valve 1, so that the pressure in the storage tank gradually returns to the set value. When the set value is reached, the signal valve 2 is closed and the gas sealing valve 1 is also closed accordingly. If the pressure in the storage tank is higher than the set value, the pressure relief valve (breathing valve) 5 with a flame arrester on the storage tank opens to release the gas inside and reduce the pressure in the storage tank to the set value. 1.0.2.2 In order to prevent the failure of the pressure relief valve and (or) the gas sealing device and the occurrence of overpressure or negative pressure in the storage tank, a system combining liquid sealing and gas sealing devices can be used. The schematic diagram of its composition is shown in Figure 1.0.2-2. Gas sealing
Liquid sealing liquid
Figure 1.0.2--2 Schematic diagram of the combined system of liquid seal and gas seal device The role of the gas seal device equipped with liquid seal is:
(1) When the pressure relief valve fails, the liquid seal can play the role of exhaling gas. That is, when the pressure in the tank exceeds the set value, the gas in the tank can be depressurized through the liquid seal. (2) When the gas seal device fails, such as when the pressure in the tank is higher than the set value, the pressure can be released through the liquid seal to reduce the load of the pressure relief valve.
(3) When the pressure relief valve and the gas seal device fail at the same time and negative pressure appears in the tank, air can be sucked in through the liquid seal to protect the tank from deformation and damage.
2.0.1 Calculation of air supply volume
2 Calculation of air sealing devicebzxz.net
2.0.1.1 The air supply volume of the tank air sealing device should be greater than or equal to the sum of the amount of supplementary air required for the pump to extract the liquid stored in the tank and the amount of supplementary air required for the condensation and contraction of the gas in the tank caused by the change in external temperature.
(1) The amount of supplementary air required for the pump to extract the liquid stored in the tank is equal to the maximum output capacity of the pump. (2) The amount of gas that needs to be replenished due to condensation and contraction of gas in the storage tank caused by temperature changes is specified in the American Petroleum Institute Standard 2000 "Venting of Atmospheric and Low-Pressure Storage Tanks": For storage tanks with a volume ≥3180m2, this amount of gas is related to the surface area of ​​the tank shell and tank top. For every square meter of tank shell and tank top surface area, 0.6m2 of gas sealing gas needs to be replenished per hour. For storage tanks with a volume <3180m2, 0.178m2 of gas sealing gas needs to be replenished per cubic meter of volume per hour. The above amount of gas can allow the temperature of the gas in the tank to change by 37.8℃ per hour, and it is relatively safe. Table 2.0.1 lists the gas supply required for common storage tanks due to changes in external temperature. Table of required gas volume for gas sealing device of tank under temperature change Tank volume
Tank volume
Tank volume
Note: When the tank volume is inconsistent with that listed in the table, the required gas volume can be calculated by interpolation. The gas volume in the table is standard cubic meters per hour. (3)
Add the required gas volumes of (1) and (2) to get the required gas volume for the gas sealing device. 2.0.2 Calculation of gas sealing valve selection
Different gas sealing valve manufacturers have different recommended calculation formulas. According to the calculation formula and size coefficient provided by the selected product manufacturer, the gas volume and valve selection calculations are carried out according to the required working conditions. 463
2.0.3 For atmospheric pressure tanks with breathing valves, in order to prevent air from entering, the gas sealing pressure value can generally be taken as 0.0005~～0.001MPa water column (table). This is an empirical value. 464
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