1 Types of liquid seals
Common types of liquid seal sets are as follows:
1.0.1 Liquid seal tank type liquid seal set
This type of liquid seal set uses the liquid level of the liquid seal tank to maintain a certain pressure in the equipment system through the tube inserted, thereby preventing air from entering the system or medium from leaking out. In order to prevent the seal liquid from flowing backward into the system, inert gas is also used to inflate the system through the liquid seal to keep the pressure in the system constant, as shown in Figures 2.0.2-1~2. Inert gas can be automatically charged into the system through the pressure regulating system. Usually, seal liquids are water or other liquids not reacting with the materials chemically. This type of liquid seal is widely used in venting systems of atmospheric and micro pressure distillation columns and storage tanks.
1.0.2 U-shaped tube type liquid seal set
U-shaped tube type liquid seal set relies on the liquid seal height of the U-shaped tube, which is filled with liquid, to prevent the material in the equipment system from discharging without bringing out gases, and maintain a certain pressure in the system.
The liquid seal medium is usually the material/liquid in the system itself. This type of liquid seal set has many applications, as shown in Figures 2.0.2-3~4.
1.0.3 II-shaped tube type liquid seal set
This type of liquid seal set mainly uses the height of the II-shaped tube to maintain a certain liquid level height in the equipment and prevent the liquid discharged without bringing out gases, which is realized by the liquid seal height of the II-shaped tube. The height of the II-shaped tube shall be determined according to the liquid level required by the process, as shown in Figures 2.0.2-9~10. This type is usually used in situations where a certain liquid level needs to be controlled in equipment, such as emulsion column.
1.0.4 Automatic drainer type liquid seal set
This type is usually used in the drainage occasions of gas-liquid separation systems with high pressure, for example, compressor gas storage tanks, separation tanks, etc. discharging condensed liquid automatically. It makes use of the buoyancy principle that floating ball in the fluid will rise and fall with the change of liquid level due to its buoyancy, and opens and closes the nozzle hole at the same time to realize automatic liquid discharge and block gas leakage, as shown in Figure 2.0.2-8. This type of liquid seal sets are widely used for the intercoolers, gas-liquid separators and gas storage tanks of various compressors to discharge the condensed liquid inside.
2 Setting of liquid seals
2.0.1 Cases requiring liquid seals
2.0.1.1 Where equipment stores flammable liquids or combustible liquids with a flash point lower than or equal to the ambient temperature of the site; for example, the drain or exhaust pipe of the storage tank shall be provided with liquid seal.
2.0.1.2 Where, for system equipment, the entering of air may form explosive mixed gas with the materials or the entering of wet air may affect the product quality in normal production or an accident as well as during shutdown overhaul and hot work with the materials in the system not completely discharged.
2.0.1.3 Where equipment needs to discharge liquid continuously or intermittently and prevent the gas in the system from being brought out or leaking, for which, a liquid seal set shall be set at the liquid outlet.
2.0.1.4 Where equipment needs to maintain a certain liquid level, for which, a liquid seal tube shall be set at the liquid outlet.
2.0.1.5 Other cases that liquid seal shall be set as required by the process.
2.0.2 Examples of liquid seal setting
2.0.2.1 Offgas venting system of columns
For atmospheric and micro-pressure distillation columns, if moisture in the air is not allowed to be brought into due to the materials in the system, or explosive mixed gas may be formed by the materials and the air, the venting system needs to be provided with a liquid seal set, as shown in Figures 2.0.2-1~2. In order to prevent the sudden decrease of nitrogen pressure, which may lead to the seal liquid flowing into the system, the upper part of the liquid seal tube shall maintain a certain height and pipe diameter/volume.
1 Types of liquid seals
2 Setting of liquid seals
3 Precautions for liquid seal setting
4 Determination of liquid seal height
