We often use Seal pot as a safety device in chemical plants.
The structure and functions are simple and reliable.
Besides sealing hazardous material tanks, the principle of water sealing can be used for many purposes.
We use several possible patterns for the structure of the seal pot, and you may be surprised at what should be a simple facility.
If you read this article, you will understand the basics of water seals and will be able to apply them.
Seal pot for maintaining internal pressure
The purpose of the seal pot is to maintain the internal pressure of the tank within very small range.
As shown in the figure below, we often use for the purpose of sealing atmospheric pressure tanks.
It is very dangerous to open the gas line to the atmosphere without using seal pot.
For example, when a tank becomes pressurized, the gas inside the tank leaks into the atmosphere.
When the tank becomes negative pressure, the atmosphere (air) leaks into the tank.
If gas leaks, it will cause damage to the global environment and the human body.
Flare stacks and scrubbers can be considered if the only mechanism is to prevent gas from leaking, but seal pots have the advantage of being inexpensive.
If air gets into the tank, for example, if it is Class 4 hazardous materials, a fire or explosion can cause a serious accident.
To prevent this situation, use seal pot.
Structure of Seal pot
Introduce the structure of the seal pot.
Simply put, dipped pipe and container.
Create two lines: a line that dips inside the container from the canopy, and a line that removes only the nozzle from the top plate.
Connect this line to the tank and the atmosphere, fill it with liquid, and seal pot is complete.
By connecting the gas line and air port of the tank to seal pot, it is possible to use both the pressurized type and the negative pressure type.
For example, the left side of the above figure is a pressure type, and the right side is a negative pressure type.
Dangerous goods tanks require a structure that can be sealed under both pressurization and negative pressure, so it is necessary to create two upper seal pots and connect them.
With a little ingenuity, the following confluence type can also be considered.
Seal pot material
The material used is generally stainless steel.
It is good to use SUS304 and SUS316L properly according to the material of the tank side.
When using high-grade metal materials for the tank, it is better to use PTFE lining or resin lining.
In this case, it is better to think that the above confluence type cannot be created.
Seals and linings are quite troublesome.
If you try to realize it, the number of flanges will increase, and the risk of leakage will increase.
Be careful with stainless steel if it contains even a very small amount of acid or salt.
By the time I realized it, it was in tatters. . . It can also happen.
Seal pot performance changes depending on the type of liquid
A seal pot is a liquid sealing device.
The type of liquid is also a consideration.
Generally, we use cheap water.
In areas where water may freeze in winter, an antifreeze such as liquid paraffin should be used.
If the seal liquid is water, it is ideal to run it constantly.
The water in the seal pot absorbs the gas and changes its properties.
If this is stored in the seal pot for a long time, for example, the gas absorption properties will deteriorate or become clogged.
For this reason, a constant amount of water is constantly drained to keep the properties of the sealing water constant.
The depth of the seal can be designed by appropriately determining the height of the drainage pipe to create the liquid height and by determining the dip height.
In the case of liquid paraffin, this is difficult, so you will have to replace it periodically.
For that reason, we set a valve for draining liquid on the bottom.
Dimensions Determine Seal Pot Capabilities
I will explain the dimensions of the seal pot.
The key indicator is capacity.
It will be used properly depending on the type of gas to be sealed.
For example, once the seal liquid is put into the seal pot, the amount of liquid that needs to be delayed for one day until the gas can no longer be absorbed is determined.
In practice, however, it is often determined by the performance of each company.
The height is determined in relation to the seal height.
The seal height must be lower than the design pressure of the tank.
If the sealable pressure is too high, the tank will explode.
Diameter is determined as a secondary factor of volume → height.
Strictly speaking, it is related to the diameter and dip depth of the tank’s gas line and atmosphere release line, but I don’t think there is much to be aware of.
Various designs in a hazardous materials manufacturing plant are very important for mechanical and electrical engineers.
The following books are very helpful for dangerous goods tanks.
I explained the structure and design considerations of seal pots in chemical plants.
This is an internal pressure maintenance device to maintain a slight pressurization/negative pressure in a hazardous material tank.
There are many structures in which two dip-type tanks are arranged side by side so that they can be used for both pressurization and negative pressure, and water is constantly flowing.
Stainless steel is the common material.
Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (Comments are at the bottom of this article.)
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