I will briefly explain how to select a flame arrestor.
Flame arresters are essential for storing and using large amounts of hazardous materials in chemical plants under stable conditions.
It is a safety device that is also regulated by the Fire Service Act.
It is better to have the basic knowledge to use it more safely than just purchasing regular equipment on a regular basis and installing it in a fixed form.
What is a flame arrestor?
A flame arrestor is a flashback prevention device .
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From a design point of view, it can be simply called a net .
Gas can pass through the fine mesh, but flame cannot.
A flame arrester is a device that uses this principle to minimize damage in the event of a fire or explosion.
With this kind of feeling, it will be installed on the gas line connecting the tank containing the dangerous goods and the atmosphere.
- Even if a flame occurs inside the tank, it does not flow outside.
- Prevents flames generated outside from entering the tank
In terms of flame, it acts as an isolation valve between the tank and the outside.
Role of flame arrestor
You might think that the role of a flame arrestor is simply to prevent a flashback, but batch-type chemical plants end up using it with an unexpected function.
I expect this kind of function from a flame arrester.
- Flashback prevention
- Mist collection
- Prevention of powder scattering
As long as it’s a net, it’s possible that it should have the function of collecting mist and preventing scattering of powder, but it should be considered as a comfort.
If the emission of mist or powder into the atmosphere is not a problem, flame arresters can be expected.
How to select a flame arrestor
The method of selecting a flame arrestor is fairly simple.
It is good to say that once the piping is decided, it will be decided automatically.
Material
The material of the flame arrestor should be matched to the piping material or one rank up.
- Piping material is SUS304 or SUS316L → Flame arrestor material is SUS304 or SUS316L
- Pipe material is glass lining → Flame arrestor material is equivalent to Hastelloy C
You can use it with this feeling.
Selecting a Hastelloy material as a flame arrester requires considerable thought.
Some companies may have the idea of replacing SUS316L flame arresters because they are expensive .
caliber
The design of the caliber is also easy.
It is OK if it matches the pipe diameter of the gas line.
The diameter of the gas line is basically determined by the diameter of the incoming pipe to the tank and the outgoing pipe from the tank .
You don’t have to think about it because you just need to select a flame arrester that matches the gas line pipe diameter.
Actually, it seems that there are elements that cannot be selected with this alone, but at least this understanding is enough for batch chemical plants, at least from the user’s point of view.
Inspection of flame arrestor
The flame arrestor must be inspected.
It seems unlikely that flame arrestor inspections will decrease even at chemical plants that are reducing the risk of on-site work.
As with strainer inspection, this is a high-risk task.
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Check the flame arrestor during operation.
In the case of a batch run, you would check when the batch is finished and no process fluid is present .
Since the inside of the tank is not completely cleaned, the flame arrestor will be opened with some of the hazardous materials remaining.
This is dangerous, isn’t it?
Choking
Even if the process liquid is stopped, nitrogen is still flowing in the system.
Otherwise air will be entrained in the process.
Nitrogen leaks outside when the flame arrestor is opened.
When removing the flame arrestor, if you bring your face in front of the flame arrestor, you may inhale nitrogen .
This means that when you remove the flame arrestor, you have to hold your breath and remove the net while turning your face in another direction.
Dangerous goods spill
In addition to the suffocation potential, workers may be exposed to hazards .
This is because the organic solvent leaks into the atmosphere along with the nitrogen.
Acids and alkalis may leak out.
It would be nice to open it with appropriate protective equipment, but I think there are many cases where this is not the case.
electrostatic ignition
If the nitrogen leaks out and the organic solvent leaks out when the container is opened, there is a risk of electrostatic ignition .
The risk of electrostatic ignition is low in a nitrogen-filled space, but the risk increases the moment it leaks into the atmosphere.
Opening the lid, removing the net, attaching the net, and attaching the lid are all dangerous.
The state without a flame arrestor, which is a shutoff valve, is still uneasy.
bypass? valve?
If the inspection work of the flame arrestor is dangerous, the idea of installing a bypass will come up.
But the difficulty with flame arresters is that they can’t do that properly.
In order to attach a bypass, you must attach a valve, but basically a valve cannot be attached to the gas line .
This is because if the valve is closed by mistake, the tank may fall under the first class pressure vessel .
In order to maintain a safe atmospheric pressure in the tank, the gas line is vented to the atmosphere.
On the other hand, if a valve is not installed, there is a high risk of leakage during inspection work.
This is the difficult part.
Mist separation and powder scattering prevention
I wrote that the flame arrester has a certain role to separate mist and prevent scattering of powder.
However, you should avoid relying on this feature.
This is because inspecting the flame arrestor itself is dangerous .
- Mist is generated → Mist is removed with a demister, heat exchanger, cyclone, etc.
- Powder scatters → Increase the pipe diameter, remove powder with a cyclone, etc.
If this is not done, mist or powder will easily adhere to the flame arrestor and cause clogging .
This increases the frequency of inspection work and increases the risk.
reference
A flame arrestor is a dangerous goods tank.
The following books are very useful for understanding the knowledge about the dangerous goods manufacturing site.
Related article
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lastly
I explained the role of flame arresters in chemical plants.
It is basically a flashback prevention device, but it also has the role of preventing mist and powder from scattering. Overconfidence is prohibited.
You can match the material and diameter with the piping, so let’s design the piping first and decide the flame arrester later.
Particular attention should be paid to the installation location.
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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