A Common Misconception
“It’s hard to flare liquid propane in a tank that has been water injected.”
By: Ron Huffman, 06/05/2021 Updated 04/22/2023
Whether you’re conducting a training evolution or on an actual incident, if the propane tank has water in it, you’ll need to remove the water prior to liquid flaring operations. If you don’t, you’ll most likely freeze your system up and not be able to flare the tank.
Just like freon, ammonia and a few other products, as propane passes through a restriction to a lower pressure area it gets colder. That restriction or orifice can be the opening in the tank, a seated excess flow valve, the valve in your flaring system, or any other restriction. As the liquid propane continues towards the tip of your flare and atmospheric pressure, it loses more of its pressure the farther it gets away from the tank. As the propane liquid flows through the hose it’s getting colder, it’s auto-refrigerating. An easy way to identify where this begins is to look at your system and see where frost starts forming.
In areas with low humidity, the use of a Thermal Imaging Camera (TIC) or infrared thermometer can help identify the point where auto-refrigeration starts. It’s not recommended to use a bare hand due to the potential of extreme cold (propane’s boiling point is -44F).
If waters been injected and you need to flare liquid propane:
As propane and water sit in the tank, both maintain the same temperature. But when you open a valve and allow the two to flow together, the propane will start to auto-refrigerate causing the water to freeze. When this happens, your system will lock up and need to be thawed before you can continue. But there’s an easy remedy, you must remove the water prior to flaring operations. During our water injection training program, we must remove the water that was just pumped in prior to the next evolution. We’ve done this for years at every class, time after time with no freeze ups. If you do it correctly, you’ll never freeze a line or your flare.
So, then the question is how do we do it correctly?
The first issue is managing where the water starts to freeze. It’s really quite easy, first maintain full tank pressure to the release point. Next, have nothing beyond the release point that can trap the water and create ice blocking the flow, I recommend the use of a ball valve. As long as you can maintain tank pressure, you can bleed the water at the most distant end of your hose, even next to your flare. If the tip freezes up thaw it with your hand line. Then, utilize the handline to disperse any propane vapors prior to igniting your flare.
Clearing Water From a Propane Tank Prior to Flaring Operations
Step by Step
- Slowly release/vent the water in the tank to the atmosphere.
- When propane liquid starts to escape with the water stop the release of water. Allow the water to gather and open the valve slowly again. When propane liquid starts mixing with the water again, close the valve, allow the water to gather and open the valve slowly. Continue this process until all the water has been removed and just propane liquid is released when the valve is opened.
- Open the valve fully and verify that all the water has been removed. There will still be moisture in the system, but if done correctly there will not be enough water to freeze the system closed.
- If you suspect that you may still have water in the system, install a valve at the base of your flare and close it enough to maintain tank (or back) pressure up to the flare. That way if you do have a freeze up it will be easy to identify and hopefully remedy.
Once all the water has been vented to the atmosphere it will be safe to connect your flare and begin your liquid flaring operation. As I stated above, it’s quite easy. But if you do lock up your system just thaw everything and start again.
And feel free to call me if you have any questions.
Ron Huffman,
Owner/Senior Instructor,
Responder Training Enterprises, LLC.
(765) 524-4848
