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Compressed natural gas fuel tank defueling, decommissioning, and disposal

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  • Compressed natural gas fuel tank defueling, decommissioning, and disposal

    This Clean Cities Video is great for those of you who may have to deal with draining, or disposing of decommissioned CNG tanks.

    https://www.youtube.com/watch?featur...&v=vTxQPfsm8n0
    [ATTACH=CONFIG]temp_4586_1441434431016_578[/ATTACH]

  • #2
    i recently changed out a tank - installed new tank and hooked everything up and went to fill tank. the tank will not take much fuel. it only takes about 50 cents worth at a time. the most i got it to take was $1.25. it is an older gfi system on a 1994 ford bronco. i installed a 3600 psi tank and fill valve. it seems to be getting gas to the tank as i hear the hissing in the tank. the line at the tank gets very cold and ices up a little. the pump pressure will read about 4500 then drop quickly as i fill. i tried 2 different stations and both had the same result. do i need to purge the tank of air? is there some sort of shut off on the system??. i cleaned the old tank and drilled holes in it to dispose of it properly. but i am stuck with no gas.....

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    • #3
      Originally posted by furdog55 View Post
      i recently changed out a tank - installed new tank and hooked everything up and went to fill tank. the tank will not take much fuel. it only takes about 50 cents worth at a time. the most i got it to take was $1.25. it is an older gfi system on a 1994 ford bronco. i installed a 3600 psi tank and fill valve. it seems to be getting gas to the tank as i hear the hissing in the tank. the line at the tank gets very cold and ices up a little. the pump pressure will read about 4500 then drop quickly as i fill. i tried 2 different stations and both had the same result. do i need to purge the tank of air? is there some sort of shut off on the system??. i cleaned the old tank and drilled holes in it to dispose of it properly. but i am stuck with no gas.....

      You have a major restriction in the line. Was the system operational before the tank change ?

      Info on the new tank ? size, date ? Pictures. This stuff is not complicated, but errors in installation and service can be very dangerous due to the pressures. Be sure of what you are doing. Mistakes can cost you your life.

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      • #4
        the new tank is a lincoln tufftank it is 48x16. the system was not used for some time as the tank expired in 09. but i hear gas getting into the tank i hear a hissing in the tank so it must be getting there. also the line at the tank valve is getting white with the cold so i must be getting gas to the tank. just stops for no apperant reason. ever heard of this ?? system was 3000 psi but i was told by gfi that it could be converted to 3600 with a tank and fill valve. which is what i did

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        • #5
          The cold at the one point is the symptom of a restriction. Sim to how a refrigeration or AC system works, high pressure gas or liquid forced thru a small opening will cause freezing. Natural gas has a lot of moisture in it, even after drying to a standard acceptable for CNG. Its building an ice plug inside. Something is partially blocked. Who did you buy this tank and valve from ? was it new, or used / surplus. Don't even think of trying to remove it from the tank yourself, now that an unknown amount of gas is in it. Get some prof. help on this.

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          • #6
            used tank but the valve is from my old tank. (used of course) is there a need to pull a vacume on the tank? do i need to purge it? could my system be set up for only a slow fill and not a fast fill??

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            • #7
              Take it to a qualified shop. Used cylinders are generally acceptable if it has a current 3 year inspection cert, but re-using valves is a dicey thing. One more thing, the pressure relief device within the valve must be replaced if the valve is put on another cylinder. The relief device must be sized and compatible with the cylinder , not just with the valve. Some are not replaceable, so the valve must be discarded in that case. Also, most shops are venting with method that renders the valve un- usable at end of tank service date. Did you ever have the old tank in use ? or did you buy the vehicle without the CNG system working ?

              AGAIN, this is not a do it yourself thing. people have been killed working on valves, thinking the cylinder was empty.
              Last edited by Lakewood90712; 10-10-2016, 02:41 PM.

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              • #8
                Agreed with Lakewood. You are experiencing a pressure drop in the line feeding the tank which causes the icing. Note that this will "improve" if you keep squirting little bursts of CNG in the tank as the internal tank pressure gets higher and closer to the pressure from the dispenser. But I don't recommend you put any more gas in there... it only creates more safety risk to the person who eventually has to fix your high-pressure side problems.

                Please click on the link above all pages here "Find Certified CNG Tank Inspectors" and locate an expert near you to get this resolved.

                A few other notes:
                1. Upgrading an old 3000 psi system to 3600 psi is more than simply changing out the tank and fill connector. You also need to take into account other high-pressure components which are rated for the lower pressure, especially the pressure regulator and high-pressure filter housing. And, importantly for your situation, the tank valve must also be rated for 3600 psi. By re-using the old valve you have introduced risk of valve fatigue at pressures it was not designed to handle. Which is another reason to not fill this system to capacity. The valve has had a long life of holding pressures up to 3600 psi (this is what a 3000 psi system might see in warm ambient temperatures), and now it could be subjected to 4500 psi (the pressures a 3600 psi fill will provide in hot ambient temps).

                2. Air in the cylinder prior to installing the valve and having its first fill will have no impact on cylinder capacity. Whatever was in there at 14 psi (or 1 bar atmosphere) will be compressed to 3600 psi (or 250 bar atmospheres) anyway. It becomes 1/250th of the gas in the cylinder and is negligible. Generally, cylinder manufacturers place inert nitrogen in there and install the valve at the factory.

                I should also say kudos to you for doing the right thing in rendering the old tank unusable.

                My other question is if gas is getting OUT of the tank? Does the vehicle run on CNG?

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                • #9
                  truck ran for about one minute when i first got it and then was out of gas. i do not believe it was run on cng much as the hour meter is only 15 hours. not much in 20 years.
                  i talked to a tech at gfi and he told me that i just needed fill valve and tank for the upgrade. i guess a valve was understood with the tank.but the system is 20 years old so it might be bad info.
                  then to top it all off , i got this truck to run on cng and find that my local cng pump has shut down. i have been driving 60 miles each way to the closest fill station to test this thing out.
                  i did learn that it was set up for a slow fill station, the fill nozzle was for a forklift, golf cart according to the manufacture. there is no cng company here in el paso texas that i can find. so i have been relying on internet and phone calls for help

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                  • #10
                    Furdog55,
                    Where did you buy the "new" tank from? Did it have pressure in it when you bought it? Lincoln Composite Type 4 cylinders have a plastic bladder inside the carbon fiber tank, inside the sacrificial fiberglass outer cover . If the cylinder had no pressure in it when you got it, odds are good that the bladder collapsed and the cylinder is unusable and dangerous with pressure in it. I have run into too many "junkyard" cylinders in the Southwest that are not safe for reuse because of this problem. I have a collection.
                    I regularly get that size cylinder and have to drain the pressure and the compressor oil out of them. Lately, sometimes as much as a gallon of condensate.I then inspect them inside(borescope)and out before re-pressurizing them for storage and use.
                    Please find an experienced CNG professional in your area or PM me. I do service and cylinder replacement/upfits on vehicles from Dallas/Fort Worth to Southern California due to the lack of qualified technicians.

                    Your Friendly Nazi Squirrel Administrator

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                    • #11
                      Clean Cities University is offering free courses in Alternative Fuels. Your regional chapter can get you set up with a login and password, or use this forum to private message me with your email for access:

                      Compressed Natural Gas Fuel Tank Defueling, Decommissioning, and Disposal Course Description

                      This course covers the steps involved in compressed natural gas (CNG) fuel tank defueling, decommissioning, and disposal. Note that the course is composed of four modules, each consisting of a video page and a quick quiz related to that video. The entire course takes about 25 minutes to complete.
                      .

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                      • #12
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