Announcement

Collapse
No announcement yet.

LNG What is the difference????

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • LNG What is the difference????

    What is the difference on a LNG vehicle. Okay, I know that LNG is "liquefied natural gas" and that NG is a liquid if cold enough, but what are the differences on a LNG vehicle. I was down in orange county and saw numerous buses that has a LNG sticker on it. The tanks on the roof also appeared to be much smaller. Anyone know? Surely the natural gases on the buses isn't in liquid form. I also see that there are two LNG stations planned for Utah.
    Last edited by dbd; 10-26-2009, 09:22 PM.

  • #2
    Re: LNG What is the difference????

    Methane, unlike Propane (for example) will not turn into a liquid under pressure at reasonable temperatures. Therefore, to get enough volume of fuel to be usable in a vehicle, it must be compressed to high pressure. In large vehicles, even under high pressure there isn't enough room to store the required amount of fuel. An alternative is to cool the Methane until it turns into a liquid. It vaporizes as the temperature rises somewhat like Propane. As a liquid, a greater amount of energy can be stored in a given volume then can be stored as a gas at any reasonable pressure. At least this is as I see it . Time for the experts to report in on this one.

    Comment


    • #3
      Re: LNG What is the difference????

      You're off to a good start. The nicest thing about LNG is that it is almost pure methane. Just about all of the impurities and odorants drop out during the liquification process; -260 deg F (darn cold). Nitrogen (-320), Hydrogen, and heilum will still be in a gaseous form.

      LNG systems are usually liquid draw (like LP) and have to go through a vaporizor so you won't get any of the other inmpurity gases, hence almost a pure product. You will also get better drivability because of the consistant quality and purity of the product. You will also get maximum octane, 130. The other gases that drop out would lower the octane of the fuel

      Being a cryogenic liquid (anything below -100 deg F) LNG requires special handling and storage. Storage is a big thermos bottle called a Dewar, usually double walled stainless with a vacuum between the two containers along with some insulating material. Handling; full coverage with a face shield. NO short sleves, shorts, sandles, etc. This stuff will give you a nasty burn and a single drop will put out an eye.

      Depending on the ambient temperature a Dewar will hold pressure for a couple of days if the vehicle is parked. Pressure in Dewar is around 150 psi and it will vent at about 225 psi.

      When LNG boils off it can get up to around 4,000 psi. That is why some transit properities use LNG that is run through a heat exchanger to fuel their CNG buses -- no compressors to deal with. On the down side LNG is odorless and therefore a vehicle needs a gas detection system to warn of leaks.

      So much for the short version.


      Larrycng

      Comment


      • #4
        Re: LNG What is the difference????

        I would like to clear up a few things here:
        -LNG is produced by refrigerating pipeline natural gas. This can be a tricky process and requires a fairly complex process plant though there are many efforts under way to simplify the process and reduce the production costs.
        -LNG is odorless, colorless and non toxic
        -1 cubic foot of LNG = 600 cubic feet of gas at atmospheric pressure and 70 deg F. This high energy density is why LNG is the preferred alternative fuel for heavy vehicles such as buses and class 8 rigs.
        -LNG has the same basic properties as methane gas (flammable only between 5-15% mixture with air). LNG liquid will not burn or explode, only the off gassing or vapors mixed with air (or oxygen) will burn.
        -LNG is perishable, as it warms the storage pressure vessel builds pressure and eventually activates a safety relief to vent gas and not exceed the pressure rating of the storage container. Use it or lose it.
        -LNG is stored in double wall containers that are vacuum insulated which extends the shelf life of the fuel up to 1 month (assuming cold LNG and a good tank to start). Some older storage tanks or poorly insulated/maintained tanks will allow LNG to warm quickly and may allow venting within 1-2 days and total LNG loss within a few days. This is not acceptable behavior but some systems just don't get maintained.
        -Vehicle engines do not burn the LNG liquid. The liquid is converted to vapor through a small heat exchanger. The engine does not know the difference between LNG vapor and regular CNG though LNG is very dry where CNG typically has some oil atomized in the gas stream which helps with injector lubricity.
        -Because LNG has no odorant, LNG fuel stations and LNG vehicles utilize electronic gas detectors that will alarm if gas is detected in the local environment (from a leak). CNG is typically odorized to allow for leak detection.
        -Lastly LNG fuel stations compress the liquid LNG to make CNG, they do not just allow the liquid to warm and build pressure. Compressing a liquid is more energy efficient than compressing gas and the pump is fairly simple so making CNG from LNG is a cost effective process and high volumes of gas (400-1000+ SCFM) can be generated with minimal footprint and equipment.

        Hope this helps and I look forward to other comments/information.
        Last edited by gastronaut; 10-27-2009, 11:32 PM.

        Comment


        • #5
          Re: LNG What is the difference????

          So, one bottom line is that you want to fill the tank, then use most of it that day. Ok for vehicles like buses and trucks. I fuel my GX fairly often at Tulare which also has LNG, mostly for Tulare's trash trucks, and found the city drivers very friendly and happy to discuss LNG.
          02 GX
          01 GX
          03 Crown Vic
          06 GX
          Home Fueler

          Comment


          • #6
            Re: LNG What is the difference????

            Barstow is another good example of an L/CNG station. If you fill there notice the little compressor that often kicks in during refueling -- it's no louder than an electric bicycle pump and is located near the bathroom.

            Comment


            • #7
              Re: LNG What is the difference????

              Okay, so a LNG vehicle is completely different than a CNG vehicle? A CNG vehicle cannot use LNG correct? The LNG fill stations that questar is building is basically a CNG fill station as far as the vehicle is concerned correct? Are there any LNG vehicles, like cars, or is it only used on buses and large trucks? Thanks for all the info.

              Comment


              • #8
                Re: LNG What is the difference????

                Dear dbd,

                This subject has already been covered well by Larry and gastronaut. But, no, once LNG is vaporized, there is no difference between LNG and CNG.

                So, to simplify, what's under the hood is the same, the difference is in the storage system.

                Oh, BTW, LNG will have significanly greater range...600:1 ratio.

                b/r,

                afvman

                Comment


                • #9
                  Re: LNG What is the difference????

                  You might also mention, that If want to run the vehicle on LNG, the tank will cost over $10,000 in addition to the vaporizer and regulator. But after that it is the same.

                  Larrycng

                  Comment


                  • #10
                    Re: LNG What is the difference????

                    Originally posted by larrycng View Post
                    You might also mention, that If want to run the vehicle on LNG, the tank will cost over $10,000 in addition to the vaporizer and regulator. But after that it is the same.

                    Larrycng
                    Thats cheaper than an "EPA" approved cng kit!

                    Comment


                    • #11
                      Re: LNG What is the difference????

                      LNG really isn't a realistic option for private owners. There are too many complcations. The Cryogenic safety issues are one, but more importantly is the boil off effect. Busses and such use up their whole tank over the course of a day, so boil off over night is not a problem. inconsistent home use, on the other hand, would require the vehicle be parked only outdoors, as it will eventually vent off the excess gas as it boils. Also, the lack of odorizer makes it that much more dangerous.
                      1997 Factory Crown Victoria w/ extended tanks ~~ Clunkerized!
                      2000 Bi-Fuel Expedition --> ~~ Sold ~~ <--

                      Comment

                      Working...
                      X