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  • LNG heat value question?

    Does anyone know the fuel value of a gallon of LNG? I've read some contradictory info. One article claimed that it took 1.5 gallons of LNG to equal 1 gallon of gasoline. Another stated that there are 600 standard cubic feet of natural gas in a gallon of LNG. This sounds about right to me, making 1 gallon of LNG equivalent to just under 5 gallons of gasoline.

  • #2
    Re: LNG heat value question?

    Depending on the saturation pressure of LNG, there area approximately 644 cubic feet of natural gas per gallon of LNG. If one assumes a btu value of 120 cubic feet of natural gas equal to a gallon of gasoline, we get about 5.3 gallons to 1 of LNG.

    Note that the key is the saturation pressure. There is technically no LNG with a saturation pressure of zero, it starts to climb almost immediately. 80 to 120 lbs saturation is the average.

    Franz

    Comment


    • #3
      Re: LNG heat value question?

      Franz,

      Now...explain saturation pressure.

      afvman

      Comment


      • #4
        Re: LNG heat value question?

        LNG is a cryogenic fuel, meaning, that to keep it in liquid state, it must be kept cold. The point where LNG liquefies is -259 deg F, and at that temperature, it is at zero pressure. LNG is kept liquid by keeping it cold and that is handled by a unique fuel tank called a “dewar”. A dewar is a double wall tank made of nickel and stainless steel alloys and thermally insulated with mylar, Styrofoam, and importantly, vacuum between the two walls. Regardless of how carefully the tank is formed, there are two mechanical connections from the inside wall to the outside wall, and that is at the two ends. A mechanical connection also means that there are no thermal barriers, and that means heat absorption, and that also means that it is for all purposes, practically impossible to keep LNG at zero pressure.

        LNG has a pressure rise based upon temperature. Dewars typically have two pressure relief valves, one set at 250 psig, the second at 350 psig (this depends on the tank construction and certification but these numbers are close enough). These two valves vent LNG if the internal heat absorption is enough to cause a resultant rise in pressure.

        LNG tanks also have a unique means of fuel withdrawal, in liquid state and in vapor state. If the vapor is withdrawn, the pressure will drop, and if liquid is withdrawn, the pressure will remain the same but over time it will slowly increase

        Saturated LNG is at the maximum temperature at which it can remain in a homogenous liquid state at a given pressure. Heat added to the saturated liquid yields an increase in pressure as some of the saturated liquid is converted to gas. Saturation permits effective control of the pressurization of the fuel system. As the pressure rises, the amount of liquid that is converted to gas also increases. Drawing the vapor pressure down decreases saturation pressure. On LNG vehicles, saturation pressure is critical since a combination of liquid and vapor is pulled simultaneously through a pressure regulator that pulls either liquid or vapor to maintain its set pressure. If too much vapor is pulled, the vehicle will “run out of fuel” since the system relies on vapor pressure to push the fuel to the engine. If more liquid is pulled, the saturation pressure will increase.

        If the saturation pressure is too high, there will be less storage or hold time for the fuel before the internal pressure reaches the 250 psig relief valve.

        In some transport LNG tankers, it is possible to circulate the LNG liquid fuel through the vapor space to chill the vapor fuel back to liquid. Common transport pressure is around 10 psig. It is possible to cool LNG below its zero saturation stage but a cryogenic pump must be used to provide fuel to the engine, and that adds a lot of complexity.

        My typical two dollar answer to a five cent question.

        Franz

        Comment


        • #5
          Re: LNG heat value question?

          Hope these pictures help understand the LNG tank. I have a few more. The vertical bar is the fuel level sender. The space betwen the 2 shells is about 1-1/8 on an inch.

          Larrycng
          Attached Files
          Last edited by larrycng; 03-20-2009, 12:43 PM. Reason: add correct measurement

          Comment


          • #6
            Re: LNG heat value question?

            Originally posted by Franz View Post
            LNG is a cryogenic fuel, meaning, that to keep it in liquid state, it must be kept cold. The point where LNG liquefies is -259 deg F, and at that temperature, it is at zero pressure. LNG is kept liquid by keeping it cold and that is handled by a unique fuel tank called a “dewar”. A dewar is a double wall tank made of nickel and stainless steel alloys and thermally insulated with mylar, Styrofoam, and importantly, vacuum between the two walls. Regardless of how carefully the tank is formed, there are two mechanical connections from the inside wall to the outside wall, and that is at the two ends. A mechanical connection also means that there are no thermal barriers, and that means heat absorption, and that also means that it is for all purposes, practically impossible to keep LNG at zero pressure.

            LNG has a pressure rise based upon temperature. Dewars typically have two pressure relief valves, one set at 250 psig, the second at 350 psig (this depends on the tank construction and certification but these numbers are close enough). These two valves vent LNG if the internal heat absorption is enough to cause a resultant rise in pressure.

            LNG tanks also have a unique means of fuel withdrawal, in liquid state and in vapor state. If the vapor is withdrawn, the pressure will drop, and if liquid is withdrawn, the pressure will remain the same but over time it will slowly increase

            Saturated LNG is at the maximum temperature at which it can remain in a homogenous liquid state at a given pressure. Heat added to the saturated liquid yields an increase in pressure as some of the saturated liquid is converted to gas. Saturation permits effective control of the pressurization of the fuel system. As the pressure rises, the amount of liquid that is converted to gas also increases. Drawing the vapor pressure down decreases saturation pressure. On LNG vehicles, saturation pressure is critical since a combination of liquid and vapor is pulled simultaneously through a pressure regulator that pulls either liquid or vapor to maintain its set pressure. If too much vapor is pulled, the vehicle will “run out of fuel” since the system relies on vapor pressure to push the fuel to the engine. If more liquid is pulled, the saturation pressure will increase.

            If the saturation pressure is too high, there will be less storage or hold time for the fuel before the internal pressure reaches the 250 psig relief valve.

            In some transport LNG tankers, it is possible to circulate the LNG liquid fuel through the vapor space to chill the vapor fuel back to liquid. Common transport pressure is around 10 psig. It is possible to cool LNG below its zero saturation stage but a cryogenic pump must be used to provide fuel to the engine, and that adds a lot of complexity.

            My typical two dollar answer to a five cent question.

            Franz
            two dollar hell thats a hundurd dollar answer but lots of good information

            Comment


            • #7
              Re: LNG heat value question?

              Originally posted by Franz View Post
              LNG is a cryogenic fuel, meaning, that to keep it in liquid state, it must be kept cold. The point where LNG liquefies is -259 deg F, and at that temperature, it is at zero pressure. LNG is kept liquid by keeping it cold and that is handled by a unique fuel tank called a “dewar”. A dewar is a double wall tank made of nickel and stainless steel alloys and thermally insulated with mylar, Styrofoam, and importantly, vacuum between the two walls. Regardless of how carefully the tank is formed, there are two mechanical connections from the inside wall to the outside wall, and that is at the two ends. A mechanical connection also means that there are no thermal barriers, and that means heat absorption, and that also means that it is for all purposes, practically impossible to keep LNG at zero pressure.

              LNG has a pressure rise based upon temperature. Dewars typically have two pressure relief valves, one set at 250 psig, the second at 350 psig (this depends on the tank construction and certification but these numbers are close enough). These two valves vent LNG if the internal heat absorption is enough to cause a resultant rise in pressure.

              LNG tanks also have a unique means of fuel withdrawal, in liquid state and in vapor state. If the vapor is withdrawn, the pressure will drop, and if liquid is withdrawn, the pressure will remain the same but over time it will slowly increase

              Saturated LNG is at the maximum temperature at which it can remain in a homogenous liquid state at a given pressure. Heat added to the saturated liquid yields an increase in pressure as some of the saturated liquid is converted to gas. Saturation permits effective control of the pressurization of the fuel system. As the pressure rises, the amount of liquid that is converted to gas also increases. Drawing the vapor pressure down decreases saturation pressure. On LNG vehicles, saturation pressure is critical since a combination of liquid and vapor is pulled simultaneously through a pressure regulator that pulls either liquid or vapor to maintain its set pressure. If too much vapor is pulled, the vehicle will “run out of fuel” since the system relies on vapor pressure to push the fuel to the engine. If more liquid is pulled, the saturation pressure will increase.

              If the saturation pressure is too high, there will be less storage or hold time for the fuel before the internal pressure reaches the 250 psig relief valve.

              In some transport LNG tankers, it is possible to circulate the LNG liquid fuel through the vapor space to chill the vapor fuel back to liquid. Common transport pressure is around 10 psig. It is possible to cool LNG below its zero saturation stage but a cryogenic pump must be used to provide fuel to the engine, and that adds a lot of complexity.

              My typical two dollar answer to a five cent question.

              Franz
              I don't quite understand why - If more liquid is pulled, the saturation pressure will increase. Can you explain?

              Comment


              • #8
                Re: LNG heat value question?

                ok if you have evaporation say on a hot day you put water on your arm it will cool your arm as the water evaporates the lng evaporates faster as the pressure drops so by pulling vapor when the pressure is high the pressure inside of the tank drops and the lng starts to boil off or evaporate and this causes it to cool the remaining lng to drop the pressure if the pressure gets to low then the regulator will pull liquid and the evporation slows and the liquid starts absorbing heat form the surounding air and the pressure will rise. that is the simple scoop of how it works. there is probley someone here that can explain it better but that is the jest of it

                Comment


                • #9
                  A "Refer" for perishable goods trucks evolves into "Refers" to keep the LNG cold...

                  Chart also claims “the longest hold-times in the industry,” better than seven days for popular sizes, with a heat management system that auto-refrigerates the tank.

                  http://www.fleetsandfuels.com/fuels/...m_medium=email
                  .

                  Comment


                  • #10
                    Re: A "Refer" for perishable goods trucks evolves into "Refers" to keep the LNG cold.

                    So when this is parked in the driveway venting off pressure (GNG) can you plug it into your house? will the gas company meter run backwards?
                    I use LN2 dewars, when it vents, no big deal, most of the air we breath is nitrogen, another story with methane gas.

                    Comment


                    • #11
                      Re: A "Refer" for perishable goods trucks evolves into "Refers" to keep the LNG cold.

                      No Kuma, it doesn't work that way. Line gas at your home is 6"- 7" water column (about 1/4 psi) you would overpressure the system with out even thinking about it. Gas meters are not like some electric meters. They don't run backwards. (to my knowledge)

                      You could however compress the off gas into storage, but not at home as storage at home is illegal unless it is the fuel tank of a vehicle.

                      Comment


                      • #12
                        Re: A "Refer" for perishable goods trucks evolves into "Refers" to keep the LNG cold.

                        So, if you don't use it, you loose it, I guess for a truck running all the time it would be OK but doesn't sound like an option for a daily driver.

                        Comment


                        • #13
                          Liquid nitrogen was also used in Space Shuttle to cool rocket nozzles.

                          Linde Energy Solutions strategic marketing and business development chief Bryan Luftglass called the compact fueling station design a potential “game-changer” (F&F, May 24, 2012).

                          Details of the new design will be discussed by Jonathan Harris, merchant LNG technology manager for the Linde division, on April 19 at the LNG 17 conference in Houston...

                          “The station is designed to eliminate station boil-off gas by using novel applications of on-the-fly saturation and LIN-assist cryogenic cooling techniques.” LIN stands for liquid nitrogen.

                          “Linde’s new station design is the latest in a series of initiatives we are implementing to facilitate broader adoption of LNG to fuel vehicles, oil and gas drilling and completion equipment and marine vessels,” Harris said in the company’s announcement this week. “We intend to continue to escalate our commitment to making it easy, safe and economical for fleets to switch to LNG fuel.”

                          Linde says it will apply the new LNG station design at its facility in Springville, Ind., where it will support LNG-fueled company trucks...

                          http://www.fleetsandfuels.com/fuels/...m_medium=email
                          .

                          Comment


                          • #14
                            It seems the rocket industry is well ahead of simply keeping moisture out of a fuel. No mention of the pressures, if any, that are used. Was very surprised when reading this news item because it was thought that SpaceX used the low-tech kerosene used in Russian rockets for reliability and cost reasons (A Soyuz launch is ten times cheaper than what the Space Shuttles missions cost.) When digging further, the Wiki writeup on SpaceX had this gem:

                            Musk goes for methane-burning reusable rockets as step to colonise Mars. We are going to do methane, Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years. The energy cost of methane is the lowest and it has a slight Isp (Specific Impulse) advantage over Kerosene. And it does not have the pain in the ass factor that hydrogen has.

                            SpaceX said it suspected the explosion that destroyed the Falcon 9 rocket on the launch pad in Sept 2016 had something to do with one of three carbon fiber helium tanks that sit inside the main fuel tank. The liquid oxygen fuel froze solid as it was flowing into the rockets second stage, which set off the chain of explosions. Elon Musk didnt share any details about how the frozen oxygen may have affected the helium tanks, but he did offer a vague explanation and confirmed that his engineers had been able to replicate a ruptured helium tank. It basically involves a combination of liquid helium, advanced carbon fiber composites and solid oxygen, Musk said. Oxygen so cold that it actually enters solid phase.

                            Oxygen freezes at –219 degrees Celsius and the latest Falcon 9 rockets use supercooled liquid oxygen that is usually around –207 degrees. The helium inside the carbon fiber tanks is even colder at –269 degrees and may have caused the liquid fuel to freeze.

                            https://www.engadget.com/amp/2016/11...ocket-mystery/

                            .

                            Comment


                            • #15
                              The Shell LNG station at Travel Centers of America 12310 S Highway 33 Santa Nella CA has a liquid nitrogen tank half the height of the LNG tank.

                              In all kinds of industries, expendable coolant chambers use cryogenic LN2 (liquid N2) to achieve low temperatures for keeping other things cold. In the case of these LNG stations, nitrogen boils off in the course of cooling the LNG. Nitrogen already makes up over 3/4 of the atmosphere.

                              Why is any of this important for vehicles needing CNG? A brief look at the major players putting in LNG stations reveals:

                              - BLU LNG re-injects LNG boil-off back into a gas pipeline (interesting, since a LNG station does not need to have natural gas service since pipeline gas is not used to make the LNG)


                              - CLEAN ENERGY will add a compressor, storage tubes, and dispenser to supply CNG from an LNG station - sometimes. Photo shows that all the tubes are connected together to work as one, so the compressor must be keeping at least 3600 psi in the tubes. As more LNG boils off, more CNG is added to the storage tubes until the max working pressure is reached - which can be as high as 5500 psi.

                              - SHELL is using the LIN-assist cryogenic non-boil off cooling mentioned developed by LINDE mentioned in the above
                              04-27-2013, 08:56 PM
                              post. At atmospheric pressure, Methane boils at -260F and Nitrogen (N2) boils at -320F. These stations will have a tall LNG tank and a smaller N2 tank.

                              Naturally, if LNG is being dispensed regularly into trucks, the boil off situation is avoided.


                              http://www.lngworldnews.com/usa-shell-opens-lng-fueling-lanes-in-santa-nella/


                              http://www.ngvjournal.com/shell-opens-second-lng-refueling-site-in-california/


                              https://www.ta-petro.com/about-us/press-center/945016/travelcenters-of-america-opens-lng-fueling-lanes-at-ta-santa-nella-california


                              LNG_gustine_shell_b.jpg LNG_gustine_shell_6.jpg LCNG_CPoint_d.jpg
                              .

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