Liquified natural gas, energy transition friend or foe?
Storage tanks and gas-chilling units are seen at Freeport LNG, the second largest exporter of U.S. liquified natural gas, near Freeport, Texas, U.S., February 11, 2023. Reuters/Arathy Somasekhar/File Photo
Since the 1920's natural gas has been used by humans for energy generation. The components of natural gas are >90% methane (CH4), and the remainder being other light hydrocarbons such as ethane, propane, and butane. It's popularity took off after world war 2 with advancements in technology specifically liquefaction and turbines. Recently natural gas, specifically liquefied natural gas or, LNG, has been put in the spotlight due to the war in Ukraine and the global green energy transition. Natural gas is a cleaner alternative to coal with the by products of combustion of its hydrocarbons being CO2 and H2O. However many environmentalist still oppose the use of natural gas since it still emits CO2. In January 2025 the United States un-paused the permits for several LNG export plants. This was seen as controversial due to the aforementioned CO2 emissions coming from the burning of natural gas. One of the big issues with LNG is that it takes ~10% of the energy contained by a kilogram of natural gas to liquefy it. Unfortunately the media in their coverage of the LNG export terminals has not focused on this. However, thankfully industry physical chemists have been hard at work to make LNG even cleaner and closer to green. The import terminals of LNG in the receiving country can actually recoup up to ~50% of this energy in models, currently ~25-30% is recovered. What a great deal for the buyer they can potentially get 5% more energy! This is where the chemistry comes in. How can this energy be recovered at the import terminals and why can it not be done at the export terminals?
This energy is stored in the LNG as thermal energy since it is cooled to -162C. The energy is then extracted when it is re-gassed to flow into the gas mains at the terminal, try using liquid gas in your stove or heater. Through a thermodynamic processes called the Rankine cycle. This technology utilizes a heat exchanger with saltwater as the working fluid, meaning it receives the cold. In fact so cold that it crystallizes and the impurities are able to be separated and you are left with clean potable water. This is how the energy is recovered. There are other ways to recover the energy as well like making dry ice or liquefying air gasses. Media coverage should focus more on making the import terminals in Europe and the rest of the world more efficient and highlight the breakthroughs of scientists trying to improve life for all of us.
https://www.reuters.com/business/energy/us-lng-projects-boosted-by-trumps-export-permit-restart-2025-01-21/
https://www.google.com/url?sa=i&url=https%3A%2F%2Fenergyeducation.ca%2Fencyclopedia%2FRankine_cycle&psig=AOvVaw0GH5loswpG1Oeq1WCkdHtm&ust=1740700182194000&source=images&cd=vfe&opi=89978449&ved=0CBcQjhxqFwoTCOCmydHD4osDFQAAAAAdAAAAABAE
Your piece makes some interesting points about using LNG efficiently. I don't see that discussed in the Reuters piece so I assume you found that somewhere else. Reuters really just reports the end of the moratorium on new LNG terminal permits. They put this in the context of actions of the incoming and outgoing administrations and in the context of current and projected volumes of LNG exports. You pick up on related issues that are in fact more relevant to chemistry. First you review the use of natural gas as a fuel and its impact on the environment. It is always useful to note in any such discussion that basic chemistry tells us that as fuels coal produces 2.4 times as much CO2 as NG per kilowatt hour of electrical energy produced. Then you proceed with a very interesting discussion on the efficiency of transporting NG as a liquid. You should probably give us some sort of media source for this. You give us a nice figure on the Rankin cycle, but your specifics on the quantitative efficiency of energy recovery from the liquefaction and re-gasification of NG at LNG terminals must have come from somewhere. It would be interesting to know if this kind of sophisticated physical chemistry is turning up in general interest media. Your title and graphic would attract interest and attention. Your discussion is clear if a little dense. I am not sure what you mean with your suggestion that energy now recovered at import terminals could be recovered at export terminals. I would recommend breaking up the material into three or four paragraphs.
ReplyDeleteOverall an interesting post.