Saturday, May 10, 2014

Ethane as a Transportation Fuel - To Our Rescue

The world is looking for a lower carbon intensive liquid fuel for transportation.  The massive logistical hassles of liquefying, transporting, and storing natural gas (methane) have made this fuel hardly available for motorists and truckers even after many years of effort and the massive amount of dollars invested.   Converting gas to liquids through chemical synthesis is very wasteful of the energy content of the natural gas and is also extremely capital intensive.   As an example we should consider Shell Oil with their massively cost overrun Qatar Pearl GTL Project and their now abandoned GTL project in Louisiana that are linked below.

Lindsay Leveen The Green Machine (CTO of ITZ A GAZ Inc. Tiburon, CA) has formulated a simple yet elegant solution for a USA sourced liquid fuel that is economic, is less carbon intensive than gasoline or diesel, and is still widely available with the fuel actually is in large surplus.   This fuel is ethane (C2H6).  Yes ethane is the step sister of the other natural gas liquids propane and butane.  It is also the step sister of methane in pipelined natural gas.   There are limits to the quantity of ethane that can be sold in pipeline natural gas.  The shale gas revolution in the USA has brought about vast coproduction of ethane with natural gas.   The USA is actually swimming in ethane.

Companies are planning ethane crackers to convert ethane to ethylene and ethylene’s petrochemical derivatives such as polyethylene and PVC.  More plastics are not what the world needs!   Other companies are lining up to cryogenically liquefy and transport ethane to far off lands in Europe and Asia in specialty LNG type cryogenically refrigerated ships.  This is also a waste of our ethane resource and an expensive and non-green option to deal with the glut of ethane.

The Green Machine proposes to simply compress ethane to a sufficient yet fairly low pressure at which it liquefies at room temperature.   Yes in a welding tank in an auto shop or an oxygen tank you see at a hospital, ethane will become a liquefied gas at moderate and safe pressure.   Ethane like carbon dioxide, propane, and butane are all stored as liquid in those gas cylinders.  The basic welding cylinder is 90% filled with liquid ethane.  By storing the ethane fuel as a liquid under pressure, many more BTUS of fuel can be stored in the same volume of cylinder compared with CNG.  Compared with LNG there is much less logistical and infrastructure hassle in the supply chain to get the liquid ethane fuel aboard a vehicle.  Ethane is a really good fuel on a gaseous per cubic foot basis and has 70% more BTUs per scf than methane.  It is also clean burning and low in sulfur like methane.

The Green Machine estimates that only 3% of the energy content of the ethane will be lost to compress it into liquid state in a gas cylinder.   For the same size gas cylinder the ethane powered vehicle will travel more than twice the range of a similarly equipped CNG vehicle.  The ethane powered vehicle will emit less CO2 per mile than a gasoline fueled vehicle as ethane is less carbon intensive and richer in hydrogen than gasoline (3 hydrogen atoms for each carbon atom in ethane versus only 2 to 1 in gasoline).

Companies are considering projects to covert ethane gas to liquids by reforming the gas and then synthesizing methanol, DME, gasoline, or diesel from the synthesis gas produced in the reforming.   This is massively capital intensive and wastes over half of the energy content of the gas with large amounts of CO2 being emitted due to the low efficiency of the gas to liquids synthesis process. 

The Green Machine is suggesting a national energy policy for the USA that adds ethane directly as liquid ethane into the transportation fuel mix.  Railroad locomotives are a first target for the proposed ethane fueling conversion.  Railroads have investigated and considered LNG but the logistics and costs of a cryogenic fuel are simply too high.  It is very simple and easy for a train to have several tube trailers of ethane on flat bed carriages behind the locomotive that supply the ethane fuel to the locomotive for the long haul propulsion of trains.  For shunting and rail-yard work the locomotive could easily be fueled from a single tube trailer on a carriage behind the locomotive.

If the Green Machine Ethane Idea is adopted it is quite possible that as much as a quarter million barrels a day of surplus ethane that is now being reinjected or flared could compliment the gasoline and diesel the USA uses in transportation.  This is about 2% of the total gallons of transport fuel other than jet airplane fuel that is consumed in the US on a daily basis.   Note a gallon of ethane has approximately half the fuel content of a gallon of diesel.   Hence two gallons of ethane will substitute for one gallon of diesel.   All that is needed is for larger companies to join the ethane bandwagon.  No government subsidy is needed as liquid ethane is only worth about 30 cents a gallon (at its trading point in Mont Belvieu Texas) and when expressed on a diesel equivalent basis this is only 60 cents a gallon of diesel equivalent.   There is a lot of value add to pay for the logistics of compression and hauling of ethane to get it aboard cars, trucks, and trains.

To the right is a photo of a jumbo tube trailer that will hold approximately 5,200 gallons of liquid ethane or 2,600 gallons equivalent of diesel.  A diesel locomotive typically has a similar quantity of diesel in its storage tank.

Lindsay Leveen is the recipient of the 2011 Professional Development Award from the Northern California Section of the American Institute of Chemical Engineers.  He also wrote the primer on energy and sustainability titled Hydrogen Hope or Hype? and is available as an Ebook.

Kimberly King an Energy and Sustainability Engineer and Lindsay Leveen have submitted the ethane transportation fuel idea to the Climate Colab at the MIT Center for Collective Intelligence.

  If you like the idea please hit the “support proposal” tab on the link below.

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