Location: Pantego, Texas, United States

Wednesday, April 14, 2010

T. Boone Pickens has advocated making a major switch to compressed natural gas (CNG) to fuel vehicles in the United States. He says that switching large trucks and buses to CNG fuel would reduce US use of foreign oil by 3 million barrels per day. With the development of shale gas with horizontal drilling and slick water hydraulic fracturing has significantly increased the NG reserves in the US. Officially the NG reserve is 2000 trillion Cubic Feet (Tcf), and Pickens says the probable reserve is 8300 TCF. The US currently consumes just over 20 Tcf/year, so there is many years of supply available. There is a lot of mis-information put out by politicians regarding energy independence of the United States. The US is independent in terms of electricity generation. It is fuel for transportation that uses most of the imported oil. Windmills, etc. can aid in reducing oil importation only to the extent that electric automobiles can be adopted. Many people outside of the east coast need a vehicle with more range than 40 miles, and many people would like an SUV rather than a glorified golf cart. (Assuming they don't have $120,000 to buy one of those slick Tesla sports cars.) The problem with CNG fuel is that it is not volume efficient. This is not a major issue for large trucks and buses, and probably not for pickups and SUV's. The conversion rate for CNG to gasoline is about 8 gallons per 1000 cubic feet (mcf). So on a cost basis CNG at $6 or 7/mcf would take a vehicle about the same distance as $22 of gasoline (at $2.75/gal). (Actually the CNG vehicle will probably go farther because the engine is more efficient.) So CNG is an economic winner. But volume efficiency is another issue. The NG has to be compressed to a high pressure (3000 to 4000 psi) and stored in a cylindrical tank. Not much of a problem for a large vehicle, but perhaps a problem for a small car. In comparing CNG to electric vehicles it is often overlooked that the electricity to charge the battery comes from an electricity generation plant. About half of the electricity in the US comes from coal fired plants, with 20% coming from gas fired plants. The efficiency of the wheels on the ground is actually better for the CNG fueled vehicle than for electricity provided by a coal or gas fired electric power plant. In terms of pollution for one billion BTU's of energy input natural gas beats coal (using numbers from a Chesapeake Energy Presentation in April 2010.) Natural gas produces 117,000 pounds of CO2 compared to 208,000 for coal, 92 pounds of nitrogen oxides compared to 457, 1 pound of sulfur dioxide vs. 2591, 7 pounds of particulates vs. 2744, and no mercury compared to 0.016 pounds. Some of the CNG engine manufacturers claim that they produce virtually no pollution (they don't consider CO2 to be a pollutant). The manufacturers also claim that the engines have demonstrated over one million miles without any repair. Some countries have a large part of their vehicle fleets fueled by CNG. Pakistan, for example, has about 1 million cars fueled by CNG. The US has about 350,000 CNG fueled cars. Some people buy compressors and fuel their CNG vehicle from their home NG supply. I think I would much rather have a CNG fueled car than an electric car.


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