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Clean Truckin' for Clean Air
The traffic light changed from amber to red. The big diesel rig slowed to a stop, noise from the throbbing engine engulfing nearby cars and inky smoke puffing from gleaming exhaust pipes. For the driver in the car behind the diesel, there was no escape. When the light changed to green, the diesel began to move, and the car was again enveloped in smoke and stench.

For millions of drivers in the U.S. and around the world, an experience like that is a daily occurrence. Diesel-powered trucks and buses crowd the nation's roads, and each one contributes to the fouling of the air we breathe. Beverly Miller is Director of the Salt Lake Clean Cities Coalition (SLCCC), a non-profit organization dedicated to promoting the use of alternative, cleaner fuels for transportation. "What we really need to be doing," she says, "is addressing those big diesels, because they are the big polluters, puffing and snorting around." 

Is there an alternative to the big rigs powered by diesel fuel? Yes, and for several years the Idaho National Engineering and Environmental Laboratory has converted vehicles in INEEL's fleet from gasoline and diesel to a cleaner, less-polluting fuel. Furthermore, if engineers and scientists in Idaho Falls have their way, they will establish INEEL as a national center of expertise in developing this alternative source of energy, especially for heavy-duty transports like trucks and buses. The alternative fuel is liquefied natural gas, or LNG. 


The INEEL has converted 
several diesel and gasoline buses to 
cleaner-burning liquid natural gas engines.

Used in a test fleet in California, LNG was almost unbelievably clean. Emission of ozone-forming compounds was down 70-80 percent, of carcinogenic particulate matter, down 90 percent, and of unburned fuel, down 50-60 percent. These were among the lowest levels ever measured from heavy-duty vehicles.

Scientists and engineers at INEEL know that before this cleaner fuel can be widely used in heavy-duty vehicles, several things have to happen. Facilities must produce liquefied gas that is uniform in quality, refueling stations must be built, and vehicles must be modified to take the fuel. Above all, if LNG is to become a permanent part of transportation, the fuel must be competitive in price with gasoline and diesel. 
Hydrocarbons form ground-level ozone, a major component of smog and a cause of reduced lung function in humans when they combine (in the presence of sunlight) with other emissions like nitrogen oxides. 

U.S. Environmental Protection Agency

After researching the problems for several years, engineers and scientists at INEEL now know that they can make an LNG system work. Advisory Engineer Bruce Wilding is principal investigator on the project to make the idea of a low-cost methane plant and refueling station a reality. "We sat down," he says, "and took this approach: What is the bare minimum that we need, and how can we do it cheaper?" For the LNG project, Wilding and his colleagues achieved their results by simplifying technology that already existed. 

Wilding's group designed and patented an ingenious methane plant, a low-cost refueling station, and an engine modification that will allow the efficient use of LNG in trucks and buses. With an increase in public awareness of how clean LNG burns, and with the right kind of support, they believe that within a couple of years, LNG vehicles could be a common sight in Idaho and Utah. Prove the concepts and the vehicles to be successful in those two states, and they could soon be in use nationwide; all because of three licensable technologies developed at the INEEL.

Microscopic life in the oceans is the principal source of oil and natural gas. The death of an organism releases organic tissue, most of which scavengers and bacteria consume, but some of the organic matter will be deposited with sediment on the ocean floor. Over millions of years, as more and more sediment accumulates, increasing temperature at depth transforms the buried organic matter into both liquid and gaseous compounds of carbon and hydrogen, the so-called hydrocarbons. We know hydrocarbons as oil and gas, which provide more than 65 percent of the energy used in the U. S.

Neither oil nor gas is a single chemical substance. Oil may be solid as wax, as thick as the tar on our roads, or as clear and volatile as kerosene or gasoline. Most often it is a mixture of liquids, which are separated by the refining. Natural gas is not one gas, but many: butane, pentane, propane, ethane, methane, and even incombustible ones like carbon dioxide, nitrogen, helium and water vapor. 

Separate the individual components of liquid petroleum and you have gasoline, lubricating oil, wax, kerosene, road tar and diesel fuel. Separate the components of natural gas and you have fuels we are familiar with: butane for camp-stoves, propane for gas lighters and domestic heating, and methane, the most common household gas used for cooking and heating. The most convenient way to use natural gas as a fuel in vehicles is to convert it to a liquid, either by compressing it to make compressed natural gas (CNG), or chilling it to make liquefied natural gas (LNG). Since natural gas is a combination of gases, when you compress it you include in the final liquid all the original gases that came out of the pipeline or storage tanks. The composition of natural gas varies from place to place along the thousands of miles of pipelines criss-crossing the country, collecting from hundreds of fields. Here it may have 15 percent propane and five percent ethane, there it may have a little butane, no ethane and only 10 percent propane. This is not a problem if the gas is to be used in the home, but it is a problem in an internal combustion engine, which is usually tuned for fuel of a specific composition. When the fuel deviates from that ideal, the engine runs poorly. And worse still, if there is more than six percent of ethane in CNG, the fuel causes pre-ignition knock and damages the engine. 

LNG, however, because of the way it is liquefied in the INEEL-designed methane plant, is usually more than 98% methane and creates neither of those problems for the internal combustion engine. 

The Methane Liquefaction Plant 

Natural gas flows from oilfields and gasfields across the country, through high-pressure pipelines to distribution centers and ultimately to consumers. To liquefy natural gas, you can compress it, or you can chill it. If you compress it, you get a liquid that is a mix of substances and variable in quality, not always suitable for vehicles. But just as water vapor condenses to liquid water on a cold surface, so natural gas will liquefy if you lower its temperature far enough. And as you lower its temperature, the different components in the mixture become liquid one by one and can then be removed. Butane, propane, and ethane become liquids at successively lower temperatures, until the only gas left is the one you need to liquefy for the heavy-duty vehicles: methane, with a purity of 98% or better. The ingenious part of this chilling process lies in the use that can be made of the separated liquids during the purification of the methane. For as a liquid expands to become a gas, its temperature drops. The butane, propane and ethane liquids are each separated and then allowed to expand, whereupon they become cold gas again, which can then be used to cool the complete natural gas mixture coming into the plant to be processed. Eventually, the separated gases are pumped into tanks for storage and sale, but in the meantime, they have also contributed to an inexpensive, efficient process for producing clean and pure LNG.

The Refueling Station

The typical LNG stations are expensive, because of the special equipment needed to store and dispense a liquid at a temperature of -200 to -260 degrees Fahrenheit and a pressure of 25 to 135 psi. Researchers at INEEL sought simple ways to store and pump the fuel. Their design for the refueling station uses the physical properties of the liquefied fuel to provide the force needed to transfer the LNG from the tank of the station to the tank of the vehicle, and reduces the cost to $100,000 or less, competitive with gasoline stations.

Liquefied natural gas must be stored cold and sealed. If its temperature rises, some of the liquid vaporizes to gas above the liquid surface, and raises the pressure of that gas. The INEEL plan is to store the fuel very cold, so that the pressure of the gas above the liquid is about 25 psi. In the vehicles coming in for refueling, however, the temperature of the fuel in their tanks may be higher than that in the station, and the pressure of the gas correspondingly greater. This means that an expensive pump would be needed to force the fuel from low pressure in the station to higher pressure in the vehicle. But the staff at INEEL devised a way of maintaining a high pressure above the liquid in the storage tanks of the station, thereby eliminating the need for the pump.

Their design is to bleed off the liquid gas from the bottom of the tank, warm it and vaporize it in a coil that draws its heat from the surroundings. The gas is then discharged into the top of the storage tank, increasing the pressure there, which can drive the refueling process. At the same time, a small pump sends a quick surge of very cold fuel into the tank of the vehicle. This chills the fuel, causing some of the gas above the liquid to condense, thereby lowering the pressure. The fuel is then being transferred from high pressure to low pressure so that no more pumping is needed. Gravity and the "false pressure" created in the storage tank combine to fill the tank in the vehicle.

The Engine Modification

In an LNG vehicle, the engine draws liquid from the bottom of the tank, or gas from the top, depending on the pressure of the gas and the setting of a special valve called the economizer valve. With a pressure below the valve setting, the engine draws liquid; with a higher pressure, gas. When the fuel is very cold, the engine can suffer fuel starvation during acceleration or when under a heavy load. Engineers at the INEEL changed the piping of the fuel system to prevent fuel starvation.
The State of California has recently concluded that exhaust particulates are carcinogenic.

Ingenious and economical though these innovations may be, the real test of LNG will come on the road. For several years the INEEL has operated buses and trucks running on LNG, and four buses went to Atlanta to serve as part of the transportation fleet for the 1996 Olympic Games. Based upon that success, the engineers and scientists at the INEEL proposed a project to expand the use of LNG heavy-duty vehicles in Idaho and Utah. It will be a collaborative effort with the Utah Energy Office, the Salt Lake Clean Cities Coalition, Utah Transit Authority, and Questar Regulated Services Company to install a methane liquefaction plant and a refueling station to supply transit buses and other heavy-duty vehicles in Salt Lake City and its suburbs.

"We are absolutely delighted and thrilled to be part of INEEL's project," says Beverly Miller, "for we need to convince owners and drivers that if they use LNG, they can save dollars. And natural gas as a transportation fuel has an extremely impressive safety record." As an example she cites the experience of the Newspaper Agency Corporation, the company that home-delivers the Salt Lake City Tribune and the Deseret News. Of their 250 vehicles, 238 are powered by natural gas in one form or another, and they drive six million miles a year. Miller believes that the tradition of using natural gas vehicles in the Salt Lake City area makes it an ideal market for the INEEL proposal.

Safe, effective and cleaner than diesels, the LNG vehicles would also be as economical as the big rigs and buses if there were filling stations and liquefaction plants around the country. The vision of the framers of the INEEL project is to achieve that goal. Build an economical LNG infrastructure in Idaho and Utah, and then convince the rest of the country to do the same. California would be one of the first candidates, with its smog problems in the Los Angeles basin and elsewhere. 

Already in the Sacramento area, one company is trying out heavy-duty LNG trucks. Raley's, a chain of grocery markets in northern California and Nevada, bought eight big trucks in 1997. Kathleen Tschogl (pronounced Shagle), Manager of Governmental and Regulatory Affairs for Raley's says "We are very pleased with the program and are looking at ways to expand it. They were unbelievably clean."

They are clean of that cloud of smoke and particles that comes from diesels. Not merely unpleasant, the emissions from the big rigs are dangerous. The U.S. Environmental Protection Agency describes hydrocarbons from incomplete burning as toxic and possibly carcinogenic. When they combine (in the presence of sunlight) with other emissions like nitrogen oxides ("noxes"), they form ground-level ozone, a major component of smog and a cause of reduced lung function in humans. The black and sooty particulate matter that is spewed by the exhausts of diesel-powered vehicles lodges in the lungs, perhaps causing premature death. The State of California has recently concluded that exhaust particulates are carcinogenic.

Kevin Chandler is principal research scientist for Battelle, contractor for the National Renewable Energy Laboratory, monitoring the Raley program. He compared the emissions from LNG vehicles from Raley's fleet and the emissions from diesels. "The values [from the LNG trucks] were low enough that we thought there was a mistake." With a 70-80 percent reduction in "noxes", a better than 90 percent reduction in particulates, and a 50-60 percent reduction in hydrocarbons, "they were the lowest levels from heavy-duty engines we have ever received," Chandler says.

Unaware of all that the researchers at INEEL had done to advance the cause of using clean LNG fuel instead of diesel, an automobile driver sits at a light. When it changes to green, a nearby tractor and the bus move. She hears the roar of their engines, but sees no dark and billowing clouds come out into the air. The dream of engineers and scientists at the INEEL is for the moment a reality. "I want the world to get our vision," says Richard Rice, Department Manager of Advanced Fossil Fuel Products: the vision of clean, heavy-duty transportation.

Written by Robert Evans for INEEL Research Communications.