CNG is Compressed Natural Gas. It is 95% Methane and 5% a combination of butane, propane, ethane, other trace gases and water vapor. Methane is made of hydrogen and carbon. Its simple structure of one carbon atom and four hydrogen atoms makes nearly complete combustion possible.
CNG is not new. Legend says that the Chinese have been using natural gas for 4,000 years. As early as 1,000BC, they were piping from shallow wells with bamboo pipes to salt-water boilers used to make salt. In the 1800's gas lighting was the modern way to light a house or building. It was common until the twentieth century when electrical power replaced it. Gas is still used to power stoves, lamps and refrigerators... and buses.
Compressed natural gas - natural gas under high pressure: A "Natural" Choice
You can cook with it and heat your house with it. You may even power a car or truck with it. So what is it? ... natural gas. Like oil (petroleum), this common fuel comes from underground. However, natural gas, as the name implies, is a gas much like air, rather than a liquid like petroleum. It has been found to be one of the most environmentally friendly fuels, and its popularity is growing.
Natural gas is mostly made up of methane, about 95 percent of the natural gas in California. The other 5 percent is made up of various gases along with small amounts of water vapor. These other gases include butane, propane, ethane and other trace gases. Methane is a hydrocarbon, meaning its molecules are made up of hydrogen and carbon atoms. Its simple, one carbon, molecular structure (CH4) makes possible its nearly complete combustion.
Because of its clean burning nature and the fact that it is not made from petroleum, as gasoline and diesel are, many automakers around the world are developing vehicles to run on natural gas. Cars, vans, buses and small trucks generally use natural gas that has been compressed (called compressed natural gas or CNG) and stored in high-pressure cylinders.
Several vehicles are available today that operate on compressed natural gas. Some run on natural gas only and others can run on natural gas or gasoline (called bi-fuel vehicles).
Where does CNG come from?
CNG comes from the ground. We do not know exactly how it was formed, but we believe that for millions of years in the past, the remains of dead plants and animals sank to the bottoms of lakes and oceans. There, they were covered by silt and other debris. Over millenia, the accumulation of tons of materials exerted high pressures and temperatures on the buried materials. This caused chemical reactions that converted the remains into gas and oil. There, the oil, gas and natural gas was trapped under the soil. All oil and gas deposits contain Natural Gas, but it is also found without oil and gas.
How do we get CNG?
We drill for CNG just as we drill for oil. Geologists look for places where porous, gas-bearing soil is capped by solid rock. It is found in many places around the world including the United States, Canada, the former Soviet Union, Algeria, Mexico and Venezuela, under the North Sea , Romania, Indonesia, Iran, China, France, and Italy.
Exploratory wells are drilled at likely locations. Only one of nine of these wells will produce gas. If the exploratory well produces gas, then other wells are drilled nearby to tap the whole pocket of gas.
The well is a deep hole. As it is drilled into the earth, a casing is put around the hole to keep dirt from falling in. When the bottom of the pocket is reached, drilling stops and the casing is opened at the bottom of the well with a small explosion. That is all that is needed to start the well flowing. The pressure of the gas underground keeps it flowing smoothly until about 85% of the gas has been pumped out.
Then the gas must be processed. First sand and dust are separated from the raw gas by allowing the heavier particles to drop out and then bubbling the gas through oil. The fine dust sticks to the oil and the clean gas rises to the surface. Then the gas is cleaned of heavier hydrocarbons like gasoline by bubbling it through a tank of mineral oil. The mineral oil traps the heavier hydrocarbons. The mineral oil is then later treated to recover, butane, propane, LPG, kerosene and gasoline. Then water is removed from the gas by passing it through towers with water-absorbing granules. As a final step, any carbon dioxide and hydrogen sulphide is removed from the gas by passing it through a solution of monoethanolamine. And then the gas is ready to be used.
The gas is pumped in high pressure pipelines from refinery to where it is to be used. It can also be transported in pressurized tanks or chilled to -161 C (-258 F) where it becomes liquid. This liquified natural gas is called LNG. It is very compact and pours like water or gasoline.
How does CNG compare to gasoline?
The gasoline in your car has an octane rating of about 87-92. CNG has an octane rating of about 130. In addition, because it's compressed CNG gives you natural fuel injection. This gives you a little more power than a gasoline engine. The engine is usually tuned to give you more fuel economy.
