CNG stands for compressed natural gas and used as a substitute for petrol,
gasoline or diesel fuel. As the name suggests, it is natural gas compressed
at high temperature. Composed of 95% methane and 5% of a combination of
propane, ethane, butane, other trace gases and water vapor, this gas is
supposed to be a very environmentally clean fuel compared to other fuels.
CNG plants are CNG gas generating systems.
The gas produced is stored in hard containers, at a normal pressure of
200/220 bar. These containers are usually in spherical or cylindric shapes
to maintain equal pressure on the walls of the containers. CNG gas has
become very popular for driving vehicles today because of the constant rise
in petrol and diesel prices. In response to high fuel prices and
environmental concerns, CNG is used widely in light and medium duty
passenger vehicles, buses and pickup trucks.
Where does CNG come from?
CNG is available from the ground. Everyone knows that millions of years ago
the remains of dead animals and plants sank to the bottoms of lakes and
oceans. There, they were covered by debris and silt and over the years, the
collection of tons of materials imposed high pressures and temperatures on
the buried materials. This led to a chemical reaction which transformed the
remains into gas and oil. The oil, gas and natural gas was trapped under the
soil. All oil and gas deposits contain Natural Gas, and this gas when
transformed at a certain temperature was transformed into CNG.
Manufacturing
Process: The CNG plant
CNG is produced in gas plants by pressing natural gas at a very high
pressure, about 3,000 psi pressure. It is generally produced on the fueling
station site by using a compressor based system. Natural gas is transferred
through pipelines to refueling stations. Compressed at the specific pressure,
the natural gas is transformed into CNG and then it is loaded in gas
cylinders for vehicles. The manufacturing process involves the drawing of
the natural gas from underground pipelines using the compressor. Depending
on the time of year, pipeline demand, and pipeline system, the composition
of the natural gas vary considerably. It may contain impurities, like
particulates, hydrogen sulfide, oil, oxygen or water. Hence today, quality
CNG Plant system also consists of facilities to address problems caused by
them.
CNG Refuelling Stations
The collective term used for the complete installation needed to refuel a
vehicle using CNG is a CNG refuelling station. The CNG refuelling station
consists of a gas supply, storage cylinders, gas compressor, priority panel
and dispenser. All CNG stations contain these basic components. However,
these stations come in many shapes and sizes. There are two types of
refuelling stations:
Time Fill (or Slow fill)
Here, the station uses the compressor to directly fill the vehicle over a
certain period usually whilst the vehicle is parked up overnight. Expensive
electronic dispensers are not required here but they are not suited to
public refuelling. This type of station is preferable to large bus depots
where all the vehicles come back to a known base every night.
Fast Fill
This is a common approach for light vehicles. The gas is dispensed here
from static storage cylinders which hold the gas at high pressures. The gas
compressors keep the pressure topped up at all times. This is done by
cutting in and out as and when required to replenish the gas taken out by
each vehicle filling. It is suited to public stations or where a fast fill
is required. Though any kind of vehicle can be refuelled this way, it is
most suited for cars, taxis, vans, and HGV's.
Benefits of CNG
- Abundance availability.
- A clear burning fuel, with no black smoke and hence environmental
friendly.
- CNG being lighter than air, diffuses upwards.
- Due to its very narrow flammability limits it is very safe fuel.
- Such a gas has an excellent knock resistant, lower compression ratio.
- Another benefit of using CNG is that there is low noise level of the
engine.
CNG
Plant
