About CNG Station:
For transportation of natural Gas within the city, pipeline is being laid from City Gate Station (CGS) where natural gas is pushed at a pressure of 15 barg or even lower. In order to dispense the gas to CNG vehicles, there are CNG stations at various locations, where the gas is being compressed upto 250 barg initially and then dispensed to vehicles at a pressure of 200 barg. Typically following are the types of CNG Stations.
Online stations are directly connected with the Natural Gas Pipeline. At online station, natural Gas is received at a pressure of 19 barg and then compressed upto a pressure of 250 barg with the help of a reciprocating compressor in order to enhance the on board storage capacity of vehicle. Then, it is dispensed to vehicles locally through CNG dispensers at a pressure of 200 barg. Typically a CNG Online Stations consists of following equipments:
- CNG Compressor
- CNG Dispenser
- Storage Cascade
Mother stations are similar to an online station, where it has the facility to refuel the mobile cascades in addition to the local demand of vehicles. These mobile cascades are then dispatched to other stations, which do not have the connectivity of pipeline.
Daughter stations do not have the connectivity of natural gas pipeline. At these stations, compressed natural gas (CNG) is transported through mobile cascades (bunch of cylinders mounted on trucks) at a pressure of 240-250 barg and then dispensed to vehicles through CNG dispensers. In fact, under stopped condition of CNG Compressor, a mother/online station acts as a Daughter Station and dispensed the gas from the local storage cascades.
Principle of CNG Refueling/Dispensing:
CNG is dispensed to vehicles on the principle of Pressure Equilibrium. Once the pressure of mobile cascade drops below 200 barg at daughter stations, the customers (vehicles) gets lesser amount of gas, which is below 200 barg. With each fill there after, the amount of gas dispensed to vehicles starts decreasing and the filling time starts increasing, leaving the customer un-satisfied.
Daughter Booster Station:
Daughter booster stations are similar to Daughter stations. However, in order to satisfy the customers w.r.t. amount of gas dispensed as well as filling time, a booster compressor (hydraulic type with variable suction pressure) is installed in between the mobile storage and the CNG dispenser. Booster compressor increases the pressure above 200 barg once the pressure of the mobile cascade falls below 200 barg and works upto the pressure of the mobile cascade falls below 30 barg. Thus maximum amount of gas stored in the mobile cascade is used at Daughter Booster station.