City gas station is a cluster of pipelines & appliances for converting high pressure gas from the main trunk line to a medium pressure distribution grid and subsequently to service pipelines. The gas is then supplied to domestic, industrial or commercial premises and CGD stations located in specified charge areas or geographical areas.
According to PNGRB guidelines, CGD network in India comprises of one or more or all of the following: 1) Primary network, 2) Secondary network & 3) Tertiary Network.
The primary network is a medium pressure distribution system comprising of pipelines normally constructed using steel pipes. The operating pressure is between 7 to 49 bars. The objective is to supply gas to secondary distribution network or service line to bulk customers.
The secondary network is a low pressure distribution system comprising of pipelines normally constructed using thermoplastic piping (MDPE) (Medium Density Polyethylene). In the secondary network the operating pressure is between 7 bar and above 100mbar.
The tertiary network is a service pressure distribution system comprising of service lines, service regulators & customer metering systems constructed using a combination of thermoplastic (MDPE) piping & GI/Copper tubing components. In a tertiary network, the operating pressure is less than 100 mbar.
Distribution mains are designed to ensure uninterrupted supply to tertiary network or to industrial consumers through service lines. Sub transmission pipelines connect the main transmission pipelines to the City Gas Station (CGS) but are owned by CGD entity.
Natural gas is supplied to customers in two forms i.e. Piped Natural Gas (PNG) & Compressed Natural Gas (CNG). Gas from transmission pipelines is sent to City Gas Stations (located at the outskirts of a city), & then it is further distributed to automobile users in the form of CNG and to domestic, industrial & commercial customer in the form of PNG. Natural gas from CGS is transferred to PNG & CNG segment for distribution at a pressure of 15-19 bars.
In the PNG segment, gas from CGS is sent to District Regulating Station (DRS) for domestic users & Common Pressure Reduction Skid (CPRS) for industrial users. In DRS/CPRS pressure of gas is further reduced to 4 bar. Meter Regulating Station (MRS) is installed after CPRS to reduce the gas pressure to 4-1.5 bars for industrial usage. For domestic customers, Service Regulators (SR) are installed after DRS to reduce the pressure from 4 bar to 100 mbar. For domestic usage, gas pressure is further reduced from 100 mbar to 21 mbar by a meter regulator, and then gas is supplied safely to households.
In the CNG segment, natural gas from CGS is transferred to CNG Station where it is compressed to 200-250 bar pressure. The gas is then filled in the vehicle cylinders.