This is second post of city gas network series. For the first post, please check “City Gas Flowrate Requirement”.
City gas distribution is one of Indonesia national priority program which purpose is to diversify energy, to reduce energy subsidiary, to provide clean and cheap energy, and as complementary program to convert cerosene into Liquified Petroleum Gas (LPG).
The total installed city gas until now is 56,888 house connection. It will be increased year by year. For example in 2013, the government planned to installed 16,000 connection.
In this post I want to share you overview of city gas distribution system from transmission pipeline to service pipeline at house.
Figure below shows overview of gas distribution from high pressure pipeline to low distribution service line. There are several important parts.
According to Indonesia Oil and Gas General Directorate, the pipe shall be designed for 20 years life time. Pipe diameter that can be used are 6”, 4”, 10 mm, 125 mm, and 90 mm
Tapping from Transmission Pipeline
Tapping from transmission pipeline can be done by hot tap. We use carbon steel pipe for tapping from transmission pipeline to inlet MRS.
Metering and Regulating Section
Gas pressure from transmission pipeline is high, therefore it must be reduced to guarantee safety operation of city gas. Reduction and meter of gas is conducted in Metering and Regulating Section (MRS).
Design of MRS must comply with the following specification:
- MRS must be designed based on its design pressure and must have accuracy better tahn 1%-volume.
- MRS must be designed according to approved engineering drawing.
- MRS must be designed to remove dirt or contaminant in gas.
In general, MRS have this configuration:
- MRS must be provided with standby stream with the same configuration and capacity as main stream
- MRS must be provided by by pass provided that can be switched from main line to ensure continuity of gas supply
- Every pipe connection must be design with maximum velocity 20 m/s for gas before entering filter and 40 m/s for gas leaving filter at the same condition. This requirement is not valid for tube meter and valve regulator
- Inlet and outlet of gas connection must be installed with cathodic protection
- Emergency valve must be operated quickly (less than 1 second to detect over pressure at upstream of gas supply)
- Gas filter must be designed and fabricated according to ASME VIII or BS5500 or equal. Pressure drop of filter element must be less than 0.1 bar for filter size 50 micron.
- Meter must be turbine type with full type flow. It must be provided with pressure and temperature correction.
- Regulating valve must be in monitor/active mode
- Every regulating valve must be provided with pressure relief valve for over pressure protection. Gas is directly released to atmosphere.
- MRS must be provided with wafer-type check valve which can withstand back pressure of 10 bar for item 1-4 and 15 barg for item 5 and have differential pressure less than 0.1 bar.