Design and function
Natural gas metering and regulating stations can be delivered based on the specific requirement by the user or as standard types.
Depending on the flow capacity, available inlet pressure, required outlet pressure, custom designs of metering and regulating
stations are available. Metering and regulating gas stations usually are designed as skid mounted, on steel skid frame in metal cabinet,
for convenient transport and mounting.
Gas metering station are used as city gate, in distribution network, industrial, commercial, underground or domestic use.
Gas metering and regulating stations can be with one, two or even more regulating lines, depending on the flow capacity requirement
and available flow capacity by regulators, related to inlet pressures. Each regulating line consists of ball valves on the begging
and on the end of regulating line, gas cartridge filter with drainage ball valve, natural gas pressure regulator with safety shut of valve,
safety relief valve with exhaust ball valve for emptying gas line and pressure gauge with connections for pressure and temperature transmitters.
For natural gas users which require constant gas supply without potential risk of gas supply shortage, and basically for every station that has capacity over
150 Sm3/h, it is recommended to use metering and regulating stations with two parallel regulating lines with the same capacities.
In that way, eventual malfunction of pressure regulator on the first regulating line which may lead to safety shut off valve activation,
the second regulating line will take action and continue to operate, preventing gas supply cut off. Periodical check of safety shut off valve position is required, to check if one has been activated, as it can be deactivated only
by hand operation.
In situations where pressure reduction can cause freezing, gas preheaters are used. Preheaters are mounted after the inlet ball valve, and
before cartridge filters preventing freezing of installation. Usually preheters are working with hot water that is produced in boilers using gas
from the installation. For that boiler, additional pressure regulating line is required, with all equipment as stated above.
Integral part of gas metering and regulating station is line for metering of gas consumption. Each metering line consist of ball valves
on the beginning and on the end of gas line, gas meter and connections for pressure and temperature transmitters. Regularly for gas metering
several types of gas meters are used, like turbine gas meters, rotary gas meters, or for very high flow rates, ultrasound flow meters and orifice
flow meters. For calculation of gas flow at standard condition, electronic volume correctors are used, which convert the real gas flow measured by
gas meter into the flow on standard condition which is used for pay bills.
For precise gas metering turbine and rotary gas meters are used, with measuring range from 1:20 to 1:160 and measuring error less than 2%.
If the gas consumption is in the range that one flow meter can not cover, than two flow meters should be used where the bigger one is for
higher values of flow, and the smaller one is for measuring flows that are bellow the range of bigger flow meter measurement.