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Natural gas is one of the most commonly used fossil fuels, powering industries. Statistics suggest that the world’s total annual consumption for 2022 was 4.04 trillion cubic meters. If we look at the last 20 years, the annual gas consumption displays an uprising trend, meaning the consumption increases.
This tremendous amount of gas has to be measured and modulated to the correct pressure range to be distributed and used. Natural gas stations are responsible for these duties. In this article, we’ll mention the types of different stations and station equipment.
Types Of Stations
If a natural gas station performs both pressure modulation and measurement, called Metering and Regulation (M&R) stations. In contrast, if the station only performs measurement, it’s an MS station.
Different networks operate with various pressures. To indicate which pressure range a gas station operates under, letter coding is used. Type A stations regulate pressure levels from 35-70 bars to 12-25 bars. Type B stations are the ones with a maximum inlet pressure of 25 bars. Finally, Type C stations operate between 4 bars and 0.3 bars.
To sum it all up with one example, an RMS-C station performs measurement and pressure modulation between 4-0,3 bars.
Different countries have various regulations about M&R stations, however, the piping inside the station is made out of steel pipes. All the measurement and emergency alarm systems have to be exproof to prevent explosions and usually, the station is built inside a stainless steel cabin to protect against weather elements.
Accurate marking of possible risks is a must, along with fencing around the station and keeping it locked. All welding joints inside an RMS go under the same inspection as any other gas line which is connected by welding. Finally, an RMS must be maintained and operated only by authorized and licensed personnel.
All M&R equipment must be licensed for use in the natural gas industry. A typical set of RMS equipment includes ball valves, bypass tubes, filters, regulators, flanges, grounding plates, rotary or turbine meters, and electronic volume correctors.
Many of the mentioned equipment is familiar to most engineers and technicians but electronic volume correctors or EVCs may not be that familiar. EVC is a piece of equipment that picks up mechanical movements from the gas meter, turning them into electronic pulses. These pulses keep the gas measurements on record. However, the EVC serves a much bigger purpose than recording consumption.
Gas is fuel in the gas phase and its measured and billed by volume. However, materials in the gas phase can change their volume depending on temperature and relative pressure. To measure gas in a way that is not affected by pressure changes, the number of gas that is measured in relative conditions needs to get corrected. To correct readings under relative conditions, the measured amounts need to get multiplied with a correction coefficient. This coefficient is calculated based on the relative conditions of the environment. EVC considers these factors and calculates the coefficient automatically to correct relative readings accurately. Corrected data can be stored separately or can be sent on a SCADA system via radio transmitters or GPRS modems. Transferred data is used on billing.
Flow Diagram of an M&R
The gas enters the M&R from underground and immediately passed through a filter to trap any loose debris. Gas filters need to get checked and cleaned regularly, otherwise, they’d block gas flow. After the initial filtering, the gas passes through a meter to get measured. Depending on the capacity of the station, different types of meters are used. The correct choice of meter is vital since different meters have various minimum, and maximum reading and sensitivity levels. Incorrect reading of consumption usually gets heavily fined by the network operator. After measurement, the gas passes through a regulator to get modulated into the desired pressure and then it travels towards the next destination.
Ball valves placed on the main lines of an RMS provide the ability to shut down the station in case of an emergency, maintenance, or malfunction. Many stations have two mainlines and meters to ensure uninterrupted gas flow during any of the mentioned scenarios. Any one of the main lines can be isolated with the entry valves and the gas remaining inside the pipe is drained by exhaust lines.
After shutting down a section of an RMS, repressuring that section can be challenging. The pressure difference between both ends of a station damages the ball of the valve. That’s why bypass tubings are used to equalize pressure between two sections before repressuring.
Correct measurement and modulation of gas are extremely important to provide users with an accurate and uninterrupted supply of gas. RMS is the equipment responsible for handling those duties.