City gas distribution (CGD) operators have gradually started using advanced metering solutions. The key areas of improvement for local gas distribution utilities are enhancing operational efficiencies and bringing down costs. Technological advancements in meter-to-cash, distribution, customer service, leakage detection, workforce management and asset management can help in revenue protection and operational efficiency.
Smart Utilities takes a look at various gas metering options, their key characteristics and benefits, and different metering systems installed by CGD utilities in India…
There are several kinds of gas meters including diaphragm meters, rotary meters, turbine gas meters, electronic volume converter and ultrasonic meters.
Diaphragm meters are volumetric meters that are suitable for small industrial and commercial consumer loads at low pressures. The typical turndown ratio (the ratio of maximum measured flow to minimum measured flow) of such meters stands at 150:1. Some of the advantages of using a diaphragm meter are good turndown, and high tolerance for installation effects and load characteristics. Also, these meters have low maintenance requirements. The size of the meter, particularly at large capacities, is however a concern. Further, the accuracy specification of these meters is lower than that of other meters.
Rotary meters are also volumetric meters and are appropriate for medium-sized loads at lower pressures. The typical turndown ratio of such meters is in the range of 35:1 to 50:1. Rotary meters have good turndown, and high tolerance for installation effects and load characteristics. These meters have a very long shelf life and are much smaller in size as compared to diaphragm meters. However, they require lubrication and in case of a meter failure, they can result in gas supply disruption. Also, these meters are comparatively expensive.
Turbine gas meters are inferential meters, which are sensitive to gas velocity instead of volume flow. Such meters are capable of processing high pressure steady loads. The typical turndown ratio of these meters is 20:1. These meters are smaller in size, cost less as compared to its alternatives and have higher accuracy rates. Unlike rotary meters, there is no gas supply disruption in case of a turbine gas meter failure. However, these meters are sensitive to installation effects and load behaviour, and gas filtration is necessary to ensure accurate reading. These meters also require frequent lubrication.
The usage of different kinds of meters is generally determined on the basis of a common usage area. Diaphragm meters are used for a 100 cubic metre per hour flow rate; rotary positive displacement (RPD) meters are preferred for a 1,000 cubic metre per hour flow rate; and turbine meters are considered for a 10,000 cubic metre per hour flow rate.
Traditional meter reading practices are prone to human errors. Also, demand analysis, gas audits, loss identification, etc. cannot be undertaken using traditional meters. Automatic meter reading gas meters are based on four different technologies. These include technologies that are radio based, telephone based and power line carrier based. A hybrid of these technologies can also be used. Smart meters are designed to transmit pricing and energy information from the utility company to the consumer, enabling two-way communication.
Smart gas metering offers several advantages such as walk-by metering, fixed SMS/global positioning system metering and fixed cluster metering. Under walk-by metering, radio frequency (RF) data loggers with 50 metre to 200 metre effective communication distance (2 km in open space) can be used. These are compatible with different types of meters and are easy to retrofit.
Under SMS-based metering, data loggers compatible with different types of meters are used. These are capable of storing data with a 24-hour consumption profile and can communicate via general packet radio service. For fixed cluster metering, readouts from meters with RF data loggers are collected by a concentrator installed on one of the meters. These systems are helpful for residential customers, particularly in multi-storey buildings.
Metering systems installed by CGD utilities in India
GAIL Gas Limited
GAIL Gas utilises metering options such as turbine gas meters, RPD meters and diaphragm gas meters, depending on the flow and pressure requirements. Turbine gas meters are used to measure gas flow and large gas volumes; RPD meters measure gas mixtures; and diaphragm gas meters are installed in households and on industrial premises for measuring gas usage.
The company utilises diaphragm gas meters with AGA 7/T4S standards for domestic and commercial users. These meters are beneficial for measuring lower volumes accurately. On the other hand, for industrial customers, turbine meters and RPD meters along with flow computer/electronic volume correctors are used. Further, these meters are equipped with a communication device that can send online data to the control centre. For the compressed natural gas (CNG) segment, GAIL Gas has installed mass flow meters in line with the International Organisation of Legal Metrology’s standards.
Central UP Gas Limited (CUGL) uses ultrasonic flow meters, process gas chromatograph and a computerised workstation to check gas flow and quality. While the ultrasonic flow meter helps in the accurate estimation of gas flow, the process gas chromatograph determines the gas composition and calculates its gross heating value.
Further, to keep track of the quantity of gas sold, CUGL has adopted advanced metering systems. In this context, GSM-based metering facilities have been installed for industrial users. These ensure high efficiency without any lag. With reference to the domestic and commercial segments, mechanical meter reading facilities are being used to reduce costs for customers.
CNG sales are monitored through coriolis flow meters. According to CUGL, these meters do not require any moving parts and therefore result in low operation costs as well as high measurement accuracy.
In addition, CUGL has adopted diaphragm and RPD flow meters in the commercial, domestic and, to some extent, industrial segments. The company has also installed RPD volumetric flow meters with electronic volume correctors, which are used to measure the quantity of gas sold to customers.
Mahanagar Gas Limited (MGL) uses a variety of metering options such as ultrasonic flow meters, mass flow meters, turbine meters, RPD meters and diaphragm meters.
The company receives gas from GAIL India at its four existing gas receiving stations, which are equipped with ultrasonic flow meters. Although GAIL India has installed ultrasonic flow meters for custody transfer applications, MGL has installed them to serve as check meters. To measure the mass of gas at its CNG stations, MGL utilises mass flow meters. It has installed about 1,000 mass flow meters at its CNG stations. These meters have a flow range of 1-100 kg per minute and an operating pressure of 250 bar.
To measure gas flow, MGL has adopted turbine meters and has installed RPD meters for the measurement of gas mixtures. Both these meters are used depending on their applications in the industrial and commercial sectors. The flow range of these meters is up to 1,600 cubic metres per hour and the operating pressure is in the range of 0.1-4 bar.
MGL has also installed diaphragm meters to measure gas usage by small commercial and domestic customers. The flow range of these meters is up to 65 cubic metres per hour. While the operating pressure for domestic diaphragm meters stands at 20 millibar, commercial diaphragm meters operate at a pressure of 100 millibar.
With inputs from a presentation made by Pramod Karwa, Divisional Manager, Raychem RPG, at a recent Indian Infrastructure conference