Technical Blog
Technical Blog
May. 22, 2024
Natural gas transmission and distribution systems connect gas sources with industrial, commercial and residential users through an integrated network of pipelines, process stations, pressure regulating and metering facilities, and distribution networks.
Natural gas may travel over long distances at relatively high pressure before reaching a city gate station, industrial receiving station or regional distribution facility. At different stages of this process, the gas may require filtration, separation, pressure regulation, flow metering, heating, monitoring and other forms of treatment before it can be safely delivered to downstream users.
Understanding how these different stages work together is important when selecting equipment for a natural gas supply project.
This guide introduces the basic structure of a natural gas transmission and distribution system, the functions of its major facilities, and the equipment commonly used from the transmission pipeline to the downstream gas distribution network.
A natural gas transmission and distribution system is the infrastructure used to transport natural gas from a supply source to downstream consumers.
Depending on the project, the gas source may be a gas field, gas processing facility, upstream pipeline network, LNG regasification facility or another gas supply system.
A simplified process can be represented as:
Gas Source → Gas Processing → Transmission Pipeline → Transmission Station → City Gate Station → Distribution Network → End Users
Each part of the system has a different function.
Transmission pipelines are generally used to transport relatively large quantities of natural gas over long distances. Distribution systems receive gas from the transmission network, reduce and control the pressure as required, measure the gas flow and distribute it to industrial, commercial or residential users.
Between these two networks, various process stations provide the filtration, separation, pressure control, metering and monitoring required for reliable gas delivery.
Although transmission and distribution are parts of the same gas supply chain, they perform different functions.
Natural gas transmission refers primarily to the long-distance transportation of gas from production or processing areas to regional receiving facilities, city gate stations, industrial users or downstream distribution networks.
Transmission systems typically operate at higher pressures and larger flow capacities than local distribution networks.
Depending on the pipeline and operating requirements, transmission facilities may perform functions such as:
Gas receiving and delivery
Filtration and separation
Compression
Pressure regulation
Flow metering
Gas quality monitoring
Pig launching and receiving
Pipeline isolation and control
For a more detailed explanation of transmission station types and equipment, see:
Natural Gas Transmission Stations: Equipment & Functions
Natural gas distribution begins after gas is transferred from the transmission network to a regional or local distribution system.
Before entering the downstream network, gas pressure normally needs to be reduced and controlled according to the operating requirements of the distribution pipeline. Gas flow may also be measured, filtered, heated and monitored.
The distribution network then delivers gas to different types of users, including:
Industrial plants
Power generation facilities
Commercial users
Residential distribution networks
Other gas-consuming facilities
The exact configuration depends on gas demand, upstream pressure, downstream pressure requirements, local regulations and project specifications.
A complete gas supply system can contain several major stages.
Before entering a transmission pipeline, natural gas may require processing to remove components or contaminants that could affect pipeline transportation or downstream equipment.
The required treatment depends on the composition and quality of the gas.
After processing, natural gas can be transported through high-pressure transmission pipelines.
Pipeline diameter, operating pressure, gas flow capacity and distance are determined according to the design requirements of the transmission system.
Compressor stations may be used along long-distance pipelines where additional compression is required to maintain gas transportation capacity.
Different types of stations are installed along a transmission pipeline according to their location and function.
These may include receiving stations, compressor stations, regulating and metering stations, delivery stations, pigging facilities and other process stations.
Their configuration depends on the required process functions rather than on a single standard station arrangement.
[Internal Link: Natural Gas Transmission Stations: Equipment & Functions]
A city gate station or receiving station provides an important interface between an upstream gas transmission pipeline and a downstream distribution network.
Gas arriving from the transmission pipeline may require filtration, pressure reduction, metering, heating and monitoring before entering the downstream network.
Depending on local requirements, gas odorization may also be incorporated into the gas distribution process.
After the required pressure control and metering processes, natural gas enters the downstream distribution network.
The network may contain several pressure levels, with additional regulating facilities used to progressively reduce gas pressure according to downstream operating requirements.
Natural gas can ultimately be supplied to industrial, commercial, power generation and residential users.
The final pressure, flow and gas quality requirements vary considerably depending on the application.
Transmission stations are important process nodes within a long-distance natural gas pipeline system.
Depending on their purpose, they may receive gas from an upstream pipeline, remove entrained solids or liquids, measure gas flow, regulate pressure, support pipeline pigging operations or distribute gas into different downstream pipelines.
Typical station functions can include:
Gas receiving and delivery
Filtration and separation
Gas compression
Flow metering
Pressure regulation
Temperature and pressure monitoring
Pig launching and receiving
Process control and communication
Not every transmission station contains all of these functions. Equipment configuration should be determined according to the role of the station and the operating conditions of the project.
For a detailed discussion of station types, functions and typical process equipment, refer to:
[Internal Link: Natural Gas Transmission Stations: Equipment & Functions]
A city gate station is typically located between a high-pressure transmission pipeline and a regional or urban gas distribution network.
Its main purpose is to receive gas from the upstream transmission system and condition it according to the requirements of the downstream network.
A typical city gate or receiving station may include several process stages.
Natural gas can first pass through filters or filter separators to remove solid particles and entrained liquids that could affect downstream metering and pressure regulating equipment.
When natural gas undergoes significant pressure reduction, its temperature may decrease.
Depending on the operating conditions and process calculations, gas heating equipment can be installed upstream of pressure regulation to maintain the required gas temperature.
Gas flow is measured for operational monitoring, gas allocation or commercial measurement according to project requirements.
Different metering technologies can be selected depending on flow range, pressure, required accuracy and applicable specifications.
Pressure regulating equipment reduces the upstream gas pressure to the level required by the downstream distribution network.
Multiple regulating trains or regulators may be used according to required capacity, control philosophy and redundancy requirements.
Pressure, temperature, flow and other process parameters can be monitored through instrumentation and control systems.
Remote communication can also be incorporated when required by the project.
Natural gas odorization may be required before gas enters certain distribution networks.
An odorization system introduces a controlled quantity of odorant into the gas stream according to the project design and applicable requirements.
[Internal Link: Gas Odorization Systems]
Integrated filtration, metering and pressure regulating functions can be assembled into skid-mounted systems to reduce field assembly and simplify equipment integration.
[Internal Link: Gas Pressure Regulating & Metering Equipment]
For an example of this type of configuration:
[Internal Link: City Gate Natural Gas Regulating & Metering Skid]
The equipment required for a natural gas transmission and distribution project depends on the process conditions and station functions.
Some commonly used equipment includes the following.
Filters and separators help remove solid contaminants and entrained liquids from the gas stream.
They can be installed upstream of metering, regulating and other process equipment to support downstream equipment operation.
[Internal Link: Gas Treatment & Auxiliary Equipment]
Gas heating may be required when pressure reduction could cause the gas temperature to fall below the required operating range.
Water bath heaters, heat exchangers and other heating configurations can be selected according to the process conditions.
Pressure regulating systems control downstream pressure despite variations in upstream pressure and gas demand.
The number of regulating trains, regulator configuration and control strategy are determined according to the project requirements.
Natural gas metering systems measure gas flow for operational monitoring, allocation or commercial purposes.
Depending on project requirements, metering technologies may include ultrasonic, turbine or other suitable flow measurement methods.
[Internal Link: Natural Gas Metering Skid]
For many stations, filtration, metering, pressure regulation, instrumentation, valves and process piping can be integrated into a factory-assembled skid-mounted system.
The skid configuration is engineered according to gas flow, pressure, temperature, metering requirements and control philosophy.
[Internal Link: Gas Pressure Regulating & Metering Equipment]
Pig launching and receiving facilities are used to support pipeline inspection, cleaning and maintenance operations.
Their configuration depends on pipeline diameter, design pressure, pigging requirements and station arrangement.
Gas odorization systems inject a controlled quantity of odorant into natural gas where odorization is required.
Automatic or other project-specific configurations can be selected according to gas flow conditions and operating requirements.
[Internal Link: Gas Odorization Systems]
Pipeline gas is not the only source that can supply a natural gas distribution network.
LNG can also be used as a gas supply source, particularly for locations without direct pipeline access, satellite gas supply projects, industrial gas supply facilities and other applications where LNG is delivered to the site.
A simplified LNG supply process can be represented as:
LNG Storage → LNG Vaporization / Regasification → Pressure Regulation → Metering → Gas Distribution Network
LNG is stored as a cryogenic liquid and must be vaporized before it can be supplied as gaseous natural gas.
Depending on the project, LNG vaporization can be performed using ambient air vaporizers, water bath vaporizers or other suitable heat exchange systems.
After regasification, the gas may require pressure regulation, metering and other process functions before entering the downstream gas network.
This means LNG regasification equipment can function as an alternative gas supply interface for a downstream natural gas distribution system.
[Internal Link: LNG Equipment]
The final LNG system configuration depends on LNG supply conditions, required gas flow, operating pressure, ambient conditions and downstream gas requirements.
Natural gas transmission and distribution equipment should be selected according to actual project operating conditions rather than only by nominal pipeline size or gas flow.
Before determining the equipment configuration, several key process parameters should normally be confirmed.
Gas composition affects material selection, treatment requirements and process design.
Where relevant, information on components such as methane, heavier hydrocarbons, carbon dioxide, hydrogen sulfide, water content and other constituents should be provided.
Normal, minimum and maximum gas flow requirements help determine equipment sizing and operating range.
The normal operating range and maximum design conditions of the upstream gas supply should be identified.
The downstream operating pressure determines the required pressure reduction and regulating configuration.
Minimum and maximum gas and ambient temperatures may affect material selection, heating requirements, instrumentation and equipment design.
The expected contaminants and required gas cleanliness should be considered when selecting filters and separators.
The purpose of metering, required operating range, accuracy requirements and applicable measurement standards should be defined before selecting a metering system.
Where significant pressure reduction occurs, process calculations can be used to determine whether gas preheating is required and the necessary heating duty.
Projects may require local PLC control, remote monitoring, SCADA communication or integration with an existing control system.
Ambient temperature, hazardous-area classification, installation location, local codes and customer specifications should also be considered during equipment engineering.
For this reason, gas regulating, metering and treatment systems are commonly engineered according to project-specific process data rather than supplied as one fixed standard configuration.
Natural gas transmission generally refers to transporting large quantities of gas over longer distances through higher-pressure pipelines. Distribution refers to delivering gas from transmission or receiving facilities through downstream networks to industrial, commercial and residential users.
A city gate station is a facility located between an upstream gas transmission system and a downstream distribution network. Depending on the project, it can perform filtration, heating, metering, pressure regulation, monitoring and odorization functions.
Typical equipment may include filters or filter separators, gas heaters, flow meters, pressure regulators, valves, instrumentation, control systems and process piping. The actual configuration depends on the operating conditions and project requirements.
Gas temperature can decrease during pressure reduction. Depending on the inlet conditions, pressure reduction ratio and required downstream temperature, preheating may be used to maintain suitable operating conditions.
Different flow-metering technologies can be used depending on gas flow, pressure, operating range, required accuracy and project specifications. Ultrasonic and turbine flow meters are among the technologies used in natural gas applications.
LNG can be stored at the supply site and vaporized through a regasification system. After vaporization, the gas can undergo pressure regulation, metering and other required process steps before entering the downstream gas distribution network.
A natural gas transmission and distribution system is not a single piece of equipment, but an integrated infrastructure that connects gas sources with downstream users through pipelines, process stations and distribution networks.
From long-distance transmission to city gate stations and downstream gas distribution, each stage requires equipment selected according to specific gas flow, pressure, temperature, gas quality and operating requirements.
Filtration, separation, heating, metering, pressure regulation, pigging and odorization can all form part of the overall gas supply process.
HUAYI provides gas equipment and engineered skid-mounted systems for natural gas transmission, distribution and industrial gas supply applications, including pressure regulating and metering systems, gas treatment equipment, LNG equipment and gas odorization systems.
[Internal Link: Natural Gas Equipment]
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