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What is a long distance natural gas pipeline project?

With the increase of natural gas exploration and development in China and the increasing material and environmental protection needs of the people, the development of natural gas long-distance pipeline is very rapid in recent years. With the continuous extension of the pipeline, the social responsibility, political responsibility and economic responsibility of pipeline enterprises are also increasing. Therefore, it is particularly important to popularize the knowledge of long-distance natural gas pipeline.

20200726084634 29529 - What is a long distance natural gas pipeline project?

What is a long distance natural gas pipeline project?

Gas transmission pipeline engineering refers to the project of transporting natural gas and gas by pipeline, which generally includes gas transmission line, gas transmission station, pipeline crossing (crossing) and auxiliary production facilities.
The pipeline project is divided into gas transmission trunk line and gas transmission branch line. The gas transmission trunk line is the main operation pipeline from the first gas transmission station to the gas transmission terminal station; the gas transmission branch line is the pipeline that inputs gas to the gas transmission trunk line or outputs the gas transmission pipeline from the gas transmission trunk line.
The line block valve chamber is a part of the line engineering, and the main equipment includes pigging tee, line block ball valve, upstream and downstream vent bypass process, vent riser, etc. its function is to block the line in sections under extreme conditions or line maintenance. The valve chamber is set with different spacing according to the regional level of the line.
Valve chamber system includes manual valve chamber and RTU valve chamber.

Manual valve chamber

The manual valve chamber realizes automatic shut-off of overpressure, low pressure and pressure drop rate detection and local indication of process parameters in the valve chamber. The main local measurement and control parameters are: pipeline temperature display, pressure display before and after emergency shutdown valve.

RTU valve chamber

RTU system can realize remote data acquisition, monitoring, management and monitoring of combustible gas leakage in valve chamber.
Main functions of RTU system:

  • 1) Data acquisition and transmission function: collect process operation parameters in valve chamber and transmit them to control center system.
  • 2) Control function: execute the command issued by the control center; start and stop control of the whole valve chamber; remote control and local manual control of the gas-liquid linkage valve of the line.
  • 3) Other functions: self diagnosis and self recovery; exchange information with third-party system or intelligent equipment through communication interface.

Process station

Gas transmission station is the general name of various process stations in gas transmission pipeline engineering. Generally, it includes initial gas transmission station, gas transmission terminal station, compressor station, gas receiving station, gas distribution station, pigging station, etc.
Gas transmission station is an important part of gas transmission piping system. Its main functions include pressure regulation, filtration, metering, pigging, pressurization and cooling. The purpose of voltage regulation is to ensure that the input and output gases have the required pressure and flow rate; the purpose of filtration is to remove solid impurities in natural gas, avoid increasing resistance to gas transmission, wear instruments and equipment, and pollute the environment; metering is essential for gas sales and business handover; at the same time, it is also the basis for automatic control of the entire pipeline. The purpose of pressurization is to provide certain pressure energy for natural gas, while cooling is to reduce the temperature of gas due to pressurization, so as to ensure the gas transmission efficiency. According to the location of gas transmission stations, their functions are also different.

First station

The first station is the starting point of the gas pipeline. The first gas transmission station is usually near the gas field, and the first station of Sichuan East gas pipeline is close to Puguang gas field.
Main functions of the first station:

  • Receive the gas from the natural gas purification plant for on-line gas quality analysis and chromatographic analysis;
  • The natural gas is filtered and separated;
  • Measure and calibrate the natural gas after filtration and separation;
  • The metered natural gas is sent to the downstream station through bypass pipeline or pressurization;
  • Pig launching;
  • Emergency cut-off;
  • Venting and blowdown during accident and maintenance;
  • Station data acquisition and monitoring.

Terminal station

The terminal station is the terminal station of the gas pipeline. The gas is supplied to users through the terminal station. Therefore, the terminal station has the functions of pressure regulation, filtration, metering and pig acceptance. In addition, in order to solve the problem of imbalance between pipeline transportation and user gas consumption, peak shaving facilities, such as underground gas storage and gas storage tank, are also set up. There are six special line and branch terminal stations in the Sichuan East gas pipeline, including Dahua terminal station, SVW terminal station, Jiujiang terminal station, Yangzi Petrochemical Terminal Station, Nanjing terminal station and Jinling terminal station, and one terminal station of trunk line, which is Shanghai terminal station.
Main functions of terminal station:

  • Pig receiving;
  • Gas filtration and separation treatment;
  • Gas flow measurement, online calibration;
  • Gas pressure regulation;
  • Station gas supply;
  • Station emergency cut-off and venting;
  • Station sewage discharge;
  • Station data acquisition and monitoring.

Pigging station

Pigging station is a process station with pig receiving and receiving, natural gas separation equipment and facilities and pigging operation functions. There are 2 stations with simple pigging function along the Sichuan East gas pipeline, which are respectively set in Huangjin and Yesanguan to carry out sectional pigging on the pipeline regularly.
Main functions of pigging station:

  • Pig receiving and launching;
  • Cyclone separation of trunk gas;
  • Station gas supply;
  • Station emergency cut-off and venting;
  • Station data acquisition and monitoring.

Compressor station

The compressor station is located along the gas transmission pipeline to pressurize the pipeline gas with compressor. There are three compressor stations in Sichuan East gas pipeline, namely Puguang initial station, Lichuan compressor station and Qianjiang compressor station.
Main functions of compressor station:

  • Receive the gas from the purification plant and conduct on-line gas quality analysis and chromatographic analysis;
  • The natural gas is filtered and separated;
  • Measure and calibrate the natural gas after filtration and separation;
  • After pressurization, the natural gas will be sent to the downstream pipeline after pressurization;
  • Pig launching;
  • Emergency cut-off;
  • Venting and blowdown during accident and maintenance;
  • Station data acquisition and monitoring.

Distribution station

Along the gas transmission pipeline, the stations set up for distributing gas to users generally have the functions of separation, pressure regulation, metering and pigging.

Gas receiving station

Along the gas transmission pipeline, the stations set up to receive the gas from the gas transmission branch line generally have the functions of separation, pressure regulation, metering and pigging.

Automatic control system

With the development of electronic computer, instrument automation technology, communication technology and information technology, “supervisory control and data acquisition (SCADA system)” has been widely used to complete the automatic monitoring and protection of natural gas pipeline transportation, and has become the basic mode of pipeline automatic control system. The automatic control system of Sichuan East gas pipeline project adopts the computer-based monitoring and data acquisition (hereinafter referred to as SCADA) system.
Under normal conditions, the dispatching control center is responsible for the automatic control and dispatching management of the whole line, and the backup control center takes over the monitoring of SCADA system of the whole line in case of dispatching control center failure or war, natural disaster, etc.
The pipeline SCADA system implements remote data acquisition, monitoring control, safety protection and unified dispatching management for each station. The dispatching control center can send dispatching instructions to each station control system, and the control function is completed by the station control system; the dispatching control center realizes resource sharing, real-time collection and centralized processing of information through the communication system. The three-level control mode of dispatching center control level, station control level and local control level is adopted for Sichuan East gas pipeline.
The first level is the central control level: remote monitoring of the whole line and unified dispatching management. Under normal conditions, the dispatching control center monitors and controls the whole line. The control of each station along the line does not need manual intervention, and the SCS and RTU of each process station complete their respective monitoring work under the unified command of the dispatching control center.
The second level is station control level: in the initial station, each off load station, compressor station and terminal station, the station control SCS system is used for data acquisition, monitoring control and interlocking protection of process variables and equipment operation status in the station. Remote terminal unit (RTU) is set in unattended pigging station to collect, monitor and control process variables and equipment operation status. The control authority of station control level is determined by the dispatching control center, and the operator is allowed to operate the station within the authorized scope through SCS or RTU after authorized by the dispatching control center. When the communication system breaks down or the system is overhauled, the station control system is used to monitor and control each station.
The third level is local control level: the local control system carries out manual / automatic local control of process unit or equipment. In case of equipment maintenance or emergency cut-off, local control mode can be adopted.
SCADA system configuration and function:

Dispatching control center

The configuration hardware part includes all kinds of servers and workstations, and the software part includes operating system software, SCADA system software, database management, alarm and event management and special software packages (receiving and sending tracking, simulation software and gas management system (GMS) software, etc.).
The main functions include: data acquisition and processing; dispatching and operation commands; display of dynamic process flow; alarm and event management; collection, archiving and trend display of historical data; report generation and printing; implementation of standard configuration software and user generated software; clock synchronization; real-time simulation of gas transmission process and training of operators; Pressure and flow regulation; gas transmission process optimization; fault diagnosis and analysis of instruments and systems; network monitoring and management; automatic switching of main and standby communication channels; trade settlement management; emergency shutdown of the whole line; pipeline leakage detection.

Backup control center

The configuration hardware part includes all kinds of servers and workstations, and the software part includes operating system software, SCADA system software, database management, alarm and event management and special software packages (receiving and sending tracking, simulation software and gas management system (GMS) software, etc.).
The main functions include: data acquisition and processing; dispatching and operation commands; display of dynamic process flow; alarm and event management; collection, archiving and trend display of historical data; report generation and printing; execution of standard configuration software and user generated software; clock synchronization; pressure and flow regulation; fault diagnosis and analysis of instruments and systems; network monitoring Visual and management; automatic switching of main and standby communication channels; emergency shutdown of the whole line; pipeline leakage detection.

Monitoring terminal of gas transmission management department

The management office has two monitoring terminals respectively, which can only realize data monitoring, but not control.
The main functions of the monitoring terminal are as follows: dynamic process display; alarm and event display; historical data trend display; instrument fault diagnosis and analysis display.

Station control system

Each station is equipped with SCS, with different number of workstations, station control system PLC and ESD system PLC.
The main functions of the station control system are as follows: data acquisition and transmission function, control function, display function, printing function, ESD off function, data management and other functions.

Remote control terminal RTU

RTU of remote control line block valve chamber is set in the whole line. RTU can realize the following main functions: data acquisition and processing; logic control; receiving instructions from dispatching control center; sending real-time data with time tag to dispatching control center; self diagnosis function; fault alarm.

Flow measurement and trade management

Trade Measurement

Gas ultrasonic flowmeter or gas turbine flowmeter is selected for trade transfer flowmeter, and the diameter of turbine flowmeter is generally less than DN 100. When the gas ultrasonic flowmeter is between 5% Qmax ~ Qmax (Qmax is the inherent maximum flow range of the flowmeter), the measurement accuracy is better than ± 0.5%. The measurement accuracy of gas turbine flowmeter is better than ± 0.5% in the range of 20% Qmax ~ Qmax, and the measurement accuracy of gas turbine flowmeter is better than ± 1% in the range of qmin ~ 20% Qmax. The metering system uses an independent flow computer as the flow accumulation unit, and transmits the data to the SCS system.
The first station is equipped with online chromatography, H2S and water dew point analyzer to detect the gas quality and parameters.
Other metering stations are equipped with on-line chromatographic analyzers to detect gas quality and parameters.
The dispatching control center is equipped with gas management system (GMS), which calculates the field natural gas flow, temperature and pressure data, and provides data for the trade management system.

Self use gas metering

The station shall be equipped with the station service gas treatment skid, and the turbine flowmeter shall be used for the metering of self used gas. The station gas includes flare ignition gas, natural gas generator gas and domestic gas.

Gas management system (GMS)

Gas management system (GMS) is a gas / energy trade management system, which can automatically manage the handover, sales and transportation of natural gas, provide data required by the company’s finance, provide users with the data required for inquiry, complete the functions required by trade settlement and archive the data.
The software structure of gas management system (GMS) is divided into the following parts: real-time data and historical database management platform, pipeline operation plan, management and financial information system, gas metering system, etc.

Simulation system

In order to accurately evaluate the past of the pipeline, explain the current events of the pipeline, and predict the future of the pipeline. The real-time simulation software is used in Sichuan East gas pipeline, which can provide reference for operators and dispatchers and provide training platform for operators to ensure safe, stable, efficient and economic operation of gas transmission pipeline.
The simulation software configures the pipeline model according to the actual situation of the pipeline. According to the needs of calculation results, such as pipeline leakage alarm, natural gas component tracking, flow rate of each pipeline section, gas storage capacity, pressure distribution status, pig position in the pipeline, etc., are written into the real-time database of SCADA by simulation software, and displayed on the operator workstation, as a reference for the operator on pipeline operation scheduling.
The simulation system consists of real-time transient, hydraulic characteristics, gas component tracking, instrument analysis, pipe filling management, pipeline efficiency, pig tracking, process prediction, SCADA training, etc.

Communication system

The communication system provides a variety of communication services for the production scheduling, administrative management, line inspection and repair, life logistics, etc. of the long-distance pipeline, and opens video services such as remote monitoring and video conference. At the same time, it provides reliable channel for the data transmission of the pipeline SCADA system and provides communication support for the digital pipeline. Due to the high degree of automation and less maintenance personnel, the communication system is required to be advanced in technology, stable and reliable, with high transmission quality, so as to reduce the workload of daily maintenance as much as possible and meet the needs of future communication development.
The general pipeline communication part includes: optical transmission system, television monitoring system and perimeter security system, video conference system, program-controlled telephone exchange system, local area network office automation (OA) system, line patrol repair and emergency communication system and public network backup communication system.
Generally, optical fiber communication, DDN public network communication, GPRS wireless communication and satellite communication are used.

Power supply and distribution system

Station power supply and distribution

For compressor station and other stations with large power load, 110 kV or 35 kV substation shall be built to provide power. Other stations with small power load are generally reported to install 10 kV external power lines, which are supplied by 10 kV / 0.4 kV transformer transformer.
In order to ensure the normal operation of gas transmission production, the automatic natural gas generator set is selected as the emergency self-contained power supply. In case of external power failure, the generator set shall provide power for the first and second level loads in the station. Rated voltage selection of natural gas generator set: AC 380 / 220 V, 50 Hz, 3-phase, 4-wire. The operation mode is automatic switching between mains power and power generation.

Power supply and distribution of valve chamber system

RTU valve room power supply

There are three main power supply modes, such as RTU and gas power supply system.
According to the geographical location of RTU valve chamber, solar power system and small capacity gas power generation device are set respectively to provide power for automatic control, communication, anti-corrosion and lighting in RTU valve chamber. According to the similar meteorological conditions of RTU valve chamber, the solar power supply is determined for plain area with no light day less than or equal to 11 days and the place without sunlight blocking. The valve chamber uses 1000ah valve controlled sealed lead-acid battery as standby power supply, and the backup time is about 48 hours. Remote monitoring and control are realized through SCADA system. All alarm signals are transmitted to SCADA system through common alarm contact.
The RTU valve chamber powered by external power supply adopts a 10kv High-voltage external power supply, and a 10 / 0.4kV transformation and distribution room is built in the station, and a single indoor dry-type transformer is set. In order to meet the requirements of level I power load, redundant UPS UPS UPS is adopted in case of power loss of external power supply, and the battery configuration is considered for uninterrupted time of 3 days. At the same time, the power supply device has local and remote monitoring functions.

Manual valve chamber power supply

The power demand of manual valve chamber is mainly to meet the electronic control unit of the actuator of the line block valve chamber. The power load is very small. Small solar panels are used to supply power with sealed lead-acid batteries. In the case of light, the solar power supply floats the lead-acid battery, and the lead-acid battery maintains the normal working voltage of the electronic control unit of the actuator.

Pipeline corrosion protection

Anticorrosion of pipeline

(1) The pipeline is generally protected by the combination of external anti-corrosion coating and cathodic protection. The external anti-corrosion coating of the pipeline adopts three-layer PE, the cathodic protection adopts the forced current cathodic protection, and the cathodic protection station is set along the pipeline according to the protection distance requirements.
The design parameters of cathodic protection are as follows:

  • Spontaneous potential: – 0.55v (relative saturated copper sulfate reference electrode)
  • Junction potential: – 1.15V (relative saturated copper sulfate reference electrode)
  • Minimum protection potential of pipeline: – 0.85 V (relative saturated copper sulfate reference electrode)
  • Pipeline protection current density: 5 μ A / m2
  • Design life: 30 years
  • Three coating for gas transmission: PE coating

(2) Basic situation of external joint coating:

  • Solvent free liquid epoxy coating + heat shrinkable joint coating shall be used for joint coating of three-layer PE of general pipe section and joint coating of simmering elbow.
  • Solvent free liquid epoxy coating + special heat shrinkable joint tape for directional drilling crossing section shall be selected as reinforced 3-layer PE joint coating for directional drilling.

(3) Internal coating of pipeline
In general, the internal surface of main pipeline adopts two-component liquid epoxy coating, and the dry film thickness is more than or equal to 65 μ M.
In order to improve the performance of cathodic protection system for long-distance pipeline and effectively protect the pipeline, an independent cathodic protection monitoring system can be adopted. Intelligent test piles are set at key positions along the pipeline, and potential collectors are set in RTU valve chamber. The intelligent test post uses GPRS communication mode, uses long-life battery power supply, uses low-power technology to complete GPRS communication wireless potential acquisition function, automatic GPRS connection and data transmission. RTU valve chamber potential collector uses optical cable for data transmission. The cathodic protection monitoring center is located in the main control center.

Anticorrosion of process pipeline in valve chamber

Impressed current cathodic protection is adopted for the connecting part of valve chamber process and main line; insulated joint is set for valve chamber vent system, and cathodic protection mode of sacrificial anode is adopted.
(1) Surface of above ground natural gas pipeline, vent pipeline and vent riser

  • Primer: epoxy zinc rich primer, 2 layers, 80-100 mm
  • Intermediate paint: epoxy micaceous iron intermediate paint, 1 coat, 100 mm
  • Finish: acrylic polyurethane finish, 2 coats, 80-100 mm
  • Total dry film thickness ≥ 260mm

(2) External surface of buried pipeline

  • Primer: epoxy zinc rich primer, 2 layers, 80-100 mm
  • Finish: solvent free liquid epoxy coating, 1 coat, 500mm
  • Total dry film thickness ≥ 580mm

Anti corrosion of station process pipeline

For pipeline process stations, the impressed current cathodic protection method is generally adopted for booster stations; the cathodic protection mode of sacrificial anode is adopted for other stations, and insulated joints are set for incoming and outgoing pipelines.
(1) External surface of above ground process piping

  • Primer: epoxy zinc rich primer, 2 coats, 80mm
  • Finish: epoxy siloxane finish, 1 coat, 125mm
  • Total dry film thickness ≥ 205mm

(2) External surface of buried process pipeline

  • Primer: epoxy zinc rich primer, 2 coats, 80mm
  • Finish: solvent free liquid epoxy coating, 1 coat, 500mm
  • Total dry film thickness ≥ 580mm

Gas storage

The gas consumption is constantly changing, with monthly, daily and hourly non-uniformity. However, the original supply can not be changed at any time according to the change of gas consumption. Especially for long-distance gas transmission pipeline, in order to obtain high efficiency and the best economic benefit, it is always hoped to work under a certain optimal throughput. In this way, the imbalance between gas supply and gas consumption often occurs. In order to ensure uninterrupted gas supply according to the requirements of users, the balance between production and use of gas transmission must be considered.
There are three ways to solve the imbalance between gas consumption and gas supply:

  • Changing the production capacity of gas source and setting mobile gas source;
  • The buffer users are used to play the role of scheduling;
  • All kinds of gas storage facilities are used.

The first two points can not completely solve the imbalance between supply and demand due to the limitation of the possibility and range of change of gas production load, as well as the requirements of safety and reliability and technical and economic rationality of gas supply. Due to the flexibility of gas storage facilities and methods, the use of various gas storage facilities is one of the most effective methods to solve the problem of uneven use of gas. Gas storage can be divided into underground storage, gas tank storage, liquid or solid storage and gas storage pipeline end storage.

Source: China Natural Gas Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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