GDS - gas distribution station, equipped with equipment to reduce the pressure of the gas coming from the main network to the required level. In addition, the tasks of the station include filtration and odorization, distribution and metering of consumed gas.
Appointment
The gas distribution station is the last facility in the gas transmission system chain and, at the same time, the main building for urban gas supply systems. Due to the fact that the interruption of gas supply to cities and large industrial enterprises is unacceptable, protective automatic equipment is provided in the gas distribution system. Moreover, protective automation is made on the principle of redundancy. The backup line turns on when the main reduction line fails.
GDS is intended for:
- gas intake from gas pipelines;
- cleaning it from various mechanical impurities;
- lowering the pressure to the values required in urban systems;
- maintaining pressure at a constant level;
- odorization and heating of gas;
- determine its consumption.
Types of stations
GDS and AGDS are divided according to their purpose:
- Automatic on the branches of the main gas pipelines - to provide gas to small settlements. Additionally subdivided into gas control points (1000-30000 m 3 / h) and gas control units (up to 1500 m 3 / h).
- Control and distribution points - feed industrial and agricultural facilities, ring gas pipelines around large settlements and cities 2000-12000 m 3 / h).
- Field gas distribution stations - are installed at gas fields, purify the extracted raw materials from moisture and impurities.
- End stations - are built directly at the consumer (enterprises, settlements).
Automation
In recent years, automated gas distribution stations have become widespread. AGRS with a capacity of up to 200,000 m 3 / h are operated without maintenance. In this case, the stations have a set of equipment and instrumentation, allowing it to be operated in an automated mode.
Maintenance of such gas distribution systems is carried out remotely. The operator of the gas distribution station is usually located in the premises of the service organization, monitoring can even be carried out at home. In the event of an emergency, sound and light signals are transmitted to the premises and residential buildings of the operators, which are located at a distance of no more than 0.5 km from the controlled station. GDS service with a capacity of more than 200,000 m 3 / h is carried out on a shift basis.
Equipment
The gas distribution station includes a series of technological equipment:
- input disconnecting device;
- Filters
- heater;
- a line for reducing and regulating gas pressure ;
- a device for measuring the flow of incoming gas;
- output disconnecting device.
As pressure regulators at the station, direct-acting regulators of the RD type and indirect ones of the RDU type are used.
Technological cycle
The received gas is received by the gas distribution station. The scheme of its movement along the technological chain is as follows:
- From the main gas pipeline, the gas first passes the disconnecting device and enters the filter.
- After that, it is pumped into the first stage of reduction, which has two or three lines, one of which is reserve. In the presence of two reduction lines, the reserve thread is calculated for one hundred percent productivity, and in the case of three lines - for 50%. The backup line in this scheme can be used to bypass the first stage.
- If the pressure at the inlet to the gas distribution system is 4 MPa, then in the first stage the gas pressure decreases to 1-1.2 MPa, and in the second stage to 0.2-0.3 MPa. After the second stage, the gas pressure will have a value of 0.6-0.7 MPa.
Filter installation and pressure control
The choice of filter installation location depends on the inlet pressure and on the gas composition. If the gas distribution station receives wet gas, then the filters must be installed before the 1st stage of reduction. Filters in this case will trap both condensate and mechanical impurities. After this, a mixture of dust and condensate enters the sumps. The settled product is sent to containers, from where it is periodically pumped and exported in tankers.
If the working pressure at the inlet to the GDS is less than 2 MPa, then the filters are installed after the 1st stage of reduction. With this filter installation scheme, bypassing (installation of a bypass line) of the first stage is performed. Filters in this case are adjusted to a pressure of 2.5 MPa. If the inlet gas pressure rises above 2.5 MPa, the shutdown device on the bypass line is closed and the gas is directed to the line of the 1st reduction stage. After its passage, the gas is sent to the second stage, and after the 2nd - to the outlet gas pipeline.
If the gas distribution station requires replacement of equipment on the main reduction line, as well as during the creation of an emergency situation, this line is switched off and the bypass line equipped with a disconnecting device and a pressure reducing valve is opened. In this case, the gas flow rate and its pressure are adjusted manually.
Automated GDS device
Automated gas distribution stations have several equipment layout options. However, all of them must take into account the danger of both hydrate formation and external freezing of the external reduction units. In this regard, in winter, station staff have to pay special attention to the above factors. To prevent hydrate formation in gas distribution stations, gas heating units are used.
The heating unit includes a heater and a hot water boiler. Water enters the boiler from a special tank, the actual heating of water in the boiler is carried out by burning gas supplied to the gas distribution system and undergoing a reduction system. The gas burner device of the boiler operates at low gas pressure. To prevent the flow of gas going to the combustion chamber of the boiler with a pressure above the specified limits, there is a safety device. Thus, the gas with the inlet pressure entering the GDS is directed first to the filters for cleaning, and then to the heater. The gas is heated in the heater, as a result of which hydrate formation is removed from it. After passing the heater, the drained gas enters the reduction line and then into the exhaust gas pipeline.
Security measures
In order to avoid explosions and fires, special installations are installed on the gas distribution system to give a gas odor. These installations are installed when gas is not odorized at the main facilities or its degree is below the established limits. Gas odorization plants are divided into bubble, drip and wick. The latter are also called evaporative.
Gas distribution station automation
The principle of operation of automated GDS with home-based service is as follows. If the gas outlet pressure deviates above the permissible value, the sensor tuned to a certain value gives a command to switch the valve with a simultaneous notification of station personnel using sound and light alarms located on the switchboard.
In the case when there is an increase in gas pressure at the outlet of the gas distribution system by 5% in excess of the set nominal pressure value, the corresponding sensor is triggered. As a result, the control valve on one of the reduction working lines will begin to close, thereby reducing the gas outlet pressure. If the pressure does not decrease, then another sensor will trigger, which will give a command to cover the control valve even more, until the entire reduction line is completely turned off. If the output pressure drops to 0.95P, the backup line opens.
Technical condition
Despite the simplicity of the device, gas distribution stations need updating. The construction of gas distribution stations in most cases was carried out in the 70s, when thousands of kilometers of gas pipelines were laid from Siberian fields to European consumers, and mass gasification of settlements and enterprises of the Soviet Union was carried out. Almost 34% of gas distribution stations celebrated their 30th anniversary, 37% - over 10 years old, only less than a third of the stations are equipped with modern equipment under 10 years old. At the moment, a comprehensive program of technical re-equipment and reconstruction of gas distribution stations is being considered.