Automated gas distribution station

GDS - gas distribution station, equipped with equipment that allows to lower the pressure of gas coming from the main gas pipeline to the required level. In addition, the tasks of the station include filtration and odorization, distribution and accounting of consumed gas.

Appointment

The gas distribution station is the last facility in the chain of the gas transmission system and at the same time the main facility for urban gas supply systems. In view of the fact that the cessation of gas supply to cities and large industrial enterprises is unacceptable, the GDS provides for a protective automatic system. Moreover, the protective automatics is executed on the principle of reservation. The backup line is switched on when the main reduction line has failed.

The GDS is designed for:

• Reception of gas from gas mains;
• Cleaning it from various mechanical impurities;
• Lowering the pressure to the values required in urban systems;
• Maintaining the pressure at a constant level;
• Odorization and heating of gas;
• Determine its consumption.

Types of stations

GDS and AGRS are divided according to their purpose:

• Automatic on the branches of the main gas pipelines - to provide gas to small settlements. In addition, they are divided into gas control points (1000-30000 m ³ / h) and gas regulating 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).
• Commercial GDS - installed on 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 is operated by non-emergency maintenance. In this case, the stations have a set of equipment and instrumentation, allowing to operate it in an automated mode.

Servicing such GRS is carried out remotely. The operator of the gas distribution station, as a rule, is in the premises of the service organization, monitoring can be carried out even at home. In the event of an emergency, sound and light signals are transmitted to the premises and apartment houses of operators, which are located at a distance of no more than 0.5 km from the controlled station. Maintenance of a gas turbine with a capacity of more than 200,000 m ³ / h is carried out in the watch regime.

Equipment

The gas distribution station includes a series of technological equipment:

• A disconnect device at the input;
• Filters;
• heater;
• A line for reducing and regulating the gas pressure;
• Device for measuring the flow rate of incoming gas;
• Disconnecting device at the output.

Regulators of direct action of type RD and indirect action of RDU type are used as pressure regulators at the station.

Technological cycle

The received gas is taken by the gas distribution station. The scheme of its movement along the technological chain is as follows:

1. From the main gas pipeline, gas is first passed by the disconnecting device and enters the filter.
2. After that, it is pumped into the first reduction stage, which has two or three lines, one of which is reserved. If there are two reduction lines, the backup thread is calculated to 100% performance, and in the case of three lines - to 50%. The reserve line with this scheme can be used to bypass the first stage.
3. If the pressure at the inlet to the GDS is 4 MPa, then in the first stage the gas pressure is reduced 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.

Filtration and pressure control

The choice of the location of the filters depends on the inlet pressure and the composition of the gas. If the gas distribution station receives wet gas, the filters must be installed before the 1st reduction stage. Filters in this case will trap both condensate and mechanical impurities. After that, the mixture of dust and condensate enters the sedimentation tanks. The retarded product is sent to the tanks, from where it is periodically pumped out and taken out in tank trucks.

If the working pressure is less than 2 MPa at the inlet to the GDS, the filters are installed after the 1st reduction stage. With this scheme, the filters are installed bypassing (bypass line installation) of the first stage. The filters in this case are adjusted to a pressure of 2.5 MPa. If the gas pressure at the inlet increases above 2.5 MPa, the cut-off 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 second - to the off-gas pipeline.

If the gas distribution station requires a replacement of the equipment on the main reduction line, as well as during the emergency situation, this line is disconnected and a bypass line equipped with a disconnecting device and a reducing valve is produced. Adjustment of the gas flow rate and its pressure is carried out in this case manually.

The device of automated GDS

Automated gas distribution stations have several options for assembling equipment. However, all of them must take into account the danger of both hydrate formation and external freezing of external reduction nodes. In connection with this, in winter, the station's maintenance personnel have to pay special attention to the above factors. To prevent hydration in gas distribution units, 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 the water in the boiler is carried out by burning gas coming to the gas distribution system and passed the reduction system. The gas burner of the hot water boiler operates at a low gas pressure. To prevent the supply of gas to be burned into the furnace of a hot-water boiler with a pressure above the set limits, there is a safety device. Thus, the gas with input pressure entering the GDS is sent first to the filters and then to the heater. In the preheater, the gas is heated, as a result of which hydrate formation is removed. After passing the heater, the dehydrated gas enters the reduction lines and then into the off-gas pipeline.

Security measures

To avoid explosions and fires on the gas distribution system, special installations are installed to smell gas. These installations are established when the head facilities do not gasify or its degree is below the established limits. Installations for gas odorization are divided into bubble, drop and wick. The latter are also called evaporative.

Automation of gas distribution station

The principle of operation of an automated GDS with home-based services is as follows. If the output gas pressure deviates beyond the permissible value, a sensor adjusted to a certain value gives the command to switch the crane with simultaneous notification of the station's attendants with the help of sound and light signaling placed on the switchboard.

In the event that there is an increase in gas pressure at the outlet from the gas distribution system by 5% above the set nominal pressure value, the corresponding sensor is triggered. As a result, the control valve on one of the operating reduction lines starts to close, thereby reducing the outlet gas pressure. If the pressure does not decrease, another sensor will trigger, which will command an even greater cover of the control valve, until the entire reduction line is completely turned off. In the case of reducing the output pressure to 0.95P, the reserve line is opened.

Technical condition

Despite the simplicity of the device, the gas distribution stations need to be updated. Construction of gas distribution stations in most cases was carried out in the 70's, when thousands of kilometers of gas pipelines were laid from Siberia to European consumers, and massive gasification of settlements and enterprises of the Soviet Union was carried out. Almost 34% of the GDS noted the 30th anniversary, 37% - over 10 years, only less than a third of the stations are equipped with modern equipment under 10 years. At the moment, a comprehensive program of technical re-equipment and reconstruction of gas distribution stations is under consideration.