Gas distribution stations (GDS) are the final objects of main lines or branches from them and the main ones for distributing gas networks to consumers. The main functions of the gas distribution system are to reduce and maintain the output gas pressure at a level that meets the requirements (technological and household) of the consumer, to take into account and regulate the flow of supplied gas. In addition, the GDS carries out additional gas purification from mechanical impurities and, if the degree of odorization is insufficient, additional introduction of an odorant. The gas pressure in the pipeline is provided in a wide range - from 10 to 55 kgf/cm2, at the outlet - from 3 to 12 kgf/cm2, sometimes (for industrial consumption and a medium pressure distribution network) up to 25 kgf/cm2.
Gas distribution stations (GDS) are designed to supply gas from main and field gas pipelines to the following consumers:
1) for the own needs of gas and oil field facilities;
2) for the own needs of gas compressor station facilities (GKO);
3) objects of small and medium-sized settlements;
4) power plants;
5) industrial, public utility enterprises and settlements of large cities.
GDS provide:
1) gas purification from mechanical impurities and condensate;
2) reducing to a given pressure and maintaining it with a certain accuracy;
3) gas flow measurement with multi-day recording;
4) Odorization of gas in proportion to its consumption before supply to the consumer;
5) supplying gas to the consumer bypassing the gas distribution system in accordance with the requirements of GOST 5542-87.
By design, all GDS are divided into:
1) individual design stations;
2) automatic (AGRS): AGRS-1/3, AGRS-1. AGRS-3, AGRS-10, “Energia-1M”, “Energia-2”, “Energia-3”, “Tashkent-1 and -2”.
3) block-packaged (BK-GRS) - with one (BK-GRS-1-30, BK-GRS-1-80, BKRS-1-150) and two consumer outputs (BK-GRS-P-70. BK-GRS-P-130, BK-GRS-P-160).
All GDS are intended for outdoor operation in areas with seismicity up to 7 points on the Richter scale, with a temperate climate (in conditions normalized to execution V, placement category I according to GOST 15150-69*), with ambient temperatures from -40 to 50°C, with relative humidity 95% at 35°C.
Depending on the productivity, gas distribution stations are divided into two groups: the first group is designed for small and medium-sized gas consumers with gas consumption less than 250 thousand m 3 /h, the second group
designed for large gas consumers with a flow rate of more than 250 thousand m 3 /h. As a rule, gas distribution stations of the first group are built according to standard designs. GDS for large cities and industrial centers, whose gas consumption is determined by millions of cubic meters per day, are created according to individual projects.
When placing gas distribution stations on the ground, it is necessary to maintain safe distances from populated areas, industrial enterprises and individual buildings and structures specified in SNiP
II.45-75. For example, with diameters of gas supply pipelines exceeding 800 mm, the distance of the gas distribution system from populated areas, individual buildings and industrial enterprises should be 250-300 m, from agricultural facilities and railways- 200 m, from bridges - 225-300 m. The distance from the gas distribution station to the operator’s house for home service should be at least 200 m.
The GDS has the following equipment systems:
Units for purifying incoming gas from dust and liquid, equipped with viscine filters, oil dust collectors or gas separators;
Reducing units, where gas pressure is reduced and automatically maintained at a given level using pressure regulators RD of various capacities;
Gas quantity metering units with chamber diaphragms on outlet gas pipelines and flow meters/differential pressure gauges:
Switching units with shut-off devices for directing gas flows directly into output gas pipelines along base lines, bypassing the gas distribution system in emergency situations or when repairing installations; Spring springs are installed on the output lines safety valves through which, in the event of an unexpected increase in pressure in the system, gas is automatically released into the atmosphere;
Gas heating units to prevent the formation of hydrate plugs; Usually for this purpose water heating boilers “Neris” or VNIISTO with heat exchangers are used, which simultaneously serve for heating
captivity of GRS;
Gas odorization installations with odorization columns and odorant containers;
External inlet and outlet pipelines - a comb with a large number of shut-off valves;
Instrumentation and automation devices;
Electrical equipment and control devices for electrochemical protection of the adjacent linear part of the gas pipeline.
All gas distribution stations are equipped with automatically operating control valves complete with pressure regulators or pneumatic relays, flow meters and other installations.
The most widely used for average gas consumption are automated gas distribution stations in block-packaged design with a capacity of 100-150 thousand m 3 /h, developed by the Giprogaz Institute (Fig. 1). According to this project, gas distribution stations are constructed from factory-made technological and building complete blocks, which ensures high level industrialization of construction.
Depending on the specific conditions, the gas distribution system can be assembled from various units assembled into blocks for shutdown, cleaning, reduction of the first consumer and reduction of the second consumer.
GDS in block-packaged design are produced in six standard sizes, three of them for one consumer and three for two consumers. Such GDS are distinguished by their simplicity of design, operational reliability, low construction cost and low metal consumption. As indicated, the maximum productivity of these types of gas dispensers at a gas outlet pressure of 20 kgf/cm 2 is 100 - 150 thousand m 3 / h; with increasing pressure, the productivity can be increased to 200 thousand. m 3 / h. Transportable blocks have a width of up to 3350 mm and a height of up to 2800 mm.
The operation scheme of the GDS in a block-complete design is as follows (Fig. 2.3-2). Through the connection unit, the gas enters the purification unit, then to the reduction unit and after that to the flow meter lines. Having passed through the shut-off valve, the gas is odorized as necessary and enters the consumer’s gas pipeline. If necessary, heating units are connected to the inlet line after gas purification.
Instrumentation and automatic gas distribution systems provide liquefaction of gas pressure, automatic maintenance of gas pressure at the outlet within specified limits with wide fluctuations in gas consumption, automatic protection and uninterrupted gas supply to consumers.
Gas purification is carried out in battery-powered cyclonic dust collectors designed by the Giprogaz Institute, and reduction is carried out by direct-acting regulators RD. The GDS building is assembled from complete blocks, which include a building block of instrumentation and automation, as well as a set of building elements that allow the assembly of reduction blocks and shutdown devices, foundations - crushed stone preparation for base slabs, walls and coverings made of VNIIST panels with a steel frame.
The heating of the premises of only the building block of instrumentation and A-water is from the AGV-120 installation, and in the version with heating of the reducing valves - water from the gasified boiler VNIISTO-M.
Ventilation of the GDS premises is supply and exhaust with natural impulse. Power supply - from networks with voltage 380/220 with cable input.
At the GDS, as a rule, an intermediate selective communication control point with a tone call is installed. Master plan The GDS in block-complete design is shown in Fig. 8.3.
To reduce gas when supplying gas to large industrial, domestic and agricultural facilities, automatic gas distribution stations AGRS are used in cabinet design, manufactured entirely in the factory. AGDS provide gas supply from the main gas pipeline to the consumer at a given pressure and with normal odorization. They are equipped with monitoring sensors with electrical output, allowing for remote monitoring of their operation from the control center. The weight of cabinet-mounted AGRS 1/3 is a little more than 2 tons.
The industry has developed several standard sizes of block AGDS, produced with complete blanks of equipment components, support structures, heating, ventilation, instrumentation and automation systems. For example, AGRS-3 and AGRS-10 (VNIPIGazdobycha Institute) are distinguished by their transportability, ease of installation on reinforced concrete slabs, and operational reliability.
Fig.8.3. General plan of the block gas distribution station:
1 - container for condensate; 2 - petrol dispenser; 3 - container for odorant; 4 - lightning rod; 5 - GDS building block; 6 - supports for pipelines, 7 - cleaning unit; 5 - building block of disconnecting devices; 9 - fence; 10 - candle
To supply gas to small associated household and technological consumers, in particular thermoelectric heaters of radio relay points and cathodic protection stations, cabinet-type automatic reducing points RP, developed by the VNIPIGazdobycha Institute, are used.
When reducing wet gas at the gas distribution station, hydrate formation and freezing of regulators and control valves can occur. To prevent these undesirable phenomena, general gas heating is currently widely used in front of the reduction units at gas distribution stations using shell-and-tube heat exchangers.
According to the form of service, GDS are divided into:
1) with rotational service - gas distribution stations with a capacity of more than 250 thousand m 3 /h and gas distribution stations supplying enterprises where gas is a technological raw material;
2) with home and cluster service by operators - GDS with a capacity of up to 250 thousand m 3 /h.
Shift service, which is used very rarely in practice, involves the constant presence of duty personnel of 5-9 people at the gas station. The responsibilities of the maintenance personnel, in addition to ensuring the specified gas supply to consumers, include production current repairs technological equipment, direct participation in the production of medium and major repairs of equipment and communications of the gas distribution system, as well as maintenance of instrumentation and control instruments and installations for gas purification and odorization.
Unattended, or, as is commonly called, home-based service is provided at automated gas distribution stations, which ensure, without the constant presence of personnel, an uninterrupted supply of gas to consumers at specified pressure parameters and with the required degree of odorization. Such gas distribution systems are serviced by two operators on duty at home. In the event of a malfunction, undeciphered light and sound signals are transmitted to the operators' apartments, upon receipt of which the operator on duty must come to the gas distribution station and fix the problem. IN recent years Cluster service has become widespread, in which two operators service 5-6 nearby gas distribution stations.
The conditions for the creation and number of structural units of the EO branch responsible for the operation of the gas distribution system are established in accordance with the regulatory and methodological documents provided for by the List of regulatory and methodological documents for standardizing the work of employees of PJSC Gazprom.
The form of GDS servicing is established based on the following factors:
Station performance;
Level of automation and telemechanization;
Time of arrival of the crew for servicing the gas distribution system by motor transport from the industrial sites of the EO branch to the gas distribution system;
The need to supply gas to non-switchable gas consumers.
6.2.2 When operating GDS, they are used following forms services:
Centralized;
Periodic;
Home-based;
Watch room.
| 6.2.3 Centralized form of maintenance - maintenance without the constant presence of maintenance personnel, when scheduled maintenance and repairs are carried out at least once every 10 days by personnel of the structural units of the EO branch. With a centralized form of maintenance, the gas distribution system must meet the following requirements: - design capacity no more than 30 thousand m 3 /h; - availability of devices for automatic removal of condensate from the gas purification unit; - presence of an automatic odorization unit; - availability of self-propelled control systems for gas distribution stations, telemechanics, automatic control of gas contamination, ITSO, fire alarm systems with the ability to automatically transmit warning and emergency signals via technological communication channels to the DP of the EO branch and receive control commands from it; - availability of registration and automatic transmission via technological communication channels of the main operating parameters gas (gas pressure and temperature at the inlet and at each outlet of the gas distribution system, gas flow at each outlet); - presence of remotely controlled fittings on the bypass line; - availability of automated backup power supply sources; - the arrival time of the crew for servicing the gas distribution system by motor transport did not exceed two hours (for areas equated to the regions of the Far North - three hours). Notes 1 The recommended scope of automation and the list of typical functions performed by the ACS of the GDS are determined in accordance with the requirements of the RD, which define the general technical requirements for the GDS. 2 For gas distribution stations that do not fully comply with the above requirements, a centralized form of maintenance is allowed with a design capacity of no more than 15 thousand m 3 /h. |
6.2.4 For periodic maintenance, the GDS must meet the following requirements:
Design capacity no more than 50 thousand m 3 /h;
Availability of devices for automatic removal of condensate from the gas purification unit;
Availability of automatic odorization unit;
Availability of self-propelled control systems for gas distribution stations, telemechanics, automatic control of gas contamination, security and fire alarms with the ability to automatically transmit warning and emergency signals via technological communication channels to the DP of the EO branch and receive control commands from it;
Availability of registration and automatic transmission via technological communication channels of the main gas operating parameters (gas pressure and temperature at the inlet and at each outlet of the gas distribution system, gas flow at each outlet);
Availability of remotely controlled fittings on the bypass line;
Availability of automated backup power supply sources.
2 For gas distribution stations that do not fully comply with the above requirements, periodic maintenance is allowed with a design capacity of no more than 30 thousand m 3 /h.
6.2.5 For home-based service, the GDS must meet the following requirements:
Design capacity no more than 150 thousand m 3 /h;
Availability of a telemechanics system, emergency, security and fire alarms with a warning signal sent to the DP of the branch of the EO and subsidiaries;
Availability of devices for removing condensate and mechanical impurities from the gas purification unit;
Availability of a pulse gas preparation system for regulation, protection, and control devices.
6.2.6 When servicing on a watch basis, the GDS must meet the following requirements:
Design capacity more than 150 thousand m 3 /chile number of outlet collectors more than two;
Availability of emergency, security and fire alarms with a warning signal sent to the control room, if there is a telemechanics system in the DP branch of the EO branch;
Availability of a unit for preventing hydrate formation in communications and equipment;
Availability of registration of basic gas parameters (gas pressure and temperature at the inlet and at each outlet of the gas distribution system, gas flow at each outlet);
availability of a pulse gas preparation system for regulation, protection, and control devices.
Each subdivision's GDS must have the following technical documentation:
Land allotment act;
Certificate of acceptance of the gas pipeline - tapping to the gas distribution station and as-built technical documentation;
Scheme of gas pipeline maintenance - branch and situational plan of the area;
Schematic diagrams(technological, automation, control and alarm, electric lighting, heating and ventilation, lightning protection and grounding, etc.);
Technical passport;
Passports for equipment, devices and factory instructions;
GDS operating instructions;
Other regulatory and technical documentation established by the association.
The following documentation must be provided directly to the GDS:
Schematic flow diagram;
GDS operating instructions;
Operator log;
Other documentation at the discretion of the department.
Equipment, structures and systems, operational documentation for the gas distribution system must be checked by the person responsible for the operation of the gas distribution system and take the necessary measures to ensure the appropriate level of operation of the gas distribution system, equipment and systems of the compressor station.
Description of the technological process, equipment and
Technological production diagram.
GDS equipment.
Blocks, units, devices of GDS.
The composition of the equipment at the gas distribution station must correspond to the design and passports of the manufacturers. Any changes in the composition of the equipment must be in accordance with the requirements of the Federal Law “On Industrial Safety of Hazardous Facilities”, agreed with the design organization, Gaznadzor of OJSC Gazprom, Gosgortekhnadzor of Russia with simultaneous adjustment of the technological scheme and other technical documentation located in the LPUMG and at the GDS. GDS fittings and equipment must have numbers or tags with a number corresponding to the designation in the process diagram.
Figure 1 shows a technological diagram of the GDS, where the main components of the GDS are indicated, each of which has its own purpose.
Main components of the GDS:
1. switching unit;
2. gas purification unit;
3. heating unit;
4. reduction unit;
5. gas metering unit;
6. gas odorization unit.
The GDS switching unit is designed to switch the gas flow high pressure from automatic to manual regulation of pressure along the bypass line, as well as to prevent an increase in pressure in the gas supply line to the consumer using safety valves.
The GDS gas purification unit is designed to prevent the ingress of mechanical (solid and liquid) impurities into process and gas control equipment and control and automation equipment for the GDS and the consumer.
The hydrate formation prevention unit is designed to prevent freezing of fittings and the formation of crystalline hydrates in gas pipelines and fittings.
The gas reduction unit is designed to reduce and automatically maintain the specified gas pressure supplied to the consumer.
The gas metering unit is designed to record the amount of gas consumption using various flow meters and counters.
The gas odorization unit is designed to add substances with a strong unpleasant odor (odorants) to the gas. This allows you to promptly detect gas leaks by smell without special equipment.
Switching block (node).
Switch block designed to protect the consumer's gas pipeline system from possible high gas pressure and to supply gas to the consumer, bypassing the gas distribution system, through a (bypass) bypass line using manual regulation of gas pressure during repair and maintenance work at the station. The switching block consists of: cranes on the inlet and outlet gas pipelines, bypass line And safety valves.
Bypass line – to switch the high pressure gas flow from automatic to manual pressure control. The normal position of the shut-off valves on the bypass line is closed. Cranes the bypass line must be sealed by the State Registration Service. The bypass line must be connected to the outlet gas pipeline before the odorizer (along the gas flow). There are two shut-off devices located on the bypass line: the first along the gas flow – shut-off valve; second – for throttling, faucet regulator.
Safety valves. A safety valve is an automatic device for relieving pressure, actuated by static pressure arising in front of the valve, and characterized by rapid full lifting of the spool due to the dynamic action of the jet of released medium emerging from the nozzle.
Safety valves are most often used to protect vessels of devices, tanks, pipelines and other technological equipment in case of excessive pressure. The safety valve ensures safe operation of equipment under conditions of high gas or liquid pressure.
When the pressure in the system increases above the permissible level, the safety valve automatically opens and releases the required excess working medium, thereby preventing the possibility of an accident. After the release is completed, the pressure decreases to a value less than when the valve begins to operate, the safety valve automatically closes and remains closed until the pressure in the system again increases above the permissible level.
The main characteristic of safety valves is their throughput, determined by the amount of liquid discharged per unit of time when the valve is open.
The number of safety valves, their sizes and capacity must be selected according to calculations so that the protected object does not create a pressure exceeding the operating pressure more than indicated in Table 3.
Table 3
The most widely used are spring safety valves (PPVs).
The GDS uses full-lift flanged safety valves PPK-150-16 and PPK-150-40, intended for liquid and gaseous non-aggressive media, at operating pressures up to 16 and 40 kg/cm 2, respectively. The design of the valves is closed and hermetically sealed. They are installed on the outlet gas pipelines and are set to response pressures of 3.3 and 13.2 kg/cm 2 .
Valves of the type SPPK (special full-lift safety valve) Fig. 1 and PPK (spring full-lift safety valve) Fig. 2 are used. A three-way valve is placed between the safety valves, always open to one of the safety valves. Shut-off valves should not be installed between the gas pipeline and the valves.
During operation, valves should be tested for operation once a month, and winter time- once every 10 days with an entry in the operational log.
Safety valves are checked and adjusted twice a year, and a corresponding entry is made in the journal.
Each safety valve must have a plate (tag) on which the registration number, operating pressure (Prab), response pressure (Psrab), adjustment date, and next adjustment date must be indicated.
The tag must be made of aluminum or on a paper base with a laminated coating and have a shank with a hole for the sealing wire and a pin for the flange connector of the PPK body.
Each safety valve must be sealed. The sealing wire must connect: the tag, the adjustment screw cap and the seat position adjustment screws.
The rod of the SPPK4R safety relief valve is acted on one side by gas pressure from the outlet gas pipeline, and on the other by the force of a compressed spring. If the gas pressure at the outlet of the gas distribution system exceeds the specified value, then the gas, overcoming the force of the compressed spring, lifts the rod and connects the outlet gas pipeline to the atmosphere. After the gas pressure in the outlet gas pipeline decreases, the rod returns to its original position under the action of the spring, blocking the passage of gas through the valve nozzle, thus disconnecting the outlet gas pipeline from the atmosphere. Depending on the setting pressure, safety valves are equipped with replaceable springs.
In addition to valves of the SPPK type, spring safety valves of the PPK-4 type for a nominal pressure of 16 kgf/cm 2 are widely used. valves of this type are equipped with a lever for forced opening and control purging of the gas pipeline. The spring is adjusted with an adjusting screw.
Gas pressure from the gas pipeline enters the shut-off valve, which is held in the closed position by a spring through a rod. The spring tension is adjusted with a screw. The cam mechanism allows for control purging of the valve: by turning the lever, the force is transmitted through the roller, cam and guide bushing to the rod. It rises, opens the valve and a purge occurs, which indicates that the valve is working and the discharge line is not clogged.
PPK-4 valves, depending on the number of the installed spring, can be configured to operate in a pressure range of 0.5 to 16 kgf/cm 2 .
To discharge gas into the atmosphere, it is necessary to use vertical pipes (columns, candles) with a height of at least 5 m from ground level; which lead beyond the GDS fence to a distance of at least 10 m. Each safety valve must have a separate exhaust pipe.
It is allowed to combine exhaust pipes into a common manifold from several safety valves with the same gas pressures. In this case, the common collector is designed for simultaneous discharge of gas through all safety valves.
3.3. Gas purification unit (unit).
Gas purification unit (unit) at the gas distribution station allows you to prevent mechanical impurities and condensate from entering the equipment, process pipelines, control and automation devices of the station and gas consumers.
The greatest difficulty in gas purification is the formation of hydrocarbon gas hydrates: white crystals resembling a snow-like crystalline mass. Solid hydrates form methane and ethane, propane forms liquid hydrates. When hydrogen sulfide is present in a gas, both solid and liquid hydrates are formed.
Hydrates are unstable compounds that, when pressure decreases and temperature increases, easily decompose into gas and water. They fall out when the gas is reduced, enveloping the valves of the gas pressure regulators and disrupting their operation. Crystalline hydrates are also deposited on the walls of measuring pipelines, especially in areas of restriction devices, thereby leading to an error in measuring gas flow. In addition, they clog impulse tubes, disabling instrumentation.
To purify gas at gas distribution stations, dust and moisture collection devices must be used, various designs, ensuring gas preparation for stable operation of GDS equipment.
The gas purification unit must be equipped with devices for removing liquid and sludge into collection containers equipped with level measuring devices, as well as a mechanized system for their removal into transport containers, from which the liquid, as it accumulates, is removed from the territory of the gas distribution station. The containers must be designed for the maximum permitted operating pressure of the inlet gas pipeline.
This unit must provide such a degree of gas purification when the concentration of solid particles 10 microns in size should not exceed 0.3 mg/kg, and the moisture content should not exceed the values corresponding to the state of gas saturation.
The GDS provides single-stage gas purification. Natural gas is purified from mechanical impurities and condensate using gas separators according to OST 26-02645-72. Three gas separators operating in parallel are installed at the GDS installation site. The speed of gas movement in them should not be more than 0.5-0.6 m/s. Gas separators are selected in such a way that when one of them stops, the gas speed in operation does not exceed 1 m/s. Gas separators must be thermally insulated and installed on separate foundations. The distance between them is not less than their diameter from the thermal insulation
Gas purification from mechanical impurities and condensate in the gas separator occurs due to:
1) changing the direction of gas movement by 180 0 C;
2) reducing the gas speed to 0.5-0.6 m/s (v in< v 0 , где v в – скорость витания механических частиц в газосепараторе; v 0 – скорость оседания механических частиц в газосепараторе);
3) the movement of gas in the nozzle, where mechanical impurities and drops of condensate are separated (released), which fall to the conical bottom of the gas separator. As practice shows, the least condensate droplet loss occurs in gas separators with mesh nozzles.
For gas purification, mesh gas seperators of the GS-8.8-1600 type are installed at the gas distribution station. Fig.3
At the small gas distribution station bandwidth Viscine and mesh filters are used to purify gas from mechanical impurities
Rice. 4. Viscine filter
1- inlet pipe; 2 - filter housing; 3- perforated mesh; 4 - loading hatch; 5- backfill (small metal or ceramic rings 15x15 mm); 6- fitting; 7-output pipe: 8 - unloading hatch: 9- fender sheet.
Such filters consist of a housing, inside of which a cassette (nozzle) filled with Raschig rings is mounted.
These rings come in metal and ceramic. Metal 15×15×0.5 mm are mainly used. Raschig rings are lubricated with viscine oil (60% cylinder oil plus 40% solar oil).
The principle of operation of the viscine and mesh filter is as follows: particles of mechanical impurities, entering the filter with the gas flow, pass through Raschig rings moistened with viscine oil, changing their direction, and stick to the surface of the rings.
As soon as the gas pressure difference at the inlet to the filter and at the outlet from it increases, which indicates contamination of the nozzle, the filter rings are cleaned with steam, washed with a soda solution, after which they are lubricated with pure viscine oil. The process of cleaning and restoring the functionality of the viscin and mesh filter is very labor-intensive, as it is carried out manually. Frequent cleaning and restoration of the filter is due to the fact that the active oil film from the Raschig rings quickly dissolves and is washed away by the condensate found in natural gas.
Viscine and mesh filters are designed to purify gas only from mechanical impurities
When operating a gas purification device, ensure visual monitoring of the condition of the filtering and absorption elements of the gas treatment device;
regularly replace the filtering and absorption elements of the device by connecting backup equipment.
Drainage and drain lines and shut-off valves on them must be protected from freezing.
To prevent spontaneous combustion of the pyrophoric compounds of the cleaning apparatus, before opening it, it must be filled with water or steam.
During opening, inspection and cleaning, the internal surfaces of the walls of the devices must be abundantly moistened with water.
Sediments containing pyrophoric iron removed from the apparatus must be collected in a metal container with water, and upon completion of work, immediately removed from the GDS territory and buried in a specially designated place that is safe in fire and environmental terms.
Gas heating unit (unit).
Gas heating unit (hydrate formation prevention unit),serves for general heating of gas passing through the gas distribution system. The greatest difficulties in reducing (lowering pressure) gas arise due to the formation of hydrates, which settle in the form of solid crystals on the walls of pipelines at the installation sites of restriction devices, on gas pressure regulator valves, and in instrumentation impulse lines. Methods for preventing hydrate formation include general or partial heating of gas, local heating of pressure regulator housings, and injection of methanol into gas pipeline communications. The first method is most widely applicable, the second is less effective, and the third is expensive.
Fire and water heaters are used for general heating. The main elements of fire heaters: fire chamber, coil through which heated gas passes, burner, bypass line, chimney, control and ignition device and automatic control.
For general gas heating at the gas distribution station in Nadym, STPS, water heaters of the PTPG-30 type are used; at the gas distribution station-107km, a water heater "SEKOMETAL" made in France, since their circuits are almost identical, we will consider a heater based on PTPG-30.
The fuel and starting gas heater PTPG-30 is a tubular furnace and is designed for indirect heating before throttling fuel and starting gas at compressor stations, as well as for heating gas at gas distribution stations and for other gas consumers.
The heater automatically maintains the temperature in the range from 15 o C to 70 o C.
Basic technical data and characteristics.
The gas distribution station includes:
a) switching stations;
b) gas purification;
c) preventing hydrate formation;
d) gas reduction;
e) gas heating;
f) commercial measurement of gas flow;
g) gas odorization (if necessary);
h) autonomous power supply;
i) gas selection for own needs;
Systems:
a) control and automation;
b) communications and telemechanics;
c) electric lighting, lightning protection, protection against static electricity;
d) electrochemical protection;
e) heating and ventilation;
f) security alarm;
g) gas control.
The GDS switching unit is designed to switch the high-pressure gas flow from automatic to manual pressure regulation along the bypass line, as well as to prevent an increase in pressure in the gas supply line using safety valves.
The GDS gas purification unit is designed to prevent mechanical (solid and liquid) impurities from entering process and gas control equipment and control and automation equipment.
The hydrate formation prevention unit is designed to prevent freezing of fittings and the formation of crystalline hydrates in gas pipelines and fittings.
The gas reduction unit is designed to reduce and automatically maintain the specified pressure of the supplied gas.
The gas metering unit is designed to record the amount of gas consumption using various flow meters and counters.
The gas odorization unit is designed to add substances with a strong unpleasant odor (odorants) to the gas. This allows you to promptly detect gas leaks by smell without special equipment.
These units and systems consist of equipment that performs functions intended for the elements included in the gas distribution system.
3.1 Industrial fittings
Industrial valves are a device installed on pipelines, units, vessels and designed to control (switch off, regulate, reset, distribute, mix, phase distribute) flows of working media (gaseous, liquid, gas-liquid, powder, suspension, etc.) by changing flow area.
There are a number of state standards regulating the requirements for fittings. In particular, the main parameters of the cranes must be looked at according to GOST 21345-2005.
Industrial valves are characterized by two main parameters: conditional passage(nominal size) and conditional (nominal) pressure. The nominal bore DN or DN is understood as a parameter used for pipeline systems as a characteristic of the connected parts (GOST 28338-89). Conditional pressure PN or Py is the highest excess pressure at a working medium temperature of 20 °C, at which a specified service life of fittings and pipeline connections of certain dimensions is ensured, justified by strength calculations for the selected materials and characteristics, their strength at a temperature of 20 °C. The values and designations of nominal pressures must correspond to those specified in GOST 26349-84.
Industrial fittings can be classified according to several criteria.
Functional purpose (type).
Constipated. Designed to completely shut off (or completely open) the flow of the working medium, depending on the requirements of the technological regime.
Regulating (reducing). Designed to regulate the parameters of the working medium by changing its flow rate. This includes: pressure regulators (Figure 7), control valves, liquid level regulators, throttling valves, etc.
Safety. Designed for automatic protection equipment and pipelines from unacceptable pressure by releasing excess working fluid. These include: safety valves, impulse safety devices, diaphragm burst devices, bypass valves.
Protective. Designed to automatically protect equipment and pipelines from unacceptable or not provided for by the technological process changes in the parameters or direction of flow of the working medium and to shut off the flow without discharging the working medium from the technological system. This includes check valves and shut-off valves.
Phase separation. Designed for automatic separation of working media depending on their phase and condition. This includes condensate drains, oil separators, gas separators, and air separators.
Figure 7 - Pressure regulator device
Constructive types.
Valves. Their working body moves back and forth perpendicular to the flow of the working medium. Used primarily as shut-off valves.
Valves (gates) (Figure 8). Their shut-off or regulating working body moves back and forth parallel to the axis of the flow of the working medium.
Cranes. Their shut-off or regulating working body has the shape of a rotating body or part thereof, and rotates around its axis, arbitrarily located in relation to the flow of the working medium.
Shutters. Their shut-off or regulating body, as a rule, has the shape of a disk and rotates around an axis that is not its own.
Figure 8 - Three-way valve (valve)
3.2 Gas pressure regulators
The hydraulic operating mode of the gas distribution system is controlled using pressure regulators. A gas pressure regulator (GP) (Figure 9) is a device for lowering (reducing) gas pressure and maintaining the output pressure within specified limits, regardless of changes in inlet pressure and gas flow, which is achieved by automatically changing the degree of opening of the regulator's control body, as a result of which also The hydraulic resistance to the passing gas flow automatically changes.
RD is a combination of the following components:
A sensor that continuously monitors the current value of the controlled variable and sends a signal to the control device;
A controller that generates a signal for the set value of the controlled variable (required output pressure) and also transmits it to the control device;
A control device that performs algebraic summation of the current and set values of the controlled variable, and sends a command signal to the actuator;
An actuator that converts the command signal into a regulatory action, and into the corresponding movement of the regulatory body due to the energy of the working environment.
1 - control valve; 2 - direct action control regulator; 3.4 - adjustable throttle; 5 - throttle.
Figure 9 - Gas pressure regulator RDBK1P
Due to the fact that the gas pressure regulator is designed to maintain constant pressure at a given point in the gas network, it is always necessary to consider the automatic control system as a whole - “the regulator and the object of regulation (gas network)”.
The correct selection of a pressure regulator should ensure the stability of the “regulator - gas network” system, i.e. its ability to return to its original state after the cessation of disturbance.
Depending on the maintained pressure (location of the controlled point in the gas pipeline), the RDs are divided into “before” and “after” regulators.
Based on the regulation law underlying the operation, pressure regulators are astatic (working out the integral law of regulation), static (working out the proportional law of regulation) and isodromic (working out the proportional-integral law of regulation).
In statistical RD, the magnitude of the change in the control hole is directly proportional to the change in gas flow in the network and inversely proportional to the change in the outlet pressure. An example of static pressure regulators are regulators with a spring output pressure setter.
A RD with an integral regulation law, in the event of a change in gas flow, creates an oscillatory regime caused by the regulation process itself. As the gas flow rate changes, the difference between the initial and set output pressure values increases until the amount of gas passing through the regulator is less than the new flow rate and reaches its maximum when these values are compared. At this moment, the opening speed of the control hole is maximum. But the regulator does not stop there, but continues to open the hole, allowing more gas to pass through than required, and the outlet pressure, accordingly, also increases. The result is a series of oscillations around a certain average value, at which a constant mode (as in the case of a static regulator) will never be achieved.
Representatives of astatic regulators are RDs with a pneumatic output pressure controller, and a typical example of such a process can be considered the undamped self-oscillations of certain types of pilot RDs in certain transient operating modes.
Isodromic regulator (with elastic feedback) when the regulated pressure deviates, it will first move the regulated element by an amount proportional to the magnitude of the deviation, but if the pressure does not reach the set value, then the regulating element will move until the pressure reaches the set value. Such a controller combines the accuracy of integral and the speed of proportional control. Representatives of isodromic RDs are “direct-flow” regulators.
3.3 Gas filters
Gas filters are designed to clean gas from dust, rust, resinous substances and other particulate matter. High-quality gas purification increases the tightness of shut-off devices and increases the overhaul time of these devices by reducing wear of sealing surfaces. This reduces wear and increases the accuracy of flow meters (meters and measuring diaphragms), especially those that are sensitive to erosion. The correct choice of filters and their qualified operation are one of the most important measures to ensure reliable and safe operation of the gas supply system.
According to the direction of gas movement through the filter element, all filters can be divided into direct-flow and rotary, according to design - into linear and angular, according to the body material and method of its manufacture - into cast iron (or aluminum) and welded steel.
When developing and selecting filters, the filter material is especially important, which must be chemically insensitive to gas, provide the required degree of purification and not be destroyed under the influence of the working environment and during periodic cleaning of the filter.
Depending on what filter material is chosen for the filter, they are divided into mesh (Figure 10) and hair (Figure 11). In mesh they use wicker metal mesh, and in hair - cassettes stuffed with nylon thread (or pressed horsehair) and soaked in viscine oil.
1 - body; 2 - cassette; 3 - mesh; 5 - cover.
Figure 10 - Mesh filter type FS
1 - body; 2 - bumper sheet; 3 - cassette; 4 - perforated sheet; 5 - filter element; 6 - cover; 7 - fittings; 8 - flange.
Figure 11 - Hair filter type FG
Mesh filters, especially double-layer ones, are characterized by increased fineness and cleaning intensity. During operation, as the mesh becomes clogged, the filter fineness increases while the filter throughput decreases. For hair filters, on the contrary, during operation the filtering capacity decreases due to the entrainment of particles of the filter material by the gas flow and during periodic cleaning by shaking.
To ensure a sufficient degree of gas purification without entrainment of solid particles and filter material, the gas flow rate is limited and is characterized by the maximum permissible pressure drop across the filter mesh or cassette.
For mesh filters, the maximum permissible pressure drop should not exceed 5000 Pa, for hair filters - 10000 Pa. In the filter before use or after cleaning and washing, this difference should be 2000-2500 Pa for mesh filters, and 4000-5000 Pa for hair filters. The design of the filters has fittings for connecting devices, with the help of which the magnitude of the pressure drop across the filter element is determined.
3.4 Safety valves
An increase or decrease in gas pressure after the pressure regulator beyond the specified limits can lead to emergency situation. If the gas pressure increases excessively, the flames of the burners may come off and an explosive mixture may appear in the working volume of gas-using equipment, seal failure, gas leakage in the connections of gas pipelines and fittings, failure of instrumentation, etc. A significant decrease in gas pressure can lead to the penetration of the flame into the burner or the extinguishing of the flame, which, if the gas supply is not turned off, will cause the formation of an explosive gas-air mixture in the furnaces and flue ducts of units and in the premises of gasified buildings.
A common reason for a sharp drop in pressure for any network may be a violation of the tightness of gas pipelines and fittings, and therefore a gas leak.
To prevent an unacceptable increase or decrease in pressure, fast-acting safety shut-off valves (SSV) (Figure 12) and safety relief valves (Figure 13) (PSV) are installed.
Housing -- 1; Adapter flange - 2; Cover - 3; Membrane -- 4; Large spring -- 5; Cork -- 6; Small spring -- 7; Rod -- 8; Valve -- 9; Guide post -- 10; Plate -- 11; Fork -- 12; Rotary shaft -- 13; Lever -- 14; Anchor lever -- 15; Rocker - 16; Hammer -- 17.
Figure 12 - Safety shut-off valve
SCPs are designed to automatically stop gas supply to consumers in the event of an increase or decrease in pressure above specified limits; they are installed after pressure regulators. SPDs are triggered in “emergency situations”, so their spontaneous activation is unacceptable. Before manually turning on the shut-off valve, it is necessary to detect and eliminate malfunctions, and also make sure that the shut-off devices are closed in front of all gas-using devices and units. If, due to production conditions, an interruption in the gas supply is unacceptable, then instead of a shut-off valve, an alarm system should be provided to alert service personnel.
PSK are designed to discharge into the atmosphere a certain excess volume of gas from the gas pipeline after the pressure regulator in order to prevent pressure from increasing above a predetermined value; they are installed after the pressure regulator on the outlet pipeline.
1 - body; 2 - cover; 3 - valve with guide; 4 - spring; 5 - adjusting screw; 6 - membrane; 7 - plate; 8 - spring plate; 9 - cover.
Figure 13 - Safety relief valve
If there is a flow meter (gas meter), the PSK must be installed after the meter. After the controlled pressure has decreased to a predetermined value, the PSC must close hermetically.
3.5 Gas metering devices
Metering devices of the highest accuracy must be installed at the gas distribution station.
If gas transportation volumes exceed 200 million m3 per year, it is recommended to use redundant measuring instruments (MI) to increase the reliability and reliability of gas volume measurements. Duplicate measuring instruments should not affect the operation of the main measuring instruments. It is recommended that the primary and backup metering systems use different methods for measuring gas flow and quantity.
At measuring units with a maximum volumetric gas flow rate of more than 100 m3/h, at any excess pressure or range of volumetric flow rate from 16 m3/h to 100 m3/h, at an excess pressure of more than 0.005 MPa, gas volume measurement is carried out only using calculators or correctors volume of gas.
At an excess pressure of no more than 0.005 MPa and a volume flow of no more than 100 m3/h, the use of flow converters with automatic correction of gas volume based only on its temperature is permitted.
Composition of SI and auxiliary devices, on the basis of which the gas metering unit is made, is determined by:
The applied measurement method and the requirements of the measurement methodology regulating the measurements;
Purpose of the metering unit;
A given gas flow rate and the range of its change;
Pressure and gas quality indicators, taking into account gas sampling modes;
The need to include metering units in automated commercial gas metering systems.
In general, gas metering includes:
Flow transducer for measuring gas volume and flow;
Measuring pipelines;
Gas quality preparation facilities;
Gas quality analyzers;
A set of technical automation equipment, including processing, storing and transmitting information.
3.6 Gas odorizers
The gas odorizer is designed for dosed supply of an odorant (a mixture of natural mercaptans) into the gas flow at the output line of a gas distribution station with a working pressure of up to 1.2 MPa (12 kgf/cm2), in order to give the gas a characteristic odor.
The gas odorizer is used as part of the gas distribution system and provides:
Metered supply of odorant into the pipeline;
Control of the administered dose of odorant and automatic correction of odorant consumption depending on the current gas consumption;
Automatic accounting of total odorant consumption;
Display of the following information on the display screen of the odorizer control unit (OCU):
a) the level of odorant in the working container;
b) the current value of hourly gas consumption obtained from the flow meter;
c) operating time of the odorizer;
d) the accumulated total value of odorant consumption since the launch of the ODDC;
e) emergency and warning signals.
Contact with various systems top level according to an agreed protocol.
Odorizers are intended for use outdoors in areas with seismicity up to 9 points with a temperate and cold climate in conditions standardized for the UHL design, placement category 1 according to GOST 15150-69. The location of the odorizer control unit is determined by the project for linking the ODDC or GDS in an explosion-proof zone, in a heated room.
3.7 Gas heaters
Gas heaters are designed to heat and automatically maintain a given gas temperature before throttling it at gas distribution stations. Gas is heated to ensure reliable operation of process equipment. Working environment: gaseous media that do not contain aggressive impurities.
The thermal power of heaters produced by Russian enterprises exceeds the real needs of gas distribution stations. As a result, 75% of heaters operate with a load of less than 50%, 51% with a load of less than 30%, 15% with a load of less than 10%. Of the more than 150 modifications of direct-heated gas heaters and with an intermediate coolant produced by the domestic industry, the direct-heated gas heaters PGA-5, PGA-10, PGA-100 satisfy the thermal power requirements.
PGA heaters with an intermediate coolant are designed to heat natural, associated and petroleum gas to a given temperature and can be used both as part of gas distribution stations and independently. As a rule, PHA heaters are equipped with modern system automation designed for autonomous and remote control.
The main advantage of PGA heaters is that the gas is heated through an intermediate coolant, which can be diethylene glycol or coolant. Thanks to this, PHA heaters have higher reliability and operational safety compared to heaters that heat fuel gas directly with gas.
The main advantages of PGA heaters are their high reliability and safety.
INTRODUCTION
In industry, along with the use of artificial gases, natural gas is increasingly used. In our country, gas is supplied over considerable distances through large-diameter gas pipelines, which represent complex system structures.
The system for delivering gas field products to consumers is a single technological chain. From the fields, gas flows through a gas collection point through a field manifold to a gas treatment plant, where the gas is dried and purified from mechanical impurities, carbon dioxide and hydrogen sulfide. Next, the gas enters the main compressor station and the main gas pipeline.
Gas from main gas pipelines enters city, town and industrial gas supply systems through gas distribution stations, which are the final sections of the main gas pipeline and are, as it were, the border between city and main gas pipelines.
A gas distribution station (GDS) is a set of installations and technical equipment, measuring and auxiliary systems for gas distribution and regulation of its pressure. Each GDS has its own purpose and functions. The main purpose of the gas distribution system is to supply gas to consumers from main and field gas pipelines. The main consumers of gas are:
Gas and oil field facilities (own needs);
Compressor station facilities (own needs);
Objects of small, medium and large settlements, cities;
Power plants;
Industrial enterprises.
The gas distribution station performs a number of specific functions. Firstly, it cleans the gas from mechanical impurities and condensate. Secondly, it reduces the gas to a given pressure and maintains it with a given accuracy. Thirdly, it measures and records gas consumption. Also at the GDS, gas is odorized before supply to the consumer and gas is supplied to the consumer, bypassing the main blocks of the GDS, in accordance with the requirements of GOST 5542-2014.
The station is a complex and responsible energy (technological) facility of increased danger. The technological equipment of the GDS is subject to increased requirements for the reliability and safety of gas power supply to consumers, and industrial safety as an explosion- and fire-hazardous industrial facility.
Depending on the performance, design, and number of outlet manifolds, gas distribution stations are conventionally divided into three large groups: small gas distribution stations (1.0-50.0 thousand m3/h), medium (50.0-160.0 thousand m3/h ) and high productivity (160.0-1000.0 thousand m3/h and more).
GDS are also classified according to their design (Figure 1). They are divided into the following types: individual design stations, block-packaged GDS (BK-GDS) and automatic GDS (AGDS).
Figure 1 - Classification of gas distribution stations
1.1 Custom design stations
GDS design is carried out by specialized design organizations in accordance with current standards, process design rules and sections of SNiP.
Stations individual design- these are stations that are located near large settlements and in permanent buildings. The advantage of these stations is the improvement of service conditions for technological equipment and living conditions for operating personnel.
1.2 Block-packaged gas distribution stations
BK-GDS can greatly reduce construction costs and time. The main design of the GDS is a block box made of factory-made three-layer panels.
The largest mass of the block box is 12 tons. Fire resistance degree - Sha. The estimated outside air temperature is 40°C, for the northern version - 45°C. The supply of all elements of a block-complete gas distribution system is carried out by the manufacturer. At the installation site, the blocks are connected by gas pipelines and cables, equipped auxiliary equipment(lightning rod, purge candle, spotlights, security alarm, etc.) and a fence, forming a complete complex.
BK-GRS are designed for gas supply to cities, towns and industrial enterprises from main gas pipelines with a gas pressure of 12-55 kgf/cm2 and maintaining the outlet pressure of 3, 6, 12 kgf/cm2.
Block-packaged GDS can have one or two output lines to consumers (Figures 2 and 3). BK-GRS are known in six standard sizes. With one outlet to the consumer, three standard sizes - BK-GRS-I-30, BK-GRS-I-80, BK-GRS-I-150. And also three standard sizes with two consumer outlets - BK-GRS-II-70, BK-GRS-II-130 and BK-GRS-II-160.
Figure 2 - Block diagram GDS with one consumer
Figure 3 - Block diagram of a gas distribution station with two consumers
BK-GDS of all standard sizes are used in Russia and the CIS countries, but all of them at the installation site are subject to reconstruction according to individual projects, as they have significant design flaws in the cleaning, heating, gas reduction and metering units.
1.3 Automatic gas distribution stations
Automatic gas distribution stations contain basically the same technological units as individual or block-assembled gas distribution systems. At the installation site, they are also equipped with auxiliary equipment and fencing, like the BK-GRS. AGDS, unlike other types of gas dispensers, operate using unmanned technology.
These stations are designed to reduce high pressure (55 kgf/cm2) of natural, associated petroleum, artificial gases that do not contain aggressive impurities to a given low pressure (3-12 kgf/cm2), maintaining it with a given accuracy of ±10%, as well as for gas preparation before supply to the consumer in accordance with the requirements of GOST 5542-2014.
All AGRS are intended for outdoor operation in areas with seismicity up to 7 points on the Richter scale, with a temperate climate, at an ambient temperature of minus 40 to 50°C with a relative humidity of 95% at 35°C.
During the operation of the AGDS, significant design flaws are revealed, which for the most part boil down to the following:
Failure of gas pressure regulators due to the loss of condensate in the process of gas reduction in the form of ice flakes and their seizure of the regulator valve;
Failure of instrumentation devices in winter due to low temperatures in instrumentation and alarm units heated by lighting lamps.