CA2325756C - Multi-step gas saver - Google Patents
Multi-step gas saver Download PDFInfo
- Publication number
- CA2325756C CA2325756C CA 2325756 CA2325756A CA2325756C CA 2325756 C CA2325756 C CA 2325756C CA 2325756 CA2325756 CA 2325756 CA 2325756 A CA2325756 A CA 2325756A CA 2325756 C CA2325756 C CA 2325756C
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- CA
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- Prior art keywords
- gas
- equipment
- pressure
- source
- source gas
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- Expired - Lifetime
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C7/00—Methods or apparatus for discharging liquefied, solidified, or compressed gases from pressure vessels, not covered by another subclass
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
- F17C2205/01—Mounting arrangements
- F17C2205/0123—Mounting arrangements characterised by number of vessels
- F17C2205/013—Two or more vessels
- F17C2205/0134—Two or more vessels characterised by the presence of fluid connection between vessels
- F17C2205/0142—Two or more vessels characterised by the presence of fluid connection between vessels bundled in parallel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
- F17C2205/01—Mounting arrangements
- F17C2205/0123—Mounting arrangements characterised by number of vessels
- F17C2205/013—Two or more vessels
- F17C2205/0134—Two or more vessels characterised by the presence of fluid connection between vessels
- F17C2205/0146—Two or more vessels characterised by the presence of fluid connection between vessels with details of the manifold
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
- F17C2205/03—Fluid connections, filters, valves, closure means or other attachments
- F17C2205/0302—Fittings, valves, filters, or components in connection with the gas storage device
- F17C2205/0323—Valves
- F17C2205/0326—Valves electrically actuated
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2221/00—Handled fluid, in particular type of fluid
- F17C2221/03—Mixtures
- F17C2221/032—Hydrocarbons
- F17C2221/033—Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
- F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
- F17C2223/0107—Single phase
- F17C2223/0123—Single phase gaseous, e.g. CNG, GNC
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
- F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
- F17C2223/035—High pressure (>10 bar)
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
- F17C2227/01—Propulsion of the fluid
- F17C2227/0128—Propulsion of the fluid with pumps or compressors
- F17C2227/0157—Compressors
- F17C2227/0164—Compressors with specified compressor type, e.g. piston or impulsive type
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
- F17C2250/03—Control means
- F17C2250/032—Control means using computers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
- F17C2250/07—Actions triggered by measured parameters
- F17C2250/072—Action when predefined value is reached
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2260/00—Purposes of gas storage and gas handling
- F17C2260/04—Reducing risks and environmental impact
- F17C2260/044—Avoiding pollution or contamination
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2270/00—Applications
- F17C2270/01—Applications for fluid transport or storage
- F17C2270/0102—Applications for fluid transport or storage on or in the water
- F17C2270/0118—Offshore
- F17C2270/0123—Terminals
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2270/00—Applications
- F17C2270/01—Applications for fluid transport or storage
- F17C2270/0134—Applications for fluid transport or storage placed above the ground
- F17C2270/0136—Terminals
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2270/00—Applications
- F17C2270/05—Applications for industrial use
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
Natural gas and other industrial gases presently vented to the atmosphere can contribute to global warming or have other harmful effects.
In this invention a multi-step process has been devised to save high-pressure gas contained within equipment that is being temporarily de-pressurized, gas which would otherwise be vented to atmosphere or burned, and return a portion of this saved gas directly to the equipment, when this equipment is to be returned to high pressure service.
Depending on equipment size, saver vessel size, gas pressures, and the requirements of the user, gas venting could be reduced by amounts of from 70% to 99%.
This invention is applicable to natural gas compressor stations and other facilities where natural gas is vented during operation or maintenance, or for use in other industries where toxic or harmful gases might otherwise be vented to atmosphere
In this invention a multi-step process has been devised to save high-pressure gas contained within equipment that is being temporarily de-pressurized, gas which would otherwise be vented to atmosphere or burned, and return a portion of this saved gas directly to the equipment, when this equipment is to be returned to high pressure service.
Depending on equipment size, saver vessel size, gas pressures, and the requirements of the user, gas venting could be reduced by amounts of from 70% to 99%.
This invention is applicable to natural gas compressor stations and other facilities where natural gas is vented during operation or maintenance, or for use in other industries where toxic or harmful gases might otherwise be vented to atmosphere
Description
SPECIFICATION
Field of the Invention This invention relates to gas containing equipment in the natural gas industry, or any industry where gases may be vented to the atmosphere or burned in a flare and where reducing this venting or flaring may be of benefit to the environment, or to the health and safety of persons in the vicinity.
Background The natural gas industry seeks to contain its product as much as practical however the gas is relatively inexpensive so the practice is to vent it to the atmosphere during many operating procedures rather than spend time and money to save the gas. Venting natural gas releases methane (a typical proportion is 95%) and burning it releases carbon diaxide, both of these gases are potential contributors to global warming.
Some facilities in the natural gas industry vent or burn large amounts on a regular basis, such as at compressor stations. Gas compressor stations are located along transmission pipelines to increase gas pressure and propel it toward its destination. There may be one or more compressors in a station, the centrifugal type being the most common.
When such a compressor is shut down for operational or maintenance purposes it is usually necessary to quickly reduce the pressure inside the machine to atmospheric. A
common method is to vent or flare.
The natural gas industry also vents gas during other activities such as in processing plants and in the maintenance of meter stations and other equipment. Other industries also vent hazardous or harmful gas to the atmosphere. This invention could be used in many instances as an effective method to save a large portion of the gas being vented or burned.
Present Practice in Industry Many in the natural gas industry recognise that venting should be reduced, but the practice of venting or flaring persists because the gas is not a costly loss and because not all are convinced of the harm in venting natural gas, which is similar to the gas given off by decaying vegetation.
Some companies have tried to reduce venting by discharging gas to large lower pressure systems and the evacuation of equipment using small auxiliary compressors. These methods are slow and may require special operating procedures.
Brief Description of the Invention The invention is a process consisting of three or more gas saving pressure vessels capable of being connected to a piece of equipment containing a gas source, and a vent or flare, via piping arrangements that include controllable valves. In a fixed facility these pressure vessels may also be connected to other process functions, such as a fuel gas header, and the inlet of an ancillary gas compressor which can return the saved gas to a higher pressure system in the facility, but at a slower rate.
The principle of operation of this invention is an application of a basic law of thermodynamics: P, V, = P2 V2, where P is the absolute pressure of a gaseous material and V is the volume which this gaseous material occupies. The principle is applied in steps to gain the quickest pressure reduction while minimizing the size of equipment required.
Other thermodynamic effects including those due to temperature and gas composition occur but they are minor and are approximately equalized in both the gas source equipment and the (Gas Saver) pressure vessels.
This invention is the process concepts and the interconnection of equipment.
The process could be incorporated into a new installation or retrofitted into an existing facility.
The equipment used would be based on the standards for the industry including foundations and structures, high-pressure piping and vessels, valves, actuators, gauges, overpressure protection, monitoring and controls.
Piping and valve size would depend on gas flow rates and the time requirements for depressurizing as recommended by the source equipment manufacturer. The main control valves between the gas source equipment and the Saver vessels should be quarter-turn ball valves if flow modulation was required during the initial high pressure drop service, but low pressure drop full flow was required as the Saver vessel and equipment pressures near equalization. The monitoring and controls could be a separate package or incorporated into the control system of the industrial facility; at a fixed facility the process could operate automatically and unattended.
This process invention could be adaptable to many industrial operations, including natural gas transmission stations using centrifugal compressors. The compressors used in these stations may be of various manufacture and size, but an operational requirement is a quick reduction of pressure (formerly by gas venting or flaring) when an item of gas source equipment is being shut down.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are illustrated and described with reference to the accompanying drawings:
Figure 1 is a schematic process and instrument (P 8 I) diagram showing the embodiment of the basic components of the invention and their required interconnection in order to perform the operation of the invention, and from which details the process equipment is sized and configured;
Figure 2 is a schematic process and instrument (P & I) diagram showing the embodiment of the invention in a fixed facility and the interconnection of the components of the invention within such facility to fixed equipment containing sources of gas and facilitating disposal of gas; and Figure 3 is a schematic process and instrument (P & I) diagram showing the embodiment of the invention as a portable facility and the interconnection of the components of the invention temporarily to fixed equipment containing sources of gas and other equipment facilitating the disposal or utilisation of gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Saving the Gas Referring now to the drawings, Figure 1, at the start of the saving process sequence the gas to be saved is contained in the source operating equipment at its operating pressure, and the pressure vessels (Gas Savers PV-A, PV-B, PV-C, PV-D) are normally at atmospheric pressure. The gas to be saved flows from the source equipment to the pressure vessels, propelled by differential pressure, through the connecting piping. The gas saving operation proceeds as follows:
During the first step of saving the gas, valve V-A1 is opened to allow gas to flow from the source equipment into the first pressure vessel (Gas Saver) PV-A, reducing the source equipment internal pressure; when the pressure in PV- A and the source equipment are almost equal, valve V-A1 closes.
During the second step valve V-B1 is opened to allow gas to flow from the source equipment into the second pressure vessel (Gas Saver) PV-B, further reducing the source equipment internal pressure; when the pressure in PV-B and the source equipment are almost equal, valve V-B1 closes.
During the third step valve V-C1 is opened to allow gas to flow from the source equipment into the third pressure vessel (Gas Saver) PV-C, further reducing the source equipment internal pressure; when the pressure in PV-C and the source equipment are almost equal, valve V-C1 closes.
During the fourth step, in a 4-Step system, valve V-D1 is opened to allow gas to flow from the source equipment into the fourth pressure vessel (Gas Saver) PV-D, further reducing the source equipment internal pressure; when the pressure in PV-D and the source equipment are almost equal, valve V-D1 closes.
During the final step the blow-down valve V-BD is opened directing the remaining excess gas in the source equipment to atmosphere, or if available to a flare system, or perhaps a low pressure facility; in either case the source equipment pressure is reduced to near atmospheric pressure, at which point the blow-down valve V-BD is closed.
Depending on the equipment and the user's operational requirements, only three steps may be needed to reduce venting to a reasonable amount, or more than four steps could be used. It may be more feasible to increase the size of pressure vessels rather than increase the number of steps.
Returning the Gas A significant portion of the gas saved can be returned to the source equipment when the operating equipment is being restarted. The return sequence is in reverse order to the saving sequence; the lowest pressure gas is returned first.
During the first step of returning the gas, valve V-D1 is opened to allow gas to flow from (Gas Saver) PV-D (for a 4-Step system) into the source equipment, increasing the source equipment internal pressure; when the pressures in PV-D and the source equipment are almost equal, valve V-D1 closes. The first part of this step could include a purging action if the equipment had been opened and de-gasified for maintenance purposes.
During the second step valve V-C1 is opened to allow gas to flow from (Gas Saver) PV-C into the source equipment, further increasing the source equipment internal pressure;
when the pressures in (Gas Saver) PV-C and the source equipment are almost equal, valve V-C1 closes.
During the third step valve V-B1 is opened to allow gas to flow from (Gas Saver) PV-B
into the source equipment, further increasing the source equipment internal pressure; when the pressures in PV-B and the source equipment are almost equal, valve V-B1 closes.
During the fourth and final step valve V-A1 is opened to allow gas to flow from (Gas Saver) PV-A into the source equipment, further increasing the source equipment internal pressure; when the pressures in PV-A and the source equipment are almost equal, valve V-A1 closes.
This completes the gas return process, it may then be necessary to bring the equipment up to operating pressure by adding gas from an operating facility using conventional methods.
Page Restoration of Savers The pressure vessels (Gas Savers) can now be restored to atmospheric pressun:
for the next time there is gas in the source equipment needing to be saved. The restoration method will depend on the facility and the application but the most probable methods would be the use of a small compressor.
The pressure vessel PV-A with the highest pressure would probably be the first to be restored. Valve V-A2 would open and allow gas to flow to the suction of the Restoration Compressor, which would deliver the gas to the source equipment or facility piping. The other pressure vessels could be restored in a similar manner, or an alternate might be to open all the valves (V-A2, V-B2, V-C2, and V-D2) at the same time, thereby equalizing the pressures in all the vessels and allowing them to be restored in unison.
If the Multi-Step Gas Saver vessels were not immediately restored they could still be used but the capacity to save gas would diminish.
Application of a Multi-Step Gas Saver in a Fixed Facility Referring now to Figure 2 the operational example shows the embodiment of the invention applied in a fixed industrial facility.
The example is a natural gas compressor station, which typically use centrifugal compressors, which may be shut down many times per year, depending on operating conditions, and they often require depressurizing whenever shut down takes place, depending on design. If there were more than one pipeline compressor using the same (Multi-Step Gas Saver) invention process, then separate valves (V-1 S and V-2S) would be required on the connection of each compressor's piping to the invention.
In this example Gas Compressor #1 is to be shut down and the gas inside it and adjacent piping saved. This shutdown is triggered by the facility control system. The invention's control system could be separate and linked with the facility's automatic control system, or the logic could be incorporated into the facilities control system.
The gas source equipment is isolated from the remainder of the facility by its inlet and outlet valves V-1 i and V-10, and the connecting valve V-1s is open. The gas saving process is then carried out as described in "Saving the Gas" above.
When the compressor is to be restarted it has to be re-gasified, so the startup program can incorporate the "Returning the Gas" sequence described above, using a portion of the gas from the Savers. The remainder of the gas required to repressure Gas Compressor #1 during startup would come from the pipeline in the usual manner.
Page Restoration of the (Gas Saver) pressure vessels would take place as described in "Restoration of Savers" once the main gas compressor has restarted. In a gas compressor station, gas with high enough pressure in a (Saver) vessel could be used directly as fuel gas for the turbine drive via valve V-AFG. The remainder could be utilized at a lower pressure or with the aid of the Restoration Compressor be transferred via valves V-A2, V-B2, V-C2 and V-D2 to the fuel gas system or the main transmission pipeline.
This invention could apply to small or very large compressors, the size of the (Saver) pressure vessels and connecting pipe would be proportional to the volume of the compressor and adjacent piping. If a second and subsequent compressor was to be shut down before the Saver restoration was complete, it could be done but a lower percentage of gas would be saved, and a higher percentage vented or flared. Other compressor station equipment such as gas coolers and oil separators could also be piped into the Multi-Step Gas Saver for removal and storage of the gas when these facilities are to undergo inspection or maintenance.
Application of a Multi-Step Gas Saver as a Portable Facility Referring now to Figure 3 the operating example shows the embodiment of the invention in a portable assembly and applied to an item of gas source equipment that may need to be depressurised for operational or maintenance purposes. Equipment such as natural gas meter assemblies, or other industrial facilities, may need to be taken out of service and the operating company may wish to save the gas within this equipment for reuse rather than vent this gas to the atmosphere or burn it.
The gas saving process is carried out as described in "Saving the Gas" above.
The process could be controlled manually by the trades-person connecting an appropriately sized version of the Multi-Step gas Saver to the equipment to be taken out of service, and simply operating the valves to each Gas Saver vessel by hand, using the sound of flowing gas and pressure gauges as guides.
When the work on the source equipment is finished the gas in the Multi-Step Gas Saver can be used to purge and partially repressurise the equipment as described in "Returning the Gas" above, with the remainder of the repressurising gas coming from the pipeline in the normal manner.
If the (Saver) pressure vessels were not immediately restored they could still be used but the capacity to save gas would diminish. Depending on the intended use, these savers could be made larger to handle more than one field operation. Operational techniques such as reserving a spare low-pressure vessel could minimize venting.
The portable vessels could be restored to atmospheric pressure at some central facility, probable using a small compressor, or by partial utilization of the gas at a lower pressure. It might be possible to use the natural gas as a vehicle fuel if the service vehicle was so equipped.
BRIEF DESCRIPTION OF UTILITY AND BENEFITS
Appendices A and B which follow are tables showing the invention's step logic sequence of events and the effective performance of the invention for different size configurations and different typical operating pressures. Appendix A shows processes using four (Gas Saver) pressure vessels (4-Step Savers), and Appendix B shows processes using three pressure vessels (3-Step Savers). Each appendix explores the performance using different source equipment pressures and vessel volumes. The volumes of the pressure vessels are not absolute volumes; rather they are a volume as compared to the volume of the gas source equipment.
The invention would be able to reduce gas venting significantly. In an example shown in Appendix B page 2, for a 3-Step process operating at 50 bars (approx. 700 psig) and vessels at one-half the volume of the gas source equipment, gas venting could be reduced by about 70%. In an example shown in Appendix A page 3, for a 4-Step process also operating at 50 bars but with vessels at double the volume of the gas source equipment gas venting could be reduced by about 99%.
Many industries are attempting to reduce venting to the atmosphere of gases that could contribute to global warming or have other harmful effects so the major benefit is expected to be environmental but there could also be cost savings. Installing a Multi-Step Gas Saver could reduce the need and cost of other industrial equipment, such as for vent gas noise attenuation.
Reduced venting of toxic or harmful gases could improve employee and public safety, and save costs over other methods or mitigation. Other benefits are: improved safety by containing the greater part of a hazardous and/or flammable material, reduced odours of escaping natural gas or other material, plus increased satisfaction of employees, neighbours, and customers.
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Field of the Invention This invention relates to gas containing equipment in the natural gas industry, or any industry where gases may be vented to the atmosphere or burned in a flare and where reducing this venting or flaring may be of benefit to the environment, or to the health and safety of persons in the vicinity.
Background The natural gas industry seeks to contain its product as much as practical however the gas is relatively inexpensive so the practice is to vent it to the atmosphere during many operating procedures rather than spend time and money to save the gas. Venting natural gas releases methane (a typical proportion is 95%) and burning it releases carbon diaxide, both of these gases are potential contributors to global warming.
Some facilities in the natural gas industry vent or burn large amounts on a regular basis, such as at compressor stations. Gas compressor stations are located along transmission pipelines to increase gas pressure and propel it toward its destination. There may be one or more compressors in a station, the centrifugal type being the most common.
When such a compressor is shut down for operational or maintenance purposes it is usually necessary to quickly reduce the pressure inside the machine to atmospheric. A
common method is to vent or flare.
The natural gas industry also vents gas during other activities such as in processing plants and in the maintenance of meter stations and other equipment. Other industries also vent hazardous or harmful gas to the atmosphere. This invention could be used in many instances as an effective method to save a large portion of the gas being vented or burned.
Present Practice in Industry Many in the natural gas industry recognise that venting should be reduced, but the practice of venting or flaring persists because the gas is not a costly loss and because not all are convinced of the harm in venting natural gas, which is similar to the gas given off by decaying vegetation.
Some companies have tried to reduce venting by discharging gas to large lower pressure systems and the evacuation of equipment using small auxiliary compressors. These methods are slow and may require special operating procedures.
Brief Description of the Invention The invention is a process consisting of three or more gas saving pressure vessels capable of being connected to a piece of equipment containing a gas source, and a vent or flare, via piping arrangements that include controllable valves. In a fixed facility these pressure vessels may also be connected to other process functions, such as a fuel gas header, and the inlet of an ancillary gas compressor which can return the saved gas to a higher pressure system in the facility, but at a slower rate.
The principle of operation of this invention is an application of a basic law of thermodynamics: P, V, = P2 V2, where P is the absolute pressure of a gaseous material and V is the volume which this gaseous material occupies. The principle is applied in steps to gain the quickest pressure reduction while minimizing the size of equipment required.
Other thermodynamic effects including those due to temperature and gas composition occur but they are minor and are approximately equalized in both the gas source equipment and the (Gas Saver) pressure vessels.
This invention is the process concepts and the interconnection of equipment.
The process could be incorporated into a new installation or retrofitted into an existing facility.
The equipment used would be based on the standards for the industry including foundations and structures, high-pressure piping and vessels, valves, actuators, gauges, overpressure protection, monitoring and controls.
Piping and valve size would depend on gas flow rates and the time requirements for depressurizing as recommended by the source equipment manufacturer. The main control valves between the gas source equipment and the Saver vessels should be quarter-turn ball valves if flow modulation was required during the initial high pressure drop service, but low pressure drop full flow was required as the Saver vessel and equipment pressures near equalization. The monitoring and controls could be a separate package or incorporated into the control system of the industrial facility; at a fixed facility the process could operate automatically and unattended.
This process invention could be adaptable to many industrial operations, including natural gas transmission stations using centrifugal compressors. The compressors used in these stations may be of various manufacture and size, but an operational requirement is a quick reduction of pressure (formerly by gas venting or flaring) when an item of gas source equipment is being shut down.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are illustrated and described with reference to the accompanying drawings:
Figure 1 is a schematic process and instrument (P 8 I) diagram showing the embodiment of the basic components of the invention and their required interconnection in order to perform the operation of the invention, and from which details the process equipment is sized and configured;
Figure 2 is a schematic process and instrument (P & I) diagram showing the embodiment of the invention in a fixed facility and the interconnection of the components of the invention within such facility to fixed equipment containing sources of gas and facilitating disposal of gas; and Figure 3 is a schematic process and instrument (P & I) diagram showing the embodiment of the invention as a portable facility and the interconnection of the components of the invention temporarily to fixed equipment containing sources of gas and other equipment facilitating the disposal or utilisation of gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Saving the Gas Referring now to the drawings, Figure 1, at the start of the saving process sequence the gas to be saved is contained in the source operating equipment at its operating pressure, and the pressure vessels (Gas Savers PV-A, PV-B, PV-C, PV-D) are normally at atmospheric pressure. The gas to be saved flows from the source equipment to the pressure vessels, propelled by differential pressure, through the connecting piping. The gas saving operation proceeds as follows:
During the first step of saving the gas, valve V-A1 is opened to allow gas to flow from the source equipment into the first pressure vessel (Gas Saver) PV-A, reducing the source equipment internal pressure; when the pressure in PV- A and the source equipment are almost equal, valve V-A1 closes.
During the second step valve V-B1 is opened to allow gas to flow from the source equipment into the second pressure vessel (Gas Saver) PV-B, further reducing the source equipment internal pressure; when the pressure in PV-B and the source equipment are almost equal, valve V-B1 closes.
During the third step valve V-C1 is opened to allow gas to flow from the source equipment into the third pressure vessel (Gas Saver) PV-C, further reducing the source equipment internal pressure; when the pressure in PV-C and the source equipment are almost equal, valve V-C1 closes.
During the fourth step, in a 4-Step system, valve V-D1 is opened to allow gas to flow from the source equipment into the fourth pressure vessel (Gas Saver) PV-D, further reducing the source equipment internal pressure; when the pressure in PV-D and the source equipment are almost equal, valve V-D1 closes.
During the final step the blow-down valve V-BD is opened directing the remaining excess gas in the source equipment to atmosphere, or if available to a flare system, or perhaps a low pressure facility; in either case the source equipment pressure is reduced to near atmospheric pressure, at which point the blow-down valve V-BD is closed.
Depending on the equipment and the user's operational requirements, only three steps may be needed to reduce venting to a reasonable amount, or more than four steps could be used. It may be more feasible to increase the size of pressure vessels rather than increase the number of steps.
Returning the Gas A significant portion of the gas saved can be returned to the source equipment when the operating equipment is being restarted. The return sequence is in reverse order to the saving sequence; the lowest pressure gas is returned first.
During the first step of returning the gas, valve V-D1 is opened to allow gas to flow from (Gas Saver) PV-D (for a 4-Step system) into the source equipment, increasing the source equipment internal pressure; when the pressures in PV-D and the source equipment are almost equal, valve V-D1 closes. The first part of this step could include a purging action if the equipment had been opened and de-gasified for maintenance purposes.
During the second step valve V-C1 is opened to allow gas to flow from (Gas Saver) PV-C into the source equipment, further increasing the source equipment internal pressure;
when the pressures in (Gas Saver) PV-C and the source equipment are almost equal, valve V-C1 closes.
During the third step valve V-B1 is opened to allow gas to flow from (Gas Saver) PV-B
into the source equipment, further increasing the source equipment internal pressure; when the pressures in PV-B and the source equipment are almost equal, valve V-B1 closes.
During the fourth and final step valve V-A1 is opened to allow gas to flow from (Gas Saver) PV-A into the source equipment, further increasing the source equipment internal pressure; when the pressures in PV-A and the source equipment are almost equal, valve V-A1 closes.
This completes the gas return process, it may then be necessary to bring the equipment up to operating pressure by adding gas from an operating facility using conventional methods.
Page Restoration of Savers The pressure vessels (Gas Savers) can now be restored to atmospheric pressun:
for the next time there is gas in the source equipment needing to be saved. The restoration method will depend on the facility and the application but the most probable methods would be the use of a small compressor.
The pressure vessel PV-A with the highest pressure would probably be the first to be restored. Valve V-A2 would open and allow gas to flow to the suction of the Restoration Compressor, which would deliver the gas to the source equipment or facility piping. The other pressure vessels could be restored in a similar manner, or an alternate might be to open all the valves (V-A2, V-B2, V-C2, and V-D2) at the same time, thereby equalizing the pressures in all the vessels and allowing them to be restored in unison.
If the Multi-Step Gas Saver vessels were not immediately restored they could still be used but the capacity to save gas would diminish.
Application of a Multi-Step Gas Saver in a Fixed Facility Referring now to Figure 2 the operational example shows the embodiment of the invention applied in a fixed industrial facility.
The example is a natural gas compressor station, which typically use centrifugal compressors, which may be shut down many times per year, depending on operating conditions, and they often require depressurizing whenever shut down takes place, depending on design. If there were more than one pipeline compressor using the same (Multi-Step Gas Saver) invention process, then separate valves (V-1 S and V-2S) would be required on the connection of each compressor's piping to the invention.
In this example Gas Compressor #1 is to be shut down and the gas inside it and adjacent piping saved. This shutdown is triggered by the facility control system. The invention's control system could be separate and linked with the facility's automatic control system, or the logic could be incorporated into the facilities control system.
The gas source equipment is isolated from the remainder of the facility by its inlet and outlet valves V-1 i and V-10, and the connecting valve V-1s is open. The gas saving process is then carried out as described in "Saving the Gas" above.
When the compressor is to be restarted it has to be re-gasified, so the startup program can incorporate the "Returning the Gas" sequence described above, using a portion of the gas from the Savers. The remainder of the gas required to repressure Gas Compressor #1 during startup would come from the pipeline in the usual manner.
Page Restoration of the (Gas Saver) pressure vessels would take place as described in "Restoration of Savers" once the main gas compressor has restarted. In a gas compressor station, gas with high enough pressure in a (Saver) vessel could be used directly as fuel gas for the turbine drive via valve V-AFG. The remainder could be utilized at a lower pressure or with the aid of the Restoration Compressor be transferred via valves V-A2, V-B2, V-C2 and V-D2 to the fuel gas system or the main transmission pipeline.
This invention could apply to small or very large compressors, the size of the (Saver) pressure vessels and connecting pipe would be proportional to the volume of the compressor and adjacent piping. If a second and subsequent compressor was to be shut down before the Saver restoration was complete, it could be done but a lower percentage of gas would be saved, and a higher percentage vented or flared. Other compressor station equipment such as gas coolers and oil separators could also be piped into the Multi-Step Gas Saver for removal and storage of the gas when these facilities are to undergo inspection or maintenance.
Application of a Multi-Step Gas Saver as a Portable Facility Referring now to Figure 3 the operating example shows the embodiment of the invention in a portable assembly and applied to an item of gas source equipment that may need to be depressurised for operational or maintenance purposes. Equipment such as natural gas meter assemblies, or other industrial facilities, may need to be taken out of service and the operating company may wish to save the gas within this equipment for reuse rather than vent this gas to the atmosphere or burn it.
The gas saving process is carried out as described in "Saving the Gas" above.
The process could be controlled manually by the trades-person connecting an appropriately sized version of the Multi-Step gas Saver to the equipment to be taken out of service, and simply operating the valves to each Gas Saver vessel by hand, using the sound of flowing gas and pressure gauges as guides.
When the work on the source equipment is finished the gas in the Multi-Step Gas Saver can be used to purge and partially repressurise the equipment as described in "Returning the Gas" above, with the remainder of the repressurising gas coming from the pipeline in the normal manner.
If the (Saver) pressure vessels were not immediately restored they could still be used but the capacity to save gas would diminish. Depending on the intended use, these savers could be made larger to handle more than one field operation. Operational techniques such as reserving a spare low-pressure vessel could minimize venting.
The portable vessels could be restored to atmospheric pressure at some central facility, probable using a small compressor, or by partial utilization of the gas at a lower pressure. It might be possible to use the natural gas as a vehicle fuel if the service vehicle was so equipped.
BRIEF DESCRIPTION OF UTILITY AND BENEFITS
Appendices A and B which follow are tables showing the invention's step logic sequence of events and the effective performance of the invention for different size configurations and different typical operating pressures. Appendix A shows processes using four (Gas Saver) pressure vessels (4-Step Savers), and Appendix B shows processes using three pressure vessels (3-Step Savers). Each appendix explores the performance using different source equipment pressures and vessel volumes. The volumes of the pressure vessels are not absolute volumes; rather they are a volume as compared to the volume of the gas source equipment.
The invention would be able to reduce gas venting significantly. In an example shown in Appendix B page 2, for a 3-Step process operating at 50 bars (approx. 700 psig) and vessels at one-half the volume of the gas source equipment, gas venting could be reduced by about 70%. In an example shown in Appendix A page 3, for a 4-Step process also operating at 50 bars but with vessels at double the volume of the gas source equipment gas venting could be reduced by about 99%.
Many industries are attempting to reduce venting to the atmosphere of gases that could contribute to global warming or have other harmful effects so the major benefit is expected to be environmental but there could also be cost savings. Installing a Multi-Step Gas Saver could reduce the need and cost of other industrial equipment, such as for vent gas noise attenuation.
Reduced venting of toxic or harmful gases could improve employee and public safety, and save costs over other methods or mitigation. Other benefits are: improved safety by containing the greater part of a hazardous and/or flammable material, reduced odours of escaping natural gas or other material, plus increased satisfaction of employees, neighbours, and customers.
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Claims (3)
1. A process for accepting gas at high pressure from an item of source gas equipment and quickly saving a major portion of this gas, for return of a portion of the saved gas to the item of equipment at a later time, the basic concepts of said process being the transferring of gas to be saved from a source within high pressure equipment via piping, valves and controls, to pressure vessels, each initially being at a pressure lower than the gas source equipment and capable of containing a portion of the source gas, in three or more steps, by:
a) connecting from the source gas equipment to a first pressure vessel (PV-A) thus transferring by differential pressure a portion of the source gas, and when the pressures in this first pressure vessel and the source equipment have been approximately equalized, blocking the connection; and then connecting from the source gas equipment to a second pressure vessel (PV-B) thus transferring in similar manner a second portion of the source gas, and when the pressures in this second pressure vessel and the source gas equipment have been approximately equalized, blocking the connection; and then connecting and transferring to a third and possibly a fourth or more vessels (PV-C and PV-D) in a similar manner; and when the pressures in the last vessel and the source gas equipment have been approximately equalized, blocking the connection, then blowing down to a vent, or a flare, or a storage device, the excess residual gas in the source equipment; and b) when the source equipment is to be re-pressurized and returned to operation, to return a portion of the saved gas from the saver pressure vessels to the source equipment, beginning from the pressure vessel with the lowest pressure, in similar operating steps as in 1a), to finally the highest pressure vessel; and to restore the saver vessels to atmospheric pressure all by conventional means; and c) the overall performance of this invention being predictable and determined by the size of equipment selected, which is based on the operating requirement of the user.
a) connecting from the source gas equipment to a first pressure vessel (PV-A) thus transferring by differential pressure a portion of the source gas, and when the pressures in this first pressure vessel and the source equipment have been approximately equalized, blocking the connection; and then connecting from the source gas equipment to a second pressure vessel (PV-B) thus transferring in similar manner a second portion of the source gas, and when the pressures in this second pressure vessel and the source gas equipment have been approximately equalized, blocking the connection; and then connecting and transferring to a third and possibly a fourth or more vessels (PV-C and PV-D) in a similar manner; and when the pressures in the last vessel and the source gas equipment have been approximately equalized, blocking the connection, then blowing down to a vent, or a flare, or a storage device, the excess residual gas in the source equipment; and b) when the source equipment is to be re-pressurized and returned to operation, to return a portion of the saved gas from the saver pressure vessels to the source equipment, beginning from the pressure vessel with the lowest pressure, in similar operating steps as in 1a), to finally the highest pressure vessel; and to restore the saver vessels to atmospheric pressure all by conventional means; and c) the overall performance of this invention being predictable and determined by the size of equipment selected, which is based on the operating requirement of the user.
2. A process as defined in Claim 1, installed in a fixed facility, in which said process may be shared by one or more fixed natural gas compressors or other fixed items of industrial equipment containing high pressure source gas, within the fixed facility, and provision is made to connect these items of equipment so as to share the use of the said process.
3. A process as defined in Claim 1, arranged as a portable facility for the purpose of accessing items of industrial equipment containing high pressure source gas at various locations, and provision being made to connect these facilities so as to share the use of the said process in a portable mode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2325756 CA2325756C (en) | 2000-12-13 | 2000-12-13 | Multi-step gas saver |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2325756 CA2325756C (en) | 2000-12-13 | 2000-12-13 | Multi-step gas saver |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2325756C true CA2325756C (en) | 2001-10-23 |
Family
ID=4167623
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2325756 Expired - Lifetime CA2325756C (en) | 2000-12-13 | 2000-12-13 | Multi-step gas saver |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2325756C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113432032A (en) * | 2021-05-21 | 2021-09-24 | 长沙中益气体有限公司 | Industrial gas safety intelligent gas supply device with filling and metering functions |
| US20230313947A1 (en) * | 2021-05-17 | 2023-10-05 | Estis Compression, LLC | Methane Retention System |
-
2000
- 2000-12-13 CA CA 2325756 patent/CA2325756C/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20230313947A1 (en) * | 2021-05-17 | 2023-10-05 | Estis Compression, LLC | Methane Retention System |
| US20240133521A1 (en) * | 2021-05-17 | 2024-04-25 | Estis Compression, LLC | Methane Retention System |
| CN113432032A (en) * | 2021-05-21 | 2021-09-24 | 长沙中益气体有限公司 | Industrial gas safety intelligent gas supply device with filling and metering functions |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20201214 |