LPG is a hydrocarbon compound consisting mainly of carbon and hydrogen atoms. LPG means liquefied petroleum gas.
As per NFPA 58 Section 3.3.36 LP-Gas or LPG is any material having a vapour pressure not exceeding that allowed for commercial propane that is composed predominantly of the following hydrocarbons, either by themselves or as mixtures: propane, propylene, butane (normal butane or isobutane), and butylene’s.
LPG is used for various applications including industrial, commercial, power generation, agricultural and manufacturing applications. LPG is widely used for cooking; it can also be used for heat generation as well as a source of fuel to power cars.
LPG is a product of gas and crude processing activities usually gotten as gas but conditioned to liquid state. LPG is stored in pressure vessels, when LPG is released from the storage vessel at ambient temperature it automatically changes to gas.
It should be noted that this article is tailored toward the requirements and recommendations of NFPA 58 code (Liquefied Petroleum Gas Code).
1.1 LPG Manufacturing Process
LPG is manufactured from two main sources; the processing of natural gas and the refining of crude oil.
Natural gas contains high percentage of methane and other smaller percentage of hydrocarbons including propane and butane etc. During the processing of natural gas Liquefied Petroleum Gas (propane and butane) are extracted.
During crude oil refining process, LPG is produced as one of the products of the refining process. Crude oil refining processes, include catalytic cracking, crude distillation, etc. The gas recovered during this refining process is liquefied to form LPG.
1.2 Categories of LPG Facilities
There are no distinct ways to categorise LPG storage facilities, however they may be categories based on the volume of LPG stored.
The first category is bulk storage terminal which are generally used to store large quantity of LPG for onward delivery to smaller storage facilities.
Distribution facilities are medium sized facilities that supply LPG to either final consumer or to small retailers. This type of facilities are more prominent than the bulk storage facilities especially in Africa.
Lastly there are mini LPG facilities which serves as retailer’s outlet to final consumers. These facilities are usually sited at designated location in a city or community.
The siting of an LPG facility is highly regulated; various level of permitting is required before approval is granted.
2 LPG TRANSPORTATION
Liquefied petroleum gas (LPG) can be transported using any appropriate means. Prior to selecting a transportation methodology, various factors including the under listed has to be analysed.
The volume of LPG to be transported
Available transportation infrastructure
The below modes of transportation may be used for LPG transfer.
2.1 Road Transportation
This is mostly used to transport small volumes of LPG to either medium capacity storage facilities, retailers or final consumers. Road transportation of LPG is usually limited to medium and short distances. Road transportation may be any of the following
Transportation using Iso containers or vessels mounted on trailers. This is usually employed when LPG is transported from bulk storage facilities to medium storage facilities. This is a common practice in in Africa.
LPG is most times transported using bobtail trucks, these small trucks convey LPG to retailers or major LPG consumers
Small LPG storage cylinders (gas bottles) are also transported on roads, the bottles filled with LPG are properly arranged on vans for onward delivery to customers.
It should be noted that when LPG is transported on roads all necessary safety considerations must be analysed to prevent accident.
2.2 Rail Transportation
This method is usually employed when large volume of LPG is transported from either LPG reception facilities or bulk storage facilities to other storage facilities. This mode of transportation is employed when large volume of LPG is to be conveyed over a long distance.
2.3 Ship/ Ocean Vessel Transportation
This mode of transportation is mostly employed when high volume of LPG is transported over a long distance especially from one country to another, from processing facilities to bulk storage facilities etc. This is the most preferred means of transporting LPG over a long distance. The liquefied gas is stored in special storage vessels mounted on Ships for onward transportation to bulk storage facilities. The Ship usually berth at a jetty constructed on a river banks, seaports etc. The river should be of appropriate depth for easy sailing of ship. It should be noted that there must be a connecting pipeline to transfer the LPG from the Ship to the storage facility. The connection between the Ship and the pipeline may be achieved using unloading arms or hose connection.
LPG is mostly transported with pipeline from Jetties to Bulk storage facilities, process facilities to Ships berthed at Jetties, reception stations to storage terminals etc. It should be noted that there are communities/estates with built LPG distribution network. The LPG to each home is supplied from a central storage facility through a pipeline distribution network.
3 COMPONENTS OF LPG FACILITIES
LPG facility is an integration of various component forming a functional unit for product reception and transfer. LPG facility may contain varying components depending on the complexity and size of the facility. In this section I will try to summarize some of the components of LPG facilities and their functions. See below schematic of a typical LPG facility.
Figure 1: Typical LPG Facility Schematics
3.1 LPG Storage Containers
Storage containers are used for storing LPG products, these vessels are pressurised, designed in accordance to ASME Boiler and Pressure Vessel Codes, BS Standard or any other approved code. In a typical LPG facility, you may see specific vessels for storing propane, Butane or missed LPG. Storage vessels may be classified in accordance to their shapes. It should be noted that this article does not cover other types of storage vessels or tanks except Spherical and cylindrical storage vessels.
Prior to selecting the type of storage vessel, understanding the advantages and disadvantages of the vessel type is critical.
Below are some of the pros and cons of these vessels.
Spherical storage vessel can store larger volume of LPG products compared to cylindrical storage vessels. In some cases spherical storage vessel stores over 120,000 gallons of LPG.
When large volume of LPG is stored, spherical vessels occupy lesser space compared to cylindrical vessels. When there is space limitation, Spherical storage vessel provides the best solution for space utilization.
More time is required to fabricate spherical vessels compared to cylindrical vessels. Due to their large size they cannot be entirely shop fabricated and transported to site. Part of the vessels are shop fabricated and assembled on site to complete the installation. On the other hand, cylindrical vessels can be entirely shop fabricated and transported to site for installation.
Due to uniform distribution of stresses across the entire shell of Horton spheres, lesser plate thickness is used for a designated design pressure. In cylindrical pressure vessels due to uneven stress distribution, the plate thickness used for storage vessel head fabrication may be different to that used to form the shell.
Piping cost for spherical vessels is usually lesser than cost of piping attached to cylindrical vessels. Assuming one sphere stores the volume of LPG in three cylindrical vessels, only one discharge piping and connected fittings is requires compared to the three times quantity required for the three cylindrical vessels.
The cost of fabricating spheres on site is usually higher than the equivalent cost of fabricating cylindrical vessels.
Planned and unplanned maintenance favours the cylindrical vessels, because of their quantities, individual vessel can be maintained or repaired while others are in-service.
The content of a cylindrical vessel can be easily empties and isolated compared to large volume of LPG stored in Horton spheres. This is usually a big advantage if there is vessel failure in a cylindrical vessel.
Vessel relocation favours cylindrical storage vessels. In some cases, there is a possibility of relocating LPG storage vessels, this is very easy for cylindrical vessels because they can be easily transported to another location compared to the extra effort required to disassemble a spherical vessel and reassemble in a new site.
3.1.1 Spherical Vessels
The technical name for a spherical storage vessel is Horton Sphere. Like the name they are spherical in shape. These vessels are used for storing large volume of liquefied petroleum gas. They usually occupy lesser space than cylindrical storage vessels. One of the main advantage of this type of storage vessel is the uniform distribution of stress on the sphere compared to the non-uniform stress distribution on cylindrical vessels. The uniform stress distribution results in reduced shell plate thickness.
These vessels are cylindrical in shape they are also called LPG storage bullets. They have hemispherical, ellipsoidal head or a combination of various heads. They may be installed horizontally or vertically however they are mostly installed horizontally either below ground or above ground. When installed above ground they may be mounded, semi mounded or unmounded.
Below is a brief explanation of the types of Cylindrical storage vessels
18.104.22.168 Underground Storage Vessels
These vessels are installed below ground to provide additional safety to the vessels, surrounding structures and environment. Various codes and standards including NFPA, BS standards permits LPG storage vessels to be installed below ground. Installing vessels below ground results in reduced spacing between vessels, reduced spacing between vessels and building/structures etc.
22.214.171.124 Mounded Vessels
Cylindrical storage vessels can be installed above ground and mounded. Mounding entails building a wall (may be made of concrete) around the storage vessels to a specified height, filling the concrete structure with earth, sand or other material above the tank. A concrete cover or gravel pack may additionally be placed on top of the sand cover. Cylindrical storage vessels can be totally mounded or partially mounded. When they are totally mounded, the entire shell and head are not visible however provision is made for piping and instrument connection. When they are semi-mounded one of the heads including a section of the shell may be visible.
This is one of the most common type of installation especially when the storage capacity is small. The vessels usually have attached saddle supports resting on concrete base. Details of the spacing and installation requirements for unmounded tanks will be discussed in further sections however the spacing between buildings and unmounded tank is greater than the required spacing between mounded tanks and buildings (this is applicable for tanks with water storage capacity greater than or equal to 7.6m3). Refer to table 6.3.1 of NFPA 58 for separation distance between tanks and buildings.
Pumps are used for transferring LPG from trucks/bobtail to storage vessels, storage vessels to bobtail, storage vessel to storage vessel, from storage vessels to dispensing stations etc. When the pump is turned on it sucks LPG from the bottom of the tank to its destination. Note the pump suction must be connected to the bottom of the vessels. One of the major shortfalls of using pump to transfer LPG is its inability to recover LPG vapour.
Compressors are used for LPG transfer. Compressors are very efficient in transferring LPG. They utilised the vapour generated in the LPG storage vessel to transfer LPG products from (Trucks, Ships etc.) to the storage vessel. Some of the most common compressors in LPG facilities are manufactured by Corken.
Below is a simple illustration of how LPG is transferred from Truck A to a Storage Vessel B.
The compressor is equipped with a four way valve the compressor is turned on and the 4-way valve adjusted such that vapour is sucked from Vessel B to Truck A, the vapour creates higher pressure in the truck vessel and force the LPG through the Liquid transfer line into the storage Vessel until the liquid is emptied. After this the 4-way valve position is reversed and the compressor sucks the vapour from Truck A back into Vessel B.
Figure 7: Installed LPG Transfer Compressors
3.4 LPG loading and Unloading Bay
This is the location in the facility where LPG transfer is performed. The loading/unloading arms or transfer hose will be installed here for LPG transfer. A bay may not be covered however NFPA permits a weather shed or canopy installed over the bay.
Figure 8: LPG Loading Bay
3.5 LPG Loading and Unloading Arm
These are specialised equipment installed in a loading bay for product transfer from or into a vessel. They are equipped with swivel joints that permits vertical and sideways movement thereby making it easy to operate. The end connection to the LPG truck is equipped with a quick connect coupling which fits into the discharge nozzle of the trucks. LPG transfer using loading/unloading arm is safer and more efficient. Section 126.96.36.199 of NFPA 58 requires that an isolation valves shall be located at the point of loading/unloading arm connection to the manifold
Figure 9: Installed LPG Loading and Unloading Arms
3.6 Loading/Unloading Hose
Hoses are sometimes used for LPG transfer they are however less efficient connection compared to loading and unloading arms. They are usually equipped with a quick connect/disconnect coupling or flange coupling at their free end. Hoses have expiry dates therefore replacement is required after years of usage. Bigger transfer hoses are more difficult to operate. Section 188.8.131.52 of NFPA 58 requires that an isolation valves shall be located at the point of loading/unloading hose connection to the manifold
Figure 10: LPG Transfer Hose
3.7 LPG Measurement
There are measurement instruments installed in a facility to measure the quantity of LPG transferred. Typically, there are two measurement techniques used; They are volumetric measurement and weight or mass measurement.
3.7.1 Volumetric Measurement (Flowmeter)
This entail installing a flow meter on the discharge line to measure the volume of LPG transferred from a container to truck etc. This is the measurement procedure employed at the loading bay. The meter is installed on the inlet piping to the loading arm or hose. There are various manufacturers of flowmeters used in LPG facilities however some of the most used meters are the Smith meters. Meters shall be installed as per the manufacturers guidelines and procedures.
Figure 11: Installed LPG Flowmeter
3.7.2 Weight Measurement (Weighbridge)
This is mostly employed for measuring bulk LPG conveyed into or out of a facility by truck or bobtail. Small weight measurement devices are also available to measure the weight of cylinders before and after been filled with LPG. To measure quantity of LPG conveyed by a truck into or outside a facility, a Weighbridge is used. The Weighbridge is installed at a designated location in the facility preferably on the facility access road. When a truck conveying LPG to the facility arrives, it is directed to the location of the weighbridge. The truck stops on top of the weighbridge and the load cells in the Weighbridge senses the weight of the truck and transmit these data to a display or control room. The Truck proceeds to the unloading bay and discharges its LPG content. If the empty weight of the truck is not known the truck drives back and stop on the weighbridge and the weight is measured. The difference between the truck weight filled with LPG and when empty is the weight of the LPG content discharged by the truck. The weight measured can as well be converted to volume of LPG discharged.
Figure 12: Installed Weighbridge at The Entrance of an LPG Facility
Figure 13: Weighbridge Field Display
3.8 LPG Transfer Sales Unit
This is a location where LPG is sold in small quantities to retailers or final consumers. This unit may contain a carousel where LPG bottles are automatically filled or offline sales scales where LPG is sold based on weight measurement. A decanting unit may as well be installed very close to the transfer sales unit.
3.9 Pump Suction Line
This line is usually connected to a nozzle at the bottom of the storage vessel. Upstream of the pump a strainer and an isolation valve should be installed on the pump suction line. This line is used when the pump is used for LPG transfer to another storage, LPG sales point etc. It should be noted that there may be piping interconnection between the pump suction line and the Compressor liquid transfer line.
3.10 Compressor Liquid Transfer Line
This line is usually connected to a nozzle at the bottom of the vessel. This line is only used when the compressor is used for liquid transfer. Assuming we intend to transfer LPG from the vessel to a bobtail, the compressor draws vapour into the storage tank and the vapour pushes the liquid through the compressor liquid transfer line into the bobtail.
3.11 Vessel Fill Line
This line is used to fill a storage vessel. The vessel fill line may be connected to the discharge of a pump or a compressor liquid transfer line.
3.12 Liquid Bypass Line
The bypass line is connected to the discharge of the flow control valve. This line is only used when there is excess LPG transfer in the pump discharge line. When the FCV opens LPG flows back into the storage tank via the Liquid bypass line.
3.13 Vapour Lines
These line are connected to the compressor. The vapour line connected to storage vessel are usually connected to a nozzle at the top of the vessel. Vapour lines are only used when compressor is used for LPG transfer. There are two vapour lines: Vapour line connected to the discharge nozzle of the compressor and vapour line connected to the suction nozzle of the compressor. Since the compressor has a 4-way valve the suction and discharge of the compressor are interchangeable. When the compressor is turned on it suck vapour from a storage tank ad discharge into a truck after liquid transfer the compressor sucks back the vapour from the truck back to the storage vessel
Various types of valves are installed in a typical LPG facility; these valves perform various functions. The type of valves in a facility may vary however the below valves are very prominent
3.14.1 Ball valves
These valves are used for isolation. They are quarter turn valves this implies they can be easily closed or open. Ball valves also provide tight shutoff to flow. They are installed at suction lines, discharge lines, manifolds etc.
3.14.2 Check valves
Check valves are installed on pump discharge lines and other piping that return flow is anticipated. They are also called non return valves because they allow flow in only one direction. When two or more pumps discharge line are connected to a common header, each individual pump discharge line shall have a check valve installed.
Figure 14: Installed Check Valves
3.14.3 Internal Valves/Excess Flow Valves
As per table 4.1.1 of NFPA 58, storage vessels with water storage capacity greater than 7.6m3 shall have excess flow valves installed. Section 6.1 requires that a storage vessel with storage capacity 4000 gallons shall be equips with internal valves. Internal valves al installed in vessels to provide shutoff of stored content from piping connections. Internal valves are also equipped with excess flow control capacity. When there is excess flow through any of the nozzle the valve regulates the flow or cut off flow.
3.14.4 Pressure Relief Valves
A Pressure relief valve is very essential in an LPG facility. They are installed on top of the pressure vessels and may find small relief valves installed on the piping network. All relief valves have a set point, when there is pressure build up in the vessel or piping up to the set point the relief valve opens until the pressure drops below the set point.
Figure 15: Installed Pressure Relief Valve on a Storage Vessel
3.14.5 Flow Control Valve
A flow control valves is installed on pump discharge lines or discharge header. The valves are pre-set to a particular value. When the pump is operating normally i.e. the discharge flow is lesser than the set point of the FCV, the valve remains closed. When there is excess flow in the line up to the set point of the FCV the valve opens gradually to reduce the flow by diverting the excess volume into a bypass line. The FCV outlet piping is usually piped back to the storage vessel. An isolation valve may be installed upstream and downstream of the FCV; these valves are normally open during operation. The isolation valves are only closed when there is need to maintain/repair the flow control valve.
Figure 16: Flow Control Valve
3.15 Pressure Indicators
Pressure indicators are very important instrument in an LPG facility. They are installed on the storage vessels, inlet and outlet piping of pumps and compressors, manifolds etc. In automated facility the recorded pressure is transmitted to the control room. If the recorded pressure is higher than a set value, the pump or compressor is shutdown down or the pressure relief valve opens and depressurise the system. When the pressure in storage vessels increases beyond a set point, the Pressure relief valve opens and depressurise the storage vessel.
Figure 17: Pressure Indicator Installed on Pump Discharge Piping
3.16 Gas Detectors
Gas detectors are very important in an LPG facility. They have the capability to sense little gas leakage in the facility. They are installed at strategic locations in the facility to detect gas leakages. In automated facility if gas leakage is detected the emergency shutdown and firefighting system is activated.
3.17 Temperature Sensors
These are key components of an LPG facility. They maybe small in size but perform key functions especially around the product storage area and LPG transfer locations. When they sense high temperature they may automatically activate the sprinkler system installed in the product storage and transfer area. They may also activate the shutdown of the facility.
3.18 Temperature Indicators
Temperature indicator are mostly installed on LPG storage vessels, loading bays, unloading bays and LPG transfer points. They continually measure the temperature and turns on the sprinkler system when the temperature reaches a set point. Temperature indicator transmitters may also be integrated into the emergency shutdown system of the facility.
Figure 18: Temperature Indicator
3.19 Sight Flow Indicator
They are also called sight glass; they are usually installed upstream of the pump suction i.e. on the suction line to the pump. It is no mandatory to install a sight flow indicator, however they are installed to promote the efficiency of pumps and to observe the flow through the pipe. The operator observes the flow through the pipe using the sight flow indicator and can adjust the pump speed accordingly to obtain maximum flow rate without cavitation. Sight flow glass may be equipped with swing type check valve to prevent back flow of LPG.
3.20 Breakaway Coupling
Breakaway Couplings are used when hoses are used for LPG transfer. They provide a safe parting point within the hose assembly. They are installed to separate at the tie in point of the hose to the metallic piping. Assuming a truck has completed unloading activities and the operator forget to disconnect the hose from the pipe connection point this can cause a fatal accident if the truck starts moving with the hose still connected. The breakaway coupling senses the scenario by measuring tensile forces, once the forces exceed predetermined tolerances, the Breakaway Coupling automatically activates by first sealing the flow preceding and succeeding the coupling and secondly separates.
3.21 Instrument Air Compressor
The instrument air compressor provides the air used for instrumentation control. The compressor takes air from the atmosphere compresses the air to a designated pressure and sends and stores the pressurised air in a vessel. The instrument air header is connected to the vessel storing the pressurised air. All actuated valves take air from the instrument air header for their opening and closing.
Figure 19: Instrument Air Compressor
3.22 Emergency Shutdown Push Buttons
The level of automation in facilities varies however it is recommended that LPG facilities are automated. When facilities are not fully automated emergency shutdown push buttons are installed at designated locations. These buttons are only put into use in the event of an accident. Any of the button can activate the total shutdown of the entire facility.
Figure 20: Emergency Shutdown Push Button
3.23 Instrumentation Control Room
This is the brain of the facility. In Automated facilities the appearance of the control room may be more complex compared to semi-automated facilities. All field instrument reading are transmitted to the control room where they are monitored. The control room also has the capacity to turn on any pump, compressor for loading and unloading operation. Actuated valves can as well be remotely open or closed at the control room. The emergency shutdown system is also an integral part of the control room.
Figure 21: A Control Room Under Construction
Figure 22: Instrumentation Control Panel( Internals Showing Wiring)
3.24 Earthing System
For an LPG facility to be operated safety earthing system should be installed. All metallic structures are usually earthed by connecting them to the earthing grid. All trucks unloading or loading LPG should be properly grounded until operation has ended. Grounding ensures there is no build of static electricity on the vessel and chassis of the truck.
3.25 Firefighting System
This is a safety system installed in an LPG facility to help in combating fire. Components of a firewater system are mostly painted red. A firefighting system may contain any of the following
3.25.1 Firewater Storage Tank
The tank stores the water that is used for firefighting. The tank must be appropriately sized based on the firewater demand calculation performed by the process engineer. The tank must be equipped with level gauge this is to ensure that sufficient water is always stored in the tank. In automated system when the level gauge senses the volume of water is lesser than a set limit, the raw water pump is automatically turn on and fill the tank.
Figure 23: Firewater Storage Tank
3.25.2 Raw Water Pum
These pumps are used to pump water into the storage tank, they may take their suction from boreholes or from open river. The water may undergo some level of purification before entering the tank.
3.25.3 Jockey Pumps
Jockey pumps are small centrifugal pumps installed in a firefighting system. They are mostly electrically driven. Jockey pumps are primarily used to maintain pressure on the firewater ring main. They provide the initial water that is used to fight fire however due to the low volume of water generated there will be significant pressure drop in the ring main. The pressure drop activates the main firewater pump to provide the required pressure for firefighting.
These are the main pumps for firefighting. They maybe diesel driven or electrically driven. In minimum there must be a spare pump always available for firefighting this is to provide backup for the primary pumps if it is faulty. In automated facilities when the temperature sensors measures temperature beyond set point or the gas detectors senses gas leakage, the main firewater pump is turned on to pressurise the firewater ring main. The pumps can as well be manually turned on for firefighting. The discharge pressure of the pump must be sufficient to provide firefighting coverage when the firefighting monitors and hydrants are operational. Main firewater pumps may take their suction from firewater storage tanks or from a river source depending on the facility design philosophy
Figure 25: Diesel Engine Driven Firewater Pump
Figure 26: Electric Motor Driven Firewater Pump
3.25.5 Firewater Ring Main
The Ring Main is the major pipe header routed around the LPG facility. The ring main may be buried or installed above ground. It does not necessarily mean the ring main must be routed along the perimeter of the facility. The ring main is appropriately sized by the process engineer to ensure it supply the require flowrate to the firewater monitors and hydrants.
Figure 27: Fire Monitor Connected to a Ring Main Pipe (Red in Colour)
3.26 Fire Monitors
Fire monitors or water cannons are devices used to deliver large volume of water for firefighting purpose to the fire source. They may be automatically controlled to open or manually turned on for firefighting. They can efficiently deliver high volume of water to the fire source. In selecting the monitor, the reach of the monitor and the volume of water delivered are some of the major considerations. The monitor can be manually turned on by opening the valve, and directing the monitor to the fire source.
Figure 28: Fire Monitors
3.27 Fire Hydrants
Fire Hydrants are connection point for firefighting hose. They are made of pipes, valves and outlet connections for hose. They are strategically located on the firewater ring main. Close to the hydrant is a hose reel. In the event of fire, the hose is connected to the hydrant and can be pulled to a firefighting location.
Figure 29:installed Firewater Hydrant
3.28 Fire extinguishers
Thy constitute part of the firefighting system. They are strategically located in the facility where they can be easily accessed for firefighting. Fire extinguishers shall only be used by trained personnel.
Figure 30: Fire Extinguisher at Loading Bay
3.29 Water Sprinklers
The water sprinklers are primarily used for cooling and preliminary fire suppression. The sprinklers are installed in the LPG storage area, loading and unloading bay and LPG transfer points. During LPG transfer the sprinklers are turn on especially when the temperature increases beyond a set point. The sprinklers installed in the storage area must provide a total coverage for the entire storage vessels. When the temperature sensors measures temperature beyond set point the sprinkler system is activated to cool the tanks.
Figure 31: Activated Water Sprinklers
3.30 Utility Water System
The utility water system consists of storage tank and piping, this water is what is used in toilets and for other general purpose.
3.31 Portable Water System
Portable water simply means water that is safe to drink.
Portable water system is the connection of equipment, piping and fittings installed to process and transfer drinkable water to appropriate locations in the LPG facility. The portable water system consists of water purification units, tanks etc.
3.32 Power Generating System
Electricity is key to the effective operation of an LPG facility. The control room is electrically powered; pumps may be electrically powered etc. the source of power should be carefully analysed. Primary source of power may be the National grid, however alternative power source such as electricity generator may be provided
4 LPG FACILITIES DESIGN CODES AND STANDARDS
LPG facilities are designed, constructed and operated as per various codes and standards depending on local requirements, client requirement. The code requirement for facility design shall be selected prior to the commencement of design activities
4.1 LPG Facility Design Requirements
The below requirements are just few of the guidelines set by NFPA as stated in NFPA 58. For details of these requirement refer to NFPA 58 code.
4.1.1 Container Requirements
As stated in section 4, table 4.1 of NFPA 58 containers storing LPG with water storage capacity greater than 7.6m3 shall have
Container excess-flow valves, backflow check valves, or alternate means of providing this protection such as remotely controlled internal valves Container gauging devices Regulators and container pressure relief devices.
Refer to table 4.1 for container requirement where container water storage capacity is lesser than 7.6m3.
4.1.2 Vessel Separation Spacing Requirement
Spacing requirements and guidelines are stated in section 6.3 of NFPA 58. Also refer to table 6.3.1 for minimum spacing.
4.1.3 Separation Distance Between Container Pressure Relief Valve and Building Openings
Spacing requirements are stated in section 6.3.9, Table 6.3.9 of NFPA 58.
4.1.4 Burial Depth Requirements for Underground and Mounded Containers
Guidelines for burial depth are stated in section 6.6.6 of NFPA 58. When containers are installed in an area with no vehicular traffic, the minimum burial depth from grade shall be 15cm.
When non interchangeable containers are installed in an area with foreseen vehicular movement, the minimum burial depth shall be minimum 46cm
4.1.5 Minimum Separation Distance between point of LPG transfer and Exposures
Some of these requirements are clearly spelt out in section 6.5 of NFPA 58. Some of the requirement are
LPG shall only be transferred into containers (Cylinders, tanks, vessels etc.) outdoor and not inside buildings
LPG transfer into containers is permitted under weather shelter or canopy, however section 184.108.40.206 states that a vehicle fuel dispensing points installed under a weather shelter or canopy shall not be enclosed for more than 50 percent of its perimeter
When a container point of transfer is located outdoors in a stationary installation, the minimum separation horizontal distance between the transfer point and other infrastructure shall be as per Table 6.5.3 of NFPA 58.
LPG can be transported by Vessels/containers mounted on trailers, Vessels on rail tracks and by Ships.
LPG storage facilities may be classified as per the volume of liquid stored, the design of LPG facility should take into considerations all safety requirements.
LPG facilities may be design as per NFPA codes, BS standard and other approved codes. Minimum requirements for vessel spacing, location of dispensing units, separation distance between containers are properties etc. are stated in these codes and standards.
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