Vol 4 SNG and LPG Systems Overview

Vol: 4

SNG and LPG Systems Overview

A Handbook from theSNG Academy™

Tulsa, Oklahoma, USA

LPG and SNG Systems OverviewTable of ContentsHistory & Abstract � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 2General Business Description � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 2The Company � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 2Purpose of the handbook� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 4SNG System Overview � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 4TTU � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 6SNG System Owner Responsibility� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 8LPG Cylinder Filling� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 9LPG Storage Tanks � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 11LPG Pumps� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 16LPG Vaporizer� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 17SNG Blenders � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 19 Venturi SNG Systems � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 20

Proportional SNG Systems � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 23Old Fashioned Piston Type Mixers � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 25

SNG to NG � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 27Properties of LPG � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 28Codes & Standards (USA)� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 30LPG Safety Components� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 31Combustion Characteristics of LPG � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 33SNG System Operation, Maintenance and Malfunctions � � � � � � � � � � � � � � � � � � � � � 34Emergency Procedures� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 38

Disclaimer of Responsibility: Ely Energy Inc. does not warrant or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process described herein. Ely Energy Inc. assumes no liability for the misuse, abuse, or incorrect application of data presented. This Handbook does not pur-port to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation, operation, maintenance or training. Should further information be desired or should particular prob-lems arise which are not covered sufficiently for the readers purposes the matter should be referred to Ely Energy Inc. [email protected]

LPG and SNG Systems Overview

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History & AbstractSynthetic Natural Gas (SNG), plays a niche role, yet a critical role in meeting the energy

needs of nations around the world� SNG is a term that describes a variety of “manufactured gases”� In our language, SNG is a blend of Liquefied Petroleum Gas (LPG) and air that provides a direct replacement for natural gas.

This handbook provides basic information and describes concepts and equipment com-mon to the SNG industry� Our presentation is intended to assist personnel who are involved with SNG systems and equipment�

History of Ely Energy, Inc.From 1898 to the 21st-Century…

In 1898, Energy Systems, Inc� (ESI) began as a mechanical contractor located in south-ern Minnesota (USA)� By the 1950’s ESI had branched out into associated mechanical engineering activities that grew to include design and manufacture of Synthetic Natural Gas (SNG) systems� Their applications included peak shaving for natural gas utilities and industry, backup fuel systems and CityGas distributed gas systems� Around 1980, ESI was acquired by the RJ Ely Company of Tulsa, Oklahoma (USA) and began operations as Ely Energy Systems, and later as Ely Energy Inc� — a subsidiary of the RJ Ely Company� In 1998, under a corporate consolidation, the corporation formally changed to Ely Energy, Inc� (EEI)�

General Business Description

EEI specializes in specific niche market opportunities that typically involve LPG (liquid fired petroleum gases) or NH3 (ammonia)� The cornerstone of EEI’s business is the so-called synthetic natural gas (SNG) group that offers solutions to assist in natural gas management� Most people have heard of natural gas� Some have heard of liquefied petroleum gas (LPG)� Few outside the energy sector, however, understand SNG� We create SNG by blending LPG with air to a specific ratio that results in a fuel with combustion characteristics essentially identical to natural gas� This precise and controlled mixing of LPG and air allows it to be used as an alternative to natural gas for “backup” use, ‘peak shaving’, and CityGas supply in regions where natural gas is not yet available� No orifice changes, pressure changes or any other changes are required to the natural gas consuming equipment! SNG is a direct replacement for natural gas (NG)!

The technology of blending LPG and Air to simulate natural gas is not new — SNG extends back to the 1950’s� What is new is our ability to provide much higher degrees of control, gas quality consistency and safety to the process�

Our SNG solutions assist in natural gas energy management for private industry, the fed-eral government, the U�S� military, municipalities, educational and correctional institutions and the medical-health care sector� We offer solutions in various forms, typically involving the installation of an on-site SNG system for either ‘standby’ or ‘base load’ use�

With ancestral roots that trace to 1898, EEI is easily one of the most respected SNG

AQUA-GAS® under manufacture at Ely Energy.

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equipment and service providers in the world� Our commitment is to optimize our avail-able resource base to make every project successful� We provide a variety of SNG energy services including:

■ SNG Backup Systems: Allow the industrial natural gas customer to change from a FIRM to an INTERRUPTIBLE Natural Gas rate structure� The savings will often pay for an installation within 6 mo� or less, up to 4 years�

■ SNG Peak Shaving Systems of NG: SNG is used by both NG Companies and Industrial Clients to augment their NG demand during peak demand periods�

■ SNG Base-Load Systems: Provide SNG in regions where NG is currently not avail-able� SNG provides a bridge fuel or a long-term solution for an energy need�

The CompanyWe can be contacted at fax (918) 254-5412 (USA) or at our e-mail: sales@elyenergy�com�

Our telephone switchboard is at (918) 250-6601� Touch ‘0’ for the Operator to direct your call� Or visit us on the Internet at www.elyenergy.com� Our physical address is 11385 East 60th Place South, Tulsa, Oklahoma 74146 (U�S�A�)�


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Purpose of the Handbook

The purpose of this handbook is to provide information on the properties of LPG and basic operation of an SNG system� This includes basic safety and operational information� Any training must be conducted by a technician trained in the properties of LPG and the application of LPG equipment to “real life” scenarios�

Handbook Includes:An overview of LPG and SNG systems•An introduction to the basic properties of LPG and how those properties impact •the operation of an SNG systemAn introduction to applicable codes and standards used to design, manufacture, •and maintain safe operation of an SNG systemTheory of operation of major subsystems of an SNG system•Basic maintenance requirements•How to recognize non-standard operating and emergency situations•

Handbook Does Not Include:Details of combustion or “plant specific” burner applications•Review of • all code requirementsKnowledge or training necessary to make design changes to an LPG or SNG system•

SNG System OverviewPurpose of an SNG System:

To provide a substitute synthetic natural gas (SNG) to replace or augment natural gas�SNG burns with similar characteristics as natural gas�•SNG requires no changes to pressure regulators or burner orifices�•SNG is introduced at the same pressure as natural gas� •SNG provides a similar “energy value” to natural gas (wobbe index) at the burner tip�•

SNG systems utilize five basic subsystems:Truck Transfer Unloading• facility (TTU) to receive liquid LPG from a transport (~ 9,000 US gallons/load)�LPG Storage Tanks• to store the liquid LPG�An LPG • pump system to transfer and elevate the pressure of the liquid LPG from the tanks to the vaporizer�An LPG • vaporizer to heat the liquid LPG and change it into the vapor (gaseous) phase� An LPG/Air • blender to blend the necessary air with the LPG vapor to create SNG�

Typical small capacity SNG System Layout

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Note: A “tie-in” point to the existing natural gas piping is another subsystem� Almost always, this point is just downstream of the existing service regulator/meter at the natural gas entrance to the plant.

Discussion Topics Five Key Subsystems of an SNG systemTTU/cylinder filling1. LPG Storage2. LPG Pump System3. LPG Vaporizer4. SNG Blender5.

Optional components may also be associated with an SNG system (examples include):Methanol injector system• located at the TTU to inject methanol into the storage tanks to remove water which may be in the LPG�SNG metering system• usually located at the outlet of the SNG blender to provide an accurate measurement of the SNG used�A• ‘Gas Quality Instrument’ to ensure the SNG has the proper energy content to repli-cate the energy valve of the natural gas� Flare Stack• allows testing the LPG air system at any time without running it into the plant or to ensure the SNG mix is good prior to sending it into the plant�Natural Gas peak shaving configurations• allow SNG to augment the flow rate of natu-ral gas either by pressure or ratio control�Remote monitoring system• to provide annunciation of key safety limits and the abil-ity to adjust flow rates from a remote location�


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TTU (Truck Transport Unloading Facility)

A normal TTU off-loads a 9000 gallon (34m3) transport in about 1 hr and 15 minutes� This rate of off-loading is based on using a 2" liquid line and 1 ¼" vapor line with valving sized for the pipe� Liquid is extracted from the transport via the larger diameter line� The smaller diameter line prevents a vacuum forming in the truck by allowing the pressures to equalize between the truck and the storage tank�

A common cause of accidental spills of LPG is a pull-away at an LPG transfer area� The term “pull-away” refers to an accident caused by a bulk truck moving away from the trans-fer point with the transfer hoses still connected to the TTU� A pull-away could break a hose, or in a severe case, pull out the piping network� In either case, a pull-away would cre-ate a large LPG spill and possibly result in a fire� To avoid these problems the TTU design incorporates a robust steel bulkhead set in a massive concrete foundation� The TTU utilizes shear fittings that “break away” in a designed fashion in the event of an accidental truck pull-away� The TTU is protected by large steel or concrete posts to prevent vehicles from colliding with the critical piping�

Industry studies prove a point of failure can be predicted and that a specific pull-away force can be determined at which the piping will rupture in a “clean break�” These studies have resulted in designs and connections using Schedule 80 pipe nipples and couplings� An example of a TTU bulkhead is shown on the opposite page�

The key components of the TTU include:Steel bulkhead configured to meet code, including risers and concrete�•“Acme” fittings to connect to hoses which normally come with the transport�•Back Check Valve on the liquid line�•Hand-operated back check valve on the vapor line�•Emergency Safety Shutdown system (ESS Station)�•

About the TTU

The TTU is designed to cause a predictable shear failure by utilizing forged steel pipe couplings welded vertically into a reinforced steel channel member and mounted onto two legs� The TTU is set into a hole approximately 4ft by 4ft filled with concrete� This design protects the structural integrity of plant piping and equipment should a pull-away occur from any angle or position�

Force applied to the vertical pipe nipples above the horizontal bulkheads channel results in deformation of the pipe nipple threads� The threads continue to deform as more force is applied until the pipe nipple pulls out of the coupling� Automatic valves on the tank side of the TTU will then immediately shutdown the flow of LPG from the piping system� A pull-away force can be selected that would be greater than any force expected in normal operations and smaller than that which might cause hose rupture or which could pull out

Typical TTU (Truck Transport Unloading) Station with Emergency Pull Cable. Refer to the current or appropriate version of NFPA 58 for requirements.

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the valves from the vehicle tank� Testing indicates a 2-inch hose requires almost 8000 lb� to break (or pull off certain fittings); a 3-inch hose requires about 11,000 lb� to failure�

There are several additional desirable features of this vertical coupling breakaway system� Tests show that nipples pulled out completely will result in sudden release of LPG� This will cause slugging of the system’s excess flow valves� Additionally, if the pullout nipple is mounted above the coupling, the released LPG will go straight up� This is the most desirable direction for safe dissipation of the LPG� The most important attribute of this system is that the pulling force can come from any direction without compromising the design�


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SNG System Owner Responsibilities: LPG Transfer

According to NFPA 58, during the LPG transfer process, at least one qualified and trained person must remain in attendance from the time connections are made from the truck to the TTU, until the valves are closed and the transfer hoses are disconnected�

Without direct control as provided by the person delivering LPG, it is difficult to insure all steps are properly and safely completed� Often SNG system owners leave all transfer responsibility with the LPG supplier� Since most accidents happen during LPG transfer, a greater role should be taken by the SNG system owner�

At a minimum, SNG system owners should:Keep a log of tank volumes and make their own calculations to confirm •that the tank(s) can accept the volume of LPG ordered�When the SNG system has more than one tank, provide a plant person •during the transfer to insure the LPG goes into the correct tank(s)�If your LPG supplier handles more products than LPG, make your own •confirmation that the delivered product is LPG�Take any additional steps necessary to improve the reliability and safety •of LPG delivery�Confirm that the tank(s) are not over filled�•

The LPG vendor making delivery of LPG should:Inspect the general area for hazards and access for their truck�•Position the truck correctly and chock the wheels�•Inspect the truck for damage�•Check the contents of the truck to confirm the product is LPG�•Perform a ‘sniff’ test to confirm an odorant is present�•Record the pressure and temperature readings of the LPG tank�•Determine the maximum amount of LPG which can be added to each tank�•Connect the transfer hoses�•Transfer the LPG�•Disconnect the transfer hoses�•Prepare the truck for departure�•

UFM Filling machineModern LPG cylinder filling machine using a small PLC and weight based filling.

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LPG Cylinder Filling

Filling Cylinders

This brief training overview does not include sufficient detail to instruct the readers to become fully competent to perform full inspections of cylinders prior to filling� However, all operators are expected to follow the procedures and set aside all suspect cylinders for fur-ther inspection by your LPG supplier or cylinder supplier�

Inspect the Cylinder Filling AreaLPG filling or dispensing stations should be kept clear of trash and debris� An accu-

mulation of leaves and other combustible materials pose a significant fire hazard and may interfere with operation of the transfer equipment�

During transfer operations, remove all sources of ignition within 25 feet of a point of transfer� Shut down internal combustion engines within 15 feet of a point of transfer when a transfer operation is in progress�


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LPG Cylinder FillingInspect the Containers and Valves

Check the retest date on each cylinder and be aware of the inspection periods and type of retests required for various DOT cylinders� Note that relief valves in forklift cylinders must be replaced 12 years after manufacturer and every 10 years there after� You must also confirm that all cylinders are fitted with an OPD (overfill prevention device)�

Check containers to be filled for visual evidence of damage to valving or to the container walls from any of the following:

Fire damage.• If there is evidence that the protective coating has been burned off any portion of the cylinder surface, or the cylinder body is warped or distorted, it must be assumed that the cylinder has been overheated and must be removed from service� Check with your cylinder supplier�Dents.• Dents are deformations caused by the cylinder coming in contact with a blunt object in such a way that the thickness of the metal is not materially impaired� Some dents which do not include a weld or are not sharp or defined may be tolerated� Check with your cylinder supplier�Cuts, Gouges and Digs.• Cuts, gouges, and digs are deformation caused by contact with a sharp object in such a way as to cut into or upset the metal of the cylin-der, decreasing the wall thickness at that point and raising the stresses in the material� Refer all gouged cylinders to your cylinder supplier�Corrosion.• Corrosion or pitting involves the loss of wall thickness by corrosive action� Refer these cylinders to your supplier�Leaks.• Permanently remove ALL cylinders with leaks, other than leaks at fittings which can be tightened, from service�Neck Flange or Foot Ring Defects.• Check both areas for damage along with damage to valves or gauges�Markings.• Code requires labels on each cylinder, indicating LPG as the contents�

When filling by volume, open then close the fixed liquid level gauge to be sure vapor vents from the bleeder orifice� If no vapor escapes, the orifice may be blocked and must be reopened before the gauge will operate properly� Do not attempt to fill a cylinder by volume if the fixed level gauge is damaged or inoperable�

Connect the filler hose and follow your written instructions to operate your filling equip-ment� Open the fixed liquid level gauge and fill until a white mist appears�

When filling by weight set the container on the scale and set the scale for the tare weight of the cylinder plus the weight of the LPG plus the weight of the hose and fittings� When fin-ished filling, verify weight to insure cylinder is not overfilled�

Simplified depiction of a typical LPG storage vessel with appropriate trim components.

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LPG Storage TanksCapacity of Storage Tanks

The amount of LPG storage to have on site is based on the maximum time desired between LPG fills� Since LPG liquid (propane) contains 91,500 Btu/Gallon, there are about 11 gallons required for every one million BTU’s (1 MMBTU) required by the facility� Note also that one MMBTU = 1 decatherm as 10 therms x 100,000 BTU/therm = 1,000,000 BTU�

ExaMPLE: a factory uses a maximum of 800 Decatherms, or 800 MMBTU per day. The equivalent LPG consumption would be 800 x 11 or 8,800 gallons/day. When selecting the appropriate size of your storage tanks, consider:

average • daily consumption of LPG.The logistics of LPG deliveries. •LPG tanks cannot be filled completely; assume 85% usable.•Larger standard size tanks come in 18,000 US gallons [67m• 3], 30,000 [112m3] and 60,000 [224m3] sizes.

According to code, LPG storage tanks are required to have specific fittings. These fittings include:Relief valve(s) •Excess flow and shutoff valves on vapor opening•Back check and shutoff valves on liquid inlet openings•Internal valve•Fixed liquid level gauge•Variable liquid level gauge•Pressure gauge•Temperature gauge•


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LPG Storage Tanks

The available storage of LPG is about 85% of the total water gallon capacity of a tank� This filling technique provides for approximately 15% vapor space to allow for liquid expansion and “boil off” of the LPG�

Tanks are typically, but not always, rated for a maximum operating pressure of 250 psig� If rated at 250 psig, the “burst” or “design” pressure is 4 times the operating pressure or 1000 psig� The point is, they do not break apart for any reason except for fire or similar catastrophic events�

Pressure in an LPG storage tank is related to temperature� That temperature is •normally at or near the ambient temperature of the outside air� The corresponding pressure is called equilibrium pressure.For propane at 0• oF, the pressure is 24 psig� At 110oF, the pressure is 197 psig� The tanks pressure relief valves are generally designed to relieve at 250 psig� The release valves are located on the top of the storage tanks�Tanks are required to be painted silver or white — • only� These colors reflect sunlight and keep the tank as cool as possible� In most parts of the world, it is rare that the ambient temperature ever gets high enough to cause the relief valves to discharge� However, regions such as the Middle East and Southeast Asia are exceptions�Tanks are normally installed to provide at least 3 feet from the belly of the tank to •the ground� This allows the tank to provide enough hydraulic head to the feed the LPG to the pumps�Pressure in the tank is generated by the LPG boiling off in the same way that •water boils at 212oF� When water boils steam is created and if the steam is contained, as with a tea kettle, pressure builds� With our tea kettle, the pitch increases as the temperature climbs (above the 212oF due to the confining pres-sure) and this increase in pressure is heard as a higher pitch� In the same way, propane creates higher and higher pressures as its temperature rises above its boiling point of -44°F�

Note: The boiling point of propane is –44oF! Thus, if the outside air temperature was say, -45°F (very cold), propane would simply flow onto the ground and remain as a liquid — no vapor� We could carry propane with an open bucket�

At 100oF, if liquid propane leaks out of the pipe, it will immediately boil and become vapor and dissipate into the atmosphere� A cooling effect occurs when LPG vaporizes and this is the reason why a storage tank cannot normally be used as a vaporizer� If you contin-ually remove vapor via a vapor line on the top of a storage tank, you are relieving pressure from the tank� But the tank will stay at equilibrium, so this results in LPG boiling (vapor-izing) to restore the tank back into equilibrium� Obviously, this boiling requires heat and this heat comes from the available ambient temperature of the LPG� The result is the tem-

Moving the pointer on the Rotary dial causes the end of the tube to rotate until it contacts liquid in the tank. At that point, discharge from the bleed orifice turns from LPG vapor to liquid. The rotary gauge dial provides the volume percentage of liquid in the tank.

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perature of the LPG will be reduced as heat, or energy is extracted� This result in a lower vapor pressure in the tank which also reduces the rate at which the LPG can boil or vaporize� Over time, the LPG temperature continues to drop so low that there is little vapor avail-able to be fed to the vapor consuming process� The solution to this problem, of course, is to have an LPG vaporizer installed�

It should be noted that any significant leak in an LPG system usually results in ice for-mation at the point of the leak� The ice is created because of the cooling effect of the LPG vapor as it hits the atmosphere which contains moisture� Another way to find leaks is to see if there are any flies hovering around the tank or piping� For some reason flies love the stuff!

Liquid Level in a Storage Tank

The level of the liquid LPG in a tank is usually measured by one of two available devices�

A “Magnetel” gauge consists of a float on a long arm installed internal to the •storage tank� The float rides up and down on the surface of the liquid LPG as the level changes� A pointer on the face of the gauge indicates the percentage of liquid LPG in the tank�Another type is a “rotary” gauge or so called “Spit Gage”� This is a long tube •inside the liquid you can manually rotate through the LPG liquid surface� A small hole on the face of this gauge allows the LPG to “spit” out when the end of the arm inside the tank hits the surface� At this point you simply look at the indicator dial to estimate the % full of the tank�

An 85% outage gauge should be mounted on every tank at the 85% full level� Normally, during the filling process this needle type valve is opened by the person filling the tank to ensure the tank isn’t over filled� If liquid LPG gets to this level, there is a small release of liquid indicating that the tank is full�


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LPG Storage Tanks

Determining Maximum Fill Volume for LPG Storage Tanks

NFPA 58 Section 4-4�2�2 lists the maximum fill allowed in any LPG container� The basis of the calculation is that LPG liquid expands dramatically on a rise in temperature� A vapor expansion space must always be allowed in the tank�

Each tank is required to have a fixed maximum liquid level gauge� Since the gauge is fixed, it may not be suitable for determining the proper amount to fill a tank if the temperature of the LPG is low�

Refer to the table (right) to determine the maximum level per-mitted for LPG:

There are two common misconceptions regarding the maximum fill volume of LPG tanks:If you never fill over 85% you will be safe�•The colder it is, the more LPG you can safely put in the tank�•

Both are wrong! The 85% figure is wrong because it only applies when the liquid tempera-ture is above 35°F� The second myth is wrong because if you overfill when it is cold, and then the temperature rises — you will over pressurize the tank and the relief valves will relieve�

Safety Considerations for an LPG Storage Tank:

Steel integrity: Properly paint the tank and rest it on felt pads in the concrete saddles� Otherwise, rust will “pit” the tank surface and eventually threaten the tank integrity� Pitting also reduces potential resale value of a tank�

Connections: The greatest risk points with a tank are its penetration points� These points are where LPG, either liquid or vapor, enter or exit the tank� Typically there are three bot-tom connections to an LPG tank� These include: a) liquid LPG into the tank from the TTU, liquid LPG out of the tank to the vaporizer or process, and LPG a bidirectional flow of vapor into and out of the tank (In the case of vapor, one pipe accomplishes this�)

ProPane Storage tank MaxiMuM Fill level

TankTemperaTure

aboveground

belowground

-10 80 % 82 %

0 81 % 83 %

-10 82 % 84 %

20 83 % 85 %

30 84 % 86 %

40 86 % 87 %

50 87 % 89 %

60 88 % 90 %

70 90 % 91 %

80 91 % 93 %

90 93 % 95 %

On the left are two LPG rated stainless steel braided flex connectors, from the tank valving to the tank systems headers. On the right, conventional swing joints at 90° are built into the system piping to accept expansion and contraction.

Ely Energy, Inc.


Protect Penetrations into the Tank — Several techniques and components are used:

The connections must be 6,000 psig steel fittings welded to the tank accord-•ing to ASME and DOT standards� (Both NPT and flanged connections are available�)

The vapor connection is protected using an excess flow valve and isolation valve� •The liquid inlet is protected using an inline back check valve or a combination internal/excess flow valve with remote shut off. The liquid outlet opening is protected by the combination internal/excess flow valve with remote shut-off�

Immediately downstream of these valves, manual isolation valves are usually •installed� These valves may be either a ball valve or globe valve rated for LPG service�

Another means of protection for piping susceptible to damage due to tank set-•tling, or expansion / contraction is use of a “swing” joint� A swing joint consists of two 90 degree bends in transition piping� Another option would be to use a stainless steel braided flex connector rated for LPG service� Either method satisfies NFPA 58 and 59 code requirements for pipe protection� All LPG piping must be Schedule 80 if screwed (i�e� with NPT connections) or Schedule 40 if welded�

Typical STABILIZER™ LPG pump package configuration utilizing a pilot operated back pressure regulator, a differential pressure BV valve, gauges, hydrostats and isolation valves as required.


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LPG Pumps

The LPG pumping system is a critical link in an LPG or SNG system� Faulty motors, leaks in the pump seals or problems with the back pressure regulator can cause the entire system to go down� That is why nearly all installations utilize a “duplex” pump design� Two pumps are provided in parallel with either pump available for immediate use� See the dia-gram below for basic pump components and operation�

The pump and its controls ensure LPG is delivered at the proper pressure and flow� The pumping system and its associated piping and valves are part of an overall system specially designed for the application� It should not be changed in any way unless the designer is well experienced in LPG pumping systems�

Pumps installed at Venturi type SNG Blending systems increase the LPG pressure to provide the required motive pressure to the venturi� This allows the venturi to properly mix the correct air to LPG ratio to create the SNG� Any pressure created above the desired pressure set point is relieved back to the LPG storage tank� To protect the pump and the downstream piping from excessive pressure in the event the primary control valve failed, a secondary relief valve or bypass is used�

During warm or hot weather, exercise caution with an LPG pump� The high ambi-ent temperatures could allow the pump to develop very high pressures downstream� If the tank pressure is sufficient, a standby system might be operated without a pump during very warm temperatures�

AQUA-GAS® WB-V Series Waterbath Vaporizer, front

Ely Energy, Inc.


LPG Vaporizers

An LPG vaporizer heats liquid LPG to the vapor phase� This helps ensure that only vapor is delivered to the gas supply system or to an SNG Blender� In a small capacity LPG only system, it is possible to obtain vapor directly from the vapor space of the storage tank� This process is called natural vaporization� The energy required to vaporize the liquid LPG comes from the sun as energy is transmitted through the wetted walls of the tank� Various factors limit the amount of vapor that can be created in this way, including the size of the tank, the temperature difference between the liquid LPG and the ambient air and the degree of fill of the tank�

Typical Waterbath Type Vaporizer

A vaporizer is engineered to convert liquid LPG to the vapor phase� If the vaporizer is part of an SNG system, this vapor will then be diluted with air to provide a fuel that is interchangeable with natural gas�

In a Waterbath vaporizer, the vaporization process works as follows:Liquid LPG is pumped into inlet of a waterbath vaporizer’s process coil�•The process coil is immersed in a solution of heated water and glycol� This •waterbath solution is typically heated to 180o to 200oF [80o to 93oC] by a gas fired burner which also utilizes the LPG vapor it is creating as its own fuel�As the liquid LPG passes through the process coil, it is heated to its boiling •point, vaporized and then super-heated in the last section of the coil�Vapor leaves the process coil by passing through a liquid float switch assembly�•

The purpose of a vaporizer is to add heat to liquid LPG causing it to boil and become a vapor� This process does not increase the pres-sure in the LPG vapor delivery line� The reason pressure does not build in the delivery line is that the entire LPG system is pressure balanced� The liquid delivery line from the tank, through the pump and to the vaporizer can flow in both directions — it is bidirectional� Any pressure increase that results from the added heat from the vaporizer will flow back to the storage tank as soon as the pressure in the return direction exceed the pressure in the opposite direction� Again — this is a pressure balance system�

Most large (200GPH or larger) vaporizers are gas fired waterbath type� Again, in this design

Typical AQUA-GAS® WB-H Series vaporizer with Optional Maintenance House installed in Peru.


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the liquid LPG is piped through a water/glycol solution� This prevents freeze ups in the win-ter — just like with your automobile radiator� The waterbath is heated to approximately 160 to 200oF depending on the LPG composition� The LPG vapor exits the vaporizer with a minimum of approximately 20°F of superheat� The vaporizer’s gas fired burner uses the vaporized LPG as its fuel source� During start-up, even on very cold days, there is gener-ally sufficient vapor coming from the LPG process coil to satisfy the burner, allowing it to begin the process of heating the water/glycol solution�

Other types of vaporizers include steam fired vaporizers and electric vaporizers� Direct fired vaporizers, which are very uncommon, heat LPG in a metal container heated directly by flame impingement on the bottom of the container� This type vaporizer has a poor safety record and a greater potential for leaks and fires than other type vaporizers� Such units are considered dangerous and are not recommended by Ely Energy�

There are a number of basic safety limits on a typical gas fired waterbath vaporizer. These usually include:

Low waterbath level cutoff switch•High waterbath temperature switch•Low and high gas pressure switch to burner•Liquid LPG carry over switch•Safety relief valve for high pressure LPG in the coil (set for 250 psig)•

Simplified depiction of SNG and NG interchangeability.

Ely Energy, Inc.


SNG Blenders

The purpose of an SNG blender is to blend air with LPG vapor from a vaporizer in the correct ratio to create a gas interchangeable with natural gas� As you know, natural gas has a BTU content of approximately 1000 BTU/Ft3� Undiluted propane vapor has a BTU content of about 2520 Btu/Ft3� However, a mixture of about 45% air and 55% propane vapor results in SNG with a BTU content of around 1420 Btu/Ft3 and a specific gravity of 1�31� So — our SNG has a BTU/ft3 content of 1420 versus natural gas at 1000 — Why are they so different?

Why 1420 BTU/Ft 3?The reason involves

the relative specific grav-ity (weight) of the gases� SNG is approximately twice as heavy as natu-ral gas� SNG has a SG of about 1�31 versus natural gas at about �65� Physics states that the flow of a gas through any orifice, (e�g�, a burner orifice) is directly proportional to the square root of the specific gravity ratio� In our example, the square root of 1�3 ⁄�65 is the square root of “2” which is 1�414� So, the heavier SNG flows through a burner orifice more slowly� You can think of the SNG as being thicker or more viscous then the “lighter” NG� Since SNG flows more slowly, each cubic foot of gas must have a proportionately higher BTU content in order to make up for the fact that less gas is flowing to the burner! Again, the formula shows us that because of the specific gravity difference, there must be approximately 1�414 times as many BTUs in the heavier SNG than in the NG�

Types of blenders:

There are two basic SNG Blending processes:Venturi Blenders• (No air compressor required; can provide 5-12 PSIG of propane/air pressure)Proportional Blending• (Air compressor required; can provide whatever SNG pressure is required)


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Venturi Blending

Venturi blenders use the kinetic energy in the LPG vapor stream to create the desired mixture� The theory of operation is similar to a typical atmospheric burner�

ExaMPLE:

The venturi is named after an Italian physicist: Giovanni Venturi� He observed that when a fluid — either a gas like LPG or a liquid, is passed through a constricted chan-nel, it will increase in velocity� With SNG venturi systems, this occurs as LPG vapor passes through the throat of the venturi nozzle� During venturi operation, the LPG is gaining kinetic energy�

Let’s think for a moment:

Due to the First Law of Thermodynamics (“Conservation of Energy”) kinetic energy must come from some place — it does not just “occur”�

If you look up the First Law of Thermodynamics in a reference book you will learn that energy can be neither created nor destroyed� However, energy can be converted from one form to another. For example, potential energy can be converted to kinetic energy� But, total energy remains constant�

In a venturi, kinetic energy increases as the LPG is accelerated� The “pressure” (i�e�, energy) is reduced — and hence total energy again remains constant�

The venturi creates “negative pressure” in the venturi chamber� Consequently, the atmo-spheric pressure is “greater” than the pressure in venturi housing� Air flows as we would expect, from the higher pressure zone (atmosphere) to the lower pressure zone (into the ven-turi housing) — to mix with the LPG�

This is a simple explanation, but it describes the principle�

Ely Energy, Inc.


From the previous example it should also be apparent that the 1most energy the atmo-spheric pressure can contribute is about (1) atmosphere or (14�7 PSIG)� You will also notice that as the SNG pressure gets higher — the inlet pressure to our venturi (the pressure from our pumpset) must also increase! There are limits on what LPG pressures are feasible based on vaporization and pumping�

In summary, without using an air compressor or blower, Venturis can provide:7 PSIG• max of SNG pressure if the LPG is ~ 50% butane and 50% propane (* this can vary slightly)12 PSIG• max of SNG pressure if the LPG is 100% propane 6 • PSIGmax of SNG pressure if the LPG is 100% butane

If we want to increase SNG pressure above these pressures with a venturi — we must increase the available air pressure above atmospheric pressure� This requires use of an air compressor or blower�

Typical Venturi Blending System

1 Technically – this depends on elevation, etc. but for sake of this discussion, this is adequate.


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Operation of the Venturi System

A venturi Solenoid Valve is energized by a Pressure Control Switch which senses 1� pressure of the SNG in the SNG Surge Tank�

The Pressure Regulator controls the undiluted LPG vapor pressure to the 2� Venturi Nozzle�

As SNG from the Surge Tank is consumed by the downstream gas consuming 3� equipment, the SNG pressure in the Surge Tank drops� The Pressure Control Switch senses the pressure of the SNG Surge Tank dropping and energizes the Solenoid Valve allowing LPG vapor at a regulated pressure to be fed through the venturi Nozzle and then through the Venturi Chamber�

The LPG Vapor passes through the Plenum Chamber between the Nozzle and 4� the Venturi throat at a high velocity� A negative pressure is created and this inspirates the required volume of air throughout the Venturi throat into the expansion section (diffuser) of the Venturi where the velocity of the mixed gases are converted to static pressure�

Air entering the Plenum Chamber passes through the Inlet Back Check Valve�5�

SNG leaving the Venturi passes through the manual shut off valve and into the 6� SNG Surge tank�

When pressure in SNG Surge Tank rises to its set point, the Pressure Control 7� Switch opens, thus deenergizing the Solenoid Valve which then closes�

The Inlet Ball Check Valve in the venturi housing prevents escape of SNG back 8� to the atmosphere�

Safety limits include a High/Low SNG Pressure Limit Switch, Low Input 9� Pressure Limit Switch and the Low Water Temperature Limit Switch on the vaporizer� Any of these devices will de-energize the Solenoid Valve on the vapor discharge side of the vaporizer and shut down the SNG system�

Venturi Blending

Ely Energy, Inc.


Proportional Blending

The AFC™ proportional mixer provides SNG mixtures at pressures from 13 PSIG to over 150 PSIG in a capacity range from 38 million BTU/HR to 2000 million BTU/HR)

AFC™ stands for Active Flow Control� The AFC™ can use both ‘feed forward’ and ‘feed-back’ control for fast response and unparalleled accuracy� In conventional ‘feedback only’ control systems the response to an error can only be identified and corrected after the event occurs� For example, with a mixing valve type system, a gas quality problem is identified by a calorimeter after the problem occurs� Then a correction is attempted� This slow reac-tion coupled with multiple correction attempts then causes more control oscillations and creates further unstable gas quality outputs� The AFC™ feed forward control design elimi-nates the problem!

When the AFC™ is started, the LPG flow meter sends a flow value to the control system� The control system responds instantaneously and pre-determines the approximate required position of the air flow control valve relative to the LPG vapor flow rate� Within seconds, the actual measured air flow rate is compared with the calculated flow rate and the control system makes the necessary fine adjustments� The AFC™ is now on line� Perfect gas — no wild swings and no “bad gas” typical of old conventional mixing valve systems�

The AFC™’s Automatic Load Tracking option allows pressures and flow parameters to be pre-set in the Control System� Mixing with intelligence, the AFC™ automatically closes the mixed gas outlet valve and then automatically reopens it at a lower down stream pressure! No manual steps are required and the concern of “turndown” is eliminated� The Flow Schematic illustrates the basic operation of the AFC™ Blender� LPG vapor and compressed air enter the AFC™ in parallel streams� Flow meters instantaneously and continu-ously send flow data to the Control System� The Control System pro-vides both feed forward and feedback control� The feed forward control constantly calculates the required air to achieve the desired mixing ratio and adjusts the airflow control valve accordingly� Simultaneously, the feedback control loop compares the actual valve (i�e� Wobbe, BTU/SCF, KCAL/Nm3, etc�) of the mixed gas with the desired set-point value and makes any necessary fine adjust-ments� These small adjustments compensate for any errors inherently associated with instrumentation�


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The Human Machine Interface (HMI) is a simple Touch Screen Panel provided with the sys-tem� A single cable connects with HMI to the AFC™ J-box� Installation couldn’t be easier!

Proportional Blending

1 8 Pressure Regulators (Not provided)

2 9 Butterfly-type Isolation Valve

3 10 Wafer-type Back Flow Check Valve

4 11 Pressure Transmitters (Pressure correction of the flow data)

5 12 Flow Meters

6 13 Temperature Sensor [RTD] (Temperature correction of the flow data)

7 air Flow Control Valve (Controls air flow based on flow and control parameters)

14 LPG Vapor automatic Safety Valve (Pneumatically opens – spring close; Valve closes where there is a safety violation)

15 Turbulators (Internal to header)

16 Pressure Indicator (Displays mixed gas discharge pressure)

17 Pressure Transmitter (Provides mixed gas discharge pressure signal to the control system)

18 SNG Discharge Safety Valve (Pneumatically opens – spring close; Valve closes when there is a safety violation)

19 Butterfly-type Isolation Valve

20 Local Explosion-proof Junction Box (Mounted on the AFC Blender)

21 Profibus Cable (Single cable link from the AFC Junction Box to the Control Panel)

22 Control Panel (With “Touch Screen;” Operator-friendly and compact)

Single Profibus Cable

AFC Control Panel with Touch Screen for HMI

Interior View of Control Panel

Local J Box on AFC

Ely Energy, Inc.


Piston Type Blending System

Operation

Modern gas blenders such as the AFC™ Blender have no moving parts� The design uses highly accurate flow meters and a sophisticated but simple to use Human Machine Interface (HMI)� However, there is another type of mixer – the piston, or floating orifice type�

Even today piston type mixers are still sometimes used, especially outside the USA and Europe� The old fashioned piston mixing valve design date from the late 1940’s� The basic mixing valve design utilized a piston, a sleeve and some type of cast or fabricated valve body� The air and LPG vapor enter the “mixing chamber” through “ports” cut in the valve bodies� Depending on the manufacturer, the sleeve (i�e� cylinder to the piston) either used rotational movement or is stationary� As for the piston, it had either vertical movement, or a combination of both vertical and rotational depending on the design�

Mixing valve type mixers were “ported” to admit gas and air at the relative proportions required at a flow rate� The piston moved vertically inside the sleeve – sometimes by a dia-gram located below the piston that senses the line pressure� Rotation of the sleeve (or the piston in other designs), allowed the proportions of gas and air to change as the exposure of the port inlet increased or decreased in size� This rather primitive method of ratio adjust-ment formed their basis of their mixing control�

Like any piston and cylinder design, this style of mixing was a totally mechanical process� However, contamination from the LPG, for example the C5’s, oils and so called heavy ends made this difficult and potentially dangerous� LPG is laden with contaminants� Dirt and heavy ends from the LPG built up and on occasion effectively “locked” the mixer� When that occurred, the cylinder and piston stuck together! Some gas utilities reported perform-ing maintenance on their old mixing valves every day or 3-4 times a week!

It is also important to understand that LPG-air mixing valves were typically slaved blenders� That means the air and gas side of the system were pneumatically “slaved” to each other� The performance of one side dictated the performance of the other� Consequently, they did not maintain the same mixing ratio at all flow rates� This resulted in substantial gas quality variations depending on flow rate� Sleeve and piston type blenders operating at lower flow rates tended to produce lean (lower Wobbe values) mixtures compared to the Wobbe at higher flow rates� This was poten-tially dangerous with negative impact on end users of the gas� The calorific value devi-ated dramatically from set value when flow dropped below 15 % of their rated capacity�

Inoperable old style piston blending system that was removed from service in 2003.


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At lower flow rates (e�g� 10%) the mixing ratio could go out of control! Auto-Ratio-Control, a standard function on most modern mixers, is not standard on

the old piston type mixer� For the pistons types, the Auto-Ratio-control is an option� The option typically involves adding an awkward and sometimes problematic servo motor to rotate the piston or sleeve in an attempt to control the Wobbe� With this design, the servo motor receives a signal from a gas quality instrument and attempts to adjust the output of the gas quality by rotating the port on the mixer� This type control is inferior in response time and accuracy�

Piston to sleeve faces must also be machined (often by hand) to as precise to its original shape in order to operate properly� Care must also be taken regarding corrosion problems that might severely affect piston-sleeve faces� Carbon dioxide can readily cause an acid to form in presence of water or humidity in both the LPG vapor or air supply� Given the qual-ity of most LPG, avoiding a build up from paraffin’s and bituminous ends is impossible� This type build up leads to sticking of the piston in the sleeve� Several documented cases occurred where the vertical shaft for piston rotation and adjusting the gas air ratio have broken from the torque of the Auto-Ratio-Control systems� The piston gets locked by the impurities, but the Auto-ratio controller continues to rotate the shaft – finally the shaft simply breaks�

If you encounter this type of a mixer at a location, we strongly suggest you attempt to contact the manufacturer� As about half the US manufacturers of this design are now out of business, you may encounter difficulty� Feel fee to contact Ely Energy service with ques-tions� Most important – be cautious and do NOT operate the device if you lack knowledge or experience�

The tie-in of the SNG to the NG piping requires expertise and knowledge of both the NG and the LPG system. As with all work associated with hazardous fuels and materials, we recommend such work only be done by appropriately trained and licensed professionals.

Ely Energy, Inc.


SNG to NG

Tie-In

The connection of any SNG system to a natural gas distribution line (i�e�, tie-in) is made downstream from the client’s metering and pressure regulating equipment� There are two choices in selecting the pressure at which the SNG is delivered�

If the SNG mixture is delivered at a pressure below the natural gas delivery pressure, the natural gas system must be isolated with a valve in order to use the SNG�

If the SNG is delivered at a pressure above the natural gas delivery pressure, the SNG will automatically replace the natural gas in the distribution system� This happens because either the check valve installed in the natural gas piping or the utility’s regulator stops the flow of natural gas� In this case, no valves need be closed at the connection between the SNG and natural gas piping�

An additional advantage of this arrangement is that if the SNG system shuts down for any reason, the natural gas will automatically begin to flow when the SNG pressure falls below the natural gas delivery pressure�


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Properties of LPG

LPG is different from the liquids and gases people typically encoutner� These unique properties can be dangerous if not understood� Caution is required! The following proper-ties must be understood in order to avoid unsafe actions regarding an LPG system�

The boiling point of propane is -44°F.

LPG is stored in pressure vessels� Unlike water, LPG boils at a temperature well below common ambient temperatures� This means that anytime LPG liquid is released from a pipe or container and exposed to common atmospheric pressure and temperature, the liq-uid will boil and convert instantly to vapor�

Several safety issues arise when LPG liquid is released:When LPG converts to vapor, it expands 270:1 times its liquid volume� This •will displace air and potentially becoming a breathing hazard as the air is pushed away!Liquid LPG will boil! Remember, propane’s boiling point is -44°F� At this tem-•perature it will cause instant frostbite to any exposed skin� Heavy vinyl gloves with cuffs should be worn� A face shield or eye protection is also required�The LPG vapor cloud is an explosion hazard� • Keep any and all ignition sources away.Any remaining liquid will continue to boil, converting into more vapor�•Liquid can travel some distance when released — be careful!•

When LPG liquid is released, the conversion from liquid to vapor refrigerates the air it comes in contact� A white cloud often forms� This white cloud is actually frozen water vapor in the air; this is not LPG liquid or LPG vapor� The cloud’s presence can indicate the approximate location of the vapor cloud� However, do not rely on the presence or lack of a cloud to judge the potential danger from LPG in the vicinity�

LPG has a low flammability limit.

We describe the mixture of air and LPG needed for combustion in terms of flamma-bility limits� A flammability limit is simply the percentage of LPG needed in an LPG/air mixture to support combustion� Normally, this value is given in both upper and lower lim-its of flammability� The upper limit is the percentage of gas in the richest (most gas rich) mixture that will support combustion� The lower limit is the percentage of gas in the lean-est (least gas rich) mixture that will support combustion� Refer to the following table for limits of flammability of LPG�

Ely Energy, Inc.


* Note that a concentration of only 2.15% propane in air will create a flam-mable or explosive mixture. This limit is half the lower limit of natural gas.

LPG is both odorless and colorless� Because of its hazard as a flammable material, safety codes require an odorant be added to LPG sufficient to be detectable at 20% of its lower flammability limit� The presence of the odorant suggests the presence of LPG, but does not indicate its concentration� If LPG has passed through soil or placed in a new container or pipe, the odorant could be significantly stripped from the LPG�

When checking for possible leaks from underground piping, a detector sensitive to LPG must be used� Never rely only on your sense of smell! Substantial underground leaks can develop with little or no odor apparent�

LPG vapor is heavier than air.

Always remember that LPG vapor is heavier than air� If a leak develops in an LPG line or container, the LPG vapor will settle in low areas and can become concentrated, particularly if there is lit-tle or no air movement� This trait is important to know and understand when trying to identify the source of a leak, or working in an area where a leak has occurred� If a leak originated with a liquid release, the refrigerating effect of the conversion to vapor will also tend to make LPG vapors sink�

The weights of gases are compared using specific gravity� The specific grav-ity of a vapor is the comparison of the weight of a given volume of a gas at a certain temperature with the same vol-ume of air at the same temperature and pressure� LPG vapor has a specific grav-ity of 1�50 at 60° F�

FlaMMability liMitS (Fuel in air)

ProPane natural gaS

upper 9.6 % 15 %

Lower 2.15 % 5 %

NaTURaL GaS

aIR


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Codes and Standards

Codes and standards have been developed to promote safety in the operation of many activities� Plumbing, electrical and building codes are a few examples� For LPG equipment, the primary resource is the National Fire Protection association Pamphlet 58 (NFPA 58)� NFPA 58 covers the storage and handling of Liquefied Petroleum Gases and references a number of other codes or standards� The three major components of the code are:

Equipment design•Equipment installation•Operating procedures•

EEI recommends reviewing NFPA 58 and maintaining a copy at each facility with LPG equipment as a reference� NFPA also publishes a ‘Handbook’ in conjunction with Pamphlet 58� The handbook includes many descriptive passages to help interpret the code and is also a recommended reference�

Chapters in NFPA 58:

CH a P T ER T IT LE DE SCR IP T IoN

1 General Provisions Definitions, scope, etc.

2 LP-Gas Equipment and appliances

Standards for tanks cylinders, valves, piping, and appliances (i.e., vaporizers)

3 Installation of LP-Gas Systems

Guidelines for installing equipment in bulk plants, cylinder filling stations and on industrial and road vehicles

4 LP-Gas Transfer Guidelines for filling tanks and cylinders

5 Storage of Portable Containers awaiting Use or Resale

Includes scope, general provisions, storage, and fire protection

6 Vehicular Transportation of LP-Gas

Includes scope, transportation modes and parking and garaging vehicles

7 Buildings or Structures Housing LP-Gas Distribution Facilities

Includes scope, separate and attached structures

8 Engine Fuel Systems Application, general purpose and industrial vehicles, engine installation and garaging of vehicles

9 Refrigerated Storage Containers, impoundment and locating aboveground containers

10 Marine Shipping and Receiving Piers, pipelines, and actions prior to transfer

Ely Energy, Inc.


LPG Safety Components

Safety ValvesThere are a number of types of safety valves used on LPG systems

Back Flow Check ValveThe back flow check valve, also called the back check or just

check valve, functions to permit the flow of LPG in only one direction through piping� With no flow or flow in the reverse direction, the valve closes by spring pressure or system pressure on the back of the valve disk� When flow in the proper direction is sufficient to overcome the combination of spring force and the weight of LPG on the other side of the valve disc, the valve opens�

This valve is used where flow is normally in one direction only and protection is desired from flow in the opposite direction; i�e�, the fill opening into the storage tank�

Excess Flow Valve Excess flow valves prevent the catastrophic loss of product in

the event of line breakage� Excess flow valves are used where the normal flow is in the same direction as the protection is required� Should any connecting line become damaged or broken, any leak-age created in excess of a designed quantity, will cause the Excess flow valve to close� This prevents the possibility of losing the entire contents of a container� A common application of this type of valve is the process opening in the storage tanks�

It is important to remember that tank valves should be fully opened in order to allow the excess flow valves to perform as designed� If a tank valve is not fully opened it could provide a greater restriction than the setting of the excess flow check valve, thus preventing the excess flow check valve from operating as designed�

Note the excess flow valve is not normally designed as a positive shut off valve� When the valve closes as a result of flow above its design flow, a small weep hole remains open allowing an eventual equalization of pressure if the excess flow was caused by opening a downstream valve too fast and not a line break� When the pressure on either side of the valve equalizes, the valve will open and be ready again�

Pressure Relief ValveThe pressure relief valve is possibly the most important valve

installed in an LPG installation� It is designed specifically to protect tanks or cylinders from over pressure� If this valve cannot perform its function properly, the tank or cylinder could rupture�

Although all pressure relief valves perform similar functions, certain types have features and characteristics that uniquely affect their capacity, selection,


32 Phone (918) 250-6601 / Fax (918) 254-5412

and use� For this reason, pressure relief valves are separated into different types� Each pressure relief valve has special markings that provide information about its size

and capacity� For example, all pressure relief valves are marked with a pressure rating� This rating indicates the pressure at which the valve will start to open� If a pressure relief valve with the wrong pressure rating is installed in a tank or cylinder, high pressures could build up inside the container and the valve could relieve prematurely�

Every pressure relief valve must be carefully sized and matched to a particular type and size of container� NFPA 58 specifies how to properly size a relief valve�

Hydrostatic Relief Valves LPG expands dramatically with a rise in temperature� It can exert excessive forces on pip-

ing, valves and other equipment if trapped between closed valves� Hydrostatic relief valves are therefore installed where liquid LPG can be trapped between two valves�

Hydrostatic relief valves are simple in construction� At the bottom of the valve body is a threaded inlet port� The valve screws into a fitting on the system to be protected� Inside the valve body, a spring held in place by a vented retainer presses down on the poppet at the bottom of the valve� The valve poppet is fitted with a soft seat disc made of a synthetic material to ensure it forms a tight seal against the inlet port�

Under normal conditions, the force exerted by the spring holds the valve poppet down (closed) over the inlet port so no LPG can escape through the valve� If expansion of the trapped liquid causes the pressure in the valve inlet to rise above its preset setting, the pres-sure forces the poppet off of its seat and releases a small amount of LPG into the atmosphere through the vent in the retainer at the top of the valve� This quickly relieves the excess pressure in the system and the spring again forces the poppet back over the inlet opening, reclosing the valve�

Hydrostatic relief valves should be fitted with rain caps to prevent moisture and debris from accumulating inside the valve� It is also a good practice to provide a vent stack or pipe away for hydrostatic relief valves� This is important for Hydrostats located in low lying areas or where discharge from the valve might impinge on sources of ignition�

Emergency Shutoff Valves (ESVs)Excess flow check valves have been used to prevent large LPG spills at transfer points�

These excess flow valves are installed at a point where the hose joins the rigid piping system� In the event a hose is sheared off completely, the excess flow valve will slug shut� This can prevent a major spill of LPG� In certain situations, however, an excess flow valve may not close properly� Even when an excess flow valve closes properly, LPG will continue to discharge through the equalizing orifice� If the spill is ignited, the resulting fire

LPG Safety Components

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may prevent the operator from closing the manual shutoff valves upstream from the break in the hose�

Combustion characteristics of LPGCombustion is a chemical reaction that changes a fuel source into a different form of energy — heat.

Three ingredients needed to start and sustain combustion are: fuel, oxygen, and an igni-tion source� All three must be present in the proper proportions for combustion to occur�

The combustible molecules in LPG are hydrocarbons� Hydrocarbons are chemical com-pounds consisting of hydrogen and carbon atoms� The oxygen needed to burn LPG vapor is obtained from the air� Air is made up of 20% oxygen, 79% nitrogen, and about 1% of other miscellaneous gases� The ignition source must provide enough heat to the mixture of fuel and oxygen to raise the temperature of the LPG to its ignition temperature, which is between 920 oF — 1,120oF�

Combustion Ratio

The combustion ratio is the ratio of air to fuel� A ‘perfect’ ratio exists when all of the hydrogen and carbon combine with air and no oxygen or fuel is left over during combus-tion! This is called the stoichiometric ratio� For LPG the stoichiometric ratio is 23�9:1 and for Natural Gas 9�6:1�

LPG will burn anytime at a ratio of 2�15% to 9�6% LPG in air exists� However, for proper combustion in appliances, a ratio approaching the stoichiometric ratio is required�

When LPG and air burn in the correct ratio, complete combustion occurs� Since LPG is a mixture of hydrogen and carbon, water vapor and carbon dioxide are combustion by-products�


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SNG System Operation

Basic Safety Precautions

These are basic procedures for operating your system safely:Do not perform any actions which you have not been trained•Be very deliberate about any actions you take, think them through!•If need to know about aspects of the system (valve positions, etc) prior to • performing a function, check them out personallyRead and be familiar with your operating manuals•Be familiar with any pertinent emergency procedures•Keep the system maintained•Repair any non-functioning or damaged components promptly•Remember that an empty tank is no less dangerous than a full one•Remember that most accidents happen during transfers of LPG•

Operating Manuals

Operating manuals should include the following sections:Startup to standby procedure•Standby to operating procedure•Operating to standby procedure•Shut down procedure•Troubleshooting procedures•

Receiving LPG

The most important aspect of receiving LPG is knowing in advance if you have suffi-cient tank capacity to accept the anticipated load�

Maintenance

General annual maintenance requirements:Check for any visible damage•Check all valves for easy operation•Remove weeds and other combustible hazards from the area•Test for corrosion •Check entire system for leaks and correct•Check fire extinguishers•Test and document operation of Emergency Shutoff Valves•

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SNG System Maintenance Requirements

TTU

Check gaskets, seals, and sealing surfaces•Check condition of caps and replace if necessary•Check operation of Emergency Shutoff Valve•

Tank

Check condition of paint•Check condition of pressure gauges and temperature gauge•

Pump

Check for seal leaks and piping leaks•Check condition of pressure gauges•Open strainer valve and check for the presence of water•

Vaporizer

Check condition of gauges•Check condition of glycol mixture; pH maintenance is critical•Check for any leaks•Check to ensure safety devices work•

System Malfunctions and Emergencies

How to Identify Problems

Be familiar with equipment when operating and not operating •Note the typical temperatures and pressures shown on gauges.Listen for leaks and other unusual sounds•Look for visible damage•

How to Check for Ammonia in LPG

Some LPG dealers use their vehicles to transport ammonia during the summer and LPG during the winter� Contamination of LPG by ammonia is possible� If you suspect the pres-ence of ammonia, test by wetting a piece of red litmus paper in distilled water and exposing to LPG vapor for 30 seconds� A blue color indicates the presence of ammonia�


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How to Recognize Combustion Problems

An SNG standby system creates a mixture of LPG and air compatible with natural gas� When a compatible mixture is created, it will be difficult for the untrained observer to deter-mine whether an appliance is burning natural gas or SNG� With the higher carbon content, SNG will tend to have slightly more yellow in its flame�

Appliances burning natural gas must be tuned to create proper combustion� With nat-ural gas, the limits of flammability range from 5% to 15%� The limits of flammability of LPG are 2�15% to 9�6%� As a result, a natural gas appliance can be out of tune and still burn, but when supplied with a perfect SNG mixture can be out of tune�

The best method to handle apparent combustion problems is to first tune the appliance on natural gas� Then switch fuels to SNG for confirmation� Most combustion problems can be addressed in this manner� If problems still exist, it is possible that the mixture generated by the SNG system does not have the correct Wobbe index� It is either too lean or too rich� When the mixture is too lean, appliance burners will flash back or pop� A rich mixture will appear yellow or with sooting� The SNG must be adjusted to provide the optimum com-bustion match with natural gas�

One appliance which seems to have more problems than most is the high intensity infra-red heaters� These devices mix all the air required for combustion at the burner rather than depending on secondary air for complete combustion� They operate at the edge of the capa-bility of the burner Venturi to entrain the correct amount of air� As a result they are very sensitive to the delivered gas pressure and the plant air pressure� Proper operation by infra-red heaters may require individual adjustment of gas pressure and air shutter�

Most Common Minor Problems

Leaks. • Leaks are probably the most common SNG system problem� Leaks in gas lines and components impact safety, operational capability and plant econom-ics� An air leak of sufficient volume can impact measuring or controlling loops and may compromise safety of the system�Water in LPG. • Water is a contaminant in LPG� It can seriously interfere with the proper operation of pumps and regulators� If water is suspected, a ‘freeze off’ test can be performed to determine the presence of water� In cold climates, if water is present in concentrations of more than a few parts per million, cor-rective action must be taken� Larger concentrations can result in liquid water collecting in low points in the system� The remedy for water in the LPG is addi-tion of methyl alcohol (methanol)� The easiest method to introduce methanol is to request its inclusion from your LPG supplier in your next LPG order� Add a maximum of 20 gallons of methanol to an 18,000 gallon tank and a maximum

System Malfunctions and Emergencies

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of 30 gallons to a 30,000 gallon tank� Leaking Pump Seals. • Pump seals are a common problem� Check the pump fre-quently for signs of leakage or excessive wear�Temperature and Pressure Controls. • All controls are subject to damage and require calibration checks�Burner controls. • Check for proper operation�Venturi check valves. • Check for leaks�

Typical Accidents and How to Avoid Them

Pull-awayThe most common accident is a truck pulling away from an unloading station without

disconnecting the hoses�Upgrade your TTU to current code�•Use LPG vendors with trained drivers�•

Hose breakCheck hoses at frequent intervals for damage and leaks�•

Accidents at cylinder fill stationsTrain operators well and • only allow trained operators, from a certified training program, to fill cylinders�

Pump seal failureCheck pumps for leaks and wear regularly�•

Non-Standard Situations

A “non-standard” situation exists when equipment is not operating within its normal parameters� A hazard thus exists which is easily controlled or self controlling� This hazard is limited in scope and can be controlled without endangering lives or significant property�

Examples of Non-Standard Situations Include:

Process pump seal failure. Follow these steps:Notify appropriate supervisor or personnel�1� Turn off electrical power to the pump motors�2� Close the pump inlet and discharge valves�3� Close all tank valves�4� Turn off all operating electrical equipment to prevent ignition of leaking gas� 5�


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Large liquid or vapor discharges at truck unload area (no fire involved). Notify appropriate supervisor or personnel�1� Assist any person in the plant to move away from the hazardous area� 2� If possible shutdown all operating electrical equipment by tripping main breaker� 3� When safe to do so, isolate the LPG source feeding the leak� 4�

General Precautions in the Event of a LPG Leak, Spill, or Discharge

Because LPG is flammable, everyone involved with its handling must know and follow fire prevention rules� An LPG fire is one hazard that everyone wants to avoid� Any fire, large or small, has the potential to destroy property and take human lives� As a result, general fire prevention rules and general fire precautions in the event of a LPG leak, spill, or discharge, are topics that must be considered everyday when working with LPG� The only way to reduce this chance is to be aware of fire hazards and always follow fire prevention rules�

Emergency Procedures

Definition of Emergency Incident

An “emergency” condition exists when extraordinary procedures, equipment, manpower and supplies must be employed to protect life and property� These hazards may include:

Overpressure in the system�•Large volumes of uncontrolled escaping gas�•Fire or explosion, etc�•Any leak considered hazardous�•The endangerment of continued safe operation of a major segment of the system;•Natural disasters such as floods, hurricanes, earthquakes or other severe forces •of nature which make emergency provisions necessary�Civil disturbances or riots which require special procedures�•

An emergency manual cannot possibly address every situation arising and it is therefore incumbent on each employee to become familiar with:

Physical and chemical properties of LPG� •Safety procedures and equipment�•Current codes and standards�•Operating procedures for all installed equipment�•

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as is the case with all potentially hazardous facilities, public safety must be given the greatest consideration. The important point to remember about LPG fires is the only effective way to put out a LPG fire is to cut off the supply of gas to the flame� If the flame is extinguished before the gas supply is cut off, the gas can spread to a much larger area� If the fire then reignites, it can easily create a much more serious problem� If the gas cannot be turned off without personal injury then let it burn until fire-fighting personnel arrive at the scene� The main concern in any fire caused by or involving LPG should be to prevent injury�

Some precautions that should be followed are listed below.Do Not Panic.• This is the “Golden Rule” of handling emergencies�Move upwind from the fire as quickly as possible� This will help to avoid burns •from radiant heat�If the fire is caused by LPG, move all people in the area to a point at least 1,000 •feet upwind from the fire�Immediately call the local fire department and the companies to notify them of •the fire as soon as everyone is safely clear of the area� Be sure to report the exact location of the fire and, if possible, the extent of the damage�If it is possible without danger to personnel, spray water on the vapor space area •of the container to keep it cool�

If the fire is at the loading bulkhead, go to the nearest remote emergency shutoff valve control that is upwind and away from the fire and close the emergency shutoff valve� Remember: Do not move to an area downwind of a leak or fire or into any area where you may become trapped or have no upwind escape route.

If there is a small fire caused by another flammable material, extinguish the flame with a dry chemical fire extinguisher� Remember to approach the fire from upwind�

How to Spot System Malfunctions

Be familiar with equipment when running and when not running� Note the •typical temperatures and pressures shown on gauges�Listen for leaks and other unusual sounds•Look for visible damage•

Thank YouThanks for taking the time to read this booklet and for being interested� When we can

help — call us� We’re dedicated to serving your needs�


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Percentage of Propane in an SNG Mixture vs. Dewpoint

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Percentage of Isobutane in an SNG Mixture vs. Dewpoint


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Percentage of N-Butane in an SNG Mixture vs. Dewpoint

L-Pressure

l-te

mpe

ratu

re (

C)

l-Pressure (bar_g)

L-Temperature

l-te

mpe

ratu

re (

C)

l-Pressure (bar_g)

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Dew Point Data for SNG with 100% Butane Blended with air

FoR REFERENCE oNLY – not for design use! Contact Ely Engineering

FoR REFERENCE oNLY – not for design use! Contact Ely Engineering

Dew Point Data for LPG with 33% Propane and 67% Butane Blended with air


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Pressure-Temperature Diagram for Various Propane-air Mixtures

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Various LPG Compositions:Vapor Pressures of Typical Butane-Propane Mixtures


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Thermodynamic Properties of Saturated Propane

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Thermodynamic Properties of Saturated Butane


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Physical Constants of Hydrocarbons

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Physical Constants of Hydrocarbons


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Vaporization Rate from a 30,000 Gallon Tank

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Pressure Conversion Table

A) Example: 16 psig Converts to 1.17 kg/cm2

B) Example: 6 kg/cm2 Converts to 85.3 psig


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Propane Vaporization Rates at 0° F at Varying Tank Levels

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Typical LPG/air Consumption Profile for a City Distribution Grid with 100% Connected Load

Typical SNG Consumption Profile for a City Distribution Grid with 10% Connected Load


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Electric Currents for Specific Countries

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Temperature Conversion Table

11385 E. 60th Place So.Tulsa, Oklahoma 74146Phone: (918) 250-6601

Fax: (918) 254-5412Visit us at: www.elyenergy.comEmail: [email protected]

Copyright 2008 – Ely Energy, Inc.Publication: SNG/LPG Overview 10-08

Vol 4 SNG and LPG Systems Overview

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Transcript of Vol 4 SNG and LPG Systems Overview