SNG and LPG Systems Overview_ELY Energy

5/28/2018 SNG and LPG Systems Overview_ELY Energy

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Vol: 4

SNGandLPGSystems Overview

A Handbook from theSNG Academy

Tulsa, Oklahoma, USA


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LPG and SNGSystems OverviewTable of ContentsHistory & Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

General Business Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Te Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose of the handbook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4SNG System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

SNG System Owner Responsibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

LPG Cylinder Filling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

LPG Storage anks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

LPG Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

LPG Vaporizer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

SNG Blenders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Venturi SNG Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Proportional SNG Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Old Fashioned Piston ype Mixers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

SNG to NG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Properties of LPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Codes & Standards (USA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

LPG Safety Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Combustion Characteristics of LPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

SNG System Operation, Maintenance and Malfunctions . . . . . . . . . . . . . . . . . . . . . 34

Emergency Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Disclaimer of Responsibility: Ely Energy Inc. does not warrant or assume any legal liability or responsibility for theaccuracy, completeness, or usefulness of any information, apparatus, product, or process described herein. Ely EnergyInc. 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 connectionwith 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 [email protected]


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LPG and SNG Systems Overview

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

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 manufacturedgases. In our language, SNG is a blend of Liquefied Petroleum Gas (LPG) and air that provides adirect replacement for natural gas.

Tis 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 1950s ESI had branched out into associated mechanicalengineering activities that grew to include design and manufacture of Synthetic NaturalGas (SNG) systems. Teir applications included peak shaving for natural gas utilities andindustry, backup fuel systems and CityGas distributed gas systems. Around 1980, ESI wasacquired by the RJ Ely Company of ulsa, Oklahoma (USA) and began operations as ElyEnergy Systems, and later as Ely Energy Inc. a subsidiary of the RJ Ely Company. In1998, 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 (liquidfired petroleum gases) or NH3 (ammonia). Te cornerstone of EEIs business is the so-calledsynthetic 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. Tis precise and controlled mixing of LPG and air allows it to beused as an alternative to natural gas for backup use, peak shaving, and CityGas supplyin regions where natural gas is not yet available. No orifice changes, pressure changes orany other changes are required to the natural gas consuming equipment! SNG is a directreplacement for natural gas (NG)!

Te technology of blending LPG and Air to simulate natural gas is not new SNGextends back to the 1950s. What is new is our ability to provide much higher degrees ofcontrol, 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 institutionsand the medical-health care sector. We offer solutions in various forms, typically involvingthe 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


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AQUA-GASunder 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 energyservices including:

SNG Backup Systems:Allow the industrial natural gas customer to change from aFIRM to an INERRUPIBLE Natural Gas rate structure. Te savings will oftenpay 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 andIndustrial 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: [email protected].

Our telephone switchboard is at (918) 250-6601. ouch 0 for the Operator to direct yourcall. Or visit us on the Internet atwww.elyenergy.com. Our physical address is 11385 East60th Place South, ulsa, Oklahoma 74146 (U.S.A.).


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

Purpose of the Handbook

Te purpose of this handbook is to provide information on the properties of LPG andbasic operation of an SNG system. Tis includes basic safety and operational information.

Any training must be conducted by a technician trained in the properties of LPG and theapplication of LPG equipment to real life scenarios.

Handbook Includes:

An overview of LPG and SNG systemsAn introduction to the basic properties of LPG and how those properties impactthe operation of an SNG system

An introduction to applicable codes and standards used to design, manufacture,

and maintain safe operation of an SNG systemTeory of operation of major subsystems of an SNG systemBasic maintenance requirementsHow to recognize non-standard operating and emergency situations

Handbook Does Not Include:

Details of combustion or plant specific burner applicationsReview of all code requirements

Knowledge or training necessary to make design changes to an LPG or SNG system

SNG System OverviewPurpose of an SNG System:

o 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 (U) to receive liquid LPG from a transport(~ 9,000 US gallons/load).LPG Storage Tanks to store the liquid LPG.

An LPG pump systemto transfer and elevate the pressure of the liquid LPG fromthe tanks to the vaporizer.

An LPG

vaporizerto heat the liquid LPG and change it into the vapor (gaseous)phase.An LPG/Air blenderto blend the necessary air with the LPG vapor to create SNG.


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Typical small capacity SNG System Layout

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Note:A tie-in point to the existing natural gas piping is another subsystem. Almostalways, this point is just downstream of the existing service regulator/meter at the natural gasentrance 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 U to inject methanol into the storage tanksto remove water which may be in the LPG.SNG metering system usually located at the outlet of the SNG blender to provide anaccurate measurement of the SNG used.

A Gas Quality Instrumentto 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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6 Phone (918) 250-6601 / Fax (918) 254-5412

TTU (Truck Transport Unloading Facility)

A normal U off-loads a 9000 gallon (34m3) transport in about 1 hr and 15 minutes.Tis rate of off-loading is based on using a 2"liquid line and 1 "vapor line with valvingsized for the pipe. Liquid is extracted from the transport via the larger diameter line. Tesmaller diameter line prevents a vacuum forming in the truck by allowing the pressures toequalize between the truck and the storage tank.

A common cause of accidental spills of LPG is a pull-away at an LPG transfer area. Teterm 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 U. A pull-away could break ahose, 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. o avoid these problems the U designincorporates a robust steel bulkhead set in a massive concrete foundation. Te U utilizesshear fittings that break away in a designed fashion in the event of an accidental truckpull-away. Te U is protected by large steel or concrete posts to prevent vehicles fromcolliding with the critical piping.

Industry studies prove a point of failure can be predicted and that a specific pull-awayforce can be determined at which the piping will rupture in a clean break. Tese studieshave resulted in designs and connections using Schedule 80 pipe nipples and couplings. Anexample of a U 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

Te U is designed to cause a predictable shear failure by utilizing forged steel pipecouplings welded vertically into a reinforced steel channel member and mounted onto twolegs. Te U is set into a hole approximately 4ft by 4ft filled with concrete. Tis designprotects the structural integrity of plant piping and equipment should a pull-away occurfrom any angle or position.

Force applied to the vertical pipe nipples above the horizontal bulkheads channel results

in deformation of the pipe nipple threads. Te threads continue to deform as more force isapplied until the pipe nipple pulls out of the coupling. Automatic valves on the tank sideof the U will then immediately shutdown the flow of LPG from the piping system. Apull-away force can be selected that would be greater than any force expected in normaloperations and smaller than that which might cause hose rupture or which could pull out


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Typical TTU (TruckTransport Unloading)Station with EmergencyPull Cable. Refer to the

current or appropriateversion of NFPA 58 forrequirements .

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

Tere are several additional desirable features of this vertical coupling breakaway system.ests show that nipples pulled out completely will result in sudden release of LPG. Tis

will cause slugging of the systems excess flow valves. Additionally, if the pullout nipple ismounted above the coupling, the released LPG will go straight up. Tis is the most desirabledirection for safe dissipation of the LPG. Te most important attribute of this system is thatthe pulling force can come from any directionwithout 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 andtrained person must remain in attendance from the time connections are made from thetruck to the U, 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 insureall steps are properly and safely completed. Often SNG system owners leave all transferresponsibility with the LPG supplier. Since most accidents happen during LPG transfer, agreater 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 personduring the transfer to insure the LPG goes into the correct tank(s).If your LPG supplier handles more products than LPG, make your ownconfirmation that the delivered product is LPG.ake any additional steps necessary to improve the reliability and safetyof 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.ransfer the LPG.Disconnect the transfer hoses.Prepare the truck for departure.


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UFM Filling machineModern LPG cylinder filling

machine using a small PLCand weight based filling.

Ely Energy, Inc.

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LPG Cylinder Filling

Filling Cylinders

Tis brief training overview does not includesufficient detail to instruct the readers tobecome 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 Area

LPG 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 whena transfer operation is in progress.


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

LPG Cylinder Filling

Inspect the Containers and Valves

Check the retest date on each cylinder and be aware of the inspection periods and typeof retests required for various DO cylinders. Note that relief valves in forklift cylindersmust be replaced 12 years after manufacturer and every 10 years thereafter. You must alsoconfirm 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 containerwalls from any of the following:

Fire damage. If there is evidence that the protective coating has been burned offany 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 removedfrom service. Check with your cylinder supplier.Dents. Dents are deformations caused by the cylinder coming in contact witha blunt object in such a way that the thickness of the metal is not materiallyimpaired. Some dents which do not include a weld or are not sharp or definedmay 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 thematerial. Refer all gouged cylinders to your cylinder supplier.Corrosion. Corrosion or pitting involves the loss of wall thickness by corrosiveaction. 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 damageto 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 ventsfrom the bleeder orifice. If no vapor escapes, the orifice may be blocked and must be reopenedbefore the gauge will operate properly. Do not attempt to fill a cylinder by volume if thefixed 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 weightset the container on the scale and set the scale for the tare weight ofthe 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.


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Simplified depiction ofa typical LPG storagevessel with appropriate

trim components.

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LPG Storage Tanks

Capacity of Storage Tanks

Te amount of LPG storage to have on site is based on the maximum time desired betweenLPG fills. Since LPG liquid (propane) contains 91,500 Btu/Gallon, there are about 11 gallonsrequired for every one million BUs (1 MMBU) required by the facility. Note also thatone MMBU = 1 decatherm as 10 therms x 100,000 BU/therm = 1,000,000 BU.

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 dailyconsumption 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

Te available storage of LPG is about 85% of the total water gallon capacity of a tank.Tis filling technique provides for approximately 15% vapor space to allow for liquidexpansion and boil off of the LPG.

anks are typically, but not always, rated for a maximum operating pressure of 250psig. If rated at 250 psig, the burst or design pressure is 4 times the operating pressureor 1000 psig. Te point is, they do not break apart for any reason except for fire or similarcatastrophic events.

Pressure in an LPG storage tank is related to temperature. Tat temperature isnormally at or near the ambient temperature of the outside air. The correspondingpressure is called equilibrium pressure.

For propane at 0 oF, the pressure is 24 psig. At 110oF, the pressure is 197 psig.Te tanks pressure relief valves are generally designed to relieve at 250 psig. Terelease valves are located on the top of the storage tanks.anks are required to be painted silver or white only. Tese colors reflectsunlight and keep the tank as cool as possible. In most parts of the world, itis rare that the ambient temperature ever gets high enough to cause the reliefvalves to discharge. However, regions such as the Middle East and Southeast

Asia are exceptions.

anks are normally installed to provide at least 3 feet from the belly of the tank tothe ground. Tis allows the tank to provide enough hydraulic head to the feed theLPG 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 iscontained, as with a tea kettle, pressure builds. With our tea kettle, the pitchincreases 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 itsboiling point of -44F.

Note:The boiling point of propane is44oF! Tus, if the outside air temperature was say,-45F (very cold), propane would simply flow onto the ground and remain as a liquid novapor. We could carry propane with an open bucket.

At 100oF, if liquid propane leaks out of the pipe, it will immediately boil and becomevapor 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 pressurefrom 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 andthis heat comes from the available ambient temperature of the LPG. Te result is the tem-


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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 ofliquid in the tank.

Ely Energy, Inc.


perature of the LPG will be reduced as heat, or energy is extracted. Tis result in a lowervapor 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. Te 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. Te ice is created because of the cooling effect of the LPGvapor as it hits the atmosphere which contains moisture. Another way to find leaks is to see ifthere are any flies hovering around the tank or piping. For some reason flies love the stuff!

Liquid Level in a Storage Tank

Te level of the liquid LPG in a tank is usually measured by one of two availabledevices.

A Magnetel gauge consists of a float on a long arm installed internal to thestorage tank. Te float rides up and down on the surface of the liquid LPG asthe level changes. A pointer on the face of the gauge indicates the percentage ofliquid LPG in the tank.

Another type is a rotary gauge or so called Spit Gage. Tis is a long tubeinside 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 endof the arm inside the tank hits the surface. At this point you simply look at theindicator 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 personfilling the tank to ensure the tank isnt 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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14 Phone (918) 250-6601 / Fax (918) 254-5412

LPG Storage Tanks

Determining Maximum Fill Volumefor LPG Storage Tanks

NFPA 58 Section 4-4.2.2 liststhe maximum fill allowed in anyLPG container. Te basis of thecalculation is that LPG liquidexpands dramatically on a rise intemperature. A vapor expansionspace 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 notbe suitable for determining theproper amount to fill a tank if thetemperature of the LPG is low.

Refer to the table (right) to

determine the maximum level per-mitted for LPG:

Tere aretwo common misconceptionsregarding the maximum fill volume of LPG tanks:If you never fill over 85% you will be safe.Te colder it is, the more LPG you can safely put in the tank.

Both are wrong!Te 85% figure is wrong because it only applies when the liquid tempera-

ture is above 35F. Te second myth is wrong because if you overfill when it is cold, and thenthe 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. Pittingalso reduces potential resale value of a tank.

Connections:Te greatest risk points with a tank are its penetration points. Tese pointsare where LPG, either liquid or vapor, enter or exit the tank. ypically there are three bot-tom connections to an LPG tank. Tese include: a) liquid LPG into the tank from theU, liquid LPG out of the tank to the vaporizer or process, and LPG a bidirectional flowof 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%


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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.

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

Te connections must be 6,000 psig steel fittings welded to the tank accord-ing to ASME and DO standards. (Both NP and flanged connections are

available.)

Te vapor connection is protected using an excess flow valve and isolation valve.Te liquid inlet is protected using an inline back checkvalveor a combinationinternal/excess flow valve with remote shut off.Te liquid outlet opening is protectedby the combination internal/excess flow valve with remote shut-off.

Immediately downstream of these valves, manual isolation valves are usually

installed. Tese valves may be either a ball valve or globe valve rated for LPGservice.

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 consistsof two 90 degree bends in transition piping. Another option would be to use astainless steel braided flex connector rated for LPG service. Either method satisfiesNFPA 58 and 59 code requirements for pipe protection. All LPG piping must be

Schedule 80 if screwed (i.e. with NP connections) or Schedule 40 if welded.


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Typical STABILIZER LPG pump package configuration utilizing apilot operated back pressure regulator, a dif ferential pressure BVvalve, gauges, hydrostats and isolation valves as required.


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LPG Pumps

Te 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 entiresystem to go down. Tat is why nearly all installations utilize a duplex pump design. wopumps are provided in parallel with either pump available for immediate use. See the dia-gram below for basic pump components and operation.

Te pump and its controls ensure LPG is delivered at the proper pressure and flow. Tepumping system and its associated piping and valves are part of an overall system speciallydesigned for the application. It should not be changed in any way unless the designer is wellexperienced in LPG pumping systems.

Pumps installed at Venturi type SNG Blending systems increase the LPG pressure toprovide the required motive pressure to the venturi. Tis allows the venturi to properlymix the correct air to LPG ratio to create the SNG. Any pressure created above the desiredpressure set point is relieved back to the LPG storage tank. o protect the pump and thedownstream piping from excessive pressure in the event the primary control valve failed, asecondary relief valve or bypass is used.

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

warm temperatures.


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AQUA-GASWB-V Series Waterbath Vaporizer, front

Ely Energy, Inc.


LPG Vaporizers

An LPG vaporizer heats liquid LPG to the vapor phase. Tis helps ensure that onlyvapor is delivered to the gas supply system or to an SNG Blender. In a small capacity LPGonly system, it is possible to obtain vapor directly from the vapor space of the storage tank.Tis process is called natural vaporization. Te energy required to vaporize the liquidLPG 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 sizeof the tank, the temperature difference between the liquid LPG and the ambient air andthe 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 ispart of an SNG system, this vapor will then be diluted with air to provide a fuel that isinterchangeable with natural gas.

In a Waterbath vaporizer, the vaporization process works as follows:Liquid LPG is pumped into inlet of a waterbath vaporizers process coil.Te process coil is immersed in a solution of heated water and glycol. Tis

waterbath solution is typically heated to 180oto 200oF [80oto 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 boilingpoint, 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.

Te purpose of a vaporizer is to add heatto liquid LPG causing it to boil and become avapor. Tis process does not increase the pres-

sure in the LPG vapor delivery line. Te reasonpressure does not build in the delivery line isthat the entire LPG system is pressure balanced.Te liquid delivery line from the tank, throughthe pump and to the vaporizer can flow in bothdirections it is bidirectional. Any pressureincrease that results from the added heat fromthe vaporizer will flow back to the storage tank

as soon as the pressure in the return directionexceed the pressure in the opposite direction.

Again this is a pressure balance system.Most large (200GPH or larger) vaporizers

are gas firedwaterbathtype. Again, in this design


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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. Tis prevents freeze ups in the win-ter just like with your automobile radiator. Te waterbath is heated to approximately160 to 200oF depending on the LPG composition. Te LPG vapor exits the vaporizer witha minimum of approximately 20F of superheat. Te vaporizers 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 tobegin the process of heating the water/glycol solution.

Other types of vaporizers include steam fired vaporizers and electric vaporizers. Directfired vaporizers, which are very uncommon, heat LPG in a metal container heated directlyby flame impingement on the bottom of the container. Tis type vaporizer has a poor safetyrecord and a greater potential for leaks and fires than other type vaporizers. Such units areconsidered 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 switchHigh waterbath temperature switchLow and high gas pressure switch to burnerLiquid LPG carry over switchSafety relief valve for high pressure LPG in the coil (set for 250 psig)


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Simplified depict ion of SNG and NG interchangeabil ity.

Ely Energy, Inc.


SNG Blenders

Te 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 hasa BU content of approximately 1000 BU/Ft3. Undiluted propane vapor has a BUcontent of about 2520 Btu/Ft3. However, a mixture of about 45% air and 55% propanevapor results in SNG with a BU content of around 1420 Btu/Ft3 and a specific gravityof 1.31. So our SNG has a BU/ft3 content of 1420 versus natural gas at 1000 Whyare they so different?

Why 1420 BTU/Ft3?

he reason involvesthe relative specific grav-ity (weight) of the gases.SNG is approximatelytwice as heavy as natu-ral gas. SNG has a SG ofabout 1.31 versus naturalgas at about .65. Physicsstates that the flow of agas through any orifice,(e.g., a burner orifice) isdirectly proportional tothe square root of thespecific gravity ratio. Inour example, the square root of 1.3.65 is the square root of 2 which is 1.414. So, theheavier SNG flows through a burner orifice more slowly. You can think of the SNG as beingthicker or more viscous then the lighter NG. Since SNG flows more slowly, each cubic

foot of gas must have a proportionately higher BU content in order to make up for thefact that less gas is flowing to the burner! Again, the formula shows us that because of thespecific gravity difference, there must be approximately 1.414 times as many BUs in theheavier SNG than in the NG.

Types of blenders:

Tere 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 SNGpressure is required)


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Venturi Blending

Venturi blenders use the kinetic energy in the LPG vapor stream to create the desiredmixture. Te theory of operation is similar to a typical atmospheric burner.

EXAMPLE:

Te venturi is named after an Italian physicist: Giovanni Venturi. He observedthat 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 vaporpasses through the throat of the venturi nozzle. During venturi operation, the LPGis gaining kineticenergy.

Lets think for a moment:

Due to the First Law of Thermodynamics(Conservation of Energy) kinetic energy mustcome from some place it does not just occur.

If you look up the First Law of Termodynamics in a reference book you will learn thatenergy can be neither created nor destroyed. However, energy can be converted from one formto another.For example, potential energycan be converted to kinetic energy. But, total energyremains constant.

In a venturi, kinetic energy increases as the LPG is accelerated. he pressure(i.e., energy) is reduced and hence total energy again remains constant.

Te 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 wouldexpect, from the higher pressure zone (atmosphere) to the lower pressure zone (into the ven-turi housing) to mix with the LPG.

Tis is a simple explanation, but it describes the principle.


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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 noticethat as the SNG pressure gets higher the inlet pressure to our venturi (the pressure fromour pumpset)must also increase! Tere are limits on what LPG pressures are feasible basedon vaporization and pumping.

In summary, without using an air compressor or blower, Venturis can provide:

7 PSIG maxof SNG pressure if the LPG is ~ 50% butane and 50% propane(* this can vary slightly)

12 PSIG maxof SNG pressure if the LPG is 100% propane6 PSIGmaxof SNG pressure if the LPG is 100% butane

If we want to increase SNG pressure above these pressures with a venturi we mustincrease the available air pressureabove atmospheric pressure. Tis requires use of an aircompressor 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 senses1.pressure of the SNG in the SNG Surge ank.

Te Pressure Regulator controls the undiluted LPG vapor pressure to the2.Venturi Nozzle.

As SNG from the Surge ank is consumed by the downstream gas consuming3.

equipment, the SNG pressure in the Surge ank drops. Te Pressure ControlSwitch senses the pressure of the SNG Surge ank dropping and energizes theSolenoid Valve allowing LPG vapor at a regulated pressure to be fed throughthe venturi Nozzle and then through the Venturi Chamber.

Te LPG Vapor passes through the Plenum Chamber between the Nozzle and4.the Venturi throat at a high velocity. A negative pressure is created and thisinspirates the required volume of air throughout the Venturi throat into the

expansion section (diffuser) of the Venturi where the velocity of the mixed gasesare 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 the6.SNG Surge tank.

When pressure in SNG Surge ank rises to its set point, the Pressure Control7. Switch opens, thus deenergizing the Solenoid Valve which then closes.

Te Inlet Ball Check Valve in the venturi housing prevents escape of SNG back8.to the atmosphere.

Safety limits include a High/Low SNG Pressure Limit Switch, Low Input9.Pressure Limit Switch and the Low Water emperature Limit Switch on the

vaporizer. Any of these devices will de-energize the Solenoid Valve on the vapordischarge side of the vaporizer and shut down the SNG system.

Venturi Blending


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Ely Energy, Inc.


Proportional Blending

TeAFCproportional mixer provides SNG mixtures at pressures from 13 PSIG to over150 PSIG in a capacity range from 38 million BU/HR to 2000 million BU/HR)

AFCstands for Active Flow Control. Te AFCcan use both feed forward and feed-back control for fast response and unparalleled accuracy. In conventional feedback onlycontrol systems the response to an error can only be identified and corrected after the eventoccurs. For example, with a mixing valve type system, a gas quality problem is identifiedby a calorimeter after the problem occurs. Ten a correction is attempted. Tis slow reac-tion coupled with multiple correction attempts then causes more control oscillations andcreates further unstable gas quality outputs. Te AFCfeed forward control design elimi-nates the problem!

When the AFCis started, the LPG flow meter sends a flow value to the control system.Te control system responds instantaneously and pre-determines the approximate requiredposition 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 controlsystem makes the necessary fine adjustments. Te AFCis now on line. Perfect gas no

wild swings and no bad gas typical of old conventional mixing valve systems.Te AFCs Automatic Load racking option allows pressures and flow parameters to be

pre-set in the Control System. Mixing with intelligence, the AFCautomatically closes the

mixed gas outlet valve and then automatically reopens it at a lower down stream pressure! Nomanual steps are required and the concern of turndown is eliminated. Te Flow Schematicillustrates the basic operation of the AFCBlender. LPG vapor and compressed air enterthe AFCin parallel streams. Flowmeters instantaneously and continu-ously send flow data to the ControlSystem. Te Control System pro-vides both feed forward and feedback

control. Te feed forward controlconstantly calculates the required airto achieve the desired mixing ratioand adjusts the airflow control valveaccordingly. Simultaneously, thefeedback control loop compares theactual valve (i.e. Wobbe, BU/SCF,KCAL/Nm3, etc.) of the mixed gas

with the desired set-point value andmakes any necessary fine adjust-ments. hese small adjustmentscompensate for any errors inherentlyassociated with instrumentation.


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Te Human Machine Interface (HMI) is a simple ouch Screen Panel provided with the sys-tem. A single cable connects with HMI to the AFCJ-box. Installation couldnt 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] (Temperaturecorrection of the flow data)

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

14 LPG Vapor Automatic Safety Valve

(Pneumatically opens spring close; Valvecloses where there is a safety violation)

15 Turbulators (Internal to header)

16 Pressure Indicator (Displays mixed gasdischarge pressure)

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

18 SNG Discharge Safety Valve (Pneumatically

opens spring close; Valve closes when there isa 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 AFCJunc tion Box to the Cont rol 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


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Ely Energy, Inc.


Piston Type Blending System

Operation

Modern gas blenders such as the AFC Blender have no moving parts. Te design useshighly 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 andEurope. Te old fashioned piston mixing valve design date from the late 1940s. Te basicmixing valve design utilized a piston, a sleeve and some type of cast or fabricated valvebody. Te air and LPG vapor enter the mixing chamber through ports cut in the valvebodies. 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, ora combination of both vertical and rotational depending on the design.

Mixing valve type mixers were ported to admit gas and air at the relative proportionsrequired at a flow rate. Te 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 thepiston in other designs), allowed the proportions of gas and air to change as the exposureof the port inlet increased or decreased in size. Tis 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 C5s, oils and so called heavy endsmade this difficult and potentially dangerous. LPG is laden with contaminants. Dirt andheavy ends from the LPG built up and on occasion effectively locked the mixer. Whenthat 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 slavedblenders. Tat means the air and gas side of the system were pneumatically slaved to each

other. Te performance of one side dictatedthe performance of the other. Consequently,they did not maintain the same mixing ratioat all flow rates. Tis resulted in substantialgas quality variations depending on flow rate.Sleeve and piston type blenders operating atlower flow rates tended to produce lean (lower

Wobbe values) mixtures compared to the

Wobbe at higher flow rates. Tis was poten-tially dangerous with negative impact onend users of the gas. Te calorific value devi-ated dramatically from set value when flowdropped below 15 % of their rated capacity.


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


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

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. Teoption 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 servomotor receives a signal from a gas quality instrument and attempts to adjust the output ofthe gas quality by rotating the port on the mixer. Tis type control is inferior in responsetime and accuracy.

Piston to sleeve faces must also be machined (often by hand) to as precise to its originalshape in order to operate properly. Care must also be taken regarding corrosion problemsthat might severely affect piston-sleeve faces. Carbon dioxide can readily cause an acid toform 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 paraffins and bituminous ends is impossible. Tistype 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 fromthe torque of the Auto-Ratio-Control systems. Te piston gets locked by the impurities, butthe 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 tocontact the manufacturer. As about half the US manufacturers of this design are now outof business, you may encounter difficulty. Feel fee to contact Ely Energy service with ques-

tions. Most important be cautious and do NO operate the device if you lack knowledgeor experience.


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The tie-in of the SNG to the NG pipingrequires expertise and knowledge ofboth the NG and the LPG system. As withall work associated with hazardous fuelsand materials, we recommend such workonly be done by appropriately trainedand licensed professionals.

Ely Energy, Inc.


SNG to NG

Tie-In

Te connection of any SNG system to a natural gas distribution line (i.e., tie-in) is madedownstream from the clients metering and pressure regulating equipment. Tere are twochoices 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, thenatural 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 SNGwill automatically replace the natural gas in the distribution system. Tis happens becauseeither the check valve installed in the natural gas piping or the utilitys regulator stops the

flow of natural gas. In this case, no valves need be closed at the connection between theSNG and natural gas piping.

An additional advantage of this arrangement is that if the SNG system shuts down forany reason, the natural gas will automatically begin to flow when the SNG pressure fallsbelow the natural gas delivery pressure.


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Properties of LPG

LPG is different from the liquids and gases people typically encoutner. Tese uniqueproperties can be dangerous if not understood. Caution is required! Te following proper-ties must be understood in order to avoid unsafe actions regarding an LPG system.

The boiling point of propane is -44F.

LPG is stored in pressure vessels. Unlike water, LPG boils at a temperature well belowcommon ambient temperatures. Tis means that anytime LPG liquid is released from apipe 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. Tiswill displace air and potentially becoming a breathing hazard as the air ispushed away!Liquid LPG will boil! Remember, propanes boiling point is -44F. 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.

Te 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 airit comes in contact. A white cloud often forms. Tis white cloud is actually frozen watervapor in the air; this is not LPG liquid or LPG vapor. Te clouds presence can indicate theapproximate 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/airmixture to support combustion. Normally, this value is given in both upper and lower lim-its of flammability. Te upper limit is the percentage of gas in the richest (most gas rich)

mixture that will support combustion. Te lower limit is the percentage of gas in the lean-est (least gas rich) mixture that will support combustion. Refer to the following table forlimits of flammability of LPG.


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Ely Energy, Inc.


* Note that a concentration of only2.15% propane in air will create a flam-mable or explosive mixture. This limit ishalf the lower limit of natural gas.

LPG is both odorless and colorless. Because of its hazard as a flammable material, safetycodes require an odorant be added to LPG sufficient to be detectable at 20% of its lowerflammability limit. Te presence of the odorant suggests the presence of LPG, but does notindicate its concentration. If LPG has passed through soil or placed in a new container orpipe, the odorant could be significantly stripped from the LPG.

When checking for possible leaks from underground piping, a detector sensitive to LPGmust be used. Never rely only on your sense of smell! Substantial underground leaks candevelop with little or no odor apparent.

LPG vapor is heavier than air.

Always remember that LPG vapor isheavier than air. If a leak develops in anLPG line or container, the LPG vapor

will settle in low areas and can becomeconcentrated, particularly if there is lit-tle or no air movement. Tis trait isimportant to know and understand

when trying to identify the source of a

leak, or working in an area where a leakhas occurred. If a leak originated with aliquid release, the refrigerating effect ofthe conversion to vapor will also tend tomake LPG vapors sink.

Te weights of gases are comparedusing specific gravity. Te specific grav-ity of a vapor is the comparison of the

weight of a given volume of a gas at acertain temperature with the same vol-ume of air at the same temperature andpressure. LPG vapor has a specific grav-ity of 1.50 at 60 F.

FLAMMABILITY LIMITS (FUEL IN AIR)

PROPANE NATURAL GASUpper 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 manyactivities. 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). NFPA58 covers the storage and handling of Liquefied Petroleum Gases and references a numberof other codes or standards. Te three major components of the code are:

Equipment designEquipment installationOperating procedures

EEI recommends reviewing NFPA 58 and maintaining a copy at each facility with LPGequipment as a reference. NFPA also publishes a Handbook in conjunction with Pamphlet58. Te handbook includes many descriptive passages to help interpret the code and is alsoa recommended reference.

Chapters in NFPA 58:

CH AP T ER T IT LE DE SCRIP T ION

1 General Provisions Definitions, scope, etc.

2 LP-Gas Equipmentand Appliances

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

3 Installation of LP-GasSystems

Guidelines for installing equipment in bulk plants, c ylinderfilling stations and on industrial and road vehicles

4 LP-Gas Transfer Guidelines for filling tanks and cylinders

5 Storage of Portable ContainersAwaiting Use or Resale

Includes scope, general provisions, storage, and fireprotection

6 Vehicular Transportationof LP-Gas Includes scope, transportat ion modes and parking andgaraging vehicles

7 Buildings or Structures HousingLP-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 abovegroundcontainers

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


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LPG Safety Components

Safety Valves

Tere are a number of types of safety valves used on LPG systems

Back Flow Check Valve

Te back flow check valve, also called the back check or justcheck valve, functions to permit the flow of LPG in only onedirection through piping. With no flow or flow in the reversedirection, the valve closes by spring pressure or system pressureon the back of the valve disk. When flow in the proper direction is sufficient to overcomethe combination of spring force and the weight of LPG on the other side of the valve disc,

the valve opens.Tis 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 lossof product inthe event of line breakage. Excess flow valves are used where thenormal 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 Excessflow valve to close. Tis 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 couldprovide a greater restriction than the setting of the excess flow check valve, thus preventingthe excess flow check valve from operating as designed.

Note the excess flow valve is not normally designed as a positive shut off valve. When thevalve closes as a result of flow above its design flow, a small weep hole remains open allowingan eventual equalization of pressure if the excess flow was caused by opening a downstreamvalve 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 Valve

Te pressure relief valve is possibly the most important valveinstalled in an LPG installation. It is designed specifically to protecttanks or cylinders from over pressure. If this valve cannot performits 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,


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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. Tisrating 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 buildup inside the container and the valve could relieve prematurely.

Every pressure relief valve must be carefully sized and matched to a particular type andsize 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 valvesare 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 isa threaded inlet port. Te valve screws into a fitting on the system to be protected. Insidethe valve body, a spring held in place by a vented retainer presses down on the poppet atthe bottom of the valve. Te valve poppet is fitted with a soft seat disc made of a syntheticmaterial 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 thetrapped 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 atmospherethrough the vent in the retainer at the top of the valve. Tis quickly relieves the excesspressure 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 debrisfrom accumulating inside the valve. It is also a good practice to provide a vent stack or pipeaway for hydrostatic relief valves. Tis is important for Hydrostats located in low lying areasor 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.Tese excess flow valves are installed at a point where the hose

joins the rigid piping system. In the event a hose is sheared offcompletely, the excess flow valve will slug shut. Tis can prevent

a major spill of LPG. In certain situations, however, an excessflow valve may not close properly. Even when an excess flowvalve closes properly, LPG will continue to discharge throughthe 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 breakin the hose.

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

Tree 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.

Te combustible molecules in LPG are hydrocarbons. Hydrocarbons are chemical com-

pounds consisting of hydrogen and carbon atoms. Te oxygen needed to burn LPG vaporis obtained from the air. Air is made up of 20% oxygen, 79% nitrogen, and about 1% ofother miscellaneous gases. Te ignition source must provide enough heat to the mixture offuel and oxygen to raise the temperature of the LPG to its ignition temperature, which isbetween 920oF 1,120oF.

Combustion Ratio

Te combustion ratio is the ratio of air to fuel. A perfect ratio exists when all of thehydrogen and carbon combine with air and no oxygen or fuel is left over during combus-tion! Tis is called the stoichiometric ratio. For LPG the stoichiometric ratio is 23.9:1 andfor Natural Gas 9.6:1.

LPG will burn anytime at a ratio of 2.15% to 9.6% LPG in air exists. However, for propercombustion in appliances, a ratio approaching the stoichiometric ratio is required.

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


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SNG System Operation

Basic Safety Precautions

Tese are basic procedures for operating your system safely:Do not perform any actions which you have not been trainedBe very deliberate about any actions you take, think them through!If need to know about aspects of the system (valve positions, etc) prior toperforming a function, check them out personallyRead and be familiar with your operating manualsBe familiar with any pertinent emergency proceduresKeep the system maintained

Repair any non-functioning or damaged components promptlyRemember that an empty tank is no less dangerous than a full oneRemember that most accidents happen during transfers of LPG

Operating Manuals

Operating manuals should include the following sections:Startup to standby procedure

Standby to operating procedureOperating to standby procedureShut down procedureroubleshooting procedures

Receiving LPG

Te 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 damageCheck all valves for easy operationRemove weeds and other combustible hazards from the areaest for corrosionCheck entire system for leaks and correctCheck fire extinguishersest and document operation of Emergency Shutoff Valves


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SNG System Maintenance Requirements

TTU

Check gaskets, seals, and sealing surfacesCheck condition of caps and replace if necessaryCheck operation of Emergency Shutoff Valve

Tank

Check condition of paintCheck condition of pressure gauges and temperature gauge

Pump

Check for seal leaks and piping leaksCheck condition of pressure gaugesOpen strainer valve and check for the presence of water

Vaporizer

Check condition of gaugesCheck condition of glycol mixture; pH maintenance is criticalCheck for any leaksCheck to ensure safety devices work

System Malfunctions and Emergencies

How to Identify Problems

Be familiar with equipment when operating and not operatingNote the typical temperatures and pressures shown on gauges.Listen for leaks and other unusual soundsLook for visible damage

How to Check for Ammonia in LPG

Some LPG dealers use their vehicles to transport ammonia during the summer and LPGduring 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 exposingto 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%. Te limits of flammability ofLPG are 2.15% to 9.6%. As a result, a natural gas appliance can be out of tune and stillburn, but when supplied with a perfect SNG mixture can be out of tune.

Te best method to handle apparent combustion problems is to first tune the applianceon natural gas. Ten switch fuels to SNG for confirmation. Most combustion problems canbe addressed in this manner. If problems still exist, it is possible that the mixture generatedby 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 willappear yellow or with sooting. Te 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. Tese devices mix all the air required for combustion at the burner rather thandepending on secondary air for complete combustion. Tey operate at the edge of the capa-bility of the burner Venturi to entrain the correct amount of air. As a result they are verysensitive 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 gaslines and components impact safety, operational capability and plant econom-ics. An air leak of sufficient volume can impact measuring or controlling loopsand may compromise safety of the system.Water in LPG. Water is a contaminant in LPG. It can seriously interfere with theproper operation of pumps and regulators. If water is suspected, a freeze offtest 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. Te remedy for water in the LPG is addi-tion of methyl alcohol (methanol). Te easiest method to introduce methanol isto request its inclusion from your LPG supplier in your next LPG order. Add amaximum 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-away

Te most common accident is a truck pulling away from an unloading station without

disconnecting the hoses.Upgrade your U to current code.Use LPG vendors with trained drivers.

Hose break

Check hoses at frequent intervals for damage and leaks.

Accidents at cylinder fill stations

rain operators well and

only allow trained operators, from a certified trainingprogram, to fill cylinders.

Pump seal failure

Check pumps for leaks and wear regularly.

Non-Standard Situations

A non-standard situation exists when equipment is not operating within its normalparameters. A hazard thus exists which is easily controlled or self controlling. Tis hazard islimited 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.urn off electrical power to the pump motors.2.

Close the pump inlet and discharge valves.3.Close all tank valves.4.urn 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 followfire prevention rules. An LPG fire is one hazard that everyone wants to avoid. Any fire, largeor small, has the potential to destroy property and take human lives. As a result, general fireprevention 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. Te only way to reducethis 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, manpowerand supplies must be employed to protect life and property. Tese hazards may include:

Overpressure in the system.Large volumes of uncontrolled escaping gas.Fire or explosion, etc.

Any leak considered hazardous.Te endangerment of continued safe operation of a major segment of the system;Natural disasters such as floods, hurricanes, earthquakes or other severe forcesof 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 thereforeincumbent 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. Te important point to remember about LPG fires is the only effective way toput out a LPG fire is to cut off the supply of gas to the flame. If the flame is extinguishedbefore 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 offwithout personal injury then let it burn until fire-fighting personnel arrive at the scene. Temain 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. Tis is the Golden Rule of handling emergencies.Move upwind from the fire as quickly as possible. Tis will help to avoid burnsfrom radiant heat.

If the fire is caused by LPG, move all people in the area to a point at least 1,000feet upwind from the fire.Immediately call the local fire department and the companies to notify them ofthe fire as soon as everyone is safely clear of the area. Be sure to report the exactlocation 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 areaof the container to keep it cool.

If the fire is at the loading bulkhead, go to the nearest remote emergency shutoff valvecontrol that is upwind and awayfrom 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 trappedor have no upwind escape route.

If there is a small fire caused by another flammable material, extinguish the flame witha 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 thetypical temperatures and pressures shown on gauges.Listen for leaks and other unusual soundsLook for visible damage

Thank YouTanks for taking the time to read this booklet and for being interested. When we can

help call us. Were 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


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L-Pressure

L-Tem

perature(C)

L-Pressure (bar_g)

L-Temperature

L-Temperature(C)

L-Pressure (bar_g)

Ely Energy, Inc.


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 Convert s 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 Gridwith 100% Connected Load

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


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Electric Currents for Specific Countries


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Temperature Conversion Table


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

Fax: (918) 254-5412

Visit us at: www.elyenergy.comEmail: [email protected]

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

SNG and LPG Systems Overview_ELY Energy

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