The University of Salford

School of Computing, Science and Engineering

MSc/PgDip in Petroleum and Gas Engineering

Fundamentals of Natural Gas & Production Systems & Design – Module 1: Assignment

Liquefied Petroleum Gas (L.P.G) Technology

Student : Constantinos Christodoulou - @00316650

Tutor : Mr. N.E. Connor, Dr. M.L. Burby

Semester : 1st

Table of contents

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TABLE OF FIGURES – TABLES 31. LPG

1.1. Properties1.1.1. Composition1.1.2. Viscosity1.1.3. Combustion1.1.4. Vapor Pressure1.1.5. Gross Calorific Value1.1.6. Specific Gravity (Relative Density) of Vapor and Liquid1.1.7. Boiling Point1.1.8. Dew Point1.1.9. Flame Temperature1.1.10. Latent Heat1.1.11. Flash Point1.1.12. Co-Efficient of Cubical Expansion of Liquid LPG1.1.13. Flammability Limits1.1.14. Odorization of LPG1.1.15. Colour1.1.16. Toxicity

1.2. Production1.3. Storage

44455556666667777789

2. CYLINDER FILLING PLANT 113. TRANSPORTATION

3.1. Transportation by Road Tankers3.2. Transportation by Rail3.3. Transportation by Ships

13131415

4. APPLICATIONS4.1. Industrial Uses4.2. Residential and Domestic Uses4.3. Motor Fuel

16161718

BIBLIOGRAPHY – REFERENCES 19

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Table of figures - tables

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FIGURESFig. 1. Constituents of Natural Gas 4Fig. 2. Constituents of LPG 4Fig. 3. Refining process 8Fig. 4. Refining process 8Fig. 5. Spherical storage vessels for LPG 9Fig. 6. Cylindrical storage vessels for LPG 10Fig. 7. LPG tank analytical view – main parts 10Fig. 8. Cylinder filling plant automatic procedure 1 11Fig. 9. Cylinder filling plant automatic procedure 2 11Fig. 10. Cylinder filling plant operating individually 12Fig. 11. Cylinder filling plant operating simultaneously 12Fig. 12. LPG large capacity tanker 13Fig. 13. LPG medium capacity tanker 13Fig. 14. LPG rail tanker passing through a station 14Fig. 15. LPG rail tanker waiting to connect with the rail engine 14Fig. 16. LPG ship with spherical vessels 15Fig. 17. Safety Importance in Ships Transportation 15Fig. 18. LPG world demand 16Fig. 19. CO2 emissions 16Fig. 20. Generating energy by using LPG as main fuel 16Fig. 21. LPG bulk tank 17Fig. 22. Residential use 17Fig. 23. Different sizes of vessels easily found on market 17Fig. 24. LPG re-filling station, pump and nozzle 18Fig. 25. LPG cylinder in the trunk and switch 18

TABLESTable 1.Gross and Net Calorific Values of Propane and Butane in different units of measurement

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Table 2. Boiling Points of the main constituents of LPG 6Table 3. Approximate limits of flammability of LPG (P = atmospheric, T = 15 oC) 7

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1. LPG

Liquefied Petroleum Gas also known as LPG, is a flammable mixture consisted by hydrocarbon gases (mainly propane C3H8 and butane C4H10) and is derived from crude oil and/or natural gas. Also the mixture can contain more chemical compounds like Propylene (C3H6), butylene (C4H8) and more.

Figure 1 .Constituents of Natural Gas (www.pttplc.com – natural gas pdf)

1.1. Properties

1.1.1. Composition

As we concluded for figure 1, LPG is a more than an individual gas. It’s a composition of gases as shown below to the analytical chemical formulas.

Propane – 2D Propane – 3D Butane – 2D Butane – 3D

Propylene – 2D Propylene – 3D butylene – 2D butylene – 3D

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Figure(s) 2. Constituents of LPG (www.wikipedia.com)

Also, the LPG has some impurities in the early stages of the process and must be removed before the gas will be delivered for use. These impurities exist in very small percentages (traces) on the original mixture. The most known impurities are oil, wax, sludge, water (as liquid) and hydrogen sulfide (H2O), carbonyl sulfide (COS), ethyl mercaptan (C2H5SH) (as gas).

1.1.1. Viscosity

It’s very important to know the viscosity of a gas because that will help us in designing the pipelines of distribution systems. The LPG viscosity is smaller than water viscosity. In liquid phase, the temperature is inverse proportion with viscosity. When temperature is increasing, the viscosity is decreasing and vice versa. This property helps also in leak detection and the easy movement of the leaked LPG through the water avoiding the change of explosion if something goes wrong.

1.1.2. Combustion

The combustion of LPG is using basic chemistry equations. These equations are correct if there is excess air for the combustion. In the opposite case, we are going to have incomplete products like carbon monoxide (CO) and carbon dioxide (CO2). Both products are considered as toxic gases.

C3H8 + 5O2 3CO2 + 4H2O + Q

2C4H10 + 13O2 8CO2 + 10H2O + Q

1.1.3. Vapor Pressure

Vapor pressure expresses a measure of the volatility of the gas. Knowing the vapor pressure, we will be able to specify the design conditions for the pressurized system (tanker, pipework, tank or cylinder). The vapor pressure inside an LPG vessel varies dependent on the type of gas (propane, butane or the mixture ratio of these two gases), the quantity of the gas stayed unconsumed in the vessel and the ambient conditions (temperature, pressure). The pressure is not constant in the vessel but with the use of a regulator, we can get steady outlet pressure of the gas. The determination of gauge vapor pressure usually based on BS EN ISO 4256 or ASTM 1267.

1.1.4. Gross Calorific Value

The gross calorific value is defined as the amount of energy (heat) obtained by a complete combustion when a gas is burned at atmospheric pressure and steady temperature. The calorific value of commercial LPG is considerably higher than the natural gas and that’s one of the reasons that LPG is preferred in some cases than natural gas.

Measurement UnitsCommercial Propane Commercial Butane

Gross Net Gross NetMJ/m3 (dry) 93,1 86,1 121,8 112,9Btu/ft3 (dry) 2500 2310 3270 3030MJ/kg 50 46,3 49,3 45,8Btu/lb 21500 19900 21200 19700

Table 1.Gross and Net Calorific Values of Propane and Butane in different units of measurement

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1.1.5. Specific Gravity (Relative Density) of Vapor and Liquid

At ambient conditions (pressure and temperature), LPG is a gas that is heavier than air ≈ 1,5 – 2 times. Propane has density around 1,4 – 1,55 and butane around 1,9 – 2,1. But on liquefaction, these properties changes and LPG volume is reduces considerably. At ambient conditions, the ratio of gas volume to liquid volume is 274 for propane and 233 for butane. As individual gas, both gases exist as clear liquid with very low density (propane ≈ 0,50 and butane ≈ 0,58) that is about half of water density.

1.1.6. Boiling Point

Commercial LPG mixture is consisted of gases with very low boiling points and under atmospheric conditions exists as vapor. For higher temperatures than ambient, the gases perform an increasing vapor pressure and increase the pressure needed for archiving liquefaction.

Propane n - Butane iso - ButaneCommercial

PropaneCommercial

ButaneEthylene

Boiling Point oC at 1 atm

- 42,1 - 0,05 - 11,7 - 45 - 2 - 103,7

Table 2. Boiling Points of the main constituents of LPG

1.1.7. Dew Point

LPG usually is stored and distributed in liquid phase but regularly is used as vapor under controlled pressure and temperature. The important rule is that within the system, the temperature must be above dew point or else the vapor will be re-condensed (become back in liquid phase). The dew point is not constant and as temperature increases, the pressure will increase also.

1.1.8. Flame Temperature

The maximum flame temperature that can be produced from the combustion of LPG is 1977 oC. This temperature is the same for propane and butane combustion individual burned or as a mixture in any ratio.

1.1.9. Latent Heat

The latent heat of a liquid product can be expressed as the quantity of heat required to enable vaporization and the liquid product becomes gas. When LPG vaporizes naturally , the latent heat needed is taken by the liquid itself and that cause a temperature drop. This phenomenon is known as “auto-refrigeration”. Because the vaporization of propane can be achieved only at very low temperatures, operators must wear protective clothing for not receiving cold burns.

1.1.10. Flash Point

By using the term “flash point” we mean that this is the lowest temperature at which a flammable liquid/gas can receive an ignition source and be ignitable. However, once the ignition source is removed, the flammable nature may cease and the flame stops. The flash point for LPG is -104 oC

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and this temperature states that LPG is only safe when storage is under controllable conditions (although it will not auto-ignited since that temperature is around 410 – 580 oC) and consider as a very high flammable gas.

1.1.11. Co-Efficient of Cubical Expansion of Liquid LPG

Cubical expansion means that LPG in liquid phase expands considerably as its temperature increase. The co-efficient of cubical expansion at 15 oC is about 0,0020/ oC for propane and 0,0029/ oC for butane. If we make a comparison, the value for LPG is four times the equivalent for fuel oil, ten times for water and one hundred times for steel. The high rate of expansion has to be considered when we will have to specify the maximum quantity of LPG that will be permitted to be filled into pressure vessels. The filling ratio is determining the maximum quantity allowed.

1.1.12. Flammability limits

When a mixture of LPG and air is combustible within certain concentrations, then it’s known as a flammable range. The flammability limits at atmospheric pressure are 1,8% (lower) – 8,4% (higher) for butane and 2,4% (lower) – 9,5% (higher) for propane. If higher pressure than atmospheric is detected, the flammability limits will change. We are assuming that the gas and air are mixed thoroughly for taking the flammability limits below as standard.

Commercial Butane

Commercial Propane

Methane Hydrogen Acetylene

Lower Limit 1,8 2,2 5,3 4 2,5

Upper Limit 8,4 9,5 14 74 80

% gas in stoichiometri

c mixture3,2 4,2 9,5 29,6 7,75

Table 3. Approximate limits of flammability of LPG (P = atmospheric, T = 15 oC)

1.1.13. Odorization of LPG

LPG at refining state, is almost odorless. This is dangerous because in everyday use, we wouldn’t be able to detect any possible leakages. Usually, ethyl mercaptan is used to provide the characteristic smell of LPG. This chemical compound is selected because is non-corrosive, is a low sulfur content and the boiling point is very near to LPG boiling point.

1.1.14. Colour

LPG is considered as a colourless gas but in case of leakage, the atmosphere around the gas will change to foggy.

1.1.15. Toxicity

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LPG is considered non-toxic in vapour phase but when large quantity is gathered, LPG is replacing the oxygen in the air and might cause faints or even death when there is no appropriate ventilation.

1.2. Production

LPG is a mixture of gaseous hydrocarbons, produced from natural gas and oil extraction (≈66%) and from oil refining (≈34%). It is automatically generated during the production of methane as an associated gas and during the refining process itself. If LPG was not captured at this point, it would be destroyed through venting or flaring. Because LPG is an immediately available and exceptional energy source, that would be an unacceptable waste.

For processing the LPG, we use the integration of four units (acid gas removal, extraction, fractionation and product treatment unit). The main categories that consists the products of refining of crude oil are : Methane and Ethane (permanent gases), Hydrocarbons (5 or more atoms of Carbon) and Alkanes (3 or 4 atoms of Carbon).

LPG manufacture involves separation and collection of the gas from the petroleum sources. The gas/oil hydrocarbon mixture is piped out of the well and into a gas trap, which separates the stream into crude oil and "wet" gas, which contains natural gasoline, liquefied petroleum gases, and natural gas. Crude oil is heavier and sinks to the bottom of the trap. Then it’s pumped into an oil storage tank for later refinement. The "wet" gas comes off the top of the trap and is piped to a gasoline absorption plant, where it is cooled and pumped through an absorption oil to remove the natural gasoline and liquefied petroleum gases. The remaining dry gas, about 90% methane, comes off the top of the trap and is piped to towns and cities for distribution by gas utility companies. The absorbing oil, saturated with hydrocarbons, is piped to a still where the hydrocarbons are boiled off. This petroleum mixture is known as "wild gasoline." The clean absorbing oil is then returned to the absorber, where it repeats the process. The "wild gasoline" is pumped to stabilizer towers, where the natural liquid gasoline is removed from the bottom and a mixture of liquefied petroleum gases is drawn off the top. This mixture of LPG, which is about 10% of total gas mixture, can be used as a mixture or further separated into its three parts - butane, iso-butane, and propane (about 5% of the total gas mixture). (LPG manufacturing process source – www.madehow.com)

Below, we can see analytical two figures of the refining process.

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Figure 3. Refining process (www.npra.com) Figure 4. Refining process (www.howstuffworks.com)

1.3. Storage

Since the production of LPG has finished, we must storage it at liquid phase until it will be distributed for several uses. Storage of LPG is a combination of temperature and pressure. We must choose if we want to store the LPG in refrigerated mode under atmospheric pressure conditions or in controllable pressure vessels under atmospheric temperature. Usually for large storage quantities (more than 5000 tons), we prefer the first method with atmospheric pressure.

The considerations regarding storage of LPG are :

Vessel design & fittings (max pressure, min temperature, max liquid level, relief valve design)

Siting & installation layout (easy access, ventilation, space arrangement of vessels) Area classification & electrical equipment (safe area, division 1, division 2) Fire protection (pump areas, firewall, retaining walls, stream curtains) Operation (Recharge of vessels, commission, decommission) Maintenance (inspection of vessels internal & external, relief valves tests)

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Figure 5. Spherical storage vessels for LPG (www.cnipvc.com)

For refrigerating storage at atmospheric pressure, we can have low pressure vessels (dome or conical roof tanks) and high pressure vessels (cylindrical or spherical). It may also be needed to have double skin construction vessels if we have very low ambient temperature in the place where the vessels will be placed.

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Figure 6. Cylindrical storage vessels for LPG (www.tootoo.com)

Design of pressure vessels must be based on international standards as ASTM D-6849-02, ASTM D-6897-09 and BS 5500.

Figure 7. LPG tank analytical view – main parts (www.catskillhouse.us.blog)

The area of installation of the storage vessels must be selected carefully and keep the safety standards. The ground must be smooth and without slope. Also, heat sources must be far away from the installation to exclude the possibility of ignition of the vessels.

2. CYLINDER FILLING PLANT

The cylinder filling plants are in the market for more than 60 years. They usually contain propane and/or butane. They can be found in the market in range 10 to 110 liters capacity. The design of cylinders in the UK, are based on BSEN 1920:2000, BSEN 13365:2002, BSEN 13385:2002, BSEN 12205 and 97/720071 DC (ISO/DIS 10691:2004). The cylinders are sold according to the weight of LPG it’s contained inside. So checking and measurement is necessary during the filling and even after. Before the cylinders get on market, must be checked for leak, corrosion, hits and must marked as appropriate for the market. Also the maximum allowed filling should be not exceeded for avoiding any problems because of the volumetric expansion of the liquid. For maintenance, we use the ISO 10464:2004 and BSEN 1440:2008. As for safety, relief valves should be installed for cylinders that are loaded with more than 3 kg.

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Figure 8. Cylinder filling plant automatic procedure 1 (www.pochcorp.com)

Figure 9. Cylinder filling plant automatic procedure 2 (www.siraga.com)

The cylinder filling plants can operate even individually or simultaneously in some cases but only be connected to one source. These can be shown by the figures below.

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Figure 10. Cylinder filling plant operating individually (www.eko.com.cy)

Figure 11. Cylinder filling plant operating simultaneously (www.eko.com.cy)

3. TRANSPORTATION

Demand for LPG is rising, particularly in the residential and commercial sectors of developing and more developed countries. The use of cleaner liquid and gaseous fuels is expected to continue to increase as population grows and total demand for energy in these regions rises proportionally. Transportation means the way of delivering LPG from production to consumption. Transportation can be achieved by road (trucks), by rail and by sea (ships)

3.1. Transportation by Road Tankers

Transportation by road mainly used for customers’ consumption. We are using road tankers for delivering the products to the consumers. Tankers are specially designed motor vehicle to carry

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liquefied products and the capacity can be from 2000 L (2m3) until 45000 L (45m3). The capacity depends on the kind of the tanker and if LPG is carried out pressurized or non-pressurized.

Figure 12. LPG large capacity tanker (www.truck.co.za)

In all stages before, during and after the transportation, safety rules must be followed. The personnel must know the dangers, the safety rules and must be educated for acting in emergency situations.

Figure 13. LPG medium capacity tanker (www.eximclub.com)

3.2. Transportation by Rail

Also tankers are used and in these conditions, but the capacity and pressure are much bigger than the road tankers. Again, we can have pressurized or non-pressurized transportation. Because rail is passing by places that road approach is not easily accessed, the tankers are equipped for fire incidences (fire extinguishers and water spray or foam). A lot of manifolds and valves are installed to prevent leakages. The capacity or each tanker can be up to 165000 L (165m3) but under pressurized environment.

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Figure 14. LPG rail tanker passing through a station (www.trainweb.org)

For a train to be allowed to transport LPG, must satisfy the international carriage of dangerous goods by rail (RID - Reglements Internationale Relatif au Transport des Marchandises Dangereuses par Chemin de Fer). This international agreement is updated every two years.

Figure 15. LPG rail tanker waiting to connect with the rail engine (www.veritecsolutions.com)

3.3. Transportation by Ships

In the marine transportation market, LPG is typically transported by dedicated vessels suitable for carrying pressurized, semi-pressurized or refrigerated LPG.

Pressurized ships (18 bar, ambient temperatures) can carry from 3m3 up to 10000 m3 and semi-pressurized (5-8 bar, -10 to -20 oC) can carry up from 10m3 up to 30000m3. If we want to transport larger volumes than 30000m3 we must use the refrigerated solution. Fully refrigerated ships (atmospheric pressure, until -43 oC temperature), can carry up from 35000m3 up to 100000m3.

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Usually, for a cargo sheep to be loaded and un-loaded needs about 24 hours. (Trip time is excluded).

Figure 16. LPG ship with spherical vessels (www.ilo.org)

Safety is very important because the ships are travelling in very long distances, in the middle of the oceans and they are experiencing big temperatures changes. How important is the safety in ships transportation, is shown below to figure 17.

Figure 17. Safety Importance in Ships Transportation (www.snc.ro)

4. APPLICATIONS

LPG has a large scale of uses because of its properties. Also the fact that it’s much more environmentally friendly than other fossil fuels make it more preferable for use and can be call as the fuel of future. That’s happening because LPG is consisted by light molecule hydrocarbons and when the combustion takes place, very few particulates released. The most common uses of LPG are : industrial, rural heating, motor fuel, refrigeration and cooking. The increasing demand for

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LPG around the world can be shown clear from the figure 18 below. Also we can see the difference in CO2 emissions compare with other kind of fuels.

Figure 18. LPG world demand (www.ogj.com) Figure 19. CO2 emissions (www.forestfuels.co.uk)

4.1. Industrial Uses

LPG is used widely for power generation combined with heat generation. This is a usual phenomenon in isolated areas where no energy supply exists. Also it’s used in metal forming, metal cutting, thermal treatment, ceramics and glass manufacture, to heat the bitumen in road construction and much more.

Figure 20. Generating energy by using LPG as main fuel (www.mprservices.com)

4.2. Residential and Domestic Uses

The most common uses of LPG are : space heating at winter, air conditioning at summer, hot water supply in big facilities (hotels, federal buildings), lighting, cooking and refrigeration. It’s preferred from other conventional fuels because it’s cheaper and it’s easier to re-supply the units that using it.

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We are using LPG for cooking because of its low boiling point, for refrigeration because it’s cheaper than other chemical compounds and friendlier to the environment. Also it can be found easily in the market in different sizes and that means every potential buyer can find the amount of LPG needed for demanding his needs.

Figure 21. LPG bulk tank (www.calor.co.uk) Figure 22. Residential use (www.primagas.com)

Figure 23. Different sizes of vessels easily found on market (www.uklpg.org)

4.3. Motor Fuel

LPG is also used as an alternative fuel source. We are referring to LPG more as auto-gas or auto-propane when it’s used as a motor fuel. The main characteristics of auto-gas are :

Tetra-ethyl lead-free and clear burning fuel Non-toxic

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Non-corrosive Very high octane rate (102 – 110 RON depending on gas specifications) Less emissions of sulfur Much more cheaper than other motor fuels

The only disadvantage that LPG has as a motor fuel comparing with conventional motor fuels, is the low calorific value (in comparison with other motor fuels). That means higher consumption but the low cost and the reduce need of maintenance, makes it more affordable for the consumers.

The LPG vessel is placed on the trunk for more protection (ex. frontal collision) and can be used individually as the only fuel source or in combination with other motor fuel. The change from the one fuel to another can be done easily, pressing only one switch.

Figure 24. LPG re-filling station, pump and nozzle (www.caradvice.com.au) (www.brecorder.com)

Figure 25. LPG cylinder in the trunk and switch (www.carsguide.com)

BIBLIOGRAPHY – REFERENCES

LPG Book, Mr. N. E. Connor, School of Computing, Science and Engineering, Salford Univ. http://buildingcriteria2.tpub.com/ufc_3_460_01/ufc_3_460_010041.htm http://en.wikipedia.org/wiki/Liquefied_petroleum_gas http://en.wikipedia.org/wiki/Tank_truck

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http://mellcon.com/LPG-Storage-Tank.html http://science.howstuffworks.com http://standby.com/propane/tanks.html http://ts.nist.gov/WeightsAndMeasures/upload/LPG-Chptr2May-05.pdf http://www.altenergy.com/technology/lpgproperties.htm http://www.answers.com/topic/liquified-petroleum-gas http://www.ashgas.com/lpg_cylinder.htm http://www.bluewater.com/products.asp?refID=185&ID=310&contentID=309 http://www.bluewater-offshore.com/downloads/PT26_LPG%20SPM_bluewater.pdf http://www.budgetgas.co.uk/how%20lpg%20works.html http://www.cne-siar.gov.uk/buildingstandards/documents/guidance/LPG%20Storage.pdf http://www.cvrenergy.com http://www.daviddarling.info/encyclopedia/A/alkane.html http://www.eere.energy.gov/vehiclesandfuels http://www.elmhurst.edu/~chm/onlcourse/chm110/outlines/distill.html http://www.explainthatstuff.com/lpg.html http://www.flogas.co.uk/132/lpg-properties-hazards http://www.flogas.co.uk/81/what-is-lpg-gas http://www.gas-plants.com/lpg-bottling-plant.html http://www.hse.gov.uk/comah/sragtech/techmeasplant.htm http://www.hse.gov.uk/foi/internalops/hid/ din /546.pdf http://www.ideamarketers.com/?The_use_of_LPG&articled=429100 http://www.ilo.org/safework_bookshelf/english?content&nd=857171254 http://www.indiastudychannel.com/resources/83758-Precautions-for-Using-LPG.aspx http://www.iocl.com/Products/LPGSpecifications.pdf http://www.lpgasmagazine.co.uk/cylinders/Speeding-up-the-Lpg-Cylinder-Filling-Process-

with-RFID.html http://www.madehow.com/Volume-3/Propane.html http://www.maritimesun.com/downloads/inspection/1_GasTankersAdvanceCourse.pdf http://www.nationalgasco.net/portals/0/Characteristics%20of%20LPGas.pdf http://www.npra.org http://www.originenergy.com.au/2363/What-is-LPG http://www.propane.tx.gov/publications/lpg_safetyrules.pdf http://www.siegelgas.com/propane.htm http://www.teekay.com/?page=lpg_main http://www.total.co.in http://www.tucsonaz.gov/fire_prevention/Resources/LPGrequirements.pdf http://www.window.state.tx.us/specialrpt/energy/nonrenewable/lpg.php

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