Well, it's an acronym for Liquefied Petroleum Gas and it's derived from petroleum refine processing and natural gas extraction which is stored in liquid form, and used for heating appliances and vehicles. It's an eco-friendly product and known to be one of the world's most important fuels. It's very flexible as a fuel and it reach most parts of the world because of its portability, which is an advantage. Another advantage is the ease to control and the clean combustion process with results minimal pollution. They are two types of LPG for commercial uses, which are Butane and Propane. Commercial propane has a lower 'boiling point', that way it turns into a gas at a lower temperature and its storage pressure is therefore higher. As a consequence, Commercial propane cylinders should not ever be stored or utilized inside residential premises. This vital property discriminates the two produce and their spans of request, with butane being utilized nearly completely in cylinders for its portability and propane in both cylinders and fixed or perpetual installations. The last gives customers all the benefits obtainable from natural gas, alongside the connection established on a customer tank whose size is reliant on the consumption of the installation. (Ritter, T.J , 2000)
BENEFITS OF LPG
LPG offers significant benefits to both the end-user and society as a whole which are listed below:
Clean Energy: LPG has low particle emissions, low NOx emissions (term for term for mono-nitrogen oxides NO and NO2 ), and low sulphur content meaning that it does not pollute the air as far as countless supplementary power sources. LPG can consequently give considerably to both indoor and outdoor air quality.
Availability: LPG is obtainable nowadays in numbers that can service the power needs of millions of residents across Europe and the world. Looking forward, LPG will stay in abundance globally for the instant future. LPG , a source of energy which the society can depend on for countless years to come .
Portability: LPG can be utilized anywhere. From emergency relief procedures to remote isles to ski resorts at altitude - LPG can grasp locations, other energies cannot. In Europe, LPG has a flexible and decentralized allocated network that that reaches beyond energy grids, enabling progress and attention in low are alongside a low populace density.
Efficiency: Gaseous fuels such as LPG offer inherently huge efficiency, a supremacy that has been considerably enhanced by the rise of performance-optimizing knowledge such as condensing boilers and renewable/LPG hybrid systems.
Lower Carbon: LPG is a low carbon alternative to standard fossil fuels.
(2)
And now, we go have a look at the properties of LPG , both physical and chemical.
PROPERTIES OF LPG
CHEMICAL PROPERTIES OF LPG
The source of LPG, has one public element which is the hydrocarbons (HC) it comprises containing 3 or 4 carbon atoms. It's only these HC gases that are liquefied by reasonable compression at ambient temperature, which are in form of the following below:
PROPANE C3H8
PROPYLENE C3H6
BUTANE C4H10
BUTYLENE C4H8
Thus, it's important to know that we are dealing with commercial products rather than pure chemicals.
PHYSICAL PROPERTIES OF LPG
In this regard, the physical attributes of the product is derived from the chemical composition. Therefore, in its physical state that LPG is normally encountered. Thus, the major physical attributes and their impact are studied.
Vapor Pressure: This is an amount of uncertainty of the gas and its liquid are in equilibrium at any given temperature. At the simmering point, it is equal to the atmospheric pressure and tends to increase as the temperature elevates to critical state. Commercial propane and butane frequently encompass comprehensive proportions of the corresponding unsaturated analogues and tinier numbers of similar hydrocarbons, as well as these hydrocarbons themselves. Fig 1 below shows the vapor pressure/temperature of propane and butane specifically, and Due to its lower boiling point, higher rates of vaporization for comprehensive periods are obtainable from propane than from butane, and at the same period, appreciable pressures are upheld even at low ambient temperatures. (Connor N.E)
http://zenstoves.net/Canister/GasCanisterFuelVaporizationPressureVsATM+PSIBasic2.png
Figure 1: Vapor pressure/ Temperature curves of butane, propane, and isobutene.
(Courtesy of Zen Stoves)
Calorific Value: This is the amount of heat dissipated from complete combustion of gas with air under standard temperature and pressure. The Gross calorific value is total heat content of gas, after the water that is formed during combustion of gas is reduced at the temperature.
The net calorific value is the total heat content of gas, after the water is formed during combustion of gas is still at the gas phase at the temperature. From the table 1 below shows various calorific values, and it's seen that LPG has high calorific values. Watkins, D.E (2011)
Fuel
CV in MJ/Kg
CV in MJ/M³
Butane
45.8
112.9
Propane
46.3
86.1
Natural gas
-
34.9
Kerosene
43.6
-
Gas oil
42.7
-
(Courtesy: Heating services in buildings, page 347)
Table 1: Comparison of net calorific values of common fuels.
Viscosity: This is simply the resistance of fluid to shear motion, thus internal friction. For LPG, the absolute viscosity held as liquid under vapor pressure, is by far less than that of water, thus demanding a very high integrity in the pressurized system, if leakage doesn't occur. Knowledge of the viscosity features in LP gases is required for the design pipe network and pumping systems. Williams & Lorn (1974).
Limits of Flammability: A mixture of LPG with air is a flammable mixture. The flammable range at ambient temperature and pressure is bounded by lower and upper limits of flammability which are approximately 2 percent to 8.4 percent for butane and 3percent to 9.5 percent for propane. Beyond this range, either the mixture is weak or strong, it generates flame. The limits of flammability for propane and butane are much narrower than most supplementary gas fuels, making LPG safer in this respect.
Odor: In a refined state, LP gases are almost odorless. Therefore, to detect leaks easily, commercial butane and propane have a featured smell, such that its odor shall be unpleasant and distinctive, and the mixture shall be such that it is detectable.
Note: Odorants such as ethanediol, tetrahydrothiophene or dimethyl sulfide may be added so that the gas complies with the specified requirements for odor. (5)
Relative Density: The density of liquid butane and propane is concerning half that of water, and as such is far lower than supplementary liquid fuels.
As for vapor, the major difference between LPG vapor and natural gas is that natural gases are lighter than air. Thus, LPG vapor are slightly twice heavy than air. This is vital in two areas. First, after converting equipment running on usual gas to run on propane or butane, the number of gas that subjects from a fixed orifice at a fixed pressure is inversely proportional to the square root of its density. Second, if there is a leak of LPG vapor it will collect at ground level or in depressions, drains or cellars if appropriate precautions are not taken. This is a major protection thought when designing or installing LPG systems. (Ritter, T.J, 2000)
Specific Gravity: LPG vapor is nearly 1 ½ to 2 times as heavy as air. This would mean that any escaping vapors of LPG would tend to settle down. Hence, there should be adequate ground level ventilation where LPG cylinders are stored. For this very reason LPG cylinder installations should not be undertaken in cellars or basements which have no ventilation at ground level. Also, cylinder installation should not be within 1 meter of drain openings.
PROPERTIES OF LPG
There are two main sources from which LPG are produced, namely:
(a) Natural Gas Production
(b) Refinery operations
Refinery Production from Crude oil
Mainly, we take about the refinery process were crude oil is refined by the process of fractional distillation, heating it to about 350 °C to turn into a mixture of gases. This is piped into a tall cylinder known as the fractional tower. Inside the tower, the very long chain carbon liquids such as bitumen and paraffin wax are piped out to be broken down elsewhere. The hydrocarbons rise up inside the tower passing through a series of horizontal trays and bubbles called " bubble caps", the temperature in each tray is controlled so as to the exact temperature for the particular hydrocarbon will condense into a liquid, the distillation process is based on this fact. The different hydrocarbon condense out of the gas cloud when temperature drop below a specific boiling point, so the higher the gas rises to the tower's apex, the lower the temperature becomes. The precise details are different in every refinery and also depend on the type of crude oil being distilled. Around 260°C diesel condenses out of the gas, Around 180°C kerosene condenses out of the gas, around 110°C petrol condenses out of the gas, and finally the LP gases which are less than 25°C. The figure below is a diagram of how LPG is distilled from crude oil due to heating.
http://www.energybulletin.net/image/uploads/40234/Fractional_distillation.gif
Figure 2: Fractional distillation processing of petroleum refining (Courtesy: the Physics of Petroleum Refining)
Natural gas processing
When gas is drawn from the earth, it is a mixture of several gases and liquids. Commercial natural gas is mainly composed of methane. However, it also contains ethane, propane and butane in accordance with the specifications for natural gas in each country in which it is distributed. Therefore, before natural gas is marketed, some NGLs, including LP Gases (propane and butane) are separated out, depending on the "wetness" of the gas produced: NGLs represent 1 to 10% of the unprocessed gas stream. Some NGLs are also trapped in crude oil. In order to stabilize the crude oil for pipeline or tanker distribution, these "associated" or "natural gases" are further processed into LP Gas. Worldwide, gas processing is the source of approximately 60% of LP Gas produced.
STORAGE AND HANDLING OF LPG
LP-Gas is stored and shipped as a Liquid and utilized as a gas. Because it is a gas under ordinary temperatures and pressures, it has to, if it is to be handled as a liquid, be retained below a reasonable pressure. Consequently, unless butane, with its lower vapor pressure, is to be handled completely, tanks possessing a design pressure of 250 psig are used. Tanks of this design pressure are suitable for commercial propane, all butane-propane mixtures, or business butane. This affords a desirable degree of flexibility. Lower design pressure storage tanks can be utilized merely for commercial butane or the low-vapor-pressure butane-propane mixtures. The use of minimum design pressure tanks is an vital commercial thought, particularly in large-volume storage. Storage is vital at countless points alongside the shackle of distribution. It is required at the point of creation, at the point of allocation, and at the point of consumption. Either the producer or distributor could additionally have secondary storage installations. Producer storage could be of the pursuing types:
Underground: (1) disappeared salt cavities, (2) mined caverns
Aboveground: (1) globes, (2) horizontal or vertical cylindrical tanks
Dissolved salt cavities are probable whereas suitable salt domes or salt layers exist. The NGAA has industrialized Tentative Standards for the Underground Storage or Liquefied Petroleum Gas. These tentative standards encompass precise safety standards for the assembly, assessing, and fitting of these underground storage installations. Spheres are frequently utilized for butane storage and 5,000 to 10,000-bbl globes are quite common. A little have capacities up to 20,000 bbl. Horizontal cylindrical tanks used for LP-Gas storage normally are of 30,000 gal capacity, nevertheless tanks of 60,000 to 70,000 gal capacity are becoming accepted, chiefly at terminals. The per-gallon price of these larger tanks is merely somewhat lower, but the saving on footings, piers, piping, and accessories makes them attractive. There have been insufficient distinct storage installations of large-diameter pipe in constituents of 950- to 1,100-ft lengths, but space limitations usually discourage such installations. Most producer storage is at the point of creation, even though there is a growing tendency to craft and work large-volume storage nearer main consuming areas. Most of this secondary storage is placed on pipelines or at water terminals. However, several major storage terminals receive their product by tank car during the "off" season. Storage by the distributor is largely in the horizontal cylindrical containers of American Society of Mechanical Engineers (ASME) construction for 250-psig design pressure. Butane storage may utilize tanks having a design pressure of 125 psig (the minimum set forth in NFPA Pamphlet 58). Although 12,000-, 18,000-, and 30,000-gal tanks are the most common for bulk storage plants, these tanks may vary in capacity from 1,000 to 30,000 gal. A few distributors have developed their own underground storage where their operations are large enough to justify the investment and where their marketing area is close to suitable geological formations. Consumer storage may include all types and sizes mentioned above for producers and distributors. The size and type will vary with the load demand by the domestic, commercial, industrial, petrochemical, or utility user. Guthrie. V (2005)
CYLINDER STORAGE AND FILLING PLANT
LPG bottling plant is a plant where LPG is filled into bottles (cylinders) for storage and distribution among various LPG distributors. The plant has the facility to receive bulk LPG by Tank trucks (of various capacities e.g. 12MT, 17MT etc) or pipeline from a reliable source e.g. Refinery or any other LPG Bottling Plant. After receipt of Bulk LPG, filling of LPG into cylinders is done. Here we shall discuss the filling operations in LPG Bottling Plant. Below is a schematic of a LPG filling station,
Full-size image (61 K)
Fig 3: a schematic diagram of Bucheon LPG filling station. (Courtesy: Bucheon LPG)
In this station, Propane is pumped to the cylinder filling area at about 0.8 MPa of operating pressure and butane is pumped to vehicle dispenser at about 0.5 MPa of operating pressure through 50 mm diameter pipeline. The filled cylinders are stored at stack area or loaded on cylinder truck to be distributed to the agents.
SAFETY IN STORAGE
Safe storage and handling of LPG is of paramount importance, whether it is in bulk or in cylinders. This is achieved by ensuring the mechanical integrity of the storage vessels or cylinders and by strict observance of the recommended separation distances between storage and buildings or boundaries. This passive protection has to be supplemented by rigorous observance of operational procedures.
Both the LPGITA (UK) and the Health and Safety Executive have issued codes of practice on the subject. (Ritter, T.J, 2000)
TRANSPORTATION OF LPG
Liquids may be transported in numerous ways depending upon the quantity and distance involved. The associated hazards are chemical-specific and also depend upon the physical condition, i.e.:
• Liquid at atmospheric pressure and ambient temperature;
• liquefied gas under pressure and at ambient temperature; or
• liquefied gas at atmospheric pressure and at low temperature (i.e. fully-refrigerated transport).
Water spreading will be more extensive, and vaporization will be more rapid, because of the increased rate of heat transfer. Unstable chemicals may pose an explosion risk. Toxic chemicals may be released as a liquid which spreads or as a vapor cloud. The risk of environmental damage is likely to be potentially serious in most cases.
The common means for transport are:
• In bottles, plastic drums, steel or resin-lined drums (e.g. of 210 liter capacity).
• Glass bottles which are used only for small quantities, e.g. 2.5 liters, but should be protected in specially designed carriers.
• Plastic drums, which must not be subjected to excessive loading and, if returnable, require checking for degradation, e.g. due to cracking, impact, distortion.
• By road or rail tanker.
• By ship, e.g. crude petroleum.
• By pipeline, e.g. LPG.
A generic supply chain model for the LPG industry is shown below:
http://www.progas.cc/images/transportation.jpg
Fig 4: chain model of LPG industry (courtesy: PROGAS)
Accidents may be caused by impact, failure of container or pipeline, or during loading/unloading.
The hazards arise from:
• Fire and/or explosion.
• Toxic release:
- Of a conventional type; or
- Of an ultra-toxic; either instantaneous or prolonged.
• Environmental pollution.
These mirror those at fixed installations, but loss of containment due to the triggering event can occur anywhere en route. Thus accidents may occur in populated or environmentally sensitive locations, or where domino effects are less easily controlled. Common risks are also associated with all vehicular movements and mechanical/manual loading/unloading activities. Problems may arise with switch-loading of road tankers, ships or pipelines and with the use of returnable containers.
The important considerations for safety are:
• Compatibility of the chemical with the materials of construction.
• Adequacy of cleaning out, and removal of residues from, the previous chemical carried to avoid cross-contamination and potential reactive hazards on refilling.
• A sound information transfer system to avoid confusion of chemical identities and to ensure the specific risks of each load are identified and made known to the carrier/transporter.
• Adequacy of decontamination of 'empty' containers, tankers, etc. before return.
APPLICATIONS OF LPG
The uses of LP-Gas are countless and varied. The first uses were undeviatingly attributable to its skill to produce heat and power. Later, credit of its convenient chemical structure made it a vital chemical building block. A finished tabulating of all of the uses of LP-Gas is tough, as new requests are being made continually .Table 2 catalogs a little of the normal applications of LP-Gas.
Category
Examples
Domestic and farm
Crop drying, air conditioning, scalding, cooking, refrigerating, weed burning
Commercial
Baking ovens, hot plates, tar kettles, lead pots
Industrial
Heating, carbonizing, die casting, core baking, mold drying, torches
Raw materials
Alcohols, organic acids, plastics, acetates, detergents,
Chemical use
Color control of soaps, solvent extraction of vegetable oils
Utility
Peak shaving, standby
Transportation
Buses, cars, tractors, automobiles,
Table 2: Uses of LP gases (Courtesy: BP Gas)
CONCLUSION
