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LIQUIFIED PETROLEUM GAS

Introduction:

Liquefied Petroleum Gas (LPG) is a colourless, odourless and environment friendly. Liquefied petroleum gas (LPG) is a subcategory of variety of class of petroleum products known as Natural Gas Liquids (NGLs). LPG are produced and extracted along with the natural Gas. It is also produced by refining the crude oil, though it is commercially defined as a product of propane, butane and a mixture of propane-butane. To be precise, commercial availability is limited to propane. It is gaseous at normal temperature and pressure, and liquefiable under reduced temperature or moderate pressure. A chemical ethyl mercaptan is added to impart a pungent odour for leak detection. Because of its characteristics LPG is fast becoming a fuel of choice in the areas, where natural gas distribution network is not available.

Properties of LPG:

LPG, being a mixture of gases possesses a large number of properties. Let's divide the properties into two categories:

* Commercial Properties and

* Physical Properties.

The typical commercial properties of LPG are:

(i) LPG is gaseous by nature but under the application of pressure and temperature it is turned into liquid state.

(ii) LPG is colourless as a liquid and under vapour state it cannot be seen.

(iii) LPG is odourless but, during the production a stenching agent is added to give a pungent and an unpleasant smell indicating aid detection.

(iv) It is non-toxic but at very high concentration in air, LPG acts as anesthetic and subsequently acts as an asphyxiate agent reducing the oxygen content in the atmosphere.

(v) A highly flammable mixture is produced when it is mixed with air. Flammability range is between 2% to 11% by volume of gas to air.

(vi) It has a high vapour density. Due to high vapour density, LPG is heavier than air.

(vii) LPG liquid is lighter than water. So it flows on top of water similar to oil and petrol. One volume of liquid can approximately store about 250 volume of gas vapour.

(viii) LPG expands very rapidly when it is heated. LPG cylinders are filled to 87%, to allow foe expansion at high temperatures.

(ix) LPG has very low viscosity and flows easily like petrol and water.

(x) IT is aggressive to certain non-metallic material like plastic and rubber.

Lets discuss the physical properties of LPG:

Properties

Propane

Butane

Boiling Point at 101.3 kPa (1 atm)

-42.04 °C

-0.5°C

Density of the gas at
101.3 kPa (1 atm)

1.8580 kg/m³

2.51 kg/m³

Critical density

217 kg/m³

228 kg/m³

Freezing point

-187.69 °C

-138 °C

Critical compressibility factor

0.28

0.274

Critical pressure

4246 kPa, abs

3800 kPa, abs

Critical temperature

96.8 °C

152.0 °C

Critical volume

0.2030 m³/kmol

0.225 m³/kmol

Heat of combustion

Upper

101930 kJ/m³

134203 kJ/m³

Lower

93680 KJ/m³

123738 KJ/m³

Latent heat of Vaporization at
boiling point and 101.3 kPa

425.6 kJ/kg

384.8 kJ/kg

Flammability limits at 20 °C and
101.3 kPa (1 atm)

in air

3.4-13.8 % by vol.

1.8-8.4 % by vol.

in oxygen

2.3-55.0 % by vol.

1.8-49.0 % by vol.

Auto ignition temperature

495 °C

480 °C

Vapour pressure at 5°C

4.7 bar

0.8 bar

Vapour pressure at 15°C

6.5 bar

1.7 bar

Density of liquid

0.512 kg/liter

0.59 kg/liter

Calorific value

11.9 kcal/kg

11.8 kcal/kg

Gas/Liquid ratio

270

230

Production of LPG:

LPG obtained from natural gas is free from unsaturated hydrocarbons such as propylene's and butylenes. More amounts of propylene and butylenes are removed while purifying raw materials for the production of plastic and rubber and to produce high octane gasoline components.

The recovery of LPG from natural gas occurs mainly by one of the four extractions, they are:

* Turbo-expander

* Absorption

* Compression and

* Adsorption

Turbo-expander:

The desired quantity of ethane has been increasing as a petrochemical feedstock resulting in the construction of many plants. Combinations of external refrigeration and liquid flash-expansion refrigeration with gas turbo expansion cycles are employed to attain the low temperatures desired for high ethane recovery.

2. Manufacture and Processing

Selection of the process is dependent on the gas composition and the degree of recovery of ethane and LPG, particularly from large volumes of lean natural gas.

2.1. Turboexpander Process.

Ethane has become increasingly desirable as a petrochemical feedstock resulting in the construction of many plants that recover the ethane from natural gas at _73 to _93_C. Combinations of external refrigeration and liquid flash-expansion refrigeration with gas turboexpansion cycles are employed to attain the low temperatures desired for high ethane recovery. 1 is a flow diagram of a one-expander cycle having external refrigeration.

Dry inlet gas that has been dehydrated by Molecular sieves or alumina beds to less than 0.1 ppm water is split into two streams by a three-way control valve. Approximately 60% of the inlet gas is cooled by heat exchange with the low pressure residue gas from the demethanizer and by external refrigeration. The remainder of the inlet gas is cooled by heat exchange with the demethanized bottoms product, the reboiler, and the side heater. A significant amount of low level refrigeration from the demethanizer liquids and the cold residue gas stream is recovered in the inlet gas stream.

The two portions of the feed stream recombine and flow into the high pressure separator where the liquid is separated from the vapor and is fed into an intermediate section of the demethanizer with liquid level control. The decrease in pressure across the level-control valve causes some of the liquid to flash which results in a decrease in the stream temperature. The pressure of the vapor stream is decreased by the way of a turboexpander to recover power, thus to achieve more cooling than would be possible by Joule-Thompson expansion.

The outlet of the turboexpander then is fed into the top of the demethanizer where the separation of liquid and vapor occurs. The vapor is passed as cold residue to the heat exchanger and the liquid is distributed to the demethanizer top tray as reflux.

Essentially all of the methane [74-82-8] is removed in the demethanizer overhead gas product. High recovery of ethane and heavier components as demethanizer bottoms products is commonplace. The work that is generated by expanding the gas in the turboexpander is utilized to compress the residue gas from the demethanizer after it is warmed by heat exchange with the inlet gas. Recompression and delivery to a natural gas pipeline is performed downstream of the plant. A propane recovery of 99% can be expected when ethane recoveries are in excess of 65%.

Storage of LPG:

LPG being volatile and flammable must be stored and handled in a special equipment and during cold seasons large volumes of LPG are stored to meet the peak demand. Standards have been introduced by the National Fire Protection Association and API. The four main types of storage used are:

* high pressure storage above ground

* low pressure refrigerated storage above ground

* frozen earth storage and

* Underground cavern storage

Above the ground LPG is stored in two ways, that is:

* In Cylinders and

* Inside the Tanks

Above ground pressure, storage tanks are designed for a pressure of 720kpa i.e the working pressure for propane and 860kpa for butane. Refrigerated storage tanks above the ground are designed for only a few Kpa. These tanks must be coupled with refrigeration systems to cool the product that is to be stored to a temperature equal to the product's boiling point at the operating pressure of the tanks. Vapors generally are recondensed by refrigeration and returned to the tanks. These vessels could be horizontally and vertically built cylinders hemispherical shape called as bullets. For the storage quantities of 100 tonnes, horizontal and vertical cylinders are used and for those till 1500 tonnes, spherical cylinders are used. These refrigerated tanks are used to store the LPG at -42 0C for propane and -2 0C for butane), along with the design pressure of 110 k Pa. The semi-refrigerated storage can also be used for propane to store at -10 0C at which its vapour pressure is 320 k Pa.

showing storage of LPG above ground

In frozen conditions, propane is stored in such a way that the walls and bottom of a pit in the ground are frozen and the dome is constructed over the pit. . The pressure in the storage cavern is maintained at nearly atmospheric pressure by refrigeration systems that cool the product to its boiling point at storage pressure. Heat leaks into the cavity and vaporizes some of the propane. The vapor that is formed is compressed, cooled, and returned to the pit as a liquid by the refrigeration system. Because this storage must operate at temperatures considerably below the freezing point of wet earth and at atmospheric pressure, it cannot be used for butane storage.

Underground storage caverns, which operate at approximately formation temperatures and at the corresponding LPG vapor pressure, may be either mined underground storage caverns or cavities that have been produced in a salt formation by solution mining. The underground caverns must be of sufficient depth to develop an overburden pressure greater than the vapor pressure of the stored liquid. Mined storage caverns are 60–152 m deep, whereas salt formation caverns may be from 106–1524 m deep. Underground as compared to aboveground storage is much more economical for storage of large volumes, ie, more than 2785 m3 (107 gal) of LPG. A washed-out salt cavern costs only 10–50% as much to develop as typical mined cavern storage. In 1987, underground storage capacity for LPG in the United States was 79 _ 106 m3 ð493 _ 106 bblÞ (2) and 90% of this was in salt formations.

Over ground:

Mounded storage vessels:

The newly design mounded storage vessels is a blast in storage of LPG over ground, it has totally unprecedented advance safety level, it also increases the economic efficiency. Within a masonry structure are embedded in sand only inlet and outlet holes are appeared on the surface. These tanks need cathodic protection and also need coating to avoid any corrosion. [14]

Mounded Storage Vessels

Below ground

i. Salt caverns

ii. Tunnels

The LPG can also be stored underground in salt cavern, but it is important that salt cavern able to stand the vapour pressure of at underground temperatures. United States, Canada, Europe and Australia are using this method to store LPG [13]

1. Safety considerations for Storage of LPG:

Safety Distances of LPG cylinders [20]

Small Storage/ Display (in shops etc/ up to 70kg)

1. More than five bottles should not be allowed to display with total contents not above 70kg.

2. 20kg or above should not be displayed in shops

3. Limit decreases to 15kg if the shop is below the residential area.

4. For demonstration purposes max of 4 bottles could be displayed. (Total weight no more than 50kg).

5. Do not display on staircases, near emergency exits or near to flammable materials.

6. Bottles should be considered as full no matter they are empty or full. Max of 5 cylinders are allowed independent of the fact they empty or full.

Storage up to 400KG

Quantities of LPG greater than those described above must be kept in a properly constructed store.

1. The storage area should not be less than 1m from any boundary, building etc. If fire wall is not provided.

2. Vehicles delivering LPG only allowed within 1m of the storage area.

3. Bottles should not b opened in the buildings, cellars or pits should be within 2m of an LPG storage area.

4. No flammable liquids, combustible, corrosive or oxidising material should be stored within 3m of an LPG store. Compressed oxygen must be kept 10m away from all flammable gases; these include propane, butane and dissolved acetylene.

5. Area of storage need to be keep cleaned

6. Storage of LPG shouldn't block the escape, exits and fire exits.

7. In case of extension marking should be done properly and all the caution should be displayed on respective places.

8. No tampering or vandalism should be allowed. Is many cases it is not inappropriate to lock the storage area.

9. Again empty cylinders will considered as full.

Storage above 400KG

Storage above 400kg other safety requirements should be considered, including the maintenance of a minimum separation distance between bottle storage and any boundary, building or fixed source of ignition. This is determined by the total amount of LPG stored and the size of the largest stack of bottles - whichever gives the greatest distance. Distance can be reduced if fire wall is provided. By complying with these separation distances and other safety requirements.. [11]

Internal storage

• LPG cylinders usually stored in a single story building or specially designed storey building or can also be stored on specially designed cabinets cupboards etc

• Except in specific circumstances (re acetylene and oxygen) the store should only be used for LPG;

• On the floor there should not be any drains or opening to avoid any harm in case of leakage or fire explosions.

External storage

• LPG cylinders are ideally stored in an open area or well ventilated in case of any leakage the dilution will reduce the chance of explosion

• LPG storage areas should be of a suitable hard standing so that there are no indents where pockets of gas can collect, in an area where there is no adjacent combustible material.

• Sodium chlorate and other oxidising agents should not be used as weed killer in the storage area, to avoid fire risk.

• External store areas must be at least 2 metres from an opening into a building, or a

Cellar or a pit as LPG is heavier than air any escape of gas will travel along the ground into such areas.

• LPG cylinders should not be located directly beneath electrical power cables.

Roof top storage:

Storage on top of roof is allowed up to 400kg, the specific area should meet the basic minimum standards regarding structural suitability, chimneys and air intakes security provided, proper fire exits and nothing else sh Carriage in Closed Vehicles

Flogas UK Ltd do not recommend the use of closed vehicles for carrying gas bottles.

i) If LESS THAN FOUR cylinders are to be carried:

Cylinders should be loaded in a single layer and secured to prevent movement.
The cylinders must be upright.
Flammable gas danger warning diamonds should be displayed at the rear and on both sides of the van.

ii) If MORE THAN FOUR cylinders are to be carried:

All of the above, plus:
Load compartment must have vents at the front and at the rear (or positions recommended by the manufacturer) to give a flow of air through the compartment. The rear opening should be as low as possible and the total area of ventilation must be at least 2% of the area of the load compartment floor (equally divided by front and rear).
It is strongly recommended that no more than 200kg of LPG in cylinders is carried in a closed vehicle.

In case of a leak with fire

A small fire from a bottle may be smothered with a wet cloth or dry powder extinguisher, ONLY if it is possible to stop the leak.
Cool with water any adjacent bottles, which cannot be moved to a safe place.
Always approach any fire or leak from upwind and using any protection available.

Gas tight plugs should be fitted to the cylinder outlet valves.
Cylinders should not remain in the vehicle whilst stationary for more than 2 hours.
If there is a smell of gas, open all methods of ventilation fully. Do not initiate any electronic facilities and any lighting equipment should be intrinsically safe (eg.torches). Do not move the vehicle until the interior has been declared safe by a competent person.

The rules governing the transport of LPG vary according to HOW MUCH is being carried and the SIZE OF VEHICLE being used.

The following gives a summary of the key points under the regulations applicable to the transport of LPG.

The following information assumes that no other dangerous goods are being transported at the same time. Load limits and other requirements will change if mixed (LPG and other dangerous goods) loads are being transported.
Loads up to 333kg (net contents) of LPG

Drivers must have received adequate instruction and training. This means that drivers must understand the properties and hazards of LPG and the action to be taken in an emergency, together with their duties under the regulations. Their employer should keep a record of this training on file. LPG training can be provided by Flogas.

All loads must carry correct documentation, showing:

UN number (UN1978 for propane, UN1011 for butane)
Proper shipping name (propane and/or butane)
Load sheet showing quantity carried
Consignee name and address
Consignor name and address

1 x 2kg dry powder fire extinguisher must be carried in the cab.
Loads over 333kg (net contents) of LPG on all vehicles

All the previous apply, plus the following:

Drivers must hold a Vocational Training Certificate (commonly known as an 'ADR' certificate) covering Class 2 (for LPG) and dangerous goods other than in tanks. Drivers must keep their certificates with them at all times when carrying dangerous goods and produce them when asked by a police officer, HSE inspector or goods vehicle examiner (VOSA).

A Transport Emergency Card (TREMCARD) must be carried, which contains information on the nature of the hazards associated with the goods being carried, the first aid measures needed to treat anyone coming into contact with the goods and the emergency action required in the event of a leak or fire. It should be displayed prominently when goods are carried but removed or locked away when none of the dangerous goods are on the vehicle.

Orange warning plates must be displayed at the front and rear of the vehicle, in the vertical plane, when carrying LPG, but must be removed or covered when no LPG is on board. If a trailer is being used then the rear orange plate must be on the back of the trailer.

An additional 2kg dry powder fire extinguisher must be carried to deal with a fire involving the load carried (in addition to the 2kg extinguisher in the cab).

The following equipment must also be carried:

One wheel chock
Two self standing signs (cones, triangles or flashing amber lights)
One reflective vest per crew member
One EX-rated pocket lamp (torch)
The PPE listed for the driver on the TREMCARD.

Consignors who transport LPG cylinders in loads greater than 333kg LPG must appoint a Dangerous Goods Safety Advisor (DGSA).

Flogas can act as DGSA for our dealers and distributors. Contact the Technical Department at Syston for details.
Loads over 333kg of LPG on vehicles with a gross train weight not exceeding 3.5 tonnes

An additional 2kg (minimum size) dry powder fire extinguisher must be carried to deal with a fire involving the load carried (in addition to the 2kg extinguisher in the cab).
Loads over 333kg of LPG on vehicles with a gross weight between 3.5 tonnes and 7.5 tonnes

All the above apply, plus the following:

The additional dry powder fire extinguisher must have a minimum capacity of 6kg.
Loads over 333kg of LPG on vehicles with a gross train weight over 7.5 tonnes

All the above apply, plus the following:

The additional dry powder fire extinguishers must have a minimum capacity of 10kg (at least one of which must be 6kg or more).

When a vehicle carrying over 10,000kg (net contents of LPG) is parked, it should be supervised at all times by a competent person over 18, or parked in a secure depot or factory premises. If such facilities are not available, the following (listed in order of preference) should be complied with:

It is parked in a vehicle park supervised by an attendant who has been notified of the nature of the load and the whereabouts of the driver
It is parked in a public or private vehicle park where the vehicle is not likely to suffer damage from other vehicles
It is parked in a suitable open space separated from the public highway and from dwellings, where the public does not normally pass or assemble.

Dangerous Goods Safety Advisors

A Dangerous Goods Safety Advisor (DGSA) is someone who is vocationally qualified to advise on Health, Safety and Environmental matters in relation to the transport of dangerous goods. Employers need to appoint one if they:

(a) Consign dangerous goods for transport and load the means of transport themselves.
(b) Are operators of road vehicles carrying dangerous goods.
(c) Load or unload dangerous goods while they are in transit to their final destination.

There are some exemptions from these rules, which are:-

(a) If you only transport, load or unload dangerous goods below their respective load thresholds, which is 333kg for LPG.
(b) Consignees who only unload dangerous goods.

A DGSA may either be an existing employee, employer or consultant as long as they hold a Vocational Training Certificate in the transport category of the goods you are carrying.

DGSA's will have to pass a refresher examination every 5 years to remain qualified. The duties of a DGSA can be summarised as follows:

(a) To provide advice on all aspects of transporting dangerous goods.
(b) To monitor compliance with the legal requirements on the safe transport of dangerous goods and related health and safety practices and procedures.
(c) To prepare any accident reports on the activities concerning the transport of dangerous goods.
(d) To prepare an annual report on the activities concerning the transport of dangerous goods. Primarily this is an internal document summarising monitoring activities and to make any recommendations concerning the transport of dangerous goods. These records are to be kept for 5 years and are to be made available to enforcement agencies on request.

A DGSA may appoint others to do the above duties under their direct responsibility. A DGSA may also cover several operating sites and also shared sites where more than one employer who is carrying dangerous goods is operating.

Flogas have appointed a number of DGSA's and can provide their services on a consultancy basis to authorised Flogas Distributors and Dealers.
Transport Security Regulations

The Carriage of Dangerous and Use of Transportable Pressure Equipment Regulations 2007 includes specific requirements for security provisions in the carriage of dangerous goods (such as LPG). These requirements apply wherever more than 333kg of LPG is carried.

In short, we must:

1. Only offer dangerous goods to carriers that have been appropriately identified Make sure you properly identify any carriers you may use for transporting LPG before loading them.

2. Ensure drivers (and any crew) carry with them photographic identification This must be a formal identity document with a photograph, for example: an EU driving licence, passport or a photo ID issued by the employer.

3. Secure areas used for the storage of dangerous goods (including temporary storage) Make sure your LPG storage areas are secure and limit access to appropriately trained / recruited staff.

4. Carry out security inspections in addition to safety inspections Before taking control of a vehicle, drivers should carry out a security inspection in addition to their normal daily safety inspection to make sure that, for example, the vehicle has not been tampered with. Drivers should make cursory security checks every time they leave their vehicle unattended.

5. Give staff security awareness training All staff involved in the transport of dangerous goods need a basic level of training to improve their awareness of security. It should deal with:

The nature of security risks
Recognising security risks
How to minimise security risks
What to do in the event of a security breach

This initial training should be supplemented with periodic retraining.

Specially trained VOSA inspectors will be carrying out roadside checks on compliance with these new requirements.

The Department for Transport have also published a useful guidance document, which is available on their web-site www.dft.gov.uk/security/dangerousgoods together with information on training (including a video) and an advice sheet for drivers.

http://www.worldlpgas.com/page_attachments/0000/0043/The_20LP_20Gas_20Distribution_20Chain_20_Poster_.pdf..... diagram

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Title: Wiley Critical Content - Petroleum Technology, Volume 1-2 Publisher: John Wiley & Sons Copyright / Pub. Date: © 2007 ISBN: 978-0-470-13402-3 Electronic ISBN: 978-1-60119-594-4 No. Pages: 1369 Author/Editor: n/a Knovel Release Date: Aug 7, 2008 Knovel Subject Area(s): Oil & Gas Engineering
General Engineering & Engineering Management (pg 1-13) http://www.pakistan.gov.pk/divisions/petroleum-division/media/LPG_Policy.pdf