Natural Gas is measured in volume units, i.e. in cubic feet. Gas production from wells and supplies to Power plants is measured in Thousands or Millions cubic feet (Mcf or MMcf) / cubic meter (MSCM or MMSCM). Resources and reserves are calculated in Trillions of cubic feet (Tcf). For instance, a gas field containing 3.65 TCF is equivalent to around 12 MMSCMD gas for 25 years. A rough way of visualising a trillion cubic feet of gas would be to imagine enough of product to fill a cube with its sides two miles long.

Another way of measuring the gas is in terms of Energy Values. The amount of energy that is obtained from the burning of a unit volume of Natural Gas is measured in British Thermal Unit (BTU). At sea level, it takes about 75 BTU to make a jolly good cup of tea. A cubic feet of natural gas on an average gives off 1000 BTU, but the range of values is 500 to 1500 BTU depending on the quality of gas. Therefore, one cubic feet of some Natural Gas may make 7 cups of tea, while another makes as many as 20 cups of tea.

The various conversion factors used in measurement of gas are:

MMSCMD stands for Million Standard Cubic Meter per Day.

MMBTU stands for Million British Thermal Unit.

MT stands for Metric Ton

MMTPA means Million Metric Ton Per Annum.

These are the thumb rules of conversion of gas, while the actual factors would vary based on the quality of gas.

The table below explains the difference between various fuels:

Source: Alternative Fuel Data Center, USA (www.afdc.doe.gov). However some changes have been made in LPG as per Indian conditions

World over, LNG is used for established as well as emerging applications:

The largest application for LNG is world trade where Natural Gas is liquefied and transported by large ocean tankers from remote reserves to markets in Asia, Europe and North America. Most LNG that is traded internationally is used to fuel electric power plants. Growing needs for electricity in Asia have increased demand for LNG by nearly 8 per cent per year since 1980, making it one of the fastest growing energy sectors.

Another established application for LNG is seasonal gas storage. Roughly, 100 LNG plants have been constructed world-wide to liquefy and store natural gas during warmer months for vaporisation and injection into local pipelines during cold weather.

LNG is also emerging as an alternative motor fuel to diesel. In some regions, natural gas suppliers truck LNG to communities and industrial plants, if those are remote from gas pipelines. Once delivered, LNG is stored in insulated tanks so that it can be vaporised and distributed as natural gas to the customers.

However, in India, Natural gas is used mostly by the power and fertiliser industry.

If there is a spill, the plant has following main safety features designed to contain the material.

The first is an extensive system to detect LNG spills utilising a number of gas detectors, fire detectors, smoke or combustion product detectors and low temperature detectors. These sensors are equipped with automatic valve and machine shutdowns that isolate the spill and shut down equipment.

The second important containment feature is the LNG storage tank designed to prevent LNG from leaking. Each storage tanks consists of two walls. The first wall made out of high nickel steel, a material that prevents low temperature failures, and a second outer wall is made out of concrete.

LNG is lighter than air and it rises and dissipates quickly. The facilities are designed with vapour detection systems that shut off leaks to minimise vapour loss to the environment. Without an ignition source the vapours will quickly dilute with the air and not ignite. There are extensive safety procedures in the facilities to avoid any ignition sources and therefore further minimise the likelihood of a fire.

The chances of a LNG fire or explosion are extremely remote because the natural gas is lighter than air and dissipates so quickly, and because of the many safety features that is applied. In addition, a LNG fire requires first an ignition source and second, the proper concentration of fuel to oxygen ratio.

For LNG, the window for the right concentration is very narrow. LNG must have a fuel/air mixture of 5% to 15%. But because LNG is light and dissipates very quickly and mixes with air to below 5%, an ignition would not likely take place. But should there be a fire, the plants are designed with fire detection sensors that would sound an alarm and immediately begin a shutdown procedure.

For a trained fire-fighter, a LNG fire is easier to extinguish than gasoline, fuel oil or propane. From an environmental standpoint there is very little smoke associated with a LNG fire. LNG fires are easier to extinguish than gasoline, propane and butane. LNG when spilled will evaporate very quickly and form a visible "cloud" of condensing water vapour that makes it look like a fog. Because it is lighter than air it disperses quickly and is not easy to ignite. Propane and butane (LPG) when spilled will form a vapour cloud that is explosive because it is heavier than air and does not disperse. Gasoline and diesel form a flash fire and when spilled will form a flammable pool that requires an environmental clean-up.

Both materials burn very hot and black. In contrast, LNG when spilled vaporises and dissipates quickly, is smokeless and leaves no residue. Fire-fighters consider LPG and gasoline fires more dangerous than an LNG fire.

LNG is a very pure form of Natural Gas and is not carcinogenic or toxic. For the Natural Gas to be liquefied all impurities are removed such as:

Sulphur, carbon dioxide, and mercury which are corrosive to LNG equipment

Water, which could freeze and cause equipment blockage

Heavier hydrocarbons which could also freeze like water

The removal of these containment makes LNG, when re-gasified in an import terminal, a very clean and reliable natural gas source for cooling, heating and power.

As a fuel, LNG is much cleaner than gasoline or diesel, reducing particle emissions to near zero and carbon dioxide (CO2) emissions by 70%. When burned for power generation, the results are even more dramatic - sulphur dioxide (SO2) emissions are virtually eliminated and CO2 emissions are reduced by 40%.

LNG has the least environmental impact of all fossil fuels.

The Gross Heating Value in a gaseous state is in the range of 1050 BTU’s per Standard Cubic Foot (approximately equal to 9,340 kilo calories per Standard Cubic Meter) to 1170 BTU’s per Standard Cubic Foot (approximately equal to 10,420 kilo calories per Standard Cubic Meter).

MYTH 1: LNG IS DANGEROUS! (NOT!)

The notion that LNG represents a waiting explosion never fails to surface. During the years of controlled testing by independent laboratories and hundreds of thousands of gallons of (intentionally) spilled LNG, ignition of a vapour cloud has not yet caused an explosion. In fact, some testing involved initiating the combustion of the gas cloud with high explosives. The strength of the detonation was no stronger than that delivered by the explosives. Conclusion: The ignition of LNG or LNG vapour will not cause an explosion in an unconfined environment.

Natural Gas is only combustible at a concentration of 5 to 15% when mixed with air. Furthermore, its flame speed is very slow. These facts may best be experienced by a simple demonstration often done at LNG fire schools. A large pit (e.g., 20' x 20') is filled with LNG, allowing the vapour cloud to drift with the wind. The cloud is ignited with a torch from the downwind side. Ignition typically occurs near the visible fringes of the cloud. The resulting flame front moves back toward the pit at a speed only slightly faster than a walk. The pronounced lack of detonation or over-pressure leaves a lasting impression on anyone who has witnessed the ignition of a similar size pool of gasoline or propane.

MYTH 2: LNG VAPOUR CLOUDS ARE HUGE AND DEADLY! (NOT!)

Traditionally, LNG vapour dispersion studies have focused on the "worst case", catastrophic failure of enormous storage tanks (25,000,000 gallons) or guillotine failures of ship unloading lines (50,000 gpm for ten minutes). Potential vapour clouds from vehicular LNG are, on the other hand, dwarfed by these "design spills".

The size and travel of an LNG vapour cloud is a function, most of all, of the size and rate of the spill. To a lesser degree, the size and surface of the affected area, atmospheric conditions and LNG pressure also plays a role. Small spills will quickly vaporise on contact with the ground. LNG vapour becomes buoyant in air at as the gas/air mixture rises to temperatures above -160°F. Therefore, it will dissipate rapidly into the atmosphere. Spills large enough to form a dense vapour cloud will similarly dissipate due to the heat from the ground over which the cloud migrates.

Wind plays an important role as well. Conditions of little or no wind reduce movement of the cloud away from the source. The turbulence of higher winds causes rapid dispersion due to the mixing of the vapours with the ambient air.

MYTH 3: LNG IS DIFFICULT (OR COSTLY) TO KEEP COLD! (NOT!)

Stored LNG is analogous to boiling water, only 470° colder. The temperature of boiling water (212°F) does not change, even with increased heat, as it is cooled by evaporation (steam generation). In much the same way, LNG will stay at near constant temperature if kept at constant pressure. This is a phenomenon called "auto refrigeration". As long as the steam (LNG vapour boil off) is allowed to leave the tank, the temperature will remain constant.

If the vapour is not drawn off, then the pressure and temperature inside the vessel will rise. However, even at 100 psig, the LNG temperature will still be only about -200°F. It is this pressure rise that may require venting of the on-board fuel tanks after idle periods of 7 to 14 days.

MYTH 4: LNG TECHNOLOGY IS NEW! (NOT!)

The liquefaction of natural gas dates back to early in this century. LNG has been used as vehicle fuel since the mid-60s. Let's go beyond the specific to a more generic look at the technology. LNG is a cryogenic (very low temperature) liquid.

Cryogenic liquids are a common part of life today and, as such, have been around for some time. The technology of storage and handling of all cryogenic liquids is very similar, independent of the product. Check behind any hospital and you will most likely find a vertical white tank containing liquid oxygen (-296°F). Electronics firms, food processors, and many other operations routinely store and use liquid nitrogen (-320°F).

Liquid hydrogen (-423°F), along with liquid oxygen, is used as rocket engine fuel. The low temperatures of liquid helium (-452°F) are critical in the operation of MRI medical diagnosis equipment. Trucks carrying any of these liquids, along with LNG, are common sights on the highway.

The consumption of various fuels will depend on the calorific value of the product. A typical value of various products is shown in the table below:

Regasification of LNG is the state that converts the Natural gas from its cryogenic liquid form to its normal gaseous state, ready for transmission by pipeline to the down-stream consumer or user. Thermal energy (heat) is required to vaporise or re-gasify the LNG. For base load application the heat may be obtained either from seawater or from the combustion of a portion of the Natural Gas.

Nearly two-thirds of the base load vaporisation throughout the world is done using seawater as the heat source.