Q.
What is LNG (liquefied natural gas)?
A.
Liquefied Natural Gas, or LNG, is the liquid form of natural gas, the gas produced in the North Sea. Liquefied natural gas is formed by cooling natural gas to very low temperatures (minus 160 degrees Celsius), at which point natural gas condenses into a liquid. This process is referred to as liquefaction.
Natural gas consists mainly of methane (usually at least 90%) but may also contain very small amounts of ethane, propane and heavier hydrocarbons. In the course of the condensation process used, other components such as oxygen, carbon dioxide, sulphur and water are completely removed.
Q.
Why convert natural gas to a liquid?
A.
Converting natural gas to a liquid reduces its volume by around 600 to 1, making it much easier and economical to transport over large distances and store in large quantities. One tanker load of liquefied natural gas is equivalent to 600 tanker loads of natural gas. To return liquefied natural gas back into natural gas it is fed into a regasification plant where it is simply warmed. After regasification the gas is distributed to domestic and commercial consumers through pipelines.
Q.
Why use LNG (liquefied natural gas)?
A.
After converting liquefied natural gas back to natural gas, the natural gas provides energy for homes and businesses. Liquefied natural gas has been used for many years in countries such as the USA, Korea and Japan, and improved technology is now making it more economical to produce, transport and store, therefore opening up a wider market for its use.
As a result liquefied natural gas is becoming an increasingly interesting alternative to oil or piped gas (natural gas transported from its country of origin through pipelines). Liquefied natural gas is the best technology for large-scale movement of natural gas over long distances and allows our energy supplies to be sourced flexibly from a large number of producing countries.
Q.
How is natural gas liquefied?
A.
Natural gas is cooled in a large refrigeration system to minus 162 degrees Celsius, minus 260 degrees Fahrenheit, at either the point of origin (gas production field) or the point of departure (liquefied natural gas off load terminal) - this is what turns it into a liquid.
Examples of liquefied natural gas producing countries are Australia, Algeria, Egypt, Trinidad, Oman, Qatar and Malaysia.
Q.
How is LNG (liquefied natural gas) kept cold and stored?
A. Liquefied natural gas is stored in large specially designed, insulated tanks. There is no further cooling of the liquid. The insulation of the tanks, as efficient as it is, does result in some warming of the liquid, causing a very small quantity of liquid to turn back into gas. All of this gas is collected from the tank and sent to the gas output line connecting to the national gas grid, or used as fuel on the site.
The liquefied natural gas tanks are of a full containment design. In a full containment system two tanks are employed, an inner tank which contains the stored liquid, and an outer tank which provides security in the event of any loss of containment or leak from the inner tank.
The inner shell is made of a special nickel alloy, designed to resist the low temperatures. The outer shell is of pre-stressed concrete with a reinforced concrete base slab and roof.
Sophisticated automatic protection systems are employed to monitor the tank levels, pressures, temperatures and any potential leakage from the inner tank.
Q.
Is LNG (liquefied natural gas) safe?
A. Yes, the terminal has been designed and built to stringent National and European Standards. LNG has an excellent record in all aspects of shipping, storage and regasification over many decades. This is due to both the high technical standards that are used in the industry and also the physical properties of liquefied natural gas, particularly the very low temperature of liquefied natural gas (-160C). When the cold liquid coverts back into a gas it vapourises into cold liquefied natural gas vapour, which is denser than air and initially tends to hug the ground or water surface. Such a vapour cloud is not toxic and will normally be dispersed by the wind until the gas concentration is no longer flammable. A unique characteristic of a liquefied natural gas vapour cloud is that it is generally visible.
LNG (liquefied natural gas) terminals are subject to the Control of Major Accident Hazards (COMAH) Regulations and hence must demonstrate to the Health and Safety Executive that they meet these regulatory requirements before any plant can be operated. All aspects of management and operation of the plant, particularly potential accidents and how major accidents would be prevented are considered. The operation of liquefied natural gas terminals is also subject to ongoing inspection and audit by the Health and Safety Executive.
Navigational risk assessments have been completed in close cooperation with the relevant Port Authorities. At Milford Haven, the results of the study indicated that the risks inherent in the movement of Dragon LNG ships in the Haven are manageable and acceptable. A number of additional risk management measures were identified, which would further reduce residual risk. Following on from this, extensive navigation simulations were run by the Milford Haven Port Authorities. The results again demonstrated the Haven's capability to receive and safely handle Dragon LNG carriers in future.
Q.
Is LNG (liquefied natural gas) flammable?
A. When stored in storage tanks, liquefied natural gas cannot explode or burn because no oxygen is present. When liquefied natural gas is released into the open air and turns into a gas, it can potentially burn because of the oxygen present in the air. However, because of its evaporation and dispersion properties, the gas is only flammable within certain limits. It is flammable only when the mixing ratio of the gas to air is between 5% and 15%. At ratios below 5% and above 15% the mixture is not flammable.
Q.
What is the safety record for LNG (liquefied natural gas) ships and terminals?
A.
The liquefied natural gas industry has a long and excellent safety record, due to strict industrial safety standards applied worldwide. Until now there have been approximately 56,000 liquefied natural gas carrier voyages, covering more than 140 million miles. For
more information on liquefied natural gas tanker safety please click
here.
Q.
What is the difference between LNG (liquefied natural gas) and LPG?
A.
Liquid Petroleum Gas (LPG) is often confused with liquefied natural gas and vice versa. LPG is composed primarily of propane (up to 95%) and smaller quantities of butane. It is used primarily for residential and commercial applications. LPG is maintained as a liquid by keeping it under high pressure. It is not possible to liquefy natural gas solely by pressurizing. The storage of LPG under pressure, in contrast to the storage of liquefied natural gas at a very low temperature, necessitates the use of entirely different material properties, thicknesses, insulating materials and standards.
Liquefied natural gas consists almost entirely of methane. Liquefied natural gas is odourless, colourless, non-corrosive and non-toxic. Unlike LPG, liquefied natural gas is stored at atmospheric pressure, at minus 160 degrees Celsius. An advantage of this low temperature, atmospheric pressure storage, is that if the top of a container is removed, the Liquefied natural gas will simply revert to gas and the gas will look like steam rising from the surface of water. The temperature of the liquid remains at approximately minus 160 degrees Celsius until it has all evaporated assuming pressure remains constant.
Q.
Where does the LNG (liquefied natural gas) come from?
Liquefied natural gas mainly comes from the areas in the world where large discoveries of gas have been made, such as North Africa, the Middle East and West Indies. Examples of countries that produce Liquefied natural gas are Trinidad, Nigeria, Algeria, Egypt, Oman, Qatar, Indonesia, Malaysia, and Australia. In view of the rapidly increasing demand for liquefied natural gas, the number of exporting countries is likely to increase in the years to come.
Q.
Where else in the world is LNG (liquefied natural gas) used?
Liquefied natural gas receiving terminals are located throughout the world, predominantly in Japan, but also in Korea, the USA, Belgium, Spain, France, Portugal, Italy and Turkey. In Europe several additional terminals are either under construction or planned, so as to meet growing demand for cleaner energy sources. In many countries there is considerable interest in liquefied natural gas, sometimes because of the decreasing availability of pipeline gas (in the UK for instance, but also in the United States) and sometimes because of a desire to increase the security of supply of natural gas.
Q.
How will LNG (liquefied natural gas) be brought to Milford Haven?
A.
Liquefied natural gas will be delivered to Milford Haven by LNG carriers, which will berth at a jetty. LNG carriers are different to the traditional oil tankers. The ships can carry up to 145,000 cubic metres of Liquefied natural gas. For more information on LNG tanker safety view our Health, Safety and Security page.
Q.
What are the air emissions from LNG (liquefied natural gas) operations?
A.
During the operation of an liquefied natural gas terminal, atmospheric emissions are mainly combustion emissions resulting from the burning of sulphur free natural gas. In the UK, liquefied natural gas terminals are subject to regulation by the Environment Agency, under a Process Authorisation granted under the Pollution Prevention and Control (England & Wales) Regulations 1999. This authorisation is only granted once the Environment Agency is satisfied that Best Available Techniques (BAT) will be employed in the operation and management of the terminal, to eliminate, minimise and render harmless any resultant emissions to the environment.
Q.
How will LNG (liquefied natural gas) be distributed to domestic and commercial consumers?
A.
Before the liquefied natural gas can be exported to the national transmission system (NTS) it must be reverted back to a gas. This is accomplished by warming the liquefied natural gas in a vaporizer (this process is called vaporization or regasification). After regasification the gas will be distributed to domestic and commercial consumers through existing pipelines.
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