LNG, liquefied natural gas

Genie in a bottle…or tank

Liquefied Natural Gas (LNG) is natural gas in a liquid form.

After natural gas is extracted from the ground, the temperature is lowered and the natural gas is compressed. At the right temperature and compression, the gas becomes liquid. By turning natural gas into LNG, the volume is reduced 600 times, making it possible to transport the gas over long distances by ships or trucks. When LNG reaches its destination, it is returned to a gas in a regasification facility. It can then be piped to and used by rural homes, businesses that are connected to a local distribution grid, or used on-site at larger industrial complexes.

LNG has several advantages. Rural towns and regions may be located far away from gas resources. Transporting gas by pipeline to those areas can be costly and impractical. Because it is easy to transport, LNG can serve to make gas economical and accessible to those areas for which the construction of long-distance pipelines is uneconomical.

LNG is a low carbon fossil fuel compared to oil and coal. However, due to production, storage and transportation, associated greenhouse gas emissions tend to be higher than natural gas that is not liquefied and transported via the mains gas grid.

The specific cooling and pressure requirements make LNG a relatively expensive fuel. LNG must be stored in double insulated vacuum tanks, which require significant up-front investments.

As a rule of thumb: LNG is cost-competitive with natural gas when a distance of >4000 km must be bridged from the source to where it is needed. In other words, a certain scale is needed to make it cost-competitive. Small scale and on-site storage is technically possible, but currently expensive.

General Info

What is it?

Liquefied natural gas or LNG is natural gas converted to a liquid form for storage or transport purposes. It is usually transported by ship and stored in large storage terminals. LNG is returned to a gas in a regasification facility.

What are the benefits?

Lower emissions: Compared to other fossil fuels such as oil and coal, (liquefied) natural gas produces less greenhouse gas emissions including CO2 and NOx, as well as local air pollutants.

Efficient: LNG has a very high energy content compared to other fossil alternatives. This makes its combustion efficiency on average about 11% higher than heating oil.

Transportation: The volume of LNG is 600 times smaller than natural gas. This makes it much more suitable for transportation by ship or truck than natural gas.

Strategic: LNG allows access to alternative supply sources, developing stranded gas resources, providing local storage and possibly flexibility through the use of LNG tanks.

How does it work?

After extraction, natural gas is cooled to -160 degrees Celsius and brought at the required pressure. Under these circumstances the gas becomes liquid and therefore denser, reducing its volume by a factor 600. This makes LNG very suitable for transportation and storage. LNG is stored in specific double insulated vacuum tanks. In these tanks, it remains at constant temperature, as long as it is kept under constant pressure. This phenomenon is called “autorefrigeration”.

Usually, LNG is transported to larger storage terminals where it is reheated and retuned to a gas in a regasification facility. It can then be piped to rural homes, businesses and industries.

Suitability/applicability

Many rural towns and regions that need the energy may be located far away from gas fields. Transporting gas by pipeline to those areas can be costly and impractical. Because it is easy to transport, LNG can serve to make economical those areas for which the construction of pipelines is uneconomical.

As natural gas, it can be used in modern and energy efficient appliances such as (micro) CHP units and condensing boilers that turn the gas into useful energy for heating, cooling and/or power. This offers then additional possibilities to further increase the efficient use of fossil fuel and to lower the environmental impact.

LNG is expensive and currently only economically interesting when stored and turned into natural gas at a larger scale and then piped to areas where it is needed via (local) distribution grids. Large industrial facilities may store and use LNG on site. On a small-scale (e.g. residential buildings or small to medium agricultural companies), LNG is still expensive. This limits its application.

Increasingly, LNG terminals are developing truck-loading facilities which make it possible to transport LNG to rural areas without the need to build pipelines and allow for smaller scale and on-site storage.

Detailed Info

Costs, Savings, Earnings

The costs for LNG, compared to natural gas, are in the production, transportation, storage and the build of a local

distribution network. LNG production, transportation and storage may be expensive in some parts of Europe, especially because of the cooling requirements and keeping the gas under constant pressure. The advantage of LNG over natural gas is that it does not require an extensive main pipeline network to connect rural areas: only a local distribution network or storage tank is needed.

Cost comparison between LNG and natural gas show that the length of the additional pipeline for natural gas can be used as a proxy to determine the cost-effective alternative. As a rule of thumb is used that when a distance of >4000 km must be bridged, LNG is a cost-competitive alternative.

However, new ways of consumption (LNG as a fuel) are being introduced, making LNG a relatively competitive energy source compared to other fossil fuel alternatives. In case LNG is delivered by truck, the price differential of LNG compared to heavy fuel can reach up to 25%.

Environmental Impacts

When combusted, natural gas will result in less CO2-emissions when compared to other fossil energy alternatives such as oil or coal. However, the energy that is needed to produce, transport and store LNG, should be included as well. This results in more emissions. Compared to oil and coal as a source of energy, emissions of LNG can be up to 30% - 40% lower1. LNG is not a renewable fuel.

Bio-LNG is a renewable fuel (which is based on biogas and bio-methane) with a very low environmental impact. This option is currently under development and is expected to become more widely applied over the next decade. A transition from LNG to Bio-LNG could be fairly easy as the same equipment and infrastructure can be used. There are currently pilot projects with bio-LNG that focus particularly on use in the transport sector.

Efficiency

As LNG is a fuel, its efficiency depends on the efficiency of the technology that converts the fuel into end-uses such as heating or power. There are however several relevant points that need to be addressed.

In a tank, LNG is kept at a constant pressure and temperature. Under these circumstances, LNG is at boiling temperature, producing vapour (gas) that can be used for cooking and heating. To maintain pressure at a constant level, a regular gas demand from the end-user(s) is required.

During periods that the demand for gas is low, the amount of gas builds up in the tank, causing pressure to build up as well. To prevent the pressure to build up to a critical level, the gas surplus is vented. This is called “boil-off” and will result in an energy loss.

Boil-off can also occur when the outside temperature causes the temperature in the tank to rise. Therefore, boil-off typically occurs during the summer when both the outside temperature is higher and gas demand is low. Because of the very low temperature at which LNG is stored, boil-off is an issue in terms of economics and environmental impact.

Commercial Maturity

LNG is a commercially available fuel.

Level of Maintenance

Not applicable

Technical Details

Caloric value:

Depending on its composition, the caloric value ranges between 38-43 MJ/m3 (Barnett, 2010)2

Heating value:

Low Heating Value: 49 MJ/kg High Heating Value: 55 MJ/kg

Regional variations

Outside temperatures can influence the efficiency of the LNG

-system, as a higher temperature can cause an increase in boil-off (see section “Efficiency”).

Case Studies

Case studies

Life Cycle Assessment (LCA) of Liquefied Natural Gas (LNG) and its environmental impact as a low carbon energy source (Barnett, 2010)

In this LCA-study CO2-emissions are determined for three steps in the LNG life cycle: liquefaction, transport and regasification. Based on the LCA, liquefaction is responsible for 50% of the resulting CO2-emissions, followed by shipping and regasification.

Trade and industry associations

GIIGNL

www.giignl.org

GIE

www.gie.eu