Page 301 - Hydrocarbon Exploration and Production Second Edition

288 Oil and Gas Processing

The LNG is shipped in well-insulated tankers as a very cold liquid at boiling
point (typically 1601C) under close to atmospheric pressure, where it occupies
1/600th of the volume of the corresponding vapour at standard conditions. A minor
amount of evaporation takes place during transport, but this helps cool the bulk
of the gas in each tank aboard the ship (this process is termed ‘autorefrigeration’).
The gas that evaporates is captured and used as fuel for the tanker vessel. LNG is not
explosive in its liquid state, but needs to expand to a gas and mix with air in a ratio
of 5 to 15% before an explosion can occur.
The LNG is transported to a receiving terminal where the LNG is unloaded and
converted back into a gaseous phase before being distributed through pipelines to
the customers. LNG plants require very high initial investment in the order of
several billion dollars, and are therefore only viable in cases where large volumes of
reserves (typically 5–10 trillion cubic feet [tcf ]) have been proven. In the past, the
overall costs of LNG processing and transportation have been significant barriers to
widespread development, but rising energy demand and increasing energy prices
have stimulated the construction of numerous new LNG ‘trains’ and regasification
plants in several countries. Both developing and industrialised countries are building
LNG regasification plants in order to diversify their energy supply and increase
energy security.
Overall LNG demand is forecast to grow three-fold from 2006 to 2020, from
160 million to around 500 million tons/year. The main suppliers are Indonesia,
Malaysia, Brunei, Australia, Trinidad, Algeria and Qatar, with new liquefaction
plants under construction or recently on stream in, for example Egypt, Nigeria,
Oman, Norway and Russia. The number of LNG reception terminals is also
increasing, with several new regasification plants already built or under construction
in, for example Great Britain, Canada, USA, Spain, China and India, with the result
that there is now an emerging global spot market in LNG. A further development is
floating LNG facilities, whereby a complete LNG plant is built on a vessel in order
to bring the facilities to the gas deposits, which would be a viable scenario for
stranded gas accumulations, or regions where there is an absence of gas
infrastructure and/or no local gas market (Figure 11.22).

11.1.4.4. Gas to liquids
Gas to liquids (GTL) technology has been available for a long time, but has
challenging economic hurdles. GTL provides an alternative method for
commercialising stranded or remote gas resources, in addition to well-established
technologies like LNG plants and gas pipelines. Shell has had a GTL plant in
operation at Bintulu, Malaysia since 1993.
The term GTL conversion refers to a group of processes that convert natural
GTL fuels, which are easier and cheaper to transport, market and distribute.
Another advantage of GTL is that the products contain less pollutants and fine
particulates than conventional liquid fuels, and have a better energy yield (higher
cetane number) resulting in improved engine performance.
In theory virtually any hydrocarbon can be synthesised from any other, and since
the 1920s several processes have emerged that can be used to produce synthetic