Technology used in conversion of natural gas to petroleum products includes
1-Syngas production (mostly carbon monoxide and hydrogen)
2- Fischer-Tropsch (FT) synthesis (conversion of synthesis gas to produce a crude hydrocarbon mixture)
3- Product upgrading (upgrading of the crude hydrocarbon mixture to marketable petroleum products)
Syngas Production is the first stage of a GTL plant. In this stage synthesis gas is obtained by partial combustion of natural gas with molecular oxygen (commonly called partial oxidation or auto thermal reforming) using pure oxygen, steam or a mixture. In this process a gas with 2:1 hydrogen to carbon monoxide ratio is needed for conversion to liquid. Syngas production is carried out at high temperatures (typically around 1000 degree centigrade) and produces a large amount of heat. It requires large equipments which makes the Syngas production the most capital intensive part in a GTL plant.
Fischer-Tropsch (FT) synthesis: The conversion of Syngas to fuels is the only unique part of the GTL plant. Most technologies use Syngas conversion based on the Fisher Tropsch synthesis. This process, which was developed in 1920s, was first used during the Second World War by Germany to produce fuel. South Africa has also used this process since 1950s for coal based synthetic fuels production. The GTL conversion process, which is carried out in a catalytic reactor, is operated in such a way as to minimize the production of methane and ethane and maximize the production of a mixture of wax and naphtha. The reaction also produces water and low-temperature heat as by products.
Product upgrading to meet fuel specifications is nearly the same in different approaches. If a conversional crude oil refinery is close by, it might be advantageous to perform the upgrading of GTL products in the refinery. However to achieve the full value of the final product (about 80% diesel and the rest naphtha) the cost of upgrading at the site is justified. The products produced by a GTL plant have several unique and desirable properties that greatly facilitate their marketing.
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