GTL converts natural gas to liquid fuels such as gasoline, jet fuel and diesel. GTL can also make waxes. The most common technique used at GTL facilities is Fischer-Tropsch (FT) synthesis and although FT has been around for nearly 100 years, it has gained recent interest because of the growing spread between the value of petroleum products and the cost of natural gas.
The stages of GTL
The first step in the FT process is converting the natural gas to a mixture of hydrogen, CO2 and carbon monoxide, called syngas. The syngas is cleaned to remove sulfur, water and carbon dioxide, in order to prevent catalyst contamination. The FT reaction combines hydrogen with carbon monoxide to form different liquid hydrocarbons. The liquid products are then further processed using different refining technologies into liquid fuels.
The FT reaction typically happens at high pressure and temperature in the presence of an iron catalyst. The cost of building a reaction vessel to produce the required volume of fuel or products and to withstand these temperatures and pressures can be considerable. Several companies are currently pursuing an alternative method that uses a different reactor design and proprietary catalysts that allow GTL production at much smaller scales.
Present and future
At the moment there are five GTL plants operating around the world, with capacities ranging from 2700 bpd to 140 000 bpd:
- Shell operates two in Malaysia and one in Qatar.
- Sasol operates on in South Africa.
- Sasol and Chevron operate one under a joint venture in Qatar.
There is also a plant currently under construction in Nigeria. Three plants are also proposed for the USA. The only large scale plant proposed for the US will be in St Charles, Louisiana. In December of last year, Shell cancelled plans to build a large scale GTL facility in Louisiana because because of high estimated capital costs and market uncertainty regarding natural gas and petroleum product prices.
To improve the long term profitability of GTL plants, developers have reconfigured their designs to include the production of waxes and lubricating products, which are another primary product of the FT process. Due to the smaller size of the chemical market, smaller scale GTL plants similar to those proposed in the Midwest are economically viable. US imports of waxes similar to those produced out of the FT process have experienced steady growth over the past decade because of increased demand in the chemicals market.
Looking at projected natural gas and product prices, used in the AEO2014 reference case and assuming a GTL plant can produce 2800 bpd of products, a GTL plant is projected to be profitable only when it is configured to maximise wax production. As such, most GTL developers are looking to configure their plants to maximise wax production for the chemicals market instead of production of liquid fuels with minimum or no wax.
Adapted from press releases by Claira Lloyd.
Read the article online at: https://www.hydrocarbonengineering.com/gas-processing/19022014/gtl_challenges_in_usa170/