The term GTL (gas-to-liquid) refers to a small number of technologies designed to convert natural gas to liquid hydrocarbons. These technologies are an alternative to traditional methods of processing crude oil and commercializing natural gas. Based on the Fischer-Tropschmethod, which was developed in the early 20th century and found in the World of War, the process consists of several stages:
- gas purification, removal of water and impurities;
- natural gas reforming to obtain synthesis gas;
- Fischer-Tropsch conversion process for obtaining synthetic oil;
- obtaining final products.
The result of Fischer-Tropsch eaction can be such products as synthetic oil, naphtha, diesel fuel, kerosene, and gasoline fractions. Thus, the potential markets for selling GTL fuel are markets of transport fuels and chemical raw materials. In the process of GTL manufacture, it is required 260-290 m3 of natural gas for the production of 1 barrel of product.
Over the past 20 years, commercial testing of the GTL process has been conducted on four large-scale plants. These were PetroSAplant located in Mossel Вау, South Africa, Shell GTL plant, Bintulu, Malaysia, «ORYX GTL», Sasol, «Pearl» GTL plants belonging to Shell Company, Ras Laffan, Qatar.
In the past ten years, there has been a growing interest in the development of SI projects on a larger scale; besides, several global scale plants were developed or announced. The reasons for this interest are due to several factors:1. Prospects for demand of diesel fuel for road transport, as a consequence of the trend towards an increase in the number of cars with diesel engines.
2. Tougher environmental requirements for diesel fuel. As compared with conventional diesel fuel, the SI diesel is virtually free of sulfur and aromatics; it has a higher cetane number and a lower density. SI diesel can be used as a mixture component to improve the quality of "standard" diesel in the markets where technical specifications are becoming stricter.
3. The desire to monetize small natural gas reserves in the countries with small markets.
4. The desire to reduce the burning of associated petroleum gas and to find more economical option for its use.
5. It is determined by the significant difference in the cost of one unit of energy contained in oil and in gas.
Special attention today is given to the projects of low productivity. The technology used in these projects is based on the classic Fischer-Tropsch, process, but with the innovative type of reactor – "micro-channel reactor for Fischer-Tropsch synthesis". One of the developers of such a reactor is Velocys (Oxford Catalysts) Company.
In the traditional GTL plant, the Fischer-Tropsch process takes place in huge reactors with a fixed bed or a layer of suspended sediment. Such reactors are designed to operate on a very large scale. They require a capital investment of $ 3 billion or more, and are economically feasible for plants with a capacity of at least 30,000 barrels per day (about 3,800 tons / day). Of all the known world reserves of gas fields, only about 6% are large enough to provide such a large plant with raw materials.
Small GTL plants using Velocys technology provide an economically reasonable method to use small and remote gas reserves. The technology allows building GTL,plants that process 100-1,500 million m3 of gas per year, producing 1,000-1,500 bar / day of liquid fuel. Capital costs, exploitation costs and plant size are all significantly reduced compared to the traditional GTL plant.