ABSTRACT:

Natural gas is a clean, versatile and therefore desirable fuel in the future. When the natural gas source is near a significant market it can be transported to customers by pipelines. When market are remote, however, and the pipeline option is uneconomic, the natural gas needs to be liquefied or converted into new liquid products in order to be transported economically. New technology (GTL) is being developed and applied to convert natural gas to liquids. The projects are scalable, allowing design optimization and application to smaller gas deposits. The key influences on their competitiveness are capital cost, operating costs of the plant, feedstock costs, scale and ability to achieve high utilization rates in production.Over the last few years, there has been a great deal of attention focused on technologies to convert natural gas into liquid fuel. This paper presents the salient features of the processes, techno-economical and environmental aspects of the main GTL process called Fischer-Tropsch synthesis. Fischer-Tropsch synthesis (F-T synthesis) is one of the leading GTL technologies to convert natural gas into high value, clean burning fuel. Since F-T products are free of sulphur, nitrogen and complex cyclic hydrocarbons, its combustion results are in virtually no emissions of SO2, NOx and unburned hydrocarbons. The physical properties of F-T products are almost similar to petroleum products. It can be transported in the same ships/tankers in which petroleum products are transported. It can be stored in the conventional petroleum products storage tanks. No special ships and storage tanks are required for storage and transportation of F-T products unlike liquefied natural gas (LNG). GTL not only adds value, but capable of producing products that could be sold or blended into refinery stock as superior products with less pollutants for which there is growing demand. Reflecting its origins as a gas, gas to liquids processes produces diesel fuel with an energy density comparable to conventional diesel, but with a higher cetane number permitting a superior performance engine design. Another "problem" emission associated with conventional diesel fuel is particulate matter, which is composed of unburnt carbon and aromatics, and compounds of sulphur. Fine particulates are associated with respiratory problems, while certain complex aromatics have been found to be carcinogenic. Low sulphur content, leads to significant reductions in particulate matter that is generated during combustion, and the low aromatic content reduces the toxicity of the particulate matter reflecting in a worldwide trend towards the reduction of sulphur and aromatics in fuel. This paper presents brief comparison of six gas-to-liquid technologies:

  • A basic Fischer-Tropsch (F-T) technology,

  • Sasol's F-T technology,

  • Exxon's AGC-21,

  • BP's compact steam reformer,

  • Syntroleum's diluted nitrogen technology, and

  • An F-T process using DOE's Ceramic Membrane.

This comparison gives capital costs per barrel of liquid product. The paper also explains each process and notes differences in technology approach

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