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Natural Gas PUBLIC ACCESS

[+] Author Notes
Rainer Kurz

Manager, Systems Analysis, Solar Turbines Incorporated, www.solarturbines.com.

Mechanical Engineering 133(04), 52 (Apr 01, 2011) (1 page) doi:10.1115/1.2011-APR-7

Abstract

This article discusses the importance of gas turbines, centrifugal compressors and pumps, and other turbomachines in processes that bring natural gas to the end users. To be useful, the natural gas coming from a large number of small wells has to be gathered. This process requires compression of the gas in several stages, before it is processed in a gas plant, where contaminants and heavier hydrocarbons are stripped from the gas. From the gas plant, the gas is recompressed and fed into a pipeline. In all these compression processes, centrifugal gas compressors driven by industrial gas turbines or electric motors play an important role. Turbomachines are used in a variety of applications for the production of oil and associated gas. For example, gas turbine generator sets often provide electrical power for offshore platforms or remote oil and gas fields. Offshore platforms have a large electrical demand, often requiring multiple large gas turbine generator sets. Similarly, centrifugal gas compressors, driven by gas turbines or by electric motors are the benchmark products to pump gas through pipelines, anywhere in the world.

Article

In a recent article in Mechanical Engineering (Vol. 133, No.1, Jan 2011), John Reilly and Allison Crimmins discuss the future of energy supply in the light of economic, political and technological reality. Primary energy use, closely related to income, may more than double by the end of the century. And, it has to be asked how much of that increase will be from alternative energies, and how much from fossil fuels. It is a common misunderstanding that we are running out of fossil fuel (and I remember learning that in high school in the 70's, with clearly defined dates for the end of oil reserves in the early 2000's), but that is not the case. A study by MIT concludes that, absent climate policies that would impact energy prices, 80% of primary energy in 2100 will be supplied by fossil fuels, despite a ten fold increase in renewable energy and a 8.5 fold increase in nuclear energy. And just recently, in the latest State of the Union address, President Obama mentioned the importance of natural gas for the future energy mix in the United States.

The authors also point out that renewable energy sources are not free of environmental risks, either:

Wind turbines, deployed on a scale to meet 10% of the energy demand, could result in the stagnation of surface air, with potential impact on local warming and large-scale precipitation patterns. Bio fuels may create large indirect emissions and have indirect effects on water use and food supply.

While advanced new technologies will be needed in later years, significant emissions reductions can be achieved now, with current technologies. Due to the composition of natural gas, as well as the very high efficiency of modern gas turbines, electricity from natural gas causes much lower greenhouse gas emissions, as well as other emissions, than electricity from coal or oil fired power plants. Natural gas is found in reservoirs in many parts of the world. Lately, huge additional gas reservoirs have been exploited in the United States and elsewhere in the world.

This article intends to highlight the importance of gas turbines, centrifugal compressors and pumps, and other turbomachines in processes that bring natural gas to the end users.

To be useful, the natural gas coming from a large number of small wells has to be gathered. This process requires compression of the gas in several stages, before it is processed in a gas plant, where contaminants and heavier hydrocarbons are stripped from the gas. From the gas plant, the gas is recompressed and fed into a pipeline. In all these compression processes, centrifugal gas compressors driven by industrial gas turbines or electric motors play an important role.

Natural gas is also produced as a by-product of oil production: so-called associated gas. Turbomachines are used in a variety of applications for the production of oil and associated gas. For example, gas turbine generator sets often provide electrical power for offshore platforms or remote oil and gas fields. Offshore platforms, or FPSO's, have a large electrical demand, often requiring multiple large gas turbine generator sets. The natural gas is separated from the oil and cleaned before being used as a fuel for these gas turbines. Gas turbines are also used to drive compressors that re-inject gas into the well or the reservoir to maximize oil recovery.

The remaining gas is pumped via gas turbine driven export compressors to an onshore gas plant. Since oil production is often conducted off shore, these export pipelines run sub-sea.

Centrifugal gas compressors, driven by gas turbines or by electric motors are the benchmark products to pump gas through pipelines, anywhere in the world. Many developing countries with booming economies, such as China, India and Brazil, invest heavily in the expansion of their gas pipeline infrastructure. The pipelines transport gas from the oil and gas fields to gas fired power plants, industrial and residential users, sometimes thousands of miles away from the gas reservoir. Gas is also transported to large LNG plants, where the gas is liquefied to be shipped on tankers around the world. Along the way, gas may be stored in large underground cavities to balance supply and demand – and for this duty we also find many opportunities for gas turbine or electric motor driven centrifugal compressors.

Innovation in this key application of industrial turbomachinery will further increase efficiency, safety and reliability in the operation, and reduce the environmental impact. Many of these developments, including the integration of turbomachinery in the users’ process, are possible by close cooperation between manufacturers and users of these machines.

Copyright © 2011 by ASME
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