The gas turbine, as developed for aircraft propulsion, is an extremely reliable, efficient and robust machine. Safety and reliability are of prime importance to the airline industry and airline power units must meet exacting standards.
It can be assumed that aeroderivative gas turbines, based directly on aviation propulsion units, will show the same levels of reliability and efficiency as the machines from which they are derived provided no significant design modifications have been introduced. Design modification of these highly optimised machines is extremely costly, and design alteration for power generation applications makes little sense since its most likely service will be to increase costs. Consequently the risks associated with the use of aeroderivative gas turbines should be minimal. It is important, however, to clarify the relationship between the stationary machine and the aviation machine.
The same does not apply to heavy-frame gas turbines developed specifically for the power generation industry. These units do not have to meet the same exacting safety standards as the aviation units. Consequently they are generally not so thoroughly tested before entering service. Given the cost of a single 200-300 MW class gas turbine, it is perhaps not surprising to learn that some of the testing of these new heavy gas turbines has taken place in service. As a result there have been a number of instances of failure and the need for modification. Though the manufacturers are frequently coy about discussing such issues, it is clear that most if not all have been affected.
Part of this problem has arisen from the speed with which the market for heavy gas turbines for power generation has evolved and the high levels of competition this has engendered. Manufacturers may have learned from their recent experience, but even so a developer would be wise to establish the history of any gas turbine under consideration for a power project.
Natural gas appears to be the fuel of the moment for the power generation industry. Demand is high, but supplies remain plentiful in most areas of the world. As a result, gas prices have remained low in most parts of the world (though there have been significant price fluctuations in the USA). This situation cannot be expected to continue.
The economics of gas-fired power generation rely heavily on low gas prices. Once gas prices start to rise coal-fired plants, even when fitted with costly emission-control systems, soon become more cost effective.
This presents a dilemma for companies planning to develop new gas-fired generating capacity. Over the short term it looks economically attractive - though recent experience in North America suggest that an open gas market can lead to rather large price fluctuations (see Table 4.2) - but longer-term uncertainties must remain. New technologies to gasify coal and use the gas generated to fire gas turbines offer one solution to this dilemma, but the technology has not been demonstrated widely enough to make coal gasification a realistic option in the near term. Besides gas turbines optimised for natural gas may not perform as well with coal gas.
The second factor is security of supply. In Europe and North America the construction of national and international gas transmission systems have made the supply and availability of gas stable. In most other parts of the world this gas infrastructure does not yet exist. Networks are being developed in Asia and South America but the cost of development is high, particularly as long distance gas transmission pipelines are often required. Under such circumstances, security is likely to be higher when the development of a gas-fired power project takes place close to a source of fuel.
A well-organised supply infrastructure will aid gas security but cannot ensure it. Western Europe is already being forced to import gas from remote regions of Russia and from Algeria to supplement its own dwindling resources. The USA is eying fields in Alaska to boost its resources. Such extended supply lines are vulnerable to both technical failure and terrorist attack, either of which could cripple gas supply in the future.
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