An Introduction to Gas-Fired Power Generation
Abstract
Natural gas is the second most important fossil fuel for generating electricity after coal. Although it has a long history as a fuel for power generation, it is only since the 1990s that its use has soared, mainly on the back of the development of the high-efficiency combined cycle power plant. These plants are cheap to build and can produce cheap electricity if the cost of gas is low. They emit less carbon dioxide than coal-fired power plants. The commercial exploitation of natural gas began during the 19th century when it was first used for lighting. Electricity generation was initially in gas-fired boilers with steam turbines but the development of the gas turbine offered an alternative route to power generation, one that has come to dominate production from natural gas.
Keywords
Natural gas; fossil fuel; power generation; gas turbine; gas boiler; steam turbine; global production; renewable grid support
Natural gas is the second most important fossil fuel for generating electricity after coal. Its exploitation as an energy source for electrical power generation dates from the early part of the 20th century. However it was in the latter part of the century that capacity accelerated alongside the development of efficient gas turbine-based power stations. The use of natural gas for power generation has continued to grow into the 21st century, particularly among the developed nations. In the United States, where the economic extraction of natural gas from shale rocks in the past decade has dramatically increased the amount of natural gas available and reduced the cost of the gas, this has been especially noticeable. Other regions are now trying to exploit the potential for shale gas, with varying success.
While cost has been one factor driving the use of natural gas for power generation, another has been climate change. Combustion of natural gas produces significantly less carbon dioxide for each unit of electricity generated than would be emitted by a coal-fired power station during production of the same unit of power. A natural gas-fired power station can be as large as a coal-fired power station and it can generate electricity continuously like a coal-fired plant,1 making it a good substitute for the latter. Switching from coal to natural gas has therefore provided a simple means for companies to meet climate-change emission control limits more easily and for nations to achieve targets for carbon dioxide emissions.
While a switch from coal to natural gas will reduce overall emissions for each unit of power it will not eliminate them. To achieve that requires either abandoning the combustion of fossil fuel for power generation or the introduction of carbon capture and storage technologies to natural gas-fired power plants. The technologies for both carbon capture and its storage already exist but they have yet to be tested the scale of a large natural gas-fired power station. So, while power companies and some governments are promoting natural gas—with or without carbon capture—as a stage on the way to a carbon free energy economy, environmental campaigners generally consider it to be a distraction, sapping investment that could otherwise be used to develop more extensive renewable generation resources.
The recognition of natural gas as a source of energy can be traced back to around 500 BC. Natural gas seeping from the ground will often ignite to create a flame but in earlier times its significance as an energy source was not recognized. More often the flame was instead considered a sacred sign. It was in China for the first time that this seeping gas was collected and transported in bamboo pipes, then used to boil sea water and produce salt.
Commercial use of gas for energy originated in Great Britain in the 18th century although this was based on gas manufactured from coal rather than natural gas extracted directly from the earth. The modern natural gas industry probably started in the United States in the middle of the 19th century when gas was first pumped from a natural gas well and distributed for lighting. At this stage, however, long distance transportation of gas was not possible and gas was all used locally. It took the development of gas pipeline technology in the 20th century to make natural gas widely available.
Pipelines are a key technology in the growth of the natural gas industry. The cheap, easy transportation of natural gas though pipelines gives the fuel one of its main attractions. Pipeline delivery has allowed gas to be used as a source of domestic energy for both heating and cooking, as a commercial energy source, and in industrial processes. This ease of transportation has also allowed natural gas to be traded globally, like oil, and this has led to large global and regional fluctuations in the cost of natural gas over the past 30 years. Such fluctuations can have serious economic consequences, particularly for power plants that use the fuel.
The commercial electricity industry began at the end of the 18th century when electric power started to replace gas as a source of light, incidentally removing one of the main uses of gas at the time. This prompted gas companies to search for other uses for their product. One of those was electricity generation. The production of electricity from natural gas began during the first half of the 20th century with the use of gas in combustion boilers similar to those used for the combustion of coal. While this practice continues in some parts of the world, particularly where natural gas is abundant, it was the development of gas turbines for power generation that led to a dramatic rise in the global use of natural gas by the power industry. Gas turbine-based power plants, particularly combined cycle plants that add a steam turbine to exploit the waste heat from gas turbine exhausts, have much higher efficiencies than traditional boiler plants and are both cheap and quick to build. This has made then extremely attractive commercially. Piston engines fired with natural gas are also popular for smaller capacity generation.
Large natural gas-fired power stations have become an important component of the electricity supply industries in many parts of the world, particularly in the developed nations of Europe and in North America. However the arrival of renewable energy has changed the complexion of the electricity industry and with it the function of these gas-fired power stations. Their use is now being adapted to help accommodate the large volumes of renewable electricity generation that is being introduced into national grids in many parts of the world, with the natural gas plants providing back up for the intermittent renewable supplies. This renewable support duty is likely to provide a role for natural gas-fired power plants well into the 21st century.
1.1 The History of Natural Gas as an Energy Source and for Power Generation
Natural gas, the product of the fossilization of organic material in the earth’s crust, has made its presence known for millennia when gas leaking from reservoirs close the earth’s surface has ignited to create a flame bursting from the earth. The temple to the Oracle of Delphi, an ancient Greek temple on Mount Parnassus, is reputed to have been founded after a goat herd found a flame issuing from a fissure in the rock, a flame that was considered to be divine. Similar divine flames have been identified from ancient Persian and Indian religions and are probably the original source of “eternal flames” that still have symbolic meaning today in both religious and secular contexts.
It was in China that the nature and utility of natural gas was first recognized as a source of energy. Having realized that the gas emerging from the ground was a useful source of heat, Chinese craftsmen collected the gas and then transported it using simple bamboo pipelines to sites where the heat could be exploited. The best documented example is the use of natural gas to produce sea salt from salt water by using the heat to evaporate the water. Simple use of the gas in this way is not recorded elsewhere but French explorers in North America in the early 17th century reported that native Americans were igniting gas that seeped into and around Lake Erie.
The commercial gas industry from which the natural gas industry evolved began with the large scale gasification of coal in England around 1785 to produce “illuminating gas.” This process involved heating bituminous coal in a vessel in the absence of air, driving off a combustible gas and leaving a solid residue, coke, which was used in the iron industry. The coal gas produced by this method was used for street lighting and eventually for domestic lighting. The gas production and distribution industry developed on the back of this process which continued to be used for gas production well into the middle of the 20th century in the United Kingdom and elsewhere. In the United Kingdom the gas, often called “town gas,” was finally replaced with natural gas from the North Sea when exploitation of these reserves began in the second half of the 20th century, stimulating the construction of a UK national gas grid.
The use of coal gas in the United States began in 1816 when the gas was used for street lighting in Baltimore. It was in the United States later in the century that the true natural gas industry began when gas was raised from wells and used to provide lighting. Meanwhile in 1855 the German scientist Robert Bunsen developed a stable and safe means of burning natural gas efficiently. His invention was an improvement on earlier designs and is now known widely as the Bunsen Burner. The burner design allowed the exploitation of natural gas as a source of heat to develop and expand.
Natural gas could still only be used locally because of the inability to transport it over long distances. Where it was produced in conjunction with oil2 it was often burned (flared) at the wellhead, a practice that continues today in some parts of the world. Some progress was made with pipeline technology during the early decades of the 20th century and in the United States the first interstate pipelines were built. However it was the development of new metallurgical and iron-working techniques after the Second World War that made the construction of extensive modern pipeline networks possible.
The exploitation of natural gas for power generation began with the use of gas in boilers to raise steam for a steam turbine. Where natural gas was readily available this offered a cheap and reliable means of generating electricity, particularly in oil producing countries that had large volumes of natural gas available for which there was no obvious use. Such boilers are similar to coal-fired boilers but without the necessity for coal handling and preparation. While this offered a viable option where it was available, coal was the fuel of choice for most large fossil-fuel power stations.3
It was during the 1930s and 1940s that gas turbines, which were being developed as aero engines, began to be used in stationary applications such as electricity generation too. The first commercial gas turbine was installed in 1949 in the United States and the technology became established during the 1950s. Until the early 1980s the most common use of these “aeroderivative” gas turbines was for providing power during peak demand periods. However, the development of heavy duty gas turbines, and of the combined cycle power plant, led to a massive growth in this type of power station during the 1980s and 1990s, growth that has continued into the second decade of the 21st century. It is these combined cycle power stations that have promoted natural gas to become the second most important fossil fuel for power generation after coal.
1.2 Global Electricity Production from Natural Gas
Until the 1970s, most natural gas used for power generation was burned in steam-raising boilers. The gas, usually a by-product of oil production, was cheap and burning it to raise steam was an economic alternative to flaring which was widely practiced. Figures detailing the amount of electricity generated from natural gas, globally, are not available for the first half of the 20th century. However, data from the International Energy Agency (IEA) show that in 1973 there were 740 TWh of electricity generated from natural gas-fired power stations. That represented 12.1% of total global electricity production during the year as shown in Table 1.1.4
Table 1.1
Annual Electricity Production from Natural Gas
| Year | Annual Production of Electricity From Natural Gas (TWh) | Total Global Annual Electricity Production (TWh) | Natural Gas Production as a Proportion of Annual Global Electricity Generation (%) |
| 1973 | 740 | 6117 | 12.1 |
| 2004 | 3420 | 17,450 | 19.6 |
| 2005 | 3623 | 18,239 | 19.7 |
| 2006 | 3805 | 18,930 | 20.1 |
| 2007 | 4132 | 19,771 | 20.9 |
| 2008 | 4299 | 20,181 | 21.3 |
| 2009 | 4292 | 20,055 | 21.4 |
| 2010 | 4758 | 21,431 | 22.2 |
| 2011 | 4846 | 22,126 | 21.9 |
| 2012 | 5100 | 22,668 | 22.5 |
Source: International Energy Agency.
The use of natural gas for electricity generation began to accelerate during the 1980s, as outlined above, and by 2004, the total production from natural gas had risen to 3420 TWh. This now represented 19.6% of total world electricity production (Table 1.1). Since then the consumption of natural gas for power generation has continued to rise steadily both in absolute terms and in terms of the proportion of power generated from gas. In 2006 natural gas provided over 20% of total global electricity production and in 2012 the proportion was 22.5%, when total production from natural gas was 5100 TWh.
Nationally, the largest user of natural gas for electricity generation is the United States which in 2012 produced 1265 TWh from the fuel according to figures from the IEA shown in Table 1.2.5 This is far more that the second largest user, the Russian Federation, which generated 525 TWh from natural gas in 2012, while the third largest, Japan produced 397 TWh. Other big users in the table include the Islamic Republic of Iran, Egypt, Mexico, Saudi Arabia and Thailand, all of which are major producers of natural gas.
Table 1.2
National Production of Electricity from Natural Gas, Top 10 Leading Nations in 2012
| Country | Electricity Production From Natural Gas (TWh) |
| United States | 1265 |
| Russian Federation | 525 |
| Japan | 397 |
| Islamic Republic of Iran | 170 |
| Mexico | 151 |
| Italy | 129 |
| Egypt | 125 |
| Saudi Arabia | 121 |
| Thailand | 117 |
| Korea | 112 |
| Rest of the world | 1988 |
Source: International Energy Agency.
The growth in the use of natural gas for power generation in combined cycle power plants can be seen from the rapid rise in the consumption of gas by utilities in the United States over the past two decades. In 1993 total US natural gas electricity production was 415 TWh according to the US Energy Information Administration (US EIA) and generating capacity based on natural gas was 66 GW. By 2004 production was 709 TWh while the installed natural gas-fired generating capacity was 224 GW. As shown in Table 1.2, in 2012 the total production was 1265 TWh, three times the production in 1993. The US natural gas-fired generating capacity in 2011 was 415 GW.