Sparks About Gas

Gas: the next generation

 By Robin Wylie
About gas

For a long time, natural gas played only a minor role in the world’s energy mix. But its lower carbon emissions, coupled with major improvements in efficiency are making this fuel an increasingly popular choice for power generation as we progress into the 21st century…

Natural gas is far from a new fuel. Humans were using it as early as 600 BC, when Chinese engineers transported seeping natural gas through bamboo pipes before burning it to desalinate seawater. Around 100 AD, the King of Persia, in modern day Iran, had natural gas piped to his home to fuel the royal kitchen. In the modern age, however, natural gas has long been outshone as a fuel source by coal and petroleum. Although natural gas has a long history of use in the residential sector, its share of total global energy production has until recently been relatively small. In the power sector, for example, coal was the dominant fuel source for most of the 20th century. Before 1990, the share of global electricity which was generated using natural gas was less than 10 percent.

But in the last few decades, the use of natural gas in power generation has surged around the world. The share of the world’s electricity being generated by natural gas has steadily grown from around 10 percent in 1989 to around 22 percent today. The trend looks set to continue. The rising popularity of natural gas is linked to the exploitation of unconventional gas resources (such as tight sands and coal-bed methane) which began in the mid-late 1990s, as well as the shale revolution, which began in the early 2000s and continues to revolutionize the industry. But in an increasingly carbon-conscious world, the shift towards natural gas is also due to the fuel’s environmental credentials. As well as being the cleanest-burning fossil fuel, producing about half the CO2 emissions per unit energy of a coal-fired power plant, natural gas is gaining popularity due to its ability to merge with and supplement renewable sources of energy such as solar and wind power, enabling more widespread, reliable and affordable deployment of these low-carbon technologies.

The ability of natural gas to support the development of renewable energy is being proven by the various hybrid natural gas power plants which have been constructed around the world in recent years, such as the Ivanpah Solar Electric Generating System in the Mojave desert (pictured above). Natural gas-fired electricity generation is also enabling the transition to a low-carbon economy by offering increasing emissions reductions over coal-fired power. Not only does natural gas produce fewer greenhouse gas emissions per unit energy than coal, but today’s natural gas plants produce that energy much more efficiently than coal plants.

For a long time, natural gas played only a minor role in the world's energy mix.

Efficiency rising

Even the least efficient natural gas plants — so called “simple cycle” plants — have thermal efficiencies of between 32 and 38 percent, which is similar to the efficiencies of coal power plants, most of which are between 32 and 42 percent. But a second generation of power plants has made natural gas the most efficient fossil fuel around. Natural gas combined cycle (NGCC) power plants use two turbines to generate electricity in tandem, with the waste heat from a primary gas turbine being used to drive a secondary steam turbine.

Since the first NGCC plant became operational in the early 1960s, the thermal efficiency of these plants has increased to around 50 to 60 percent, significantly greater than the efficiencies attainable using coal. This efficiency boost not only reduces the cost of electricity, but also amplifies the existing environmental advantages of natural gas, resulting in less than half the CO2 emissions per megawatt-hour as coal power plants. Due partly to the widespread adoption of NGCC plants, the global average power generating efficiency for natural gas today stands at approximately 48 percent, compared to approximately 35 percent for coal. There are signs that these efficiencies could increase even further in the future, with state-of-the-art NGCC plants claiming efficiencies of up to 64 percent. But by using waste heat in another way, natural gas can already generate electricity with even greater efficiency. And it involves leaving power plants, as we know them, behind.

Combined heat and power (CHP), also known as cogeneration, is a method of power generation which reuses the waste heat for an alternative purpose, usually heating air or water. CHP has a long history, dating back to the United States’ first central power station, Pearl Street Station, which opened in 1882 in Manhattan, and provided both electricity and heat to nearby buildings. Pearl Street Station (which was built by one of Thomas Edison’s construction companies) was powered by coal. But in the 21st century, natural gas is at the forefront of CHP generation, and providing some of the highest efficiencies around.

Combined Heat and Power generation in Uppsala, Sweden. Credit: Vattenfall

By reusing waste heat from electricity generation in factories, commercial or residential buildings, today’s CHP systems — approximately half of which use natural gas as the fuel source — achieve extremely high thermal efficiencies of between 75 and 90 percent by generating heat and electricity from the same fuel supply. The efficiency boost provided by CHP power generation translates into CO2 emission reductions of up to 30 percent compared to the separate means of conventional generation via a boiler and power station. However, if natural gas fuel cells are used the reduction can be up to approximately 50 percent.

According to the International Energy Agency, CHP could reduce global greenhouse emissions by at least 10 percent in 2030, which translates into a 7-percent overall cost reduction in the power sector, or $795 billion. Today CHP accounts for approximately 8 percent of global electricity generation capacity, most of it concentrated in Europe: Denmark is the world leader, with CHP meeting around half of its electricity needs, with Finland close behind on around 40 percent, as well as Russia and the Netherlands, with around 30 percent each. Currently CHP is largely restricted to the industrial sector, such as paper and printing, oil refining, chemicals and food processing. However in Denmark, the majority of CHP output is used for district heating systems, demonstrating that this technology could have a much wider application than it currently does.

Natural gas has made significant inroads to the electricity sector in recent years, and with technologies such as CHP and high efficiency NGCC power plants, this fuel has the potential to significantly aid decarbonization efforts in the 21st century.

SEE MORE: Gas as a Bridge by Robin Wylie

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.