Cleaner Coal

Since the industrial revolution, the word coal has become synonymous with air pollution. London in the late 19th and early 20th centuries was characterized by a dense, noxious fognamed by Sir Henry Antoine des Voeux in 1905 as smog, or smoke and fog. In December 1952, the smog in London got so bad that over 4000 people died in one week due to respiratory illnesses.

Today, coalsupplies of which they say could last, in Canada, another 143 years, and 250 years in the U.S.is being re-examined as a source of energy. Oil and natural gas supplies are dwindling as concerns about the environment and demand for energy simultaneously grow. No one source of renewable energywhether wind, solar, or geothermal poweris a reliable enough solution to be implemented on its own on a large scale. Most power plants are, in fact, still powered by coal, and countries like China and India are building new coal-powered electricity plants in order to keep up with the energy demands of rapid industrialization.

So what do we do? Well, one option is to take what is already working and at least temporarily plentiful, and clean it up.

Older coal-fired power plants burn coal at a reliable, economical, and inefficient subcritical levelthe steam used to transform thermal energy into electrical power is kept at a relatively low pressure and temperature. However, raising the temperature and pressure of the steam to supercritical or ultra-supercritical levels can increase a plant’s efficiency from about 36% to about 40% and 47%, respectively.

Oxy-fuel combustion, when coal is burned in the presence of pure oxygen, produces flue gas that is richer in carbon dioxideit sounds worse, but in fact makes the CO2 easier to remove from the gas for potential geological sequestration, or for other uses.

Another alternative that could increase the efficiency of combustionthereby reducing greenhouse gas and smog-inducing emissionsis to purify the coal before it is burned. Removing inorganic elements from coal reduces waste products like ash and the toxic sulfur-rich slag that is typical of traditional coal-fired plants. Unfortunately, the process of purification involves the use of acids, caustic agents, and organic solvents, exposure to which can cause health problems and whose disposal is cause for environmental concern.

A process known as Integrated Gasification Combined Cycle (IGCC) is an alternative to combustion for extracting energy from coal. The coal is reacted with steam and air (sometimes pure oxygen) at a high temperature and pressure. Hydrogen, carbon monoxide, and smaller amounts of methane and carbon dioxide are producedcalled synthesis gas, or syngas. Syngas is then passed through a gas-cleaning unit so that impurities like sulfur and mercury can be removed. The gas goes on to be expanded in a gas turbine and produces electricity through a generator. The turbine exhaust passes through a heat recovery system generator (HRSG), which removes additional heat and produces additional energy, further increasing the efficiency of the process.

Gasification is a much more efficient way of harnessing coal’s energy. In addition, the large amounts of H2 produced during gasification could be harnessed and used to make hydrogen fuel cells. Syngas can also be used to make other chemicals, like fertilizer, instead ofor as well asproducing power. Low-grade heat can also be recovered and used for steam-driven applications such as district heating.

Coal-burning power plants haven’t actually come very far since their inception. Smog is certainly still a problemon hot summer days in Toronto, for example, the very old, the very young, and anyone with respiratory problems are advised to stay indoors and turn on their air conditioners (which helps with the pollution problem, I’m sure).

The main obstacle standing in the way of cleaner coal is, in fact, the power companies themselves. There have been legislations passed and incentives offered, even lawsuits filed, and power plants still haven’t changed. The truth is, it is still much cheaper to run a plant based on combustion than one using IGCC, and all the plants are already built.

Clean coal is probably not the ideal solution to our pollution problems, but it would be better than the dirty coal we’re using now. I’m waiting for the day when the health of the planet and everyone on it becomes more important than profit.

Getting to Clean Coal
Clean Coal Technology Pathways
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Met Office

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Sarah Nelson | My Bio & Articles

Sarah Nelson was born and raised in rural eastern Ontario, where she spent her childhood frolicking in fields and hugging trees. Off to Toronto to experience the city life, she found her passion and pen for writing. She has been ...