Coal is an abundant fuel source, but burning coal is problematic for the environment. In this lesson, you will learn about clean coal technologies, such as coal washing, flue gas desulfurization systems, low-NOx burners, gasification, and Carbon Capture and Storage (CCS).
Coal is a promising fuel for the future. Even though it's a nonrenewable fossil fuel that takes millions of years to form, coal is still thought to be abundant.
In the year 2007, the U.S. coal resources totaled approximately 486 billion short tons, which is enough to provide hundreds of years of energy. While some of that coal is found in inaccessible locations (such as under towns) or otherwise too difficult to mine, there is still a lot of coal to be utilized for energy. However, coal is a problematic fuel when it comes to the environment. In this lesson, we will learn about some of the problems associated with burning coal, and discover technologies that are being used to make coal a cleaner source of energy.
Coal is comprised mostly of carbon and is found underground. When it's lying in the earth undisturbed, it does not impact the environment. However, when we pull coal out of the ground and burn it to generate electricity, the coal is converted to carbon dioxide, which is released into the atmosphere along with other pollutants. Carbon dioxidegreenhouse gas
To recall the term 'greenhouse effect,' it may help you to note that the glass of a greenhouse acts similarly to the gases in the atmosphere, keeping some of the heat inside the greenhouse; kind of like the way car windows absorb heat and help to keep it inside the car on a summer day.
Clean Coal Technologies
Coal is an abundant fuel source and could be a source of electricity for many years to come, if we could just find a way to make coal cleaner. Fortunately, there are many teams of scientists hard at work to solve this problem; and thanks to the clean coal technologies that they have developed, we may see a reduction in the environmental effects of coal burning in the future.
Now, if you have ever seen a coal burning plant, one of the things that likely caught your attention was the billowing smoke and gases that pour out of the smokestacks. This is called 'flue gas.' This flue gas can contain many impurities, such as sulfur and nitrogen, and these impurities combine with water vapor and fall to the earth as acid rain.
Coal washing is a type of coal preparation that removes impurities. The process involves crushing the coal into small chunks and washing it. During the washing process, the coal floats to the surface while the sulfur and other impurities sink.
Another way to make coal burning cleaner is to use flue gas desulfurization systems, which are also known as 'scrubbers.' These systems remove sulfur dioxide from the flue gas. This is an easy term to recall if you remember that the prefix 'de' means to remove, and the term 'sulfur' is found in the word. Therefore, flue gas desulfurization systems literally remove sulfur dioxide from the flue gas. During this process, the flue gas is sprayed with limestone and water. The limestone and sulfur combine with each other to form a wet paste that looks somewhat like the toothpaste you use to scrub your teeth clean in the morning. Although, I wouldn't recommend using this type of paste to freshen your breath.
Nitrogen is a normal part of the air we breathe, and we tolerate nitrogen just fine. However, when air is heated, as it is when coal is burned, the nitrogen atoms break apart and join with oxygen to form 'nitrogen oxide,' or 'NOx,' which is the abbreviation and rhymes with socks. Nitrogen oxide is a pollutant that causes smog and acid rain. Low-NOx burners reduce nitrogen oxide emissions by restricting oxygen and manipulating the combustion process when coal is burned.
Gasification is another method that scientists have found to make coal cleaner, and as its name suggests, it involves the conversion of coal into gas. With gasification, coal is subjected to steam and hot pressured air to break the carbon molecules apart. This results in a mixture of carbon monoxide and hydrogen, which can be used to spin a gas turbine to generate electricity. Gasification can remove impurities from coal and is a great way to clean pollution out of coal.
We have looked at a number of ways to clean coal and remove impurities so they are not released into the atmosphere. But scientists have also discovered that they can catch carbon dioxide after coal is burned, and prevent it from harming the atmosphere.
This process is called carbon capture and storage, or CCS. CCS is defined as the process of capturing carbon dioxide and transporting it to permanent underground storage. When carbon capture and storage is utilized at a coal burning plant, much of the carbon dioxide generated during the burning of coal is transported by pipeline or other mode to sites where it can be stored deep underground in areas, such as depleted oil or gas fields, preventing it from being released into the atmosphere.
Let's review. Coal is a relatively cheap fossil fuel and will remain abundant long after oil and natural gas reserves are used up. However, burning coal creates problems for the environment. When coal is burned, it releases carbon dioxide and other impurities into the atmosphere. Carbon dioxide is a 'greenhouse gas,' which is a gas in the atmosphere that absorbs infrared radiation and traps heat. Greenhouse gases contribute to the warming of the surface of the earth and the lower atmosphere, which is known as the 'greenhouse effect.'
Even though there is no such thing as 'clean coal,' there are new technologies that are helping to make coal burning less harmful for the environment. One of these technologies is called coal washing, which is a type of coal preparation that removes impurities by allowing the coal and impurities to separate.
Flue gas desulfurization systems remove sulfur dioxide from the flue gas by spraying the flue gas with limestone and water to create a less harmful paste. Low-NOx burners reduce nitrogen oxide emissions when coal is burned, which prevents nitrogen oxide from turning into smog and acid rain.
Gasification is the conversion of coal into gas, which removes impurities from the coal. This gas is then used to spin a gas turbine to generate electricity. Carbon capture and storage, or CCS, does not prevent carbon dioxide emissions; instead, it captures carbon dioxide and transports it to permanent underground storage, keeping it from being released into the atmosphere.
After viewing this video lesson, you should be able to:
- Explain the negative environmental effects of burning coal
- Discuss coal cleaning technologies that have been developed