- The chemical energy stored in coal is released when it is burned and changed to thermal (heat) energy that is used to produce steam.
- The steam turns a turbine, and that mechanical energy is used to turn a generator to produce electricity.
Steps in Electricity Generation from Lignite
- Lignite is delivered to the power plant.
- Depending on the power plant, the lignite is crushed to approximately ¼ inch size coal or pulverized into a fine powder so it will burn more quickly.
- The crushed or pulverized coal is then blown into a boiler combustion chamber, or furnace.
- Pipes inside the boiler carry water, which is turned to steam by the extreme heat of the combustion.
- The steam reaches temperatures of up to 1,000⁰ F.
- The steam is injected at high pressure into a turbine.
- The steam reaches pressures up to 3,500 pounds per square inch (psi).
- The high-pressure steam causes the turbine blades to spin, turning a drive shaft.
- The drive shaft is connected to a generator, where magnets spin within wire coils to produce electricity.
- The exhaust steam from the turbine is drawn into a condenser, which changes the steam back to its liquid state.
- The steam water is then returned to the boiler to repeat the cycle.
- Burning coal results in the production of bottom ash, fly ash, and various gases.
- The ash is captured and converted into useful by-products; the gases are "scrubbed" and then released through the emission stacks.
- Bottom ash is the large ash material that is removed from the bottom of the furnace.
- Its uses include aggregates in road bases, pavement, and as a product for sanding icy winter roads.
- Fly ash consists of particles that are removed from the exhaust.
- It is recycled and used for construction and other commercial purposes.
- Fly ash got its name because it could fly out from the power plant if it were not captured.
- Fly ash added to concrete results in a concrete that is easier to work with, stronger, lasts longer, and is of higher quality than concrete made with Portland cement.
- Some ready-mix concrete producers are replacing more than 30 percent of their cement with fly ash.
- It is used in the construction business for roads, bridges, sidewalks, curbs, foundations, commercial buildings, and homes.
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Fly ash was used in the construction of the Fort Mandan Visitors Center in Washburn.
- Other products enhanced by fly ash include carpet, paint, insulation, ceiling and flooring tiles, lumber, bricks, and shingles.
- Fly ash is also used to strengthen soil and as a soil stabilizer to prevent soil erosion.
- The stack on a power plant acts like a chimney and allows exhaust to leave the plant.
- The visible plume that comes out of the stack at a coal-based power plant, particularly in winter, is almost all water vapor.
- North Dakota power companies have spent approximately 2 billion dollars ($2,000,000,000) in new technologies to control emissions from the power plants.
- Emissions Control Technology is used to remove pollutants from the exhaust before it is released into the air.
- Two types of particulate control devices for particulate matter are the baghouse and the precipitator.
- A baghouse is a giant filter that removes particles from plant exhaust.
- An electrostatic precipitator uses the attraction of positive and negative electrical particles to trap particles in the flue gas.
- Flyash trapped by the baghouse or electrostatic precipator is recycled and used for construction and other commercial purposes.
- Scrubbers are used to remove SOx or sulfur-based emissions.
- This is done with a chemical process.
- The flue gas mixes with a spray of water and a chemical (usually lime) to let the gasses combine with the spray to be removed.
- Nitrogen Oxides (NOx) are reduced by boiler enhancements and/or chemical additives.
- NOx occurs in nature with events such as lightning strikes and forest fires. NOx occurs in a boiler, car or furnace due to high temperature and the presence of Nitrogen and Oxygen.
- According to the US Environmental Protection Agency (EPA), 50 percent of NOx emissions are from automobiles and other mobile sources, 20 percent from electric power plants, and 30 percent from a variety of other sources such as industrial furnaces and manufacturing of materials.
- North Dakota's power plants have invested around $1 billion since 2006 in new technology to reduce emissions and increase efficiencies.
- North Dakota is one of only seven states that meets all of the EPA's clean air quality standards as of 2014.
- North Dakota plants are investigating the potential of capturing the CO2 from coal fired power plants and sequestering it deep underground.