Last blog post I discussed some of the basics about how electricity was generated, and introduced the basic steam cycle. This blog I would like to share some information about the primary heat sources for steam cycles of power plants; coal, natural gas, and nuclear.
In order to increase the efficiency of coal, which also helps minimize emissions, coal is ground up into a very fine particulate. This is performed inside of a Pulverizer, which uses large steel balls to crush and grind the coal into the very fine powder. The pulverizer is also combined with a Primary Air fan, which blows a large amount of air into the pulverizer that serves two purposes:
- Blows the pulverized coal out of the pulverizer
- Mixes a specific amount of air with the coal fines to increase burning efficiency
After the coal leaves the pulverizer, it is directed into coal burners, which assist in directing the coal, and the fire to maximize efficiency and minimize emissions. At the burners, coal is lit off into fire (initially by a natural gas flame, but the coal fire becomes self-sustaining and the natural gas is removed). The fires heat the tubes inside the furnace, which contain water, causing the water to boil into steam. The steam is then “superheated” by sending it through another heat exchanger downstream from the fires. After being superheated, the steam is then sent to the turbine, starting the steam cycle.
There are two different methods for using natural gas – through a gas furnace, or by using a gas turbine. A gas furnace is perhaps the simplest of all the power sources for the steam cycle plants – it is simply done by burning natural gas through burners, similar to how coal is burned after it is pulverized.
The gas turbine is not necessary for a steam cycle, however, they are typically used in conjunction with a steam cycle to increase the efficiency of the gas – these are called combined cycle natural gas plants. In a combined cycle natural gas plant, natural gas feeds a gas turbine, where it is mixed with air and burned. The burning creates additional gasses, and heat, causing the gasses to expand, building up pressure. This pressure from the gas and heat is used to drive the turbine, which also has a generator attached to it. After it exits the turbine, the gas is directed through a water heat exchanger, where it boils the water to steam – this allows these plants to reclaim some of the energy, which would have been lost in the form of heat. Some of these plants also have supplemental natural gas burner elements to aid in controlling and increasing the output of the steam cycle. (http://energy.gov/fe/how-gas-turbine-power-plants-work, https://www.edfenergy.com/energyfuture/generation-gas)
Thanks for continuing to read my blog! Next week I will continue this discussion of fuel sources, moving to nuclear fuel – please check back, and leave comments!