Wednesday, October 02, 2013
Natural Gas Combustion Turbines
1. Air Intake
When the unit is put into operation, air is pulled in from outside and compressed.
2. Combustion Chamber
This compressed air is ignited by burning fuel (low sulfur fuel oil or natural gas) and expands. The resulting combustion develops 300,000 horsepower. Combustion turbines operate differently from coal-fired or nuclear plants. Rather than using steam to drive a turbine, combustion turbines harness the nature of air to expand when it is heated.
The expanding air pushes the turbine generators much like steam does in a steam-electric station. The turbines then turn the electric generators. In simplest terms, a turbine is a series of many long, thin blades similar to propeller blades. Two-thirds of the horsepower generated rotates the air-compressor turbine. The remaining energy spins the electric generator.
Gas turbines and combustion engines are also used to generate electricity. In these types of units, instead of heating steam to turn a turbine, hot gases from burning fossil fuels (particularly natural gas) are used to turn the turbine and generate electricity. Gas turbine and combustion engine plants are traditionally used primarily for peak-load demands, as it is possible to quickly and easily turn them on. These plants have increased in popularity due to advances in technology and the availability of natural gas. However, they are still traditionally slightly less efficient than large steam-driven power plants.
Combined Cycle Units
Many of the new natural gas fired power plants are known as 'combined-cycle' units. In these types of generating facilities, there is both a gas turbine and a steam unit, all in one. The gas turbine operates in much the same way as a normal gas turbine, using the hot gases released from burning natural gas to turn a turbine and generate electricity.
In combined-cycle plants, the waste heat from the gas-turbine process is directed toward generating steam, which is then used to generate electricity much like a steam unit. Because of this efficient use of the heat energy released from the natural gas, combined-cycle plants are much more efficient than steam units or gas turbines alone. In fact, combined-cycle plants can achieve thermal efficiencies of up to 50 to 60 percent. (Duke Energy, Natural Gas . org)