U.S. Net Generation
Source: U.S. Energy Information Administration
The issue
The recent increase in the generation of electricity by natural gas power plants is a result of an increase in the supply of natural gas, increasing focus on power plant emissions and short construction times for natural gas plants. The increase in supply of natural gas is a result of gas production from unconventional sources, such as shale gas and tight gas. Natural gas has a much lower emissions of sulfur dioxide and carbon dioxide than coal when burned to generate electricity. Finally, natural gas plants have much shorter construction times than coal plants making them a more practical for increasing generating capacity.
Types of natural gas plants
There are three types of natural gas plants currently used to generate electricity: steam generation, simple cycle and combined cycle.
Steam generation plants use natural gas to heat water and create steam that spins a turbine, just as it would be in a conventional solid fuel plant such as a coal plant.
U.S. Summer Capacity
Source: U.S. Energy Information Administration
Simple cycle plants burn natural gas to produce a high pressure gas that is then used to spin the turbine. These plants have short start-up times compared to other generating facilities and, therefore, are used during periods of peak demand. They are very inefficient in their ability to convert heat into electricity so their use is often limited to periods of high demand.
Combined cycle plants incorporate simple cycle turbines and a heat recovery steam generator. As gas is burned to create high pressure gas, the waste heat from that process is captured and used to generate steam to spin a steam turbine. These plants are the most efficient form of natural gas plant but have longer start-up times, so they are primarily used for intermediate-load and base-load generation.
Efficiency of natural gas plants
The International Energy Administration (IEA) indicates that combined cycle gas plants have a higher average efficiency than coal plants. Simple cycle plants have efficiencies ranging from 35 - 42% and combined cycle plants have efficiencies of 52 - 60% compared to efficiencies of up to 46% for supercritical coal plants to 50% for ultra supercritical coal plants.
EPA Emissions Data Coal vs. Natural Gas Electric Generation
| Natural Gas | Coal |
|---|
| Nitrogen Oxides (lbs/MWh) | 1.7 | 6 |
| Carbon Dioxide (lbs/MWh) | 1,135 | 2,249 |
| Sulfur Dioxide (lbs/MWh) | 0.1 | 13
|
| Ash Content | 0% | 10% |
Construction lead times
Natural gas generating plants are constructed much more quickly than coal fired generation. Simple cycle plants are typically constructed in 18 to 30 months and combined cycle plants are constructed in about 36 months. These lead times are significantly less than the average for solid fuel plants (i.e. coal plants), about 72 months.
Natural gas plants at AEP
Natural gas generating facilities account for about 16% of AEP generating capacity. The complete list of AEP natural gas generating facilities is presented in the table to the left.
AEP Natural Gas Generating Plants
| Operating Company | Plant & Capacity |
|---|
| AEP Generating Company | Lawrenceburg - 1,162 MW |
| Appalachian Power Company | Ceredo – 523 MW |
| Columbus Southern Power Company | Waterford – 850 MW |
| Darby – 518 MW |
| Public Service Company of Oklahoma | Tulsa – 433 MW |
| Riverside – 1,047 MW |
| Northeastern Units 1 & 2 – 922 MW |
| Southwestern – 642 MW |
| Comanche – 277 MW |
| Weleetka – 167 MW |
| Southwestern Electric Power Company | Arsenal Hill – 110 MW |
| Lieberman – 268 MW |
| Knox Lee – 488 MW |
| Wilkes – 882 MW |
| Lone Star – 50 MW |
| Mattison – 340 MW |
