 |
Air Injection Technology
Validation
of Humid Air Injection Technology
Performance Tests on GE7FA Engine
In 2001, Calpine obtained a license from ESPC to apply air injection technology to its fleet of gas turbine engines. As part of this license agreement, Calpine conducted validation tests on a General Electric PG7241FA peaking engine. Unit #3 at the Broad River Energy Center in Cherokee County, South Carolina. This engine is equipped with a once-through-steam-generator and has ports for injecting high-pressure steam for power augmentation. These same ports were adapted for air injection. Read the article that appeared in Gas Turbine World: Air Injected Power Augmentation Validated by Fr 7FA Peaker Tests, Gas Turbine World April-May 2002.
Test measurements were made while operating with humid air injection, dry air injection, steam injection and without any injection. Power and heat rate were recorded at various ambient temperatures under each of these operating conditions.
As a precaution, the moisture content of the injected air was limited to 3.5% of the inlet air flow since this is the moisture limit GE specifies for steam injection into engines with DLN combustors. Humid air injection should be able to have higher moisture levels than deemed acceptable for steam injection because humid air has heat transfer characteristics that are more similar to normal compressor discharge air than does injected steam. The higher heat transfer coefficient of steam relative to air can create localized thermal spikes wherever steam comes into contact with metal surfaces such as combustors, transition pieces or turbine blades. These thermal spikes can lead to overheating, and eventually metal damage. Steam injection can reduce the life of hot gas path parts by a factor of two, but humid air injection should have little or no impact on part life. Because of the heat transfer characteristics of injected steam, GE recommends gas turbine operation on the "dry" control curve, which reduces firing temperature as steam is injected.
The Calpine tests measured a 18.3 MW increase in gas turbine power at 95 F ambient temperature with 3.5% moisture in the injected air while operating on the normal engine control curve, called the "dry control curve" on the figures below. GE recommends operating on this dry control curve for steam injection becasue it results in a lowering of the engine firing temperature as steam is injected (about 50 F lower with 3.5% steam injection).
The test results closely match the predicted performance (using a GateCycle model of the engine) for the test conditions. Based on these results, the predicted power increase for a GE7FA engine at 95 F with 5% moisture in the injected humid air, operating at constant firing temperature, is nearly 32 MW, and is approximately 28 MW on the "dry" control curve.
| GE7FA Humid and Dry Air Augmentation Predicted performance at 95 F ambient temperature, sea level, at constant firing temperature. |
||||
| Design | Humid Air | Humid Air | Dry Air | None |
| Moisture (% of combustor inlet air mass flow) |
7.5% | 5.5% | n/a | n/a |
| Net Power (MW) | 182.6 | 177.0 | 166.4 | 150.4 |
| LHV Heat Rate (Btu/kWhr) | 9160 | 9380 | 9720 | 9760 |
| Incremental Power | 32.2 | 26.6 | 16.0 | Base |
| Incremental Heat Rate | 6360. | 7230. | 9345. | Base |
The validation tests were performed with steam injection, dry air injection and with humid air injection. The following figures show predicted GE7FA performance with various levels of air and steam injection, and are based upon the results of the validation tests.
Click below to view a pdf file of the Calpine test results:
| Back to Top |
|
Contact: |
Telephone: |
Fax: |
E-Mail: |