TRAX’s goal in this study was to help Southern California Edison (SCE) load their gas turbine as quickly as possible to reach the minimum emissions-compliant load. In addition, TRAX models provided an array of secondary information about how these load tests affected the unit ― such as how the tests affected temperatures to the SCR and NOx removal efficiency.
The scope of this study was focused on the gas turbine effects on the heat recovery steam generator (HRSG) and steam turbine performance. To accomplish this, TRAX first created a highly responsive model of SCE’s gas turbine. TRAX then modeled the HRSG and balance of plant, including high pressure, intermediate pressure and low pressure steam turbine sections, seal steam, condenser and vacuum pumps, condensate pumps, and gland steam condenser and exhausters. The modeling omitted much of the fuel system, as this was not of interest for this study.
TRAX was able to modify exhaust gas profiles to mimic gas conditions entering HRSGs and replicate any ambient condition at the plant.
The detailed modeling approach was used first for load maneuvering tests, to test increased ramp rates, lower minimum turndown and reduce startup times. During these tests, TRAX could examine thermal stresses and estimate emission levels. TRAX closely analyzed plant dynamics during startup, shutdown and load maneuvering events to determine potential effects of gas turbine exhaust profile events, as well as the effects of these operational strategies on the HRSG and steam turbine performance.
TRAX also examined turndown, modifications to duct burners, changes in heat transfer surface areas, addition or removal of SCR catalysts layer(s), operation at different ambient conditions, and other plant configuration changes to optimize the plant ramp rate, minimize turndown and decrease startup time. TRAX encountered several operational transient potential pitfalls and physical limits, including steam turbine and drum thermal stress and unacceptable levels of emission during various tests.
For this client, TRAX was able to presentsuggestions to increase ramp rate, including IGV improvements to enable fasterstartup. TRAX also provided the client with suggestions for furtherexamination, such as investigating thermal blanketing of the steam turbine andbattery testing.
By testing differentscenarios and comparing the impacts on temperatures, flows and pressures aroundthe equipment, TRAX could help optimize the client’s cold startup whilemaintaining steam quality.
The various transient event testing also acted to find excessive outcomes, measure the severity of excursions and establish the need for mitigation. TRAX highlighted opportunities for controls optimization and encouraged SCE to test and revise operating procedures.
With the provided model, the client could continue to independently test further scenarios by causing equipment to malfunction within the model, demonstrating broken shafts, valves failed open/closed/stuck, tube ruptures or fouled tubes.
