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Products > Combined Cycle > GT MASTER > Sample 2

Performance of a 350 MW Condensing Combined Cycle with Cogeneration at Varying Loads

Whereas in GT PRO you often create many different designs for a single project when you are scoping out various options, in GT MASTER, you want to run many different operational scenarios using a single plant configuration.  This sample focuses on using a single plant model to compute expected performance under different loading situations, at a fixed ambient condition.

This is a model of a three pressure non-reheat combined cycle in 2-on-1 configuration with cogeneration steam taken from IP header.  The plant is based on two ALSTOM GT 11N2 gas turbines, nominally rated at 115.4 MW, 865 lb/s / 392 kg/s airflow, 33.6% LHV efficiency and 988 F / 531 C exhaust temperature.  Nominal ISO net plant performance is 344 MW electric output at 50.6% LHV efficiency (6740 BTU/kWhr LHV heat rate) with no process steam flow.

The E-LINK utility lets you run batches of cases from MS Excel.  The plant design here is used to generate expected performance plots shown below using E-LINK.

This chart shows how this plant’s efficiency changes on a given day when operated with a specific loading logic.  Each line represents fixed process steam extraction, where higher efficiencies are associated with lower process flows.  The plant load is varied by increasing engine load from minimum allowed to base load with no duct firing.  Additional power (at lower efficiency) is available by duct firing when the gas turbine reaches full load.  Plant efficiency varies by about four points between minimum and base load.  Full firing reduces plant efficiency by almost one percent relative to base load unfired condition.  This data is essential for determining incremental heat rate versus power output at known process demand.

This chart shows the plant heat consumption from the same set of runs.  It is useful to nominate gas consumption based on projected ambient conditions and process steam demand.