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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

SIMULATION OF NATURAL GAS COMBINED CYCLE POWER PLANT AT ELEVATED TEMPERATURES

Achyut Paudel
Interdisciplinary Thermal Science Laboratory Colorado State University, Fort Collins, CO 80524

Todd M. Bandhauer
Interdisciplinary Thermal Science Laboratory Colorado State University, Fort Collins, CO 80524

Abstract

It is well known that increasing ambient temperature negatively impacts the performance of natural gas combine cycle (NGCC) power plants. However, no simplified model that adequately accounts for this effect has been presented in the literature. In the present study, a coupled heat transfer, thermodynamic, and gas turbine performance model for a NGCC power plant was developed to investigate the impact of increase ambient temperature on cycle performance. Using this model, a 565 MW NGCC power plant was simulated to study the effects of increasing ambient air temperature on overall performance. Because the gas turbine exhaust temperature and flow rate change significantly with ambient temperature, the most challenging portion of this system was the bottoming Rankine cycle of the power-plant, which has a heat recovery steam generator (HRSG) with a single reheat cycle, multiple pressure steam turbines, and an evaporatively cooled condenser. The overall conductances (UAs) of the HRSG heat exchangers were scaled to predict performance at elevated temperatures. Additionally, the steam mass flow rates and superheat temperatures were adjusted accordingly with the resulting HRSG flue gas temperature and flowrates. The simulation results show that, as the ambient temperature increases from 15°C to 40°C, the low pressure steam turbine back pressure increases from 6.89 kPa to 23.6 kPa, and the condenser load decreases by 3.92%. As a result, there was a drop in efficiency of the power-plant by 3.55%, and total power output was reduced by 16%. Future investigations will use this modeling approach to determine optimal waste heat recovery strategies that can minimize the drop in overall performance.

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