Optimal dynamic operation of natural gas combined cycles accounting for stresses in thick-walled components

Jairo Rúa,Roberto Agromayor,Magne Hillestad,Lars O Nord

doi:10.1016/j.applthermaleng.2019.114858

Jairo Rúa, Roberto Agromayor + Show 2 more

Open Access

https://doi.org/10.1016/j.applthermaleng.2019.114858

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Abstract

Flexible natural gas combined cycles will play a fundamental role in future electric markets. Stresses in thick-walled components and gas turbine load ramps are arguably the main limiting factors during transient operation. Classical control strategies as PID are not suitable to incorporate technical constraints such as stress limits. This work presents a control methodology based on model predictive control where the stress in the walls of the high pressure drum and the first high pressure steam turbine rotor are computed simultaneously with the optimal control sequence. Thus, the maximum allowable stress in this equipment can be set as a constraint and the control actions imposed in the power plant ensure that these limits are not exceeded. Two cases simulating flexible operation under realistic conditions and tight constraints on the stress limits are included. Results show that with the proposed control methodology the natural gas combined cycle can respond to load step changes of 165 MW in 300 s, and can operate close to the material maximum stress limit without exceeding it. The robustness and flexibility of this methodology allows its application to different operation conditions such as start-ups and shut-downs.

Highlights

Anthropogenic greenhouse emissions have continuously increased since the industrial revolution
The performance of the NGCC during the load ramp is analysed under reasonable stress limitations that can be expected in current modern power plants
This work proposes a control methodology based on linear Model predictive control (MPC) with stress control

Summary

Introduction

Anthropogenic greenhouse emissions have continuously increased since the industrial revolution. If this tendency is maintained, global warming is expected to reach temperatures of 1.5 °C above pre-industrial levels between 2030 and 2050 [1]. Electricity is progressively gaining relevance in the energy sector. It currently accounts for 20% of the final energy global consumption and this amount is only expected to increase [3], reaching almost 40% in 2050 [4]. Renewable energy sources will play a major role in this new energy scenario and will have large shares in the electricity mix, predicted to reach about 40% of the power generation in 2040 [3]. Traditional thermal power plants will remain the largest source of electricity production [3]

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