Evaluation of Novel Configurations of Natural Gas Combined Cycle (NGCC) Power Plants for Load-Following Operation using Dynamic Modeling and Optimization

Abstract

With increasing penetration of intermittent renewable energy sources into the electric grid, conventional thermal power plants are being forced to cycle their load and operate under low-load conditions much more frequently. A high-fidelity dynamic model of a natural gas combined cycle (NGCC) power plant with rigorous equipment level submodels is developed in this work. A model of the gas turbine (GT) for estimating its performance under off-design conditions, a thermo-hydraulic model for the heat recovery steam generator (HRSG), and a model of the steam turbine (ST) with moisture detection and model adaptation capability are also developed. Five novel configurations are proposed for controlling the main steam and reheat steam temperatures while avoiding “spraying to saturation” during fast load-following by considering different final high-pressure superheater (HP SH2)/reheater (RH) arrangements (in series or in parallel) and attemperation strategies (single-stage, two-stage, and damper-assisted attemperation). Load-following operation is studied under two operational strategies, i.e., the industry-standard coordinated control strategy and dynamic optimization. Dynamic optimization is used to maximize the plant efficiency while satisfying the operational constraints and state transition constraints. It was observed that while more than one configuration can avoid spraying to saturation and maintain the steam temperatures within their limits even during very fast load transients, their efficiency can greatly vary and that dynamic optimization, when feasible, can lead to superior efficiency than the coordinated control system. The parallel HP SH2/RH configuration using the damper-assisted attemperation strategy shows the highest efficiency.

Multiobjective Dynamic Optimization for Optimal Load-Following of Natural Gas Combined Cycle Power Plants under Stress Constraints

“…Only a brief summary of various sections of the NGCC model will be described here. More details can be found in our earlier publication …”

“…Therefore, a methodology was developed that can detect moisture formation and account for it in the model, if moisture is formed. More details about the ST model, including the algorithm for moisture detection and its accounting, can be found in our previous work …”

“…In our previous paper, a dynamic model of the entire NGCC plant was developed. Different configurations of NGCC plants were modeled, and operating strategies were evaluated to maximize the plant efficiency while avoiding a two-phase condition at the inlet of the superheater (SH)/reheater (RH) attemperator due to attemperator spray, a phenomenon known as “spraying to saturation.” , It should be noted that in power plants, the main steam temperature to the ST is tightly controlled . A lower main steam temperature not only results in lower plant efficiency but can also lead to undesired moisture formation in intermediate ST stages where steam condensation is not expected and/or a higher amount of moisture formation in the last stage or last few stages than what those stages are designed for.…”

Dynamic Optimal Dispatch of Energy Systems with Intermittent Renewables and Damage Model

“…The dynamic models of the energy systems considered are linearized models of the high-fidelity first-principle models of the charge and discharge models of the sodium sulfur (NaS) batteries [12], natural gas-fired combined cycle (NGCC) power plant [17,18], and supercritical pulverized coal-fired (SCPC) power plant [22], as depicted in Figures 1-3, respectively. The wind and solar power generation are considered as forcing functions based on historical data [25].…”

“…This constraint is expressed in Equations ( 16) and (17). The NaS batteries range of operation considering the regression data fit is shown in Equation (18).…”