Optimal Operation of a Semi-Closed Oxyfuel-Combustion Combined Cycle Power Plant
Abstract/Contents
- Abstract
- Gas turbines provide flexibility to electricity systems today. In a low-carbon future energy system, natural-gas-based power systems with CO2 capture may take over that role. In this thesis, I analyze the operations of an oxyfuel-based natural gas system with CO2 capture and storage that is designed to operate flexibly on timescales of order one hour. Specifically, I present optimal hour-to-hour operation of a flexible semi-closed oxyfuel-combustion combined cycle (SCOC-CC) power system. Our method includes co-optimization of the required air separation unit used to produce O2. Computational optimization is used to maximize operating profit. The system consists of a cryogenic air separation unit (ASU), oxygen storage facilities, a natural gas combustion turbine, a heat-recovery steam generator, a steam turbine, and a CO2 purification and compression unit. In this integrated system, I represent all components in a modular fashion using energy and mass balances. The air separation unit is modeled for operation at full capacity and part load based on industrial data. The gas turbines, steam turbines, and CO2 purification and compression units have part-load operation modeled based on existing literature. In order to model the oxyfuel-combustion gas turbine, the part-load gas turbine model is expanded with pure oxygen combustion and a recirculation fluid cycle. The optimal operation maximizes daily operating profit using a Sparse Nonlinear OPTimizer (SNOPT) algorithm with multiple starting points due to the nonconvexity of the problem. Whereas previous studies have only optimized performance of oxyfuel-combustion combined cycles, the system in this work is able to operate flexibly, and its overall operation, including time-varying electricity prices, is optimized. It also includes the air separation unit and an oxygen storage facility within the system boundary. I show that the oxyfuel-combustion system can be operated more flexibly than generally perceived. Operating profit is increased, especially at high price differentials throughout the day, by running the air separation unit at full capacity at times of low electricity prices, storing oxygen and running the oxyfuel gas turbine at full load in times of high electricity prices. This avoids energy-intensive air separation when the economic penalty is the greatest. Sensitivity studies show no significant improvements in operating profit with increased ASU ramp rate for day-ahead market participation but show increased profit with added oxygen storage up to a threshold of maximum oxygen storage capacity (7% maximum increase in profit over the base case). They also show that oversizing the ASU does not result in gains in operational profit but undersizing it results in decreasing operational flexibility and thus decreasing operating profit (undersizing to 80% of original capacity leads to a 17% reduction in operating profit). Furthermore, the system`s profitability strongly depends on the natural gas price (March 2016: 57.4 k$/day vs. March 2014: -77.6 k$/day, both in the high variability case).
Description
| Type of resource | text |
|---|---|
| Date created | June 2016 |
Creators/Contributors
| Author | Teichgraeber, Holger |
|---|---|
| Primary advisor | Brandt, Adam R. |
| Degree granting institution | Stanford University, Department of Energy Resources Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
Bibliographic information
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Preferred citation
- Preferred Citation
- Teichgraeber, Holger. (2016). Optimal Operation of a Semi-Closed Oxyfuel-Combustion Combined Cycle Power Plant. Stanford Digital Repository. Available at: https://purl.stanford.edu/gt217kt6500
Collection
Master's Theses, Doerr School of Sustainability
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