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Dynamic Simulation and Operational Flexibility Assessment of Integrated Solvent-based CO2 Capture Process with Combined Cycle Power Plants in Iran

Khorshidi, Mahshad | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58202 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Vafa, Ehsan
  7. Abstract:
  8. Solvent-based absorption is one of the most effective methods for reducing carbon dioxide emissions in combined cycle power plants. In such integrated systems, a portion of the steam from the intermediate-pressure turbine is utilized to supply heat to the carbon capture unit, and its condensate is returned to the heat recovery steam generator. This tight integration forms a coupled system. Key challenges include variations in flue gas flow rate and composition due to load changes and fuel switching. Therefore, the integrated system must be operationally flexible in both design and control. To assess these aspects, the development of a dynamic model of the integrated system is essential, and for this purpose, Aspen Plus software was used to perform steady-state and dynamic simulations of the combined cycle power plant and carbon capture unit. In this study, due to the slower transient response of the carbon capture unit compared to the power plant, dynamic simulation of the power plant was omitted, and the focus was placed on the dynamic behavior of the capture unit using a decentralized control structure. The designed control system effectively managed disturbances caused by changes in the flow rate and composition of the gas entering the absorber column. The results showed that implementing load changes in a stepwise manner helps to minimize severe disturbances in the system. The steady-state simulation of the integrated system was carried out under three conditions: 1) natural gas as the plant fuel, 2) diesel as the plant fuel, and 3) partial load operation of the plant. As a result, when the plant operated at 90% and 80% load, the net power output of the plant decreased to 89.87% and 70.30% of the full-load condition, respectively. Although the steam turbine output (and thus steam generation in the water/steam cycle) was reduced, sufficient steam was still available at the crossover between the intermediate- and low-pressure turbines for solvent regeneration. Additionally, switching the plant fuel from natural gas to diesel reduced the CO₂ capture rate from 90% to 71%, in order to maintain the gas and liquid loads within the absorber columns within design limits
  9. Keywords:
  10. Combined Cycle Power Generation ; Integrated System ; Operational Flexibility ; Steady State Simulation ; Dynamic Simulation ; Solvent Based Absorption ; Decentralized Control Structure

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