(181f) Dynamic Modeling, Validation and Optimization of a Solvent-Based CO2 Capture Process Under Flexible Operation

Amines-based CO₂ capture technology is the most matured technology for post combustion CO₂ (PCC) capture. However, the parasitic loss in the capture plant and its dynamics can adversely affect the efficiency and load-following capability of the host plant. One way of mitigating these problems is flexible capture in the PCC unit where the extent of CO₂ capture can be considered as a degree of freedom. However, during load-following operation of the host power plant, the CO₂ capture unit is subjected to significant variability due to changing flue gas flowrate and composition. Flexible capture in the PCC unit under load-following operation requires excellent tracking control performance along with good disturbance rejection while maximizing the efficiency. Optimal design and operation of the capture plant using an accurate dynamic model is the key to satisfying such challenging operational requirements.

Development of dynamic models of the amine-based capture units including model validation with limited industrial data has been reported by various authors.^1-5 However, a rate-based dynamic model with an accurate two-film model and electrolyte NRTL-based thermodynamic model is still missing in the literature. In this talk, development of such a rigorous dynamic model and its validation with large amount of industrial data will be presented.

The dynamic model is developed using the Institute for Design of Advanced Energy Systems (IDAES) Process System Engineering (PSE) computation platform.⁶ The tower model includes mass and heat transfer between the liquid and gas phases using a two-film model. Extended Fick’s law and Maxwell-Stefan equations are applied to describe the transport in the films. An electrolyte-NRTL model is developed for modeling the vapor-liquid equilibrium at the interface of the two films. The models are developed considering the ion-ion, ion-molecule and molecule-molecule interactions.^7-9 The reaction kinetics are modeled so that the complex equilibrium behavior of these electrolyte systems can be captured in a thermodynamically consistent manner. The enthalpy model is developed so that it remains consistent with the thermodynamic model. A rigorous dynamic reboiler model is also developed. The tower models are validated with the dynamic test run data collected from the National Carbon Capture Center (NCCC) located in Wilsonville, Alabama, USA. These data sets are generated under considerable variation of solvent flowrate, gas flow rate, CO₂ concentration in the gas, and steam flowrate to the reboiler as would be expected under the part-load operation of the host power plant. As the plant data are noisy and do not satisfy the mass and energy balances, a dynamic data reconciliation problem is solved. The validated dynamic model is used for optimal design and operation considering various flexible operation scenarios.

References

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