(681d) Optimization of the Various Modes of Flexible Operation for Post-Combustion CO2 Capture Plant
Adding a post-combustion CO2 capture plant to a power plant comes with a substantial energy penalty as significant amounts of steam must be used to strip off the absorbed CO2 and regenerate the solvent. This leads to a decrease in the power output of the plant, typically by ~30 %. One option to mitigate the adverse effect of power plant output loss is to operate the CO2 capture plant in flexible modes in response to the varying electricity market price. This way the overall profit can be improved while meeting the peak electricity demand. Flexible operation can be done, for example, by reducing the capture level (through CO2 venting, by-passing a part of flue gas, CO2 capture level reduction, etc.), or by reducing the amount of regenerated spent solvent on a periodic or temporary basis, i.e., storing the CO2 rich solvent in a tank for a time while ensuring a constant CO2 capture level by using the already regenerated solvent stored in another tank. The objective of this work is to simulate, optimize, and analyze the economics of the various modes of flexible operation including the CO2 capture level reduction, solvent storage, and the both options simultaneously. An equilibrium based model for complete absorption/regeneration system has been used and its optimizations are performed in the gPROMS interface.
There are three novel features in this work when compared to the previous works [1-5]: 1) A more detailed, accurate process flow sheet model is used for the analysis and optimization rather than first-order approximations more suitable for quick screening purposes. 2) Many previous works treated captured CO2 as products of market value. They then posed the problem as optimizing the flexible operation in light of varying energy price and CO2 market price. In contrast, we consider penalties on the CO2 emission. We assume that captured CO2 holds no market value as the market for CO2 is likely to be highly limited in view of the huge CO2 quantity once CO2 capture becomes ubiquitous. 3) Both options of dynamically varying the capture level and storing the solvent (with varying storage capacities and different input energy cost profiles) are considered simultaneously. Therefore, the simultaneous operation can have advantages in optimizing both capture reduction level and regeneration level for the solvent storage. The Simultaneous mode of the flexible operation has been shown to offer the greatest advantage over the inflexible operation.
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