Dynamic Integration of Solar Assisted Carbon Capture with Thermal Energy Storage for Flexibilization of Natural Gas Combined Cycle Power Plant

Abstract A fast increase in power generation from renewable sources is creating the need for a larger contribution from power generation from other sources. This demands more flexible power generation systems, making energy storage a necessity to integrate flexible power generation with the grid demand. Thermal energy storage is a good option to be integrated with Rankine power cycles. Particularly, sensible heat stored in concrete offers the option for integration with power plants in a flexible and cost competitive way. This document reports research results for the development of a thermal battery cell (TBC) capable of operating at temperatures up to 425°C. The TBC integrates a concrete matrix, engineered to provide enhanced thermal and mechanical properties, and thermosiphon elements capable of dual action operation, engineered to enable charging and discharging on a single thermal battery unit. Components for the TBC were researched in the laboratory. Two integrated single-thermosiphon TBC's with storage capacities of 1.5 kWhth and 10 kWhth and an additional 150 kWhth TBC were designed and tested. Efficient heat transfer to/from the storage media, was demonstrated in the laboratory. All three TBC's were tested under several different charging and discharging conditions and proven to be resourceful. Test results demonstrate the feasibility of the concept to store sensible thermal energy in concrete between 300°C and 400°C, with fast charging and discharging performance provided by the thermosiphons, suited for power generation unit fast ramping. In the second part of this research, a typical NGCC plant equipped with PCC was modeled in Aspen Plus and validated against similar models generated by the National Energy Technology Laboratory (NETL), and then adjusted to match the conditions of a plant located at Poza Rica, Mexico. After validation of the NGCC plant model with PCC, heat integration options were considered where heat from the flue gas cooler, CO2 dryer, and CO2 compressor intercoolers was used for heating of feedwater or low pressure (LP) steam in the steam cycle. The model was further modified to include solar-assisted carbon capture (SACC), to offset the detrimental impact of the PCC system on plant operations. The use of parabolic trough solar thermal collectors for heating of the stripper reboiler in the PCC system was considered in the Aspen Plus modeling. It was found that by using solar thermal energy for PCC reboiler heating, the LP steam extraction used to supply heat to the carbon capture reboiler element could be reduced in flow rate or eliminated depending on the quantity of solar thermal energy available. Modeling showed that if 100% of the reboiler duty could be supplied via solar thermal energy, net plant power would increase significantly relative to the case without solar thermal collectors. The availability of the solar resource was also predicted for the target location in Mexico using the System Advisor Model (SAM) developed by the National Renewable Energy Laboratory (NREL). By coupling the modeling results from SAM with those produced by Aspen Plus, annual plant energy production for an NGCC plant with PCC and using solar thermal energy for reboiler heating was found. A final case was modeled in both Aspen and SAM, where solar thermal energy was used for LP steam heating. While this case has marginally better performance than the case where solar thermal heat was applied to the reboiler, the added complexity of this system outweighs the slight increase in net annual power generation. This modeling effort demonstrated that solar thermal heating of the stripper reboiler in an NGCC plant with PCC could meaningfully offset the detrimental impact of carbon capture on plant efficiency and power generation loss, offering an attractive renewable energy option to NGCC carbon mitigation.