(724g) Comparison in Dynamic Response of Energy-Storing Cryogenic and Chemical Absorption Carbon Capture Systems to Electricity Demand

Authors: 
Safdarnejad, S. M., Illinois Institute of Technology
Strahl, W., Brigham Young University
Hedengren, J. D., Brigham Young University
Baxter, L. L., Brigham Young University
Projections of energy production from different resources shows that fossil fuel will remain the primary energy source by 2040 [1]. Concerns over CO2 emission from the combustion of fossil fuels have necessitated the technology development to mitigate the CO2 emission from these resources. Several technologies are developed for carbon capture such as physical and chemical absorption, oxyfuel combustion, pre-combustion, membrane and cryogenic separation [2]. In this study, the dynamic performance of two of these carbon capture systems is compared in response to volatile electricity prices and demand. The systems in consideration are amine-based chemical absorption and cryogenic carbon capture (CCC). Amine-based chemical absorption is a mature technology in gas processing units and is under investigation and commercialization for the power industry. The CCC process is a novel technology that requires less energy in comparison to many carbon capture systems including amine-based chemical absorption. This system captures CO2 from power plant flue gas by cooling it to the desublimation temperature of CO2. Solid CO2 is then separated from the remaining gases by filtration that is followed by its liquefaction. To liquefy CO2, the heat integration inside the carbon capture plant it utilized, resulting in significantly lower energy consumption in comparison to other capture systems. The CCC process is able to capture 99% of CO2 from the flue gas as well as other pollutants such as SOx, NO2, mercury, and particulate matter. Additionally, the CCC process is able to store energy in large-scale and in the form of liquefied refrigerant that can be used in peak hours, resulting in a more stable power grid [3-11].

This investigation considers the integrated system of a coal-fired power generation unit and the above mentioned capture systems. The energy-storing versions of both capture systems are considered in this analysis, which allows for more flexibility toward volatile electricity prices. Unlike many of the previous analyses that consider a constant electricity demand, the goal in this analysis is to compare the performance of both carbon capture systems in response to the dynamic electricity demand while maximizing the operational profit. Inability of both systems in meeting the electricity demand is severely penalized. Thus, meeting the power demand is given the higher priority in comparison to maximization of the profit. The dynamic model of the CCC process is developed previously by the authors and is used in this analysis [3-7]. The model from [12-16] is also adopted for the analysis of the amine-based carbon capture. Some modifications are needed, however, to develop a common basis for comparison. The dynamic models of both systems are developed in the GAMS modeling language and are run for 8 days of simulation time on the NEOS Server [17]. Nonlinear solvers such as KNITRO, CONOPT, and IPOPT are used in analysis to solve the models. A 2014 electricity demand profile from a residential area in San Diego, CA, with a maximum demand of 2000 MW is adopted in this study. A common assumption in comparing the carbon capture systems is 90% capture rate. Thus, 90% capture rate is also assumed in this study while a penalty of $50/tonne is applied for the emission of remaining CO2 to the atmosphere. Wind power is also utilized in meeting the total electricity demand and results in a more sustainable power production. In both systems, it is observed that they are capable of meeting the dynamic electricity demand throughout the simulation horizon while priority is given to using the wind power in meeting the demand. The remaining power requirement is met from coal. It is also observed that the CCC process consumes less total energy than the amine system to capture the same amount of CO2. Additionally, the operational profit of running the CCC process is significantly higher than the amine system. The lower energy consumption of the CCC process, higher operational profit, and the large-scale energy storage capability of it suggest that the CCC process could be a promising system for large-scale integration with the power grid which helps in stabilizing the grid.

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