In the previous section the context, framework and opportunity for the development of this thesis has been presented. Following, the specific objectives addressed along the thesis are described.
The present thesis aims to contribute to the CFPP-CaL integration research with the following objectives:
1) Developing models based on lab-scale tests using realistic process conditions. From the analysis of full-scale plant operation, a set of operation conditions should be defined to be later reproduced at lab-scale. Results of lab-scale tests can be used in the development of a novel carbonator model which considers realistic CaO regeneration conditions. The new model would allow a more accurate evaluation and prediction of the carbonator performance, which is relevant for the development of process configurations and reactors design for the integration in real power plants.
This objective intends to respond to the research opportunity (a) discussed in the previous section.
2) Improving the process scheme to reduce the energy consumption in realistic CaL operation. CO2 capture efficiency and heat integration within the CFPP-CaL plant should be designed by considering the important role of the diffusion-controlled carbonation phase, which becomes relevant when CaO regeneration is carried out under high CO2 partial pressure as is the case in the CaL process for CO2 capture.
This objective intends to respond to the research opportunity (b) discussed in the previous section.
3) Evaluating the performance of several natural CaO precursors, such as limestone, dolomite, and steel slag. Even though there is a large number of synthetic sorbents that are being currently analyzed within the CaL process, the present thesis is focused on the study of sustainable, environmental-friendly, low cost and widely available precursors as required to make possible the CaL large scale deployment.
Experimental results on their multicycle capture capacity behavior at realistic CaL conditions are needed to evaluate the feasibility of using these CaO precursors.
Furthermore, the energy penalty that arises from the integration of the CaL process into a coal fired power plant using these CaO precursors should be addressed. This objective intends to respond to the research opportunity (h) discussed in the previous section.
4) Developing a new hybrid process based on the CaL technology which could improve state-of-the-art configurations. Hybrid processes, which take advantage of synergies
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between different CO2 capture systems (such as CaL, oxy-combustion or membranes technology), could reduce the energy consumption and the equipment size associated to integrate CO2 capture in fossil-based power plants. This objective intends to respond to the research opportunity (c) discussed in the previous section.
Regarding the development of the CaL process as TCES system, the present thesis aims to contribute to the CSP-CaL integration research through the following objectives:
5) Developing models based on realistic operation and multicyclic behavior of CaO within TCES schemes. Thus, a specific carbonation model for TCES should consider optimal integration conditions of the CaL process within CSP facilities, such as reducing the receiver temperature and increasing, as much as possible, the carbonation temperature. Moreover, carbonation under high pressure is an interesting option to improve the power cycle efficiency in TCES schemes, which requires the analysis of how the carbonation (kinetics, sorbent deactivation, etc.) is affected by increasing the reactor pressure. This objective intends to respond to the research opportunity (e) discussed in the previous section.
6) Performing a critical assessment about the advantages and challenges of developing the CaL process for high temperature thermochemical energy storage. This objective intends to respond to the research opportunity (d) discussed in the previous section.
7) Gaining knowledge about the possibilities of integrating the CaL process in both new and operating CSP plants. Power production from the stored energy by means of a Brayton CO2 closed cycle could improve both the reliability and the power plant efficiency regarding previously proposed schemes, which are based on air open schemes. This objective intends to respond to the research opportunity (d) discussed in the previous section.
8) Exploring the integration with the TCES core system of alternative direct and indirect cycles (steam turbine, closed Brayton CO2 and indirect-supercritical CO2) for relevant CSP-CaL integration conditions. This objective intends to respond to the research opportunity (g) discussed in the previous section.
9) Enhancing the CSP-CaL plant efficiency by improving heat integration. An interesting possibility of the CaL process is to store energy at ambient temperature for long term energy storage. However, due to the high temperatures in both the calciner and carbonator reactors, a low temperature storage involves a large streams temperature change along the entire cycle, which makes crucial an optimized heat integration to achieve an adequate system efficiency. This objective intends to respond to the research opportunity (f) discussed in the previous section.
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10) Another possibility is to store the solids at high temperature. In this case the process scheme is simplified by requiring fewer heat exchangers due to a lower temperature difference between the reactors and storage. On the other hand, long term storage cannot be considered because of the temperature losses. However, the CSP-CaL system could be operated under a solar multiple (defined as the ratio of the solar thermal power to the power block design thermal input) in a similar way than in currently CSP plants. The development of specific schemes for this configuration could reach a compromise between the overall plant efficiency and heat integration complexity. This objective intends to respond to the research opportunity (f) discussed in the previous section.
11) Assessing the technologies to be used within the CSP-CaL scheme, with special focus on solar receiver and solids management. This objective intends to respond to the research opportunity (d) discussed in the previous section.
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