A parametric investigation of the Chilled Ammonia Process from energy and economic perspectives
Highlights
► First, the CAP integrated with USC power plants is investigated parametrically. ► Then, the optimal integration is analyzed in details. ► Capturing 88.4% of the CO2 reduces the power by 19% and the efficiency by 8.6% points. ► The specific heat duty is and the SPECCA index is . ► The cost of avoided CO2 is and the cost of electricity 82.4 €/MWhe.
Introduction
The ongoing scientific discussion does not focus on whether fossil fuels will have to meet a major portion of the short- and the mid-future energy demand, but rather on how they will be most effectively exploited in doing so, in terms of the overall efficiency and the environmental impact. At the same time, renewable sources will have to be more diffusely implemented in the energy infrastructure to allow independence from fossils in the far future. In this outlook, coal will play most likely a primary role among the conventional sources, being the most abundant and diffuse of all. However, as carbon dioxide anthropogenic generation and climate change appear to be correlated, the capture of that generated carbon dioxide and its storage in geological formations turns to be advisable. There are three classes of capture technologies that are being investigated worldwide: (i) those that capture the carbon before the combustion process, named pre-combustion capture, (ii) those after the combustion, called post-combustion capture, and (iii) those that have the combustion occur in high-purity oxygen, said oxy-combustion, in order to generate flue gases at a high concentration of carbon dioxide that can be sequestered after a less energy-intensive clean-up with respect to the previous two classes.
Post-combustion capture has the large benefit of being readily applicable to already existing power plants, both coal- or natural gas-fired. The carbon capture can be accomplished by adsorption or chemical absorption. The use of amine aqueous solutions for the chemical absorption is widely used in other industrial sectors, such as the oil&gas or the urea industries. Currently, the so-called advanced amines are under intensive analysis by industrial and academic centers with the common scope of reducing the energy demand when applied to the power generation industry. In the recent years, the alternative chemical absorption in ammonia aqueous solutions has been proposed. In particular, the absorption in chilled working conditions, a process commercially named Chilled Ammonia Process (CAP), is considered a promising technology that still needs further numerical modeling and pilot testing to prove its viability.
As a continuation of an older investigation [1] and an extension of a more recent one by the authors [2], this work simulates in details the integration between modern Ultra Super Critical (USC) power plants and the conventional layout for CAP, which was implemented by the company Alstom in the pilot plant that has recently concluded the experimental operation, as indicated by Sherrick et al. [3], but outdated by a modified version for the plants that will be built, as depicted by Black et al. [4]. The numerical results referred to the former layout have the advantage of being comparable against the experimental results, which however have been limitedly diffused so far. The extension includes (i) a review of the literature of experimental studies that may be adopted in calibrating or validating the thermodynamic codes, (ii) the modeling of the removal of the ammonia slipping out of the absorber and (iii) an estimation of the investment as well as the operation costs of both capture and power islands and their influence on the Cost Of Electricity (COE).
The following sections describe in sequence: (i) the scope of the work and the methodology adopted in seeking it, (ii) the review of a number of articles from the open literature providing experimental vapor–liquid equilibrium data in the region of interest for CAP, (iii) the modeling approach, comprising both the energy and the economic analyses, and the simulations launched with the developed models and (iv) the results along with the discussion of the trends.
Section snippets
Scope and methodology
The scope of this work is (i) to identify the design parameters of the capture block and (ii) to quantify their influence on the energy performance indexes of the overall plant through a parametric investigation in order to determine the optimal set of values. This optimal set is used to define the best case. Moreover, (iii) to model precisely the integration between the carbon capture and the power generation through a specific investigation of the best case. Finally, (iv) to evaluate the
Experimental data bibliography review
This paragraph reviews the experimental vapor–liquid and vapor–liquid-solid equilibrium data that can be found in the open literature and exploited for either the calibration or the validation of the thermodynamic models used to simulate CAP. The NH3–H2O is widely studied for application as a refrigerating fluid or as a working fluid in the Kalina cycle. The CO2–H2O is considered for various physical chemistry phenomena. The CO2–NH3–H2O system is researched for process water treatment and for
Models and simulations
The overall plant consists of a power block and a capture block. The power side includes Flue Gas Desulfurization (FGD) from which the exhausts are directed to the capture side. The power block, either in the approximated model or in the detailed one, is treated as a whole system whereas, in contrast, the islands comprising the capture block are simulated separately. These islands are: (i) exhaust chilling, (ii) carbon dioxide absorption, regeneration and gas washing (which will be shorten as
Results and discussion
Before presenting the parametric and best case investigation results, some preliminary considerations are introduced that, despite approximate, may be of use in the critical review of results of any study on CAP.
Conclusions
The integration of USC plants with CAP is assessed by way of a parametric investigation to determine the optimal design parameters of the capture block from an energy perspective and by a more detailed best case investigation of the overall plant from both energy and economic perspectives. The thermodynamic model of the chemical absorption is validated against experimental data from the open literature indicating a good agreement for binary mixtures and acceptable for ternary. In the parametric
Acknowledgments
The authors acknowledge gratefully the support by Enel SpA.
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