Exergetic Analysis of a Natural Gas Combined-Cycle Power Plant with a Molten Carbonate Fuel Cell for Carbon Capture

This study aims to propose the repowering of an existing Italian natural-gas fired combined cycle power plant through the integration of Molten Carbonate Fuel Cells (MCFC) downstream of the gas turbine for CO2 capture and to pursuit an exergetic analysis of the two schemes. The flue gases of the turbine are used to feed the cathode of the MCFC, where CO2 is captured and transported to the anode while generating electric power. The retrofitted plant produces 787.454 MW, in particular, 435.29 MW from the gas turbine, 248.9 MW from the steam cycle, and 135.283 MW from the MCFC. Around 42.4% of the exergy destruction has been obtained, the majority belonging to the combustion chamber and, in minor percentages, to the gas turbine and the MCFC. The overall net plant efficiency and net exergy efficiency are estimated to be around 55.34 and 53.34%, respectively. Finally, the specific CO2 emission is around 66.67 kg/MWh, with around 2 million tons of carbon dioxide sequestrated.

Exergy analysis of a reversible chiller

The work presents the results of exergetic analysis of a reversible chiller providing both cooling and space heating in varying operational modes. The year values of avoidable parts of exergy destruction occurring in each system component are used for the analysis. The outcomes obtained showed that the both inside and outside heat exchangers have the highest priority for improvement revealing more than 718 kW-hr avoidable year exergy destruction within the system.

A monitoring framework based on exergetic analysis for sustainability assessment of direct laser metal deposition process

With the constant increase of energy costs and environmental impacts, improving the process efficiency is considered a priority issue for the manufacturing field. A wide knowledge about materials, energy, machinery, and auxiliary equipment is required in order to optimize the overall performance of manufacturing processes. Sustainability needs to be assessed in order to find an optimal compromise between technical quality of products and environmental compatibility of processes. In this new Industry 4.0 era, innovative manufacturing technologies, as the additive manufacturing, are taking a predominant role. The aim of this work is to give an insight into how thermodynamic laws contribute at the same time to improve energy efficiency of manufacturing resources and to provide a methodological support to move towards a smart and sustainable additive process. In this context, a fundamental step is the proper design of a sensing and real-time monitoring framework of an additive manufacturing process. This framework should be based on an accurate modelling of the physical phenomena and technological aspects of the considered process, taking into account all the sustainability requirements. To this end, a thermodynamic model for the direct laser metal deposition (DLMD) process was proposed as a test case. Finally, an exergetic analysis was conducted on a prototype DLMD system to validate the effectiveness of an ad-hoc monitoring system and highlight the limitations of this process. What emerged is that the proposed framework provided significant advantages, since it represents a valuable approach for finding suitable process management strategies to identify sustainable solutions for innovative manufacturing procedures.

Exergy analysis of an atmospheric residue desulphurization hydrotreating process for a crude oil refinery

The exhaustion of petroleum reserves and the declining supply of conventional feedstock have forced refineries to use heavier crude oil in their production. Removing the undesirable components containing sulphur and metals in the atmospheric residue (AR) fraction requires extensive catalytic hydrotreating (HT) atmospheric residue desulphurization (ARDS) process. In this work, we endeavour to collect and present a comprehensive dataset to develop and simulate the ARDS HT model. This model is then used for an exergetic analysis to evaluate the performance of the ARDS HT model regarding the exergy destruction, the location of losses and exergetic efficiency. The massive exergy destruction is caused by significant differences in chemical exergy of source and product streams during separations, fractionation and reactions. The exergy destruction in the equipment independent of chemical exergies such as heat exchangers, pumps and compressors is relatively low. This exergetic analysis revealed that the majority of the processing equipment in the ARDS HT process performed satisfactorily. However, the remaining equipment requires improvement for its performance in regards to exergetic efficiency or/and avoidable exergetic losses. To enhance the efficiency of the equipment that is intensive in terms of exergy and energy use, the use of clean and high purity renewable hydrogen and several process rectification is proposed.

Energetic & exergetic analysis of a parabolic trough: concentrated solar power plant

Solar energy is the most affordable source of energy. Parabolic trough systems are used to concentrate and extract heat, therefore it’s very significant to analyse its performance in terms of energy and exergy. Exergy based analysis of the system ensures the eradication of losses, resulting in the yield of energy of the highest quality. In this paper, an investigation has been carried out using numerical simulation with an objective of analysis of Parabolic Trough Collectors on the basis of energy and exergy. Detailed second law analysis has been performed by varying the system and operating parameters through computer simulation. Exergy output has been determined by analysing the effect of major system parameters, namely, mirror reflectivity, glass transmissivity, absorptivity, the diameter of glass envelop, and the receiver. The operating parameters considered in the investigation are insolation and temperature rise parameters. The extensive investigation of the parabolic trough of a concentrated solar power plant for various design parameters in the range of operating parameters reveals that it is beneficial to operate the system at higher temperature as opposed to the preference of the operating system at lower temperature from purely thermal considerations.