열확산계수가 다른 균일물질에 대한 동적 엑서지 분석법과 비정상상태 엑서지 분석법의 비교

조하빈(Jo, Ha-Bin),최원준(Choi, Wonjun) 대한건축학회 2023 대한건축학회 학술발표대회 논문집 Vol.43 No.1

Small temperature differences between a target system and reference state characterize thermal exergy phenomena in the built environment. Exergy analysis results change significantly with temporal changes in environmental conditions, limiting the applicability of steady-state exergy analyses. Dynamic exergy analyses have been used to mitigate these limitations, but they neglect the effect of heat capacity and only change the boundary condition over time. Recently, an unsteady-state exergy analysis method that does not violate the thermodynamic integrity has been established. In this study, the difference between dynamic and unsteady-state analyses are compared with materials of different thermal diffusivity to clarify the limitation of the dynamic analysis and the necessity of unsteady-state exergy analyses.

Exergoeconomic analysis of an LNG integrated - air separation process

Hamayun Muhammad Haris,Ramzan Naveed,Faheem Muhammad 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.12

An integrated LNG regasification - air separation process is investigated using exergy and exergoeconomic analyses. The objective of developing this integrated process is to lower the calorific value of LNG by mixing regasified LNG with high purity nitrogen, while simultaneously recovering and utilizing valuable cryogenic energy from the LNG during its regasification to minimize the power consumption of the air separation unit (ASU) for nitrogen production. The overall exergy efficiency and exergy destruction of the integrated process are 76.47% and 28.52MW, respectively, with the compression section causing the most exergy destruction. Further exergoeconomic analysis of the proposed process reveals that the air compressors have the highest capital investment (CI) and operating and maintenance (O&M) cost rates, the pumps for cooling water and LNG have the highest exergoeconomic factors, and the low-pressure column and a multistream heat exchanger have the highest exergy destruction cost rates. A parametric study is also conducted to examine the impact of economic variables including interest rate, plant life, and compressor performance on exergy destruction, CI and O&M cost rates, and exergoeconomic factor. The findings of this study offer valuable insight into the design and optimization of similar integrated processes, with potential benefits for the energy industry.

Investigation of the thermodynamic performance of an existing steam power plant via energy and exergy analyses to restrain the environmental repercussions: A simulation study

Muhammad Haris Hamayun,Murid Hussain,Iqrash Shafiq,Ashfaq Ahmed,Young-Kwon Park 대한환경공학회 2022 Environmental Engineering Research Vol.27 No.1

Exergy analysis is an important tool to identify the improvements in various industrial processes. In this study, the existing steam power plant is examined based on energy and exergy analyses. The steam network in the power plant is comprised of two sections, one of them is used for paddy drying, while other portion is used to operate the turbine for in-house electricity production. Mass, energy, and exergy balances are applied to individual equipment of the plant. The power plant is modeled and simulated using Aspen HYSYS® V10. The calculated thermodynamic values are used for in-depth analysis of the power plant. Case-studies are included in this study to show the effect of various operational parameters on the process efficiency. The analysis shows that the boiler is the major source of exergy destruction, because of the incomplete combustion process, and inappropriate insulations. The remedial actions are also suggested in the study.

순산소 연소를 위한 초저온 공기분리장치의 엑서지 분석

최형철,문흥만,조정호 한국가스학회 2019 한국가스학회지 Vol.23 No.1

In order to solve the global warming and reduce greenhouse gas emissions, CO2 capture technology was developed by applying oxy-fuel combustion. But there has been such a problem that its economic efficiency is low due to the high price of oxygen gases. ASU is known to be most suitable method to produce large quantity of oxygen, to reduce the oxygen production cost, the efficiency of ASU need to be improved. To improve the efficiency of ASU, exergy analysis can be used. The exergy analysis provides the information of used energy in the process, the location and size of exergy destruction. In this study, the exergy analysis was used for process developing and optimization of large scale ASU. The process simulation of ASU was conducted, the results were used to calculate the exergy. As a result, to reduce the exergy loss in the cold box of ASU, a lower operating pressure process was suggested. It was confirmed the importance of heat leak and heat loss reduction of cold box. Also, the unit process of ASU which requires thermal integration was confirmed.

Multi-scale smart management of integrated energy systems, Part 1: Energy, economic, environmental, exergy, risk (4ER) and water-exergy nexus analyses

Ifaei, Pouya,Safder, Usman,Yoo, ChangKyoo Pergamon 2019 Energy Conversion and Management Vol. No.

<P><B>Abstract</B></P> <P>A holistic analytical approach is proposed to study the performance of fossil fuel burning integrated energy conversion systems considering energetic, economic, exergetic, environmental and risk (4ER) aspects in a framework. For this, life cycle assessment is conducted to study environmental impacts while other analyses are performed using the algebraic thermo-mathematical programming. The hazardous risks are also investigated using a hazard and operability approach. The external hot and cold utilities are also studied using a novel water-exergy nexus (WExN) analysis. Accordingly, two configurations are developed that integrate a Rankine cycle (RC) and an ejector refrigeration cycle (ERC) for two purposes: power and cooling co-generation (CGS) and power generation (MGS). Water losses in both systems are studied considering three cold utilities and two fossil fuel cycles using the WExN analysis, and the performance of the CGS and the MGS are compared employing several organic fluids. The results showed that the MGS had greater energetic and exergetic efficiencies, better environmental performance, and less hazardous risk impacts compared to the CGS employing almost all working fluids. The smallest exergy loss in the cooling system was 3.90 MW and 7.94 MW in the MGS allocating R123 and the CGS using R718, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A comprehensive analysis for evaluating energy conversion systems is described. </LI> <LI> A novel water-exergy nexus analysis is employed to evaluate hot and cold utilities. </LI> <LI> A mathematical program is developed to model two integrated energy systems. </LI> <LI> According to 4ER, power generation was preferred to power/cooling cogeneration. </LI> <LI> Allocating steam caused less risks and costs but great water losses in cold utility. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Performance, economic and exergy analyses of carbon capture processes for a 300 MW class integrated gasification combined cycle power plant

Lee, Woo-Sung,Lee, Jae-Cheol,Oh, Hyun-Taek,Baek, Seung-Won,Oh, Min,Lee, Chang-Ha Pergamon Press 2017 Energy Vol.134 No.-

<P><B>Abstract</B></P> <P>The techno-economic analysis of the CCPs was performed for a 300 MW class integrated coal gasification combined cycle (IGCC) power plant. In the study, the a-MDEA and Selexol processes were selected for the analysis as the representative of the chemical and physical solvent-based carbon capture process (CCPs). A rigorous evaluation of dual-stage CCPs, including power generation, economic evaluations, and exergy destruction, was performed. The net power of a-MDEA and Selexol processes was 267.3 MW and 291.4 MW, respectively, which corresponded to the thermal efficiencies of the dual-stage a-MDEA process of 32.3% and Selexol process of 35.2%. According to the economic analysis, the CAPEX of the Selexol process was approximately 1.39 times more expensive than that of the a-MDEA process. However, the OPEX of the Selexol process for removing a ton of CO<SUB>2</SUB> was approximately one third of that of the a-MDEA process. The exergy flow and destruction were also discussed to evaluate the associated impact on the major components of CCPs. Based on the exergy analysis, the suggestion to improve thermal efficiency was made and result was also briefly discussed. These results can aid in decision-making and in process development for commercial-scale CCPs with respect to thermodynamic and economic analyses.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Process simulation of dual-stage CCPs was carried out and used for thermodynamic and economic analysis. </LI> <LI> Technical analysis of dual-stage CCPs was performed to identify thermal and carbon capture efficiency. </LI> <LI> Economic performance of dual-stage CCPs was compared by CAPEX and OPEX. </LI> <LI> The direction of process improvement was suggested by means of exergy flow and destruction. </LI> </UL> </P>

Conceptual design and exergy analysis of combined cryogenic energy storage and LNG regasification processes: Cold and power integration

Lee, Inkyu,Park, Jinwoo,Moon, Il Pergamon Press 2017 Energy Vol.140 No.1

<P><B>Abstract</B></P> <P>This study aims to develop an efficient cryogenic energy storage (CES) process using the exergy from liquefied natural gas (LNG) regasification. While LNG has low internal energy, it has high exergy because of its cryogenic characteristics, and much of this exergy is wasted in the process of regasification. Thus, this work focuses on the recovery of LNG cold exergy to store cryogenic energy using air as a working fluid. The cold exergy of LNG is transferred in two forms: cold transfer by heat exchange to liquefy air, and shaft work transfer by direct expansion of LNG to compress the air. Thermodynamic analysis of the proposed process is carried out in three exergy flow steps: the LNG regasification step, the air liquefaction step, and the air expansion step. In addition, the proposed system has an advantage which system can store and release the energy simultaneously. Therefore, daily produced energy by CES system is more than double compare to the most recent contributions that have divided operation modes for energy storage and release. This study not only proposes an efficient energy storage process that can generate power flexibly but also highlights further possibilities for performance enhancement by thermodynamic analysis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The integrated Cryogenic energy storage (CES) and liquefied natural gas (LNG) regasification process is proposed. </LI> <LI> Exergy efficiency of the air storage process is 94.2%, and the air release process is 61.1%. </LI> <LI> The specific power output per 1 kg of LNG is about 160.92 kJ. </LI> </UL> </P>

Performance Enhancements in LiCl-H2O and LiBr-H2O Absorption Cooling Systems through an Advanced Exergetic Analysis

Parth Mody,Jatin Patel,Nishant Modi,Bhargav Pandya 대한설비공학회 2021 International Journal of Air-Conditioning and Refr Vol.29 No.1

This research study compares the thermodynamic performance of 10 kW lithium chloride–water (LiCl–H2O) and lithium bromide–water (LiBr–H2O) absorption cooling systems through first and second law of thermodynamics. Further, the exergy degradations happening in each component have been split into unavoidable and avoidable exergy degradations as well as endogenous and exogenous exergy degradations through advanced exergy analysis. Pressure–temperature–concentration (P–T –X) diagrams are drafted to clarify the real, ideal, and unavoidable cycles for LiCl–H2O and LiBr–H2O absorption cycles. Moreover, this paper exhibits the sensitivity of various system components towards the generator, condenser, and absorber temperature for both pairs. Energetic observation proves that LiCl–H2O pair is 10% more efficient as compared to LiBr–H2O pair. Exergetically, LiBr–H2O cycle struggles with additional (nearly 13.45%) exergy destruction than LiCl–H2O cycle. The major contribution (around 70% to 80%) of irreversibility comes from the generator and absorber. Comprehensively, the parametric partitions of irreversibility rate in each component provide broad indications to prioritize the system components for enhancements.

Development of partial liquefaction system for liquefied natural gas carrier application using exergy analysis

Jungho Choi 대한조선학회 2018 International Journal of Naval Architecture and Oc Vol.10 No.5

The cargo handling system, which is composed of a fuel gas supply unit and cargo tank pressure control unit, is the second largest power consumer in a Liquefied Natural Gas (LNG) carrier. Because of recent enhancements in ship efficiency, the surplus boil-off gas that remains after supplying fuel gas for ship propulsion must be reliquefied or burned to regulate the cargo tank pressure. A full or partial liquefaction process can be applied to return the surplus gas to the cargo tank. The purpose of this study is to review the current partial liquefaction process for LNG carriers and develop new processes for reducing power consumption using exergy analysis. The developed partial liquefaction process was also compared with the full liquefaction process applicable to a LNG carrier with a varying boil-off gas composition and varying liquefaction amounts. An exergy analysis showed that the JouleeThomson valve is the key component needed for improvements to the system, and that the proposed system showed an 8% enhancement relative to the current prevailing system. A comparison of the study results with a partial/ full liquefaction process showed that power consumption is strongly affected by the returned liquefied amount.

Development of partial liquefaction system for liquefied natural gas carrier application using exergy analysis

Choi, Jungho The Society of Naval Architects of Korea 2018 International Journal of Naval Architecture and Oc Vol.10 No.5

The cargo handling system, which is composed of a fuel gas supply unit and cargo tank pressure control unit, is the second largest power consumer in a Liquefied Natural Gas (LNG) carrier. Because of recent enhancements in ship efficiency, the surplus boil-off gas that remains after supplying fuel gas for ship propulsion must be reliquefied or burned to regulate the cargo tank pressure. A full or partial liquefaction process can be applied to return the surplus gas to the cargo tank. The purpose of this study is to review the current partial liquefaction process for LNG carriers and develop new processes for reducing power consumption using exergy analysis. The developed partial liquefaction process was also compared with the full liquefaction process applicable to a LNG carrier with a varying boil-off gas composition and varying liquefaction amounts. An exergy analysis showed that the Joule-Thomson valve is the key component needed for improvements to the system, and that the proposed system showed an 8% enhancement relative to the current prevailing system. A comparison of the study results with a partial/full liquefaction process showed that power consumption is strongly affected by the returned liquefied amount.