Exergy

In this paper, the exergy analysis of “(56MW) the rmal power plant Raipur (India); a case study” are presented. The main objectives of this paper are to analyze the plant’s component separately and to id entify the parts having largest exergy losses. This paper will also justify the major sources of losses and exergy dest ruction in the power plant. According to the study, percentage rat io of the exergy destruction to the total exergy de struction was found to be maximum in the boiler system (57 %) followed by the turbine (33.3%), and then the condense r (5.34%). the exergy efficiency of the power plant was 31.12% . Which are low compared to modern power plants. According to analysis found that boiler is the major source o f irreversibility in the power plant, but exergy de struction rate in boiler can be reduced by reheating the system. It i s a suitable technique for decrease boiler’s irreve rsibility. How reheating is the best tool for improvement of overa ll performance and com...

Hybrid photovoltaic-thermal (PVT) collector has been developed by combining photovoltaic (PV) technology and solar thermal collector in one module. The combination of two technologies in the same module has the potential to reduce cost of materials and the required space also improves performance of collectors. The hybrid PVT collectors were designed to generate electrical and thermal energy simultaneously. PV technology converts solar radiation into electrical energy while solar thermal collector will be converting solar energy to thermal energy. The main components of PVT collectors are PV panel, absorber plate, working fluid and insulator. According to the previous research, PVT collectors were developed by using air and water as a heat transfer medium. The benefits of heat removal are increasing PV panel efficiency by removing excessive heat from module. Parameters affecting the overall performances of PVT collectors included mass flow rate, area of collector, irradiance and PV cell materials. This paper presents a review of energy and exergy analysis of air-based and water-based PVT collector with different designs. The performances of PVT collectors were studied using First Law and Second Law of Thermodynamics. This study has found that generally the energy and exergy efficiency are range from 40%-70% and 5%-25%, respectively.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. Department of Mechanical Engineering, University of Mazandaran, Babolsar, Iran

A conceptual trigeneration system is proposed based on the conventional gas turbine cycle for the high temperature heat addition while adopting the heat recovery steam generator for process heat and vapor absorption refrigeration for the cold production. Combined first and ...

Although water is a cheap and effective medium for thermal energy storage, other options are currently being studied, to increase the storage density or to reduce the cost of the storage. The authors have been developing a system which combines the advantages of stratified sensible heat storage and latent, phase change heat storage; i.e. a hot water storage tank with stratification where a phase change material (PCM) is included into a spiral tube installed in the top of the tank. The PCM used was a granular PCM–graphite compound of about 90 vol.% of sodium acetate trihydrate and 10 vol.% graphite. This paper presents the results of an experimental investigation of the performance of the new storage concept, and of a conventional hot water storage tank for comparison. The data are further analysed with respect to the energetic and exergetic performance of the two systems. Copyright © 2007 John Wiley & Sons, Ltd.

Exergoeconomic (thermoeconomic) analysis is performed on Alkhoms steam power plant. The nominal power of the plant is 120 MW. The analysis is based on real-time data and performed for three different loads. The main factor of load variation is the variation of the steam mass flow rate. These loads are 120 MW (full load), 60 MW (part load), and 100 MW (real-time operation). It is worth to mention that high-pressure heaters are out of service these days. A systematic and general methodology for defining and calculating exergetic efficiencies, exergy destruction, and exergy related to costs in thermal systems is presented. The methodology is based on the Specific Exergy Costing (SPECO) method. Results of the exergy analysis showed the exergetic efficiency (effectiveness) increases from 34.74% at the real-time operation to 40.96% at full operating load, and hence the ratio of the total exergy destruction to fuel input exergy decreases from 64.46% at a real-time operation to 59.6 at part load up to 57.88% at full operating load. The exergoeconomic analysis results the average specific cost is 0.177 $/kWh at real-time operation and 0.113 $/kWh at part load, and 0.102 $/kWh at full operating load taking into consideration the escalation of fuel price (levelized fuel cost). It is found that the cost of exergy destruction in the steam generator presents the main contribution to the total cost of exergy loss; its value varies in the steam generator from 8296 $/h at the real-time operation to 6560 $/h at full operating load, while exergy destruction cost at part load is at a notable value of 3495 $/h due to low fuel consumption. The contributions and the variation of exergy destruction cost with load are lower for the other components.

In this study, we study and evaluate a zero emission integrated system, as taken from the literature, for coproduction of electricity and methanol. The investigated integrated system has three subsystems: water electrolysis, Matiant power plant (oxy-fuel combustion of pure methane), and methanol production unit. The system and its components are analyzed energetically and exergetically. The rates of exergy destructions, relative irreversibilities, and sustainability indexes of each subunit of each subsystem, as well as the overall system are analyzed to identify the greatest exergy losses and possible future research directions. The total rate of exergy destruction of the overall system is calculated to be around 280 MW. The greatest rate of exergy destruction, therefore the greatest irreversibility, occurs within the power plant unit (about 60 % of the total rate of exergy destruction). The energy efficiencies of electrolysis, power plant, and methanol synthesis unit are found to be 30 %, 76 %, and 41 %, respectively. The exergy efficiencies of electrolysis, power plant, and methanol synthesis unit are found to be 30 %, 64 %, and 41 %, respectively. Depending on the utilization of the heat rejected from the different units of each subsystem, the overall system could have energy and exergy efficiencies up to 68 % and 47 %, respectively.

This study reviews gas engine-driven heat pump (GEHP) systems for residential and industrial applications in terms of energetic and exergetic aspects for the first time to the best of the authors’ knowledge. These systems are novel heat pump systems (one of today's promising new technologies). Although the first investigations had been performed at late 1970s, the first merchandized GEHP was produced and introduced in the market in 1985. Gradually, it has become widespread all over the world for various purposes. Main application of GEHPs are for space and water heating/cooling purposes. However, they can be integrated to industrial applications, especially to drying processes.In this study, historical development of GEHP systems was briefly given first. Next, the operation of these systems was described, while studies conducted on them were reviewed and presented in tabulated forms. GEHPs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, an illustrative example was given, while the results obtained were discussed. In addition, a new project on integration of GEHP systems to food drying processes in Turkey initiated by the authors was introduced. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis and performance of assessment of GEHP systems.

ABSTRACT Thermo–economic analysis of Heat Pipe Heat Exchanger (HPHE) for waste heat recovery in thermal systems using the P1–P2 and NTU methods is presented. The optimum effectiveness of a HPHE is given as a polynomial equation, whereas the net savings and payback period are given in closed form to enable the HPHE designer to determine the optimised values directly. In addition to this, exergy analysis of HPHE for waste heat recovery in thermal systems is formulated. The variation of exergy efficiency with respect to change in inlet temperature is also presented.

An exergy modeling and optimization of an industrial ammonia unit based on steam methane reforming (SMR) process is presented. The base-case unit produces about 1000 t NH3/day [1], as well as power and steam, with no auxiliary exergy use. Some critical operation parameters are analyzed and the base-case and optimal operating conditions of the major components are compared. Since the ammonia synthesis process is highly exothermic, higher per-pass conversions in industrial adiabatic reactors are often achieved by using various sequential catalyst beds, where a near-optimum profile of reaction rate vs temperature can be attained by regulating the inlet temperature of each bed. This is performed via internal heat recovery, either by preheating reactor feed gas or by using waste heat boilers, which results in an increase of the steam production and a smaller fuel consumption. But, although such near-optimum operation conditions may lead to higher reaction rates and, thus, lower catalyst volumes could be required, it is found that the optimal design of the ammonia loop is rather determined by the performance of each component and their interdependencies. Moreover, since the proposed objective function (exergy destruction minimization) is very sensitive to specific process variables, the convergence of the solution algorithm is sometimes hindered. The exergy destruction breakdown shows that the ammonia converter and the refrigeration system are together responsible for more than 71e82% of the total exergy destruction in the ammonia loop, which in turn varies between 25.6 and 38.8 MW for optimal and base-case operation conditions, respectively.

In the second part of this study, heat-pump drying systems were comprehensively reviewed in terms of applications and performance evaluations. In this regard, these systems were classified in terms of type of heat pump systems, type of dryer and product types first. The performance assessments included coefficient of performance (COP), specific energy consumption (SEC) and specific moisture extraction rate (SMER), while types of energetic, exergetic and cost analyses were covered. It may be concluded that the most preferred method used to determine the HPD efficiency is SMER, while in recent years exergetic analysis method has been widely used.

This study involved the performance of energy and exergy analysis on a 200 MW Steam cycle power plant (SCPP). The aim is to investigate the effect of using different number of feed water heaters (FWHs) on the cycle performance. Several simulation analyses were conducted in this study on a MATLAB platform. The computer model used was based on natural gas combustion, enthalpy balances, energy balances, and entropy changes of the SCPP. The real case study was simulated on a validated model of the SCPP for Shahid Montazeri Power Plant. The exergy destroyed within each components system and the exergy efficiency are determined to study the irreversibility of the system and identify the chances for the enhancement of the power system. Based on the result of the analyses, the energy and exergy efficiencies of the SCPP were determined to be about 37.52 % and 41.7 %, respectively. In the SCPPs, the combustion chamber (boiler) contributes the highest exergy destruction rate (around 48 % of the exergy value of the gas) among the main components of the power system.

The Second Law of Thermodynamics talks about the entropy and exergy of a thermodynamic system in its own state of internal thermodynamic equilibrium. It is an empirical finding that has been accepted as an axiom of thermodynamic theory. This law is explained through Statistical thermodynamics either classically or through quantum formulation. Although the first­law aspects of thermodynamics readily understood & accepted, people fail to comply with the second­law aspects. It is viewed as a topic more of theoretical interest rather than being an important engineering tool well applicable to our life aspects. In view of human efficiency, the second law discussion disregards the availability of time to a person being a problem and rather focuses upon its effective utilization. The irreversiblity of a process cast the difference between the actual work delivered and the maximum work (reversible work) that could have been derived from the system. Here we try to identify the major sources of irreversibilities and the way to minimize them in order to maximize performance.

This paper presents an exergy and environmental assessment of a 1000 metric t/day ammonia production plant based on the steam methane reforming (SMR) process, including the syngas production, purification (CO 2 capture) and compression units, as well as the ammonia synthesis and purge gas treatment. An integrated heat recovery system produces power and steam at three pressure levels, besides exporting hot water, CO 2 and fuel gas, with no additional heat or power consumption being required. Two configurations for ammonia refrigeration process (À20 C) are compared in terms of power consumption. Exergy cost data for upstream processing stages of natural gas is used to calculate the extended exergy cost of the products of the plant, namely ammonia, CO 2 and fuel gas. Moreover, an appropriated methodology is employed to properly allocate the renewable and non-renewable exergy costs, as well as the CO 2 emissions of the reforming, shift and furnace stack among the products of the plant. By considering that the cost reduction of the combustion gases is a linear function of the exergy flow rate reduction in each component of the heat recovery system, an improved allocation of the CO 2 emission cost along the convection train is performed. A breakdown of the total exergy destruction rate of the plant (136.5 MW) shows that about 59% corresponds to the reforming process followed far behind by the ammonia synthesis and condensation (18.3%) and the gas purification units (13.2%). The overall exergy efficiency of the ammonia plant is calculated as 66.36%, which is enhanced by recovering the hydrogen-rich and fuel gases in the purge gas treatment process. The total and non-renewable exergy costs and CO 2 emission cost of the ammonia produced are calculated as 1.7950 kJ/kJ and 0.0881 kg CO2 /MJ, respectively. In addition, a rational exergy cost of 1.6370 kJ/kJ and CO 2 emission cost of 0.0821 kg CO2 /MJ are allocated to the CO 2 gas, which can be supplied as feedstock to an associated chemical plant (urea, methanol, polymers, etc.).

In this study, we investigate the economic, environmental and social impacts of various hydrogen production methods,
based on fossil fuel and renewable energy resources with a special emphasis on hybrid photoelectrochemical systems perform
comparative assessments of these methods for applications. The sources considered for hydrogen production in this
study are water, fossil hydrocarbons, and biomass. Furthermore, the primary energy sources considered in this study are
natural gas, coal, biomass, wind and solar. In order to address sustainability, the relationship between efficiency and environmental
impact is also investigated. The results show that solar based hydrogen production options (photocatalysis,
photoelectrolysis, and photoelectrochemical methods) provide near zero global warming potentials and air pollutants, while
coal gasification has the highest ones. In regards to the exergy efficiencies, biomass gasification gives the highest exergy
efficiency, while photoelectrochemical method ends up with the lowest one.

 These notes were created for various energy engineers who may not have originated from a mechanical or related engineering program.

 The notes are intended for civil and electrical engineering students. Additionally they support the studies of renewable energy and energy engineering students at undergraduate and graduate level. Notes may also be used by practising engineers.

 There is an associated PDF of an Excel file complementing these notes with solved example problems. This file is on this page titled 'Exergy Example Problems (1-12). Accompanying: Exergy Notes_KSB_12 Aug 2019. Resource-PK Nath'.This PDF of an Excel file has additional notes specific to example.

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... Various criteria in optimization of a geothermal air conditioning system with a horizontal ground heat exchanger Hoseyn Sayyaadi Ć,y and Emad Hadaddi Amlashi Faculty of Mechanical Engineering—Energy Division, KN Toosi University of Technology, Tehran, Iran SUMMARY ...

... Ahmet Koca a , Hakan F. Oztop b , Tansel Koyun c and Yasin Varol a , Corresponding Author Contact Information , E-mail The Corresponding Author. ... from 1.22 to 2.63 kW, whereas the rate of heat stored in the LHS unit were 111.2 and 79.9 W. Sari and Kaygusuz [11] conducted ...