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1

Exergy life cycle assessment indicators in Colombian gold mining sector

Cano Natalia A., Hasenstab Christian, Velásquez Héctor I.

Journal of Sustainable Mining

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2020

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Vol. 19, iss. 3

151--165

EN

Thermodynamic methods, such as exergy analysis allow the assessment of environmental load (environmental impacts), by calculating the entropy generated or exergy destroyed due to the use of renewable and non-renewable resources along the entire production chain. In this research, exergy analysis will be approached as an extension of LCA to ExLCA (Exergy Life Cycle Assessment), as complementary tools, for sustainability assessment of two gold mining systems in Colombia: open-pit and alluvial mining. It is quantified exergy life cycle efficiencies; Cumulative Energy/ Exergy Demand, by distinguishing between renewable and non-renewable resources used in the process. The energy contained in renewable and non-renewable resources, interpreted as a measure of its utility potential, and which inefficient use generates waste streams with an exergy content that may be a measure of its potential to cause environmental damage. For open-pit mining 53% of exergy consumed comes from fossil energy, and 26% of energetic use of water, while in alluvial mining, 94% of exergy flow comes from water as a resource used within process activities. In order to reduce the environmental impact associated with gold generation life cycle described in this study, four strategies should be implemented; 1) Increasing efficiency, by reducing the exergy required in tails and extraction stages in open-pit mining process and, casting and molding stage in alluvial mining process, where large exergy supplies are required. 2) Increasing efficiency through the reduction of exergy emissions and residues in casting and molding stage in alluvial mining, and stripping stage in open-pit mining. 3) Using external exergy resources, such as renewable resources from nature (solar, wind, hydraulic). 4) Applying the concept of circular economy, which implies the reduction in consumption of resources.

2

Exergy-based control strategy in a dwelling ventilation system with heat recovery

Voloshchuk Volodymyr, Polishchuk Mariya

Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska

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2020

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T. 10, nr 2

44--47

EN

The paper presents energy and exergy analysis of a typical dwelling ventilation system with heat recovery for Ukrainian climatic conditions using a quasi-steady state approach over 24-hour time-steps. Evaluation of such systems on the base of the first law of thermodynamics demonstrates that heat recovery is beneficial for the whole variety of operational modes. Such methodology identifies as a thermodynamic inefficiency only energy losses to the surroundings with the exhaust air. The exergy-based analysis can detect additional inefficiencies due to irreversibilities within the components of the system. As a result the exergetic investigations show that for the ventilation systems there are operating conditions for which heat recovery increases exergy of fuel expended to provide the ventilation air compared to cases without bringing any recovery of heat and additional power consumption to drive the air flow by the fans. For the specified system, in case of switching ventilation unit to the operation mode of lower values of spent fuel exergy it is possible to provide annual saving of the primary energy sources from 5 to 15%.

PL

W pracy przedstawiono analizę energetyczną i egzergetyczną typowego systemu wentylacji mieszkań z odzyskiem ciepła dla ukraińskich warunków klimatycznych z zastosowaniem podejścia quasi-stabilnego w 24-godzinnych krokach czasowych. Ocena takich systemów w oparciu o pierwsze prawo termodynamiki wykazuje, że odzysk ciepła jest korzystny dla całego szeregu trybów pracy. Taka metodologia identyfikuje jako nieefektywne termodynamicznie tylko straty energii do otoczenia wraz z powietrzem wylotowym. Analiza egzergetyczna może wykryć dodatkowe nieefektywności wynikające z nieodwracalności elementów systemu. W rezultacie badania egzergetyczne wykazują, że w systemach wentylacyjnych występują warunki pracy, dla których odzysk ciepła zwiększa egzergię paliwa zużytego do dostarczenia powietrza wentylacyjnego w porównaniu do przypadków, w których nie występuje żaden odzysk ciepła i dodatkowe zużycie energii elektrycznej do napędzania przepływu powietrza przez wentylatory. Dla określonego systemu, w przypadku przełączenia urządzenia wentylacyjnego na tryb pracy o niższych wartościach egzergii zużytego paliwa możliwe jest zapewnienie rocznych oszczędności pierwotnych źródeł energii od 5 do 15%.

3

Simplified exergy analysis of ship heating systems with different heat carriers and with the recovery of waste heat

Zeńczak Wojciech

Archives of Thermodynamics

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2019

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Vol. 40, no 3

211-228

EN

The application of waste heat from exhaust gas of ship’s main engines has become widely practiced as early as in the 1930s. Thus the increase of ship’s overall efficiency was improved. Nowadays all newly built ships of the 400 gross tonnage and above must have specified energy efficiency design index, which is a measure for CO2 emissions of the ship and its impact on the environment. Therefore, the design of waste heat recovery systems requires special attention. The use of these systems is one of the basic ways to reduce CO2 emissions and to improve the ship’s energy efficiency. The paper describes the ship’s heating systems designed for the use of waste heat contained in the exhaust gas of self-ignition engines, in which the heat carriers are respectively water vapor, water or thermal oil. Selected results of comparative exergy analysis of simplified steam, water and oil heating systems have been presented. The results indicate that the oil heating system is comparable to the water system in terms of internal exergy losses. However, larger losses of exergy occur in the case of a steam system. In the steam system, a significant loss is caused by the need to cool the condensate to avoid cavitation in boiler feed pumps. This loss can in many cases cause the negative heat balance of ship during sea voyage while using only the exhaust gas boilers.

4

Exergetic Analysis of Hybrid Photovoltaic - Thermal Solar Collectors Coupled to Organic Rankine Cycles

Pinto C., Mady C. E.

Civil and Environmental Engineering Reports

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2018

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Vol. 28, no. 4

1--12

EN

In this work, the application of hybrid solar modules that combine photovoltaic panels and solar thermal collectors coupled with a low-temperature thermal cycle such as the Organic Rankine Cycle is discussed, their main purpose being an increase in the total electric power production per available area. This work will study the thermal and electrical power production efficiency of the hybrid system, the increase in the PV module electric conversion efficiency due to their cooling through heat transfer to the thermal cycle and the total exergetic efficiency of the system. A simplified simulation of the system in steady state conditions based on a thermal efficiency model will be performed with the aid of the EES (Engineering Equation Solver) software using climate data from Campinas, São Paulo, Brazil. The study shows that while the PV/T+ORC system does fulfill the purpose of increasing the electrical power generation both from the generator coupled to the thermal cycle and from the increase in the PV module efficiency due to its cooling. Thus, there is an increase the overall exergy efficiency of the system compared to uncoupled PV/T collectors.

PL

W pracy omówiono zastosowanie hybrydowych modułów słonecznych łączących panele fotowoltaiczne z kolektorami słonecznymi w połączeniu z niskotemperaturowym cyklem termicznym, takim jak cykl organiczny Rankine'a, którego głównym celem jest zwiększenie całkowitej produkcji energii elektrycznej. W pracy zbadano wydajność produkcji energii cieplnej i elektrycznej w systemie hybrydowym, wzrost sprawności konwersji energii modułu fotowoltaicznego ze względu na ich chłodzenie poprzez przeniesienie ciepła do cyklu termicznego i całkowitą efektywność energetyczną układu. Uproszczona symulacja systemu w warunkach stanu ustalonego w oparciu o model sprawności cieplnej została przeprowadzona za pomocą oprogramowania EES (Engineering Equation Solver) wykorzystującego dane klimatyczne z Campinas, São Paulo, Brazylia. Badania wykazały, że system PV/T + ORC spełnia cel zwiększenia wytwarzania energii elektrycznej zarówno z generatora połączonego z cyklem termicznym, jak i ze wzrostu sprawności modułu PV ze względu na jego chłodzenie. W ten sposób zwiększa się ogólna efektywność egzergii systemu w porównaniu z niezwiązanymi kolektorami PV/T.

5

Thermal analysis of heat and power plant with high temperature reactor and intermediate steam cycle

Fic A., Składzień J., Gabriel M.

Archives of Thermodynamics

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2015

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Vol. 36, no. 1

3--18

EN

Thermal analysis of a heat and power plant with a high temperature gas cooled nuclear reactor is presented. The main aim of the considered system is to supply a technological process with the heat at suitably high temperature level. The considered unit is also used to produce electricity. The high temperature helium cooled nuclear reactor is the primary heat source in the system, which consists of: the reactor cooling cycle, the steam cycle and the gas heat pump cycle. Helium used as a carrier in the first cycle (classic Brayton cycle), which includes the reactor, delivers heat in a steam generator to produce superheated steam with required parameters of the intermediate cycle. The intermediate cycle is provided to transport energy from the reactor installation to the process installation requiring a high temperature heat. The distance between reactor and the process installation is assumed short and negligable, or alternatively equal to 1 km in the analysis. The system is also equipped with a high temperature argon heat pump to obtain the temperature level of a heat carrier required by a high temperature process. Thus, the steam of the intermediate cycle supplies a lower heat exchanger of the heat pump, a process heat exchanger at the medium temperature level and a classical steam turbine system (Rankine cycle). The main purpose of the research was to evaluate the effectiveness of the system considered and to assess whether such a three cycle cogeneration system is reasonable. Multivariant calculations have been carried out employing the developed mathematical model. The results have been presented in a form of the energy efficiency and exergy efficiency of the system as a function of the temperature drop in the high temperature process heat exchanger and the reactor pressure.

6

Exergy analysis of the Szewalski cycle with a waste heat recovery system

Kowalczyk T., Ziółkowski P., Badur J.

Archives of Thermodynamics

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2015

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Vol. 36, no. 3

25--48

EN

The conversion of a waste heat energy to electricity is now becoming one of the key points to improve the energy efficiency in a process engineering. However, large losses of a low-temperature thermal energy are also present in power engineering. One of such sources of waste heat in power plants are exhaust gases at the outlet of boilers. Through usage of a waste heat regeneration system it is possible to attain a heat rate of approximately 200 MWth, under about 90°C, for a supercritical power block of 900 MWel fuelled by a lignite. In the article, we propose to use the waste heat to improve thermal efficiency of the Szewalski binary vapour cycle. The Szewalski binary vapour cycle provides steam as the working fluid in a high temperature part of the cycle, while another fluid – organic working fluid – as the working substance substituting conventional steam over the temperature range represented by the low pressure steam expansion. In order to define in detail the efficiency of energy conversion at various stages of the proposed cycle the exergy analysis was performed. The steam cycle for reference conditions, the Szewalski binary vapour cycle as well as the Szewalski hierarchic vapour cycle cooperating with a system of waste heat recovery have been comprised.

7

Exergy analysis of the performance of low-temperature district heating system with geothermal heat pump

Sekret R., Nitkiewicz A.

Archives of Thermodynamics

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2014

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Vol. 35, no. 1

77--86

EN

Exergy analysis of low temperature geothermal heat plant with compressor and absorption heat pump was carried out. In these two concepts heat pumps are using geothermal water at 19.5°C with spontaneous outflow 24 m3/h as a heat source. The research compares exergy efficiency and exergy destruction of considered systems and its components as well. For the purpose of analysis, the heating system was divided into five components: geothermal heat exchanger, heat pump, heat distribution, heat exchanger and electricity production and transportation. For considered systems the primary exergy consumption from renewable and non-renewable sources was estimated. The analysis was carried out for heat network temperature at 50/40°C, and the quality regulation was assumed. The results of exergy analysis of the system with electrical and absorption heat pump show that exergy destruction during the whole heating season is lower for the system with electrical heat pump. The exergy efficiencies of total system are 12.8% and 11.2% for the system with electrical heat pump and absorption heat pump, respectively.

8

Exergy analysis of the coal gasification process in ex-situ conditions

Janoszek T.

Journal of Sustainable Mining

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2013

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Vol. 12, iss. 3

32--37

EN

In this article the possibilities of implementing exergy analysis of coal gasification processes in ex-situ conditions was presented. The analysis was performed in order to detect the sources of exergy loss. The experimental results of the coal gasification process are also presented and was used as input data to perform the exergy analysis of the coal gasification process.

9

Thermodynamic modeling and second law based performance analysis of a gas turbine power plant (exergy and exergoeconomic analysis)

Ameri M., Enadi N.

Journal of Power Technologies

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2012

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Vol. 92, nr 3

183--191

EN

It this research paper, a complete thermodynamic modeling of one of the gas turbine power plants in Iran is performed based on thermodynamic relations. Moreover, a complete computer code is developed for the simulation purposes using the Matlab software. To assess the system performance, exergy and exergo-economic analysis are conducted to determine the exergy destruction of each component and cost of each flow line of the system. A complete parametric study is also carried out to study the effect of some design parameters such as exergy efficiency and total cost of exergy destruction on the system performance variation. The exergy analysis results have revealed that combustion chamber (CC) is the most exergy destructor component compared to other cycle components. Also, its exergy efficiency is less than other components which is due to the high temperature difference between working fluid and burner temperature. In addition, it was found that by an increase in the TIT (gas turbine inlet temperature), the exergy destruction of this component can be reduced. On the other hand, the cost of exergy destruction, which is a direct function of exergy destruction, is high for combustion chamber. The effects of design parameters on exergy efficiency have shown that an increase in the air compressor pressure ratio and TIT increases the total exergy efficiency of the cycle. Furthermore, the results have revealed that by an increase in the TIT for about 350 K the cost of exergy destruction can be decreased for about 22%. Therefore, TIT is the best option to improve the cycle losses.

10

Comparison of a dual-fuel internal combustion engine performance for CNG and gasoline fuels

Ameri M., Kiaahmadi F., Khanaki M. M.

Journal of Power Technologies

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2012

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Vol. 92, nr 4

214--226

EN

In this paper, comparison of a dual-fuel internal combustion engine performance for CNG and gasoline fuels is evaluated at the steady-state condition by application of energy and exergy analysis using the experimental test results. The energy and exergy balances are calculated at different engine speeds. The results show that the energy and exergy of the heat rejection for gasoline and CNG fuels increases with increasing engine speed and the exergy efficiencies are slightly higher than the corresponding energy efficiencies. Moreover, the results show that the exergy efficiency for gas-fuel is higher than the gasoline-fuel exergy efficiency at all engine speeds. The results show that due to volumetric efficiency drop, power and torque of the gas-fuel engine is lower than gasoline-fuel one. Furthermore, the specific fuel consumption of the gas-fuel engine is lower than gasoline-fuel one. The results of this study have revealed that the most important source of the system inefficiency is the destruction of exergy by irreversible processes, mostly by the combustion. Moreover, it should be noted that liquid fuels like gasoline have many important advantages like much greater volumetric energy density, ease of transport and storage, which have made them as the preferred fuels for IC engines.

11

Exergy analysis of internal regeneration in supercritical cycles of ORC power plant

Borsukiewicz-Gozdur A.

Archives of Thermodynamics

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2012

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Vol. 33, no. 3

51-63

EN

In the paper presented is an idea of organic Rankine cycle (ORC) operating with supercritical parameters and so called dry fluids. Discussed is one of the methods of improving the effectiveness of operation of supercritical cycle by application of internal regeneration of heat through the use of additional heat exchanger. The main objective of internal regenerator is to recover heat from the vapour leaving the turbine and its transfer to the liquid phase of working fluid after the circulation pump. In effect of application of the regenerative heat exchanger it is possible to obtain improved effectiveness of operation of the power plant, however, only in the case when the ORC plant is supplied from the so called sealed heat source. In the present paper presented is the discussion of heat sources and on the base of the case study of two heat sources, namely the rate of heat of thermal oil from the boiler and the rate of heat of hot air from the cooler of the dinkier from the cement production line having the same initial temperature of 260[degrees]C, presented is the influence of the heat source on the justification of application of internal regeneration. In the paper presented are the calculations for the supercritical ORC power plant with R365mfc as a working fluid, accomplished has been exergy changes and exergy efficiency analysis with the view to select the most appropriate parameters of operation of the power plant for given parameters of the heat source.

12

Exergy analysis of an externally-fired combined cycle power plant using the concept of avoidable thermodynamic inefficiencies

Cziesla F., Tsatsaronis G., Gao Z.

Czasopismo Techniczne. Mechanika

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2004

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R. 101, z. 4-M

51--62

EN

The real thermodynamic inefficiencies in a thermal system are related to exergy destruction and exergy loss. An exergy analysis identifies the system components with the highest exergy destruction and the processes that cause them. However, only a part of the exergy destruction in a component can be avoided. A minimum exergy destruction rate for each system component is imposed by physical, technological, and economic constraints. The difference between the total and the unavoidable exergy destruction rate represents the avoidable exergy destruction rate, which provides a realistic measure of the potential for improving the thermodynamic efficiency of a component. This concept is applied to the exergetic analysis and evaluation of an externally-fired combined cycle power plant.

PL

W pracy przedstawiono analizę strat termodynamicznych w rzeczywistych układach cieplnych odnoszącą się do egzergii i umożliwiającą identyfikację elementów systemu wykazujących największe jej rozpraszanie. Wielkość rozpraszanej egzergii dla każdego składnika zależy od czynników fizycznych, technologicznych i ekonomicznych. Różnica pomiędzy całkowitym a niemożliwym do uniknięcia rozpraszaniem egzergii przedstawia możliwą do uniknięcia jej stratę i stanowi miarę możliwego zwiększenia efektywnej wydajności termodynamicznej elementu. Koncepcję tą zastosowano do analizy egzergii w systemach energetycznych z zewnętrzną komorą spalania.