Exergy Emissions Research Articles

Determination of the sustainability index along with energy–exergy–emission–economic analysis of a VCR diesel engine fuelled with diesel–bioethanol–Al2O3 nanoparticles

Different percentages of bioethanols made from waste rice straw blended with diesel mixed with Al2O3 nanoparticles were tested in a VCR CI engine under varying load intensities and at different compression ratios.

Energy, exergy, exergoeconomic and exergoenvironmental analysis and optimization of a novel partially covered parabolic trough photovoltaic thermal collector based on life cycle method

Efficient utilization of solar energy could effectively alleviate dependence on fossil fuels and contribute to the ambitious target of carbon neutrality. This study first proposes a novel partially covered parabolic trough photovoltaic thermal (PCPTPVT) collector to efficiently exploit solar energy. The thermodynamic model and iterative procedure are built based on the thermal resistance circuit method. Energy, exergy, exergoenvironmental, and exergoeconomic analyses are conducted to evaluate the thermodynamic, environmental, and economic performances of the novel PCPTPVT collector. Besides, multi-objective optimization of the tradeoff between cost-effectiveness and environmental friendliness is also carried out. The results show that 12.42% of the solar energy beamed on the PCPTPVT is converted into solar electricity and 61.38% of that is transformed into thermal energy for heating fluid. The electrical and thermal efficiencies of the PCPTVPT can reach 27.9% and 64.3%, respectively, and the energy and exergy efficiencies have notable improvements of 11.11% and 6.19% when the solar irradiation changes from 300 W/m2 to 1100 W/m2. The unit exergy emissions of CO2, NOX, and SO2 of the PCPTPVT under design conditions are 18.39 g/kWh, 117.8 mg/kWh, and 149.4 mg/kWh, and life cycle pollutant emission reductions reach 136.08 t, 971.92 kg, and 1125.35 kg, respectively.

Assessment of eco‐thermal sustainability potential of a cluster of low‐cost solar dryer designs based on exergetic sustainability indicators and earned carbon credit

• Environmental sustainability performance of different solar dryer designs from the same cluster area were compared • The sustainability indices varied despite having equal collector area • The wind powered solar dryer with triple air path on a single pass collector was more environmentally sustainable than others • The study outcome is indicative for improved sustainable solar dryer design choice for the studied zone This research aims to establish the interconnectivity between solar dryer designs and the exegetic-sustainability performance of solar dryers. This is to assist energy policymakers and fabricators to establish design standards and make the right choice for waste exergy management strategy for environmental sustainability. Therefore, in this study, the exergy-based sustainability indicators and earned carbon credit were used to assess and compare the performance of four different designs of solar dryers of equal collector capacity under the same external environmental conditions in the same town. In terms of better sustainability indicators that include high exergy efficiency, lower waste exergy emission, higher sustainability index and lower lack of productivity, solar dryer designs with single-pass triple air movement direction with inlet air powered by wind generator had the best indices for environmental sustainability. In contrast, the natural convection mix-mode solar dryer design had the lowest environmental effect factor and destruction coefficient while the indirect natural convection solar dryer had the highest energy recovery ratio based on exergy output from water evaporation. However, the mix-mode solar dryer powered by the wind generator earned the highest carbon credit. The exergy efficiency ranged from 19.09 to 52 % for the four cases, whereas the waste exergy ratio ranged from 0.52 to 0.81. The LOP value ranged from 2.95 to 19.96. Similarly, the sustainability index ranged from 1.28 to 2.5, the average environmental destruction coefficient varied from 3.96 to 20.96, the exergy recovery ratio for the four dryers varied from 0.001825 to 0.12405, and the earned carbon credit ranged from $442. 3 to $2630.5.

Thermodynamic-Based Exergy Analysis of Precious Metal Recovery out of Waste Printed Circuit Board through Black Copper Smelting Process

Exergy analysis is one of the useful decision-support tools in assessing the environmental impact related to waste emissions from fossil fuel. This paper proposes a thermodynamic-based design to estimate the exergy quantity and losses during the recycling of copper and other valuable metals out of electronic waste (e-waste) through a secondary copper recycling process. The losses related to recycling, as well as the quality losses linked to metal and oxide dust, can be used as an index of the resource loss and the effectiveness of the selected recycling route. Process-based results are presented for the emission exergy of the major equipment used, which are namely a reduction furnace, an oxidation furnace, and fire-refining, electrorefining, and precious metal-refining (PMR) processes for two scenarios (secondary copper recycling with 50% and 30% waste printed circuit boards in the feed). The results of the work reveal that increasing the percentage of waste printed circuit boards (PCBs) in the feed will lead to an increase in the exergy emission of CO2. The variation of the exergy loss for all of the process units involved in the e-waste treatment process illustrated that the oxidation stage is the key contributor to exergy loss, followed by reduction and fire refining. The results also suggest that a fundamental variation of the emission refining through a secondary copper recycling process is necessary for e-waste treatment.

Computer-aided exergy analysis of microalgal biodiesel production using Chlorella vulgaris

Background: Exergy analysis has been recognized as a feasible approach to evaluate and improve industrial processes by identifying major irreversibilities in a system. Objectives: This work attempts to apply exergy analysis to a third-generation biodiesel production from Chlorella vulgaris microalgae. Methods/Analysis: Commercial industrial process simulation software was used to simulate this process. The specific exergy of many substances were found in literature and the others were calculated using Szargut, Morris & Steward’s equation. A global exergy balance around the system was carried out in order to determine total irreversibilities. The contribution of unit operations and equipment to total irreversibilities was also considered. In addition, exergy efficiency and exergy emission were calculated for each stage (pretreatment, reaction, separation, biodiesel purification, and glycerol treatment). Findings: The global exergy efficiency was calculated in 86% similar to the results reported in other researches. The equipment that contributes the most to total irreversibility was the separation column used to remove alcohol with 487.55 kJ/kg BD. In addition, the highest irreversibilities (5.22 MJ/kg BD) and exergy emission (2.71 MJ/ kg BD) per stage were reached during biodiesel purification. Novelty/Improvement: The application of exergy analysis allowed to identify potential improvements in this case of study, mainly in biodiesel purification stage and process modifications are suggested to reduce total irreversibilities as reutilizing methanol and glycerol streams. Keywords: Biodiesel, Exergy Analysis, Microalgae, Process Simulation, CAPE

Thermodynamic evaluation of a kerosene pre- Fraction unit using energy and exergy analysis

Abstract This work applies the method of energy and exergy analysis over first step of linear alkyl benzene (LAB) production namely kerosene pre fraction plant, to determine unit energy and exergy performance and loss, besides of opportunities for improvement based on operational data. For this purpose macroscopic energy and exergy balance was developed over main equipment including electro pumps, heat exchangers, air coolers, and distillation columns. The results shows that total energy performance of plant is 92.62% by 19.76 MW energy lost, while from exergy perspective, unit performance is 78.08% by 17.92 MW exergy lost. Maximum local exergy lost occurs in the feed pre heater exchanger by 27% performance which is designed to recover energy from top product of second column, furthermore results shows that upgrading low quality energy in air coolers based on heat pump concept would protect energy and exergy emission to the environment and reduce 40% of total lost energy and 16% of total lost exergy in plant.

Exergy evaluation of emitted waste gas and fuel consumption in food delivery process

Food delivery from restaurants and fast food shops by motorbikes is one of the major modes of its distribution. We aim to investigate the environmental impact of food delivery process by motorbikes. The environmental impact was described from the viewpoint of waste gas emission and emission exergy. A university campus was selected as the test site. We extracted the number of food delivery, average fuel consumption and driving distance per motorbike by collecting data from restaurants. We did an experiment to find how much fuel is consumed if a driver does idling during delivery. The experiment gives us 20.8 ± 8.3 ml for 5 min idling. In cruising state there is a high value of CO2 emission (~90% of total waste per year) into the environment mainly in September and December, although from exergy analysis CO contributes more to the exergy emission than CO2 in most cases.

Analysis on exergy consumption patterns for space heating in Slovenian buildings

Problem of high energy use for heating in Slovenian buildings is analyzed with exergy and energy analysis. Results of both are compared and discussed. Three cases of exterior building walls are located in three climatic zones in winter conditions. Results of energy analyses show that the highest heating energy demand appears in the case with less thermal insulation, especially in colder climate. If the comparison is made only on the energy supply and exergy supply, the results of exergy analysis are the same as those of energy analysis. The main difference appears, if the whole chain of supply and demand is taken into consideration. Exergy calculations enable us to analyze how much exergy is consumed in which part, from boiler to building envelope. They also reveal how much energy is supplied for the purpose of heating. Results show that insulation has much bigger effect than effect of boiler efficiency. However, the most effective solution is to improve building envelope together with boiler efficiency. Better thermal insulation also makes an important contribution to the improvement of thermal comfort conditions. It causes higher surface temperatures resulting in a larger warm radiant exergy emission rate and consequently better thermal comfort.

A STUDY ON THE RELATIONSHIP BETWEEN THERMAL COGNITION OF ROOM SPACE CONTROLLED BY HIGH-TEMPERATURE RADIANT COOLING PANEL COMBINED WITH NATURAL VENTILATION AND HUMAN-BODY EXERGY BALANCE

This paper discusses the relationship between the indoor thermal conditions provided by a high-temperature radiative cooling system mounted on the ceiling and thermal cognition given by the subjects experiencing its thermal environment in an experimental room simulating common living conditions in residential buildings. The subjects accepted the indoor thermal environment with high relative humidity over 70 % provided that both of the mean radiant and air temperatures kept at 29°C and the air movement exceeds 0.15m/s. We also calculated the human-body exergy balance for indoor thermal conditions that the subjects voted most for “comfort”. Under such a condition, the cool radiant exergy received by the human body was approximately 30mW/m2 and thereby the warm exergy was emitted efficiently from the human body by radiation and convection into the room space. This amount of warm exergy emissions was are larger than that in an air-conditioned room space. Therefore, radiant cooling is not to provide a large amount of cool radiant exergy with occupants, but to provide a sufficient amount in order for the human body to release warm exergy smoothly from the human body surface; that is for spontaneous entropy disposal.

Unified account of gas pollutants and greenhouse gas emissions: Chinese transportation 1978–2004

To facilitate the aggregation of both quantity and quality of waste emissions, the concept of chemical exergy combining the first and second laws of thermodynamics is introduced for a unified account of gas pollutants and greenhouse gases, by a case study for the Chinese transportation system 1978–2004 with main gas pollutants of NO, SO2, CO and main greenhouse gases of CO2 and CH4. With chemical exergy emission factors concretely estimated, the total emission as well as emission intensity by exergy of the overall transportation system and of its four modes of highways, railways, waterways and civil aviation are accounted in full detail and compared with those by the conventionally prevailing metrics of mass, with essential implications for environmental policy making.

Assessing and improving the efficiencies of a steam power plant using exergy analysis. Part 1: assessment

Energy and exergy analyses are used to examine the performance of a coal-fired steam power plant and to identify and evaluate possible modifications to improve the efficiency of the plant. The exergy analysis provides a detailed breakdown of the exergy losses (including waste exergy emissions and internal irreversibilities) for the overall plant and its components. The results show that irreversibilities are the largest source of exergy loss for the plant and that the irreversibility rate in the steam generator is much larger than that in the other plant components.

Thermodynamics, Exergy and Environmental Impact

Environmental problems associated with energy utilization span a growing spectrum of environmental quality and natural ecosystem.The second law of thermodynamics is considered to be instrumental in providing insights into environmental impact. In conjunction with this, exergy appears to be an effective measure of the potential of a substance to impact the environment. This article discusses the relations between environmental impact and thermodynamics in general, and the thermodynamic property exergy in particular. Historical and modern examples demonstrate these concepts. Three main relations between exergy and environmental impact are identified: (1) order destruction (chaos creation),(2) resource degradation, and (3) waste exergy emissions. An apparent paradoxis described between the usefulness of a high-exergy quantity and the simultaneous potential for environmental disruption it possesses. It is concluded that the potential usefulness of exergy analysis in addressing and solving environmental problems is substantial.

ON EXERGY AND ENVIRONMENTAL IMPACT

Environmental problems span a continuously growing range of pollutants, hazards and eco-system degradation factors that affect areas ranging from local through regional to global. Some of these problems may arise from observable, chronic effects on, for instance, human health, while others may stem from the perceived risk of a possible accidental release of hazardous materials. A significant number of these environmental issues are caused by or relate to the production, transformation and end use of energy. In this regard, energy and environment studies which lead to increased energy efficiency can reduce environmental impact by reducing energy losses. Within the scope of exergy methods, such activities lead to increased exergy efficiency, which is of great importance for practical applications. In this study, the main relationships between energy and environmental impact are identified. Historical and modern examples are used to illustrate some of the concepts. The relationships introduced are: order-destruction/chaos-creation, resource degradation and waste exergy emissions. Some examples are given demonstrating the use of exergy analysis in addressing and solving environmental problems. © 1997 by John Wiley & Sons, Ltd.