Exergy Output Research Articles

Optimal design of solar concentrator in multi-energy hybrid systems based on minimum exergy destruction

The paper presents a systematic approach to designing an imaging dish for a concentrator photovoltaic (CPV) system to minimize exergy destruction. The designed CPV system uniformly distributes light rays on the receiver (TPV/multi-junction PV) to enhance the conversion technology efficiency and lifetime. To this end, a parametric dish is designed using imaging optics and the numerical solution of a differential equation. Afterward, a Monte Carlo simulation is used to estimate the output energy and exergy of the CPV system with the parametric dish. Finally, an optimization algorithm finds the optimal design parameters to minimize the system's exergy destruction. The optimal design leads to a CPV with a concentration factor of 100–150 that is fitted to utilize TPV/multi-junction PV as its receiver. Moreover, it can produce a temperature of 1019° C. Finally, the overall system energy and exergy efficiency with conventional commercial components at solar irradiance of 1000 W/m2 are estimated to be 74.07% and 66.36%, respectively.

Energy and exergy based study on a box type solar cooker coupled with a Fresnel lens magnifier

ABSTRACT The variation of energy and exergy efficiency of a Box-type solar cooker (BTSC) incorporated with a Fresnel lens magnifier (FLMG) is evaluated in this study. The comparison in energy and exergy efficiency was investigated in the absence and presence of the FLMG to determine the efficiency variation of the BTSC by addition of the FLMG. With the implementation of FLMG, the average values of energy and exergy efficiencies had increased by 10% and 8.52%, respectively. The magnitude of energy efficiency with and without FLMG decreased with time, whereas the exergy efficiency enhanced with time for both cases. The manuscript discusses the effect of different thermodynamic parameters like temperature difference, energy and exergy output, absorber mean plate temperature, and heat losses in the modified cooker. The total heat loss coefficient ranged from 5.48 to 8.44 W/m2K and depended on the variation of wind velocity. The maximum heat loss and mean plate temperature were found to be 120 kJ and 128.3°C, respectively. The time for sensible heating was reduced by 16 mins by the implementation of the FLMG. The addition of the lens showed an increase in the Area concentration ratio (AR) of the BTSC by 48.7%. By comparing the cost and energy usage of LPG (Liquefied Petroleum Gas), the payback period and the quantity of carbon dioxide reduced per month were calculated as 3.19 years and 8.265 kg, respectively.

Experimental and numerical study on thermodynamic characteristics of a vacuum membrane distillation system based on mechanical vapor recompression for sulfuric acid waste

Energy conservation and emission reduction in the field of industrial wastewater treatment have attracted worldwide attention. This study focused on the concentration and recovery of industrial sulfuric acid waste by a vacuum membrane distillation system based on mechanical vapor recompression (VMD-MVR). Mathematical models were built considering the mass and energy conservation principles and relevant thermal equilibrium theory, and an experimental platform, which was suitable for sulfuric acid solution, with excellent corrosion resistance was also constructed. Initially, the performance of VMD-MVR from the energetic and exergetic standpoints was evaluated based on the experimental data. Furthermore, the effects of critical parameters on compression and condensation heat transfer in VMD-MVR were simulated and revealed, and exergy destruction analysis was conducted using various selected parameters. The obtained experimental results indicated that VMD-MVR exhibited a membrane flux of 1.7 kg·m−2·h−1, separation efficiency of 99.9%, and performance coefficient (COP) of 7.88 under the following conditions: feed concentration: 5%; feed temperature: 353.0 K; feed velocity: 1.6 m·s−1; permeate side pressure: 45 kPa; heat transfer temperature difference (ΔThex): 2 K; and compressor frequency: 40 Hz. The exergy input, exergy destruction, exergy output, and exergy efficiency were 4.95 kW, 4.691 kW, 0.259 kW, and 5.24%, respectively. Moreover, according to the numerical simulation results, with a decrease in the feed concentration and ΔThex or with an increase in the feed temperature, feed velocity, and permeate side pressure, the compression ratio and exergy destruction in VMD-MVR decreased, whereas the COP increased.

Multi objective optimization of MSF and MSF-TVC desalination systems with using the surplus low-pressure steam (an energy, exergy and economic analysis)

Water is consumed as one of the main fluids in the natural gas refinery which becomes wastewater after undergoing different process. Therefore, it is not possible to reuse or dispose the wastewater to the environment due to contaminant issues. At the same time, a huge amount of heat is wasted in surplus low pressure (LP) steam flow, which is used in natural gas refining process. In present study, it is attempted to model Multi Stage Flash (MSF) and multi stage flash coupled with thermal vapor compressor (MSF-TVC) systems for desalination of existing refinery wastewater utilizing different heat losses occur in the refinery process. In order to optimize the MSF and MSF-TVC systems, effective parameters in the field of energy, exergy and economic including gain output ratio (GOR), exergy efficiency and payback ratio (PBR) are used simultaneously. For this purpose, the Pareto solution and TOPSIS methods are used as the multi objective optimization. As a result, the optimum values of the first stage temperature (maximum system temperature) and number of desalination stages are obtained 130 °C and 32 stages for MSF and 115 °C and 25 stages for MSF-TVC systems. Finally, it is found that the amount of 46,335 ton/year CO2 emission reduction can be achieved by using surplus LP steam heat potential in refinery wastewater desalination.

Optimization of geothermal- and solar-driven clean electricity and hydrogen production multi-generation systems to address the energy nexus

Given the limited sources of fossil fuels, mankind should find new ways to meet its energy demands. In this regard, geothermal and solar energy are acknowledged as reliable, safe, promising, and clean means for this purpose. In this research study, a comparative analysis is applied on geothermal- and solar-driven multi-generation systems for clean electricity and hydrogen production through energy and exergy assessments. The systems consist of an organic Rankine cycle, a proton electrolyte membrane electrolyzer, and a thermoelectric generator subsystem. The Engineering Equation Solver software has been utilized in order to model the system and obtain the output contours, sensitivity analysis, and exergy destruction. The results were obtained considering the ambient temperature of Bandar Abbas city as a case study. The geothermal system was performant over the solar system, with 11.21% higher hydrogen production and 0.17 % higher exergy efficiency. According to the sensitivity analysis, the turbine efficiency, evaporator inlet temperature, thermoelectric generator suitability criterion, pump efficiency, and evaporator inlet mass flow rate were the most influential parameters. Also, the exergy analysis showed that the utmost system's exergy destruction is pertinent to the evaporator and the least is related to the pump. In addition, the system produces 352,816 kWh and 174.913 kg of electrical power and hydrogen during one year.

Energy, exergy, economic and environmental analysis of a novel direct-expansion solar-assisted flash tank vapor injection heat pump for water heater

Energy, exergy, economic and environmental analysis of a novel direct-expansion solar-assisted flash tank vapor injection heat pump for water heater is conducted by simulation method. Two working modes are designed for the presented system. The solar-assisted mode is recommended for most solar radiation conditions, and the air-source mode maintains more superior performance under extremely low or no solar radiation situations. By utilizing solar energy, the system heating efficiency and capacity can be respectively improved by up to 29.6% and 25.9% under the considered condition. The performance analysis shows that the presented system can respectively enhance the average heating capacity and efficiency by 11.7% and 10.6% in a typical winter day of Lanzhou City, compared with the conventional flash tank vapor injection heat pump system. The exergy analysis expresses that the heat exergy output increases with the solar radiation intensity, while the system exergy efficiency presents an opposite variation trend because of the greater increment of the exergy destruction in the solar collector. The economic analysis indicates that the presented system achieves a payback period of 8 years under the given assumptions. Benefiting from the electricity consumption reduction, the presented system can remarkably reduce the carbon dioxide and air pollution emissions.

Exergy analysis and optimisation of a two-stage solar thermoelectric generator with tapered legs

Numerous previous studies indicate that the performances of thermoelectric generators are enhanced by incorporating legs with variable area geometries. However, there is a dearth of comprehensive optimisation studies on these new thermoelectric generator designs. More so, the few optimisation studies that exist have rather employed unrealistic isothermal boundary conditions in their numerical models. Furthermore, these new leg geometries have not been applied to multi-stage systems. Accordingly, to address these gaps, a numerical optimisation, using ANSYS 2020 R2 software, is performed on a two-stage thermoelectric generator with variable area leg geometries; with optimisation parameters that include: leg geometry (height and area), intensified insolation with external load resistance, i.e., geometrical, thermal and electrical operation of the device. An exergy/irreversibility analysis is also carried out and techniques of minimising thermodynamic losses while allowing for the useful exergy output after solar energy conversion are proposed. Results indicate that, for an optimum leg height, area, concentrated solar radiation intensity and load resistance of 10 mm, 0.7 mm2, 20 suns and 1.3 Ω, respectively. Maximum energy and exergy efficiencies of 7.03% and 7.55% respectively, were obtained for the proposed system. This improves the energy and exergy efficiencies of the standard device by 23.44%.

Energy, exergy performance and analysis of 50w solar photovoltaic module

With the speedy exhaustion of fossil fuels, chances for renewable energy including solar energy are limitless. The solar photovoltaic (PV) system produces both thermal energy and electrical energy by using solar radiation. In this article, an experimental study has been conducted for evaluating the electrical, thermal and exergy output of solar PV panel installed. Energy analysis was performed on the solar PV module by using first law of thermodynamics; exergy analysis was performed to determine the exergy efficiency and losses during the PV conversion by using the second law of thermodynamics. The various electrical and operating factors such as temperature, open-circuit voltage, short-circuit current, and overall heat loss coefficient for solar PV module.

ANALYSIS OF EXERGY LOSSES IN HEAT RECOVERY SYSTEMS OF BOILER PLANTS WHEN IMPLEMENTING THE BYPASS METHOD TO PROTECT CHIMNEYS

The results of the analysis of exergy losses in the heat recovery systems of boiler plants during the implementation of one of the thermal methods of anticorrosion protection of gas exhaust ducts - the bypass method - are presented. Gas-consuming boiler plants with a heat recovery system for heating heat supply water are considered. The choice of a complex technique for the analysis of exergy losses in a heat recovery system with gas bypass is substantiated. The technique includes structural-variant and integral balance methods of exergy analysis and is effective due to the small number of parameters required for the calculation, the simplicity of the calculation and analytical methods for obtaining exergy characteristics, and the high accuracy of the results obtained. The principal and structural diagram of the heat recovery system in the implementation of the bypass method is given. In the block diagram, the input and output exergy flows between the individual elements of the heat recovery system are identified. According to the block diagram, an exergy balance equation was compiled, on the basis of which the exergy losses and the heat exergy efficiency criterion were determined. The exergy characteristics of the heat recovery system are given with an increase in the amount of bypassed gases and different values of the heat load of the heat recovery system. It is shown that the nature and extent of the impact of these parameters depend on the specified load. It has been established that an increase in the amount of bypassed gases at all values of the heat load of the heat recovery system leads to a decrease in exergy losses and the heat power criterion. The value of the heat load of the heat recovery system is determined, at which its exergy efficiency in the implementation of the bypass method is the highest.

Energy and exergy analyses of a hybrid system integrating solar-driven organic Rankine cycle, multi-effect distillation, and reverse osmosis desalination systems

This study analyzes the energy and exergy of a novel arrangement of a solar driven organic Rankine cycle (ORC), two reverse osmosis (RO) desalination systems, and a multi-effect distillation (MED) desalination unit. The ORC power is used as power sources of the high-pressure pump of the RO unit and pumping system of the MED unit. Also, the waste heat of the ORC condenser is utilized as the heat impetus of the MED unit. The results demonstrate that increasing the solar radiation intensity and collector module length leads to increase in the ORC power output, produced freshwater, and total exergy destruction. Increasing the volumetric flow rate of the collector reduces the temperature of the output fluid from the solar collector field, but the mass flow rate is increased, resulting in the highest net output power from the ORC system at a volume flow rate of 11000 lit/min. The exergy analysis reveals that the solar collector, as the system heat source, has the highest total exergy destruction share of 65% in the system. Also, among the organic fluids, toluene, n-decane, n-nonane and n-octane have the highest ORC power, the highest amount of produced freshwater, and the least exergy destruction for ORC, respectively.

Development of a new CO2 liquefaction system using the Linde–Hampson process, Kalina power generation unit, and flat plate solar collectors with Al2O3/H2O nanofluid

AbstractGreenhouse gas emissions into the atmosphere have had devastating environmental effects, including ozone depletion and global warming. Carbon dioxide (CO2) is widely used in oil and gas plants, the food industry, and as a working fluid in the power industry. Carbon dioxide is liquefied for long‐term storage, to be transported to remote areas, and is used for peak shaving in the power plants. Solar flat plate collectors and wasted heat from the CO2 liquefaction system can be used in power plant systems. Also, the use of nanoparticles in the collectors improves the thermal properties of the working fluid and increases the efficiency of solar collectors. This study has developed a new hybrid system for CO2 liquefaction using Linde–Hampson system, Kalina power generation unit, and flat plate solar collectors. The Linde–Hampson system's dissipated heat and solar collectors are used to supplying part of the power of the CO2 liquefaction system. The combined system produces 9416 kmol/h of liquid CO2 by absorbing 35.97 MW of power. The Kalina power generation unit provides 9.546 MW of power by absorbing 76.98 MW of the CO2 liquefaction cycle's dissipated heat and 91.18 MW from flat plate collectors. Based on the output of exergy assessment, exergy efficiency and exergy degradation of the developed integrated structure are 44.16% and 118.3 MW, respectively. Moreover, significant portions of exergy destruction in the combined process belong to solar collectors (74.68%), heat exchangers (12.47%), and compressors (7.157%), respectively. The use of Al2O3 nanoparticles in pure water has been investigated for heat transfer in flat panel solar collectors. According to the sensitivity analysis results, as the volume ratio of particles in nanofluid increases to 6%, the production capacity of the Kalina cycle and exergy efficiency improves to 9.56 MW and 9.522%, respectively. Also, as the pressure of the pumped fluid in the Kalina cycle increases from 800 to 1600 kPa, the exergy yield of the Kalina cycle and the exergy yield of the whole combined system increase to 36.34% and 44.26%, respectively.

Effects of Compressor Blade Profile Change on Thermo-economic Performance of Gas Turbine

This study investigates the effects of variations in compressor blade profile on the thermo-economic performance of gas turbines. The compressor's thermo-economic performance was determined using data obtained from the power plant. The method used for the analysis was simplifying the compressor, combustion chamber, and turbine into control volumes. Each flow was analyzed based on exergy, economic, and exergy cost principles. As 1 was increased, rotor blade deflection and diffusion were reduced while outlet velocity, stage efficiency, and pressure ratio increased. Pressure ratio increased by up to 20 percent when 1 increased by 10 and decreased by 7.5 percent when  2 increased by 10 . Equipment cost, annualized cost and total capital investment, operation, and maintenance cost increased by 27.68 percent, 27.31 percent, and 22.86 percent as 1 increased by 10 while equipment cost, annualized cost and total capital investment, operation, and maintenance cost increased by 12.44 percent, 12.12 percent, and 12.45 percent as  2 decreased by as much as 10 . Cost of exergy destruction, average unit cost of exergy input and average unit cost of exergy output increase by 2.64 percent, 2.62 percent, and 4.65 percent as 1 increase by 10 . It was recommended that the gas turbine filtration system be improved to suit the harsh environmental conditions of the area to reduce the amount of foulants on compressor blades. This will increase compressor life expectancy and efficiency, save operating and maintenance costs, and increase the reliability of the gas turbine to deliver maximum power. Furthermore, the research findings could serve as a useful reference for designers in selecting a reasonable compressor blade angle.

RETRACTED: Exergy analysis and optimization of Rankine power and ejector refrigeration combined cycle

This article proposes a combined cycle which consists of the hybrid Rankine power cycle and Ejector refrigeration cycle. This cycle is capable of producing thermal and refrigeration powers simultaneously. The proposed cycle can function through the heat exhausting from gas turbines, energy dissipations of factories, solar energy, or geothermal energy. In this research, Exergy analysis is used to improve the cycle; and Parametric analysis is used to investigate the effects of thermodynamic characteristics on the performance of the cycle. The results indicate that the most exergy dissipations occur as a result of irreversibilities and that ejectors have a significant role in such irrevesibilities. It has also been noted that factors such as the inlet pressure to turbine, turbine outlet pressure, and the temperature of condenser and evaporator have a considerable effect on turbine's output power and exergy efficiency of the cycle. The optimized exergy efficiency is 24.52% under the given condition. • Proposing a combined hybrid Rankine power cycle and Ejector refrigeration cycle. • Using exergy and parametric analysis to improve the performance of the cycle. • Calculating the energy and exergy equations using ESS software.

Exergoeconomic and Environmental Analysis and Multi-Objective Optimization of a New Regenerative Gas Turbine Combined Cycle

Combined cycle systems have an important role in power generation. In the present study, three different configurations of combined Brayton and Rankine cycle system are studied from the perspective of energy, exergy, exergoeconomic and environmental perspectives. Results indicate that it depends on the preferences and criteria of each decision maker to select the best configuration among the three proposed configurations as the final configuration. For the purpose of parametric analysis, the effect of changing various parameters such as compressor pressure ratio, gas turbine inlet temperature on the output work, exergy efficiency, exergy-economic and environmental parameters is studied. In addition, an attempt is made to optimize the performance of combined cycle systems considering three objective functions of exergy efficiency, total cost rate and exergy unit cost of produced electricity.

Modified methods for assessing photovoltaic solar thermal collectors

Photovoltaic solar thermal collector (PVT) is a promising hybrid technology for generating heat and electricity simultaneously. Recently, vast research has been conducted to improve its performance. Most of the time, the manufacturing cost is needed to be taken into consideration by PVT designers and/or manufacturers, to justify producing certain PVT designs. In the existing methods, the assessment of PVT with different designs was governed only by their total energy or exergy output, area, volume and weight, making the PVT designs comparison becomes difficult if the manufacturing cost is to be considered. This paper is intended to link the manufacturing cost parameter into the existing methods. The modified methods are yield per area per cost, yield per volume per cost and yield per weight per cost factors which are defined and derived. Based on the modified methods, the optimum PVT design will have higher values of the proposed factors. The significance, applicability conditions, limitations and the influential parameters of the proposed factors are illustrated. It is shown that the modified methods are helpful in classifying PVT with different designs based on their energy or exergy output, area, volume, weight as well as manufacturing cost. These methods may have a potential to be used by the designers and/or manufacturers of PVT in making their design decisions.

Proposal of a new low-temperature thermodynamic cycle: 3E analysis and optimization of a solar pond integrated with fuel cell and thermoelectric generator

The present research deals with a novel hybrid system that comprises of a salinity gradient solar pond (SGSP) integrated with a proton exchange membrane fuel cell (PEMFC) and a thermoelectric generator (TEG). The key novelty of this research is the use of PEMFC waste heat to increase the performance of the low-temperature heat source (solar pond). Also, a thermoelectric generator is employed in the proposed setup for complete waste energy recovery. In this paper, the proposed system's energy, exergy, and economic (3E) performance are investigated, as well as compared with two additional systems that were modelled by excluding TEG and PEMFC to showcase the benefits of the sub-systems in the final configuration. A parametric study is also conducted to investigate the effect of significant parameters on the overall system performance. The simulation results indicated that the integrated system's net output power is 2288.8 kW at a base case operating condition, with energy and exergy efficiency of 11.26% and 13.17%, respectively, and a system cost rate of 394 $/h. In comparison to other components in the integrated system, SGSP alone accounts for 75% of total exergy degradation and has the highest investment cost rate of 66.70 $/h. Further, to achieve the best system performance, a multi-criteria optimization is performed for the suggested system with net output power, energy efficiency, exergy efficiency, and system cost rate as objective functions. Besides, the multi-criteria decision analysis (MCDA) is also carried out on the obtained Pareto front using TOPSIS decision-maker to select the best operating condition that improves the output power, energy, and exergy efficiency by 52.6%, 49.6%, and 61.8%, respectively, at the expense of 5.2% increase in the system cost rate. The current investigation demonstrates how an appropriate optimized design of an integrated energy system using SGSP, PEMFC, and TEG can improve the overall performance with reasonable cost increment.

Potential of hydrogen/diesel reactivity controlled compression ignition (RCCI) combustion from the perspective of the second law of thermodynamics

The potential of reactivity controlled compression ignition (RCCI) combustion fueled with hydrogen and diesel (i.e. hydrogen/diesel RCCI) was evaluated using multi-dimensional simulations embedded with a reduced chemical mechanism. In hydrogen/diesel RCCI, the premixed hydrogen is ignited by the diesel, which is directly injected into the cylinder well before the top dead center. To investigate the potential benefits of hydrogen/diesel RCCI, its combustion characteristics were compared with that of gasoline/diesel RCCI from the perspective of the second law of thermodynamics. Meanwhile, the impacts of premixed energy ratio and initial pressure on the exergy distribution for hydrogen/diesel RCCI were explored. The results show that hydrogen/diesel RCCI has an advantage over gasoline/diesel RCCI in the reduction of exergy destruction due to higher combustion temperature, shorter combustion duration, and the distinctive oxidation pathways between hydrogen and gasoline. A higher proportion of exergy output work can be achieved for hydrogen/diesel RCCI under the conditions with the same total input energy and 50% heat release (CA50) point. Moreover, a larger premixed energy ratio (i.e. larger hydrogen proportion) is helpful to elevate exergy output work and reduce exergy destruction owing to higher combustion temperature and the undergoing oxidation pathways of hydrogen with less exergy destruction. A higher initial pressure yields raised exergy destruction because of lower combustion temperature and longer combustion duration, but exergy output work is increased owing to the significantly reduced exergy transfer through heat transfer.

Exergoeconomic, environmental, economic, and energy-matrices (4E) analysis of three solar distillation systems equipped with condenser and different heaters

The water scarcity in the world in the near future become to a global challenge. The main aim of present study was to elucidate the performance of the three identical solar distillation units with different configurations under climatic conditions of the city of Tehran. All systems were equipped with different heating source that are thermoelectric heating modules (TEH), copper heater (CH), and solar water heater (SWH) while all system assisted with an active external condenser. Performance of all systems is scrutinized from different thermodynamic, thermoeconomic, environmental, and energy-matrices viewpoints. Findings revealed that the highest daily and annual productivity obtained by the system with CH. Economic analysis on the basis of uniform annual cost (UAC) revealed that the system with SWH has the lowest cost per liter (CPL) rather than other system while the highest CPL was for the case of TEH. Furthermore, it was concluded that the system with TEH obtain the most promising results in terms of exergoeconomic, enviroeconomic, and energy payback time (EPBT) because of the highest daily and annual energy and exergy output. Eventually, the environmental analysis indicated that the solar still with CH with 6342, 48.169, 18.46 kg emission of CO2, SO2. And NO have the best results rather than other systems

Design, exergy analysis, and optimization of a hydrogen generation/storage energy system with solar heliostat fields and absorption-ejector refrigeration system

In the current work, a solar-based energy plant that includes an organic Rankine cycle, an NH3−LiNO3 operated refrigeration system, reverse osmosis desalination, and hydrogen production device are integrated, modeled, and optimized. A parametric examination is designed with Matlab software to show the impact of varying primary system variables on outputs like system total energy, exergy efficiency, and total exergy output. All processes have been carried out for different working fluids, namely iso-butane, Propane, n-octane, and the results are compared. Parametric analysis reveals that at solar radiation of 800 W/m2, which is reasonable for the sun in most of the Middle East, selecting n-Octane as a working media results in an increase in the hydrogen production rate of about 150%. This also confirms the importance of selecting the right working fluid for the ORC unit. Moreover, the influence of substantial decision variables on the hydrogen production, net out pout power, exergy efficiency indicated that multi-criteria optimization is necessary. The multi-objective optimization strategy suggests the TIP = 1753 kPa, Toil = 99°C, ηistur = 0.9, ηispump = 0.87, and AHeliostat = 2800 m2, for the optimum state of the studied system. Additionally, the scatter distribution and sensitivity analysis for optimum point introduced by multi-criteria optimization utilized for better understanding the optimization process.

Exergy-environment assessment for energy system: Distinguish the internal and total exergy loss, and modify the contribution of utility

Improving the efficiency of energy system is a way to reduce its environmental impact. However, high efficiency always means high system complexity and high expense, and will again increase the environmental impact. This work proposed an exergy-environment assessment method for energy system. With the exergy balance calculation, the method converted the internal and total exergy loss flows, as well as the life-cycle consumed material (including utility), to the values of environmental impact points. This work also proposed indexes to assess whether the energy transformation (exergy loss) or the life-cycle consumption dominates the environmental impact. Then, this work adopted a sludge digestion system to show the application of the proposed method. The exergy analysis and environmental impact points of the system were calculated. The entire system has a positive exergy output of digestion gas (4.18 GJ h−1). The objective exergy efficiency of system is 27.11%, and the general exergy efficiency of digester unit (80.10%) is over two times that of heating unit (35.00%). Heating unit also has a much higher environmental impact than digester unit (about 1.00: 0.15). Results show that the exergy-environment assessment does not breach the classical thermodynamic analysis and provides the understanding of environmental impact. Compared to previous studies, this work resolves the issue of unreasonable data for the exergy-environment impact factor in methodology by amending its value from <0 or ≈0 to 0.40, clarifying the significance and rationality of exergy-environment assessment. The case study result shows the feasibility and advantage of the proposed method, which can be flexibly selected by decision maker. Impact factor based on the internal exergy loss is relatively preferred from the perspective of sustainability.