Chemical Exergy Research Articles

Exergy evaluation of equivalence ratio, compression ratio and residual gas effects in variable compression ratio spark-ignition engine using quasi-dimensional combustion modeling

This study is founded on previously validated, in-house, comprehensive, two-zone, quasi-dimensional combustion model, predicting performance and emissions in spark-ignition engines. The model is extended to include exergy terms complementing the first-law analysis results, which provide further useful information by implementation on test results acquired from an experimental, Ricardo E6, variable compression ratio (VCR) gasoline engine at the authors’ laboratory, operated under various CR and equivalence ratio (EQR) values at wide-open throttle. The model consists of unburned and burned zones simulating the combustion process, following strictly the flame-front movement in combustion chamber. The eventual combustion of the unburned mixture turbulent entrainment into burned zone through the flame-front area is followed closely. The exergy terms of each simulated zone are identified and computed, considering also chemical exergy components (diffusion plus reactive). The accurate account of temperature and species histories in burned zone after entrainment from the unburned one, should lead to more precise evaluation. This is important if irreversibility is computed from balance of all other exergy terms. The investigation examines and compares exergy-wise various EQR, CR and residual gas fractions. Presented diagrams of exergy terms for each zone and cylinder charge provide detailed information for chemical exergy, irreversibility and exergy losses.

Proposal and analysis of a poly-generation process for coal gasification and ironmaking

The novel gasification-reduction coupling process (GRCP) was proposed to obtain higher coal gas/hot metal poly-generation system efficiency. The hematite particles replaced previous moderators (H2O/CO2) in the entrained-flow gasifiers, and direct reduced iron (DRI) can be obtained simultaneously. In this study, the thermodynamic model was established to predicate material streams in GRCP. Numerous cases with different material ratios were also examined to investigate the relevant effects, such as effective gas ratio ([CO] + [H2]), metallization ratio (Fe wt.%), and reduction degree (R). To further quantify energy streams, the exergetic analysis was also conducted according to different definitions. The results indicated that both chemical and physical exergy of high temperature reducing gas transferred into DRIs through the coupling process. Therefore, a significant decrease was observed in cold gas efficiency (72.7%). The exergetic evaluation also shows that GRCP still kept a high-level (83.6%) based on all substances. Since the chemical exergy of DRI was stable exergy storage during the subsequent utilization, higher system efficiency can be expected in the further development of GRCP.

Accurate prediction of chemical exergy of technical lignins for exergy-based assessment on sustainable utilization processes

The exergy-based assessment on the sustainable utilization processes of technical lignin is important for potential identify and process optimization. In this study, chemical exergy of technical lignin was evaluated for the first time based on the Gibbs free energy relation. The chemical exergy of technical lignin was from 17653.89 to 33337.92 kJ kg−1.The effects of O/C and H/C ratios on the chemical exergy and standard entropy were investigated by using contour plot analysis. The chemical exergy of technical lignin is more significantly influenced by the O/C ratio, compared with the H/C ratio. Three types of prediction models including artificial neural network model with the input of elemental composition, HHV-based correlation, and element-based correlation were developed. The artificial neural network model has an excellent performance of predicting the chemical exergy of technical lignin, with the prediction relative error of less than ±0.15% under the confidential level of 97%. The prediction relative errors of the HHV-based correlation and the element-based correlation are within ±1.0% and ±2.5%, respectively. This work will provide the basic data for exergy-based assessment on the valorization processes of technical lignin, which is an important aspect of improving the economic level of biorefinery industry.

Thermodynamic Limitations and Exergy Analysis of Brackish Water Reverse Osmosis Desalination Process.

The reverse osmosis (RO) process is one of the most popular membrane technologies for the generation of freshwater from seawater and brackish water resources. An industrial scale RO desalination consumes a considerable amount of energy due to the exergy destruction in several units of the process. To mitigate these limitations, several colleagues focused on delivering feasible options to resolve these issues. Most importantly, the intention was to specify the most units responsible for dissipating energy. However, in the literature, no research has been done on the analysis of exergy losses and thermodynamic limitations of the RO system of the Arab Potash Company (APC). Specifically, the RO system of the APC is designed as a medium-sized, multistage, multi pass spiral wound brackish water RO desalination plant with a capacity of 1200 m3/day. Therefore, this paper intends to fill this gap and critically investigate the distribution of exergy destruction by incorporating both physical and chemical exergies of several units and compartments of the RO system. To carry out this study, a sub-model of exergy analysis was collected from the open literature and embedded into the original RO model developed by the authors of this study. The simulation results explored the most sections that cause the highest energy destruction. Specifically, it is confirmed that the major exergy destruction happens in the product stream with 95.8% of the total exergy input. However, the lowest exergy destruction happens in the mixing location of permeate of the first pass of RO desalination system with 62.28% of the total exergy input.

Exergetic comparison of electrical heating gasification and water electrolysis assisted gasification for renewable electricity storage

To develop an efficient solution for the storage of renewable electricity and utilization of biomass or waste within the power-to-X concept, the electrical heating gasification (EHG) technology for industrial-scale application was proposed and compared with water electrolysis-assisted gasification (WEG). The two technologies were compared in terms of composition, yield, and exergy efficiency. The results indicate that EHG consumes less electricity and generates syngas with higher chemical exergy. The maximum exergy efficiency of EHG was calculated as 80.76%. Electrical heating gasification is more efficient than WEG based on either the current state or the potential progress in the future. Additionally, the exergy efficiency of water electrolysis ranges between 54.1% and 79.1%, which implies that more efforts are needed in the future to reduce the specific electricity consumption. This work is valuable to guide the development of an electrical heating gasifier and to improve performances of power-to-X technologies.

Comparative analysis of methods for determining the flammability of municipal solid waste as railway transport cargo

A statistical analysis of information about fires that occurred on the railroads shows that it is necessary to enhance the fire protection measures while transporting the fire-hazardous materials (FHM). A comparative analysis of the use of the exergetic index and the flammability potential for forecasting the fire risks connected to the railroad FHM transportation has been performed. The studies considered municipal solid waste (MSW) as promising railway cargo. The values of the MSW chemical exergy and the heat of combustion have been calculated. The conditions and behavior of their variations have been investigated. A system of the substances and materials classification that is based on the exergetic coefficient was introduced. The proposed approach allows us to resolve methodological problems caused by the requirement to account for the technical, economical criteria, and the fire risk indexes into a unified classification system. The conception of the exergetic index improves the objectivity of the procedure for the estimation of the MSW flammability properties.

Применение модели Хольта — Уинтерса и эксергетического метода для прогнозирования безопасного обращения с отходами в Российской Федерации

The problem of waste management is acute in the Russian Federation. Not enough attention is paid to the systematic studies of their composition and properties. The purpose of the work is to conduct a comprehensive analysis of data on waste generated, to select models for predicting their mass, composition, and properties, to substantiate the feasibility of using exergetic analysis to assess safety and make informed decisions on the management of solid municipal waste management. To predict the volume of waste generation, the following were used: an integrated autoregression model — a moving average and exponential smoothing models. The study of changes in the composition and properties of the municipal solid waste, the choice of technology and the assessment of safety in waste management were carried out using the exergetic method. Its advantages are determined by the possibility of conducting a comprehensive energy-ecological assessment and determining the fire hazard of waste and the processes of handling them. The application of the Holt-Winters model for predicting the mass of the generated waste is substantiated. The analysis of changes in the morphological composition of waste, their distribution by types of economic activity is carried out. The values of chemical exergy of municipal solid waste are determined, and a forecast of its further growth is constructed. The dependences of chemical exergy on the heat of combustion of waste are found. It is determined that it is advisable to consider chemical exergy as a heat engineering characteristic and an indicator of fire and environmental hazard of waste. It is proved that the exergetic efficiency of the incineration process is higher than that of composting and burial. Transportation of garbage from the large cities by road and rail transport for subsequent disposal and recycling can be considered as a forced temporary measure during the development of the branch of industry and the formation of a waste management culture. For the application of the exergy method in the system for ensuring safety when handling solid municipal waste, a data mining system was developed. It is advisable to use the obtained results for the development of safety requirements for the management of production and consumption waste in the Russian Federation.

Modelling and simulation of industrial multistage flash desalination process with exergetic and thermodynamic analysis. A case study of Azzour seawater desalination plant

Abstract Despite the fact of being intensive energy consumption, MSF is a mature technology that characterised by a high production capacity of high-quality water. The multistage flash (MSF) desalination process is one of the prominent thermal desalination used in the industry of seawater desalination to produce high quantity and high quality of freshwater. However, this process consumes large amount of energy and faces thermal limitations due to its high degree of exergy destruction at several units of the process. Therefore, the research of MSF is still existed to elevate the performance indicators and to resolve the concern of high energy consumption. To rectify these limitations, it is important to determine the units responsible in dissipating energy. This study aims to model an industrial MSF process validated against real data and then investigate the exergy destruction and thermodynamic limitations of the process. As a case study, Azzour MSF seawater desalination plant, located in Al Khiran in Kuwait is under the focus. A comprehensive model is developed by analysing several published models. Specifically, the calculation of exergy destruction has embedded both physical and chemical exergies that identified as a strong point of the model developed. As expected, the highest exergy destruction (55.5%) occurs within the heat recovery section followed by the brine heater with exergy destruction of 28.26% of the total exergy destruction. This study identifies the sections of the industrial process that cause the highest energy losses.

Optimal configuration and economic analysis of PRO-retrofitted industrial networks for sustainable energy production and material recovery considering uncertainties: Bioethanol and sugar mill case study

In this study, an optimal scheme is proposed by utilizing waste streams at a plant-wide scale along with pressure retarded osmosis (PRO) membrane allocation in complex industrial networks for energy recovery. Chemical exergy pinch analysis (ChExPA) and process graph (P-graph) are used to address the problem. The ultimate goals of utilizing the tools are (1) determine the optimal external load consumption, (2) minimizing the waste discharge, and (3) sustainable energy production while utilizing high chemical exergy potential waste discharges. A reliability assessment assisted with Monte-Carlo simulation is further performed to evaluate the proposed solutions from P-graph considering uncertainties. The effectiveness of the proposed methodology is explained using three industrial case studies which covered both intra-plant and inter-plant networks. The results indicated that ChExPA and P-graph can effectively identify the optimal location of the PRO membrane in industrial networks. Upon analyzing the complex inter-plant industrial networks 7.795 MW net power output was harnessed, and significantly higher waste of 384.92 kg/s was recovered with a levelized cost of energy of 0.073 $/kWh. The inter-plant network shows the greatest net profit which accounted for approximately $1,191,000 (i.e., 5.84 times higher than stand-alone plants) with a reasonable payback-period of 4.5 years.

Key issues on the exergetic analysis of H2O/LiBr absorption cooling systems

This paper deals with the key aspects of the exergy analysis of H2O/LiBr absorption refrigeration cycles where, instead of agreement, disparity of opinion exists among researchers. As a result, comparisons with the literature are often difficult or meaningless. Based on an in-depth literature review, the key issues highlighted were: a) the identification of the dead state, b) the calculation of the exergy of the currents, and c) the definition of the exergy efficiency of the devices and of the overall system. This study clarifies controversial and divergent assumptions and proposes a coherent approach. In addition, a comparison with the literature is performed. As a case study, a single effect absorption cycle, refrigerated with water, has been considered here. Related to the dead state, consideration of different subsystems results in practical interest. The results highlight the importance of the correct calculation of the chemical exergy for the exergy analysis of the absorption refrigeration system. It is also described here how to define the rational exergetic efficiency, or fuel-product exergy, according to physical and chemical exergies of the streams. The comparison with the literature shows discrepancy specially in the exergy analysis of the desorber and the absorber, where the chemical exergy plays an important role.

Exergy analysis of an atmospheric residue desulphurization hydrotreating process for a crude oil refinery

Abstract The exhaustion of petroleum reserves and the declining supply of conventional feedstock have forced refineries to use heavier crude oil in their production. Removing the undesirable components containing sulphur and metals in the atmospheric residue (AR) fraction requires extensive catalytic hydrotreating (HT) atmospheric residue desulphurization (ARDS) process. In this work, we endeavour to collect and present a comprehensive dataset to develop and simulate the ARDS HT model. This model is then used for an exergetic analysis to evaluate the performance of the ARDS HT model regarding the exergy destruction, the location of losses and exergetic efficiency. The massive exergy destruction is caused by significant differences in chemical exergy of source and product streams during separations, fractionation and reactions. The exergy destruction in the equipment independent of chemical exergies such as heat exchangers, pumps and compressors is relatively low. This exergetic analysis revealed that the majority of the processing equipment in the ARDS HT process performed satisfactorily. However, the remaining equipment requires improvement for its performance in regards to exergetic efficiency or/and avoidable exergetic losses. To enhance the efficiency of the equipment that is intensive in terms of exergy and energy use, the use of clean and high purity renewable hydrogen and several process rectification is proposed.

Prediction of chemical exergy of syngas from downdraft gasifier by means of machine learning

The rapid consumption of fossil fuels because of the increasing energy demand caused the increase in greenhouse gas emissions. However, biomass gasification is attracting much attention as an environmentally friendly and highly efficient thermochemical conversion due to its high carbon conversion and low greenhouse gas emissions. Further, downdraft gasifiers are known as the most suitable technology for biomass gasification processes because they offer an easy-to-control working environment and low investment cost. In recent years, artificial neural network models (ANN) have been used in the literature as a machine learning approach to predict gasification parameters. In this work, the parametric study was carried out for the variation of gasifier temperature (873.15 K–1173.15 K) and steam/biomass ratio (0.1–1.5) for 22 lignocellulosic biomass samples. Thus, 32,025 different experimental conditions generated by Aspen Plus® were used with Bayesian regularized ANN as a machine learning approach to predict the chemical exergy of the syngas from the downdraft gasifier. The operating parameters of gasifier temperature and steam/biomass ratio were found to be highly influential on the syngas quality and chemical exergy value of the syngas. Therefore, the operating conditions and biomass properties (carbon, hydrogen and oxygen content) were selected as input parameters for the ANN model. The regression coefficients (R2) were found to be convincingly 0.9992, 0.9991 and 0.9942 for training, test and hazelnut shell gasification data, respectively. Moreover, the results for root mean squared error (RMSE) were within satisfactory limits for the developed ANN model.

An investigation of recovering the energy of exhaust heat for improving conventional compression ignition to low temperature combustion by adding diesel vapor

Reducing exhaust emissions and, consequently, recovering wasted energy and exergy of an engine are the primary purposes of engine research. In previous studies, improving the combustion efficiency and reducing the exhaust emissions by homogeneous combustion, and the recovery of engine wasted energy (especially exhaust wasted energy) to use in the downstream cycles have been researched. In the present study, the feasibility of recovering exhaust energy to evaporate diesel fuel and the effects of adding diesel vapor on combustion efficiency, exhaust emissions, and overall engine efficiency have been investigated. To achieve these purposes, an experimental investigation on the effects of adding diesel vapor was performed. And, the numerical analysis was used to investigate the feasibility of the diesel evaporation by recovering exhaust energy. The experimental tests were performed at a constant speed (1000 rpm) and three amounts of fuel injection. In each amount of fuel injection, the amount of diesel vapor increased in three steps up to the knock threshold. In the experimental investigation, the share of the indicated work, combustion irreversibilities, heat transfer loss, and exhaust gas from the inlet exergy have been shown. Also, the effects of adding diesel vapor on exhaust emissions (PM, NO, CO and HC) and the cycle variation were investigated. Furthermore, the chemical exergy of each one of the species in the exhaust stream was investigated in detail. In the numerical investigation, the following results were investigated: the available exhaust gas exergy up to the dew point, the share of the exhaust recoverable energy from the diesel evaporation energy, the improvement of the second law efficiency by recovering exhaust gas energy, the reduction of exhaust gas temperature, and the required length of heat exchanger for increasing the diesel temperature from ambient temperature up to the exhaust gas temperature. According to the achieved results, adding diesel vapor reduces combustion irreversibility and heat transfer loss; also, the second law efficiency improves from 30% to 44%. Using a heat exchanger can recover 20–45% of the required evaporation heat of diesel. The reduction of exhaust gas temperature after the heat exchanger is less than 2%. The maximum required heat exchanger length for increasing the diesel temperature from ambient temperature up to the exhaust gas temperature is 50 cm. The addition of diesel vapor decreases NO and soot emissions and, simultaneously, increases CO and HC emissions. The addition of diesel vapor decreases the cycle variation, especially in low-load conditions. According to the chemical exergy of the various species in the exhaust gas mixture, the CO2 and H2O emissions have the most destructive effect on the environment; also, the detrimental environmental impact of CO emission is more than NO until being oxidated by a catalyst.

Exergy analysis in the processes of municipal wastewater treatment plants

ABSTRACT The produced sludge in WWTPs can be used as a renewable energy source to supply a part of their energy demands. The condition of the wastewater entering the treatment plant changes after passing through different units in terms of pollution and exergy. In this research, exergy analysis of raw wastewater entering the WWTPs in the south of Tehran has been studied. Six other WWTPs have also been examined in general in terms of exergy. The results show that physical exergy compared to chemical exergy in the WWTPs south of Tehran is insignificant and negligible. Also, a small part of the wastewater exergy in the Screening units and Grit chamber units is removed from the treatment plant cycle and energy is not recyclable. Other results include the destruction of most of the exergy of WWTPs in the aerobic reactor, which is about 30% of the exergy of the inlet wastewater and about 93% of the total exergy destruction. Also about 3700 kW of exergy is removed through the expulsion of dewatered sludge from the treatment plant. In the study of 6 other treatment plants, it was found that the larger the capacity of the treatment plant, the exergy of consumable work will have a smaller share in the exergies entering the treatment plant compared to the exergy of the inlet wastewater. Also, with increasing biogas exergy, the exergy rate of dewatered sludge decreases. In addition, the exergy change of inlet wastewater in treatment plants of 3 and 5 is about 10% while this variation for other treatment plants is more than 40%.

Chemical and Mechanical Aspect of Entropy-Exergy Relationship.

The present research focuses the chemical aspect of entropy and exergy properties. This research represents the complement of a previous treatise already published and constitutes a set of concepts and definitions relating to the entropy–exergy relationship overarching thermal, chemical and mechanical aspects. The extended perspective here proposed aims at embracing physical and chemical disciplines, describing macroscopic or microscopic systems characterized in the domain of industrial engineering and biotechnologies. The definition of chemical exergy, based on the Carnot chemical cycle, is complementary to the definition of thermal exergy expressed by means of the Carnot thermal cycle. These properties further prove that the mechanical exergy is an additional contribution to the generalized exergy to be accounted for in any equilibrium or non-equilibrium phenomena. The objective is to evaluate all interactions between the internal system and external environment, as well as performances in energy transduction processes.

Evaluation of dual crude palm and kernel oil production in North Colombia via computer-aided exergy analysis

Palm production chains in Colombia have some unsatisfied demands that affect their competitiveness. Specific demands include efficiency in energy use. Therefore, in the present report, an exergy analysis for the dual crude palm and kernel oil production process was carried out to determine the main energy sinks and suggest technological improvements that allow better use of energy. For this study, the process was initially simulated in the Aspen Plus ® software, where the chemical and physical exergies of the species and streams involved were quantified. The process irreversibilities, the exergy loss, the exergy of waste, and the exergy of utilities were calculated for each stage and the whole process. An overall exergy efficiency of 18% was achieved, while the highest process irreversibilities contribution was due to the destroyed exergy with the waste in the threshing stage. To increasing the global exergy efficiency of dual crude palm and kernel oil production, it is proposed the evaluation of palm rachis use to obtain biofuels and/or high-value products.

A conceptual biomass liquefaction system with supercritical water for bio-oil, power and heating trigeneration: Thermodynamic and environmental analysis

Advanced energy conversion systems on biomass-based are essential for high-efficient utilization of biomass energy. This work proposed a conceptual biomass liquefaction system with supercritical water for combined bio-oil, power and heating trigeneration. Both thermodynamic and life cycle environmental assessment are performed to verify the potential benefits of this novel system. Mass flow in the overall process is configured using Aspen Plus, with detailed energy and exergy flow modelling for the whole system. At the optimal operation parameters, where reactor temperature and pressure are around 390°C and 25 MPa, feedstock concentration is ∼33.3 wt%, water recycle ratio is ∼50%, and gas combustor temperature is about 1000°C, system energy and exergy efficiency reach their highest values, i.e. 58.53% and 50.65%, which are comparable to those of other biomass-based energy conversion system. Effects of those key parameters on exergy and energy efficiency are also discussed. The maximum exergy loss is induced by chemical exergy loss in liquefaction reactor and energy loss is mainly caused by heat transfer. From environmental assessment, GWP, AP, EP and TP values at the optimal operation parameters are lower than those of other biomass-based liquefaction system. When CCS and wastewater treatment units are applied, GWP, AP and EP values can be reduced by 50.0%, 33.2% and 61.5%, respectively. The comparison of thermodynamic and environmental performance among different biomass-based energy conversion systems shows that biomass liquefaction with SCW is a relatively efficient and clean technology to produce carbon-neutral bio-oil.

Exergy study of amine regeneration unit for diethanolamine used in refining gas sweetening: A real start-up plant

Diethanolamine (DEA) solutions are used in refineries to sweeten gas. DEA is responsible for absorbing H2S from sour gas. In an Amine Regeneration Unit (ARU), the rich amine with H2S is regenerated. A refining column in the Middle East started commercial production in 2020. Using Aspen HYSYS V.11, an amine regeneration unit in the refinery that supplies lean amine to the delayed cooker unit for gas sweetening was simulated, and an exergy study was performed on various equipment. Exergy is destroyed in an irreversible process, while energy is converted from one type to another. The sum of the physical and chemical exergy is the total exergy. The chemical exergy was calculated using a series of equations embedded in Excel, while the physical exergy was calculated using HYSYS. The DEA concentration used is25 wt%. Each equipment's exergy destruction rates, destruction efficiency, and percentage share of destruction were determined. The regenerator had the highest destruction rate of 2144.11 kW and an 80.21 percent share of total destruction. With a value of 326.00 kW and a percentage share of 12.20 percent of total destruction, the air cooler has the second-highest exergy rate. Exergy has a 99.70 percent overall efficiency. Due to system losses, the DEA concentration fell from 25% to 20% of the design value. The regenerator had the highest destruction rate of 2616.74 kW followed by the air cooler with a value of 294.61 kW. In DEA 20%, an exergy analysis was carried out. Exergy research showed the same percentage share distribution for equipment at a concentration of 20 DEA wt. percent. To find related equipment relationships, the results of the unit's exergy analysis were compared to those of another ARU exergy study at the same refinery plant. The regenerators were found to have the highest exergy destruction of the two units with a percentage share of the overall destruction reaching 80% followed by the air coolers with values reaching 9%.

Mid/low-temperature solar hydrogen generation via dry reforming of methane enhanced in a membrane reactor

Dry reforming of methane (DRM) is a promising approach for hydrogen generation and decreasing CO2 emission. However, the high reaction temperature of DRM (~800 °C) has strict requirements on materials and sealing, which also has high heat losses during the reaction process. In this study, a solar thermochemical system integrated with a parabolic trough solar collector and a membrane reactor is proposed for decreasing the reaction temperature of DRM to a mid/low-temperature range (300–500 °C). Due to the selective H2 separation via the H2 permeation membrane reactor, the equilibrium of the DRM reaction shifts forwards, leading to a lower reaction temperature, and high-purity hydrogen can be collected during the one-step process. The conversion rate of CH4 in this experimental research could reach 20.47% at 400 °C and 30.00% at 425 °C, which is higher than state-of-the-art results. Besides, the thermodynamic analysis of the proposed system indicates that the first-law thermodynamic efficiency and the solar-to-fuel efficiency could reach as high as 74.73% and 38.92%, respectively. The chemical exergy of methane can be utilized efficiently by enhancing the energy level of solar thermal energy. This research provides a novel approach for efficient solar energy storage and hydrogen generation with negative CO2 emissions.

Exergy Study of Sour Water Stripper Unit of Delayed Coker Unit in a Refinery plant: A Real Start-Up Plant

Process sour water produced from refinery contains some hazardous pollutants as (H2S and NH3). Sour water stripper units remove both compounds from water. The two stripped pollutants are sent to Sulphur recovery unit to produce Sulphur and prevent any acidic emissions against environmental regulations. The sour water stripper unit serving the delayed Coker unit was simulated with Aspen HYSYS V.11 and an exergy study was conducted on different equipment. While energy is transformed from a form to another, exergy is destructed in an irreversible process. The total exergy is equal to physical and chemical exergies. Physical exergy is calculated through HYSYS and chemical exergy is calculated through a series of equations embedded in excel. The exergy destruction rates, the destruction efficiency and the percentage share of the destruction of each equipment was calculated. The total unit destruction rate was 2996.25 kW. The stripper showed the highest destruction rate 2592.23 kW and a percentage share of 86.52 % of total destruction. The overall efficiency of exergy is 81.58%. A comparison was conducted between the exergy results of this study with two other exergy studies performed in the same refinery plant. The columns in the three studies showed the highest destruction rates exceeding 78% of the total destruction of each unit. The air coolers showed the second- highest destruction rates in their units with a percentage share exceeding 7% of total destruction. The pumps showed the lowest destruction rates with values of less than 1% of the total destruction of each unit.