Largest Exergy Loss Research Articles

Exergy and exergoeconomic analyses of multi-energy complementary system based on different natural gas and biogas co-firing ratios considering carbon tax

This study analyzes the exergy and exergoeconomic performances of a combined cooling, heating, and power (CCHP) system powered by natural gas and biogas. First, the exergy of the energy and material flows in the investigated co-firing CCHP system is obtained. In addition, the exergy loss and exergy loss distribution ratios of each component as well as the exergy efficiency of the entire system are investigated. Furthermore, the effects of the co-firing ratio of natural gas and biogas on the exergy and exergoeconomic performances are analyzed. Meanwhile, a carbon tax is considered in the exergoeconomic analysis. The results show that the gasifier, two-stage LiBr-H2O absorption chiller, and internal combustion engine indicate the largest exergy loss and exergy loss distribution ratios under different co-firing ratios. The exergy efficiency of the entire system decreases by 3.81% and 4.93% as the co-firing ratio decreases from 1:1–1:10 (natural gas: biogas) in the summer and winter, respectively. The unit exergoeconomic cost (UEC) of multiple products decrease with the co-firing ratio. Finally, a sensitivity analysis is performed to reveal the effects of the co-firing ratio and natural gas price on the UEC of multiple products.

The exergetic approach for the analysis of HDH desalination process using a pulverized column

In the process of humidification-dehumidification, the cross transfer of heat and mass is due to the affinity between water and air. In the present work, a mathematical model was developed basing on the mass, thermal and exergy balances in order to analyse the performance of a freshwater productivity by desalination of seawater. Firstly, we acquired the thermodynamic properties of the binary system (air-vapour water) through the use of the virial equation of state. To determine the impact of operating variables on the performance of the unit, the concept of degrees of freedom has been introduced. Basing on a rigorous algorithm, the performance of HDH was approached by calculating the productivity of fresh water and exergetic efficiency in relation with the operating variables. The results of the simulation show that the productivity and the gained-output ratio (GOR) increase with the increase of the ratio of the flow rates and the temperature of the inlet air in the humidifier. However, it decreases simultaneously with the outlet water temperature. Besides, the humidifier and dehumidifier exergetic efficiencies increase simultaneously by increasing of the mass flow rates ratio and the temperature of the air at the inlet of the humidifier. Also, we note that the exergetic efficiency of the dehumidifier decreases with outlet water temperature. The simulation results establish that the collector performance diminishes with the liquid mass flow rate. Nevertheless, these results show that the major part of exergy destruction in the unit is localized in the collector with the lowest exergetic efficiency. The largest exergy losses are caused by increasing of the pinch of temperature.

Analysis of thermal efficiency in Star Energy Gothermal Darajat

After years of operation, the plant will no longer operate optimally according to its design. The practice of the work cycle shows that the original value of thermal efficiency will always be below 100%, this is because during the cycle process of creating work, the energy received by the system by heat transfer will not be fully received and will be absorbed by the environment. In this research, thermal efficiency analysis was carried out in accordance with the first and second laws of thermodynamic efficiency and thermoeconomic calculations to calculate losses. Based on calculations that have been carried out, the thermal efficiency of the Star Energy Geothermal Darajat unit-3 geothermal power plant system is 21.72% with the largest exergy loss being in the condenser component of 62,219,418 kW with an exergy loss cost of 252,766,682.24 Rp/ days and the smallest is in the cooling tower of 599,362 kW with exergy loss costs of 23,655,907.11. Rp/day from the following results it can be seen that this efficiency value depends on the performance of each component.

Comprehensive performance analysis of cold storage Rankine Carnot batteries: Energy, exergy, economic, and environmental perspectives

Rankine Carnot batteries have demonstrated promise as a viable solution for electricity storage due to their high energy density at low temperatures. A specific variant of these batteries, known as the Cold Storage Rankine Carnot Battery (CSRCB), utilizes a vapor compression refrigeration (VCR) unit to store cold energy at sub-ambient temperatures. In this paper, three different configurations of CSRCB are constructed: the Basic CSRCB (B-CSRCB), CSRCB with a recuperator in VCR (R-CSRCB), and CSRCB with a recuperator in VCR and a preheater in ORC (RP-CSRCB). The system is analyzed from four perspectives: energy, exergy, economic, and environmental (4E). The impact of key parameters, such as heat source temperature, ambient temperature, and pinch point temperature, on the system's performance is evaluated. The results indicate that the RP-CSCBR configuration outperforms others in terms of energy, exergy, and economic analysis. The evaporator in ORC-subsystem is the component with the largest exergy loss. When the three configurations of CSRCB achieve the maximum exergy efficiency under different conditions, the ORC-subsystem evaporator accounts for 41.9 %, 41.9 % and 17.6 % of the exergy loss of B-CSRCB, R-CSRCB and RP-CSRCB, respectively. The lowest levelized cost of storage (LCOS) can be obtained when the system is operating at high heat source temperature, low ambient temperature and small pinch temperature difference. The environment assessment results show that the changes of the key parameters of the system have different effects on the annual emission reduction (AER) and total equivalent warming impact (TEWI) of CSRCB with different configurations.

Energy, exergy, economic and environmental (4E) analyses of a cleaner fused magnesia system

This study performed a comprehensive energy, exergy, economic, and environmental analysis to evaluate the thermodynamic performance of a cleaner fused magnesia system (CFMS), compare with light burned magnesia process system (LMPS) and fused magnesia process system (FMPS). The analysis considered the multi-energy supply and exergy efficiency of the system, and determined its irreversibility under different processes. The yield rate of fused magnesia (34.2%) in CFMS, higher than that of LMPS (12.8%) and FMPS (7.7%). The energy and exergy efficiencies of the CFMS were 35.4 and 26.3%, higher than those of LMPS (29%; 21.2%) and FMPS (22.4%; 16.8%), the energy consumption per unit product were 3410.2 kWh/t, higher than those of LMPS (4800 kWh/t) and FMPS (3640 kWh/t), and the economic benefit of the fused magnesia product was 1476 ￥/t, higher than that of LMPS. The carbon dioxide emission in CFMS was 2.116 kgCO2/kgMgO, which is lower than that of LMPS (4.226 kgCO2/kgMgO), and almost equal to that of FMPS (2.077 kgCO2/kgMgO). The largest exergy loss in CFMS, which was caused by the heat transfer among magnesia products, furnace gas, and air, can be partially recovered using a waste heat recovery system. The improved fused magnesia system was more energy-saving and environmentally friendly. The findings of this study can be used to improve decision making in the smelting system.

Optimization of combined heat and power cogeneration via modification of low-pressure regenerative system with absorption heat exchanger

The large exergy loss during heat transfer is a key problem for the combined heat and power cogeneration. Instead of the traditional heat source coming from high-grade extracted steam at the outlet of the intermediate-pressure turbine, a novel combined heat and power configuration is proposed for large heat demand by modifying the low-pressure regenerative system. By adding a new LP unit with sufficient extracted flow and heat exchange, a part of the heat source from high-grade extracted steam at the outlet of the intermediate-pressure turbine is replaced by low-grade extracted steam within the LP turbine, avoiding the off-design operation of the LP turbine in the traditional combined heat and power configuration. In addition, the new combined heat and power configuration is optimized by introducing an absorption heat exchanger. The absorption heat exchanger lowers the return temperature of the PHS, which further reduces the energy grade of the heat source. The thermodynamic results show that the electric efficiency of the novel combined heat and power configuration is increased by 4.24% in total at a given heat demand of 241.37 MW. Exergetic results reveal that the exergy loss of two heat exchange links is drastically reduced from 30.47 MW and 26.04 MW to 8.80 MW and 11.81 MW respectively. An economic analysis of the new CHP configuration indicates that the dynamic payback period counteracting the investment increment is only 2.15 years, and the net present value increment over a 25-year period can reach $55.818 million.

Typical case of CO2 capture in Chinese iron and steel enterprises: Exergy analysis

The iron and steel industry is not only a major energy consumer but also a major CO2 emitter. Thus, this industry is now actively improving its energy utilization efficiency and reducing carbon emissions in the production process through process development, equipment upgrades, and CO2 capture and utilization. Based on typical CO2 capture and utilization cases in Chinese iron and steel enterprises, this study analyzes the exergy efficiencies and exergy losses of different CO2 capture processes, confirming that the main reasons for low exergy efficiencies and large exergy losses in such processes are the consumption of steam, electricity, and converter gas, and further analyzes the impacts of converter gas and steam recycling on the exergy efficiency of CO2 capture. The results show that the product exergy efficiency of the C-PRO-4 process is increased by 19.97% compared with that before recycling, and 21.35%, 24.4%, and 6.8%, respectively, compared with those of the C-PRO-1, C-PRO-2, and C-PRO-3 processes after recycling, providing data reference for improving energy utilization in CO2 capture.

Energy, Exergy, and Economic (3E) Analysis of Transcritical Carbon Dioxide Refrigeration System Based on ORC System

This paper used the energy, exergy, and economic analysis of a carbon dioxide (CO2) transcritical two-stage compression system based on organic Rankine cycle (ORC) waste heat recovery technology. When the intermediate pressure and high-pressure compressor outlet pressure were changed, respectively, this study simulated the change in system energy efficiency by adding the ORC for waste heat recovery, calculated the ratio of exergy loss of each component, and performed an economic analysis of the coupled system. The results show that adding waste heat recovery can effectively increase the energy efficiency of the system, and among all components, the heat exchanger had the largest exergy loss, while the evaporator had the highest capital investment and maintenance costs.

Thermo-economic analysis and multi-objective optimization of a reversible heat pump-organic Rankine cycle power system for energy storage

The rapid growth in renewable energy has reinforced the efforts to develop new scalable energy storage to balance the mismatch between energy production and demand. The reversible heat pump-organic Rankine cycle (HP-ORC) Carnot battery system is a possible candidate for this. Further investment cost reduction and the utilization of low-temperature energy were extremely beneficial to its development and application. A low-temperature and simple reversible HP-ORC storage system based on a compression and expansion dual-function unit was developed in this paper. A screening of 3 candidate working fluids was performed and R1233zd (E) was selected as the final candidate for the demonstrator. A mathematical model of the presented system was built to analyze the energy, exergy, and economic performance. Additionally, a multi-objective optimization of the system was carried out to find the optimal storage temperature taking economic and energy criteria into account. Finally, exergy analysis was performed under the optimal condition. The results show that the higher isentropic efficiency and temperature of the heat source are, the better the performance of the system is. When the optimal upper and lower storage temperatures are 126 ℃ and 99 ℃, the power-to-power efficiency (P2P), electrical storage capacity (ESC), levelized cost of storage (LCOS), and exergy efficiency are 28.16 %, 1.77 kW∙h/t, 0.36 $/kW∙h, and 61.82 %, respectively. The condenser and evaporator need to be improved in terms of their large exergy loss rate and low exergy efficiency.

Transient behavior and thermodynamic analysis of Brayton-like pumped-thermal electricity storage based on packed-bed latent heat/cold stores

Pumped-thermal electricity storage has the advantages of high energy storage density, no geographical restrictions and low costs, making it the most promising large-scale electricity storage technology. In this paper, a numerical model of the Brayton-like pumped-thermal electricity storage based on packed-bed latent heat/cold stores is established and a recuperator is added between the hot store and the expander. The rated power of the system is 150 kW and the charging/discharging time is 4 h. The dimensionless analysis is applied to the energy storage units including transient temperature, charging/discharging time as well as axial position. Moreover, based on the finite element method, an extensive thermodynamic analysis is carried out in MATLAB. It is concluded that compared with the non-recuperated system, the total input power of the recuperated system can be reduced by 18.1 kW in the charge duration and the energy density of the system using PCMs instead of sensible heat storage materials can be improved from 202.4 kWh/m3 to 267.4 kWh/m3. The roundtrip efficiency of the system could reach 0.55. In addition, detailed exergy flow and exergy loss of each component are studied. It is found that the total exergy loss of the recuperated system is 52.27 kW, a 22.4 % decrease compared to that of the non-recuperated system and the compressor has the largest exergy loss, accounting for 36 % of the total loss, which can be ameliorated by improving the level of industrial manufacturing in the future.

Energy and exergy analysis of supercritical/transcritical CO2 cycles for water injected hydrogen gas turbine

This paper investigated the supercritical/transcritical carbon dioxide cycles for water injected hydrogen gas turbine with the advantages of zero carbon emission, low pollution, high efficiency, low cost and so on. This paper selected several typical combined cycles from more than a dozen layouts studied by our team. We constructed a thermodynamic energy and exergy analysis model and verified it with the experimental models from GE. The maximum energy efficiency and its corresponding exergy efficiency that each layout can achieve are obtained after parameter sensitivity analysis, water mixing research and exergy analysis. It can be found that the combined cycle energy efficiency decreases as the water-hydrogen ratio increases. The component with the largest exergy loss is the combustor, accounting for 23.58%. And the transcritical CO2 dual recuperated combined cycle is the best layout with the combined cycle energy efficiency of 64.39% and the combined cycle exergy efficiency of 62.96%. The research done in this paper can provide a basis for the design of next-generation gas turbine.

Absorption Chiller/Kalina Cycle Coupled System for Low-Grade Waste Heat Recovery in Hydrate-Based CO2 Capture Process: An Economic and Exergetic Study

This study investigates a coupled system combined by a LiBr/H2O absorption refrigeration cycle and a Kalina cycle, to recover waste heat from a hydrate-based CO2 capture process. The optimal system operation has been obtained. Payback time, Return on investment, Net present value and Discounted cash flow rate of return are selected as the evaluation indicators for a comprehensive economic analysis. Cash flow patterns are obtained for different discounted interest rates and electricity prices. Exergy analysis is conducted and the exergy loss of each component is calculated. Results show that in comparison with the individual Kalina cycle, the net electricity generation is increased by around 45%. The highest thermal efficiency of this coupled system is 16.78%. Payment balance can be achieved with a payback time of 6 years. The purchase price of heat exchanger occupies the largest capital investment. Exergy efficiency of this system is obtained as 36.89%. Major system irreversibility occurs in heat transfer processes of heat exchangers and the largest exergy loss is found in generators of both subcycles. Reducing the heat transfer irreversibility and the size of heat exchangers are greatly encouraged in future efforts.

Performance assessment and multi-objective optimization of a geothermal-based tri-generation system in hot Summer Continental Climate: Tianjin case study

Considerable interest in the investigation of energy supply systems that effectively utilize renewable energies is being aroused due to the shortage of fossil energy and serious environmental pollution. Geothermal energy is a considered as a promising alternative to fossil energy due to its advantages of large reserves, good stability, and strong sustainability. This paper developed a geothermal-driven tri-generation system to generate power and supply heating and cooling demand. The tri-generation system is composed of an absorption refrigeration cycle, a heat exchange cycle, and an organic Rankine cycle. The paper begins with an introduction to the thermodynamic, economic, and environment models of the presented system. The effects of the geothermal water parameters on the system performance were originally investigated based on the actual data of a sports center (zero energy building). This building is located in Jiefang South Road, Tianjin, which belong to Hot Summer Continental Climate. In addition, the multi-objective optimization of this system was carried out based on the TOPISIS decision-making method considering economic and environmental criteria. The minimum payback period and maximum carbon emission reduction were chosen as the optimization factors. Finally, the optimal temperature of geothermal water is obtained and the exergy analysis was performed under the optimal conditions. The results indicate that the presented system possesses an optimal geothermal water temperature of 83 °C. Under this temperature, the total thermal efficiency in cooling season and heating season were 41.17 % and 84.93 %, respectively. The exergy efficiency in cooling season and heating season were 47.28 % and 62.23 %, respectively. Our proposed system has equivalent annual operating cost of 12.9 k$/year, with a payback period (PBP) of 2.57 years and carbon emission reduction of 2379 ton/year. The condenser and evaporator need to be improved in terms of large exergy loss rate and low exergy efficiency.

Performance analysis of an adiabatic compressed air energy storage system with a pressure regulation inverter-driven compressor

Adiabatic compressed air energy storage provides an efficient and emission free approach for large-scale energy storage. In adiabatic compressed air energy storage system with isochoric air storage tank, the throttle valves cause large exergy losses. To reduce throttling loss, a novel system is proposed by regulating the discharging pressure with an inverter-driven air compressor. Variable- and constant-output power operation modes of the novel system are proposed and studied from the aspects of exergy, economic and dynamic characteristic analysis. Furthermore, parametric analysis of the novel system is conducted from the perspective of the system discharge total output power, inverter-driven compressor efficiency and equipment purchase cost. The results indicate that for the novel system, the round-trip efficiency is improved by 1.8–2.7%, and the levelized cost of electricity decreases by 0.57–0.85 ¢/kWh. Hence, the proposed novel system is verified an effective way for adiabatic compressed air energy storage system optimization.

Thermodynamic analysis and optimization of a vapor injection organic Rankine cycle system for low-grade heat recovery

The organic Rankine cycle (ORC) system has been widely used in waste heat recovery and geothermal utilization, but the system efficiency is limited due to the large exergy loss in the evaporation process. To improve the performance of ORC systems, in this paper, a vapor injection organic Rankine cycle (VIORC) system using positive-displacement expanders was proposed. The thermodynamic model of the proposed system was developed in views of energy and exergy. The effects of system operation parameters on system performance were investigated, and the system was optimized under different waste heat temperatures. Furthermore, the optimized systems were compared with basic ORC (BORC) systems. Results showed that compared with the BORC system, the proposed system increased the net output power by 3-8% and the exergy efficiency by 0.8-3.2% under the heat source temperature of 90-150 °C. The exergy loss analysis further showed that the reduction of the exergy loss in the evaporation process was the main contribution to the efficiency improvement of the proposed system.

Thermodynamic analysis and optimization of auto-thermal supercritical water gasification polygeneration system of pig manure

A large amount of livestock manure is produced every year around the world, which requires harmless utilization to reduce environmental pollution and produce energy. As a promising and pollution-free technology in recent years, Supercritical water gasification (SCWG) can utilize pig manure with high moisture to produce hydrogen. In this paper, a novel process modeling an auto-thermal SCWG polygeneration system of pig manure was established with thermodynamic analysis, coupled with in-situ hydrogen separation and waste heat recovery method. Simultaneously, the environmental significance was analyzed through Life cycle assessment (LCA), and the GWP was 1.73 kgCO2-eq/kgH2 under optimal conditions with CCS. The results showed that the system with in-situ hydrogen separation would produce more H2 to improve energy efficiency. Adding a waste heat recovery unit could reduce the exergy loss of 89.14% of the cooling unit, which had the largest exergy loss in the system. In this study, there were 5081Nm3/h of H2 and 16377 kW of hot steam produced when the SCWG system was auto-thermal (620 ℃, 25 MPa, 650 t/d dry manure and 10 wt% reactor concentration), where the energy efficiency of the system could reach 79.85% that had a 3.6–35.64% increase to the previous SCWG systems. In addition, the optimal operating parameters of this polygeneration system were obtained, which the exergy efficiency could reach 54.25%. A lower complete gasification temperature and a larger in-situ H2 separation ratio were conducive to achieving higher H2 yield when the optimal ratio of preheated water to dry material was 8.

Thermodynamic analysis of a tri-generation system driven by biomass direct chemical looping combustion process

Chemical looping process (CLP) is a promising technology for in-situ CO2 capture without energy penalty. Direct CLP has more compact structure, favorable economic competitiveness, and larger reduction of exergy loss compared to syngas CLP. In this work, a novel biomass direct chemical looping combustion (CLC) driven tri-generation system for the production of cooling, heating, and power is proposed. The proposed system contains a direct CLC section as the prime mover, two gas turbines and an organic Rankine cycle for power generation, an absorption chiller for cooling production, and two heat exchangers to generate heat. First, a thorough thermodynamic analysis is implemented to assess the energy and exergy efficiencies of the proposed system under evaluated design conditions, as well as identify the exergy loss distribution. Second, Sensitivity analysis is conducted to investigate the effects of major operating parameters on the system performances. Third, the performances of the proposed system are compared to syngas CLC based tri-generation system. Thermodynamic analysis results show that the proposed system has high energy efficiency of 90.92% and exergy efficiency of 33.82%. The largest exergy loss takes place in the air reactor, accounting for 34.42% of total exergy loss, followed by fuel reactor and absorption chiller, which are 30.09% and 15.37%, respectively. Besides, the proposed system has better thermodynamic performances than syngas CLC driven tri-generation, whose energy and exergy efficiencies are 69% and 23.4%, respectively.

Multi-objective optimization of a clean, high-efficiency synthesis process of methyl-ethyl-ketone oxime from ammoximation

The ammoximation of ketones is an important chemical reaction, as oximes have a wide range of industrial applications. In this study, the process of preparing methyl ethyl ketone oxime by ammoximation of methyl ethyl ketone was studied. The modeling of the reaction unit was based on the kinetic data, and the reaction conditions were analyzed. Based on the total annual cost, an economic evaluation of the process was carried out, and a sequential iterative optimization algorithm integrating the reaction conditions was used to complete the process optimization. The minimum annual total cost was 2.41 × 107 USD/yr. The exergy of methyl ethyl ketone ammoximation to methyl ethyl ketone oxime process was analyzed, and the unit with the largest exergy loss was determined. The exergy loss rate was 65% for the minimum annual total cost. Considering exergy and annual total cost as the two optimization objectives, the process was comprehensively optimized by a multi-objective optimization algorithm. The annual total cost after multi-objective optimization was 2.55 × 107 USD/yr, which is 5.8% higher than minimum total annual cost, and the exergy loss rate was 64%, which is 1.54% lower than maximum exergy-loss rate. Compared with single-objective optimization, multi-objective optimization has a better comprehensive performance.

Exergy analysis of hydrogen-reduction based steel production with coal gasification-shaft furnace-electric furnace process

Carbon-free energy utilization in steel production is an effective way for China's iron and steel industry to achieve low carbon development. Thus, coal gasification-shaft furnace-electric furnace (CSE) technology, which use hydrogen-enriched gas for steel production, has recently become a sustainable topic of great concern. In the current study, the material flow analysis (MFA) and exergy assessment of the CSE process are conducted to investigate the material consumption and energy efficiency of this new steelmaking process. The exergy efficiency of the CSE process is calculated to be 50.11%, indicating a great potential for energy-saving. The results indicate that the coal gasification & gas purification that responsible for hydrogen-enriched gas production is the system with the largest exergy loss (account for 23.13% of the total exergy input), while the pelletizing system has the lowest efficiency (13.33%) due to heat loss. The key to further improve the thermal performance of this process lies in the heat recovery of the coal gasifier and pelletizing. It is also found that when the H2 content in reducing gas rise from 57.00% to 100.00%, the exergy efficiency of the shaft furnace is only increased by 1.58%, while the demand volume of reducing gas significantly increases from 1326.30 Nm3/t to 2201.50 Nm3/t. The environmental benefits of hydrogen reduction based steelmaking must be considered together with energy utilization and production cost. The present work should do helpful effort for the application and further improvement of the CSE process in China.

Thermodynamic modeling and analysis of a novel PEMFC-ORC combined power system

In this study, a novel proton exchange membrane fuel cell (PEMFC) system is proposed, which uses organic working fluid to cool the fuel cell stack directly and recovers the waste heat by combining with an Organic Rankine Cycle (ORC) system. A thermodynamic model of each component and subsystem is established for the combined PEMFC-ORC system. The influence of the PEMFC stack inlet temperature and current density, the ORC working fluid, superheat temperature and saturation pressure on the system performance is studied. The flow and distribution of energy and exergy in the whole PEMFC-ORC system are analyzed comprehensively. It is found that the system performance indicators reach the optimum when the stack inlet temperature is about 343.15 K. Lower current density improves the system efficiency, but reduces the system power density. R245fa shows the best performance among the five organic working fluids investigated for the designed ORC system. Higher superheat temperature and saturation pressure of the organic working fluid in the cycle improves the ORC efficiency. The PEMFC stack has the largest exergy loss in the system, and the cathode side heater and air compressor also contribute much to the large power and exergy loss. The optimization of these components should be the focus of system performance improvement.