Utilization Exergy Efficiency Research Articles

Thermodynamic and thermoeconomic evaluation of integrated hybrid solar and geothermal power generation cycle

The present investigation examines geothermal and solar energy for electricity generation. The proposed cycle can generate electricity independently or jointly using geothermal and solar sources. Organic Rankine Cycles (ORCs) have been employed due to their positive effects, including improved efficiency, comprehensive performance and economic analysis, adaptability, and the benefits of using ORCs with refrigerants in the hybrid power generation system. The proposed system is designed to include two evaporators, each working at distinct temperature levels, with one running at a high temperature and the other at a low temperature. Consequently, the system is outfitted with a pair of turbines functioning at elevated and moderate pressures. The analysis of the performance of the suggested cycle was conducted considering both energy and exergy perspectives; this leads to the determination of the efficiency of the first and second laws of thermodynamics. As a result, the exergy loss amount was calculated, and the exergy utilization efficiency for each component was determined. To assess the financial implications of the end product, a comprehensive study including electricity and exergy economic factors was conducted. A sensitivity analysis for many different aspects of the design factors and a parametric study, such as the difference in temperature at the pinch point and the temperature of the evaporator and their effects on energy and exergy performance, as well as the cost, are done. Findings revealed that the high-pressure turbine is directly related to the highest second-law efficiency. In contrast, the low-pressure turbine had the highest value for the exergy economic component. The average cost of energy production, obtained by evaluating power generation through low-pressure and high-pressure turbines, was calculated as 27.23 S/Gj. The system presented in this article can expand and adapt to diverse case analyses and can be effectively applied under various climatic conditions.

Efficient cascade waste heat utilization using thermoacoustic engine with variable temperature heat sources

Waste heat recovery is vital for greenhouse gas emissions reduction and meeting increasing power demands. Thermoacoustic engines present a promising solution. However, existing research predominantly focuses on single heating temperatures, which restricts their efficiency in harnessing heat sources with variable temperatures. To overcome this limitation, this work proposed a novel concept of thermoacoustic engine containing multistage heat exchangers capable of cascade waste heat recovery by incorporating bypass orifices to address this issue. By organizing decreasing temperatures of heat source across heat exchangers with decreasingly lower temperatures, multiple heat-to-power energy conversions can be achieved. Theoretical analyses demonstrate that the total exergy utilization efficiency of single-stage (37.7 %), two-stage (47.6 %), and three-stage systems (51.2 %) significantly increases when increasing the stage number up to three. Further increasing the stage number results in less efficiency improvement (only a 1.3 % increase in a four-stage system). Simulation results show that the three-stage thermoacoustic engine can achieve an acoustic power of 2.7 kW and a total exergy utilization efficiency of 51.2 % for recovering 12 kW variable-temperature heat sources. Coupling the engine with a linear alternator increases electricity production by 12 % with higher waste heat utilization rate compared to traditional single-stage thermoacoustic generators. The experimental results further underscore the capability of the proposed thermoacoustic generator to effectively utilize heat sources with variable temperatures.

A multi-parameters evaluation on exergy for hydrogen metallurgy

The traditional iron and steel industry (ISI) began to implement technological innovations aimed at lowering carbon footprint and emissions, resulting in hydrogen metallurgy gradually becoming a new trend of green development in ISI. However, there is a lack of comprehensive and in-depth analysis of energy-exergy based on the second law of thermodynamics in the current research of hydrogen metallurgy. To address these issues, a numerical calculation model of hydrogen metallurgy based on material-energy-exergy is established. Two novel evaluation indexes are introduced to better evaluate the impact of various parameters on hydrogen metallurgy. It was found that the exergy intensity is mainly affected by the amount of reducing gas, and increasing the preheating temperature of the ore cannot always reduce the exergy intensity due to the influence of element conservation. And when the ore preheating temperature is higher than 623 K, the exergy utilization efficiency decreases. After calculation, the lowest exergy intensity is 1.23 × 107 kJ/t-DRI when the H2 content is 41.37% and the ore temperature is 773 K. Furthermore, a simple process is designed to recover a substantial volume of unreacted gas from the furnace top gas. Overall, this study can serve as a reference for actual hydrogen metallurgy production.

A novel design of absorber surface of solar chimney power plant (SCPP): Thermal assessment, exergy and regression analysis

Clean and emission-free renewable energy production has attracted more demand. In this context, solar energy, being the most promising renewable energy source with low emission, is utilized for power generation such as solar chimney power plants (SCPP). The present work proposes a modification of the absorber surface with multiple triangular wavy peaks (n) at different amplitudes (h) and analyzes the performance of SCPP of the Manzaranes plant (utilizing velocity, temperature, pressure, different efficiencies, power output, and exergy). For this, a three-dimensional study is conducted by using ANSYS Fluent, RNG k-ε turbulent modeling, discrete ordinates (DO), and solar ray-tracing model. The study reveals the modified wavy ground absorber performs better than the traditional flat ground absorber. An increase in wavy wall amplitude enhances the power generation of SCPP markedly. Maximum gain in power generation and efficiency is noted for a single triangular wavy wall with higher amplitudes (58.61 % and ∼82.5 kW enhanced power and 61.83 % augmented efficiency). The exergy utilization efficiency of the collector rises with wall undulations (n); however, the exergy output drops with amplitude (h). Furthermore, through regression analyses, mathematical correlations are developed for major performance parameters. This novel concept may help the research community to establish a plant either in the hilly area or on any surface wavy nature to supply generated power for the remote area.

Multi-criteria assessment of an environmentally-friendly scheme integrating solid oxide fuel cell hybrid power and renewable energy auxiliary supply

The current severe energy and environmental crisis seriously hinder sustainable development and carbon neutrality. To deal with the current situation, it is imperative to replace traditional fuels with sustainable energy and develop efficient conversion technologies. Therefore, this study develops an environmentally-friendly polygeneration system that combines solid oxide fuel cell power system, renewable energy system, and waste heat recovery system. The mathematical model of each subsystem is first established and validated with reference to the published literature. Subsequently, the power source potential investigation, subsystem performance analysis, multi-objective optimization, energy storage adjustment, and positive effects are carried out. Ultimately, the thermoeconomic, sustainability, and environmentally-friendly throughout the life cycle are thoroughly assessed. The numerical results demonstrate that the equivalent work, fuel exergy utilization efficiency, sustainability index, and carbon footprint reduction of the polygeneration system are 2671 kW, 70.8%, 3.49, and 2268 kg/h, respectively, and that the capex can be recovered within 3.99 years. Due to the synergistic effect of the storage system and renewable energy system, the cooling and heating are increased to 134 kW and 259 kW, respectively, thereby, effectively responding to dynamically changing demands. This configuration scheme offers considerable advantages in terms of thermoeconomic, sustainability, and environmentally-friendly, meets the carbon neutrality goals, and provides an important reference for the development of a new concept energy system with solid oxide fuel cell integrated renewable energy.

Thermodynamic Analysis in Bubbling Fluidized Bed Dryers With Spiral and Cone Angles

Abstract Effective thermodynamic analysis is quite necessary for proper system design performance and optimization of system processes. Energy is concerned with the quantitative evaluation of system processes. Nonetheless, exergy gives a qualitative analysis of the system processes. The present investigation deals with the study of exergy and energy analysis of the paddy drying processes in two tapered fluidized bed dryers having the tapered angle 5 deg and 10 deg, respectively, and one cylindrical bubbling fluidized bed dryer. The energy utilization (EU) and energy utilization ratio (EUR) for various operating parameters such as inlet air velocity, mass of paddy, temperature, a spiral, and cone angle are investigated. Similarly, the exergetic efficiency and the rate of exergy destruction are also studied for the same operating parameters. The EU and EUR are found to have an increasing order when the inlet air velocity, temperature, and mass of paddy increase. The trend of EU and EUR also increases with an addition of a spiral inside a dryer. The increasing cone angle of the dryer has a similar impact on EU and EUR as that of other operating parameters. Similarly, exergy utilization and exergetic efficiency also show an increment with the rise in inlet air velocity, mass of paddy, cone angle of dryer, and temperature. The incorporation of a spiral inside a dryer improves exergy utilization and exergetic efficiency. Hence, the conical dryer with a higher cone angle is found to be the best option for drying.

Organic Rankine cycle integrated with hydrate-based desalination for a sustainable energy–water nexus system

Clathrate hydrate-based desalination (HyDesal) is a promising desalination technology but it is energy intensive. Developing strategies to reduce the high energy consumption of HyDesal process is necessary for its industrial application. The need for refrigeration requirement for the operation of HyDesal can be offset by LNG cold exergy to reduce its energy consumption. However, the LNG cold exergy utilization efficiency is low due to the large temperature difference between LNG and seawater and hydrate former. In this work, we propose a sustainable process that integrates HyDesal and organic Rankine cycle by utilizing LNG cold exergy to generate fresh water and electricity simultaneously. This integrated process was optimized by adopting particle swarm optimization algorithm to achieve maximal power and fresh water generation. Further, an economic analysis was performed to compare the economic performance of the proposed system and the base case. The results showed that the proposed process could achieve zero specific energy consumption for desalination and generate extra power. The largest fresh water production and power generation of 165.3 tonne/h and 3480 kW were achieved by adopting cyclopentane as hydrate former and mixed working fluid in organic Rankine cycle based on 100 tonne/h of LNG flowrate. The lowest levelized cost of water of the proposed process was 1.946 $/m3, which was 21.05% lower than that of the base case. Thus, the proposed sustainable process can strengthen the energy–water nexus and reduce the greenhouse gas emission by utilizing LNG cold exergy.

Optimization of a novel cryogenic air separation process based on cold energy recovery of LNG with exergoeconomic analysis

Oxyfuel combustion is deemed as one of the most potential technology to reduce CO2 emission from power plant. Exploring the technology of low-cost high-purity oxygen is a key issue to the implement of oxyfuel combustion. Cryogenic air separation is routinely used in large-scale production of high-purity oxygen. However, the relatively high power consumption of traditional cryogenic air separation no longer satisfies the requirement for cost-effective high-purity oxygen generation in the industrial field. A novel three-column cryogenic air separation process integrated with liquefied natural gas (LNG) regasification is introduced and evaluated in this paper. Waste nitrogen full utilization, cascade heat transfer and multi-column air distillation strategies are employed. To confirm the rationality and validity of the process, pinch point, energetic, exergetic and exergoeconomic analyses are performed. The obtained results indicate that the specific power consumption of liquid oxygen and liquid nitrogen are 0.252 kWh·kg-1 and 0.258 kWh·kg-1 in the proposed integrated system. The overall exergy efficiency and the LNG cold exergy utilization efficiency reach 0.7165 and 0.5318, respectively. Furthermore, sensitivity analysis is employed to investigate the effects of the outlet temperature of sub-coolers and stage number of low pressure column on total power consumption and equipment investment of the proposed process.

Effect of coal powder mass‐energy conversion efficiency on oxygen coal ironmaking and parameter optimization

AbstractA new process of prereduction of rotary kiln‐oxygen coal combustion and melting ironmaking was developed. The core is to realize the conversion of mass and energy of pulverized coal through high‐density injection of pulverized coal and high‐density combustion in the molten pool to provide the required energy for the ironmaking process. By calculating the combined energy values of working conditions under different metallization rates (η), gas oxidation degrees (α) and blast oxygen content (μ), the pulverized coal consumption, exergy income, exergy expenditure, four gas exergy values, and process of the process system under different working conditions were analyzed. Exergy using efficiency, quantitatively evaluated the interaction between the mass‐energy conversion efficiency of coal powder and process parameters and used orthogonal analysis to determine the combination of working conditions with the highest energy utilization rate. The results show that increasing the metallization rate, gas oxidation degree, and blasting oxygen content will change the exergy value, and the exergy utilization efficiency will increase with the increase of metallization rate, gas oxidation degree, and blast oxygen content, but the various parts exergy the value does not reach the optimum with the increase of the process operating parameters. After comparing and analyzing the overall working conditions, it can be known that when the charge metallization rate is 70%, the melting furnace gas oxidation degree is 12% and the blast oxygen content is 98%, the rotary kiln‐oxygen coal combustion melting furnace has the best operating conditions and the highest energy utilization efficiency. A mathematical relationship model including metallization rate, gas oxidation degree, blast oxygen content, and process exergy utilization efficiency was established: y = η × 0.1908+α × 0.467227383+μ × 0.137069+0.522508.

Multi-criteria investigation of a pumped thermal electricity storage (PTES) system with thermal integration and sensible heat storage

In the present paper a multicriteria analysis of a Rankine Pumped Thermal Electricity Storage (PTES) system with low-grade thermal energy integration is performed. The system is composed by an ORC for the discharging phase and a high-temperature heat pump for the charging phase. As previously demonstrated, the low-grade thermal energy can be provided at the heat pump evaporator to boost the PTES performances. As it regards the multi-criteria analysis, a tradeoff is required when electric-to-electric energy ratio ηrt, total exergy exploitation efficiency ψut and energy density ρen, are maximized concurrently. By means of multi-objective optimization, theoretical performances of the system are derived in two different layouts, which are differentiated by the presence, or not, of internal regeneration in charge and discharge subsystems. Results showed that regeneration can be very effective, as it relaxes the tradeoff between the objectives, thus yielding better global performances. Pareto fronts are built and explored to characterize the PTES system. Configurations of interest are proposed, and PTES performances are compared with other storage technologies. Theoretical results showed that, by exploiting thermal energy at temperature lower than 80 °C, ηrt≈0.55 and ρen≈15 kWh/m3 can be concurrently achieved. This can be done at the cost of an inefficient exploitation of the thermal source, as ψut≈0.05. If higher total exergy utilization efficiency is required, storage density can still be maintained high, but ηrt must drop down to 0.4.

A study of the optimal control approach for a Kalina cycle system using a radial-inflow turbine with variable nozzles at off-design conditions

To maximize the exergy utilization efficiency of a Kalina cycle system with an ammonia-water radial turbine at off-design conditions, this study proposes a novel control approach named optimal control approach. An off-design model for ammonia-water radial-inflow turbine using variable nozzles is constructed. The optimal control approach is realized by changing the outlet angle of the radial-inflow turbine nozzle and the turbine inlet pressure. Design parameters of heat source (waste hot water) are 130 °C and 10 kg/s. To find out the performance advantage for the novel control approach, it is compared with two traditional control approaches. The results show that the proposed novel control approach presents the highest exergy utilization efficiency and net power at off-design conditions. The net power ratio of the optimal control approach to the traditional sliding pressure control approach reaches 111.22% as the heat source mass flow rate declines to 5 kg/s. Compared with the traditional approach for constant pressure control (changing turbine nozzle outlet angle), the optimal control approach has a potential to produce 3.11% more net power. The exergy utilization efficiency is generally declined with the elevated heat source mass flow rate at the approach for optimal control, while the system thermal efficiency is slowly increased.

Steady state modeling on energy and exergy analysis of a pulverized coal fired thermal power plant

AbstractSteady state concept has relevance in many fields, particularly in economics, engineering and thermodynamics. In a steady state system, the recent observed behavior will continue to be so in future. Energy and exergy analysis (first and second law of thermodynamic) in steady state condition of a thermal power plant provides in‐depth information to find out areas for potential improvement in efficiency. This study deals with the performance analysis of a pulverized coal fired power plant using energy and exergy analysis in steady state condition. The overall plant performance is assessed by undertaking detailed modeling and simulating thermal cycle of the plant scheme. Off design energy and exergy utilization efficiencies and thermodynamic properties are assessed from the model simulation based on actual operating data collected from the plant Distributed Control System (DCS) at operating load of 460 MW on 15‐min average for a period of 8 h. The analysis revealed that the combustion chamber and boiler are the major source of exergy destruction with 40.29% and 53.20% respectively. Whereas gross energy and exergy efficiency of overall plant are calculated as 34.33% and 31.47% at 460 MW gross generation as compared to the design rating of 37.77% and 34.53% respectively at 500 MW. This paper deals with methodology and assessment of exergy destruction in the plant and how to reduce it. Simultaneously a comparison has been made of energy losses vis‐a‐vis exergy destruction of various plant components, which brings out advantages of using exergy method over energy method calculation. Copyright © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Exergoeconomic analysis of energy utilization of drying process in a ceramic production

Thermo economic cost analysis of a ceramic plant, with a yearly production capacity of 24 million m2, was performed based on the actual operational data. The ceramic drying system was analyzed at the spray dryer, the vertical dryer and the furnace stages. The performances of these three processes and the effects of the process conditions on the process performance were evaluated using energetic, exergetic, and exergoeconomic analysis methods. The performance assessment was performed through energy and exergy efficiencies, the improvement potential rate, the total cost, and the exergoeconomic factor terms. The ratio of the thermodynamic loss rate to the capital cost values was obtained in the range of 53.38–135.83 MW/$. In this process, there is a great potential towards increasing the energy and exergy utilization efficiencies.

Energy and exergy utilization efficiencies and emission performance of Canadian transportation sector, 1990–2035

Transportation sector of Canada is the second largest energy consuming sector which accounts for 30% of the total energy consumption of the country in 2009. The purpose of this work was to analyze the energy, exergy, and emission performance for four different modes of transport (road, air, rail, and marine) from the year 1990–2035. For historical period, the estimated overall energy efficiency ranges from 22.41% (1991) to 22.55% (2006) with a mean of 22.48 ± 0.07% and the overall exergy efficiency ranges from 21.61% (2001) to 21.87 (2006) with a mean of 21.74 ± 0.13%. Energy and exergy efficiencies may reach 20.95% and 20.97% in the year 2035 respectively based on the forecasted data. In comparison with other countries, we found that in the year 2000 the overall energy and exergy efficiencies for Canadian transportation sector were higher than Jordan, China, Norway, and Saudi Arabia but lower than Turkey and Malaysia. Between the year 1990–2009, the highest amount of emission produced in each subsector was: road CO2 (80%), NOx (72%), and CO (carbon monoxide) (96%); air SO2 (86%); rail NOx (6%) and marine NOx (7%). The road subsector produced the highest amount of emissions.

Study on Heating System of Solar Energy Combined with Bioenergy

In order to employ the solar energy and bioenergy efficiently and economically, a new model of heating system is established for theoretically studying the exergy and energy utilization of solar energy and bioenergy on the basis of the Integrated Cascaded Utilization of Chemical and Physical Energy Principle. The results indicate, the low temperature floor radiation heating way is better than the traditional radiator heating way, and compared with traditional direct burning biomass heating, the energy and exergy utilization efficiency of the new system are more than 89% and 20% respectively, and the capital recovery period is less than 3 years.

Analysis of Exergy Utilization Efficiency of Combined Cooling Heating & Power on Gas Engine-Driven Heat Pump System

The exergy utilization efficiency is the better reasonable to measure quantity and quality of thermal system then energy utilization efficiency .This text analyzed the exergy utilization efficiency of gas engine-driven heat pump(GEHP) at different combined supply energy modes. . Simulation computes gives that the heat recover plays the important action for increases exergy utilization efficiency of GHP system, especially at combined heating and electricity operational models, and the rules of heat recollection ratio and heat recollection temperature to exergy utilization efficiency of CHCP system were provided.

Energy and exergy utilization efficiencies in the Japanese residential/commercial sectors

Unlike the manufacturing sector, the residential/commercial sectors of Japan struggle to meet their environmental requirements. For instance, their CO 2 emission levels have increased tremendously since 1990. This research estimates energy and ‘exergy (available energy)’ efficiencies in Japan's residential/commercial sectors during the period 1990–2006. Since an exergy analysis reveals ‘available energy losses’, it is an effective tool to achieve sustainable societies. The primary objective of this paper is to examine the potential for advancing the ‘true’ energy efficiency in Japan's residential/commercial sectors—by observing energy and exergy efficiency disparities. The results show large differences between the overall energy and exergy efficiencies in the residential (60.12%, 6.33%)/commercial sectors (51.78%, 5.74%) in 2006. This implies great potential for energy savings in both sectors. Furthermore, this research suggests that the residential sector may face more difficulties than the commercial sector, although the latter appears to be less energy-efficient, according to recent statistics. This is because the disparity between energy and exergy efficiencies has expanded in the residential sector since 2000. This study illustrates the importance of exergy analyses in promoting sustainable energy policies and new adaptation strategies.

Exergoeconomic aspects of sectoral energy utilization for Turkish industrial sector and their impact on energy policies

This study deals with this thermo-economic analysis of energy utilization in the industrial sector (IS) towards establishing energy policies. The relations between capital costs and thermodynamic losses for subsectors in the IS are investigated. In the analysis, Turkey is taken as an application country based on its actual data over the period from 1990 to 2003. Energy and exergy analyses are performed for eight industrial modes, namely iron–steel, chemical–petrochemical, petrochemical–feedstock, cement, fertilizer, sugar, non-metal industry, other industry. The energy and exergy utilization efficiency values for the entire Turkish IS are obtained to range from 63.45% to 70.11%, and from 29.72% to 33.23%, respectively. The ratio of thermodynamic loss rate-to-capital cost values is also calculated to vary from 0.76 to 1.01.

A novel Brayton cycle with the integration of liquid hydrogen cryogenic exergy utilization

Stored or transported liquid hydrogen for use in power generation needs to be vaporized before combustion. Much energy was invested in the H 2 liquefaction process, and recovery of as much of this energy as possible in the re-evaporation process will contribute to both the overall energy budget of the hydrogen use process, and to environmental impact reduction. A new gas turbine cycle is proposed with liquefied hydrogen (LH 2) cryogenic exergy utilization. It is a semi-closed recuperative gas turbine cycle with nitrogen as the working fluid. By integration with the liquid H 2 evaporation process, the inlet temperature of the compressor is kept very low, and thus the required compression work could be reduced significantly. Internally fired combustion is employed to allow a very high turbine inlet temperature, and a higher average heat input temperature is achieved also by internal heat recuperation. As a result, the cycle has very attractive thermal performance with a predicted energy efficiency over 73%. The choice of nitrogen as the working fluid is to allow the use of air as the oxidant in the combustor. The oxygen in the air combines with the fuel H 2 to form water, which is easily separated from the N 2 by condensation, leaving the N 2 as the working fluid. The quantity of this working fluid in the system is maintained constant by continuously evacuating from the system the same amount that is introduced with the air. The cycle is environmentally friendly because no CO 2 and other pollutant are emitted. An exergy analysis is conducted to identify the exergy changes in the components and the potential for further system improvement. The biggest exergy loss is found occurring in the LH 2 evaporator due to the relatively high heat transfer temperature difference, dictated by the fixed temperatures of the LH 2 and of the ambient combustion air, which are far apart. The exergy efficiency is 45%. The system has a back-work ratio only 1 4 of that in a Brayton cycle with ambient as the heat sink, and thus can produce 72.7% more work, with the LH 2 cryogenic exergy utilization efficiency of 50%.

Assessment of the Turkish utility sector through energy and exergy analyses

The present study deals with evaluating the utility sector in terms of energetic and exergetic aspects. In this regard, energy and exergy utilization efficiencies in the Turkish utility sector over a wide range of period from 1990 to 2004 are assessed in this study. Energy and exergy analyses are performed for eight power plant modes, while they are based on the actual data over the period studied. Sectoral energy and exergy analyses are conducted to study the variations of energy and exergy efficiencies for each power plants throughout the years, and overall energy and exergy efficiencies are compared for these power plants. The energy utilization efficiencies for the overall Turkish utility sector range from 32.64% to 45.69%, while the exergy utilization efficiencies vary from 32.20% to 46.81% in the analyzed years. Exergetic improvement potential for this sector are also determined to be 332 PJ in 2004. It may be concluded that the methodology used in this study is practical and useful for analyzing sectoral and subsectoral energy and exergy utilization to determine how efficient energy and exergy are used in the sector studied. It is also expected that the results of this study will be helpful in developing highly applicable and productive planning for energy policies.