Exergy Utilization Research Articles

The mode of interaction of the constituents of a microbial system determines the attainable exergy utilisation

The typical text book definition of exergy is the work that this system can produce if it is brought to thermal, mechanical and chemical equilibrium with its surroundings via reversible processes. In microbial systems, this ability depends on the interaction, e.g., collaboration, competition or antagonism, between the constituents of the system. Leavening of dough with mixed cultures of microorganisms is a typical example, where the microbial constituents of a system may present different modes of interaction depending on the temperature and their relative amounts. Data pertinent to leavening at four different temperatures and six different inoculum ratio of Saccharomyces cerevisiae and Lactobacillus plantarum were processed. The maximum carbon dioxide production (42.7 g CO2/kg dough), expansion work (0.334 kJ/kg dough) and dough volume increase (3,300 cm3/kg dough) were obtained at 35°C with the inoculum consisting of 80% S. cerevisiae and 20% L. plantarum. The system achieved the highest exergy utilisation (2000 kJ/kg dough) under these conditions, demonstrating that the microbiological and the exergy optima were not independent and achieved under the same conditions.

The renewability indicator and cumulative degree of perfection for gamboeng tea; part.1, exergy calculation of fresh tea leaf

Renewability Indicator (RI) and Cumulative Degree of Perfection (CDP) are employed as tools to assess sustainability of Gamboeng Tea. The assessment then compared with black tea process in Black Sea Region in Turkey from the previous study. Exergy analysis for Gamboeng tea was decribed in two part of articles. This first part was desribing the energy and exergy calculation for producing fresh tea leaf in Gamboeng tea plantation. The energy and exergy utilization for black sea fresh tea leaves was calculated to be 807.83 MJ/t of fresh leaf, 273.43MJ/t of fresh leaf, respectively. For the Gamboeng green tea, the energy and exergy utilization were 1496.38 MJ/ t of fresh leaf and 821.86 MJ/t of fresh leaf, respectively.The second part desribed cooperation of wood pellet with ambient-adapting controller uin tea factorywas a contribution from Gamboeng Tea for achieving Sustainable Development Goal which is affordable and clean energy and also an applicable climate action.

The mode of interaction of the constituents of a microbial system determines the attainable exergy utilisation

The mode of interaction of the constituents of a microbial system determines the attainable exergy utilisation

Effect on Vehicle Turbocharger Exhaust Gas Energy Utilization for the Performance of Centrifugal Compressors under Plateau Conditions

This paper is focused on the performance of centrifugal compressors for vehicle turbochargers operating at high altitude. The reasons for turbocharged diesel engine power loss increases and bad economy performance caused by exhaust gas energy utilization are investigated. The atmosphere’s impact on the turbocharger centrifugal compressor’s energy distribution characteristics under the plateau is discussed. The key parameters that affect compressor characteristics are concluded in a theoretical method. A simulation calculation model is established to accurately predict compressor performance at high altitude. By comparing the experimental results, the calculation results are validated. The details of the internal flow fields analysis, including critical parameters of a compressor operating at high altitude, are analyzed. The results show that with the increase of altitude from 0 m to 4500 m, the peak efficiency of the compressor is reduced by 2.4%, while the peak pressure ratio is increased by 7%. The main influence characters of the plateau environment on the turbocharger centrifugal compressor performance, such as blade loads, exergy utilization and entropy distribution are concluded. The key factors for compressor performance and compressor energy flow control design method operated at high altitude are obtained.

A case study of an ORC geothermal power demonstration system under partial load conditions in Huabei Oilfield, China

Liubei reservoir of Huabei oilfield, a typical mature oil and gas field in China, now has a water cut of 98% and the traditional “oil” field has become a “water” field. To further exploit the oilfield, a 500kW organic Rankine cycle using R245fa as the working fluid was designed and set up to use the coproduced fluid. Experiments under partial load conditions indicate that it is a good choice to use a plate heat exchanger as the preheater to be responsible for part load of the evaporator. In addition, dynamic test results show that the fluctuating of the geothermal water strongly affects the stability of the system’s performances, so attention should be paid on the stability of the geothermal water flow rate. Compared with the design generating capacity, the system did not get as much electricity as expected. Besides, exergy comparison analysis between design and partial load condition reveals that the intermediate heat exchanger (IHE) used to transfer heat from geothermal water to hot water becomes the main obstacle in view of exergy utilization ratio. Therefore, methods should be adopted to decrease the heat transfer temperature difference between the geothermal water and hot water, to reduce the exergy loss of the system.

Energy, exergy utilization and CO2 emission of strawberry production in greenhouse and open field

There is intensive energy use in crop production in agriculture. Efficient energy usage is a key factor for sustainable production in agricultural production. Optimization of the inputs used according to the efficiency of the production of the product is generally performed by the researchers through energy analysis. The optimization of srawberry production is evaluated by thermodynamic approach in this study. The study identified energy and exergy utilization, CO2 emissions, loss of exergy, and cumulative of degree perfection values of one tonne strawberry production in the open field and in the greenhouse. Energy utilization required for the strawberries production in the open field is higher than the greenhouse. The cumulative degree of perfection values of one tonne strawberry production in open field and greenhouse found 0.29 and 0.18, respectively. Along with that, the exergy loss values of one tonne strawberry production in open field and greenhouse found 6163 MJ and 11598 MJ, respectively.

Exergy and economic analyses of indirect coal-to-liquid technology coupling carbon capture and storage

Coal-to-liquids (CTL) technology has been developed steadily for producing gasoline and diesel fuels as the demand for energy security issue and liquid fuels in China outpaces production capacities. In this light, given the importance of CO2 emissions in climate change, carbon dioxide capture and storage (CCS) is considered as an integral part of CTL processes. In this study, CTL coupling with CCS technology (CTL-CCS) were simulated using the Aspen Plus software. Based on it, this study conducted exergy and economic analyses to the CTL-CCS system for five different coal types, including anthracite, meager, lean, coking and gas. Results show that the exergy utilization ratios ranged from 40.3% to 43.7%, revealing only a limited effect of the choice of coal type; although anthracite, meager, and gas coal were marginally better. Results also indicate the largest sources of exergy loss to be firstly from gas generation and secondly from the combined process of synthesis and separation. The economic analysis compared the cost, net present value, internal rate of return, and payback period. The cost of liquid fuel produced by CTL-CCS system was in the range from 4117 to 5627 yuan RMB/t, indicating economic feasibility. The system using lean coal revealed the best economic performance, while those using coking coal and gas coal were the second best performers. This research suggests that gas coal can achieve relatively reasonable values for both the exergy utilization ratio and cost in comparison to other coal types processed through a coupled CTL-CCS system.

Thermodynamics analysis for a new approach to agricultural practices: Case of potato production

Nowadays, studies are focused on the effective use of energy resources in sustainable agricultural applications. These studies include the use of less energy resources and less environmental pollution in agricultural applications. However, in order to optimize the use of energy resources in sustainable agriculture and to provide less environmental pollution, a thermodynamic analysis of crop production is needed as a more comprehensive analysis. In this study, thermodynamics analysis was performed as a new approach model according to the inputs of potato production. Cumulative energy consumption, cumulative exergy consumption, cumulative carbon monoxide emissions and cumulative degree of perfection occurring in potato production process were determined and interpreted within the scope of thermodynamics analysis. The total energy and exergy utilization and total CO2 emission for production of one ton of potatoes were found as 2206 MJ, 4832.5 MJ and 67.3 kg, respectively. Along with that the cumulative degree of perfection in potato production was found to be 1.09. To increase the cumulative degree of perfection in potato production, the use of manure must be reduced. Reducing manure use will increase the cumulative degree of perfection of potato production. In addition, use of manure must be reduced to reduce cumulative carbon monoxide emissions occurring in potato production.

Design and optimization of a novel cryogenic Rankine power generation system employing binary and ternary mixtures as working fluids based on the cold exergy utilization of liquefied natural gas (LNG)

A fundamental double-stage Rankine cycle system using the single-component working fluid in each stage for liquefied natural gas (LNG) cold exergy recovery is used as a base case in the present paper. An advanced scheme of three-stage Rankine cycle system with the cooling output part is then proposed and designed. A series of cases are simulated within the fundamental and the advanced system schemes by employing the single-component working fluid and binary or ternary mixture working fluids. To settle the optimization problem of the poly-stage system with the multi-component working fluids, the priority-oriented composition optimization is performed based on the Genetic Algorithm in the advanced three-stage system. The thermal efficiencies, the exergy efficiencies and the exergy analysis are conducted in all the cases. As a result, the performances of the thermal and exergy efficiencies rise from 3.5% and 7.16% in the initial case to 17.33% and 25.7% in the fully optimized case respectively. The heat transfer analysis and the parameter study of the pump outlet pressure of the working fluids in the advanced three-stage Rankine cycle system are presented. Furthermore, the economic analysis is conducted as well to evaluate the novel cryogenic Rankine power system for future engineering design.

Exergy Analysis of a Heat Exchange Substation based on Cascading Heat Supply

When radiator and floor radiant heating users coexist in the same heat exchange substation, simply parallel connection of the user systems or the heat exchangers cause high return water temperature. Since the return water temperature of radiator heating system is generally about equal to the supply water temperature of floor radiant heating system, a cascading heat supply connection is proposed to apply in heat exchange substation. The cascading heat supply connection considers eleven conditions to meet the combination of flow rate and water temperature from each user. Using exergy analysis method, each condition is analyzed. The results of case study show that the return water temperature of secondary network in the cascading connection can be reduced by 2-11℃; the flow rate of secondary network decreases by 7%-30%; and the exergy utilization rate is higher than traditional connection. According to the analysis of influencing factors, reference temperature and primary supply temperature correlate negatively with exergy utilization rate, while flow rate ratio and secondary supply temperature have positive correlation. During heating period, the cascading heat supply connection performs better exergy utilization as the rise of outdoor temperature.

Energy and exergy utilization of some agricultural crops in Turkey

Energy and exergy analysis gives valuable information to policy maker in order to make the right decision with regard to agricultural policies. In this present study, an investigation was carried out to reveal the energy and exergy consumption of some agricultural crops cultivated in Turkey for the year of 2014. Wheat, corn, cotton, sunflower, potato, and sugar beet are the massively harvested crops in Turkey. Therefore, energy and exergy analysis of these crops were evaluated. The analysis was based on the thermodynamics concept and covers the direct energy usage (i. e. electricity for pumping and diesel fuel for farm machinery) in the agricultural activity. Three different irrigation methods namely, flooding, sprinkler, and drip irrigation were considered. According to the results of the present study, wheat is the most energy and exergy consuming crop and potato is the least energy and exergy consuming crop. In addition to this flooding irrigation method requires the least energy and exergy values. On the other hand, sprinkler irrigation method requires the most energy and exergy values.

Thermodynamic analysis of a novel power plant with LNG (liquefied natural gas) cold exergy exploitation and CO2 capture

The LNG (liquefied natural gas) regasification process is a source of cold exergy that is suitable to be recovered to improve the efficiency of thermal power plants. In this paper, an innovative power plant with LNG (liquefied natural gas) exergy utilisation and the capture of CO2 proceeding from the flue gases is presented. It is characterised by the recovery of LNG cold exergy in a closed Brayton cycle and through direct expansion in an expander coupled to an electrical generator. Moreover, this novel power plant configuration allows CO2 capture, through an oxy-fuel combustion system and a Rankine cycle that operates with the flue gases themselves and in quasi-critical conditions. The greatest advantage of this plant is that all the recoverable LNG exergy is used to increase the efficiency of the CBC (closed Brayton cycle) and in direct expansion whereas, in other power cycles found in literature that associate LNG regasification and CO2 capture, part of the LNG exergy is used for condensing flue gas CO2 for its subsequent capture. As a result, a high efficiency power plant is achieved, exceeding 65%, with almost zero greenhouse gas emissions.

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.

Exergy analysis of network temperature levels in Swedish and Danish district heating systems

Exergy concept is applied on district heating systems with different network temperature levels in their distribution networks. These district heating systems use a combination of renewables and heat recovery from other primary processes. The aim is to show simplicity and value of using exergy concept when comparing current and future temperature levels. Both the traditional exergy factor and the novel exergy utilisation rate are used in these analyses. Exergy utilisation rate expresses the ratio between the exergy delivered to customer heating systems and the exergy content in heat supply input to the distribution network. The analyses are performed on four different generations of district heating technologies, two national groups of district heating systems in Denmark and Sweden for revealing variations among systems, and two municipal systems for revealing variations within systems. The main conclusions are simplifications can be introduced in order to analyse the network temperature levels, current exergy factors reveal that current temperature levels can be reduced, and that almost two thirds of the exergy content in heat supply input are lost in the heat distribution chain. These conclusion will be vital input in developing the future fourth generation of district heating systems using both renewables and heat recovery.

Analysis of an optimal resorption cogeneration using mass and heat recovery processes

This paper presents an optimised resorption cogeneration using mass and heat recovery to improve the performance of a novel resorption cogeneration fist proposed by Wang et al. This system combines ammonia-resorption technology and expansion machine into one loop, which is able to generate refrigeration and electricity from low-grade heat sources such as solar energy and industrial waste heat. Two sets of resorption cycle are designed to overcome the intermittent performance of the chemisorption and produce continuous/simultaneous refrigeration and electricity. In this paper, twelve resorption working pairs of salt complex candidates are analysed by the first law analysis using Engineering Equation Solver (EES). The optimal resorption working pairs from the twelve candidates under the driven temperature from 100°C to 300°C are identified. By applying heat/mass recovery, the coefficient of performance (COP) improvement is increased by 38% when the high temperature salt (HTS) is NiCl2 and by 35% when the HTS is MnCl2. On the other hand, the energy efficiency of electricity has also been improved from 8% to 12% with the help of heat/mass recovery. The second law analysis has also been applied to investigate the exergy utilisation and identify the key components/processes. The highest second law efficiency is achieved as high as 41% by the resorption working pair BaCl2–MnCl2 under the heat source temperature at 110°C.

Energy Analysis and Exergy Utilization in the Residential Sector of Cameroon

In this paper, we present an analysis of energy and exergy utilization in the residential sector of Cameroon by considering the sectoral energy and exergy flows for the years of 2001-2010. Exergy analysis of Cameroon residential sector utilisation indicates a less efficient picture than that obtained by the energy analysis. Cooking stands out as the most inefficient end use in the Cameroon’s residential sector. In 2010, the energy and exergy efficiency are determined and were respectively 58.74% and 22.63%. Energy and exergy flows diagrams for the overall efficiencies of Cameroon residential sector are illustrated and a comparison with the residential sector of other countries is also done. To carry out this study, a survey of 250 households was conducted and the sharing of the end uses of energy was done and data were gathered.

An application of energy and exergy analysis at the transportation sector of Cameroon

This paper presents energy analysis and exergy utilisation in the transportation sector of Cameroon by considering the sectoral energy and exergy flows for the last decade. The transportation sector, in Cameroon, is a two-mode system, including roads, which cover almost all domestic passenger and freight transport, and air. The latter is mainly used for international flights. In 2010, the average estimated overall energy and exergy efficiencies were 22.15% and 20.78%, respectively. This simply indicates that there is a large potential for improvement and efficiency enhancement. A comparison of the overall energy and exergy efficiencies of Cameroon transportation sector with the transportation sector of other countries for the year 2001 is also presented based on the data available. This reveals that the Cameroon transportation sector is least effective.

Modelling the energy and exergy utilisation of the Mexican non-domestic sector: A study by climatic regions

This paper presents the development of a bottom-up stock model to perform a holistic energy study of the Mexican non-domestic sector. The current energy and exergy flows are shown based on a categorisation by climatic regions with the aim of understanding the impact of local characteristics on regional efficiencies. Due to the limited data currently available, the study is supported by the development of a detailed archetype-based stock model using EnergyPlus as a first law analysis tool combined with an existing exergy analysis method. Twenty-one reference models were created to estimate the electric and gas use in the sector. The results indicate that sectoral energy and exergy annual input are 95.37PJ and 94.28PJ, respectively. Regional exergy efficiencies were found to be 17.8%, 16.6% and 23.2% for the hot-dry, hot-humid and temperate climates, respectively. The study concludes that significant potential for improvements still exists, especially in the cases of space conditioning, lighting, refrigeration, and cooking where most exergy destructions occur. Additionally, this work highlights that the method described may be further used to study the impact of large-scale refurbishments and promote national regulations and standards for sustainable buildings that takes into consideration energy and exergy indicators.

Wichit Prakaypan, Anthony Paterson

The fiber cement composite production process consumes extremely high fuel especially boiler and autoclave leading to the release of a lot of waste energy. In this study, the concept of energy and exergy utilization is analyzed and illustrated in the form of the Sankey diagram. It was found that the energy and exergy efficiencies of the boiler were 72.04 and 69.98%, respectively. The exergy destruction of the boiler system is 30% or 3.89 MW. Which can also be represented in the Power Available Diagram (PAD). In the exergy analysis, there are 2 methods in reducing the energy loss of the boiler by increasing the steam outlet temperature or reducing the temperature of the exhaust gas of the boiler. For the autoclave system, the energy analysis showed the total energy input at 43.67 GJ/batch. The three main energy losses are; the exhaust steam (49.74% or 23.74 GJ/batch), condensate (16.42% or 7.83 GJ/batch) and autoclave shell heat loss (13.67% or 6.25 GJ/batch). For the exergy, the exergy destruction in the autoclave is at 87.14%. However, the PAD of the autoclave cannot present the relation of the exergy loss. The main causes of the exergy destruction are the three main energy losses; the exhaust steam (50.80%), condensate (16.47%) and autoclave shell loss (10.01%) respectively.

Exergy Based Performance Analysis of a Solid Adsorption Solar Refrigerator

The exergy based performance analysis of a solid adsorption solar refrigerator is presented. The analysis is based on an exergy balance applied to each component of the refrigeration machine, leading to a general exergy balance equation. The dead state temperature was chosen to coincide with the ambient temperature. Results reveal that maximum exergy destruction occurred in the collector/generator/adsorber during heat up and adsorbate desorption phases with a value of 3747.77 kJ. Values recorded in the condenser and evaporator were 10.51 and 20.11 kJ, respectively while the exergy efficiency was in the range of 0.0008 – 0.012. It was also found that the rate of exergy destruction reduced as soon as adsorbate generation commenced; indicating superior energy and exergy utilization during desorption phase. Thus use of adsorbent and adsorbate with the potential of very early commencement of desorption can significantly improve the exergetic efficiency of the system.