Results Of Exergy Analysis Research Articles

A high performance solar-assisted ejector expansion refrigeration cycle for residential air conditioning

Introducing a solar collector between the compressor and condenser of an ejector expansion refrigeration cycle (EErc) can improve the performance of the system by further superheating the refrigerant. Hence, this paper proposes a new configuration of a vapor compression refrigeration system, solar compression-ejector expansion refrigeration cycle (SCEErc) with energy saving in the compressor via an ejector and an evacuated tube solar collector. The performance improvement of the proposed system under a wide range of operating conditions such as condenser and evaporator temperatures, superheating and subcooling degrees, nozzle and diffuser efficiencies, and solar radiation intensities has been evaluated and compared with EErc under the same operational conditions and for four different refrigerants. The results indicate that the coefficient of performance (COP) of the SCEErc increased by 26.53 % compared to the EErc for the solar radiation energy of 0.2 kW. Moreover, exergy analysis results indicate a 59 % increase in the exergy destruction of the condenser in the SCEErc compared to the EErc. This is due to the increase in heat rejected from the condenser to the environment, which can be beneficial if the condenser cooling air outlet is utilized for applications like heat recovery technologies. The R152a, boasting a COP of 3.963, presents itself as a more favorable alternative to R134a.

Analysis of Exergy Efficiency and Influencing Factors of Tube Heating Furnace in Oilfield Enterprises

Abstract In the energy consumption of surface engineering systems in oilfield enterprises, heating furnaces account for a significant proportion. Therefore, it is necessary to analyze and study their operational performance. This paper conducts an exergy analysis on tubular heating furnaces from the perspective of energy quality. Firstly, an exergy balance model and exergy analysis evaluation criteria are established for the energy system of the heating furnace. Then, the internal and external exergy losses in the heating furnace's energy system are comprehensively considered to identify weak points in the energy system and reflect the utilization of energy quality. The exergy analysis results show that the highest proportion of exergy losses in the heating furnace system is attributed to the heat transfer process. The excess air coefficient, exhaust gas temperature, and external surface temperature of the furnace are inversely proportional to exergy efficiency. Based on the static exergy analysis results, measures to improve the exergy efficiency of the heating furnace are proposed: controlling the excess air coefficient within a reasonable range, reducing the exhaust gas temperature, and lowering the external surface temperature of the furnace. These measures can effectively enhance the energy utilization level of the tubular heating furnace and provide reference and assistance in meeting emission reduction requirements.

Exergy and pinch assessment of an innovative liquid air energy storage configuration based on wind renewable energy with net-zero carbon emissions

Given the rising global energy demands and the fluctuating nature of load demand, advancing various energy storage systems to enhance their efficiency is essential. Moreover, the increase in greenhouse gas emissions from various industries has prompted governments to implement carbon dioxide (CO2) capture systems and invest in renewable energy sources. In this research, a cryogenic energy storage configuration is developed according to the air liquefaction process, liquefied natural gas (LNG) regasification operation, CO2 capture cycle, and organic Rankine plant. During off-peak times, the air entering the energy storage system is compressed and liquefied using wind energy and the cold energy from LNG vaporization, producing 83.12 kg/s of liquid air. During on-peak times, the liquid air and LNG after recovering the cold energy enter the power generation cycle, generating 119 MW of electrical power. This power generation cycle includes a combustion chamber, gas turbine power plant, and organic Rankine cycles. Flue gases from the power generation cycles enter the amine-based CO2 capture and then the output CO2 is stored in liquid form. The storage and round-trip efficiencies of the present energy storage configuration are 67.97 % and 62.50 %, respectively. The results of exergy analysis show that the exergy efficiency of the whole system, off-peak, and on-peak sections are calculated as 64.88 %, 82.40 %, and 74.03 %, respectively. The pinch method for multi-stream exchangers (HX6, HX7, and HX8) is accomplished and the exchanger network related to each one is determined. Three-dimensional sensitivity analysis indicates that storage and round-trip efficiencies increase up to 80.45 % and 66.20 %, respectively when the power generation section pressure increases up to 110 bar and compressed air pressure decreases to 135 bar.

Design and performance estimate of a novel linear fresnel reflector solar-gas combined system for producing electricity and hydrogen

Multi-energy complementary technology is meaningful for promoting the development of solar energy utilization, and the main novelty of this paper is the proposal of a novel linear Fresnel reflector solar-gas combined (LSGC) system which utilizes the organic Rankine cycle driven proton exchange membrane hydrogen production (PEM-HP) subsystem as well as is designed for generating electricity and hydrogen. By using the Ebsilon, the operation performance and exergy analyses of the LSGC system are launched. The results show that the output power and electric efficiency of the LSGC system are 424.8 MW and 45.4%. The solar field contributes a power of 34 MW. The hydrogen production rate of the LSGC system is 182.88 kg/day. The solar field, GTCC and PEM-HP section can reach the coordinated operation effectively during a long term, revealing the technical feasibility of the LSGC system. The exergy analysis results indicate that the solar field has the second maximum exergy destruction and the smallest exergy efficiency, and the combustion chamber has the maximum exergy destruction. The economic analysis shows that the levelized costs of electricity and hydrogen of the LSGC system are 0.045 $/kWh and 5.67 $/kg. The environment effect evaluation shows that compared with the coal power, the LSGC system can reduce the annual emissions of CO2, NOx, SO2 and dust effectively. Those reveal relatively acceptable economic feasibility and environment protection effect of the LSGC system.

4E assessment of ejector-enhanced R290 heat pump cycle with a sub-cooler for cold region applications

Currently, the worldwide implementation of the Montreal Protocol has accelerated the development of low GWP refrigerants. R290 as an alternative refrigerant with low GWP has great advantages over R134a for heat pump applications. However, the use of expansion valve throttling in the heat pump cycle has a large irreversible loss. Therefore, an ejector-enhanced sub-cooler vapor injection heat pump cycle (ESVIC) with R290 for water heating is proposed in this paper to improve the energy efficiency by applying ejector. The thermodynamic models are established based on the 4E (energy, exergy, economic and environmental) analysis to compare its performance with the basic ejector-enhanced heat pump cycle (BEEC) and the sub-cooler vapor injection heat pump cycle (SVIC). The energy analysis results show that compared with the BEEC and SVIC, the volumetric heating capacity of the ESVIC is improved by 42.0 % and 21.2 %, and the heating coefficient of performance (COPh) of the ESVIC is improved by 27.6 % and 5.3 %, respectively. The exergy analysis results indicate that in BEEC, SVIC and ESVIC the exergy destruction of the expansion valves is 0.3 %, 13.5 % and 0.8 %, respectively. It is indicated that the adoption of ejector can significantly decrease the exergy destruction of expansion valves. Moreover, the environmental analysis results reveal that the carbon emissions of ESVIC is 21.5 % and 5.0 % lower than those of BEEC and SVIC, respectively. Besides, for the ESVIC system, the carbon emissions of the life cycle climate performance when using R290 are 9.9 % lower than that of using R134a, indicating that the R290 is a potential substitute for R134a in heat pump applications. The economic analysis results demonstrate that the unit exergy production costs of ESVIC is 21.6 % and 5.1 % lower than BEEC and SVIC, respectively.

Extended exergy analysis of a novel integrated absorptional cooling system design without utilization of generator for economical and robust provision of higher cooling demands

The focus of this study is on designing a novel system for the provision of high-capacity cooling and heating loads (4000 kW) with the utilization of absorption technology to increase economic viability and COP value of existing cooling plants via lower-grade waste heat sources (70 °C-90 °C). To achieve this aim, in the novel system, an integration including the LiBr-water solution based absorptional heat transformer (AHT), and absorptional cooling cycle (ACC), and flat plate solar collector (FPSC) systems was proposed. In the integration, the utilization of the generator in the cooling cycle was avoided with the interaction of the high-temperature LiBr-water solution (120 °C-150 °C) from the AHT system and ACC system evaporator. In this way, both the additional cost of the boiler and heat source and the enhancement of economic viability and COP value were achieved. Energy, economic, traditional, and extended exergy, sustainability, and environmental analyses were implemented in this novel system. The COP value for the cooling system was determined to be 3.10 from energy analysis. This result forms a significant indicator for achieving of the main focus of the current study with the proposed novel system. The annual heating and cooling duty generations with this novel system were computed as 52.37 GWh and 52.40 GWh, respectively. In the context of economically comparing the proposed system to other plants with similar scale that already exist, the initial overall expenditure, yearly operational expenses, and the time it takes to recover the investment for the proposed system were set at $4.56 million, $3.12 million, and 1.75 years, respectively. It is worth noting, though, that these figures fall within the range of $6–8 million, $5–7 million, and 5–10 years, respectively, for the currently operational plants. This result indicated that the proposed system provides a robust alternative to the existing cooling-heating cogeneration systems in terms of main output generation and is more economically viable. Also, the novel system gained annually US$3.89 million in energy costs. The conventional exergy analysis results were summarized by forming an exergy flow and loss diagram, namely, the Grassmann diagram. In addition, in this current study, the novel extended exergy flow diagram indicating extended exergy content components, energy carriers of the proposed system, and exergy product rate streams was also proposed and drawn for the proposed system.

Energy, exergy and exergo-economic analysis of a novel HT-PEMFC based cogeneration system integrated with plasma gasification of food waste

Landfill and incineration of food waste would result in a significant waste of resources. Plasma gasification, as a novel solid waste treatment technology with cleaner product, is suitable for this perishable kitchen waste with high water and oil content. In present research, a food waste plasma gasification driven HT-PEMFC cogeneration system is proposed. Based on the established models, a comprehensive study is conducted from the perspective of energy, exergy and exergo-economy. Effects of key operational parameters on critical performance indicators are investigated. Results show that current density imposes an obvious effect on the cogeneration efficiency, this efficiency is obtained as 0.523–0.457 at low current density varying from 0.1 to 0.4 A/cm2. Exergy analysis results indicate that the plasma gasifier and the stack have the largest exergy destructions, accounting for 62.1 % and 32.2 % of the total, respectively. Gasification temperature has a great effect on the system exergy efficiency which is 0.603–0.384 when this temperature increases from 1000 K to 1300 K. Current density also has an obvious effect on the exergo-economic performance, the exergy cost per unit is obtained as 46.1–51.8 $/GJ when current density varies from 0.2 to 0.4 A/cm2. The optimization results are obtained as cogeneration efficiency of 0.4636, exergy efficiency of 0.6125 and exergy cost per unit of 24.58 $/GJ. This research provides a novel solution for substantial treatment of food waste, and guidelines for sustainable development of efficient and clean utilization technology of municipal solid waste.

Entransy based heat exchange irreversibility analysis for a hybrid absorption-compression heat pump cycle

Thermally-coupled hybrid absorption-compression heat pump cycle could achieve large temperature lift and high output temperature, which is promising for the decarbonization of industrial heat demand. However, the cycle also has many heat exchange processes, resulting in irreversible losses in different components and performance degradation. In this study, entransy dissipation is used for the heat exchange irreversibility analysis of different components in the cycle. Heat and mass transfer model and entransy dissipation model for combined heat and mass transfer components such as absorber and generator are proposed. By comparing with the exergy loss, it proved that the entransy dissipation calculation model is reasonable. In addition, the T-Q diagram obtained by entransy dissipation analysis visually illustrates the heat exchange processes in each heat exchange component, which shows that entransy dissipation analysis has the characteristics of focusing on heat exchange, process-oriented and visualization. Results of entransy dissipation analysis are then used to guide the heat exchange enhancement of different components, thus optimizing the performance of whole heat pump cycle. Reducing the heat exchange irreversibility in internal heat recovery part can obtain the maximize improvement on COP by 3.92 %. The effect of thermal coupling temperature on exergy based and entransy based parameters of the heat pump cycle is investigated. The entransy increment states the optimal coupling temperature as 73.9 °C, in agreement with the COP and exergy analysis results. Therefore, from entransy dissipation to entransy increment, entransy analysis is expected to be a powerful tool to guide from the heat transfer optimization to the thermodynamic system optimization.

Advanced exergy and exergoeconomic analysis of a multi-stage Rankine cycle system combined with hydrate energy storage recovering LNG cold energy

In recent years, liquified natural gas (LNG) cold energy utilization technology has been widely investigated due to the increasing global use of LNG. The LNG stored at −162 °C needs to be regasified. To efficiently recover the large amount of cold energy released during the regasification process of LNG with lower investment, a multi-stage Rankine cycle system combined with hydrate energy storage and seawater ice-making cycle was carried out, and the advanced exergy and exergoeconomic analysis was conducted in this paper. The Aspen HYSYS V11 was selected to establish the LNG cold energy recovery process. The result of exergy analysis shows that the exergy destruction rate and exergy efficiency of the total system are 1662.655 kW and 41.149 %, respectively. For conventional analysis results, the burner gives the highest exergy destruction and total cost rate, while considering the result of advanced exergy and exergoeconomic analysis, the condenser 2 gives the highest avoidable exergy destruction, and the turbine 1 gives the highest avoidable total cost rate. In addition, 26.49 % of exergy destruction, 31.6 % of exergy destruction cost rate and 6.59 % of investment cost rate are avoidable, which indicated the optimization potential of the proposed system.

Process design and improvement for hydrogen production based on thermodynamic analysis: Practical application to real-world on-site hydrogen refueling stations

An energy source transition is necessary to realize carbon neutrality, emphasizing the importance of a hydrogen economy. The transportation sector accounted for 27% of annual carbon emissions in 2019, highlighting the increasing importance of transitioning to hydrogen vehicles and establishing hydrogen refueling stations (HRSs). In particular, HRSs need to be prioritized for deploying hydrogen vehicles and developing hydrogen supply chains. Thus, research on HRS is important for achieving carbon neutrality in the transportation sector. In this study, we improved the efficiency and scaled up the capacity of an on-site HRS (based on steam methane reforming with a hydrogen production rate of 30 Nm3/h) in Seoul, Korea. This HRS was a prototype with low efficiency and capacity. Its efficiency was increased through thermodynamic analysis and heat exchanger network synthesis. Furthermore, the process was scaled up from 30 Nm3/h to 150 Nm3/h to meet future hydrogen demand. The results of exergy analysis indicated that the exergy destruction in the reforming reactor and heat exchanger accounted for 58.1% and 19.8%, respectively, of the total exergy destruction. Thus, the process was improved by modifying the heat exchanger network to reduce the exergy losses in these units. Consequently, the thermal and exergy efficiencies were increased from 75.7% to 78.6% and from 68.1% to 70.4%, respectively. The improved process was constructed and operated to demonstrate its performance. The operational and simulation data were similar, within the acceptable error ranges. This study provides guidelines for the design and installation of low-carbon on-site HRSs.

Thermodynamic performance comparison of SOFC-MGT-CCHP systems coupled with two different solar methane steam reforming processes

Multi-energy complementary distributed energy system integrated with renewable energy is at the forefront of energy sustainable development and is an important way to achieve energy conservation and emission reduction. A comparative analysis of solid oxide fuel cell (SOFC)-micro gas turbine (MGT)-combined cooling, heating and power (CCHP) systems coupled with two solar methane steam reforming processes is presented in terms of energy, exergy, environmental and economic performances in this paper. The first is to couple with the traditional solar methane steam reforming process. Then the produced hydrogen-rich syngas is directly sent into the SOFC anode to produce electricity. The second is to couple with the medium-temperature solar methane membrane separation and reforming process. The produced pure hydrogen enters the SOFC anode to generate electricity, and the remaining small amount of fuel gas enters the afterburner to increase the exhaust gas enthalpy. Both systems transfer the low-grade solar energy to high-grade hydrogen, and then orderly release energy in the systems. The research results show that the solar thermochemical efficiency, energy efficiency and exergy efficiency of the second system reach 52.20%, 77.97% and 57.29%, respectively, 19.05%, 7.51% and 3.63% higher than those of the first system, respectively. Exergy analysis results indicate that both the solar heat collection process and the SOFC electrochemical process have larger exergy destruction. The levelized cost of products of the first system is about 0.0735$/h that is lower than that of the second system. And these two new systems have less environmental impact, with specific CO2 emissions of 236.98 g/kWh and 249.89 g/kWh, respectively.

Techno-economic examination and optimization of a combined solar power and heating plant to achieve a clean energy conversion plant

Renewable energies are one of the best alternatives to fossil fuels, which have disadvantages such as exhaustibility and emission of environmental pollution. An alternative system consisting of a parabolic trough collector (PTC) and a photovoltaic thermal (PVT) is used to produce electric power and heating. By using the Kalina cycle and the organic Rankine cycle (ORC) coupled with the PVT unit, an attempt was made to recover as much as possible heat from the solar energy. Exergy and exergy-economic analyzes were performed on the proposed system, and appropriate criteria for evaluating the system were defined based on energy, exergy, and economic analyses. The exergy analysis results indicate that the highest exergy destruction rate in the ORC sub-system is associated with the PVT unit. The value of electrical cost for three studied cities, Doha, Tehran, and Ankara were calculated. Results present that the highest and lowest net output power were for Doha and Ankara and these cities also have the maximum and minimum electrical cost. In addition, using multi-objective optimization, the optimum states of introduced system in the Pareto diagram are presented and with the help of ideal point concept, the final optimum state is determined.

Energy and exergy assessments of supercritical water oxidation of wet organic wastes under hydrothermal flames with a Y-shape reactor for power generation

A novel Y-shape reactor combined the concepts of transpiring wall reactor (TWR) and hydrothermal flame was proposed for supercritical water oxidation (SCWO) of wet organic wastes. Hydrothermal flames can enhance feed degradation, and the Y-shaped structure enables the efficient gas–solid separation and allows extracting a part of uncooled supercritical fluids for power generation. The proposed reactor and corresponding system were simulated using Aspen Plus 8.2, and simulation results agree well with experimental flame temperatures and reaction products. Exergy analysis results indicate the reactor, heat exchanger 7, heat exchanger 1, and turbine contribute to the main destruction of the system, with exergy distribution coefficients of 18.65%, 17.75%, 11.95%, and 7.64%, respectively. The exergy destruction coefficient for the reactor has been greatly reduced compared with previous TWR-SCWO systems, indicating great improvement in exergy efficiency with the Y-shape reactor. The exergy efficiency can be increased from 24.83% to 40.50% when hot water output is replaced with steam production because of the great reduction in exergy destruction. Lower ratios of fuel flow to feed flow contribute to higher exergy efficiencies on the premise of the safety and economy of the system. The increases of separation efficiency and split coefficient are helpful for increasing system efficiency for more supercritical fluids can be converted into high-grade energy. The increase of feed concentration is beneficial for the increase of system economy even though at a relative low exergy efficiency.

Plasma gasification based monetization of poultry litter: System optimization and comprehensive 5E (Energy, Exergy, Emergy, Economic, and Environmental) analysis

Plasma gasification (PG) based tri-generation process for dimethyl ether (DME) and power generation has been developed to valorize the poultry litter with an objective of energy, exergy, emergy, economic, and environment (5E) sustainability. PG process has been optimized by the application of a radial basis function surrogate optimization algorithm. Comparative analysis of the base and the optimized process has been performed. The results reveal that the economic performance of the optimized process is better than base process with 6% additional DME generation. The energy efficiencies of the optimized process and the base process are 44% and 48%, respectively while there is no significant difference in the results of exergy analysis. Process thermal energy has been converted into electrical energy through steam turbine powered generator, and 1271 kW electricity can be produced through it. Emergy analysis indicates that the sustainability index of the process is 2.509, to some extent, which means that the process is sustainable. Finally, the economic analysis shows that the capital payback period of the optimized process (7.2 year at 70% process efficiency) is shorter while the base process is not feasible when the process efficiency is below 90%. Therefore, this PG tri-generation optimized process is a feasible solution for biomass waste valorization based on 5E analysis.

Exergy Analysis of Biomass-Based Ethyl Levulinate Fuel for Whole Life Cycle

Hydrolysis of agricultural residues into ester fuels is an important way to alleviate energy shortage and reduce greenhouse gas emissions, which is in accord with the major demand of sustainable energy development strategy. Based on the production and application of biomass-based ester fuel, this paper analyzed the growth, collection, pretreatment, hydrolysis and esterification of bagasse, transportation and distribution of fuel, and the vehicle use of fuel, make clear the exergy efficiency and distribution law of pollutant exergy consumption over the whole life cycle. The results are as follows: the overall exergy efficiency of the system for preparing ethyl levulinate (EL) by hydrolysis of bagasse is 64%. The exergy consumption proportion of CO2 is the largest (72%), the second is SO2 (7%) in the distribution of exergy consumption of different emissions in the whole life cycle. The exergy consumption of VOC, CO, NOx and PM10 in gas pollutants is less than 2%, while the exergy consumption of N2O, CH4 and HC is between 2% and 4%. The exergy consumption of industrial sewage accounted for the lowest of 1%, while the exergy consumption of agricultural sewage accounted for 5%. The exergy consumption of CO2 in the whole system is much higher than that of the sum of other pollutants. Based on the results of exergy analysis, the preparation of biomass-based EL can be optimized. It is suggested to improve the environmental index of the whole life cycle of the system, reduce the dependence on pesticides and fertilizers in the process of crop planting, reduce the electricity consumption in the process of ester fuel production as much as possible, and increase the proportion of clean power generation using renewable energy, so as to control the greenhouse gas emissions at the source.

New insight into contradictory distillation sequence heuristics: exergoeconomic and environmental analysis

This research focuses on possible sequences for the distillation of quaternary mixture to assess the performance of a system, where the general design heuristics are contradictory. In cases of contradictory heuristics, the most fitting operating scenarios for referencing each heuristic have not been explored in previous publications. The main objective of this research is to identify the most environmentally friendly and thermodynamically efficient processes, as well as to gain a better understanding of the effect of the objective function on the synthesis of separation trains, through environmental, economic and exergy analyses. To address this, 855 simulations are carried out with capital costs (CAPEX) and total annual costs (TAC) evaluations and environmental impact assessment. Global warming potential (GWP), along with exergy analysis results are also presented. The results of the current study reveal that in contrast to the heuristic criteria and recommendations, it is possible that a heuristically discouraged separation train may work very well, depending on operating conditions. It was also discovered that switching from liquid to vapour feed significantly reduces the direct sequence's superiority. Moreover, it was shown from exergy analysis that selecting the most thermodynamically efficient process does not guarantee optimal solutions in terms of economic and environmental aspects.

Effect of hydrothermal flame generation methods on energy consumption and economic performance of supercritical water oxidation systems

Hydrothermal flames are critical to solving preheating problems and enhancing feed degradation in supercritical water oxidation (SCWO) systems. In this work, different hydrothermal flame generation methods including hot water injection, evaporation concentration, and addition of auxiliary fuel are proposed for SCWO of cutting fluids. The proposed systems are simulated using Aspen Plus 8.2, and the simulation model is validated by comparisons with experimental temperature profiles and product properties. A low ratio between the heat source flow and the feed flow (FR) requires a high heat source temperature to keep the hydrothermal flame stable and results in a high electricity consumption, and FR = 2 is chosen as the optimum condition for the SCWO system with hot water injection (SCWOH). The increase in concentration ratio and fuel concentration can effectively reduce the energy consumption for the SCWO systems with evaporation concentration (SCWOE) and addition of auxiliary fuel (SCWOF), respectively. The exergy analysis results indicate that most of exergy inputs are destructed inside the system, and the exergy distribution coefficients of the reactor exceed 80% in the SCWOE and SCWOF. Economic analysis results show the SCWOE has the lowest treatment cost of 95.9 USD/t.

Energy, exergy, economic and environmental comprehensive analysis and multi-objective optimization of a sustainable zero liquid discharge integrated process for fixed-bed coal gasification wastewater

For a long time, China's regional water resource imbalance has restricted the development of coal chemical industry, and it is imperative to achieve zero liquid discharge (ZLD). Therefore, the game relationship between technical indicators, costs and emissions in ZLD process of fixed-bed coal gasification wastewater treatment process should be explored in detail. According to the accurate model, the simulation for ZLD of fixed-bed coal gasification wastewater treatment process is established, and this process is assessed from the perspective of thermodynamics, economy, and environment. The total energy consumption of ZLD process before optimization is 4.032 × 108 W. The results of exergy analysis show exergy destruction of ZLD process is 94.55%. For economic and environmental results, the total annual cost is 1.892 × 107 USD·a−1 and the total environmental impact is 4.782 × 10−8. The total energy consumption of the optimal six-step ZLD process based on multi-objective optimization is 4.028 × 108 W. The CO2 content in the treated wastewater is 0.1%. This study will have an important role in promoting the establishment of the ZLD process for coal chemistry industry.

A Comparative Energy and Exergy Analysis Between Organic Rankine Cycle and Kalina Cycle System 11 for the Waste Heat Recovery of a PEM Fuel Cell Power Station

Abstract In this study, the performance analysis of waste heat recovery systems in a power generation system consisting of 13000 Proton Exchange Membrane Fuel Cells (PEMFC) in a stack has been investigated. Organic Rankine Cycle (ORC) and Kalina Cycle System 11 (KCS11) as bottoming cycles to convert generated waste heat of stack into electricity were compared with each other in a defined hybrid system. The improvement of system with an exact energy and exergy analysis after utilizing the waste heat in the hybrid system has been analyzed. Results show that the energy efficiency of combined system using Organic Rankine Cycle and Kalina Cycle System 11 increase by about 5% and 1.75% respectively. In addition, exergy analysis results indicate that exergy efficiency of combined system using Organic Rankine Cycle and Kalina Cycle System 11 increases by about 4% and 1.5% respectively. The total exergy destruction rate obtained for the hybrid power systems is 235.5 kW when ORC is used and 329.7 kW when KCS11 is used respectively. Results show that in presented systems ORC has higher energy and exergy efficiencies than KCS11 but different used working fluids and equipment of systems must also be considered from an economical point of view.

Thermodynamic analysis and process optimization of organosilicon distillation systems

The technical barrier of organosilicon production mainly lies in the separation of crude monomers, which has low product purity and high energy consumption. A novel Light Split distillation process was proposed in this work. Based on the root mean square deviation and the average absolute deviation models, Willson was selected as the thermodynamic model. Taking the total annual cost and gas emissions as the objective function, the traditional distillation process and the Light Split distillation process were improved simultaneously by multi-objective optimization based on the nondominated sorting genetic algorithm II. Furthermore, based on the results of exergy analysis and heat exchange network analysis, the heat matching between cold and heat flows is carried out to achieve the optimization of energy. Results show that the total annual cost and gas emissions of the improved distillation process are reduced by more than 50% compared with the basic distillation process. The total annual cost and gas emissions of the improved Light Split distillation process were reduced by 13.28% and 4.47% compared with the improved traditional distillation process, respectively. Comprehensive consideration, the improved Light Split distillation process has excellent economic and environmental performance, which is of great significance to the efficient separation of organosilicon.