•Possibility of integrating thermoelectric with gasifier cycle is investigated.•Different locations for adding TEG in a biomass power generation is investigated.•Adding thermoelectric to the ...condenser section increases efficiency from 16.76% to 17.93%.•Economic evaluation indicated the conditions under which the system is profitable.
Thermoelectric waste heat recovery systems (WHRSs) can be used appropriately to recover wasted heat from various industrial processes. In the current work, new thermodynamic modeling was developed to harvesting waste heat from an integrated system includes an externally fired gas turbine and a biomass gasifier by three thermoelectric WHRSs. The biomass system consisted a gas turbine cycle, an organic Rankine cycle (ORC) and a domestic water heater were first thermodynamically modeled, and then effects of adding thermoelectric WHRSs to different locations of the system were investigated. It is observed that first law efficiency of the system (η1) will become 17.11% (an increase of 0.35%) if the total output heat from the stack enters WHRSs. The efficiencies of the system can be increased from 16.76% to 17.93% by placing a WHRS on the condenser of ORC. Moreover, the operating parameters have a significant effect on the integrated system efficiency; the influence of increasing αGE on the efficiencies is in contrast to the effect of enhancing αcond. In addition, an economic assessment of integrating WHRSs with the biomass gasifier integrated system is conducted and the conditions are indicated under which the proposed system is profitable. Furthermore, the results of genetic algorithm based multi-objective optimization shows that with the use of γDU = 2 and γL,ORC=30 defined thermal efficiencies are at their optimum state.
In this paper, a novel fluid-thermal-electric multiphysics numerical model is presented to predict the performance of a thermoelectric generator system applied in automobile waste heat recovery. The ...model considers the complete geometry, temperature-dependent material properties, topological connection among thermoelectric modules, and impedance matching, which can simulate the actual working conditions. Numerical simulations are carried out on the COMSOL platform combined with the exhaust temperature and exhaust mass flow rate under different vehicle speeds. In addition, the detailed physical field distribution characteristics of the automobile thermoelectric generator system, as well as the variations of output power, conversion efficiency, power losses, and net power with vehicle speed, are obtained. The position of thermoelectric modules on the hot side heat exchanger plays an important role in output uniformity, and the higher the vehicle speed is, the more uniform the output will be. At the vehicle speed of 120 km h−1, the output power and conversion efficiency of the automobile thermoelectric generator system are 38.07 W and 1.53% respectively. Considering the weight power loss and coolant pumping power loss, the net power is 23.66 W. This work fills the gap in evaluating the performance of automobile thermoelectric generator systems at different vehicle speeds comprehensively.
•A fluid-thermal-electric multiphysics numerical model for automobile TEG systems is proposed.•Complete physical field distribution characteristics of the automobile TEG system is obtained.•Performance of the automobile TEG system under different vehicle speeds is investigated.•The effect of TEM location on the output performance is studied.•The net power analysis under different vehicle speeds is performed.
•Review of methods used for heat integration of Organic Rankine Cycle.•Integration of Organic Rankine Cycle with industrial waste heat.•Influence of working fluid selection, architecture and low ...temperature waste heat.•Problems in integration with continuous and batch industrial processes.
Production systems represent a significant source of waste heat. The waste heat cannot be reused often. Many optimization methods can give a solution for waste heat recovery. However, the results do not depend only on the method. The low-temperature waste heat makes difficulties for its recovery within the processes. Organic Rankine Cycle units can be used for low-temperature heat transformation into electricity. Linking the Organic Rankine Cycle within the heat integrated system is not simple. This depends on the influence of a few important factors. The process parameters of the working medium, the physical and chemical characteristics of the working fluid, the continuity of heat supply, and the temperature level of waste heat are necessary conditions that must be included in optimization. The optimization method should determine the optimal operating point of the Organic Rankine Cycle. The displacement of the operating point leads to decrease in the effective transformation of heat into electricity. These problems are analyzed through a review of the methods and approaches used for the integration of Organic Rankine Cycle in thermal process systems. These include Pinch technology, Non-Linear Programming, Multiple Integer Linear Programming, Genetic Algorithm, Artificial Neural Network and many different approaches for polygeneration systems. All methods were compared and systematized in a general scheme for integration of an Organic Rankine Cycle with low-temperature industrial waste heat supply. This work also includes experience in implemented and designed projects of an integrated Organic Rankine Cycle.
Heat pump is effective to recover ultra-low grade waste heat, and includes compression and absorption heat pumps. However, the driving source of these heat pumps are different. This makes the ...efficiency comparison unfair, and multi-criterion comparison is necessary. In this paper, the compression and absorption heat pumps are compared under the same condition, where 30 °C waste heat is recovered to provide 60 °C domestic heating supply. Analyses with coefficient of performance (COP), second law efficiency, exergy efficiency and exergy rate are carried out. Exergy-to-energy ratio of driving source, instead of temperature, is used to unify the evaluation of different driving sources. Results show that compression heat pump has higher COP but lower exergy efficiency, indicating more irreversible loss. This is followed by double effect, single effect and double lift absorption heat pumps. The high COP lead to effective recovery of exergy from waste heat, with higher exergy rate. However, the strong sensitivity of COP versus temperature lift in compression heat pump makes it more effective under small temperature lift, while absorption heat pumps are more effective under higher temperature lift. The multi-criterion comparisons provide both deeper understanding about heat pumps and useful framework for waste heat recovery analysis.
•Absorption and compression heat pumps are analyzed for ultra-low heat utilization.•Carnot factor of driving source is used to unify different forms of driving source.•Multi-criterion analysis is done with COP, exergy efficiency and exergy rate.•Compression heat pump is more effective under lower temperature lift condition.
•A supercritical carbon dioxide Brayton-Kalina combined cycle system is presented.•The parameter analysis and optimization of the proposed cycle system are conducted.•The combined cycle system can ...make full use of marine diesel engine waste heat.•Using the system can reduce the Energy Efficiency Design Index by 15.01%.
With the continuous rise in world oil prices and increasing environmental awareness, how to improve ship energy efficiency and reduce ship pollution emissions has become a common concern of the shipping industry. Waste heat recovery technology is an effective method to improve the fuel economy of ships and help the future ships to meet the increasingly stringent Energy Efficiency Design Index of the International Maritime Organization. Under the thermodynamic analysis results of the 8S90ME-C10.2 low-speed marine diesel engine, this paper proposed a waste heat recovery scheme that combined the supercritical carbon dioxide Brayton cycle power generation system with the Kalina cycle power generation system. According to the energy and exergy balances of the combined cycle system, a MATLAB program based on the REFPROP database was established. With the application of control variate method, the influence of the key operating parameters including the main compressor inlet temperature, the turbine inlet temperature, the main compressor outlet pressure, the expander inlet pressure, and the ammonia solution mass concentration on the system performance was thoroughly analyzed. Moreover, the multi-objective optimization matching between the diesel engine and the combined power generation system was carried out from the viewpoints of the thermodynamic performance and economic performance and the impact of the system on the fuel economy and the Energy Efficiency Design Index of the ship was calculated. The results showed that the combined power generation system was used to recycle the waste heat of diesel engine exhaust gas and bypass exhaust gas to generate electricity, which reduced the annual fuel consumption and the Energy Efficiency Design Index to 16.62% and 15.01%, respectively. Finally, this study provides a reference for researchers to study the combined use of supercritical carbon dioxide Brayton cycle and Kalina cycle to recycle the waste heat of the marine diesel engine.
The focus of this study is to review the latest developments and technologies on waste heat recovery of exhaust gas from internal combustion engines (ICE). These include thermoelectric generators ...(TEG), organic Rankine cycle (ORC), six-stroke cycle IC engine and new developments on turbocharger technology. Furthermore, the study looked into the potential energy savings and performances of those technologies. The current worldwide trend of increasing energy demand in transportation sector are one of the many segments that is responsible for the growing share of fossil fuel usage and indirectly contribute to the release of harmful greenhouse gas (GHG) emissions. It is hoped that with the latest findings on exhaust heat recovery to increase the efficiency of ICEs, world energy demand on the depleting fossil fuel reserves would be reduced and hence the impact of global warming due to the GHG emissions would fade away.
•Eight advanced HTHP configurations and nine low GWP refrigerants were studied.•The modelling process was optimized to obtain the most optimum solution.•The cost and carbon emissions of different ...scenarios were obtained.•Two-stage configurations are benefited from temperature lifts above 60 K.•Advanced configurations reduce the carbon footprint compared to traditional natural gas boilers.
High temperature heat pumps (HTHPs) have a great potential to improve industrial processes with thermal demand through industrial waste heat recovery and revalorization. Vapor compression HTHPs are very sensitive to the cycle configuration, refrigerant, components, and operating temperatures. This study compares eight advanced cycle configurations and nine low global warming potential (GWP) refrigerants from an energetic, economic, and environmental comprehensive perspective to illustrate an optimum selection for different HTHP applications. Firstly, several single-stage and two-stage compression cycles are proposed adding different components, such as the ejector, economizer, parallel compressor, flash tank, or additional evaporators and condensers. Moreover, an internal heat exchanger (IHX) has been included in all configurations to maximize the energy performance and ensure dry compression. Secondly, HC-601, HC-600, HC-600a, HFO-1336mzz(Z), HFO-1336mzz(E), R-514A, HCFO-1233zd(E), HCFO-1224yd(Z), and HFO-1234ze(Z) are considered as alternative low GWP refrigerants to replace the hydrofluorocarbon HFC-245fa. The results indicate that a two-stage cascade becomes the most appropriate configuration for high temperature lifts (60 K and above). In contrast, single-stage cycles with economizer and parallel compression are suitable for low temperature lifts (50 K and below). HCFO-1233zd(E) and HCFO-1224yd(Z) show a trade-off between coefficient of performance (COP) and volumetric heating capacity (VHC). Advanced HTHPs configurations can save up to 68% of the equivalent CO2 emissions compared to a natural gas boiler.
•A novel system is proposed to supply power and cooling.•Carbon dioxide is employed as working fluid of power and refrigeration.•Energy and exergy performances are comprehensively analyzed for the ...system.•A thermoeconomic performance comparison between the proposed and the reference systems is conducted.•Effects of key parameters on the system performance are investigated.
With excellent physical properties, carbon dioxide has been widely employed as a working fluid in efficient energy conversion technologies, which are represented by supercritical carbon dioxide Brayton cycle and transcritical carbon dioxide refrigeration cycle. In this contribution, with the aim to recover the waste heat of shipboard, a combined system coupling carbon dioxide Brayton cycle and refrigeration cycle is proposed to simultaneously produce power and cooling. In order to alleviate the temperature mismatch in recuperator and effectively utilize the discharged heat of refrigeration cycle, low temperature recuperator and gas cooler are shared by power and cooling cycles. For this novel waste heat recovery system, thermodynamic and economic models are developed to conduct energy, exergy and economic analysis. Thereafter, key cycle parameters including gas cooler pressure, evaporation temperature and turbine inlet temperature are investigated to reveal the effects on the system performances. The obtained results indicate that the energy and exergy efficiencies of the proposed system are respectively 42.42% and 39.05% under design conditions. The corresponding average energy cost is 9.28 $/GJ. At lower evaporation temperature and higher gas cooler pressure, the advantages of low temperature recuperator can be fully utilized and more work is produced. However, lower cooling capacity is obtained. Furthermore, the turbine inlet temperature has no effects on refrigeration cycle, and the net work decreases with the increase of inlet temperature. These results will be beneficial to improve the design and performance of combined power and cooling system for future shipboard applications.
•Performance trends are discussed and addressed as functions of first principles.•Majority of experimental ORC published work is below 10 kWe power.•Heat to electrical power conversion efficiency is ...44% of the Carnot cycle efficiency.•R245fa was the most popular working fluid, followed by R123 and then R134a.•The average values of Back-Work Ratio were 25.9% for ORC experiments.
Organic Rankine Cycle (ORC)-based systems are being extensively investigated for heat-to-electric power conversion from various sources, such as biomass, waste heat recovery, concentrated solar thermal and geothermal. The ORC technology has a promising future as it helps to meet energy requirements, arguably with a minimal environmental impact. This work summarizes the current state-of-the-art of actual i.e., experimental ORC system performance, derived from a comprehensive analysis of the most significant, relevant and up-to-date experimental data published in scientific literature. A survey of more than 200 scientific works is scrutinized according to specific selection criteria and data is extracted to develop a database containing thermodynamic cycle information along with component-level performance information. Performance trends are discussed and addressed as functions of first principles. One of the least surprising results indicate that the performance follows economies of scale. More revealing is the fact that the Organic Rankine Cycle conversion efficiency (mechanical to electrical) was around 70%. Furthermore, it becomes clear that there is a large gap between research and development for source and sink temperature differences above 150 °C. In general, the overall heat to electrical power conversion efficiency was around 44% of the Carnot cycle efficiency of the cycle. A host of other relevant thermodynamic parameters are cross-compared, as well as compared to theoretical results, allowing a level of practical ORC system design target homologation to be achieved which is useful for the engineer as well as the scientist in the design of ORC components, systems as well as advanced cycles.
In the context of the stringent automobile emission legislations, this paper proposes a novel compression-assisted decomposition thermochemical sorption energy storage system for recovering engine ...exhaust waste heat, which is utilized to produce cooling capacity for a refrigerated vehicle. In this system, the desorption pressure of sorbent can be flexibly adjusted by changing the suction pressure of compressor embedded between the sorption bed and condenser, which ensures the stable operation of system even at relatively low exhaust temperatures. Simultaneously, the decomposition reaction increases suction pressure of compressor, so the coefficient of performance (COP) is thus greatly improved. Furthermore, the sorption bed can output cooling capacity for refrigerated compartment when the vehicle is parked. Currently, vehicle emission standards generally adopt World Harmonized Stationary Cycle test, and 13 engine operating points are selected. At an operating point 3 (a low engine load), i.e. 55% speed and 25% torque, the COP of the novel system at an evaporating temperature of −25 °C and a condensing temperature of 45 °C is 1.65, 1.5 times higher than that of conventional one. The weighted average COP under 13 operating points is still up to 1.48. Eventually, the novel system promotes the realization of low-carbon and low-cost refrigerated transportation.
•A thermochemical sorption energy storage system is designed for a refrigerated vehicle.•Compression-assisted decomposition is employed to recover more exhaust waste heat.•The system performance is analyzed based on World Harmonized Stationary Cycle test.•Low and medium-temperature exhaust waste heat of engine is utilized efficiently.•Low-carbon and low-cost refrigerated transportation is realized.
