Performance evaluation of integrated trigeneration and CO2 refrigeration systems

Food retailing is one of the most energy intensive sectors of the food cold chain. Its environmental impacts are significant not only because of the indirect effect from CO₂ emissions at the power stations but also due to the direct effect arising from refrigerant leakage to the atmosphere. The overall energy efficiency of supermarkets can be increased by integrating the operation of CO₂ refrigeration and trigeneration systems. This paper compares three alternative schemes in a medium size supermarket. Experimental results and simulation studies have shown that the best scheme for energy and GHG emissions savings is the one where the cooling produced by the trigeneration system is used to condense the CO₂ fluid in the refrigeration system to ensure subcritical operation throughout the year. It is shown that this system can produce 30% energy savings and over 40% greenhouse gas emissions savings over conventional refrigeration and indoor environment control systems in supermarkets.     

Design and performance analysis of a solar-geothermal-hydrogen production hybrid generation based on S–CO2 driven and waste-heat cascade utilization

In the present paper, a multi-energy complementary power generation is designed. It's a hybrid plant of solar power, geothermal power and hydrogen power based on S–CO₂ and T-CO₂ brayton cycle driven. The thermal power for hydrogen production is gained from the extracting S–CO₂ of solar power side and power consumption is 0.2% of PEM. The hybrid plant has the novel feature of time and energy complementarity. Through the thermodynamic analysis, the results reveal that energy efficiency and exergy efficiency could reach 78.14% and 84.04%, comparing with some other hybrid plans, the values have increased by about 20% and 30%, respectively. Through a sensitivity analysis, three optimal split radios have been put forward and the values are 0.68, 0.93 and 0.96, respectively. The Mg–Cl thermochemical cycle is used to hydrogen production and producing hydrogen energy is about 0.902 GJ/h. The economic analysis is investigated by COE_S and CRF, and the net economic profit is at least 42.11 million USD. The proposal system is based on the S–CO₂ and T-CO₂ driven and the daily average CO₂ circulating flow could get 55.0 × 10⁶ kg, it could decrease lots of greenhouse-gas emissions.     

Performance comparison of three trigeneration systems using organic rankine cycles

In this paper, energetic performance comparison of three trigeneration systems is presented. The systems considered are SOFC-trigeneration, biomass-trigeneration, and solar-trigeneration systems. This study compares the performance of the systems considered when there is only electrical power and the efficiency improvement of these systems when there is trigeneration. Different key output parameters are examined: energy efficiency, net electrical power, electrical to heating and cooling ratios, and (GHG) GHG (greenhouse gas) emissions. This study shows that the SOFC-trigeneration system has the highest electrical efficiency among the three systems. Alternatively, when trigeneration is used, the efficiencies of all three systems considered increase considerably. The maximum trigeneration efficiency of the SOFC-trigeneration system is around 76% while it is around 90% for the biomass-trigeneration system. On the other hand, the maximum trigeneration efficiencies of the solar-trigeneration system is around 90% for the solar mode, 45% for storage and storage mode, and 41% for the storage mode. In addition, this study shows that the emissions of CO₂ in kg per MWh of electrical power are high for the biomass-trigeneration and SOFC-trigeneration systems. However, by considering the emissions per MWh of trigeneration, their values drop to less than one fourth.     

SusDesign – An approach for a sustainable process system design and its application to a thermal power plant

This paper presents a structured process design approach, SusDesign, for the sustainable development of process systems. At each level of process design, design alternatives are generated using a number of thermodynamic tools and applying pollution prevention strategies followed by analysis, evaluation and screening processes for the selection of potential design options. The evaluation and optimization are carried out based on an integrated environmental and cost potential (IECP) index, which has been estimated with the IECP tool. The present paper also describes a flowsheet optimization technique developed using different thermodynamic tools such as exergy/energy analysis, heat and mass integration, and cogeneration/trigeneration in a systematic manner.The proposed SusDesign approach has been successfully implemented in designing a 30 MW thermal power plant. In the case study, the IECP tool has been set up in Aspen HYSYS process simulator to carry out the analysis, evaluation and screening of design alternatives.The application of this approach has developed an efficient, cost effective and environmentally friendly thermal system design with an overall thermal efficiency of 70% and CO₂ and NO emissions of 0.28 kg/kW h and 0.2 g/kW h respectively. The cost of power generation is estimated as 4 ¢/kW h. These achievements are significant compared to the conventional thermal power plant, which demonstrates the potential of the SusDesign approach for the sustainable development of process systems.     

Integration of gas switching combustion in a humid air turbine cycle for flexible power production from solid fuels with near-zero emissions of CO2 and other pollutants

This work presents a novel plant configuration for power production from solid fuels with integrated CO₂ capture. Specifically, the Gas Switching Combustion (GSC) system is integrated with a Humid Air Turbine (HAT) power cycle and a slurry fed entrained flow (GE-Texaco) gasifier or a dry fed (Shell) gasifier with a partial water quench. The primary novelty of the proposed GSC-HAT plant is that the reduction and oxidation reactor stages of the GSC operation can be decoupled allowing for flexible operation, with the oxygen carrier serving as a chemical and thermal energy storage medium. This can allow the air separation unit, gasifier, gas clean-up, CO₂ compressors and downstream CO₂ transport and storage network to be downsized for operation under steady state conditions, while the reactors and the power cycle operate flexibly to follow load. Such cost-effective flexibility will be highly valued in future energy systems with high shares of variable renewable energy. The GSC-HAT plant achieves 42.5% electrical efficiency with 95.0% CO₂ capture rate with the Shell gasifier, and 41.6% efficiency and 99.2% CO₂ capture with the GE gasifier. An exergy analysis performed for the GE gasifier case revealed that this plant reached 38.9% exergy efficiency, only 1.6%-points below an inflexible GSC-IGCC benchmark configuration, while reaching around 5%-points higher CO₂ capture rate. Near-zero SO_x and NO_x emissions are achieved through pre-combustion gas clean-up and flameless fuel combustion. Overall, this flexible and efficient near-zero emission power plant appears to be a promising alternative in a future carbon constrained world with increasing shares of variable renewables and more stringent pollutant (NO_x, SO_x) regulations.     

Comparative studies of augmentation in combined cycle power plants

The attractive features of a combined cycle (CC) power plant are fuel flexibility, operational flexibility, higher efficiency and low emissions. The performance of five gas turbine‐steam turbine (GT‐ST) combined cycle power plants (four natural gas based plants and one biomass based plant) have been studied and the degree of augmentation has been compared. They are (i) combined cycle with natural gas (CC‐NG), (ii) combined cycle with water injection (CC‐WI), (iii) combined cycle with steam injection (CC‐SI), (iv) combined cycle with supplementary firing (CC‐SF) and (v) combined cycle with biomass gasification (CC‐BM). The plant performance and CO₂ emissions are compared with a change in compressor pressure ratio and gas turbine inlet temperature (GTIT). The optimum pressure ratio for compressor is selected from maximum efficiency condition. The specific power, thermal efficiency and CO₂ emissions of augmented power plants are compared with the CC‐NG power plant at the individual optimized pressure ratios in place of a common pressure ratio. The results show that the optimum pressure ratio is increased with water injection, steam injection, supplementary firing and biomass gasification. The specific power is increased in all the plants with a loss in thermal efficiency and rise in CO₂ emissions compared to CC‐NG plant. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison between single-shaft and mutli-shaft gas fired 800 MWel combined cycle power plant

Multi-shaft and single-shaft configurations allow customization to optimize plant performance, capital investment, construction and maintenance access, operating convenience, and minimum space requirements. Technical comparison between both configurations at partial loads has not been published before. This paper will primarily address a comparison between the two configurations based on thermodynamic simulation results for a gross power capacity of approximately 800 MWel at ISO conditions. This capacity has been chosen based on power market requirements. The analysis approach for each configuration is divided into three components: (1) Performance, (2) Plant configuration, and (3) Environmental impact. The first component dealt with plant gross power output, plant gross efficiency, plant auxiliary power demand, plant generator losses and plant shaft power. The second component dealt with space limitations and extension capability. The third component dealt with specific emissions of NO_x and specific emissions of CO₂. The thermodynamic simulations have been carried out using Thermoflow^® at base load and part load respectively. The results show that the single-shaft configuration is more suitable with regards to performance, NO_x specific emissions, CO₂ specific emissions, start-up and extension possibilities. The multi-shaft configuration is more suitable with regards to space limitations, steam turbine shaft power, availability, and reliability.     

Design,testing and mathematical modelling of a small-scale CHP and cooling system (small CHP-ejector trigeneration)

Trigeneration is the production of heat, cooling and power from one system. It can improve the financial and environmental benefits of combined heat and power (CHP) by using the heat output from the CHP unit to drive a cooling cycle, as demonstrated in existing large-scale installations. However, small-scale systems of a few kW_e output present technological challenges. This paper presents the design and analysis of possible trigeneration systems based on a gas engine mini-CHP unit (5.5 kW_e) and an ejector cooling cycle. Analysis shows that an overall efficiency around 50% could be achieved with systems designed for applications with simultaneous requirements for heat and cool. While using part of the CHP electrical output into the cooling cycle boosts the cooling capacity, it does not improve the overall efficiency and increases the CO₂ emissions of the system. Emissions savings compared to traditional systems could be achieved with improvements of the heat transfer from CHP to cooling cycle.     

Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants

A comprehensive exergy, exergoeconomic and environmental impact analysis and optimization is reported of several combined cycle power plants (CCPPs). In the first part, thermodynamic analyses based on energy and exergy of the CCPPs are performed, and the effect of supplementary firing on the natural gas-fired CCPP is investigated. The latter step includes the effect of supplementary firing on the performance of bottoming cycle and CO₂ emissions, and utilizes the first and second laws of thermodynamics. In the second part, a multi-objective optimization is performed to determine the “best” design parameters, accounting for exergetic, economic and environmental factors. The optimization considers three objective functions: CCPP exergy efficiency, total cost rate of the system products and CO₂ emissions of the overall plant. The environmental impact in terms of CO₂ emissions is integrated with the exergoeconomic objective function as a new objective function. The results of both exergy and exergoeconomic analyses show that the largest exergy destructions occur in the CCPP combustion chamber, and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction. The optimization results demonstrates that CO₂ emissions are reduced by selecting the best components and using a low fuel injection rate into the combustion chamber.     

Analysis of a novel solar energy-powered Rankine cycle for combined power and heat generation using supercritical carbon dioxide

Theoretical analysis of a solar energy-powered Rankine thermodynamic cycle utilizing an innovative new concept, which uses supercritical carbon dioxide as a working fluid, is presented. In this system, a truly ‘natural’ working fluid, carbon dioxide, is utilized to generate firstly electricity power and secondly high-grade heat power and low-grade heat power. The uniqueness of the system is in the way in which both solar energy and carbon dioxide, available in abundant quantities in all parts of the world, are simultaneously used to build up a thermodynamic cycle and has the potential to reduce energy shortage and greatly reduce carbon dioxide emissions and global warming, offering environmental and personal safety simultaneously. The system consists of an evacuated solar collector system, a power-generating turbine, a high-grade heat recovery system, a low-grade heat recovery system and a feed pump. The performances of this CO₂-based Rankine cycle were theoretically investigated and the effects of various design conditions, namely, solar radiation, solar collector area and CO₂ flow rate, were studied. Numerical simulations show that the proposed system may have electricity power efficiency and heat power efficiency as high as 11.4% and 36.2%, respectively. It is also found that the cycle performances strongly depend on climate conditions. Also the electricity power and heat power outputs increase with the collector area and CO₂ flow rate. The estimated COP_power and COP_heat increase with the CO₂ flow rate, but decrease with the collector area. The CO₂-based cycle can be optimized to provide maximum power, maximum heat recovery or a combination of both. The results suggest the potential of this new concept for applications to electricity power and heat power generation.     

Life cycle GHG assessment of fossil fuel power plants with carbon capture and storage

The evaluation of life cycle greenhouse gas emissions from power generation with carbon capture and storage (CCS) is a critical factor in energy and policy analysis. The current paper examines life cycle emissions from three types of fossil-fuel-based power plants, namely supercritical pulverized coal (super-PC), natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC), with and without CCS. Results show that, for a 90% CO₂ capture efficiency, life cycle GHG emissions are reduced by 75–84% depending on what technology is used. With GHG emissions less than 170 g/kWh, IGCC technology is found to be favorable to NGCC with CCS. Sensitivity analysis reveals that, for coal power plants, varying the CO₂ capture efficiency and the coal transport distance has a more pronounced effect on life cycle GHG emissions than changing the length of CO₂ transport pipeline. Finally, it is concluded from the current study that while the global warming potential is reduced when MEA-based CO₂ capture is employed, the increase in other air pollutants such as NO_x and NH₃ leads to higher eutrophication and acidification potentials.     

An experimental investigation of a household size trigeneration

A household size trigeneration based on a small-scale diesel engine generator set is designed and realized in laboratory. Experimental tests are carried out to evaluate the performance and emissions of the original single generation (diesel engine generator); and the performances of the whole trigeneration including the diesel generator within the trigeneration system, the heat exchangers which are used to recover heat from engine exhaust, the absorption refrigerator which is driven by the exhaust heat; and the emissions from the whole trigeneration.Comparisons of the test results of two generations are also performed. The test results show that the total thermal efficiency of trigeneration reaches to 67.3% at the engine full load, comparing to that of the original single generation 22.1% only. Within the range of engine loads tested, the total thermal efficiencies of trigeneration are from 205% to 438% higher than that of the thermal efficiency of single generation.The CO₂ emission per unit (kW h) of useful energy output from trigeneration is 0.401 kg CO₂/kW h at the engine full load, compared to that of 1.22 kg CO₂/kW h from single generation at the same engine load. Within the range of engine loads tested, the reductions of CO₂ emission per unit (kW h) of trigeneration output are from 67.2% to 81.4% compared to those of single generation.The experimental results show that the idea of realizing a household size trigeneration is feasible; the design and the set-up of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, produce heat and drive a refrigeration system, simultaneously from a single fuel (diesel) input.     

Experimental tests of a small‐scale microturbine with a liquid desiccant cooling system

In a trigeneration plant, the thermal energy recovered from the prime mover is exploited to produce a cooling effect. Although this possibility allows the working hours of the plant to be extended over the heating period, providing summer air conditioning through thermally activated technologies, it is rather difficult to find in the literature experimental data on trigeneration plants operation, and the availability of performance characteristics at off‐design conditions is anyway limited. The paper has the aim of showing the experimental data of a real trigeneration system installed at the Politecnico di Torino (Turin, Italy), composed of a natural gas 100 kW_el microturbine coupled to a liquid desiccant system. The data are presented for both cogeneration and trigeneration configurations, and for full and partial load operations. An energetic and economic performance assessment at rated power operation is presented, and compared with the partial load operation strategy. The primary energy savings are calculated through a widely accepted methodology, proposed by the European Union, and through another methodology, reported in literature, which seems to the Authors more suitable to describe the energetic performances of trigeneration plants. Copyright © 2012 John Wiley & Sons, Ltd.     

Parametric optimization design for supercritical CO2 power cycle using genetic algorithm and artificial neural network

Supercritical CO₂ power cycle shows a high potential to recover low-grade waste heat due to its better temperature glide matching between heat source and working fluid in the heat recovery vapor generator (HRVG). Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the cycle performance and exergy destruction in each component. The thermodynamic parameters of the supercritical CO₂ power cycle is optimized with exergy efficiency as an objective function by means of genetic algorithm (GA) under the given waste heat condition. An artificial neural network (ANN) with the multi-layer feed-forward network type and back-propagation training is used to achieve parametric optimization design rapidly. It is shown that the key thermodynamic parameters, such as turbine inlet pressure, turbine inlet temperature and environment temperature have significant effects on the performance of the supercritical CO₂ power cycle and exergy destruction in each component. It is also shown that the optimum thermodynamic parameters of supercritical CO₂ power cycle can be predicted with good accuracy using artificial neural network under variable waste heat conditions.     

Solid oxide fuel cell/gas turbine trigeneration system for marine applications

Shipping contributes 4.5% to global CO₂ emissions and is not covered by the Kyoto Agreement. One method of reducing CO₂ emissions on land is combined cooling heating and power (CCHP) or trigeneration, with typical combined thermal efficiencies of over 80%. Large luxury yachts are seen as an ideal entry point to the off-shore market for this developing technology considering its current high cost.This paper investigates the feasibility of combining a SOFC-GT system and an absorption heat pump (AHP) in a trigeneration system to drive the heating ventilation and air conditioning (HVAC) and electrical base-load systems. A thermodynamic model is used to simulate the system, with various configurations and cooling loads. Measurement of actual yacht performance data forms the basis of this system simulation.It is found that for the optimum configuration using a double effect absorption chiller in Ship 1, the net electric power increases by 47% relative to the electrical power available for a conventional SOFC-GT-HVAC system. This is due to more air cooled to a lower temperature by absorption cooling; hence less electrical cooling by the conventional HVAC unit is required. The overall efficiency is 12.1% for the conventional system, 34.9% for the system with BROAD single effect absorption chiller, 43.2% for the system with double effect absorption chiller. This shows that the overall efficiency of a trigeneration system is far higher when waste heat recovery happens.The desiccant wheel hardly reduces moisture from the outdoor air due to a relative low mass flow rate of fuel cell exhaust available to dehumidify a very large mass flow rate of HVAC air, Hence, desiccant wheel is not recommended for this application.     

Energy analysis of a trigeneration plant based on solid oxide fuel cell and organic Rankine cycle

In this study, energy analysis of a trigeneration plant based on solid oxide fuel cell (SOFC) and organic Rankine cycle (ORC) is conducted. The physical and thermodynamic elements of the plant include an SOFC, an ORC, a heat exchanger for the heating process and a single-effect absorption chiller for cooling. The results obtained from this study show that there is at least a 22% gain in efficiency using the trigeneration plant compared with the power cycle (SOFC and ORC). The study also shows that the maximum efficiency of the trigeneration plant is 74%, heating cogeneration is 71%, cooling cogeneration is 57% and net electricity is 46%. Furthermore, it is found that the highest net power output that can be provided by the trigeneration plant considered in this study is 540 kW and, the highest SOFC-AC power is 520 kW. The study reveals that the inlet pressure of the turbine has an insignificant effect on the efficiency. The study also examines the effect of both the SOFC current density and the SOFC inlet flow temperature on the cell voltage and voltage loss.     

Thermodynamic analysis of the CO2‐based Rankine cycle powered by solar energy

Using carbon dioxide as working fluid receives increasing interest since the Kyoto Protocol. In this paper, thermodynamic analysis was conducted for proposed CO₂‐based Rankine cycle powered by solar energy. It can be used to provide power output, refrigeration and hot water. Carbon dioxide is used as working fluid with supercritical state in solar collector. Theoretical analysis was carried out to investigate performances of the CO₂‐based Rankine cycle. The interest was focused on comparison of the performance with that of solar cell and those when using other fluids as working fluids. In addition, the performance and characteristics of the thermodynamic cycle are studied for different seasons. The obtained results show that using CO₂ as working fluid in the Rankine cycle owns maximal thermal efficiency when the working temperature is lower than 250.0°C. The power generation efficiency is about 8%, which is comparable with that of solar cells. But in addition to power generation, the CO₂‐based solar utilization system can also supply thermal energy. Copyright © 2007 John Wiley & Sons, Ltd.     

Construction and testing of a wet-compression absorption carbon dioxide refrigeration system for vehicle air conditioner

The environmental benefits of the transcritical carbon dioxide (CO₂) refrigeration cycle are considerable. But its application is greatly challenged by the high operation pressure, which could be as high as 120 bar. A wet-compression absorption (WCA) CO₂ refrigeration cycle was constructed by adding a non-volatile liquid into a CO₂ refrigeration cycle. CO₂ is highly soluble in the liquid and easily absorbed and desorbed by it. In the WCA CO₂ refrigeration cycle, the high side pressure was less than 35 bar, which was tremendously reduced compared to the transcritical CO₂ refrigeration cycle.In this paper, following a thermodynamic analysis of working fluid, a WCA CO₂ refrigeration demonstrator plant was constructed within the restricted physical and operational envelope of an existing vehicle refrigeration unit. This unique plant operated satisfactorily, delivering sustainable cooling for refrigerated vehicle. The relationship between system performance and the cycle ratio and IHX (internal heat exchanger) efficiency was tested. The components used in the demonstrator were entirely based on existing components and not optimized and considerable potential exists for efficiency improvements.     

Design and energy evaluation of a stand‐alone copper‐chlorine (Cu‐Cl) thermochemical cycle system for trigeneration of electricity,hydrogen, and oxygen

In this article, a new stand‐alone Cu‐Cl cycle system (SACuCl) for trigeneration of electricity, hydrogen, and oxygen using a combination of a specific combined heat and power (CHP) unit and a 2‐step Cu‐Cl cycle using a CuCl/HCl electrolyzer is presented. Based on the self‐heat recuperation technology for the CHP unit and the heat integration of the Cu‐Cl cycle unit, the power efficiency of the SACuCl for 5 prescribed scenarios (case studies) is predicted to achieve about 48% at least. The SACuCl uses the technologies of the dry reforming of methane and the oxy‐fuel combustion to achieve a relatively high CO₂ concentration in the flue gas, and CO₂ emissions for power generation could be almost restricted by 0.418 kg/kWh. From the aspect of the electricity required for hydrogen production, it is verified that the 2‐step Cu‐Cl cycle system is superior to the conventional water electrolyzer because the CHP process supplies the heat/electricity for Cu‐Cl thermochemical reactions and a thermoelectric generator is connected to the exhaust gas for recovering the power consumption from the compressor and the CuCl/HCl electrolyzer. Finally, the heat exchanger network and the pinch technology are employed to determine the optimum heat recovery of the Cu‐Cl cycle. In case 5 analyzed for the SACuCl, the electricity required for the heat‐integrated 2‐step Cu‐Cl cycle is predicted to dramatically decrease from 4.39 to 0.452 kWh/m³ H₂ and the cycle energy efficiency could be obviously increased from 23.77 to 31.97%.     

Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal

Based on the results of previous studies, the efficiency of a Brayton/Hirn combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO₂ removal by chemical absorption reached 33.94%, considering also the separate CO₂ compression process. The specific CO₂ emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO₂ chemical absorption (38–39% efficiency, 130 kg/MW h specific CO₂ emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilisation. The LCA shows the important environmental advantages of biomass utilisation in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilisation.