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Abstract A new air-cooled gas-steam combined cycle cogeneration system with absorption heat pump for recovering waste heat from exhausted steam of the steam turbine to achieve double effects of waste heat recovery and water saving is proposed based on a conventional water-cooled gas-steam combined cycle cogeneration system in the paper. The property criteria variation is analyzed before and after modification. In addition, the exergy analyses of primary equipments are carried out based upon the exergy analysis theory. The results demonstrate that the net generating power is approximately increased by 11,082 kW, equivalent coal consumption is reduced by 2.71 g/kWh, the net overall thermal efficiency is improved by 0.91% with 334,245 kW heating load at 100% load of the gas turbine in the modified system. Besides, the overall exergy loss is decreased by 6448 kW and exergy efficiency is improved by 0.98%. The overall property of the whole system is improved. The results show that the property reduction caused by air-cooling modification can be made up by the property improvement due to waste heat recovery. Moreover, the cooling circulating water can be saved by 1196.34 kg/s. The presented measure can not only improve performance of the system but also simultaneously achieve energy and water saving on the premise of satisfying user needs, which has a wide application potential in the water-shortage regions.

Abstract The coal gasification process is one of the main exergy destruction contributors in polygeneration systems and has considerable energy saving potential. In the present study, for improving the performance of the polygeneration system, the coal-steam gasification method was employed to integrate a novel methanol-electricity polygeneration system. The results indicated that the energy efficiency of the novel system was 63.3% with a chemical-to-power output ratio of 8.4, while the energy efficiency of the traditional system is 51.3% at the optimal unreacted syngas recycling ratio. Exergy analysis results revealed that the system exergy destruction in the coal–steam gasification process is 7.5% smaller than that in the GE gasification process, and eliminating the air separation unit can reduce the exergy destruction of the system by 4.3%. Additionally, the energy saving contributions of gasification process improvement and system integration were quantitatively evaluated. When the chemical-to-power output ratio increased from 1.9 to 11.9, the energy saving contributions of the system integration and gasification process improvement ranged from 9.8% to 15.1% and 11.9% to 12.9%, respectively.

Abstract Organic solvent upgrading Indonesian lignite was performed in a 1 L autoclave under moderate temperature. The chemical structure and functional groups transformation of lignite upgraded by two organic solvents (ethanol and n-hexane) were analyzed to explore the upgrading mechanism of solvent thermal treatment by using Fourier transform infrared (FTIR) and 13 C nuclear magnetic resonance (NMR). In addition, the characteristics of pyrolysis of treated samples were investigated using thermo gravimetric (TG) to clarify the variance of pyrolysis reactivity. Results showed that the carbon content and calorific value of upgraded lignite were significantly improved, and H/C and O/C ratios of treated samples were significantly reduced with the temperature increasing. The relative percentage of carbonyl and carboxyl carbon, oxygenated aliphatic carbon and methoxyl carbon of lignite upgraded at 300 °C decreased by 20–30%. However, the carbon-substituted and protonated aromatic carbon at 120–135 ppm and protonated aromatic carbon at 90–120 ppm were significantly increased after lignite was upgraded by the two solvents at above 200 °C. These transformations indicated that oxygen-containing functional group was substituted by hydrogen or carbon-substituent as temperature increased, and were intensified at above 200 °C. In addition, oxygen-loss in the treated samples was attributed to the loss of carbonyl group at 175 ppm, dihydric phenol at 147 ppm, and methoxyl group at 55 ppm. The activation energy of upgraded lignite at 300 °C were higher than those of raw lignite and upgraded lignite at 100 and 200 °C, indicating the low reactivity of pyrolysis of the treated lignite with the temperature increasing.

Remanufacturing has received extensive attention due to its advantages in material and energy saving, emission reduction and is often considered a viable approach for the realization of a circular economy. Remanufacturing ecological performance reflects the ability of an enterprise to balance economic and environmental benefits. Therefore, evaluating the remanufacturing ecological performance is of great significance for leveraging the benefits of remanufacturing and promoting the concept of sustainability and the implementation of a circular economy in the industry. To this end, a set of data-driven techniques, i.e., data envelopment analysis, R clustering and grey relational analysis, are deployed to analyze and evaluate the ecological performance of a remanufacturing process. The effectiveness and feasibility of the proposed method are illustrated via a case study of remanufacturing for hydraulic cylinder and boom cylinder. Furthermore, a number of critical factors, e.g., energy-saving rate, remanufacturing process cost and rate of remanufacturing, for end-of-life products have been identified as the key drivers impacting the remanufacturing ecological performance. So as to improve remanufacturing ecological performance, optimizing production technology, implementing lean remanufacturing and raising public acceptability over remanufacturing products are effective measures. The research results of the present work can provide support for remanufacturing enterprises to guide and improve their ecological performance and formulate better development strategies.

Abstract Direct de-ionized (DI) water immersion cooling has been verified to be an effective method of managing the operating temperature of silicon solar cells under concentration. However, the stable electrical performance is difficult to be achieved. Possible factors from bare cell self, materials for tabbing cells were investigated in this study for understanding the degradation mechanism. Long term immersion results showed that no significant degradation on bare cells operated in DI water at 65 °C. When cells were tabbed using lead-based solder and flux, the short circuit current ( I sc ) of cells decreased with exposure time, notably under sunlight, but it was not observed for cell open circuit voltage ( V oc ). The epoxy tabbed cells test also demonstrated that the tabbed cells without lead-based solder and flux involved were also found drop in I sc , but with slower rate. The presence of lead and tin black oxides on the lead based-soldered tabbed cells and red deposition on the epoxy tabbed cells confirmed the occurrence of galvanic corrosion. However, particular cleaning recovers the I – V towards its initial values for the former tabbed cells, and partial recovery for the latter tabbed cells, which indicates that the cells are not damaged after long-time DI water immersion.

Abstract A novel combined power and cooling system based on the organic Rankine cycle and the ejector refrigeration cycle for highly efficient utilization of low-grade heat is presented, in which the endothermic process adopts a dual-pressure evaporation approach and the two vapor generators are connected in series. A mathematical model is developed to evaluate the system thermodynamic and exergoeconomic characteristics. The effects of key parameters on system performance are evaluated. Results show that a higher low-pressure evaporation temperature and a higher vapor fraction at the low-pressure vapor generator are conducive to increasing the system cooling output. An optimal high-pressure evaporation temperature exists that gives the maximum exergy efficiency and the minimum sum unit cost of product. Compared with the net power output of the system, the cooling output is more sensitive to the variation of condensation temperature. Among the system components, the ejector has the highest exergy destruction rate and the lowest exergy efficiency. Furthermore, optimization of the system’s performance and working fluid selection for fixed cooling outputs was conducted. The results show that reducing the exergy destruction in the endothermic process is the key to improving system performance, while perfluoropropane was found to be the most suitable working fluid for the proposed system. In the cooling output range of 300–700 kW, a minimum sum unit cost of product of 45.79–58.87 $/MWh can be achieved, and corresponding ranges of net power output, energy efficiency and exergy efficiency are 614.93–430.58 kW, 14.32–19.25%, and 32.3–22.62%, respectively. Finally, the performance of the proposed system is compared with two typical systems for a cooling output range of 300–700 kW. The results show that the sum unit cost of product is reduced by 7.9–11.1%, and the net power output increased by 23.6–40.6% compared with the system with parallel vapor generators. Compared to the system with the ejector installed after the turbine, the sum unit cost of product is increased by 9.16–13.28%, and the net power output is increased by 129.73–118.38%.

Abstract This paper investigated a combined solar/air dual source heat pump water heater system for domestic water heating application. In the dual source system, an additional air source evaporator is introduced in parallel way based on a conventional direct expansion solar-assisted heat pump water heaters (DX-SHPWH) system, which can improve the performance of the DX-SHPWH system at a low solar radiation. In the present study, a dynamic mathematical model based on zoned lump parameter approach is developed to simulate the performance of the system (i.e. a modified DX-SHPWH (M-DX-SHPWH) system). Using the model, the performance of M-DX-SHPWH system is evaluated and then compared with that of the conventional DX-SHPWH system. The simulation results show the M-DX-SHPWH system has a better performance than that of the conventional DX-SHPWH system. At a low solar radiation of 100 W/m2, the heating time of the M-DX-SHPWH decreases by 19.8% compared to the DX-SHPWH when water temperature reaches 55 °C. Meanwhile, the COP on average increases by 14.1%. In addition, the refrigerant mass flow rate distribution in the air source evaporator and the solar collector of the system, the allocation between the air source evaporator and the solar collector areas and effects of solar radiation and ambient air temperature on the system performance are discussed.

Abstract In this paper, secondary solar action to biomass, focused on the conceptualized intersection of solar energy and biomass, is presented to illustrate how “breaking” of biomass to biofuels plus hydrogen can be utilized for the adaptation of Solar Thermal Electrochemical Process (STEP) chemistry. This Solar Thermal Electrochemical Process (STEP) system was designed and employed for the synergetic solar energy and corresponding chemistry to provide an action of biomass for efficient solar and biomass utilization - production of biofuels plus hydrogen. The control and modulation of solar fields and sub-chemical reactions were adopted to achieve a high utilization of solar energy, high chemical conversion rate, and high selectivity of the biomass to achieve rich biofuels and abundant hydrogen. The Solar Thermal Electrochemical Process (STEP) temperature of the breakdown reaction was greatly lowered by using electrolysis, as compared with the conventional pyrolysis. Based on their structural complexity and thermal stability, cellulose and lignin are well-suited for the production of biofuel and hydrogen. Through the coupling of thermolysis and electrolysis, the Solar Thermal Electrochemical Process (STEP) hydrogen production from cellulose was 7.2 times higher under a current of 100 mA and 8.8 times higher at 400 mA compared with pyrolysis at 200 °C. The Solar Thermal Electrochemical Process (STEP) lignin conversions were significantly improved by reaching 87.22%, 21.78%, 57.72%, and 7.22% (340 °C, 400 mA), while the pyrolysis achieved only 52.39%, 19.48%, 25.81%, and 7.10% (340 °C, 0 mA), respectively, for the total rate, solid, liquid, and gas fractions. With electrochemical synergy to help, the Solar Thermal Electrochemical Process (STEP) process efficiently and selectively produced gas hydrocarbons, liquid biofuel, and hydrogen. The light hydrocarbons in the gas phase, such as methane, ethane, and n-pentane, became more abundant via thermo-electrolysis. The Solar Thermal Electrochemical Process (STEP) chemistry for converting biomass to biofuels and hydrogen was also elucidated in this paper. The simplified mechanism can best be described by a series of thermo/electro-induced free radical reactions. The system, built on solar energy and specific chemical reactions, features a perfect, green, sustainable, and recyclable operation to transform solar biomass to biofuels and hydrogen.

Abstract Anaerobic Digestion (AD) is identified to be a promising method to address the dilemma of solid waste recycling, and biogas produced from AD has also been identified as an important alternative to fossil fuels, pertaining to energy crisis and climate change. As the applied technology of anaerobic digestion is fixed, required thermal energy for biogas production in an anaerobic digester varies dramatically with the ambient temperature. The conventional way is to combust the biogas on the spot for heat preservation in the digester, and the additional natural gas will be needed for supplement in colder area. To mitigate the consumption of fossil fuel and increase the amount of available biogas for bio-methane production, a hybrid system by integration of Concentrated PhotoVoltaic Thermal (CPVT) collectors and biogas upgrading technology is proposed. The heat produced from CPVT collectors is for heat preservation in the digester, and generated electric power is used in the biogas plant and biogas upgrading unit for bio-methane production. The annual performance analysis indicates that, comparing with the conventional design, the new design saves 2.6% amount of natural gas consumption, reduces 48.38% amount of electricity from power grid and increases 86.08% amount of biomethane production. Besides, the new design can supply 829.4 MWh electricity to the power grid in a year. This research provides a new way to utilize biogas by integration with solar utilization technologies.