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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.

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 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.

Abstract Sustainability is an important and difficult consideration for the stakeholders/decision-makers when planning a biofuel supply network. In this paper, a Mixed-Integer Non-linear Programming (MINLP) model was developed with the aim to help the stakeholders/decision-maker to select the most sustainable design. In the proposed model, the emergy sustainability index of the whole biodiesel supply networks in a life cycle perspective is employed as the measure of the sustainability, and multiple feedstocks, multiple transport modes, multiple regions for biodiesel production and multiple distribution centers can be considered. After describing the process and mathematic framework of the model, an illustrative case was studied and demonstrated that the proposed methodology is feasible for finding the most sustainable design and planning of biodiesel supply chains.

Abstract Advanced energy conversion systems on biomass-based are essential for high-efficient utilization of biomass energy. This work proposed a conceptual biomass liquefaction system with supercritical water for combined bio-oil, power and heating trigeneration. Both thermodynamic and life cycle environmental assessment are performed to verify the potential benefits of this novel system. Mass flow in the overall process is configured using Aspen Plus, with detailed energy and exergy flow modelling for the whole system. At the optimal operation parameters, where reactor temperature and pressure are around 390°C and 25 MPa, feedstock concentration is ∼33.3 wt%, water recycle ratio is ∼50%, and gas combustor temperature is about 1000°C, system energy and exergy efficiency reach their highest values, i.e. 58.53% and 50.65%, which are comparable to those of other biomass-based energy conversion system. Effects of those key parameters on exergy and energy efficiency are also discussed. The maximum exergy loss is induced by chemical exergy loss in liquefaction reactor and energy loss is mainly caused by heat transfer. From environmental assessment, GWP, AP, EP and TP values at the optimal operation parameters are lower than those of other biomass-based liquefaction system. When CCS and wastewater treatment units are applied, GWP, AP and EP values can be reduced by 50.0%, 33.2% and 61.5%, respectively. The comparison of thermodynamic and environmental performance among different biomass-based energy conversion systems shows that biomass liquefaction with SCW is a relatively efficient and clean technology to produce carbon-neutral bio-oil.

Abstract Methanol is considered a favorable renewable fuel for use in diesel engines owing to its advantageous features including sustainability, accessibility, and reasonable price. However, some drawbacks, such as the phase separation problem, low cetane number, and high latent heat of vaporization, hinder its utilization in diesel engines. This study attempted to improve the usability of methanol in diesel engines using n-octanol and diethyl ether as cosolvents and ignition improvers. The experimental part was divided into two stages. First, the stabilities of pure methanol and hydrous methanol, with waste cooking oil biodiesel as a base fuel, were investigated under different temperatures: 10 °C, 20 °C, and 30 °C. The results demonstrated that the pure methanol/waste cooking oil biodiesel mixtures remained stable at all temperatures. To improve the solubility of the hydrous methanol/waste cooking oil biodiesel blends, n-octanol was applied as a cosolvent. Next, the engine combustion and emission features were assessed using three ratios of pure methanol/waste cooking oil biodiesel blends with n-octanol and diethyl ether additives. The three combinations included 15%, 25%, and 35% methanol with 10% n-octanol and 2.5% diethyl ether. The waste cooking oil biodiesel was produced via the transesterification method, and the final product was characterized using Fourier transform infrared spectroscopy, gas chromatography–mass spectrometry, and thermogravimetric analysis. The fuels were evaluated via thermogravimetric analysis, and their physicochemical properties were determined according to the American Society for Testing and Materials standards. The highest cylinder pressure, heat release rate, and pressure rise rate were lower for the methanol/waste cooking oil biodiesel/n-octanol/ diethyl ether blends compared with the waste cooking oil biodiesel. In addition, the thermal efficiency reduced, while the brake specific fuel consumption increased for the mixtures compared with the waste cooking oil biodiesel. Relative to engine emissions, the nitrogen oxide levels also reduced, while the carbon monoxide and smoke opacity increased for the combinations compared with the waste cooking oil biodiesel.

Abstract The combined heat and power system is a highly efficient energy source for many applications because heat and power are often of high demand. Although fuel cells and thermoelectric generators are popularly known to be used separately for combined heat and power purposes, there is little research on combining these two components for this application. This research proposes to analyze the hybrid fuel cell and thermoelectric system specifically when it is used as a combined heat and power system – thus forming a newly proposed fuel cell and thermoelectric combined heat and power (FC-TE-CHP) system. The key idea is to use the thermoelectric device to further improve the exergetic and temperature performance of the conventional fuel cell based combined heat and power (FC-CHP) system. Both systems are analyzed and compared by using a steady state thermodynamic model from both the temperature and exergetic perspectives. The exergetic efficiency and temperature results are reported by performing parametric sweeps of several key parameters such as fuel cell stack electric power, operation in thermoelectric cooler mode, water mass flow rate and radiator air convection coefficient. Subsequently, recommendations on how the FC-TE-CHP system can be operated efficiently in terms of exergy are drawn.