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Abstract A novel dual functional heat pump and power generation integration system (DFHPPGIS) using a scroll machine as compressor and expander is proposed in this paper. It can be operated in both reverse Carnot cycle (RCC) heat pump mode and organic Rankine cycle (ORC) power generation mode. Compared with single system, this system can improve the utilization efficiency of geothermal water and generate more economic benefits. Three kinds of ORC and RCC working fluids are compared to select refrigerant R245fa as the most suitable fluid for the system. Then the model of DFHPPGIS is built to analyze its energy, exergy and economic performance as the variation of geothermal water inlet temperature. Results of theoretical calculation show that there is a conflict between total cost and payback period of the system. The system with lower total cost shows high payback period and vice versa. Thus, a multi-objective optimization for the system is conducted to determine the optimal geothermal water inlet temperature based on the ideal point decision making method. Exergy loss of the system under the optimal condition is analyzed to reveal which component has the largest exergy loss. The results indicate that in this proposed system, if the total cost based optimized design is chosen, payback period is 136.4% higher than its minimum value. If the method of payback period based optimized design is selected, total cost is 15.3% higher than its minimum value. The system has a heat capacity of 250.19 kW and a power output of 17.83 kW at the optimal geothermal water inlet temperature of 80℃ as well as the total cost and payback period of the system are 37.31 k$ and 4.87 years. In addition, the scroll machine has the largest exergy loss in both RCC and ORC mode, which is the component that needs to be mostly optimized in the further development.

Abstract This study proposed and investigated two novel absorption combined power and cooling cycles using ammonia-water as working fluids driven by low-grade heat sources. The two proposed systems which combined the Kalina cycle and the absorption refrigeration cycle were named the double-pressure series cycle (DSC) and the double-pressure parallel cycle (DPC) according to the different configurations. The thermodynamic and economic models were developed and then the combined system performances were evaluated. The results showed that, under given conditions, the exergy efficiency and the total exergy efficiency of DSC (34.44%, 24.63%) were higher than those of the DPC (30.05%, 23.81%), but the higher cost rate of DSC was achieved, which is 3.6% higher than DPC’s. Moreover, the parameter analysis showed that increasing the heat source temperature and the basic ammonia concentration has a positive effect on the thermodynamic performance of DSC and DPC, while increasing the separation pressure, rectification pressure and the pinch temperature difference led to performance degradation. Furthermore, the multi-objective optimization genetic algorithm (NSGA-Ⅱ) was employed to obtain the Pareto frontier, and the optimal solution was obtained through the comprehensive decision-making method (TOPSIS). The research results can provide references for the establishment and evaluation of innovative combined cycles driven by low-grade waste heat.

This study develops a multi-level programming model from a life cycle perspective for performing shale-gas supply chain system. A set of leader-follower-interactive objectives with emphases of environmental, economic and energy concerns are incorporated into the synergistic optimization process, named MGU-MEM-MWL model. The upper-level model quantitatively investigates the life-cycle greenhouse gas (GHG) emissions as controlled by the environmental sector. The middle-level one focuses exclusively on system benefits as determined by the energy sector. The lower-level one aims to recycle water to minimize the life-cycle water supply as required by the enterprises. The capabilities and effectiveness of the developed model are illustrated through real-world case studies of the Barnett, Marcellus, Fayetteville, and Haynesville Shales in the US. An improved multi-level interactive solution algorithm based on satisfactory degree is then presented to improve computational efficiency. Results indicate that: (a) the end-use phase (i.e., gas utilization for electricity generation) would not only dominate the life-cycle GHG emissions, but also account for 76.1% of the life-cycle system profits; (b) operations associated with well hydraulic fracturing would be the largest contributor to the life-cycle freshwater consumption when gas use is not considered, and a majority of freshwater withdrawal would be supplied by surface water; (c) nearly 95% of flowback water would be recycled for hydraulic fracturing activities and only about 5% of flowback water would be treated via CWT facilities in the Marcellus, while most of the wastewater generated from the drilling, fracturing and production operations would be treated via underground injection control wells in the other shale plays. Moreover, the performance of the MGU-MEM-MWL model is enhanced by comparing with the three bi-level programs and the multi-objective approach. Results demonstrate that the MGU-MEM-MWL decisions would provide much comprehensive and systematic policies when considering the hierarchical structure within the shale-gas system.

Abstract The effects of hot-water outlet temperature, compressor discharge pressure, compressor rotation speed, and expansion valve opening on the ejector and overall system performance were investigated for tap water outlet temperatures ranging from 50 to 90 °C. The coefficient of performance (COP) of the ejector–expansion heat pump system reaches 4.6 when the tap water outlet temperature is 70 °C, which is 10.3% higher than the corresponding basic cycle. Compared to the basic system, adding an ejector is more effective for the generation of high-temperature hot water. The COP of the ejector–expansion heat pump system increases; however, the COP improvement ratio ΔCOP decreases with the increase in the discharge pressure because of lower pressure lift ratio and ejector efficiency. The COP and ΔCOP increase when the compressor rotation speed decreases under our test conditions; simultaneously, the heat capacity decreases.

Abstract In this paper, a new geothermal combined cooling, heating and power system that integrates flash power cycle and ammonia-water absorption refrigeration cycle, is proposed to supply electricity, refrigerant water and domestic hot water simultaneously to users. In the system, the refrigeration cycle serves as the bottom cycle of the power cycle by further utilizing the exhausted geothermal water from the flasher of the power cycle, meanwhile all waste heat of the power and refrigeration cycles is recovered for supplying heat, thus effectively improving the energy conversion efficiency of whole system. This paper establishes detailed mathematical models of the proposed system and conducts a valid model validation. Then a preliminary design condition of the system is given and the results show that the exergy efficiency of system could reach 43.69% under the condition of 170 ℃ geothermal water. An exergy loss analysis is carried out based on the design condition, demonstrating that the maximal exergy destruction exists in the condenser of flash cycle, accounting for 48.53% of the total exergy destruction of the system; the components used for separating or mixing fluids including rectification column, absorber and flasher, occupying 17.68%, 9.02% and 9.30% respectively, are prone to generate exergy destructions. Finally a thermodynamic parameter analysis, in order to assess the effects of seven key parameters on the system performance, is performed. The results show that there are an optimal flash pressure (about 300 kPa) and an optimal generator temperature (about 120 ℃) respectively that could make the exergy efficiency of system maximal. Within some scopes, lower turbine back pressure and rectification column pressure, higher ammonia concentration of ammonia-strong solution, bring about higher exergy efficiency of system. Additionally the evaporation pressure and the reflux ratio of rectifier just make little difference on the exergy efficiency of system.

Abstract The drying characteristics and kinetics of Shengli lignite were investigated using four different drying methods, namely, the fluidized bed (FB), vibrated fluidized bed (VFB), medium fluidized bed (MFB), and vibrated medium fluidized bed (VMFB) methods, at various inlet air temperatures (80–160 °C). Seven thin layer models were used to analyze the lignite drying kinetics. The drying characteristics results showed that a higher temperature contributed to the drying process in all of the drying methods. Different drying methods also had significant effects on the drying characteristics and kinetics. The VMFB had the best drying characteristics with the shortest drying time and fastest drying rate. The Midilli–Kucuk model best simulated the lignite dewatering processes in all of the drying methods. Moreover, the VMFB obtained the fastest drying kinetics with the highest apparent diffusion coefficients and lowest activation energy.

Abstract To increase the photocatalytic reaction rate and make full use of electricity generated by photovoltaics (PV), a water purification system (SOL&PID) with solar and ultraviolet-light emitting diode (UV-LED) powered by a hybrid PV photocatalytic reactor was designed and tested in this paper. The SOL&PID system is based on Solar Water Purification and Renewable Electricity Generation system (SOLWAT). Photovoltaic and photocatalytic performances of SOL&PID system were evaluated in comparison with SOLWAT by the degradation of Acid Red 26 (AR 26) and 4-chlorophenol (4-CP) using suspended TiO2. To assess the directly-coupled performance between PV and UV-LED array, the power consumption percentage of UV-LED array from the maximum output power of PV was analyzed. The results show an adequate coupling between the UV-LED array and the photovoltaics. More than 92% of the maximum output power generated by PV modules is used to drive the LED array. The photocatalytic reaction rate constants in SOL&PID system increase respectively 29–37% and 31–78% during AR 26 and 4-CP experiments, in comparison with SOLWAT system. Besides, the SOL&PID system achieved lower solar module temperature and lower UV-LED pin temperature than the reference systems by the addition of flow channel.

Abstract Earth–air–pipe systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on numerical heat transfer and computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth–air–pipe systems. Superposition technology is used in the model, incorporating the natural ground temperature field and the turbulent air flow inside the buried pipe. The model developed is validated against experimental investigations on an experimental set-up in Southern China. Good agreement between simulated results and experimental data is obtained. The model is then implemented on the CFD (Computational Fluid Dynamics platform), PHOENICS, to evaluate the effects of the operating parameters (i.e. the pipe length, radius, depth and air flow rate) on the thermal performance and cooling capacity of earth–air–pipe systems. A daily cooling capacity up to 74.6 kW h can be obtained from an earth–air–pipe system installed in that region.

Abstract Co-combustion characteristics of refining and chemicals wastewater solid (RS) and Huolinhe lignite (HL) were studied through thermogravimetric analysis (TGA). The combustion behaviors of the blends at various RS to HL ratios were compared with those of the individual samples. Co-combustion experiments showed that the combustion performance of the blends would be improved with the percentage of RS rising. The interactions between RS and HL during the co-combustion could be divided into four phases, and there were no interactions below 120 °C (PH 1) and beyond 700 °C (PH 4), inhibitive effects at the temperature range of 120–700 °C (PH 2 and PH 3). The results of SEM and XRD indicated that the sintering and fusion degree of residues after combustion became more severe with the percentage of RS increasing. The iso-conversional methods, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), were used for the kinetic analysis of the combustion process. The results showed that the activation energy of RS was higher than that of HL, and the minimum value was obtained at 75HL/25RS.