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Abstract Waste heat recovery has attracted a significant attention because of the world growth in energy demand. In this paper, we report the study on an energy recovery system utilizing low-grade waste heat below 100 °C. This system called a thermal-driven electrochemical generator is composed of reverse electrodialysis (RED) power generation and thermal separation using waste heat. We especially focus on the experimental characterization of the RED process with ammonium bicarbonate (NH4HCO3) solution, which is known to be easily decomposed at the temperature around 60 °C. We characterized this NH4HCO3-RED system with various parameters including the concentration difference, the membrane type, the inlet flow rate, and the compartment thickness. We found the best power density at the concentrated solution of 1.5 mol L−1 and the diluted solution of 0.01 mol L−1. The maximum power density increases as the inlet flow rate increases or the compartment thickness decreases owing to the decrease in the internal resistance. We obtained the excellent power density of 0.77 W m−2, compared with the previous studies.

Abstract Waste heat recovery has attracted a significant attention because of the world growth in energy demand. In this paper, we report the study on an energy recovery system utilizing low-grade waste heat below 100 °C. This system called a thermal-driven electrochemical generator is composed of reverse electrodialysis (RED) power generation and thermal separation using waste heat. We especially focus on the experimental characterization of the RED process with ammonium bicarbonate (NH4HCO3) solution, which is known to be easily decomposed at the temperature around 60 °C. We characterized this NH4HCO3-RED system with various parameters including the concentration difference, the membrane type, the inlet flow rate, and the compartment thickness. We found the best power density at the concentrated solution of 1.5 mol L−1 and the diluted solution of 0.01 mol L−1. The maximum power density increases as the inlet flow rate increases or the compartment thickness decreases owing to the decrease in the internal resistance. We obtained the excellent power density of 0.77 W m−2, compared with the previous studies.

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 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.

A thermoelectric distillation system has recently been demonstrated to have a great potential of improving the efficiency of distillation processes due to the use of waste heat from the hot side of thermoelectric module to assist evaporation while the cold side for condensation. This work investigates the key factors that affect the water production in a thermoelectric distillation system. An experimental investigation was performed to investigate the influence of evaporation temperature, vapour volume, Peltier current and input power on the water production rate. The results of the experiment show that an increase in the sample water temperature from 30 °C to 60 °C led to an increase in total water production by 47%. In addition, an increase in total water production by 58% was obtained by reducing the vapour volume from 600 cm3 to 400 cm3 during a 3-h operation. The maximum water production rate is achieved by appropriate selection and control of the Peltier current to the thermoelectric device based on the operating condition of the distillation system.

A thermoelectric distillation system has recently been demonstrated to have a great potential of improving the efficiency of distillation processes due to the use of waste heat from the hot side of thermoelectric module to assist evaporation while the cold side for condensation. This work investigates the key factors that affect the water production in a thermoelectric distillation system. An experimental investigation was performed to investigate the influence of evaporation temperature, vapour volume, Peltier current and input power on the water production rate. The results of the experiment show that an increase in the sample water temperature from 30 °C to 60 °C led to an increase in total water production by 47%. In addition, an increase in total water production by 58% was obtained by reducing the vapour volume from 600 cm3 to 400 cm3 during a 3-h operation. The maximum water production rate is achieved by appropriate selection and control of the Peltier current to the thermoelectric device based on the operating condition of the distillation system.

Abstract There is an enormous untapped potential for hydropower generation in rivers with large head and high flow variation, currently not feasible for conventional hydropower dams. Conventional dams make use of the potential energy, but waste kinetic energy from spillage during periods of high flows. This article studies the possibility of harnessing energy from potential and kinetic energy from hydropower dams with large head and flow variation, analyses its potential, and shows possible technologies. Focus is given to a Moveable Hydro-Electric Power Plant (HEPP) system in which the turbine module can be adjusted according to the flow and water level in the river. During floods the exceeding flows can pass above and below the Moveable HEPP results in a sub-pressure environment after the turbine module, thereby reducing the dam’s downstream head, increasing the pressure difference between the turbine inlet and outlet and the flow through the turbine, which increases the electricity generation of the dam. Dams with head increaser arrangement have been implemented in several dams in the 1930–1950s and now are regaining attention in Middle Europe. The main intention for its implementation is harnessing hydropower generation at run-of-river plants, with low-head, with a 20%–30% cost reduction, lower flooded area at the dam site, the resulting evaporation and the impact on the aquatic fauna. A case study was performed with the proposal of the Aripuana Moveable HEPP in the Madeira River with a 26 ms height dam and a generation capacity of 1400 MW. The increase in generation with the head increaser effect is as high as 21%. The estimated potential for this technology in the Amazon region is 20 GW. Other potential locations are discussed in the article. Dams with head increaser effect have been successfully implemented and have the potential to become a major alternative for base load renewable energy in the future.

Abstract There is an enormous untapped potential for hydropower generation in rivers with large head and high flow variation, currently not feasible for conventional hydropower dams. Conventional dams make use of the potential energy, but waste kinetic energy from spillage during periods of high flows. This article studies the possibility of harnessing energy from potential and kinetic energy from hydropower dams with large head and flow variation, analyses its potential, and shows possible technologies. Focus is given to a Moveable Hydro-Electric Power Plant (HEPP) system in which the turbine module can be adjusted according to the flow and water level in the river. During floods the exceeding flows can pass above and below the Moveable HEPP results in a sub-pressure environment after the turbine module, thereby reducing the dam’s downstream head, increasing the pressure difference between the turbine inlet and outlet and the flow through the turbine, which increases the electricity generation of the dam. Dams with head increaser arrangement have been implemented in several dams in the 1930–1950s and now are regaining attention in Middle Europe. The main intention for its implementation is harnessing hydropower generation at run-of-river plants, with low-head, with a 20%–30% cost reduction, lower flooded area at the dam site, the resulting evaporation and the impact on the aquatic fauna. A case study was performed with the proposal of the Aripuana Moveable HEPP in the Madeira River with a 26 ms height dam and a generation capacity of 1400 MW. The increase in generation with the head increaser effect is as high as 21%. The estimated potential for this technology in the Amazon region is 20 GW. Other potential locations are discussed in the article. Dams with head increaser effect have been successfully implemented and have the potential to become a major alternative for base load renewable energy in the future.

Abstract Oil reservoirs are deep underground, with the oil and gas contained in porous rock at high temperatures and pressures. Around 5 – 20%, of the oil can be produced from the field under its own pressure (primary production), but in most fields water is injected to displace the oil. This still leaves at least 50% of the oil behind in the reservoir. Further recovery can be obtained by injecting carbon dioxide that both displaces and dissolves the remaining oil. At least 71 projects worldwide use CO2 flooding and produce a total of over 170 000 barrels of oil a day, worth around $1.3 billion a year. The cost of producing an extra barrel of oil ranges from $5 to $8 and thus is profitable at the present price of nearly $20 a barrel. In the majority of these cases, the carbon dioxide comes from natural underground sources and is piped to the oil field. The potential use of CO2 flooding would be considerably greater, if large quantities of the gas, extracted from power stations, were available at low cost. For every kilogramme of CO2 injected, approximately one to one quarter of a kilogramme of extra oil will be recovered. For most projects about as much carbon dioxide is disposed of in the reservoir as is generated when the oil is burnt. When CO2 is at a sufficiently high pressure to form mixtures with the crude oil that are miscible in laboratory tests, up to 40% of the oil remaining in the field after water flooding can be recovered. Approximately half the water flooded oil fields in the US could be exploited profitably by CO2 injection. Carbon dioxide flooding of the larger North Sea fields is a particularly attractive prospect, because the crude oil is light (composed of low molecular weight hydrocarbons) and the geology of the reservoirs is less heterogeneous than the American fields. A profitable project would be possible if the gas could be provided and piped to the reservoir at a cost of around $3.50 per thousand cubic feet or less.