• Energy Research
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The increasing depletion of natural resources, combined with a wider set of pressures on the environment, has, in recent years, highlighted the need for a more efficient use of energy and a development process that involves alternative energy sources. Energy efficiency has received much attention as a solution, implying both monetary and emissions savings. However, the latter may be partially offset by the income and demand effects of the former, both in more efficient sectors and in spreading to the wider economy. This is the problem of rebound effects. Taking Spain as a case study, and introducing an energy-related CGE model that develops the inclusion of renewables, this paper evaluates a combination of efficiency initiatives to deliver both reduced energy use by households and a more sustainable supply of energy. Our findings suggest that a package aimed at improving efficiency in household electricity and petroleum use, combined with a more competitive supply of energy from renewable sources, may be the only way to get reductions in all energy use, and thus benefit the economy. Specifically, we consider how this package may lead to positive economic impacts and associated rebound effects, where the latter are focused on a greener energy supply.

Abstract The residential sector accounts for most of energy-consumption in developing countries in the form of traditional energy. The use of commercial energy is nominal and confined mostly to urban areas where fuelwood is already monetized. A model, based on an end-use/process analysis approach, is developed on a spreadsheet, which is capable of simulating scenarios to address issues of increasing traditional energy-demand caused by population growth, sustainable supply capacity of the existing energy resources, potential for development of new and renewable energy resources, technology. This paper is divided into two parts: general energy issues and the modelling approach, and the application of this approach to Nepal in the context of fuelwood-supply sustainability.

Abstract One of the most important research areas searches for new sources of energy and for the highest efficiency from existing energy sources. Radio frequency (RF) energy harvesting is a promising alternative to obtain energy for wireless devices directly from RF energy sources in the environment. In this paper, we provide a broad overview of the main blocks of RF energy harvesting systems, which are the wireless transmission medium, the antenna and impedance matching circuit, the rectifier, the voltage multiplier, and the energy storage device or load. The characteristics of these blocks directly affect the performance of an RF energy harvesting system. We mainly focus on the ratio of output and input powers at each block, named as the conversion efficiency and the impedance matching efficiency, which determines the overall efficiency of system. We present detailed information about the system parameters. Thus, we characterize an RF energy harvesting system, which makes the design of system possible to obtain the maximum efficiency and correspondingly the maximum output power, providing the necessary insight about the design of RF energy harvesting systems.

Abstract Small-scale hydroelectric plants, primarily run-of-the-river designs, are regularly subjected to hard particle wear and cavitation erosion due to the wide range of operating points. Depending on the severity of the operating conditions and erosion damage experienced by the machine throughout its service life, the operating companies of these facilities will be impacted. The impact will be technical, operational, logistical, and economic. A small-scale generation plant located in Amaime River in Colombia, is one such case, where severe wear occurs in the turbine components, with a consequent reduction of efficiency. In this study, the analysis of the erosion damage has been expanded and supplemented by computational fluid dynamics (CFD). From this approach, correlations between the wear rate and power output were obtained. Likewise and in conjunction with the computer estimates, a methodology to analyse the costs associated with wear based on historical data of operation was developed, creating a strategy of operation based on a stopping criterion that depends primarily on sediment concentration, turbinated flow, and wear level. The methodology optimizes the use of generators, which takes into consideration the revenue generation and the costs associated with operation and maintenance of pieces under conditions of intrinsic erosion wear in the facility.

Abstract Liquefaction of poly-isoprene based rubber (PIR) was performed using ethanol as a solvent for the production of liquid fuel and chemicals. An autoclave batch reactor was used to perform the ethanolysis of PIR at different temperature ranges (250–375 °C), with different ethanol to PIR ratio (0.5:1 to 4:1), and at different reaction times (15–75mins). The experimental results showed that a maximum yield of 86 wt % was achieved at temperature of 325 °C, ethanol to PIR ratio 1/1, and reaction time of 30 min. This liquid oil yield is about 14% higher than the yield obtained from the pyrolysis of PIR at 500 °C and about 10% higher than the yield obtained from hydrothermal liquefaction of PIR at 375 °C. Moreover, the utilization of ethanol in the process was also incorporated and product yields were redefined. Furthermore, ethanol contributed to enhance the quality of liquid-oil, particularly in term of viscosity, acidity, and energy density. Furthermore, the FTIR analysis showed methyl and methylene were most dominating functional groups found in the liquid product and GCMS analysis identified that they were presented by alkenes, aromatics, and alkyls.

Abstract For a fixed bed gasifier, coal gas is mainly derived from dry distillation zone and gasification zone. The upstream gas from gasification zone will inevitably affect the composition and production of dry distillation gas. Therefore, the composition of upstream gas and the reaction conditions of dry distillation zone were simulated to perform experiments of Yining coal pyrolysis under a series of atmospheres. Some new discoveries are obtained. H2O and the hydrogen-containing gas have a significant impact on the release of dry distillation gas. H2O inhibits the release of CO, CO2 and CH4, but promotes the release of H2 which is not from char−H2O gasification. When the hydrogen-containing gas passes through dry distillation zone, the path of stabilizing radicals is completely changed, resulting in that coal pyrolysis changes from a process of generating H2 under inert atmosphere to a process of consuming a large amount of H2. In addition, water gas shift reaction is the only homogeneous reaction observed obviously in dry distillation zone, which can promote the production increase of CO2, but can not prevent the production decrease of H2 in coal gas.

Abstract The supercritical power plant analyzed in this paper consists of the following elements: a steam turbine, a hard-coal-fired oxy-type pulverized fuel boiler, an air separation unit with a four-end-type high-temperature membrane and a carbon dioxide capture unit. The electrical power of the steam turbine is 600 MW, the live steam thermodynamic parameters are 650°C/30 MPa, and the reheated steam parameters are 670°C/6 MPa. First of all the net efficiency was calculated as functions of the oxygen recovery rate. The net efficiency was lower than the reference efficiency by 9–10.5 pp, and a series of actions were thus proposed to reduce the loss of net efficiency. A change in the boiler structure produced an increase in the boiler efficiency of 2.5–2.74 pp. The range of the optimal air compressor pressure ratio (19–23) due to the net efficiency was also determined. The integration of all installations with the steam turbine produced an increase in the gross electric power by up to 50.5 MW. This operation enabled the replacement of the steam regenerative heat exchangers with gas–water heat exchangers. As a result of these alterations, the net efficiency of the analyzed power plant was improved to 5.5 pp less than the reference efficiency.

Abstract The absorption refrigeration system driven by low grade heat sources, especially the waste heat sources, becomes more and more attractive in recent decades. However, most traditional absorption systems cannot achieve a high utilization rate of the waste heat with limited heat capacity. These systems are usually designed to obtain heat in the generator, which means that the waste heat sources cannot be utilized to the temperature lower than the generator temperature. This paper proposed a new structure heated by heat conduction oil in the generator and electric heating rings around the stripping section. This structure can simulate the temperature-distributed heat sources when the electric heating rings work. It can also simulate a traditional generator when the electric heating rings do not work. Influences of different heat distributions are analyzed in detail in this paper. The results show that the heat sources utilization rate will increase with the increase of the heat in the stripping section, while the coefficient of performance will be negatively affected by the increasing heat in the stripping section. By optimizing the heating structure, the coefficient of performance can be similar to that of a traditional system when the heat is just added in the middle and lower part of stripping section. The optimum utilization rate of heat sources in this test model can reach 1.8 times to that of a traditional system. Under this heating model, the lowest temperature required in the heating section is 82 °C when the heat conduction oil inlet temperature is 169 °C. It is much lower than the temperature inside the generator, which is 137.3 °C.

Abstract For biomass/waste fueled power plants, stricter regulations require a further reduction of the negative impacts on the environment caused by the release of pollutants and withdrawal of fresh water externally. Flue gas quench (FGQ) is playing an important role in biomass or waste fueled combined heat and power (CHP) plants, as it can link the flue gas (FG) cleaning, energy recovery and wastewater treatment. Enhancing water evaporation can benefit the concentrating of pollutant in the quench water; however, when FG condenser (FGC) is not in use, it results in a large consumption of fresh water. In order to deeply understand the operation of FGQ, a mathematic model was developed and validated against the measurements. Based on simulation results key parameters affecting FGQ have been identified, such as the flow rate and temperature of recycling water and the moisture content of FG. A guideline about how to reduce the discharge of wastewater to the external and the withdrawal of external water can be proposed. The mathematic model was also implemented into an ASPEN Plus model about a CHP plant to assess the impacts of FGQ on CHP. Results show that when the FGC was running, increasing the flow rate and decreasing the temperature of recycling water can result in a lower total energy efficiency.

Abstract Variable electricity generation from wind and solar influences the design of a cost-efficient and reliable energy system. This paper presents a method that uses stochastic programming to represent variable renewable electricity generation in long-term energy system models, and demonstrates this on a Norwegian TIMES model. First, we derive hourly PV- and wind-generation data by modifying satellite-based data, based on a comparison with historical generation data. Second, the satellite-based dataset is transformed into a manageable set of scenarios that is used as an input to the stochastic energy-system model. This is done using six different scenario generation methods. Third, we solve the energy-system model with three of the scenario-generation methods and evaluate the quality of the corresponding model value by stability tests. We demonstrate that scenarios generated from the six methods have significantly different moment-based and Wasserstein distance error relative to the dataset. Further, the energy system model results show that the number of scenarios needed to achieve stability differs between the three used scenario generation methods.