1,721,004 research outputs found
IMPROVEMENT OF THE ENERGY MANAGEMENT OF THE GAS GRID IN FUTURE ENERGY SCENARIOS
Full text linkThe thesis aims at improving the energy management of the natural gas grid as a whole, focusing on both i) the possible opportunities of energy recovery and ii) the utilization of the grid as storage capacity of renewable energies. The basic motivation is to exploit completely this infrastructure in the transition phase fossil-to-renewable energy conversion system.
As regards energy recovery, the goal is to identify all possible solutions of energy recovery, both the more complex and costly ones based on expanders for power generation and the simpler and more inexpensive ones based on dissipation processes and aimed to avoid gas preheating. In the expander field, special focus is on micro-turbines where novel designs are proposed with the support of an original CFD analysis criterion and of an extended campaign of experiments. The new prototypes show a power output almost doubled in comparison with the current machines available in the market. On the other hand, novel solutions based on “smart throttling” are proposed, designed, and tested. Although these solutions dissipate the majority of the energy content of an expanding gas as the traditional throttling valves, they allow exploiting part of the available energy to avoid the preheating of natural gas or to produce small amounts of electricity. Considering Italy as a case of study, the study indicates that 90% of the energy consumptions for preheating can be avoided within acceptable return of investments even without financial incentives and with beneficial consequences for the environment.
As regards the utilization of the gas grid for renewable energy storage, the main goal is to verify the capability of the grid to store and transport “green gas”, and the practical mode of utilization in this circumstance. The analysis is performed at increasing share of renewable penetration to simulate possible realistic scenarios in the next future. Results supply a reliable spectrum of RES systems to be progressively installed by the time new restrictions imposed by the regulation will appear.
Overall, the thesis shows wide margins for improvement on the “energy recovery side”, where many solutions are available and economically feasible but mostly unexplored because of established technological “habits” and, perhaps, a scarce environmental sensitivity. On the “storage side”, the thesis traces interesting paths for the utilization of the gas network as conjunction node between RES generation and use. In spite of some necessary simplifying assumptions made at this step and the need to add all local constraints in the practical application of the proposed solutions, these paths have solid foundations and can be used to implement a general strategy for a faster transition to a renewable system. On the other hand, the utilization of the gas grid as storage capacity poses new challenges also on the energy recovery side, where the technologies must be adapted to the constantly evolving operation constraints.The thesis aims at improving the energy management of the natural gas grid as a whole, focusing on both i) the possible opportunities of energy recovery and ii) the utilization of the grid as storage capacity of renewable energies. The basic motivation is to exploit completely this infrastructure in the transition phase fossil-to-renewable energy conversion system.
As regards energy recovery, the goal is to identify all possible solutions of energy recovery, both the more complex and costly ones based on expanders for power generation and the simpler and more inexpensive ones based on dissipation processes and aimed to avoid gas preheating. In the expander field, special focus is on micro-turbines where novel designs are proposed with the support of an original CFD analysis criterion and of an extended campaign of experiments. The new prototypes show a power output almost doubled in comparison with the current machines available in the market. On the other hand, novel solutions based on “smart throttling” are proposed, designed, and tested. Although these solutions dissipate the majority of the energy content of an expanding gas as the traditional throttling valves, they allow exploiting part of the available energy to avoid the preheating of natural gas or to produce small amounts of electricity. Considering Italy as a case of study, the study indicates that 90% of the energy consumptions for preheating can be avoided within acceptable return of investments even without financial incentives and with beneficial consequences for the environment.
As regards the utilization of the gas grid for renewable energy storage, the main goal is to verify the capability of the grid to store and transport “green gas”, and the practical mode of utilization in this circumstance. The analysis is performed at increasing share of renewable penetration to simulate possible realistic scenarios in the next future. Results supply a reliable spectrum of RES systems to be progressively installed by the time new restrictions imposed by the regulation will appear.
Overall, the thesis shows wide margins for improvement on the “energy recovery side”, where many solutions are available and economically feasible but mostly unexplored because of established technological “habits” and, perhaps, a scarce environmental sensitivity. On the “storage side”, the thesis traces interesting paths for the utilization of the gas network as conjunction node between RES generation and use. In spite of some necessary simplifying assumptions made at this step and the need to add all local constraints in the practical application of the proposed solutions, these paths have solid foundations and can be used to implement a general strategy for a faster transition to a renewable system. On the other hand, the utilization of the gas grid as storage capacity poses new challenges also on the energy recovery side, where the technologies must be adapted to the constantly evolving operation constraints
EFFECTS OF BLADE SOLIDITY AND ASPECT RATIO ON A 0.5 HUB-TO-TIP RATIO TUBE-AXIAL FAN
Full text linkSolidity and aspect ratio are the two geometrical parameters bridging the fan preliminary sizing with the blade aerodynamic design. In a previous work, the topic has been investigated by experimental testing of 16 propeller fans with 0.2 hub-to-tip ratio, all designed for approximately 0.075 flow rate coefficient and 0.008 pressure coefficient. As a further research step, this paper investigates the influence of solidity and aspect ratio on the global aerodynamic performance of 0.5 hub-to-tip ratio tube-axial fan rotors. Aim of the work is twofold: first, to extend the aerodynamic performance data set of comparable axial-flow industrial fans characterised by different blade solidity and aspect ratio; second to investigate by experiments the role of the hub-to-tip ratio on the effects of the two design parameters. To this end, 18 additional fans with 0.5 hub-to-tip ratio were designed and tested according to ISO-5801, and the collected data were compared to those already available from the 16 fans with 0.2 hub-tip ratio. The results confirm that the aerodynamic performance at best efficiency operation is primarily set by the hub-to-tip ratio. Solidity plays a role comparable to the hub-to-tip ratio only within the minimum-to-low solidity range, whereas the aspect ratio contributes to the fan efficiency – in high hub-to-tip ratio designs only – and to the best efficiency flow rate coefficient – in low hub-to-tip ratio designs only
Experimental analysis of a novel Savonius based spline geometry with flexible blades for Vertical Axis Wind Turbines (VAWT)
No full textCurrently, the wind-power market is dominated by Horizontal Axis Wind Turbines (HAWT) owing to
their high efficiency. Vertical Axis Wind Turbines (VAWT) are far behind in popularity. However, the
interest for future applications of vertical axis wind rotors is increasing because of the simple geometry,
low cost, low sensitivity to turbulent flow conditions and simple and affordable maintenance. Thus, an
improvement in the efficiency of vertical rotors could close the existing gap and make HAWT more
attractive as wind energy conversion devices. In this paper, a new blade spline concept of Savonius
rotor with flexible blades is studied experimentally. The idea is to check the performance improvements
previously achieved by computational CFD simulations. Two Savonius rotors were built using fiber
glass: a rigid rotor with a spline blade shape and a flexible one with the same blade shape but with a
morphing section located at the blade’s tips. Important improvements were registered using the flexible
rotor compared to the same but rigid rotor, in a large working conditions range, validating the CFD
simulation results. The low speed wind tunnel at San Diego State University was utilized for the tests
considering a wind speed in the range of 3.5 to 9.5 m/s. A combined analysis of performance and
flexibility was also performed to find the deformation associated with the best performance for this kind
of rotor. Finally, a comparison was made between the energy conversion of the rigid and flexible rotors
at low wind speed for a possible urban application. Results show a 50% power coefficient improvement
for the flexible rotor compared to the rigid one at the most optimum working condition. A 90% increase
of energy produced by the flexible rotor during one year in the city of San Diego was calculated.
Eventually the most productive wind speed for the flexible rotor was found to be 9m/s. Thus, the
deformation angle obtained at that value (22°- 32°) was considered as the best deformation for this
kind of rotor
Effect of Solidity and Aspect Ratio on the Aerodynamic Performance of Axial-Flow Fans With 0.2 Hub-to-Tip Ratio
No full textAspect ratio and solidity play complementary roles in the aerodynamic design of axial fan rotor blades. Few studies have experimented the effect of the aspect ratio of rotor blades on the performance of low-speed axial fans or its interaction with blade solidity in terms of fan aerodynamic performance. This study examined the selection of the solidity and blade aspect ratio in the preliminary design of low-pressure industrial fans with minimized hub-to-tip ratios. The aim of this study was to make available to the fan community experimental data that allow the determination of the optimal aspect ratio for practical applications as a function of the blade solidity. Various aspects of the performance of 16 prototypes
of a 315-mm-diameter propeller fan were compared. The industrial fan prototypes all had a hub-to-tip ratio of 0.2 and were derived from four baseline designs conceived to ideally achieve the same best efficiency operation with different values of the aspect ratio. In addition, the prototypes’ assemblies were conceived to allow operation with different blade counts, i.e., with different rotor solidities at a fixed blade aspect ratio. The aerodynamic performance of the fans, measured in accordance with the ISO-5801 standard, was evaluated to assess the sensitivity and trends of the fan pressure and efficiency with respect to the
blade aspect ratio and solidity at fixed tip clearance. The measured effects of the aspect ratio and solidity are discussed on the basis of data available in the literature. The results of the experimental analysis were used to formulate general guidelines for the preliminary design of propeller fans with minimized hub-to-tip ratios
Supercritical CO2 and air Brayton-Joule versus ORC systems for heat recovery from glass furnaces: Performance and economic evaluation
No full textThis paper evaluates the thermodynamic and economic performance of four different heat recovery systems (HRSs) applied to two hollow glass furnaces providing 1.2 to 4 MWt of wasted heat at 450°C. Organic Rankine Cycle (ORC), two configurations of supercritical CO2 Brayton-Joule cycle (sCO2) and an innovative regenerative air Brayton-Joule cycle generating compressed air and/or power are modeled at both design and off-design conditions. The aim is to find the most commercially attractive HRS for the considered glass furnaces, as representative of small-to-medium size ones, taking into account all physical and technological constraints. The optimized designs of all systems are first obtained by identifying “average” heat recovery conditions from real data. Off-design simulations are then conducted to predict the behavior of the HRSs considering ambient temperature variations and furnaces ageing process. Results show that the ORC systems are the most attractive HRS available in the market for small-size furnaces while the air Brayton-Joule cycle appears to be the best choice when bigger furnaces are
considered. On the other hand, the sCO2 cycle systems show the highest power output in the whole range of furnace sizes while being still penalized by the too high costs deriving by their early-stage precommercialization
phase
Thermodynamic evaluations on the potential energy recovery from the Italian natural gas network
Full text linkA novel micro-cogeneration unit for market applications based on a biomass-fired ORC system
No full textIn the transition towards smart grid systems, a problem of increasing importance is the distributed generation of thermal and electric power at low cost and low environmental impact. This work proposes a novel cogeneration system based on a biomass boiler and a micro-Organic Rankine Cycle (ORC) unit. The biomass boiler heats up an unpressurised thermal oil circuit, which, in turn, supplies heat to an ORC unit that produces electricity and hot water for the users. The ORC system is based on a single-pressure regenerative cycle that works in the subcritical region. The goal of this study is twofold: i) the analysis of the design choices that were made to achieve a good compromise between efficiency and cheapness of the micro-CHP system, and ii) the performance evaluation of the system for variations of key parameters, such as temperature and flow rate of the thermal oil, mass flow rate of the cooling water and operational assets of the ORC unit. An in-depth experimental campaign has been carried out, where the rotational speeds of the pump and expander of the ORC unit have been varied to choose first the best operating asset, and then investigate the influence of the other key parameters. The best combination of the speeds has been identified as 2250 rpm for the pump and 2300 rpm the expander. In these conditions, maximum values of electrical efficiency (7.4%) and total energy utilization factor (62%) are found. With an oil temperature of about 150°C, the achieved power production is 2530 W, the ORC utilization factor 93% and the expander global efficiency 57%. Simplicity and low specific cost contribute to increase the efficiency-to-cost ratio, making this novel system appealing for the customer
A common thread in the evolution of the configurations of supercritical CO2 power systems for waste heat recovery
Full text linkPerformance and economic comparison of heat recovery systems for regenerative glass furnaces
No full textGlass industry produces a large amount of medium temperature flue gas that is commonly released to the atmosphere after it has been filtered. This paper summarizes the thermodynamic and economic performance of three different heat recovery systems applied to an existing hollow glass furnace with a production capacity of 150 ton/day, which generate electricity and the compressed air required by the furnace. The aim is to find the best commercially attractive system for medium temperature heat recovery. Different configurations of Organic Rankine Cycles (ORC), supercritical CO2 Brayton cycle and an innovative regenerative air Brayton cycle are modeled, optimized and compared. The economic analysis is then performed using the module costing technique. ORC systems working with cyclopentane results the best choice for the case study. It shows a Return of Investment (ROI) lower or equal than five years, which makes this system commercially attractive. The utilization of the air Brayton cycle is effective only when the efficiencies of the turbomachinery are very high. The system configuration including a supercritical CO2 Brayton cycle and a preheating system of the furnace combustion air shows higher performance than the ORC system but also higher cost (ROI is higher than five years). However, results show also that sCO2 cycle is a promising technology that could overcome the ORC cycle performance for medium to high temperature heat sources and medium to large flue gas mass flow rates
Collection Efficiency of Cyclone Separators: Comparison between New Machine Learning-Based Models and Semi-Empirical Approaches
Full text linkCyclones are employed in many waste treatment industries for the dust collection or abatement purposes. The prediction of the dust collection efficiency is crucial for the design and optimization of the cyclone. However, this is a difficult task because of the complex physical phenomena that influence the removal of particles. Aim of the paper is to present two new meta-models for the prediction of the collection efficiency curve of cyclone separators. A Backpropagation Neural Network (BPNN) and Support Vector Regression (SVR) models were developed using Python environment. These were trained with a set of experimental data taken from the literature. The prediction capabilities of the models were first assessed by comparing the estimated collection efficiency for several cyclones against the corresponding experimental data. Second, by comparing the collection efficiency curves predicted by the models and those obtained from classic models available in the literature for the cyclones included in the validation dataset. The BPNN demonstrated better predictive capability than the SVR, with an overall mean squared error of 0.007 compared to 0.015, respectively. Most important, a 40% to 90% accuracy improvement of the literature models predictions was achieved
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