In recent years, pumps operated as turbines (PaTs) have been gaining the interest of industry and academia. For instance, PaTs can be effectively used in micro hydropower plants (MHP) and water ...distribution systems (WDS). Therefore, further efforts are necessary to investigate their fluid dynamic behavior. Compared to conventional turbines, a lower number of blades is employed in PaTs, lowering their capability to correctly guide the flow, hence reducing the Euler’s work; thus, the slip phenomenon cannot be neglected at the outlet section of the runner. In the first part of the paper, the slip phenomenon is numerically investigated on a simplified geometry, evidencing the dependency of the lack in guiding the flow on the number of blades. Then, a commercial double suction centrifugal pump, characterized by the same specific speed, is considered, evaluating the dependency of the slip on the flow rate. In the last part, a slip factor correlation is introduced based on those CFD simulations. It is shown how the inclusion of this parameter in a 1-D performance prediction model allows us to reduce the performance prediction errors with respect to experiments on a pump with a similar specific speed by 5.5% at design point, compared to no slip model, and by 8% at part-loads, rather than using Busemann and Stodola formulas.
In the next few years, even though there will be a continuous growth of renewables and a loss of the share of fossil fuel, energy production will still be strongly dependent on fossil fuels. It is ...expected that coal will continue to play an important role as a primary energy source in the next few decades due to its lower cost and higher availability with respect to other fossil fuels. However, in order to improve the sustainability of energy production from fossil fuels, in terms of pollutant emissions and energy efficiency, the development of advanced investigation tools is crucial. In particular, computational fluid dynamics (CFD) simulations are needed in order to support the design process of low emission burners. Even if in the literature several combustion models can be found, the assessment of their performance against detailed experimental measurements on full-scale pulverized coal burners is lacking. In this paper, the numerical simulation of a full-scale low-NO x , aerodynamically-staged, pulverized coal burner for electric utilities tested in the 48 MW th plant at the Combustion Environment Research Centre (CCA - Centro Combustione e Ambiente) of Ansaldo Caldaie S.p.A. in Gioia del Colle (Italy) is presented. In particular, this paper is focused on both devolatilization and char burnout models. The parameters of each model have been set according to the coal characteristics without any tuning based on the experimental data. Thanks to a detailed description of the complex geometry of the actual industrial burner and, in particular, of the pulverized coal inlet distribution (considering the entire primary air duct, in order to avoid any unrealistic assumption), a correct selection of both devolatilization and char burnout models and a selection of suited parameters for the NO x modeling, accurate results have been obtained in terms of NO x formation. Since the model parameters have been evaluated a priori, the numerical approach proposed here could be suitable to be applied as a performance prediction tool in the design of pulverized coal burners.
Como consequência da pandemia da COVID-19 foram observadas reduções nas concentrações de dióxido de nitrogênio (NO2) na atmosfera em diversos países, pois esse gás está altamente relacionado à queima ...de combustíveis fósseis provenientes de meios de transportes. O objetivo deste trabalho é identificar as mudanças no padrão de emissão de NO2 associadas às medidas de restrição de circulação e confinamento durante a pandemia, nas áreas urbanas de Brasília (DF), Anápolis e Goiânia (GO). Coletamos dados de NO2 troposférico, por meio do sensor TROPOMI, do satélite Sentinel-5P, e dados de precipitação por monitoramento de satélite provenientes da rede de Medição de Precipitação Global (GPM). Calculamos as médias dos valores de NO2 e precipitação (mm/h) para cada uma das imagens entre os anos de 2019 e 2021, bem como as médias móveis semanais para cada área urbana. Assim, delimitamos seis períodos de dois meses, e calculamos a razão da média móvel entre os anos 2020/2019 e 2021/2019. No período supracitado observamos queda na densidade da coluna de NO2 em 2020, com aumento posterior, em 2021, no mesmo período e nas três regiões. Em Brasília a queda foi mais expressiva, sendo, em média, -9,35%, seguida de Goiânia com -2,61% e Anápolis com -1,34%. Apesar da queda das emissões em 2020, no ano seguinte ocorreu o aumento de emissão de NO2. A maior alta observada foi em Goiânia, com +30,3%, seguida de Anápolis, +19,30%, e +16,08% em Brasília.
The introduction of piezo-electric sensor on mass produced engines for in-cylinder pressure measurement represents a near future step in order to improve combustion control. Piezo-electric sensors ...provide pressure measurements affected by offset error and drift due to thermal sensitivity: a pressure reference is needed for each cycle in order to obtain the actual pressure value (pegging). Three methods for the evaluation of the offset, based on the hypothesis of polytropic compression, have been analyzed in this work: (1) a three-point referencing method, (2) a linear least-square method and (3) a non-linear least-square method. From such a comparison the three-point referencing method appeared the best suited for on-board calculation since it has the lowest computational cost even if it suffers from noise sensitivity. Hence, the accuracy and the efficiency of this method have been improved by means of an original methodology. The proposed method has been applied both to simulated and to experimental signals gathered from a 4-stroke spark-ignited engine. The results are compared to those obtained by using the other two methods showing much better accuracy in all the examined tests. Finally, a computational cost analysis proves the feasibility of the proposed method for efficient on-board pegging calculation with modern engine control units.
A fully 3D unsteady Computational Fluid Dynamics (CFD) approach coupled with heterogeneous reaction chemistry is presented in order to study the behavior of a single square channel as part of a Lean ...NOx Traps. The reliability of the numerical tool has been validated against literature data considering only active BaO site. Even though the input/output performance of such catalyst has been well known, here the spatial distribution within a single channel is investigated in details. The square channel geometry influences the flow field and the catalyst performance being the flow velocity distribution on the cross section non homogeneous. The mutual interaction between the flow and the active catalyst walls influences the spatial distribution of the volumetric species. Low velocity regions near the square corners and transversal secondary flows are shown in several cross-sections along the streamwise direction at different instants. The results shed light on the three-dimensional characteristic of both the flow field and species distribution within a single square channel of the catalyst with respect to 0-1D approaches.
Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly valid when biomass fuels are used. In most cases, the ...use of both heat and electricity to serve on site energy demand is a key to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and it is influenced by climatic conditions. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale biomass CHP plants, a bottoming ORC system can be coupled to the cycle, however this decreases the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper proposes a thermo-economic analysis of small scale CHP plants based on steam turbine (ST) or externally fired micro gas turbine (EFGT) coupled to different typologies of bottoming Organic Rankine Cycles (ORC). The research assesses the influence of the thermal energy demand and CHP plant operational strategies on the global energy efficiency and profitability of the proposed cogeneration options, taking into account the part load efficiency and the heat to electricity ratio flexibility that could be achieved through a switch on-off of the bottoming ORC. The thermodynamic cycles and their part load efficiency are modeled by Gate-Cycle (Brayton cycles) and Cycle-Tempo (Rankine cycles). The research explores the profitability of bottoming ORC in view of the higher efficiency and electricity generation revenues but higher costs and reduced heat available for cogeneration in the case of bottoming ORC. The results indicate the optimal CHP technology and configuration for each energy demand segment and the relative key technical and economic factors in the Italian legislative framework.
Convection within a latent heat thermal energy storage (LHTES) shell-and-tube device filled with phase change material (PCM) has been studied by means of numerical simulations. Both, the heat ...transfer fluid and the PCM mass, momentum and energy equations are solved and coupled with a conjugate heat transfer model. The study highlights three specific zones within the PCM: the top convective-dominated part, the curvilinear solid-liquid interface, and the bottom conductive-dominated part. The PCM melts from the top to the bottom, therefore the main mechanism of melting appears to be confined in the top part of the solid PCM. However, the flow details reveal a convective cell that includes the whole melted PCM from the top to the bottom of the PCM enclosure. Even though the problem is widely studied by means of experiments and numerical simulations, here the convective flow has been studied quantitatively. During the melting phase the viscous and thermal boundary layers at the walls has been reported at different heights from the bottom of the device. Results show in detail the phenomenology of the melting process within a shell-and-tube LHTES supporting the development of design solutions that could enhance the heat transfer of such device.
•Methodology to design the bottoming ORC cycle coupled to a biomass fired EFGT.•The influence of thermodynamic parameters in the ORC turbine design is investigated.•The fluid selection affects more ...the heat recovery ratio than the energy efficiency.•Bottoming ORC is promising to increase energy efficiency and profitability of EFGT.•Energy demand type is a key factor for the selection of the cycle configuration.
This paper focuses on the energy analysis of a combined cycle composed by a topping 1.3MW Externally Fired Gas Turbine (EFGT) with direct combustion of biomass and a bottoming Organic Rankine Cycle (ORC). A non recuperative scheme is assumed for the EFGT in order to avoid the costs of the recuperator. This scheme presents lower conversion efficiency in comparison to a recuperative one, however the heat available for the bottoming cycle is at a higher temperature (about 400°C). In the present work, evaporation pressure and superheating temperature of ORC cycle are ranged in order to examine different bottoming cycles, including supercritical ones. Different organic fluids are investigated, such as siloxanes and toluene, aiming to analyze how the fluid choice influences both the plant performance and important features for the ORC turbine design. On the basis of the results of the thermodynamic simulation, a thermo-economic assessment is proposed, to investigate the profitability of the bottoming ORC in comparison to only topping EFGT, and the most influencing techno-economic factors that influence the selection of the optimal cycle. In order to propose real case studies, the Italian bioenergy subsidy framework is assumed, and the sensitivity assessment includes the options of only electricity and CHP, at different biomass cost, thermal energy demand and heat selling price values.
In this paper technical-economic feasibility is analyzed about a gas-steam combined-cycle, fueled by syngas produced in a local downdraft gasifier. At first, the downdraft gasifier model is briefly ...described, where a biomass mix of Refused-Derived Fuel, RDF, and sewage sludge is transformed into syngas; then, the economic model is introduced with the graph about the economic trends of the most important plant components. Starting from the Design of Experiment (DOE) analysis, this paper proposes a multi-objective optimization methodology to obtain the Pareto Frontier of micro gas turbine technologies. In particular, this study allowed us to determine which micro gas turbine technology is more suitable to attract investment capital. The considered performance parameters are: the nominal power of the cycle; the total plant efficiency; the net revenues; the pay back period. On the other hand, the input design variables are represented by the turbine intake temperature, the compression ratio and the biomass chemical composition.
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