Yazar "Gungor, Afsin" seçeneğine göre listele
Listeleniyor 1 - 19 / 19
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A study on the effects of operational parameters on bed-to-wall heat transfer(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Gungor, AfsinIn this study the effects of operational parameters on bed-to-wall heat transfer in CFBs are investigated such as solids volume fraction, particle diameter, suspension density, solid circulation rate. Based on a previously developed 2D CFB model, a modified cluster renewal model is used in this investigation. The model uses the particle-based approach (PBA) and integrates the hydrodynamics and combustion aspects. The study is also validated with experimental data. As a result of this study, it is observed that the bed-to-wall heat transfer coefficients are strongly dependent on particle diameter and solids concentration at the riser wall. The smaller particles result in higher heat transfer coefficients than larger particles for the same solids volume fraction values. The heat transfer coefficient increases with suspension density. However, at a constant suspension density, the superficial velocity does not have a significant influence on the heat transfer coefficient. PBA is satisfactorily adapted to cluster renewal model so that to define the bed-to-wall heat transfer mechanisms for the upper zone. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Analysis of combustion efficiency in CFB coal combustors(ELSEVIER SCI LTD, 2008) Gungor, AfsinFluidized bed technology is well known for its high combustion efficiency and is widely used in coal combustion. In this study, the combustor efficiency has been defined and investigated for CFB coal combustor based on the losses using a dynamic 2D model. The model is shown to agree well with the published data. The effect of operating parameters such as excess air ratio, bed operational velocity, coal particle diameter and combustor load and the effect of design variables such as bed height and bed diameter on the mean bed temperature, the overall CO emission and the combustion efficiency are analyzed for the small-scale of CFBC in the presently developed model. As a result of this analysis, it is observed that the combustion efficiency decreases with increasing excess air value. The combustion efficiency increases with the bed operational velocity. Increasing coal particle size results in higher combustion efficiency values. The coal feed rate has negative effect on the combustion efficiency. The combustor efficiency considerably increases with increasing combustor height and diameter if other parameters are kept unchanged. (C) 2007 Elsevier Ltd. All rights reserved.Öğe Determining the best model for estimation the monthly mean daily global solar radiation on a horizontal surface - A case study in Nigde, Turkey(EMERALD GROUP PUBLISHING LTD, 2015) Gungor, Afsin; Gokcek, Murat; Yalcin, Fusun; Kocer, Abdulkadir; Yaka, Ismet Faruk; Sardogan, Gozde TugceKnowledge of the local solar radiation is important for many applications of solar energy systems. The global solar radiation on horizontal surface at the location of interest is the most critical input parameter employed in the design and prediction of the performance of solar energy systems. In this study, 3 empirical sunshine based models are compared correlating the monthly mean daily global solar radiation on a horizontal surface with monthly mean sunshine records for Nigde, Turkey. Models are compared using coefficient of determination (R-2), the root mean square error (RMSE), the mean bias error (MBE) and the t-statistic. According to our results, all the models fitted the data adequately and can be used to estimate the specific monthly global solar radiation. The t-statistic was used as the best indicator; this indicator depends on both, and is more effective for determining the model performance. The agreement between the estimated and the measured data were remarkable and the method was recommended for use in Nigde, Turkey.Öğe Effects of operational parameters on emission performance and combustion efficiency in small-scale CFBCs(CHINESE INST CHEMICAL ENGINEER, 2008) Gungor, Afsin; Eskin, NurdilA well-designed CFBC can burn coal with high efficiency and within acceptable levels of gaseous emission. In this theoretical study effects of operational parameters on combustion efficiency and the pollutants emitted have been estimated using a developed dynamic 2D (tow-dimensional) model for CFBCs. Model simulations have been carried out to examine the effect of different operational parameters such as excess air and gas inlet pressure and coal particle size on bed temperature, the overall CO, NO(x) and SO(2) emissions and combustion efficiency from a small-scale CFBC. It has been observed that increasing excess air ratio causes fluidized bed temperature decrease and CO emission increase. Coal particle size has more significant effect on CO emissions than the gas inlet pressure all the entrance to fluidized bed. Increasing excess air ratio leads to decreasing SO(2) and NO(x) emissions. The gas inlet pressure at the entrance to fluidized bed has a more significant effect on NO(x) emission than the coal particle size. Increasing excess air causes decreasing combustion efficiency. The gas inlet pressure has more pronounced effect on combustion efficiency than the coal particle size, particularly at higher excess air ratios. The developed model is also validated in terms of combustion efficiency with experimental literature data obtained from 300 kW laboratory scale test unit. The present theoretical study also confirms that CFB combustion allows clean and efficient combustion of coal. (C) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Öğe Effects of operational parameters on the thermodynamic performance of FBCC steam power plant(ELSEVIER SCI LTD, 2009) Eskin, Nurdil; Gungor, Afsin; Ozdemir, KorayIn this study, the effects of operational parameters on the thermodynamic performance of a FBCC steam power plant with a rated output of 7.7 MW are investigated by the developed model such as excess air, coal type and steam pressure based on the first and second laws of thermodynamics. The plant consists of a FBCC, a WHB and an economizer as subsystems and fans, pumps, cyclone and chimney as auxiliary systems. The model results are shown to agree well with plant operational data. As a result of this study. it is observed that the first and the second law efficiencies of the system decrease 5.1% and 5.2%, respectively, as the excess air increases from 10% to 70%. As the steam pressure increases from 4 to 12 bar, the energy efficiency of the system decreases to 2.1% but the exergy efficiency of the system increases to 19.9%. The amount of irreversibility occurring in the system is also calculated at each location through the developed model. The FBCC has the largest irreversibility, of about 80.4% of the total irreversibilities in the plant, mostly due to the irreversible combustion process. It is also observed that the coal type does not affect the first and the second law efficiencies considerably. (c) 2008 Elsevier Ltd. All rights reserved.Öğe Exergy analysis of Eregli sugar factory(EMERALD GROUP PUBLISHING LTD, 2015) Sahin, Necmettin; Kaplan, Erkan; Bayrak, Mustafa; Yaka, I. Faruk; Gungor, AfsinProgressive decline in world energy resources, rising costs, on behalf of the various studies has led businesses to use energy resources efficiently. This work is at the top of the exergy analysis. In this study, using data from Eregli Sugar Factory 2010-2011 campaign year for sugar production processes, the first law of thermodynamics (energy analysis) and analysis of these condlaw (exergy analysis) were conducted. Depending on there sults of this analysis of the sugar production process yields the first and these cond law is calculated. Obtained in the light of the secalculation stoin crease theen ergy efficiency of the plant, was tetoprovide energy to gainth embackand give direction to the development of new technologies Eregli Sugar Factory recommendations were made.Öğe Fossil fuel sustainability: Exergy assessment of a cogeneration system(JOHN WILEY & SONS LTD, 2011) Bayrak, Mustafa; Gungor, AfsinThermodynamics plays an important role to perform the energy and exergy analyses of the industrial processes. The first law is widely used in engineering practice and is the basis of the heat-balance method of analysis that is commonly used in energy systems performance analysis. However, the second law involves the reversibility or irreversibility of processes and is a very important aspect in the exergy method of energy systems analysis. From the viewpoints of energy conservation and environmental benefits, cogeneration system can be considered as one of sustainable energies. The exergy analysis allows for improvements not necessarily attainable via energy methods, like increased efficiency, reduced fuel use, and reduced environmental emissions. From this point of view, in this study, exergy analysis of an actual Diesel engine-based cogeneration plant with a total capacity of 11.52 MW electrical powers, 9 t h (-1) of steam and 140 t h (-1) of hot water is carried out by analyzing the components of the system separately. The results show that 39.86% of the exergy entering the plant is converted to electrical power. The net steam production of the plant constitutes 8% of the total exergy input and the hot water production of the plant constitutes only 1.26% of the total exergy input. The remaining 50.88% of the exergy input is lost. Total exergy destruction in the engine is mostly due to the highly irreversible combustion process in the engine, heat losses from engine and friction. Small improvements in engine design and operation can provide better utilization of plant performance compared to large and expensive improvements in other components. Copyright (C) 2010 John Wiley & Sons, Ltd.Öğe In view of sustainable future energetic-exergetic and economic analysis of a natural gas cogeneration plant(INDERSCIENCE ENTERPRISES LTD, 2013) Gungor, Afsin; Bayrak, Mustafa; Beylergil, BertanThermodynamics plays an important role in performing energy and exergy analyses of industrial processes. The first law is widely used in engineering practice, and is the basis of the heat-balance method of analysis that is commonly used in energy systems performance analysis. However, the second law involves the reversibility or irreversibility of processes, and is a very important aspect of the exergy method of energy systems analysis. For a sustainable future, exergy analysis allows for improvements not necessarily attainable via energy methods, like increased efficiency, reduced fuel use and reduced environmental emissions. From the viewpoints of energy conservation and environmental benefits, cogeneration systems can be considered as systems of sustainable energies. From this point of view, in this study, the energy, exergy and economic analysis of an actual natural gas cogeneration plant with a total capacity of 121.5 MWh electrical powers is carried out. The first and second law efficiency of the cogeneration plant is calculated as 40.8% and 90.2%, respectively. The pay-back period of the cogeneration plant is calculated as three years, which means this plant runs quite efficiency and economically.Öğe Modeling the effects of the operational parameters on H-2 composition in a biomass fluidized bed gasifier(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Gungor, AfsinIn this study, effects of the operational parameters such as gasifier temperature, bed operational velocity, equivalence ratio, biomass particle size and biomass-to-steam ratio on hydrogen production from an atmospheric biomass FB gasifier is simulated by presently developed model. The model is one-dimensional, isothermal and steady state, and the fluid-dynamics are based on the two-phase theory of fluidization. Tar conversion is taken into account in the model. The model simulation results are also compared with and validated against experimental data given in the literature. As a result of this study, it is observed that H-2 composition increased remarkably with the rise of the gasifier temperature. Small biomass particles improves H-2 composition. It is unfeasible to apply too small or too large ER in biomass air steam gasification. The increases in the mole fractions of H-2 with increases in the steam flow rate indicated that the gas shift reaction has a substantial effect in air steam gasification. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Numerical Simulation of Nano Particles in a Fluidized Bed(AMER SCIENTIFIC PUBLISHERS, 2011) Gungor, AfsinIn this study, two dimensional numerical model is developed to simulate the hydrodynamic characteristics of nano particles such as the solids fraction and bed pressure drop in a fluidized bed. The model results are compared with and validated against experimental data given in the literature for the solids fraction in the bubble phase and emulsion phase, and for bed pressure drop as a function of superficial velocity. General trend of the solid fraction is high in the central region and gradually decreases towards the wall for bubbling fluidization. The solid fraction value is slightly different in dense region for fast fluidization regime. Whereas in the dilute phase there are not significant differences between fluidization regimes.Öğe One dimensional numerical simulation of small scale CFB combustors(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Gungor, AfsinIn this study, a one-dimensional model which includes volatilization, attrition and combustion of char particles for a circulating fluidized bed (CFB) combustor has been developed. In the modeling, the CFB combustor is analyzed in two regions: bottom zone considering as a bubbling fluidized bed in turbulent fluidization regime and upper zone core-annulus solids flow structure is established. In the bottom zone, a single-phase back-flow cell model is used to represent the solid mixing. Solids exchange, between the bubble phase and emulsion phase is a function of the bubble diameter and varies along the axis of the combustor. In the upper zone. particles move upward in the core and downward in the annulus. Thickness of the annulus varies according to the combustor height. Using the developed simulation program, the effects of operational parameters which are the particle diameter, superficial velocity and air-to-fuel ratio on net solids flux, oxygen and carbon dioxide mote ratios along the bed height and carbon content and bed temperature on the top of the riser are investigated. Simulation results are compared with test results obtained from the 50 kW Gazi University Heat Power Laboratory pilot scale unit and good agreement is observed. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Predicting axial pressure profile of a CFB(ELSEVIER SCIENCE SA, 2008) Gungor, AfsinThe numerical simulation of CFBs is an important tool in the prediction of its flow behavior. Predicting the axial pressure profile is one of the major difficulties in modeling a CFB. A model using a Particle Based Approach (PBA) is developed to accurately predict the axial pressure profile in CFBs. The simulation model accounts for the axial and radial distribution of voidage and velocity of the gas and solid phases, and for the solids volume fraction and particle size distribution of the solid phase. The model results are compared with and validated against atmospheric cold CFB experimental literature data. Ranges of experimental data used in comparisons are as follows: bed diameter from 0.05 to 0.305 m, bed height between 5 and 15.45 m, mean particle diameter from 76 to 812 mu m, particle density from 189 to 2600 kg/m(3), solid circulation fluxes from 10.03 to 489 kg/m(2) s and gas superficial velocities from 2.71 to 10.68 m/s. The computational results agreed reasonably well with the experimental data. Moreover, both experimental data and model predictions show that the pressure drop profile is affected by the solid circulation flux and superficial velocity values in the riser. The pressure drop increases along the acceleration region as solid circulation flux increases and superficial velocity decreases. (C) 2007 Elsevier B.V. All rights reserved.Öğe Prediction of SO2 and NOx emissions for low-grade Turkish lignites in CFB combustors(ELSEVIER SCIENCE SA, 2009) Gungor, AfsinThe CFB technology is widely used for combustion of coal because of its unique ability to handle low quality. high ash, high sulphur and low heating value coals. This paper presents a modeling study of pollutant emissions such as sulphur dioxide (SO2) and nitric oxide (NOx) resulting from coal combustion in a CFBC. Using this model, overall SO2 and NOx emissions are predicted for the combustion of three different kinds of low-grade Turkish lignites. The contents of these lignites are as follows: ash from 23.70% to 45.31%. sulphur from 1.81% to 8.40% and calorific values (LHV) from 10,283 to 15.215 kJ/kg. The data is obtained from two pilot scale CFBCs (50 and 80 kW) and an industrial scale CFBC (160 MW). The present study proves that CFB combustion demonstrated by both experimental data and model predictions produces low and acceptable level of SO2 and NOx emissions resulting from the combustion of low-grade lignites. Developed model can also investigate the effects of different operational parameters on overall SO2 and NOx emissions. As a result of this investigation, it is observed that increase of excess air decreases SO2 and NOx emissions. However, NOx emission increases with the operational bed velocity while SO2 emission decreases. A bigger inlet bed pressure value results in lower emissions of SO2 and NOx if other parameters are kept unchanged. (C) 2008 Elsevier B.V. All rights reserved.Öğe Second law analysis of heat transfer surfaces in circulating fluidized beds(ELSEVIER SCI LTD, 2009) Gungor, AfsinThe correct sizing of the heat transfer surfaces is important to ensure proper operation, load turndown, and optimization of circulating fluidized beds (CFBs). From this point of view, in this study, the thermodynamic second law analysis of heat transfer surfaces in CFBs is investigated theoretically in order to define the parameters that affect the system efficiency. Using a previously developed 2D CFB model which uses the particle-based approach and integrates and simultaneously predicts the hydrodynamics and combustion aspects, second law efficiency and entropy generation values are obtained at different height and volume ratios of the heat transfer surfaces for CFBs. Besides that, the influences of the water flow rates and heat exchanger tube diameters on the second law efficiency are investigated. Through this analysis, the dimensions, arrangement and type of the heat transfer surfaces which achieve maximum efficiency are obtained. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Simulation of bed-to-wall heat transfer in circulating fluidized beds(TURKISH SOC THERMAL SCIENCES TECHNOLOGY, 2008) Gungor, AfsinIn this study, the numerical simulation of bed-to-wall heat transfer in CFBs is presented which based on previously developed 2D CFB model which uses the particle-based approach and integrates and simultaneously predicts the hydrodynamics, combustion aspects. The study is also validated with published data. The comparisons of the model predictions and experimental data indicate that the model is flexible enough to operate under different operational conditions concerning superficial velocity, particle diameter and suspension density values. Additionally, the simulation matches the measured data quite faithfully for heat transfer coefficient as a function of the suspension density at different temperature values which is also an indicator that that the simulation is valid for both cold and hot CFB units.Öğe Simulation of emission performance and combustion efficiency in biomass fired circulating fluidized bed combustors(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Gungor, AfsinIn this study, the combustion efficiency and the emission performance of biomass fired CFBs are tested via a previously published 2D model [Gungor A. Two-dimensional biomass combustion modeling of CFB. Fuel 2008; 87: 1453-1468.] against two published comprehensive data sets. The model efficiently simulates the outcome with respect to the excess air values, which is the main parameter that is verified. The combustion efficiency of OC changes between 82.25 and 98.66% as the excess air increases from 10 to 116% with the maximum error of about 8.59%. The rice husk combustion efficiency changes between 98.05 and 97.56% as the bed operational velocity increases from 1.2 to 1.5 m s(-1) with the maximum error of about 7.60%. CO and NO(x) emissions increase with increasing bed operational velocity. Increasing excess air results in slightly higher levels of NO(x) emission. A significant amount of combustion occurs in the upper zone due to the high volatile content of the biomass fuels. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Simulation of NOx Emission in Circulating Fluidized Beds Burning Low-grade Fuels(AMER CHEMICAL SOC, 2009) Gungor, AfsinNitrogen oxides are a major environmental pollutant resulting from combustion. This paper presents a modeling study of pollutant NOx emission resulting from low-grade fuel combustion in a circulating fluidized bed. The simulation model accounts for the axial and radial distribution of NOx, emission in a circulating fluidized bed (CFB). The model results are compared with and validated against experimental data both for small-size and industrial-size CFBs that use different types of low-grade fuels given in the literature. The present study proves that CFB combustion demonstrated by both experimental data and model predictions produces low and acceptable levels of NOx emissions resulting from the combustion of low-grade fuels. Developed model can also investigate the effects of different operational parameters on overall NOx emission. As a result of this investigation, both experimental data and model predictions show that NOx, emission increases with the bed temperature but decreases with excess air if other parameters are kept unchanged.Öğe Thermodynamic analysis of a FBCC steam power plant(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Eskin, Nurdil; Gungor, Afsin; Ozdemir, KorayThis article presents the analysis of first and second laws of thermodynamics in a 7.7 MW steam power plant located in Torbali (Izmir, Turkey). it involves a fluidized bed, a waste heat boiler (WHB) and an economizer as subsystems. Fans, pumps, cyclone and chimney are also considered through the analysis as auxiliary systems in the thermal plant. The analysis is performed for the whole system and subsystems by considering the available energy balance. In this analysis which consists of a detailed fluidized bed coal combustor (FBCC) model, the amount of irreversibilities occurring in the system is calculated at each location. Analysis results are compared with the test results obtained from the measurements at several locations in the system and good agreement is observed. These measured values are the temperatures at three levels in the FBCC and boiler, economizer exit temperatures as well as flue gas composition at the boiler exit and steam flow rate. The maximum error observed in temperature values and steam flow rate is about 3.03% and 4.03%, respectively. Through the developed and validated model, effects of excess air and ambient temperature on first and second law efficiency of the subsystems and overall system are investigated. The second-law analysis reveals that the FBCC has the largest irreversibility, with about 80.4% of the total system exergy loss. The FBCC temperature, first and second law efficiencies decrease 19.8%, 5.1% and 5.2%, respectively, as the excess air increases from 10% to 70%. Also steam flow rate decreases 5.1%. As the ambient temperature increases from 25 to 45 degrees C, the FBCC temperature, system first and second law efficiencies increase 0.8%, 1.3%, and 1.3%, respectively. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Two-dimensional biomass combustion modeling of CFB(ELSEVIER SCI LTD, 2008) Gungor, AfsinIn this study, a 2D model for a CFB biomass combustor has been developed which integrates and simultaneously predicts the hydrodynamics, heat transfer and combustion aspects. Combustor hydrodynamic is modeled taking into account previous work. Simulation model calculates the axial and radial distribution of voidage, velocity, particle size distribution, pressure drop, gas emissions and temperature at each time interval for gas and solid phase both for bottom and upper zones. The model results are compared with and validated against experimental data both for small-size and industrial-size biomass combustors which uses different types of biomass fuels given in the literature. As a result of sensitivity analysis, it is observed that: major portion of the combustion will take place in the upper zone, the air staging could improve combustion, for industrial-size CFB biomass combustors and the decrease of NO, adversely results in high CO emissions as air ratio decreases. Unexpected results concerning the emissions is caused by using data of different sized CFBs and is clearly an indicator of the necessity to compare the model results with various sized CFBs as far as possible. (C) 2007 Elsevier Ltd. All rights reserved.
