The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
T A G Langrish - One of the best experts on this subject based on the ideXlab platform.
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discounted cash flow analysis of greenhouse type solar Kilns
Renewable Energy, 2016Co-Authors: Mahmudul Hasan, Mengze Zhang, T A G LangrishAbstract:This paper describes the overall discounted cash flow (DCF) analysis of two greenhouse-type solar Kilns (Oxford and Boral) for hardwood drying processes. The financial performance of both the Kilns was found to be mainly dominated by the costs/benefits associated with the model-predicted future thermal energy flows. All the costs and benefits were calculated based on the current energy prices, while adjusting all future cash flows (either costs or benefits) to their respective present values by incorporating appropriate inflation and discount rates. The overall results indicated that the net present cash benefit and the present drying energy benefit were larger for the Oxford kiln than those for the Boral kiln, by approximately 38% and 16%, respectively, while the present energy-loss cost was smaller for the Oxford kiln by 23% than that for the Boral kiln. A sensitivity analysis was carried out in order to assess the robustness of the results against the uncertain parameters. In general, the Oxford kiln design was found to be more cost-effective and environmentally beneficial than the Boral kiln design for hardwood drying.
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time valued net energy analysis of solar Kilns for wood drying a solar thermal application
Energy, 2016Co-Authors: Mahmudul Hasan, T A G LangrishAbstract:This paper describes a LNEA (life-cycle net energy analysis) for solar thermal applications with particular reference to two typical greenhouse-type solar Kilns (Oxford and Boral) for wood drying. The analysis included the simulation of future flows of OE (operational energy), and the assessment of EE (embodied energy) for the two Kilns over an expected service life of 20 years. The OE streams associated with the drying of a hardwood species (Eucalyptus pilularis) were estimated by solving a solar kiln model, while a LCA (life cycle assessment) model was used for the assessment of EE components. The key objective of this paper was to carry out a time-valued net energy analysis for two significantly different kiln designs. This approach of evaluating the energy-intensive facilities (e.g. solar Kilns) is novel, and may result in a robust framework for further performance/design optimization study of solar kiln designs. Based on the chosen life-cycle performance parameters, the Oxford kiln was generally found to be more productive and energy efficient than the Boral kiln for hardwood drying in Australia.
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time valued net energy analysis of solar Kilns for wood drying a solar thermal application
Energy, 2016Co-Authors: Mahmudul Hasan, T A G LangrishAbstract:This paper describes a LNEA (life-cycle net energy analysis) for solar thermal applications with particular reference to two typical greenhouse-type solar Kilns (Oxford and Boral) for wood drying. The analysis included the simulation of future flows of OE (operational energy), and the assessment of EE (embodied energy) for the two Kilns over an expected service life of 20 years. The OE streams associated with the drying of a hardwood species (Eucalyptus pilularis) were estimated by solving a solar kiln model, while a LCA (life cycle assessment) model was used for the assessment of EE components. The key objective of this paper was to carry out a time-valued net energy analysis for two significantly different kiln designs. This approach of evaluating the energy-intensive facilities (e.g. solar Kilns) is novel, and may result in a robust framework for further performance/design optimization study of solar kiln designs. Based on the chosen life-cycle performance parameters, the Oxford kiln was generally found to be more productive and energy efficient than the Boral kiln for hardwood drying in Australia.
Marie Debacq - One of the best experts on this subject based on the ideXlab platform.
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Characterization of solids transport within flighted rotary Kilns : Synthesis of numerous experiments and modeling.
2017Co-Authors: Marie Debacq, Stéphane Vitu, Clément Haustant, Jean-louis DirionAbstract:Over the years, rotary Kilns have become an inescapable benchmark in several industrial sectors. This is because they offer special possibilities regarding a wide range of materials which can be continuously processed with little or no operating labor, especially when they are automatically controlled. The wider the scope of applications, the greater the variety of kiln designs and sizes. Rotary Kilns are widely used for the drying or cooling of solid particles, for instance in the food processing industry when dealing with wet or dry granular materials, for the calcination of limestone, petroleum coke, or production of cement. Other applications include: regeneration of spent catalyst, hazardous waste reclamation, defluorination and reduction of uranyl difluoride and so on. Industrial rotary Kilns are usually equipped with internal fixtures such as lifters, baffles, constrictions or exit dams. The complex hydrodynamic behavior of the granular materials within rotary Kilns has led to extensive research over the years. Most of these publications report on the influence of operating parameters (rotational speed, kiln slope, mass flow rate or exit dam height) on the residence time distribution (RTD) and axial dispersion of solid particles. However, few of these studies analyze the effect of the presence of lifters, their number or shape. We therefore decided to conduct a systematic experimental investigation of RTD, kiln holdup and axial dispersion coefficient for the continuous flow of granular materials in rotary Kilns equipped with lifters. To do so, we used two different pilot scale rotary Kilns. One is about twice the size of the other. We investigated both the influence of operating parameters (rotational speed, kiln slope, mass flow rate) and of the presence of internal devices (grid, different shapes and number of lifters, different height of exit dam) on a large range of size and shape of particles (two different sands, rice and beech chips). The large set of experimental data obtained, allowed us to build a model based on dimensional analysis, which is useful for industrial applications.
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Residence Time Distribution of Fine to Coarse Particles in Rotary Kilns
2016Co-Authors: Maryanna De Melo Soledade, Jean-louis Dirion, Stéphane Vitu, Alex Stéphane Bongo Njeng, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or an exit dam at the kiln outlet end. They usually require very little labor to operate. Though the operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solid flow and heat transfer. The objective of this presentation is to provide a new model to predict the mean residence time, axial dispersion coefficient and hold-up of fine to coarse solid particles within the rotary kiln based on a dimensional analysis. Flow of material through a rotary kiln depends on many factors: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material. Experiments were carried out on two pilot-scale rotary Kilns at room temperature, whether equipped or not with different kinds of lifters or fitted with a dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the Residence Time Distribution of solid particles. The tracer impulse-response technique was used to establish residence time distribution curves. Four granular solids having different properties were used: fine and medium sand, broken rice and beech chips. The other operational parameters were also varied, maintaining the cascading (tumbling) motion. We have already presented* the results on the smaller kiln with two types of particles. In the present study, we will show that the correlation established with these earlier results had a good predictive ability over the larger kiln with coarser particles. New results with fine particles will also be presented. These new experiments will be used for the consolidation and validation of the previous model. * Alex Stéphane Bongo Njeng, Stéphane Vitu, Marc Clausse, Jean-Louis Dirion and Marie Debacq « Modeling of Mean Residence Time of Solid Particles in Rotary Kilns » 14AIChE annual meeting, Atlanta, November 2014 [paper 374307]
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Convective and wall-to-solids heat transfer coefficient in flighted rotary Kilns: experimental measurement and modeling
2015Co-Authors: Alex Stéphane Bongo Njeng, Jean-louis Dirion, Stéphane Vitu, Marc Clausse, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide range of material processing operations: mixing, heating or cooling, reacting of coarse, free-flowing or cohesive solids. Therefore rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of biomass or hazardous waste, calcining of petroleum coke, conversion of uranium fluoride for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, these units consist of a cylindrical shell that can be inclined, into which the solids burden is fed continuously at one end and discharged at the other. Most of them are equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They can be classified into two main heating modes; they can be either directly heated or indirectly heated, depending on the heating source position with respect to the kiln’s tube wall. They usually require very little labor to operate in comparison with other industrial reactors. Though operational cost of these units is usually high, their design and intended operating conditions are often conservative due to the lack of fundamental understanding notably upon the solids flow behavior and the heat transfer mechanisms. Heat transfer in rotary Kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms that are, conduction, convection, and radiation. There have been quite a few studies dealing with this subject in the literature. Although many researchers studied the main phenomena occurring in the kiln, the heat transfer between the wall and solid particles, or the (free) convection of non forced gas are not yet well understood. The present study investigates the convective gas-to-wall heat transfer coefficient, in the case of a non-forced air flow, and the wall-to-solids heat transfer coefficient. These coefficients were first experimentally determined, and then correlated based on a dimensional analysis, so to be used in a global model for rotary Kilns. A series of experiments were carried out on a pilot scale rotary kiln at atmospheric pressure, whether or not equipped with lifters and fitted with a dam at the outlet end. The experimental apparatus, 1.95m in length and 0.01m in (internal) diameter, can be externally heated in two independent consecutive zones by electrical resistance up to 1000°C. Regarding the thermal metrology, thermocouples are positioned at five and four cross-sections, respectively in and outside along the kiln tube. Hence, after turning on the heating system, axial temperature profiles of gas, wall and solids were measured until steady state is achieved. Both coefficients were determined from the temperature profiles measurements data for low and medium wall temperature set point comprises between 100 and 500°C. In particular for the wall-to-solids heat transfer coefficient, the bulk materials used was quartz sand (average size about half a millimeter) with a narrow distributed size fraction; No solids were fed into the kiln when studying the air convection inside the kiln. Two shapes of lifters were compared to determine the influence of lifters presence and their geometry on the heat transfer: straight (one-section) lifters and rectangular (two-section) lifters (RL). The kiln operating conditions examined also include: the rotational speed (2-12 rpm), the mass flow rate (0.8-2.5 kg/h) and the exit dam height at the kiln outlet end (23.5-33.5 mm). An experimental matrix of about eighty experiments was achieved. For the determination of the experimental value, the lumped system analysis and a heat balance accounting for the measured power supplied for the heating are used. Results showed that the wall-to-gas convective heat transfer coefficient is significantly lower that what can be expected for natural convection. Though only small variations were observed, still some trends could be observed in presence of lifters, and when varying the rotational speed. The wall-to-solids heat transfer coefficient was notably lower in presence of lifters. It was also found to increase with the temperature set at the wall and the filling degree, which is imposed by the operating conditions set. Dimensional correlations were developed to describe these two heat transfer mechanisms from the experimental results.
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Modeling of Mean Residence Time of Solid Particles in Rotary Kilns
2014Co-Authors: Alex Stéphane Bongo Njeng, Jean-louis Dirion, Stéphane Vitu, Marc Clausse, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They usually require very little labor to operate. Though operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solids flow and heat transfer. The objective of this presentation is to provide a new model to predict the residence time of solid particles within the rotary kiln based on a dimensional analysis. This model can be used for process control as well as for design purposes. Progress of material through a rotary kiln is affected by a number of factors, namely: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed, and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material. Experiments were carried out on a pilot scale rotary kiln at room temperature, whether or not equipped with lifters or fitted with dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the mean residence time of solid particles; the mean residence time was determined from residence time distribution measurements data. The tracer impulse-response technique was used to establish residence time distribution curves. Two granular solids having different properties were used: sand and broken rice. Furthermore, two shapes of lifters were compared to determine the influence of lifter geometry: straight lifters (SL) and rectangular lifters (RL). The other operational parameters were also varied so that a matrix of 69 experiments (without including repeatability tests) was achieved. These experiments were used for the consolidation and validation of the presented model. The model not only gave good agreement with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other Kilns, having different design, materials, and order of magnitude of the operating parameters. The excellent predictive capacity of the model compared to other semi-empirical models shows its capacity to handle a wide range of conditions and operating variables. The model is applicable for inclined Kilns that process materials in cascading (tumbling) motion, whether or not equipped with lifters or fitted with dams at the outlet end.
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Heat transfer in an externally heated rotary kiln: Preliminary results obtained with a new experimental device
2011Co-Authors: Phahath Thammavong, Marie Debacq, Stéphane Vitu, Marc DupoizatAbstract:Rotary Kilns are widely used gas/solid reactors encountered in several branches of the chemical industry. They are a key element in the production processes of cement, lime and pigments, for the reduction of ore in extractive metallurgy and for the pyrolysis of solid waste. They are also used to convert uranium fluoride into uranium dioxide for the production of nuclear fuel. In this kind of device, hydrodynamic, thermal and chemical modelling processes are linked, as it is clear that the temperature profiles of the solid and the gas in the kiln directly influence the chemical reaction kinetics that occur. It is thus essential to be able to calculate precisely the temperature of the solid and of the gas at any point in the kiln and to understand the heat exchanges in the kiln. Various correlations are reported in the literature for estimating the heat transfer coefficients in rotary kiln. However, for a given kiln, the heat transfer coefficient values calculated by using these correlations are highly scattered. Moreover, experimental measurements of heat transfer in rotary Kilns are scarce. The aim of this work is thus to design and construct an adaptable experimental setup to study heat exchange in rotary Kilns. A key point is that the operating mode of the experimental setup must be similar to those of the rotary Kilns used for the conversion of uranium. In particular, our kiln is externally heated and equipped with lifters. The design of our experimental device will be described, focusing on the heating mode chosen and on the instrumentation. A special attention will also be devoted to the preliminary results obtained concerning the influence of the solid flow rate and the rotational speed on the heat transfer coefficient between the wall of the rotary kiln and the solid flowing through the kiln.
Mahmudul Hasan - One of the best experts on this subject based on the ideXlab platform.
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discounted cash flow analysis of greenhouse type solar Kilns
Renewable Energy, 2016Co-Authors: Mahmudul Hasan, Mengze Zhang, T A G LangrishAbstract:This paper describes the overall discounted cash flow (DCF) analysis of two greenhouse-type solar Kilns (Oxford and Boral) for hardwood drying processes. The financial performance of both the Kilns was found to be mainly dominated by the costs/benefits associated with the model-predicted future thermal energy flows. All the costs and benefits were calculated based on the current energy prices, while adjusting all future cash flows (either costs or benefits) to their respective present values by incorporating appropriate inflation and discount rates. The overall results indicated that the net present cash benefit and the present drying energy benefit were larger for the Oxford kiln than those for the Boral kiln, by approximately 38% and 16%, respectively, while the present energy-loss cost was smaller for the Oxford kiln by 23% than that for the Boral kiln. A sensitivity analysis was carried out in order to assess the robustness of the results against the uncertain parameters. In general, the Oxford kiln design was found to be more cost-effective and environmentally beneficial than the Boral kiln design for hardwood drying.
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time valued net energy analysis of solar Kilns for wood drying a solar thermal application
Energy, 2016Co-Authors: Mahmudul Hasan, T A G LangrishAbstract:This paper describes a LNEA (life-cycle net energy analysis) for solar thermal applications with particular reference to two typical greenhouse-type solar Kilns (Oxford and Boral) for wood drying. The analysis included the simulation of future flows of OE (operational energy), and the assessment of EE (embodied energy) for the two Kilns over an expected service life of 20 years. The OE streams associated with the drying of a hardwood species (Eucalyptus pilularis) were estimated by solving a solar kiln model, while a LCA (life cycle assessment) model was used for the assessment of EE components. The key objective of this paper was to carry out a time-valued net energy analysis for two significantly different kiln designs. This approach of evaluating the energy-intensive facilities (e.g. solar Kilns) is novel, and may result in a robust framework for further performance/design optimization study of solar kiln designs. Based on the chosen life-cycle performance parameters, the Oxford kiln was generally found to be more productive and energy efficient than the Boral kiln for hardwood drying in Australia.
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time valued net energy analysis of solar Kilns for wood drying a solar thermal application
Energy, 2016Co-Authors: Mahmudul Hasan, T A G LangrishAbstract:This paper describes a LNEA (life-cycle net energy analysis) for solar thermal applications with particular reference to two typical greenhouse-type solar Kilns (Oxford and Boral) for wood drying. The analysis included the simulation of future flows of OE (operational energy), and the assessment of EE (embodied energy) for the two Kilns over an expected service life of 20 years. The OE streams associated with the drying of a hardwood species (Eucalyptus pilularis) were estimated by solving a solar kiln model, while a LCA (life cycle assessment) model was used for the assessment of EE components. The key objective of this paper was to carry out a time-valued net energy analysis for two significantly different kiln designs. This approach of evaluating the energy-intensive facilities (e.g. solar Kilns) is novel, and may result in a robust framework for further performance/design optimization study of solar kiln designs. Based on the chosen life-cycle performance parameters, the Oxford kiln was generally found to be more productive and energy efficient than the Boral kiln for hardwood drying in Australia.
Zhuo Zhenxi - One of the best experts on this subject based on the ideXlab platform.
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study on the compositional differences of tang sancai from different Kilns by inaa
Journal of Archaeological Science, 2005Co-Authors: Lei Yong, Feng Songlin, Feng Xiangqian, Fan Dongyu, Xu Qing, Sha Yin, Cheng Lin, Chai Zhifang, Jiang Jie, Zhuo ZhenxiAbstract:Many kinds of Tang Sancai specimens were excavated in the Shaanxi and Henan Provinces. However, the provenances of some kinds of Tang Sancai have not been well identified until now. In order to group the Tang Sancai specimens of the unknown provenance to the respective Kilns according to their chemical compositions, we studied the element abundance patterns of different kiln's Tang Sancai samples by Instrumental Neutron Activation Analysis (INAA). Our experimental results indicate that the differences of the element abundance pattern of the studied specimens from different Kilns are significant. The separation is clear on the basis of factor analysis mainly using the contents of 13 elements, i.e. Ce, Nd, Eu, Yb, Lu, Ta, Th, Sc, Cs, La, Sm, U and Tb. The composition database of the Tang Sancai body samples from different Kilns has been set up and can be used for the identification of the unknown Tang Sancai samples. The result also implies that similar raw materials have been used for Tang Sancai production at different Kilns and the technical exchange between those Kilns during the period of Tang Dynasty.
Stéphane Vitu - One of the best experts on this subject based on the ideXlab platform.
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Characterization of solids transport within flighted rotary Kilns : Synthesis of numerous experiments and modeling.
2017Co-Authors: Marie Debacq, Stéphane Vitu, Clément Haustant, Jean-louis DirionAbstract:Over the years, rotary Kilns have become an inescapable benchmark in several industrial sectors. This is because they offer special possibilities regarding a wide range of materials which can be continuously processed with little or no operating labor, especially when they are automatically controlled. The wider the scope of applications, the greater the variety of kiln designs and sizes. Rotary Kilns are widely used for the drying or cooling of solid particles, for instance in the food processing industry when dealing with wet or dry granular materials, for the calcination of limestone, petroleum coke, or production of cement. Other applications include: regeneration of spent catalyst, hazardous waste reclamation, defluorination and reduction of uranyl difluoride and so on. Industrial rotary Kilns are usually equipped with internal fixtures such as lifters, baffles, constrictions or exit dams. The complex hydrodynamic behavior of the granular materials within rotary Kilns has led to extensive research over the years. Most of these publications report on the influence of operating parameters (rotational speed, kiln slope, mass flow rate or exit dam height) on the residence time distribution (RTD) and axial dispersion of solid particles. However, few of these studies analyze the effect of the presence of lifters, their number or shape. We therefore decided to conduct a systematic experimental investigation of RTD, kiln holdup and axial dispersion coefficient for the continuous flow of granular materials in rotary Kilns equipped with lifters. To do so, we used two different pilot scale rotary Kilns. One is about twice the size of the other. We investigated both the influence of operating parameters (rotational speed, kiln slope, mass flow rate) and of the presence of internal devices (grid, different shapes and number of lifters, different height of exit dam) on a large range of size and shape of particles (two different sands, rice and beech chips). The large set of experimental data obtained, allowed us to build a model based on dimensional analysis, which is useful for industrial applications.
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Residence Time Distribution of Fine to Coarse Particles in Rotary Kilns
2016Co-Authors: Maryanna De Melo Soledade, Jean-louis Dirion, Stéphane Vitu, Alex Stéphane Bongo Njeng, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or an exit dam at the kiln outlet end. They usually require very little labor to operate. Though the operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solid flow and heat transfer. The objective of this presentation is to provide a new model to predict the mean residence time, axial dispersion coefficient and hold-up of fine to coarse solid particles within the rotary kiln based on a dimensional analysis. Flow of material through a rotary kiln depends on many factors: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material. Experiments were carried out on two pilot-scale rotary Kilns at room temperature, whether equipped or not with different kinds of lifters or fitted with a dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the Residence Time Distribution of solid particles. The tracer impulse-response technique was used to establish residence time distribution curves. Four granular solids having different properties were used: fine and medium sand, broken rice and beech chips. The other operational parameters were also varied, maintaining the cascading (tumbling) motion. We have already presented* the results on the smaller kiln with two types of particles. In the present study, we will show that the correlation established with these earlier results had a good predictive ability over the larger kiln with coarser particles. New results with fine particles will also be presented. These new experiments will be used for the consolidation and validation of the previous model. * Alex Stéphane Bongo Njeng, Stéphane Vitu, Marc Clausse, Jean-Louis Dirion and Marie Debacq « Modeling of Mean Residence Time of Solid Particles in Rotary Kilns » 14AIChE annual meeting, Atlanta, November 2014 [paper 374307]
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Convective and wall-to-solids heat transfer coefficient in flighted rotary Kilns: experimental measurement and modeling
2015Co-Authors: Alex Stéphane Bongo Njeng, Jean-louis Dirion, Stéphane Vitu, Marc Clausse, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide range of material processing operations: mixing, heating or cooling, reacting of coarse, free-flowing or cohesive solids. Therefore rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of biomass or hazardous waste, calcining of petroleum coke, conversion of uranium fluoride for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, these units consist of a cylindrical shell that can be inclined, into which the solids burden is fed continuously at one end and discharged at the other. Most of them are equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They can be classified into two main heating modes; they can be either directly heated or indirectly heated, depending on the heating source position with respect to the kiln’s tube wall. They usually require very little labor to operate in comparison with other industrial reactors. Though operational cost of these units is usually high, their design and intended operating conditions are often conservative due to the lack of fundamental understanding notably upon the solids flow behavior and the heat transfer mechanisms. Heat transfer in rotary Kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms that are, conduction, convection, and radiation. There have been quite a few studies dealing with this subject in the literature. Although many researchers studied the main phenomena occurring in the kiln, the heat transfer between the wall and solid particles, or the (free) convection of non forced gas are not yet well understood. The present study investigates the convective gas-to-wall heat transfer coefficient, in the case of a non-forced air flow, and the wall-to-solids heat transfer coefficient. These coefficients were first experimentally determined, and then correlated based on a dimensional analysis, so to be used in a global model for rotary Kilns. A series of experiments were carried out on a pilot scale rotary kiln at atmospheric pressure, whether or not equipped with lifters and fitted with a dam at the outlet end. The experimental apparatus, 1.95m in length and 0.01m in (internal) diameter, can be externally heated in two independent consecutive zones by electrical resistance up to 1000°C. Regarding the thermal metrology, thermocouples are positioned at five and four cross-sections, respectively in and outside along the kiln tube. Hence, after turning on the heating system, axial temperature profiles of gas, wall and solids were measured until steady state is achieved. Both coefficients were determined from the temperature profiles measurements data for low and medium wall temperature set point comprises between 100 and 500°C. In particular for the wall-to-solids heat transfer coefficient, the bulk materials used was quartz sand (average size about half a millimeter) with a narrow distributed size fraction; No solids were fed into the kiln when studying the air convection inside the kiln. Two shapes of lifters were compared to determine the influence of lifters presence and their geometry on the heat transfer: straight (one-section) lifters and rectangular (two-section) lifters (RL). The kiln operating conditions examined also include: the rotational speed (2-12 rpm), the mass flow rate (0.8-2.5 kg/h) and the exit dam height at the kiln outlet end (23.5-33.5 mm). An experimental matrix of about eighty experiments was achieved. For the determination of the experimental value, the lumped system analysis and a heat balance accounting for the measured power supplied for the heating are used. Results showed that the wall-to-gas convective heat transfer coefficient is significantly lower that what can be expected for natural convection. Though only small variations were observed, still some trends could be observed in presence of lifters, and when varying the rotational speed. The wall-to-solids heat transfer coefficient was notably lower in presence of lifters. It was also found to increase with the temperature set at the wall and the filling degree, which is imposed by the operating conditions set. Dimensional correlations were developed to describe these two heat transfer mechanisms from the experimental results.
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Modeling of Mean Residence Time of Solid Particles in Rotary Kilns
2014Co-Authors: Alex Stéphane Bongo Njeng, Jean-louis Dirion, Stéphane Vitu, Marc Clausse, Marie DebacqAbstract:Rotary Kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary Kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or exit dam at the kiln outlet end. They usually require very little labor to operate. Though operational cost of these units is usually high, their design is often conservative due to the lack of fundamental physical understanding of both solids flow and heat transfer. The objective of this presentation is to provide a new model to predict the residence time of solid particles within the rotary kiln based on a dimensional analysis. This model can be used for process control as well as for design purposes. Progress of material through a rotary kiln is affected by a number of factors, namely: length and diameter of the kiln, design and number of lifters distributed around the circumference, rotational speed, and slope of the kiln, exit dam height at the kiln outlet end, flow rate and physical properties of the material. Experiments were carried out on a pilot scale rotary kiln at room temperature, whether or not equipped with lifters or fitted with dam at the outlet end. These experiments aimed at determining the effects of most of the factors listed above on the mean residence time of solid particles; the mean residence time was determined from residence time distribution measurements data. The tracer impulse-response technique was used to establish residence time distribution curves. Two granular solids having different properties were used: sand and broken rice. Furthermore, two shapes of lifters were compared to determine the influence of lifter geometry: straight lifters (SL) and rectangular lifters (RL). The other operational parameters were also varied so that a matrix of 69 experiments (without including repeatability tests) was achieved. These experiments were used for the consolidation and validation of the presented model. The model not only gave good agreement with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other Kilns, having different design, materials, and order of magnitude of the operating parameters. The excellent predictive capacity of the model compared to other semi-empirical models shows its capacity to handle a wide range of conditions and operating variables. The model is applicable for inclined Kilns that process materials in cascading (tumbling) motion, whether or not equipped with lifters or fitted with dams at the outlet end.
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Heat transfer in an externally heated rotary kiln: Preliminary results obtained with a new experimental device
2011Co-Authors: Phahath Thammavong, Marie Debacq, Stéphane Vitu, Marc DupoizatAbstract:Rotary Kilns are widely used gas/solid reactors encountered in several branches of the chemical industry. They are a key element in the production processes of cement, lime and pigments, for the reduction of ore in extractive metallurgy and for the pyrolysis of solid waste. They are also used to convert uranium fluoride into uranium dioxide for the production of nuclear fuel. In this kind of device, hydrodynamic, thermal and chemical modelling processes are linked, as it is clear that the temperature profiles of the solid and the gas in the kiln directly influence the chemical reaction kinetics that occur. It is thus essential to be able to calculate precisely the temperature of the solid and of the gas at any point in the kiln and to understand the heat exchanges in the kiln. Various correlations are reported in the literature for estimating the heat transfer coefficients in rotary kiln. However, for a given kiln, the heat transfer coefficient values calculated by using these correlations are highly scattered. Moreover, experimental measurements of heat transfer in rotary Kilns are scarce. The aim of this work is thus to design and construct an adaptable experimental setup to study heat exchange in rotary Kilns. A key point is that the operating mode of the experimental setup must be similar to those of the rotary Kilns used for the conversion of uranium. In particular, our kiln is externally heated and equipped with lifters. The design of our experimental device will be described, focusing on the heating mode chosen and on the instrumentation. A special attention will also be devoted to the preliminary results obtained concerning the influence of the solid flow rate and the rotational speed on the heat transfer coefficient between the wall of the rotary kiln and the solid flowing through the kiln.
