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Hermann Hofbauer - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the solid Circulation Rate in circulating fluidized bed systems
Powder Technology, 2018Co-Authors: Michael Stollhof, Stefan Penthor, Karl Mayer, Hermann HofbauerAbstract:Abstract The results of experiments performed in four different fluidized bed units (two pilot plants and two cold flow models, with a wide range of operating conditions) together with correlations from literature are used to establish methods to estimate the solid Circulation Rate in a circulating fluidized bed system. The estimation is based on the measured pressure drop in the upper part of the riser as well as particle properties and geometry of the riser exit. Investigations included smooth as well as abrupt riser exit configurations. In case of a smooth riser exit geometry (direct gas solids separation exit), the assumption of a uniformly upflow of solids in the riser is sufficient for the estimation of the solid Circulation Rate. Further, for an abrupt exit (L-shape exit), two methods were developed. Both methods are based on the assumption that the Rate of reflected particles at the top of the riser increases with the so-called exit Froude number. One method is based on a correlation between interstitial gas velocity in the riser, slip velocity, mean particle velocity in the riser, and exit Froude number where it was possible to keep the difference between measured and estimated solid Circulation Rate in the range of approximately +75% and −40%. Further, this method is not able to consider the local mass flow distribution in the riser. For the other method, the output of a detailed mathematical model, based on information from literature, was used to establish a correlation between, exit Froude number, exit reflecting coefficient and local mass flow to estimate the solid Circulation Rate. Using this method it was possible to keep the difference between measured and estimated solid Circulation Rate in the range of ±40%. For both methods, the accuracy of the measurement of the pressure drop in the upper part of the riser is a significant parameter for the prediction of the solid Circulation Rate.
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Estimation of solids Circulation Rate through magnetic tracer tests
Powder Technology, 2017Co-Authors: Diana Carolina Guío-pérez, Florian Dietrich, Jorge Nicolay Ferreira Cala, Tobias Pröll, Hermann HofbauerAbstract:Abstract This work assesses the solids Circulation Rate in a circulating fluidized bed cold model based on measuring the particles mean residence time ( τ ). The tracking method detects fluid-dynamically similar ferromagnetic tracer particles, and is based on inductance changes of a coil due to changes in the concentration of ferromagnetic particles in its core. A section of the model was selected to perform the tracer measurement, such that the variations in the solids volumetric fraction and the solids velocity were negligible, and a correlation between the Circulation Rate and the mean residence time of solids could be established. The Circulation Rate was calculated in this manner for a range of operation conditions, variations of riser fluidization velocity and total inventory were performed. The results were validated measuring the Circulation Rate by the accumulation method as well, the results show a satisfactory correlation between the tracer and the accumulation methods. The magnetic tracer method appears thus to be suitable for the measurement of solids Circulation Rates in low temperature applications. This method offers as advantages the possibility for on-line measurement, good sensitivity, non-intrusiveness, cost efficiency, and does not require a calibration.
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Comparison of Four Different Methods for Measuring the Solids Circulation Rate in Circulating Fluidized Beds
2013Co-Authors: Florian Dietrich, Tobias Pröll, Gregor Tondl, David Wöss, Hermann HofbauerAbstract:In this work four different methods are proposed for the measurement of the solids Circulation Rate in the scaled cold flow model of a circulating fluidized bed (CFB) facility; the study is ultimately aimed to transfer the most suitable method to the corresponding oxyfuel combustion CFB pilot plant. The configuration of a screw conveyor by-passing the loop-seal provides additional possibilities for the determination of the Circulation Rate. Further the influence of the Circulation Rate on the horizontal pressure difference in the loop-seal was investigated. Method 1 and 2 cannot be applied for the hot oxyfuel pilot plant as optical principles are used in both cases. Method 3 as well as method 4 are suitable for a transfer to the oxyfuel pilot plant as they can be performed on-line and require only simple calibration. Further the results indicated a linear correlation between the Circulation Rate and the horizontal pressure difference in the loop-seal for the conditions studied here. INTRODUCTION In many chemical processes gas-solids contact is an important requirement. In these processes contact between the particle and the fluid is realized in form of a circulating fluidized bed, where “the fluid phase opeRates in a “flow through” mode, whereas the solid phase circulates in a closed loop” (1). An important parameter to quantify heat and mass transportation and thus showing the quality of the reactor, is the Circulation Rate. Circulation Rate measurements can be categorized into 6 groups, these being: “optical, radioactive, electrical, tracer, acoustical, heat/mass transfer and mechanical” (2). Additionally, a distinction must be made between methods which are invasive and ones which are not, furthermore some methods will require calibration, others won’t. The ideal method of measuring the Circulation Rate of a fluidized bed facility is non-invasive; it would also need no calibration, and would be flexible in terms of fluidization Rates and temperatures (2). Numerous experiments have been conducted in order to measure the solids Circulation Rate in CFB-facilities. Burkell et al.(3) measured the Circulation Rate by means of closing a permeable butterfly valve in the return leg, this led to an accumulation of solids. The temporal pressure difference across the valve is monitored and measured. The method was only classified appropriate for smallscale models due to higher interference in large-scale models. Burkell et al. (3) also used a method in which “the time for identifiable particles to descend through a known distance in a transparent section of a standpipe through which the solids return in moving packed bed flow” (3) was measured. Although both mentioned methods cannot be used for on-line measurement of the Circulation Rate, the latter method is very accuRate and reliable, can however be impractical for small particles. A particularly elegant calorimetric method was also investigated by Burkell et al. (3). A cooling jacket, through which cooling water or air flows, is mounted to a heat transfer section of the facility. Both temperature difference and mass flow of the cooling medium before and after the jacket is measured; along with the temperature difference of solids before and after the heat transfer section. The Circulation Rate can then be estimated from a simple heat balance. Despite elaboRate calibration, this on-line method proved to be dependable over a broad range of conditions. By conducting two sets of experiments in a section of the downcomer where plug-flow was provided Bhusarapu et al. (2) as well as Roy et al. (1) used noninvasive radioactive methods to measure the solids Circulation Rate. The fundamental idea was to determine the solids volumetric flow by measuring the cross-sectional area, the cross-sectional averaged solids holdup along with the solids velocity. Mass flux can then be calculated with knowledge of the particle density. Initial experiments determined solids holdup by scanning the cross section of the downcomer using one radioactive source and one detector. These experiments were conducted in various operating modes so a calibration curve could be established. Subsequently, solids velocity was determined in various operating modes by measuring the falling time of a single radioactive tracer particle between two detectors mounted on the downcomer. The requirement for the tracer particle, besides similar size and density as the particles used as inventory, is a relatively short half-life so it is harmless once it is no longer needed. After these experiments, a calibration curve for the Circulation Rate as a function of the fluidization Rate can be created. Detailed information on these experiments can be found elsewhere (1; 2).
Pallippattu Krishnan Vijayan - One of the best experts on this subject based on the ideXlab platform.
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Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed
Industrial & Engineering Chemistry Research, 2018Co-Authors: Palash Kumar Mollick, Aniruddha B. Pandit, Pallippattu Krishnan VijayanAbstract:Solid Circulation Rate in a draft tube spouted bed is an important parameter for its industrial use. It can be manipulated adjusting the dimensions of the draft tube and entrainment height above the gas inlet nozzle and is studied here for a wide range of spouting gas velocities. A maximum entrainment height is identified and seen to show strong correspondence with the ratio between the projected volumes of annulus and spout zones below the draft tube. Overall energy loss at the spout-annulus interface has been reported for the first time as a function of particle size. Solid Circulation Rate is seen to be highly affected by flow resistance due to the passage of solid flow between conical apparatus wall and the draft tube and solid pressure in the annulus and can be well varied by changing the spouting gas velocity and fixing at a critical value.
Palash Kumar Mollick - One of the best experts on this subject based on the ideXlab platform.
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Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed
Industrial & Engineering Chemistry Research, 2018Co-Authors: Palash Kumar Mollick, Aniruddha B. Pandit, Pallippattu Krishnan VijayanAbstract:Solid Circulation Rate in a draft tube spouted bed is an important parameter for its industrial use. It can be manipulated adjusting the dimensions of the draft tube and entrainment height above the gas inlet nozzle and is studied here for a wide range of spouting gas velocities. A maximum entrainment height is identified and seen to show strong correspondence with the ratio between the projected volumes of annulus and spout zones below the draft tube. Overall energy loss at the spout-annulus interface has been reported for the first time as a function of particle size. Solid Circulation Rate is seen to be highly affected by flow resistance due to the passage of solid flow between conical apparatus wall and the draft tube and solid pressure in the annulus and can be well varied by changing the spouting gas velocity and fixing at a critical value.
Lawrence J. Shadle - One of the best experts on this subject based on the ideXlab platform.
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Phase-Shift Method to Estimate Solids Circulation Rate in Circulating Fluidized Beds
Industrial & Engineering Chemistry Research, 2013Co-Authors: J. Christopher Ludlow, Rupen Panday, Lawrence J. ShadleAbstract:While solids Circulation Rate is a critical design and control parameter in circulating fluidized bed (CFB) reactor systems, there are no available techniques to measure it directly at conditions of industrial interest. Cold flow tests have been conducted at NETL in an industrial scale CFB unit where the solids flow has been the topic of research in order to develop an independent method which could be applied to CFBs operating under the erosive and corrosive high temperatures and pressures of a coal fired boiler or gasifier. The dynamic responses of the CFB loop to modest modulated aeration flows in the return leg or standpipe were imposed to establish a periodic response in the unit without causing upset in the process performance. The resulting periodic behavior could then be analyzed with a dynamic model and the average solids Circulation Rate could be established. This method was applied to the CFB unit opeRated under a wide range of operating conditions including fast fluidization, core annular flow...
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Improvement of continuous solid Circulation Rate measurement in a cold flow circulating fluidized bed
Powder Technology, 2008Co-Authors: J. Christopher Ludlow, Esmail R. Monazam, Lawrence J. ShadleAbstract:A method is described to independently estimate the solids velocity and voidage in the moving bed portion of the NETL circulating fluidized bed (CFB). These quantities are used by a device that continuously measures the solids Circulation Rate. The device is based on the use of a rotating Spiral vane installed in the standpipe of a circulating fluid bed (CFB). Correlations were developed from transient experiments and steady state mass balance data to correct the solids velocity and solids fraction in the standpipe as a function of standpipe aeration Rate. A set of statistically-designed experiments was used to establish the need for these corrections and to verify the accuracy of solid Circulation Rate measurements after correction. The differences between the original and corrected measurements were quantitatively compared.
C. Jim Lim - One of the best experts on this subject based on the ideXlab platform.
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Measurement of solids Circulation Rate in a high temperature dual fluidized bed pilot plant
Powder Technology, 2017Co-Authors: M. Hafizur Rahman, John R. Grace, C. Jim LimAbstract:Abstract A number of fluidized bed reactor processes operating at high temperature require that solid particles be circulated back and forth between two reactor vessels. Since the Circulation Rate strongly affects mass and energy balances, and therefore greatly influences hydrodynamics and performance of the system, a reliable technique for its accuRate measurement would be helpful in monitoring and modeling the process. However, there are no reported techniques suitable for measuring solid Circulation Rates at elevated temperatures typical of gasification systems. A novel thermal-tracing technique was developed for measuring the solids Circulation Rate between two reactors. Particles at room temperatures (cold particles) are injected into a downward-moving packed bed of solids at elevated temperature (hot particles), creating reduced-temperature zones inside the moving bed. The transit time of the cold-particle-clusters between pairs of thermocouples is determined by cross correlation allowing the flux to be estimated. The technique was shown to provide sensitive and reproducible data for a cold model unit with injection of dry ice. The technique was then applied to determine the solids Circulation Rate between the bubbling bed gasifier and the riser combustor of a pilot scale dual fluidized bed gasification system. A number of conditions are imposed on the data to eliminate unsatisfactory data at high temperatures. Data which satisfy the discrimination criteria are shown to lead to measured solids Circulation fluxes up to 133 kg/m2-s at temperatures up to 856 °C in the gasifier test section. The technique provides high-temperature solids Circulation Rate information beyond the capability of other techniques.