scholarly journals Fluidized bed hydrodynamic modeling of CO2 in syngas: Distorted RTD curves

2021 ◽  
Author(s):  
Ariane Berard ◽  
Bruno Blais ◽  
Gregory Patience
Keyword(s):  
Gas Phase ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Dispersion Model ◽  
Operating Conditions ◽  
Fluid Catalytic Cracking ◽  
No Adsorption ◽  
Axial Dispersion Model ◽  
Chromatographic Effect ◽  
Bubble Sizes

Bubbles rising through fluidized beds at velocities several times superficial velocities contribute to solids backmixing. In micro-fluidized beds, the walls constrain bubble sizes and velocities. To evaluate gas-phase hydrodynamics and identify diffusional contributions to longitudinal dispersion, we injected a mixture of H2, CH4, CO, and CO2 (syngas) as a bolus into a fluidized bed of porous fluid catalytic cracking catalyst while a mass-spectrometer monitored the effluent gas concentrations at 2 Hz. The CH4, CO, and CO2 trailing RTD traces were elongated versus H2 demonstrating a chromatographic effect. An axial dispersion model accounted for 92% of the variance in the data but including diffusional resistance between the bulk gas and catalyst pores and adsorption explained 98.6% of the variability. At 300 °C, the CO2 tailing disappeared consistent with expectations in chromatography (no adsorption). H2 and He are poor gas-phase tracers at ambient temperature. We recommend measuring the RTD at operating conditions.

Comparing ANSYS Fluent® and OpenFOAM® simulations of Geldart A, B and D bubbling fluidized bed hydrodynamics

2019 ◽  
Vol 30 (1) ◽  
pp. 93-118 ◽  
Author(s):  
Cesar Martin Venier ◽  
Andrés Reyes Urrutia ◽  
Juan Pablo Capossio ◽  
Jan Baeyens ◽  
Germán Mazza
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Internal Diameter ◽  
Ansys Fluent ◽  
Content Type ◽  
Current State ◽  
Bubbling Fluidized Bed ◽  
Bubble Sizes

Purpose The purpose of this study is to assess the performance of ANSYS Fluent® and OpenFOAM®, at their current state of development, to study the relevant bubbling fluidized bed (BFB) characteristics with Geldart A, B and D particles. Design/methodology/approach For typical Geldart B and D particles, both a three-dimensional cylindrical and a pseudo-two-dimensional arrangement were used to measure the bed pressure drop and solids volume fraction, the latter by digital image analysis techniques. For a typical Geldart A particle, specifically to examine bubbling and slugging phenomena, a 2 m high three-dimensional cylindrical arrangement of small internal diameter was used. The hydrodynamics of the experimentally investigated BFB cases were also simulated for identical geometries and operating conditions using OpenFOAM® v6.0 and ANSYS Fluent® v19.2 at identical mesh and numerical setups. Findings The comparison between experimental and simulated results showed that both ANSYS Fluent® and OpenFOAM® provide a fair qualitative prediction of the bubble sizes and solids fraction for freely-bubbling Geldart B and D particles. For Geldart A particles, operated in a slugging mode, the qualitative predictions are again quite fair, but numerical values of relevant slug characteristics (length, velocity and frequency) slightly favor the use of OpenFOAM®, despite some deviations of predicted slug velocities. Originality/value A useful comparison of computational fluid dynamics (CFD) software performance for different fluidized regimes is presented. The results are discussed and recommendations are formulated for the selection of the CFD software and models involved.

Combustion Characteristics of Natural Gas in a Circulating Fluidized Bed

2003 ◽  
Author(s):  
Dennis Y. Lu ◽  
Edward J. Anthony
Keyword(s):  
Natural Gas ◽  
Gas Phase ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Pilot Scale ◽  
Combustion Characteristics ◽  
Air Pollutant ◽  
Operating Conditions ◽  
Fluidized Bed Combustion ◽  
Gas Combustion

Recently there has been interest in extending the application of fluidized bed combustors (FBCs) to fuels with difficult handling properties or ones that are associated with non-conventional air pollutant problems. These fuels, such as biomass, plastic wastes, black liquors and heavy liquid fuels, have very high volatiles contents and, because they are often treated as easily-burned materials, they have received much less attention than has been given say to the combustion processes for char in FBCs. Understanding their gas-phase chemistry is helpful in optimizing their combustion. This paper describes the study of natural gas combustion in a fluidized bed as a simple model for studying gas-phase reactions involving C/H/N/O chemistry in the absence of char. The experimental work was conducted using a pilot-scale CFBC unit. Combustion characteristics and emissions were investigated by varying the operating conditions and in particular the combustion temperature, fluidizing velocity and bed material. The results indicated that fluidized bed combustion chemistry is associated with superequilibrium free radical processes, similar to high-temperature flame systems. In this system, prompt-NO mechanisms are the only routes for NO formation and this work shows that they can lead to significant NOx production.

Modelling of gaseous phase in bubble columns

1991 ◽  
Vol 56 (6) ◽  
pp. 1238-1248
Author(s):  
Jana Vašáková ◽  
Jan Čermák
Keyword(s):  
Gas Phase ◽  
Driving Force ◽  
Bubble Column ◽  
Dispersion Model ◽  
Correlation Method ◽  
Axial Dispersion ◽  
Bubble Columns ◽  
Axial Dispersion Model ◽  
Impulse Characteristics ◽  
Dispersion Layer

An axial dispersion model of a bubble column was verified by an experimental method based on pseudo-random binary signals of maximum length. The diameter of the column was 0.292 m and the height of the dispersion layer was 1.33 m. Water formed a stagnant liquid layer and a mixture of air with up to 5 vol.% of CO2 formed a streaming gas phase. The model was evaluated from the response of the bubble column to pseudo-random binary signals and from impulse characteristics calculated from this response by the correlation method. The use of the axial dispersion model with mass transfer was evaluated in dependence on the driving force.

Frequency Domain Analysis of Fluidized Beds with Vibration Time Series of the Bed Wall

2013 ◽  
Vol 391 ◽  
pp. 477-481
Author(s):  
H.R. Norouzi ◽  
H. Azizpour ◽  
R. Zarghami ◽  
J. Chaouki ◽  
Navid Mostoufi
Keyword(s):  
Time Series ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Vibration Signal ◽  
Frequency Domain Analysis ◽  
Industrial Applications ◽  
Operating Conditions ◽  
High Frequencies ◽  
Power Spectral ◽  
Vibration Time

Monitoring of fluidized beds operation is important in industrial applications. Collecting fluidize bed wall vibration is a non-intrusive method that can be used to characterize bed hydrodynamics. In the present work, the vibration of a lab-scale fluidized bed was measured at different operating conditions as well as the empty bed. It was shown that vibration of the empty bed is as significant as that of the fluidized bed. Therefore, the vibration signal was decomposed into two distinct signals, coherent and inherent signals. The inherent signal was used to reflect the bed hydrodynamics. The power spectral density of inherent vibration signal showed that the increasing aspect ratio of the bed leads to an increase in the intensity of vibrations especially at high frequencies. Moreover, there are first, second and so forth harmonics for which their intensities decrease as the frequency is increased.

Comparative Bio-sorption of Cadmium and Nickel Ions from Aqueous Solution onto Fibers of Date Palm using Fluidized Bed Column

2019 ◽  
Vol 70 (5) ◽  
pp. 1507-1512
Author(s):  
Baker M. Abod ◽  
Ramy Mohamed Jebir Al-Alawy ◽  
Firas Hashim Kamar ◽  
Gheorghe Nechifor
Keyword(s):  
Aqueous Solution ◽  
Heavy Metal ◽  
Metal Ions ◽  
Fluidized Bed ◽  
Removal Efficiency ◽  
Heavy Metal Ions ◽  
Date Palm ◽  
Operating Conditions ◽  
Initial Concentration ◽  
Bed Height

The aim of this study is to use the dry fibers of date palm as low-cost biosorbent for the removal of Cd(II), and Ni(II) ions from aqueous solution by fluidized bed column. The effects of many operating conditions such as superficial velocity, static bed height, and initial concentration on the removal efficiency of metal ions were investigated. FTIR analyses clarified that hydroxyl, amine and carboxyl groups could be very effective for bio-sorption of these heavy metal ions. SEM images showed that dry fibers of date palm have a high porosity and that metal ions can be trapped and sorbed into pores. The results show that a bed height of 6 cm, velocity of 1.1Umf and initial concentration for each heavy metal ions of 50 mg/L are most feasible and give high removal efficiency. The fluidized bed reactor was modeled using ideal plug flow and this model was solved numerically by utilizing the MATLAB software for fitting the measured breakthrough results. The breakthrough curves for metal ions gave the order of bio-sorption capacity as follow: Cd(II)]Ni(II).

Expulsion of particles from a buoyant blob in a fluidized bed

1994 ◽  
Vol 278 ◽  
pp. 63-81 ◽  
Author(s):  
G. K. Batchelor ◽  
J. M. Nitsche
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Particle Concentration ◽  
Small Concentration ◽  
Numerical Calculations ◽  
Significant Feature ◽  
Average Particle ◽  
Remarkable Property ◽  
Gas Fluidized Beds ◽  
Secondary Instabilities

It is a significant feature of most gas-fluidized beds that they contain rising ‘bubbles’ of almost clear gas. The purpose of this paper is to account plausibly for this remarkable property first by supposing that primary and secondary instabilities of the fluidized bed generate compact regions of above-average or below-average particle concentration, and second by invoking a mechanism for the expulsion of particles from a buoyant compact blob of smaller particle concentration. We postulate that the rising of such an incipient bubble generates a toroidal circulation of the gas in the bubble, roughly like that in a drop of liquid rising through a second liquid of larger density, and that particles in the blob carried round by the fluid move on trajectories which ultimately cross the bubble boundary. Numerical calculations of particle trajectories for practical values of the relevant parameters show that a large percentage of particles, of such small concentration that they move independently, are expelled from a bubble in the time taken by it to rise through a distance of several bubble diameters.Similar calculations for a liquid-fluidized bed show that the expulsion mechanism is much weaker, as a consequence of the larger density and viscosity of a liquid, which is consistent with the absence of observations of relatively empty bubbles in liquid-fluidized beds.It is found to be possible, with the help of the Richardson-Zaki correlation, to adjust the results of these calculations so as to allow approximately for the effect of interaction of particles in a bubble in either a gas- or a liquid-fluidized bed. The interaction of particles at volume fractions of 20 or 30 % lengthens the expulsion times, although without changing the qualitative conclusions.

Study on De-Nitrification of Improved Step-Feed Progress

2014 ◽  
Vol 703 ◽  
pp. 171-174
Author(s):  
Bing Wang ◽  
Yi Xiao ◽  
Shou Hui Tong ◽  
Lan Fang ◽  
Da Hai You ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Fluidized Bed ◽  
Removal Efficiency ◽  
Nitrogen Removal ◽  
Removal Rate ◽  
Operating Conditions ◽  
Removal Mechanism ◽  
Aerobic Zone

Improved step-feed de-nitrification progress combined with biological fluidized bed was introduced in this study. The progress had good performance and capacity of de-nitrification and organic matter. The experiment result showed that the de-nitrification efficiency of the improved biological fluidized bed with step-feed process was higher than the fluidized bed A/O process under the same water quality and the operating conditions. When the influent proportion of each segment was equal, the system showed good nitrogen removal efficiency with the change of influent C/N ratio, HRT and sludge return ratio. The removal rate of TN reached up to 88.2%. It showed that the simultaneous nitrification and de-nitrification phenomenon happened in the aerobic zone. The nitrogen removal mechanism was also studied.

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