Optimum Gas Velocity Research Articles

Separation performance of 0.5–1 mm fine coal in a gas–solid fluidized bed without dense medium

The polluting elements in coal are mainly concentrated in gangue, and it is difficult for existing dry coal preparation technologies to separate fine gangue below 1 mm effectively. Because 0.5–1 mm raw coal particles belonging to the Geldart B group can form a stable bubbling fluidized bed, the fluidization and segregation of simulated coal particles composed of 0.5–1 mm quartz sand and clean coal were investigated in this study. The results showed that the optimum operation gas velocity was slightly higher than the minimum fluidization gas velocity when the content of quartz sand was less than 60%; when it was higher than 60%, the optimum gas velocity was somewhat less than or equal to the minimum fluidization velocity. When the content of quartz sand was 60%, the separation effect was the most obvious, and the segregation standard deviation was 0.37. The initial bed height was in the range of 150–210 mm, and the separation effect was good. In addition, the separation tests of three raw coal samples showed that the research results of binary-simulated coal particles composed of quartz sand and clean coal were valid. Under the optimal conditions, the ash content of clean coal products of three raw coal samples can be reduced by 75.65%, 79.03%, and 83.03%, respectively.

Numerical simulation of a novel fluidized bed for gas-solid non-catalytic reactions (NRFB)

This study proposed a novel fluidized bed (NRFB) to realize gas-solid non-catalytic continuous reaction. Gas and solid flowed in reverse direction in NRFB, achieving high-efficiency contact between particles and gas to form particles. The discrete phase model was used to simulate the gas-solid two-phase flow in NRFB. Basis on an optimum operating gas velocity, the characteristics of the gas-solid two-phase flow field and sodium phenolate carboxylation in NRFB were analyzed. The equal-area torus method was proposed to explore the radial particle distribution. The results showed that the gas in NRFB could be in full contact with solid particles. The introduction of the grid trays could significantly improve radial distribution and increase the residence time of sodium phenolate particles in the dense phase section, thereby improving the reaction efficiency. The simulation results can provide guidance for the determination of the operation parameters in pilot and industrial production of gas-solid non-catalytic reactions.

A General-Purpose Procedure for the Calculation of the Optimum Gas Velocity in Gas Exhaust Ducts of Stacks at Thermal Power Stations

A General-Purpose Procedure for the Calculation of the Optimum Gas Velocity in Gas Exhaust Ducts of Stacks at Thermal Power Stations

Catalytic Oxychlorination Process Optimization for the Conversion of Ethylene to Ethylene Dichloride

The catalytic oxychlorination of ethylene is widely used for the production of ethylene dichloride (EDC) which is an essential step for the production of poly-vinyl chloride (PVC). However, catalyst entrainment from the fluidization reactor has formed a problem and caused the loss of expensive catalyst powder with the outlet gas, hence less conversion in achieved. In this research we studied the catalytic oxychlorination of ethylene over the surface of geldart A powder with average particle size of 80 microns. Simulation was developed using Aspen plus and Mat Lab. It was validated against the industrial data and they were matching. Various operating conditions and variables were studied. The effect of fluidized gas velocity, bubble diameter, temperature and pressure on solid catalyst entrainment rate. In addition, the copper content from the quencher bottom was analyzed. It was found that the entrainment rate increased with the increase in fluidized gas velocity, bubble diameter, reactor temperature and pressure. While on the other hand increasing orifice diameter decreased the amount of entrained catalyst within the fluidized bed. It was found that the optimum superficial gas velocity is 2570.4 m3/hr.and the optimum orifice diameter is 1 cm. At this condition the lowest rate of solids entrainment out of the bed will be reached. This will decrease the amount of lost catalyst and the process will be more economic with higher gas conversion.

Numerical study and optimization of thermoelectric-hydraulic performance of a novel thermoelectric generator integrated recuperator

Abstract Thermoelectric modules are usually sandwiched between hot-side and cold-side heat exchangers to generate electrical power. But the sandwiched structures are unsuitable for recuperators because large thermal resistance caused by the thermoelectric modules significantly reduces the heat transfer efficiency. In order to maintain heat transfer efficiency and generate more electrical power, a novel concept of a thermoelectric generator integrated recuperator is proposed, with fins made of thermoelectric materials rather than steel. A numerical model is developed using FLUENT software with User Defined Function codes. Compared with conventional plate-fin recuperators, the new recuperator has similar thermal-hydraulic performance and generates additional electrical power. The effects of Reynolds number on open circuit voltage, internal resistance, heat transfer, output power, and pumping power are studied. The optimum hot gas velocity is 1.5 m/s, which produces a temperature difference of 147.6 K, an open circuit voltage of 31.5 mV, and an output power of 0.23 mW. The Taguchi method is employed to design numerical cases for geometrical optimization. Results show that the effect order is: channel width > TE fin thickness > TE fin height. The optimum values of channel width, fin thickness, and height are 1 mm, 3 mm, and 1 mm, respectively.

Adsorption modeling of CO2 in fluidized bed reactor

A model was proposed for studying the adsorption of CO2 in fluidized bed reactor based on combination of two-phase fluidization with tanks-in-series model. Logical combinations of ideal reactors can be of critical importance in gaining insights into the nature of FBRs and might better be further utilized in process simulation software. Implementation of the tanks-in-series model, in addition, is more consistent with hydrodynamics of the bed compared to one-phase and two-phase models. Considering this model, the fluidized bed was divided into 4 equal-volume stages, in which gas flows as completely mixed flow in emulsion phase and in bubble phase as plug flow. Using experimental data, the number of sections was found as a function of Hata number, superficial gas velocity and minimum fluidization velocity. The experimental results in a laboratory scale fluidized bed reactor with two particle sizes (335 and 605μm) at different superficial gas velocities (0.47, 0.62, 0.79, 0.94 and 1.25m/s) and aspect ratios were used for model validation. Obtained breakthrough curves from modeling were compared against experimental data to verify the validity of the model and acceptable agreement was observed. By fitting the results of the proposed model with experimental data, the reaction constant and Langmuir equilibrium constant were determined to be 0.041/s and 0.019m3/mol, respectively. Increasing the superficial gas velocity and better mixing of adsorbent result in greater adsorption capacity. Moreover, it was observed that smaller particles have higher adsorption capacity due to higher specific surface area and mass transfer coefficient than larger particles. It has also been found that the optimum superficial gas velocity was in the range of 0.62 and 0.79m/s for both particles sizes.

THEORETICAL STUDY OF GRANULATION KINETICS IN A BATCH FLUIDIZED BED

The objective of the study is to build a simple but informative model to estimate qualitatively the influence of process parameters on granulation kinetics in a batch fluidized bed. A Markov chain approach is used to build the model. The height of fluidized bed reactor is separated into a certain number of perfectly mixed cells, and two parallel chains of such cells are introduced: one chain for original particles and another chain for already granulated particles. The particles can move stochastically along their chains and transit from one chain to another due to their size enlargement during granulation. It is supposed that the granulation itself occurs only in the cell of original particles where a binder suspension is supplied to. The volume of suspension, which enters the cell during the time step, is spread over the original particles that can be covered by the suspension up to their desired size. These particles transit to the neighboring cell of another chain for already granulated particles. Then the both sorts of particles move along their chains according to corresponding matrices of transition probabilities. This “could” model can be easily combined with the Markov chain model of drying in fluidized bed developed in our previous works. The numerical experiments with the developed model allowed qualitative estimating the influence of the process parameters on the granulation kinetics. The existence of the optimum superficial gas velocity that provides the maximum rate of granulation is shown. For citation:Mitrofanov A.V., Mizonov V.E., Tannous K., Ovchinnikov L.N. Theoretical study of granulation kinetics in a batch fluidized bed. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 5. P. 81-87

Methane Hydrate Formation and Decomposition Properties During Gas Migration in Porous Medium

Natural gas hydrate is a clean energy source with significant potential. It's significant to elucidate the formation and dissociation properties of natural gas hydrate during exploitation process. In this study, methane hydrate reformation under dynamic conditions was simulated to provide essential data for hydrate safe and efficient exploitation. The changes of vessel pressure, methane hydrate saturation (Sh) and residual water saturation (RWS) were measured and analyzed. Residual water distribution is illustrated by images obtained by magnetic resonance imaging (MRI). The experimental results indicated that an optimum gas velocity exist to maximize hydrate generation under a certain initial water saturation when constant velocity of methane was injected into the porous media. Compared to downward methane, upward methane is more likely to cause structure changes of porous medium and the structure changes can’t recover after hydrate dissociation. Comparing the axial residual water distribution porous media during the process of hydrate formation and decomposition, the axial residual water distribution in formation process is more non-uniform than that in dissociation process. Moreover, the hydrate dissociation boundaries moving from vessel wall to core can be observed by MRI images. This study provides important basic data for natural gas hydrate exploitation.

Development of a hollow fiber membrane micro-reactor for biocatalytic production of formate from CO2

A hollow fiber membrane (HFM) micro-reactor was developed for the conversion of CO2 to formate for the first time by combining hydrophobic polymer HFMs as a gas distributor and modified polyethylene (PE) HFMs for enzyme immobilization in the same module. The effects of the ventilation mode, polymer type and parameters of bubbling membrane, gas velocity and configurational parameters of the HFM module on the reaction were investigated. Using HFM for aeration, the specific activity of enzyme increased, and the Michaelis constant decreased remarkably. For most membranes investigated, when the porosity and pore size of the aerating membrane increased, the reaction rate initially increased and later decreased. The maximum rate was achieved with PE when the porosity was 50% and the pore size was 0.625µm. For the membranes made of the same type of polymer, a higher value for the contact angle corresponded with a higher reaction rate. Upgrading the number of bubbling HFMs and packing density intensified the reaction. The optimum upstream gas velocity decreased as the bubbling HFM number increased. The HFM number for bearing enzyme and the height-diameter ratio of the module had no significant effects on the reaction. HFM-attached enzyme showed excellent reusability and storage stability.

De-mixing characteristics of fine coal in an air dense medium fluidized bed

An air dense medium (magnetite) fluidized bed (ADMFB) provides an alternative method for dry coal beneficiation. The de-mixing (segregation) characteristics can significantly affect the quality of the final products. In this study, the segregation characteristics of fine coal (1–3mm) in an ADMFB were compared to those in an ordinary fluidized bed (FB). Specifically, the pressure drop, density-segregation behaviors, segregation degree, motions of the coal/magnetite mixture, and bubble size were determined with various gas velocities. Density-segregation occurred at a low gas velocity in the ADMFB. However, the particles started to mix when the gas velocity was increased. There was an optimum gas velocity to produce the maximum amount of segregation. The comparative analysis (ash segregation degree and bubble size characteristics) between ADMFB and FB suggested that the bubble-drive flotsam-jetsam mechanism can explain the particle segregation. Furthermore, adding dense medium to a fluidized bed led to a higher amount of segregation because of the reduction in bubble size.

Foam fractionation in recovery of captopril

Toxic effect caused due to the presence of pharmaceuticals in waste water has been recognized as one of the emerging issue in the presentday environmental pollution. The aim of the present work is to investigate the feasibility of foam fractionation technique in batch mode for the recovery of captopril from dilute aqueous solution and to compare the performance of drug recovery from two feed solutions, one containing pure drug and the other containing formulated drug (tablet). Captopril is an anionic compound used as antihy- pertensive drug. Presence of this drug can cause aquatic toxicity. The performance of recov- ery was investigated as a function of gas velocity, pH of feed solution, collector-colligend ratio (j), colligend (drug) concentration, feed volume, column height and aliphatic chain length of the collector (surface active agent) and finally, optimum condition had been deter- mined. Percentage recovery was enhanced to 90% (approx) for pure drug at the optimum pH value of 3.75, j = 4 at an optimum gas velocity. The optimum gas velocity depends on feed volume. Percentage recovery (Rp) decreases with increase of chain length. Enrichment ratio (Er) was enhanced with the increase of foam height in the column. Rp and Er were found lower in formulated type of captopril in comparison to the pure drug due to the presence of other soluble ingredients in tablet.

Comprehensive two-dimensional gas chromatography with a multi-capillary second dimension: A new column-set format for simultaneous optimum linear velocity operation

Comprehensive two-dimensional gas chromatography (GC×GC) suffers from the impossibility to operate both dimensions at their optimum carrier gas velocity at the same time due to the different inner diameters of the columns typically employed. The use of multiple parallel capillary columns in the second dimension (GC×multi-GC) is studied as a means to achieve simultaneous optimum-velocity operation. A programme written in Microsoft Excel® was developed to calculate the efficiency of the two dimensions in GC×multi-GC for different numbers of columns in the second dimension. With the aid of this programme the appropriate number of columns was selected. Columns with maximum repeatability were specifically manufactured to grand suitable performance, i.e. to avoid band broadening effects caused by inter-column variations. 1D-GC experiments were carried out on the columns separately and combined in parallel. The performance of the parallel column set was consistent with that of the individual columns, with over 9100plates generated (approximately 10,000plates/m). A GC×multi-GC set-up was successfully installed. Model experiments proved the possibility to operate both dimensions at their optimum linear velocity simultaneously. The suitability of the novel second dimension column format to perform multidimensional separations was also shown for a number of selected applications.

Performance of Membrane Bio-Reactor Equipped with Air-Sparged Side-Stream Tubular Membrane: Treatment Efficiency and Membrane Fouling

We conducted a high-load operation of a baffled bio-reactor equipped with air-sparged side-stream tubular membrane modules for treating actual municipal wastewater at two different periods (high- and low-temperature). Although nitrogen removal efficiency slightly decreased at the low-temperature period, this baffled bio-reactor showed excellent nitrogen and phosphorus removal efficiencies. We also investigated the developments of both physically reversible and irreversible fouling during operation with two-phase flow (mixed-liquor and gas) at various gas velocities and the mixed-liquor velocity was fixed at 0.50 m/s. The membrane flux was fixed at 80 L/m2/hour throughout the experiments. Regardless of the difference in temperature, the trends in the development of these two types of membrane fouling caused by the difference in gas velocity were similar. For physically reversible fouling, an optimum gas velocity, in which the development of this type of fouling was minimized, was found to be around 0.42 m/s (corresponding void fraction was 0.45). A further increase in gas velocity resulted in more reversible fouling. On the other hand, the degree of physically irreversible fouling decreased as gas velocity increased. The results obtained in this study indicated the effect of gas velocity on fouling control differs depending on the type of membrane fouling.

Prediction of the Maximum Heat Transfer Coefficient Between a Horizontal Tube and Gas–Solid Fluidized Beds

Average heat transfer coefficient between a horizontal tube and fluidized bed reaches a maximum at an optimum superficial gas velocity. Prediction of the optimum superficial gas velocity and maximum heat transfer coefficient in gas–solid fluidized beds was obtained based on a cluster-based mechanistic model that properly takes into account the thermal and fluid dynamic properties of the solids and the fluidizing gas. Experiments were carried out in a 15 cm diameter fluidized bed using 280, 490, and 750 μ m sand particles fluidized by air with an 8 mm diameter horizontal tube immersed in the bed. The predicted values were compared with the experimental data of this work as well as those from the literature under a wide range of operating conditions with good agreement. The model presented in this work for prediction of maximum heat transfer coefficient and optimum superficial gas velocity is considerably more reliable than existing correlations.

Single fiber-in-capillary annular column for gas chromatographic separation

A method for preparation of a stationary phase-adjustable column with in-column stationary phase-coated fused-silica fiber annular column was successfully developed. The surface of a 0.12 mm o.d. bare optical fiber was first coated with a stationary phase and then inserted into a fused-silica capillary (non-coated or coated) as an annular column for gas chromatographic study. The optical fiber and capillary were coated with polydimethylsiloxane (SE-30) and polyethylene glycol 20M (PEG-20M) as nonpolar and polar stationary phases, respectively. Among the investigated annular and open tubular columns, the PEG-20M-coated fiber-in-PEG-20M-coated capillary annular column showed the highest column efficiency with a minimum plate height of 0.35 mm and an optimum gas velocity of 25 cm/s. When a SE-30/PEG-20M-coated fiber-in-uncoated capillary annular column was applied to separate a 9-component complex mixture, the total analysis time was 5.3 min and the column length was 12 m. By contrast, when a SE-30-coated fiber-in-PEG-20M-coated capillary annular column was used to separate the same 9-component mixture, the analysis time was reduced to 3.5 min and the column length was shortened by half to 6 m. Our results show that the stationary phase-coated fiber-in-stationary phase-coated capillary annular column is a better choice for gas chromatographic separation as it is more efficient and flexible. In addition, the proposed annular column design provides flexibility in using two or even more types of stationary phases to achieve optimal analytical separation.

Studies on segregation of binary mixture of solids in continuous fast fluidized bedPart III. Quantification of performance of the segregator

Abstract Segregation of particles due to difference in either size or density was studied in a continuous fast fluidized bed of 69 mm ID and 3.65 m height [1] . Binary feed mixtures of either flotsam-rich or intermediary or jetsam-rich mixtures were utilized for the study. The influence of the operating variables on the particles segregation was examined. All the considered feed mixtures, showed similar segregation effect even though the fluidization behavior of the binary mixtures differ [1] , [2] . Empirical correlations were suggested for the entrainment of solids and purity of the top and bottom products for all the three categories of binary feed mixtures considered. The optimum gas velocity for maximum separation of the lighter/fine and heavier/coarse particles is identified. The effect of the operating variables on the identified optimum gas velocity and optimum purity/recovery is presented.

Production of hydrogen and carbon nanofibers by thermal decomposition of methane using metal catalysts in a fluidized bed reactor

Thermo catalytic decomposition (TCD) of methane using Ni–Cu–Al catalyst in a pilot scale fluidized bed is studied. The conventional method of catalyst preparation based on co-precipitation is compared versus an easier preparation method based on the fusing of the metallic nitrates. Catalysts prepared by both methods shown similar behavior. Fluidodynamic studies have shown that TCD can be carried out in a fluidized bed reactor without reactor clogging provided that a methane velocity of two times the minimum fluidization velocity is used. This high spacial velocity resulted in a reduction of the fraction of methane converted, but not in the quantity of carbon deposited per gram of catalyst. The optimum gas velocity should be chosen in terms of hydrogen production rates and fluidization quality. A semi-continuous fluidized bed installation has been started up and operated to produce at the scale of 60 l h - 1 of hydrogen and 15 g h - 1 of carbon nanofibers.

Hydrodynamic and Thermal Modelling of Gas-Particle Flow in Fluidized Beds

In this study a mathematical model has been developed to simulate two dimensional fluidized beds with uniform fluidization. The model consists of two sub models for hydrodynamic and thermal behavior of fluidized beds on which a FORTRAN program entitled (NEWFLUIDIZED) is devolved .The program is used to predict the volume fraction of gas and particle phases, the velocity of the two phases, the gas pressure and the temperature distribution for two phases. Also the program calculates the heat transfer coefficient. Besides that, the program predicts the fluidized bed stability and determines the optimum input gas velocity for fluidized beds to achieve the best thermal behavior. The hydrodynamic model is verified by comparing its results with the computational fluid dynamic code MFIX [1]. The thermal model was tested and compared to the available previous experimental correlations. The model results show good agreement with MFIX results and the thermal model of the present work confirms Zenz [2] and Gunn [3] equations.

Photocatalytic degradation of trichloroethylene over TiO2/SiO2 in an annulus fluidized bed reactor

The effects of superficial gas velocity (Ug), wavelength and intensity of ultraviolet (UV) light, oxygen and H2O concentration on the photocatalytic degradation of TCE (Trichloroethylene) over TiO2/SiO2 catalyst have been determined in an annulus fluidized bed photoreactor. The key factor in determining the performance of the annulus fluidized bed photoreactor is found to be an optimum superficial gas velocity (Ug) that provides the optimum UV lighttransmit through the proper size of bubbles in the photoreactor. The degradation efficiency of TCE increases with light intensity but decreases with wavelength of the UV light and H2O concentration in the fluidized bed of TiO2/silica-gel photocatalyst. The optimum concentration of O2 for TCE degradation is found to be approximately 10%. The annulus fluidized bed photoreactor is an effective tool for high TCE degradation with efficient utilization of photon energy.

Biological treatment of mixed industrial wastewaters in a fluidised bed reactor

A study has been carried out on the operating parameters that influence the biodegradation of petroleum and brewery wastewaters, with a low-density biomass support. The biodegradation rate of a mixture of two wastes was compared with that of the separate wastes. A low aspect ratio reactor was employed, and this made it possible to operate at low superficial gas and liquid velocities. The gas distributor used created a fluid flow pattern similar to that of a draft tube, which enhanced axial mixing. At a particles loading of 12% (v/v), the optimum superficial gas velocity was 2.5 cm/s for the mixture. The interstice structure of the biomass-support particles, improved microbial attachment due to the resulting large surface area. There was a low biomass concentration when petroleum wastewater was treated alone, however, for a mixture of petroleum and brewery wastewaters, an increase in the concentration was observed. There was a higher gas hold up in the mixture than in the petroleum wastewater, but lower than in the brewery wastewater. An improved biodegradation was achieved when a mixture of brewery and petroleum wastewaters was treated, and this gave an indication that nutrient deficient wastes can be treated together with phosphate and nitrate rich food industry wastewaters.