Fluidization behavior in a circulating slugging fluidized bed reactor. Part II: Plug characteristics

In the transporting square nosed slugging fluidization regime () a bed of polyethylene powder with a low density () and a large particle size distribution () was operated in two circulating fluidized bed systems (riser diameters 0.044 and 0.105 m). A relation was derived for the plug velocity as a function of the gas velocity, solids flux, riser diameter, particle size range and particle and powder properties. The influence of the plug length on the plug velocity, the raining rate of solids onto and from the plugs and the influence of the particle size range on the plug velocity is accounted for.     

Flow behavior and regime transition in a high-density circulating fluidized bed riser

Flow behavior and flow regime transitions were determined in a circulating fluidized bed riser (0.203 m i.d. × 5.9 m high) of FCC particles (, ). A momentum probe was used to measure radial profiles of solids momentum flux at several heights and to distinguish between local net upward and downward flow. In the experimental range covered (; ), the fast fluidization flow regime was observed to coexist with dense suspension upflow (DSU). At a constant gas velocity, net downflow of solids near the wall disappeared towards the bottom of the riser with increasing solids mass flux, with dense suspension upflow achieved where there was no refluxing of solids near the riser wall on a time-average basis. The transition to DSU conditions could be distinguished by means of variations of net solids flow direction at the wall, annulus thickness approaching zero and flattening of the solids holdup versus G_s trend. A new flow regime map is proposed distinguishing the fast fluidization, DSU and dilute pneumatic transport flow regimes.     

Solid circulation rate in a circulating fluidized bed in the presence of fine powders

Fine powders (Geldart's group C) are added to a circulating fluidized bed (CFB) of coarse particles (Geldart's group A) and the solid circulation rate (SCR) is investigated with addition of fine powders of different sizes and different fractions (different hold-ups) to the bed. Experiments were carried out in a CFB of 2 m in height and 0.052 m in diameter, using FCC catalyst particles of as the coarse particles and cohesive aluminum hydroxide powders of 0.5- as the fine powders. The effects of hold-up of fine powders in the bed, fine powders size, and superficial gas velocity on the SCR were investigated.The SCR strongly depended on the hold-up of fine powders of 0.5- in size and noticeably decreased with increasing the hold-up of fine powders under constant gas velocity. This dependency disappeared when the size of fine powders was larger than . Thus, depending on the size of fine powders added to the CFB, two distinct regions for the changes of SCR could be clearly identified.     

Influence of carbon dioxide partial pressure and fluidization velocity on activated carbons prepared from scrap car tyre in a fluidized bed

The effect of carbon dioxide partial pressure and fluidization velocity on activated carbons produced by carbon dioxide activation of scrap car tyre rubber in a fluidized bed has been studied. The method consisted of carbonization at under nitrogen followed by activation at . Three types of activated carbons were produced using activated gas concentrations of 20, 60 and 100% carbon dioxide by volume, the rest nitrogen, at a constant fluidization velocity (0.0393 m/s) to investigate the influence of carbon dioxide partial pressure. Within the experimental setup and activation time of 4 h, it was observed that BET surface area and total pore volume increased with carbon dioxide partial pressure reaching and , respectively, for 100% activation with carbon dioxide. Three other types of activated carbons were produced using 100% carbon dioxide at two (0.0393 m/s), three (0.0589 m/s) and four (0.0786 m/s) times the minimum fluidization velocity (U_mf). The BET surface area and total pore volume were observed to increase with fluidization velocity (which can be viewed as an indicator of the intensity of mixing in the bed), reaching and , respectively, at four times the minimum fluidization velocity.     

Non-catalytic recovery of phenol through decomposition of 2-isopropylphenol in supercritical water

The decomposition of 2-isopropylphenol (IPP) was studied in supercritical water at 723- with a water density of 0- in the absence of catalyst. The main products were phenol, 2-propylphenol (PP), 2-cresol and 2-ethylphenol. The reaction was determined to proceed as follows. At first, the dealkylation and rearrangement of IPP yielded phenol and PP, respectively. Next, the dealkylation of PP lead to the formation of 2-cresol and 2-ethylphenol. The conversion of IPP and the selectivity of phenol increased with the increasing water density, which led to an increase in the yield of phenol. The recoveries of phenol as high as 43% can be obtained in the high water density region at . The rate constant for decomposition of IPP was correlated with a global reaction model for a range of temperatures from 613 to .     

CFD simulation of gas solid flow in FCC strippers

In this paper, the hydrodynamic characteristics in bubbling fluidized beds (FCC Strippers) were simulated by using computational fluid dynamics (CFD) code (Fluent 6.2.16). The modified Gidaspow drag model based on the effective mean diameter of the particle clusters predicted the expected bubbling fluidization behavior and bed expansion. Compared with the bed densities of in the empty-cylinder stripper, bed densities in the V-baffled stripper were at the superficial gas velocity of 0.10-0.20 m/s. The overall trend of the time-averaged bed density at various superficial gas velocities were in agreement with the experimental data. The results illustrated that internal baffles had an important effect on the fluidization hydrodynamics. Internal baffles improved break-up and redistribution of bubbles and intensified the gas-solid contact. The simulation results also indicated that appropriate modification of the internal configuration eliminated the dead flow region in the strippers, and enhanced the gas-solid mixing remarkably, showing benefit for the mass and heat transfer in the fluidized bed.     

Electrochemical performances of gel polymer electrolytes using tetra(ethylene glycol) diacrylate

A gel polymer electrolyte (GPE) was prepared using tetra(ethylene glycol) diacrylate monomer, benzoyl peroxide, and (). The LiCoO₂/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures.The viscosity of the precursor containing the tetra(ethylene glycol) diacrylate monomer was around . The ionic conductivity of the gel polymer electrolyte at 20°C was around . The gel polymer electrolyte had good electrochemical stability up to vs. Li/Li⁺. The capacity of the LiCoO₂/GPE/graphite cell at rate was 63% of the discharge capacity at rate. The capacity of the cell at −10°C was 81% of the discharge capacity at 20°C. Discharge capacity of the cell with gel polymer electrolyte was stable with charge-discharge cycling.     

Temperature variations in the oxygen carrier particles during their reduction and oxidation in a chemical-looping combustion system

A particle reaction model including mass and heat transfer has been developed to know the temperature variations produced inside the oxygen carrier particles during the cyclic reduction and oxidation reactions taking place in a chemical-looping combustion (CLC) system. The reactions of the different oxygen carriers based on Cu, Co, Fe, Mn, and Ni during the reduction with fuel gas (CH₄, CO, and H₂) and oxidation (O₂) have been considered. In these systems, the oxidation reaction is always exothermic with subsequent heat release; however, the reduction reaction can be exothermic or endothermic depending on the metal oxide and the fuel gas. The heat generated inside the oxygen carriers during the exothermic reactions increases the particle temperature, and could affect the particle structure if the temperature increase is near to the melting point of the active materials. Several variables that affect the reaction rate and the heat transport process have been analyzed to know their effect on the internal particle temperature. For a given oxygen carrier and reaction, the maximum temperature of the particles depended mainly on the particle size, the reaction rate, and the external heat transfer resistance, being lower than the effect of the oxygen carrier porosity, type of inert material, and metal oxide content. The highest temperature variations were reached for the oxidation reactions, with the maximum corresponding to the Ni and Co oxygen carriers with values of for particles. The highest temperature increase observed during the reduction reactions corresponded to the reaction of CuO with CO, with values of for particles. For the rest of the reactions and metals, the variations in the particle temperature were below for particle sizes below . Under the typical operating conditions that exist in a CLC system, with particle sizes lower than , % of metal oxide content, and overall conversion times lower than , the increases of temperature with respect to the bulk conditions were lower than for any reaction of any oxygen carrier. Moreover, the temperature profiles inside the particles were near flat in most of the practical conditions, and no local points with high temperatures were found. Thus, changes in the solid porous structure of the carrier due to sintering during oxidation in fluidized bed reactors are not expected working at typical temperatures of CLC systems (1000-).     

Fixed bed studies for the sorption of chromium(VI) onto tea factory waste

The adsorption of Cr(VI) ions from aqueous solutions onto waste of tea factory in fixed beds was investigated. Experiments were carried out as a function of liquid flow rate, initial feed of Cr(VI) concentration, particle size, feed solution pH and bed depth. The bed capacities were found to increase with decreasing flow rate and particle size. The maximum bed capacities for the tested flow rates were found to be 55.65, 40.41 and at 5, 10 and , respectively. When the initial Cr(VI) concentration is increased from 50 to , the corresponding adsorption bed capacity appears to increase from 27.67 to . The longest breakthrough time and maximum of Cr(VI) adsorption is obtained at the lowest examined pH value. Decrease in the particle size from 1.00-3.00 to 0.15-0.25 mm resulted in significant increase in the treated volume, breakthrough time and bed capacity. Breakthrough volume varies with bed depth and the treated volume considerably increases from about 4200 to 11 800 ml as the bed depth increases from 5 to 30 cm. Thomas model for tea factory waste on Cr(VI) adsorption was used to predict the breakthrough curves under varying experimental conditions. This study indicated that the tea factory waste can be used as an effective and environmentally friendly adsorbent for the treatment of Cr(VI) ions in aqueous solutions.     

A vibrating membrane bioreactor (VMBR): Macromolecular transmission—influence of extracellular polymeric substances

The vibrating membrane bioreactor (VMBR) system facilitates the possibility of conducting a separation of macromolecules (BSA) from larger biological components (yeast cells) with a relatively high and stable macromolecular transmission at sub-critical flux. This is not possible to achieve for a static non-vibrating membrane module. A BSA transmission of 74% has been measured in the separation of 4 g/L BSA from 8 g/L dry weight yeast cells in suspension at sub-critical flux . However, this transmission is lower than the 85% BSA transmission measured for at pure 4 g/L BSA solution. This can be ascribed to the presence of extracellular polymeric substances (EPS) from the yeast cells. The initial fouling rate for constant sub-critical flux filtration of unwashed yeast cells is 3-4 times larger than for washed yeast cells . At sub-critical flux, an EPS transmission of around 32% is measured for a pure yeast cell suspension. Thus, EPS and BSA are “competing” in being transmitted which might explain the lowered BSA transmission in the presence of yeast cells. Additionally, EPS heavily foul the membranes, leading to a 86% permeability drop and a fouling resistance 6 times larger than the membrane resistance after 5  h of constant sub-critical flux filtration of pure 8 g/L dry weight yeast cell suspensions. Thus, the addition of hydraulic resistance caused by EPS might also explain the lowered BSA transmission, in the presence of yeast cells, since the membrane pores might be narrowed or partly blocked. EPS is, furthermore, able to cause a relatively large permeability drop even on a membrane module pre-fouled by EPS.     

Effect of N(4)-substituent groups on transfer of 2-benzoylpyridine thiosemicarbazone derivates at the water/1,2-dichloroethane interface

Dependent on the pH of the aqueous phase, the transfer of protonated forms of 2-benzoylpyridine N(4)-phenyl thiosemicarbazone (BPPT) (which has antimicrobial, antifungal and anticytotoxic activities) and 2-benzoylpyridine N(4)-ethyl thiosemicarbazone (BPET) across water/1,2-dichloroethane (1,2-DCE) interface has been studied by cyclic voltammetry. The protonation constants of the ligands ( and ) were determined by spectrophotometry. The standard partition coefficients () and the standard Gibbs energies of ionic (cationic) species of ligands () were calculated from the standard transfer potentials (). The standard Gibbs energies of their transfer () and partition coefficients of neutral species (log P_N) were determined by shake-flask method. These thermodynamic parameters were evaluated as a quantitative and qualitative measure of the lipophilicities of two compounds. The differences between the partition coefficients of cationic and neutral form of compounds [diff(log PI⁺−N)] were interpreted by results obtained from voltammetric data. Effect of N(4)-phenyl and ethyl groups for transfer of 2-benzoylpyridine thiosemicarbazone derivatives at macro-liquid/liquid interface was investigated. The antimicrobial activity of BPET was tested against four types of bacteria and found to be active against Staphlylococcus aureus.