Single-stage Fluidized Bed Research Articles

Evaluation Of Germination Quality Of Wheat Seeds Dried In Fluidized Bed Dryer

An attempt was conducted taking three wheat varieties (BARI gom-24, Shatabdi, Bijoy) to investigate the application and suitability of single-stage fluidized bed drying for quality wheat seeds in terms of germination percentage. Drying of wheat seed was conducted in a fluidized bed dryer at three temperatures of 35°C, 40°C, and 45°C at a constant bed thickness of 13 cm and 4.5 m/s of air velocity. Total drying time required for drying of each variety 210 min (3.5hr), 150 min (2.5hr) and 80 min (1.3hr) at temperature 35°C, 40°C, and 45°C respectively for reduction of moisture from 16.98±0.15% to 12±0.1% wb. In contrast, sun drying (33±2°C) took 270 min (4.5 hr). It was shown, the drying time required in the fluidized bed drying method was almost 22-71% shorter than the sun drying method. The germination percentage was 94.67%, 97.33%, 88% for the variety “BARI gom-24” 93.67%, 97%, and 91.33% for the variety Shatabdi and 95%, 96.67%, 89.67% for the variety Bijoy while dried in a fluidized bed dryer at temperature 35°C, 40°C, and 45°C respectively. The germination percentage of sun-dried samples was 90.67% (BARI gom-24), 92.33%. (Shatabdi) and 92% (Bijoy). In the comparison of germination, wheat seed samples dried in the fluidized bed dryer at 35°C, 40°C showed a higher germination percentage than sun drying wheat seed samples. Therefore, the proposed drying technique does not only facilitate faster removal of moisture content, and also a higher germination percentage was found than the existing sun drying method. So, fluidized bed drying can be effective for wheat seeds in Bangladesh.

Self-agglomeration mechanism of iron nanoparticles in a fluidized bed

Aided by self-agglomeration, a two-stage reduction process conducted at a higher temperature (600 °C) than the single-stage process resulted in an enhancement of the k constant to more than twice that of the single-stage process. A force balance model coupled with the reduction kinetics of Fe2O3 is first proposed to explain the self-agglomeration mechanism of iron nanoparticles (NPs) during the reduction. This force balance model successfully elucidates the reason for the prevention of defluidization via a two-stage fluidized bed method. At lower temperatures, there is a long stationary phase, which is of great importance in overcoming the sintering of agglomerates and in promoting the reduction reaction. At lower temperatures, the initial NPs first self-agglomerate into particles that are tens of microns in size; they then gradually agglomerate into larger particles (>100 μm) at higher temperatures. By contrast, the sudden growth of iron NP agglomerates causes sintering and defluidization in the single-stage fluidized bed method.

Introduction and evaluation of a double loop staged fluidized bed system for post-combustion CO2 capture using solid sorbents in a continuous temperature swing adsorption process

A double loop staged fluidized bed system operated with solid amine sorbents is proposed and evaluated for temperature swing adsorption (TSA) CO2 separation from flue gas streams. The proposed system features effective counter-current movement of gas and sorbent streams in both gas–solid contactors, i.e. the adsorber and the desorber. The counter-current movement enables the realization of axial CO2 concentration profiles within both contactors that is exploited within the TSA process to reach high CO2 capture rates as well as concentrated CO2 from the desorber. The system comprises two multi-stage fluidized bed contactors where the sorbents move downwards through a series of bubbling fluidized bed stages. The stages are made up by nozzle or sieve plates and feature downcomers or dip tubes to allow for downward directed particle flow. The gas is fed at the bottom and serves as fluidizing agent in the stages. The particles are removed from the bottom stage through chutes and are directed through a sealing device (loop seal or purged moving bed) towards a transporting riser. The particles are lifted up, separated from the transport gas via gravitational or centrifugal separators and sent to the respective other contacting device through simple chutes. Lean/rich heat transfer may be possible using fluidized bed heat exchangers within the dense bed phase of both transport risers. The process is thermodynamically evaluated for a well-studied sorbent material consisting of a porous silica support that is functionalized with a mixture of two different amines (PEI+APTES). It is shown that application of the double loop staged system leads to a significant reduction of sorbent circulation rate and stripping steam demand compared to single-stage fluidized bed systems and thus to a significant reduction of the energy demand of the CO2 capture process. It is found that when implementing five stages in each contacting device, it is possible to capture 90% of the CO2 from a typical flue gas stream (10vol% CO2 content), even when the process is operated with moderate sorbent circulation and stripping steam rates. The corresponding overall heat requirement of the capture process without accounting for CO2 compression and effective heat integration is 3.5MJ per kg CO2 captured and, thus, equal or even below the values reported for liquid amine capture systems. Improved heat transfer through immersed fluidized bed heat exchangers as well as a significantly lower number of theoretical stages indicate that the proposed TSA contacting devices will allow for a more compact design as compared to gas–liquid systems, which would lead to reduced capital costs. In conclusion, CO2 capture within the proposed TSA system using solid amine sorbents may be regarded as a promising post-combustion CO2 capture technology.

Conversion of methanol to aromatics in fluidized bed reactor

Conversion of methanol to aromatics (MTA) was conducted over a fresh or a spent Zn/ZSM-5 catalyst in single stage fluidized bed (SSFB) and two stage fluidized bed (TSFB). Sampling at different stages of TSFB and operation in the temperature range of 250, 275, 300, 325, 350, 380 and 475°C revealed the consecutive reaction mode from methanol to DME, C1–C4 hydrocarbons, C5+ nonaromatics to aromatics finally. High weight ratio of para-xylene (PX) in xylene in wide temperature range suggested that PX was the primary product of MTA, and other xylenes are produced by the iosmerization of PX. Other aromatics such as benzene, toluene and trimethylbenzene are finally produced by the dealkylation, alkylation or disproportionation of xylene. The adoption of TSFB reactor was effective to increase the yield of aromatics, compared to that using SSFB, due to the inhibition of backmixing of gases. Combination of TSFB and highly active catalyst with strong acids was effective to get high yield of aromatics under high space velocity of methanol.

Gas-Phase Catalytic Hydrochlorination of Acetylene in a Two-Stage Fluidized-Bed Reactor

Production of vinyl chloride monomer (VCM) by the hydrochlorination of acetylene with HCl was investigated in both a single-stage fluidized bed (SSFB) and a two-stage fluidized bed (TSFB) at different reaction temperatures and space velocities of acetylene. The conversion of acetylene increases with increasing temperature and decreases with increasing space velocity. Over a wide range of operating conditions, a higher conversion of acetylene was achieved in the TSFB than in the SSFB, with the selectivity of VCM being almost 100%. This process can be described by a two-dimensional dispersion and reaction model. A new catalyst, HgCl2 supported on a coconut-shell-type activated carbon, which has a much higher mechanical strength than the industrial catalyst (HgCl2 supported on a coal-based activated carbon), was employed in the fluidized beds. Evaluation of the catalyst lifetime in a fast sublimation experiment at high temperature showed that the new catalyst has a longer lifetime than the industrial catalys...

On the Plate Design in a Countercurrent Single-Stage Fluidized Bed System

A countercurrent continuous single-stage fluidized bed system using different perforated plate designs was studied. The results indicated that the plate design significantly affected the operation of the countercurrent staged fluidized bed. The triangular hole arrangement plates accumulated more particles above the plates compared to the equilateral square hole arrangement plates at the same operating conditions. When the plate open ratio was increased from 0.37 to 0.4 and 0.44, the size of the operating window increased and the location of the window shifted upward in the solids feeding rate versus superficial gas velocity figure. The increase of the operating window was due to the different discharging mechanisms at different flow regimes. When the position(s) of the large hole(s) was/were moved from the center of the plate to the column wall, the size of the operating window increased.

Gaseous catalytic hydrogenation of nitrobenzene to aniline in a two-stage fluidized bed reactor

Gaseous hydrogenation of nitrobenzene over a Cu/SiO 2 catalyst has been studied in a two-stage and in a single-stage fluidized bed reactor, at 513–553 K and atmospheric pressure. The placement of the second perforated plate in the fluidized bed reactor inhibits the backmixing of gases and solids and consequently increases the local molar ratio of hydrogen to nitrobenzene in the second stage. Thus, the conversion of nitrobenzene and the selectivity of aniline production and the stable life of the catalyst are significantly increased in the two-stage fluidized bed reactor, as compared with those in the single-stage one. A comparison of the coke formation and the burning characteristics of cokes in different reactors has also been presented. It suggests the simple catalyst regeneration for the two-stage fluidized bed technology. This work provides an effective method to produce aniline with higher purity.

Design, process simulation and construction of an atmospheric dual fluidized bed combustion system for in situ CO 2 capture using high-temperature sorbents

An atmospheric dual fluidized bed combustion system using high-temperature sorbents for in situ CO 2 capture has been designed and simulated and is now under construction. The pilot plant is expected to burn petroleum coke and coal or biomass in a clean and efficient manner, generating a carbonator flue gas containing 2–5 mol% CO 2, while producing a relatively pure carbon dioxide stream ready for compression. The concentration of sulphur dioxide in the resulting flue gas is expected to be on the order of a few parts per million by volume. Initial investigations are to be carried out using limestone-derived sorbents enhanced using a simple single step process for pore modification developed at CETC-Ottawa. Carbonation occurs in a two-stage fluidized bed carbonator–combustor allowing for optimal temperature control for both combustion (850–950 °C) and carbonation (650–750 °C). Calcination occurs in a single-stage fluidized bed combustor burning petroleum coke. Pilot plant operational data will be used for on-going scale-up activities using the ASPEN Plus process simulator.

Role of Pressure Drop in the Counter-current Multistage Fluidized Bed of the Solid-Liquid System. Effect of Non-uniform Liquid Flow.

An experimental study on the pressure drop has been carried out for a counter-current multistage fluidized bed having a downspout as well as on the particle holdup relating to a pressure drop. Three kinds of fluidized beds were used; a 3-stage column with 48.6 mm i.d., a 2-stage column with 99.6 mm i.d. and a batch-wise single stage column without downspout. The holdups for three kinds of ion exchange resins in the multistage fluidized bed are expressed by the correlation obtained for a batch-wise single stage fluidized bed. The pressure drop of the 48.6 mm column, however, varied little with the superficial liquid velocity, while that of the single stage column with the same diameter decreased with an increase in liquid velocity as expected from the theoretical consideration. A 99.6-mm column, where diameter of the downspout is small in comparison with the column diameter, shows that the pressure drop in the multistage column was the same as in the single stage column. By covering a part of stage-partitioning screen of the 99.6-mm column with a plate producing a non-uniform liquid flow, the pressure drop behavior approached the one that is observed for a 48.6-mm column. Discrepancy of the observed and the estimated pressure drops for the multistage fluidized bed is ascribed to the non-uniform flow generated by the downspout which is indispensable to the multistage operation.

Drying characteristics of millet in a continuous multistage fluidized bed

The effects of gas velocity, inlet gas temperature and the solid feed rate on the drying efficiency, the outlet solid moisture content, bed temperature in each stage, the outlet gas humidity and temperature in a rectangular acryl multistage fluidized bed (0.172 m×0.192 m×1.5 m-high) with a downcomer (0.04 m-I.D.) were investigated. The experiments were performed by using 1.9 mm millet particles. The final moisture contents of the solids increased with increasing the solid feed rate. The drying efficiency increased with increasing the wetted solid feed rate but decreased with increasing the inlet gas temperature. The drying performance of the multistage fluidized bed was compared with the single-stage fluidized bed and found to be superior under identical operation conditions. The model predicted values were well matched with the experimental data in the multistage fluidized bed dryer.

An experimental study of the release of nitrogen from coals pyrolyzed in fluidized-bed reactors

Nitrogen release has been measured from a suite of Australian, German, and U.S. coals pyrolyzed under rapid heating conditions in two bench scale reactors. The first reactor was a single-stage fluidized bed reactor: the second was a two-stage reactor in which a fluidized bed was coupled with a tubular reactor. The two-stage reactor enabled cracking reactions of the volatiles to be studied in isolation from reactions of the char. The results show that the gas-phase N-containing species, HCN and NH3, are formed from both brown and bituminous coals. In addition, HNCO is also observed from bituminous coals: HNCO is a plausible precursor for NH3 formation. At high temperatures low-volatile coals give lower yields of HCN and NH3 than high-volatile coals. This observation, however, does not imply that tar cracking is the only source of HCN and NH3. In fact, the results obtained in the two-stage reactor suggest that a significant proportion of the HCN is released from the char and that tar cracking is not a significant source of NH3. A major part of the NH3 is produced by interactions of N-containing species with the char. These results, together with previous studies of N release, demonstrate that there is no simple relationship between N functionality in coals and the composition and rate of release of the nitrogen.

Leaching by Means of Fluidized Bed

The purpose of this study is to obtain data available for the design of a continuous fluidized-bed-type leaching equipment.Concerning the leaching of the extractable material from the sphere of a solid particle, theoretical analyses have been developed, taking into consideration the diffusion in the solid particle as well as in the film of the fluid.When the concentration of solution contained in a solid particle is uniform, or when the leaching interface can be assumed to exist in the solid particle, the following equations will be applicable, -Eqs. (4) and (10) for the distribution of the concentration of solute in solid phase, Eqs. (7) and (16) for the rate of solute leaving the surface of the solid particle due to diffusion, Eqs. (5) and (14) for the mass of extractable material remaining unextracted, Eqs. (6) and (15) for the nonleached fraction, and Eqs. (8) and (17) for the concentration of solute on the surface of the particle.Based on the diffusion in the film of fluid and in the solid phase, and on the assumption that solid particles are completely mixed in the bed, theoretical equations representing the longitudinal distribution of the concentration of solute in the leaching operation by a single-stage fluidized bed have been derived, -e. g., Eqs. (19)-(23) and Eq. (27).Experiments on the dissolution of solid particles in fluidized bed have been performed in order to compare the results with those of the theoretical curves obtained from Eq. (19).In Figs. 9 and 10 are illustrated graphical solutions for determining the number of stages necessary for a multistage-fluidized-bed-type extractor, when the diffusion in the film of the fluid is controlling.