Coal desulfurization in a fluidized bed reactor

Fluidized bed reactor technology was investigated as a means of developing a new simple and low cost process for coal desulfurization. Preliminary experimental results obtained in a 2.54 cm batch fluidized bed reactor have shown that over 80% total sulfur reductions can be achieved by sequential chlorination and dechlorination/ hydrodesulfurization of high sulfur pulverized coals. Proximate and ultimate analyses of desulfurized coals have revealed enhanced carbon and fixed carbon levels and substantially reduced volatile, oxygen and hydrogen contents. While there was a minor increase in the ash content and heating value, nitrogen and chlorine contents were essentially unchanged. Compared to an earlier slurry phase process, the fluidized bed reactors process has specific advantages such as shorter reaction times, fewer processing steps and reduced reactant requirements. A fluidized bed reactor process may thus have a potential of being developed into a simple and economic means of converting high sulfur coals to environmentally acceptable fuels.

Immobilization of Aspergillus oryzae alpha-galactosidase in gelatin and its application in removal of flatulence-inducing sugars in soymilk

Raffinose oligosaccharides (RO) are the major factors responsible for flatulence following ingestion of soybean-derived products. Removal of RO from seeds or soymilk would then have a positive impact on the acceptance of soy-based foods. In this study, alpha-galactosidase from Aspergillus oryzae was entrapped in gelatin using formaldehyde as the hardener. The immobilization yield was 64.3% under the optimum conditions of immobilization. The immobilized alpha-galactosidase showed a shift in optimum pH from 4.8 to 5.4 in acetate buffer. The optimum temperature also shifted from 50 degrees C to 57 degrees C compared with soluble enzyme. Immobilized alpha-galactosidase was used in batch, repeated batch and continuous mode to degrade RO present in soymilk. In the repeated batch, 45% reduction of RO was obtained in the fourth cycle. The performance of immobilized alpha-galactosidase was tested in a fluidized bed reactor at different flow rates and 86% reduction of RO in soymilk was obtained at 25 ml h(-1) flow rate. The study revealed that immobilized alpha-galactosidase in continuous mode is efficient in reduction of RO present in soymilk.

Catalytic dehydrogenation of 2-propanol to acetone

Catalytic dehydrogenation of 2-propanol over Cu-SiO2 catalyst was investigated. The undesired side reaction of dehydration can be controlled by a selective catalyst and choice of proper operating conditions. The kinetics of the heterogeneous catalytic reaction can be adequately expressed by a forward first-order and reverse second-order mechanism. The rate-controlling step with chemically pure 2-propanol is single-site surface reaction, while for the technical grade alcohol the adsorption of alcohol is rate-controlling. The static bed data are compared with the fluidized bed dat

Mathematical model of COREX melter gasifier: Part I. Steady-state model

The COREX melter gasifier is a countercurrent reactor to produce liquid iron. Directly reduced iron (DRI), noncoking coal, and other additives are charged to the melter gasifier at their respective temperatures, and O-2 is blown through the tuyeres. Functionally, a melter gasifier is divided into three zones: a moving bed, fluidized bed, and free board. A model has been developed for the moving bed, where the tuyere region is two-dimensional (2-D) and the rest is one-dimensional (1-D). It is based on multiphase conservation of mass, momentum, and heat. The fluidized bed has been treated as 1-D. Partial equilibrium is calculated for the free board. The calculated temperature of the hot metal, the top gas, and the chemistry of the top gas agree with the reported plant data. The model has been used to study the effects of bed height, injection of impure O-2, coal chemistry, and reactivity on the process performance.

Bed Shear from Velocity Profiles: A New Approach

A new binary law of velocity distribution has been developed to describe the velocity profile for the entire flow region. The law is a combination of logarithmic law, valid in the wall (inner) region, and parabolic law, valid in the core (outer) region of the flow. The validity of the law has been established based on earlier data on flat plates, rough and smooth pipes and experimental data obtained from rigid-walled open channels with plane sand beds. A procedure of estimating bed shear stress from the proposed law of velocity distribution using the measured velocity profile has been evolved. Bed shear estimates made according to this procedure are in agreement with the values obtained from uniform flow analysis in the case of open channel flow over a sediment bed. The proposed method of estimating the bed shear stress from the observed velocity profiles is found to be particularly useful in cases where it is difficult to determine precisely the true bed level, such as in the case of flow over sediment beds.

New main group ligands for complexation with transition and inner transition elements

Symmetrical and unsymmetrical diphosphinoamines of the type X(2)PN(R)PX(2) and X(2)PN(R)YY' offer vast scope for the synthesis of a variety of transition metal organometallic complexes. Diphosphinoamines can be converted into their dioxides which are also accessible from appropriate (chloro)phosphane oxide precursors. The diphosphazane dioxides form an interesting series of complexes with lanthanide and actinide elements. Structural and spectroscopic studies have been carried out on a wide range of transition metal complexes incorporating linear P-N-P ligands and judiciously functionalized cyclophosphazanes and cyclo-phosphazenes.

Bearing capacity of circular footing on geocell-sand mattress overlying clay bed with void

The potential benefits of providing geocell reinforced sand mattress over clay subgrade with void have been investigated through a series of laboratory scale model tests. The parameters varied in the test programme include, thickness of unreinforced sand layer above clay bed, width and height of geocell mattress, relative density of the sand fill in the geocells, and influence of an additional layer of planar geogrid placed at the base of the geocell mattress. The test results indicate that substantial improvement in performance can be obtained with the provision of geocell mattress, of adequate size, over the clay subgrade with void. In order to have beneficial effect, the geocell mattress must spread beyond the void at least a distance equal to the diameter of the void. The influence of the void over the performance of the footing reduces for height of geocell mattress greater than 1.8 times the diameter of the footing. Better improvement in performance is obtained for geocells filled with dense soil. (C) 2008 Elsevier Ltd. All rights reserved.

Adsorption isotherms for neutral organic compounds - A hierarchy in modelling: Part V. Models for the inner layer potential difference in the presence of dipolar adsorption

The relations for the inner layer potential &fference (E) in the presence of adsorbed orgamc molecules are derived for three hterarchlcal models, m terms of molecular constants like permanent &pole moments, polarlzablhtles, etc It is shown how the experimentally observed patterns of the E vs 0 plots (hnear m all ranges of $\sigma^M$, non-linear in one or both regions of o M, etc ) can be understood in a serm-quantltatlve manner from the simplest model in our hierarchy, viz the two-state site panty version Two-state multi-site and three-state (sxte panty) models are also analysed and the slope (3E/80),,M tabulated for these also The results for the Esm-Markov effect are denved for all the models and compared with the earlier result of Parsons. A comparison with the GSL phenomenologlcal equation is presented and its molecular basis, as well as the hmltatlons, is analysed. In partxcular, two-state multa-slte and three-state (site panty) models yield E-o M relations that are more general than the "umfied" GSL equation The posslblhty of vaewlng the compact layer as a "composite medium" with an "effective dlelectnc constant" and obtaimng novel phenomenological descnptions IS also indicated.

Hydrodynamic pressure on a dam with a periodically corrugated reservoir bed

The problem of determining the hydrodynamic pressure, caused by earthquake forces, on a dam with a vertical upstream face and a periodically corrugated reservoir bed is solved approximately by employing a Fourier cosine transform technique to the linearised equations of inviscid and incompressible flow. A particular case of the present problem giving rise to results valid for dams with flat reservoir beds is shown to produce known results as a check of the method used.

Stream power criterion and design of sand bed channels at incipient motion

The critical stream power criterion may be used to describe the incipient motion of cohesionless particles of plane sediment beds. The governing equation relating ``critical stream power'' to ``shear Reynolds number'' is developed by using the present experimental data as well as the data from several other sources. Simultaneously, a resistance equation, relating the ``particle Reynolds number'' to the``shear Reynolds number'' is developed for plane sediment beds in wide channels with little or no transport. By making use of these relations, a procedure is developed to design plane sediment beds such that any two of the four design variables, including particle size, energy/friction slope, flow depth, and discharge per unit width in the channel should be known to predict the remaining two variables. Finally, a straightforward design procedure using design tables/design curves and analytical methods is presented to solve six possible design problems.

Oxidation Of Sodium Sulfide In A Foam Bed Contactor

Oxidation of sodium sulphide to sodium thiosulphate has been experimentally investigated in a foam bed contactor using air as oxidizing medium. The var.

Oxidation of sodium sulphide in the presence of fine activated carbon particles in a foam bed contactor

The oxidation of sodium sulphide in the presence of fine activated carbon particles (4.33 μm) has been studied at 75°C in a foam bed contactor. The existing single-stage model of a foam bed reactor has been modified to take into account the effect of heterogeneous catalyst particles and the absorption in the storage section. The variables studied are catalyst loading, initial sulphide concentration and the average liquid hold-up in the foam bed. It is seen that the rates of oxidation of sodium sulphide are considerably enhanced by an increase in the loading of activated carbon particles. The rate of conversion of sodium sulphide also increases with an increase in the average liquid hold-up in the foam. The modified model predicts these effects fairly well. The contribution of reaction in the storage section is found to be less than 2% of the overall rate of conversion in the contactor.

A Transient surface renewal model for heat transfer in bubbling fluidized beds

Abstract is not available.

Mass transfer with chemical reaction in a foam bed contactor

On the basis of dodecahedral structure of a foam bed, a model to predict conversion in a foam bed contactor with mass transfer with chemical reaction has been developed. To verify the proposed model, experiments have been carried out in a semi-batch apparatus for the absorption of lean CO2 gas in a foam of sodium hydroxide solution. The proposed model predicts fairly well the experimentally found absorption values.