Leonardo Goldstein

A study of the effect of high inlet solids loading on a cyclone separator pressure drop and collection efficiency

The effect of high inlet solid loadings on cyclone pressure drop and separation efficiency was studied. The particles used were FCC catalyst. An extended range of concentrations, up to 20 kg of solids/kg of gas was used, well beyond the loading range reported before. The average entrance velocities were 7, 18 and 27 m/s. The experiments showed that, in the range of concentrations tested, the cyclone pressure drop for the solids laden air flow was about 47% of that for clean air. A trend of increasing separation efficiency with concentration was observed, up to 12 kg of solids/kg of gas, above which, the efficiency decreased. At test conditions, the collection efficiency was higher for the entrance velocity of 18 m/s than for 27 m/s.

Experiments on the local heat transfer characteristics of a circulating fluidized bed

Abstract The role of particle diameter in the heat transfer of a gas–solid suspension to the walls of a circulating fluidized bed was studied for particles of uniform size. This work reports and analyzes new experimental results for the local bed to wall heat transfer coefficient, not including the radiation component, in a long active heat transfer surface length laboratory bed, which extend previous findings and clear up some divergences. The research included determining the effects of extension and location of the heat transfer surface, circulating solids mass flux and average suspension density. An experimental set-up was built, with a 72.5 mm internal diameter riser, 6.0 m high, composed of six double pipe heat exchangers, 0.93 m high, located one above the other. Five narrow sized diameter quartz sand particles − 179, 230, 385, 460 and 545 μm − were tested. Temperature was kept approximately constant at 423 K and the superficial gas velocity at 10.5 m/s. The major influence of suspension density on the wall heat transfer was confirmed, and contrary to other authors, a significant effect of particle size was found, which becomes more relevant for smaller particles and increasing suspension density. It was observed that the extension of the heat transfer surface area did not influence the heat transfer coefficient for lengths greater than 0.93 m.The heat transfer surface location did not show any effect, except for the exchanger at the botton of the riser. A simple correlation was proposed to calculate the heat transfer coefficient as a function of particle diameter and suspension density.

A procedure for calculating pressure drop during the build-up of dust filter cakes

Abstract Gas flow through the cake formed over the surface of a filter generates an aerodynamic drag that increases mechanical compression on the layers closer to the filter surface, reducing their thickness and permeability. A procedure was developed to calculate the pressure drop during cake build-up, taking into account the adjustment of the cake properties to the compressive stress through a constitutive equation. The rise of pressure drop with time in a cycle was determined assuming that the gas velocity was constant and that the layers were formed in equal time intervals. Darcys law, the Happel cell model and the Carman–Kozeny equation were tested in calculating the pressure drop through each layer of filter cake. Part of the particles from the incoming gas stream may settle down before reaching the filter, and not participate on cake formation. Prior knowledge of the settling process was shown to be necessary in order to predict the filter cleaning period, more so when the gas face velocity was lower. Three laboratory filtration experiments, under coal gasification conditions, were used to exemplify the procedure.

Performance of a tuyère gas distributor

The flow discharge coefficient of tuyere gas distributors with six radial holes was obtained as a function of the tuyere head holes diameter Reynolds number, with the holes to riser flow cross-sectional area ratio as parameter. The fraction of the pressure drop which occurred in the tuyere head holes, a significant parameter for satisfactory operation of a fluidized bed, was also determined. The flow phenomena in the thin-plate standard square-edged orifice meter and in the tuyere discharge holes were studied; the differences in the corresponding discharge coefficient values are discussed in the light of the flow pattern dissimilarities. The possibility of adopting the standard thin-plate square-edged orifice meter or perforated-plate discharge coefficients to calculate the tuyere coefficient was analyzed, as well as the influence of the presence or absence of a solids fluidized bed over the distributor plate.

THE THREE-DIMENSIONAL NUMERICAL AERODYNAMICS OF A MOVABLE BLOCK BURNER

Computational fluid-dynamics techniques were employed to study the aerodynamics of a movable block swirl burner, developed by the International Flame Research Foundation, IFRF, which is characterized by the ability to adjust continuously and dynamically the intensity of the swirl by means of the simultaneous rotation of eight movable blocks, inserted between eight fixed blocks. Five three-dimensional grids were constructed for the burner, corresponding to five positions of the movable blocks. Both the k-e and RNG k-e isotropic turbulence models were applied. Only the latter described the existence of a central reverse flow along the annular duct. The employment of first-order and second-order interpolation schemes provided distinct results. The later provided results closer to the experimental tests. The swirl number decayed in the annular duct. The predicted swirl numbers for this movable block swirl burner were lower than the corresponding IFRFs experimental data, as was also observed by other researchers. This gave rise to the suspicion of some possible measurement error in the IFRFs experiments. On the other hand, the lack of agreement between the experimental data and the predictions regarding swirling flows could be attributed to the possible inadequate performance of the k-e model, as a consequence of its isotropic approximation. Still another possible explanation could be a phenomenon called bifurcation, in which one given swirl number can be associated with two distinct conditions of steady state flow. In addition, this complex flows requires a scrupulous development of the grids for the boundary condition and the employment of adequate interpolation schemes.

Experimental study of secondary air diffusion effects on soot concentration along a partially premixed acetylene/air flame

Abstract Soot emission is determined by the competition between soot formation and oxidation in a flame. Several factors affect these processes, including the type of fuel, the air-to-fuel ratio, flame temperature, pressure, and flow pattern. In this paper, the influence of external air diffusion on the soot axial concentration and centerline flame temperature in a partially premixed acetylene/air flame was assessed. The flame was generated in a vertical axis burner in which the discharge of the fuel-oxidant mixture was surrounded by a coaxial annular flow of nitrogen, which provided a shield which controlled the contact between the flame and secondary air. When primary air premixing decreased, the average soot concentration of the flames without the N 2 shield increased more than the concentration of the flames with the shield. The effect of the shield became more intense, in general, as partial premixing increased.

Heat Transfer Analysis of Digital Transmission Equipment with Horizontally Arranged Printed Circuit Boards

Printed circuit boards (PCBs) may be arranged horizontally in many situations, as for example in some digital transmission equipment being used in Brazil. Such pieces of equipment, known as slim racks, have a high aspect ratio (height/width) and are assembled side by side and back to back. The present work deals with the steady-state thermal dissipation in the so-called thermal unit of the slim rack made of the PCB, the magnetic shield above it and the bounding walls constituting an enclosure. The heat transfer in each thermal unit was investigated by assuming isothermal enclosure surfaces with uniform radiosities. Once the thermal paths are identified, an electric circuit analogy is employed to obtain the overall thermal resistance network. Most of the thermal resistances are temperature-dependent, so the associated nonlinear algebraic equations can be solved only by an iterative method. An experimental investigation was carried out in a module of the slim rack with simplified boundary conditions in orde...

In Developping a Bench-Scale Circulating Fluidized Bed Combustor to Burn High Ash Brazilian Coal-Dolomites Mixtures

This work considers some of the questions in burning high ash Brazilian coal-dolomite mixtures in a bench-scale circulating fluidized bed combustor (CFBC). Experimental tests were performed with the CE4500 coal from Santa Catarina State, in southern Brazil, with a Sauter mean diameter d p =43 μm. The coal particles were mixed with dolomite particles of d p = 111 μm and this fuel mixture was fed into the circulating fluidized reactor, previously loaded with quartz sand particles of d p =353 μm. This inert material was previously heated by the combustion of liquefied petroleum gas up to the ignition temperature of the fuel mixture. The CFBC unit has a 100mm internal diameter riser, 4.0m high, as well as a 62.8mm internal diameter downcomer. The loop has a cyclone, a sampling valve to collect particles and a 62.8mm internal diameter L-valve to recirculate the particles in the loop. A screw feeder with a rotation control system was used to feed the fuel mixture to the reactor. The operational conditions were monitored by pressure taps and thermocouples installed along the loop. A data acquisition system showed the main operational conditions to control. Experimental tests performed put in evidence the problems found during bed operation, with special attention to the solids feed device, to the L-valve operation, to particle size, solids inventory, fluidized gas velocity, fuel mixture and recirculated solids feeding positions.

A numerical investigation of the aerodynamics of a furnace with a movable block burner

In this work the air flow in a furnace was computationally investigated. The furnace, for which experimental test data are available, is composed of a movable block burner connected to a cylindrical combustion chamber by a conical quarl. The apertures between the movable and the fixed blocks of the burner determine the ratio of the tangential to the radial air streams supplied to the furnace. Three different positions of the movable blocks were studied at this time. A three-dimensional investigation was performed by means of the finite volume method. The numerical grid was developed by the multiblock technique. The turbulence phenomenon was addressed by the RNG k-e model. Profiles of the axial, tangential and radial velocities in the combustion chamber were outlined. The map of the predicted axial velocity in the combustion chamber was compared with a map of the experimental axial velocity. The internal space of the furnace was found to be partially filled with a reverse flow that extended around the longitudinal axis. A swirl number profile along the furnace length is presented and shows an unexpected increase in the swirl in the combustion chamber.

New particulate solids pneumatic feeding device with mass flowrate control

Abstract A new solids feed valve design was developed, based on the destruction of the repose cone resulting from the deposition of solid particles over a horizontal surface by fluidization of its base, followed by pneumatic transport of the fallen particles. Tests were carried out to determine the mass flowrate of solids of types A, B, C and D, according to Geldarts classification, as a function of the air flowrate.