Morris H. Morgan

Design and scale-up of a spouted-bed combustor

This paper discusses the effect of the second (heterogeneous) phase on the extent of heat recycle, lowering of the lean flammability limit, stability and performance of a spouted-bed combustor. Experiments suggest that the extent of heat recycle, and therefore the lowering in the lean flammability limit, is controlled by both particle circulation rate and particle physical properties. This concept of heat recycle can be utilized in the burning of low heating value chemical and toxic wastes. The stability of a spouted-bed combustor depends upon the geometric design ratios di/Dc,di/dp, and hd/H, based on studies with columns of two different sizes burning propane. The introduction of a draft tube improves the flexibility of the combustor in terms of residence time control and bed stability. A well-designed draft tube spouted bed combustor can yield a destruction and removal efficiency, i.e. conversion, of ⩾99.99.

Measurements of spout voidage distributions, particle velocities and particle circulation rates in spouted beds of coarse particles—II. Experimental verification

Experimental data are presented using 2.7 mm and 4.9 mm spherical glass particles spouted with air to verify the particle circulation theory presented in Morgan et al. (Chem. Engng Sci.40, 1367–1377 (1985)) The particle mass flowrate, particle circulation rate and spout voidage profiles are in excellent agreement with the theory. To fit the particle velocity profile, the spout must contract slightly near the inlet to the bed and then expand to the average spout diameter.

Spout voidage distribution, stability and particle circulation rates in spouted beds of coarse particles. I: Theory

Abstract Mass and momentum balance equations are used with a derived expression for the interaction force between the fluid and particle phases to calculate the axial spout voidage distribution and particle circulation rate in a spouted bed of coarse particles. The voidage profiles above minimum spouting are found to follow a similarity relationship and an explicit equation for the circulation rate is developed using that relationship and the calculated voidage at the top of the spout. Criteria for stability and spouting regime identification are discussed.

Variational model for prediction of the fluid-particle interphase drag coefficient and particulate expansion of fluidized and sedimenting beds

Abstract An equation for prediction of the fluid-particle interphase drag coefficient in particulately fluidized and sedimenting beds is derived and experimentally verified. This equation is obtained by modeling the dimensionless drag coefficient-voidage relationship in a bed in which the superficial fluid velocity varies from minimum fluidization to terminal as a single constraint isoperimetric problem of the calculus of variations. The solution contains a single dimensionless parameter, U mF 2 / U 2 t ϵ mF 3 , and no adjustable constants. An equation for the superficial velocity-voidage relationship in the bed is also derived and experimentally verified. Fluidization and sedimentation experiments were conducted using water and spherical glass particles 1.20, 1.94 and 2.98 mm in diameter in columns 36, 40 and 50 mm in diameter to verify the model. Both the drag coefficient and velocity for voidages varying from minimum fluidization to 0.96 are predicted extremely well. Several empirical equations are shown to give limited descriptions of the data when considered over the whole range of voidages from minimum fluidization to terminal.

Modeling and measurement of the effective drag coefficient in decelerating and non-accelerating turbulent gas—solids dilute phase flow of large parti

Abstract The one-dimensional modeling of decelerating and non-accelerating turbulent dilute phase flow has been studied by transporting 1 mm glass spheres with

A new choking velocity correlation for vertical pneumatic conveying

A new choking correlation is presented here, based on the assumption that choking occurs at the inlet to the transport line when a parameter γ(e)=0. The voidage at the inlet required to calculate γ(e) is obtained using a correlation for the slip velocity. This new correlation is shown to give better predictions than Yangs (1983) correlation for monodisperse particles. A significant improvement in the prediction of the choking velocity of polydisperse particle, compared with the Briens and Bergougnou (1986) model, is also illustrated

Effect of particle diameter, particle density and loading ratio on the effective drag coefficient in steady turbulent gas-solids transport

Abstract Extending earlier work [1], effective drag coefficients for particles in steady turbulent gas-solids transport in a 28.45 mm vertical transport pipe 5.49 m long have been determined for 1 and 2 mm glass spheres and 1.99 mm rapeseed. The data are well represented by the equation C dn = 4 3 ∈Ar Re p 2 so that in the range studied, Cdn increases proportionally with dp and (ϱ p −ϱ f ) ϱ f and is essentially independent of loading ratio. Slip Reynolds numbers ranged from 469 to 1847 and pipe Reynolds numbers from 21400 to 33600. Loading ratios were varied from 7.03 to 45.4. The data reported here for Cdn fall below the standard drag curve as the slip velocity is increased due to the effects of freestream turbulence. The effect of neglecting particle-wall friction in our two-fluid model on the calculation of the solids fraction, slip velocity and drag coefficient is discussed.

Particle circulation and liquid bypassing in three phase draft tubed spouted beds

Abstract The design of any fluid-solid contacting system is based on a knowledge of certain intrinsic parameters and their functional dependence on extrinsic or easily measurable parameters such as system geometry, flow rates, etc. For Three Phase Draft-Tubed Spouted Bed systems(TPDS) , the important intrinsic design parameters are the particle circulation and the liquid distribution between the draft tube and the annulus. The extrinsic parameters are liquid and gas flow rates, solid loading, particle size, inlet size and draft tube size and spacing. In this paper a semi-empirical model is developed which relates the intrinsic design parameters to extrinsic variables at a constant draft tube size. The model is based on the earlier work of Grbavcic (1991a,b) who used a variational drag in transport systems and Matthews (Ph.D thesis, RPI, Troy NY) work on pressure profiles in draft tubed spouted beds.

An axisymmetric model for fluid flow in the annulus of a spout-fluid bed

Abstract The axisymmetric model previously developed for spouted beds is adapted to describe fluid flow in the annulus of a spout-fluid bed at the minimum spout-fluid flow rate. Experimental axial pressure profiles provide the boundary condition at the spout-annulus interface. The fluid streamlines, residence time distribution, average residence time, average axial fluid velocity in the annulus and the fluid flow rate entering the annulus from the spout are all calculated. The fluid streamlines in spout-fluid beds are shown to be very different from those of spouted beds in the lower part of the annulus. Although the residence time distribution of the fluid percolating through the annulus of a spout-fluid bed is more uniform than that of a spouted bed, the average residence time does not vary significantly with the inlet fluid flow to the annulus.

A pseudo-Stokes representation of the effective drag coefficient for large particles entrained in a turbulent airstream

Abstract Recently published data by Littman et al., Powder Technol., 77 (1993) 267 and Powder Technol., 84 (1995) 49, for the effective drag coefficient in the vertical pneumatic transport of 1 and 2 mm glass and 1.99 mm rapeseed particles are represented by the pseudo-Stokes equation, C d = 24/ R e pc . The effects of freestream turbulence are represented using Lees ( Int. J. Multiphase Flow, 13 (1987) 247) correlation for the apparent turbulent kinematic viscosity of the fluid felt by the particles in a suspension flow. These results not only confirm the importance of freestream turbulence in lowering the drag coefficient for those particles significantly below that on the standard drag curve but suggest that the turbulence intensities are high enough to largely or completely eliminate the particle wake. These low drag coefficients increase corresponding slip velocities above terminal suggesting that solids residence times in the pipe are much higher than predicted by use of the standard drag curve.