Ajit V. Sapre

Heater probe technique to measure flow maldistribution in large scale trickle bed reactors

Abstract Novel flow distribution measurement probes were used in a large-scale commercially operating trickle-bed reactor. The probes consist of long heated pipes designed to measure local heat transfer coefficients at multiple points along their length. Local flow rates are correlated with the heat transfer coefficient based on independent laboratory data. The results of our study showed significant point-to-point variation in flow distribution. The pattern of maldistribution would vary with alternate operating conditions of flow rates, temperature, and liquid volatility. Results included an increase in the nonuniformity of flow moving down the reactor in the direction of flow. And severe maldistribution with poor reactor performance occurred at high liquid mass flux.

Catalyst deactivation kinetics from variable space-velocity experiments

Abstract Reliable estimates of catalyst deactivation parameters are difficult to get from conventional experiments at constant space velocity where conversion declines with time on stream, or when temperature is adjusted to compensate for the loss of catalyst activity. An alternate technique, where space velocity is adjusted to maintain constant conversion, is shown here to give reliable rate information for both the catalyst deactivation and the primary catalytic reactions. This technique, at constant temperature, provides kinetics data on a deactivating catalyst in which the catalyst is exposed to reactant and product concentrations that are relatively constant. In principle, the kinetics of deactivation are obtained directly as the kinetic regime remains unchanged. This technique is used quite successfully for many catalytic processes of industrial significance. In this paper, the variable-space-velocity experimental technique is demonstrated for the methanol to hydrocarbons process on a ZSM-5 catalyst. The deactivation kinetic parameters were determined at several temperatures in a fixed-bed reactor. This rate information was then used to determine the temperature-time policy for maintaining constant reactor outlet conversion at a fixed space-velocity. The predicted temperature-time policies are in good agreement with experimental data on fixed-bed and fluid-bed reactors. Mathematical analysis of interpreting experimental data, as well as predicted temperature-time policies for practical applications, is illustrated.

FCC Regenerator flow model

Abstract Catalyst flow patterns in FCC cross-flow and swirl-type dense-bed regenerators affect regenerator efficiency. A two-dimensional, pseudo-homogeneous flow model describing such flow patterns is developed. The predicted catalyst flow patterns for swirl regenerators indicate catalyst bypassing and recirculating zones. More severe bypassing is predicted for cross-flow regenerators, the severity of bypassing increases with increasing Reynolds number. The calculated flow patterns are combined with a radial mixing-cell model to account for radial mixing in fluidized beds. Radial mixing rates in commercial size regenerators counteract somewhat the effect of bypassing. Model calculations coupling coke burning kinetics with the flow model, however, show that bypassing leads to non-uniform coke levels and oxygen breakthrough. This modeling technology is used to optimize FCC regenerator operation.

Development of trickle-bed heat transfer correlation for flow measurement probe

Abstract The heat transfer coefficient from a heated pipe in a trickle-bed catalytic reactor was correlated with combined gas and liquid flow rates along with fluid and packing physical properties. The correlation is readily applicable for flow rate measurements in commercial-scale trickle-bed reactors. Data for the correlation were obtained using petroleum distillate liquid fed to a laboratory reactor over a range of temperatures along with hydrogen and nitrogen as gases. Our analysis showed that the heat transfer coefficient data are represented based on the combined thermal mass flux of the fluids plus the effective conductivity of the packed bed. The latter depends on gas, liquid, and solid thermal conductivities, but not significantly on flow rates or flow regime.

Use of preconditioned bi-conjugate gradient method in modeling two-phase fluid flow in porous media

We have found the preconditioned bi-conjugate gradient method superior to the standard conjugate gradient method for iterative solution of linear systems occurring in solving the finite difference form of partial differential equations describing multi-dimensional two-phase flow in porous media. The matrices involved in these systems are typically non-symmetric and not positive definite. Fully vectorizable preconditioning was effective in our solutions using the bi-conjugate gradient method, whereas more extensive, non-vectorizable preconditioning is often necessary when using the conjugate gradient method.