S.B. Reddy Karri

Dynamics of gas-particle flow in circulating fluidized beds

Abstract The flow of gas—particle mixtures in a circulating fluidized bed has been studied, probing the flow behavior under both stable and unstable operating conditions. A novel feature of our work is the use of electrical capacitance tomography to image particle distribution over the cross-section at one elevation in the standpipe. In addition, we have also obtained data on pressure profile and aeration rate in the standpipe, particle circulation rate in the circulating fluidized bed and riser gas flow rate under various operating conditions. Here, we report experimental results obtained for two different particles, both belonging to Geldart type A. At low aeration rates, a stable dense phase flow is obtained in the standpipe. At high aeration rates, the flow became unstable, manifesting low frequency oscillations in the flow characteristics. Our results suggest that, under conditions explored in the present study, this instability originates in the standpipe and that any attempt to model it should consider the interaction between the various components of the circulating fluidized bed system.

4 – Gas Distributor and Plenum Design in Fluidized Beds

This chapter discusses the gas distributor and plenum design in fluidized beds. The gas distributor in a fluidized bed reactor is intended to induce a uniform and stable fluidization across the entire bed cross-section, operate for long periods without plugging or breaking, minimize weepage of solids into the plenum beneath the grid, minimize attrition of the bed material, and support the weight of the bed material during start-up and shut-down. In practice, grids have taken a variety of forms, and the chapter discusses a few of them. Whatever the physical form, all are fundamentally classifiable in terms of the direction of gas entry: either upward, laterally, or downward. Gas flowing from the grid holes can either take the form of a series of bubbles or a permanent jet, depending on system parameters and operating conditions.

Dynamics of bubble departure in micro-gravity

The effect of gravity on nucleate pool boiling is considered. The static and dynamic forces acting on a growing vapor bubble on a heating surface are evaluated and how their interaction causes the bubble to detach from the surface is presented. By using a force balance, an estimate of the bubble departure radius is calculated and compared with experimental measurements from literature under micro-gravity conditions. In addition, five well known theoretical correlations are used to predict the bubble departure radius and are compared for several gravitational accelerations.

Graphical solution of multistage fluidized bed heat exchanger

Methode type McCabe et Thiele pour lits fluidises multietages a contre-courant et a courant croise. Application a un calcineur multietage

Computer-aided graphics in distillation columns design

Abstract A portable computer simulator has been developed to aid in the design of distillation columns with either an internal reboiler or an open steam. The program (PANCHN) uses the traditional Ponchon-Savarit method and a modified form which incorporates a more exact analysis of the feed region in the case of a partially vaporized feed. Examples of this simulation program and its computer graphics output are presented to illustrate the programs capability and usefulness in studying the effect of operating parameters in the design of distillation columns. While equilibrium data for some systems are stored in its data bank, the present simulator has the flexibility of reading equilibrium data for other systems, as well as overriding stored data.

ANALYSIS OF THE PERFORMANCE OF NON-UNIFORMLY ACTIVE CATALYST PELLETS FOR A NON-ISOTHERMAL SERIES REACTION

An analysis of the influence of the non-uniform distribution of the active species in a catalyst pellet on the effectiveness factor and selectivity for the case of a series non-isothermal reaction is carried out. The case in which the desired reaction has a lower activation energy than the undesired reaction is considered. The effect of different reaction parameters on the selectivity for a single pellet is studied, and the optimum activity distribution is determined for high values of Thiele modulus. It is shown that temperature gradients within the pellet have a detrimental effect on local and overall selectivity and that these gradients are a strong function of the distribution of catalytically active material within the pellet.