Ted M. Knowlton

L-valve equations

Abstract Non-mechanical valves, especially the L-valves, have been used extensively in fluidized beds and circulating fluidized beds for solids recycling or to serve as a pressure seal. Despite their widespread use, reliable characterization equations for L-valves are still not available, though design principles have been proposed by Knowlton of the Institute of Gas Technology. This paper presents a set of L-valve equations which relate the solids flow rate to the L-valve design, aeration rate, and pressure drop across the L-valve. The equations were developed by visualizing a L-valve as a pneumatically-operated pseudo-mechanical valve. The valve opening is activated pneumatically by L-valve aeration. The physical interpretation of the L-valve operation corresponds to that observed by Knowlton and other researchers, and the proposed equations correlate well with the extensive data base. The data base covers L-valve diameter from 38 mm to 152 mm for particles ranging from 175 μm to 509 μm, particle density ranging from 1230 kg m −1 to 4150 kg m −3 , and shape factor ranging from 0.56 to 0.915.

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.