Spouting stability

It was explained in Section I that the regime of stable spouting is critically dependent on certain conditions unless these are satisfied, the move- 

The first part of this section briefly summarizes the main findings concerning the effect of the various factors on spouting stability, while the second part deals with methods proposed for calculating the maximum spoutable bed depth. 

The stabilizing effect of a slightly protruding inlet pipe has been confirmed by Reddy et al. (Rl), who obtained better results with a converging nozzle inlet (Fig. 28b) than with a straight pipe. These workers consider 

From the few observations cited above, it is clear that the exact design of the gas inlet has an important effect on spouting stability. However, the question of inlet construction has received insufficient attention. Indeed, it is even possible that some of the discrepancies in other aspects of spouting behavior observed by different investigators may be due to unspecified differences in inlet designs. 

Using a very small air orifice, he was able to obtain a miniature spouted bed with glass beads as fine as 80-100 mesh (mean diameter of 0.16 mm). Spouting of such fine material, however, is of little practical interest since it cannot be achieved on a larger scale, except perhaps by the use of a bed with multiple spouts in parallel, such as that developed by Peterson (P3). 

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Split-boundary problems 123, 644 Spouted bed reactor 466 Stability of chemical reactors 361 Stage... 

The geometric factors and the design requirements for stability have been delimited and the operational conditions of the jet spouted bed have been compared with those of the other gas-solid contact techniques [2,3]. 

M.J. San Jose, Operation regimes in conical spouted beds. Stability conditions and hydrodynamics, Ph.D. Dissertation, University of the Basque Country, Bilbao, Spain, 1991. 

Steam ejectors Operability of steam ejectors is very sensitive to the stability in the motive fluid (steam) pressure. Prefer vacuum pumps to steam ejectors (H). Keep diameter of pipes = diameter of inlet and discharge flanges of ejectors. As the column overhead mass flowrate increases above design, so will the column overhead pressure and vice versa. Compression ratios per ejector 6 1 to 15 1. If inlet gas temperature < 0 °C or below the triple point of water (0.61 Pa) then add steam jacketing to cope with ice formation. Seal for the hot well submerge > 30 cm. The volume in the hotwell between the pipe and the overflow weir should be 1.5 times the volume in the down spout sealed. Replace any nozzles or diffusers where the area is > 7 % larger than design. 

Since removal of dry material from the dryer is critical for the hydrodynamic stability of dryers with inert carriers, the preferential configuration is the conical spouted bed as it offers intense motion of the particulate phase, which promotes fracture of the dried coat by interparticle collisions and resulting attrition. Moreover, the conical drying chamber has been shown to result in better energy efficiency than the cylindrical one (Kutsakova et al., 1964). Consequently, most of studies aimed at process modeling have been carried out with conical spouted beds. 

Menshutma NV, Tsoukanov VA, Kudra, T. Definition of hydrodynamic stability for a jet spouted bed of inert particles. Proc. 12 Inti. Drying Symposium (IDS 2000), Coumans Wl, Kerkhof PIAM, eds. Noordwijkerhout, The Netherlands, Paper 264, 2000. 

Olazar M, San Jose MJ, Penas FJ, Aguayo AT, BUbao J. The stability and hydrodynamics of conical spouted beds with binary mixtures. Ind Eng Chem Res 32 2826 2834, 1993c. 

The third parameter to be determined is the range of stable operation, and in particular the lower limit of this range that defines the gas volume flow rate which is at least necessary in order to reliably operate the spouted bed. A stable operation means the stability of particle circulation trajectories, which may be different depending on equipment construction (as noted above), but should not fluctuate too much in time. Investigations of the stable operating range have been conducted... 

Visual observation of the entrainment region, with the use of a high speed video camera, has allowed a careful interpretation of the trends in the results. In particular, the solids circulation rates have been correlated with the size and stability of the jet, forming over the entrainment region. Also, non-uniformities of the solids distribution within the spouting jet have been studied. 

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