Porous plate distributors

The differences in behavior between small laboratory beds and larger demonstration units can, in part, be attributed to a switch from porous plate distributors in the small bed to discrete hole or bubble caps in... 

Again, as in the case of jet attrition, attention must be paid in the experimental determination of Ra bub to the isolation of the attrition that is due to bubbles. There are basically two ways to do this. The one is to use a porous plate distributor in order to avoid any grid jets. The other is the procedure suggested by Ghadiri et al. (1992a) which is depicted in Fig. 7 the measurement of the production rate of fines at different values of the static bed height permits to eliminate the grid jet effects. 

High-pressure conditions favour a smaller bubble size and narrower bubble-size distribution, and therefore lead to higher gas hold-up in BSCR, except in systems operated with porous plate distributors and at low gas velocities. For design purposes in BSCR at high pressure, where the liquids operate in the batch mode, Luo et al. [31] proposed the following formula for the calculation of the gas hold-up, based on their proper experimental data and those of many other authors [1,26,31-34] for various systems of gas, liquid and solids ... 

Fig. 34. Dependence of average slip velocity m, on the superficial gas velocity column diameter has little effect on u,. A porous plate distributor seems to give smaller u,.

The catalytic cracking of cumene to propylene and benzene was studied at 800°F using a fiuidized bed 3 inches in diameter [7]. The silica-alumina catalyst had 13% AI2O3 and a BET surface of 490 m /g. The 100-to 200-mesh fraction of the catalyst was used after fiuidizing for several hours to remove fines. The predicted equilibrium conversion was 0.77, and in many of the fixed bed tests this value was almost reached. With a porous-plate distributor and 8-inch initial bed height, the conversion was 62% at 0.1 ft/sec and 50% at 0.2 ft/sec. Treating the reaction as pseudo-first-order, Nf was estimated to be 8.4 for 0.1 ft/sec and 4.2 for 0.2 ft/sec. 

Initial bubble diameter (porous plate distributor) ... 

Figure 23 shows a comparison of the experimental data depicted in Fig. 22 with the calculation from the model equation (27). The required attrition rate constants Cj, K, and Q that describe the materials susceptibility to attrit in the respective regions have been determined by the corresponding attrition tests as described in Sec. 4.3. Cj has been determined from exactly that Gwyn-type test facility that is shown in Fig. 14 and was set to zero in the case of the porous plate distributor has been measured in a 200 mm ID Gwyn-type test apparatus, and Q has been determined from exactly that cyclone attrition-test procedure that is described in Sec. 4.3.4 using the equipment sketched in Fig. 11. The parameters me,in and dpc were measured in the apparatus sketehed in Fig. 21 under the assumption that mc n may be...

Use the packet model to estimate the convective heat transfer coefficient for the above case of a horizontal tube in a bubbling bed. Additionally, the bed has a porous plate distributor, and the center line of the heat transfer tube is located of Lt = 0-19m above the distributor. 

Figure 4 shows a schematic of the detector positions in the CARPT Facility which consists of the column, the detector support structure and the signal processing and data acquisition system. The set-up consists of 16 Nal detectors (2.54 x 2.54 cm crystals) positioned around the bubble column at known locations. The column makes use of a Plexiglass plenum which can accommodate test sections of various diameters. A stainless steel porous plate distributor with an average pore size of 40 pim is sandwiched between the two sections. A positioning device was fabricated and attached to the top of the column for calibration purposes. Air to the column is supplied by a compressor and the flow rate is monitored by three parallel rotameters. 

CARPT experiments were performed with bubble columns of three different diameters (11.4 cm 19 cm 29.2 cm) using air-water. Four superficial velocities, spanning the range from 2 cm/s to 18.4 cm/s were used in each column. This covers all flow regimes from bubble to churn turbulent flow. All runs were done with batch liquid (i.e. zero liquid superficial velocity). A porous plate distributor was employed. 

Figure 13, Bubble sizes at h = 1.5Dt as a function of bed size U =, 15m/sec, IJmf < < Uo, porous plate distributor.

These results are in line with an earher report by Fligner et al (1994) that the origin of clusters in gas—solid riser flows was seen to be associated with the way the oil is injected at the base of the riser. In addition, it is known in the fluidization Hterature that too low a pressure drop across the gas distributor may provoke convective instabilities and bubble formation in the bed—an effect that was also found in a linear stability analysis by Medlin and Jackson (1975) for a porous plate distributor. 

---