Distributor Grid

Fig. 15. Schematic of a distributor grid shroud used to allow jets to expand and enter the fluid bed at lower velocity.

Fig. 16. Typical distributor grid designs for fluidized-bed applications (a) porous plate, (b) cone, (c) perforated plate, (d) downward dish, (e) upward dish,...

Distributed feedback (DFB) lasers, 22 177 Distributed fiber sensors, 11 152-153 Distribution function, 26 1020 Distributor design, in fluidized beds, 11 810 Distributor grid shroud, 11 813 Distributor jets, 11 812-813 Distributors... 

The UOP rotary valve has been used in hundreds of Sorbex units across a variety of applications. The purpose of the rotary valve is to simply move the inlet and outlet ports of the net streams (feed, desorbent, raffinate, extract) around the 24 beds in stepwise fashion, creating a semi-continuous countercurrent flow of adsorbent relative to the entry and exit points of the net streams to and from the adsorbent chambers [25]. The rotary valve consists of a rotor plate pressed against a stator plate inside a pressure vessel that indexes the net desorbent, feed, extract and raffinate streams around the adsorbent chambers [26]. An alternative method of moving the inlet and outlet streams around the adsorbent chambers is used in other technologies where multiple automatic on-off valves at each distributor grid inlet are employed [5]. 

Solids of group A have small particle diameters (% 0.1 mm) or low bulk densities this class includes catalysts used, for example, in the fluidized-bed catalytic cracker. As the gas velocity u increases beyond the minimum fluidization point, the bed of such a solid first expands uniformly until bubble formation sets in at u = //mb > mr. The bubbles grow by coalescence but break up again after passing a certain size. At a considerable height above the gas distributor grid, a dynamic equilibrium is formed between bubble growth... 

Distributor Grid, or a plate with holes, through which the fluid is injected into the bed. 

It is worth pointing out that a general observation made by Chavarie and Grace (1975) was that none of the models (tested correctly) accounted for the considerable end effects observed at both the inlet and the outlet, i.e., near the distributor (grid region) and in the space above the bed surface (freeboard region). 

When both solids and gases pass through the distributor, such as in catalytic-cracldng units, a number of variations are or have been used, such as concentric rings in the same plane, with the annuli open (Fig. 17-9a) concentric rings in the form of a cone (Fig. 17-9b) grids of T bars or other structural shapes (Fig. 17-9c) flat metal perforated plates supported or reinforced with structural members (Fig. 17-9d) dished and perforated plates concave both upward and downward (Fig. 17-9e and f). The last two forms are generally more economical. 

Figure 4-51. Air distributor— pipe grid design version. (Source Enpro Systems, Channelview, Texas.)...

D. Hold-Down Grid (see Figure 3). According to Strigle, Normally, the upper surface of the packed bed is at least 6 in. below a liquid distributor or redistributor. The bed limiter or hold-down plate is located on top of the packed bed in this space. It is important to provide such a space to permit gas disengagement from the packed bed. Such a space allows the gas to accelerate to the velocity neces-... 

Overall distributor height is approximately 24". The distributor is leveled from a supporting grid, which normally restson the top of the packed bed. The vessel manway is usually located at or above the header elevation. 

Phj sically the redistributions may be a simple and relatively inefficient side wiper as in Figure 9-12 or 9-13 a conventional support grid or plate plus regular distribution plate as used at the top a combination unit similar to Prym support and distributor or a support plate as shown in Figures 9-14 and 9-7D and 7E, a circular plate with holes. 

Figure 7-5. Typical layout of a pipe grid distributor.

Liquid Distributor/ Redistributor Hoki-Down Grid 7 Rsndom Packing... 

Grid Jets as a Source of Attrition. Jet attrition affects only a limited bed volume above the distributor, which is defined by the jet length. As soon as the jet is fully submerged its contribution to the particle attrition remains constant with further increasing bed height. Figure 6 shows some respective experimental results by Werther and Xi (1993). The jet penetration length can be estimated by various correlations, e.g., Zenz (1968), Merry (1975), Yates et al. (1986) or Blake et al. (1990). 

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. 

Arena etal. (1983) and Pis etal. (1991) also found that Eq. (15) gave a good description of their experimental results. As an example, Fig. 11 shows the results of Pis etal. (1991), which were obtained in a fluidized bed column of 0.14 m in diameter. The distributor had 660 orifices of 1 mm in diameter. Unfortunately, no distinction was made between the measured attrition rate and the influence of the grid jets. However, their influence might be negligible in the present case due to the relatively smalljet velocity. 

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