Plant tray types

In a contact sulphuric acid plant the secondary converter is a tray type converter, 2.3 m in diameter with the catalyst arranged in three layers, each 0.45 m thick. The catalyst is in the form of cylindrical pellets 9.5 mm in diameter and 9.5 mm long. The void fraction is 0.35. The gas enters the converter at 675 K and leaves at 720 K. Its inlet composition is ... 

Scaling Up from Laboratory Data Laboratory experimental techniques offer an efficient and cost-effective route to develop commercial absorption designs. For example, Ouwerkerk (Hydrocarbon Process., April 1978, 89-94) revealed that both laboratory and small-scale pilot plant data were employed as the basis for the design of an 8.5-m (28-ft) diameter commercial Shell Claus off-gas treating (SCOT) tray-type absorber. Ouwerkerk claimed that the cost of developing comprehensive design procedures can be minimized, especially in the development of a new process, by the use of these modern techniques. 

The smallest feasible tower diameter size is 2 ft, but any size over 2 ft may be chosen. For pilot plant units, however, you may use the special optional inputs shown in Table 3.4. These same inputs are required for any of the three tray types, and allow accurate program answers for diameters smaller than 2 ft. 

In the second tower the gas must be cooled to meet the required water balance for acid production. This is usually a packed- or tray-type tower with liquor coolers in the recirculated weak acid stream. The temperature to which the gas must be cooled is determined by its sulfur dioxide content, the product acid strength desired, and the elevation of the plant above sea level. As shown in the chart, each of these factors has an important effect on the required temperature. An allowance has... 

It is therefore desirable to minimize the heat leak by reducing the size of the distillation column (which is usually of the tray type) for a given separation efficiency as much as possible, particularly in plants producing gaseous products. This implies a small column height and diameter in relation to the throughput, i.e., the following requirements are desired ... 

After 1980 a gradual displacement of the tray-type contactors by packet columns began in the distillation plants, and until 1990 it was considered the greatest novelty in the area of distillation [42]. 

FIG. 14-79 Cost of trays in plate towers. Price includes tray deck, bubble caps, risers, downcomers, and structural-steel parts. The stainless steel designated is type 410 Peters and Timmerhaus, Plant Design and Economics for Cbemical Engineers, 4th ed., McGraw-Hill, New York, 1.9.91). 

Final H2S removal takes place in four vertical vessels each approximately 60 feet (18.3 m) in height and 8 feet (2.4 m) in diameter and equipped with five trays of iron-oxide absorbent. Each vessel is provided with a locking lid of the autoclave type. The total pressure drop across these vessels is 5 psi (35 kN/m2). Gas leaving this section of the plant contains less than 1 ppm of H2S and passes to the C02 removal stage at a temperature of 35°C. 

Trays of type (a) are pushed through the plant between the heated shelves without contact (System Atlas Industries A/s, DK 2750 Ballerup, Danmark). The ribbed trays (b) are made... 

The process data from manifold installations can hardly be transferred to chamber-type plants. This applies, practically, also to the process transfer from belljar-type installations to chamber plants. Results obtained in laboratory plants of the chamber type must be analyzed carefully, if they are be transferred to another plant. If the product, the layer thickness of the product and the vials or trays are identical, the following conditions should be observed and compared ... 

Fig. 2.56. Freeze drying plant, type CONRAD 800, as shown in Fig. 2.54. In this plant, two trays are pushed in parallel through the tunnel. The two heating systems can be seen, and in front of these are the two lifts, which hoist the tray to required level. The two locks for the trays are on the left and right side, in the lower part of the tunnel. This plant produces approx. 3000 tonnes of freeze dried coffee granulate per year (photograph Atlas Industries A/S, DK-2750 Ballerup).

Possibly 90 percent of the trays seen in the plant are of these types. Perforated tray decks all have one feature in common they depend on the flow of vapor through the tray deck perforations, to prevent liquid from leaking through the tray deck. As we will see later, if liquid bypasses the outlet weir, and leaks through the tray deck onto the tray below, tray separation efficiency will suffer. 

Tray dryers, the simplest type of dryer, are commonly used for batch drying of biological materials, where the wet solids are placed on trays which are then transferred into a chamber. The chamber may have a heating jacket, heated tray supports, or a hot air supply. Vacuum may be applied to reduce the temperature at which the liquid evaporates, preserving heat labile products. These are well suited to low-volume products or flexible plants where a number of different products with different characteristics must be dried. They are relatively inefficient to operate, difficult to clean, and labor intensive to operate. The product is exposed when being loaded and unloaded, so the dryer may need to be located in a clean room or area for pharmaceutical products. 

These models use experimental data from drying kinetics tests in a laboratory, pilot-plant or full-scale dryer, and are thus more accurate and reliable than methods based only on estimated drying kinetics. They treat the dryer as a complete unit, with drying rates and air velocities averaged over the dryer volume, except that, if desired, the dryer can be subdivided into a small number of sections. These methods are used for layer dryers (tray, oven, horizontal-flow band, and vertical-flow plate types) and for a simple estimate of fluidized-bed dryer performance. For batch dryers, they can be used for scale-up by refining the scoping design calculation. 

---