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This type of plate oan also find wide application in separating thermally unstable substances (with a limited liquid residence time in the column). In processes which take place under a significant excess pressure, where large loads with respect to liquid are observed but there are no fluctuations in load, it is expedient to use columns with mesh-work plates. S-shaped plates (Fig.2), which are basic column units, determine column dimensions and the quality of column operation (Table 1). The plate consists of S-shaped elements of identical profile which, being connected with each other, form caps and gutters. On one side are located trapezoidal slots for vapor passage, and on both ends of the vapor part of the element (the cap) are vapor chokes to prevent The first and last elements (reckoned along the course of liquid movement) are prepared respec- tively in the form of a cap and a gutter. Fulfilling its direct purpose as a bubbling" set-up, the S-shaped element is also a supporting construction which eliminates the necessity for any special supporting beams for element lengths of up to 4m. The working part of the plate, starting from the overflow, is composed of S-shaped elements, which, overlapping one another, form channels for vapor passage. For convenience in demounting any part of the plate (without disturbing another plate), the S-shaped elements after 6-8 steps are made demountable. The elements rest on a bearing ring, welded to the column body. If there is a necessity to remove liquid from the plate, a pocket is recessed, which en- sures complete flooding of the connecting pipe to remove liquid. The S-shaped elements are made of St.3, 0Khl3 or Khl8N10T steel, or from Monel metal, by cold rolling according to specially developed technology. For this, the elements were supplied with a length of 12 m, which decreases the amount of waste in laying out and reduces the cost of making them. The free cross section of the plates was varied in the limits 10-12%. The working area amounted to about 80% of the column cross section, and the overflow length was 0.7-0.74 times the column diameter. The norms worked out by the 'Giproneftemash" include 202 styles of S-shaped plates, among which 64 are single-stream, 120 are two-stream, and 18 are four-stream. In Fig.3 we show a graph which characterizes stable plate operation at various charges with re- spect to vapor and liquid. In Fig.4b we show data on entrainment of liquid from bubble cap plates under average conditions. As is evident from Fig~ entrainment of liquid at large gas velocities is greater in the plate of the bubble cap type. The hydraulic resistance of the S-shaped plate compared to bubble cap plates is shown in Fig.4a, from which it is evident that the resistance of the S-shaped plate at large gas loads is less than that of the bubble cap plate; the overall resistance coefficient referred to the narrowest section for vapor pas- sage was ~ = 4.5. As a result of the investigative work, three characteristic types of plate operation have been es- tablished: unstable, even and stable, and uneven. This gradation was fixed mainly in determining the region of stable plate operation. Depending on the operating conditions, the plate efficiency (Murphy efficiency, or overall efficiency) varies over wide limits. The maximum value of overall efficiency obtained in the unit was 90%, which confirmed the high effectiveness of the plates in operation under optimum conditions. Comparative values of plate efficiency are shown in Fig.5. In 1963 the machinery factories of the petroleum refining industry began serial output of columns with S-shaped plates. In 1966 the output of such columns was about 10,000 tons. Thereby, in 1966 alone, because of the iowest amount of metal in columns with S-shaped elements, 1.8 million rubles was saved. Industrial tests of columns with S-shaped elements and diameters up to 5m, carried out in 1966, confirmed the high degree of separation obtainable in these columns. It should be noted that the "Gipro- neftemash" has also developed a method of designing columns with S-shaped plates. The basic element of column plates with valved once-through plates is a valve of circular form which has two long legs and one short one, stamped out together with the valve, which fix the position of the valve in the plate opening and limit its rise. The short leg is positioned In a special groove in the base of the plate and ensures a fixed position of the valve when it is open. Because of the fact that the center of gravity of the valve is shifted in the direction of the long leg, opening of the valve on increase of gas velocity takes place in the following manner (see Fig.6). Initially the valve opens on the side of the short leg, up to its stop against the base, toward the stream of liquid. Then the valve opens its other part and occupies a horizontal position. After this, at higher gas flow rates, the valve opens to an angle of approximately 20 ~ to the plate base. The indicated valve rise en- sures highly effective operation of the plate over the whole range of change in gas load; therebythe first and second positions of the valve correspond to a plate operating schedule in a cross-over stream; the third position, to a direct stream or mixed stream schedule. The operating part of the plate or its base is composed of sheets about 400 mm wide; they are supported on longitudinal and transverse beams. On the sheets, valves are laid out in a checkerboard arrangement in vertices of a triangle with a spacing of 80 mm in transverse rows and one of 50 mm be- tween neighboring rows. To avoid free passage of liquid along the plate without contact with vapor, special grids of 100 mm height were set up on the longitudinal supports and at the column walls. In ordinary execution the base of the overflow assembly is made on the same level as the plate base. For plates with liquid sampling, the overflow pocket is recessed by 250-300 mm. The basic plates and all their welded parts were made up of carbon steel or alloy steel (depending on the aggres- siveness of the medium in the column) and the valves, of 0Khl3 steel 2 mm thick (so that the valve weight would not exceed 36g). The free cross section of the plates varied from 10 to 16%, and the plate working area was 60-80% of the column cross section; the weir length was 0.7-0.8 times the column diameter (see Tables 2 and 3). One hundred ninety styles of valved once-through plates were worked out according to standards (64 single-stream and 126 double-stream). Besides this, an improved variant of construction of valved once-through plates from stamped out elements has also been devised. In Fig.7 we show the region of stable operation of valved once-through plates and designate the regions of effective and highly effective operation. In Fig.4b we give data on liquid entrainment from valved once-throughplates, obtained on U } II111, "kL J lllIli N I I l lllt el IIIIII I I IIIII, 4 5678910" 3 5678.qlOx=} Fig. 8. Region of stable operation of grid plate (L = 57 m3/m2.h; a = 4 ram): 1) Line of maximum allow- able load; 2) line of minimum al- lowable load. the "cold" unit of 1200 mm diameter, which show that liquid entrainment at high gas rates does not exceed 10-20% by wt. and decreases with increase in liquid flow rate. In Fig.4a we give curves for the hydraulic resistance of valved, once-through plates which show that this resistance changes but little at maxi- mum gas loads and over a wide range in its velocity, and do not exceed the resistance of bubble cap or S-shaped plates. The ef- ficiency of plate operation is shown in Fig.5.