Levelness of trays

The common reason for out-of-levelness of trays is sagging of the tray decks. Sags are caused by pressure surges and sloppy installation. Sometimes, the tray support rings might not be installed level or the tower itself might be out-of-plumb (meaning the tower itself may not be truly vertical). 

The net result of this unpleasant scenario is loss of both vapor-liquid contacting and tray efficiency. Note how the mechanical problems (i.e., levelness) of tray 1 ruins the tray efficiency of both trays 1 and 2. 

Out of level of Tray Support Rings See Tolerances for Trays ... 

Burning Pyrites. The burning of pyrite is considerably more difficult to control than the burning of sulfur, although many of the difficulties have been overcome ia mechanical pyrite burners. The pyrite is burned on multiple trays which are subject to mechanical raking. The theoretical maximum SO2 content is 16.2 wt %, and levels of 10—14 wt % are generally attained. As much as 13 wt % of the sulfur content of the pyrite can be converted to sulfur trioxide ia these burners. In most appHcations, the separation of dust is necessary when sulfur dioxide is made from pyrite. Several methods can be employed for this, but for many purposes the use of water-spray towers is the most satisfactory. The latter method also removes some of the sulfur... 

At higher vapor loads, the kinetic energy of the vapor rather than the bubble burst supphes the thrust for jets and sheets of hquid that are thrown up as well as the energy from breakup into spray. This yields much higher levels of entrainment. In distillation trays it is the most common limit to capacity. 

Bottoms Level. Trays are particularly vulnerable to damage during shutdown and startup operations. Glitsch. Inc., (Reference 14) provides several good tips to minimize the possibility of tray damage during such periods. 

Tough transparent sheet may be produced by blending standard polystyrene with block copolymer in an extruder in the ratios 80 20 to 20 80, depending on the application of the products subsequently thermoformed from the sheet. For example, sheet for thermoforming an egg tray will not require the same level of impact strength as that required for jam jars. 

Tray, Truck, and Tunnel Driers In order to accelerate drying, the closet is factory-built with tight walls. It forms a box, and the air is passed by means of a fan over a radiator or over finned tubes and then over the trays. A portion of the air escapes at the discharge opening the remainder is reheated and recirculated. An amount of new air equivalent to the volume discharged is admitted at the fan. Secondary heating tubes are placed in the path of the air to restore their temperature and heat content. In the tray drier, shallow pans 2 ft by 3 ft by 2 in. deep, for example, are placed on a rack, forming part of the drier. In the truck drier, the rack is on wheels, and the whole may be wheeled in and out of the drier. There may be one or several trucks to each drier, and each truck may have twelve, sixteen or more levels for trays. 

The term inventory refers to liquid hydrocarbon contents at the top of the working level range. Tray holdup is included, but piping contents are disregarded. 

Fractionating columns usually operate with a normal liquid level in the bottom of the column and a level of liquid on each tray. It is reasonable to assume that the wetted surface be based on the total liquid within the height limitation—both on the trays and in the bottom. 

Top of Trays out of Level to a Horizontal or Designated Plane Along Any Diameter, and Variation From True Flatness. 

Ov Crall, the careful design of a distributor for liquid in the top of a packed tower, and for the redistribution of liquid flowing dow n multi-section packing in the tower, is essential to good consistent tower performance. However, the liquid flow is not alone, the uniformity of vapor distribution is likewise essential, because non-uniform vapor distribution can cause non-uniform liquid downflow. Then, there is the selection of the packing itself and its characteristics and requirements/sensitivity to the uniform distribution of the liquid and vapor. As earlier emphasized, the level of the distributor tray or trough can be critical to the consistent uniform liquid distribution. 

In the physical arrangement, make certain that the pressure balance level, plus an allowance for froth, establishes a height that is below the bottom tray of the column to avoid flooding the column. In addition, the estimated froth height on top of the liquid should still be below the level of the vapor return from the reboiler. 

Providing the surrounding air is reasonably still, the lids may be omitted. It helps to have glass walls at the sides to reduce draughts, which would disturb the layer of very cold air in the cabinet. The evaporator may be pipe coils on the outside of the inner wall, but is more usually a finned coil at the back or sides. It is important that produce is kept below the design level of the cold air blanket. The construction with discrete cold trays is now taken a stage further, where several trays may be arranged one above the other. 

Example 11.8 With highly reactive absorbents, the mass transfer resistance in the gas phase can be controlling. Determine the number of trays needed to reduce the CO2 concentration in a methane stream from 5% to 100 ppm (by volume), assuming the liquid mass transfer and reaction steps are fast. A 0.9-m diameter column is to be operated at 8 atm and 50°C with a gas feed rate of 0.2m /s. The trays are bubble caps operated with a 0.1-m liquid level. Literature correlations suggest = 0.002 m/s and A, = 20m per square meter of tray area. 

The most significant feature of the bubble-cap plate is that the use of risers ensures that a level of liquid is maintained on the tray at all vapour flow-rates. 

In the arrangement discussed, the feed is introduced continuously to the column and two product streams are obtained, one at the top much richer than the feed in the MVC and the second from the base of the column weaker in the MVC. For the separation of small quantities of mixtures, a batch still may be used. Here the column rises directly from a large drum which acts as the still and reboiler and holds the charge of feed. The trays in the column form a rectifying column and distillation is continued until it is no longer possible to obtain the desired product quality from the column. The concentration of the MVC steadily falls in the liquid remaining in the still so that enrichment to the desired level of the MVC is not possible. This problem is discussed in more detail in Section 11.6. 

Conceptualizations, once arrived at, interact to produce new conceptualizations, new technology, from which, once more, new concepts and new needs may emerge. Television, for instance, derives as a concept from motion pictures and radio and, even though it was introduced only a comparatively short time ago, has rapidly become a central part of homes at all levels of society in our culture. Watching television has tended to produce a more uniform culture through greater exposure to common stimuli, has reduced the amount of time available for free interaction by members of any particular household, and has resulted in the creation of such implements as "TV trays" and "TV dinners" to accommodate the need for more time around the television set. Automobiles have made possible the movement to the suburbs, the virtual end of public transportation in many parts of our country, and a resultant increased dependency on private means of transportation. In its turn, this has produced a more mobile population, a proliferation of roads, a tendency to think of distance in terms of units of time, the destruction of the countryside, and an increased need to deal with air pollution. 

Once in the column, volatile compounds vaporize and less-volatile liquids drop to the bottom of the column. Reflux begins and oil fractions condense and collect in various trays throughout the column. Heating within the column can influence the rate of reflux and holdup within the column. Steam is introduced into the column at the level of the lower trays and strips lighter compounds from the condensed fractions on these trays. As a result, the flash point of the fractions remaining on the lower trays increases. 

Guymon (21) reported the composition of tray liquids for brandy distilled in continuous column, respectively, at 130°, 170°, and 181° proof. The maximum level of fusel oil occurred on the tray nearest in proof to about 130°. This is the second tray below the product tray for the customary 170° proof of distillation of the product. 

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