Column handling

A continuous rectifying column handles a mixture consisting of 40 per cent of benzene by mass and 60 per cent of toluene at the rate of 4 kg/s, and separates it into a product containing 97 per cent of benzene and a liquid containing 98 per cent toluene. The feed is liquid at its boiling-point. 

Most columns handle multicomponent feeds. But many can be approximated by binary or pseudobinary mixtures. For this example, however, we will make several additional assumptions and idealizations that are sometimes valid but more frequently are only cmde approximations. 

Most methods for pressure drop calculation assume the column handles a nonfoaming mixture. Therefore, they do not strictly apply to the high-pressure column in this example, where systems do show a tendency to foam. The only published method that applies for these conditions is Strigle s [15 Eq. (8,29)]. This method was used earlier in this example to check compliance with the maximum pressure drop criterion. Here it is used to calculate the average bed pressure drop. 

A distillation column was designed to separate a 1000 kmol/h binary mixture of 50% mole component 1 to produce a distillate of 95% mole component 1 and to recover in this product 90% of component 1 in the feed. The column was constructed to handle a liquid traf-flc of 2500 kmol/h. Due to upstream process changes, the column feed composition dropped to 40% mole component 1 at the same total rate of 1000 kmol/h. While maintaining the required 95% distillate composition and operating at optimum performance, what recovery of component 1 is achievable, and can the column handle the required liquid traffic The column operates with a partial condenser at 100 kPa. The feed is a saturated liquid at feed tray conditions. Thermodynamic data given in Problem 6.1 may be used in this problem. 

The author recommends that for adequate vapor disengagement, liquid residence time should be at least 1 minute, based on the above definition. The author is familiar with experiences where sump residence times of the order of 20 to 40 s were insufficient to adequately disentrain vapor from liquid in sumps and draw pans of columns handling nonfoaming liquids. A greater residence time may be required... 

The absorption column handles large amounts of comparatively lean gas and needs to have a large diameter, short column and low pressure drop. In contrast, the stripper has a large liquid load and a comparatively small amount of vapour (the recaptured solvent), tending to lead to a tail column with a small diameter. 

In this arrangement, the first column handles about 40% of the total feed. Therefore, with a boil-up of 1.5 X 0.32 of the total feed, it provides, via its condenser, the heat to evaporate the feed of the second column. The latter operates under vacuum to provide the temperatiue difference for the condenser/vaporizer. 

Purity fractionated through a low-temperature column. Handling, Storage, and Precautions pentafluorosulfanyl chloride is stable at room temperature. Since it is toxic, it should be used in a fume hood. 

Purification fractionally distilled through a "Wgreaux column. Handling, Storage, and Precautions flammable. Chlorobis(tri-methylsilyl)methane is irritating to the eyes, skin, and respiratory system and should only be handled in a well-ventilated fume hood. In addition, proper protective clothing, gloves, and eye/face protection should be worn when title compound is in use. In case of contact with eyes, rinse immediately with water and seek medical advice. 

A 7-ft 0-in. ID CO2 absorber in an ammonia plant presentiy is equipped with 20 valve trays on 24-in. spacing. The gas to the absorber is 79,400 Ib/h at 130°F with a density of 0.792 Ib/ft. The inlet gas contains 18.2 mol % CO2, which must be reduced down to 90 mol ppm CO2 in the outlet gas stream. The absorber operates at a top pressure of 325 psia. The liquid feed is 30.2 wt % monoethanolamine solution at a temperature of 110°E This lean solution flow is 575,000 Ib/h, which contains 0.12 mol CO2 per mol MEA. It is desired to increase the rates by 35%, which the present trays will not accommodate. Can the existing column handle these higher rates with tower packing ... 

The one-column and two-column systems are both controllable using several types of control structures. The two-temperature control scheme for the neat reactive column handles most disturbances, but it cannot handle one type of feed composition disturbance. The use of an internal composition measurement provides more robust control. 

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