Tube Evaporators

Inclined tube evaporators sometimes perform well in foaming services because of the sharp change in flow direction at the vapor head. It sometimes offers advantages when treating heat sensitive materials. Inclined tube evaporators require low headroom and permit ready accessibility to the tubes. 

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Screw-pressed oil is aUowed to stand to settle out suspended soUds, filtered through plate filter presses, and then pumped to storage. The oil-rich solvent (miscella) from the solvent-extraction process is filtered or clarified, and most of the solvent is removed in a long tube evaporator. FinaUy, the concentrated oil passes through a stripping column where sparging steam is injected to remove the residual solvent. A metric ton of cottonseed yields ca 91... 

A number of options for controlling scale formation are used in plant operations around the world. One approach is use of mechanical means, including thermal shock. Although rare today (ca 1997), this practice can be found ia use with the few obsolete submerged tube evaporators. 

Heat-transfer coefficients in clean coiled-tube evaporators for seawater are shown in Fig. 11-24 [Hillier, Proc. Jn.st. Mech. Eng. (London ), 1B(7), 295 (1953)]. The tubes were of copper. 

Heat Transfer from Various Metal Surfaces In an early work, Pridgeon and Badger [Jnd. Eng. Chem., 16, 474 (1924)] pubhshed test results on copper and iron tubes in a horizontal-tube evaporator that indicated an extreme effect of surface cleanliness on heat-transfer coefficients. However, the high degree of cleanhness needed for high coefficients was difficult to achieve, and the tube layout and... 

FIG. 11-23 Heat-transfer coefficients for water in short-tube evaporators. °C = (°F — 32)/1.8 to convert British thermal units per hour-square foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply hy 5.6783. 

FIG. 11-122 Evaporator types, a) Forced circulation, (h) Siibmerged-tiihe forced circulation, (c) Oslo-type crystallizer, (d) Short-tube vertical, (e) Propeller calandria. (f) Long-tube vertical, (g) Recirculating long-tube vertical, (h) Falling film, (ij) Horizontal-tube evaporators. G = condensate F = feed G = vent P = product S = steam V = vapor ENT T = separated entrainment outlet. 

The tube proportions in the basket evaporator are about the same as in the standard vertieal. One important feature of the basket-type evaporator is the ease with which a deflector may be added in order to reduce entrainment from spouting. The boiling in the vertical-tube evaporator is quite violent, and this tends to cause entrainment losses. This condition is accentuated if the liquor level in the evaporator is low. A baffle such as shown in Figure 9 largely prevents these losses and is much more easily added to the basket type than to the standard type. Other differences between the standard and the basket type are largely details of construction. 

Figure 11. Vertical tube evaporator (A) Tube sheets (B) Downtake (C) Condensate outlet (D) Non-condensed gas outlet (E) Liquor inlet (F) Thick liquor outlet.

Evaporators, Horizontal-Tube Type - The basic horizontal-tube evaporator is illustrated in Figure 12. The body of this evaporator is the liquor compartment and is in the form of a vertical cylinder. It is closed, top and bottom, with dished heads, although the bottom may be conical. The lower body ring is provided on opposite sides with steam compartments, closed on the outside by cover plates and on the inside by tube sheets. Between these tube sheets are fastened a number of horizontal tubes. The two steam chests with their connecting mbes form the steam compartment, and the tube wall heating surface. Steam is introduced into one steam chest and as it flows through the tubes it washes non-condensed gases and condensate ahead of it, so that these are withdrawn from the opposite steam chest. 

There are many modifications of the horizontal-tube evaporator, but these consist largely of changes in the shape of the body castings and not at all in the general arrangement or interrelationship of the parts. The horizontal-tube evaporator is best suited for non-viscous solutions that do not deposit scale or crystals on evaporation. Its first cost per square foot of heating surface is usually less than that of the other types of evaporators. 

Figure 13. Steam outside tube evaporator (A) Shell (B) Tube sheets (C CJ Distributing plates (D) Vapor head (E) Baffles (F) Steam inlet (G) Condensate outlet (H) Non-condensed gas vent (J) Thick liquor outlet (K) Vapor outlet (L) Liquor feed box.

Evaporation. The process of evaporation or distillation in the past was carried out in submerged-tube evaporators. These have been superseded by flash-type evaporators, which are more economical to run and reduce scale problems. The prcKess is suitable for brackish water, where the cost of chemical methods is excessive. The resulting distilled water is not palatable and re quires aeration to make it potable. 

Natural circulation Forced circulation Short-tube evaporators 200-600 400-2,000 hio = (16.1/dJ [Bik(cjx/k)f ... 

Evaporate 25,000 Ib/hr of CCI4 at 55 psia and saturation temperature on shell side of a ketde-type U-tube evaporator. Use steam as heating medium ... 

Most fish is still caught at sea and must be cooled soon after it is taken on board, and kept cold until it can be sold, frozen or otherwise processed [45]. The general practice is to put the fish into refrigerated sea water tanks, kept down to 0°C by direct expansion coils or a remote shell-and-tube evaporator. The sea water must be clean and maybe chlorine dosed. At this condition, fish can be kept for up to four days. 

Chilling of brines for pre-cooling will generally be in shell-and-tube evaporators. The Baudelot cooler within the pressure vessel may be cooled by flooded or dry expansion refrigerant, or by brine. 

Prohexadione-calcium standard solutions Dissolve 10 mg of prohexadione-calcium in 100mL of water to prepare a lOOmgL" solution. Transfer 100 p.L of this solution into a 30-mL test-tube, evaporate water to dryness under reduced pressure and to methylate prohexadione-calcium according to Section 6.3. Dissolve the product in acetonitrile to prepare the 0.05,0.2,0.4,0.6 and 0.8 mgL acetonitrile solutions. 

Figure 10.32. Long-tube evaporators (a) Rising film (b) Falling film...

Short-tube evaporators, also called callandria evaporators, are used in the sugar industry see Volume 2. 

Over-all heat transfer coefficients54 Long tube evaporators... 

Place 100 pi of plasma in each of two tubes and add 2.5 ml of methylene chloride. Shake the contents of the tube vigorously for 10 minutes and transfer 0.5 ml of clear extract (i.e.. the lower layer) to another tube. Evaporate the methylene chloride either at 35°C in an oven or in a stream of N2. The extract thus obtained is employed in the following step. 

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