Evaporators Horizontal tube

The earliest fabricated evaporator designs incorporated horizontal tubes. A vertical tank-like cylinder housed a horizontal tube bundle in the lower portion of the vessel, and the vapor space above the tubes served to separate the entrained liquid from the rising vapors. A later design based on a horizontal body and a removable U-type bundle is illustrated in Fig. % i). Another modification, the kettle type re-boiler, is similar and is more often employed as a bottoms heater for a distillation column than as an evaporator. 

Initial investment for horizontal tube evaporators is low, but heat transfer rates may also be relatively low. They are well suited for non-scaling, low viscosity liquids. For several scaling liquids, scale can sometimes be removed from bent-tube designs by cracking it off periodically by shockcooling with cold water or, removable bundles can be used to confine the scale to that part of the heat transfer surface which is readily accessible. 

Horizontal tube evaporators may be susceptible to vapor-binding, and foaming liquids cannot usually be handled. The short tube variety is seldom used today except for preparation of boiler feed water. The kettle-type reboiler is frequently used in chemical plant applications for clean fluids. 

The first evaporator to receive general recognition was a design utilizing horizontal tubes. This type is seldom used except for a few special applications. 

Modifications include the use of U-bend tubes to facilitate bundle rentoval for inspection and cleaning. 

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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. 11-122 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. 

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. 

Figure 12. Horizontal tube evaporator (A) Steam inlet (B) Vent for non-condensed gas (C) Condensate outlet (D) Liquor inlet (E) Liquor outlet (F) Sight glass (G) Vapor outlet.

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. 

Tube evaporators may be designed as vertical tube evaporators (VTE) or horizontal tube evaporators (HTE). In the VTE. vapor produced in one effect is condensed in the next effect. The effect is an evaporator chamber receiving heat from an external source or from a higher effect and producing vapor and brine which may serve as a heat source for ihc next elfecl. To obtain high efficiency in the use of heal energy, the process is repeated in several evaporator effects arranged in series. Sec also Evaporation. 

In horizontal tube evaporators, the liquor is usually on the outside of the tubes and the heating medium on the inside. Rather than submerging the tubes, the boiling liquid is sometimes sprayed on the outside of the tubes. This gives a performance approaching that of falling film evaporators. ... 

KocamustafaoguUari, G. Chen, I.Y. Ealling film heat transfer analysis on a bank of horizontal tube evaporator. AIChE J. 1988, 34 (9), 1539-1549. 

Chen, I.Y. KocamustafaoguUari, G. An experimental study and practical correlations for overall heat transfer performance of horizontal tube evaporator design. In Heat Transfer Equipment Fundamentals, Design, Applications, and Operating Problems Shah, R.K., Ed. The American Society of Mechanical Engineers New York, 1989 108, 23-32. 

A series of articles, "Studies in Evaporator Design, by W. L. Badger, has also been published in 1920 and 1921 in Chemical and Metallurgical Engineering, Badger gives experimental data with special reference to the horizontal-tube evaporator. 

The condensed steam forms a layer of water on the heating surface, and it is necessary especially in coils and horizontal tube evaporators that this condensate is removed as quickly as possible to avoid reduction in capacity. 

Barium Chloride.—The usual concentration is from 10 to 50 per cent, and with a horizontal-tube evaporator the capacity will be 1 gal. per square foot, with a steam pressure of 5 lb. and a vacuum of 26 in. Number of effects depends on quantity of liquor. Evaporators are built of cast iron or steel, with steel or wrought-iron tubes. 

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