Evaporation short-tube vertical evaporator

Fig. 1. Natural ckculation evaporators where C = condensate, E = entrainment return, F = feed, N = noncondensibles vent, P = product or concentrate, S = steam, V = vapor, and M = knitmesh separator (a) horizontal-tube, (b) short-tube vertical, (c) propeUer calandria, and (d) long-tube reckculating.

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. 

Circffiation in the standard short-tube vertical evaporator is dependent entirely on boiling, and when boihng stops, any sohds present settle out of suspension. Consequently, this type is seldom used as a ciystaUizing evaporator. By instalhng a propeller in the downtake, this objection can be overcome. Such an evaporator, usually called a pro-... 

FIG. 11 -28 Effect of viscosity on heat transfer in short-tube vertical evaporator To convert centipoises to pascal-seconds, multiply by f0 to convert British thermal units per hour-square foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply by 5.6783. 

Best applications of short-tube vertical evaporators ... 

Mechanical cleaning is fairly easy with such units, and the capital investment is relatively low. Circulation stops, however, if the heat input is interrupted, creating the danger of the settling of any solids suspended in the liquor. This type of unit is not well suited to viscous liquids because of the low heat transfer coefficients associated with the low velocities of natural convec-tion.f Short-tube vertical evaporators have largely been surpassed by other types, particularly for applications involving liquors that foam, deposit excessive scale, are excessively viscous, or are heat sensitive. 

The short-tube vertical evaporator. Fig. %(d), also known as the calandria or Robert evaporator, was the first evaporator to be widely used. Tubes 4 and 8 long, often 2" to 3" in diameter, are located vertically inside a steam chest enclosed by a cylindrical shell. The early vertical tube evaporators were built without a downcomer but did not perform satisfactorily, so the central downcomer appeared very early. There are many alternatives to the center downcomer different cross sections, eccentrically located downcomers, a number of downcomers scattered over the tube layout, downcomers external to the evaporator body. 

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