Short-tube evaporators

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. 11-23 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. 

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-... 

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

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

Several types of evaporators exist.34 The older, more traditional, evaporators are the Roberts and the Kestner, both rising film, tubular evaporators. The Roberts, first introduced in the 1800s, is known as a short tube, natural circulation, vertical tube evaporator. The tubes, inside which the evaporation takes place, are in the range of 1.5 to 3 meters in length. The Kestner evaporator consists of numerous long vertical tubes, 6 to 7.5 meters long, inside a cylindrical shell. In both, the juice to be concentrated is fed to the bottom of the tubes and heated, causing the juice to... 

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. 

---