Long-Tube Vertical Evaporators

Fig. 3. Film-type evaporators (a) long-tube vertical, (b) falling film, and (c) horizontal tube. Terms are defined in Figure 1. M represents end view of (a).

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. 

FIG. 11-123 Temperature variations in a long-tube vertical evaporator. 

Best applications of long-tube vertical evaporators ... 

Major evaporator designs include forced-circulation, long-tube vertical (both rising and falling film), and calandria-type evaporators. The economics of a particular process will dictate the evaporator style and model best suited to a particular application. Forced-circulation and calandria evaporators are required for processes where crystals are formed. These evaporators are designed to keep crystals suspended in solution to prevent scaling of the equipment. Long-tube vertical evaporators are used to concentrate a liquid that does not have solids present. 

Long tube vertical evaporators with either natural or forced circulation are most popular. Tubes are 19-63 mm dia and 12-30 ft long. 

Stroebe, G. W., Baker, E. M., and Badger, W. L. Trans. Am. Inst. Chem. Eng. 35 (1939) 17. Boiling film heat transfer coefficients in a long-tube vertical evaporator. 

This is a process mainly used in power plants for separation of dissolved matters by evaporation of the water. Multistage flash distillation, multiple-effect vertical long-tube vertical evaporation, submerged tube evaporation, and vapor compression are effective process equipment. It may require pH adjustment. The process removal efficiency is about 100%. 

Figure 8.16. Some types of evaporators, (a) Horizontal tube, (b) Calandria type, (c) Thermocompressor evaporator, (d) Long tube vertical, (e) Falling film, (f) Forced circulation evaporator-crystallizer, (g) Three types of Oslo/Krystal circulating liquid evaporator-crystallizers.

Evaporation of Sea Water in Long-Tube Vertical Evaporators... 

That the highest performance evaporator could be used for sea water. By performance was meant heat transfer coefficient not in B.t.u./hr./° F./sq. ft. but in B.t.u./ hr./° F./dollar of installed cost. For a long time, the long-tube vertical (LTV) evaporator has best fitted this description, at least under favorable operating conditions, such as at relatively high temperature differences (usually), and with little scale formation. 

STANDIFORD AND BJORK—EVAPORATION IN LONG-TUBE VERTICAL EVAPORATORS... 

FIG. 11-20 General range of long-tube vertical- (LTV) evaporator coefficients. °C = (°F - 32)/1.8 to convert British thermal units per hour-square foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply by 5.6783. 

Little work has been published on the effect of viscosity on heat transfer in the long-tube vertical evaporator. Cessna, Leintz, and Badger [Trans. Am. Inst. Chem. Eng., 36, 759 (1940)] found that the overall coefficient in the nonboiling zone varied inversely as the 0.7 power of viscosity (with sugar solutions). Coulson and Mehta [Trans. Inst. Chem. Eng., 31, 208 (1953)] found the exponent to be -0.44, and Stroebe, Baker, and Badger (loc. cit.) arrived at an exponent of -0.3 for the effect of viscosity on the film coefficient in the txriling zone. 

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