Falling Film Vaporizers

The temperature gradient across the iiquid film must be kept relatively low (less than 15°C). Excessive temperature differences between the process and utility fluids may result in boiling of the fluid on the heat transfer surface with resultant fouling. Film boiling may also be effected with subsequent reduction in the rate of heat transfer. 

Inert gases are sometimes Injected into a falling film evaporator in order to reduce the partial pressure required to vaporize the volatile component. This technique will often eliminate the need for vacuum operation. Enough inert gas must be injected to achieve the desired results, but too much can produce flooding and entrainment with resultant poor control. 

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This criterion establishes the maximum amount of material that can be vaporized with a falling-film vaporizer. Approximately 85 percent of the entering material can be vaporized in a single pass without destroying the film. If tube loadings below the terminal loading are attempted, the film will break and form rivulets. Part of the tube surface will not be wetted, and the result will be reduced heat transfer with possible increased fouling of the heat-transfer surface. 

Keep the pressure drop between the last effect and the inlet to the vacuum device < 3 kPa. Consider vapor recompression for conventional low-ATevaporators such as falling film, forced circulation and horizontal tube falling film. Vapor recom-... 

The application of evaporators, in particular vertical tube falling film vapor compression evaporators, to treat PW is increasing, in particular in SAGD applications. The system provides a clean water stream that can be used by a once-through steam generators (OTSG) or drum boilers for stream production. Evaporator blowdown is disposed either... 

The Diikler theory is applicable for condensate films on horizontal tubes and also for falling films, in general, i.e., those not associated with condensation or vaporization processes. 

For example, vaporization may occur as a result of heat absorbed, by radiation and convection, at the surface of a pool of hquid or as a result of heat absorbed by natural convect ion from a hot wall beneath the disengaging surface, in which case the vaporization takes place when the superheated liquid reaches the pool surface. Vaporization also occurs from falling films (the reverse or condensation) or from the flashing of hquids superheated by forced convec tion under pressure. 

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. 

Multistrand wire, close-knit in two layers, holds stable liquid film by surface tension. Falling films of liquid form expansive contact surface with rising vapor layers. 

Mixed titania/alumina collodiai spheres were prepared in an apparatus consisting of two falling film generators in series upstream of the manifold. In the first generator, Ti(OEt)4 was vaporized at temperatures ranging between 78 and l0l°C, and the droplets, obtained by condensing this vapor, were then introduced into the... 

Figure 1 Flowsheet of the RCH/RP hydroformylation process 38 1 Continuous flow stirred tank reactor,424 2 Phase separator, 3 Stripping column, 4 Distillation column, 5 Heat exchanger, 6 Falling film evaporator, 7 Liquid vapor separator.

Fig. 4. Flow diagram of the Ruhrchemie/Rhone-Poulenc process (137) 1, continuous-flow, stirred tank reactor 2, phase separator 3, stripping column 4, distillation column 5, heat exchanger 6, falling film evaporator 7, liquid-vapor separator.

Fig. 3. Triple-effect steepwater evaporator. The third effect (forced circulation) Is shown in background second effect (falling film, recirculating) is middle unit. The first effect vapor head is shown in foreground. (Swenson. Whiting Corp)...

The vast majority of sulfonic acids were produced using continuous falling film sulfonation technology, which utilizes vaporized SO3 mixed w ith air. This technology dominates the sulfonation industry owing to the capability of high product throughput and low by-product waste streams. 

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