Plate Evaporator

Plate units were first known as liquid/liquid heat exchangers. 

In the meantime, these advantages are also used for evaporation. The achieved k values are similar as those achieved in a tube climbing-film evaporator. A separate preheater is not required since the heat transfer in the liquid phase is already good. 

A throttling of the evaporation is not recommended since the plates only can take up a limited pressure difference between heating and product side. The plates which support each other are imprinted. Thus, they can resist to higher pressure differences, but the supporting points are always a starting point for the formation of coatings. 

The distribution of the liquid over the plates is very important. The complete transfer surface has to be flushed well in order to avoid incrustations. Plate evaporators can be chemically cleaned, but a mechanical cleaning with high-pressure ejector is very difficult. For this reason, plates are only used for evaporation for pure liquids, such as sugar juice. 

Plates are also operated as falling-film evaporator. 

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Concentration and Aroma Recovery. Concentration of juice from deciduous fmit is best carried out using an evaporator that causes as httle thermal degradation as possible and that permits recovery of volatile materials important to the aroma of the fresh fmit, ie, essence. Evaporators that use a high temperature for a short time and operate under a vacuum, such as the APV Crepaco falling film plate evaporator or the Alfa Laval centrifugal... 

For new components, the nickel coating is usually 25-250 im thick. Normally, the deposits are not machined. Applications include pump bodies, laundry plates, heat exchanger plates, evaporator tubes, alkaline battery cases and food-handling equipment of various sorts. 

Plate evaporators (Figure 7.8) are formed by cladding a tubular coil with sheet metal, welding together two embossed plates, or from aluminium extrusions. 

The major use for flat plate evaporators is to cool a solid product by conduction, the product being formed in rectangular packages and held close between a pair of adjacent plates. 

Figure 7.8 Plate evaporators, (a) Single embossed, (b) Double embossed, (c) Extruded, (d) Holdover (brine filled) (Courtesy of Elliott Turbomachinery Ltd)...

The study concluded that Once wash steps are optimized, samples prepared by solid phase extraction are cleaner than those prepared by protein precipitation. Samples prepared by extraction with a Multi-SPE plate resulted in lower LOQs than samples prepared by solvent precipitation. Drug recoveries were acceptable (>80%) for both the SPE and the solvent precipitation methods. Well-to-well reproducibility of samples was slightly better with extraction with a Multi-SPE plate. Evaporation and reconstitution, while more time-consuming, yield better chromatographic performance, allow analysis of lower concentration samples, and require optimization for good analyte recovery. 

Dissolve in a solvent and then use a liquid sampling cell to measure the solution 2) dissolve in a solvent, place several drops of the solution on a salt plate, evaporate the solvent, and measure the residue 3) KBr pellet 4) Nujol mull and 5) reflectance. 

Both the vapour evaporated from the boiling film and the concentrated product are discharged from the evaporator to a vapour-liquid separator from which the product is pumped, the vapour passing to the next effect of the evaporator, or the condenser. Compared with tubular evaporators, plate evaporators can offer important advantages in terms of headroom, floorspace, accessibility and flexibility. 

APV, whose Paraflow plate heat exchanger is illustrated in Volume 1, Chapter 9, supply climbing and falling-film plate evaporators with evaporative capacities up to 10 kg/s. Such units offer the advantages of short contact and residence times and low liquor hold-up, and hence are widely used for the concentration of heat-sensitive materials. 

Heat-assisted evaporation strategies, such as the falling-film evaporator, plate evaporator, forced-film evaporator, and centrifugal forced-film evaporator have been developed and are used to remove vyater from solutions of small peptides, such as antibiotics. But most recombinant proteins are heat labile and may not survive this strategy. 

Fig. 2.19.2. Inside view of a condenser show ing two evaporators. 1, Tube condenser cooled by direct expansion of refrigerant, e.g. R404A (see Table 2.2) 2, plate evaporator...

Morgenroth B, Austmeyer KE, Mauch W. Experiences with the falling-film plate evaporator and concept for energy-efficient process schemes in the cane sugar industry. Zuckerindustrie 1995 120. 

Magnesium (as MgO) Place 400.0 mg of sample, 5 mL of 2.7 A hydrochloric acid, and about 10 mL of water in a small beaker, and dissolve the sample by heating on a hot plate. Evaporate the solution to a volume of about 2 mL, and cool. Transfer the residual liquid into a 100-mL volumetric flask, dilute to volume with water, and mix. Dilute 7.5 mL of this solution to 20 mL with water, add 2 mL of 1 A sodium hydroxide and 0.05 mL of a 1 1000 solution of Titan yellow (Clayton yellow), mix, allow to stand for 10 min, and shake. 

Fig. 1 Exploded view of rising/falling film plate evaporator. (Courtesy of APV Crepaco, Inc., APV Americas, Rosemont, IL—An Invensys Company.)...

Another evaporator type is the plate evaporator (APV (21), GEA-TUCHENHAGEN (22), SCHMIDT (23)). The advantage of plate evaporators is that the plate sections can be opened for cleaning and inspection. The number of plates can also be adjusted... 

Plate evaporators may be constructed of flat plates or corrugated plates, the latter providing an extended heat transfer surface and improved structural rigidity. Two basic types of heat exchangers are used for evaporation systems plate-and-frame and spiral-plate evaporators. Plate units are sometimes used because of the theory that scale will flake off such surfaces, which can flex more readily than curved tubular surfaces. In some plate evaporators, flat surfaces are used, each side of which can serve alternately as the liquor side and the steam side. Scale deposited while in contact with the liquor can then be dissolved while in contact with the steam condensate. There are still potential scaling problems, however. Scale may form in the valves needed for cycling the fluids and the steam condensate simply does not easily dissolve the seale produced. 

Spiral-plate evaporators may be used instead of tubular evaporators, and offer a number of advantages over conventional shell-and-tube units centrifugal forces improve heat transfer the compact configuration results in a shorter liquid pathway they are relatively easily cleaned and resistant to... 

Figure 11. Plate evaporator, rising/falling film type. (APVCompany, Inc.)...

Frequently, it is quite difficult to grind up plastic or rubbery substances, and such materials lend themselves more readily to casting as a film on a sodium chloride or potassium bromide plate. This is done by dissolving the sample in a volatile solvent, pouring the solution onto a salt plate, evaporating off the solvent, and mounting the plate in a holder, as shown in Fig. 3.1. 

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