Details of Evaporators

Types and Design

In the evaporation process, concentration of a product Is accomplished by boiling out a solvent, generally water. The recovered end product should have an optimum solids content consistent with desired product quality and operating economics. It is a unit operation that is used extensively in processing foods, chemicals, pharmaceuticals, fruit juices, dairy products, paper and pulp, and both malt and grain beverages. Also it is a unit operation which, with the possible exception of distillation,is the most energy intensive.While the design criteria for evaporators are the same regardless of the industry involved, two questions always exist: is this equipment best suited for the duty, and is the equipment arranged for the most efficient and economical use? As a result, many types of evaporators and many variations in processing techniques have been developed to take into account different product characteristics and operating parameters.

Types of Evaporators

The more common types of evaporators include:

Batch pan Rising film tubular
Forced circulation Plate equivalents of tubular evaporators
Natural circulation Falling film tubular
Wiped film Rising/ falling film tubular



Although plate evaporators can be used on a broad range of products, the main application has been with products that are heat sensitive and therefore benefit from the high HTC's and low residence time. Products that are being processed in this evaporator include:

Apple Juice Coffee Pear juice
Amino acids Fruit purees Pectin
Beef broths Gelatin Pharmaceutical products
Beet juice Grape juice Pineapple juice
Betacyclodextrin Lime juice Skim milk
Caragenan Liquid egg Sugars
Cheese whey Low alcohol beer Vegetable juices
Chicken broth Mango juice Whey protein
Citrus juice Orange juice Whole milk
Falling film tubular Rising/falling film tubular


Multi-Effect Evaporation

Multi-effect evaporation uses the steam produced from evaporation in one effect to provide the heat to evaporate product in a second effect which Is maintained at a lower pressure . In a two effect evaporator, it is possible to evaporate approximately 2 kgs of steam from the product for each kg of steam supply. As the number of effects is increased, the steam economy increases. On some large duties it is economically feasible to utilize as many as seven effects. Increasing the number of effects,for any particular duty, does increase the capital costsignificantly and therefore each system must be carefully evaluated. In general, when the evaporation rate is above 3,000 lbs/h (1,350 kg/h), multi-effect evaporation should be considered.

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