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Evaporators
Evaporators: The goal of evaporation is to vaporise most of the water from a solution containing a desired product.
Evaporation can be distinguished from some other drying methods in that the final product of evaporation is a concentrated liquid, not a solid.
Falling Film Evaporator: This type of evaporator is generally made of long tubes (4-3 meters in length) which are surrounded by steam jackets. The uniform distribution of the solution is important when using this type of evaporator. The solution enters and goins celocity as it flows downward. This gain in velocity is attributed to the vapor being eolved against the heating meduim, which flows downward as well. This evaporator is applicable to highly viscous solutions so it is grequently used in the chemical, food, and fermentation industry.
Plate Evaporator: Plate Evaporators have a relatively large surgace area. The plates are usually corrugated and are supported by frame. During evaporation, steam flows through the chammels formed by the free spaces between the plates. The steam alternately climbs and falls parallel to the concentrated liquid. The steam foolos a co-current, counter-current path in realtion to the liquid. The concentrate and the vapor are both fed into the separation stage where the vapor is sent to a condenser. Plate evaporators are frequently applied in the diary and fermentation industries since they have spatial flexibility.
Multiple-effect Evaporator: Unlike single-stage evaporators can be made of up to seven evaporator stages of effects. The energy consumption for single-effect evaporators is very high and makes up most of the cost for an evaporation system. Putting together evaporators saves heat and thus requires less enegery. Adding one evaporator to the original decreases the energy consumption to 50% of the original amount. Adding another effect reduces it to 33% and so on. A heat saving % equation can be used to estimate how much one will save by adding a certain amount of effects.
There are two types of feeding that can be used when dealing with multiple-effect evaporators. Forward feeding takes place when the product enters the system through the first effect, which is at the highest temperature. The product is then partially concentrated as some of the water is transformed into vapor and carried away. It is then fed into the second effect which is a little lower in temperature. The second effect uses the heated vapor created in the first stage as its heating source (hence the saving in energy expenditure). The combination of lower temperatures and higher viscosities in subsequent effects provides good conditions for treating heat-sensitive products like enzymes and proteins. I using this system, an increase in the heating surface area of subsequent effects if required. Another way to porceed is by using backward feeding. In this process, the dilute products is fed into the last effect with has the lowest temperature and is transferred from effect to effect with the temperature inclreasing. The final concentrate is collected in the hottest effect which provides an advantage in that the product is highly viscous in the last stages so the heat transfer is considerably better.
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