Water can be removed from solutions in ways other than evaporation, including membrane processes, liquid-liquid extractions, crystallization, and precipitation. Evaporation can be distinguished from some other drying methods in that the final product of evaporation is a concentrated liquid, not a solid. It is also relatively simple to use and understand since it has been widely used on a large scale. In order to concentrate a product by water removal, an auxiliary phase is used which allows for easy transport of the solvent (water) rather than the solute. Water vapor is used as the auxiliary phase when concentrating non-volatile components, such as proteins and sugars. Heat is added to the solution and part of the solvent in converted into vapor. Heat is the main tool in evaporation, and the process occurs more readily at high temperature and low pressures.

Heat is needed to provide enough energy for the molecules of the solvent to leave the solution and move into the air surrounding the solution. The energy needed can be expressed as an excess thermodynamic potential of the water in the solution. Leading to one of the biggest problems in industrial evaporation, the process requires enough energy to remove the water from the solution and to supply the heat of evaporation. When removing the water, more than 99% of the energy needed goes towards supplying the heat of evaporation. The need to overcome the surface tension of the solution also requires energy. The energy requirement of this process is very high because a phase transition must be caused; the water must go from a liquid to a vapor.

When designing evaporators, engineers must quantify the amount of steam needed for every mass unit of water removed when a concentration is given. An energy balance must be used based on an assumption that a negligible amount of heat is lost to the system’s surroundings. The heat that needs to be supplied by the condensing steam will approximately equal the heat needed to heat and vaporize the water. Another consideration is the size of the heat exchanger which affects the heat transfer rate.

q = UA(T1-T2)where
U = overall heat transfer coefficient
A = heat transfer area
q = overall heat transfer rate

Falling Film Evaporator

This type of evaporator is generally made of long tubes (4-8 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 gains velocity as it flows downward. This gain in velocity is attributed to the vapor being evolved against the heating medium, which flows downward as well. This evaporator is applicable to highly viscous solutions so it is frequently used in the chemical, food, and fermentation industry.

 

Falling Film Evaporator with boiling inside the tubes.
The feed to the evaporator is fed to the top of the Calandria through efficient liquid distributors. Steam is given on the shell side. The concentrate is collected at the bottom. The same operation is repeated in multiple effects to achieve steam economy.
 

Rising Film Evaporator

The feed at near boiling is fed to the bottom of the Calandria. It is then pumped inside the tubes. Steam is provided on the shell side. Liquid and vapor are separated in the vapor separator at the top. Multiple effects are used to achieve higher steam economy.




   

Flash Evaporator

Flash (or partial) evaporation is the partial vaporization that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through a throttling valve or other throttling device. This process is one of the simplest unit operations. If the throttling valve or device is located at the entry into a pressure vessel so that the flash evaporation occurs within the vessel, then the vessel is often referred to as a flash drum.

If the saturated liquid is a single-component liquid (for example, liquid propane or liquid ammonia), a part of the liquid immediately "flashes" into vapor. Both the vapor and the residual liquid are cooled to the saturation temperature of the liquid at the reduced pressure. This is often referred to as "auto-refrigeration" and is the basis of most conventional vapor compression refrigeration systems.

If the saturated liquid is a multi-component liquid (for example, a mixture of propane, isobutane and normal butane), the flashed vapor is richer in the more volatile components than is the remaining liquid.
 

The liquid is heated in a heat exchanger and flashed in a flash vessel to achieve desired concentration. Multiple pass are provided to get required flow rate. Evaporative Crystallization can be efficiently achieved in ECOVAP FC.
 

Plate evaporator
Plate evaporators have a relatively large surface area. The plates are usually corrugated and are supported by frame. During evaporation, steam flows through the channels formed by the free spaces between the plates. The steam alternately climbs and falls parallel to the concentrated liquid. The steam follows a co-current, counter-current path in relation 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 dairy and fermentation industries since they have spatial flexibility. A negative point of this type of evaporator is that it is limited in its ability to treat viscous or solid-containing products.

Applications:

• Starch Industry: Liquid Glucose, Maltodextrine, Dextrose, Anhydrous Dextrose, High Fructose Syrup, Sorbitol, CSL, HDLS.
• Dairy Industry: Skimmed milk, Whole milk, Dairy Whitener, Baby Foods, Whey.
• Food Industry: Fruit juice concentration, Purees, Curry, Convenience Foods, Honey.
• Pulp and Paper: Black Liquor.
• Textile Industry: Caustic Recovery, Dye Bath Effluent.
• Alcohol Industry: Sugar Syrup, Spent Wash, Grain Thin Slop, DDGS.
• Pharmaceutical Industry: Active Ingredient Concentration, Pharma Effluent.
• Natural Products: Herbal Extracts, Dietary Fibres, Psyllium Husk, Licorice.
• Chlor-Alkali: Caustic evaporator.
• Petrochemical and Polymer Industry: High Density Polymer
• Beer and Beverages: Wort extract, Malt extract.
• Falling Film Reboilers.
• Edible Oil Industry: Lecithin, Lysolecithin, Hexane recovery.
• Soap and Biofuels: Glycerine
• Dyes and Pigments
• Specialty Chemical: Organic Acids, MSG, Hexamethy tetra mine, Ascorbic acid, Citric acid, Lactic acid.

 The goal of evaporation is to concentrate a target liquid, and this needs to be achieved for many different targets today. One of the most important applications of evaporation is that on the food and drink industry. Many foods that are made to last for a considerable amount of time or food that needs a certain consistency, like coffee, need to go through an evaporation step during processing. It is also used as a drying process and can be applied in this way to laboratories where preservation of long-term activity or stabilization is needed (for enzymes for example). Evaporation is also used in order to recover expensive solvents such as hexane which would otherwise be wasted. Cutting down waste handling cost is another major application of evaporation for large companies. Legally, all producers of waste must dispose of the waste in a methods that abides by environmental guidelines; these methods are costly. If up to 98% of a wastes can be vaporized, industry can greatly reduce the amount of money that would otherwise be allocated towards waste handling.