An evaporator is a device in the process used to convert the liquid form of a chemical such as water into its gas/vapor form. The liquid is evaporated, or evaporated, into a gas form of the substance targeted in the process.
Video Evaporator
Usage
One type of evaporator is a kind of radiator coil used in the circulation of a closed compressor driven by a coolant. It is called an air conditioning system (A/C) or a cooling system to allow compressed refrigerant chemistry, such as R-22 (Freon) or R-410A, to evaporate from liquid to gas in the system while absorbing heat. from a closed cooling area, such as a refrigerator or room indoors, in the process. It works in closed A/C or cooling system with a condenser radiator coil that exchanges heat from the coolant, such as to the surrounding environment.
Different types of evaporators can be used for heating and may boil liquid-containing products to cause liquid to evaporate from the product.
Appropriate processes can be used to remove water or other liquids from a liquid-based mixture. The evaporation process is widely used to concentrate liquid foods, such as soups or make condensed milk called "condensed milk" which is done by evaporating water from milk. In the process of concentration, the purpose of evaporation is to vaporize most of the water from a solution containing the desired product.
Evaporator/evaporative process can be used to separate liquid chemicals and also for salvage solvents.
In the case of seawater desalination or in the Zero Liquid Discharge plant, the opposite purpose applies; evaporation removes the desired drinking water from the unwanted solute/product, salt.
One of the most important evaporation applications is in the food and beverage industry. Foods or beverages that must last long enough or require certain consistency, such as coffee, through evaporation steps during processing.
In the pharmaceutical industry, the evaporation process is used to remove excess moisture, provide products that are easily handled and enhance product stability. Preservation of long-term activity or enzyme stabilization in the laboratory is greatly assisted by the evaporation process.
Another example of evaporation is the recovery of sodium hydroxide in kraft pulping. Reducing waste handling costs is another major reason for large companies to use evaporation applications. By law, all waste manufacturers must dispose of waste using methods compatible with environmental guidelines; this method is expensive. By eliminating moisture by evaporation, the industry can greatly reduce the amount of waste products that must be processed.
Maps Evaporator
Energetics
Water may be removed from the solution by means other than evaporation, including membrane processes, liquid-liquid extraction, crystallization, and precipitation. Evaporation can be distinguished from several other methods of drying because the final product of evaporation is a concentrated, non-solid liquid. It is also relatively easy to use and understand because it has been widely used on a large scale, and many techniques are generally well known. To centralize the product by removing water, additional phases are used which allow for easier transport of solvents (water) rather than solutes. Water vapor is used as an additional phase when concentrating non-volatile components, such as proteins and sugars. The heat is added to the solution, and part of the solvent is converted to vapor. Heat is the main tool in evaporation, and the process is easier to occur at high temperatures and low pressures.
Heat is required to provide enough energy for the solvent molecule to leave the solution and move into the air around the solution. The energy required can be expressed as an excessive thermodynamic potential of water in solution. Leading to one of the biggest problems in industrial evaporation, the process requires enough energy to remove water from the solution and to supply the heat of evaporation. When discharging water, more than 99% of the energy required flows to the provision of evaporating heat. The need to overcome the surface tension of the solution also requires energy. The energy requirements of this process are very high because the transition phase must be caused; water must go from liquid to vapor.
When designing the evaporator, the engineer shall calculate the amount of vapor required for each unit of water mass that is discarded when a concentration is given. The balance of energy should be used based on the assumption that the amount of negligible heat is lost to the system environment. The heat that condensing steam needs to be supplied is about the same as the heat required to evaporate water. Another consideration is the size of the heat exchanger that affects the heat transfer rate.
Some general terms for understanding heat transfer: A = heat transfer area, q = overall heat transfer rate, and U = overall heat transfer coefficient.
How the evaporator works
The solution containing the desired product is fed into the evaporator and passes through the heat source. The heat used converts water in solution to steam. The vapor is removed from the rest of the solution and condensed while the now concentrated solution is introduced into the second evaporator or discarded. Evaporator, as a machine, generally consists of four parts. The heating section contains heating media, which may vary. Steam is incorporated into this section. The most common media consists of parallel tubes but others have plates or coils made of copper or aluminum. The concentrating and separating parts remove the vapor produced from the solution. The condenser condenses a separate vapor, then the vacuum or pump provides pressure to improve circulation.
The type of evaporator currently in use
Forced circulation evaporator
The natural circulation evaporator is based on the natural circulation of the product caused by the difference in density arising from heating. In the evaporator using tubing, once the water begins to boil, the bubbles will rise and cause circulation, facilitating the separation of fluids and vapors at the top of the heating tube. The amount of evaporation that occurs depends on the temperature difference between the vapor and the solution.
Problems can arise if the tube is not immersed in the solution. If this happens, the system will be dry and circulation disturbed. To avoid this, forced circulation can be used by inserting pumps to increase pressure and circulation. Forcible circulation occurs when the hydrostatic head prevents boiling on the surface of the heating. Common uses of forced circulatory evaporators include waste streams, crystallisations, viscous liquids, and other difficult process fluids because suppressed damping can reduce scaling and fouling. Pumps can also be used to avoid fouling caused by boiling liquid on a tube; pump suppress bubble formation. Another problem is the non-defined residence time and the steam consumption is very high, but at high temperatures, good circulation is easily achieved.
Falling film evaporator
This type of evaporator is generally made of 4-8 m tubes (13-26 feet) coated by a steam jacket. The uniform distribution of these solutions is important when using this type of evaporator. The solution comes in and gains speed as it flows down. The gain in this velocity is associated with steam evolving to the heating medium, which flows downward as well. This evaporator is usually applied to a very thick solution, so it is often used in chemical, sugar, food, and fermentation industries.
Rising (Long Tube Vertical) evaporator movie
In this type of evaporator, boiling takes place inside the tube, because the heating is made (usually by steam) outside the same. Therefore, dislike is not desirable; the creation of a water vapor bubble inside the tube creates an ascensional flow enhancing the heat transfer coefficient. Therefore this type of evaporator is quite efficient, its disadvantage is susceptible to rapid scaling of the internal surface of the tube. This design is then usually applied to a clean, non-salt solution. The tube is usually quite long, usually 4 meters (13 feet). Sometimes there is small recycling. The size of this type of evaporator is usually a difficult task, as it requires a proper evaluation of the true level of the liquor process inside the tube. Recent apps tend to prefer falling-film patterns rather than movie-climbing. And also very useful.
Climbing and dropping the film plate evaporator
Rock climbing and falling film plates have relatively large surface area. Plates are usually wavy and supported by a frame. During evaporation, the vapor flows through channels formed by empty space between the plates. The steam alternates up and down parallel to the dense liquid. Steam follows the current co-path, the opposite current in relation to the liquid. The concentrate and vapor are both introduced into the separation step where the steam is sent to the condenser. Evaporator plates of this type are often used in dairy and fermentation industries because they have spatial flexibility. The negative point of this type of evaporator is that it is limited in its ability to treat products containing thick or solid. There are other types of evaporator dishes, which work only by climbing films.
Multi-effect Evaporator
Unlike a one-stage evaporator, this evaporator can consist of up to seven evaporator stages (effects). Energy consumption for one-effect evaporator is very high and most of it costs for the evaporation system. Putting together evaporator saves heat and thus requires less energy. Adding one evaporator to the original reduces energy consumption by up to 50%. Adding another effect reduces up to 33% and so on. The heat-saving equation can be used to estimate how much will be saved by adding a certain number of effects.
The number of securities in a multi-effect evaporator is usually limited to seven because afterwards, equipment costs are close to cost savings in decreasing energy demand.
There are two types of food that can be used when dealing with multi-effect evaporators. Future feeding occurs when the product enters the system through the first effect, which is at the highest temperature. This product is then partially concentrated because some of the water is converted to steam and carried away. Then put in a second effect which is slightly lower in temperature. The second effect uses heat vapor made in the first stage as the heat source (hence the savings in energy expenditure). Lower temperature combinations and higher viscosities in subsequent effects provide favorable conditions for treating heat-sensitive products, such as enzymes and proteins. In this system, an increase in the surface area of ​​the next heating effect is required.
Another method uses feed backwards. In this process, dilute products are incorporated into the last effect which has the lowest temperature and is transferred from effect to effect, with increasing temperature. The final concentrate is collected in the hottest effect, which gives an advantage because the product is very thick at the last stage, so heat transfer is better. Since a few years there is also in operation of a multi-effect vacuum evaporator with heat pumps, renowned energetically and technically more effective than systems with recompression of mechanical steam (MVR) because due to lower boiling temperatures they can handle highly corrosive liquids or can form incrustations.
Hardened thin film evaporator
The agitation of thinning thin films has been very successful with hard-to-handle products. Simply put, this method quickly separates the volatiles from the less volatile components using indirect heat transfer and mechanical agitation of film products that flow under controlled conditions. This separation is usually done in vacuum to maximize? T while maintaining the most favorable product temperature so that the product sees only the equilibrium conditions in the evaporator and can maximize stripping and volatile recovery.
Problem
Technical problems can arise during evaporation, especially when the process is applied to the food industry. Some evaporators are sensitive to viscosity differences and consistency of aqueous solutions. This evaporator can work inefficiently because of loss of circulation. The evaporator pump may need to be changed if the evaporator needs to be used to concentrate a very viscous solution.
Fouling also occurs when hard deposits are formed on the surface of the heating medium in the evaporator. In foods, proteins and polysaccharides can create such precipitates that reduce heat transfer efficiency. Foaming can also create problems because handling excess foams can be costly in time and efficiency. An antifoam agent should be used, but only a few can be used when the food is being processed.
Corrosion can also occur when acidic solutions such as orange juice are concentrated. The resulting surface damage can shorten the lifetime of the evaporator. Quality and taste of food can also suffer during evaporation. Overall, when choosing an evaporator, the quality of the product solution needs to be carefully considered.
Sea use
Large vessels usually carry evaporated crops to produce fresh water, thus reducing their dependence on coastal based supplies. Steamers must be able to produce high-quality distillates to maintain boiler water levels. Diesel-engined vessels often use waste heat as a source of energy to produce fresh water. In this system, engine cooling water is passed through a heat exchanger, where it is cooled by concentrated sea water (salt water). Since the cooling water (which is chemically treated fresh water) is at 70-80 ° C (158-176 ° F), it is not possible to extinguish any water vapor except the pressure on the vessel heat exchangers is dropped.
To solve this problem, the venturi pump air fountain is used to create a vacuum inside the vessel. Partial evaporation is achieved, and the steam passes through the demister before it reaches the condenser portion. The sea water is pumped through the condenser section to cool the steam enough to precipitate it. The distillate is assembled on a tray, from which it is pumped into the storage tank. The salinometer monitors the salt level and diverts the distillate flow from the storage tank if the salt level exceeds the alarm limit. Sterilization is performed after the evaporator.
Evaporators are usually of the shell-and-tube type (known as the Plant Atlas) or plate type (such as the type designed by Alfa Laval). Temperature, production and vacuum are controlled by regulating the system valves. Sea temperatures can disrupt production, as well as fluctuations in machine loads. For this reason, the evaporator is adjusted for changes in sea water temperature, and dies altogether when the vessel maneuvers. Alternatives in some vessels, such as ships and passenger ships, are the use of the reverse osmosis principle for freshwater production, rather than using evaporators.
See also
- Flash evaporation
- Vacuum evaporation
- Centrifugal Evaporator
- Rotary evaporator
- Evaporator vapor evaporator
- Evaporative cooler
- Pumpable ice technology
- Circulatory Evaporator
References
- Source
- Fennema, Owen R., Marcus Karel, and Daryl B. Lund. Physical Principles of Food Conservation. Marcel Deker, Inc. New York and Basel, 1975.
- Krijgsman, Ir J., Chief Scientist and Research Project Manager, Gist-brocades, Delft and Delft University of Technology, Delft, and the Netherlands. Product Recovery in Bioprocess Technology. Butterworth-Heinemann, 1992.
Source of the article : Wikipedia
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