Evaporation process

Evaporation, evaporation equipments, and factors effecting the evaporation rate

1. evaporation : 18ch17

2. Contents; Evaporation process Objectives of evaporation Evaporation equipment (Evaporator) Parts of evaporator Problems occurring in evaporator Types of evaporator Potential hazards Environmental applications of evaporator

3. Objective of evaporation: The objective of evaporation is to concentrate a solution consisting of a non volatile Solute and a volatile solvent. Evaporation is conducted by vaporising a portion of the solvent to produce concentrated solution of thick liquor. In evaporation the thick liquor is the valuable product and the vapours are condensed and discarded.

4. Evaporation differs from other operations Evaporation VS Drying Distillation Crystallization Water distillation ( large scale evaporation)

5. Evaporator; An evaporator   is a device used in a process to turn the liquid form of a chemical substance such as water into its gaseous-form/vapor.

6. Components of an evaporator: Thermoexpansion Valve (TEV): Meters refrigerant flow and converts  hot high pressure liquid to a cold low-pressure liquid. Differential Pressure Switch: Monitors the cleanliness of the air filter Evaporator Coil : Absorbs heat through the vaporization of low-pressure liquid. Low-Pressure Cut Out Switch: Shuts off compressor when pressure drops from 27.3 psi. EMI Filter and EMI Gasket: Dissipates and prevents EMI from affecting the operation of other electronic equipment located within close proximity. Handle: Allows two people to lift evaporator assembly. Terminal Board, Single Row: Allows for ease of troubleshooting and repair. Condensate Drain Pan: Collects condensation from coil and discharges through drain hole. Evaporator Fan Motor: Drives evaporator  h ousing  f an. Evaporator Fan Housing: Draws air across evaporator coil to increase heat transfer from refrigerant.

7. Problems The practical solution of evaporation problems is profoundly effected by character of the liquor is to be concentrated. It is the wide variation in liquor characteristics which demands experience and judgement in designing and evaporator . Some of the most important properties of the evaporatong liquid are as follows. Concentration : On evaporation the concentration of solution increases. The density and viscosity increases with solid content until the liquor becomes more viscous for adequate heat transfer. Continued boiling of saturated solution causes crystals to form; these must be removed or the tubes clog. Foaming : Some materials specially inorganic substances foam during evaporation. A stable foam accompanies the vapour out of the evaporator, causing heavy entertainment. In extreme cases the entire mass of the liquid may boil into vapour outlet and be lost.

8. Continue... 3. Temperature Sensitivity : Many fine chemicals, Pharmaceutical products, foods are damaged when heated to moderate temperatures for relatively short times. In concentrating such materials special techniques are needed to reduce both the temperature of liquid and the time of heating. 4. Scale : Some solutions deposit scale on the heating surface. The overall coefficient then diminishes until the evaporator may shut down and the tubes cleaned. When the scale is hard and insoluble, the cleaning is difficult and expensive. 5. Materials of construction: Whenever possible, evaporators are made of some kind of steel.Many solutions, however, attack ferrous metals or contaminated by them. Special materials such as copper, nickel, stainless steel, aluminium, impervious graphite and lead are then used. Since these materials are expensive, high heat transfer rates becomes specially desirable to minimize the first cost of the equipment.

9. Types of evaporators used today The chief types of steam heated tubler evaporator in use today are; 1. Shell and tube type Long-tube vertical evaporator a . Upward flow ( Rising film evaporator) b . Downward flow ( Falling film evaporator) c . Forced circulation 2. plate type Agitated-film evaporator

10. Also Flash evaporation Vacuum evaporation Centrifugal evaporator Rotary evaporator Vapor-compression evaporator Evaporative cooler Pumpable ice technology Circulation evaporator

11. a . Upward flow ( Rising film evaporator): a . Upward flow ( Risin The liquid being evaporated is feed from the bottom into long tubes and heated with steam condensing on the outside of the tube from the shell side. This is to produce steam and vapour within the tube bringing the liquid inside to a boil. The vapour produced then presses the liquid against the walls of the tubes and causes the ascending force of this liquid. As more vapour is formed, the centre of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards. This phenomenon of the rising film gives the evaporator its name.

12. b . Downward flow ( Falling film evaporator): In falling film evaporators, the liquid product usually enters the evaporator at the head of the evaporator. In the head, the product is evenly distributed into the heating tubes. The liquid enters the heating tube and forms a thin film on the tube wall where it flows downwards at boiling temperature and is partially evaporated. In most cases, steam is used for heating the evaporator. The product and the vapor both flow downwards in a parallel flow. This gravity-induced downward movement is increasingly augmented by the co-current vapor flow. The separation of the concentrated product from its vapor takes place in the lower part of the heat exchanger and the vapor/liquid separator.

13. c . Forced circulation Developed for processing fluids which are fouling, scaling, and crystallizing, The raw material liquid is circulated through circulation pump in the heating chamber and separation chamber at a high speed and heated up in the heating chamber while flashed in the separation chamber, to achieve efficient vapour-liquid separation. The high flow speed of material liquid in the heat exchange tube can improve heat transfer efficiency. Evaporation process takes place in the separator instead of the heater. Therefore, the scaling caused by crystallization and precipitation in the tube can be effectively avoided.

14. Agitated-Film evaporator The feed enters evaporator at top, tangential to shell and gets distributed along the shell by the distributor. The rotor blades spread the feed evenly on the heated surface into a thin film and further agitate the film. Heating medium passing through the jacket evaporates the volatile component in feed. The vapor generated flow counter currently to feed and gets cleared in entrainment separator before leaving through vapor nozzle. The concentrate product comes out at bottom.

15. Performance of evaporator The principal measures of performance of a steam-heated tubler evaporator are the capacity and the economy of the evaporator. Capacity is defined as number of kilograms of water vaporized per hour. Economy is defined as number of kilograms of water vaporized per kilogram of stream feed to the unit. Steam consumption is defined as the ratio of capacity of evaporator to the economy of evaporator (kilograms of steam per hour).

16. Potential hazards of evaporator

17. Environmental applications of evaporator Brine Wastewater treatment Manure Sludge By-product from bioethanol production Food and agricultural waste Fruit concentrate Cement industries Etc.