The Wide Production Of Evaporators Of KASRAVAND Technology Allows Proposing, The Most Suitable Evaporators For Plant Requirements.
Evaporation - Involves Vaporizing The Water To Separate It From The Dissolved Solids. Vapor Compression and Multistage Flash Evaporators Have Largely Replaced the Traditional Submerged-Tube Evaporators Because Of Better Energy Efficiency and the Capability, With Appropriate Water Treatment, Of Operating Free Of Scale for Relatively Longer Periods. Vapor Compression and Flash Evaporators Can Produce Water Of High Purity from Brackish And Sea Waters.
Operating Costs Are Related Principally To The Cost Of Heat, And, To A Lesser Extent, The Cost Of Utilities (Cooling Water, Electricity, Etc.) And Water Treating Chemicals. Heat (Energy) Costs Are Relatively Independent Of The Feed Water Composition.
TYPE OF EVAPORATORS
Evaporator Consists Of A Heat Exchanger For Boiling The Solution With Special Provisions For Separation Of Liquid And Vapor Phases.
Most Of The Industrial Evaporators Have Tubular Heating Surfaces.
The Tubes May Be Horizontal Or Vertical, Long Or Short; The Liquid May Be Inside Or Outside The Tubes.
1- FALLING FILM EVAPORATORS
Are Known As Vertical Shell-And-Tube Heat Exchanger With Laterally Or Concentrically Arranged Centrifugal Separator.
The Liquid To Be Concentrated Is Supplied To The Top Of The Heating Tubes And Distributed To Flow Down The Inside Of The Tube Walls As A Thin Film. The Liquid Film Starts To Boil Due To The External Heating Of The Tubes And Is Partially Evaporated As A Result. The Downward Flow, Caused Initially By Gravity, Is Enhanced By The Parallel, Downward Flow Of The Vapor Formed.
Residual Film Liquid And Vapor Is Separated In The Lower Part And In The Downstream Centrifugal Droplet Separator. It Is Essential That The Entire Film Heating Surface, Especially In The Lower Regions, Be Evenly And Sufficiently Wetted With Liquid. Where This Is Not The Case, Dry Spots Will Result That Will Lead To Incrustation And The Build-Up Of Deposits.
For Complete Wetting It Is Important To Select A Suitable Distribution System For The Head Of The Evaporator.
Wetting Rates Are Increased By Using Longer Heating Tubes, Dividing The Evaporator Into Several Compartments Or By Recirculating The Product.
This will use in water treatment plants.
2- FORCED CIRCULATION EVAPORATORS
Are Known As Horizontal Or Vertical Shell-And-Tube Heat Exchanger Or Plate Heat Exchanger, With Flash Vessel/Separator, Circulation Pump.
The Liquid Is Circulated By Means Of A Circulation Pump, Where It Is Superheated At An Elevated Pressure, Higher Than Its Normal Boiling Pressure. Upon Entering The Separator, The Pressure In The Liquid Is Rapidly Reduced Resulting In Some Of The Liquid Being Flashed, Or Rapidly Boiled Off. Since Liquid Circulation Is Maintained, The Flow Velocity In The Tubes And The Liquid Temperature Can Be Controlled To Suit The Product Requirements Independently Of The Pre-Selected Temperature Difference.
3- PLATE EVAPORATORS
Are Known As Plate Heat Exchanger, Separator. A Plate-And-Frame Configuration Employs Special Plates, With Alternate Product And Heating Channels. The Plates Are Sealed.
Product And Heating Media Are Transferred In Counter Flow Through Their Relevant Passages. Defined Plate Distances In Conjunction With Special Plate Shapes Generate Strong Turbulence, Resulting In Optimum Heat Transfer.
Intensive heat transfer causes the product to boil while the vapor formed drives the residual liquid, as a rising film, into the vapor duct of the plate package. Residual liquid and vapors are separated in the downstream centrifugal separator. The wide inlet duct and the upward movement ensure optimum distribution over the total cross-section of the heat exchanger.
4- CIRCULATION EVAPORATORS
Vertical Shell-And-Tube Heat Exchanger Of Short Tube Length, With Lateral Separator Arranged At The Top.
The Liquid To Be Concentrated Is Supplied To The Bottom And Rises To The Top Of The Heating Tubes In Accordance With The “Mammoth Pump” Or Rising Film Principle. Due To The External Heating Of The Tubes The Liquid Film On The Inside Walls Of The Tubes Starts To Boil Releasing Vapor. The Liquid Is Carried To The Top Of The Tubes As A Result Of The Upward Movement Of The Vapors.
The Liquid Is Separated From The Vapors In The Downstream Separator And Flows Through A Circulation Pipe Back Into The Evaporator, Ensuring Stable And Uniform Circulation. The Larger The Temperature Difference Between The Heating Chamber And The Boiling Chamber, The Greater The Intensity Of Evaporation And, Consequently, The Liquid Circulation And Heat Transfer Rates.
Where The Boiling Chamber Of The Circulation Evaporator Is Divided Into Several Separate Chambers, Each One Equipped With Its Own Liquid Circulation System, The Heating Surface Required For High Final Concentrations Can Be Considerably Reduced Compared To An Undivided System.
The Final Concentration Is Only Reached In The Last Chamber. In Other Chambers, The Heat transfer is considerably higher due to the lower viscosities and boiling point elevations.
5- OTHER TYPES OF EVAPORATOR
5.1. FLUIDISIED BED EVAPORATORS
5.2. FALLING FILM, SHORT PATH EVAPORATORS
5.3. RISING FILM EVAPORATORS
5.4. COUNTERFLOW-TRICKLE EVAPORATORS
5.5. STIRRER EVAPORATORS
5.6. SPIRAL TUBE EVAPORATORS