Various types of Evaporators and their working principle
Various types of Evaporators and their working principle
1) Vertical Falling Film Evaporator
The process fluid to be vaporized is feed to the evaporator at the top of the tube sheet. A suitable distribution unit is nessecary in order to achieve an even liquid distribution. It is paramount the for this process minimal wetting rate is achieved.In general the process liquid flows at the tue inside. But there are also applications where the liquid is applied on the tube outside.Due to gravity the liquid forms a continious liquid film with hydrodynamic characteristics which are determined by the Fil Reynods and Kapitza number.In general steam is used as a heating source. The steam condenses on the tube outside of the tube and flows also gravity controlled to the bottom of the unit
Inside the tubes the two phase flow is separated by means of a separator at the bottom of the unit.
In multieffect falling film evaporators the vapour produced is
used in order to heat a so called second effect on a lower temperature and
pressure level. This is possible due to the very low required meant temperature
difference between heating medium and process liquid. In seawater desalination
up to 12 effects are possible in order to evapoate most efficently.
2) Horizontal film evaporator
In case of horizontal film evaporation the liquid to be
vaporised is distributed evenly on the top of a horizontal tube bundle.
For this purpose perforated plates and special designed jet nozzles are
applied. A minimum recirculation rate is required in order to maintain a
minimum wetting rate. The liquid chraracteristics between the tubes are
determined by the Film reynods number and Kapitza number. The fluid can be
encounter between the tubes as droplets, jet or continious sheet. Due to
the liquid imingment the heat transfer in horizontal units is in general
higher compared to vertical evaporators
3) Atmospheric Forced Draft Evaporator
Where the quantity of wastewater is small and difficult to treat, atmospheric forced draft evaporator is the ideal choice. Various models from 100 to 5000 Liters per day capacities are standard.Advantages and Features
Working Principle
Atmospheric evaporator consists of Feed Pump, Evaporator Tank with
Electrical or Diesel Heater, Circulation Pump, Blower, Mixing tube, Mist
Eliminator and Humid air Outlet. The wastewater from the wastewater
tank is pumped by the feed Pump to the evaporator tank. Electric or
Diesel heater heats the effluent in the evaporator tank. The hot
effluent is pumped into the Mixing Tube, through which air is blown from
atmosphere by the blower. The air and wastewater are thoroughly mixed
in the mixing tube and passes to the evaporator tank, before getting out
through the Mist eliminator and humid air outlet. Electrical controls
limits the operation of feed pump, circulation pump and blower depends
on the levels in the evaporator tank and wastewater tank. Control system
with automatic ON/OFF, safety shut off and switch gears with control
panel are provided with the system.
Applications
4) Low Temperature Vacuum Evaporator
The low temperature vacuum evaporator vaporizes water at lower temperature around 40 Deg. C than normal 100 Deg. C due to vacuum. Hence vacuum evaporators are useful for- recovery of heat sensitive chemicals such as cyanide plating baths,
- recovery of chemicals sensitive to air oxidation such as
cyanide plating bath and Stannous tin bath
- recovery of solutions containing volatile components
Working Principle
Advantages and features
Application
5) Mechanical Vapor Recompression
MVR (Mechanical Vapor Recompression) and Multiple Effect Evaporators for large volumes and energy economy.MVR is very energy efficient, since the latent heat of vaporization is fully utilized through vapor recompression and condensation. Typical layout of a MVR Evaporator is shown in figure.
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