Page 535 - Industrial Wastewater Treatment, Recycling and Reuse

Zero Liquid Discharge Solutions 505

The system primarily consists of the following units:
1. Stripper
2. Stripper reboiler
3. Stripper condensers.
Feed effluent is fed to the preheater where it is preheated before being intro-
duced to the distillation column. The distillation column operates under
vacuum. Heat required for distillation is provided through indirect steam
heating in the stripper reboiler. Vapors from the top of the column are con-
densed in stripper condensers. Part of the condensate is sent back as reflux,
while the remaining condensate is taken out as distillate.

Distinct advantages of the distillation:
• Operation-specific design
• Energy efficient distillation system
• Optimal heat usage to conserve energy
• Vacuum operation reduces chances of scaling
• Well-engineered plants with high efficiency trays to ensure thorough sep-
aration and removal of impurities with almost 100% separation efficiency
• Proper care in the design of the calming zone, focusing on trays, the large
area of the down-comers, gas-liquid separators with tangential entry, and
vapor bottles (such focus ensures proper gas-liquid disengagement and
eliminates chances of liquid carryover)
• Column with hyper-stat Rh grid trays ensure high on-tray turbulence
and thus minimize chances of scaling and choking. (This special con-
struction of trays and tray access points also aids in the cleaning of column
internals. Comparisons between the packed column design and the tray
column design are given in Table 13.3)
• Condensers designed with multiple passes to ensure high velocity and to
minimize scaling inside tubes
• Preheated feed promotes proper stripping of impurities from water

13.5.1.7 Evaporation System: Multiple Effect Evaporator
“ECOVAP” Evaporation System. In this system, feed effluent is preheated by
processcondensate,vaporfromfirst,secondand thirdeffectfollowedbyvapors
whicharecomingoutfromTVRthroughseriesofpreheatersrespectively.The
preheated effluent is then fed into the first effect. The effluent flows in the for-
ward feed manner in evaporators, all four effects being of the forced
circulation type.
2
A live steam of 8 kg/cm (g) is fed to the inlet of the TVR system as a
motive fluid. The TVR system then sucks up a portion of the vapors from