Abstract:
An experimental investigation was undertaken that involved the design, construction
and operation of an evaporation unit which would concentrate dilute caustic soda from
the mercerizing unit wastewater of a textile mill. The concentration of caustic soda in
the wastewater was to be raised to 20 w/w % by evaporating the water from the dilute
solution containing caustic soda 4 w/w % using waste heat from flue gases.
The process unit designed for this purpose consists of an evaporator, flash chamber,
preheater, natural gas fuelled furnace, feed tank, storage tank and circulating pump.
Parameters such as the amount of water evaporated, volume of natural gas burnt,
pressure drop, circulation rate and concentration change of caustic soda solution were
measured. From these, the rate of evaporation, LMTD, total heat supplied, overall heat
transfer coefficient etc. were determined.
From the experiments, it was has been found that the rate of evaporation ranged from
0.08 liters/hr to 19.00 liters/hr with an average of 6.91 liters/hr. Overall heat transfer
coefficient in the evaporator varied from 20.70 W/m2 K to 52.58 W/m2 K.
Cost analysis carried out showed the process is economically operable in a textile mill
with mercerizing operation. The experimental results suggest that this process can be
implemented in the industry.
