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# Answer to Question #248778 in Chemical Engineering for Kamo

Question #248778

An evaporator is used to concentrate 12 000 kg/h of a 15% solution of NaOH entering at 60oC to a product of 50% solid. The pressure of the saturated steam used is 300 kPa and the pressure in the vapour space of the evaporator is 11.7 kPa. The overall heat transfer coefficient is 1 560 W/m2K. Calculate the steam used and the steam economy in kg vaporised/kg steam.

1
2021-10-10T09:32:10-0400

Given:

F = 4536 kg/h

TF = 60 ºC

xF = 0.2

S = ?

Solution

For the total balance,

"F = 4536 = L + V"

For the balance on the solute alone,

"F \\times F = L \\times L"

"4536 (0.2) = L (0.5)"

L = 1814 kg/h of liquid

Substituting into total balance and solving,

V = 2722 kg/h of vapor

To determine T1 = Tsat + BPR of the 50 % concentrate product, first we obtain Tsat of pure water from steam table. At 11.7 kPa,

Tsat = 48.9 ºC.

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