1000 kg/h of an aqueous feed solution containing 38 wt.% potassium nitrate (KNO3) and 0.2 wt.% CaCO3 (the rest is water) is crystallised in an evaporative crystalliser. 450 kg/h of water vapour are evaporated from the crystalliser to create a super‐saturated solution which then causes crystals to form and grow. The product crystal slurry is then fed to a centrifuge where perfectly dry KNO3 crystals are recovered.1 The filtrate solution (which still contains some dissolved KNO3 as well as dissolved CaCO3) is recycled back to the crystalliser. However, a bleed (purge) stream is split off and removed in order to keep the concentration of CaCO3 in the return solution from climbing above 1 wt.% (in order to prevent crystallisation of CaCO3 when its concentration builds up too high). Once this bleed is removed, the remaining 500 kg/h of solution is recycled. See diagram. Determine: 1. Unknown flows and compositions in this system. 2. KNO3 fraction in the feed solution that is recovered as product crystals.

Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
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Chapter1: Introduction
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1000 kg/h of an aqueous feed solution containing 38 wt.% potassium nitrate (KNO3) and 0.2 wt.%
CaCO3 (the rest is water) is crystallised in an evaporative crystalliser. 450 kg/h of water vapour are
evaporated from the crystalliser to create a super‐saturated solution which then causes crystals to
form and grow. The product crystal slurry is then fed to a centrifuge where perfectly dry KNO3
crystals are recovered.1 The filtrate solution (which still contains some dissolved KNO3 as well as
dissolved CaCO3) is recycled back to the crystalliser. However, a bleed (purge) stream is split off and
removed in order to keep the concentration of CaCO3 in the return solution from climbing above 1
wt.% (in order to prevent crystallisation of CaCO3 when its concentration builds up too high). Once
this bleed is removed, the remaining 500 kg/h of solution is recycled. See diagram. 

Determine:
1. Unknown flows and compositions in this system.
2. KNO3 fraction in the feed solution that is recovered as product crystals. 

Water Vapour
W = 450 kg/h
XH20,W = 1.0
Feed Solution
F = 1000 kg/h
XKNO3,F=0.380
= 0.002
xCaCO3,F
XH20,F= 0.618
Evaporative
Crystalliser
Slurry
S = __ kg/h
XKNO3,S
xCaCO3,S
XH20,s=
Recycle
R = 500 kg/h
XKNO3,R=
XCaCO3,R = 0.01
XH2O,R=
xij = mass fraction of componenti in stream j.
Centrifuge
Product
P=
XKNO3,P=
= 1.0
Filtrate
A =____ kg/h
Bleed
B =___ kg/h
Transcribed Image Text:Water Vapour W = 450 kg/h XH20,W = 1.0 Feed Solution F = 1000 kg/h XKNO3,F=0.380 = 0.002 xCaCO3,F XH20,F= 0.618 Evaporative Crystalliser Slurry S = __ kg/h XKNO3,S xCaCO3,S XH20,s= Recycle R = 500 kg/h XKNO3,R= XCaCO3,R = 0.01 XH2O,R= xij = mass fraction of componenti in stream j. Centrifuge Product P= XKNO3,P= = 1.0 Filtrate A =____ kg/h Bleed B =___ kg/h
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