Bangladesh University of Engineering and Technology
ChE 408
Design of A 100 MTPD Caustic Soda Plant
A Report on “Activity-3 (Material Balance)”
Submitted by
Group – 06
Abrar Rafid Siddique – 1802020
Sadman Nasif – 1802038
Md. Faisal Bin Rahman – 1802050
Md. Wasif Haider Rakin - 1802058
Submitted to
Dr. Mohidus Samad Khan,
Professor
Department of Chemical Engineering, BUET.
Level – 4, Term -1
Department of Chemical Engineering, BUET.
Date of submission: 28-08-2023
Table 1:Data for mass flowrate of major process streams
Stream
No
NaCl
(MTPD)
NaOH
(MTPD)
H2O
(MTPD)
Cl2
(MTPD)
H2
(MTPD)
CaCl2
(MTPD)
MgCl2
(MTPD)
Na2SO4
(MTPD)
Insoluble
(MTPD)
NaOH as
reactant
(MTPD)
Na2CO3
(MTPD)
BaCl2
(MTPD)
Flocculant
(MTPD)
CaCO3
(MTPD)
Mg(OH)2
(MTPD)
Ba(SO4)2
(MTPD)
Total
Flow Rate
(MTPD)
1
2
3
4
143.27
342.28
342.28
197.50
-
3.06
700.23
974.00
974.00
-
-
0.65
0.65
0.65
0.14
0.13
0.13
0.83
0.83
0.83
0.87
0.87
0.87
0.12
0.62
1.21
-
-
-
-
148.82
897.73
1317.5
1319.40
5
6
14
17
22
26
27
28
29
30
33
34
35
36
37
40
42
43
44
45
48
49
50
55
56
57
58
59
64
65
71
342.28
342.28
342.28
197.50
-
112.50
112.50
13.50
13.50
99.00
99.00
99.00
99.00
99.00
99.00
99.00
-
974.00
974.00
974.00
700.23
9.89
9.89
2.81
239.00
239.00
28.69
31.50
9.89
9.89
210.38
63.30
99.00
63.30
99.00
1.00
1.00
173.67
35.70
270.90
62.30
87.86
87.86
-
2.47
2.47
-
-
-
-
0.87
0.13
0.74
-
0.12
-
0.62
-
1.21
-
0.66
0.66
-
0.58
0.58
-
0.086
0.086
-
1.35
1.35
-
1320.60
1316.63
1316.28
897.73
97.75
87.86
9.89
2.81
351.56
351.56
42.19
45.00
12.36
2.47
9.89
309.38
162.30
198.00
162.30
198.00
100.00
100.00
173.67
1.21
0.62
0.12
0.66
2.76
35.70
270.90
62.30
1
Material Balance
3rd effect Evaporator (EV3)
NaOH balance:
Total mass balance:
2nd effect Evaporator 2 (EV2)
NaOH balance:
Total mass balance:
2
1st effect Evaporator (EV1)
NaOH Balance:
Total mass balance:
Table 2:Material Balance around triple effect evaporator
First Effect
Inlet
Evaporator
Stream
Flowrate (MTPD)
32% NaOH
309.375
50% NaOH
198
Vapor, mw1
111.375
50% NaOH
198
61% NaOH
162.3
Vapor, mw2
35.7
61% NaOH
162.3
99% NaOH
100
Vapor, mw3
62.3
Outlet
Inlet
Second Effect
Evaporator
Outlet
Inlet
Third Effect
Evaporator
Outlet
3
Vapor condensing tank
Intermediate caustic tank (ICT) and mixing point (M)
Consulting Samuda Chemical Complex Ltd., the mass fraction of NaOH in the electrolyzer
caustic outlet is 0.32, a portion of which is diluted to 0.30 by demineralized water at the mixing
point M.
Total mass balance around ICT:
Total mass balance around M:
NaOH balance around M:
It is assumed that 12% of mCT is recycled as mCR to the mixing point, M
4
Electrolyzer
NaOH mass flow rate = 45 × (0.30) = 13.5 MT/day
NaOH molar flow rate:
Weight fraction of NaOH = 0.30
Therefore, mole fraction,
And since mCT = 351.56 MT/day ⇒ NaOH mass flow = 351.6 × (0.32) = 112.50 MT/day
Molar flow:
Weight fraction = 0.32
Therefore, mole fraction,
5
Weight fraction of salt in saturated brine = 0.26
[1]
Therefore, mole fraction,
Weight fraction of salt in unreacted brine = 0.22
[2]
Therefore, mole fraction
6
Total mass balance on electrolyzer (ELEC):
The electrolyzer outlets are at 70oC.
[3]
The vapor pressure of H2O at 70oC is 233.7 mm-Hg
[4]
Performing atomic balance of Na, Cl, O and H
Na balance:
Cl balance:
O balance:
7
H balance:
Solving (4), (5), (6) and (7) simultaneously, we find:
nSE = n1 = 60320.5 kmol/day
nDE = n2 = 42735.16 kmol/day
n3 = n4 = 1787 kmol/day
So,
NaCl molar flow into electrolyzer = (60320.5) × (0.097) = 5851.04 kmol/day
Therefore, NaCl mass flow = (5851.04) × (58.5) = 342285.84 kg/day
Therefore, brine solution mass flow,
NaCl molar flow in unreacted brine = (42735.16) × (0.079) = 3376.06 kmol/day
Therefore, NaCl mass flow in unreacted brine = (3376.06) × (58.5) = 197500 kg/day
Therefore, unreacted brine mass flow,
Also,
n3 = 1787 kmol/day
Therefore, H2O molar flow rate in Cl2 stream = (1787) × (0.3075) = 549.5 kmol/day
And,
H2O mass flowrate in Cl2 stream = (549.5) × (18) = 9891 kg/day
Cl2 molar flowrate = (1787) × (1 – 0.3075) = 1237.5 kmol/day
Cl2 mass flowrate = (1237.5) × (71) = 87862.5 kg/day = 87.86 MTPD
Total mass flowrate = (87.86+9.891) MTPD =97.751 MTPD
8
Also,
n4 = 1787 kmol/day
Therefore, H2O molar flow rate in H2 stream = (1787) × (0.3075) = 549.5 kmol/day
And,
H2O mass flowrate in H2 stream = (549.5) × (18) = 9891 kg/day =9.891 MTPD
H2 molar flowrate = (1787) × (1 – 0.3075) = 1237.5 kmol/day
H2 mass flowrate = (1237.5) × (2) = 2475 kg/day = 2.475 MTPD
Total mass rate = (9.891 + 2.475) MTPD = 12.372 MTPD
H2 mass fraction = (2.475) / (2.475+9.891)) =0.2
Table 3: Material Balance around electrolyzer
Electrode
Stream
Recycled caustic
solution
Cathode
Produced caustic
solution
Produced hydrogen
Purified brine
Anode
Unreacted brine
Produced chlorine
In/Out
Component
Mass percent
(%)
NaOH
30
In
Flow rate
(MTPD)
45
H2O
70
NaOH
32
Out
351.56
H2O
68
H2
20
Out
12.372
H2O
80
NaCl
26
In
1316.484
H2O
74
NaCl
22
Out
897.73
H2O
78
Cl2
89.88
Out
95.751
H2O
10.12
9
Balance around Saturator:
Table 4: Composition of raw salt
Salt component
Weight fraction
Form
NaCl
0.9627
NaCl
Ca2+
0.0016
CaCl2
Mg2+
0.00024
MgCl2
SO42-
0.00382
Na2SO4
Insoluble
0.00584
Insoluble
Source: ChE308 Chloro-Alkali Plants slide prepared by Professor Emeritus Dr Iqbal Mahmud
10
Saturator (SAT)
Basis: 100kg raw salt
Table 5:Adjusted mass basis composition of raw salt
Salt component
Weight %
NaCl
96.27
CaCl2
0.44
MgCl2
0.095
Na2SO4
0.5538
insoluble
0.584
H2O
2.06
11
Mass balance of water:
Reactor (RX)
Reactions:
12
CaCl2 in salt,
For a 1:1 reaction,
Na2CO3 required = 0.000039×msalt
NaOH required,
BaCl2 required,
NaCl produced in reactor due to dosing,
Total NaCl in reactor outlet,
Reactor outlet is a saturated brine, with 26wt% NaCl. Therefore,
NaCl in reactor outlet is therefore,
13
From eqn (8),
Requirements of dosing chemicals:
Therefore,
14
So, Reactor inlet mass flowrate,
Table 6: Material balance around saturator
Stream
Raw salt
DM water
Unreacted brine
Saturator outlet
In/Out
Component
Mass percent
(%)
NaCl
96.27
CaCl2
0.44
MgCl2
0.095
In
In
Flow rate
(MTPD)
148.82
Na2SO4
0.5538
H2O
0.584
Insolubles
2.06
H2O
100
NaCl
22
In
270.9
897.73
H2O
78
NaCl
25.88
CaCl2
0.049
MgCl2
0.01
Out
1317.45
Na2SO4
0.062
H2O
74
Insolubles
0.066
15
Reactor outlet:
16
Reactor outlet mass flowrate
Table 7: Material Balance around reactor
Stream
Saturator outlet
Dosing chemicals
Reactor outlet
In/Out
Component
Mass percent
(%)
NaCl
25.88
CaCl2
0.049
MgCl2
0.01
In
In
Flow rate
(MTPD)
1317.45
Na2SO4
0.062
H2O
74
Insolubles
0.066
NaOH
100
0.12
Na2CO3
100
0.62
BaCl2
100
1.21
NaCl
26
H2O
73.8
CaCO3
0.044
Out
1319.4
Mg(OH)2
0.0065
BaSO4
0.102
Insolubles
0.066
17
Clarifier (CLR)
Thickener used: sodium polyacrylamide 0.06%w/v [5]
Mass of thickener,
We assume that 85% of the insoluble will be removed with the sludge.
Mass of sludge,
The remaining 15% of insoluble, having a mass flow rate of
(869) × (0.15) kg/day = 130.35 kg/day is to be removed by anthracite and polishing filters.
Purified brine from the filters and Ion-exchange resin will be fed to the electrolyzer.
18
Table 8: Material balance around clarifier
Stream
Reactor outlet
Thickener
Clarified brine
In/Out
Component
Mass percent (%)
NaCl
26
H2O
73.8
CaCO3
0.044
In
In
Out
Flow rate
(MTPD)
1319.4
Mg(OH)2
0.0065
BaSO4
0.102
Insolubles
0.066
Sodium
polyacrylamide
0.06% w/v
H2O
73.99
NaCl
25.99
Insolubles
0.02
0.658
1316.63
CaCO3
Mg(OH)2
Sludge
—
Out
2.76
BaSO4
Insolubles
19
Table 9: Data for Composition of major components and total flow rates of major streams
Stream No.
Composition (%w/w)
Flow rate (MTPD)
1
96.27 % NaCl
148.82
2
22% NaCl (unreacted brine)
897.73
3
-
1317.5
4
-
1319.40
Reactor outlet mixed with 0.06%
1320.60
5
(w/v) Na Polyacrylamide
6
-
1316.63
14
-
1316.28
17
22% NaCl
897.73
22
89.88% Cl2
97.75
26
100% Cl2
87.86
27
100% H2O
9.89
28
100% H2O (DM water)
2.81
29
32% NaOH
351.56
30
32% NaOH
351.56
33
32% NaOH
42.19
20
Stream No.
Composition (%w/w)
Flowrate (MTPD)
34
30% NaOH
45.00
35
20% H2
12.36
36
100% H2
2.47
37
100% H2O
9.89
40
32% NaOH
309.38
43
50% NaOH
162.30
42
61% NaOH
198.00
44
61% NaOH
162.30
45
50% NaOH
198.00
48
99% NaOH
100.00
49
99% NaOH
100.00
50
100% Water vapor
173.67
55
100% BaCl2
1.21
56
100% Na2CO3
0.62
57
100% NaOH
0.12
58
0.06% (w/v) Na Polyacrylamide
0.66
21
Stream No.
Composition (%w/w)
Flowrate (MTPD)
59
Sludge
2.76
64
100% Water vapor
35.70
65
100% H2O (DM water)
270.90
71
100% Water vapor
62.30
22
References
1. Sensorex. (n.d.). Brine Concentration Measurement. Sensorex. Retrieved August 28,
2023, from https://sensorex.com/brine-concentration-measurement/
2. Rutherford, J. A., & Rutherford, J. (2000). Concentration of chlor-alkali membrane
cell depleted brine. Patent No. US6309530B1. Retrieved from
https://patents.google.com/patent/US6309530B1/en
3. Carmo, M; Fritz D; Mergel J; Stolten D (2013). "A comprehensive review on PEM
water electrolysis". International Journal of Hydrogen Energy. 38 (12): 4901–4934.
doi: 10.1016/j.ijhydene.2013.01.151.
4. Wired Chemist. (n.d.). Vapor Pressure Data. Retrieved August 28, 2023, from
https://www.wiredchemist.com/chemistry/data/vapor-pressure
5. Gaule, H. (n.d.). Vocational training report on manufacturing of caustic soda flakes.
23
Workload Distribution
Name
Student ID
Md Wasif Haider Rakin
1802058
● Full handwritten material
balance calculation
● Preparation of tables
Sadman Nasif
1802038
● Typography, figures
● Proofreading of
calculations
1802050
● Material balance
calculation in Excel,
● Preparation of stream table
1802020
● Proofreading
● Assistance in material
balance
Md Faisal Bin Rahman
Abrar Rafid Siddique
Workload distribution
24