Material Balance
Material balances are the basis of process design. A material balance taken over complete process
will determine the quantities of raw materials required and products produced. Balances over
Individual process until set the process stream flows and compositions. The general conservation
equation for any process can be written as;
Material out = material in + accumulation
For a steady state process the accumulation term is zero. If a chemical reaction is taking place a
particular chemical species may be formed or consumed. But if there is no chemical reaction, the
steady state balance reduces to:
Material out = Material in
A balance equation can be written for each separately identifiable species present, elements,
compounds and for total material
4.1
basis 75000 Nm3/hr. of hydrogen gas produced
(0.044 * 2) * 75000 = 6600 kg mol/hr. hydrogen produced
4.2 Refinery Off-Gases Required
The reactions involved are as followed:
CH4 + H2O  CO + 3H2 ………………………… (4.1)
C2H6 + 2H2 O  2 CO + 5H2 ………………………… (4.2)
C3H8 + 3H2O  3 CO + 7H2 …………………………... (4.3)
C4H10 + 4H2O  4 CO + 9H2 ……………………………. (4.4)
CO + H2O  CO2 + H2 …………………………………… (4.5)
IF x kg mol / hr. of refinery off-gas be supplied then the
H2 content as based on the refinery offgas composition is given by:
= (3*0.9248 + 5*0.0169 + 7*0.0013) * X
= 2.8121X
Hence, 2.8121 X = 6600 kg mol/hr
 X = 2347 kg-mol / hr
Hence, refinery off-gas required = 2347 kg-mol / hr.
4.3 Material Balance of Individual Equipment
4.3.1 Desulfurizer
In the desulfurizer, there is removal of sulfur, since, the concentration of the sulfur being
encountered is less than 3 ppm, we can neglect desulfurization.
Input = 2347 kg-mol / hr of the refinery off-gas
Output = 2347 kg-mol / hr of the refinery off-gas.
Both the input and output have the same composition and this composition is seen in the table
below for feed to the primary reformer.
Table-2 refinery off-gas composition at reformer inlet
component
mol %
mol wt
kgmol/hr
kg/hr
CH4
78.81
16
1849
29584
C2H6
10.46
30
245.5
7365
C3H8
4.62
44
108.43
4770.92
C4H10
0.79
58
18.31
1061.98
C4H10
0.97
58
22.77
1320.66
C5H12
0.31
72
7.28
524.16
C5H12
0.27
72
6.34
456.48
C6H14
0.21
86
4.93
423.98
C7H16
0.1
100
2.35
235
CO2
2.59
44
60.79
2674.76
N2
0.61
28
14.32
400.96
H2O
0.26
18
6.1
109.8
H2S
0.001
34
0.02
0.68
TOTAL
100.001
660
2346.14
48928.38
4.3.2 Reformer:
Total carbon in ROG = (0.7881*1) + (0.1046*2) + (0.0462*3) + (0.0079*4) + (0.0097*4) +
(0.0031*5) + (0.0027*5) + (0.0021* 6) + (0.001*7) + (0.0259*1) = 1.2808
Here taking the steam to carbon mole ratio is 3:1 we have.
Steam = 3 *1.2808*2346.14= 9014.808336kg mol / hr = 162266.55 Kg / hr
Total feed to reformer = ROG + steam = 2346.14 + 9014.80833= 11360.94834 kgmol / hr
For the methane reforming the following reaction take place
CH4 + H2O  CO + 3H2 --- (4.6)
C2H6 + 2H2O  2CO + 5H2 --- (4.7)
C3H8 + 3H2O  3CO + 7H2 --- (4.8)
C4H10 + 4H2O 4CO + 9H2 --- (4.9)
CO + H2O  CO2 + H2 --- (4.10)
Assume:
(1) 90% conversion of the first reaction.
(2) 100% conversion of 4.7, 4.8 and 4.9 reaction.
(3) 65% conversion of reaction 4.10
From the reaction -1
CH4 consumed = 0.9 * 1849 = 1664.1 kg mol / hr
CH4 unconverted = 1849 - 1664.1= 184.90 kg mol / hr
H2O consumed = 1664.1 kg mol / hr
H2 produced = 3*1664.1 = 4992.3kg mol / hr
CO produced = 1664.1 kg mol / hr
From the reaction-2
C2H6 consumed = 245.5kg mol / hr
H2O Consumed = 2*245.5= 491 kg mol / hr
CO produced = 491 kg mol / hr
H2 produced = 5* 245.5= 1227.5 kg mol / hr
From reaction -3
C3H8 consumed = 108.43kg mol / hr
H2O consumed = 3*108.43= 325.29 kg mol / hr
CO produced = 325.29 kg mol / hr
H2 produced = 7 * 108.43 = 759.01 kg mol / hr
From reaction -4
All components are zero in reaction-4
Total CO produced from the first four reactions 1664.1 +491 +325.29 +0 =2480.39 kg mol/hr
Total H2 produced 4992.3+1227.5 +759.01 +0 = 6978.90 kg mol/hr
Total H2O consumed = 1664.1 + 491+ 325.29 + 0 = 2480.39 kg mol / hr
H2O remaining =9014.808336– 2480.39 = 8766.42 kg mol / hr
N2 is used as an inert gas
So, N2 Input = N2 Output=14.32 kg mol/ hr
Table-3 Output of The Reformer
component
CH4
H2
N2
CO2
H2O
CO
TOTAL
mol %
0.091762606
0.346350488
0.000710676
0.0030169
0.435061951
0.123097378
1
mol wt
16
2
28
44
18
28
136
kgmol/hr
1849
6978.9
14.32
60.79
8766.42
2480.39
20149.82
kg/hr
29584
13957.8
400.96
2674.76
157795.56
69450.92
273864
4.3.3 Shift Reactor:
CO + H2O  CO2 + H2…………………………. (4.11)
CO inlet = 2480.39kg mol/hr.
.CO consume = 0.65 * 2480.39= 1612.25 kg mol/hr.
CO outlet = 2480.39–1612.25 = 868.14 kg mol/hr.
H2O consumed = 1612.25 kg mol/ hr.
H2O outlet =8766.42–1612.25 = 7154.17 kg mol/ hr
H2 produced = 1612.25 kg mol/hr.
CO2 produced =1612.25 kg mol/hr.
Table-4 Output of Shift Reactor
component
CH4
H2
N2
CO2
H2O
CO
TOTAL
mol %
0.141035978
0.122977423
0.001092285
0.122977423
0.545697869
0.066219023
1
mol wt
16
2
28
44
18
28
kgmol/hr
1849
1612.25
14.32
1612.25
7154.17
868.14
13110.13
4.3.4 CO2 Absorber
The absorption of CO2 is done by MDEA solution.
CO2 inlet = 1612.25kg mol/ hr
Assume efficiency of CO2 absorber is 99%.
CO2 outlet (remaining) = (0.01 *1612.25) = 16.12 kg mol/hr.
kg/hr
29584
3224.5
400.96
70939
128775.06
24307.92
257231.44
4.3.5 Pressure Swing Adsorber
Assume that 99.9% of CO, CO2 & CH4 are get adsorbed.
Assume that 100% H2O & 0.5% H2 get adsorbed in PSA unit.
CO outlet = 0.001 * 868.14= 0.868 kg mol/ hr.
CO2 outlet = 0.001 * 16.12 = 0.016 kg mol/ hr.
CH4 outlet = 0.001 * 1849= 1.849 kg mol/ hr.
H2O outlet = 0 kg mol/ hr.
H2 outlet = 0.995 * 1612.25= 1604.19 kg mol/ hr
Table-5 outlet composition of PSA
component
CH4
H2
CO2
CO
TOTAL
mol %
0.001150646
0.998299234
9.95692E-06
0.000540163
1
mol wt
16
2
44
28
kgmol/hr
1.849
1604.19
0.016
0.868
1606.923
kg/hr
29.584
3208.38
0.704
24.304
3262.972
ENERGY BALANCE
5.1 Energy Balance at Individual Equipment
5.1.1 Energy Balance at Steam Reformer
Table-7 Inlet Gas Properties of Reformer
component
flowrate Kg/hr
CH4
C2H6
C3H8
CO2
N2
29584
7365
4770.92
2674.76
400.96
cp at 475k
(KJ/Kg.K
2.483
1.616
1.645
0.858
1.034
Qin= MCP∆T
= {(29584*2.483) +(7365*1.616) +(4770.92*1.645) +(2674.76*0.858) +(400.96*1.034)} (475298)
= 16977240.35kJ/hr
Table-8 Outlet Gas Properties of Reformer
component
flowrate Kg/hr
H2
N2
CO
CO2
CH4
H2O
13957.8
400.96
69450.92
2674.76
29584
157795.56
cp at 698k
(KJ/Kg.K
14.57
1.064
1.017
1.126
3.602
2.08
Qout= MCP∆T = {(13957.8*14.57) +(400.96*1.064) +(69450.92*1.017) +(2674.76*1.126) +
(29584*3.602) +(157795.56*2.080)} (698-298)
= 284884586.3kj/hr
∆Q= Qout-Qin = 267907346 kJ/hr.
5.1.2 Energy Balance at Steam Generator
Q=MCP∆T
where, T1=373k
=>M=Q/CP∆T
= (267907346)/ (38.73*75)
T2=298k
CP=38.73kJ/kmol.k
= 92230.78 kgmol/hr.
Export stream= (92230.78 -9014.808336)
= 83215.97 kmol/hr.
5.1.3 Energy Balance at Shift Converter
Table-9 Inlet Gas Properties of Shift Converter
component
H2
N2
CO
CO2
CH4
H2O
flowrate Kg/hr
13957.8
400.96
69450.92
2674.76
29584
157795.6
cp at 623k (KJ/Kg.K
7.197
7.008
7.276
11.311
12.546
8.677
Qin=MCP∆T
= {(13957.8*7.197) +(400.96*7.008) +(69450.92*7.2) +(2674.76*11.311) +(29584*12.546) +
(157795.6*8.677)} (623-298)
= 773238783.4 kJ/h
Table-10 Outlet Gas Properties of Shift Converter
component
flowrate Kg/hr
H2
N2
CO
CO2
CH4
H2O
3224.5
400.96
24307.92
70939
29584
128775.1
cp at 700k
(KJ/Kg.K
7.035
7.351
7.451
11.489
11.88
8.951
Qout=MCP∆T
= {(3224.5*7.035) + (400.96*7.351) + (24307.92*7.451) + (70939*11.489) +
(29584*11.88) + (128775.1*8.951)} (700-298)
= 1015408495 kJ/hr
∆Q= Qout-Qin
= (1015408495-773238783.4) kJ/hr
= 242169712 kJ/hr
5.1.4 Energy balance at CO2 Absorber
Table-11 Inlet gas properties of CO2 Absorber
component
flowrate Kg/hr
H2
N2
CO
CO2
CH4
H2O
3224.5
400.96
24307.92
70939
29584
128775.1
cp at 366k
(KJ/Kg.K
6.974
6.991
7.013
9.871
9.736
9.185
Qin=MCP∆T
= {(3224.5*6.974) + (400.96*6.991) + (24307.92*7.013) + (70939*9.871) + (29584*9.736) +
(128775.1*9.185)} (366-298)
= 160944428.9 kJ/hr.
Table-12 Outlet Gas Properties of CO2 Absorber
component
H2
N2
CO
CO2
CH4
H2O
flowrate Kg/hr
3224.5
400.96
24307.92
70939
29584
128775.1
cp at 466k (KJ/Kg.K
6.895
6.961
6.965
8.89
8.552
8.026
Qout= MCP∆T
= {(3224.5*6.895) +(400.96*6.961) +(24307.92*6.965) +(70939*8.890) +
(29584*8.552) +(128775.1*8.026)} (466-298)
= 354736600.2 kJ/hr
∆Q= Qout-Qin
= (354736600.2-160944428.9)
= 193792171.3 kJ/hr.
5.1.5 Energy balance at PSA
Table-13 Inlet gas properties of PSA
component
H2
N2
CO
CO2
CH4
H2O
flowrate Kg/hr
3224.5
400.96
24307.92
70939
29584
128775.1
cp at 373k (KJ/Kg.K
6.972
6.921
6.015
9.723
9.736
8.185
Qin= MCP∆T
= {(3224.5*6.972) + (400.96*6.921) + (24307.92*6.015) + (70939*9.723) +
(29584*9.736) + (128775.1*8.185)} (373-298)
= 165244648.8 kJ/hr