Homework #9
Imagine that you have been hired to work at a small refinery. Youve been asked to do
calculations to support the blending of several intermediate streams to get gasoline. The
data for the blend stocks is in attached table.
You are asked to blend to the following recipe:
Blend Stock Vol%
Cat Cracked Naphtha #1 40%
Light Alkylate 20%
Heavy Alkylate 0%
Full Range Reformate 35%
Light St Run Naphtha 0%
C6 Isomerate 5%
n-Butane 0%
1. What is the RVP of the blend? (Use the appropriate blending indices.)
2. What is the benzene content of the blend (in vol%)?
3. What are the expected RON, MON, and average (i.e., road) octane numbers of the blend
using volumetric blending (linear blending rules)?
a. using the Ethyl 135-blend non-linear blending rules?
Extra: What are the expected RON, MON, and average (i.e., road) octane numbers of the
blend using the Ethyl 135-blend non-linear blending rules?
4. Wed like to blend in nC4 to increase the RVP up to the allowable amounts for summer
& winter gasoline. Use the appropriate blending indices for the RVP blending & linear
blending rules for the octane numbers.
a. Blend to a summer spec of 9.0 psi RVP.
b. Blend to a winter spec of 15.0 psi RVP.
CBEN 409 Fall 2016 -1- November 27, 2016
Blending Cat Cracked Light Heavy Full Range Light St C6
Component Naptha #1 Alkylate Alkylate Reformate Run Naptha Isomerate NC4
Gravity, API 52.1 72.3 55.8 44.2 81.8 83.0 110.8
Aromatics, vol% 35.2 0.5 1.0 61.1 2.2 1.6 0
Olefins, vol% 32.6 0.2 0.9 1.0 0.9 0.1 0
Saturates, vol% 32.2 99.3 98.1 37.9 96.9 98.3 100
Benzene, vol% 1.06 0.00 0.01 1.17 0.73 0.00 0
Bromine Number 57.1 2.3 0.3 1.2 0.5 3.8
RVP, psi 4.3 4.6 0.3 3.2 10.8 8.0 52
Distillation, F
IBP 110 101 299 117 91 118
T05 143 144 318 168 106 131
T10 158 162 325 192 113 134
T20 174 181 332 224 117 135
T30 192 196 340 244 121 135
T40 215 205 345 258 126 136
T50 241 211 354 270 132 136
T60 270 215 362 280 139 137
T70 301 219 373 291 149 137
T80 336 225 391 304 163 138
T90 376 239 427 322 184 139
EP 431 315 517 393 258 146
RON 93.2 93.2 65.9 97.3 63.7 78.6 93.8
MON 81.0 91.2 74.5 86.7 61.2 80.5 89.6
Carbon, wt% 86.94 84.00 84.39 88.11 83.58 83.44
Hydrogen, wt% 13.00 16.09 15.54 11.60 16.29 16.49
Nitrogen, ppmw 46 0 0 0 0 0
Sulfur, ppmw 321 15 15 9 325 10
CBEN 409 Fall 2016 -2- November 27, 2016
Solution
Problems 1-3
The Table 1 shows the pertinent information for the four blend stocks needed for these
problems:
Given API gravity & derived specific gravity.
Given RVP (psi) & derived volume blend factor (RVP1.25).
Given octane numbers (RON & MON) & derived road octane number ((R+M)/2) and
sensitivity (J=RON-MON).
Given aromatics, benzene, & olefins content.
The given values are shown in blue font; all calculated values are in black font. The
requested values are bordered in red.
Table 1. Results for the Blending Calculations
The overall API gravity can be calculated from the volume blending of the specific gravities
& the API gravity is then back calculated from this blended value. First, each given API
gravity must be converted to the specific gravity; for example, for the Cat Naphtha:
141.5 141.5
o 0.7707
131.5 G 131.5 52.1
Next the volume-blended value for the specific gravity is determined:
o,blend
V
i i
V i
40 0.7707 20 0.6943 35 0.8054 5 0.6597
40 20 35 5
0.7620
CBEN 409 Fall 2016 -3- November 27, 2016
Finally, the API gravity can be calculated from this specific gravity:
141.5 141.5
Gblend 131.5 131.5 54.20
o,blend 0.7620
RVP is blended volumetrically, but not directly. Rather, a volatility factor, the RVP raised to
the 1.25 power, is actually blended. So:
V P
1.25
PRVP blend
1.25 i RVP i
V i
40 4.3 1.25
20 4.61.25 35 3.21.25 5 8.01.25
40 20 35 5
599.486
100
5.99
PRVP blend 1.25 5.99 4.19 psi
The benzene content is blended volumetrically:
Bblend
V B i i
V i
40 1.06 20 0 35 1.17 5 0
40 20 35 5
0.83 vol%
The blending of octane number can be fairly complex. The simplest model (and the one
used in class) is to assume that volumetric blending is sufficiently accurate. So, the
Research Octane Number (RON) will be:
RONblend
V RON i i
V i
40 93.2 20 93.2 35 97.3 5 78.6
40 20 35 5
93.91
the Motor Octane Number (MON) will be:
CBEN 409 Fall 2016 -4- November 27, 2016
MONblend
V MON
i i
V i
40 81.0 20 91.2 35 86.7 5 80.5
40 20 35 5
85.01
and the road octane number (i.e., the arithmetic average) will be:
R+M 93.91 85.01
89.46 .
2 2
The non-linear blending rules start with the values found above and correct for the octane
number sensitivity, olefin content, & aromatic content. The blending rule equations are:
R R 0.03324 RJ R J 0.00085 O2 O 2
M M 0.04285 MJ M J 0.00066 O2 O 2 6.32 107 A2 A2
where the values with the bar indicate volume averages. So the volume averages used in
these equations are:
R 93.91 (as found above).
M 85.01 (as found above).
J
V RON MON
i i
V i
40 93.2 81.0 20 93.2 91.2 35 97.3 86.7 5 78.6 80.5
40 20 35 5
0.40 12.2 0.20 2.0 0.35 10.6 0.05 1.9
8.895
RJ 0.40 93.2 12.2 0.20 93.2 2.0 0.35 97.3 10.6 0.05 78.6 1.9
845.612
MJ 0.40 81.0 12.2 0.20 91.2 2.0 0.35 86.7 10.6 0.05 80.5 1.9
745.770
CBEN 409 Fall 2016 -5- November 27, 2016
O 0.40 32.6 0.20 0.2 0.35 1.0 0.05 0.1
13.4
O 0.40 32.6
2 2
0.20 0.2 0.35 1.0 0.05 0.1
2 2 2
425.463
A 0.40 35.2 0.20 0.5 0.35 61.1 0.05 1.6
35.65
A 0.40 35.2
2 2
0.20 0.5 0.35 61.1 0.05 1.6
2 2 2
1802.418
The values from the non-linear blending rule are:
R R 0.03324 RJ R J 0.00085 O 2 O 2
93.91 0.03324845.612 93.905 8.895 0.00085 425.463 13.42
94.46
M M M 0.04285 MJ M J 0.00066 O 2 O 2 6.32 107 A2 A2
85.01 0.04285745.770 85.01 8.895 0.00066 425.463 13.42
6.32 107 1802.418 35.652
84.55
R+M 94.46 84.55
89.50 .
2 2
Problem 4
We will apply the same blending rules as before but now we know the target RVP for the
final blend and we have to determine the nC4 amount. Starting with the blending equation
we can manipulate to get:
V P V P
1.25 1.25
Vi PRVP i
1.25
i RVP i nC4 RVP nC4
PRVP blend
1.25
i nC4
V i V Vi nC4
i nC4
CBEN 409 Fall 2016 -6- November 27, 2016
V P PRVP blend V
1.25 1.25
i RVP i i
VnC4 i nC4 i nC4
PRVP blend PRVP nC4
1.25 1.25
V P
1.25
Note that the i RVP i
term represents the RVP of the non-butane portion of the
i nC4
blend. So, we could do the calculations using the already calculated value for Problem 1
instead of redoing all of the intermediate calculations again and again. For 9.0 psi RVP:
599.486 9.0 100 7.73
1.25
VnC4
9.0 52
1.25 1.25
and for 15.0 psi RVP:
599.486 15.0 100 21.36 .
1.25
VnC4
15.0 52
1.25 1.25
The following tables show the results for all calculations. The requested values are
bordered in red.
Table 2. Results for the Adding Butane to 9.0 psi RVP
CBEN 409 Fall 2016 -7- November 27, 2016
Table 3. Results for the Adding Butane to 15.0 psi RVP
CBEN 409 Fall 2016 -8- November 27, 2016
