Hydrocarbon Processing - April 2021 - 30

Clean Fuels
TABLE 1. Economics evaluation using $150/t of acid cost and $25/bbl of alkylate margins
Description

Temperature

Design Case

7.2°C (45°F)

Acid flow, tpd Alkylate rate, bpd Acid consumption, lb/gal Acid cost, $/d Alkylate margin, $/d
101

16,000

0.3

15,120

400,000

Operating Case

15.6°C (60°F)

209

21,142

0.47

31,301

528,550

Operating Case-
Performance Optimized

14.4°C (58°F)

182

21,142

0.41

27,305

528,550

Reactor Improvements Case

11.1°C (52°F)

155

21,142

0.35

23,309

528,550

Reactor Improvements with
Increased Feed Case

15.6°C (60°F)

210

23,275

0.43

31,526

581,875

600
500
$1,000 per day

400

$481

$482

$486
$530

$370

300
200
100
0

-100
Design Case

Utility cost

Operating Case

Operating Case
Performance
Optimized

Alkylate margin

Reactor
Improvements
Acid cost

Reactor
Improvements
with Increased
Feed
Operating profit

FIG. 4. Alkylate operating economics using $150/t of acid cost and
$25/bbl of alkylate margins, electricity cost of $0.05/kWh, steam 15#
as $3/MMBtu, steam 150# as $4/MMBtu, and steam 225# as $5/MMBtu.

optimizing refrigeration section performance and
to managing spent acid analyses and control to
lower acid consumption. The alkylate rate was kept
the same, so acid consumption dropped.
* Reactor Improvements Case: This case included tube
inserts, 0.75-in. tube bundles and the proprietary internal
modifications and assumes that the refrigeration section
and spent acid management are optimized. Chillers were
not included. Acid consumption drops even further at the
same alkylate capacity.
* Reactor Improvements with Increased Feed Case:
This case is the real moneymaker. It is the same as the
previous case but assumes that refiners will maximize the
alkylate rate until they hit the reaction temperature limit.
Although the acid consumption is almost double the
design case, the profitability of the incremental alkylate
more than makes up for the additional cost.
When looking at FIG. 4, it is easy to understand why most North
American refiners continuously push their alkylation units far
beyond the original design capacity. The case studies demonstrate that the earnings from conservative alkylate margins greatly outweigh the extra cost of sulfuric acid demand.
The Operating Case-where the unit was operating at its current refrigeration limit reaction temperature [15.6°C (60°F)]-
generates a $128,000/d additional alkylate margin, while costing only $15,000/d more on acid than the Design Case. This is a
net profit gain of nearly 30%.
After optimizing the refrigeration section operations and better managing acid analyses and control, it is typical to reduce the
30 APRIL 2021 | HydrocarbonProcessing.com

acid consumption by 10%-15%. The Performance Optimized
Case saves $4,000/d on acid cost vs. the Operating Case. Most
refiners would likely use the 1.1°C (2°F) reaction temperature
decrease to produce more alkylate.
With the Reactor Improvements Case (tube inserts, 0.75-in.
bundle and proprietary internal modifications), refiners could
save $8,000/d on acid cost at the same alkylate capacity, but
would probably take advantage of the cooler reaction temperatures to process more feed.
With increased feed, the alkylate margins increase to
$180,000/d, showing why refiners continue to push their units.
This case boosts the net profit gain to 43% vs. the Operating
Case. By adding in all reactor enhancements and pushing temperature limits, the unit is nearing 150% of the design capacity.
Takeaway. Every sulfuric acid alkylation unit refiner should
tackle this low-hanging fruit to get more cooling out of their existing refrigeration section and to better manage their acid analyses/control to reduce consumption. Acid consumption savings
of 10%-15% are typically achievable through extra attention to
unit operations and with only minimal investment. The value of
additional alkylate typically far exceeds the incremental cost of
spent acid, so, when changes are made that lower reactor temperature, refiners usually take advantage of the improvement to
produce more alkylate. This explains why acid consumption for
most older units far exceeds new unit design values.
NOTES
STRATCO® XP2 technology
b
STRATCO® ST-M impellers
c
STRATCO® Contactor™ reactor technology
a

J. RANDALL PETERSON is the Alkylation Technology Manager for the STRATCO®
alkylation technology at DuPont Clean Technologies. His primary focus is
continuous improvement of the STRATCO® alkylation process, and he assists with
troubleshooting, startup assistance, plant optimization and operator training. Prior
to his employment at STRATCO Inc. in 1989, Mr. Peterson spent 3 yr at Conoco
working in FCC, catalytic reforming and HF alkylation. Mr. Peterson earned a BS
degree in chemical engineering from the University of Kansas and an MBA degree
from Rockhurst College in Kansas City, Missouri.
DIWAKAR RANA is the Technology Development Manager at DuPont Clean
Technologies for the STRATCO® alkylation business. He has three patents pending
within the sulfuric acid alkylation area. Dr. Rana has more than 16 yr of experience
in the refining and biofuels industries and has been a licensed professional engineer
for the State of Texas since 2009. He earned a BE degree in chemical engineering
from Deenbandhu Chhotu Ram University of Science and Technology, India, along
with an ME degree in chemical engineering from the Illinois Institute of Technology
and a PhD in chemical engineering from Washington State University.
ROB EWING is the Innovations and Technology Manager with DuPont Clean
Technologies for the alkylation and hydroprocessing businesses. He has more than
23 yr of experience in the refining and petrochemical industries. Mr. Ewing earned
a BS degree in chemical engineering from Kansas State University.

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