Hydrocarbon Processing - April 2021 - GP-31

PROCESS TROUBLESHOOTING
removed. The study conclusively showed
that fouling of the test element was greatly reduced after hydrocarbon removal
(FIG. 2). Deposition of foulant material
on the test elements, as well as a marked
decrease in differential temperature, was
observed in those samples where hydrocarbon was not removed prior to HLPS
testing (FIG. 3). With the results of this
testing, plant engineers in the methanol
recovery unit were able to proceed with
a better understanding of fouling reduction by focusing on hydrocarbon removal
in addition to solids filtration. However,
it is important to stress that in this case,
if filtration improvement alone had been
recommended based on the high particulate matter, the overall impact on fouling
would have been marginal. The key solution in this case was to remove suspended
solids by adequate filtration in combination with hydrocarbon separation and recovery from the feed stream.
It was established that the source of hydrocarbon contamination in the feed arose
from inefficiencies at several upstream
three-phase separators. The installation of
an oil-water separator at the methanol recovery unit feed inlet was recommended.
To understand the separation rate of the
hydrocarbon from the bulk feedwater, a
time-lapse study was performed (FIG. 4).
The feedwater sample was shaken to homogenize, and the phases were allowed to
separate into organic and aqueous component phases over the course of 1 hr. Separation was complete in 30 min-45 min, indicating that a residence time API device
for an oil/water separator would be an
efficient system for hydrocarbon removal.
The filtration system in place for the
feedwater consisted of two bag filters set

Identifying fouling causes, possible mechanisms and
tendencies is critical to eliminate or reduce process
fouling. The presence of dissolved components,
suspended solids, hydrocarbon or water phases and
emulsions should be tested, analyzed and correlated
with fouling when possible. These parameters must be
carefully monitored to anticipate potential fouling events.
in parallel and run in rotation. The filters
(FIG. 5) were nominally rated for 10-micron (nominal 80%-85% efficiency) particle capture (no efficiency information
was available) and were observed to have
low efficiency in removing smaller particle sizes. Due to the particle distribution
(FIG. 6) and hydrocarbon contamination,
the filters were also plugging rapidly, causing reduced filter lifetimes and increased
filter changeouts. An upgrade to the filtration system was recommended to improve
solids retention, accommodate smaller
particle sizes and hydrocarbon contaminants, and increase filter lifetimes. The
recommended glass microfiber-based filter was pleated to increase the available
surface area and to reduce pressure drop
across the newly installed elements. The
filter vessels in place were reconfigured to
accommodate these cartridge-style elements and improve the solids removal efficiency in the feed stream, in addition to
increasing filter online life.
Root cause troubleshooting and
analytics. A thorough and holistic un-

derstanding of process conditions and
appropriate root cause analysis are key to
resolving fouling and other issues. Specialized analytics and data interpretation
are necessary for finding and resolving
root cause problems that contribute to
fouling episodes. Filtration systems can
be analyzed for solids removal efficiency,
often revealing the real solids removal efficiency and the impact on downstream
fouling. Coalescing systems in both gas
and liquid streams also can be effectively
and quickly tested to provide valuable
insight about actual separation performance and contaminant breakthrough.
Several resources and strategies can be
used to determine the best path forward
for fouling mitigation, and the best possible solutions can be identified using
advanced analytics, expert troubleshooting and innovative, results-oriented solutions. The ability to identify sources
and mechanisms of fouling is vital to
plant operations, and every fouling issue
should be approached differently and
proactively, with proper analytical techniques. Only then can suitable separation

Differential + cumulative < volume
100

3.5
B2A4988-BA8936-01 109.$Is diff. volume
B2A4988-BA8936-01 109.$Is cum. < volume

3.0

Differential volume, %

70
60

2.0

50
1.5

Cumulative < volume, %

80
2.5

1.0

20
0.5

FIG. 5. Bag filter and filter vessel in place
at the feed to the methanol recovery
tower. The 10-μm nominal rated filters were
experiencing low solids removal efficiency,
rapid plugging and short online life.

0.0

0
0.4 0.6

6 8 10

20
40 60
Particle diameter, μm

100

200

400 600 1,000

2,000

FIG. 6. Particle size distribution of suspended solids in the feed to the methanol recovery tower.
Gas Processing & LNG | MARCH/APRIL 2021

Hydrocarbon Processing - April 2021

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