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Pre Job Info:
The customer had a vertical drum which contained multiple phases -
vapor, hydrocarbon, an emulsion phase, and water. There were both high
and low level nucleonic level indicators installed on the vessel, the
problem was that simultaneous high and low level alarms were being
indicated.
TowerScan Results: TowerScan
performed a series of neutron backscatter surveys at different process
conditions, one of which is shown. This allowed the customer to
recalibrate their installed nucleonic instrumentation.
Pre Job Info: The customer was
experiencing problems operating the column in a stable manner. The
column had been scanned the previous year, thus providing baseline data
for comparison.
TowerScan Results: The most recent
scan plotted in red, revealed that the tower had suffered extensive damage to trays 2 through 13. The damage was easily identified,
especially when compared to the blue profile showing normal operation a
year earlier.
Knowing which trays were in need of
repair, the customer was able to pre-order tray parts and arrange to have
sufficient labor on hand in order to minimize their downtime.
The customer was soon back operating profitably
again.
Trayed Column - Flooding Due to a
Mechanical Obstruction
Pre Job Info: The
client was unable to meet their product specifications, and there were
indications of liquid being carried overhead. The client suspected
either foaming or flooding. There was no reliable pressure
differential available for the tower.
TowerScan Results: The
scan revealed the tower to be flooded from tray 12 upwards. The
sharpness of the transition from a flooded condition to a normally
operating tower above and below tray 12 indicated an obstruction in the
tray 12 downcomer. As the tower had a history of solids (salts)
building up on the trays, the customer performed a water wash of the
tower, after which the tower's operation returned to normal.
Pre Job Info: This
customer's tower required regular injection of anti-foaming agents in
order to maintain stable operational conditions. However, they
wanted to ensure that they were making optimum use of the anti-foam and
not unnecessarily spending money on additional volumes that didn't provide
any benefit.
TowerScan Results:
A series of scans were performed with changing amounts of anti-foam being
injected. Gradually decreasing the volume of anti-foam, the red scan
showed foaming just starting to develop. The
next reduction in anti-foam volume showed a significant increase in the
number of trays experiencing foaming, thereby allowing the customer to
determine the threshold level of anti-foam that would allow them to
maintain stable process operating conditions and minimize cost.
Pre Job
Info: This customer had made modifications to their
tower during a shutdown. Ever since the turnaround it had not been
possible to operate the tower in a stable manner or make product that was
on specification, even though the operating parameters seemed comparable
to pre-turnaround.
TowerScan Results: The
first scan (plotted in red) revealed the trays to be severely entrained
and in a "jet" flood. In addition, the base liquid level was highly aerated and above the vapor inlet, almost reaching the
bottom tray. As changes were made to the tower's operating
conditions, especially the reboiler and base liquid level, the process
personnel were able to eliminate the entrainment (green plot) until the
tower was operating in a stable manner at the "new post turnaround
normal conditions" and the product was on specification.
Pre Job Info: The
customer had been experiencing an erratic bottoms temperature
profile, as well as unstable operation of the column for several weeks
ever since an upset in the unit. From their instrumentation and analysis,
they were confident the problem was in the bottom half of the column, but
they could not pinpoint the cause of the trouble. The customer called
TowerScan in the morning, a crew was on site that afternoon.
TowerScan Results: The
trays involved were MD or multi-downcomer trays. Due to their
generally tight tray spacing, and the large amount of metal in the form of
boxed downcomers, it is very important to obtain precise scan line
orientation. In addition, the trays should be scanned at a 1"
interval rather than the normal 2" increment or a significant loss of
definition occurs.
TowerScan had performed a baseline scan
on the same tower, offline, four years earlier (blue plot). The
current scan in red revealed that the bottom tray (45) was missing, and
the next tray up (44) was severely damaged. With this knowledge the
engineer was able to adjust the operating parameters in order to manage
the damaged tower in the best way possible. In addition, they were
provided with adequate planning time for them to go into the tower during
their next shutdown which was less than a month away, knowing what had to
be fixed.
Minor Damage Resulting in Vapor Bypassing
& Flooding
Pre Job Info: Under
normal operating conditions, this tower was experiencing a high pressure
differential across the column with liquid being carried overhead.
TowerScan Results: The
rates were reduced in order to obtain a scan under stable operating
conditions. The first scan showed trays in the middle of the tower
(11-17) to be flooded, with evidence of entrainment on the trays higher up
the tower. The unusual aspect of the scan profile was the extremely
high density seen for the liquid on tray 11. Given that tray 11 was
holding liquid, and therefore mechanically sound, TowerScan personnel were
confident in predicting that the vapor was bypassing the tray via the
downcomer, as there was no aeration of the liquid.
The mechanism causing the vapor
bypassing wasn't 100% certain from the profile. Trays 10 and 9
immediately below 11 showed reduced liquid loadings on the tray.
Typically this is due to damage, however the possibility of the trays from
11 upwards loading up with liquid and then dumping, temporarily starving
the trays below of liquid remained as an alternative explanation.
Subsequent inspection of the tower revealed that the
tray deck panel immediately underneath the downcomer from tray 11 was
damaged. As such it allowed the vapor to bypass tray 11, and most of
the liquid to bypass trays 10 and 9 even though the remainder of that
decking was mechanically sound.
Packed Bed Tower - Baseline Scans Used
for Shutdown Planning
Pre Job Info: Historically,
this tower with multiple packed beds was relatively stable in its operation
but running over several years between shutdowns it was prone to
fouling. Therefore the customer had TowerScan perform baseline grid
scans so that in the future they could minimize the time spent on turnarounds.
TowerScan Results:
The adjoining scan profile shows the grid scan performed two
years after the baseline scan, as well the profile (black) for one of the
four baseline profiles. Each of the six packed beds consisted of a
shorter section of structured packing in the top of the bed, with the
majority of the bed consisting of dumped packing.
The greatest contrast was between the
two beds shown, beds C and D. While all of the beds showed some
fouling in the smaller structured packing element at the top, the
remainder of the beds, consisting of the dumped packing, were seen to be
still operating with a uniform density profile, clear of significant
fouling. The exception was bed D below the feed inlet, which showed
appreciable fouling throughout the bed. Armed with this knowledge
going into the shutdown, the unit engineer was able to minimize the
downtime by planning to clean the distributor above each bed, as well as
the top structured packing element, while leaving in place all of the
dumped packing except for that in bed D which was replaced.
Pre Job Info: The
customer had seen a very small change in the
indicated pressure differential measured on their disengagement
drum. In addition, one of the process operators noted an unusual
“noise” in the vicinity of the drum, leading the process engineering/operations
staff to suspect that the internal riser may have sustained damage.
TowerScan was contacted to first confirm if there had been any damage to
the internal riser, and if so, to determine the current orientation of the
riser as different orientations would have various safety implications.
TowerScan Results:The scans were
conducted by erecting a square horizontal framework of scaffolding poles
at two different elevations.The
source and detector were suspended from the scaffolding frame and then
positioned so that they were past the edge of the drum, i.e. there was
nothing between the source and detector. The source and detector
were then moved in two inch increments, horizontally, to in effect take a
cross-sectional cut of the disengagement drum.The source and detector were then repositioned so that the
same process could be repeated at 90 degrees to the original orientation.This process was carried out at both the
upper and lower elevations.
If the riser was
undamaged and in position, the density profiles should essentially be that
of a smaller empty pipe (the riser walls),
centered on, and superimposed upon a larger empty pipe (the drum
walls). The scans indicated that the internal riser had in fact been
broken off.The density
profiles indicated that the top of the riser was leaning against the west
wall of the drum, offset slightly to the south of the
east-west centerline. Armed with this knowledge,
process operations determined that with additional precautions they could
continue operating the unit until the next scheduled shutdown.
