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TowerScan Case Examples

 
 
 
 

 

Note:  For the examples below, please click on the images to enlarge.  Improved printing quality will be obtained by right clicking on the image file and saving it to your computer, to be printed from a graphics program.  As an alternative, download the PDF version of the Case Example.  Adobe Acrobat Reader is required in order to open, view, and print PDF files.

If you require higher quality images of these samples, please contact TowerScan and we will be happy to provide them.  Also, these images do not incorporate all the features provided in our customer reports.  Sample reports are available upon request.  

If you have any questions in general, or specifically about the Case Examples still under construction, please don't hesitate to email or call us, we are happy to hear from you.  Or if you are looking for a sample you don't see, please ask us and we will be happy to provide you with one.

Click on the link below in order to download all Case Examples as a single file.

TowerScan Example Case Studies.pdf

Neutron Backscatter - Multiphase Level Measurement

image080.gif (21304 bytes)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.

Neutron Backscatter.pdf

Profiles of Normally Operating vs. Damaged Trays

Tray damage single pass_9673_image001.gif (21266 bytes)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.

Normally Operating vs. Tray Damage.pdf

Trayed Column - Flooding Due to a Mechanical Obstruction

Flooding_mechanical_blockage_27487_image001.gif (23444 bytes)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.

 

Flooding - Mechanical Blockage.pdf

Trayed Column - Optimizing Use of Anti-Foam

Foaming_17921_image001.gif (24214 bytes)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. 

Foaming.pdf

Trayed Column - Entrainment

Entrainment_17011_image001.gif (27059 bytes)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. 

Entrainment.pdf

MD Trays - Damaged

image082.gif (24377 bytes)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.

MD Trays Damaged.pdf

Minor Damage Resulting in Vapor Bypassing & Flooding

Vapor_bypass_up_downcomer_rev02_9505_image001.gif (23204 bytes)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.

Vapour Bypass.pdf

Packed Bed Tower - Baseline Scans Used for Shutdown Planning

Packed_Bed_2_years_after_baseline_1689_image001.gif (31380 bytes)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.

Packed Bed Tower.pdf

A TowerScan in a Different Plane

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.

Damaged_Internal_Riser_Figure_1D_22391_image001.gif (21858 bytes)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.

Damaged_Internal_Riser_Figure_1C_23992_image001.gif (22545 bytes)Damaged_Internal_Riser_Figure_1A_26905_image001.gif (26484 bytes)Damaged_Internal_Riser_Figure_1B_25164_image001.gif (25444 bytes)

A TowerScan in a Different Plane.pdf

 

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Last modified: March 05, 2013

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