Troubleshooting a C3 Splitter Tower

Troubleshooting a C3 splitter tower

Part 2: root cause and solution

The PetroLogistics giant C3 splitter started up in October 2010 and had experienced

RSHUDWLRQDO GLIFXOWLHV GXULQJ LWVLQLWLDO HLJKWPRQWK UXQ 7UD\ HI-ciency appeared to be very low, about 40-50%, compared to a typi-FDO WUD\ HIFLHQF\experienced with conventional trays in a C3 splitter. Due to the low WUD\ HIFLHQF\ LW FRXOGQRWSURGXFHon-spec polymer grade propylene. PetroLogistics, Fluor (which was not involved in the tower design), and the tray supplier formed a taskforce to conduct a troubleshoot-ing investigation to determine the root cause of this performance and WRSURSRVHDQGHQJLQHHUD[

The troubleshooting investigation combined hydraulic analysis and detailed multipass distribution calculations with the specialised technique of multichordal gamma scanning with quantitative analy-sis.7 +\GUDXOLF DQDO\VLV FRQUPHGthat the trays are prone to channel-ling and maldistribution due to their large open areas. It also ruled out several other theories.

The gamma scans showed a mald-istributed pattern on the trays, with high L/V ratios on the inside panels and low L/V ratios on the outside panels. The scans showed vapour FURVV RZ FKDQQHOOLQJ 9&)& RQthe outside panels. Flooding was observed on the inside panels well EHORZ WKH FDOFXODWHG RRG SRLQWThe scans pointed at a combination of VCFC and multipass maldistribu-tion as the root cause. ,QYHVWLJDWLRQ LGHQWLHG WKH KLJK

open slot area (15% of the active DUHD RI WKH [HG YDOYHV WR EH WKHprime factor inducing channelling

Distillation trays are prone to channelling and multi-pass maldistribution in large diameter towers. Multichordal gamma scanning is used for solving such problems

HENRY Z KISTER FluorBRIAN CLANCY-JUNDT and RANDY MILLER PetroLogistics

and maldistribution. A likely initia-tor of the multipass maldistribution ZDV OLTXLGSUHIHUHQWLDOO\RZLQJ WRthe inside panels from the false GRZQFRPHUV GLVWULEXWLQJ WKH DVK-LQJ UHX[ WR WKH WRS WUD\V SDQHOV7KLVSUHIHUHQWLDORZLVEHOLHYHGWRhave occurred through the gap at ZKLFK WKH UHX[ SLSHV HQWHUHG WKHfalse downcomers. Another likely initiator was channelled vapour blowing liquid from the outside to inside panels across the off-centre downcomers.

A short plant outage due to a problem elsewhere provided the RSSRUWXQLW\IRUDTXLFN[7KHNH\PRGLFDWLRQ ZDV EODQNLQJ DERXW Dquarter of the valves on each tray to reduce the tray open slot areas from 15% to 11%. The gaps at the UHX[SLSHHQWU\WRWKHIDOVHGRZQ-comers were sealed and the false downcomer heights were raised to HQVXUH JRRG UHX[ VSOLW WR WKH WRSWUD\SDQHOV$QWLMXPSEDIHVZHUHadded across the centre and off-centre downcomers to prevent the possibility of channelled vapour from blowing liquid from the outside to the inside panels towards the middle. Some down-comer blocks were installed to improve liquid distribution. The PRGLHG WRZHU DFKLHYHG WUD\ HI-ciencies comparable to those obtained in well-operated, smaller diameter, low pressure C3 splitters.

The investigation is described in two parts. Part 1 (see PTQ, Q4 2014) described the initial tower operation, as well as our hydraulic analysis and how it directed the investigation to focus on the combi-nation of VCFC and multipass maldistribution as the most likely

root cause. Part 2, the current arti-cle, describes the application of the specialised technique of multi-chordal gamma scanning with quantitative analysis7 to validate WKLV WKHRU\ FORVHO\GHQH DQGPDSthe channelling and maldistribution patterns, and lead to the correct solution. All of the literature refer-ences in Part 2 were listed at the end of Part 1.

Gamma scans investigationTo diagnose the nature of the suspected channelling or maldistri-bution, and to implement an HIIHFWLYH [ ZH SHUIRUPHG H[WHQ-sive multichordal gamma scans together with quantitative analysis of the gamma scans.

The gamma scanning technique normally practised for distillation trays shoots a single chord, or at most one chord per panel, with qualitative interpretation. Often, downcomer chords are also shot. The early gamma scans of the C3 splitter used this simple technique which is excellent for detecting JURVV DEQRUPDOLWLHV VXFK DV RRG-ing, missing trays, foaming, fouling, and high base levels, but is unable to detect subtle abnormalities such as channelling, abnormal froth structure, and blow-by in unsealed downcomers.

For the C3 splitter, the early quali-tative gamma scans established that WKHLQVLGHDFWLYHDUHDVZHUHRRGHGCentre and off-centre downcomers ZHUHRRGHGLQVRPHVFDQVEXWQRWRRGHG LQ RWKHUV 7KLV WLHG XSZHOOwith the conclusion based on Figure 3 in Part 1 that the trays were at LQFLSLHQW RRG DW WKH RSHUDWLQJrates.

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40 PTQ Q1 2015 www.eptq.com

tower end). For each of these chords, froth heights, froth densi-ties, entrainment indexes, and clear liquid heights were calculated. Due to scan quality issues, some chords needed re-shooting to verify repeatability.

Quantitative analysis of gammascans: resultsFigure 2 shows the results derived from the multichordal gamma scans of the active areas. These results are shown on Kistergrams,7 which are tray sketches drawn to scale with the various measure-ments also shown to scale. As such, they give a visualisation of the key hydraulic parameters.

The quantitative interpretation required several estimates. In the interpretation, allowance was made for variation in chord length and, where relevant, for the liquid in the mod arc downcomer above the outside even-numbered panels. No allowance was made for radiation absorption by the support trusses above the odd-numbered trays, but these are shown in Figure 2 and where relevant were considered in the interpretation. Also, the chords were chosen in a manner that mini-mises interference of the beams with the measurements. Even though the numbers in Figure 2 are not accurate, the inferred trends are quite independent of the estimates and are therefore real and valid.

Figure 2 shows results only for the western half of the tower. The results from the eastern and west-ern inside panels were very similar. From left to right on each diagram (west to east in the tower) are the side downcomers, the outside panels, the off-centre downcomers, WKH LQVLGH DFWLYH DUHDV DQG QDOO\the centre downcomers. Each sketch terminates just to the right (just east of) the centre downcomer.

Figure 2a shows the froth densi-ties (using 1.0 for pure liquid propane/propylene, 0 for pure vapour). The values plotted were obtained by numerical integration of the gamma scan transmission vs height above the tray for each scan chord7 and are drawn on a scale of 0 to 0.5, so that a point on the tray above means a froth density of 0.5,

To identify more subtle abnor-malities, multichordal gamma scans with quantitative analysis are inval-uable. This technique, seldom applied by gamma scan vendors GXH WR LWV KLJK FRVWV ZDV UVWproposed by Harrison,6 and later developed by Kister.7 The lead author has used it with great success to diagnose a multitude of subtle abnormalities on trays, including various modes of chan-nelling, abnormal froth structure, blow-by in unsealed downcomers, and many others. This technique requires top-quality multichordal scans of each tray panel. Froth heights, froth densities, clear liquid heights, and hydraulic gradients can be calculated as described in references 7 and 8.

Initial multichordal scans FRQUPHG WKH SUHVHQFH RI FKDQQHO-ling both on the outside and inside active areas of the trays. The scans showed a similar and quite uniform channelling pattern throughout the tower. There were no signs of unbolted manways.

The uniformity of the channelling pattern throughout the tower made it possible to focus on a relatively small section, map it in detail, and

use this section to represent most of the tower. This mapping provided a cost-effective way of gaining a FRQFLVH GHQLWLRQ RI WKH QDWXUH RIthe channelling. The costs of multi-chordal scanning with quantitative analysis rapidly escalate with the number of trays scanned and the number of chords per tray. The small section mapping permitted shooting a large number of chords SHUWUD\WRJLYHDJRRGGHQLWLRQRIthe channelling while keeping the costs down by limiting the number of trays scanned. ,Q WKLV PDSSLQJ VWXG\ YH

chords were shot on the inside east-HUQ SDQHOV DQRWKHU YH FKRUGV RQthe inside western panels, and three more chords on the outside western panels (see Figure 1). The spacing between any two succes-sive inside panel chords was about 6in, and their locations were chosen to minimise interference from the support trusses (also shown in Figure 1). Spacing between succes-sive outside chords was 23-29in. Two of the three outside chords passed through the mod arc down-comers (MOAD). These MOADs are marked as dashed lines in Figure 1 (extending to 63in from the

30 53

63

82 123 123148 1480

Figure 1 Chords used for the mapping gamma scan study

that is 50% liquid and 50% vapour E\ YROXPH ,Q WKLV JXUH EOXHVKDGLQJ LQGLFDWHV KLJK IURWKGHQVLW\ UHG VKDGLQJ ORZ IURWKGHQVLW\$KLJKIURWKGHQVLW\JHQHU-DOO\ LQGLFDWHV D KLJK /9 UDWLRZLWK D ORZ IURWK GHQVLW\ LQGLFDWLQJDORZ/9UDWLR

Figure 2a VKRZV KLJKHU IURWKdensities in the inside than in the RXWVLGH SDQHOV LQGLFDWLYH RI ORZHU/9 UDWLRV RQ WKH RXWVLGH SDQHOVDQGKLJKHU/9UDWLRVRQWKHLQVLGHpanels. 7KH RQO\ SODFHV RQ WKH RXWVLGHSDQHOVZKHUHWKHIURWKGHQVLWLHVDUHsimilar to those in the inside panels are at the outside panel inlets. The GLIIHUHQFH EHWZHHQ WKH KLJK GHQVL-ties (at the inside panels and at the inlets to the outside panels) and WKRVH LQ WKH PLGGOH DQG RXWOHWV RIWKH RXWVLGH SDQHOV LV W\SLFDOO\ RIWKH RUGHU RI 7KH VFDQV VKRZKLJKHU /9 UDWLRV DW WKH LQOHWV RIWKHRXWVLGHSDQHOV FRPSDUHG WR WKHPLGGOHDQGRXWVLGHRIWKHVHSDQHOV7KLVEHKDYLRXU LV W\SLFDO RIYDSRXUFURVVRZFKDQQHOOLQJ9&)&2Q WKH LQVLGH SDQHOV WKH IURWKGHQVLWLHV DUHKLJKHVW LQ WKHPLGGOH7KH IURWKV DW WKH WUD\ RXWOHWV DQGinlets are less dense than near the WUD\ PLGGOH 7KHUHIRUH WKH KLJKHVW/9 UDWLRV DUH DW WKHPLGGOH RI WKHLQVLGH SDQHOV ZLWK ORZHU /9ratios at the panels inlets and RXWOHWV 7KH KLJK /9 UDWLRV LQ WKHSDQHO PLGGOH VXJJHVW OLTXLG DFFX-PXODWLRQ SRVVLEO\ RRG LQLWLDWLRQULJKWWKHUH

Figure 2bVKRZVWKHIURWKKHLJKWVXVLQJDVFDOHRILQ WR WUD\VSDFLQJ$ IURWK KHLJKW RI WUD\ VSDFLQJ RUPRUH LQGLFDWHV RRGLQJ DQG VKRZVXS DV D SRLQW ULJKW RQ WKH WUD\DERYH$IURWKKHLJKW OHVVWKDQWUD\VSDFLQJ WKDW LV D SRLQW ZHOO EHORZWKH WUD\ DERYH LQGLFDWHVQRQRRGHG RSHUDWLRQ 7KH DFFX-UDF\ RI IURWK KHLJKW GHWHUPLQDWLRQLV VR PDQ\ SRLQWV VKRZSUR[LPLW\ WR RRG 7KH VKDGLQJVKRZQ RQ WKH GLDJUDP LV WKH VDPHDV WKDW VKRZQ LQ Figure 2a and UHSUHVHQWVIURWKGHQVLWLHVZLWKEOXHEHLQJ KLJK IURWK GHQVLW\ DQG UHGORZIURWKGHQVLW\

Figure 2b VKRZV WKDW PRVW RI WKHRRG RFFXUUHG QHDU WKH PLGGOH RIWKH LQVLGH SDQHOV 1R RRG ZDV


REVHUYHGLQWKHFKRUGFORVHVWWRWKHRIIFHQWUH GRZQFRPHUV DQG RQO\ LQWZR WUD\V LQ WKH FKRUG FORVHVW WR WKH FHQWUH GRZQFRPHUV ,Q WKHFKRUG FORVHVW WR WKH RIIFHQWUHGRZQFRPHUV IURWK KHLJKWV ZHUHFRPSDUDWLYHO\ ORZ 7KH UHJLRQVZKHUHWKHRRGZDVREVHUYHGZHUHWKRVHRIKLJKIURWKGHQVLW\

Figure 2b VKRZV RRG DOVR DW WKHRXWOHWV RI WKH RIIFHQWUH WR VLGHoutside panels. In the outside SDQHOV QR RRG ZDV REVHUYHG LQWKH PLGGOH QHDU WKH RIIFHQWUHGRZQFRPHUV DQG LQ DOO EXW RQH RIWKH LQOHW VLGH WR RIIFHQWUH SDQHOV7KHRRGREVHUYHGKHUHZDVGLIIHU-ent to that observed in the inside SDQHOV LQ WKDW LW DOZD\V WRRN SODFHLQ WKH ORZ GHQVLW\ UHJLRQV $JDLQWKLVRRGLVFKDUDFWHULVWLFRI9&)&

Figure 2c VKRZV WKH FOHDU OLTXLGKHLJKWV RQ WKH WUD\V 7KH VFDOH LVLQVRWKDWDSRLQWDWWKHRRURIWKH WUD\ DERYH FRLQFLGHV ZLWK LQFOHDU OLTXLG KHLJKW (DFK FOHDUOLTXLG KHLJKW LV VLPSO\ WKH IURWKKHLJKW PXOWLSOLHG E\ WKH IURWK

GHQVLW\7KH VKDGLQJ VKRZQRQ WKHGLDJUDP LV WKH VDPH DV WKDW VKRZQin Figure 2a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

Tray104105106107108109110111112113114115116117118119

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Figure 2 Results from multichordal gamma scans of active areas: (a) froth densities, (b) froth heights, (c) clear liquids heights, and (d) entrainment


chord closest to the off-centre downcomers, the index was much less, ranging from 0.07 to 0.14. For the chord closest to the centre downcomers the index ranged from 0.12 to 0.27.

For the outside panels, the entrainment index (froth densities at the peaks) ranged from 0.06 to 0.22. The only exceptions were the inlets to the side to off-centre panels, where most indices were 0.28-0.3. These were also the peaks that had high clear liquid heights in Figure 2c. These outside side to off-centre panels had entrainment gradients which tracked the clear liquid heights, showing lessening entrainment from panel inlet to outlet.

Patterns distinguished from analysis of gamma scans: resultsThe side panels appear to operate at lower L/V ratios than the centre panels. This means that either the inside panels contained more liquid, or the outside panels contained more vapour, or both.

There appears to be VCFC on the outside panels, with hydraulic gradients of the order of 3in on the

the inside panels. The only excep-tions were the clear liquid heights at the inlets to the side to off-centre panels. The clear liquid heights there ranged from 6in to 7in, except on tray 108. On these trays (the even trays) there appeared to be a hydraulic gradient of around 3in. This pattern is typical of VCFC.

Figure 2d shows entrainment from the trays. For the entrainment index, we deviated from the index we usually use7 in favour of an alternative index that we believe is more meaningful here. For the entrainment index, we took the froth density at the maximum transmission point, that is at the vapour peak. The scale is 0-0.5, the same as the froth density. The shading shown in Figure 2d is the same as in Figure 2a and represents froth densities, with blue being high and red being low.

The shading shows that the entraining regions closely track the high froth density regions.

For the three middle chords of the inside panels, most of the entrainment index values (froth densities at the peaks) ranged between 0.19 and 0.36. For the

Tray104

105

106

107

108

109

110

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112

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Figure 3 Clear liquid heights with VCFC on outside panels

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seem much, but 3% by weight is 48% vapour by volume due to the GHQVLW\ GLIIHUHQFH 7KH DVKHGUHX[ HQWHUV WKH WRZHU YLD DQH-distributor (see Figure 4). The inlet nozzle and the pipe feeding the H are 24in, branching into two short 18in pipes which later split into four 18in laterals. Each lateral has more than 40 2.5in diameter holes, squirting the feed horizon-tally onto the walls of two off-centre false downcomers that VHUYH DV DVK ER[HV (DFK IDOVHdowncomer is 43in wide at the top, tapering towards the bottom. The false downcomers begin tapering 6in below the bottom of the later-als. In the false downcomers, vapour disengages upwards, while OLTXLGGHVFHQGV DQGRZVRQWR WKHtop tray through 2in clearances in the bottom of each false downcomer. 7KH IHHG PL[WXUH LV GLVFKDUJHG

horizontally towards the wall of the false downcomer at a velocity of about 10 ft/s, and the distance from

VCFC and the multi-pass maldistribution.

The channelling pattern on the LQVLGH FKRUGVZDVPRUH GLIFXOW WRH[SODLQ 2QH K\SRWKHVLV ZDV WKDWabove the off-centre downcomers, the VCFC on the outside panels generated a strong horizontal vapour velocity component in the direction of the inside panels. This velocity component would supply the horizontal push in a direction RSSRVLWH WR WKH OLTXLG RZ RQ WKHinside centre to off-centre panels. Although possible, this hypothesis was not considered likely. It was realised that there was still a miss-ing link.

Re ux inletWhile closely reviewing the tower internals, we found our missing OLQNUHX[HQWU\PDOGLVWULEXWLRQ7KHUHX[HQWHULQJWKH WRZHU LVDDVKLQJ OLTXLG 8SRQ DVKLQJ WRthe tower top pressure, it generated about 3% vapour by weight at the operating conditions. That may not

side to off-centre panels. Figure 3 illustrates this mechanism. The low-density regions nicely corre-spond to the path of the vapour in Figure 3 . The entrainment is mostly from the inlet areas of the side to RIIFHQWUH SDQHOV 7KH RRGobserved on the outside panels is on the outlet of the off-centre to side panels (see Figure 2b). Even WKRXJK WKH RRG DSSHDUV WKHUHthere is not much entrainment (compare Figures 2b and 2d). The reason for the low entrainment there could be drying up in this region. This ties in with the low clear liquid heights observed in the middle and outlet of the off-centre to side panels. Note that the inlet weep from this panel comes from the inlet region that is much wider than the panel width near the outlet.

With the outside panels operating at VCFC, there will be an easy path for the vapour to travel without encountering a high liquid head. This will induce preferential YDSRXU RZ WKURXJK WKH RXWVLGHpanels and induce multi-pass mald-istribution. The horizontal vapour velocity component through the outlet regions of the even numbered outside panels may blow liquid across the off-centre down-comers from the outside into the inside panels. This too may induce PXOWLSDVVPDOGLVWULEXWLRQ2%DUD9 who consulted our team on maldis-WULEXWLRQ LGHQWLHG DGGLWLRQDOsources conducive to diversion of vapour and liquid into the inside panels. These include the effective OHQJWK RI WKH PRGLHG DUF GRZQFRPHU02$'EHLQJOHVVWKDQWKDWused in the design calculations, making it shorter than the centre weir length; the formation of UHJLRQV RI UHWURJUDGH RZ RQ WKHouter panels caused by the impact of the liquid on the outlet weir near the tower wall on both sides of the 02$' DQG WKH LQ GHHS LQWHJUDOtrusses perpendicular to the liquid RZ ZKLFK ZRXOG FDXVH PRUHhydraulic resistance on the side panels.

This theory of VCFC alone H[SODLQHG WKH UHVXOWLQJRRG LQLWLDtion on the inside panels. The lower HIFLHQF\ LV WKHQ ERWK GXH WR WKH

18 18

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Figure 4 Re ux inlet arrangement


rich. The high liquid heads generated on the inside panels would induce vapour to preferen-WLDOO\ RZ LQWR WKH RXWVLGH SDQHOVWith the high open area of the trays, the dry tray pressure drop would be too low to counter this maldistribution, so the maldis-tribution would persist throughout the tower. The result is high froth densities on the inside panels and low froth densities on the outside panels as seen in the gamma scans.

Modi cations for overcoming theproblemFollowing the diagnosis, the team GHOLEHUDWHG RQ WKH RSWLPXP [ WRthe problem. During these delibera-tions, the heat pump main FRPSUHVVRU H[SHULHQFHG D KLJKvibration incident. It was discov-ered that the compressor had thrown a blade and that the unit would be out of service for several weeks. The team discussions turned immediately from What can we do? to What will we do?

With the tower problem identi-HG DV LQWHUDFWLRQ EHWZHHQ 9&)&and the inside-to-outside pass maldistribution, it was necessary to mitigate the channelling and mald-istribution. The key to eliminating the channelling is to reduce the H[FHVVLYH RSHQ DUHD IURP WRDERXWRQWKHWUD\V7KHNH\WReliminating the maldistribution is WR FORVH WKH JDSV DW WKH UHX[ SLSHentry into the false downcomers to DYRLGSUHIHUHQWLDORZ WRZDUGV WKHinside passes, and to raise the heights of the false downcomers to SUHYHQWRYHURZ

Less critically, it was regarded as EHQHFLDO WR DGG DQWLMXPS EDIHVto block the horizontal velocity component from the outside panels that may blow vapour or carry liquid or froth into the inside SDQHOV 7KLV PRGLFDWLRQ ZDVoverkill since eliminating the channelling should be enough to mitigate the horizontal velocity component, yet was a small price to SD\ WR JDLQ FRQGHQFH WKDW WKHchannelling will be completely mitigated. Finally, off-centre down-comer clearance blocks were added to improve the split of liquid from

PDOGLVWULEXWLRQ ZLWK H[FHVV OLTXLGpouring through the gaps into the inside panels.

The validity of the assumption of pure liquid may be questioned. The region of the gap did not have any pipe holes on either side of the pipe, so it is likely to be liquid-rich. So while the assumption may not be precise, it should be quite a UHDVRQDEOHUVWDSSUR[LPDWLRQ

Mysteries explained7KH9&)&REVHUYHGRQ WKHRXWVLGHpanels can now be combined with WKH UHX[ GRZQSRXU WKURXJK WKHgaps in Figure 5 WR H[SODLQ DOO WKHREVHUYDWLRQV 7KH UHX[ GRZQSRXUthrough the gaps would be totally directed to the inside panels, making the inside panels liquid-

the holes to the false downcomer walls is only about a foot. This is likely to produce some upward lift on the feed liquid when it hits the false downcomer walls, and gener-ate turbulence in this region. The downward liquid velocity in the false downcomer at the holes eleva-tion is about 0.2 ft/s, which is quite typical of downcomer entrance velocities, a region of considerable turbulence. The presence of vapour at this region will aggravate the turbulence. The top of the false GRZQFRPHU LV RQO\ LQ DERYH WKHcentreline of the holes, and it is possible that some of the feed OLTXLGOLIWHGXSZRXOGRYHURZWKHtop of the false downcomers. Such RYHURZ LV OLNHO\ WR EHmaldistributed.

Figure 5 shows the entry of one of WKHLQEUDQFKSLSHV LQWR WKH IDOVHdowncomer. Where each pipe HQWHUV WKHUH LVDQLQ[LQJDSmostly above the pipe, through which liquid would pour out if froth or liquid built up above the UHX[ SLSH RU LI WKHUH ZDV WXUEXlence in the region. A calculation using the Francis weir formula

showed that if liquid built to the WRSRIWKHIDOVHGRZQFRPHURIWKH UHX[ZRXOG SRXU WKURXJK WKHgap above the pipe. If it only built up to 6in above the gap, this frac-WLRQ ZRXOG GHFOLQH WR (LWKHUway, there would be a large scale

Figure 5 Re ux pipe entering the false downcomer, showing gap at the entrance to the downcomer

The modi ed tower achieved tray ef ciencies comparable to those obtained in well-operated, smaller diameter, low pressure C

3 splitters


Post-modications tower operation$SSUR[LPDWH WUD\ HIFLHQF\ DIWHUUHYDPS KDV EHHQ REVHUYHG WR EH ZLWK GRZQFRPHU YHORFLWLHVDV KLJK DV IWVHFZHLU ORDGLQJVRIURXJKO\JSPLQDQG&IDFWRUVEDVHGRQEXEEOLQJDUHDDERYHIWVHF7KHPRGLHGWRZHUDFKLHYHGWUD\HIFLHQFLHV FRPSDUDEOH WR WKRVHREWDLQHG LQ ZHOORSHUDWHG VPDOOHUGLDPHWHU ORZ SUHVVXUH &3 VSOLWWHUV7KLV LV LQFUHGLEOH FRQVLGHULQJ WKDWWKH RZ SDWK OHQJWKV ZHUH VRPH-ZKDWFRPSURPLVHGE\WKHEODQNLQJVWULSV WKDW WKHEODQNLQJVWULSVZHUHVRPHZKDW ZLGHU WKDQ LGHDO DQGthat the time was too short to LPSOHPHQW VRPH RI WKH DGGLWLRQDOLGHDV RQ RXU ZLVK OLVW )ORRGLQJDQG LQVWDELOLW\ ZHUH IXOO\ HOLPL-QDWHG 7KH WRZHU VXFFHVVIXOO\SURGXFHV RQVSHF SRO\PHU JUDGHSURS\OHQH2XUH[SHULHQFHVKRZVWKDWFRUUHFWGLDJQRVWLFV JRRG HQJLQHHULQJ DQGD PXOWLGLVFLSOLQHG WHDP ZRUNLQJWRJHWKHU FDQ VROYH HYHQ WKH PRVWFKDOOHQJLQJSUREOHPVZLWKVXFFHVV

AcknowledgementThe authors express their gratefulness to Tracerco, in particular to Lowell Pless, for the excellent gamma scans.

Henry Z Kister is a Fluor Corp. Senior Fellow and Director of Fractionation Technology. He is the author of three books, 100 articles and has taught the IChemE-sponsored Practical Distillation Technology course more than 400 times. He holds BE and ME degrees from the University of NSW in Australia, is a Fellow of IChemE and AIChE, a Member of the NAE.Email: [email protected].

Brian Clancy-Jundt currently works in one of the largest propane dehydrogenation plants in the world with PetroLogistics and has had direct engineering oversight over all aspects of an olens plant. He graduated from Texas Tech University with a BS in chemical engineering.

Randy Miller served as Vice President, Engineering for PetroLogistics (2007-2014), instrumental in the design and development of the facility since the commencement of front end engineering design. He has worked in the petrochemical industry for over 20 years and holds a BS in chemical engineering from Texas A&M University, an MBA from University of Houston at Clear Lake, and is a Registered Engineer in Texas.

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