TRACERCO Diagnostics FCCU Study Bro 16pp A4 HR.pdf · Tracerco is a world leading industrial...

TRACERCO Diagnostics™

FCCU Study

26782 Diagnostics Bro 16pp A4 02/10/2013 09:50 Page 2


FCCU StudyIntroductionThe Fluidised Catalytic Cracking Unit (FCCU) is the economic heart of a modern refinery. Even small increases in its yield can bring about significant overall gains in productivity and revenue.

Tracerco is a world leading industrial technology

company providing unique and specialised detection,

diagnostic and measurement solutions.

A TRACERCO Diagnostics™ FCCU Study will provide youwith the information you need to optimise or trouble-shootyour specific process:

• All testing is performed while the FCCU is online.

• There is no interference with normal unit operations or production scheduling.

• Data collected can be used to identify operating parameter changes to improve unit productivity or gauge the accuracy of process modelling and simulation.

• Tracerco’s experience involves numerous studies performed on units worldwide.

TRACERCO Diagnostics™ FCCU Studies utilise both sealedsource and tracer technologies. A typical study will usethese technologies to measure the velocity, distribution and residence time of the catalyst or vapour phase through eachpart of the FCCU, including:

• Reactor Riser

• Reactor

• Reactor Stripping Section

• Regenerator

• Spent Catalyst and Regenerated Catalyst Standpipes

The operation of the associated downstream Main Fractionator column can also be investigated using TRACERCO Diagnostics™ Tower Scan technology.

In order to offer our customers a fast response we operatefrom a number of regional bases strategically close to majorindustrial centres. Same or next day service is part of our normal service provision.

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Reactor Riser - page 4

Riser Density Profile

Catalyst and Vapour Distribution

Catalyst and Vapour Velocities (Slip Ratio)

Reactor - page 6

Cyclone Operation and Distribution Study

Cyclone Blockage Detection

Catalyst Bed Level Measurement

Efficiency of Riser Termination Device

Residence Time Distribution

Regenerator - page 10

Cyclone Operation

Cyclone Blockage Detection

Catalyst Bed Level Measurement and Extent of Bed Dilute - Phase

Catalyst and Air Distribution Study

Residence Time Distribution

Spent Catalyst and Regenerated Catalyst Standpipes - page 12

Catalyst Slugging Study

Catalyst Density Profile

Stripping Section - page 8

Density Profile

Catalyst and Steam Flow Distribution


FCCU Study

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Reactor Riser

Riser Density ProfilePoor fluidisation or poor mixing of catalyst and oil causes localised variances in the oil-to-catalyst ratio and crackingreactions. The over-cracked portion of the feed generateslow-value light components, while at the same time theunder-cracked portion produces more residue.

A TRACERCO Diagnostics™ scan of the riser provides thecatalyst density profile down the height of the riser. Results illustrated in figure 1 show the density profiles at high andlow steam rates. In this example, the overall catalyst densityin the riser feed zone at scan elevation 13-18 ft. decreaseswith the higher steam rate. The scan also indicated that thecatalyst and oil mixture travelled upward approximately 8 ft.from the oil feed nozzles before the oil was completelyvapourised.

Catalyst and Vapour DistributionThis method generates a detailed cross-sectional densityprofile of the reactor riser at a fixed elevation or riser cross section.

The information is used to determine the uniformity of distribution between the catalyst and feed and to identifyflow inefficiencies, such as catalyst mal-distribution. A TRACERCO Diagnostics™ tomographic scan is often used to evaluate changes in design and operation of feed injection or lift steam nozzles. An example of this is shown infigure 2, where two tomography scans were performed, onewith all six feed nozzles open and another with one of thenozzles shut (nozzle number 3) to simulate a plugged orfouled nozzle.

Figure 1: Source and detector placement and density profile. Figure 2: Tomography Scan Simulated Plugged Nozzle.

Tomography Scan Scanline Orientation.

GammaSource

RadiationDetector

CatalystParticles

FeedFeed

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Reactor Riser

One common application applied to an FCCU is measurement of stream velocities. Ideally, catalyst andvapour should be in plug flow condition to eliminate back-mixing, which can produce undesirable secondary reactions. However, because of its greater density, the catalyst always flows up the riser slower than the hydrocarbon vapour. This phenomenon is known as “catalyst slip”. An ideal plug flow riser should have a slip ratio of 1.0.

Discrepancy from 1.0 or design expectation is often used as a measure of the fluidisation performance. The slip ratiocan be determined by measuring the velocities of the hydrocarbon vapour and catalyst via a TRACERCO Diagnostics™ flow study. Figure 4 represents test results that involve two tracer injections, one for the vapour phaseand the other for the catalyst phase. The velocities of thevapour phase and catalyst phase can be measured over the same section of the riser.

Catalyst and Vapour Velocity Measurements

Injection DetectorRiser DetectorInjection DetectorRiser Detector

Catalyst Slip Factor = 1.8042.2 ft/s 23.5 ft/s

-5 5 15 25Time In Seconds

Radi

atio

n In

tens

ity

Figure 4: Riser traffic velocity.

5

Radiation DetectorNumber 2

Radiation DetectorNumber 1

Distance X

RadiotaggedFeed

CatalystPulsed Injection

RE

AC

TOR

RIS

ER

TO FR

AC

TION

ATOR

Figure 3: Riser traffic velocity tracer test detector positions.


Reactor

Cyclone OperationThe loss of catalyst through the reactor or cyclones is a fairly common problem. Identifying the reason for the loss is often difficult. TRACERCO Diagnostics™ gammascans can be a powerful tool for gathering essentialinformation about the problem. In figure 5, fourTRACERCO Diagnostics™ gamma scans were used to obtain a density profile of each reactor cyclone. The scans identified that there was one plugged cyclone and a dipleg that was full of catalyst.

Catalyst Bed Level MeasurementTRACERCO Diagnostics™ gamma scans can be performed to obtain information on the reactor bed level. In the example below, operations personnel were suspicious of the calibration of the level gauge. Results from the threescans performed (figure 6) found that at the low level (100” of pressure), the bed was so low that the bottom of the diplegs were uncovered, allowing vapour and catalyst to pass up the diplegs. Using the TRACERCO Diagnostics™scan data results, the appropriate height was found to coverthe diplegs and the level instrument was recalibrated.

West Secondary CycloneSouth Primary Cyclone

East Secondary CycloneNorth Primary Cyclone

1000 10000

Plugged Cyclone Dipleg

BRACING

MANWAY

FLAPPER VALVE

2'

4'

6'

8'

10'

12'

14'

16'

18'

20'

22'

24'

26'

28'

30'

Catalyst

EXTERNAL LINING

N

Figure 6: Scan results assist with level instrument calibration.Figure 5: Reactor cyclones distribution study.

Flooded Cyclones @ 125" PressureUnsealed Diplegs @ 100" PressureNormal Operations @ 112" Pressure

100 1000

BRACING

CYCL

ONES

BRACING

2'

4'

6'

8'

10'

12'

14'

16'

18'

20'

22'

24'

26'

28'

30'

32'

SECONDARY CYCLONE DIPLEGS

FREEBOARD INTENSITY

PRIMARY CYCLONE DIPLEGS

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Reactor

Since FCCUs have been modified to achieve the crackingreaction in the riser instead of the reactor, the reactor’s roletoday is to minimise post riser reactions by providing efficient catalyst/hydrocarbon disengagement.

A TRACERCO Diagnostics™ distribution study is used to determine relative amounts of vapour or catalyst traffic entering the primary reactor cyclones. A group of radiationdetectors are placed at the cyclone inlets and outlets (figure 7). Usually only the primary cyclone inlet and thesecondary cyclone outlets can be monitored, because thecyclone pairs are internally coupled. For a normal cyclonesystem, each of the primary cyclones should receive thesame amount of vapour and catalyst traffic, so all of thedetectors should receive the same amount of tracer radiation response. Comparing the integration of the areasbeneath each of the distribution detector responses allowsidentification of flow mal-distribution (figure 8).

Cyclone Distribution StudyOutlet Detector

Secondary Cyclone OutletRing of Detectors

Primary Cyclone InletRing of Detectors

Bed LevelRing of Detectors

6 Detectors ateach elevation

Injection Detector

Vapor Distribution at Cyclone Inlets

Time (seconds)

Rad

iatio

n In

tens

ity

Figure 8: The TRACERCO Diagnostics™ Distribution study illustrated is an example of a typical distribution profile exhibiting maldistribution at theReactor cyclone inlets.

Figure 7: Illustrated above is a typical set-up showing the placement ofradiation detectors used in a TRACERCO Diagnostics™ Distribution study.

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Stripping Section

Density ProfileThe Spent Catalyst Stripper is designed to prevent hydrocarbon from being carried from the reactor to the regenerator with the catalyst. Steam is injected counter current to the flow of catalyst to strip the hydrocarbon adsorbed onto the catalyst.

A TRACERCO Diagnostics™ scan of the reactor strippingsection can identify differences in the density of the aeratedcatalyst to show:

• If maldistribution of the stripping steam is occurring.

• If excessive catalyst hold-up is occurring on any of the trays.

• Whether or not the trays are in place.

Four scans are performed through the stripper in an orthogonal grid pattern (figure 9). When the results of thescans are overlaid on a single plot (figure 10), areas where the scan results do not overlay are areas of the stripperwhere the aerated catalyst density is different. The absenceof low density areas under each tray is an indication offlooded trays.

West ScanlineNorth Scanline

100 1000 10000

MANWAY

STEAM NOZZLES

BOTTOM TANGENT

MANWAY

Tray 5

2'

4'

6'

8'

10'

12'

14'

16'

East ScanlineSouth Scanline

Tray 3

Tray 1

Figure 9: Scanline Orientation. Figure 10: Response Profiles.

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Stripping Section

At the base of the reactor, stripping steam is used to strip the adsorbed hydrocarbons from catalyst. In the strippingsection, trays or packing are installed to improve the stripping efficiency. Steam/catalyst distribution can be identified from the TRACERCO Diagnostics™ scan resultspreviously described. However, if superficial velocities andmean residence times are to be measured, then the relativesteam/catalyst distribution can be measured simultaneouslyusing a tracer injection technique. Uniform distribution of catalyst and steam in the stripper is critical to achieve highstripping efficiency (less carry-down of the hydrocarbonproducts from reactor to regenerator).

A TRACERCO Diagnostics™ distribution study of the stripping section of an FCCU requires two groups of radiation detectors (four or more detectors for each group),placed respectively at the top and bottom of the stripper (figure 11). The steam and catalyst response profiles can be overlaid and interpreted for superficial velocity and distribution (figures 12 and 13).


18000

16000

14000

12000

10000

8000

6000

4000

2000

030 7050 90 190170150130110 230210 250 270 290 310 330

Time (seconds)

Inte

nsity

North Top- 27%

East Top- 32%

South Top- 20%

West Top- 21%

North Bottom- 62%

East Bottom- 10%

South Bottom- 20%

West Bottom- 7%

Figure 11: Detector placement.

Figure 12: Catalyst Flow and Distribution.

900

800

700

600

500

400

300

200

100

070 75 80 85 90 95 100 105 110 115 120 125 130

Time (seconds)

Inte

nsity

North Top- 28%

East Top- 34%

South Top- 18%

West Top- 20%

North Bottom- 19%

East Bottom- 20%

South Bottom- 25%

West Bottom- 36%

Figure 13: Steam Distribution.

Figure 12 and 13: Study of the catalyst and steam flow requires two tracers injected separately, one for tracing the catalyst and one for tracing the steam.

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Regenerator

Catalyst Bed Level MeasurementThe dense bed level elevation in a regenerator can be determined using TRACERCO Diagnostics™ scan technology. The scan will produce a density profile at thecatalyst bed level area that will indicate dense phase and dilute phase levels. It can be performed over varying operational conditions to assess the changes in level and help calibrate level control.

By using four scan lines in a grid arrangement (figure 14), a more accurate indication of the regenerator’s catalyst bed level can be determined. Overlaying the four scan lineswill identify the dense and dilute phase catalyst levels anddetermine if the levels are uneven which may be indicative of air mal-distribution and air grid problems (figure 15).

Cyclone Operation and CycloneBlockage DetectionAs with reactor cyclones, a scan can be performed on each regenerator cyclone to search for high catalyst levels in diplegs or plugged cyclones that will explain high catalyst loss.

Northwest ScanlineSouthwest Scanline

100

FCC REGENERATORDate 10:32 - 12:22 X-Axis: 50 - 20000

1000 10000

Cyclones

Upper Set of Detectors

Bracing Level B

DenseCatalyst

Manway

Lower Set of Detectors

(Top Tangent)

Weld

Bracing Level C

Primary Dipleg Valve ElevationSecondary Depleg Valve Elevation (Bottom Tangent)

Dilute PhaseCatalyst

2'

4'

6'

8'

10'

12'

14'

16'

18'

20'

22'

24'

26'

28'

30'

32'

34'

36'

Southeast ScanlineNortheast Scanline

Figure 15: Scan results to determine the Regenerator catalyst bed level.Figure 14: Illustration of a grid Scan orientation used on a Regenerator.

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Regenerator

A TRACERCO Diagnostics™ flow study can measure several flow parameters around the regenerator with a singleinjection of radiotracer. For example, both the air rate andflue gas rate can be determined simultaneously with a studyof the air distribution from the air grid and/or the vapour distribution to the cyclones.

This is accomplished by placing a group of detectors at a known distance apart on the air supply line to the regenerator and another set on the flue gas line leaving the regenerator (figure 16). The flow rates will be calculated byconverting the measured velocities to volumetric flow with respect to line diameter, process pressure and temperature.

Figures 17 and 18 illustrate vapour distribution test resultsfrom when eight detectors were positioned near the eight primary cyclone inlets (figure 17) and twelve detectors werepositioned in a ring just above the upper air ring (figure 18).Test results showed that some detectors had much larger responses than others, indicating mal-distribution from the air grid and preferential distribution to some of the cyclones.


Y1: N CycloneY1: S CycloneY1: Overhead Line

200

150

RADI

ATIO

N IN

TENS

ITY

TIME (seconds)

100

50

0470 480 490 500 510 520 530 540 550 560

Y1: NE CycloneY1: SW Cyclone

Y1: E CycloneY1: W Cyclone

Y1: SE CycloneY1: NW Cyclone

N CycloneNE Cyclone

E CycloneSE CycloneS Cyclone

SW CycloneW Cyclone

NW Cyclone

30.8%23.6%

6.9%2.5%3.7%3.4%5.0%

24.1%

PercentArea

Position

Y1: Air 1Y1: Air 5Y1: Air 10

220

200

180

160

140

120

100

80

60

40

20

TIME (seconds)

0135 145 155 165 175 185 195 205



Y1: Air 4Y1: Air 9Y1: Overhead Line

Air 1Air 2Air 3Air 4Air 5Air 6Air 7Air 8Air 9

Air 10Air 11Air 12

14.4%13.4%4.0%6.0%

10.5%5.3%7.4%

10.6%5.3%

10.0%5.8%7.3%

PercentArea

Position

RADI

ATIO

N IN

TENS

ITY

Figure 16: Detector placement.

Figure 17: Vapour distribution at cyclone inlets.

Figure 18: Vapour distribution above air grids.

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Spent Catalyst and RegeneratedCatalyst StandpipesCatalyst Slugging StudyStationary Monitoring Slugging Study

This test uses TRACERCO Diagnostics™ scan technologydesigned to measure density variations over time as the catalyst circulates. A small source and detector are positioned vertically on the standpipe being inspected andthe transmitted radiation is continuously monitored (figure19). Fluctuations in the transmitted radiation are recordedand provide a relative measurement of the fluid density variations within the pipeline over time (figure 20).

Figure 20: This case study was performed because of catalyst circulation problems. A TRACERCO Diagnostics™ stationary monitoring test was designed to observe and record density fluctuations. The sources anddetectors were positioned and connected to a computer tocollect data over time. These results justified a short outagewhere a hole was found in the overflow well. The hole allowed air to leak into the downward flowing catalyst and be entrained into the standpipe. Operations can also makechanges to the re-circulation rate to see the effect of the fluidised flow density profile in the standpipes.

Figure 20: This case study was performed because of catalyst circulation problems. A Tru-Scan® stationary monitoring test was designed to observe and record density fluctuations. The sources anddetectors were positioned and connected to a computer to collect dataover time. These results justified a short outage where a hole was foundin the overflow well. The hole allowed air to leak into the downward flowing catalyst and be entrained into the standpipe. Operations can also make changes to the re-circulation rate to see the effect of the fluidised flow density profile in the standpipes.

Actual Time

12:4

9:13

12:5

0:13

12:5

1:13

12:5

2:13

12:5

3:13

12:5

4:13

12:5

5:13

12:5

6:13

12:5

7:13

12:5

8:13

12:5

9:13

100

1000

10000

Tran

smis

sion

TOPMIDDLEBOTTOM

Figure 19: Set-up for Slugging Study.

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Spent Catalyst and RegeneratedCatalyst Standpipes

A TRACERCO Diagnostics™ scan of the spent catalyststandpipe can be performed to investigate the cause of circulation problems. Scan results from two scans of a spentcatalyst standpipe showed an increase in density in thestandpipe, but the red scan (N-S vertical scan, figure 21)showed an area of very low density below the area of highdensity. This was theorised to be a blockage that caused thecatalyst to flow to one side of the standpipe, leaving the areaunder the blockage clear of catalyst. With this information, ashutdown was authorised and a large piece of refractorywas found to be causing the blockage.

Catalyst Density Profile

NW-SE Vertical

1000

RingRing

Ring

Ring

Area of High Densityin Both Scans -Probable Blockage

Area of Lower thanNormal Density

Area of Much Lower thanNormal Density -Probably Void Space

5m

6m

7m

8m

9m

10m

11m

N-S Vertical

Figure 21: A scan of the Spent Cat standpipe can be performed toinvestigate the cause of circulation problems.

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Main Fractionator Scan

Tracerco has provided TRACERCO Diagnostics™ tower scanservices worldwide to evaluate trayed and packed towers inorder to identify damage, fouling, flooding, mal-distributionand many other problems that can exist inside of the tower.This service is provided online, externally to the column, withno interference to normal plant operations. The ability to accurately determine what is happening inside the column,without having to shut it down for a visual inspection, effectively provides our customers with ‘insight onsite’.

A main fractionator was not operating properly at normal capacity and was showing symptoms of flooding from tray 2 (red trace, figure 22). A TRACERCO Diagnostics™ towerscan pinpointed the location of flooding that was probablydue to fouling (coking).

After the main fractionator was cleaned, a baseline scan(blue trace) was performed to use for future diagnosis ofcoking problems at an earlier stage before the floodingreached such a severe condition.

A scan a few months later (green trace) showed that tray 2 was again starting to show the same problem with cokingand the subsequent liquid hold-up and flooding. Using this data, plant operations and maintenance were able to determine where the limitation in the column was occurringand prepare corrective action. Figure 22: TRACERCO Diagnostics™ Tower scan baseline and

troubleshooting results provided operations and maintenance personneladvance warnings of approaching problems so they could prepare for corrective action.

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Tracerco’s operational offices acrossthe worldBillingham, UKTel +44 (0) 1642 375500

Aberdeen, UKTel +44 (0) 1224 650650

Alblasserdam, The NetherlandsTel +31 (0) 78 890 7640

Villefontaine, FranceTel +33 (0) 4 74 94 79 88

Milan, ItalyTel +39 02 90989971

Bergen, NorwayTel +47 55 36 55 40

Brussels, BelgiumTel +32 (0) 2 465 85 20

Oldenburg, GermanyTel +49 441 361109-0

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Abu Dhabi, UAETel +971 (0) 2 5541672

Muscat, OmanTel +968 9270 7498

SingaporeTel +65 6336 3377

Kuala Lumpur, MalaysiaTel +603 7803 4622

Maharashtra, IndiaTel +91 22 27401427/428 (Extn: 321)

Amphur Muang Rayong, ThailandTel +66 38 691 5357

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Perth, AustraliaTel +61 (0)8 9209 3905

Concord, CA, USATel +1 925 687 0900

Pasadena, TX, USATel +1 281 291 7769

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Rio de Janeiro, BrazilTel +55 21 3535 7600

Sarnia, CanadaTel +1 519 332 6160

Edmonton, CanadaTel +1 780 469 0055

Calgary, CanadaTel +1 403 931 6705

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For further details please contact:

Pavilion 11, Coxwold Way, Belasis Hall Business Park,Billingham, Cleveland TS23 4EA UK

Tel: +44 (0)1642 375500Fax: +44 (0)1642 370704Email: [email protected]: www.tracerco.com

XM1015/0/B

@oil_diagnostics

Front cover image supplied by Praxis Technical Group www.praxistech.com

Tracerco Limited is a subsidiary of Johnson Matthey PLC, 5th Floor, 25 Farringdon Street, London EC4A 4AB.Registered in England No. 4496566. Tracerco is a trading name of Tracerco Limited.

TRACERCO Diagnostics, Johnson Matthey and the Johnson Matthey logo are trademarks of the Johnson Matthey Group of companies.


TRACERCO Diagnostics FCCU Study Bro 16pp A4 HR.pdf · Tracerco is a world leading industrial...

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Transcript of TRACERCO Diagnostics FCCU Study Bro 16pp A4 HR.pdf · Tracerco is a world leading industrial...