Radioisotope Applications for...

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RAD I01SO TOPE APPL ICAT IONS FORTROUB LESHOO TING AND OPT 'IM 1Z I,NG

INDU STR IAL PRO CESSES ,

INTERNATIONAL ATOMIC ENERGY AGENCYREGIONAL COOPERATIVE AGREEMENT


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CONTENTS

Introduction 2Gamma scanning of Columns, Vessels and Pipes 3Gamma-ray Scan Methodology 5Planning of a Gamma-ray scan Investigation 12Raclioisotope Activity Calculations 13Gamma scanning of clifferent columns, case studies 18Pipe Scanning 34

eutron Backscattering - Detection of Level and Interface 40Radiation Safety 46The Benefits of Industrial Applications of Radioisotopes 47Conclusions 52References 52


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RADIOISOTOPE APPLICATIONS FORTROUBLESHOOTING AND

OPTIMIZING INDUSTRIAL PROCESSESFOREWORDRadioisotopes were first applied for industrial problem solving around themiddle of the last century. Si.nce then, their use has increased steadily. Todayradioisotope techniques are used extensively throughout the world fortroubleshooting and optimization of industrial process plants.The economic benefits that may be derived from the use of radioisotopetechnology are large, a fact that has not been fully recognized by thegovernments of developing countries. Among the developing Member Statesof the IAEA) nearly fifty have radioisotope application groups.This Brochure on Radioisotope applications for troubleshooting andoptimizing industrial processes is intended to present the state-of-the-artin technigues for gamma scanning and neutron backscattering fortroubleshooting inspection of columns, vessels, pipes and tanks in manyindustrial processing sectors. It aims to provide not only an extensivedescription of what can be achieved by the application of radioisotopesealed sources but also sound experience-based guidance on all aspects ofdesigning, carrying out and interpreting the results of industrial applications.Though it is written primarily for the radioisotope practitioners, theBrochure is also intended to function as an ambassador for the technologyby promoting its benefits to governments, to the general public and toindustrial end-users.The Brochure is prepared under the RCA activities. The IAEA/RCA isgrateful to many RCA experts in the field who contributed to thispublication, in particular to A. Hills, who drafted the Brochure, as well asto J .S. Charlton and Gursharan Singh, who reviewed it . The IAEA/RCAofficers responsible for the publication were C. Aleta, RCA Coordinator andJ . Thereska of the Division of Physical and Chemical Sciences.

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RADIOISOTOPE APPLICATIONS FORTROUBLESHOOTING AND OPTIMIZING

INDUSTRIAL PROCESSES

1. INTRODUCTIONPetrochemical and chemical process industries are the main users andbeneficiaries of the radioisotope technology. Radiosotope techniques are verycompetitive and are largely applied for troubleshooting and process analysis oftechnically complex, continously operating industrial plants. The success ofthese applications is attributed to their unique ability to provide informationwhich otherwise cannot be obtained by alternate techniques.The benefits of applying radioisotope techniques in industry are derived from;

Troubleshooting - Radioisotope technology is used to diagnose specificcauses of inefficiency in plant or process operations. In many cases,the benefit is derived due to the savings associated with minimizationof plant shut-down and prevention of production losses.

Process Optimisation - Radioisotope measurements provideinformation that facilitate improvements either in the throughput orthe product quality

TIlls Brochure on "Radioisotope applications for troubleshooting and optimizingindustrial processes" aims to provide sound, experience-based guidance on allaspects of designing, carrying out and interpreting the results of industrialapplications. Though it is written primarily for the radioisotope practitioners,the Brochure is also intended to function as an ambassador for the technologyby proa:oting its benefits to governments, to the general public and to industrialend-users.The major radioisotope s~aled source techniques and applications presented inthis Brochure are gamma scanning of columns, vessels and pipes and level andinterface detection using neutron backscatter technique. These largely used

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techniques help to obtain a clear "inside view" of processing equipment forprocess troubleshooting without the expensive costs of a shutdown. These aremost useful on-line and non-invasive techniques to troubleshoot and optimiseunit performance.The examples described in this Brochure clearly demonstrate the potential valueof industrial radioisotope applications. Probably, an average benefit to cost ratioof 20:1 - 50:1 is reasonably representative. There are a few short-terminvestments, which will give a return of this magnitude. The cost effectivenessof radioisotope applications should be widely promulgated to encourageindustrialists to take full advantage of the technology. That being the case, it issomewhat surprising that industry does not use the technology more widelythan it does at present.1.1. Gamma Scanning of Columns, Vessels and PipesGamma Scanning is the best technique to carry out an internal inspection ofany process equipment, without interrupting production. A collimated beam ofpenetrating gamma rays is allowed to pass through the shell of a vessel, getsmodified by the vessel internals and then comes out of the other side. Bymeasuring the intensity of the transmitted radiation, valuable information canbe obtained about the densities of the materials present inside the vessel. Thehigher the density of the material, the less radiation gets through; so significantlymore gamma rays are transmitted through a vapour compared to a liquid phase.Density scanning of distillation columns is the most commonly used applicationof this technique. \Xlithout affecting processing unit, this reliable and accuratetechnique can be used to determine:

The liquid level on trays The pr~sence or absence of internals, such as trays, demister pads,

packing and distributors The extent and position of jet and liquid stack flooding The position and the density characteristics of foaming

Gamma ray source and radiation detectors are moved simultaneously downopposite sides of the column. The intensity is recorded at appropriate intervals

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and a profile of the instantaneous operating state is obtained by plotting thedetector response against the column elevation. The tray structure and the liquidon the trays give high absorption, while the presence of foam and entrainmentslightly moderates the expected vapour profile. Studies of the degree of foamingcan be carried out by generating density profiles at different concentrations ofantifoam additive.The scanning of pipelines for detection of blockages or build-up is anotherexcellent use of Gamma Scanning because it is faster and uses lower intensitysources than conventional radiography testing techniques.Level and interface detection by neutron backscatter technique;'Without affecting the process, neutron back scatter techniques can:

Determine liquid and sludge levels in storage vessels Locate water/organic interfaces Measure foam levels Determine absorption tower packing levels Calibrate level gauges quickly and easily

Neutron backscatter level measurement gauge can detect interfaces betweensolids, liquids and vapour to an accuracy of approximately 2 ems. Vessels canbe almost any diameter, with wall thickness up to about 100 mm. The detectionequipment is external to the vessel so these measurements are applicable to anyprocess material- whether it is toxic, corrosive, or viscous) and at any temperatureor pressure. These techniques even permit calibration of installed level gauges.Solid/liquid and liquid/liquid interfaces are best detected using Neutron Backscattertechnique. High energy or " fast" neutrons from a radioactive source are beamedonto the vessel and slowed down by collision with hydrogen atoms in the processmaterial. A direct hit results in a slow neutron being bounced back towards thesource. By placing a slow neutron detector next to the source, these backscatteredneutrons can be measured and their intensity is directly proportion to theconcentration of hydrogen atoms in process material As the source and detectormove down the side of the vessel, interfaces can be detected provided theyinvolve a change in hydroge~ atom concentration in contents of vessel.

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2. GMfMA-RAY SCAN METHODOLOGY2.1. General principlesThe intensity of gamma radiation absorbed in the material between theradioactive ource and detector is described by the transmission law:

where:I is the inten ity of radiation transmitted through the material1 0 is the intensity of incident radiationjJ - is the mass absorption coefficient of the test materialp is the density of materialx is the thickness of material (radiation path length)

This basic equation is used for experimental design, measurment, data processingand interpretation of gamma-ray absorption scans in column, vessel and pipes.

Table 1 .: CommonJy used gamma sealed sources for industrial scanningRadioisotope T1/l Energy (MeV) Gamma constant

Riht CLmCs-137 30,2 y 0,662 (89,9%) 0,399

5,27 y 1,173 (100%) 1,31Co-60 1 . ,332 (100%)The experimental design of gamma scanning is presented in the figure 1.

Radiationdetector

r " " 'II ,I I

I~I I

, ,........ iiIi_

sourceiGammaFlg . 1 . S ource-de te t tor c OJJ fig ura lio 17 ill p flljo rJ7 Jil1 g g aJ 1lm a SCa 17 Jlm g o f a column

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The radioactive source is positioned into a panoramic collimator (360 grade)(Fig. 2)

Panoramic scan pot container

F ig . 2. S ou rce pa no ram ic co ll im ato rThe principle of gamma scanning profile is illustrated by the figure (3):

Liquid line Gas line

...._ .....)u------ _------ ------ f7. . J ,_ _

1/

Count rateF ig . 3. Principle o f g am m a sc ann ing profile

When scanning a distillation column or a similar vessel, a small suitably sealedgamma radiation source and a detector (NaI/Tl) are moved concurrently insmall increments on opposite sides, along the exterior length of the vessel. Arelative density profile of the contents of the column is thus obtained; areascontaining relatively high density material (such as liquid and/or metal) providea relatively low intensity of transmitted radiation, while areas of relatively lowdensity (vapour spaces between trays) result.in a high intensity le el. Deductions

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can be made regarding possible mechanical damage of trays inside the unit, aswell as with regard to certain operational conditions in the unit, such as flooding,blockages, weeping and other process anomalies. The figure below shows on-stream gamma scanning in petrochemical plant in progress (Fig.4).

F ig .4. P eJjo rm in g g am m a sca nn in g 0 / d is tilla tio n c olu m n in p etro le um rifin eryComparing mechanical drawings with relative density profile (gamma absorptionprofile) of a unit, deductions can be made with regard to:

Presence or absence of trays and other internals inside a column Presence and formation of coke Location and extent of flooding Blockages caused by ;

downcomer obstruction tray fouling, dirt or high liquid loading on trays

Location and severity of entertainment Presence of liquid weeping Top and bottom positions of packed beds Maldisrribution of packing material in packed beds Liquid levels on trays

Repeating scans under different operating conditions such as, temperature,pressure, feed flow rate and reflux ratios can obtain additional information ondegree of entertainment (carry over of liquid) , tray and "jet" flooding and foamingor "weeping".

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Importan t Points :When radiation from a radioactive source passes through a mediumcontaining a tray with aerated liquid, much of the radiation is absorbedand the amount of radiation reaching the detector is relatively smallIf a radiation beam passes through unaerated liquid, most of theradiation is absorbed by the medium, and the intensity is low

When radiation beam passes through vapour, there is little mass presentto absorb the radiation and therefore high radiation intensities are

transmitted to the detector.A gamma scan of a vessel can detect and locate liquid and vapour regionswithin a column. It can discriminate between aeration of liquid and detect foamor spray heights invapour regions. By measuring and analysing density changes,many parameters indicating column performance can be obtained. Each trayand the vapour space above it "tells the story" of its operating status. A properlyoperating tray has a reasonable level of aerated liquid showing a rapidly decreasingdensity gradient until it reaches a clear vapour space just under the next tray. Todistinguish the above symptoms, experience is required. Gamma scanning isthe only diagnostic tool available that can be applied with confidence on anydistillation process to obtain the true hydraulic behaviour of the system. Theresults of the scan can be immedietely discussed with process engineers so thatthey can take remedial action.

Liquid line}c5::j"0u

Gas line

8F ig . 5. Scanning profile o j a norm al dis ti!!a#on colum n

Count tate


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Trayed Tower Diagnostics

Count rate

Collap ed tray

Fig. 6 . G am ma pm jile o f c olu m n p art J p i t h co/ lapsed trq)!

Count rate

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10

Flooding

Obstruction

Count rate

F 2 g . 7 . Gamma p rr ifil e o f part o f c ol umn w it h fl oo di ng

ntrainrnent

.... _ ~. '''''' h u~ ~ "" u.n, .u L.,.. u

~ ....v n.... u.u ............. ;;._ ~ t",L ~~~

Count rate

F ig .B . G am ma prq fife o f CO/f,fmn pa rt w ith en tra in men t (d ra gg in g)


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I: I

\Xieeping

..................................................... " .., - - _ . . . . . . . . . . . . . . . . . . . . . . . . _ _-Count rate

F zg .9 . G am ma pn:ftle o f tl column part lVitb lJ!eepiJlg {sboner)

Foaming

Count rate

F ig . 10 . . G am ma scanning o f t ! c ol umn s ec to r J J J i t h foamil1g

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2.2. Planning of a gamma-ray scan investigationThe following data is required before a scan can be carried out:

inside diameter and wall thickness of the column (mm)bulk density and type of packing material, for packed bedsdowncomer orientation and type of trays present (single, double passtrays)operating problems experienced, e.g. low or high-pressure problemsacross the column, or temperature differences along the length of thecolumn

detailed mechanical drawinzs of the unit showing internal structure,such as elevations, tray or packing assemblies, nozzle and pipework

locations as well as other special features.Such information is vital for interpreting data from column scan profiles obtainedand for identifying and visualising possible mechanical problems. The followingadditional information is useful:

gamma scan profiles of an "empty" column (with all the internals butnot in ~peration)

a scan profile before a maintenance shutdown a scan profile after a maintenance shutdown when the column is under

normal operating condition.There is a clear difference between an empty (dry) and normal (wet) scans( Fi g. 1 1) .

- Empty scan- 1 ormal scan

12F i g . 1 1 . Exm'1tple o f empty ( d r y ) and norm al (w et) scan profiles


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It i very important for cornpari on that the can is carried out along the samescan Lines (lines between the radioactive source and detector). Measurementsmust be taken out at small intervals (less than or equal to 50 mm).2.3..Radioisotope activity calculationsA typical radioactive sealed source used for gamma-ray scan of a distillationcolumn is only approximately 0.1 % of the strength needed to investigate weldsby radiography testing. Co-GO and Cs-137 are main sources used for gammascanning. The activity required depends of the column diameter, ranging from5-10 mCi for 1-2 m up to 60-70 mCi for 5-6 m and higher for greater diameters.Estimated source strength can be calculated as follows:

Activity A = (D. (d) 2. (2) Wt/hJ) /T\X1hereD = dose rate required (mR/Hr)d = diameter of column (m)wt = total wall thickness of column (mm) + wall thickness of scan container.h1 = half layer thickness value of material (25 rnm for steel for 60Co)T = ganuna-ray constant for a specific source

(1.31 R/h on a distance of 1 metre for a 1 Ci 60Cosource).When using the above equation it is suggested that 200 rom be added to thediameter of the column to make provision for the source and detector containeron the outside.The above equation is an approximation, and build-up factors of the materialare not taken into account. Shielding calculation software can be used to greatereffect. It is further recommended to work with a maximum count rate ofapproximately 7000 to 9000 cps through the vapour space (gas line) of thecolumn. The count rate decreases to approximately 1000 cps at the position ofthe trays and liquids (liquid line). This count rate range ensures good statistics.ExaJ7lple if activi t )! calculation: A Stripper distillation column needs to be scanned.The inside column diameter is 2.9 m. and wall thickness 15 mm. The sensitivityof a NaI/Tl detector can be measured placing a 6fJCoor a 137CSradioactive source

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at the distance from the detector, where the dose rate is ImR/h. The sensitivityof a normal scan detector (2" x 2" NaI/Tl) was found to be 7500 cps/mR/h.This means that 1 mR/h is necessary for good statistics. It fact, dose rates ofapproximately 0.5-1 mR/h at the position of the panoramic collimated detectorprovide clear gamma profiles.Lees calculate the activity of a Co-60 source that is needed to obtain a cleargamma profile of this column. The gamma-constant for Co-60 is 1.31 R/h.Calculations are based on a typical panoramic scan pot.Activity = (D . (d)2.(2)wt/hl)/T = (1.(2.9+.2f(2) 3/2.5) /1 .332 = 29.4 mCi 60(0For 2-3 m. diameter columns Co-60 source activity of 15-20 mei is quite enoughto provide a good picture of the internal structure.2.4. Scanning proceduresThe following procedures are recommended for gamma scanning set-up:

Obtain detailed mechanical drawings of the column. Request assistance from the process or chemical engineer for process

details. Obtain operational data before, during and after scanning Decide upon scan line orientation and number of scans. Check for source and detector alignment every 50 em. of scanning Note any unusual reduction ~n radiation intensity due to external

obstruction on the column.

To conduct a tray-column scan, it is advisable to execute a scan across the traysand to avoid scanning through the downcomers of the trays. Typical andrecommended scan line orientations for trayed columns are shown in the followingfigure 12.

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-. . .-.~-. .-..- . . " "Single: pass-trays Double pass-traysTwo pass-trays

Detector

Radioactive source . .@Radioactive source

,

-+.-.~-..,-.,-,...Quadruple pass-traysMulti pass-trays

Detector

. .Radioactive source

F ig 12 . 1 Jp ic a! S ca n l in e o rie nta tio nsGrid ScanningGrid scanning is recommended for packed bed columns. A typical orientationof grid scan lines is shown in the next figure 13. At least four scans arerecommended to examine a packed bed column.Grid scans may be conducted to investigate process-related conditions such as:

flooding or blockages entrainmerit or carryover of liquid or rnaldistribution of liquid flow through packed beds.

Grid scans can also be used to investigate mechanical construction problemssuch as:

collapsed packed beds or maldistribution of packing material.

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An important factor to take into account is that as far as is possible the operatingconditions (such as feed rate, temperature and other process parameters) mustremain constant especially during the scan investigation. It is very important torecord any process changes during the time of the scan. This will facilitate theinterpretation of the scan. profile if anomalies are observed. Grid scanning isrecommended on packed columns with diameters up to approximately 3m. Largerdiameter columns must be approached in a different way, since too large an area(especially in the centre) is not covered.

.~. Radioactive source

t .. ... . ..-'. . . . . _ .._ . .,_ ..I I I I _,..L,.._ ..'_..:_..'_-, .t .'.-.~( : P ) Detector

F i g . .1 3 . . Crientations oj grid s ca n l in es

Grid scannillg is also useful for investiga ring the correct installation of distributorsas well as the correct distribution of incoming liquid feed. An irregular distributorcan undermine the performance of the entire packed bed and column. Liquiddistributors must spread liquid uniformly on top of a bed, resist plugging andfouling, and also provide free space for gas flow. An incorrectly water levelinstalled distributor, that is a tilted distributor, could cause liquid to flowpreferentially on one side of the column.

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Packed Tower Diagnostics

East

South

10 c0 00 ; r00.5 I 1.5 2 ~5 1 3 . . > t5 , 5. 6 6.s 1 ?,s 8 s , . , ~

- Eesr - ,"(1e5[ - Norm _ South

F ig 1 4. Typica! packed colunm g rid scan lines

Typical Game-ray scan equipmentF z g.1 5 . T ]p ic o/ equipment usedjor ,gammo scanning

Detector Container

DetectorPanoramic scansource container

Detector cableRaterneter

Clamps

Cable reelsPalmtop Computer

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2.5. Gamma scanning of different columns, case studies2.5. 1 . S tr ip pe r c o/u ll inProduct purity problems were experienced and could not be solved during theoperation of the stripper column. It was presumed that collapsed trays ormalfunction areas inside the column could be the cause of the problems. Agamma-ray scan was consequently carried out on the entire length of the column,using a 15 mCi 6OCoradioactive source. Obtained scan profile is showngraphically (Fig. 16). The following deductions were made from the scan profile.

GAMMA SCAN PROFILE ON STRIPPER COLUMN0.0 -------~-------- ........-- ............~--.J..-REFLUX-------~ __ ~__ - -~~~ ~ TRAY I1.0 J ~ ; ; : : = = = = = = ~ = : = : : = = : - : = : " ' ~ = - -TRAY 2I : . - TRAY 32.0 --- = - - -3.0 ::::-:::::=~~-------:-_._:__= : = = ~~VlBUTOR

. ~----""""" .................--~- . ------ TRAY 54.0 L_ .___ :::::... ----- SUPPORT------------ ~ ---- TRAY 6

5.0 TRAY 7" " ! >- . _ " , , : ; ,- , , , -- - - - . . . . . . . .- - - . . . . . _- - - - = = : ; ; 0 ; : ; 0 ; ; : ; ; ; : ; ; : : ; : : - - . -_", -- TRAY S6.0 ._----- .....------...::;;;=~;;;;::;;~~----: : : . .- ~ ~ - - - - -- - - - .-oo:;;;=;;;:;;~:E~.~~~~ - - - TRAY 10:>-----------_-=-::!!El~~~---' " ' : : : : : : 08.0 - - - - - - - - - - - - -= : ;; ;W i iO W i i; :; ;; ::= ; ;: :: :~~-- - : - TRAYI2- - - - - - - - - - - - _ : a : ; ; ; y ; ; ; ~ : : : ; ; ; : _ : : : : - ; ; : ~ = ~ . : : : - = - -- - - TRAY 139.0 ~ ~e:=;:=:=:::~~3.=.---- TRAY 14~_ . . .- - - - - - - - - - - = - : : ! ! : ! ! ! l ~ ~ = = = = = =- - - - TRAY '15::t I--------------_c;;;:;--'~~:::---- TRAY 1 6:-:-">----------...,_===~~~~~=.---- TRAY 17- - - - - . . . . .- - - - ~ ~ = : : : ~ ; ; ~ ~ ~ . : : : : : : > ~ : - -- - TRAY I B1----------- TRAY 19~ - - - - - - - - - - - - - - - ~ ~ = ~ ~ ~ ~ ~ - -::::-

TRAY 9

7 . 0 TRAY II

1 0 . 0

11.012.013.0 TRAY 20

TRAY 21DRAW-OFF14.0

-----~~--~----~---~-----------,__.----._,-----~ . . . . . -~;15.0 -------'------------ -~ --- CHIM EY- ;I : = = : ; : : = = ~ ~ ; ; : = ; : = = = : : : ~ ~ : : : ~ ~ . - jBJ\SE LEVEL17.0 ... ..10016.0 1000 1 0 0 0 0 0

TRA S llTTEO RAOIATIO I TE SlTY (C NTS PER 0 D)F ig . 1 6. G am ma scan profile o f a stripper co lum n

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Tray 1 was in position and carried liquid. Tray 2 appeared to be in position.Abnormally high absorption density material was observed on tray 3 (relativelyhigher than liquid, indicating the presence of solid material on the tray, and lowcount rate). A deviation from the expected profile was measured between tray 2and tray 4. This indicated a high liquid level on tray 4, and could be attributedto a blockage on the tray or in its downcomer. Poor liquid/vapour disengagementwas measured in the vapour space between tray 2 and tray 6.An unidentified object, not indicated on the mechanical drawing of the unitwas located between tray 3 and the distributor. Distributor may be functioningabnormally.A relatively low liquid level was recorded on tray 20, indicative of partial damageto the tray. From the regular attenuation "peaks" coinciding with tray positionsit was concluded that all the trays from 6 to 19 were in position and carriedapproximately the same amount of liquid.The fact that the signal level recorded through the vapour spaces between trays20 and 21 did not return to the vapour base line, indicates poor liquid/vapourdisengagement between them. This may have been the result of weeping oftray 20. The same effect was evident between tray 21 and the draw-off line.The liquid base level was located at 16.6 m.2.5.2. Flooding in a pre-tractionetion columnThe primary function of the pre-fractionator is to split the incoming condensate(crude oil) into two components. The heavy component goes to the bottom,portion of the column, which consists mainly of components heavier thankerosene. Light components, which consist mainly of naphtha, are extracted atthe top of the column.Product problems were experienced with the operation of a pre-fractionationcolumn. Gamma-ray scans were consequently carried out to investigate andlocate possible malfunction areas or anomalies inside the column.A 7 meter portion of the column from tray 21 downwards was scanned undertwo different crude feed conditions namely 18000 barrels/day (blue line) and15000 barrels/day (black line). A 30 mCi 6 0CO radioactive source was used, andthe scan profiles obtained are shown graphically (Fig.17).

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SCAN PROFILES OBTAINED ON PRE-FRACTIONAL COLUMN

20

uuc5'"o

7.0Tray 21..-------_.._---- ~....== - _--'T' ! Iw~ ~_~-----.--:. :t- - - ~ - - - - - - - - - - - - ~ ~ - - - - -:IIIII_, _iIIif __ ... .... _I,I- - - - - . . . . .- - - - - - - - - , . - . . . .- - - ' : . : - = i ! ! ! = : ! 5 l ; ; ; ; : : ; ; ; ~ ~ : ; ; ; ~ : ~ - - - -. . . .r - - - - -tTray 25 I- - - - - - - - - - - - - - - - - - - - - ' I I . . .- : ! ! : ~ ; ; ; : : : : : : : : ~ - : - : - : _ - ~ - : - - r - - - - -~ :. ,II-- .- - - ~ - - - - - - - - - - ~ - - - - -- - ~ - - - - - - ~ = = = = ~ ~ ::t- - - - - - - - - - - . - - - - -I;1II- - - - - - - - - - - - - - - ~ - - . - - - - -I- - - - - - - - - - - - - - - - - - - - - ~ - - - - --~ III- - - - - - - . . .- - - - - . . .- - . . . .- . . . .- - . . .- . . .. _ ~ - - - - . c : : : a i : : : : : - ~. . .: - : _ - - ~ - - - - -,,:

- - - - - - - - - - - - - - - - - - - - ~ - . . I O " " ' : : : = " " " " " ' ! ! : ' : : ; ; : : : : : - : - : = : : : : : : .~ - - - - - - - - - - - - . - - - - -II

6.5 -Tray 226.0 - _ - - - - -5.5 Tray 23- - - ~ - - ~ - - - - - - - - - - - --.-.-:-5.0 Tray 24

4.5

4.0Tray 26- - - - - - - - - - - - - - - - - - - - -3.5

3 .0 Tray 27

2.5 Tray 28-------------------...--...' II!!t: ; .c:~~~i~;~~;:~~2.0 Tray 29- - - ~ - - - ~ - - - - ~ - - - -1.5 Tray 301.0

Tray 310.5

0 . 010 100 1000TRA SMITfED RADIATION JNTE SlTY (COU TS PER S CO D)

F ig . 17. G amm a s ca n p njile if a pr ejr ac tio na tio n c ol um n


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The following deductions were made from the scan profiles: An abnormally high liquid level was measured on tray 22 in the blue

scan line. This could be attributed to a partial blockage in thedowncomer of the tray or on the tray.

Poor liquid/vapour disengagement was recorded between trays 22 and21. This could be due to liquid entrainment (carry over) from tray 22to tray 21.

The relatively high liquid level recorded on tray 21 could be due liquidentrainment from tray 22 to tray 21 (most probably).

A relatively high liquid level was recorded on tray 29 during bothscans. This could be attributed to incorrect functioning of the traywith possible fouling (dirt) on the tray causing a slight downcomerbackup of liquid.

An abnormal low liquid level detected on tray 30 during both scanswas measured. This confirmed that tray 30 behaved abnormally (anindication of tray damage).

The scan carried out under a feed rate of 15 000 barrels oil per day (black line)indicates that:Try 21 and 22 were normal as expected. This behaviour confirmed that tray 22functions abnormally (blue line) under a high feed rate condition. The indicationis that under a high operating condition a resistance to the downcomer flowexists, effecting of a build-up of liquid in the downcorner of tray 22.From the regular attenuation "peaks" coinciding with tray positions it is evidentthat all the trays in tills portion of the column were in position and carriedliquid at the rime of the scan.The signal intensities recorded through the vapour spaces between the trayswere at approximately the same level, indicating good liquid/vapourdisengagement in these areas.Observing more in details the tray 22 and 21 it can be seen that:

Liquid level on: tray 22 (15 000 barrels/day black line) z; 150 rnrntray 22 (18 000 barrels/day blue line) = 360 mm

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The decrease in radiation intensity or the increase of vapour density betweentra 22 and 21 (blue line) is due to the existence of liquid entrainment andfoaming. The difference or reduction is 65% in radiation intensity. Thereforetray 22 is heavily flooded. Tray 22 is heavily flooded, with a high degree offoaming. This happens at 6.3 m to 6.5 m.2.5.3. Feints distillation column: Flooding as a result of deposit (debris)

in the downcomerThe feint column forms an important integral part of a system producing canespirits (alcohol) from sugar. The column contains sieve trays with single passdowncomers.After a certain period of production, the column appeared to be hydraulicallyunstable. The overall pressure drop across a stripping section was erratic andhigh. The column fluctuation pressure drops indicated flooding. Because thepressure drops in the fractionating stripping and rectification sections could notbe measured separately, it was not possible to locate the flood-point, In order toinvestigate and locate possible anomalies inside the column, gamma-ray scanswere carried out for two different operating conditions, under normal.productionrate and under the upset condition. .The first scan was carried out after the reflux rate was lowered until the columnbecame stable. Raising the reflux only a little, made the column unstable. Thissensitivity to a liquid rate suggested a liquid flow-path problem, such asdowncomer flooding.The 600 mm in diameter column was scanned using a 50 mCi 13 Cs radioactivesealed source. High contrast obtained using Cs-137 source allows theinvestigation of small deviations from normal operating conditions.

F~g .18 . A lc oh ol d is tifL a tio fl c ol umn22


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'=t f


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The column was opened and revealed that the clearance in the downcomer oftray 12 was completely filled with loose scale and fiberglass gasket material.The clearance problem was mainly caused by scale and dirt (rubbish) left on thetray support during installation. Corrective actions were taken and the tray anddowncomer cleaned. The column was restarted and operated properly at thedesigned capacity;2.5.4. Visbreaker distillation column, coking depositProduct quality and temperature problems were experienced with a Visbreakerdistillation column at a petrochemical plant. A gamma-ray scan was conseguentlycarried out to investigate internal tray damage, collapsed trays or other anomalies,which could have affected the performance of the column. Due to limited access,the scan was carried out through the downcorners.

I ! I, . .Malfunction area coki ng i: I : 1! ! I . .I :Distance in metres

24

JJJ


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The following observations were made from the scan profile:a) Trays 22 to 15 were undamaged and operational, but were located

approximately 200 mm above their indicated positie>nin-the mechanicaldrawing of the unit ..The width of the trays "peaks" indicated that thetrays held approx.imately the same amount of liquid at the time of thescan. The slight variation in the radiation intensity level observed inthe vapour spaces between trays were probably caused by variationsin the amount of liquid passing down the downcorners, through whichthe scan line passed.

b) A low intensity of transmitted radiation was recorded throughout theentire region between trays 15 and 5. This could have been caused eitherby a blockage in the downcomer of tray 5, resulting in a liquid build-upon tray 15, or by a solid deposit of some material in this area. Afterdiscussions with plant engineer, it turned out that the latter possibilitywas more acceptable, as recent maloperation of the column could havecaused the formation and deposit of carbon (coke) in this region. Thetemperature. distribution along the column length, as welJ.as the pressuredrop across the unit, supported this conclusion. Due to the low level oftransmitted radiation, no conclusion could be drawn with regard topossible damage to trays in this region. The additional attenuation "peak IIbetween trays 16 and 15 was also attributed to coking, as it did notcoincide with any mechanical structure in the column,

A higher radiation level was recorded in the region below tray 5 down to about20 m. The level was however, not quite as high as observed in the vapour spacesbetweentrays 22 to 15, indicating a sl ightly higher vapour density in this region.2.5:5. Gemme-ray scan investigation 011 a crude columnA gamma~ray scan was carried out on the lower portion of a crude column inorder to investigate possible tray damage and anomalies, which could haveaffected the performance of the column.

. . . . .. , ~ . , .. . \ " ' 1 .-. - iB o tom sectionw - - . . . . .

, with downcome rsTop portion

Orientation p( scan line

F ig .21 . Gamma scan line orientation on a crt/de co lum n25


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Two separate scans were carried out on the bottom portion of the urut, viz.from tray 36 downwards and from tray 41 in the bottom narrow section. Thesame scan line (lioe between the source and detector) was used during bothscans.

'" C>-' >-le , p : : ; I IL l 0C , N , I ,.J~ , ," "';j- '" , 'D 0 ::t1- - e - 'd" 'd" v , v IL l, , 0.. , Ze-, t 0-. >. ~. s-, I >. 0.. , v:'" , ee '" 8 '" , '" I < : : 5~ , . . . . t = ; ~ '-< ; : : : . , 1 - < r f~ U) , j:Q ~, ,101 2 bistance 4 6In metres

26

Scan profile obtained on a protion f a crude columnF ig .22 Gamma scan profite 0 / a po rt io n 0 / a crude o il co lum n


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The following d ductions were made from the scan profiles obtained: Trays 36 to 39 were in position and carried approximately 150 to 200

mm of liquid. ~ Tray 40 carried less liquid than trays 36 to 39 (approximately 80 mm).

This could have been caused either by a different design of tray 40, orby damage to this tray.

The scan profile showed that clear attenuation "peaks" were observedonly at the positions of trays 41 and 46. The gradual decrease of thesignal level from just below tray 41 to tray 45 suggested a build-up ofliquid in this region and from the fact that clear liquid/vapourdisengagement was not observed at the tray position i t is deducedthat trays 42 to 45 were damaged.

The scan on the bottom portion (tray 51 to tray 46) was carried out at the samedistance (distance between the source and detector) as in the case of the topportion. Due to this and the fact that no access was available to scan it closer tothe column, resolution was not as it should be. Build-up of liquid started fromtray 45 upwards and therefore tray 45 was the suspected bottleneck.2.5.6. Wash vacuum column-Collapsed bed with anomalies

\l~'-III '"

0000: : :~ ,ouu


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Observations: Bed 1 (red line) was flooded with excess liquid in the bottom section.

This can be attributed to fouling or heavy, dense dirt in the bottomportion of the bed.

Bed 2 (red line), contained less liquid than green line. Accumulationof more liquid at the top portion of the bed (red line) was assumed,which also depends on the operating condition of the column duringthe scan.

Bed 3 (green line) indicated maldistribution of packing material, thatis less densely packed in the indicated area.

Bed 4 in both cases, functioned normally and as expected with goodliquid/ vapour distribution.

Bed 5 (green scan line). Bed had collapsed, which means that therewas no packing material to be measured. This could be due to acollapsed support plate at the bottom of the bed.

The internal diameter of the column was 5000 mm, and a 50 mCi 60Co sealedsource was used. The two columns scanned were identical. Only one scan anglewas necessary, to obtain the required information.The columns were open and positive feedback was obtained. The bottom bed(green line) had collapsed and the top bed (red scan line) was heavily loadedwith dirt and broken packing material.2.5.7. Coke formationA distillation column where coke is formed during operation, was studied withgamma absorption method. First measurement was done after a thoroughcleaning of the column and successive measurements were done in order to geta picture of the temporal build up of coke.A 15 mO 60Co-source was used for the s.canning Transmitted gamma radiationwas detected using a 2x2 inch alerl) scintillation detector. A single channelanalyser was used for energy discrimination and the counts were recorded witha portable Pc. Detector and source were m ved on opposite sides of the columnusing wire ropes and winches. Vertical density profiles were obtained and changesof density were calculated. The trends for coke build up seemed to be almostlinear (Fig.24). A rapid and relatively large coke forrnati n was measured forthe present case.28


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ince energy discrimination was applied the basic absorption formula was usedto measure coke thickness with good accuracy:

I = 10, exp(-IlPx).Density of the coke was assumed as 1000 kg/m3 and mass absorption coefficient0.006 m2/kg was used.

~V>o0..v"U'-'-'"ov. . . . . .o

Gas space below the GE1vIPAC-gridGas space below the middle output

15

10

5

oo 20 40 60 80 100 120 140 16 0

Fig . 24. C oke form atio lt a t ulol! o f main COblfi11l o f a th erm o! c ra ck in g piaul2.5.8. Grid scan on a Ketone structured packed bed column

The main function of the distillation tower is to separate M.E.K. from acetoneand water. Temperatures above designed set point will cause a carryover ofM.E.K into the overhead outlet line. Temperatures below the set point indicatelight material in the bottom, which is the reason why M.E.K. is not separatedaccording to specification.After a rnaintenance shutdown and under normal operating conditions,temperature distribution and separation problems were experienced with theKetone column.

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Scan profiles obtained on packed bed

10000~'"c,~C oC~cc :s 1000ee: . : a"p o :

'Ut ; ;'EU)c'"t= :

- North_ South- East- West

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Distance in metres

Fig.25. Gamma scan pnjile o f a Ketone packed columnA grid scan was carried out on the top structured packed bed to investigateand locate malfunction areas in the bed. The scan was performed along fourequidistant cord lines as indicated in the orientation. In order to distinguishsmall deviations in the bed, a mes radioactive sealed source was used andthe results are shown graphically in the Figure 25.For a uniform distribution of packing material and liquid flow through the bed,all four-scan profiles obtained should show the same amount of gamma-raytransmission, and therefore would overlap almost exactly. This would be true,assuming there is no interference from column stiffening rings, manholes, flanges,insulation rings etc. and that a perfectly even cord distance between detectorand source are maintained. Less gamma-ray transmission through a chord wouldmean larger amounts of liquid (more liquid hold-up or more liquid flow) in thepath of the cord. Any significant deviation of the four curves is an indicationof maldistribution in the bed.From the scan profiles obtained as indicated the following deductions weremade:

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From the radiation intensities obtained at the position of the distributor it wasconcluded that the distributor was intact. Low radiation intensities were recordedbetween 0.6 m and 0.9 m just above the bed and below the distributor along aUfour-scan lines. This measurement cannot be related to struc ures in themechanical drawing of the unit, but can be attributed to liquid accumulation ontop of the bed just below the reflux distributor.The scan along the west scans line (violet line) deviates from the expectedprofile. The density of material in the path length between the source and detectoris less dense than that recorded along the other three scan lines. This can be dueto less liquid in the path length between the source and detector.After the investigation the column deteriorated and was opened. It was confirmedthat the top bed was damaged and blocked by hard paper (cardboard) whichwas left after the previous shutdown.2.5.9. Tilted distributor of a packed bed

The following case study concerns an excessive liquid flow through a packedbed resulting in non-purity due to an insufficient liquid-vapour contact. Thisleads to sharp temperature fluctuations and difficulty in controlling them. Thecolumn's efficiency is much lower than expected.The main purpose of the present vacuum column is to separate methanol andwater from ethylene. Control problems were experienced during processoperations; an excessive amount of ethylene glycol was measured at the overhead.This happened after commissioning.Itwas assumed that the following could be the cause of malfunction:

dislocation of distributor and! ordistributor plugged orifices .This in turn can lead to poor distribution of liquid through the packed bed.High separation performance of packing is achieved only with high-precisionliquid distributors.

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Gamma-ray scans were consequently carried out as an inspection tool. A 30mCi mes sealed source was used, and the resulting profiles through the relevantpacked bed are shown graphically (Fig.26).From the scan profile responses, it is clear that the packed bed column wassuffering from liquid channelling. On examining the grid scan, it was observedthat the four density profile lines did not overlap. Ifall four-scan lines are exposedto the same liquid/vapour flow path then all four-scan lines should overlapexactly. From the scan, it is clear that this was not the case, and therefore it isassumed that the most uniform (bottom line) is carrying a heavier liquid loadthan the other scan lines through the packed bed.It was concluded that the liquid distribution was uneven and the distributormight be dislodged or plugged, resulting in liquid overflowing to one side of thecollector. This caused the liquid to flow down one side through the bed ofrandom dumped packing.After shutdown of the column, the distributor was found to be tilted (Fig. 27).This caused it to dump all or most of the liquid downs one side of the column.\-'\!hen the column ~as started up again the desired separation was achieved.

Vapour Phase base line

Liquid Phase base line

> rid sc an fOT a co lum n w irh liquid ch anneling

Fig . 26 . Gamma l !, ri d s ca n p ro fi le s o f a packed bed coittm n32


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Two types of structured packing

ollapsed bed: Support plate has collapsed dumping packing bed contentsat [he bottom of m e column.

F ig .2 7. S tru rtu re d po rk iJlg ill pC lrktd bed (oIUJJlIl a nd b ed ro /la ps e

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3. PIPE SCANNING

3.1. Principles and applicationsPipe scanning technique in fact is a derivation of gamma scanning techniquefor pipes. It can be used to detect:

solids build-up refractory quality and losses slugging effects vapour and liquid presence in the line.

Adjustable handl'e

Cable !O instrumeruation

SCHEJ\ ,LATIC [l~'\\XiING OF A ;PIPE~)LANNER

F ig .2B . Gam ma pipe scanner

There are a number of radioisotope sources, which can be used; two of themare; mostly used 13 Cs with a gamma-ray energy of 662 keY (half-life 30 years),and 60CO with gamma-ray energies of 1172 keY and 1332 keY (half-life 5.27years). The source activity is calculated accepting a dose rate of approximately1.0 - 1.5 rnR/h, at the detector.Before executing any pipe scanning, the following information is needed:

the inside diameter and wall thickness of the pipe, the medium in the pipeline (gas, liquid or slurry)

A jack guide is used so that source and detector can be synchronised and alwaysmaintain the same distance. The source must be collimated with a collimator f

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6 - 8 mm and 10 rnm deep in order to obtain a narrow radiation beam. Thedetector also must be collimated suitably for best results.A reference scan is obtained on a representative area of the pipeline that ISclean and deposit-free.

Some applications of pipe scanrung

e: IS~" . P 17: 2: IG1 1 g 1 5"." s 14g 1 3~~ 1222 .,'

Detector

Detector

Detector

Radiation inre nsi cy

Sealed source

Scan profile of pipe lintI II I

" t - ~ - -, ( I ---H_::~'+, !i I I: I I I 1 i

II 5 2515 20POSlUun numbe r

Detector

Radiation in lens; t)'

:5~ ' gSour~e~

"D.-o :

~can protik of pipe hotI _.s-. . . . " t.I') L

I

I "

.3- : ; 1 9I i>Il(" 15: ; 1 4n~p~ 1 1~ Ii I, 11 1 1 5 21 1

p~)"j[HHl

C' 29 om e a to li ca ti on s Of pine scaJlnmgL 19.. rrr '1 r35


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3.2. Gamma-ray scan investigation on a FCC Transfer lineThe main function of a Fluidized Catalyst Cracking (FCC) reactor is to convertvacuum gas oils into gasoline and gas. The fine ceramic powder catalyst facilitatescracking reaction process when comes in contact with hydrocarbons.The deposit build-up of carbon catalyst on the inside walls of the transfer lineis a common problem in the FCC reactor. Gamma scanning of transfer line pipeis required to be performed periodically. A 10 mCi mes radioactive source wasused to inspect an 880 mm diameter line. This source is suitable for detectingsmall changes ill density, which can be correlated with deposits in the pipeline.The density (p) and the mass absorption coefficient ( j J . ) of the carbon/ catalystdeposit for mCs was experimentally determined in laboratory by simulating thedeposit material into the pipe. The radiation transmitted through the pipe is afunction of the initial radiation intensity without absorber (empty pipe), 10.Either of the variables x or p can be measured if one of them is kept constant.If the thickness is known or can be measured, densit; can be determined by therelation:

p = In(III) I (-~x)If the density is constant or is known, the deposit thickness can be determinedfrom a similar equation:

x = In(III)I(-jJ.p)Gamma scan profiles were obtained every month. Typical results are showngraphically (Fig.30).

From gamma profiles changes deductions can be made with regard to depositthickness rate over a .period of time. Anomalies caused by material piecescollapsed inside the columns, were detected in some cases.

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-5 0 5 10 1 5 20~E 30E 25'-"c 20

o n 15Of) 10c~ 5.~~ 0 -1 0 0 10 20 30 40 50 6 0 70 80 90 10 0 11 0 120 130

4030 SECTION 320100 I

-1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130POSITIO

F ig .30 . F CC Pipe d epo sit m ea surem en t3.3. Behaviour of gas/oil transportthroughpipelines

The oil coming from production wells from an oil field feeds a collector tank,called Primary Collecting Station (peS). In such a tank, the crude oil is primarilyseparated by gravity into slurry, water, oil and gas. From the p es the oil is fedinto to a Separation Plant, where the oil is further separated into gas and liquid.The oill gas transport pipeline was inspected using gamma pipe scanner. Thepipe internal diameter was 61 cm.

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During transit of oil-gas mixture through pipeline, irregular liquid blocks withgas in between are created. These blocks carry mechanical energy, which causesstrong pipe vibrations. This could result in mechanical damage and dangerousgas might escape. It is important for plant operators to identify liquid blocks,their frequency as well as their lengths in time and space.A pipe inspection was carried out placing the detector-source arm about 10metres before the entrance to the separator vessel. A 10 mCi Co~60 source wasused in a lead collimator ..The source ~detector arm was kept in vertical position.The calibration for liquid-oil and gas was performed in horizontal position.Experimentally was found that the count rate of 2200 c/ s represented gas phaseand 100 cis liquid phase.

Source

SourceSource

Fig .31 . Gamma s ca nn in g in sp ec tio n o f g as /o il tr an sp or t t} Jr ou gh a pipelineThe count rates recorded during one day (nearly 50000 data) were convertedinto liquid level inside the pipe, based on gamma transmission equation. Theheight and rime interval of each liquid block, the interval of gas space betweenconsecutive liquid blocks, the distribution of blocks in time and the generalbehaviour of the fluid during 24 hours were obtained.

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10090

'[ 8C lu;. 70

"V i 6 0csc 50e0 40'p'":. 0 30ee~ 20

100

1 7 : 4 6 1800/

Gas phase,U ~Gas phase (\

J f f1 / 1 \ . \- I \~ M 11 [ \ I~ ~1 \\ '\ \~. ,i r l _ l~,iitj l ~ i ~ I \.f \Iil l

f.i' ~ ~ 'vtJ \) , , ' I v v " I ""\J VfV ',,(,""Liquid phase \ Liquid PhasJ

5 0 4 3 7 5 0 5 3 7 5 0 6 3 7 5 0 7 3 7 5 0 8 3 7

Fig . 32. Transport characteristics o f g as/ oil mixture into pipeline during a dq y

This chart shows non-steady and non-uniform flow of oil-gas phases throughthe pipe during the time. Gas blocks created during transportation can causestrong vibration leading to mechanical damage of the entire pipe. Knowing thisabnormal flow regime a normal flow rate can be established to avoid pipe damage.

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4. NEUTRON BACKSCATTERING-DETECTION OF LEVEL ANDINTERFACE

4.1. Neutron backscatter principleHigh energy or "fast" neutrons from a radioactive source are beamed onto avessel. Fast neutrons are slowed down mostly by collisions with hydrogen atomsof material inside the vessel. A part of thermal neutrons are bounced backtowards the source. By placing a thermal neutron detector next to the source,these backscattered neutrons can be measured. The number of backscatterneutrons is directly proportional to the concentration of hydrogen atoms infront of the neutron detector. As the source and detector move down the sideof the vessel, interfaces can be detected provided they involve a change inhydrogen atom concentration.Neutron backscatter gauge clearly indicates solid/liquid and liquid/liquidboundaries and, with careful interpretation of the data, foam levels. Theinspection of the interface between water and oil, as well as among hydrocarbonfractions is the major application of this technique. As long as the vessel has awall thickness less than 100 mm, the use of neutrons is a quick and versatiletechnique, ideally suited if access to both sides of the vessel is not possible.

Applications of the neutron backscattering technique include: Inventory in oil storage tanks without gauges Calibration of non-contacting or conventional level gauges Determination of sludge or water layers in tanks Measurement of packing levels in absorption towers Detecting collapsed beds in packed columns Finding levels of toxic or corrosive liquids in tank cars Identifying build-up and blockages in pipes and reactor coils Measurement of catalyst levels in reactors Detecting ice formation in flare/vent systems

Helium (He-3) or BF3 neutron detectors can be used. He-3 detector has a higherefficiency and is mostly utilized in recent neutron gauges.

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The neutron source rna tl y used is 1 1241Am/Be neutron source, which producesa flux of 2.2 x 106 n/ s with energies from 0.1 Mev to 11.2 Mev, and averageenergy of approximately 5 Mev. Cf-252 neutron source is used as well, but it ismore expensIve.

Table 2: Commonly used neutron sealed sources.Neutron source Tljz Neutron Average Flux of fast neutrons

nergy(MeV)Am 241 - Be 433 y 4,46 2,6 x 106 n / Ci / sCf - 252 2 ,6 5 Y 2)2 2,3 x 106 n/mg/s

_________J~-----~-- - - - - - - - ~ - - - - - - - - ~

- - - - - - - - - - - - ,

Fig . 33. N eutron bac kscatte r g aug e for le vel and interfac e m easurem ent in sto rag e oil tank s

Storage Tank Neutron Backscatter signal

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eutrn source and He-3detector head

Palmtop computer

Typical neutron backscatter guage equipment

Fig . 3 4. Typical portable n eu tr on b ac ks ca tte r g a ug e

The following factors may influence the measurement and give wrong results: Moisture in insulation, on-uniform insulation thickness, Proximity of human body, Proximity of plant equipment, Angle and curved surfaces.

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F ig . 3 5 . N eutron ba ck sca tter lev el m ea su rem ent in pro gress o n a k no ck -ou t d ru m

eutron backscatter gauge can be used to measure level and interface oftransported liquids in pipes as well.

500 1500Count rate (0 I 20 s)

Fig . 36. leutron backscattetitlgprofile into a oil pipe/iue

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4.2. Interface level in a crude tar tankThe purpose was to measure the liquid interfaces in a crude tar tank in an oilrefinery. The tank had diameter 27 m and height 11m. Various types of liquidhydrocarbures were stored in the tank. The measurements were carried out bymeans of neutron backscatter gauge, using different neutron moderation effectdue to variation in hydrogen content of oil fractions.Two profiles along the height of the crude tar tank were performed using a 1 Ci241Am/Be neutron source. The results obtained during the measurements areshown graphically (Fig.37).Various liquid interfaces were detected inside the crude oil storage tank:

Interface one, located between 1.1 m and 1.75 m. Interface two, located between 1.75 ill and 5.7 m. Interface three, located between 5.75 ill and 7.4 m .. Interface four, located between 7.4 m and 9..6 m.

Therefore, four different hydrogen content liquids were identified. These mostprobablyed corresponded to four layers of hydrocarbon fractions separated duringstorage time. Some unidentified objects (not indicated on a mechanical dxawingof the tank) were detected at 3.7 m; 7.7 m and 8A m as well.

Scan profiles obtained on crude tankill c ~::; ~z ~ iii' C iii'; U 3 c ~ c~ ~ ~ ~ ~; : ~ g : ; a c'" @ z '" zj: f-o '. : l . ... ~

l O O < X l l J T ----'f~:___Tt:---_-'--- - 4 5 __;~~5~~_~~r ,r N r

t o . ii r . , . . ' . :f I!

r.~--~~h!I'~~~~~

' . , pz0uUlen!til~, . . .zaf : :VlZtil~6f:SasQ~b;EVJ.2, . . .

44

3 4 5 6 7 8 9 10Distance illmetre

F ig .37 . In teifa ce lev els in a cru de ta r tan k


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4.3. Neutron backscatter scanning of fractionation columnA cracking fractionation column experienced problem related with blockage oftrays by coke produced during cracking process. Plant engineers suspectedintensive coke deposition in lower part of the column. The gamma scanningcan not "see" well coke formation at its early phase of deposition at columnwalls due to low contrast of coal layers to gamma transmission. Neutron scanningis more sensitive to coal deposition in this case.The lower part of a 6 rn. diameter column was scanned by neutron backscattergauge. A relatively higher peak was obtained between trays 6 and 7. This peakwas higher than the other reaclings coming from liquid phase lying on trays.This high peak can be provided only by coke solidified at the column wallsbetween trays 6 and 7. This result was confirmed after opening the column.The coke deposit layer was quite thick (several tens of ems) disturbing all columnprocess. Itwas very hard to remove the deposited coke block from the column.A pneumatic hammer was used in this case.To follow the dynamic of coke deposition, regular neutron backscatter profileshad to be taken every month after column operation starts. The coke formationprocess was very fast, in 4-5 month time it can completely block the column.In fact, gamma and neutron scanning profiles are used as complementarytechniques for many column-troubleshooting inspections. After performing agamma scanning profile, it is recommended in some cases to obtain a neutronbackscatter profile to obtain additional information about the column insight,in particular in columns where coke formation is suspected.

P-6P -7

=c:":-----~ ------

-- .. . _ - - --.-----{ - - - - - - - - - - -_ L ! : - : : - . . . _

Fig. 38. N eu tro n b ac ks ca tte r p ro fil e 0 / a pa 11 c f fr ac ti on ati o c ol umn .C ok e b lo ck ag e is o bserv ed 0 1 7 the trq } 6

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5. RADIATION SAFETYRadioisotope technology is one of the many beneficial applications of ionizingradiation that is used around the world. To ensure that persons are protectedfrom the harmful effects of radiation, any such applications must comply withthe International Basic Safety Standards (BSS) or equivalent national regulations.Any work with radioactive materials will normally require an authorization fromthe relevant national regulatory authority. The person or organization to whomthis authorization is given, will have the prime responsibility for ensuring thatradioactive materials are used safely and in compliance with the relevantregulations/ standards. Guidance on occupational radiation protection, thedevelopment of safety assessment plans and for the safe transport of radioactivematerials has been published by IAEA.

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6. THE BENEFITS OF INDUSTRIAL APPLICATIONS OFRADIOISOTOPES

6.1. BenefitsThe benefits that can be obtained from the application of radioisotopes forprocess diagnostics are many folds. These may come in different forms:5 aft!} BenefitsFew industrialists would dispute the benefits of spending money on safetyimprovements. Indeed, in an ethically managed company, such improvementsare valued at least as much as increases in the profitability of the business. Insuch organisations, the unit engineer may well find that expenditure proposalswith safety implications are actually the easiest to justify. Thus, a proposal touse gamma ray scanning to locate the build up of ice deposits in a flare stackline is unlikely to meet with rejection because of the potential seriousness ofthe line becoming blocked.

Em ir onm en ta l BenefitsIncreasingly, as society grows more and more environmentally conscious,industrial corporations are giving as much weight to these issues as to employeesafety, though in some cases, this stems from national or international legislationwhich contains severe penalties for non-compliance with agreed standards.Whatever the motivation, expenditure proposals for projects leading to significantbenefits to the environment are at least assured of a sympathetic hearing.

E co nomic B em jitsEconomic benefit may be simply defined as a net increase in profit. That is, thegross increase resulting from the radioisotope study,lessthe total cost of performingthe measurements. Frequently, we express the benefit in terms of a "Benefit:Cost Ratio", which is defined as the ratio of the net profit increase to cost.6.2. The assessment of economic benefitsThe calculation of economic benefit is, on the face of it, straightforward. It iscertainly easy for the radioisotope practitioner to compute the cost of carrying

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out any particular study: his problem lies more in obtaining the informationneeded to calculate the resultant increase in profit. The industrialist, with hisspecialised knowledge of process economics, is in a much better position tocalculate the benefit. Unfortunately, however, for a variety of reasons, industrialcompanies are frequently unwilling to divulge the magnitude of the profits theyhave derived. It is most probably for this reason that comparatively few examplesof economic benefit have been reported.However, interesting information was provided by a survey, conducted by apetrochemical company in the UK, in which plant managers were asked toprovide information about the benefits that their units had derived fromradioisotope applications. The company in question, Imperial ChemicalIndustries, was not only the user, but also the supplier of the radioisotopetechnology. For this reason, the information obtained was considered to beunbiased, since the plant managers had no vested interest either in under-valuingor in over-valuing the benefits that they had realized.Some of the applications reported in that survey are listed in Table 3. Recognisingthat the radioisotope application may not be wholly responsible for the economicbenefit, each example takes into account an estimate, made by the manager ofthe plant in question, of the percentage contribution made by radioisotopetechnology to the solution of the problem. The study listed exemplify thedifferent ways in which the benefits are derived:1) Troubleshooting. Radioisotope technology is used to diagnose specific

causes of inefficiency in plant or process operation. In this context, it shouldbe noted that .in very many cases the benefit is derived in the form ofsavings associated with plant shutdown minimisation and loss prevention.

2) Process Optimisation. The radioisotope measurements provide informationthat facilitates improvements either in the throughput or the product quality.

The average Benefit: Cost ratio was estimated 20:1. This is within the range ofCost: Benef t figures pr vided by other authors.However, as is illustrated by the following case history, sometimes the benefitsmay be vastly greater than the above figures uggest.

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6.3. Case HistoryThe Engineering Group at the Research Centre of a major oil company wasasked to investigate the performance of a malfunctioning 'separation train onan oil production platform in the Norwegian Sector of the North Sea ..Theseparators were unable to dehydrate the oil to the level required for exportthrough their pipeline. The effect of this was to restrict production to 70,000barrels per day rather than the targeted 80,000 barrels per day. Attempts hadbeen made to improve matters by injecting various chemical agents, butthe'problem still persisted. Itwas decided to commission the services of reI Synetix,a contract supplier of radioisotope applications, to conduct a series of on-lineinvestigations of the operating parameters of the separators.Firstly, neutron backscatter scanning was used to investigate the oil/waterinterface ..The scans showed that the interface was too high, thereby allowingwater to exit the vessel with the oil phase. However, this alone was not deemedto be sufficient to fully account for the poor performance of the system.Radiotracer studies of the residence times of the organic and the aqueous phasewere therefore carried out using a standard impulse injection measuringtechnique.The results showed that the mean residence times of both the oil and the waterwere approximately 60 seconds, as opposed to the four-minute residence tim~sfor which the vessels had been designed. In essence, the process material wasshort-circuiting the vessel, allowing insufficient time for the oil and water phasesto become fully separated.The problem was solved by installing baffles in the lower section of the separatorto increase the mean residence time ..This made it possible to increase productionto the target 80,000 barrels per day and subsequently, with further modifications,to 100,000 barrels per day. With crude oil costing approximately 25 US Dollarsper barrel, the resulting benefit was, and continues to be, enormous.It would clearly be an overstatement to claim that radioisotope technology wassolely responsible for this success. However it is certainly true that the combineduse of sealed source and radiotracer techniques played a very significant part insolving a problem that had hitherto proved to be intractable. On this basis, asignificant share of the resulting benefit must be ascribed to the successfulapplication of radioisotopes.

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Table 3. Saving estimates for radioisotope studies on an leI petrochemicalcomplex.

Plant Job Details Contri Savingsbution (US$)(%)

Dimethyl Radioisotope techniques were used to 25 100,000amine investigate production limitations as part ofPlant a de-bottlenecking exercise.

Gamma ray scans on the overhead line froma stripper column revealed the presence ofserious liquid carry-over.Design changes made on the strength ofthese studies resulted in a production increaseof US$ 400,000 per annum.

Diphenyl Attempts to operate the plant at higher ratesOxide were frustrated by a bottleneck in a fractionationPlant column. Production staff believed that the problem

was caused by damage to the trays. Gamma raytransmission scanning revealed that there was nointernal damage and that the column functionedwelJ at normal rates. However, scans at differentfeed rates revealed that the column was operatingclose to its upper limit of liquid capacity: its designwas such that it was not capable of handling thehigher throughput.As a result of the study, a new column was 100 150,000designed and was ready for installation at the nextscheduled shutdown.Prior to the gamma ray scans, a special shutdownof seven days duration had been planned, in orderto conduct a visual inspection of the columninternals. The scans removed the need for thiscourse of action, thereby saving seven daylost production.

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Amines The formation of deposits in the flare system onPlant the Amines units was a potentially hazardous

occurrence, ince such deposition c uid restrict theroute for flammable gases to be safely vented toatmosphere in the event of plant malfunction.Recognising this, the plant operators periodicallyshut down the units to visually inspect and,ifnecessary clean out, the pipework. The totalshutdown time was typically ten days per year.The radioisotope applications team developed aneutron backscatter technique that was used toidentify the location of any deposits and tomeasure their thickness. The measurements wereperformed with the plants on line and withoutany break-ins.By eliminating unnecessary shut downs,production losses estimated at US$ 1,000,000pet annum were saved.

Para-xylenePlant

AnilinePlant

Pre-shutdown gamma ray transmission scans onthe suction catch-pot of a compressor unexpect-edly revealed that the internal filter was damaged.As a re ult, additional maintenance effort wasprogrammed in, to effect t.he repairs.Had the damage been discovered only after bring-ing the plant off line, the shutdown would havebeen extended by ha l f a day, equivalent toproduction losses of US$ 50000.

Gamma ray scanning, carried out in conjunctionwith radiotracer residence time measurements,was used to measure the build up of catalyst on thewalls and pipework of the aniline reactors,B y conducting the measurements at intervals overthe plant's operating cycle significant progresswas made towards understanding themechanisms responsible for catalyst deposition.Corrective actions, taken on the basis of thefindings of the radioisotope studies, extended thelife of the catalyst by approximately 3 0 [ 1 0 ,resulting in cost savings of S$ 400,000 per annum.

100

100

25

50,000

1000000

100,000

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6.4. ConclusionsThe examples described clearly demonstrate the potential value of industrialradioisotope applications. That being the case, it is somewhat surprising thatindustry does not use the technology more widely than it does at present.\Xlhatever the reasons, progress towards remedying this state of affairs can bemade by promoting, at every opportunity, the capability of radioisotopetechnology to realize substantial economic benefits for comparatively little outlay.Ultimately, economic arguments are the only quantitative way b} whichradioisotope experts can persuade industrialists to invest in the technology. Ona grander scale, they are also the ways by which governments, who must assessthe merits of competing claims on public funds, are persuaded to invest in theongoing development of the technology.For these reasons, the study of economic benefit is important and workers inthe field should strive to assess it and publish the information, wherever possible.It is hoped that the material presented in this Brochure will assist them in thistask.References.Charlton, J . S., "Radioisotope Techniques for Problem-Solving in IndustrialProcess Plants", Leonard Hill , Glasgow and London, 1986."Guidebook on Radioisotope Tracers in Industry", Technical Report Series No.316, lAEA, Vienna, 1990."Emerging New Applications of Radiotracers in Industry", Consultants' report,IAEA, Vienna, 3-6 June 1996.lAEA TECDOC 1142: Emerging new applications of NCS in industry, March2000.International Basic Safety Standards for Protection against Ionizing Radiationand for the Safety of Sources, Safety Series 0.115, IAEA, Vienna (1996)

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