On-line Diagnosing on Trayed Column of Etylene Plant Using Gamma Ray Scanning
S. Sugiharto*
Center for Application of Isotopes and Radiation Technology, National Nuclear Energy Agency Jl. Lebak Bulus Raya No 49, Jakarta 12440, Indonesia
A R T I C L E I N F O A B S T R A C T Article history:
Received 05 December 2011
Received in revised form 17 December 2012 Accepted 18 December 2012
Keywords:
Gamma-ray scanning Trayed column Liquid flooding
60Co Ethylene plant
Nuclear based technology called gamma scanning technique found its application for troubleshooting and diagnosing industrial process performance. The success of application of the gamma scanning technique is attributed to its unique ability in providing information which is cannot be obtained by any other techniques. One of the most prominent advantages of the gamma scanning technique was demonstrated by implementing this technology for scanning caustic/water wash tower DA 202 which was running in normal condition of operation. The DA 202 tower is trayed column having diameter of 4.2 m and height of 40 m. The scanning work has been performed using 70 mCi 60Co isotope as gamma emitter and scintillation detector as radiation counter to investigate condition of ten trays, starting from tray # 13 at elevation of 35050 mm to tray # 4 at elevation of 26950 mm above ground level.
Scan data show that all trays were in their position. Tray # 4 to tray #10 were functioned properly and carried approximately the same amount of liquid. Light flooding on tray # 11 and heavy flooding on tray # 12 were identified. Partial flooding was identified on tray # 13. Further examination at the time of shutdown it was found that the liquid flooding on tray # 12 was caused by presence of a bucket covered with solidified mud.
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INTRODUCTION∗∗∗∗
Ethylene is produced in petrochemical industry by steam cracking in quench tower. In this process, gaseous or light liquid hydrocarbons are heated to 750-950oC, inducing numerous free radical reaction followed by immediate quench to stop these reactions. This process converts large hydrocarbon chains into smaller ones and introduces unsaturation condition. Ethylene is then separated from the resulting complex mixture by repeating compression and distillation. Caustic/water wash tower DA 202, is one of critical components in continuous ethylene production plants of large petrochemical industry located in Banten province.
The column is designed to quench the radical reaction in ethylene line production. Problem identified was pressure increasing of the column [1].
Problem in this column leads to serious consequences to the plant operation and hence the quality of the product. It is urgently to find out the proper method in order to know what is really happening inside the column. The gamma ray scanning technique as troubleshooting tool was
∗Corresponding author.
E-mail address: [email protected]
selected to examine the cause of the problem in this column.
The gamma scanning technique is very suitable to be implemented for troubleshooting and diagnosing of technically complex, continuously operating industrial plants. The advantage of the gamma scanning technique is that this technique is applied just at the time when the plant is in operation. Petrochemical and chemical process industries are the main users and beneficiaries of the column scanning technology [2]
In engineering applications, gamma scanning technique has been used for inspection of various processing units of industrial plants and has been reviewed [3,4] and documented [5]. Gamma scanning technique with one source-one detector was used to for multiphase flow regime of hydrocarbon in the horizontal pipeline transport [6], distillation columns [7,8], and debutanizer of Fluidized Catalytic Cracking Unit (FCCU) in petroleum plant [9]. The gamma scanning technique was also used for characterization of radioactive waste in the container [10,11]. In combination with tomographic system, gamma scanning was used to assay radioactive waste [12].
In this paper on-line measurement of radiation intensity using gamma scanning technique is 138
demonstrated to figure out the sourc in trayed column of quench towe diameter of the column is 4.2 m a 40 m. The gamma emitter, 60Co 70 mCi, and scintillation detector w the column from the elevation of 2 elevation of 35950 mm above grou cover tray # 13 to tray # 4. S measurement are presented co conclusion. The problem is ident measured data. To my understandi related to this matter are rare, even therefore it is hope that this paper for dissemination of gamma scannin promising tool for industrial applic in developing countries.
Theory of gamma scanning Gamma scanning work i by moving concurrently a sealed gamma radiation source a detector, NaI(Tl), along the of the column, as schematically pre During the period of investigation source was encapsulated and placed a special housing and make no radiation detector or with the proc the column. A source holder with panoramic collimator was designed column. Scintillation detector side of the column was employ the radiation intensity emitted b source. Interaction of the ga with medium of interest in will produce change intensity of t correlated to the properties of the me
Fig.1. Schematic principle of gamma scannin Radio
Sou
Scintillation Detector
e of the problem r DA 202. The and the height is
o with activity were used to scan
6250 mm to the und level which elected data of ome with the
tified based on ing, publications nt in handbooks, r may contribute ng technology as ation, especially
is carried out small suitably and scintillation
exterior side esented in Fig 1.
n, the radiation d permanently in
contact with a cess materials in h an appropriate to exposure the
on the other yed to capture y the radiation
amma radiation the column the beam which
edium [13,14].
ng measurement.
The theory of gamma sc based on the fundamental relatio
where I (cps) is the intensity of through the material. Io (cps) incident radiation. µ (m2/kg x (m) are the mass abs the density and the thic respectively. B is buildup fac In practical application eac the column is assumed as l By using collimated beam, that intensity contribution from considered none, therefore is set equal to 1. From Eq. (1) is safely stated as:
where is linear constan each medium. It is wor gamma radiation for co should be capable of pen thickness of the column an interest. From the scanning profile of the internal column is obtained. For the following statements can be
• When the gamma radi a medium containing aerated liquid, the partially absorbed a quantity reaching the d small.
• When a radiation be a tray, most part of is absorbed and the detec
• When a radiation go only a small amount o is absorbed throug radiation intensity transm These statements can be possible mechanical damag inside the column such as damaged tray and other process
EXPERIMENTAL METHODS Column scanning w performed without any p column. All that required to the uppermost platform. N
oactive urce
( I exp
I ≡ −µι
( BI exp
I =
−µι
canning technique is on [4,5,13-15]
(1) f radiation transmitted ) is the intensity of
g), ρ (kg/m3) and sorption coefficient, ckness of medium
ctor (dimensionless).
ch medium inside linear and isotropic.
it is also assumed scattered radiation is
the buildup factor these assumptions,
(2)
nt and apply for rth to note that lumn investigation netrating the wall nd the medium of g work a density contents of the r trayed column, e derived [8]:
iation goes through a tray filled of incident beam is and the radiation detector is relatively
eam goes through f incident radiation
ted signal is weak.
oes through steam, of incident radiation gh which high mitted to the detector.
e made for analyzing
ge of components flooding, blockages,
s anomalies.
S
work is generally preparation to the
is the access way No insulation needs
) ιx
) µρx
−
to be removed, and the scan do with the operation of the colu situations, most columns hav platforms or walkway on whic detector can be suspended, b situation some additional supp scaffoldings are required.
Equipments for scannin are: 70 mCi 60Co radiation so mechanical control system with stainless-flexible slink cable movement of detector and sour detector and data acquisition data transmission, personal radi aids, laptop computer for and stationeries.
The scheme called grid performed in this experiment several radiation intensity from various scan orientations. S or scan position describes the radiation source (abbreviated as S) detector (abbreviated as D) direction. The scan orientation with respect to north direction of The grid scan of experiment in Fig. 2.
Fig. 2. Schematic scan orientation. Note direction of measurement. For example, i
The gamma scanning wo wash water tower DA 202 w as follows: both radiation source detector were put at the same
Down pipe
1050
575 S 575
0 NP
D
1050 575 0 575 D
1050
Baffle
es not interfere umn. In many
ve convenient ch source and but in certain
port such as
ng experiment ource, electro-
m equipped for controlling
rce, scintillation
n system for ation protection
data display scan has been
by conducting measurement Scan orientation
placement of and scintillation for a certain n is measured
the plant (NP).
is summarized
e that (S → D) is s scan of position 3.
rk on caustic/
was performed and scintillation
level, separated
by column construction. Th of the third man-hole (at elev above ground level) was ass point for starting level To ensure that the source were maintained in the level a single stainless-flexib used. By utilizing an automati control system, the detecto were lifted up simultaneou step approximately of 17.3 time 5 second for c intensity. Throughout ex operational condition parameter as feed-rate, temperatu process parameters were m Fixation of these conditions to record any process chang of the scan and to facilitat of the scan profile if an observed. The movemen when the detector and th close to end point of the few mm above the fourth the scan processing, data capt detector were monitored in and then saved for subsequent d
RESULT AND DISCUSSION The data of the scan Figs. 3 to 8. Material conditi DA 202 were analyzed ba In order to meaningful interpr drawing of the DA 202 col as the reference. In t data were compared with drawing which reflect t internal material in the colum the scan data many par column performance can be obt Scan data of the ca tower DA 202 show tha in their position as ind pattern having same Deep observation to each s that three of the ten trays problems. Trays # 4 to tray # properly. Serious problems trays # 11 to # 12, whereas was found on tray # 13. L on tray # 11 and heavy tray # 12 were identified. In of suspecting foreign material also observed.
1220 S
700
EP 0
700
0
Column wall
he center of flange vation of 26250 mm
signed as referenced
of measurement.
and the detector same horizontal ble slink cable was ic electro-mechanical
or and the source usly at determined
mm with delayed capturing radiation xperimentation the
rs of the column such
ure and other maintained constant.
is very important ges during the time te the interpretation ny anomalies were nt was stopped he source reached measurement, just man-hole. During tured by scintillation
n laptop computer data analysis.
N
ns are presented in ions inside of tower ased on scan data.
retation a mechanical
lumn was consulted this regard, scan h the mechanical the condition of mn. Deduction from
rameters indicating tained.
austic/ water wash at all trays were dicated by regular spaced distance.
scan data indicated s have experienced
# 10 were functioned
were found on non-serious problem ight liquid flooding
liquid flooding on n addition, presence l on tray # 12 was
Fig. 3. Profile of tower DA-202 obtained fr 1. The source and the detector were posit (25.5o) and 1050 mm (154.5o) respectiv
# 10 and tray # 13 were in position and ca the same amount of liquid. Flooding on tray were observed as indicated by their lower an
rom scan orientation tioned at 1050 mm
vely. Trays # 4 to arried approximately
y # 11 and tray # 12 nd wider scan curve.
Fig. 4. Profile of Tower DA-202 obtai 2. The source and the detector were p and 575 mm (178.5o) respectively. Tr
# 13 were in position and carried amount of liquid. Flooding on tray # observed as indicated by their lower an
ined from scan orientation positioned 575 mm (1.5o) rays # 4 to # 10 and tray
approximately the same
# 11 and tray # 12 were nd wider scan curve.
Fig. 5. Profile of Tower DA-202 obtained fr 3. The source and the detector were position and 575 mm (181.5o) respectively. Trays # 6 approximately the same amount of liquid.
trays # 11 and # 13 were observed. Floo materials on tray # 12 was observed.
rom scan orientation ned 575 mm (358.5o) 6 to # 10 was carried . Light flooding on oding and solidified
Fig. 6. Profile of Tower DA-202 obtai 4. The source and the detector we (356.8o) and 1050 mm (182.7o) res
# 10 was carried approximately the Light flooding on trays # 11 and # 13 and solidified materials on tray # 12 w
ined from scan orientation ere positioned 1220 mm spectively. Trays # 4 to
same amount of liquid.
3 were observed. Flooding were observed.
Fig.7. Profile of DA-202 tower obtained from scan orientation 5. The source and the detector were positioned at 700 mm (287.5o) and 700 mm (72.5o) respectively. Trays # 4 to # 10 was carried approximately the same amount of liquid. Light flooding on trays # 11 and # 13 were observed. Heavy flooding and solid material on tray # 12 was observed.
Fig. 8. Profile of DA-202 tower obtained from scan orientation 6. The source and the detector were positioned 700 mm (252.4o) and 700 mm (107.6o) respectively. Trays # 4 to # 10 was carried approximately the same amount of liquid. Light flooding on trays # 11 and # 13 were observed. Heavy flooding and solid material on tray # 12 was observed
It is important to observe data presented in Figs. 3 to 8. Li tray # 11 was approximately 30 cm by measuring the wide of i which corresponding to density corresponding tray. The same also applicable for measuring level on tray # 12 though that not only containing liquid but material. If it is assumed that the is fully settled or immersed or mud, therefore the liquid tray #12 was approximately 40 of all trays based on scan data in table 1
Table 1. Condition of trays based on scan da Tray # Tray condition View orien
4 Normal
5 Normal
6 Normal
7 Normal
8 Normal
9 Normal
10 Normal
11 Light flooding
12 Heavy flooding and foreign material
13 Partial flooding
Presence of solid material on disturb liquid flow either through down pipe. The location of the solid
# 12 can be predicted by analyz change of the scan data. Suppose section of the column is divided int as shown in Fig. 2. Scan on quadran not shows any significant anoma flooding on trays # 11 and # 12 onl quadrants I and IV, however, different features on which low and intensity on tray # 12 was observed that the solid material has grown on IV of the tray # 12. At the time of years after completion scanning wo that the solid material on the tray # buried in solidified mud, as shown in
Presence of metallic bucket i the tray # 12 is not expected to ex can be traced back to the time o period when plant maintenance w Somebody put the bucket in the do the surveillance of project super engineers. This fact shows a
in detail each ght flooding on
height, justified
inflected curve change on the
method was the flooding t the tray was
also solidified e solid material
in the liquid thickness on cm. Conditions
is summarized
ata
wed from scan ntation
n tray # 12 may downcomer or d material on tray
zing the density that the cross- o four quadrants nts II and III did alies except for
ly. Scan through indicates very d wide radiation d. This indicates n quadrant I and f shutdown, two ork, it was found 12 was a bucket n Fig. 9.
in down pipe of xist and it origin f last shutdown was carried out.
own pipe beyond rvisor or plant carelessness of
maintenance work during th Fortunately there was no fatal far even after three years plant o In engineering terminolo of unwanted deposits on th constructions is usually referr deposit. When the size of the de as big as the occupied stru deposit will embody as blockag of deposit (foulant) on the surfa number of different mechanism upon the fluids being processe plant operation such as tempe The overall effect is that the less efficient in terms of heat tra from other problems of operatio
Fig. 9. Suspicious solidified materi scanning was verified at the time of sh in solidified mud was found on tray #
As can be seen from F deposit was dominated by Deposit material due to chemic corrosion is also observed as metallic freak on top surface of deposit as mud may origin containing mud particles. Met other hand surely caused conditions which including h temperature and processing m such deposit including bucket to reduce its efficiency.
To sum-up, it is clear th analyzing density changes pre many parameters indicating c
he shutdown time.
accident reported so operation.
ogy the accumulation he surface of plant
red to as fouling or eposit is considerable
cture geometry, the ge. The accumulation ace may result from a ms that are dependent ed and the conditions erature and velocity.
equipment becomes ansfer and may suffer on [16,17].
ial observed by gamma hutdown. A bucket buried 12 of DA-202 tower.
ig. 9 (top-right), the particulate matter.
cal reaction including indicated by visibly f the tray. Particulate nate from feedwater
tallic deposit on the by plant operating high pressure, high materials. Presence of
on tray # 12 leading hat by measuring and esented in scan data column performance
can be obtained. Each tray with fluidized materials and the vapor space tell us ‘the story’ of its operating status. Gamma scanning technique, in this case, seems to be the only diagnostic tool available
that can be applied with confidence to obtain the true hydraulic behavior of the column performance. The results of the scan can be immediate discussed with process engineers so that appropriate remedial action should be taken as soon as possible to reduce production loss.
Learning from this experience, it is proved
that 70 mCi 60Co gamma emitter was enough to examine the column having diameter 4.2 m which is typical size of the column in industrial
process plant. In fact, the radiation activity of the source used in this experiment is very low, down to 1,000 or less, compared to the technique mostly used in industrial radiography. The source
holder was designed to fulfill radiological safety standard in order to ensure that received dose to the inspection team and plant personnel or the public do not exceed dose permissible limits as recommended by the International Commission on Radiological Protection (ICRP) [13]
CONCLUSION
Gamma scanning technique has been demonstrated for on-line diagnosing the performance of water wash tower DA 202 of ethylene plant in petrochemical industry. Scanning
data shows that all trays were in their position.
Tray # 4 to tray # 10 are carried approximately the same amount of liquid. Light flooding was observed on tray # 11. Heavy flooding in addition to suspicious solidified material was identified on tray # 12. Tray # 13 has
experienced partial flooding. The problems have been verified at the time of shutdown and it
has found that a bucket in solidified mud was found in down pipe of tray # 12. As it simple in operation and no column precondition are needed the gamma column scanning is very convenient to be applied in petrochemical plant.
ACKNOWLEDGEMENT
The authors thank to manager of utility division of PT. Chandra Asri Petrochemical Complex that allow me to publish this valuable work. Special thank to Mr. Adi Indrajaya and his team for their help and hospitality during the working carried out. PT. BATAN Technology as a stockholder of this project is acknowledged.
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