VGB PowerTech 12 l 2012

Improvement of the FGD and ESP at the Iskenderun power plant

Improving the FGD absorberand ESP performance atIskenderun power plantGürkan Atmaca, Werner Stratmann and Birgit Wortmann
Kurzfassung
Verbesserte Abscheideleistungendes Rauchgaswäschers und desE-Filters im Kraftwerk Iskenderun
Das Kraftwerk Iskenderun liegt im Süden derTürkei in der Bucht von Iskenderun in der Provinz Adana. Zwei Blöcke mit einer gesamten
elektrischen Leistung von 1,210 MW werden
durch ISKEN, einer Gesellschaft im Besitz von
STEAG (51 %) und OYAK (49 %) betrieben.
Der jährliche Brennstoffverbrauch beträgt rund
3,3 Millionen Tonnen SKE, wobei die Kohle aus
Kolumbien und Südafrika importiert wird.
Zur Einhaltung der vorgeschriebenen Schwefelund Feinstaub-Emissionsgrenzwerte mussten
die Abscheideleistungen des Wäschers und desElektrofilters verbessert werden.
In einem ersten Schritt wurde das Optimierungspotenzial des Wäschers und des Elektrofilters basierend auf dem Ist-Zustand (Referenzfall) mithilfe einer Strömungssimulation
bestimmt. Sämtliche CFD-Berechnungen wurden mit der Software FLUENT 6.3 durchgeführt. Für die Erstellung der Geometrie und desRechennetzes wurde das Programm Gambit 2.4
verwendet.
Die resultierenden Geschwindigkeits- und Konzentrationsverteilungen des Refe­renzfalls lieferten ein tieferes Verständnis für die möglichen
Verbesserungen.
In einem zweiten Schritt wurden mehrere mögliche Varianten mit verschiedenen Modifikationen an Komponenten analysiert und bewertet.
Im letzten Schritt wurde die Variante mit dem
höchsten Verbesserungspotenzial ausgewählt
und detailliert beschrieben.
lIsken Sugözü (Iskenderun)
power plant
At the Isken Sugözü power plant2 x 660 MW hard coal-fired boilers with
two FGD scrubbers are operated. Each of
the scrubbers is equipped with five levelsof recirculation pumps with a flow capacity of 4,100 m3/h. The flue gas mass flow is
1.9 million normal cubic meters per hour
and the SO2 load differs from 2,150 to2,850 kg/h according to coal quality. In
normal full load operation the FGD unit
operates with 4 levels of pumps to keep
the emissions below the legal limit of400 mg/Nm3.

Purpose of the project
The low SO2 reduction efficiency of theexisting scrubbers had to be improved toensure that the current limit values and future sulphur dioxide emissions limits at theflue duct are met.
The modification was aiming at:–– Improvement of SOx emissions withoutchanging the liquid/gas ratio. Increaseof the number of nozzles for better distribution of the slurry.
–– Meeting of the current SOx emission
limit values with 3 recirculation pumps
instead of 4 recirculation pumps by shutting down 1 pump (425 kW) to save energy.
–– Increasing the SOx capture efficiency
from 80 % to 90 % with 4 recirculation
pumps.
The first study was started in 2008. A CFD
modelling project was run by Steag Energy
Services to improve the FGD scrubber performance. The flow of the flue gas into thescrubbers was monitored.
As shown in F i g u r e 1 , the study did notreveal major uneven flow inside the scrubber tank.

Authors
Gürkan Atmaca, Mechanical Engineer
ISKEN Enerji Uretim A.S.
Ceyhan-Adana/Turkey
Dipl.-Phys. Werner Stratmann
Dr.-Ing. Birgit Wortmann
STEAG Energy Services GmbHEssen/Germany

Before CFD modelling, compact deposits
around the scrubber nozzles near the walls
were detected ( F i g u r e 2 ). Most of these
deposits were at the lowest nozzle level.
This indicated to non-uniform profiles ofvelocity, suspension concentration, andtemperature, which could also cause poor
scrubber efficiency. Other influencing factors could be the position and flow rate of
the nozzles, the upstream located guiding
vanes, and the duct form.

In the CFD modelling process, the results ofa theoretically homogeneous scrubber inletprofile did not show a significant improvement in terms of distribution of velocity, ofsuspension concentration as well as temperature profile. It became clear that whatever modification had to be implemented
for achieving a homogenous inlet profile,
it would not have any significant effect on
the situation in the scrubber. This could beexplained with the relatively high pressure
drop caused by the injected suspension
through the nozzles of 8.5 mbar. Therefore
there was no need to take influence on theinlet velocity profile by modifying guiding
vanes or other internals upstream in theflue gas duct.
The distribution profile in the scrubber was
dominated by the implemented number,position and type of nozzles. CFD modelling figured out that overall suspension
mass flow with double number of nozzles
were reaching much more homogeneous
velocity and suspension concentration
profile.
As a result, it could be seen that the recirculation rate of the scrubber suspension issufficient for the measured SO2 content.
Noticeable are the few nozzles per m2 orin sum over all layers per m2 with the consequence of a local more uneven l/g. Only
when taking into account these facts it wasrecommended to increase the number ofnozzles per layer by preserving the recirculation rate and change at the same time thetype of nozzles to full cone nozzles with aspraying angle of 90° at the wall side andin the centre to hollow cone nozzles witha spraying angle of 120° which is state of
the art. The full cone nozzles at the wallside are preventing that a great amount of
the suspension almost immediately is hitting the wall of the scrubber and is lost forthe desired deposition reaction. The 120°spraying angle of nozzles in the centre produce more droplet interactions and therefore a regeneration of the surface available
for the reaction besides a more homogeneous injection in the flue gas flow.
After CFD modelling, one of the proposed
modifications for the scrubber was increasing the nozzle quantity. Therefore, the design of the recirculation spraying headers
had to be changed. Also, new type spraying
nozzles had to be selected for better spraying quality according to the capacity of thepumps. Thus, the dimensions of headers

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87

VGB PowerTech 12 l 2012

Improvement of the FGD and ESP at the Iskenderun power plant 

Horizontal slices

Vertical slice

109.5
9.0
8.5
8.0
7.5
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6.5
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5.5
5.04.5
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Vertical slice
Isosurface for 30 m/s

Fig. 3. New design of spray bank.

that the nozzles are mounted to the Y connectors in the right orientation.
Isosurface for 7 m/s
ZXY

Fig. 1. Isosurface for 7 m/s of the FGD scrubber.

spray arms and nozzles were changed forthe new design.
Last year it was detected that the absorberrecirculation lines were damaged by abrassion. These lines had to be renewed. It wasdecided to apply the proposed modification for increasing the nozzle quantity. Thiswas realised in unit 10 by own plant staff.
Before the outage, the nozzle orientation
inside the scrubber was designed carefully
to minimise non-scrubbing areas in theabsorber. The headers were adjusted according to this nozzle orientation by theplant´s own engineering team using a CAD
software. Y connectors were used to install
new nozzles ( F i g u r e 3 ).
Twin-absorb nozzles were selected for themodification which was applied to threelevels. For each level, the number of recirculation nozzles were increased from 66 to128 with smaller diameters and flow rates
without changing the liquid/gas ratio of
each spray level. By increasing the recirculation nozzle quantity a larger scrubbing area – meaning minimisation of theamount of untreated raw gas – can be covered in the absorber. Thus, the SOx emission were reduced.
Three different types of nozzles were used
for the modification. The nozzles close to
the absorber wall were full-cone with 90˚spraying angle, nozzles close to the mainheader were hollow-cone with 90˚ spraying angle, and nozzles at the centre arehollow-cone with 120˚ spraying angle.

The new type of nozzles also reduced theSOx emission due to their secondary atomisation property which occurs by theimpingement of the recirculating slurryparticles. The impingement effect of theparticles makes the slurry droplets fragment into very small grain sizes which increases the surface area of the slurry. Thus,
the reacting surface area also increases.
The increased reaction surface area of theslurry increases the amount of the chemical reaction between slurry and SO2.

Installation process
New nozzles were installed at the newly
designed Y connectors with a special adhesive with high chemical resistance. For
reducing the curing time of the adhesive,
heating blankets were used. This processneeds extra caution because it is important

Before

The installation required a special and safe
scaffolding which in turn needed a proper
floor. Reinforced metal planks were placedon the positive-displacement bodies in theabsorber. After the preparation of the floor,
scaffolding could be constructed ( F i g u r e 4 ).
The diameter of the scaffolding was
14,500 mm with 14,250 mm height. It wasconstructed from +8 m to +22 m height(just below the first stage of the recirculation headers) in the absorber. After
construction of the main scaffolding, additional scaffolding was constructed on
top of the main scaffolding to reach level 5(+29 m). The deadweight of the scaffolding was 19,550 kg.
The old nozzles and headers were removed
from the absorber. Headers of new design
installed from their flanges and supports.
The supports and the blind ends of theheaders were fixed according to the lamination method. The Y connectors werefixed to the headers with GRP (glass-reinforced plastic) adhesive set ( F i g u r e 5 ).
After the Y connectors had been equippedwith nozzles, the connectors were rein-AfterFig. 2 Deposites around the nozzles were eliminated after modification of the spray system.

88

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VGB PowerTech 12 l 2012

forced by lamination with veil, fabric, glass
mate, and mixture of vinyl ester bonding
set (resin+hardener+accelerator) as wellas black silicon carbide have been used
( F i g u r e 6 ).
The only difference with unit 10 is the connection between Y connectors and headers. For unit 20, it was opted for flanged
connection instead of lamination. Alloy-59(2.4605) material nuts, bolts, and washers
were used for mounting to avoid corrosion.
Epdm-coated steel gaskets were also used.

Results
Due to the modifications, SO2 emissions
were reduced by 35 % at full load with only
3 pumps in operation. Apart from emission reduction the auxiliary station load
is reduced which means energy saving of
1 electrical motor with a power rating of
425 kW, which equals an annual saving of
2,800,000 kwh!
The SO2 reduction efficiency at 100 % loadwith 4 recirculation pumps was improvedby 10 %. efficiency increased from 80 to90 %.

Improving the ESP performance
Improvement of the performance of theelectrostatic precipitator (ESP) was con­Improvement of the FGD and ESP at the Iskenderun power plantsidered as very important in order to reduce the dust concentration, in view offuture limit values, and with respect to theenvironment.
Two ESP units are operated at the Isken­
derun plant. Each unit is treating an average flue gas flow 2,815,912 m3/h. The ESP
comprises 3 fields of collecting electrodes
divided with two aisles. Two more aisles
for inspecting the precipitator are locatedbefore the first and behind the last field ofcollecting electrodes. Upstream, the inlet
section is characterised by two gas distribution walls ( F i g u r e 7 ) with only one typeof perforated plates. Two guiding vanes
were implemented in the pass to improve
the profiles in the diffuser. A set of guiding
vanes was also designed directly at the gas
distribution walls. Below the gas distribution walls inclined plates are attached toprevent that a significant part of the fluegas flows through that area. In the first andlast row of the ash hoppers plates are implemented to prevent by-pass through the hoppers. Downstream of the precipitator in thenext two bends of the duct, two more guiding vanes are influencing the flow profiles.
Similar to the absorber modification, in2008, the ESP was modelled by Steag Energy Services with the aid of computational
fluid dynamics (CFD).

In a first step the potential of fluid flow
optimisation of the ESP was to be determined. The velocity distributions and ash
concentration profiles of the flue gas had
to be simulated with CFD programs ( F i g u r e 8 ) in order to understand and influence the precipitation process. The reference case (as build) and possible variants
could be analysed and evaluated to allow
for an improvement. It was possible toimprove the process at various parts, e.g.
by avoiding by-pass of the collecting electrodes and by forming a predefined velocity and ash concentration profile in theprecipitator volume. Deviations from thestate-of-the-art ideal profile could be areason for diminished efficiency of the precipitator. Other factors could be the changeof conditions during operation i.e. due toerosion or ash deposits.
It could be seen from the CFD report thatthe important area to be examined and influenced were velocity and distribution ofash concentration around the fields of collecting electrodes. Therefore, the results of
the reference case show velocity and ash
concentration profiles dominated by areasof high velocities at the sides and top of the
precipitator volume.
Ash concentration simulations have been
made for 1 and 50 µm ash particles inkg/m3.

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Jegliche Wiedergabe ist nur mit vorheriger Genehmigung des für die Freigabe verantwortlichen Mitarbeiters des VGB gestattet. Handelt es sich um ein Fremddokument, so ist die Weitergabe verboten!

89

VGB PowerTech 12 l 2012

Improvement of the FGD and ESP at the Iskenderun power plant Fig. 4. Scaffolding.

Fig. 5. Orientation of nozzles

Fig. 6. Lamination of Y-Connectors.

As a result from the CFD modelling report,
it was decided make the following modifications:–– Implementation of a diffuser outlet gas
distribution wall at the precipitator outlet with similar perforated plates as in
the inlet area,–– Removal of the existing hopper plates in
the first and nearest row to the gas distribution walls and implementation ofan hopper grid,–– Additional upwards directed horizontal
guiding vanes in the upper section of thefirst and smaller gas distribution wall
clipped in the same way as the existingguiding vanes at the gas distributionwalls,–– Implementation of flaps in the area below the gas distribution walls that open
the vanes through their weight,–– Implementation of flaps vertically to theleft side wall of the ESP inlet to divert
the excessive flue gas to the right side
because most of the flue gas flows fromthe left side wall.
The proposed modifications were carriedout 100 %. Modifications were made byown plant staff. Perforated plates, flaps,
diverter plates were welded by own plantwelders. However, it was difficult to apply
these modifications because of the confined space and ash in the ESP unit. Therefore, special caution had to be taken toobserve staff safety. Disposable protective
overalls, full face masks, dust masks, andgloves had to be worn while modifying theESP. Furthermore, special scaffolding hadbeen constructed.
The modification was aiming at–– Lowering the flue gas velocity for improving the dust capture efficiency,–– Providing of homogeneous flue gas dispersion into the precipitator, and–– Preventing the flue gas to escape fromthe sides and top of the precipitator.

All these targets were met. Besides, ash
precipitation was improved and re-suspension was lowered. The efficiency of theESP was increased which results in a reduction of average dust emissions by 15 % at
the ESP outlet. Prior to the modification,
the average dust emissions amounted toabout 65 mg/Nm3 compared to average
55 mg/Nm3 after the successful modification.
lVertical slice

Isosurface for 4·10 -3 kg/m3

Horizontal slice

Vertical slice

Fig. 7. ESP inlet gas distribution wall.

5.00e-03
4.75e-03
4.50e-03
4.25e-03
4.00e-03
3.75e-03
3.50e-03
3.25e-03
3.00e-03
2.75e-03
2.50e-03
2.25e-03
2.00e-03
1.75e-03
1.50e-03
1.25e-03
1.00e-03
7.50e-04
5.00e-04
2.50e-04
0.00e+00

Fig. 8. Ash concentration for 50 µm ash particle in kg/m3.

90

Dies ist ein internes Dokument aus dem Dokumentenmanagementsystem InfoExpert des VGB Power Tech e.V. Der Inhalt des Dokuments sowie InfoExpert selbst sind urheberrechtlich geschützt.
Jegliche Wiedergabe ist nur mit vorheriger Genehmigung des für die Freigabe verantwortlichen Mitarbeiters des VGB gestattet. Handelt es sich um ein Fremddokument, so ist die Weitergabe verboten!