USING OLI TO DESIGN SOLUTION TO MINIMIZE THE CORROSION

OF CRUDE DISTILLATION TOWERS

Benoit ALBINET – TOTAL, Belgium

Sheyla Camperos – TOTAL, France

Rasika Nimkar – OLI

THE ISSUE

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● More and more crude oil contains impurities that cause corrosion and fouling issues in the crude distillation column

● Typical damages found are mainly in the top trays, heat exchangers and lines as shown below (yellow zone).

● Typical unit arrangement, including: 2 stage desalters, a preflash and a main fractionnator:

THE ISSUE

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● The corrosion and fouling can cause:

- Bad efficiency of heat echangers and associated loss of opportunity and maintenance cost (cleaning, repair)

- Slowdown of the unit (decrease of the throughput) as the fouling of the internal trays maght end-up in flooding and unstable operation

- Loss of fractionnation leading to valorization losses

- Larger maintenance scope and cost during Turn around

- Unscheduled shutdown if the cycle of 5 years can no longer be maintained

Partially

Fouled Tray

Totally

Fouled Tray New Tray

Normal behavior Some flooding

Flooded

Line fouled

THE SOURCE OF THE PROBLEM

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● The analysis of the deposit found in the corroded/fouled zone often revealed the presence of

• Corrosion products type Iron sulphide or iron oxides (consequence of the corrosion)

• Chlorides in large quantity (could be several thousand of ppm)

• Nitrogen species balancing chloride as: Methyl diethanol amine (MDEA), Mono-ethanolamine (EA), Di-ethanolamine (DEA) or Mono-

methylamine (MMA) or Ammonia (NH3)

From a deposit analysis fround in the top pumparound heaxchanger (TPA) back in 2012, we found

Significant amount of chloride and MDEA, and traces of NH3, EA, and DEA.

● Why amine salts are formed inside the column?

FRACTIONNATION COLUMN

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● We know that a preflash/main fractionnator configuration is supposed to be structually protected from salt issues as

shown below. NH3 and HCl are mainly splitted each other and the formation of corrosive NH4Cl should not occur in

the columns.

Chlorides

Main NH3

HCL

few NH3

FRACTIONNATION COLUMN

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● What is true for NH3 is might be not for other contaminants.

● Oli was used to check if the thermodycnics predict the presence of these contaminants in the TPA area (located

between the jet and the Heavy Naphta draw).

*Split PF/MF= percentage of species sent to the preflash in comparaison with the main fractionnator

● How to protect the column? By increasing the scope of the desalter.

The presence of corrosive

amines are clearly

predicted by OLI in the

area where the

corrosion/fouling was found

UNDERSTANDING THE BEHAVIOR OF NITROGEN SPECIES

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● If the conditions to the desalter are set such that the nitrogen species (coming either from the crude or the water)

are getting out of the system with the brine water of the desalter, dowstream columns should be protected.

Fractionation

block

Desalting

Block

DESALTER (1)

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● Typical desalter arrangement is shown below.

● Main objective: Extract chloride salt (NaCl, MgCl2, CaCl2) from crude oil to prevent HCl corrosion. Secondary

objective need to go to a nitrogen contaminants removal.

● Source of Nitrogen contamination:

- Internal: from the process water: DEA, MDEA or Neutralizer used in the overhead column when recylced back to the desalter

- External: from crude oil through the H2S scavengers used:

Typical two stages desalter arrangement

DESALTER (2)

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● Nitrogen species balance was first assessed by sampling crude and water streams and analysizing amine species by ionic chromatography (directly in water or via extraction in water for oil sample).

● Then OLI was used to simulate the unit and check the consistency of the results from OLI and the one found in the field. Two cases used at low and high NH3 in the desalter water.

● As one can see consistency is good. There are no exact mach between OLI and the field but not expected as the accuracy of the measurement in the field is not very high (sampling, sample stability, extraction efficiency, low levels measured are several reasons for results deviations).

Case 1 NH3 EA MOPA

in water 160 ppm 19.4 ppm 160 ppm

out water

77 ppm 14.2 ppm 77 ppm

out oil 5.9 ppm

0.9 ppm 0.4 ppm

OLI out oil 6.1 ppm 0.41 ppm 0.59 ppm

Field data

Case 2 NH3 EA MOPA

in water 26 ppm 19.4 ppm 28 ppm

out water

48 ppm 14.2 ppm 24 ppm

out oil <1 ppm

0.3 ppm 0.8 ppm

OLI out oil 0.9 ppm 0.43 ppm 0.62 ppm

DESALTER (3)

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● Field data and extrapolation of the effect of pH using OLI.

DESALTER (4)

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● From OLI simulation, acid consumption can be optimized based on the quantity of contaminants removed

DESALTER (5)

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● Neutralization curve were also done on real sample to compare with OLI with a good similarity.

DESALTER (6)

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● The sensitivity to crude contaminants was also checked with OLI (left graph)

- The effect of the pKa of each amine clearly impacts the needed for acid

- Very usefull to design the injection skid

● One indicator was also developed to detect contaminants based on the delta pH in/out of the desalter (right graph) compare to field data. The spectra developed suggest the presence of contaminated crude when the operating point are closer to the blue curve (abnormal variation of pH).

CONCLUSION

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● OLI was used to understand the origin of the corrosion/fouling found in the main fractionnator of crude Ditillation

column

● The data clearly indicates the absence of structural protection (split) allowed by the preflash for some corrosive

species as MDEA, EA.

● OLI was able to confirm the location of the more severe area for these slat formation(btween jet and heavy naphtha

cut in the example considered).

● OLI was then used to predict the impact of running the desalter at lower pH on the control of the contaminants.

● A tool was developped, based on OLI estimation, to detect contaminated crude oil. This would allow to alert the site

and identify suspicious supply.

● More work to come to fully validate salt deposition prediction and dewpoint chemistry.