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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 2
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 3
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 4
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 5
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 6
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 7
● 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)
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 8
● 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)
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 9
● 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)
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 10
● 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)
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 13
● 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
Titre de la Présentation – Lieu et Pays – Date Jour Mois Année 14
● 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.
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