USING OLI TO DESIGN SOLUTION TO MINIMIZE THE CORROSION OF CRUDE DISTILLATION TOWERS

Transcription

1 USING OLI TO DESIGN SOLUTION TO MINIMIZE THE CORROSION OF CRUDE DISTILLATION TOWERS Benoit ALBINET TOTAL, Belgium Sheyla Camperos TOTAL, France Rasika Nimkar OLI

2 THE ISSUE 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: Titre de la Présentation Lieu et Pays Date Jour Mois Année 2

3 THE ISSUE 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 Normal behavior Some flooding Flooded New Tray Partially Fouled Tray Totally Fouled Tray Line fouled Titre de la Présentation Lieu et Pays Date Jour Mois Année 3

4 THE SOURCE OF THE PROBLEM 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 Monomethylamine (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? Titre de la Présentation Lieu et Pays Date Jour Mois Année 4

5 FRACTIONNATION COLUMN 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. Main NH3 Chlorides HCL few NH3 Titre de la Présentation Lieu et Pays Date Jour Mois Année 5

6 FRACTIONNATION COLUMN 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). The presence of corrosive amines are clearly predicted by OLI in the area where the corrosion/fouling was found *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. Titre de la Présentation Lieu et Pays Date Jour Mois Année 6

7 UNDERSTANDING THE BEHAVIOR OF NITROGEN SPECIES 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. Desalting Block Fractionation block Titre de la Présentation Lieu et Pays Date Jour Mois Année 7

8 DESALTER (1) 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 Titre de la Présentation Lieu et Pays Date Jour Mois Année 8

9 DESALTER (2) 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. Field data 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 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 6.1 ppm 0.41 ppm 0.59 ppm OLI out oil 0.9 ppm 0.43 ppm 0.62 ppm 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). Titre de la Présentation Lieu et Pays Date Jour Mois Année 9

10 DESALTER (3) Field data and extrapolation of the effect of ph using OLI. Titre de la Présentation Lieu et Pays Date Jour Mois Année 10

11 DESALTER (4) From OLI simulation, acid consumption can be optimized based on the quantity of contaminants removed Titre de la Présentation Lieu et Pays Date Jour Mois Année 11

12 DESALTER (5) Neutralization curve were also done on real sample to compare with OLI with a good similarity. Titre de la Présentation Lieu et Pays Date Jour Mois Année 12

13 DESALTER (6) 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). Titre de la Présentation Lieu et Pays Date Jour Mois Année 13

14 CONCLUSION 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. Titre de la Présentation Lieu et Pays Date Jour Mois Année 14