MODULE 3: PROCESS SIMULATION Steamcracking in general Cokes - - PowerPoint PPT Presentation

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MODULE 3: PROCESS SIMULATION Steamcracking in general Cokes - - PowerPoint PPT Presentation

Apr 29, 2023 16 likes •199 views

MODULE 3: PROCESS SIMULATION Steamcracking in general Cokes formation BASF Qtech, http://www.basf-qtech.com/p02/USWeb-Internet/basf-qtech/en/ Cokes formation Steam in steamcracking Process steam: Recycled within process Used

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MODULE 3: PROCESS SIMULATION

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Steamcracking in general

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Cokes formation

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BASF Qtech, http://www.basf-qtech.com/p02/USWeb-Internet/basf-qtech/en/

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Cokes formation

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Steam in steamcracking

  • Process steam:
  • Recycled within process
  • Used during cracking
  • Decoking steam:
  • Not recycled
  • Used during pretreatment and decoking (removal of

cokes)

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Pretreatment in steamcracking

The purpose of this pretreatment is to form a stable (oxide) layer to reduce cokes formation Goal: formation of a stable, protective oxide layer at the inner surface of the reactor, mostly Cr2O3, but in newer materials sometimes also more stable Al2O3 Method: put a mixture of steam and air through the reactor in the furnace Important parameters:

  • Steam/air ratio
  • Temperatures
  • Duration
  • Quality of steam and feed
  • As
  • Hg
  • Cl
  • Pb
  • Fe
  • Na
  • Dissolved O2
  • NH3
  • Sulphites
  • Phosphates
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Pretreatment in steamcracking

  • Comparable material composition, other pretreatments
  • Obvious big influence of pretreatment, especially in first cracking cycles

1.87 2.1 2.2 11.2 5.1 2.4 2 4 6 8 10 12 14 1 2 3 Coking rate [10-6 kg m-2s-1] Cracking Cycles

Catalytic rate

0.7 0.75 0.78 7.8 3.4 1.5 1 2 3 4 5 6 7 8 9 1 2 3 Coking rate [10-6 kg m-2s-1] Cracking Cycles

Asymptotic rate

Material A Material B

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Influence of aging at elevated temperatures

High T (EOR) Catalytic coking

1CC: COT; 6 hours 2CC: COT; 2 hours 3CC: COT; 6 hours 4CC: COT+110 °C/+160 °C*; 1.67 hours 5CC: COT = base; 12 hours *SCOPE

Reduction after high T exp Reduction after high T exp Increase after high T exp

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Coke after 2 (CC2) and 6h (CC3) ET 45 Micro and HT E + SCOPE comparable HT E significantly worse Line: estimated coking curve

Influence of aging at elevated temperatures

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Extrapolation for 12 h coke Assumptions: 2 h (CC2) = Catalytic 6 h (CC3) = asymptotic

Influence of aging at elevated temperatures

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Extrapolation based on tests prior to high T (EOR) exposure

Influence of aging at elevated temperatures

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Coke after high T exposure

Influence of aging at elevated temperatures

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Estimation coking curve

Influence of aging at elevated temperatures

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HT E better than expected ET 45 Micro worse than expected SCOPE design → Lower temperatures Lower influence high T excursion

Influence of aging at elevated temperatures

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HT E ET 45 Micro After pre-Ox Before high T After high T Oxide to carbide Transition

Jakobi, et al., “The high-Temperature Corrosion Resistance of Spun-Cast Materials for Steam-Cracker Furnaces – A Comparative Study of Alumina- and Chromia-Forming Alloys”, in NACE Corrosion, 2013.

stable

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Summary

Very important to:

  • Test aging of materials at elevated temperatures
  • Optimise pretreatments
  • Condition steam to not damage reactor materials during

pretreatment, cracking and decoking

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CONTACT

Arne Verliefde Professor Universiteit Gent Arne.Verliefde@Ugent.be 09/264.60.02