Delayed Coking Unit – How to improve the process performance ?

Delayed coking unit

Delayed Coker, n. : “Simple, clean & efficient way to upgrade heavy petroleum residues”

Back in the 30’s, vehicles’ improvements and war activities have increased the global gasoil and diesel fuel demand. In order to deal with this matter, ‘heavy residues processes’ and thermal cracking units were installed over the years (especially in US refineries at the beginning).

Thermal cracking belongs to an old process technology. Nowadays, our coking processes are quite advanced and able to answer to new environmental regulations.

The DELAYED Coking process (DCU) is the predominate coking technology available on the market :

  • Process heavy residues to produce distillates (naphtha & gas oils) that may be catalytically upgraded via Hydrotreating, catalytic cracking and/or Hydrocracking
  • Attractive for bottom of the barrel not suitable for catalytic processes as the feed contains large resins concentrations, asphaltenes & heteroatom compounds (like sulfur, nitrogen, oxygen, metals…)
  • Several metals, Sulfur & other catalyst poisons generally end up in solid coke. The solid coke will be sold for other purposes.

The typical process equipment is composed of :

delayed coking typical process equipment guichon valves solutions

The main goal: Convert residues to high valuable products such as LPG, Ethane, Propane, Gasoline, Light and Heavy Gasoil..etc.

typical delayed coking unit guichon valves solutions

More and more commercial units have been sold and results are exciting! One of the conclusion is that the global profitability of a DCU is depending on valves reliabilityDesign Improvement is worth-it!

Same thing regarding safety and environmental concerns ! Back in the years, manual decoking was a hot, dirty and absolutely unsafe job !

“Feeds and requirements are changing but technical challenges are still the same : Reliability, Safety and Performance”

Many valves are installed on a DCU, and a lot of them are considered critical :

critical valves on DCU guichon solutions

Twotypical service conditions in dcu typical services conditions met in a DCU : Dirty service and Clean Service. Both of them refer to specific technical challenges (hereunder) and designers should take care of valve matters accordingly.

The most critical valves on a DCU are :

  1. The TOP/BOTTOM UNHEADING & FEEDING SYSTEM (directly connected on the bottom and on the top of each coke drum)
  2. The SPECIAL ISOLATION VALVES (on overhead lines and feed/slurries lines)

There are a lot of technical constraints on those ones !You should, at least, consider :

  • Erosion due to coke slurries, coke particles in the lines (corrosion + sealing issues !)
  • High Temperature (Around 500°C and even more on new processes !)
  • Nominal diameter from 24” to 130”
  • Fugitive emissions and safety rules
  • 5 years maintenance free

Several custom-made valve solutions are able to fit the process requirements coming from the main Licensors Specifications (Wood, KBR, UOP, CB&I, ExxonMobil, ConocoPhillips…)

Backed with more than 40 years of experience in petrochemical applications, Guichon Valves designed several tailored valve solutions installed on DCU :

” Golden Rules – Good practices to keep in mind regarding valve selection”

  1. Do not use conventional gate valves on critical lines. They are unsafe due to coke particles (abrasion, corrosion). Coke particles buildup on the seats and the valve starts to get stuck easily. It requires several maintenance operations.
  2. Prefer single slide for feed lines to optimize tightness and safety. Seats are protected during the full bore opening.
  3. As much as possible, use seat extensions on your valves to prevent coke build-up inside the valve body. Double seats solutions can help as well.
  4. Always use steam injection on feed and cracked gas isolation valves.
  5. Use a bidirectional sealing to protect the process in case of back-flow.
  6. Ask your valve manufacturer for a reliable shut-off standard (API 598 or FCI 70.2 Class V at least).
  7. For Top and Bottom Unheading valves, use a double disc through conduit valve with the Secure Sealing System (2 separate wedges into the valve body to avoid over torqued strokes).

Many tailored solutions can improve the global process reliability !

graphic cost valves dcu

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Written by Rudy Repellin