Thermal Gasoil Process System - Preservation & Layup

February 3, 2022

The volatility of the oil and gas market means that refinery operations can fluctuate at any time. Sudden changes in the market outlook may require certain processes or equipment, such as Thermal Gasoil units, to temporarily shut down until demand and accompanying profits increase. Proper preservation during downtime is integral in maintaining assets in prime, ready-touse condition. One especially critical consideration is corrosion protection, which can be achieved with proper layup guidance and technologies. In particular, Cortec® VpCI® Technologies have a reputation for quality of protection and ease of use in many industrial preservation situations and can be beneficially applied to the Thermal Gasoil unit, as well.

Thermal Gasoil Production: The Thermal Gasoil process converts heavy gasoil or waxy distillate and atmospheric residue into a higher quality intermediate hydrocarbon (i.e., middle distillates or gasoil), which can be used for heating, diesel fuel, and other purposes. This process uses soaker visbreaking (a more efficient method of viscosity reduction than other visbreaking technologies) to convert residue, and an integrated recycle heater
system to upgrade the waxy distillate.[1-5]

General Process Flow: Atmospheric (or vacuum) residue is heated with cracked residue in preheat exchangers, then pumped to the visbreaker heater (1) and the soaker (2), where most of the conversion occurs under precise pressure and temperature controls. The resulting distillate passes to a cyclone (3) that sends overheads to an atmospheric fractionator (4) where a light gasoil and other desired distillates are formed. Bottoms from the cyclone and fractionator then travel to a vacuum flasher (6) for recovery of waxy distillate (vacuum gasoil). This is combined with recovered unconverted heavy gasoil and additional conversion is completed under high pressure in the distillate heater (5).[1-2, 4-5]

System Layup:

Engage Cortec® and Cortec® Global Services, Inc., early in the planning stage to identify potential sections of the system that can be protected before or during the shutdown process and discuss system requirements and constraints.

• Will system and/or subsystems be cleaned prior to preservation. If so, how?
• Will systems and/or subsystems be cleaned prior to startup. If so, how?
• Can the system be segmented into subsystems?
• Will subsystems or components require isolation?
• Is there a catalyst in the system and will it be removed?
• What types of non-metallic seals and gaskets are present?
• Have all access points for product application been identified?
• Which specific systems and components need to be preserved?
• Where are all isolation points from other connected systems?
• What chemistries are banned and/or controlled (e.g., chlorides)?
• What level of Cortec® and/or Cortec® Global Services, Inc., support is required?
• What kind of power supply is available, and where is it located?
• What kind of support is available from the plant?

Components:

1. Visbreaker Heater
2. Soaker
3. Cyclone
4. Atmospheric Fractionator
5. Distillate Heater
6. Vacuum Flasher
7. Piping
8. Valves
9. Pumps
10. Controls

References

1. Bee. Hydrocarbon Processing. “Thermal Gasoil Process by Shell.” 25 June, 2019. Accessed 1 November 2021
<http://hydrocarbon.processengineer.info/thermal-gasoil-process-by-shell.html>.
2. CB&I. “Shell Thermal Gasoil.” 2012. Accessed 1 November 2021 <https://nanopdf.com/download/shellthermal-gasoil_pdf>.
3. Middle Distillates / Gasoil. “Important Terms from A to Z.” Oiltanking.com. December 2015. Accessed 3 November 2021 <https://www.oiltanking.com/en/news-info/glossary/details/term/middle-distillatesgasoil.html>.
4. “Shell Thermal Conversion Technologies.” Accessed 1 November 2021 <https://visbreaking.tripod.com/STGP.htm>.
5. “Visbreaker.” Wikipedia. 8 December 2020. Accessed 1 November 2021 <https://en.wikipedia.org/wiki/Visbreaker>.

Keywords: Cooling tower, seasonal layup, cooling system, heat exchangers, corrosion, cooling system repairs, non-budgeted repairs, avoid system failure, cooling tower exterior protection, Cortec

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