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The following papers will feature in the Delayed Coking Track at RefComm Europe:
Challenges of repairing coke drum cracks and bulge repair with structural weld overlay in a tropical climate during a plant shutdown
Presented by MRCSB (Petronas)
MRCSB engaged AZZ for the repairs of two 23-year-old coke drums made from low alloy steel with stainless steel clad that were repaired and strengthened with structural weld overlay. The coke drum crack and bulge repairs were performed in a tropical country during a plant shutdown in June, 2022.
The coke drum diameter was 30 meters high. A non-engineered welding habitat was constructed for the work front to perform external structural weld overlay. The habitat was damaged twice due to heavy rain and strong winds. The challenge was to complete the repairs within the shutdown window of 28 days (with 14 repair days). This presentation covers the details of the problem, solution, and challenges faced during the repair work.
Revamp Project of the KNPC MAB Refinery Delayed Coker Unit
Presented by KNPC
Delayed coking is one of the attractive options for upgradation of residual fractions. Since commissioning, the KNPC MAB Refinery Coker Unit capacity has increased by 30%, overcoming several operational challenges, such as pumps limitations, fouling in fractionator top section trays, manual switching of coke drums, coke quality deterioration, and shorter heater run length. The revamp of the coker unit was implemented in 2019 to mitigate the challenges and address concerns related to mechanical integrity, operability, reliability, HSE and technology up-gradation.
During the initial stage of commissioning post revamp, various issues were encountered related to product yield and qualities; however, process enhancement continued until reaching unit stabilisation and meeting product specifications.
This presentation discusses the revamp work carried out in the KNPC MAB Refinery Delayed Coker Unit to achieve reliable and sustained operation at desired capacity. It explores the various challenges in commissioning and sustained operation of coker unit post revamp conditions.
Solvent Deasphalting Unit Synergies with Delayed Coking, FCC, and Hydrocracker Units
Presented by Wood.
Solvent Deasphalting is a molecular separation process which facilitates a refiner’s ability in sending the right molecules to the intended downstream units such as Delayed Coker Unit, FCC and, heavy oil treating. This simple and low-cost residue upgrading process unit offers overall higher liquid yields when used in tandem with any of the downstream units. The case studies listed below shall discuss the processing constraints such as excess fuel oil in the refinery, unavailable delayed Coker capacity margin, incompatible crude blend, heavier crudes etc. The desired economic objectives and the successful solutions implemented in the refineries in the US and Europe are explained.
- SDA Bottoms to Coker- Opportunity crudes (sweet and sour crudes) are planned while the existing Coker capacity is limited. This case also addresses some of the capacity constraints of the Vacuum Unit capacity while offering higher yields at a lower CAPEX.
- Fuel Oil reduction- SDA Unit is added to process high sulfur fuel oils due to IMO 2020 restrictions while reducing the load on the existing Delayed Coker Unit.
Unconverted Oil from H-Oil unit to SDA Unit- The asphaltenes present in the UCO are processed and removed in an SDA unit offering the highest liquid yield possible while lowering the H2 consumption. CAPEX and OPEX are also reduced.
The above case studies shall offer insight into addressing the common processing challenges faced by any refinery whether the configuration is Hydrogen addition or carbon rejection offering higher overall liquid yields at a lower CAPEX and OPEX.
Delayed Coker Heater On Line Pigging
Presented by NIS
The Delayed Coker Unit in NIS Pancevo Oil Refinery was commissioned and started up in August 2020. The process unit with long history and new technical solutions was choice for improving refinery margins and reducing emissions. One of requirements for the licensor was to have a unit that can work continuously in period of three years. To meet this requirement the NIS DCU is equipped to enable online pigging.
After 10 months of operation, an emergency shutdown, due to power loss, was performed according to procedure and all ESD systems active. Since the restart, an increase in heater cell 2 delta pressure was observed, online spalling was performed, but without improvement.
A decision was taken to perform online pigging. In order to prepare the equipment and crew for this specific activity, a detailed step-by-step procedure was developed, based on the operating manual. In addition, a thorough procedure for putting heater cells back into operation needed developing. Subsequently, activities for preparing cells for pigging, pigging operation and returning oil into the cells were successfully performed. During the pigging procedure, the unit was in continuous operation, processing above 50% capacity of design fresh feed.
DCU Sliding Un-heading Valves experience
Presented by EPROM
This practical, case-study based paper shares operator experience before and after un-heading valves.
Experiences before un-heading valve, e.g. Manual Un-heading:
Manual Un-heading was labor intensive due to the manual nature of unbolting and bolting of the heads. It also became a risky operation when shot coke was present. The feedline was attached to the bottom head for centralizing the channels inside of the drum when feeding. With shot coke, draining the drums became harder due to plugging of the feedline nozzle and the risk increased when manually unbolting. During normal operations, drum to flange leaks were common if there were bad gasket or bolting issues.
Experiences after un-heading vales, e.g. Automated Slide Valves
Less labor was needed and generally made the operation safer. With improvements, come different and unexpected problems. Side entry to the drum instead of bottom entry created drum integrity and different quenching and cutting problems. Upstream valve isolation became more important due to the fact that the feed line is no longer disconnected from the drum when open. Different leak point issues at the drum to BUD flange because it is permanently attached. Finally, challenges with the best way to lock the un-heading valves when in service.
The presentation will share experiences with grassroots and existing unit start-ups with automated un-heading valves
Design of the valves are ok, but the ergonomics around the BUD’s should to be improved. The common problem of the leak point at the drum to BUD flange still exists. The locking system for the un-heading valves can be unreliable and ergonomically difficult. Steam use and condensate system plugging are recurrent challenges. More robust vendor training for both maintenance and operations is needed, especially for those locations that are more remote. For example, Middle East project experiences have exposed challenges getting timely support for spares and technical queries solutions.
Problems with Un-heading Valves
• Incorrect inlock permissive system
• Hydraulic locking systems
• Leak valve seats
• Vacuum resid (VR) leaks
• Steam control
• Coke build up
Wish list for Operational Improvements
• Better communication between licenser and supplier of the un-headed valve
• Better arraignment for operators to get around the valve and for manual operations of the MOV
• Simpler locking
• Better service for the remote refineries
Coker Feeds and Recycles – Chemistry & Quantification
Presented by Coking.com
“Fresh” Feeds to thermal cracking units, primarily cokers, are of two fundamental types – virgin and previously cracked.
• Virgin falls into 3 types – vacuum resid, atmospheric resid and solvent deasphalter tar.
• Previously cracked falls into 3 types – visbroken, FCC product (LCCO or Bottoms) and High Pressure Hydrocracked.
Each of these six feed types has a distinctly different effect in the thermal reactor (coke drum or Fluid Reactor), due to the different chemical molecular composition.
Recycle, meaning previously cracked coker material, is analogous (but different) in behavior to previously cracked fresh feed materials. Both natural and distillate recycles will be discussed.
This presentation will explain the chemistry fundamentals for these feeds and discuss effects on yields and coke morphology. In addition, a method for improved quantification and tracking of natural coker recycle will be discussed.
Coke Drum Studies and Net Present Value Economics
Presented by Becht
As coke drums age, crack repairs occur, either in the skirt or cylinder, on a planned or unplanned basis. These eventualities raise many questions – What is the best repair approach and downtime strategy? When should I replace my coke drums? Should I adjust my coker operations, like warm-up and quench? What is the optimal coke bed level? Is a cycle time change advisable? How do I optimize module squats and turnarounds to achieve the most reliability? Becht can apply its correlative coke drum life prediction tool, understanding of coke drum stress levels, and its Net Present Value (NPV) Economics approach to help answer those difficult questions. The presentation will provide an overview that Becht has now applied for clients around the world.