Refinery Coker Unit Services and Delayed Coker Basics
Delayed Coker Project Development and Engineering Services
Whether the scope is simply a drum replacement or an extensive Coker expansion, the Team of PROCESS and APMI can identify the options, and complete a cost estimate and milestone schedule for a Coker revamp. An efficient Delayed Coker operation enhances a refinery’s profitability, safety, and long-term viability. Although Coker margins fluctuate, almost all U.S. and many international refiners have Delayed Cokers. All refiners are looking for improvements in profitability, efficiency, safety, and on-stream factor.
Process Engineering Associates, LLC (PROCESS) and Adams Project Managers, Inc. (APMI) are teaming up to perform Coker revamp and modernization studies. Study reports include a ‘roadmap’ and recommendations of path forward that provide the refiner with a plan to upgrade their Coker. Why is this important?
- The right time to analyze modernization and expansion options is before new drums are ordered as part of periodic coke drum replacement. Larger drums and shorter cycle times may be possible and will increase capacity.
- Grassroots Coker investments are difficult to predict. Some refiners have started with Engineering/Procurement/Construction (EPC) companies on grassroots cokers and stopped the process due to costs exceeding estimates which resulted in less favorable economics than initially expected. This becomes a bigger issue as refinery margins drop.
In contrast, a revamp project of an existing Coker can be more accurately estimated because the scope is smaller and all of the related process ramifications are looked at in detail. Results of revamps often include installing new larger sized drums, deheading valves, and other modernization upgrades for perhaps only one-third (1/3) of the cost of a grassroots Coker, especially when offsite systems and site development costs are considered. In many cases, this is an excellent way to provide increased capacity with lower and more certain capital cost outlay.
- Inside battery limit (ISBL) investments for grassroots units completed in 2007- 2008 increased by 15-35%+ versus 2004 estimates. This was mainly due to high EPC activities, escalating materials costs, and associated lower productivity. 2009 costs did decline as project activities were cut back.
- Outside battery limit (OSBL) investments for grassroots cokers are generally higher then most estimates indicate and can be a significant percentage of the overall capital project cost (20-40%). This is partially due to cost escalation but is also often due to scope creep.
- Foundations can normally take new drums up to one foot diameter larger with no or only minor foundation modifications. However installing automated deheading valves also adds considerable weight and must be considered.
- Drums greater than one foot in diameter larger than existing drums will typically require a new coker island, i.e., a new coker island generally includes a new foundation and derrick, new pit or pad, an upgraded or new jet water pump, and several fractionator modifications.
Here are a few things we have observed that support revamps instead of grassroots coker projects to increase capacity:
Coker modernization studies almost always include a site visit and facilities review to identify constructability and safety issues. Also included are simulations with process analyses, specific recommendations relating to the refiner’s objectives, and a milestone schedule for recommended projects. Studies typically include an analysis of cycle times, drum outages, level controls, operating conditions, heat exchanger and furnace operations, fractionator simulation and recommendations, and a pressure survey. The Coker gas plant can also be simulated, if gas plant capacity is an issue.
Our Team has project management expertise and can assist the refiner in selecting technology or drums suppliers, if needed. We also understand the Front-End-Loading (FEL) process and can complete analyses consistent with the refiner’s FEL protocol.
The expert team from PROCESS and APMI stands ready to help you modernize your Coker.
What We Provide
Analysis of Existing Coker Operations
Our analyses typically start by reviewing each of the following at the operating site:
- Coke drum replacement options, cycle times, de-heading options
- Heater design, on-line spalling considerations
- Fractionator design
- Existing interlocks
- Vacuum unit rundown
- Transfer line issues from furnace to coker
- Jet water pump and coke cutting
- Coke handling and movement
- Compressor capability
- Pipe sizes
After completing the on-site review of the existing coker operations, the coker system will be simulated using commercial simulation software. Improvements, changes, and other operating scenarios will be analyzed. Benchmarking will be done relative to best available practices. A report will be developed that will function as a road map to improve operations and maximize efficiencies. A typical report contains the following at a minimum:
- Refiner’s objectives
- Existing coker review results
- Simulation outputs
- Operating scenario analysis
- Recommendations for improving economics
- Expected results for each recommended action
- A refinery specific timeline based on coke drum change outs and expected capital availability
Typical studies are completed within 3 to 6 months and recommended actions are implemented on a schedule that fits the client's operations. Our reports include all calculations, analyses, and supporting information needed to decide the best path forward in the near term and longer term. We also have experienced staff to provide Process Hazards Analyses (PHAs) for your coker unit and Pre-startup Safety Reviews.
Implementing Coker Improvements
APMI and PROCESS will continue to support your coker improvement efforts after the revamp plan has been developed. Independent oversight of coker modifications, project management during detail engineering and implementation, upstream/downstream process design and optimization, and process safety services are just a few of the services that help to make your coker unit modernization/revamp successful.
Our goal is for your coker to operate safely and efficiently to maximize profitability.
What We Evaluate
We come to your facility prepared to review and evaluate the following areas:
- Crude oil assay
- Coke drum characteristics
- Drum metallurgy, cladding
- Drum cycle and crack history
- Design and operating pressure
- Deheading methodology (automated or manual)
- Coking cycle
- Qualified fabricator
- Schedule for turnaround
- Structure (optional)
- Foundation (optional)
- Cutting deck
- Compressor capability
- Heater design
- On-line spalling options
- Fractionator design
- Vacuum unit design and operation
- Transfer line from furnace to coke drum
- Coke cutting system and use of combination cutting tools
- Jet water pump
- Coke handling and movement
- Crane or front-end loader coke handling
- Coke water/hydrocarbon content
- Technology licensor options, if appropriate
- Environmental (optional)
Our analysis approach provides a systematic review of the refiner’s coker unit and coke drum replacement options including process simulations, FEL cost estimates, economics, and recommendations for future enhancements.
PROCESS and APMI possess expert process engineering capabilities and hands-on coker benchmarking, coke drum replacement oversight, and coker revamp experience. We can provide independent analysis not motivated by vendor or detail engineering/construction concerns. Our staff of over 40 Chemical Engineers and our in-house process safety experts are ready to help take your coker unit to the next level.
PROCESS has expertise providing a wide range of process engineering services, including:
- Process design
- Process modeling and simulation
- Process related construction oversight
- Commissioning and startup assistance
- Process safety services (PHAs, etc.)
APMI has expertise in project development and project management for Coker and refining revamps, including grassroots units. Services include:
- Coker revamp and modernization
- Coke drum replacement
- Automated deheading valve installations
- Capital project management
- Open art coker analysis
- Technology licensor selection
- Refinery unit revamps
- Grassroots refinery planning and permitting
PROCESS and APMI are available to perform coker optimization work for clients in most parts of the world. We have past experience in North America, South America, Australia, Europe, the Middle East, India, and China.
The narrative below provides a basic and somewhat simplified overview of the delayed coking process. A more detailed overview can be viewed on our web site presentation called "Coking 101".
Delayed Coker feedstock is material coming from bottoms of the refinery Vacuum Distillation Unit (VDU). The objective of the Delayed Coker (Coker) is to process the asphalt-like material from the VDU (called Vacuum Residue) to produce marketable products, such as gasoline, diesel fuel, LPG, and petroleum coke. In essence, the Coker is a unit that is able to squeeze out the last amounts of hydrocarbon materials that can be used as fuels.
[Note: for simplification the above diagram does not show pumps, heat exchangers, or minor equipment]
The Coker Fractionator is a key component of the Coker and one of the most severe distillation services in a refinery, both in terms of reliability (on-stream factor) and variability of feedstock. It receives the feedstock from the refinery vacuum unit and combines it with hot, cracked gas and liquids from the operating coke drum. The load to the fractionator varies widely with drum switches and crude feedstock quality. The coke drum feed to the fractionator contains steam, coke particles, and a 'wild' mixture of sour hydrocarbon gases and liquids. For this reason it is very important that the fractionator have on-stream clean out capability, proper metallurgy, and a selection of internals allowing critical operating flexibility. A fines removal system is also necessary in the bottom of the tower. The fractionator is not a service where "one-size-fits-all." It takes experienced process engineers to design the fractionator and its' internals to meet the specific refiner's needs.
The residue feed temperature to the tower varies, dependent on whether feedstock comes from interim storage or directly from the vacuum tower, but the fractionator flash zone temperature is usually in the 750o F range. The fractionator pressure is dependant on the coke drum pressure which varies from 25 to 50 psig, dependent primarily on when the coker was constructed. The resulting overhead pressure may be anywhere from 10 to 35 psig.
Products that may be recovered by the fractionator and associated gas plant include:
- Liquid Propane Gas (LPG) and Fuel Gas (FG) for use in fuel or other products
- Naphtha which is sent to other refinery units for processing into gasoline, etc.
- Light Coker Gas Oil (LCGO) and Heavy Coker Gas Oil (HCGO) which are sent elsewhere for hydrotreating and further processing into diesel, gasoline, and other products
- A bottoms stream which provides feed to the Coker Furnace and Coker drum
The Coker Furnace heats the heavy liquid material from the bottom of the Fractionator to a temperature in excess of 900o F (480o C.) Heating causes the heavy liquid material to 'crack' or chemically change into a combination of smaller compounds. Steam is normally injected to minimize the cracking until it reaches the Coke Drum where cracking and coke formation is desired. Cracking in the furnace and coker feed transfer line are undesirable because this lowers yields and requires more frequent furnace de-coking.
Coker units typically have 2 or more coke drums which operate in pairs in a semi-batch mode. In the Operating Coke Drum, the material from the Coker Furnace (at high temperature and low pressure) is injected into the bottom of the drum and 'cracked' into:
- Products which are returned to the fractionator for recovery
- Petroleum coke that solidifies in the drum
The offline coke drum is steamed, vented, and partially cooled prior to the drum being opened to the atmosphere. After this drum is open, the solid petroleum coke is cut from the drum using high pressure water. A jet water pump produces high pressure water that is fed to a rotating cutting bit on the end of the drill assembly. The drill assembly is lowered and raised into the coked drum via the tall drill bore cutting derrick which is a skyline feature of coker units. Petroleum coke, typically referred to as 'coke', is similar to coal and is typically blended with coal and used as fuel in power plants. Petroleum coke has a high fuel value and will therefore typically burn much hotter than mined coal.
Modern Cokers have automatic slide deheading valves on the top and bottom coke drum flanges to allow the coke drums to be opened remotely for cutting the coke out of the drum. The use of automatic slide valves greatly enhances the safety aspects of decoking the drums. These valves are remotely operated which negates the need for direct human presence at either the top or bottom of the coke drum during opening. Historically, the flanges were opened manually with great effort and potential for hazardous situations.
The coke and cutting water flow onto a Coke Pad or into a Coke Pit, where the water is separated and reused. Normally, either a bridge crane or front end loader is used to load the coke for shipment, either by rail car or dump truck.
An additional basic introduction to Cokers called Coking-101 is posted on our web site's Tech Topics section.
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