V. MANRAL and K. MAGDOZA, Chevron Lummus Global, Houston, Texas (U.S.)
Several agencies have published oil supply-demand scenarios, ranging from peak oil in 2030 by the International Energy Agency (IEA) to a demand plateau beyond 2030 by ExxonMobil’s Global Outlook report.1,2 An overall consensus has emerged that peak oil demand will be achieved within the coming decade due to improvements in energy efficiency, the spread of renewables and the continued advancement of electrification. In such a scenario, refinery and coker revamps emerge as a compelling and strategic investment.
Depending on a refiner’s specific goals, a coker revamp could deliver greater operational value in several ways. Revamps for higher capacity allow for an increase in processing capability and product throughput. Revamps for feedstock flexibility enable the unit to accommodate an alternate feedstock supply and product demand portfolio, allowing for flexible operation that can be adjusted as market conditions change. Revamps for energy efficiency and decarbonization minimize energy consumption, decreasing operating costs and lowering the unit’s carbon footprint.
Considering their minimal impact on existing plot space and changes to existing equipment, coker revamps offer a timely and strategic investment. In addition, they enable refiners to future-proof operations by enhancing flexibility, efficiency and sustainability. This article reviews how the different revamp objectives introduced above can be implemented to deliver optimal value to a refinery.
Revamps for higher capacity. The most straightforward way to increase the value of an existing coker unit is to enhance its processing capability. Such revamps typically increase capacity by up to 20%–30%. The maximum available increase in capacity depends on several constraints, such as in-built equipment design margins, availability of plot space and construction feasibility.
Changes in operating conditions also play an important role in coker revamps. For example, coking pressure may need to be increased to limit the higher superficial vapor velocity in the existing coke drums resulting from the increased capacity. Adjusting the coking pressure will affect the coke make and product yields, the impact of which would have to be carefully studied beforehand. Similarly, cycle times are expected to be lowered, as the increase in coke make might cause a bottleneck due to the size limitations of the existing coke drums.
Provided adequate space is available, additional coke drums could be added as another revamp option. For a two-drum coker, this could mean adding another pair of coke drums with an associated heater, which essentially turns the unit into a four-drum coker. For most sites, however, the plot space and/or capital are not available for such an installation.
A more attractive option may be to add a third drum in parallel to the existing pair, thus creating a three-drum configuration (FIG. 1). Requiring less space and capital, the three-drum configuration is designed such that one coke drum is in coking mode while the other two are in decoking mode. The coke drums can be operated at or slightly above the original pressure while maintaining adequate ullage in the coke drums. In addition, the decoking cycle per drum is twice as long as the coking cycle, allowing for lowered cycle times without concern of decoking schedule limitations or blowdown operation. A two-drum to three-drum coker revamp was successfully implemented for a central Indian refiner in 2019, increasing the unit’s capacity by 33.8%.3
In addition to the coke drums, the heater is another important piece of equipment for the delayed coker unit (DCU). When increasing unit capacity, the coker heater must be re-rated for the new operating conditions, and multiple modifications may be required to meet higher firing and heat flux demands. One common upgrade involves replacing the radiant coil metallurgy with stainless steel (TP347H or any austenitic alloy). This allows for higher end-of-run tube metal temperatures (EOR TMT) and enables thinner tube walls, helping to control pressure drop across the coil. In addition, layout changes, such as modifying the radiant coil geometry, can improve heat transfer and flow distribution. An example of this—if plot space and mechanical constraints allow—would be to add roof tubes to the radiant section. This increases the heat transfer surface area, reduces the tube-side heat flux and helps mitigate localized hot spots and high TMTs.
Burner replacement is another common capacity revamp activity. High-capacity, low-nitrogen oxides (NOx) burners may be installed to increase heat input while staying within emissions limits. The forced draft (FD) and induced draft (ID) fans may also need to be replaced or resized to deliver increased combustion air flow and maintain proper draft control under increased loads. Lastly, convection section upgrades, such as adding or replacing coils or installing extended surface finned tubes, can help improve the convection preheat.
For capacity revamps, in-built equipment design margins should be maximized. In cases where the design margins are exceeded, equipment modifications are required. A proper feasibility study will help ensure the optimal approach for each piece of equipment. Such a study might suggest that a pump needs a larger impeller, an additional parallel pump or must be replaced entirely. Heat exchangers and air coolers may require additional shells or bays to accommodate their increased capacity. Columns may require modifications to their internals depending on changes in the vapor and liquid traffic. A smaller, parallel wet gas compressor may be necessary to achieve the higher capacity. With such a variety of potential optimizations, a proper feasibility study is essential to ensure a successful capacity revamp.
Revamps for feedstock flexibility and coke morphology. The DCU is the most inherently flexible unit in a refinery due to its ability to process a variety of feedstocks. However, any change in feedstock will impact the unit and its products. Therefore, understanding these impacts is essential when preparing a revamp. If a refiner planned to process opportunity crudes, for example, it must first understand the effect on vacuum residue properties, such as Conradson carbon residue (CCR), metals and asphaltenes content—all of which would impact coke make, product yield rates and heater fouling. In such cases, pilot testing the new feedstock and conducting a revamp study would prove useful to determine the impacts and adjust the operating conditions accordingly to optimize performance.
The DCU can also process miscellaneous streams from the refinery, such as slop, sludge, filter backwash, slurry oil, unconverted oil and other extraneous byproducts. Typically, the flowrates from these streams are relatively small and are sent to the coker unit to extract value from their disposal. The injection location of these streams will vary, with common points including the fractionator overhead, the blowdown tower bottoms or directly into the fresh feed. The location and impact of these streams on the unit should be studied as part of the revamp effort.
With demand projections for electric vehicles and synthetic graphite expected to rise significantly in the coming years, a different coker revamp option becomes attractive: converting a conventional coker into a needle coker.4,5 Revamping a unit in this manner mainly depends on the availability of aromatic feedstock, typically fluidized catalytic cracking (FCC) slurry oil. Needle cokers operate at a higher pressure and recycle rate, achieving higher coke yields (~50%) and requiring longer cycle times compared to conventional cokers. Given these conditions, a revamp must consider several equipment modifications:
If the existing coke drum’s mechanical design pressure is inadequate, the coke drums must be replaced.
Depending on the feed quality, a fines filtration system or pretreatment package must be installed.
Coke-cutting and coke-handling equipment may require modifications or replacement due to the hardness of the needle coke.
The main fractionator’s internals and bottoms section may need to be changed to accommodate the shifts in vapor-liquid traffic and recycle rate.
With careful planning and execution, a needle coker revamp can be a strategic economic endeavor. Depending on market conditions, the revamped unit can be switched between needle coking and conventional coking modes, further enhancing the unit’s flexibility.
Revamps for energy efficiency and decarbonization. Because decarbonization remains a key trend in today’s environmental and political landscape, refiners are actively seeking ways to reduce emissions and enhance energy efficiency. Coker revamps can help achieve these objectives. A revamp study can identify ways to optimize feed preheating and pumparound circuit heat exchange, either by utilizing the in-built equipment design margins or by installing new exchangers. Pinch analyses can determine the most effective heat integration strategies for the unit.
In addition to directly improving the unit’s energy efficiency, other revamp options can reduce the unit’s carbon footprint. One such option is the installation of an ejector in the blowdown system. The ejector utilizes pressurized steam passing through an expanding nozzle to create a vacuum. By lowering the pressure of the blowdown system, the coke drums can depressurize to a lower pressure before venting, thereby reducing volatile organic compounds (VOCs) emissions to the atmosphere. This also helps ensure that the unit complies with recent U.S. Environmental Protection Agency (EPA) regulations requiring the coke drum to be lowered to 2 psig or less prior to venting.6 In addition, the ejector has the added benefit of being able to send the blowdown vapor to the fractionator overhead for recovery of hydrocarbons near the end of the coke drum cooling step. FIG. 2 shows an ejector implemented into the blowdown system.7
A water ring compressor can perform the same tasks as an ejector. This compressor utilizes a rotating impeller to form a ring of water inside an off-center cylindrical casing, creating variable-volume chambers that draw in, compress and discharge vapors. While an ejector has a lower capital cost and takes less space, its steam consumption will lead to an increase in the unit’s sour water generation. By comparison, a water ring compressor package requires only a small amount of make-up water for operation but requires more capital and a larger plot area. FIG. 3 shows the implementation of a water ring compressor into the blowdown system.7 A feasibility study would help determine which option—the ejector or the ring compressor—best suits the revamp.
The unit’s environmental impact can also be reduced by utilizing a fully enclosed coke handling and slurry system. Such a system omits an open pit/pad, thus eliminating the coke fines and VOC emissions to the atmosphere. A flow scheme of an enclosed coke slurry system is shown in FIG. 4. This system uses an in-line crusher that breaks down the coke and water from the coke drum to form a pumpable slurry. A slurry pump transports the mixture to dewatering bins that separate the water and coke. The clean water filtrate is collected in the drain water tank and routed to the hydrocyclone and the clear water tank for final cleaning and reuse. The coke is discharged from the dewatering bin via a vibration feeder directly onto a conveyor belt, which transports the coke product to the coke storage area. Aside from eliminating dust emissions, the fully enclosed system has several other advantages, including reduced water consumption, lower personnel requirements due to automation, a significantly reduced footprint and flexibility in equipment arrangement. Several fully enclosed coke handling systems have been installed in operating units worldwide.8
Opportunity for modernization. Lastly, refiners can use the time for the unit revamp as an opportunity to modernize any older equipment. For example, improvements can be made to the heater and its auxiliary systems. Ultra-Low NOx burners and SCR systems can be installed to help reduce NOx emissions.9 Cast-type air preheaters can be replaced with plate-type designs for a lighter footprint, easier maintenance and improved heat transfer efficiency. Improving the refractory or insulation can help reduce heat losses and extend equipment life. The upstream feed preheaters can also be upgraded to newer designs for enhanced thermal performance, reduced fouling rates and lower pressure drop. Finally, artificial intelligence and machine-learning can be applied to monitor and optimize heater performance in real time, potentially increasing run lengths and improving overall thermal efficiency.
The coke drums and their auxiliary systems can also be modernized. Top and bottom unheading devices, along with a remote coke cutting system, could significantly enhance the safety and ease of the decoking operation. Feed entry devices on the coke drum can provide a more uniform feed entry, resulting in less stress on the coke drums. Similarly, a vertical plate design for the coke drums can help extend their life. The variety of equipment modernization options makes a revamp feasibility study even more important.
Takeaway. Revamping a DCU presents a strategic opportunity for refiners to enhance operational performance and align with evolving environmental and economic landscapes. Whether the objective is to increase throughput, accommodate diverse feedstocks or improve energy efficiency, each revamp pathway (or combination thereof) requires a tailored approach grounded in technical feasibility and site-specific constraints. Refiners can unlock significant value from their coker units by leveraging existing design margins and incorporating modern technologies. A comprehensive revamp feasibility study remains essential to ensure that the revamp decisions are both technically sound and economically viable, ultimately supporting long-term refinery sustainability amid a time of energy transition and demand uncertainty. HP
LITERATURE CITED
International Energy Agency (IEA), “World Energy Outlook 2024,” October 2024, online: https://www.iea.org/reports/world-energy-outlook-2024
ExxonMobil, “ExxonMobil Global Outlook: Our view to 2050,” August 2024, online: https://corporate.exxonmobil.com/sustainability-and-reports/global-outlook
Magdoza, K. and V. Manral, “Delayed coker revamp for a capacity increase,” Petroleum Technology Quarterly, January 2021.
Manral, V., M. Antoniou, K. Magdoza and V. Suri, “The attractive market opportunity for synthetic graphite: Graphite as an energy transition material,” Hydrocarbon Processing, August 2024.
Manral, V., M. Antoniou, K. Magdoza and V. Suri, “Synthetic graphite demand drives attractive techno-economics for coker upgrades,” Hydrocarbon Processing, January 2025.
US EPA 40 CFR § 63.657, “Delayed coking unit decoking operation standards,” November 2018, online: https://www.ecfr.gov/current/title-40/section-63.657
Lorenc, P., K. Magdoza and V. Manral, “Design configurations for lowering quenched coke drum venting pressure,” Petroleum Technology Quarterly, January 2023.
Kaminski, M., V. Manral, B. V. Heeswijk, F. Graeter, and S. Knuedel, “Successes and challenges installing the first proprietary closed-coke slurry system,” Hydrocarbon Processing, February 2021.
U.S. Department of Energy, “Ultra-Low NOx Premixed Industrial Burner,” May 2025, online: https://www.energy.gov/eere/iedo/ultra-low-nox-premixed-industrial-burner
Virendra Manral is the Delayed Coking Technology Manager for Chevron Lummus Global. He earned a degree in chemical engineering from Panjab University in India and is a registered Professional Engineer in Texas (U.S.).
Keith Magdoza is a Senior Process Engineer with Chevron Lummus Global. He earned a degree in chemical engineering from the University of Texas at Austin and has worked in delayed coking process engineering for Lummus Technology for more than 10 yrs.