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Jun-2011

Safe, reliable and maintenance-free coke drum unheading

The process of coke drum unheading within oil refining has traditionally been one of the most dangerous activities in the industry. Even today such operations continue to result in accidents and, unfortunately, even fatalities.

David Anderson, DeltaValve
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Article Summary
According to local reports, a worker at an Oklahoma refinery in the US suffered burns to nearly 70% of his body as a result of scalding water bursting from the bottom of a coke drum and striking him. Just eight months earlier at a refinery in California, a similar incident occurred, with the refinery worker receiving second and third-degree burns over 85% of his body. Tragically, he passed away as a result of the incident at the delayed coker.

In a joint bulletin entitled Hazards of Delayed Coker Unit (DCU) Operations, released in August of 2003, the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency’s (EPA) Chemical Emergency Preparedness and Prevention Office stated: “Unlike other petroleum refinery operations, the DCU is a semi-batch operation, involving both batch and continuous stages. The batch stage of the operation (drum switching and coke cutting) presents unique hazards and is responsible for most of the serious accidents attributed to DCUs.”

The bulletin advised: “Consider equipment upgrades to further control the hazards associated with geysers and release of hot tar balls and undrained hot water during drum head removal, such as installing protective shrouds and automating both top and bottom head removal operations to keep workers away from these unprotected areas.” Such advice is given because the most common injuries to plant personnel working on delayed coker structures are burns caused by steam, hot water or coke. Also, many have suffered long-term effects from repetitive stress injuries caused from working pneumatic hammers and other impact equipment over extended periods.

A new standard
Traditional methods of coke drum unheading include manual or semi-automated unheading systems, which are labour intensive, costly to maintain, expensive to repair and include inherent risk for workers on the unheading deck. Until recently, the concept of using a valve for coke drum unheading had never been realised, held back by the severe nature of the coking and unheading process.

In the late 1990s, DeltaValve, embarked on the development of a highly engineered solution to traditional unheading. In September 2001, it installed the world’s first fully automated coke drum unheading system at the Chevron refinery in Salt Lake City, Utah. Unlike traditional coke drum unheading technologies, this fully automated unheading system created a completely sealed system from the top of the coke drum down through the discharge chute, completely and permanently isolating personnel and equipment from exposure. Since this first installation nearly nine years ago, there has never been one recorded safety incident worldwide with a DeltaValve fully automated coke drum unheading system. This technology has revolutionised coke drum unheading and has set a new global standard in safe and reliable coke drum unheading.

Safety and reliability are key
The most effective way to keep coke drum personnel safe during the unheading process is to completely remove them from the unheading deck and control the unheading process from a remote location. By introducing fully automated valve technology into coke drum unheading, remote operation has become a reality. Personnel are no longer needed on the unheading deck to unbolt the unheading flange or disconnect the feed line, but rather unheading can be accomplished by simply pushing a button from a remote location.

Counter to the objective of safe unheading is operating an unreliable unheading system. If an unheading system is unreliable, personnel must still go onto the unheading deck to resolve issues. If a breakdown occurs when the coke drum is not active, having personnel on the deck might not be a problem. However, if a breakdown occurs during a coking cycle with an energised drum or during the unheading procedure, personnel close to the drum can be exposed to significant hazards.

In addition to physical harm to workers from coke drum unheading incidents, there can be negative financial consequences, including damaged equipment, unscheduled downtime and expensive lawsuits. Additionally, in a time when refineries are coming under increased environmental scrutiny, having an unheading incident that results in a fire or hydrocarbons being released into the atmosphere can also be extremely detrimental. In difficult economic times, refineries simply cannot afford unscheduled downtime from unsafe or unreliable equipment at the delayed coker.

Ease of maintenance
Delayed cokers have a reputation for causing unplanned shutdowns largely because the equipment is subjected to severe service conditions. The problem is greatly compounded when producing coke with manual unheading systems, for which routine maintenance is a daily or weekly requirement. Constant unheading device maintenance and repairs delay coking cycles and reduce overall throughput, productivity and profitability.

Due to the inherently simple design and minimal moving parts of a fully automated single-gate unheading system, maintenance is rarely required. The valve is designed to operate from refinery turnaround to turnaround basically maintenance free. Care should be taken to avoid unheading systems that have complex internal or external moving parts, which can clog, wear or fail. A fully automated unheading system that uses a simple single-gate has proven to successfully operate from turnaround to turnaround without unscheduled maintenance.

Additional benefits
Since September 2001, fully automated single-gate unheading valves have made a significant impact on the amount of feed processed through delayed cokers around the world. A fully automated unheading valve can reduce total times from 30 minutes to more than an hour per coking cycle. For most refiners, this saving is significant. For example, if a refinery is running dual coke drums at 14-hour coking cycles, which means they fill each drum every 28 hours, the potential productivity increase for a 60-minute cycle time would be 3.5%. Meanwhile, unheading and reheading has gone from a potentially dangerous, time-consuming activity to an situation where a button is pushed and control systems with feedback devices monitor the whole process, taking less than three minutes from start to finish. With manual unheading, these activities could take one to two hours and involve a high degree of uncertainty and risk.
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