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Automated decoking solves coker safety challenges

11.01.2011  |  Botros, I. ,  Flowserve Corp., Irving, Texas

The concept improves safety and efficiency and bolsters the bottom line

Keywords: [automated decoking] [coking] [coker] [safety] [remote cutting] [efficiency] [shared information portal] [DCU] [PLC]

Safe, efficient operation of hydraulic decoking equipment is critical to the financial success of the entire refinery. Refineries report that a coker unit outage can cost up to US $1 million per day, while the financial impact of an accident in the delayed coking unit can be in the tens of millions of dollars.

Improving safety and performance are the mutual objectives of refiners and equipment manufacturers. One way to achieve better safety is through fully automated decoking. This is now possible with an integrated, intelligent technology platform coupled with a programmable logic controller (PLC). The benefits of remote and automated coke cutting are:
• Improved safety of cutting personnel
• Process efficiency and consistency
• Improved reliability of equipment
• Data recording for process optimization and troubleshooting.

Remote cutting.

Improving safety is the mutual objective of refiners and equipment manufacturers. One sure way to achieve this goal within the DCU is by removing the operator from the cutting deck. Traditional decoking combination tools require extensive handling by an operator to manually shift cutting modes (Fig. 1). This is a cumbersome and hazardous operation exposing cutting deck personnel to:
• High-pressure water discharge
• Hot spots or steam eruptions
• Hydrogen sulfide (H2S) vapors
• Mechanical hazards, including hei-ghts and high winds.

 

  Fig. 1. Traditional decoking
  combination tools require
  extensive handling by an
  operator. 



A combination cutting tool eliminates these dangers and reduces cycle time by shifting modes automatically and remotely inside the drum through water pressurization and depressurization (Fig. 2). The ability to remotely shift operating modes means operating personnel do not need to be on the cutting deck, risking exposure to the aforementioned hazards. Also, the time savings positively impact the production capacity of the refinery by reducing the decoking cycle times by 20 to 30 minutes and allowing the drum to be available for the next cycle.

 

  Fig. 2. The autoshift tool
  eliminates dangers and
  reduces cycle time by shifting
  modes automatically and
  remotely inside the drum. 


In the event of cave-ins or slumped bed conditions, the remotely operated auto-shifting combination tool provides the flexibility to remove a “stuck” tool quickly and efficiently. Shifting between modes is accomplished by switching the decoking control valve into the bypass position or, in the case of variable speed driven pumps, by slowing the pump to idle speed and then re-accelerating to rated speed.

For successful remote operation and safety in coke cutting operations, several other best-in-class equipment and information solutions are needed, including:
• A remotely operated winch and rotary joint
• Remote drum unheading capability
• Automatic guide plate and tool enclosure
• Drum vibration monitors to determine tool position and cutting progress
• Cutting equipment sensors to monitor tool rotational speed, wire rope system tension, etc.
• Interlocked safety systems for cutting water flow control
• Data monitoring, transmission and control systems within an integrated technology platform
• A remote operator enclosure with a master control panel
• Video and acoustic equipment to observe cutting deck activities, as well as coke chute and pit status (Fig. 3).

 

  Fig. 3. Looking behind the
  curtain of hydraulic decoking
  system process evolutions. 



The key element to improve coke cutting efficiency is gaining precise knowledge of the auto-shifting combination tool’s position, both inside the drum and after the coke has been removed. Coke drum monitoring instrumentation provides coke cutting personnel positive confirmation of both these conditions so the decoking process can continue.

Four vibration monitoring devices are permanently mounted at equally spaced intervals on the outer drum wall with another on the coke chute. Permanent mounting allows for a high signal-to-noise ratio to provide a more accurate readout (Fig. 4).

 

  Fig. 4. Coke drum monitoring and vibration systems.


As the coke is removed from the drum, the high-temperature accelerometers monitor the vibrations on the coke drum wall and relay the information to a data collection device. The signals are processed and the tool location and coke cutting status are displayed on a video screen where the operator can clearly see if the section of the drum being cut has been cleaned. This feature also reduces cycle time, as the tool is automatically advanced as soon as a section is cut, rather than stopping while the operator takes time to ensure a clean section. The four sensors mounted on the drum give the operator feedback at each level of cutting. The chute sensor provides information on coke exiting the bottom of the drum and is a necessary asset for safe operation in low-visibility and remote cutting operations.

In addition to the vibration sensors, feedback on cutting progress is enhanced by an audio and video system designed to help the operator determine when the section of the drum is clean. As the coke is removed from the drum, the sound of the impinging water changes, allowing the operator aural recognition of a clean section (Fig. 5). Simultaneously, a video monitoring system allows the operator to view the coke chute, thereby alerting the operator when no more coke is being removed.

 

  Fig. 5. As the coke is removed from the drum, the sound of
  the impinging water changes, allowing the operator aural
  recognition of a clean section.



This positive feedback enables the operator to advance the cutting tool at the earliest opportunity, reducing the total time needed to clean the drum and eliminating some of the guesswork currently associated with coke cutting. The coke drum monitoring system is completely integrated into the decoking control system’s master control panel. The operator display provides real-time feedback on drum cleanliness and cutting status.

One master control panel can be designed to operate the decoking equipment for each pair of drums in the DCU. The panel is designed to control and monitor:
• Drum selection and in-drum indication
• Crosshead latch/unlatch status
• Winch and rotary joint speed control and position indication
• Decoking valve position and valve condition
• Cutting water pressure and pump condition
• Cable tension indication
• In-drum cutting progress.

Additionally, safety interlocks and emergency shutdowns are integrated for cutting, water system flow control and for the unheading devices.

 

  Fig. 6. A video monitoring system allows the operator to view
  the coke chute.



Automated decoking takes remote cutting to this ultimate step by capitalizing on the advanced monitoring, diagnostic, control and instrumentation capabilities of an integrated, intelligent technology platform coupled with a PLC. DCU operators can now custom design and install the requisite computer software and algorithms, instrumentation and embedded intelligence to automatically operate the hydraulic decoking system while protecting it from unanticipated downtime. Moreover, a single operator can monitor the entire process in safety—away from the cutting deck.

An integrated technology platform makes the benefits of data acquisition, diagnostics and intelligent control more accessible to DCU operators. It helps lower life cycle costs by delivering actionable information to optimize process control and equipment operation. High-speed data acquisition of dynamic sensor signals along with the convergence of multiple data streams into embedded diagnostic and control algorithms makes this possible.

Among the benefits of an integrated, intelligent technology platform are:
• Continuous, highly accurate sensor signal condition monitoring and data logging in realtime
• Reliable detection and diagnostics to identify mechanical and hydraulic anomalies
• Intelligent control through automated control capabilities to adjust equipment and system parameters
• Data visualization through a shared information portal providing access to performance history, exception notification, reporting, etc. (Fig. 7)
• Seamless integration into distributive control and equipment health management systems
• Protection from high-risk process conditions with equipment-specific software to help operators proactively diagnose and manage unique, as well as common, operating problems.

 

  Fig. 7.  An integrated technology
  platform provides a complete
  solution for intelligent monitoring,
  visualization and anomaly control. 


The practical application of an integrated, intelligent technology platform is nearly limitless. For example, by applying onboard sensors to critical system components such as the hydraulic decoking jet pump and decoking control valve, the DCU operator is able to realize significant uptime improvements by actively monitoring for process and equipment problems that may lead to unscheduled downtime and reduced production. Using data acquisition tools and the shared information portal, experts from around the world—including the supplier’s DCU specialists and hydraulics engineers—can monitor, diagnose and communicate necessary solutions and recommend actions to increase unit uptime (Fig. 8).

 

  Fig. 8. Panel view display. 



There are two approaches to automated decoking. The first is called pre-programmed cutting, a semi-automated system in which an operator interface is required. This approach is a programmed cutting operation with a fixed sequence, but there is no feedback signal about the cutting progress. The program is customized based upon the established best practices of the unit’s operators. The basic parameters include vertical cutting position increments, dwell time and rotary joint speed control.

The second approach is a fully automated system featuring cutting control and continuous feedback signals for equipment and drum status. It includes embedded intelligence to process signals for monitoring and control, whereby operator interface is only required for sequence exceptions. Operator safety is further improved by integrating an automated cutting system with a PLC interlock.

The benefits of automated decoking with fully integrated, intelligent monitoring control systems and access to a management portal are impressive: improved safety, more efficient process cycles, greater equipment and system reliability and higher operating profit.

More specifically, these benefits include:
• Improved cutting personnel safety as an automated cutting system with PLC interlocks minimizes the possibility of operator mistakes and eliminates operator “shortcuts.” Standardized cutting procedures also reduce the risk of aggressive cutting practices.
• Process efficiency and consistency are achieved since the cutting program advances as soon as possible with consistent cutting times and standardized cutting procedures.
• Improved equipment reliability as continuous equipment condition monitoring results in predictive maintenance for the jet pump and other critical decoking equipment. Damage from aggressive or improper cutting techniques (example: ramming the tool into the coke bed during boring operation) can be eliminated.
• Data recording for process optimization/troubleshooting is collected continuously. When properly analyzed, this data can be used to optimize cycle times, troubleshoot and avoid failure events, and monitor performance for predictive maintenance.

Safety improves via automation.

Largely made possible by the auto-shifting combination cutting tool, remote coke cutting provides greatly improved safety by removing the operator from the cutting deck. Automation through an integrated technology platform further improves DCU operational efficiency and process consistency. Intelligent monitoring and control systems assist in process optimization, improved equipment reliability and maximum DCU availability. The ultimate result is safer, faster and more efficient coke cutting. HP

The author 

Ihab Botros currently serves as director of global special products for Flowserve Corp. and has global responsibility for the Flowserve special products portfolio, including hydraulic decoking systems, multiphase pumps, reciprocating pumps, subsea pumps, high energy barrels and ebullated bed reactor recycle pumps. Mr. Botros earned his bachelor of science degree in mechanical engineering from Alexandria University as well as a masters degree in mechanical engineering from California State University in Long Beach. 



Remote coke cutting

To move the operator from the cutting deck to a remote location, the following is required:
Equipment
• Remotely operated, auto-shifting combination cutting tool
• Automatic guide plate or tool enclosure
• Remote winch and rotary joint operation
• Vibration/acoustical devices
• Video equipment
• Remote operator enclosure

Information
Data sent remotely to operator:
• Cutting tool position and rotational speed
• Cable tension and auto-shifting combination cutting tool mode
• Drum status
• Video feedback for pit, winch and top of drum. 


Automated coke cutting

Fully automated decoking is achieved through a PLC with embedded intelligence and advanced algorithms to process signals and control the cutting process. Continuous feedback is provided. Operator action is only required for sequence exceptions.

Equipment
• Remotely operated, auto-shifting combination cutting tool
• Automatic guide plate or tool enclosure
• Remote winch and rotary joint operation
• Vibration drum monitoring
• Remote operator enclosure

Information
• Data received by PLC and transferred to integrated, intelligent technology platform
    – Cutting tool position and rotational speed
    – Cable tension and auto-shifting combination cutting tool mode
• Data received directly by integrated, intelligent technology platform
    – Drum status
    – Critical equipment monitoring.


The shared-information portal can make a critical difference

A powerful platform of information technology and sensor-based solutions can streamline the collection, storage, interpretation and use of essential process and equipment data. This data can be acquired and integrated with the DCU operator’s existing data management systems or displayed on a local PC or laptop.

With a shared-information portal, this data/information aggregation system enables plant managers and unit operators to:
• View ongoing performance metrics through interpreted visuals
• Monitor real-time equipment performance
• Review historical equipment information

Users can also:
• Quickly diagnose and solve equipment performance issues from anywhere in the world via the secure remote login capability
• Consult with corporate staff, industry experts and supplier specialists in real-time to analyze anomalies and provide immediate corrective recommendations
• Benchmark asset performance against industry averages
• Create a centralized view of plant asset information regardless of source. This view may include:
    – Installation and operation information
    – Bill of material data including drawings
    – Historical data including parts usage, upgrade and maintenance records.



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