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Control the burn: Part 2

Published by
World Fertilizer,


Scott W. Sexton, Haldor Topsoe Inc., discusses how digital furnace firebox monitoring technology can extend a machine's lifecycle and improve personnel safety.

Heat distribution

TFM information provides a roadmap to operations when balancing burners, by providing images and data before, during, and after adjustments. With better heat distribution, fuel gas consumption can improve from 1% to 2%, with savings up to US$100 000/year. Burner balancing also enables longer tube life by distributing heat flux across the entire surface.

Personnel training

Training of new and existing personnel on firebox operations is based on field experience from on-the-job training. This experience is difficult to obtain, costly, and limited in frequency. TFM enables the sharing of firebox images and data, providing the backbone for a training curriculum to supplement hands-on training from experience.

Personnel firebox interaction

TFM supports the remote location of personnel, reducing risks that might occur from interaction with the reformer firebox. This is important in some older plants, which are built with less consideration for risk. Modern risk analyses account for personnel risk due to exposure. With TFM, furnace interaction is less frequent than in the past, which reduces overall risk frequency.

Burner monitoring

Reformer burners can be difficult to see with the human eye and this is made worse by mixed fuels with hydrogen-based flames. The TFM sees flames that the human eye cannot and provides alarms when the flames are under-performing.

Operations support

Support groups can use TFM images and data that are also available to operations, enhancing collaboration among the entire team. Stored information, available at all times, means that the operations team is not tasked with finding and logging all plant data. Compliance data is also available at all times. Experts with access to furnace images and data can actively engage in operations troubleshooting.

Case study: new plant startup

A new reformer in a highly integrated plant was the first equipment to startup after utilities. Heat distribution and temperature control of the furnace were not yet established and burner performance, especially with mixed fuels, was not fully understood before commissioning. Startup equipment on the reformer also had challenges, including igniters, pilots, and flame scanners, which were installed on each burner.

Plant check-out process

Reformer check-out began with the pilot flame. Flame scanners did not provide constant flame verification, particularly when the flames were unstable. Burners located on six different levels on the firebox made personnel movement between levels difficult. Frustration occurred in the operations team when lighting multiple pilots, only to lose the flame signal sensed by the flame scanners. This required repetitive restarts of the lighting process.

Decisions

Operations management had to make some difficult judgements. There were two possible decisions; changes to the burner management system (BMS) was one possible decision; the human verification of the presence of a flame in each burner, which would require constant human surveillance, was another. These decisions represented compromises in core safety philosophy. Downgrading an engineered safety system, exposing personnel to firebox hazards, or both, were not attractive options.

Technology implementation

TFM was chosen to enable the lighting and stabilising of flames in the firebox, without the requirement of direct human interraction. The TFM was utilised as an engineered safeguard, administratively monitored. Flames were verified in the control room on the display screen. Flame scanner adjustments could be made prior to the trip-out of the BMS. Flame quality (size, shape, colour, and intensity) could be adjusted with fuel and air, as seen on the TFM monitor, so that safe and efficient startups could be conducted with no direct interaction required between personnel and the firebox.

Lessons learned

After the initial burner and furnace adjustments had been determined through trial and error, results were documented with digital images. These images were stored in the system’s database and operating procedures were updated for future reference.

Furnace SOPs

After safe light-off, uniform heat distribution across the process tubes was the next goal and capturing process settings in standard operating procedures (SOPs) was also very important. The TFM’s placement in the roof of the furnace enabled the continuous monitoring of all burners and all reformer tubes from the control room. Monitoring the firebox during the heat-up phase of operations aligned the operations team with the management team. Air damper modifications, the removal of refractory interference, fuel mixing, and pressure changes were all activities captured in SOPs. Then, as the furnace temperature was increased, the process tube growth and mechanical integrity of each tube was monitored and recorded. Flames impinging on the process tubes were also noted, recorded, and proper adjustments were made to eliminate them.

Incident capture

After initial startup, an unexpected tripout caused a backpressure event in the furnace. The TFM captured firebox images in its database, both before and after the incident, enabling an accurate incident investigation and its resolution in a very timely manner.

Conclusion

Furnace operations and maintenance over the machine’s entire lifecycle, which often exceedes 30 years, involves the consideration of several factors for safety, reliability, efficiency, and operability. To manage and safeguard against hazards, both engineering and administrative safeguards are implemented. Utilising the technology available today, the TFM is a proven safety option that protects both personnel and processes for furnace fireboxes, providing an engineered administrative safeguard. Immediate economic benefits accrue due to furnace incident and outage avoidance, as well as through the improvement of long term reliability with enhanced operational excellence.

Read the article online at: https://www.worldfertilizer.com/materials-handling/04012019/control-the-burn-part-2/

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