By: Thomas Fortinberry and Jim Widrig, Quest Integrity Group
As seen in the March/April 2013 issue of Inspectioneering Journal.
Steam reformers are critical assets to many refining and chemical manufacturing plants and facilities, and it is well known that the reformer is one of the most challenging assets to maintain and operate. Common problems in reformer operations include burner firing, flue gas distribution and catalyst damage. While these are only a few of the problems that can occur, all directly affect reformer tube life and lead to premature tube failure, pigtail failure, and damage to the header and convection section. In order to increase reliability and operate with a higher degree of confidence, it is increasingly important to incorporate a holistic approach to steam reformer reliability and maintenance programs. When using such an approach between turnarounds, operators should consider these essential elements:
Preventative maintenance activities during operation and planned shutdowns provide information to improve and sustain the reliability of the reformer. Historically, most of the preventive maintenance was in the form of inspection work, but many plants and facilities are seeing the value of performing engineering assessment work to better plan for future plant operations and shutdowns. The knowledge of what needs to be replaced and inspected ahead of the turnaround allows for better turnaround planning, which results in savings in time and material costs. Turnkey solutions for inspection and assessment of the entire reformer system are available today and allow operators to be proactive instead of reactive to reformer conditions.
Reformer tube inspections identify many of the problems associated with reformer operations. A comprehensive approach includes reformer tube inspection, remaining life assessment and identifying operational problems. Internal and external inspection methods assess tube condition and identify problems with burners such as flame impingement (figure 1), local hot spots due to low flow conditions from possible catalyst problems (figure 2) and problem areas of flue gas flow distribution. Many inspection and remaining life assessment services only give plant operators information late in tube life, thus reacting to the damage that has already occurred. However, a holistic approach provides plant operators with vital information early in the process, allowing them to better manage operating conditions and extend tube life.
Figure 1 ”" Flow distribution problem areas Figure 2 ”" Flame Impingement
Advanced engineering services provide plant and facility operators with access to experienced engineers with capabilities to assess the entire reformer system including high temperature components such as header systems, pigtails, risers and bull tees. One key advanced engineering capability is Computational Fluid Dynamic (CFD) modeling of reformer systems and includes modeling of furnace combustion, flue gas ductwork, convection sections, and primary and secondary burners. Additional capabilities include materials engineering and laboratory support for reformer components such as accelerated creep rupture testing.
Reformer tube life assessment methodologies incorporate creep study on HP and micro alloys, finite element analysis (FEA) and the inspection results to accurately predict remaining life of tubes. Results from a reformer tube life assessment program include the retirement dates for each tube along with an FEA analysis to show the amount of through wall damage, and the effective operating temperature for each tube. The individual tube retirement dates form the basis for a tube replacement strategy and are then figured into the operator’s turnaround schedule to help prepare for future turnarounds.
A tube remaining life report should also
be prepared that includes a remaining life assessment of each reformer tube. This
report will allow the plant to optimize the reformer operation to effectively
manage the unit production without sacrificing the reformer tube reliability. The
data associated with this report can then be combined with current process and
operating practices to fully optimize unit production.
Reformer performance monitoring is also beneficial to plant operations. Reformer operations specialists are brought in after a turnaround, when the plant is back online, to help operators balance the reformer and help correct any problems that were observed during the shutdown. A reformer performance monitoring survey should be performed for each of the reformers following a turnaround or at another predetermined interval. The primary objective of the work is to observe the reformer in operation and assist with balancing the reformer firing to deliver a reliability strategy, ensuring the safe and reliable long term operation of the reformers. This survey provides a preliminary verbal assessment of the reformer condition (prior to leaving the site) and a final written report at the conclusion of the assessment.
Infrared (IR) temperature correction software allows operators to have more accurate knowledge of reformer tube temperatures. Radiation thermometry measurements of furnace tubes (including those made with thermal imaging systems) are invariably subject to errors, principally associated with the emissivity of the tube surface and radiation reflected or scattered from surrounding surfaces. In order to determine the true tube temperatures, corrections must be made to the thermometer readings based on the geometry of the furnace, the emissivity of the tube material, atmospheric effects and knowledge of the operating characteristics of the thermometer itself. IR temperature correction software automates this process, increasing the repeatability and accuracy of temperature measurements. This allows operators to increase production without increasing safety risk or maintenance costs.
The primary benefits of employing a comprehensive inspection and remaining life assessment program are increased confidence in tube condition coupled with the knowledge of how long the reformer will continue to operate without failure. Ultimately, this allows for more reliable and confident operations between turnarounds. With additional factors including EPA sanctions, publicity and narrow profit margins, it is more important than ever for plant operators to incorporate comprehensive reliability and maintenance programs for their steam reformers.