Achieving Heater Resiliency: The Role of Radiant Tube Support and Stack Damper Performance

Paper from the AFRC 2017 conference titled Achieving Heater Resiliency: The Role of Radiant Tube Support and Stack Damper Performance

Unplanned unit shutdowns or reduction in process unit throughput is often driven by poor heater performance. Damper and tube support performance both play a key role in the resiliency of a heater, with far reaching impact to the condition of the coils, refractory linings, and steel. Additional factors such as original design, manufacturing defects, condition, years of service and operational practices all come into play in the unexpected failure of a heater. Each of these factors will be explored in detail and suggested approaches to mitigate the associated risk to the heater long term will be discussed.

Birwelco USA Presents Achieving Heater Resiliency: The Role of Radiant Tube Support and Stack Damper Performance By Walter Gull President and General Manager - Birwelco Inc. USA October 25th, 2017 Presented at the AFRC Industrial Combustion Symposium TABLE OF CONTENTS 1. Introduction - The Heater's Role in Production Losses .................................... Page 3 2. Heater Resiliency............................................................................................. Page 3 3. Reliability, Inspection and Maintenance Practices ........................................... Page 4 4. Effect of Unplanned/ Extended Heater Outage ................................................ Page 5 5. Radiant Tube Supports Resiliency Methodology .............................................. Page 6 6. Stack Dampers Resiliency Methodology .......................................................... Page 9 7. Conclusion ..................................................................................................... Page 13 Page 2 of 13 The Role of Radiant Tube Support and Damper Performance October 25th, 2017 1. INTRODUCTION - THE HEATER'S ROLE IN PRODUCTION LOSSES The overall success and profitability of a company is in direct correlation to the number of annual days of production achieved by any facility. For those facilities that utilize fired heaters or furnaces as part of the overall process, the performance of the heater becomes a critical part of operation, having the potential to profoundly impact the actual days of production in an adverse way. Industrial heaters operate at extremely high temperatures and are virtually in constant operation, exposing the internal components to conditions more severe than almost any other industrial equipment. Hours of continuous operation and the periodic heater cycling (bringing out of service and then brought back into service), shortens the remaining life of each of the components that make up a heater. Heater outages occur only in the event of a facility shutdown, heater instrumentation trip, or unexpected heater mechanical failure. Of these, the unexpected heater mechanical failures would be largely attributed to 1) the integrity of the heater's internal coils or 2) the ability of the damper(s) to maintain safe draft during all modes of operation. These failures result in unscheduled outages ranging from 1 week to 2 months. While reliability, inspection and maintenance programs of today have directionally improved heater reliability overall, there is a practical limit to what can be achieved with heaters from a reliability standpoint. Aging heater demographics and today's operational challenges will continue to adversely impact the number of future heater outages and correspondingly, overall unit production. The methodology of heater resiliency can be applied to confront these challenges, achieving the targeted days of production and resulting success and profitability of the company overall. This paper explores the methodology of heater resiliency as it applies to two critical internal heater components - radiant tube supports and stack dampers. 2. HEATER RESILIENCY Heater resiliency is best defined as; "A proactive program that builds upon existing reliability, inspection and maintenance programs, with the primary focus to reduce the magnitude of risk to production loss, every time a heater repair is required for both scheduled and unscheduled shutdowns". Page 3 of 13 The Role of Radiant Tube Support and Damper Performance October 25th, 2017 Heater Resiliency encompasses: • Records - the age of most heaters in service means that original records are often missing or no longer accurately reflect the actual heater due to modifications over the years. This can mean days ($$) of delay to not only projects but also to repair efforts when a unplanned shutdown occurs or when a scheduled shutdown has become critical path due to discovery work. • Existing Design Evaluation - this review is not only from a fitness for service standpoint, but addresses the ease of future repairs, both from a routine maintenance standpoint but also from a fast track perspective. • Conditional Evaluation - most failures are often repaired "in kind", this conditional review looks at the history of failures and current condition of the heater to consider an alternate design that could further reduce the risk of the same failure occurring in the future. 3. RELIABILITY, INSPECTION AND MAINTENANCE PRATICES Shortly after the turn of the 19th century, heater technology was still in its infancy, giving those in operation little choice but to "run it till it breaks" with no serious thought on what would be required to repair, let alone how long it would take. The risk of this operational approach was that actual production achieved from the facility from year to year was a moving target, adding one more variable for management to consider in trying to predict a company's future performance and overall profitability. The industry responded with a demand for greater heater reliability, turning the focus to understanding the condition of the heater, predicting how much longer it will last, and then scheduling the repair/ replacement prior to failure. Figure 3-1 Today's industry has continued on with this focus, the ultimate goal to eliminate any unscheduled outages from equipment failure. Heater reliability is best defined as; "A system of programs, processes and procedures, capitalizing on the failure and maintenance history of the heater to establish optimal inspection/ data collecting activities with the intent to identify possible modes of failure and frequency. Maintenance can then proactively be applied to keep unexpected outages out of service windows to a minimum" Page 4 of 13 The Role of Radiant Tube Support and Damper Performance October 25th, 2017 Most reliability programs are built around three key activities: • • • Inspection programs. Root cause analysis/ remaining life analysis Maintenance programs Over the last 20 plus years, the industry has continued to address heater reliability through 1) increased inspection and development of improved inspection techniques, and 2) ever expanding maintenance programs. The reduction in the number of unexpected or extended heater outages has slowed, while costs have continued to increase. Despite the strides made in heater reliability, the risk of unexpected outage days from a heater failure is still a regular monthly event in most facilities, expected to increase as 1) the body of heaters in service continue to age beyond the average 25 to 30 years of service, 2) heaters are being modified to address ever more stringent regulatory requirements, and 3) change in process conditions as facilities strive for greater operational flexibility to remain competitive. As extensive as the best reliability programs are, by definition, they not address a number of key factors that have a significant impact on heater reliability: • • • • • The long term performance of the original design Fitness for service of the heater for current operational process needs Availability of accurate documentation on the equipment Availability of replacement parts Ease of heater repair 4. EFFECT OF UNPLANNED/ EXTENDED HEATER OUTAGE An unplanned or extended heater outage has a number of often unrecognized consequences or risk to the bottom line of a company's safe and successful operation: • • Production Risk: While the exact value of a day's production for a unit is often not available publicly as a matter of competitive advantage between the operating companies, typically, unit production profitability values of $500,000 USD to $1,000,000 USD per day will address 90% of the facilities. With over 250 sites in North America alone that utilize one or more fired heaters as a part of the overall process, fired heater equipment is conservatively the unrecognized root cause of an estimated forfeiture of 9 to 18 lost production days annually per site or as much as $2.25 Billion USD in potential production profits annually. Personnel Safety Risk: Every shutdown and subsequent startup of a heater poses an elevated level of risk from a personnel safety standpoint if an unforeseen ignition event were to occur. These events are most likely to occur when the operation of the heater is in a transient mode, typical of startup and Page 5 of 13 The Role of Radiant Tube Support and Damper Performance • October 25th, 2017 shutdown. While this today is mitigated through the use of 1) procedures, 2) instrumentation, and 3) controls, the risk still is present. Asset Damage Risk: Every shutdown and subsequent startup of a heater poses an elevated level of asset risk; o If an unforeseen ignition event were to occur, it is highly probable that it would cause significant damage to the heater itself and surrounding equipment. While there is the associated cost to repair the damage, the significant cost is in the loss of production for the unit, a typical outage for a complete rebuild typically requiring at best between 30 and 60 mechanical working days to complete, with a possible forfeiture of $15,000,000 USD or more in loss of production for just one heater. o Beyond the risk of damage from an unforeseen ignition, cycling of a heater is a recognized key contributor to a shorter component life for all of the heater's internal components. 5. RADIANT TUBE SUPPORTS - RESILIENCY METHODOLOGY Coil failure in heaters occur when the coil components (tubes and fittings) are overstressed or damaged. Accelerated creep, tube oscillations, tube fretting, flame impingement, and coil binding all can result in a loss of process containment. This comes about through: • • • • • Over pressurization (from operation) Dual phase slug flow (from operation) Elevated tube metal temperature (increase firing, flame impingement or coking) Manufacturing defects in the fabricated coil (inspection) External mechanical loading on the coil Today's operational practices and inspection programs are very effective at addressing all of these items, falling short only when it comes to addressing external mechanical loading of the coil. External mechanical loading of the coil is a function of the coil geometry, the support/ guide locations and the restraints at the ends of the coil. Of these, it is not uncommon for the support/ guide points to fluctuate or change during operation. Page 6 of 13 The Role of Radiant Tube Support and Damper Performance October 25th, 2017 These support/ guide changes result from; • • • Tubes can bow and lift off one or more supports if not properly guided Tube supports can fail either in the main body casting (crack or creep) or where attached to the wall (crack or shear). Tube guides can crack, creep or bolting/ pins shear, no longer providing an effective guide for the coil. Traditional radiant hook support designs incorporate a cast tee or wide flange cross section and are bolted or pinned to the wall from the inside, directly to the main heater structural members or sometimes off internal clips or tabs welded to the wall. The hook support system often incorporates a separate cast guide keeper inserted in/ over or bolted to the tip of the cast hook. Figure 5-1 Figure 5-2 Figure 5-3 While the traditional support system as described above has been widely used for decades, it has a number of inherent shortcomings that ultimately lead to heater outages: • • • • • Tube support and keeper replacement can only be performed internal to the heater with the heater out of service, requiring repair to the insulation system as part of the process. Extensive internal scaffolding needed to access the support locations results in additional days of outage. Keeper designs are ineffective, lacking robustness, the minimal size severely limiting the keeper's ability to restrain the coil tube. Beyond limited observation door views, there is no inherent way to determine need of support replacement during operation. API 560 heaters are custom designs, with custom components unique to each heater. These "one-off" support or keeper alloy castings are not available if needed quickly to support a heater outage, necessitating costly high alloy plate fabricated options that typically do not perform as well long term. The main "T" or "I" casting cross section virtually guarantees poor initial insulation installation, the geometry making it difficult to install the insulation around the support resulting in poor long term performance. Page 7 of 13 October 25th, 2017 The Role of Radiant Tube Support and Damper Performance To maximize the heater's overall resiliency and avoid having to bring a heater off line due to tube support or guide issues, the support system needs to address each of these identified shortcomings. Such an example is illustrated below. Figure 5-4 Figure 5-5 Figure 5-6 For heaters with the traditional support and guide designs, there are other engineered solutions that allow for the coils to be temporarily supported while the heater remains in service, at least until the scheduled turnaround of the heater where more permanent repairs can be made. Several examples are shown below. Figure 5-7 Figure 5-8 Page 8 of 13 The Role of Radiant Tube Support and Damper Performance Figure 5-9 October 25th, 2017 Figure 5-10 6. STACK DAMPERS - RESILIENCY METHODOLOGY Safe operation of API 560 heaters rest firmly on maintaining the optimal negative pressure (draft) level internal to the heater during wide-ranging operational rates. With available heater draft capacity set by the physical heater geometry and/ or induced draft fans, dampers are critical to a heater's draft adjustment. When draft cannot be maintained, the heater will need to be brought out of service for repairs. Repeatable & reliable damper operation is essential for automated combustion control systems & for the general safe operation of the heater long term: • Safety - Personnel in close proximity to a heater are at risk when optimal draft is not maintained. Exposure to hot flue gas can result in severe burn injuries with fatalities possible if an explosion were to occur. • Safety - Too little draft can inhibit the required amount of air from being drawn in through the throat of the burners for safe combustion. Improper use of damper registers on burners can also restrict the air, even under high draft. During operation under either of these conditions, attempts to fire at increased rates will create an unsafe fuel rich situation where burners can flame out & potential afterburning or explosion occur. Page 9 of 13 October 25th, 2017 The Role of Radiant Tube Support and Damper Performance • Heater Damage (Progressive) - Heat & Corrosion damage get exponentially worse over time, requiring extensive repair or possible heater replacement (refer to photos below). Figure 6-1 Figure 6-2 Figure 6-3 • Excess air - (from too much draft) increases the flue gas volume, exposing areas within the convection section & stack to higher temperatures, causing accelerated damage over time to process coils, coil finning, coil supports, dampers, refractory linings & steel. • Heater leak points - (bolted joints, observation doors, expansion joints, etc.) are susceptible to high & low draft. High draft bringing in cold (tramp) air to promote accelerated H2S corrosion of heater steel, low draft forcing flue gas out via leak points to expose steel to elevated temperatures & distortion promoting refractory lining failure. Tramp air often poses a serious operational concern, giving a false sense to the operators of correct fuel to air ratio at the burner. Traditional damper designs are often simple pipe shafts with plate blades fixed to the shaft by bolting. The design may or not include bearings or seals where the pipe shaft penetrates the stack casing or shell. When there are multiple blades, the operation of the blades is either parallel or opposed, with the required external linkages being nothing more than flat bar steel welded to the shafts. This typical design has proven not to perform well in long term service due to a number of shortcomings inherent in the original design; • Blade Distortion - Flat plate damper blades will overtime warp or "potato chip" from the heat, the resulting gaps impacting the ability of the damper to control the flow as designed. • Shaft Deflection - Bowed damper blade shafts are a leading cause for bound up dampers, the pipe shafts lacking strength needed to prevent the distortion in the heat over time. Page 10 of 13 October 25th, 2017 The Role of Radiant Tube Support and Damper Performance • Blade Shift and Bind - Dampers can bind between the blade & the internal refractory insulation, either from blades shifting or inadequate allowance for expansion considered in the design. This binding can extend to the external shaft linkages. • Shaft / Casing Interface - without bearings, shafts can seize at the casing and the lack of sealing at the casing will result in long term (localized) corrosion. • Maintainability - with no provisions to remove damper linkages or shafts without having to cut welds, it is virtually impossible to maintain the damper long term. • Performance - there are a number of stacks in service today that the traditional damper is not capable of regulating the required draft, especially at turn down conditions. This is not a function of the damper condition, but of the wrong design being utilized. Examples of some of these shortcomings are captured in the following photos. Figure 6-4 Figure 6-5 Figure 6-6 Figure 6-7 Page 11 of 13 October 25th, 2017 The Role of Radiant Tube Support and Damper Performance If a damper driven shutdown is to be avoided, a resilient damper design would capture the following features; • • • • • • Blade Distortion - Blade design utilizes distributed reinforcement of the individual damper blades, ensuring they stay flat and true for the life of the damper. Shaft Deflection - The shaft design should be of sufficient strength. This can be achieved with damper designs that utilize a solid stub shaft, providing optimal strength where needed to keep deflection to a minimum. Blade Shift - Proper mechanical means must be employed to ensure the alignment of the blades remain true over the life of the damper, but still allow for the quick and easy replacement of the damper shafts if required. Shaft/ Casing Interface - Damper designs should support the shafts with solid lube bearings & effective sealing at the casing, ensuring corrosion is reduced & personnel safety is maintained. Maintainability - The damper design should ensure that actuators, linkages, bearings, seals, shafts & blades are designed to be 100% removable for ease of inspection & replacement, keeping heater down time to a minimum. This allows for replacement/ adjustment while the heater remains in service. Performance - CFD Modelling of the flue gas flow through the damper will ensure the damper will perform for those critical applications where stack height/ draft design margins are an operability concern, ensuring the damper controllability required under these conditions is achieved. Figure 6-8 Figure 6-9 Figure 6-10 Page 12 of 13 The Role of Radiant Tube Support and Damper Performance October 25th, 2017 7. CONCLUSION While the strides over the last 50 plus years have dramatically improved the reliability of fired heaters, there is still a gap that remains between targeted and actual days of production achieved. These unplanned days of lost production impact the competitiveness and overall profitability of a company. Implementing resiliency methodology to fired heaters can help to fill that gap, by being better prepared when the equipment breaks unexpectedly, allowing for the repair to be performed while the heater remains in service, or if a shutdown is necessary, by keeping the outage window to repair to an absolute minimum. Page 13 of 13