Rotary kilns, essential in catalyst production, require diligent maintenance. Key considerations are presented here
Rotary kilns are essential to catalyst production, facilitating the thermal treatment conditions necessary to help ensure that catalysts can meet performance expectations as efficiently as possible.
As reliable as these kilns are, their continuous operation under high temperatures and dynamic operational loads requires diligent maintenance and, occasionally, timely repairs or replacements (Figure 1). This article delves into the key aspects of rotary kiln maintenance, common issues encountered, considerations in executing repairs and replacements and measurements to keep an eye on.
FIGURE 1. This is a rotary kiln replacement in progress
Why maintenance is important
The importance of proper kiln maintenance in the catalyst industry cannot be overstated. In addition to producers relying on their kilns to meet production schedules, consistent product quality hinges on precise temperature control and material flow, both of which rely on rotary kiln integrity. Any deviation in the kiln’s mechanical condition has the potential to compromise product quality and affect downstream processes.
Beyond product quality, the mechanical condition of the kiln also has significant ramifications on process efficiency, which affects energy usage, throughput and process uptime.
A kiln in proper working order also ensures a safe and compliant working environment, reducing the opportunity for risks associated with thermal stresses, mechanical failures and gas leaks. Safe, efficient operation relies on a mechanically sound kiln.
The best approach to rotary kiln maintenance in a catalyst facility is a preventative one. Plant managers, operators and maintenance personnel should all have a sound understanding of kiln operation and maintenance and should be able to recognize the onset of potential issues or need for repairs.
Common issues and repairs
The high temperatures, dynamic loads and other operating conditions associated with rotary kilns can make them subject to a number of issues, such as misalignment, wearing of several parts, shell damage, seal leakage and a reduction in burner performance.
Misalignment. Misalignment is perhaps the most common issue catalyst producers run into with their rotary kilns. With several potential causes, misalignment occurs when the kiln’s trunnion bases fall out of perfect alignment. This could be a result of excessive skewing, settling bases, a change in process conditions or several other culprits.
While it may seem innocuous enough, misalignment worsens over time and puts increasing stress on all mechanical components, so addressing it at its onset is essential to avoid the need for additional repairs.
The remedy to a misaligned kiln is realignment (Figure 2). It’s important to note that the underlying cause must also be resolved, or misalignment will resume even after realignment.
FIGURE 2. Realignment of rotary kilns is sometimes necessary. Here, a laser alignment is in progress
Worn tires and trunnions. Wear on tires and trunnions is also not uncommon. Wear on these load-bearing surfaces may be caused by misalignment, improper or inadequate lubrication, fugitive material or excessive wheel skewing.
Depending on the cause, wear can present itself in a number of patterns, but all signs of wear should be remedied as quickly as possible to avoid further damage.
Minor wear can be addressed through a reconditioning process referred to as grinding, in which the surface of the component is ground down to remove top layers of wear (Figure 3). This resurfacing reveals the like-new surface below. However, if wear (or damage) is too deep, replacement might be the only option, because excessive grinding can change alignment of the kiln and require a re-alignment. It is recommended to align after every grinding to prevent the same issue from recurring.
FIGURE 3. Tire grinding, as shown here, may be needed to address minor wear
Worn or damaged refractory. Kilns that utilize a refractory liner, whether castable or brick, can experience wear of the liner and must be carefully monitored to avoid potential damage.
While damage to refractory is not necessarily common, it is not unusual either, and can have catastrophic consequences.
Damage to refractory can be caused by tramp material or excessive buildup moving through the drum. It can also occur as a result of chemical incompatibility. By far the most common culprit, however, is cycling, or the recurrent shutting down and starting up of the unit. Because the refractory lining and drum shell expand and contract at differing rates in response to heating and cooling, cycling increases the thermal stressors on both components.
Unfortunately, refractory wear or damage is hard to spot without regular internal inspections. One way to detect potential problems is to regularly run a temperature gun down the length of the kiln during rotation (or along the combustion chamber), looking for hot spots that could indicate heat is reaching the drum’s shell.
Refractory repair differs depending on the type of refractory and the extent of wear, with castable being easier to fix. In either case, a refractory expert must typically be called in for repair work.
Shell problems. Similarly, rotary kiln shells may experience issues such as warping or deflection due to localized or unevenly distributed heat across the kiln’s shell. Shells may also experience issues if the materials of construction and/or shell thickness were not properly selected (or if the refractory layer is insufficient). Should cracks or holes occur, they will require patches, weld repairs, or in severe cases, shell replacement.
Breeching seal leakage. A worn or damaged breeching seal allows air ingress into the carefully controlled processing environment, yielding inconsistent product quality and increasing fuel costs. A worn or damaged seal should be replaced (Figure 4).
FIGURE 4. A damaged breeching seal can allow air into the process environment. Shown here is a new replacement seal on a rotary kiln
Burner and combustion-chamber performance reduction. Burners and combustion-chamber performance may require tuning and adjustment of the controls to continue performing at maximum efficiency. This type of adjustment is especially likely when process conditions have changed.
Rotary kiln replacement
When repairs are no longer sufficient in keeping the kiln running safely and efficiently, replacement becomes the only option. While it is common to acquire a duplicate system, producers should re-evaluate the size and design of the kiln.
Resizing the kiln. The catalyst industry has historically relied on small kiln loadings, resulting in over-sized kilns. When it comes time to replace a rotary kiln, catalyst producers can garner significant cost savings while increasing throughput by increasing kiln loading and sizing the kiln more efficiently (and reducing the kiln’s spatial footprint).
Kiln loading tests can be conducted in a research and development facility to confirm proof of process and establish data for scale-up.
Additional considerations
Additional considerations to kiln maintenance include the following:
Kiln accessibility. Access to the kiln and its mechanical components is an often-forgotten, but essential aspect when it comes to rotary kiln work. Whether conducting repairs or replacing the unit entirely, service technicians must be able to safely access the necessary components, with ample room to work.
Accessibility of the kiln can also influence the decision to repair versus replace the unit, as in some cases replacement may necessitate significant modifications to infrastructure, particularly if the plant was built around the kiln.
Keep wear-critical parts on-hand. Find a reliable parts provider to collaborate with on keeping an inventory of wear-critical parts and providing additional parts as needed. This may be the original equipment manufacturer (OEM), a qualified service provider, or otherwise. Selecting a service provider that can also supply parts streamlines things by cutting out an additional middleman when parts and replacement components are needed for repairs.
A service provider that can provide comprehensive parts and service support can significantly streamline catalyst kiln maintenance programs, helping to reduce costs and avoid unnecessary downtime.
Comprehensive support should cover everything from inspections and audits to basic repair work and even retrofits.
Inspect often. As mentioned, a proactive approach is the most economic approach to kiln maintenance management. One of the least costly and most effective techniques in this regard is to have a solid inspection program (Figure 5). This should include checklists with documentation for components to check daily, weekly, monthly and every six months, tailored to the plant’s unique operating conditions.
FIGURE 5. A rotary kiln inspection, as shown here, is one of the most effective techniques for managing kiln maintenance
Operators and maintenance personnel should be well trained in proper operation, inspection and maintenance procedures. This should include taking critical measurements such as backlash (where applicable), drum float, tire creep (where applicable), cold gap and more.
It is also invaluable to bring in the OEM or other qualified service provider to thoroughly inspect the kiln both inside and out on an annual basis.
In conclusion, maintaining rotary kilns in optimal working condition is vital for ensuring the consistent performance of catalysts in industrial processes. By adhering to a proactive maintenance strategy, including regular inspections, timely repairs, and thoughtful considerations for replacement, operators can extend the life of their kilns, minimize downtime and maintain high standards of product quality and process efficiency. Partnering with a reliable service provider and ensuring accessibility to the kiln are also key components in achieving long-term operational success. As the demands of catalyst production evolve, so too should the approach to kiln maintenance, ensuring that these critical assets continue to operate at their best. ■
Edited by Dorothy Lozowski
Acknowledgement
All photos are courtesy of FEECO International
Author
Craig Peppin is the customer service manager at FEECO International (3913 Algoma Road, Green Bay, WI 54311; Telephone: 920.468.1000; Toll-free telephone: 800.373.9347; Website: www.feeco.com). He holds a B.A.S. degree in automated manufacturing technology from ITT Technical Institute and has been with FEECO for over two decades.