Pulp and Paper Machine Healthcare, Part 1: Digitalization Solutions for Condition Monitoring

Paper machine forming section. Online monitoring systems must be tailored for harsh mill conditions, including high temperatures and humidity. ISTOCK.COM/TIFONIMAGES

The pulp and paper (P&P) industry boasts a market size topping US$350 billion and an annual consumption of 414 million metric tons of paper and cardboard. This means efficient and cost-effective machine operation and maintenance is not just a necessity; it is critical for remaining competitive.

Given the competitive landscape of the P&P industry, where downtime and maintenance have heavy financial implications, putting in place the relevant maintenance and machine condition monitoring strategy that aligns itself with the specific needs of different machinery and processes becomes paramount.

MAINTENANCE CHALLENGES

There are many critical machines used in the typical P&P mill, and there are many more auxiliary machines. The auxiliary machines not only support the critical machines but also form parts of independent processes. Because the P&P industry requires a lot of energy and raw materials, and processes a lot of solid and water waste, it requires many energy, waste treatment, and production assets to deliver paper products. This makes the mill very capital intensive; capital costs can in fact add as much as 30 percent to the total production costs. This vast fleet of machines, if not properly maintained, can therefore have a significant effect on profitability.

There are many aging paper machines still being used in the industry where components are reaching end-of-life service and machine health issues are beginning to appear. There are not so many readily available replacement parts and some of these older machines have been upgraded to operate faster, which increases the stress on them. Conversely, entirely new machines that have just been commissioned or those that have just been upgraded will typically also have maintenance issues in the beginning and will therefore also need extra attention.

TIME-BASED MAINTENANCE STRATEGY

Many mills rely primarily on a time-based maintenance strategy for their balance-of-plant machinery, with no condition monitoring system at all; or monitoring is limited to routine inspections for some machines. Time-based maintenance theoretically works for those applications where there are very stable operating conditions, such as steady loads and speeds. Yet stable operating conditions are becoming a thing of the past due to changing market requirements. As production flexibility becomes an important business strategy for many mills, an increasing number of critical and auxiliary machines are operating under variable loads, which makes it more difficult to plan when the traditional time-based maintenance should be carried out.

It is not simply a question of operating the machines under variable loads—the machines also must operate more efficiently. A lot of attention is being given to protecting the environment by reducing deforestation and air and water pollution, so attention is also being given to operating P&P machines more energy efficiently and with less paper waste.

ENVIRONMENTAL CONDITIONS

Maintenance challenges in the pulp and paper industry are not only limited to the age of the machines and flexible operation requirements. They also include the effects of the traditionally harsh environmental conditions within the mill. Processes involving caustic chemicals and high temperatures, combined with abrasive paper dust and wood products, as well as pulp slurry contaminated with foreign objects like rocks and clay, can damage rotating and stationary machine components, including bearings, gearboxes, and motors. Additionally, the air ventilation system is crucial; if ventilation fans fail or are damaged, a corrosive atmosphere develops, particularly in the drying section, leading to long-term equipment damage and posing safety risks such as low visibility and slippery conditions for workers.

For all these reasons, a predictive maintenance strategy is a necessity. This means machine faults must be detected and identified early in their development—even under difficult operating and machine conditions—long before failure, so repair and replacement can be cost-effectively planned without interrupting production. The key ingredient to a predictive maintenance strategy is an effective machine condition monitoring solution.

Reel section of the paper machine. Faulty bearings on a roll or cylinder can affect paper quality, so it is important to detect the fault before this happens. ISTOCK.COM/DEDMITYAY

MONITORING CHALLENGES

There are many monitoring systems available on the market, but not all of these are applicable for monitoring the critical and auxiliary machines in a P&P mill. Many machines are quite complex, with many components, and operate under various process conditions with strict product quality and service requirements.

For mills using a condition monitoring solution, many use hand-held vibration instruments for much of their balance-of-plant machinery and even for their critical machinery. This strategy may be fine for steady-state machines where the bearing failure mechanism is predictable, but it may be a problem for monitoring other types of potential failure modes. Fast developing faults, such as lubrication problems, manufacturing faults in the equipment, bearing contamination due to worn seals, and even improper assembly or operation, may not be detected by walk-arounds because these can occur between readings.

Another disadvantage of using hand-held instruments is that there are more stringent safety regulations for operators accessing potentially dangerous areas of the mill. Finally, the hand-held instruments are also mostly designed to simply deliver data, without any actionable asset insights. This requires skilled resources to interpret the data, which may be lacking at the mill.

ONLINE MONITORING IS IMPORTANT

An online monitoring system resolves the most important shortcomings of handheld instrumentation, but there are other issues that mills must consider. First, the system must be tailored for the harsh and varied conditions of a P&P mill and must overcome significant environmental challenges, including high humidity and temperatures ranging from 70 to 130°C, along with a corrosive environment.

A robust online monitoring system is the answer, but it is not enough. There are other monitoring requirements that mill managers should take into consideration:

• Slow speed – Although paper machine (PM) output can be fast, there are several components that are turning quite slowly. These present a challenge to monitor accurately for many basic monitoring systems.
• Advanced monitoring techniques – Specialized vibration monitoring techniques are needed for early, reliable detection and diagnostics of rolling element bearing and gearbox faults, as well as felt and roll defects. Faulty bearings on a roll or cylinder can affect paper quality, so it is important to detect the fault before this happens. It is also important to have a high-resolution frequency range to detect structural resonances that can result in barring, before it occurs. The high noise encountered during operating conditions can obscure critical fault frequencies, so the monitoring techniques should account for this.
• Process data correlation – Process data plays an important role when monitoring a PM, simply because this can influence the vibration response. Therefore, process data correlation with vibration is important for diagnostics and root cause analysis of many potential failure modes. Process control systems provide basic process data such as pressure, temperature, flow and humidity values, while more sophisticated quality control systems provide much more information, especially about the paper itself, such as basis weight, moisture profile, caliper thickness, etc.
• Monitoring technique correlation – Vibration data can be combined with data from other monitoring systems for more accurate and reliable diagnostics and better asset insight. This can include oil debris analysis, motor current analysis, thermography, and ultrasonics.
• Machine states – As many PMs are producing different grades of paper at different loads and speeds, it is also important for the monitoring system to monitor these different operational conditions to individual alarm limits.
• Diagnostic decision support – For mills that do not have diagnostic specialists, this support can be a part of the monitoring system itself or offered as a service.

Although there are monitoring systems on the market that provide much of this monitoring capability, the adoption of such systems is often hindered by factors such as high initial costs, complex installation issues such as wiring, and the increased IT burden to manage the monitoring infrastructure. Additionally, the reluctance of mill managers to prioritize the healthcare of the machines to the appropriate level can be attributed to a lack of in-house expertise and/or the manpower to effectively operate advanced monitoring systems. Moreover, there is a trend toward reducing operational expenditure, which includes minimizing specialist staff, which compounds this problem further.

Despite these obstacles, there are viable monitoring solutions that can cost-effectively address these challenges and enhance the reliability and efficiency of mill operations. Two such solutions include:

• Enterprise-wide monitoring solution. One important requirement for selecting a condition monitoring solution for monitoring both critical and auxiliary machines is to evaluate how the solution manages data. There are several monitoring systems on the market that offer comprehensive condition monitoring capability, but these systems are often onsite, proprietary stand-alone systems. This means that data storage is independent from other systems, and if process data is needed for analytics or correlation in the stand-alone system, this data must be imported and saved in the proprietary monitoring system server.

An enterprise-wide data management system such as a historian is ideal for a comprehensive condition monitoring strategy. Such a system enables data from many monitoring, analytics, and process and control systems to be stored in the database. In addition to data storage, the historian can also provide additional analytics, event monitoring, notification and visualization with plots and trending. Service providers can access this information to provide additional monitoring services, including AI and machine learning.

• Cloud-based off-premises monitoring solution. In principle, the online monitoring system for auxiliary machines must be cost-effective, accurate, easy to deploy, and require no end-user specialist knowledge from mills where it is lacking. For many of the auxiliary machines, a cloud-based off-premises monitoring solution can be used for this purpose. Wireless accelerometer sensors are installed on the machines’ bearing housing and/or casing, and a gateway takes in the raw vibration data and sends it to the cloud for remote processing. This would include raw signal processing for monitoring the machine faults; performing diagnostics, AI, and machine learning of detected faults; and providing notification of maintenance action that must be undertaken.

For applications where an off-premises solution is not feasible, data from the wireless sensors can be stored in the data historian instead of in the cloud.

CONCLUSION

The digital transformation taking place in manufacturing—including within the P&P industry—is not a question of merely collecting more data to improve profitability. It is also a question of collecting the right data, storing it, and providing optimal access to it for fostering a more effective enterprise-wide culture and work team experience. In addition, the right data must be gleaned and analyzed to provide more reliable, accurate, and earlier insights into processes, operation, and maintenance. An enterprise-wide historian does all this plus it also integrates data systems to simplify processes, improve cybersecurity and avoid overloading IT. This not only improves production, quality, and profitability, but also makes the mill more agile for spur-of-the-moment demands.

Machine condition monitoring is a vital part of this digital transformation. This means the relevant machine data can be used for fault diagnostics and maintenance forecasting to optimize machine healthcare for improving safety; reducing downtime and maintenance costs; and increasing product output, agility, and quality. Not all monitoring systems can provide this value, and more is expected to be done now than what was typically done in the past.

There are many machines in a P&P mill, but most of these are auxiliary machines. For condition monitoring of these, there can be an off-premises solution and an on-premises monitoring solution based on an enterprise-wide historian. For critical machines, the rack-based solution is ideal since it can provide both protection, condition monitoring, and performance monitoring of a wide range of potential failure modes for several different machines. For a plant-wide monitoring solution, there can be a mix of all three systems.

The need for higher profitability, enhanced product quality, reduced maintenance costs, and more dependable production is becoming increasingly important in today’s competitive market. Fortunately, advancements in the accuracy, reliability, and cost-effectiveness of monitoring systems are keeping pace, and now it is possible for these systems to be effectively integrated in the enterprise-wide data management system.

Look for Part 2 of this series in the Techlink section of our July/August issue, where the author will highlight the wide array of machinery used in the pulp and paper industry and the challenges of maintaining these components.