Just like most process industry applications, papermaking is an often-delicate balancing act that requires lots of expertise and experience to consistently produce varieties of quality products. Unfortunately, again like other process industries, it’s continuing to rapidly lose its veteran engineers and operators to retirement.
Plus, many papermills are likewise unable to offset these losses with enough rookies, who don’t have sufficient know-how to maintain consistent operations and quality, or cope with rare variations or unusual problems that the veterans had experienced—and remembered how to detect and handle. Technological remedies such as archived best practices, faster data collection and analytics, remote optimization and other fixes could help, but another balancing act would be needed to apply them carefully and effectively.
For instance, WestRock’s mill in Hodge, La., operates two large, continuous-web machines, which produce 20 different grades of 26- to 42-pound paper. One of the machines makes outside liner paper for packaging, while the other makes inside corrugated paper for stabilizing packaging. Both use Honeywell’s TDC distributed control system (DCS) with an Experion Process Knowledge System (PKS) front end.
Continuous monitoring for continuous webs
The machines also require constant monitoring to align, tune and stabilize their papermaking processes. This optimization begins with weight and moisture sensors and reel scanners above and below the sheets coming from the machines, which supply data to Honeywell’s Quality Control System (QCS) 4.0 software and support equipment. WestRock also uses bump tests to check and adjust its process steps, build models, and quantify response dynamics that assist its tuning and optimization.
“Measurements must be reliable, accurate and repeatable, and machine direction and cross-direction (CD) controls must be reliable, trustworthy, responsive and stable. However, actual performance degrades below design performance as process dynamics change over time, and periodic optimization tuning is needed to improve performance,” said Jake Hubbard, process control engineer at WestRock’s papermill in Hodge, La., who presented its case study at the Honeywell Users Group 2023 this week in Orlando. “We also have two quality control technicians. However, we need to bridge the skills gap that opened up because a lot of our veterans retired, and we have much less expertise onsite.”
Closing the skills gaps with detective tools
Hubbard reported that QCS 4.0’s data analytics for equipment and control health can help WestRock’s machines and other applications and users by providing:
• Actionable alerts with probable causes;
• Control utilization, performance and quality;
• Sensor stability, standardized values and diagnostic data;
• Advanced analysis tools; and
• Links to documentation and drawings.
“These actionable alerts help our two resident technicians, not just by letting them know what’s going on, but also by telling them what they can do about it,” said Hubbard, who added that QCS 4.0 helped WestRock detect and resolve the causes of performance issues in several recent use cases.
Case 1: Audit and optimize
“We perform machine audits to set optimized base cases for investigative limits. One audit found that a machine was struggling to meet specifications at lower speeds, and that its CD reel-conditioned, weight-control performance was inconsistent across all grades with a single tuning group,” said Hubbard. “So, a second group was created, optimized, and tuned remotely, and this improved CD performance.”
Case 2: Control performance
In the second case, an alert indicated that CD moisture and CD dry weight variability had increased. Investigating this symptom revealed that 32 zones of the rewet shower weren’t functioning. “A bad batch was traced to a bad I/O module that didn’t show that spraying wasn’t occurring properly,” added Hubbard.
Consequently, CD multivariable (CDMV) control was used to sacrifice CD weight to accommodate the failure. This allowed the issue to be resolved at the next opportunity without any paper being rejected. In addition, further analytics were done after the rewet shower was repaired, which let the CDMV focus more closely on moisture-improving, steady-state control performance.
Case 3: remote expert-guided optimization
In the third case, after a new Devronizer steam box was installed, remote experts at WestRock supported the set up and tuning of the CDMV. Devronizer is Honeywell’s line of steam boxes for CD moisture profiling. This remote-guided optimization improved scheduling and created organizational efficiencies that saved on installation and other expenses. The three reasons for this were:
• Project execution didn’t have to be scheduled around the onsite availability of Honeywell’s experts;
• WestRock’s local team could schedule optimization to happen when the machine reached stable operations, instead of wasting money by keeping experts onsite, waiting to perform tuning; and
• Follow-up sessions can be performed when other paper grades are run to capture their entire product range.
Case 4: Solving a profiles issue
In the fourth case, data from an alert eventually pointed to a headbox on a machine with dirty sheets, and that it likely needed to be cleaned and restarted.
Initially, a root-cause investigation of the alert using advanced tools available in QCS 4.0 showed high-frequency variation in the first half of the profile. The CD reel-conditioned weight control wasn’t indicating the high-frequency variation shown by the actuator setpoints and control performance. A frequency analysis of the reel-conditioned weight indicated the presence of dominant short wavelengths in the power spectrum outside the controllable range of the software’s AutoSlice function. The cumulative power spectrum showed 1.5% of the total variation was in the controllable range, which meant the CD reel-conditioned weight was performing well.
The combined WestRock and Honeywell team discussed these results, and agreed the initial profile issue wasn’t caused by the CD reel-conditioned weight control but could instead be due to headbox plugging. So, the mill operations team shut down the paper machine, and found that the headbox was indeed clogged and dirtying the sheets. Once the headbox was cleaned and the paper machine was washed down, paper quality was restored, and the reel-conditioned weight profile trend showed a much-improved spread.
“This is the biggest benefit of QCS 4.0—it immediately tells you where you’re at and how to start resolving issue,” concluded Hubbard.