Gas Content

How free and dissolved gas affect wet-end stability

  • Impaired retention, drainage, and sheet formation
  • Inconsistent sizing and product performance
  • Reduced dewatering, drying efficiency, and chemical efficiency

Gas content is an important wet-end stability parameter influenced by both mechanical and chemical deaeration.

Why gas control matters

Pulp and paper suspensions contain gas in two forms: free (entrained) gas and dissolved gas. Excess gas can disturb stock flow, retention, drainage, and foam control, creating variability throughout the wet end.

As gas levels fluctuate, the efficiency of retention, fixation, and dewatering processes may become less consistent. This can affect filler distribution, sheet formation, ash retention, and internal sizing performance, leading to variation in sheet properties and overall product quality.

On grades where visual appearance and print performance are critical, this same variability can also surface as inconsistent opacity, brightness, absorbency, and print uniformity, since fine fillers such as PCC, GCC, clay, and titanium dioxide are highly retention-sensitive to changing gas levels.

 

 

 

Gas-related instability can also influence water removal. Poor drainage increases the water load carried into the press and dryer sections, potentially reducing drying efficiency and making machine performance less predictable. Excessive foam often drives higher defoamer consumption and additional process variability.

Measuring Free and Dissolved Gas

Monitoring both free (entrained) and dissolved gas provides visibility into an often-overlooked source of wet-end variability. Online measurement helps operators identify changing process conditions early, enabling more effective control of retention, drainage, sizing, and overall wet-end stability.

Gas in the pulp and papermaking process may appear as

  • Variability in formation and sheet structure
  • Changes in filler retention and ash distribution
  • Inconsistent sizing performance and Cobb values
  • Reduced drainage efficiency
  • Increased drying demand and energy consumption
  • Greater process variability and runnability challenges
  • Variation in opacity, brightness, and print uniformity
  • Inconsistent ink penetration and print density

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