A stable pH-value is an important factor for smooth machine operation as it has an influence on de-watering (a lower pH-value improves de-watering) and the pH-dependent effect of many auxiliary chemicals.
Controlling pH with carbon dioxide has many benefits:
- No disadvantageous interactions with other auxiliary materials (e.g. retention agent)
- When using carbon dioxide to carry out neutralisation on paper machines there is no risk of danger to health from dangerous fumes, or of corrosion to the hardware. In addition, the storage vessel for CO2 does not require either a water-tight drip tray or other safety hardware as is the case with mineral acids. Thus, handling carbon dioxide is simple, safe and economic.
- The process and waste water salt load is not increased by chloride or sulphate when neutralising with carbon dioxide.
- As carbon dioxide is a weak acid, the pH can be well controlled. Due to the buffering capacity of CO2, the pH in the system is additionally stabilised.
To add and dissolve the carbon dioxide in highly viscous liquid/fibre mixtures, nozzles of a special construction, which minimises their tendency to block, need to be used.