Application of CO2 for paper mill production optimisation
We can find different paper production line phases at which the application of CO2 for pH secure acidification leads to a relevant improvement by upgrading the drainage or recovering chemicals.
Reduce the pH of the pulp to have a better draining.
Replace of the strong acids to providing a smoother control.
CO2 can be used at the pH control of the pulp in two different points.
Replace part of the compressed air with CO2 as a carrier gas during the flotation.
CO2 is used to produce PCC (Precipitated Calcium Carbonate) for print paper production.
pulp to have better
draining.
factor.
black solids.
After bleaching with peroxide and NaOH, the is injected to adjust the pCO2 H level to values around 7,0 to avoid brightness reversion.
CO2 is used for the pH control of the pulp near the head box of the paper machine. This pH control provides a better draining performance at the wire in the paper machine.
Flotation System
CO2 is used in effluent treatment in flotation system to replace part of the compressed air used as a carrier gas during flotation (primary treatment of fiber recovery).
As CO2 has more affinity with the liquid phase than the air, so along the process it creates small bubbles, and improves flotation during the process, improving the flotation. Efficiency can be increased by around 15%. Usually, CO2 replaces from 40 to 60% of the total compressed air used.
PCC production
CO2 is used for PCC. Production, PCC is used as a filler in the alkaline sizing papers production (print paper).
Kraft pulp pH control tower
CO2 is used to replace strong acids (HCO2 SO4), and aluminium sulphate providing a smoother control, it avoids great variation at the CO2 .
It's used before or after the refining process, aiming a thin adjustment of the pH level, and consequently, a reduction of the consumption of aluminium sulphate or sulfuric acid dosed for pH control, which is, total or parcial to neutral/alkaline sizing of paper.
CO2 control to press high consistency
Special packaging paper bags (bags of cement, multiwall bags).
CO2 is used to eliminate aluminum sulfate provinding a smoother control, and avoiding great variation of pH values. CO2 is used in high consistency press, aiming adjustment of the pH and, consequently improve the pulp drainability. The consistency expected is around 30%. A reduction on the consumption of aluminium sulfate dosed for pH control is significant. The mechanical properties of this type of paper are improved. This is very important for tear resistance of paper bags.
