Optimization of Water Removal in Press Section

As a rule of thumb it can be said that removing one unit of water in the dryer section takes 5 times more energy compared to what is needed in the press section. There are significant energy gains to be made by optimizing water removal in the press section.

 

Press water balances will provide valuable information regarding where the sheet water is extracted within the press. However, many paper machines lack the proper equipment required to make water measurement possible from uhle boxes and press nips. There are many variables to pressing and there is not a single set of parameters to set up the press for maximum water removal on all grades. Press nip loadings need to be maximized within design limits. Also, analysis of roll coverings (soft to hard) and surface patterns (drilled, grooved, and hybrids of these) should be part of the entire press section study. Additionally, felt design changes should be considered and will require some trial and error as each step in the optimization process is taken. Typically, sheet temperature is reduced as it passes through the press, so efforts should be made to maintain, or even increase the sheet temperature as it exits the press. Additionally, higher pressing temperatures can improve water extraction from the sheet which further reduces dryer steam requirements. Increasing sheet temperature can be achieved with significantly increasing press shower water temperature (over 54.4 ºC) and/or adding steam showers at the uhle boxes, where the steam is pulled into the felt at the vacuum slot. Finally, sheet rewetting within the press should be addressed to be sure it does not exist, or is minimized (Kramer et al., 2009. p.102).

Development Status Products
Commercial

Optimization of Water Removal in Press SectionCosts & Benefits

Parent Process: Papermaking
Energy Savings Potential

A 7.8 ºC increase in sheet temperature leaving the press provides a 4% decrease in dryer steam (Kramer et al., 2009. p.102).

CO2 Emission Reduction Potential
Costs

Optimization of Water Removal in Press Section Publications

Page Number: 

102