Introduction
Raw pulp contains an appreciable amount of lignin and other discoloration, it must be bleached Raw pulp contains an appreciable amount of lignin and other discoloration, it must be bleached to produce light colored or white papers preferred for many products. The fibers are further delignified by solubilizing additional lignin from the cellulose through chlorination and oxidation. Sodium Hydroxide, a strong alkali is used to extract the dissolved lignin from fibers surface. Chemicals used for bleaching mechanical pulps selectively destroy coloring impurities but leave the lignin and cellulosic materials intact,such as sodium bisulfite, sodium or zinc hydrosulfite , calcium or sodium hypochlorite, hydrogen or sodium peroxide, and the Sulfur Dioxide-Borol Process.
In order to ensure that the whiteness of the paper is even and fine, different additives, dispersants and bleaching agents should be added. As with the use of additives in the food industry, these additives have a small flow rate and are highly corrosive.
Advantage and challenge
Advantage:
• Can be configured with a range of materials to match process needs
• Full diameter with no pressure drop across meter
• Stable, accurate measurements that represent the actual flow.

Challenge:
• The flow rate is small, and the output signal will fluctuate greatly.
• Highly corrosive medium will influence the service life
Solution
Lining: Most of them choose PTFE lining and PFA lining.
Electrode: Ta/Pt selected according to different liquid properties
Pay special attention to the concentricity when installing the small-caliber electromagnetic flowmeter.
The wrong electrode and lining material, dissatisfaction of the pipe, insufficient length of straight pipe, and misalignment during small-diameter installation are often the main factors that cause the electromagnetic flowmeter to fail to operate normally.
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