Online Monitoring and Control in the Wet-End

Abstract

From its very beginning, papermaking has been targeted to produce a homogeneous sheet structure out of large volumes of water containing small amounts of fibre and filler. Fibre concentrations of below 1% are quite common in this context.

In order to successfully control both the desired paper properties and the production process, papermakers introduce functional additives and process chemicals into the fibrous suspension. However, these chemicals have to interact with the fibres if positive results are to be obtained.

What impedes interaction are the extremely unfavourable conditions prevailing in fibrous suspensions, such as very high dilution levels, strong turbulence and high shear forces, short contact times with fibres and, not to forget, anionic trash – all of which counteract optimal adsorption of chemicals onto the fibres.

Papermakers have long been aware of the fact that a number of measurable parameters (cationic demand, Zeta Potential, COD, turbidity, conductivity, pH) enable characterisation of the pulp suspension in terms of its colloid chemistry. However, this takes a lot of time and effort. In order to obtain representative results these often dynamic and complex processes should best be monitored continuously. This is where dedicated measuring devices are needed which enable paper manufacturers to respond in time to changing system conditions.