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CACTUS


The effect of concentrating of white water to the microbial growth in paper machine

In this project, run by the Control Engineering Laboratory (HUT) and VTT Biotechnology, two paper machines with different pH values and the effect of their prevailing conditions on the growth of microbes were researched.

A paper machine is a good habitat for microbes. The range of microbe species in a machine depends on

  • the nutrients in the white water
  • the harmful microbes introduced in the process e.g. by raw materials
  • the conditions that prevail in the machine, such as pH or temperature

Closing the white water cycle in paper machines results in white water concentration and increases the amount of nutrients that are suitable for microbes.

In the laboratory experiments we looked at what effects do the changes in pH, temperature and white water concentration have on the growth of two species of harmful microbes (Bacillus coagulans and Acinetobacter lwoffii).

This project is a part of the CACTUS (1996-2000) program for research of closing the white water cycles of paper machines and its potential consequences.

  • Keywords: chemical reactions, dynamic modelling, paper and pulp industry
  • Research area: Process Control

Publications

  • Final report of the technology program CACTUS Water management in paper making, TEKES, CD-ROM (2001). (View the entire report) (This project only)
  • Ylöstalo, T., Siika-aho, M., Raaska, L. (2001). Mikrobiongelmat paperikoneella - miten mitata, mallittaa ja hallita?, Automaatioväylä 3.

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In co-operation


The Dynamic Chemical State in Unit Operations of Paper-Making

The use of precipitated calcium carbonate (PCC) and the increasing amount of recycled fibers in the paper-manufacturing processes raise the calcium levels in the aqueous solutions in the wet end of a paper machine. The calcium compounds appear both as solute ions and as precipitated solids which are often occluded with the pulp fibers. Calcium carbonate (CaCO3) is a basic salt with limited solubility to near neutral aqueous solutions. The most common ions appearing are Ca2+, HCO3- and CO32-. The solubility of calcium carbonate increases with decreasing pH and can thus be promoted by introducing acids. Undissolved calcium carbonate acts as an effective pH buffer, and thus the presence of PCC in the short circuitry has a strong effect on its pH-control and onto the chemical state of the various stages of the process.

In this work a set of studies were performed on the aqueous and suspension chemistry of calcium carbonate in conditions corresponding to the unit operations of the wet end or to those of pulp recycling. Laboratory experiments were used to study the reaction kinetics of calcite dissolution and the subsequent pH-dynamics. Batch experiments were made with de-inked pulp (DIP) suspensions with consistencies of 3, 8 and 12 %. During a plant test, tracer experiments were used to measure residence times and effect of mixing for optimal location of plant pH-measurement. Modeling tools were developed for the multi-phase equilibrium chemistry of calcite solutions in sulphuric acid and carbonaceous solutions by using the Gibbs energy minimisation techniques. It was concluded that the effect of soluble carbon dioxide from the surrounding air is essential for correct modeling of the pH-chemistry of the solutions. The transient behaviour of pH during acidifications was modelled by using combination of instantaneous (equilibrium), fast and slow reaction dynamics by fitting the reaction rate parameters from the observed experimental results.

The methods developed during the research were applied as follows:

  • dynamic models for CaCO3-dissolution in pulp suspensions
  • preparation of ChemSheet-multi-component models to evaluate process chemistry
  • improved pH-control of DIP-production at Keräyskuitu Oy

A number of situations both in pH-control of the plants and in introduction of new concepts of process chemistry could be recognized. Improved pH-control of DIP-manufacturing allowed more even product quality at the plant. The ChemSheet multi-phase models were applied in particular to evaluate effects when carbon dioxide is used to replace sulphuric acid in acidification of CaCO3-containing pulp suspensions. The work is continued by introduction of the ion-exchange between the aqueous bulk solution and the fiber phase into the multi-component models.

  • Keywords: chemical reactions, dynamic modelling, paper and pulp industry
  • Research area: Process Control

Publications

  • Jutila, V.-P., P. Jutila and J.-P. Ylén,
    "The measurement and control of the pH of thick deinked pulp",
    3rd Asia-Pacific Conference on Control and Measurement, APCCM´98, Dunhuang, P. R. China, August 31-September 4, 1998.
    Nanjing, Jiangsu, China 1998, China Aviation Industry Press, pp. 326-330.
  • Ylén, J.-P.
    "pH-value and dynamic chemical state of wet end."
    Scientific & Technical Advances in the Measurement & Control of Papermaking, Edinburg, UK, 9th & 10th November 1998.
    UK 1998, Pira International, p. 22.
  • Ylén, J.-P. & Jutila, P.
    "Dynamic chemical state modeling in paper and pulp processes."
    The 4th Asia-Pacific Conference on Control & Measurement, Guilin, P.R. China, 9-12 July 2000.
    P.R. China, 2000, China Aviation Industry Press, pp. 27-34.
  • Final report of the technology program CACTUS Water management in paper making, TEKES, CD-ROM (2001). (View the entire report) (This project only)

In co-operation