Pitch and deposit control on paper machines

The recent years ACM has worked more and with pitch- and
deposit control on paper machines. Pitch control is since a long
time a topic on paper- and board machines as agglomeration
of pitch causes quality problems, holes, spots and runnability issues. Good retention is generally desirable to avoid these problems. ACM has long experience in achieving good retention in combination with efficient pitch control.

The best results have been achieved when working in projects together with customers. The dialogue with a customer can start with discussions on problems with pitch deposits in their paper machine. The projects is defined by a common goal that is guiding a strategy and an action plan. The obvious goal is of course to reduce pitch and deposits in the paper machine so that runnability and production can be improved. Every project is unique and it normally includes the following steps:

• Analysis of the problems
• Laborations:
  – choice of chemical concept
  – dosage points
  – dosage levels
  – cationic demand
  – measurement of particle count
• Strategy plan – (step 1, 2 and 3…)
• Trial – continuous follow up, measurements, analysis, and decisions step by step
• Evaluation
• Final decision

Project time
To be able to cover variations in production and seasons with different targeted efforts, the length of the projects are often a few months up to half a year. This is necessary to be able to evaluate different strategies, in a process that varies. It has worked well in projects with customers that have opened up for this type of cooperation.

Control
To achieve an effective reduction of different
pitch and stickies, they should be fixed on to
the fibres at smallest possible size.The aim is to keep the pitch particles separate so they won’t agglomerate. This is often achieved with inorganic and organic fixatives with different charge density added in selected dosage points on the paper machine.

We use different combinations of chemicals such as bentonite, polyamine, polyDADMAC and PAC (Polyaluminiumchloride). The products we use often affect the retention in some way. Therefore we do changes in several steps to adapt these additives to the retention aids. The advantage when these chemicals work in combination is that the total machine cleanliness increases which in itself improves the runnability.

Measurement of hydrophobic particles
It’s important to know what impact different
dosages have and how they work.
We measure the amount of hydrophobic particles such as pitch, stickies and “white pitch”. We simply count the number of particles before and after the dosages with a specific analyser (flow cytometry). The samples are pre treated with a flourescent dye that is only absorbed by these specific particles. The marked particles are classified with a laser beam. The method can differentiate between fines, fillers, stickies and pitch. Measuring of turbidity can’t differentiate these different substances in a pulp or paper machine stock. On the pictures below you see TMP before and after the dosage of fixative. 

Measurement of cationic demand
Since our products are charged (cationic/anionic) they affect the pulp and stock and therefore we also have to measure how the cationic- or anionic demand is affected. We use the well-known method/equipment PCD (Particle Charge Detector).

Products – BentStar® and FixStar®
BentStar® is a micro particle that is often used in two- and three component retention systems combined with polymer and fixative. The product is in powder form and is a specifically treated clay (volcano ash). ACM also supplies bentonite as one component or in combination with other additives for pitch control.

Dosing level normally ends upp in the range
1 – 4 kg/t of pulp. Before betonite was introduced in the Swedish market in the 80’s talc was used for pitch control to a great extent. As knowledge increased with the usage of bentonite in retention systems it was discovered that it was more effective than talc for pitch control.

FixStar® is available at different charge levels and molecular weights, the most common types are polyDADMAC and polyamine. In comparison to polyacrylamide they have much higher charge density but considerbly lower molecular weight.  Most commonly the products are used for fixation and/or control of the cationic demand. The products are succesfully used together with polymer and/or bentonite on paper machines and in water treatment applications, for better retention, pitch control and cleaner water.

Written by: Jan Larsson