Brochure

The Process of Papermaking
Although not present at all mills, there are six major steps to the
papermaking process: mechanical preparation of the wood into wood
chips, turning wood chips into pulp (digestion), chemical recovery,
pulp whitening through bleaching, pulp stock preparation, and finally
paper formation.
The first of these steps uses strictly mechanical processes to form
small chips from the logs supplied to the mill. By-products such as
bark, and even some chips themselves, are used as fuel to produce
steam and electricity for mill use. Although some water may be used
for lubrication purposes, this is primarily a dry process and proceeds
with minimal process instrumentation.
The pulping process has many variations, the most common being
the kraft process, which uses caustic chemicals to digest the lignin in
the wood chips. This is different than the sulfite process, which uses
acidic chemicals to digest lignin.
No matter the process, the chemicals used are regenerated in a multi-
stage recovery process that reduces chemical costs and minimizes
waste disposal costs. Appropriate process control helps to ensure
maximum chemical regeneration.
After cooking the wood chips, pulp stock leaves the digester as a
brown slurry. Depending on the end product, it may be bleached or
remain brown. If bleaching is necessary, large quantities of expensive
bleaching chemicals like chlorine dioxide (ClO
2
) are used and must be
precisely controlled to minimize financial impact.
The slurry then heads toward the stock preparation section of the
mill. Here, different batches of pulp may be blended to produce paper
of various required properties. Starches, clays, and other retention
aids are added to improve the wetting properties of the paper so the
end product meets customer specifications.
The paper machine is the final step in the process of producing the
correctly specified end product. Reliable control valves are necessary
to ensure the appropriate percentage stock is sprayed onto the paper
machine felt, appropriate temperatures are obtained for drying the
paper, and vacuum controls are running to dispense condensate.
Control of steam pressures and temperatures are likely the most
critical applications in a pulp and paper mill. Steam is used for wood
chip preparation, process heating, paper drying, boiler cleaning,
energy production, and in many other applications.
Wherever your tough application exists, the reliability of your
control valves play a critical role in helping improve your process.
In this brochure, we’ll discuss the many application challenges you
encounter in each process and ways that Fisher control valves and
technologies can help to combat these application challenges while
ensuring your mill operates at its peak performance.
Papermaking Overview
Fisher
®
Pulp and Paper Solutions | 3