Wire
conditioner
Wire conditioner is sprayed on to the wires of the fourdrinier machine. The job of the wire
conditioner is to coat the wire and prevent stickie’s, glues, pitch and other
tacky substances from binding with the wire plugging the holes in the mesh.
Blocked parts on the wire will inhibit drainage leading to weight and moisture
deviations as well as holes/ weak spots in the sheet. these will cause a lot of issues on the paper machine.
When problems occur on the paper machines wire like marks from
stickie’s and hot melts a caustic chemical clean on the headbox can remove the hot
melts. Caustic soda is used because it breaks down inorganic materials like chalk,
ash and stickie’s.
Felt
conditioner
Felt
conditioner works in a similar way to the wire conditioner helps prevents stickie’s
and pitch from attaching to the felt and blocking the felt. An excessive amount
of pitch on the felts not only hinders dewatering but sticks off a small amount
of fibers. After time this will build up and cause defects in the sheet,
potentially leading to breaks.
Chemical felt cleaning and conditioning
Chemical precipitates found in
the press section are inorganic as well as organic. The organic or hydrophobic
types include rosin size, wet strength resin, and pitch and hydrocarbon oil.
Inorganic precipitates include clay, calcium carbonate.
Generally speaking, chemicals for
cleaning felts are applied using either a continuous or a shutdown cleaning
method. Continuous cleaning effectively keeps the felt open during its run
rather than relying on the more difficult job of cleaning a plugged felt.
Chemical felt washes are done
more infrequently on PM3/6 than on PM4, usually if the machine has been shut
for a while a chemical wash is usually done but on crawl speed to allow better
penetration of the chemicals in the felt. Using a lower speed allows the
chemicals to bed in and reacts with the dirt and contaminates.
Acid
Acid is used in two ways on the
machines, continuously dosing and shock dosing. The acid is used continuously
on all of the machines to help keep the felt open, rather than relying on the
shock cleaning on a closed felt.
The Shock dosing is done at a
high concentration of acid, it is important to ensure the water is running,
neat acid will melt the felts.
Acid is used to clean the felts
and to neutralise the caustic that has been previously dosed. The acid is dosed
through the chemical sprays on the felts. Acid is dosed for ten mins with 5
mins flushing time after. The acid removes the broken down pitch, fines etc. in
the felts. The acid is delivered in a higher concentration when shock dosed and
more dilution water is added when the acid is used continuously to keep the
felts cleaned. The caustic id a alkaline which is on the opposite spectrum to
the acid.
Caustic Soda
Caustic is used to treat the
felts. The chemical is shock dosed through the chemical sprays onto the felts
to break up the pitch, ash, fines and dirt collected in the felts. The caustic
is applied for 10 mins on each of the felts. The issue with caustic being used
on the felts is the chemical can cause the felt to close up, reducing the
efficient of water removal. After the chemical dosing the lines are flushed
with fresh water to clean the pipe work and sprays.
Anti-Scale Chemical
Anti-Scale chemical is important
chemical because the papermaking process is water based. Scale is made up of
minerals (mainly chalk and limestoneare composed mainly of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2), and calcium sulfate (CaSO4)) within
the water precipitating out and building up within water systems.
Industrial water systems using
hard water can experience breakdowns as the scale builds up in pipes, boilers,
water tanks etc. To maintain the level of scale within the water systems a
chemical is doses at specific points to dissolve/ break down the chalky
deposits preventing build up and ultimately costly breakdowns.
The effects of
scale
Can restrict the flow through pipes as the internal
diameter decreases as the scale builds up in the pipe.
Scale impairs the heat exchange between metals into the
water. this reduces the cooling/ heating efficiency and can lead to the metal
components over heating. This causes issues with the drying cylinders requiring
more steam to dry the paper because not al heat can be transferred through the
cylinder if a build up of scale occurs.
Below is a list of all the dosing
points in the site. There are problematic areas that scale is likely to build
up and can cause catastrophic breakdowns for example. If the dosing to the pump
seal water failed the pumps can clog up with scale, pumping would be reduced
and the mechanical could seize.
