Paper Technology Journal 19 - Voith

Fig. 1: Procedure for a WEP Analysis.
Procedure for solving product quality problems,
e.g. basis weight and ash content fluctuations
Periodic fluctuations Stochastic variations
Pressure pulsation
Mechanical
vibrations
Speeds and
speed variations
Paper transmission and
quality control system
Analysis
in frequency
range
(Fourier
spectra)
The approach and evaluation method of
the Wet End Process Analysis explained
here shows that it is a largely standardized
service product developed by Voith in
close partnership with the paper industry.
Goals of Wet End Process
Analysis
Since the Wet End Process Analysis is
largely standardized, it serves as a tool
for various purposes:
It can be used for troubleshooting problems
such as bad sheet profile or wrinkles.
Time signal
analysis
(statistics
and
distribution)
Paper laboratory tests
e.g. Tapio analyzer (Fig. 3)
Pressure pulsation
Stock/ash samples and
stock consistency variations
Process control system
(raw signal registration)
Gas content, temperature,
pH-value, conductivity
This tool can also be used as a condition
analysis prior to rebuilds or for assessing
optimization potential and investment,
e.g. to increase runnability or operating
speed or better profile quality.
The results from a Wet End Process
Analysis by Voith Process Solutions are
the basis for answers to various questions.
The analysis in the paper mill consists of
on-site measurements of all parameters
affecting the papermaking process, production
output and quality. Thanks to sophisticated
evaluation techniques, conclusions
can then be drawn on widely
varying aspects.
Voith
Process
Solutions
Wet End Process
Analysis
49
Fig. 1 shows the basic procedure for a
Wet End Process Analysis evaluation.
Starting with the paper characteristics,
such as basis weight or ash content stability,
potential periodic or stochastic
variation parameters are identified and
evaluated. Interrelationships for example
between pulsation and rotational frequencies,
gas content and defoamers and
sheet breaks are investigated thereby using
all available information from the
process.
Typical aspects related to the
papermaking process
● Hydraulic stability (freedom from
pulsation) of the stock and water loops
● Inflow and outflow conditions as well
as headbox pressure stability
● Stock mixing efficiency among the
various flows in the approach flow
section
● Efficiency-optimized operating ranges
of the cleaner and screen sections
● Optimized positioning of pipe elbows
and fittings
● Necessity and efficiency of mechanical
degassing systems in relation to
chemical defoamers
● Additive quality in relation to gas
content and retention of fiber and ash
● Stability of the jet impingement line
after the headbox; web pick-up
deviations on the central press roll
● Drainage element and vacuum settings
for optimal quality and water removal
19/05