Netention and u r a i n a g m
w-9
ental strategy for control
ention and drainage on a
rn paper machine
M,Sprhger,Jefsrey S. Noe, and T.H. Wegner
t and maintain control ouer contaminants in reqcled uhite uater,
ment-bked retention control strategy must be deueloped.
rates must be adjusted to compensate for this constantly
moved the paper industry toward ever in- changing environment.
To detect changes in chemical conditions at the wet end,
ees of system closure and white water reuse.
new on-line sensors will need to bedeveloped, and those that
are available will have to be used more effectively.A recent
Pete with filler and fibrous additives for survey (6) revealed that we are in our infancy in this field.
The most-needed capability is a reliable way to monitor the
costly cationic chemicals.
state of charge of the system. Knowing the state of charge of
the system is necessary, but it is not sufficient information
for controlling retention and drainage. The lack of recognition of this fact is partly responsible for the poor results
that have been experienced in trying to apply zeta potential
sensors in the paper mill.
ctivity is useful for measuring the total con- Retention and drafnage
of inorganic contaminants. The concentration
To adequately control retention and drainage, an instrument-based strategy must be developed(3-5,7). Such a
trol of retention and drainage is accomplished strategy is illustrated in Fig. 1. For this strategy, it is
combination of machine design and chemical presupposed that a good pH control program has already
he best approach is first to optimize the mech- been implemented in the mill. The strategy would contors on the machine such as headbox conditions tinuously monitor the concentration of contaminants and
eluding the number of foils and their key system responses and automatically adjust addition
control agents appropriately.
A strategy like this would likely result in substantial raw
material savings and increased productivity, while including such benefits as:
leaving the couch.
1. Reduced loss of high-cost materials such as titanium
have been studying the effects dioxide and synthetic size
s a chemical engineer for USDA Forest
Laboratory, P.O. Box 5130,
2. Increased dewatering on the paper machine, leading
to a lower water content in the sheet going to the press
section and lower energy requirements in the dryer section
3. Potential for increased machine speeds because of an
increase in drainage rate
4. Improved paper machine runnability
5. Potential for increased water reuse, which can result
in energy and raw material savings.
Lindstrom and coworkers (8) also have proposed a
retention control strategy model.
Three major generalizations can be drawn from the
extensive amount of research aimed at elucidating wet-end
chemistry mechanisms and fundamental knowledge (5).
Serving as the basis of a first-pass retention control
strategy, these three generalizations are as follows:
January 1987 TapplJoumal
43
I%"*
1. The performance of most wet-end additives and components is highly dependent on the first-pass retention.
2. On medium- to high-speed paper machines, retention
aid additives are necessary to achieve acceptable first-pass
retention.
3. The effectiveness of cationic additives is impaired by
interference from dissolved and colloidal anionic substances
at the wet end.
The proposed retention and drainage control strategy
(Fig. 1) consists of three main control loops. The first loop
measures and neutralizes the organic contaminants on the
thick-stock side of the stock preparation area. Total organic
carbon (TOC) measurements serve as a measure of the
cationic demand of the system (9). Based on the demand
measured, a cationic-charge neutralizing additive of low
molecular weight and high charge density is added to
counteract detrimental organic effects. This amount will be
affected slightly by the concentrationof dissolved inorganics
(9). In theory, as the furnish exits the stock preparation
area, the total charge of the system is checked to determine
if the charge of organics is sufficiently neutralized.
In the second loop, the first-pass retention performance is
measured, and the addition rate of the high-molecularweight retention aid is adjusted if a change in retention is
needed to achieve a targeted uniform retention. A retention
value that correlates with first-pass retention can be
derived with the M/K and Chemtronics retention meters.
The adjustment of drainage rates and couch dryness would
be controlled by this additive also. Information about the
mass of incoming fine solids (filler, pulp, and broke fines)
from the stock preparation area is also known and fed
forward to this loop.
The third loop illwtrated in the diagram monitors the
retention of filler in both the final sheet and in the recovery
system for recyclying broke. This information is fed back to
the stock preparation area to adjust the flow rates of
mineral fillers such as clay and TiO2.
Not illustrated in the diagram but quite necessary is a
feedback loop that relays information on such properties as
the optical nnd strength charaeteristicsof the paper tosome
type of process control computer. This information would
include measurements of opacity, brightness, ash contact,
strength, etc., so that product specifications would remain
acceptable.
In short, a first-pass retention and drainage control
strategy could be implemented with relatively few on-line
sensors. However, sensors which are currently unavailable
are those that measure total charge of the system,
the process stream, and wet ash in the system. G
future demands required in the paper machine wet end
from alkaline papermaking and the increased filler
loadings, higher machine speeds, lower basis weights,
white water recycling, etc., the industry needs to take a
stronger approach toward this type of on-line process
control strategy. If the needed sensors can be developed and
are sufficiently dependable, control of retention and
drainage should be possible.
We have begun to work on a reliable technique to monitor
total charge in the papermaking system, since the industry
survey ( 6 ) indicated that this was of top priority. The
measurements to characterize fine solids and wet ash still
need to be developed. Instruments for monitoring retention
are under development,and some commercial installations
exist. The sensors for monitoring sheet ash by components
exist and are readily available. They are becoming part of
I.Diagram of the proposed control strategy for retention and drainage.
44 Januaty 1987 TapplJournal
package systems for the paper machine.
ions of inorganics in the system are best
t, so the main questionsto be answered
ions of the measurement (9).
f the instruments necessary to implement the
trategy aredeveloped. What is missing are a wet
sensor,a fine solids sensor, and a technique to monitor
a papermaking system.
and pH are compensated for. TOC is
measure of the colloidal and dissolved
m!
A Manager's Guide
to Process
Simulation
Designed for the manager . . . .
0 With limited background in
simulation/computers
Considering developing a
process simulation capability
0 Wanting to improve an
existing simulation group
0
. Springer, A., Noe,J., andTaggart, T., 1985Advanced Topics in
Wet End Chemistry Seminar Notes, TAPPI PRESS, Atlanta,
4. Springer, A., McMahon, W., and Boylan, J., 1984 Papermakers
Conference Proceedings, TAPPI PRESS, Atlanta, 1984, p. 13.
. Springer, A., Boylan, J.. and McMahon, W., Southern Pulp
Paper 47(3): n(1984).
6. Scott, W.E., Tappi J. 67(11): 72(1984).
7. Scott. W.E.,1983 Retention and Drainage Seminar Notes,
TAPPI PRESS, Atlanta, p. 59.
Lindstrom, T., Rydefalk, S., Wagberg, L., Development of an
Integrated Retention Control System, New Available Techniques P"$ings
from the World Pulp and Paper Week,
Swedish A w i a t i o n of Pulp and Paper Engineers, April 10-13,
Noe. J.S., Mechanism for Control of Retention and Drainage in
ms, M.S. thesis, Miami University,
After reading the 44-pageI soft
cover report, the manager
should understand the basics of
process simulation, when to use
it as a tool, what simulators are
available, what resources are
required for simulation, and
what steps should be taken to
carry out a simulation project.
You will then be ready to direct
a person or group to:
Compare available
simulators 0 Select one for your
simulation project Arrange to
be trained to use it Start
simulating (work with
knowledgeable personnel)
0
0
0
for review April 15.1986.
1985.44 pages. 8'/2 x 11
Soft Cover.
Order Number: 01 01 R131
TAPPI Members: $8.00;
List: $12.00
TAPPI PRESS PublicationSales
Technology ParWAtlanta 0 P.O. Box loJ113
Atlanta, GA 30348 0 (404)446-1400
January 1987 TappiJournal
45