Stock
System
Papermaking nanotechnology deals with particle sizes on the order of a
billionth of a meter. At this size level, inter-particulate
forces come into play which have strong mutual attraction, binding the
particles together. In order to maximize this highly desirable
state of affairs we must do three things which are not appropriately
executed in the conventional process.
1. The bundles of chemicals must be fully dispersed by reduced surface
tension plus the application of vigorous agitation, such as ultra-sonic
energy, with the objective of creating a homogeneous stock. This
approach has several side-benefits:
A. It reduces chemical usage by one to two orders of magnitude,
or 90-99%;
B. Ultra-sonic energy destroys micro-organisms, obviating need
for biocides and boil-outs;
C. It provides a compelling incentive for reducing white water
volume from the usual gross excess, with storage silos, to the minimum
amount needed to conduct the wet end process.
2. The amount of soluble ions must be controlled at a low level,
as they physically block the particles from coming close
together. In some instances it may be economic to employ reverse
osmosis for this purpose.
3. A network of anionic nanoparticles and low molecular weight
cationic chemicals must be created to maximize water removal and
retention, by controlling the network at a net charge of zero zeta
potential.
Finally, we must increase the flow rates of anionic nanoparticles and
cationic chemicals to raise water removal to the maximum tolerable by
the machine, in a balanced manner, so as to maintain zero zeta
potential. This maximizes productivity and minimizes unit cost of
production.
Press Section
Experiments on a variable speed pilot plant press section show that
water re-wetting is a major cause of press section inefficiency.
Further experiments reveal that increasing the press section speed at a
reduced surface tension can remove sufficient water to result in a
dryer energy reduction of 20%.
It follows that a new machine, or a re-build, should run the felt
section at a reduced surface tension, and at higher speed than the rest
of the machine. This can be accomplished by extending the length
of the felt section so the web has to travel further in a given time
than on the wire or in the dryer.
Dryer Section
A significant reduction in dryer energy usage is observed when a
hydrocarbon catalyst is used to reduce wet end surface tension.
We believe it emanates from two sources: the formation of a
positive azeotrope in the dryer, and a reduction in hydrogen bonding of
water to cellulose.
The formation of a positive azeotrope results in the vaporization of
both the water and the hydrocarbon component at a lower boiling
temperature than either component individually, thereby reducing energy
consumption.
Differential scanning calorimetry experiments indicate that the energy
saving, at low levels of hydrocarbon catalyst, approximates 20%.
Our investigation of this phenomenon began with the report of an
anomaly. In the course of a consulting visit, we were informed
that a large newsprint machine, early in its history, malfunctioned and
applied kerosene to the web section, rather than to the felt, for
cleaning purposes. The first section dryer steam pressure was
reported to “drop by half.”
On return to our lab, we attempted to reproduce the result. It
took many years, much experimentation, and many dead ends to reach our
present understandings. The amount of hydrocarbon catalyst
currently used is optimized for wet end performance. We expect
that investigation of increased amounts of catalyst could result in a
total dryer energy reduction of at least 40-60%, and likely
higher.
Computer Control
Closed loop computer control of chemical feed rates is essential to a
high level of quality and uniformity. Off-line assessment of
specific performance parameters, in order to maintain on-line quality,
is inappropriate to the task.
For example, we measured Hercules Sizing Test (HST) sizing on each reel
of free sheet coating base stock for several months. The level of
sizing was approximately ten times (10X) higher than required.
Lack of an appropriate on-line method for measuring size obliged
machine management to over-shoot the amount of size required by a large
and extremely wasteful margin.
There is a large variety of indirect measurements which can be
effectively used for on-line process control, beginning with zeta
potential, specific conductance, pH, surface tension, standard
deviation, correlation coefficient, chemical feed rate, etc. It
is analogous in human health assessment to measuring body temperature,
pulse rate and blood pressure rather than analyzing for the entire
panoply of chemicals in the blood system.
In the course of design and installation of the papermaking
nanotechnology process on a given machine, manufacturing specifications
are developed which are realistic and tight. Following that, in
consultation with marketing, an additional set of sales specifications
are evolved and published.
In the course of routine production, when an aberration from the
manufacturing specs. occurs, an alarm is sent via the internet to our
remote monitoring computer. Proprietary diagnostic software
analyses the data and sends an alarm with action recommendations to the
Control Center of the manufacturing mill, enabling them to easily
resolve the issue.
In the meantime, the local machine control software has monitored the
conformance of production quality to the sales specifications, and
earmarked whatever portion of the roll needs to be excised as broke,
retaining the portion that is saleable.
The cost of each reel is output to the penny, simultaneously with its
production.
Conclusions
Nanotechnology is a game changer that enables great improvement in the
cost and quality of papermaking: at least 90% reduction in
chemical cost; 40-60% or greater energy reduction in water removal;
minimum raw material usage; maximum productivity; superb quality and
sustainability.
Quantitation of the 90-99% reduction in chemical usage was done with
four different, commonly used, wet end additives to ensure general
applicability. The 40% energy reduction was quantified by pilot
plant, differential scanning calorimetry and thermogravimetric studies,
based on the small amounts, ca 1%, of the hydrocarbon catalyst
necessary to reduce surface tension. Larger quantities would
result in greater azeotropic efficiency, not contemplated at the time
because the mechanism was not understood.
Papermaking nanotechnology uses a number of well established
engineering unit processes scaled in size appropriately to the machine
contemplated for use, and conducted under closed loop computer
control. Two processes are used to recycle the catalyst,
automatic decantation for the liquid, and carbon adsorption for the
hydrocarbon catalyst vapor.
The increased efficiencies are such that cost of a new machine, or
re-build, is significantly reduced. Size of the white water
system is reduced to the minimum necessary for conducting the process
chemistry, with the by-product of maximized effectiveness in microbial
destruction. The press section has increased vertical movement in
order to increase web speed and reduce water re-wetting, resulting in a
smaller footprint. The dryer section has about half as many dryer
cans, resulting in another large cost reduction.
The bottom line is compelling: major reductions in chemical cost;
major reductions in process cost; major reductions in machine cost;
continuously maximized productivity; unsurpassed quality and
uniformity; and the actual cost of each reel is output as it comes off
the machine.
The paper industry is finally joining the ranks of the chemical process
industry.
John G. Penniman
www.papermaking-chemistry.com
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