PAPER CHEMISTRY LABORATORY, INC.
Why the Papermaker/Chemical Supplier Relationship Isn't Working
Fundamental to the relationship between the papermaker and the chemical supplier is the objective of optimizing process chemistry in order to operate the paper machine at a uniform high level of quality and maximum cost efficiency. Our July column examines the reasons why the mutual objective consistently fails of realization.
The art of papermaking, as we presently try to conduct it, consists of cost efficiently making a finished product of uniform high quality by harmoniously balancing the properties of a variable feed stock using a variety of sophisticated chemicals in conjunction with a complex of interdependent process disciplines. The task does not fall easily to mortal man. In consequence, the papermaker narrows his efforts to what he is confident he can personally control; and delegates everything else, notably including the chemistry.
The chemical supplier plays a key role by determining the type and amount of chemicals required for the process, and providing them at a 40% gross profit. Additionally (and unlike other segments of the chemical process industry) papermakers traditionally also delegate to the chemical supplier the critically important role of supervising chemical usage in the manufacturing process. There is much room for improvement in this area.
Chemical suppliers have excelled at protecting their lucrative franchise. As a result, 'Smoke and mirrors' has long been part of the industry lingo and instead of using chemical specs, papermakers have been trained to refer to "retention aids", "drainage aids" and chemical "additives".
The industry is slowly awakening to the realization that the chemical supplier has been given key hole cards in a game the papermaker must win in order to survive in the marketplace. However, the papermaking response has varied because of needs that are often imperfectly perceived and difficult to fully express in a contract. The result is an uneasy alliance, rarely satisfactory to both parties.
In order to cope with feed stock variability, execution of the process chemistry optimization mandate requires installation and effective use of appropriate on-line sensors so that closed loop control of chemical feed rates can be mediated by a Distributed Control System (DCS). This is of little or no interest to many chemical suppliers, whose primary objective is quite different from the papermaker...it is purely and simply to keep the business.
The strategy has been perversely successful. Older engineers, i.e. those who call the shots, have avoided chemistry for their entire career and have lost whatever competence they may have had to evaluate chemistry performance. Instead of insisting on continuous optimization of process chemistry, they accept extensive machine studies and multiple voluminous reports (increasingly embellished by colored, three-dimensional graphs). The absence of supervision is not conducive to tangible quality improvement and significant, permanent cost reduction.
In the overwhelming majority of cases, the proper course of action is incontestable. Process chemistry is optimized by adjusting chemical feed rates to stabilize the process and operate the headbox at the zeta potential value that maximizes retention and/or drainage. It is necessary to use on-line sensors in order to compensate effectively for variations in feed stock quality. Remarkable benefits in quality, productivity and cost can be obtained, as will be discussed below.
Fourth generation on-line Zeta Data technology combines reliable means of on-line measurement of both zeta potential and drainage. For one particular microparticle process tested in a narrowly defined way, the optimum value turns out to be in the range +2 to +6mV.(1) One possible explanation for the positive value is that all commercial microparticles are highly anionic and therefore best attracted to a cationic, or positively charged, substrate. Conventional (i. e. non-microparticle) wet end chemistry is optimized on the negative side of the zeta potential spectrum, as most of us have long believed, and as Dr. Miyanishi has repeatedly confirmed by clever on-line use of his antique (1989 second generation) Zeta Data System (2)(3)(4).
The qualitative benefit of operating at the optimum zeta potential is described in the first web site article (1). The Series I graph shows that this is extremely sensitive, in the sensed that missing the optimum value by only 5 or 6 mV on either side decreases performance by 20 to 30%. The other side of this coin is the critically important fact that major quality, process and cost benefits attach to precise on-line control.
In Series II and III we show that a controlled process with 14% sheet ash has equivalent strength to an uncontrolled process with 4% ash, representing a potential filler for fiber savings of $15. per ton. Drainage is far superior; retention is about double; sizing efficiency is improved by an order of magnitude. The economic benefit to a particular alkaline fine paper coated free sheet (CFS) process is estimated to exceed $2,000,000 annually (5).
The measurement of cationic demand via an oscillating Teflon tube and automatic titration, as exemplified by the Mutek, has come into widespread use during the last decade. Four separate, comparative studies are reported (6). They raise questions about some aspects of data reproducibility and show that Mutek cationic demand data has a very low correlation with zeta potential. These results perhaps help to explain why Mutek has recently introduced a zeta potential instrument.
The logic is compelling for installation of on-line chemistry sensors on a world class paper machine, and for using the DCS to continuously optimize process chemistry by closed loop control of chemical feed rates.
Bibliography
Please Email your experience and suggestions, and I’ll put them on the web site with attribution, so that others can respond. Perhaps we can sort this out together.