WET END CHEMISTRY NEWS LETTER FOR NOVEMBER, 1998

Several events combine to prompt this newsletter. Following are brief descriptions:

1. During a recent visit to Europe, I visited a paper mill with an on-line zeta potential instrument that was supplied and installed by a chemical company. No correlation with paper machine performance was apparent to mill engineers, even on the addition of highly cationic chemicals. Based on my personal analysis of the (terribly primitive) design, none could be expected. It also had to be taken apart and cleaned twice a week. This travesty is a flagrant betrayal of customer confidence, and it leads me to offer specific criteria for evaluation of instruments that purport to measure charge.



Before planning on using a particular on-line zeta potential or cationic demand instrument, ask for assurance that it is capable of continuous, unattended performance, and does not require manual cleaning.

Most importantly, in the case of either an off-line or on-line instrument, ask to see process chemistry development experiments. To be completely sure that the technology will be helpful to you, ask the supplier to do experiments with your stock. Do not accept the excuse that they cannot do lab experiments with an on-line instrument, as it only requires a 30 liter stock pot, pump, and variable speed motor control.

Make sure that, in the experimental data submitted to you by the supplier, you obtain confirmation of the conclusion demonstrated on this web site that papermaking process chemistry is optimized at a sharply defined headbox charge. You can expect to observe that it falls off by 20-30% only 2 or 3mV on either side of the optimum zeta potential. Insist that the supplier spell out the precise optimum value for your particular process.

 

2. After my return from Europe, I had the pleasure of visiting installations of 6^th generation On-Line Zeta Data Systems made two months previously at the Blend Chest and the headbox of an alkaline, coated free sheet machine. Following is a brief report:



The instructions had been to apply the least rigorous of a six-phase automatic chamber and manifold cleaning protocol, and NOT to clean anything manually. After some weeks, I had been questioned on these instructions, because of a heavy slime outbreak, and I held firm to the non-manual-cleaning protocol. (This is, of course, fundamentally a biocide and chemistry balance issue.)

After two months of successful, unattended operation, I inspected the headbox System in company with the entire Instrument Service Team. There was a thin film of fiber and calcium carbonate stuck to the interior chamber plastic surface. We make little effort to automatically clean these surfaces because the issue is solely aesthetics rather than function. There was also some residual evidence of slime below the electrodes, again where we make little effort to automatically clean. The electrodes were clean and the screen function was not impaired.

The Zeta Data System had endured two months (and counting) without the touch of mortal man, using the least rigorous of our six graduated, increasingly intense cleaning protocols). The Blend Chest chamber was in even better condition, presumably because the increased stock consistency provides superior self-cleaning.

 

3. My presentation to the operating personnel centered on shifting from a monitoring mode to that of selecting the most anionic of the large volume grades, and adding a cationic scavenger plus microparticle to increase drainage until it maximized. The zeta potential at which this occurred would represent the optimum zeta potential for that system.

In addition to optimizing the electrokinetics, it is necessary to simultaneously fine-tune the chemistry. For example, monitoring data can show that the wet end goes berserk during grade changes and machine breaks. At such times, the various flow rates should be automatically adjusted to maintain a stable process, in order to minimize the broke quantity and reduce the re-start time.

Another fine-tuning example is to review the retention system as the papermaking system begins to optimize, in order to improve formation and better balance the electrokinetics. In many instances this will call for less polyacrylamide and more colloid silica.

There will likely be several machine-dependent chemistry issues to be addressed, in parallel with optimizing the electrokinetics. They might include the type, amount and addition point(s) for OBA, and improving thoroughness of mixing of chemicals with stock by minimizing headbox zeta potential standard deviation.

 

4. During the month of October, we added an On-Line Zeta Data Operating Manual to the web site. We trust that you will find it a convenience in answering basic questions concerning the principle of operation, design, construction, function and maintenance of the Zeta Data System.

After we receive an order for a System, we supply additional Confidential Information on installation, start-up, operation, trouble-shooting and maintenance.

The June Newsletter dealt with making lab handsheets that realistically reflect the use of functional chemical additives, using Mk IV or MK V Dynamic Handsheet Molds. It is well known that conventional hand sheet molds need to repeat the process many times, while saving and re-circulating the white water, in order to accomplish this. The reason is that the stock is diluted unrealistically in order to obtain good formation, and the functional chemicals quickly de-sorb, and go down the drain unless saved.

Following is a listing of the area of the handsheets generated by each of the commonly used methods:

The 8" diameter Mk V was introduced in response to the demand for much larger handsheets, and ones that could be tested for functional properties such as sizing, Scott Bond, etc.

This will announce that, in response to further expressions of demand, the Mk V will henceforth be provided in a version that includes the capability of measuring retention and drainage, as well as making dynamic handsheets.

John G. Penniman

Email your experience and suggestions, and I'll put them on the web site with attribution, so that others can respond.

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