Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2001-06-11
2002-11-05
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C073S061480, C073S061710, C137S093000
Reexamination Certificate
active
06474354
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the application of ultraviolet-visible light measurements for the determination of colloidal substances in a liquid sample. More particularly, the invention relates to the application of light attenuance and/or light scattering measurements for determining and controlling a property of colloidal substances that undergo at least one of a temperature dependent phase transition and a temperature dependent adsorption-desorption process.
BACKGROUND OF THE INVENTION
Papermaker's demands for high speed and efficiency, flexible manufacturing, stringent quality standards, and environmental compatibility coupled with new developments in on-line process control are driving the development of new sensor technology for the paper machine wet-end. The need for better systems for providing wet-end chemistry control is emphasized by recent reports stating that only 10% of the world's 150 newsprint paper machines operate at an efficiency above 88%, and that more than 60% operate in the low efficiency range below 82.5%, see for example Mardon, J., Chinn, G. P., O'Blenes, G., Robertson, G., Tkacz, A. Pulp and Paper Canada, Vol. 99 No. 5 pp. 43-46. (1998). William E. Scott addressed some of the problems that are related to wet-end chemistry control in
Principles of Wet End Chemistry
. Tappi Press, Atlanta, 1996. p. 3. “Deposits and scale usually arise from out-of-control wet end chemistry. Typical examples include chemical additive overdosing, charge imbalances, chemical incompatibility and the shifting of chemical equilibria. All of these phenomena can lead to the formation of precipitates or colloidal aggregates that produce deposits and scale. While there are numerous approaches to treating the symptoms of deposits the best approach is to determine what is out of control and fix it.”
Pitch is a generic term for the colloidal components that are suspended in the pulping process waters or water of the paper machine wet-end, wherein the composition of individual pitch particles may vary from relatively pure mixtures of fresh resin and fatty acids to heterogeneous agglomerations of wood extractives, wood-derived lignin and hemicellulose, salt, cationic polymer and filler particle. The common use of the term pitch often blurs the distinction between extractives, pitch, white pitch, and stickies as defined in the Dictionary of Paper 5
th
Edition, Tappi Press, 1996, Atlanta Ga. The degree to which temperature will alter the equilibria between colloidal pitch and dissolved substances is a complicated function of the solution conditions and the composition of the pitch particle itself. In the field of pulp and paper manufacture the maintenance of a level of stability and/or the removal of colloidal pitch is an important objective in the wet-end chemistry control programs. Deposition leading to poor paper machine efficiency is a costly problem, which is addressed through numerous strategies including pulp processing optimization and/or addition of chemical agents.
Nearly every pulp and paper mill has a strategy for controlling pitch to prevent its deposition on pulping, bleaching and papermaking machinery and to reduce pitch build-up in white water systems. Pitch control strategies include: stabilization with dispersants; coagulation and fixation with cationic polymers; and, adsorption and removal with mineral additives such as talc or bentonite clay, as described by Garver Jr., T. M. and Yuan, H.
Measuring the response of pitch control strategies
. in
PAPTAC
87
th Annual Meeting.
2001. Montreal, the contents of which are incorporated by reference herein. A strategy utilizing dispersants, such as for example non-ionic surfactants, is usually employed in open systems where the dispersed colloids can go to drain, while a strategy of removal with cationic polymers or talc is typically used in closed systems where the incoming pitch must be removed with the product. In addition, there is a plurality of pulp processing variables that may be adjusted in an attempt to reduce pitch accumulation and deposition. Ultimately the single most important reason for controlling pitch is the cost of lost production time related to cleaning pitch deposition on equipment. Other factors related to product quality include such issues as increased dirt and speck counts from agglomerated pitch or sloughed off deposits and loss of paper strength related to the interference of resinous substances with interfiber bonding and surface tension that is important for wet strength.
A method for controlling pitch using micro-particle bentonite addition with cationic polymer flocculation is disclosed in U.S. Pat. No. 5,676,796, issued to Cutts on Oct. 14, 1997. Another combination using kaolin as inorganic colloid and poly(diallyldimethyl-ammonium chloride) cationic polymer is disclosed by Lamar; Pratt; Weber and Roeder in U.S. Pat. No. 4,964,955, which issued Oct. 23, 1990. Alternatively, Dreisbach and Barton disclose a method of preventing pitch deposits by the addition of a nonionic polymeric dispersing agent in U.S. Pat. No. 5,266,166, issued Nov. 30, 1993. A physical process for reducing wood resin pitch from wood process water employing a centrifuge is disclosed by Allen and Lapointe in U.S. Pat. No. 5,468,396, issued Nov. 21, 1995. Of course, any method for controlling pitch by the addition of chemical agents requires rapid analysis of the process water to avoid accidental overdosing or underdosing of the chemical agents, which would produce undesirable results or which would increase unnecessarily the overall cost of the process control program.
A plurality of instruments for relating the intensity and/or angular dependence of scattered or absorbed light to the total concentration or size distribution of colloids are known in the prior art. For example, instruments for characterizing the amount of colloidal particles on the basis of light scattering measurements (nepholometry) and light attenuation measurements (turbidimetry) are commercially available as laboratory, hand-held and on-line instruments. On-line turbidimeters measure the intensity of light that is detected in-line and at an angle to a source of incident light. The turbidimeter relates a ratio of the detected intensities of light to a turbidity value in Jackson or NTU units. U.S. Pat. No. 4,999,514, issued Mar. 12, 1991 in the name of Silveston, discloses a method for controlling the intensity of the light source to provide a turbidimeter that operates over a broad range of particle concentrations. Kubisiak and Wilson in U.S. Pat. No. 5,331,177 describe an analog to digital turbitimeter apparatus that provides a measure of the change in turbidity over time. Other, more sophisticated methods, involving the analysis of the time and spatial dependence of light attenuation and scattering may provide information on particle size distributions, as taught by Strickland et al. in U.S. Pat. No. 5,576,827 and the patents referenced therein. Instrumentation specifically designed for measuring particle and fiber size distributions in low consistency (<1%) pulp suspensions by analysis of the time and spatial variation of scattered or absorbed light includes the BTG-Spectris RET-5300 or the Metso Automation RM200 Retention Monitoring System. These instruments employ methods taught by Lundqvist; Pettersson and Fladda in U.S. Pat. No. 4,318,180.
Unfortunately, the prior art instruments are other than capable of differentiating colloidal wood-derived pitch particles from similarly sized colloidal clay particles and hence the measured concentration represents the total concentration of all colloidal species in suspension. As such, methods to measure the amount of a specific colloidal component in a mixture or to rapidly evaluate the temperature stability of a colloidal suspension are not readily available. Additionally, systems for obtaining on-line measurements of colloid tackiness or the propensity for a colloid to agglomerate or to deposit onto a surface currently are not available. Further additiona
Boegh Kenneth
Garver Theodore M.
Hongqi Yuan
Alberta Research Council Inc.
Freedman & Associates
Hepperle Stephen M.
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