Data processing: measuring – calibrating – or testing – Measurement system – Article count or size distribution
Reexamination Certificate
2001-03-20
2004-08-17
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Article count or size distribution
C700S122000, C700S127000, C700S128000, C241S024190, C241S024200, C162S023000, C162S238000
Reexamination Certificate
active
06778936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and system for determining consistency of stock being refined by a disk refiner as well as a method and system for controlling refiner operation based on consistency.
BACKGROUND OF THE INVENTION
Many products we use every day are made from fibers. Examples of just a few of these products include paper, personal hygiene products, diapers, plates, containers, and packaging. Making products from wood fibers, cloth fibers and the like, involves breaking solid matter into fibrous matter. This also involves processing the fibrous matter into individual fibers that become fibrillated or frayed so they more tightly mesh with each other to form a finished fiber product that is desirably strong, tough, and resilient.
In fiber product manufacturing, refiners are devices used to process the fibrous matter, such as wood chips, pulp, fabric, and the like, into fibers and to further fibrillate existing fibers. The fibrous matter is transported in a liquid stock slurry to each refiner using a feed screw driven by a motor. Each refiner has at least one pair of circular ridged refiner discs that face each other. During refining, fibrous matter in the stock to be refined is introduced into a gap between the discs that usually is quite small. Relative rotation between the discs during operation causes the fibrous matter to be fibrillated as the stock passes radially outwardly between the discs.
One example of a refiner that is a disc refiner is shown and disclosed in U.S. Pat. No. 5,425,508. However, many different kinds of refiners are in use today. For example, there are counterrotating refiners, double disc or twin refiners, and conical disc refiners. Conical disc refiners are often referred to in the industry as CD refiners.
Each refiner has at least one motor coupled to a rotor carrying at least one of the refiner discs. During operation, the load on this motor can vary greatly over time depending on many parameters. For example, as the mass flow rate of the stock slurry being introduced into a refiner increases, the load on the motor increases. It is also known that the load on the motor will decrease as the flow rate of dilution water is increased.
During refiner operation, a great deal of heat is produced in the refining zone between each pair of opposed refiner discs. The refining zone typically gets so hot that steam is produced, which significantly reduces the amount of liquid in the refining zone. This reduction of liquid in the refining zone leads to increased friction between opposed refiner discs, which increases the load on the motor of the refiner. When it becomes necessary to decrease this friction, water is added to the refiner. The water that is added is typically referred to as dilution water.
One problem that has yet to be adequately solved is how to control refiner operation so that the finished fiber product has certain desired characteristics that do not vary greatly over time. For example, paper producers have found it very difficult to consistently control refiner operation from one hour to the next so that a batch of paper produced has consistent quality. As a result, it is not unusual for some paper produced to be scrapped and reprocessed or sold cheaply as job lot. Either way, these variations in quality are undesirable and costly.
Another related problem is how to control refiner operation to repeatedly obtain certain desired finished fiber product characteristics in different batches run at different times, such as different batches run on different days. This problem is not trivial as it is very desirable for paper producers be able to produce different batches of paper having nearly the same characteristics, such as tear strength, tensile strength, brightness, opacity and the like.
In the past, control systems and methods have been employed that attempt to automatically control refiner operation to solve at least some of these problems. One common control system used in paper mills and fiber processing plants throughout the world is a Distributed Control System (DCS). A DCS communicates with each refiner in the mill or fiber processing plant and often communicates with other fiber product processing equipment. A DCS monitors operation of each refiner in a particular fiber product processing plant by monitoring refiner parameters that typically include the main motor power, the dilution water flow rate, the hydraulic load, the feed screw speed, the refiner case pressure, the inlet pressure, and the refiner gap. In addition to monitoring refiner operation, the DCS also automatically controls refiner operation by attempting to hold the load of the motor of each refiner at a particular setpoint. In fact, many refiners have their own motor load setpoint. When the motor load of a particular refiner rises above its setpoint, the DCS adds more dilution water to the refiner to decrease friction. When the motor load decreases below the setpoint, dilution water is reduced or stopped.
During refiner operation, pulp quality and the load on the refiner motor vary, sometimes quite dramatically, over time. Although the aforementioned DCS control method attempts to account for these variations and prevent the aforementioned problems from occurring, its control method assumes that the mass flow of fibrous matter in the stock entering the refiner is constant because the speed of the feed screw supplying the stock is constant. Unfortunately, as a result, there are times when controlling the dilution water flow rate does not decrease or increase motor load in the desired manner. This disparity leads to changes in refining intensity and pulp quality because the specific energy inputted into refining the fibrous matter is not constant. These changes are undesirable because they ultimately lead to the aforementioned problems, as well as other problems.
In the past, consistency has been measured externally of a refiner in an effort to determine how well the refiner is operating. After evaluating the consistency measurement, there are times where an operator will manually make an adjustment to the refiner in an effort to try to get the consistency closer to a desired value or range. Unfortunately, it takes a long time, often several hours or longer, before the operator will know whether his or her adjustment had the desired impact on consistency. This hit and miss approach is inexact and inefficient.
This delay is believed to be caused by at least two problems, if not more. First, it takes a long time, often several hours or possibly even days, for the refiner to reach steady state operation before an operator will know what kind of effect that the change had. Second, consistency measurements are taken outside the refiner using equipment and methods that are slow, which also delays how fast an operator can obtain feedback. In any event, because the present methods and devices for measuring consistency are slow and there is a corresponding delay in recognizing that the refiner is operating in a steady state condition, the operator is forced to wait a long time until they know with some certainty what kind of effect their change had. This means, that the refiner can operate inefficiently for hours, if not days, before the operator, using this trial and error method, finally settles on a combination of operating settings that are more to his or her liking.
Hence, while some refiner process control methods have proven beneficial in the past, they in no way have resulted in the type of control over finished fiber product parameters and the repeatability of these parameters that is desired. Thus, additional improvements in refiner process control and consistency measurement are needed.
SUMMARY OF THE INVENTION
A system for and method of determining stock consistency. The invention includes one or more sensors that sense temperature and/or pressure of stock adjacent or in the refining zone during refiner operation. In one preferred embodiment, one or more sensors in the refining zone provide real time temperature and/or pressure d
Assouad Patrick
Boyle Fredrickson Newholm Stein & Gratz S.C.
J & L Fiber Services Inc.
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