Refiner disk sensor and sensor refiner disk

Details Refiner disk sensor and sensor refiner disk Refiner disk sensor and sensor refiner disk

2000-03-08

2003-01-07

Ostrager, Allen (Department: 3725)

Solid material comminution or disintegration

Apparatus

With automatic control

C241S261200, C241S261300, C241S296000, C241S297000, C241S298000

Reexamination Certificate

active

06502774

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a sensor, a sensor refiner disk, a system for increasing the accuracy of a measurement made from a parameter sensed in the refining zone, and a method of improving the accuracy of the measurement made.
BACKGROUND OF THE INVENTION
Many products we use everyday 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 fiber, fabric fiber 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 used to process the fibrous matter, such as wood chips, fabric, and other types of pulp, into fibers and to further fibrillate existing fibers. The fibrous matter is transported in liquid stock to each refiner using a feed screw driven by a motor.
Each refiner has at least one pair of circular ridged refiner disks that face each other and are driven by one or more motors. During refining, fibrous matter in the stock to be refined is introduced into a gap between the disks that usually is quite small. Relative rotation between the disks during operation fibrillates fibers in the stock as the stock passes radially outwardly between the disks.
One example of a disk 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 counter rotating refiners, double disk or twin refiners, and conical disk refiners. Conical disk refiners are often referred to in the industry as CD refiners.
During operation, many refiner parameters are monitored. Examples of parameters include the power of the drive motor that is rotating a rotor carrying at least one refiner disk, the mass flow rate of the stock slurry being introduced into the refiner, the force with which opposed refiner disks are being forced together, the flow rate of dilution water being added in the refiner to the slurry, and the refiner gap.
It has always been a goal to monitor conditions in the refining zone between the pairs of opposed refining disks. However, making such measurements have always been a problem because the conditions in the refining zone are rather extreme, which makes it rather difficult to accurately measure parameters in the refining zone, such as temperature and pressure.
While sensors have been proposed in the past to measure temperature and pressure in the refining zone, they have not heretofore possessed the reliability and robustness to be commercially practicable. Depending on the application, temperature sensors used in the past also lacked the accuracy needed to provide repeatable absolute temperature measurement, something that is highly desirable for certain kinds of refiner control.
Another problem grappled with in the past is how and where to mount sensors. In the past, sensors have been mounted to a bar that is received in a pocket in the refining surface. This mounting technique is undesirable because it reduces total refining surface area and can adversely affect the flow pattern during refining, leading to less intense refining and increased shives.
Hence, while sensors and sensing systems used in the past have proven useful, improvements nonetheless remain desirable.
SUMMARY OF THE INVENTION
A sensor, sensor disk, sensor correction system and method used in making a measurement of a parameter or characteristic sensed in the refining zone of a rotary disk refiner that refines fibrous pulp in a liquid stock slurry.
The sensor disk includes at least one sensor that is embedded in a refining surface of the sensor disk. The sensor disk preferably includes a plurality of spaced apart sensors that are each at least partially embedded in the refining surface. Each sensor preferably is a temperature sensor or a pressure sensor but, in any case, is a sensor capable of sensing a characteristic or parameter of conditions in the refining zone from which a measurement can be made. In one preferred embodiment, the sensor disk has at least three sensors which are radially spaced apart and which can be disposed in a line that extends in a radial direction. Even if not disposed in a line, the sensors preferably are radially distributed along the refining surface.
Each sensor is disposed in its own bore in the refining surface of the sensor disk and has a tip that is disposed no higher than the height of the axial surface of an adjacent refiner bar, such as the refiner bar that is next to the sensor. The tip of the sensor is disposed slightly below the axial refiner bar surface to prevent the tip from being physically located in the refining zone while still accommodating bar wear. In one preferred embodiment, the tip is located at least about 0.050 inch (1.3 mm) below the axial bar surface. In another preferred embodiment, the tip is located at least about 0.100 inch (2.5 mm) below axial bar height.
Each sensor preferably is disposed in a bar or groove of the refining surface. Each sensor includes a spacer that spaces a sensing element of the sensor from the surrounding material of the sensor refiner disk. The sensing element is carried by a sensor housing that is carried by the spacer. The sensor housing extends outwardly from the spacer and has its tip located flush with or below the axial refiner bar surface. The sensing element or at least one end of the sensing element can be spaced from an axial end or edge of the spacer.
In a preferred embodiment, the spacer is disposed in a bore in the refining surface. The spacer is tubular and configured to telescopically receive at least a portion of the sensor housing, which can protrude outwardly from the spacer.
At least where the sensor is a temperature sensor, the sensor housing and spacer enclose the sensing element. The housing is comprised of a thermally conductive material and at least part of the housing is immersed in the stock during refiner operation. The spacer is made of a thermally insulating material that thermally insulates the sensing element from the thermal mass of the sensor refiner disk. The sensing element preferably is disposed between the tip of the sensor housing and the spacer. The housing preferably protrudes from the insulating spacer to space the sensing element or the end of the sensing element from the spacer to minimize the impact of the insulating spacer on measurement of a temperature in the refining zone.
Where the sensor is a temperature sensor, the temperature sensor can be used to obtain an absolute measurement of temperature in the refining zone adjacent the sensor. Where a temperature sensor is used to obtain an absolute temperature measurement, the sensing element preferably is of a type that is capable of being calibrated so as to provide measurement repeatability. In one preferred embodiment, the sensing element is an RTD, preferably a three wire platinum RTD.
In another embodiment, the sensor is embedded in a plate set in a pocket in the refining surface of a refiner disk. The spacer is disposed in the bar and carries the sensor or is an integral part of the sensor. The spacer spaces the sensor, including its sensing element, from the surrounding material of the bar and the surrounding material of the refiner disk in which the bar is received. Where the sensor is a temperature sensor, the spacer preferably insulates the sensing element from the thermal mass of the surrounding material.
In one preferred refiner sensor disk embodiment, the sensor disk has a plurality of spaced apart bores in its refining surface that each receives a sensor. Each bore communicates with a wiring passage leading to the backside of the refiner disk. Each of the sensors can be carried by a fixture that is received in a pocket in the backside of the disk. In another embodiment, no fixture is used. In either embodiment, a bonding a

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