Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
1999-06-10
2001-04-03
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S263000, C162S264000
Reexamination Certificate
active
06210529
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for regulating the surface level and consistency in a stock chest for metering a component stock wherein the component stock is fed as an outward flow out of the bottom portion of a storage tower by a pump into the stock chest, a first dilution water flow is passed into the outward flow to thereby regulate the consistency of the component stock fed into the stock chest to a desired level, the component stock is stirred in the stock chest in order to obtain a uniform consistency and the component stock is then fed as a metering flow from the stock chest by another pump into the short circulation of the paper or board machine.
BACKGROUND OF THE INVENTION
Regarding its principal features, the stock feed at a paper machine is generally as follows. The stock components are stored at the paper mill in separate storage towers. From the storage towers, the stocks are fed into stock chests, and from the stock chests further into a common blend chest, in which the stock components are mixed with each other. From the blend chest, the stock is fed into a machine chest, and from the machine chest there is an overflow back into the blend chest.
From the machine chest, the stock is fed into a dilution part of the wire pit, in which the stock is diluted with white water recovered from the wire section and serving as dilution water. From the wire pit, the stock is fed through one or more centrifugal cleaners into a deaeration tank. From the deaeration tank, stock free from air is fed through a machine screen into the headbox, i.e., into the inlet header thereof, and through the slice opening of the headbox to the wire section. A bypass flow of the headbox is fed back into the deaeration tank, and the white water recovered from the wire section is fed into the wire pit.
The basis weight and the ash content of the paper are measured on-line right before reeling from a ready, dry paper, usually by means of measurement apparatuses based on beta radiation and x-radiation. Based on this measurement, the basis weight of the paper is regulated, for example, by means of a so-called basis weight valve by whose means the stock flow after the machine chest is controlled. A second possibility is regulation of the speed of rotation of the pump that feeds stock from the machine chest into the wire pit. The ash content is controlled by dosing of fillers. The basis weight profile of the paper in the cross direction is obtained when the measurement apparatus is installed to move back and forth across the web.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new and improved method for regulating the surface level and consistency in a stock chest for metering a component stock.
It is another object of the present invention to provide a method for regulating the surface level and consistency in a stock chest for metering a component stock in which attempts are made to maintain a substantially constant surface level in the stock chest constantly and to maintain the stock constantly at the desired constant consistency throughout the entire stock chest.
In order to achieve these objects and others, a method for regulating a surface level and consistency of stock in a stock chest in accordance with the invention comprises the steps of directing a flow of component stock from a bottom portion of a storage tower into the stock chest, directing a first flow of dilution water into the flow of component stock before the flow of component stock enters into the stock chest to mix with the component stock, controlling the surface level of stock in the stock chest by directing an adjustable amount of stock removed from the stock chest as a return flow into the bottom portion of the storage tower to mix with the component stock in the storage tower, and regulating the consistency of the component stock in the bottom portion of the storage tower by directing a variable second flow of dilution water into the return flow of stock from the stock chest. The component stock in the bottom portion of the storage tower is preferably mixed to thereby provide the component stock with a uniform consistency in the bottom portion of the storage tower.
To control the surface level in the stock chest, a pumping tank may be arranged to receive overflow from the stock chest, and the adjustable amount of stock pumped from the pumping tank into the storage tower via a pump. The surface level in the stock chest may be controlled to be substantially constant.
The flow of component stock may be directed from the bottom portion of the storage tower in the stock chest by passing the component stock from the bottom portion of the storage tower into an outlet line, and arranging a pump to receive the component stock from the outlet line and direct the component stock through a feed line into the stock chest. The first flow of dilution water is thus directed into the outlet line.
In some embodiments, the consistency of the mixed component stock and first flow of dilution water is measured before the stock chest and the first flow of dilution water being directed into the flow of component stock is regulated, e.g., its flow rate or quantity, based on the measured consistency.
A pump may be arranged to direct the mixed flow of component stock and first flow of dilution water into the stock chest, the consistency of the mixed flow of component stock and first flow of dilution water measured after the pump and before the stock chest and a flow property of the mixed first flow of component stock and first flow of dilution water, e.g., flow rate or quantity, measured after the pump and before the stock chest. A flow property of the first flow of dilution water is also measured before the first flow of dilution water is directed into the flow of component stock, and then, the first flow of dilution water being directed into the flow of component stock may be regulated based on the measured consistency and flow property of the mixed flow of component stock and first flow of dilution water and the measured flow property of the first flow of dilution water.
In another embodiment, a flow property of the first flow of dilution water is measured before the first flow of dilution water is directed into the flow of component stock, and the first flow of dilution water into the flow of component stock is regulated based at least in part thereon. A pump can be arranged to pump stock from the stock chest to a short circulation of a paper machine and the flow of the stock being pumped from the stock chest measured. The second flow of dilution water can then be regulated based on the measured flow property of the first flow of dilution water and the measured flow property of the stock being pumped from the stock chest to the short circulation of the paper machine. Optionally, the second flow of dilution water is also regulated in consideration of any difference between an amount of water in the stock being pumped from the stock chest to the short circulation of the paper machine and an amount of water entering into the stock chest in the mixed flow of component stock and first flow of dilution water.
In another embodiment, a pump pumps stock from the stock chest to the short circulation of a paper or board machine and this flow of the stock is measured. The flow of component stock from the bottom portion of the storage tower is regulated to be larger than the measured flow of stock from the stock chest by a substantially constant amount. Optionally, a flow property of the return flow is measured and the flow of stock from the storage tower is regulated by a flow controller in accordance with a set value based on the measured flow of stock from the stock chest to the short circulation of the paper machine and the measured flow property of the return flow.
In yet another embodiment, the surface level of stock in the stock chest is controlled by arranging a pumping tank to receive overflow from the stock chest, the return flow of stock from the stock chest being directed
Nguyen Dean T.
Steinberg & Raskin, P.C.
Valmet Corporation
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