JPH032992B2 - - Google Patents

Abstract

A surge control system for dewatering press felts on a papermaking machine which includes a suction pipe (12), a variable speed drive motor (38), a centrifugal exhauster (26) driven by the variable speed drive motor and connected to the suction pipe to provide vacuum to a felt (14) passing over a slot (18) for dewatering thereof. A surge valve (28) is provided and is opened to admit air to the centrifugal exhauster (26) so as to prevent surge when the centrifugal exhauster is operating at a predetermined level at which the centrifugal exhauster will surge.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surge control system, and particularly to a surge control system that electrically drives a centrifugal exhaust fan at variable speed, which can be used for paper dewatering. .

BACKGROUND OF THE INVENTION It is well known in the paper manufacturing industry to dewater using vacuum or suction tube systems. Such systems often employ a suction tube coupled to a tapered suction slot to dehydrate the felt as it passes through it. This type of system includes a number of devices that create the necessary vacuum during dewatering. These devices include, for example, liquid ring pumps, positive displacement pumps, and centrifugal exhaust or blowers. This type of device memorizes many situations and operating parameters to best suit the special application, and any type of vacuum pump can be selected, so they can be effectively combined and utilized in this system. possible and usually preferred.

In this regard, vacuum pumps are generally designed to maximize the vacuum in the suction tube when the felt is new. This vacuum pump is normally run at maximum speed to dewater new felt. During the dewatering process, the felt fibers fill the voids, which increases the vacuum level required for dewatering and reduces permeability. However, when the permeability of the felt decreases, the vacuum level is automatically increased since the capacity of the vacuum pump is constant.

Many systems have been proposed in the past because of the advantages of improving the vacuum state and improving economic efficiency, resulting in energy savings. That is, U.S. Patent No.
No. 4,308,077, US Pat. No. 4,329,201 issued May 11, 1982, and US Pat.
For example, as described in U.S. Pat.
Some drive a variable speed drive motor while increasing the vacuum level in the suction tube. This motor reduces the speed of the vacuum pump when the permeability of the felt decreases. Therefore, the inside of the suction pipe can be maintained at a desired vacuum level. Furthermore, while the inside of the suction pipe is maintained at a desired vacuum level, the pump is driven at a low speed, so it is sufficient to supply low driving horsepower, thereby saving power.

While such devices have proven satisfactory in suitable applications, it would be desirable to provide dewatering systems with even greater efficiency and energy savings. It would be particularly desirable to provide a dewatering system that can be used with centrifugal exhaust or blowers as compared to positive displacement pump units.

U.S. Concurrent Application No. filed January 31, 1984
No. 575447 proposes an improved version of the centrifugal feng shui machine for improved efficiency. In other words, the drive speed of the blower can be automatically adjusted when the permeability of the felt decreases. Variable speed motor drives for such types of exhaust fans are commonly used. The maximum speed of the motor is limited to certain limits by setting the maximum current and maximum frequency that can flow through the motor. For example, in the case of a variable frequency drive motor, maximum speed and maximum current can be automatically controlled using a feedback loop.

There are no examples in the prior art of combining all types of blowers, and the occurrence of surges can often cause severe damage to the system. While many different types of surge control devices are used, it is desirable to do so with an automatic surge control device. This is particularly effective when using a centrifugal fan with a variable speed drive in paper manufacturing applications. At this time, the surge point can be changed according to the speed, so
There is no need to use special signals to detect surges.

[Summary of the Invention] The main object of the present invention is to provide an automatic surge control device for variable speed drive for driving a centrifugal exhaust fan used in dewatering at variable speed.

Another object of the invention is to provide a surge control device which is of relatively simple construction and low cost, and which is especially useful in all situations.

The present invention provides an automatic surge control device for use in a variable speed drive centrifugal exhaust fan. This exhaust fan is used for dewatering, and when the flow rate of intake air (i.e., the flow rate at the intake slot, etc.) decreases due to a change in the permeability of the felt, the speed of the exhaust fan automatically increases. do. If, for example, the intake slot is completely closed, the exhaust fan will automatically speed up to its maximum speed. In such a system, the centrifugal exhaust fan does not surge even after reaching its set maximum speed. Therefore, the surge is controlled only at the maximum speed of the exhaust fan.

When the exhaust fan is operated at its maximum speed, the power is reduced as the air flow rate decreases. To eliminate the damage caused by surges, output power (hP), current (amplifier), or reduce the frequency below a preset set point to reduce the amount of power (hP), current (amplifier), or reduce the frequency below a preset setpoint to reduce the Detects the control amount of the wind machine. Therefore, the control panel opens the surge valve to allow air into the exhaust fan, preventing the air from flowing out. In this way, the exhaust fan is protected from surges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Visible from depiction 10 is a well-known type of papermaking machine that uses one or several suction tubes for dewatering papermaking felt 14 or similar fibers. The use of several intake pipes has already been described in US Pat. No. 4,329,201. This is a common arrangement of suction pipes in the compression section of a papermaking machine.

A typical suction tube 12 comprises a slot 18 and a groove 16 forming an opening at the upper end of the suction tube through which felt or fabric passes. The output pipe 20 is normally adapted to allow liquid to pass therethrough, and the output pipe 20 is connected to a gas separator 22 . The gas separator 22 has a bottom outlet for conveying separated liquid from a foot provided below to a liquid reservoir. In the case of a centrifugal separator, the gas separator 22 is connected in turn by a connecting pipe 24 which is connected to a vacuum pump 26 . Such exhaust fans include the Fuoffman air filtration system manufactured by the manufacturing division of Clarkson Industries, Inc., PO Box 214, Shiraaki Youth Eastwood Station, New York 13206. Referring to the publication No. CBE-378 "Centrifugal Exhaust Fans and Exhaust Fans" published by the former company, certain basic materials are usually placed on the exhaust fan.

Typically, such systems include a relief or surge valve located between the separator 22 and the exhaust fan 26 to prevent vacuum and, when necessary, surges.
The system is also equipped with silencers 32 and 34.

A conventional drive shaft 36 connects the exhaust fan 26 and a variable speed drive means 38, which selects, adjusts and drives a wide range of speeds, as described below.

It is noted that the drive means 38 includes a variable speed drive AC motor 8 and one manufactured by. (A-C VS Drive, Load Master
AC motor, plus mask pack). (MF Pack) manufactured by Toshiba Corporation, 3-13-12 Mita, Minato-ku, Tokyo, Japan. 77041 West Little York Road, Texas Manufactured by Toshiba/Heuston International Corporation (ESP-130 series). In addition, there is a drive means manufactured by Orange Parametics Co., Ltd. of Connecticut.

The driving means 38 is connected to an ordinary control panel 40 and a coupling portion 40 by an electric wire or the like. control panel 40
A surge valve 28 is connected through a connecting portion 44, and this surge valve 28 is also connected to the connecting pipe 24 in turn.

It can be seen that when the device is activated, the air flow through the felt decreases over time.

As mentioned above, the air flow decreases over time through the felt. Until now, drainage was carried out using a positive displacement pump unit, but in this example, the rotation speed of the vacuum pump is lowered to reduce the permeability of the felt, and the power supply section has a function to measure the pump speed. This provides an effective method for saving driving power. In a typical variable speed drive, it is normal to run to maximum speed and then reduce to the desired speed.
This is done by automatically slowing down the speed.

If the speed of the blower decreases rapidly, the centrifugal blower will not operate properly. For this purpose, the vacuum level is reduced instead of keeping the positive displacement pump unit constant.

As the blower speed is slowly reduced, the variable speed motor 38 increases in speed until a higher vacuum is achieved in the suction tube and the permeability of the felt is reduced.

At this time, the flow rate of air passing through the felt decreases, and in order to increase the degree of vacuum at the point where the air flow rate is low, the drive speed of the exhaust fan must be increased while maintaining the same torque or drive power. is required. In the system described in the aforementioned patent application, a vacuum is applied to the suction tube for dewatering the felt by means of an exhaust fan operating at variable speed, and the air flow rate is adjusted by twisting a valve. In this case, it is rather necessary to drive the exhaust fan at a variable speed so that the suction pipe, which passes from the new felt to the old felt and dehydrates the felt, reaches a desired vacuum state. In addition, such a drive system automatically adjusts the speed of the dewatering machine while dewatering fine fibers, i.e., it operates at a slow speed for light fibers and at a high speed for heavy fibers. required.

When adopting an AC motor in such a system,
The motor speed can be selected over a wide range depending on the frequency characteristics of the AC motor.
This is a standard feature common to many of the AC motors mentioned above.

Operation of drive motor 38 can be automatically controlled using a feedback loop that adjusts current and/or frequency to desired levels. The maximum speed of this motor is limited to a certain extent by the maximum current or the maximum speed of the set frequency to avoid overloading.

As mentioned above, the felt fibers are filled in between so that they are less permeable (reducing water flow). Increased dehydration is achieved by ensuring that a vacuum level is available. A variable vacuum liquid ring type pump is used to maintain a constant flow. As pump horsepower increases,
As the vacuum level increases, the permeability of the felt fibers increases. However, in a centrifugal exhaust fan, horsepower decreases as the air flow rate decreases due to passing through felt fibers that are at the end of their useful life and have reduced permeability.

The speed of the exhaust fan with a variable speed drive is adapted to automatically increase as the air flow rate decreases. Figure 2 shows the performance curve of the variable speed exhaust fan. As is clear from this figure, the surge point changes depending on the speed of the exhaust fan. That is,
The horsepower (hP) at the surge point is as shown in the figure.
It varies depending on each rotation speed. There is no special signal to indicate that the exhaust fan is entering the surge region, but it is sufficient to monitor the performance curve shown in Figure 2.

However, the speed of an exhaust fan employing such a system can automatically increase as the air flow rate decreases. The exhaust fan can therefore be predetermined, depending on the particular application, so that it does not generate surges until after the maximum speed has been reached. Therefore, by monitoring the exhaust fan at maximum speed through the control panel 40, the current power, current, and frequency can be determined. When it falls below a predetermined value, the control panel 40 sends a signal to open the surge valve 28 and draw air into the exhaust fan to prevent further reduction in air flow. In this way, surges are prevented from occurring in the exhaust fan 26.

For example, if the exhaust fan 26 has a maximum speed of 4200 RPM
When operating at less than 82 horsepower (hP), the exhaust fan enters surge territory. Therefore, the control panel 40 determines that the speed of the exhaust fan is
Horsepower output of variable drive motor 38 is 80 at 4200RPM
When it is detected that the horsepower is below, a signal is sent to the surge valve 28, which opens the valve and introduces outside air into the exhaust fan 26 through the silencer 32, as shown in FIG. As a result, a decrease in air flow rate can be suppressed, and surges generated in the exhaust fan can be suppressed. When the horsepower exceeds 82 horsepower (hP), a signal from the control panel closes the surge valve. Dead band control region (e.g.: 80-82 horsepower)
In this case, the valve cannot be controlled. At maximum speed, applications are widespread, including special exhaust fans. Once the blower is driven with a performance curve with a specific maximum speed, it can be immediately used in production. A rotation sensor for monitoring the speed of the exhaust fan monitors the output power of the variable drive engine.

Additionally, the current or frequency required to rotate the motor is monitored instead of horsepower.

Thus, it can be seen that the above objects and advantages of the present invention are highly effective. The details are given in the preferred embodiment. It goes without saying that the present invention is not limited to the scope disclosed by the dependent claims.

[Brief explanation of the drawing]

While the objects and advantages of the present invention have been described above, this description should refer to the drawings. FIG. 1 is a schematic diagram of a vacuum control device showing a part of a paper manufacturing machine, and is for specifically explaining the present invention.
FIG. 2 shows typical performance curves for certain variable speed centrifugal exhaust fans. A brief explanation of the symbols: 12 is the suction pipe, 14 is the felt, 18 is the slot, 26 is the centrifugal exhaust fan, 28
38 is a variable speed drive motor, and 40 is a control means.

Claims (1)

[Scope of Claims] 1. A suction pipe, a variable speed drive motor, and a papermaking felt driven by the variable speed drive motor, connected to the suction pipe, and passing through a slot connected to the suction pipe for dewatering papermaking felt. and a centrifugal exhaust fan for sucking moisture, and when the permeability of the felt decreases and the flow rate of air to be sucked decreases, the speed of the centrifugal exhaust fan is adjusted by the drive motor to a preset speed. A surge control system for a paper machine dewatering device that increases the speed to a maximum speed, comprising: a surge valve that introduces outside air to the centrifugal exhaust fan; and detecting when the centrifugal exhaust fan reaches a preset maximum speed; Monitoring a preset load of the drive motor at which a surge occurs when the maximum speed is reached, and detecting a preset load at which the surge occurs when the centrifugal exhaust fan is driven at the maximum speed. A surge control system characterized by comprising a control means for preventing the generation of surge in the centrifugal exhaust fan by sending a signal to the surge valve and introducing external air into the centrifugal exhaust fan when the surge occurs. 2. The surge control system according to claim 1, wherein the felt is a papermaking felt used in the papermaking industry. 3. The variable speed drive motor is an AC motor,
The control means controls its current consumption or frequency;
The surge control system according to claim 1, wherein the load is monitored by monitoring horsepower. 4 A suction pipe, a surge valve, a variable speed drive motor, and a centrifugal exhaust that is driven by the variable speed drive motor, is connected to the suction pipe, and sucks moisture from the felt passing through the slot of the suction pipe to dehydrate it. Surge control in a paper machine equipped with a suction dewatering device that increases the speed of the centrifugal exhaust fan by the variable speed drive motor when the permeability of the felt decreases and the flow rate of the air to be taken in decreases. In the system, the speed of the centrifugal exhaust fan is limited to a preset maximum speed, the preset maximum speed of the centrifugal exhaust fan is detected, and the centrifugal exhaust fan is driven at the maximum speed at which a surge occurs. monitoring a preset load of the drive motor when the centrifugal exhaust fan is driven at the maximum speed, and when the drive motor reaches the predetermined load, the centrifugal exhaust fan surges; A surge control system, characterized in that the surge valve is opened to introduce outside air into the centrifugal exhaust fan in order to prevent the above from occurring. 5. The surge control system according to claim 4, wherein an AC motor is used as the drive motor, and the load is detected by monitoring its current consumption, frequency, or horsepower.