Stock liquor pressure pulsation absorbing apparatus

Abstract: Disclosed is a stock liquor pressure pulsation absorbing apparatus of active type which is able to absorb pressure pulsation in the ordinarily demanded frequency range of 0.01 to 100 Hz. The apparatus comprises a by-pass pipe (2) for extracting a portion of a stock liquor from a master pipe (1) for supplying the stock liquor to a paper machine headbox; a control pump (7) for returning a portion of the stock liquor so extracted into said by-pass pipe; and a means (3) for detecting a stock liquor pulsation pressure at a branch point or on an upstream side thereof of said by-pass pipe and master pipe for controlling said control pump, thereby the pressure pulsation, including the low frequency range, of the stock liquor is absorbed accurately and precisely, variation in the basis weight is made small and a stable supply of final products with high quality can be attained.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a stock liquor pressure pulsation absorbing apparatus according to the preamble portion of claim 1 for carrying out an active absorption of low frequency pressure pulsation in a stock liquor piping system. Description of the Prior Art: A prior art of the above-mentioned type will be described with reference to Figs. 6 and 7. Fig. 6 shows schematically a stock liquor flow passing through an attenuator which is widely used in the prior art. Stock liquor is fed into a master pipe 03 by a fan pump 01 via a screen 02 to flow through an attenuator 04 which is disposed midway of the master pipe 03 and to enter a headbox 08 and then is injected on a wire 09 to come in a paper forming process and is formed into a paper via a downstream dewatering process and drying process which is not shown. The attenuator 04 consists of a portion of the master pipe 03, an air chamber 05 which is partitioned from the master pipe 03 by a diaphragm 06, etc. The air chamber 05 communicates with a volume tank through a passage 07, so that pressure in the air chamber 05 is set to be equal to a mean pressure in the master pipe 03 by a controller which is not shown. Thus, when there occurs a pulsation which is higher than the mean pressure in the master pipe 03, the pressure in the master pipe 03 becomes higher than the pressure in the air chamber 05 and the diaphragm 06 is pressed down. As the result, the stock liquor in the amount corresponding to volume increase in the master pipe 03 due to displacement of the diaphragm 06 is absorbed and flow variation in the master pipe 03 of the stock liquor flowing into the headbox 08 is mitigated. When there occurs a pulsation which is lower than the mean pressure in the master pipe, the diaphragm 06 is pushed up and the pulsation is absorbed. That is, the attenuator in the prior art is a pressure pulsation absorbing apparatus of passive type in which the pulsation is absorbed by a differential pressure between the pressure in the master pipe 03 and the internal pressure of the air chamber 05. Also, the Japanese laid-open patent application No. Hei 1(1989)-298291 (EP-A-0 335 343) discloses an apparatus in which water is supplied into a stock liquor piping and flow rate of that water is controlled, thereby pulsation in the stock liquor piping is absorbed. Outline of this apparatus is shown in Fig. 7, wherein a pressure gauge 016 is disposed downstream of a joining point of a stock liquor piping 015 and a water supply pipe 014 and a valve 011 is opened and closed by a pressure signal taken from the pressure gauge 016, thus flow rate of the water flowing into the stock liquor piping 015 from the water supply pipe 014 is controlled. It is mentioned there that pulsation of 1 to 50 Hz can be absorbed by this apparatus. In this apparatus, however, if a low frequency pulsation of 1 Hz or less is to be absorbed, it is necessary to supply a large amount of water and there occurs a possibility to cause a consistency variation of the stock liquor in the piping. It can be said, therefore, that absorption of the low frequency pulsation will be very difficult. It is to be noted in Fig. 7 that numeral 012 designates a controlling member for operating the valve 011, numeral 013 designates a servo valve, numeral 017 designates an electronic regulator for transmitting a command of the pressure gauge 016, numeral 018 designates a water tank, numeral 019 designates an operating oil tank and numeral 020 designates a headbox. Generally, in order to obtain a very stable operation of a paper machine, it is necessary to make a pressure pulsation level within ±0.5 to ±1% or less of a mean pressure in a range of 0.01 to 100 Hz. In an ordinary paper making plant, however, such a severe permissible pressure pulsation level will hardly be secured even if designing of piping systems therefor is done with a full deliberation. As a frequency of pressure pulsation becomes lower, flow variation becomes larger generally and stock liquor absorption amount at the attenuator increases. Because the attenuator is of a structure to absorb variation in the flow rate of the stock liquor using a diaphragm, in order to absorb pulsation of low frequency, especially of 1 Hz or less, it is necessary to enlarge an area and displacement amount of the diaphragm but there are restrictions from structure, installation space, etc., hence pulsation absorption performance of 1 Hz or less has been inevitably lowered, and moreover, not only simply due to such facilities-wise reason, pulsation absorption of 1 Hz or less has been very difficult from a functional point of view also. Above problems are applicable to the apparatuses shown in Figs. 6 and 7 generally, and as to the apparatus shown in Fig. 7 also, there are considered additional problems in securing water to be supplied for the controlling, handling and treating the water, controlling stock liquor consistency after water is added, etc. and actual apparatus will be hardly realized. Another prior art stock liquor pressure pulsation absorbing apparatus with the features of the preamble portion of claim 1 is disclosed in US-A-4 308 095. SUMMARY OF THE INVENTION: In view of such technological needs and problems in the prior art as mentioned above, it is an object of the present invention to provide a stock liquor pressure pulsation absorbing apparatus of active type which is able to detect pulsation pressure of stock liquor and to control it corresponding thereto securely even in a low frequency range. In order to attain said object, the present invention provides a stock liquor pressure pulsation absorbing apparatus as defined in claim 1. This is, in the present invention, a portion of the stock liquor is made extractable from the master pipe via the by-pass pipe and the stock liquor pulsation pressure in the master pipe is detected at the branch point from which the extraction is done or on the upstream side thereof, thereby the control pump for the by-pass pipe is controlled and the amount of the stock liquor so extracted into the by-pass pipe is regulated, thus the pressure pulsation of the stock liquor is absorbed accurately and precisely, especially the pressure pulsation in the low frequency range can be reduced greatly. Also, the present invention provides a stock liquor pressure pulsation absorbing apparatus as set forth above, characterized in that a diaphragm type attenuator is provided on the upstream side or a downstream side of the branch point of said by-pass pipe and master pipe. That is, in the present invention, the pressure pulsation in the low frequency range depends on the control by use of said by-pass pipe and the pressure pulsation in the higher frequency range is absorbed by the ordinary diaphragm type attenuator. By such division of function, respective advantageous functions are combined so as to attain a high efficiency of pressure pulsation absorption in the entire range demanded in the actual paper making machines through a high stability of control and compact sized facilities can be realized after all. Accordingly, the present invention provides a stock liquor pressure pulsation absorbing apparatus which operates with the steps of extracting a portion of a stock liquor continuously from a master pipe for supplying the stock liquor to a paper machine headbox; and increasing or decreasing an amount of the stock liquor to be so extracted corresponding to a size of pulsation pressure in the master pipe. That is, in the present invention, in addition to the piping of the master pipe for supplying the stock liquor to the paper machine headbox, a piping for extracting a portion of said stock liquor continuously is provided and the amount of said stock liquor to be so extracted is increased or decreased corresponding to the size of the pulsation pressure in the master pipe, thereby the pulsation of the stock liquor is absorbed accurately and precisely and variation in the basis weight becomes small, which results in a stable supply of final products of high quality. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is an explanatory view of a stock liquor pressure pulsation absorbing apparatus (attenuator) using a by-pass pipe and a variable speed pump of a first embodiment according to the present invention. Fig. 2 is an explanatory view of an example of a piping system constructed experimentally according to the first embodiment of Fig. 1. Fig. 3 is an explanatory view showing experimental result by the first embodiment of Fig. 1. Fig. 4 is an explanatory view of a stock liquor pressure pulsation absorbing apparatus (attenuator) in which a low frequency attenuator and a high frequency attenuator are combined of a preferred embodiment according to the present invention. Fig.5 is an explanatory view showing a variation of the preferred embodiment of Fig. 4. Fig. 6 is an explanatory view showing an example in the prior art. Fig. 7 is an explanatory view showing another example in the prior art. Fig. 8 is an explanatory view showing a variation of the first embodiment of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS: A stock liquor pressure pulsation absorbing apparatus (attenuator) of a first embodiment according to the present invention will be described with reference to Fig. 1. A small diameter by-pass pipe 2 is provided branching from a master pipe 1 which supplies stock liquor to a paper machine headbox (not shown), so that a substantially constant amount of the stock liquor may be extracted continuously into a by-pass tank 8 with opening of a valve being set. Also, a portion of the stock liquor is extracted from the by-pass tank 8 by a control pump 7 so as to be circulated to an upstream side of said valve disposed in the by-pass pipe 2. Thereby, the flow rate in the by-pass pipe 2 is regulated and thus the extraction rate from the master pipe 1 is regulated. Said control pump 7 is controlled via a controller 5 and an inverter 6 by a signal of pulsation pressure P 1 detected by a pressure gauge 3 at a branch point of the master pipe 1 and the by-pass pipe 2. The pulsation pressure P 1 may be detected alternatively by a pressure gauge 3 disposed on an upstream side of said branch point, as shown in Fig. 10. That is, a signal of reverse phase is given to the control pump 7 corresponding to pulsation of the pulsation pressure P 1 so detected and, if the pulsation pressure P 1 becomes larger, rotation of the control pump 7 is reduced so that liquor supply amount therefrom into the by-pass pipe 2 is reduced, which results in increase in amount of the stock liquor flowing into the by-pass pipe 2 from the master pipe 1 and the pulsation in the master pipe 1 is absorbed. In case the pulsation pressure P 1 becomes smaller, reverse operation to that mentioned above is proceeded so as to absorb the pulsation. It is to be noted that pulsation pressure P 2 detected by a pressure gauge 4 disposed on a downstream side of the pressure gauge 3 is what is called a value after control, which can be used as a monitor, or a signal for controlling the pulsation pressure P 2 so that it approaches to zero. Also, in Fig. 1, numeral 9 designates a flow meter and numeral 10 designates a Pitot tube. Furthermore, a surplus amount of the stock liquor beyond a predetermined amount in the by-pass tank 8 is returned to a stock liquor supply source (not shown) via a return passage (not shown). Experimental result in which the pulsation in the master pipe 1 has been absorbed by use of the first embodiment is shown in Fig. 3. Horizontal axis thereof shows frequency of the pulsation in the master pipe 1 and vertical axis thereof shows pulsation pressure in the master pipe 1. Also, broken lines drawn in an upper part thereof shows pressure in the case of "without control" and solid lines in a lower part thereof shows pressure in the case of "with control". It has been confirmed from this figure that the pulsation in the low frequency range of 0.5 Hz or less can be absorbed by the system using the control pump 7 of variable speed type. Further, an example of a piping system constructed experimentally according to the first embodiment in which flow rate in the by-pass pipe is pump-controlled will be described with reference to Fig. 2. In this example, stock liquor of consistency of 1% is supplied from a tank 40 by a circulating pump 41 into a master pipe 31 which is of a size of 150A ("A" means a designation of piping and "150A" means a pipe of inner diameter which is very near to 150 mm), and a by-pass pipe 32 of a size of 40A is provided midway of the master pipe 31 so that a portion of the stock liquor in the master pipe 31 flows into the by-pass pipe 32 continuously. Flow rate in the master pipe 31 is set to 3 m 3 /min and flow rate in the by-pass pipe 32 is changed in the range of 0.05 to 0.15 m 3 /min. Pressure P 1 before the by-pass pipe 32 (pressure before control) and pressure P 2 after the by-pass pipe 32 (pressure after control) are detected by a pressure gauge 33 and 34, respectively, and a pressure signal in the master pipe 31 is picked up by use of said pressures P 1 and P 2 . Thus, corresponding to pulsation thereof, a control unit 36 is operated actively, by which flow rate in the by-pass pipe 32 is controlled so that pulsation in the master pipe 31 is absorbed. It is to be noted that numeral 38 designates a tank which receives for a time the stock liquor flowing in the by-pass pipe 32 and numeral 42 designates a return pump for returning the stock liquor to the tank 40 from the tank 38. Next, a stock liquor pressure pulsation absorbing apparatus (attenuator) of a preferred embodiment according to the present invention will be described with reference to Figs. 4 and 5. In the present embodiment, the above-described first embodiment is combined with the prior art attenuator. That is, the first embodiment being especially effective for pulsation absorption in the low frequency range, is employed as a low frequency attenuator and the prior art attenuator operated by a diaphragm is employed as a high frequency attenuator. Fig. 4 shows one example of the preferred embodiment constructed such that a low frequency attenuator 55 having a by-pass pipe 52 is provided on an upstream side of a master pipe 51 which extends to a paper machine headbox 57 and a high frequency attenuator 56 is provided downstream thereof. Also, Fig. 5 shows another example of the preferred embodiment constructed such that the high frequency attenuator 56 is provided upstream and the low frequency attenuator 55 is provided downstream, reversely of the above example. Because the pulsation frequency in question is approximately in the range of 0.01 to 100 Hz in an actual machine, the system of the present embodiment in which the low frequency attenuator 55 of active type and the high frequency attenuator 55 of passive type are combined in series is able to absorb well the pulsation in the range of 0.01 to 100 Hz which is the demanded range in the actual machine. Also, by use of such system of combination, the high frequency attenuator 56 may be relieved from functioning to the low frequency range, hence its structural size may be reduced to a half or less.

Claims: A stock liquor pressure pulsation absorbing apparatus, comprising: a by-pass pipe (2) for extracting a portion of a stock liquor from a master pipe (1) supplying the stock liquor to a paper machine headbox and for discharging said extracted portion of the stock liquor into a by-pass tank (8); and a means (3,4,5,6) for detecting a stock liquor pulsation pressure (P 1 ) at a branch point of said by-pass pipe (2) and master pipe (1) or on an upstream side thereof; characterized by further comprising a control pump (7) for returning into said by-pass pipe (2) a portion of the extracted stock liquor, thereby regulating the extraction rate of stock liquor from said master pipe (1) through said by-pass pipe (2); and in that said means (3,4,5,6) are adapted to control the amount of said portion of the extracted stock liquor returned to said by-pass pipe (2) by controlling said control pump (7) corresponding to pulsation pressure detected in the master pipe (1), thereby reducing the pressure pulsation in the master pipe (1). A stock liquor pressure pulsation absorbing apparatus as claimed in claim 1, characterized in that said means for controlling said control pump (7) comprise a controller (5) and an inverter (6) for processing a detection signal of said pulsation pressure (P 1 ) of the stock liquor. A stock liquor pressure pulsation absorbing apparatus as claimed in claim 1 or 2, characterized in that a diaphragm type attenuator (56) is provided on the upstream side or on the downstream side of the branch point of said by-pass pipe (2,52) and master pipe (1,51).

Inventors: HIROOKA HIDEKI, MAKINO TETSUO, TAJIMA TOSHIMI, TANAKA MAMORU, HIROOKA, HIDEKI, MAKINO, TETSUO, TAJIMA, TOSHIMI, TANAKA, MAMORU, Hirooka, Hideki, c/o Mitsubishi Heavy Ind. Ltd., Makino, Tetsuo, c/o Mitsubishi Heavy Ind. Ltd., Tajima, Toshimi, c/o Mitsubishi Heavy Ind. Ltd., Tanaka, Mamoru, c/o Mitsubishi Heavy Ind. Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: D21F1
IPC codes: D21F1