Method for detecting air bubbles in water and method for adding deaerating agent using the same

Abstract

To provide a method for detecting air bubbles in water capable of accurately and simply detecting air bubbles in water even when water containing a fibrous substance and air bubbles is present in a water supply pipe, and a method for adding a degassing agent using the same.SOLUTION: An underwater air bubble detection method for detecting air bubbles in water containing a fibrous substance and air bubbles by measuring an intensity of an ultrasonic wave received by a reception unit of a transmission-type ultrasonic sensor.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for detecting air bubbles in water containing fibrous materials and air bubbles, and a method for adding a degassing agent using the same. [Background technology]

[0002] Air bubbles generated during the papermaking process, especially those remaining in the water, adversely affect the quality and productivity of paper products. For example, when air bubbles or aggregates formed by air bubbles are mixed into the product, a product defect called bubble spots occurs. Furthermore, air bubbles in the water cause fluctuations in the rotation speed of various pumps, pressure in water supply pipes, and liquid levels in papermaking equipment, leading to reduced productivity due to reduced water supply efficiency and reduced product quality.

[0003] In order to prevent such adverse effects caused by bubbles, bubbles on the liquid surface are visually observed or the liquid level is measured, and an antifoaming agent is added based on this information.

[0004] For example, Patent Document 1 describes a method for detecting the degree of foaming on the liquid surface by measuring the liquid level with an ultrasonic level meter or a laser distance meter. Furthermore, Patent Document 2 describes that the amount of dissolved gas is measured from the relationship between the volume change and the internal pressure by pressurizing and depressurizing the inside of a measurement cell. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-76059 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-133240 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 cannot accurately detect bubbles when the liquid level is not uniform, and cannot detect bubbles in a water supply pipe or the like. Furthermore, the method described in Patent Document 2 requires operations to change the internal pressure in the measurement cell, which makes measurement time-consuming and laborious, and accurate detection can sometimes be difficult due to clogging with fibrous materials, etc.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for detecting air bubbles in water that can accurately and easily detect air bubbles in water even when water containing fibrous materials and air bubbles is present in a water supply pipe, and a method for adding a degassing agent using the same. [Means for solving the problem]

[0008] The present invention is based on the discovery that by using a transmission type ultrasonic sensor, air bubbles in water can be accurately detected even in water containing fibrous materials and air bubbles in a water pipe.

[0009] The present invention provides the following means. [1] An underwater air bubble detection method that detects air bubbles in water containing fibrous materials and air bubbles by measuring the intensity of ultrasonic waves received by the receiving part of a transmission type ultrasonic sensor. [2] The underwater air bubble detection method according to [1], wherein the ultrasonic oscillation frequency is 0.5 MHz or higher. [3] A method for detecting bubbles in water described in [1] or [2], in which the water containing fibrous material and bubbles is flowing water, and the intensity of ultrasonic waves is monitored continuously and periodically. [4] The method for detecting air bubbles in water according to any one of [1] to [3], wherein the water containing fibrous material and air bubbles has a sieve residue of 100 mg / L or more with a mesh size of 20 μm. [5] The method for detecting air bubbles in water according to any one of [1] to [4], wherein the water containing fibrous material is an aqueous slurry used in a papermaking process. [6] The method for detecting air bubbles in water according to any one of [1] to [5], wherein the pressure of the water containing the fibrous material and air bubbles at the location where the intensity of the ultrasonic waves is measured is less than 0.15 MPa. [7] A method for detecting bubbles in water described in any one of [3] to [6], wherein the pressure of the water containing the fibrous material and bubbles at the point where the intensity of the ultrasonic waves is measured is 0.9 to 1.1 times the pressure at the monitoring target point for bubbles in water upstream of the measurement point. [8] The underwater air bubble detection method according to any one of [1] to [7], wherein the ultrasonic wave reduction rate represented by the following formula (1) is used as an index of the amount of air bubbles. Ultrasonic reduction rate [%]=(R0-R1) / R0×100 (1) (wherein R0 is the ultrasonic reception intensity measured for water containing no bubbles, R1: ultrasonic reception intensity measured for water containing fibrous material and bubbles, represents.)

[0010] [9] A method for adding a degassing agent, which uses the underwater bubble detection method described in any one of [1] to [7] and controls the amount of degassing agent added to water containing the fibrous material and bubbles depending on the intensity of the received ultrasound.

[10] A method for adding a degassing agent, using the underwater bubble detection method described in [8], and using the ultrasonic reduction rate as an indicator of the amount of bubbles to control the amount of degassing agent to be added to water containing the fibrous material and bubbles. [Effects of the Invention]

[0011] According to the method for detecting air bubbles in water of the present invention, air bubbles in water can be detected accurately and simply even when water containing fibrous materials and air bubbles is present in a water pipe. Therefore, the method for detecting air bubbles in water of the present invention is useful in processes such as adding a degassing agent to raw pulp slurry or white water in papermaking. DETAILED DESCRIPTION OF THE INVENTION

[0012] The underwater air bubble detection method of the present invention detects air bubbles in water containing fibrous material and air bubbles by measuring the intensity of ultrasonic waves received by a receiving section of a transmission type ultrasonic sensor. By using a transmission type ultrasonic sensor, fibrous materials and air bubbles in water containing air bubbles can be detected accurately and simply.

[0013] The water containing fibrous material and bubbles is not particularly limited, but examples thereof include aqueous slurries containing bubbles in various steps of papermaking, such as raw pulp slurries and white water. The transmission ultrasonic sensor can accurately detect only air bubbles without being affected by fibrous materials such as pulp contained in water or fillers in paper.

[0014] A transmission ultrasonic sensor has an oscillator that emits ultrasonic waves and a receiver that receives the emitted ultrasonic waves, arranged opposite each other, with the object to be measured being placed between the oscillator and receiver. The ultrasonic waves emitted from the oscillator are blocked or reflected by the object to be measured, causing the intensity of the ultrasonic waves received by the receiver to change. By measuring the intensity of the ultrasonic waves received by the receiver (hereinafter also referred to as "ultrasonic reception intensity"), it is possible to detect fibrous materials and air bubbles in water containing bubbles and obtain information about the bubbles.

[0015] In the present invention, for example, water containing fibrous material and air bubbles in a container, or water containing fibrous material and air bubbles flowing through a water pipe, can be measured. Water containing no bubbles is used as a blank, and the ultrasonic reception intensity measured for the blank is defined as R0. The ultrasonic reception intensity measured for water containing fibrous material and bubbles is defined as R1. Calculate {(R0-R1) / R0×100} [%] and define this value as the ultrasonic reduction rate. The ultrasonic reduction rate is a value indicating the reduction in the influence of environmental factors on underwater bubbles, and can be used as an index of the amount of bubbles. In addition, when it is considered that fibrous substances have almost no effect on the ultrasonic reception intensity in measurements using the transmission type ultrasonic sensor of the present invention, the blank bubble-free water may be one that does not contain fibrous substances.

[0016] Air bubbles in water are easily affected by the pressure applied to the fibrous material to be measured and the water containing the air bubbles. Therefore, when the purpose of measurement using a transmission ultrasonic sensor is to monitor air bubbles in water under atmospheric pressure, the pressure of the water containing the fibrous material and the air bubbles at the measurement part of the transmission ultrasonic sensor, i.e., the point where the ultrasonic intensity is measured, is preferably less than 0.15 MPa, more preferably 0.1 MPa or less, even more preferably 0.05 MPa or less, and is 0 MPa or more.

[0017] Furthermore, when the purpose is to monitor air bubbles in water under pressure higher than atmospheric pressure and the measurement location using a transmission type ultrasonic sensor is downstream of flowing water containing the fibrous material and air bubbles, the pressure of the flowing water at the measurement location of the transmission type ultrasonic sensor, i.e., the location where the intensity of the ultrasonic waves is measured, is preferably approximately the same as the pressure at the upstream monitoring location for air bubbles in water, more preferably 0.8 to 1.1 times, and even more preferably 0.85 to 1.05 times, the pressure at the upstream monitoring location for air bubbles in water.

[0018] The oscillation frequency of the ultrasonic waves from the oscillator of the transmission type ultrasonic sensor is preferably 0.5 MHz or higher, more preferably 1 MHz or higher, even more preferably 2 MHz or higher, and even more preferably 3 MHz or higher. If the oscillation frequency is 0.5 MHz or higher, air bubbles in water can be detected more accurately, and air bubbles in water can be measured even if fibrous materials or inorganic particulate materials are mixed in. In addition, from the viewpoint of sensitivity to air bubbles in water, the oscillation frequency is preferably 50 MHz or less, more preferably 20 MHz or less, and even more preferably 10 MHz or less.

[0019] When the water containing the fibrous material and bubbles is flowing water such as in a water pipe, the ultrasonic intensity can be monitored periodically and continuously. In this case, efficient monitoring is possible by using an instrument that can automatically measure periodically. Based on the accumulated data of the ultrasonic wave reduction rate obtained by such continuous monitoring, information corresponding to the number of bubbles and their diameters can be obtained. Based on this information, the bubble diameter distribution, volume distribution, and bubble amount of the bubbles in the water can be estimated.

[0020] The transmission ultrasonic sensor is suitable for the periodic, continuous monitoring described above of water containing fibrous materials and bubbles. The transmission ultrasonic sensor is also suitable for long-term, continuous monitoring when the water to be measured has a sieve residue of 100 mg / L or more through a 20 μm mesh. Measurement using a volumetric bubble measuring device requires changing the pressure on the fibrous material to be measured and the water containing bubbles, making the measurement operation complicated and time-consuming.In addition, the more fibrous material there is, the more likely it is that the measurement cell, etc. will become clogged. In contrast, transmission ultrasonic sensors do not come into contact with the fibrous material to be measured and the water containing bubbles, and measurement operations can be performed without being affected by the concentration of the fibrous material, allowing for easier and longer monitoring periods.

[0021] The method for detecting air bubbles in water according to the present invention as described above is useful when adding a degassing agent to water containing fibrous materials and air bubbles, particularly to aqueous slurries used in papermaking processes, and the amount of degassing agent added can be controlled according to the intensity of the ultrasonic waves received by the receiving section of the transmission-type ultrasonic sensor.

[0022] Furthermore, as described above, since the ultrasonic wave reduction rate is an indicator of the amount of bubbles, the amount of degassing agent added to water containing fibrous material and bubbles can be controlled based on the ultrasonic wave reduction rate measured for the aqueous slurry. Such a method for detecting bubbles in water using the ultrasonic wave reduction rate as an indicator of the amount of bubbles is also useful for adding a degassing agent. [Example]

[0023] Hereinafter, the present invention will be described based on examples, but the present invention is not limited to the following examples.

[0024] [Measurement method] The various measurement methods for the physical properties of the samples in the following tests are as follows.

[0025] [Ultrasonic reduction rate] Using a transmission-type ultrasonic sensor, ultrasonic waves were oscillated in the radial direction of the water supply pipe from the oscillation part contacting the side circumferential surface of the water supply pipe, and the intensity of the ultrasonic waves received by the receiving part contacting the side circumferential surface on the opposite side in the radial direction was measured. Using water without bubbles as a blank, the reduction rate {(R0 - R1) / R0 × 100} [%] of the ultrasonic wave reception intensity R1 of the sample with respect to the ultrasonic wave reception intensity R0 of the blank was defined as the ultrasonic reduction rate. <U Unless otherwise specified, the oscillation frequency of the ultrasonic wave was 3 MHz, and the ultrasonic reduction rate was obtained as the average value of the values measured 10 times at 1-minute intervals.

[0026] [Amount of air bubbles in water (volumetric air bubble measuring device)] Using a volumetric air bubble measuring device, the sample was sealed in the measurement cell, and the amount of air bubbles in water was measured at 5-minute intervals from the volume changes during pressurization (maximum: 0.5 MPa) and depressurization (minimum: -0.08 MPa).

[0027] [Average bubble diameter] The liquid to be measured was passed through at a flow rate of 10 L / min, and the median diameter (D50) was measured using a laser diffraction / scattering particle size distribution measuring device (“LA-300”, manufactured by Horiba, Ltd.; the same applies hereinafter), and this was defined as the average bubble diameter.

[0028] [SS (Suspended Solids) concentration] It was measured by a method conforming to the measurement method of the sample solid content concentration of JIS P 8225:2003.

[0029] [Residue on a sieve with a mesh size of 20 μm] The sample was emptied onto a stainless steel sieve with 20 μm openings and thoroughly washed with tap water, after which the residue on the sieve was collected. This residue was dried at 105°C for 3 hours and then its weight (bone-dry weight) was measured. The residue on the 20 μm opening (mg / L) was calculated using the formula: bone-dry weight [g] / sample volume [mL] × 1,000,000.

[0030] [Test 1] (Air bubble detection confirmation by ultrasonic intensity) Various samples shown in Table 1 below were prepared using water containing bubbles with an average bubble diameter of 100 μm, an aqueous dispersion (slurry) of LBKP (Leaf Bleached Kraft Pulp) with a Canadian Standard Freeness (CSF) of 420 mL, or an aqueous dispersion of calcium carbonate with an average particle size of 4 μm. The term "water containing bubbles with an average bubble diameter of 100 μm" refers to tap water to which a surfactant (a mixture of sodium α-olefin sulfonate and polyoxyethylene fatty acid alkanolamide) has been added, air has been pumped in at a flow rate of 0.05, 0.1, or 0.15 L / min, and the water has been passed through a stirring pump at a flow rate of 10 L / min (bubble volume: 0.5, 1.0, or 1.5% by volume), with the amount of surfactant added adjusted so that the average bubble diameter becomes 100 μm. In Examples 1-8 and 1-9, the surfactant was added to the LBKP or calcium carbonate dispersion in the same amount as in Example 1-6 (air bubble volume 1.0% by volume), and in Examples 1-10 to 1-13, the surfactant was added in an amount of 0.01% by mass of the amount added in Example 1-6 (air bubble volume 1.0% by volume), and the water was sent to a stirring pump at a flow rate of 10 L / min. Each sample was passed through a stirring pump and sent to a water supply pipe at a flow rate of 10 L / min, and the ultrasonic reduction rate was measured using an ultrasonic underwater bubble measuring device. The measurement results are shown in Table 1. The blank was tap water to which no surfactant was added and which was supplied without introducing air.

[0031] [Table 1]

[0032] As shown in Table 1, it was confirmed that the greater the amount of bubbles, the greater the ultrasonic wave reduction rate (Examples 1-1, 1-6, and 1-7). In addition, it can be said that the higher the ultrasonic oscillation frequency, the greater the ultrasonic wave reduction rate, making it easier to detect underwater bubbles (Examples 1-2 to 1-6). On the other hand, the aqueous dispersions of LBKP or calcium carbonate (Examples 1-10 to 1-13) had a small ultrasonic wave reduction rate, and it was confirmed that the ultrasonic wave intensity was not easily reduced by the dispersion. Furthermore, when the aqueous dispersion of LBKP or calcium carbonate contained air bubbles (Examples 1-8 and 1-9), the detection of air bubbles was almost the same as that of water containing air bubbles (Example 1-6). From this, it can be said that selective detection of air bubbles in water is also possible in the papermaking process, even for pulp slurries whose main components are pulp fibers such as LBKP and fillers such as calcium carbonate.

[0033] [Test 2] (Correlation between ultrasonic reduction rate and bubble volume and bubble diameter) A surfactant (a mixture of sodium α-olefin sulfonate and polyoxyethylene fatty acid alkanolamide) was added in an adjusted amount to the aerated tap water, and the water was sent to a water supply pipe so as to achieve the bubble volumes shown in Table 2. Air was sent into this water supply pipe, and the water was sent to a transmission-type ultrasonic sensor and a laser diffraction / scattering particle size distribution analyzer connected in series at a flow rate of 10 L / min, and the ultrasonic reduction rate and bubble diameter were measured at 0.1 second intervals for 10 minutes. When the ultrasonic reduction rate was less than 0.5%, it was considered to be within the detection error range and no air bubbles were present. Table 2 shows the appearance rate and average value of bubbles with an ultrasonic reduction rate of 0.5% or more, as well as the measurement results of the bubble diameter. The blank was filled with water without air.

[0034] [Table 2]

[0035] As the amount of surfactant added increased, the average ultrasonic reduction rate decreased and the average bubble diameter tended to decrease (Examples 2-1 to 2-4). From this, it can be said that the ultrasonic reduction rate can be used as an index of bubble diameter (bubble size). Furthermore, the rate of appearance of bubbles with an ultrasonic reduction rate of 0.5% or more was 0% when no bubbles were present (blank), but increased as the amount of bubbles increased when the average bubble diameter was similar (Examples 2-5, 2-3, and 2-6). From this, it can be said that the rate of appearance of bubbles with an ultrasonic reduction rate of 0.5% or more is an indicator of the number of bubbles in water. Therefore, it is possible to estimate the bubble size distribution, volume distribution, and amount of bubbles in water based on the data distribution of the ultrasonic wave attenuation rate.

[0036] [Test 3] (Continuous measurement test) Various samples shown in Table 3 below, collected during the papermaking process, were fed into the water supply pipe at a flow rate of 10 L / min, and the state of blockage in the water supply path, in which a transmission type ultrasonic sensor or a volumetric underwater bubble measuring device was installed, was observed over a period of 7 days. To prevent clogging due to slime formation, 50 mg / L of 5-chloro-2-methyl-4-isothiazolin-3-one was added at the start of the test. Table 3 shows the time it took for each sample to reach a blocked state when using a transmission type ultrasonic sensor and a volumetric bubble measuring device.

[0037] [Table 3]

[0038] As shown in Table 3, the recovered white water (Example 3-6) had a low SS concentration and a small amount of residue on a 20 μm mesh sieve. No blockages were observed for 7 days or more when either a transmission type ultrasonic sensor or a volumetric type bubble measuring device was used. For other samples (Examples 3-1 to 3-5) with high SS concentrations and large amounts of residue on the 20 μm sieve, no clogging was observed for more than seven days when a transmission ultrasonic sensor was used. On the other hand, when a volumetric bubble measuring device was used, clogging was observed within two days near the switching valves for water flow and sealing, and pressurization and depressurization. From this, it can be said that the transmission type ultrasonic sensor can detect bubbles in water containing fibrous materials continuously for a longer period of time than the volumetric type bubble measuring device.

[0039] [Test 4] (degassing agent added) A degassing agent (emulsion of a mixture of higher alcohol and paraffin) was added to the inlet slurry of a cardboard manufacturing machine in the amounts shown in Table 4, and the mixture was passed through a stirring pump at a flow rate of 10 L / min, and then degassed by retaining it in a degassing tank for 30 seconds. The amount of bubbles in the inlet slurry was adjusted so that, when the inlet slurry was filtered through a filter with a pore size of 5 μm and the filtrate was sent to the stirring pump at a flow rate of 10 L / min, bubbles with an average bubble diameter of 100 μm constituted 2% by volume. The deaerated slurry was pumped into a water pipe at a flow rate of 10 L / min, and the ultrasonic wave reduction rate and the amount of bubbles were measured using a transmission type ultrasonic sensor or a volumetric underwater bubble measuring device. The measurement results are shown in Table 4.

[0040] [Table 4]

[0041] It was confirmed that the greater the amount of degassing agent added, the smaller the ultrasonic reduction rate and the lower the amount of bubbles. Because the degassing effect of the degassing agent is reflected in the ultrasonic reduction rate, it can be said that it is possible to adjust the amount of degassing agent added based on the ultrasonic reduction rate measured with the transmission type ultrasonic sensor.

[0042] [Test 5] (Effect of pressure (1)) The raw material slurry from the fan pump outlet (pressure 0.4 MPa) of the cardboard manufacturing machine was fed into the water supply pipe at a flow rate of 10 L / min, and the pressure at the measurement part of the transmission type ultrasonic sensor was changed to measure the ultrasonic attenuation rate. The measurement results are shown in Table 5.

[0043] [Table 5]

[0044] As shown in Table 5, the ultrasonic reduction rate decreased as the pressure at the measurement section increased, and tended to decrease significantly when the pressure was 0.15 MPa or higher (Examples 5-4 to 5-7). From this, it can be said that, for example, when the purpose is to measure the amount of bubbles in the slurry on the wire at atmospheric pressure, it is preferable to measure at a pressure of less than 0.15 MPa, and more preferably at 0.1 MPa or lower.

[0045] [Test 6] (Effect of pressure (2)) The raw material slurry from the fan pump outlet (pressure 0.25 MPa) of the fine paper manufacturing equipment was fed to the water supply pipe at a flow rate of 10 L / min, and the ultrasonic reduction rate and the amount of bubbles were measured by changing the pressure at the measurement section using a transmission type ultrasonic sensor or a volumetric type underwater bubble measuring device. The measurement results are shown in Table 6.

[0046] [Table 6]

[0047] The amount of bubbles measured with a volumetric underwater air bubble measuring device was almost the same regardless of the pressure in the measuring section. This is thought to be because a volumetric underwater air bubble measuring device involves pressurization and depressurization operations during measurement, so dissolved gas becomes bubbles regardless of the pressure in the measuring section, and the measured volumetric bubble amount also includes the dissolved gas. In contrast, the ultrasonic reduction rate was almost the same when the pressure at the measurement point was 0.20 MPa or higher (Examples 6-1 to 6-3), but tended to be significantly larger when the pressure was 0.15 MPa or lower (Examples 6-4 to 6-7). This is presumably because, when measuring with a transmission type ultrasonic sensor, dissolved gas is detected as bubbles when the pressure is lower than the fan pump outlet pressure by a certain amount. Therefore, by measuring the ultrasonic reduction rate under a pressure equivalent to that near the outlet of a water pump, which is higher than atmospheric pressure, it is possible to accurately monitor air bubbles, which are a factor in reducing the efficiency of water pumping.

Claims

1. An underwater air bubble detection method for detecting air bubbles in water containing fibrous materials and air bubbles by measuring the intensity of ultrasonic waves received by a receiving unit of a transmission type ultrasonic sensor, wherein the oscillation frequency of the ultrasonic waves is 0.5 MHz or more and 50 MHz or less; A method for detecting bubbles in water, wherein the pressure of the water containing the fibrous material and bubbles at the location where the intensity of the ultrasonic waves is measured is less than 0.15 MPa.

2. An underwater air bubble detection method that detects air bubbles in water containing fibrous materials and air bubbles by measuring the intensity of ultrasonic waves received by a receiving unit of a transmission type ultrasonic sensor, wherein the oscillation frequency of the ultrasonic waves is 0.5 MHz or more and 3 MHz or less.

3. 3. The method for detecting air bubbles in water according to claim 1, wherein the water containing fibrous material and air bubbles is flowing water, and the intensity of ultrasonic waves is monitored periodically and continuously.

4. 3. The method for detecting air bubbles in water according to claim 1, wherein the water containing fibrous material and air bubbles has a sieve residue of 100 mg / L or more with a mesh size of 20 μm.

5. 3. The method for detecting air bubbles in water according to claim 1, wherein the water containing fibrous material and air bubbles is an aqueous slurry used in a papermaking process.

6. The underwater air bubble detection method according to claim 3, wherein the pressure of the water containing the fibrous material and air bubbles at the point where the ultrasonic intensity is measured is 0.9 to 1.1 times the pressure at a monitoring target point for underwater air bubbles upstream of the measurement point.

7. 3. The method for detecting air bubbles in water according to claim 1, wherein an ultrasonic wave reduction rate expressed by the following formula (1) is used as an indicator of the amount of air bubbles: Ultrasound low rate [%] = (R ０ -R １ ) / R ０ ×100 (1) (In the formula, R ０ : ultrasonic reception intensity measured for bubble-free water, R １ : ultrasonic reception intensity measured for water containing fibrous material and bubbles, Represents.)

8. The underwater air bubble detection method according to claim 7 , wherein the ultrasonic wave reduction rate is used as an index of the air bubble diameter.

9. 3. A method for adding a degassing agent, the method using the underwater air bubble detection method according to claim 1 or 2, wherein the amount of degassing agent added to the water containing the fibrous material and air bubbles is controlled according to the intensity of the received ultrasonic waves.

10. A method for adding a degassing agent, which uses the underwater bubble detection method according to claim 7 to control the amount of degassing agent to be added to the water containing the fibrous material and the bubbles, using the ultrasonic wave reduction rate as an indicator of the amount of bubbles.

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