JPH06153758A - Method of laser irradiation for preventing aquatic organism from sticking to waterline - Google Patents

Abstract

PURPOSE:To prevent aquatic organisms from sticking to waterline by irradiating aquatic organism-contg. water passing through a waterline with laser beams in a specific mode. CONSTITUTION:An aquatic organism-contg. water is passed through an irradiation water pipe 3 which is then irradiated with YAG laser beams from a laser generator 7 rectangularly or obliquely to the waterline. The YAG laser beams are branched into plural low-energy beams, the wavelength of each of which is shortened by a wavelength transformation element and then scanned in the width or height direction relatively to the waterline.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to organisms having ecological adhesiveness such as shellfish such as mussels and oysters, aquatic animals such as barnacles, aquatic plants such as algae, and aquatic microorganisms (collectively, “aquatic organisms”). Refers to a laser irradiation method for preventing the growth and reproduction of the power plant or various factories by adhering to the inner surfaces of equipment, pipes and waterways.

[0002]

2. Description of the Related Art Laser irradiation has been used in surgery and the like in the field of clinical medicine because it can irradiate an organism or a living body with its light energy at one point. However, there is no example in which laser irradiation is used to prevent the attachment of organisms in a waterway as described above.

[0003]

The laser irradiation method according to the present invention is intended to prevent the adhesion of aquatic organisms to a waterway by irradiating aquatic organism-containing water flowing through the waterway with a laser from a direction perpendicular to or oblique to the waterway. , The YAG laser beam coming from the laser oscillator is split into a plurality of low-energy beams, each split beam is passed through a wavelength conversion element to shorten the wavelength, and then the water channel is scanned in the width direction or the height direction. It is a feature.

The laser used for the energy source in the method of the present invention is a YAG laser. As the YAG laser, for example, a laser of a laser processing machine can be used. The YAG laser for processing is capable of producing an output of several hundreds of watts even with continuous oscillation, is widely used, and is easily available.

The use of an argon laser is problematic in that it has a low electro-optical conversion efficiency, is expensive because it is not widely used as an energy source, and takes time to obtain it.

The fundamental oscillation wavelength of the YAG laser is 1060
nm, and the absorption by water is extremely large, so YAG
The laser cannot directly kill and damage aquatic life.

Therefore, in the present invention, the wavelength conversion element,
For example, a YAG laser is used after converting the wavelength of the YAG laser to 530 nm, which is, for example, 1/2, using a nonlinear wavelength conversion element made of KTP crystal (potassium / titanium / phosphoric acid crystal). However, since the KTP crystal is likely to be damaged by light energy exceeding 100 watts, the YAG laser beam coming from the laser oscillator is branched into a plurality of low energy beams by using an optical fiber to be attenuated. This reduction in energy makes it possible to use a nonlinear wavelength conversion element made of a KTP crystal, and by passing each branched beam through the wavelength conversion element, a short-wavelength laser whose absorption by water is extremely small can be obtained.

By dividing the YAG laser beam, a large number of light sources can be obtained with an inexpensive system, and an efficient aquatic organism adhesion preventing effect can be realized by the laser scanning mechanism.

As means for scanning the laser beam,
As shown in Fig. 1 and Fig. 2, the rotating mirror (6) with a polygonal cross section receives and reflects the laser beam (L) coming from the laser oscillator (7), and the reflected beam by the rotating mirror (6). A fixed mirror (5) with a concave arc surface reflecting in the waterway,
A laser light receiving unit (11) provided in the water channel so as to receive the beam coming from the fixed mirror (5) is used.

Next, the scanning conditions of the laser beam will be described.

In order to kill the aquatic organisms or reduce their living ability to prevent them from adhering to the waterway wall, for example, when irradiation with an argon laser is performed, the light energy W for irradiating the aquatic organisms has an energy density Q (watt / mm). ² ) and irradiation time Δt (time), which is expressed as W = Q · Δt (1), and the effect of weakening aquatic organisms depends on the size of W. However, regarding Q, such a weakening effect does not occur unless this is a certain value or more.

In the following, water flows through a channel of width D and height Y by v ₂
When irradiating a laser beam having a spot radius r at a right angle to a water channel and scanning the laser beam in the width direction at a speed of v ₁ , the entire flowing water is irradiated with a laser, Moreover, the conditions for the irradiation light energy to be effective in preventing the adhesion of aquatic organisms will be described.

FIG. 3 shows the movement of the laser spot (S) when the flowing water is used as a reference when the laser beam is scanned in the direction perpendicular to the water channel. The laser scans at right angles to the waterway, but since water is flowing at a velocity of v ₂ ,
Based on water, the laser spot is tan
^-1 angle will be scanned in the (v ₂ / v _1).

In order to scan the entire area of the water channel without exception, the relationship D / v ₁ = 2 · r / v ₂ (2) must be established, and the scanning speed v ₁ is determined from this relationship. .

On the other hand, the energy of the laser light to be irradiated needs to be a value effective in preventing biofouling, which is defined as W _o . In order to effectively prevent the adhesion of water to the entire water flowing through the water channel, W _o should be applied to the bottom of the water channel of depth Y as well.
The above energy needs to be applied. Assuming that the attenuation rate of light energy due to water in the depth direction is k, the irradiation light energy amount W (Y) at the depth Y of the water channel is W (Y) = k ^Y · (E / πr ² ) · Δt. … (3). Here, E is the output energy of the laser used.

Δt is Δt = 2r / v ₁ (4) from the relationship between the spot diameter and the scanning speed.

Therefore, W (Y) is given by the equation (2) as follows: W (Y) = k ^Y · 4E / (πDv ₂ ) (5)

Therefore, W (Y) represented by the equation (5)
Is a condition necessary to prevent biofouling in the case of scanning with a laser, having a relationship of W (Y) ≧ W _o (6).

The method of Japanese Patent Application No. 3-110634 shows that the light energy density Q is effective at 0.01 watt / mm ² or more when an argon ion laser is used. If Q = 0.1 watt / mm ² and Δt = 1 msec, then W _o = 10 ⁻⁴ watt · sec / mm ² . In equation (5), k = 0.9, Y = 1 m, D = 0.
When the length is 5 m and an argon ion laser of 30 watts is used, the maximum flow velocity v _{2 at which} adhesion can be prevented is v ₂ = 0.68 m / sec (7). The amount of water that can be treated to prevent adhesion is Y × D × v ₂ , and Y, D, v ₂ that maximizes this under the constraint of equation (6).
It is practical to use.

The scanning conditions of the laser beam have been described above for the argon laser, but the same applies to the YAG laser.

[0021]

Embodiments of the present invention will be specifically described.

First, the structure of the experimental apparatus used in this embodiment will be described.

In FIGS. 1 and 2, filtered seawater containing the test organism is stored in the seawater tank (1). This seawater containing aquatic organisms is injected from the seawater tank (1) through the injection pipe (2) into one end of the irradiation water pipe (3), and is discharged through the discharge pipe (4) from the other end of the irradiation water pipe (3). It The amount of seawater injected into the irradiated water pipe (3) was kept constant during the experiment, and seawater containing aquatic organisms flowed in the same direction at a constant flow velocity in the same direction, and accordingly, aquatic organisms (B) also flowed in the water flow direction.

The irradiation water pipe (3) has a rectangular tube-shaped light receiving part (11) incorporated in the middle of its length, and the top wall of the light receiving part (11) is made of an acrylic resin transparent plate (10). Has been done. Transparent plate (10)
Has an antireflection film according to the wavelength of the laser.

A laser oscillator is provided near the irradiation water pipe (3).
(7) is installed, and the laser beam (L) is emitted upward from the laser head. The laser beam (L) is
It is received by a rotating mirror (6) having a horizontal axis of rotation (9).
The rotating mirror (6) has a regular hexagonal cross section, and is composed of mirrors on all six sides and is rotated about a horizontal rotation axis (9). The beam reflected by the rotating mirror (6) strikes a concave arc surface-shaped fixed mirror (5) and is reflected by the fixed mirror (5) to reach the light receiving part (11) of the irradiation water pipe (3). Then, the laser beam enters the tube through the transparent plate (10) of the light receiving section (11) and at the same time, as the rotating mirror (6) rotates, the light receiving section (1
1) Scan the inside in the width direction.

In this way, the laser beam is used as an irradiation water pipe.
(3) The light entering the inside and irradiating the aquatic organism-containing seawater in the pipe is irradiated in a direction perpendicular to the water channel while scanning the inside of the light receiving part (11) in the width direction.

In the present invention, as shown in FIG.
YA coming from the laser oscillator (7) connected to the power supply (12)
G laser is used. The YAG laser oscillator (7) is widely used as a laser processing machine and oscillates a 200 watt YAG laser beam. This YAG laser beam is guided to the branching part (13), and is branched and attenuated into four low energy beams of about 40 watts by a plurality of optical fibers (14) connected thereto. Each branched beam is passed from the optical fiber tip portion (15) through a nonlinear wavelength conversion element (8) made of KTP crystal, and the wavelength of the YAG laser is converted from 1060 nm to 530 nm. Each of these four low-energy short-wavelength branched beams is applied to the rotating mirror (6) as described above, and the same operation as above is performed to enter the irradiation water pipe (3) and to enter the aquatic organism-containing seawater in the pipe to the water channel. Irradiation is performed while scanning the inside of the light receiving unit (11) in the width direction in the right angle direction.

[0028]

Since the laser irradiation method according to the present invention is constructed as described above, it has the following effects.

Since the entire water flowing through the water channel is effectively irradiated with the laser, the aquatic animals such as shellfish, the aquatic plants such as algae, and the floating life stage larvae such as aquatic microorganisms and the larvae or adults after attachment are used as a device. It is possible to more reliably prevent the adhesion, growth and propagation to the piping and the cooling water passage.

By continuing the laser irradiation, a damaging and damaging effect on aquatic organisms can be stably generated, and the damaging effect does not decrease with time.

The apparatus used for the method of preventing attachment of aquatic organisms is compact as a whole, and the installation space is small.
Also, no complicated maintenance of the device is required.

When aquatic organisms are exterminated at the larval stage, the amount of dead organisms and organic wastes is extremely small and no pollution problem occurs.

The YAG laser used in the present invention is capable of producing an output of several hundred watts even when continuously oscillated, and is widely used.
Since it can be easily obtained, the laser irradiation treatment can be advantageously performed in terms of cost.

Further, by branching and attenuating the YAG laser beam into a plurality of low energy beams, the KT
By making it possible to use a non-linear wavelength conversion element made of a P crystal and passing each branched beam through the wavelength conversion element,
It is possible to obtain a laser having a short wavelength that is extremely absorbed by water, and it is possible to improve killing damage to aquatic organisms.

Further, by dividing the YAG laser beam, a large number of light sources can be obtained with an inexpensive system, so that an efficient aquatic organism adhesion preventing effect can be realized by the laser scanning mechanism.

[Brief description of drawings]

FIG. 1 is a perspective view showing an experimental device used in Examples.

FIG. 2 is a vertical sectional view showing an experimental apparatus used in Examples.

FIG. 3 is a schematic diagram showing an apparent movement of a laser spot on a waterway by laser scanning.

FIG. 4 is a schematic diagram showing a branched state of a laser beam.

[Explanation of symbols]

 (1)… Seawater tank (2)… Injection pipe (3)… Irradiation water pipe (4)… Exhaust pipe (5)… Fixed mirror (6)… Rotating mirror (7)… Laser oscillator (8)… Nonlinear wavelength conversion element (9)… Horizontal rotation axis (10)… Transparent plate (11)… Light receiving part (12)… Power supply (13)… Branching part (14)… Optical fiber (15)… Optical fiber tip (B)… Aquatic organism (L) ) …Laser beam

Claims (1)

[Claims] 1. A YAG laser beam coming from a laser oscillator when aquatic organism-containing water flowing through a waterway is irradiated with a laser from a direction perpendicular or oblique to the waterway to prevent aquatic life from adhering to the waterway. A plurality of low-energy beams, each branched beam is passed through a wavelength conversion element to shorten the wavelength, and then scanned in the width direction or the height direction with respect to the water channel. Laser irradiation method to prevent adhesion.