JP3795240B2 - Water jet nozzle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water jet nozzle that uses cavitation, and relates to a technique that can be applied to removal of deposits, cleaning, decomposition of harmful substances, and reaction promotion.
[0002]
[Prior art]
As a representative example of high-strength deposits, clinker-like ash that adheres and solidifies on the furnace wall and heat transfer tube of the combustion furnace will be described. In coal fired boilers and heavy oil fired boilers, ash particles melt at high temperatures and adhere to heat transfer surfaces. The ash adhering to the suspended superheater (secondary superheater) at the top of the boiler furnace grows into a large lump and becomes a hard clinker. Part of this attached hard clinker is peeled off from the heat transfer tube due to thermal shock when the boiler is stopped and falls to the furnace bottom hopper, but there are many hard clinkers that remain attached to the heat transfer tube without peeling or dropping. .
[0003]
The growth of such attached hard clinker is said to be due to combined actions such as the heat load of the boiler furnace, gas temperature, and fuel type properties (melting point of ash), but the detailed mechanism is still unknown.
[0004]
If the attached hard clinker grows significantly, if the boiler is in operation, it will become the flow resistance of the gas flow in the furnace, and if it falls to the furnace bottom, it will damage the hopper heat transfer tube, or it will be an excessive burden on the crusher In some cases. Furthermore, this hard clinker is a major obstacle to furnace maintenance work during regular inspections, and if it falls suddenly, it is very dangerous for the workers in the furnace. Therefore, much effort has been expended so far to remove the attached hard clinker.
[0005]
An example of this hard clinker removal method is a method in which a simple scaffold is built on the top of the nose, the operator operates a water-washing gun (nozzle arm), and sprays a water jet toward the hard clinker.
[0006]
Although this method can remove relatively fragile clinker, it is quite difficult to destroy all of the hard clinker, requiring a long washing time. In addition, assembling a simple scaffold is a high-place work in a boiler furnace, requiring an operator with special skills. However, this method requires a lot of time and cost to assemble and dismantle the simple scaffold, and the work on the in-furnace scaffold is environmentally good due to dust, moisture, heat, etc. in a small space. I can't say that. Accordingly, there is a need for a new technique that can complete removal work in as short a time as possible.
[0007]
This hard clinker grows into a remarkably large lump and can be very strong. This often occurs when coal with a low melting point of ash is used for a long time. Since the melting point is low, the ash melts and flows out even if the temperature is not so high, but when it cools and solidifies, it becomes high strength. Moreover, once such molten ash begins to adhere to the heat transfer tube, it adheres and grows one after another.
[0008]
In a suspended heat transfer tube, a new device is required to efficiently remove a large lump of high-strength clinker with a water jet nozzle.
[0009]
[Problems to be solved by the invention]
As shown in FIG. 11, the conventional water jet is a jet of high-pressure water 2 from a nozzle 1 in a gas phase, and utilizes the principle that a high-pressure impact force from the water jet 6 acts on the clinker 7. To do. Since the water jet 6 is disturbed, the high-pressure impact force fluctuates, and a fracture mark (erosion portion) 8 is generated in the high-strength deposit 7. In FIG. 11, 3 is an ejection hole, 4 is a high-pressure water supply flow path, and 5 is a diameter contraction part (throttle part).
[0010]
On the other hand, the prior art includes a method using cavitation. A nozzle 10 whose structure is shown in a sectional view in FIG. 12 is provided with a cup-shaped cavity 11 at the tip of a central ejection hole 12 for ejecting high-pressure water 2, and creates an underwater high-speed water jet inside the cavity 11. It is intended to generate cavitation in the jet ejected from the ejection hole 12. Since the interior of the cavity 11 is not filled with water no matter how high pressure is injected from the center ejection hole 12, this nozzle is provided with an annular opening 13 on the outer periphery of the center ejection hole 12, from which relatively low-speed water 9 And the inside of the cavity 11 is filled with water.
[0011]
A phenomenon that occurs inside the cavity 11 of the nozzle is schematically shown in FIG. A small-scale shear vortex 16 is generated between the central jet 14 ejected from the central ejection hole 12 and the ambient flow 15 ejected from the annular opening 13 due to the difference in velocity. The shear vortex 16 supplies bubble nuclei to the central jet 14 or applies pressure pulsation to cause cavitation. In the nozzle having the structure shown in FIG. However, the cavitation generated in the central jet 14 is not sufficiently developed. Therefore, it cannot be said that the impact force generated when colliding with the object to be destroyed is strong.
[0012]
An object of the present invention is to provide a new configuration and method for increasing the strength of cavitation when utilizing a water jet utilizing cavitation in order to efficiently destroy and remove high-strength deposits.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the present invention mainly adopts the following configuration.
[0014]
Injecting high velocity water jets from the spray hole in the center, providing a cavity of a substantially cup-shaped in the front end of the center jet holes, the water jet nozzle for performing decomposition of destruction removal or water harmful substances of the deposit,
Provided with a plurality of ejection holes opening in the inner wall of the substantially cup-shaped cavity or a slit-shaped opening provided in the inner wall of the substantially cup-shaped cavity,
A low- speed water stream is jetted from the plurality of nozzle holes or the slit-shaped opening toward the high-speed water jet at the same time as the high-speed water jet at an angle reverse to the high-speed water jet from the central jet hole. The water jet nozzle to configure.
[0016]
In the water jet nozzle,
A water jet nozzle that sets the nozzle position so that the deposit is present at the first peak position or the second peak position in the impact pressure distribution in the axial direction of the water jet produced by the nozzle.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an example showing an entire system when a water jet nozzle according to an embodiment of the present invention is applied to removal of high-strength deposits adhering to a heat transfer tube in a combustion furnace. Water 38 serving as a water jet is stored in a water tank 39. This water is sent to the two plunger pumps 36 and 37, boosted to a predetermined pressure, and sent to the nozzle body 17 through the respective pressure hoses 34 and 35.
[0018]
The relative low pressure water 9 is sent out from the plunger pump 36. On the other hand, relative pressure water 2 is sent out from the other plunger pump 37. The two pressure hoses pass through the nozzle arm 31 that is a tubular body and are connected to the nozzle body 17. In the nozzle body 17, as described later, high-pressure water and low-pressure water are mixed to form a water jet and collide with the high-strength deposit 7 that is an object to be removed. The nozzle arm 31 is attached to the moving mechanism 32 and adjusts the position of the nozzle body 17. The nozzle arm 31 is inserted from an inspection hole 33 that opens into the combustion furnace 29 so that the nozzle body 17 can be approached.
[0019]
FIG. 2 shows a structure of a water jet nozzle embodying the present invention as an axial sectional view and a front view. In the nozzle body 17, the high-pressure water 2 is supplied through the central high-pressure water flow path 18, and suddenly depressurized and accelerated in a narrow ejection hole 19 to be ejected to become the central jet 14. Since the dome-shaped cavity 11 is opened at the tip of the ejection hole 19, the central jet 14 becomes a high-speed water jet in water when the cavity 11 is filled with water.
[0020]
On the other hand, the low-pressure water 9 is guided through a low-pressure water flow path 20 that is an annular circulation portion on the outer peripheral side of the nozzle body 17 and is ejected through a slit-shaped annular opening 21 that opens at the outlet of the cavity 11 described above. From this annular opening 21, the low-speed water stream 22 is ejected so as to oppose the ejection direction of the central jet 14 at the ejection angle θ. In this way, the central jet 14 and the low-speed water stream 22 blown to the center are mixed in the cavity 11 and blown out from the outlet of the cavity 11 while being mixed to form a composite water jet as described later. In addition to reversing the low-speed water flow with respect to the central jet, it may be ejected in a perpendicular direction.
[0021]
In the embodiment shown in FIG. 2, the low-speed water stream 22 is ejected from the slit-shaped annular opening 21. Not limited to this, the low-speed water stream 22 ′ can be blown out from the plurality of jet holes 23. FIG. 3 shows the embodiment, and the low-speed water flow 22 ′ is ejected from the low-speed water flow ejection holes 23 that are opened at six equal intervals in the circumferential direction of the nozzle body 17. The mixing of the central jet 14 and the low-speed water stream 22 ′ inside the cavity 11 is the same as in the embodiment shown in FIG.
[0022]
FIG. 4A schematically illustrates the behavior in the nozzle according to the embodiment of the present invention. The low-speed water stream 22 that blows out from the annular opening 21 that opens at the outlet end of the cavity 11 has a relatively high relative velocity because the flow direction of the central jet 14 is opposite, and a strong shearing force is generated at the interface of the central jet 14. Due to the action, a shear vortex 24 is produced.
[0023]
On the other hand, since the low-speed water stream 22 contains a large amount of bubble nuclei that become “seeds” of cavitation, the core jet 14 is supplied with bubble nuclei from the surroundings (25).
[0024]
As described above, the present invention creates a powerful shear vortex 24 and promotes cavitation by the forced bubble nucleus supply 25, and has characteristics not found in the prior art and the prior art. Since the interior 12 of the hollow portion 11 is filled with water by the low-speed water stream 22, the central jet 14 becomes an underwater high-speed water jet. Further, the flow rate of the low-speed water flow is in a range of 1/3 to 4/5 of the flow rate of the high-speed water jet, and the flow rate of the low-speed water flow is 1.2 times or more the flow rate of the high-speed water jet. It was found that selecting from a range of 0 times or less further promotes cavitation.
[0025]
FIG. 4B schematically illustrates the behavior of the central jet 14. Immediately after ejecting from the ejection hole 19, there is a water core portion 26, and cavitation 40 is generated around it. By the action of the shear vortex 24 and the cavitation 40 described above, the water core portion 26 is split and becomes a high-speed water mass 27 and intermittently collides with the high-strength deposit 7. The water masses 27 collide one after another like a bullet from the machine gun, bite into the inside of the high-strength deposit 7 while breaking (α), and create a destructive part 8 ′ like a sharp crevasse.
[0026]
As shown in FIG. 5, the effect of embodying the present invention was evaluated by the width W and the depth h of the fracture mark (erosion part) 8 by the collision of the water jet. FIG. 6 is an experimental result using brick as a material to be destroyed, and compares the characteristics of the embodiment of the present invention, the prior art (FIG. 11) to the prior art (FIG. 12). By changing the standoff distance Xs (distance between the nozzle outlet and the target material), the depth of the erosion groove caused by the impact of the water jet was examined. The stand-off distance Xs on the horizontal axis was made dimensionless by dividing by the ejection hole diameter D. On the other hand, the depth h of the erosion groove in the vertical axis, dimensionless by dividing by the grooves of depth h _o in the prior art.
[0027]
In the prior art (FIG. 11), at Xs / D≈60, h / _ho shows a peak, but its level is much lower than the characteristics of other examples. When the water jet nozzle according to the present invention (FIG. 2) is used, it can be seen that the erosion groove deepens significantly when the stand-off distance is short, that is, when the nozzle outlet is brought close to the brick. The result regarding the level of h is overwhelming with more than twice the characteristic of the prior art (FIG. 12) showing a similar tendency. This is because the power of the collision of the water mass 27 ((2) in FIG. 4) is enhanced in the nozzle according to the embodiment of the present invention.
[0028]
FIG. 7 shows the comparison of the width W of the fracture mark in the same manner. The width W of the erosion groove on the vertical axis was made dimensionless by dividing by the maximum width W _O of the erosion groove in the prior art. In the prior art, the width of the erosion groove has a peak at a standoff distance Xs / D≈60. On the other hand, in the embodiment of the present invention, the width W of the erosion groove shows a peak under the condition that the nozzle is close to the brick, but is clearly lower than the maximum value in the prior art. Considering together with the result of FIG. 6 described above, when the water jet nozzle according to the present invention is used, an erosion groove as if it was cut narrowly and deeply is produced in comparison with the prior art.
[0029]
FIG. 8 schematically compares these features. The fracture mark (erosion part) 8 generated by the conventional water jet method spreads shallowly and is not suitable for the destruction of the hard material after all. On the other hand, since the erosion mark 14 by the water jet nozzle according to the present invention appears to be cut narrowly and deeply, it can be said that it is suitable for destructive removal of the hard material.
[0030]
Further, when the distribution of the impact pressure in the axial direction of the water jet produced by the nozzle shown in FIG. 2, for example, according to the embodiment of the present invention is observed, the impact pressure is reduced from the opening end of the nozzle to the deposit removed by destruction. There are first and second peaks that are not like but show large peak values. If the position of the nozzle is set so that the deposits are present at the location showing the peak value of such a water jet, the deposits can be effectively destroyed and removed.
[0031]
FIG. 9 compares the effect of using the water jet nozzle of the present invention with the prior art or the prior art using the construction time t for removing high-strength deposits. The construction time t for removing high-strength deposits was made dimensionless by dividing by the construction time t ^* for removing high-strength deposits in the prior art (FIG. 11). In short, the time when the prior art is applied is compared as “1”. Although the construction time can be shortened to 60% or less in the prior example shown in FIG. 12, it can be seen that the construction time can be shortened to 1/5 when the present invention is implemented.
[0032]
The fact that the construction time by the water jet can be shortened means that the amount of water used can also be reduced. FIG. 10 shows the result of comparing the amount of water used. The water flow rate Qw used for removal of high-strength deposits was made dimensionless by dividing by the water flow rate Qw ^* used for removal of high-strength deposits in the prior art (FIG. 11). Compared to the prior art, since the low speed water flow is used in the preceding example and the embodiment of the present invention, it does not have a proportional relationship with the construction time of FIG. 9 described above. It turns out that it can reduce remarkably to 1/3 or less. This characteristic is in contrast to the previous example (FIG. 12) in which the water flow rate used is not much different from the prior art. When the water jet nozzle according to the present invention is used, the construction is completed in a short time and with a small water flow rate, so that the efficiency of preventive maintenance of the plant can be improved.
[0033]
The water jet nozzle according to the present invention can be directly applied not only to the removal of the clinker-like ash adhering to the boiler heat transfer tube but also to the following completely different fields.
[0034]
(1) Cleaning of semiconductor silicon wafer As a cleaning method that does not require the use of special chemicals, there is a method of using cavitation generated in an underwater water jet as shown in FIG. According to this, the high-pressure water 2 is injected coaxially into the jet of the low-pressure water 9. The underwater water jet in which cavitation has occurred is made to collide with the wafer 28 and cleaned by the action of cavitation. However, according to this method, since the high-pressure water 2 and the low-pressure water 9 flow in parallel, the relative speed is small and the shearing action is poor. As a result, cavitation does not develop well. The application of the present invention that promotes the cavitation of a submerged water jet is also very effective for cleaning such a silicon wafer.
[0035]
(2) There is a technology for decomposing and removing harmful substances by purifying cavitation of water containing harmful substances. The present invention is suitable for purifying a large amount of water by injecting low-pressure water from the surrounding annular port in addition to the high-speed water jet from the center.
[0036]
In both (1) and (2), the water jet nozzle shown in FIG. 2 or 3 can be used almost as it is.
[0037]
As described above, the embodiment of the present invention includes the following configurations, functions, and operations.
[0038]
A substantially cup-shaped cavity is provided at the outlet tip side of the central jet hole that ejects a high-speed water jet at the nozzle, and the low-speed water jet from the central jet hole is reversed from the outer edge / outlet side of the cavity. Spouts the surrounding flow. In short, the inside of the cup-shaped cavity is filled with water, creating a situation in which a high-speed water jet spouts on the central axis, and an ambient flow blows out against it.
[0039]
A turbulent shear layer is created at the interface between the central high-speed water jet and the surrounding flow, which is opposite to the high-speed water jet, and cavitation is remarkably promoted. Also, a large amount of cavitation nuclei (Nuclei) is supplied from the surrounding flow to the central high-speed water jet. It is also effective to allow this nuclear supply to flow backward from the surroundings to the central high-speed flow. Cavitation is also greatly promoted by the nuclear supply of cavitation.
[0040]
The present invention provides a new means for promoting cavitation in the cup-shaped cavity at the tip of the nozzle ejection hole. And, in the substantially cup-shaped cavity provided at the tip of the nozzle, a strong shearing action occurs at the interface between the water flow that flows backward from the vicinity of the cavity outlet opening end to the upstream side and the high-speed water jet that blows out at a high pressure from the center, Cavitation becomes extremely active. Such a cavitation promoting effect self-amplifies the power of the two actions coupled to each other, that is, the cavitation action and the water mass splitting action.
[0041]
The ambient flow that flows backward from the vicinity of the open end of the cavity supplies a large amount of cavitation-generating nuclei to the central high-speed water jet. There is also a large velocity gradient between the ambient flow and the central high-speed water jet, and this action also promotes cavitation. As the cavitation amplification increases the turbulence of the water flow, the action of intermittently splitting the central high-speed water jet into water bodies is also strengthened.
[0042]
As a result, since the action of cavitation and intermittent breakup of the water mass becomes active, when the water flow ejected from the cup-shaped cavity collides with the deposits, the impact force is remarkably increased compared with the prior art. The kimono is easily destroyed and the efficiency of deposit removal increases. Compared with the method of FIG. 12, the method according to the present invention increases the pressure loss at the nozzle by about 3 to 6%.
[0043]
【The invention's effect】
The effects produced by the present invention are summarized as follows.
[0044]
(1) Particularly for a high-strength deposit that has a bending strength exceeding 15 MPa and adhered in a lump, the nozzle according to the present invention can be easily broken and detached from the heat transfer tube.
[0045]
(2) In connection with the effect of (1) above, since the high-strength deposit is not removed and left behind, there is no trouble that the high-strength deposit falls during the operation in the furnace. Therefore, it is effective for safety measures.
[0046]
(3) Since the construction time for removing the high-strength deposit is shortened by the effect (1), it is advantageous in terms of cost.
[0047]
(4) Even if the water jet is jetted with the same amount of water, the construction can be completed in a shorter time than the conventional method. Since the amount of water used can be reduced, it is advantageous in terms of cost. In addition, wastewater treatment costs can be reduced.
[0048]
(5) Since no special ultra-high pressure water is used, a general-purpose plunger pump or pressure-resistant hose can be used, which is advantageous in terms of equipment cost.
[0049]
(6) If the inner surface of the cup-shaped cavity member is diamond-coated by, for example, a thermal CVD method, wear due to cavitation is eliminated and nozzle replacement is not necessary.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram in the case of removing a high-strength deposit using a water jet nozzle according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the structure of a water jet nozzle according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing the structure of a water jet nozzle according to another embodiment of the present invention.
FIG. 4 is a diagram schematically illustrating a mechanism in a water jet nozzle according to the present invention.
FIG. 5 is a diagram for defining the shape and dimensions of fracture marks (erosion portions) generated in a high-strength deposit.
FIG. 6 is a diagram showing experimental results comparing the present invention with the prior art and the prior art.
FIG. 7 is a diagram showing experimental results comparing the present invention with the prior art and the prior art.
FIG. 8 is a diagram comparing the shape of a fracture portion of a high-strength deposit according to the present invention with that of a conventional technique.
FIG. 9 is a diagram showing test results and demonstrating the effect of implementing the present invention.
FIG. 10 is a diagram showing test results and demonstrating the effects of implementing the present invention.
FIG. 11 is a diagram showing a conventional technique.
FIG. 12 shows a prior art nozzle.
FIG. 13 is a diagram schematically illustrating a phenomenon in a prior art nozzle.
FIG. 14 is an example of prior art in the field of cleaning.
[Explanation of symbols]
2 High-pressure water 7 High-strength deposit 9 Low-pressure water 11 Cavity 14 Central jet 17 Nozzle body 18 High-pressure water flow channel 19 Ejection hole 20 Low-pressure water flow channel 21 Annular opening 22 Low-speed water flow 24 Shear vortex 25 Bubble core supply 27 Water mass 30 Transmission Heat pipe 31 Nozzle arm 36, 37 Plunger pump 39 Water tank 40 Cavitation

Claims (4)

Injecting high velocity water jets from the spray hole in the center, providing a cavity of a substantially cup-shaped in the front end of the center jet holes, the water jet nozzle for performing decomposition of destruction removal or water harmful substances of the deposit,
A plurality of ejection holes opening in the inner wall of the substantially cup-shaped cavity, or a slit-shaped opening provided in the inner wall of the substantially cup-shaped cavity,
A low- speed water stream is jetted from the plurality of nozzle holes or the slit-shaped opening toward the high-speed water jet at the same time as the high-speed water jet at an angle reverse to the high-speed water jet from the central jet hole. A water jet nozzle characterized by comprising: The water jet nozzle according to claim 1,
The flow rate of the low-speed water flow is in the range of 1/3 to 4/5 of the flow rate of the high-speed water jet, and the flow rate of the low-speed water flow is 1.2 times to 3.0 times the flow rate of the high-speed water jet. A water jet nozzle selected from the following ranges. The water jet nozzle according to claim 1,
The water jet nozzle, wherein the nozzle position is set so that the deposit is present at a first peak position in an impact pressure distribution in an axial direction of a water jet produced by the nozzle. The water jet nozzle according to claim 1,
The water jet nozzle, wherein the nozzle position is set so that the deposit is present at a second peak position in an impact pressure distribution in an axial direction of a water jet produced by the nozzle.

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