JPS6261325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic filter cleaning method for separating and removing magnetic substances mixed in a liquid.

In order to separate magnetic particles such as iron powder mixed in cooling water for cold and hot rolling equipment or factory wastewater, ferromagnetic materials such as permalloy or stainless steel are placed in a strong magnetic field generated by an electromagnet or superconducting magnet. Thin wire or ferromagnetic steel balls, etc. (hereinafter referred to as filter elements)
A magnetic filter is effective because it allows liquid to pass through and separates magnetic substances. This is because the force acting on a magnetic body placed in a non-uniform magnetic field is proportional to the product of magnetic field strength and magnetic field gradient, and the strong magnetic field generator increases the magnetic field strength, and the filter element increases the magnetic field gradient. . The forces acting on the magnetic particles within the magnetic filter include inertial force due to the flow of the liquid, viscous force between the liquid and magnetic particles, and gravity of the particles themselves. Conventionally, removal characteristics have been logically explained by examining the relationship between the forces acting on magnetic particles, and there are many experimental materials regarding removal characteristics. However, there is no theory regarding the cleaning of magnetic filters, and as an empirical method, a flush water cleaning method or a flush flow cleaning method using a mixture of air and water has been used.

Fig. 1 shows a conventional magnetic filter, in which 1 is an excitation coil, 2 is a yoke disposed around the excitation coil 1, and 3 is a yoke made of a non-magnetic material, such as stainless steel, disposed in the center of the excitation coil 1. A container 4 is a thin wool-like filter element 5 made of a ferromagnetic material, such as stainless steel, which is filled in the container 3.
6 is an inflow pipe for supplying the fluid to be treated from the lower part of the container 3, and 6 is an outflow pipe at the upper part of the container 3. The magnetic field direction of the excitation coil 1 in the container 3 is vertical, perpendicular to the filter element 4, and parallel to the liquid flow direction. FIG. 2 is an enlarged view of the filter element 4 of FIG. 1, and 7 indicates the magnetic flux. FIG. 3 is an enlarged view of one filter element 4, and the magnetic flux density is maximum within the filter element 4 and decreases as the distance from the filter element 4 increases, and the magnetic flux gradient on the left and right surfaces of the filter element 4 is very small.
Therefore, when a liquid containing a paramagnetic substance or a ferromagnetic substance is supplied from the inflow pipe 5 and discharged from the outflow pipe 6 while the excitation coil 1 is energized in FIG. The separated substances 8 and 9 are captured and accumulated on the lower surface 4a and upper surface 4b of the liquid, but not on the side surface 4c. On the other hand, since the filter element 4 is a thin wire, the degree of turbulence is small even if the fluid flow velocity is 1000 m/h or more. Therefore, when the outflow pipe 6 of the container 3 is flushed with the flush liquid flow and discharged from the inflow pipe 5, the captured material 9 is washed away, but most of the captured material 8 is protected by the filter element 4 and remains. do.

In cleaning with a flush flow of a mixture of air and water, the turbulence is large and the interfacial tension at the air-liquid interface is effective, so the cleaning effect on the captured objects 8 is great, but a small amount remains without being washed away. Particularly at high temperatures, the residual portion is mainly attached to the filter element 4 due to the residual magnetic field at the initial stage of capture due to changes over time, but may become even more physically and chemically attached to the filter element 4, and as the operating time increases, the magnetic The capture capacity of the filter is reduced, the frequency of backwashing is increased, the availability of the magnetic filter is reduced, and finally the filter element 4 needs to be replaced. Particularly when processing a large amount of solution containing a substance to be separated at a low concentration, if a high flow rate is used from an economical and practical point of view, the captured matter 9 will be minute, so insufficient washing of the captured matter 8 will mean that the It had drawbacks such as low effectiveness.

The present invention has been developed in view of the above-mentioned drawbacks, and improves the operating efficiency of a magnetic filter by passing a mixture of gas and fluid through a container, separating captured objects from the filter element with air bubbles, and transferring them into the liquid. An object of the present invention is to provide a method for cleaning a magnetic filter that maintains stable removal characteristics for a long period of time.

An embodiment of the present invention shown in the drawings will be described below. In FIG. 5, parts having the same functions as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. 30 is a gas supply device, 10 is a valve of the outflow pipe 6, 11 is a valve of the inflow pipe 5, 12 is a valve of a pipe that communicates from the gas supply device 30 to the inflow side of the container 3, and 13 is a valve that connects the outflow side of the container 3 to the atmosphere. Valve of the pipe communicating with 1
4 is a valve of a pipe branching from the inflow pipe 5 in parallel with the valve 11; 15 is a valve of a pipe communicating from the valve 14 to the outflow side of the container 3; 16 is a gas supply device 30
valve of the pipe communicating from the outlet side of the container 3, 17
is a valve of a pipe communicating from the inflow side of the container 3 to the atmosphere.

Next, the effect will be explained. Usually valves 10, 11
is opened, valves 12, 13, 14, 15, and 16 are closed, and with the excitation coil 1 energized and the filter element 4 magnetized, the processing fluid is fed into the container 3 from the inflow pipe 5 and the outflow pipe 6. The filter element 4 traps paramagnetic and ferromagnetic substances contained in the liquid. At a flow velocity of 300 m/h or more, the amount of captured objects 9 in Figure 4 decreases, and
At m/h or more, there is a tendency for almost only the captured object 8 to be captured. When the total amount of captured objects 8 and 9 reaches the limit capture amount of the magnetic filter, the valves 10 and 11 are closed and the excitation coil 1 is demagnetized. However, most of the captured objects remain trapped in the residual magnetic field.
In this state, the cleaning operation for the filter element 4 is started. That is, when the valves 12 and 13 are opened and a gas such as an inert gas such as nitrogen or air is supplied from the gas supply device 30 through the valve 12 to the container 3, the gas collides with the filter element 4 through the liquid remaining in the container 3. While doing so, it rises as bubbles and reaches valve 1.
It is discharged from 3. At this time, the captured matter 8 is stripped from the filter element 4 by the turbulent flow caused by the upward flow of the bubbles and the interfacial tension between the bubbles and the liquid, and transferred into the liquid. When the substances to be captured 8 have been transferred into the liquid and the valves 12 and 13 are closed, the substances to be separated that have transferred into the liquid are moved to the upper surface 4b of the filter element 4 by their own gravity.
It precipitates out. The valves 14, 15, 16, and 17 were opened, and a flash flow of a mixture of liquid and gas was supplied from above the container 3 through the outflow pipe 6, jetted out from the inflow pipe 5, and transferred onto the filter element 4 and into the liquid. The captured objects are discharged outside the container 3 and collected. The flush flow may be made of only gas, and the amount of slurry to be collected of the substance to be separated can be reduced.

According to experiments, water at 80°C containing 1 ppm of α-Fe ₂ O ₃ to be captured was supplied at a flow rate of 800 m/h, and after the capture operation was performed for 1 hour, the excitation coil was demagnetized and air was removed from the inflow pipe 5. After that, air is introduced into the container 3 from the outflow pipe 6 at a high flow rate to perform flush washing, and α-Fe ₂ O ₃ in the recovered slurry discharged from the inflow pipe 5 is removed. The ratio to the amount of α-Fe ₂ O ₃ calculated from the measured inflow amount and removal rate was determined. In Fig. 7, if the horizontal axis is the filter element filling rate (%) and the vertical axis is the backflow recovery rate (%) of captured material, then the characteristic curve 31 of the experimental results
is more remarkable than the conventional characteristic curve 32, especially when the filling factor of the filter element is large.

FIG. 6 shows another embodiment, in which 18 is a valve of a pipe communicating from the gas supply device 30 to the outflow side of the container 3, 19 is a gas acceleration pump, and 20 is a connection from the outflow side of the container 3 to the acceleration pump 19. communicating pipe valve,
21 is a recovered slurry storage tank that is sealed, and 22 is a container 3.
23 is a valve at the exhaust port of the collected slurry storage tank 21 , and 24 is a valve at the slurry discharge port of the collected slurry storage tank 21 . Valve 20, 22, 2
3 and 24 are closed, and the internal pressure of the recovered slurry storage tank 21 is made approximately equal to the pressure inside the container 3 by filling it with gas in advance. After stopping the capture operation, valves 10 and 11 are closed, then valves 20 and 22 are opened, and acceleration pump 1 is turned on.
9 to send gas from the inflow pipe 5 to the container 3,
The gas is circulated from the outflow pipe 6 to the acceleration pump 19, and the filter element 4 is cleaned by the upward flow of gas. Then, the valve 20 is closed, the valves 18 and 23 are opened, and the gas is passed from the gas supply device 30 through the outflow pipe 6 to the container 3.
A gas flushing flow is supplied to move the slurry in the container 3 along with the flushing airflow from the inlet pipe 5 to the collected slurry storage tank 21, and the gas is discharged from the valve 23 and the collected slurry accumulates at the bottom of the collected slurry storage tank 21. At this time, the valve 23 is adjusted so that the pressure within the system does not change suddenly. Slurry is at valve 2
Discharge from 4.

As described above, according to the present invention, a mixture of gas and liquid is passed through the magnetic filter, the captured substances are separated by air bubbles and transferred into the liquid, and the liquid is discharged to the outside for cleaning. At a relatively large filling rate of the filter element, trapped substances can be efficiently reverse-flow recovered, the effective operating rate of the magnetic filter is high, and stable removal characteristics can be maintained for a long period of time.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing a conventional magnetic filter.
Fig. 2 is an enlarged vertical cross-sectional view of the main part of the filter element shown in Fig. 1, Fig. 3 is an explanatory drawing showing the magnetic flux near the filter element, and Fig. 4 is an explanatory drawing showing the capture state of the captured object by the filter element. , FIG. 5 is a vertical sectional view of a cleaning device showing one embodiment of the magnetic filter cleaning method of the present invention, FIG. 6 is a vertical sectional view of a cleaning device showing another embodiment, and FIG. 7 is a vertical sectional view of a cleaning device showing another embodiment of the magnetic filter cleaning method of the present invention. It is a cleaning characteristic curve diagram. 1... Excitation coil, 2... Yoke, 3... Container,
4...Filter element, 5...Inflow pipe, 6...
... Outflow pipe, 7... Magnetic flux, 8, 9... Captured object, 1
0, 11, 12, 13, 14, 15, 16, 1
7, 18, 20, 22, 23, 24... valve,
19... Acceleration pump, 21... Recovery slurry storage tank, 30... Gas supply device.

Claims (1)

[Claims] 1. In a magnetic filter cleaning method in which a liquid is passed through a container filled with a filter element made of a ferromagnetic material and placed in a strong magnetic field to separate and remove magnetic substances mixed in the liquid, in a state where the flow is stopped and gas is introduced into the container from the lower part to generate air bubbles,
A method for cleaning a magnetic filter, characterized in that the trapped substance is separated from the filter element by the air bubbles, and then the liquid in the container is discharged from the lower part of the container while air is introduced from the upper part of the container.