JPH0716408A - Method for detaching filter cake from leaf filter - Google Patents

Abstract

PURPOSE:To easily detach cake by closing an air introducing valve with a residual liquid discharge valve being left open, opening the air introducing valve for introducing air from the outside into inside leaves through a hollow shaft and operating scrapers under these conditions. CONSTITUTION:In the initial stage of a residual liquid draw-out process, a valve V2 and a valve V6 are opened to draw out liquid remaining in a tank filter 1 to a feed liquid draw-out tank 20 from a pipe 19. Next, when the valve V2 is closed and a valve V4 is opened in its turn to do switching so that air which has been introduced into the tank filter 1 outside leaves 3 may be directed into the tank filter 1 through each leaf 3 from inside a hollow shaft 2, filter cake C is pulled off outward. When the hollow shaft 2 is rotated together with the leaves 3 in this state, the filter cake C accumulated on filter nets 4 loses touch with the filter nets 4 in the residual liquid draw-out process, causing it to be easily and surely detached by scrapers 5. The detached cake is sent to a filter cake receiver 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a type in which a filter element (leaf) surface installed inside is precoated with a filter aid such as diatomaceous earth to form a filter layer, and filtration is performed through this filter layer. The present invention relates to a method for separating a filter cake in a pressure leaf type precoat filter (generally called a "leaf type filter").

[0002]

2. Description of the Related Art A leaf type filter (1) can perform filtration at low pressure. (2) The filter material is less consumed. (3) Easy to automate. It is widely used because of its advantage.

In this leaf filter, a rotatably hollow shaft is provided at the center of a substantially cylindrical filter tank, and a plurality of leaves in the form of hollow disks are provided at predetermined intervals on the hollow shaft. It has a structure attached by. Each leaf is provided with a filter mesh, the internal space of which communicates with the internal space of the hollow shaft.

In the filtration operation, the stock solution to be filtered is supplied into the filtration tank, the liquid passes through the precoat layer composed of the filter aid on the filter net of each leaf, and then is taken out through the hollow shaft to the outside. The solids deposit on the filter mesh to form a filter cake.

This filter cake causes clogging of the precoat layer as the amount of deposition increases, so it is necessary to remove it regularly. The removal of the filter cake is performed by rotating a scraper, which is arranged close to the surface of the filter mesh, relative to the leaves.

[0006]

However, the leaf type filter as described above has a drawback that it is difficult to remove the cake depending on the properties of the cake.

That is, when the viscosity of the cake is relatively high, or when the adhesion between the cake and the leaf is high, a large resistance acts to peel the cake from the leaf, or the cake peels badly. Since the cake does not fall down and accumulates between the leaves, excessive force is applied to the scraper or leaf, causing deformation or damage, or provided in the power transmission mechanism for rotating the scraper or leaf. There is a danger of causing a serious situation such as damage to the overload operation preventing mechanism (for example, shear pin) provided.

In order to avoid such mechanical damage, it is also practiced to wash the cake adhering to the leaves with the filtrate to soften the cake, and then to remove the cake. Is lost with the cake, resulting in lower productivity and higher costs. Further, even if the filtrate was washed, the detachability of the cake was not constant under various conditions, so that it was difficult to solve the problem.

In the above cake removing step, it is possible to blow air into the hollow shaft to push up the cake adhering to the filter net from the inside, but the pressurized air is the portion with the lowest resistance. Since it flows concentratedly in the area where the cake adheres, the effect of detachment becomes weakest in the area where a large amount of cake adheres, and a sufficient effect cannot be obtained.

The object of the present invention is to remove the cake very easily, and therefore, there is no risk of damaging the parts of the apparatus, and the leaf type filtration which does not cause the loss due to the use of a part of the filtrate for washing. A method of removing a filter cake from a container is provided.

[0011]

According to the present invention, a hollow shaft having a plurality of leaves mounted at predetermined intervals is provided in a filter tank, and a filter cake is provided in the vicinity of a filter net provided on the leaves. In a leaf type filter provided with a scraper for removing, a filter cake removing method for removing the filter cake attached to the filter layer on the filter net, introducing a stock solution to be filtered into the filter tank, After the filtration step is completed, the stock solution is filtered by flowing from the leaf toward the hollow shaft through the filtration net, and the separated solid matter is captured in the filtration layer on the filtration net. A first stage in which a residual liquid discharge valve for extracting the liquid remaining in the inside to the outside and a first air introduction valve for introducing air from the outside into the filtration tank are opened; Opened the residual liquid discharge valve And a second stage in which the first air introduction valve is closed and a second air introduction valve for introducing air from the outside to the inside of the leaf via the hollow shaft is opened. A method for removing a filter cake from a leaf type filter is provided, which comprises performing the residual liquid removing step.

That is, in the filter cake removing method of the present invention, in the cake removing step, in the step of withdrawing the undiluted solution from the filter tank, each of the passages communicating with the filter tank and the hollow shaft is used as a filter aid circulation passage. Of the valves provided, at the beginning of the extraction process, the valve provided in the passage communicating with the inside of the filtration tank is opened, and then this valve is closed, and the valve provided in the passage communicating with the hollow shaft is opened. .

In this state, the liquid in the filtration tank is drawn out by the action of gravity, and the negative pressure generated thereby draws in air from the outside through the hollow shaft and each leaf. This negative pressure acts on the filter net of each leaf in the opposite direction of the liquid flow in the filtration process, regardless of the flow resistance of the air acting on it, which causes the cake to pass through each filter. The net is pulled evenly outward. Therefore, by moving the scraper with respect to the leaves in this state, a peeling action is generated on the filter cakes attached to all the leaves, whereby the filter cakes are easily separated from the leaves.

A method for removing a filter cake from a leaf type filter according to an embodiment of the present invention will be described below with reference to the drawings.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic structure of a leaf type filter to which the method for removing a filter cake according to the present invention is applied. Figure 1
In FIG. 1, reference numeral 1 indicates a substantially cylindrical filtration tank, and a hollow shaft 2 is rotatably provided at the center of the filtration tank 1. A plurality of leaves 3 in the form of hollow disks are attached to the hollow shaft 2 at predetermined intervals, and the inner space of each leaf 3 communicates with the inner space of the hollow shaft 2. A filter net 4 is attached to the leaf 3 at an end surface facing the adjacent leaf 3.

A plurality of scrapers 5 arranged on the filter net 4 of each leaf 3 at a predetermined minute interval are fixed to the filter tank 1. It should be noted that it is also possible to adopt a form in which the scraper 5 is rotated with respect to the leaf 3.

The filtration operation consists of the following steps. Filling process The stock solution is sent from the stock solution tank 11 into the filter 1 through the pipe P having the pump P1 and the valve V1. The stock solution overflows the inside of the filter 1 and the valve V
Filter aid mixing tank 1 via return pipe 14 having 2
Inflow to 3. This process is continued until the filter aid tank 13 is filled. Overflow step After the filter aid tank 13 is filled with the stock solution, the pump P2,
Filter aid tank 1 through pipe 15 having valve V3
The liquid in 3 is sent into the filter 1. In this state, the liquid circulates between the filter 1 and the filter aid tank 13, and a predetermined amount of filter aid is put into the filter aid 13 during this period. Pre-coating step The valve V2 is closed and the valve V4 provided in the pipe 16 that connects the hollow shaft 2 and the filter aid tank 13 is opened. In this state, the liquid containing the filter aid is introduced from the filter aid tank 13 into the filter tank 1 through the pipe 15, passes through the filter net 4 of each leaf 3, and enters the hollow shaft 2. Then, it circulates in a route of returning to the filter aid tank 13 through the pipe 16, during which the filter aid adheres to the surface of the filter net 4 to form a precoat film. Filtration Step When the precoating step is completed, the valve V4, then the valve V3 are closed, and then the valves V1 and V5 are opened.
As a result, the undiluted solution to be filtered enters the undiluted solution tank 11 through the pipe 12 into the unfiltered tank 1, passes through the filtration net 4 and flows from the leaf 3 to the hollow shaft 2, and is then collected through the pipe 17 into the filtrate receiving tank 18. To be As the filtration progresses, the solid matter contained in the stock solution is trapped in the precoat layer on the filter net 4 of each leaf 3 and is deposited here to form the filter cake C. Residual liquid withdrawal step This step consists of two stages. In the first stage, the valves V1 and V5 are closed, and then the valves V2 and V6 are opened to draw the liquid remaining in the filtration tank 1 through the pipe 19 into the stock solution withdrawing tank 20, and to pump this liquid with the pump P3.
Is returned from the pipe 21 to the stock solution tank 11. Valve V6
The reason for opening is to suck air from the outside into the filtration tank 1 and to smoothly flow out the residual liquid.

When the first stage has advanced to some extent, the second stage is entered. In this second stage, valve V2 is closed and valve V4 is opened instead. This allows
The air that had been introduced into the filtration tank 1 outside the leaf 3 until then is switched from the inside of the hollow shaft 2 through each leaf 3 to the inside of the filtration tank 1. In this state, the negative pressure generated when the liquid in the filtration tank 1 is extracted by the action of gravity acts on the filtration net 4 of each leaf 3 in the direction opposite to the flow of the liquid in the filtration process. As a result, the filter cake C is peeled off toward the outside. Cake removing step After discharging the residual liquid in the filtration tank 1, the hollow shaft 2 is rotated together with the leaf 3 attached thereto. Since the filter cake C deposited on the filter net 4 floats up from the filter net 4 in the above-mentioned residual liquid withdrawing step, the scraping action by the scraper 5 is easily and reliably performed.

The cake separated from the filtration net 4 is filtered by the filtration tank 1.
From the bottom to the filter cake receiving tank 23 through the pipe 22 having the valve V7.

[0020]

As described above, according to the method of the present invention, the releasability of the filter cake from the leaves is remarkably improved,
The removal of the filter cake can be carried out very efficiently and reliably. Therefore, it is possible to fully automate the filtration process without damaging the components of the leaf filter. Further, since it is not necessary to use the taken-out filtrate for removing the cake, not only the efficiency can be improved, but also the driving power, the cost, and the amount of the filter aid used can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a leaf type filter to which a method for removing a filter cake according to the present invention is applied.

[Explanation of symbols]

 1 Filter Tank 2 Hollow Shaft 3 Leaf 4 Filter Net 5 Scraper 11 Stock Solution Tank 13 Filter Aid Tank 18 Filtrate Receiving Tank 20 Raw Solution Extracting Tank 23 Filter Cake Receiving Tank C Filter Cake

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 33/44 33/58

Claims (1)

[Claims] 1. A leaf type filter comprising a hollow shaft having a plurality of leaves mounted at predetermined intervals in a filtration tank, and a scraper for removing a filter cake provided in the vicinity of a filter net provided on the leaves. A filter cake removing method for removing a filter cake adhering to the filter net, wherein a stock solution to be filtered is introduced into the filter tank, and a precoat formed with a filter aid on the filter net. After the filtration step of filtering the undiluted solution by passing it through the layer from the leaf toward the hollow shaft and capturing the separated solid matter on the filtration net, it remains in the filtration tank. A residual liquid discharge valve for extracting liquid to the outside and a first stage for opening a first air introduction valve for introducing air into the filtration tank from the outside; and a residual liquid discharge valve. Leave it open Second air introduction valve for closing the air introduction valve is closed, and a second air introduction valve for introducing air from the outside to the inside of the leaf via the hollow shaft is opened. A method for removing a filter cake from a leaf type filter, comprising: