JPH05179592A - Dehydration and washing of pigment sludge - Google Patents

Abstract

PURPOSE:To improve the dehydration efficiency in the dehydration and washing of a sludge composed mainly of pigment with a precoated filter. CONSTITUTION:In the dehydration and washing of a sludge composed mainly of pigment with a precoated filter, a sludge containing coarse pigment particles is dehydrated to form a cake, a sludge containing fine pigment particles is sprinkled on the cake and the cake is subjected to dehydration and washing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dewatering and washing method in which sludge containing a pigment as a main component is subjected to dewatering and washing with a precoat type filter, and particularly, dewatering efficiency is improved.

[0002]

2. Description of the Related Art Dewatering and washing treatment of pigment sludge has been carried out in various technical fields, and in the paper pulp industry, it is as follows in the cooking process of kraft pulp (hereinafter simply referred to as "KP"). Have been implemented in.

In the kraft pulp (hereinafter simply referred to as "KP") cooking method, an aqueous solution containing caustic soda and sodium sulfide as main components (this solution is generally called "white liquor") is added to wood chips packed in a digester. And steam to obtain pulp.
At this time, lignin, resin, a part of cellulose, etc. in the wood are decomposed and eluted into white liquor to become a cooking waste liquid (this liquid is generally called "black liquor").

In the KP method, soda and sulfur are recovered from this black liquor to produce white liquor again. That is, the black liquor is concentrated and burned, and the smelt (inorganic high temperature melt) produced is dissolved in a weak liquid (dilute alkaline water-soluble generated in the washing step described later) to dissolve green liquor (sodium carbonate). And water-soluble) whose main component is sodium sulfide).

When quicklime is added to this green liquor to cause a causticizing reaction, sodium carbonate becomes caustic soda and quicklime becomes calcium carbonate. This sludge containing calcium carbonate as the main component is washed (a weak liquid is generated here) and dehydrated,
It is burned again to form quicklime and used in the causticizing process.

A precoat type filter has been used for a long time as a dehydrating and washing apparatus for sludge containing calcium carbonate as a main component. In this device, the pigment sludge is deposited and filtered on a wire surface stretched on the surface of a drum-shaped cylinder. Specifically, instead of adopting a method of removing the sludge accumulated from the wire surface at the same time while dehydrating and washing the pigment sludge,
Currently, a base cake (precoat) layer of pigment sludge is formed on the wire surface, a new cake layer is formed on it, and the base cake part is left as it is for each revolution of the drum. The method is to scrape off only the formed cake layer with a doctor.

However, the conventional dewatering and washing method employs a method of dewatering and washing the sludge of the coarse pigment and the sludge of the fine pigment as they are, so that the precoat layer is immediately formed. Clogging causes poor dewatering efficiency. For this reason, there is a problem that the water content of the scraped cake becomes high. The higher the water content of the cake, the more adversely it affects the baking efficiency of the cake baking process. For this reason, under the conventional method, it was necessary to remove the precoat layer once to three times a day to renew it.

In a filter which requires renewal of the precoat layer 1 to 3 times a day, the condition is bad for 2 to 8 hours a day. Even if the efficiency is improved, the precoat layer must be renewed several hours after that, which makes stable operation impossible.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a method for efficiently treating fine particle sludge and coarse particle sludge with a precoat type filter without dehydration and washing. The purpose is to

[0010]

[Means for Solving the Problems] In a method of dehydrating and washing sludge containing a pigment as a main component with a precoat type filter, sludge of coarse pigment is first dehydrated to form a cake,
Further, it is a washing / dehydrating method using a pre-coat type filter, characterized in that sludge of fine pigment is further sprinkled on it for dehydration washing.

[0011]

[Function] When sludge containing a pigment as a main component is dehydrated and washed, and when coarse pigment sludge and fine pigment sludge are mixed, the sludge is divided into coarse pigment sludge and fine pigment sludge. A precoat layer is formed from sludge of coarse pigment, and sludge of fine pigment is sprinkled on the precoat layer for dehydration cleaning. By doing so, it becomes possible to improve the dehydration efficiency.

A method of separating the sludge containing a pigment as a main component into a sludge of a coarse pigment and a sludge of a fine pigment is, for example, when the sludge of the coarse pigment and the sludge of the fine pigment are in a mixed state, water sludge is set. The law can be adopted. By this method, it is divided into upper and lower layers of water,
The coarse pigment sludge of the lower layer portion can be supplied to the vat of the precoat type filter, and the dilute slurry of the upper layer portion containing many fine particles can be sprinkled on the outermost layer of the precoat layer.

Further, when the sludge containing a pigment as a main component is originally divided into sludge of a coarse pigment and sludge of a fine pigment, it may be carried out according to the method of the present invention as it is. In the present invention, the sludge accumulated on the precoat filter is not removed completely, but a new cake layer is formed on the preformed precoat layer to remove the sludge from the drum. The base cake portion remains unchanged after each rotation, and only the newly formed cake layer is scraped off with a doctor.

In the present invention, all the sludges containing a pigment as a main component can be dehydrated and washed by the precoat type filter, but all sludges cannot be described here. In particular, the dehydration cleaning of sludge containing calcium carbonate as a main component, which is generated by adding quick lime to green liquor generated in the cooking process of kraft pulp to cause a causticizing reaction, will be described.

[0015]

EXAMPLES FIGS. 1 and 2 show dehydration washing of sludge containing calcium carbonate as a main component, which occurs when causticizing reaction is caused by adding quick lime to green liquor in the KP method to produce white liquor as a cooking chemical. Then, after crushing this with a cage mill,
It shows a route to react with green liquor again.

The present invention is carried out by dewatering and washing with the precoat type filter in the figure. As for the mechanism of dehydration and washing with the precoat type filter, a precoat type filter is used as shown in FIG. In this device, the pigment sludge is deposited and filtered on a wire surface stretched on the surface of a drum-shaped cylinder.

Specifically, the method of removing the sludge accumulated from the wire surface while removing the sludge from the wire surface while removing the sludge from the wire surface is not adopted, but a base cake (precoat) layer of the pigment sludge is formed on the wire surface. Forming,
A method is used in which a new cake layer is formed thereon, the base cake portion is left as it is for each revolution of the drum, and only the newly formed cake layer is scraped off by a doctor.

The above-mentioned sludge containing calcium carbonate as a main component is generally a coarse pigment sludge in which pigments having a particle size of 10 μm or more account for 95% by weight or more of all pigments.
It includes fine pigment sludge in which pigments having a particle size of μm or less account for 20% by weight or more of all pigments. When this pigment sludge is washed and dehydrated with a precoat type filter, fine calcium carbonate is separated from the sludge in advance, and coarse calcium carbonate sludge composed of relatively large particles is first introduced into the filter vat and then placed on the filter drum. Form a cake.

Then, by the rotation of the drum, the surface of the filter drum immersed in the liquid phase of the vat moves to the air layer side, so that the cake is dehydrated and concentrated. After that, the fine calcium carbonate slurry that had already been separated was
Sprinkle on the surface of the cake. In such a filter cake configuration, the particles of the base cake layer are large, and the fine particles sprinkled afterwards form the cake on the outermost side, so it is difficult for fine calcium carbonate to penetrate to the inside of the cake. ..

Then, a new cake layer is formed, and the base cake portion is left for each rotation of the drum, and only the newly formed cake layer is scraped off by a doctor. Since the newly formed cake layer is immediately removed from the drum, there is no clogging and the underlying precoat layer having extremely high dehydration efficiency remains.

Therefore, according to the method of the present invention, there is little clogging of the precoat layer which is the underlying cake layer, and the renewal time is much longer than in the conventional case, and it is renewed once every 2 to 3 days. I can drive now. Note that burning waste gas generated in the process of firing calcium carbonate in a kiln and calcium carbonate scattered by a gaseous fluid such as air are trapped by a filter, sprinkling water, etc., and sprayed directly on the outermost layer of the precoat layer. Then, the present invention can be implemented.

[0022]

The effect of the present invention is obtained by subjecting sludge containing a pigment as a main component to dewatering and washing, sludge of coarse pigment and sludge of fine pigment are separated, and a pre-coat layer is formed in advance with sludge of coarse pigment, and then fine pigment is formed thereon. Since the sludge is sprayed for dewatering and cleaning, it is possible to enhance the dewatering efficiency and, in turn, the related operability.

[Brief description of drawings]

FIG. 1 is a pre-coating method of the present invention in which sludge containing calcium carbonate as a main component is produced when a quick lime is added to green liquor in the KP method to cause a causticizing reaction to produce white liquor as a cooking chemical. After incorporating a dehydration cleaning method with a filter to perform dehydration cleaning, and crush this with a cage mill,
It is explanatory drawing which showed the path | route made to react with a green liquor again.

FIG. 2 is a conventional method of dehydrating sludge containing calcium carbonate as a main component, which is generated when white liquor as a cooking chemical is produced by adding quicklime to green liquor in the KP method to cause causticization reaction. It is explanatory drawing which showed the path | route which makes it wash | clean, grind | pulverizes this with a cage mill, and makes it react again with green liquor.

FIG. 3 is an explanatory view showing a pre-coat type filter unit for carrying out the method for dehydration and washing of pigment sludge of the present invention.

Claims (4)

[Claims] 1. A method of dehydrating and washing a sludge containing a pigment as a main component with a precoat type filter, wherein sludge of a coarse pigment is first dehydrated to form a cake, and sludge of a fine pigment is sprayed on the sludge. A method for dehydration cleaning with a pre-coated filter, which is characterized in that 2. The sludge containing a pigment as a main component is a sludge of calcium carbonate produced by a reaction between calcium oxide and green liquor produced from the calcium carbonate firing step of the causticizing step in the kraft pulp manufacturing step. The dehydration cleaning method according to claim 1. 3. The coarse pigment sludge comprises pigments having a particle size of 10 μm or more, which account for 95% by weight or more of the total pigment.
And the method for dehydration cleaning in the precoat filter according to 2 above. 4. The fine pigment sludge comprises pigments having a particle size of 10 μm or less in an amount of 20% by weight or more of the total pigment.
And the method for dehydration cleaning in the precoat filter according to 2 above.