JPS589200B2 - Kagaku Pulp Seizou Niokeru - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides bleached wastewater that facilitates the recovery of pollutants in the bleached wastewater by removing most of the chlorine ions that promote metal corrosion from the bleached wastewater in the production of bleached chemical pulp. Concerning purification methods.

The general chemical pulp manufacturing method is as follows.

Wood chips are cooked with a chemical solution in a wooden pot while controlling temperature, pressure, time, etc. to dissolve the binding substances between wood fibers and leave pulp as a residue.

The pulp is first put into a blow tank from the wooden kettle, where large undigested materials are removed using a knot screen, and after cleaning, it is sorted using a screen to remove small undigested materials.

The black liquor from the cleaning process contains the cooking inorganic chemicals, primarily in the form of organic acids and salts, and the organic matter removed from the wood during cooking.

The recovery of black liquor is essential from the viewpoint of economics and pollution prevention, and the black liquor is concentrated to a solid content of 50 to 70% and burned in a recovery furnace to recover chemicals, steam, and power sources for electricity.

The selected pulp is subjected to a bleaching process to remove coloring impurities contained in the pulp fibers or to destructive bleaching to obtain pulp with a high level of whiteness.

The general bleaching method for chemical pulp is to first use a chlorine stage to make lignin soluble through chlorination, and then through water washing and alkaline extraction to remove most of the lignin. A small amount of remaining colored impurities is decomposed and removed using hydrogen oxide, etc., to whiten the pulp.

The wastewater from the alkaline extraction stage is blackish-brown in color with lignin eluates, and is the main source of pollution in the bleaching wastewater.

In the bleaching process of chemical pulp production using softwood wood as raw material, counter-current (recycle) the wastewater from the alkaline extraction stage to the chlorine stage is a method to eliminate alkali-soluble lignin in the wastewater after the alkaline extraction stage. is chlorinated wastewater (
It reacts with hydrochloric acid (pH 1.5-2.5) and precipitates, interfering with the subsequent bleaching process.

The present invention has found that when hardwood is used as a raw material, it is possible to counter-current the waste water from the alkaline extraction stage to the chlorine stage without any problem, and the waste water from the alkali extraction stage is diluted at the top of the chlorine tower and at the inlet vat of the washer. I learned that the amount of wastewater from the bleaching process could be greatly reduced by counter-current.

Conventionally, counter-current of wastewater from the chlorine stage of the bleaching process to the washing water of the unbleached raw material washing process has meant that soluble lignin from the wood in the black liquor is removed from the chlorine stage wastewater (pH 1.
5-2.5) The chlorine stage wastewater may react with the hydrochloric acid in the mixture and interfere with the bleaching process after precipitation, and the corrosion of equipment and equipment in the recovery process due to chlorine ions mixed into the diluted black liquor. Countercurrents were difficult.

However, the relatively small amount of afEJ dye wastewater collected in the washer after chlorination due to the countercurrent of the bleaching process, which is part of the present invention, is the gel-type anion resin which is another part of the present invention. By contacting with water, the wastewater is made alkaline and at the same time dechlorinated and ionized, counter-currented into the washing water of the washing process, and used as diluted black liquor or mixed with diluted black liquor obtained by conventional cleaning methods. This makes it possible to concentrate and burn the waste in the recovery process, thereby preventing pollutants from flowing into wastewater.

A description will be given of FIGS. 1 and 2 showing an example of application of the present invention.

However, this drawing does not limit the present invention in any way.

In Figure 1, the alkaline wastewater 14 from the alkaline extraction stage of the bleaching process is transferred to the top of the chlorine tower 2 and to the conduit 1 as dilution water for the washing machine 4 and the artificial vat.
The chlorine wastewater 11 from the washer 4 after chlorination is counter-currented through a conduit 12 as dilution water at the inlet of the chlorine stage.

Furthermore, in FIG. 2, a relatively small amount of surplus highly contaminated wastewater 13 from the chlorine stage is filtered through a sand filter 18 to remove suspended substances such as fibers, and then dechlorinated with a gel-type anion exchange resin 20, and then transferred to a conduit 2.
6, the water is heated in a heat exchanger 27, and is counter-currented as washing water 28 for the washing process.

If the ion exchange performance of the resin has decreased, use caustic soda 22
After being regenerated, the highly contaminated wastewater 13 is treated again.

In the washing process, the No. 2 washer 30 performs cleaning with the No. 3 washer filtrate 42, and the No. 1 washer 29 uses the No. 2 washer filtrate 41.
The No. 1 washer filtrate 40 is sent to a concentration step and a cooking step 52.

Example The present invention is a gel-type anion exchange resin to which the present invention is applied (
The explanation will be based on a treatment experiment of bleached wastewater using DIALON SA20A (manufactured by Mitsubishi Chemical Industries, Ltd.).

Bleaching process using gel-type anion exchange resin, treatment experiment results of chlor-alkali mixed white water

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the counter current between the chlorine treatment stage and the alkali extraction stage to which the method of the present invention is applied, and Figure 2 is the counter current to the decolorization purification and washing process of bleached wastewater to which the method of the present invention is applied. Systematic diagram showing. 1...unbleached chest, 2...chlorine tower,
3...Alkali tower, 4,5...Washing machine, 6-10...Pulp, 11...Chlorine waste water, 13... Highly contaminated wastewater, 14, 16...
... Alkaline drainage, 18 ... Sand filter, 19 ... Caustic soda tank, 20 ...
... Ion exchange resin cylinder, 21 ... Recycled waste liquid tank, 22 ... Caustic soda, 27 ... Heat exchange device, 28 ... Washing water, 29 - 31...
... Washing machine, 32-34 ... Filtrate tank, 3
5... Dilute black liquor tank, 36-39...
Pulp, 40-45...Filtrate, 46-50...
...Shower, 12, 15.23-26, 51.5
2... Conduit.

Claims (1)

[Claims] 1. In the bleaching of bleached chemical pulp made from hardwood materials, the process of using the washing waste water after the alkaline extraction stage installed following the first chlorine stage as a diluent for the pulp after chlorination, and This is a method of bleaching wastewater, which is characterized in that highly contaminated wastewater collected in a washing machine after chlorination is treated to remove chlorine ions using a gel-type anion exchange resin, and then finally concentrated and burned in a recovery process. Processing method.