A method of obtaining a bleached kraft pulp

 

(57) Abstract:

The inventive water vapor and odorous substances are separated from the hot black liquor by cooling the latter in the evaporation cyclone, mixed with the pulp slurry and oxidant at the stage oxygen-alkali delignification of unbleached pulp or oxygen-alkali delignification with the addition of hydrogen peroxide or oxidizing be chlorinated pulp. Implementation of the proposed method allows to reduce the consumption of steam as the neutralization pornopanda substances, and to reduce its consumption in the bleaching of pulp. When this is achieved a high degree of neutralization of odorous substances by oxidation to non-toxic and non-volatile oxygen derivatives of sulfur. table 2.

The invention relates to the production of bleached fibrous semi-finished and can be used to obtain bleached Kraft pulp for various purposes in the cooking apparatus of periodic action.

A method of obtaining cellulose, including boiling the pulp in the apparatus of periodic action, filler mass in the blow tank, washing, and bleaching the cellulite, tighten the high temperature and pressure (160-170aboutWith and 0.6-0.6 MPa). In the process of blowing intense boiling of the liquid in the blow tank, accompanied by release of water vapor and toxic substances (mercaptan dimethyl sulfide, dimethyl disulfide and others) in the atmosphere even when using install heat recovery type "Rosenblad". In addition, during the blowing occurs mechano-chemical degradation of cellulose, and when forced outages digester with the obtained pulp by weight deteriorate its mechanical properties due to the slow decrease of the temperature.

Closest to the technical nature of the invention is a method for bleached Kraft pulp in the cooking apparatus of periodic action, including the cooking of cellulose, the displacement of the hot black liquor, unloading cooled mass with steam, air or pump and the bleaching of pulp [2].

The known method has two significant weaknesses. First, for cooling extruded from the digester black liquor use spiral and tubular heat exchangers closed, pressure of 0.5-0.7 MPa. It is required to reduce the temperature of the black liquor 150-170 up to 80-90aboutWith that uslojnyaet the deposits. In the heat exchanger is inevitable contamination of the inner surfaces of the deposits of mineral salts and organic substances, which requires periodic cleaning. Secondly, formed during cooking odorous and toxic compounds with extruded and cooled black liquor coming to evaporation in the process of being transferred into the secondary steam condensate and in the atmosphere. For disposal of contaminated condensates requires a complex and energy-intensive to install their separation by distillation with water vapor, collection, transportation and incineration.

The aim of the invention is to increase process efficiency by reducing the consumption of steam for the cooking and bleaching of pulp and residue liquor, prevent emissions of VOC while maintaining quality indicators cellulose, as well as simplification of the system heat recovery hot black liquor.

This is achieved by the fact that in contrast to the known method of producing sulphate pulp extruded from the digester, hot black liquor is sent to the evaporation cyclone for its cooling and separation of water vapor from volatile broadnose substances that guide in the installation of oxygen-Selo is Orada or oxidative be chlorinated pulp.

The implementation of this method allows to increase by 1.5-2.0% (absolute) solids content black liquor sent to the residue (equivalent to savings of 7-8% of steam consumption per residue), separated from the black liquor up to 92% volatile odorous compounds and almost completely oxidize them to non-toxic and non-volatile oxygen-containing sulfur compounds (sulfite, sodium thiosulfate and others) at the stages of oxygen-alkali delignification of cellulose or oxidative be. The obtained filtrate after oxygen-alkali delignification can be used for washing of unbleached pulp.

In addition to the neutralization of odorous compounds proposed method allows the use of heat, water vapor formed during samosatene black liquor, during oxygen-alkali delignification of unbleached pulp or oxidative be chlorinated mass.

P R I m e R 1. Boiling cord pulp with preliminary water hydrolysis of wood chips made from pine wood, is carried out in a laboratory autoclave with a volume of 5 l equipped with electric heating and forced circulation system according to the following mode. The hydrolytic water ratio and su is aboutWith 80 minutes After extraction of the hydrolysate in the autoclave download white and black liquor to the desired water ratio and spend sulphate cooking: the consumption of alkali - 18,5% (unit Na2O), impregnation when 130aboutC - 30 min, temperature rise from 130 to 170aboutS - 60 min, Parking at 170aboutC - 90 min

In order to simulate the process by a known method using three cooking autoclave. In the first autoclave are boiling, after which the hot black liquor to a temperature of 170aboutTo displace warm black liquor temperature 70about(Autoclave N 2) in the autoclave N 3 using nitrogen gas as long as the temperature in the autoclave 1 pulp mass does not reach the 90aboutC. Then the hot black liquor temperature 155aboutServed with from the autoclave N 3 in evaporative cyclone. Pair samosatene black liquor from the cyclone is directed to the cooling and collecting in a container with a volume of 2 liters via direct water cooler. By gas chromatography to determine the content of the most toxic component of odorous gases - methylmercaptan in the condensate and cooled black liquor. The obtained experimental data show that upon evaporation of 1.1 m3water vapor per 1 ton of the Zell is Aptana - the most dangerous of which is formed with a single-component vapor-gas emissions. In the latter case, this would amount to about 91.8% of the total number found in the liquor after cooking.

P R I m m e R 2. Boiling cord pulp is carried out in conditions similar to those specified in example 1. Forced out of the autoclave 1 in the autoclave 3 hot black liquor is sent to the evaporation of the cyclone. Formed in the cyclone of water vapor samosatene together with broadnose compounds fed into the reactor with unbleached cord cellulose. Then the reactor is pumped oxygen and carry oxygen-alkali delignification according to the following mode: the concentration of the pulp 8.0%, lye concentration of 2.5%, temperature 70aboutC. Processing the mass is performed under oxygen pressure of 0.15 MPa for 60 minutes, then the reactor pressure is reduced to atmospheric and maintain the pulp mass within 150 minutes a content Analysis of odorous volatiles in the vapor condensate of samosatene black liquor and filtrate after oxygen-alkali delignification carried out by gas chromatography. Data on the degree of neutralization of VOC after stage oxygen-alkali delignification presented in the chlorination with the addition of ClO2;

SCHO2- oxidative bucking;

D - treatment with chlorine dioxide;

G - treatment with sodium hypochlorite;

To treatment with the aqueous solution SO2.

P R I m e R 3. Boiling cord pulp is carried out in conditions similar to those described in example 1. Pair samosatene black liquor is served on the stage oxygen-alkali delignification of unbleached cord pulp with the addition of hydrogen peroxide. The consumption of H2ABOUT2is 5 kg per 1 ton of pulp.

The results of the analysis and the degree of neutralization of the odorous substances are presented in table.2, column 4.

Dabelko cord pulp is carried out by the scheme: X/D - SCHO2- D - G - K.

P R I m e R 4. Boiling cord pulp is carried out in conditions similar to those described in example 1. Pair samosatene displaced from the digester black liquor together with broadnose volatile compounds is sent to the reactor before carrying out oxidative be chlorinated pulp. Conditions of oxidative be: concentration of pulp 8% , the concentration of alkali 3.0%, temperature 70aboutC. Processing the mass is performed under oxygen pressure of 0.25 MPa for 60 min, then the pressure in the re

Data quality indicators pulp after stage oxygen-alkali delignification (AMD) and oxidative be (SL2) are presented in table. 1.

Indicators cord pulp unbleached: 95,0% Kappa; Of 29.5 MPa. The results demonstrate that the addition of volatile components with pairs of samosatene black liquor when bleaching does not lead to deterioration in quality cord pulp.

The results of the analysis and the degree of neutralization of the odorous substances are presented in table.2.

Dabelko cord pulp is carried out by the scheme: X/D - SCHO2- G - d - D - D - K.

Received cord pulp after bleaching with the addition of vapor samosatene black liquor and VOC no significant differences compared with cellulose, bleached without vapor samosatene and all indicators of the quality meets the requirements of GOST 16762-82 "Cellulose sulfate prehydrolysis for cord yarns and high-modulus fibers".

Thus, implementation of the proposed method in contrast to well-known not only to avoid the consumption of steam for the disposal of odorous substances, but also to reduce its consumption in the bleaching of pulp. what I mercaptan) by oxidation to non-toxic and non-volatile oxygen derivatives of sulfur.

A method of OBTAINING a BLEACHED Kraft PULP, including periodic cooking of cellulose, the displacement of the hot black liquor, cooling it in the evaporation cyclone separating water vapor and odorous substances and the bleaching of pulp, characterized in that, to prevent emissions of odorous substances and increase process efficiency while maintaining quality indicators derived cellulose, water vapor and odorous substances separated from the extruded hot liquor, served on the stage of pulp bleaching and mixed with the pulp slurry and oxidant at the stage oxygen-alkali delignification of unbleached pulp, or oxygen-alkali delignification with the addition of hydrogen peroxide, or oxidative be chlorinated pulp.

 

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