RU2099455C1 - Method of producing cellulose for chemical processing - Google Patents

Abstract

FIELD: pulp- and-paper industry. SUBSTANCE: wood material is passed through hydrolysis, alkali digestion, and diffusion washing zones in continuous digesting apparatus. In the diffusion washing zone, hot refining and cellulose delignification are performed. EFFECT: enhanced efficiency of process.

Description

 The invention relates to the pulp and paper industry and can be used in the production of cellulose for chemical processing in continuous apparatuses of the Kamur type, having a diffusion washing zone.

 A known method of producing cellulose for chemical processing in continuous plants of the Kamur type, including the preliminary steam hydrolysis and pulping in one cooking apparatus [1] Between the hydrolysis and cooking zones there is a hydrolyzate selection zone, which allows the hydrolyzate to be taken through sieves before the hydrolyzed wood chips arrive into the cooking zone.

 White sulfate liquor is dosed in the upper and lower parts of the cooking zone, and part of it is spent on the neutralization of the acidic products of the hydrolyzate and is taken together with the hydrolyzate through the sieve selection hydrolyzate. This achieves a decrease in the amount of insoluble compounds of lignin and carbohydrates ("caramel") deposited on the sieves of the selection zone of the hydrolyzate.

 In the lower part of the cooking apparatus there is a zone of diffusive washing of the mass by the filtrate of the washing stations and a device for unloading cellulose from the boiler.

 Despite the advantages of this method, high productivity, low steam consumption, the experience in the production of cellulose for chemical processing during its implementation in Kamur devices was unsuccessful. The main difficulties in cooking pulp for chemical processing by a known method are associated with the operation of the hydrolyzate selection zone. When the hydrolyzate is mixed with white liquor in this zone, “caramel” is formed, which is deposited on the hydrolyzate screening screens, as a result of which their throughput decreases, the uniformity of the movement of the mass column in the digester is disrupted, and the cellulose quality indicators for chemical processing decrease. Due to clogging of the hydrolyzate selection sieves with “caramel”, continuous operation of the cooking plant becomes impossible due to the need to empty it and mechanically clean the sieves.

 The aim of the invention is to obtain cellulose for chemical processing with high and stable quality indicators without compromising productivity and forced equipment shutdowns.

 This goal is achieved by the fact that alkaline cooking of cellulose is proposed to be carried out in the zones of hydrolysis and cooking, and hot refinement and additional delignification of cellulose in the zone of diffusion washing of a continuous cooking plant of the Kamur type.

 The method can be implemented as follows. Technological chips made from hardwood come from the chip storage to the conveyor, with the help of which it is poured into the chip bin. From the hopper, the wood chips enter the metering funnel, from which it is transferred by the low pressure feeder to the steaming chamber. The steamed chips with the screw of the steaming chamber are fed into the feeding pipe and then to the high pressure feeder, from which it is transported via the loading pipe to the upper separator of the digester. White liquor is pumped into the digester. Cellulose is cooked in the hydrolysis and cooking zones.

 The diffusion washing zone is used for hot refinement and additional delignification of viscose pulp by supplying white liquor with a concentration of active alkali of 50 ± 10 g / l from the filtrate tank of the washing section. Strong black liquor is taken through the lower sieves of the cooking zone to the upper evaporation cyclone, the self-evaporation pairs of which are used for steaming chips, and the cooled black liquor is sent through the lower cyclone to the evaporation station. To cool the mass before unloading, the spent white liquor from the filtrate tank of the washing unit is fed to the lower part of the digester.

 The pulp is discharged into a blow tank, from where it goes to sorting, washing and to the bleaching workshop.

The proposed method for the production of cellulose for chemical processing allows to obtain unbleached pulp with the following quality indicators (data from the laboratory of mechanical tests):
Exit from wood 40-42%
The content of α-cellulose 94.0-95.0%
The degree of delignification of 4-6 units of Kappa
Viscosity 18.0-25.0 MPa • s
The increased degree of delignification of cellulose after cooking and hot refining allows to use viscose pulp with 90% whiteness and the required stable quality indicators without using molecular chlorine during bleaching according to the D-Shch-D scheme. Cellulose is environmentally friendly because it does not contain dioxins and other toxic chlorine compounds.

Claims (1)

 A method of producing cellulose for chemical processing in a continuous cooking apparatus by passing wood raw materials through zones of hydrolysis, alkaline cooking and diffusion washing, characterized in that in the diffusion washing zone, hot refinement and delignification of cellulose is carried out to dissolve hemicelluloses and residual lignin.