RU1773270C - Closed water circulation method for production of cellulose and board - Google Patents

Abstract

SUMMARY OF THE INVENTION: Recycled water is collected, which is formed at all obligatory stages of sulphate pulp and cardboard manufacture, after which the total runoff is subjected to chemical and biological treatment and divided into two streams with a concentration of the mineral part of 1.5-4.8 g / l and the content of sulfate ion in it is 50-65%. One purified stream is returned to the pulp and paperboard production, and the second is fed to the stage of washing chips, pulp and caustic sludge, and the spent washing liquids are fed to the stage of evaporation and regeneration together with the spent liquor from sulphate cooking

Description

The invention relates to methods for the disposal of wastewater, in particular pulp and paperboard production.

Various methods are known for a maximally closed water use system, offering the return of the main amount of wastewater to the process and the discharge of residual wastewater into water bodies after preliminary treatment.

A drawback of these methods is the presence of wastewater discharge containing a large amount of dissolved mineral salts.

There are also known methods of closed circulation of pulp and paper production, including the stage of demineralization by evaporation, ion exchange or reverse osmosis

The main disadvantage of the known methods requiring large capital expenditures is the presence of a discharge of regenerative wastewater

The closest tax of the proposed method is a closed-circuit method of pulp and paperboard production, including the collection of recycled water from the stage of production of sulfate pulp and the manufacture of cardboard with the formation of a common runoff, its chemical and biological treatment and its separation into two streams with a concentration of the mineral part of 1.5 -4.8 g / l and its content of sulfate ions 50-65%, one of which is returned to the pulp and paperboard industry.

In this case, in the known method, the second part of the purified total runoff in an amount of 10% is sent to a discharge into a water body, and deodorized condensate of the brewhouse in evaporation stations is used in the washing stages of chips, pulp and sludge treatment

The disadvantage of this method is the discharge of wastewater containing 1.5-4.8 g / l of mineral salts and other pollutants.

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substances. At the same time, up to 1200 kg per hour of useful salt, sodium sulfate, goes into the runoff.

An object of the invention is to prevent the discharge of wastewater while utilizing sodium sulfate from recycled water.

The essence of the invention lies in the fact that in the closed-loop water circulation method of cellulose-carton production, comprising the collection of recycled water from the stages of the production of sulfate pulp and the manufacture of cardboard with the formation of a common drain, its chemical and biological treatment and its separation into two streams with a concentration of mineral part 1, 5-4.8 g / l and with a sulfate ion content of 50-65% in it, one of which is returned to the pulp and paperboard production, the second stream of purified general runoff is fed to the washing stage of wood chips, pulp and house izatsi- onnogo slurry and the spent wash liquid is fed to the evaporation step and regeneration together with spent liquor from the kraft pulping. In this case, an excess portion of said mineral salts is removed by collecting dust particles from the resulting flue gases.

The method is implemented as follows: recycled water is collected from the steps of washing the chips, its alkaline cooking, washing the sludge, and also the steps of making cardboard, and biological and chemical treatment of this waste water collection is carried out.

Then, purified wastewater characterized by the following basic characteristics; suspended solids - 4 mg / l, VPK - 2.5 mg / l 02, mineral concentration of 1.7 g / l and sulphocationite content of 58%, are divided into two streams, one of the streams is sent to cellulose cardboard production, sent it to seal glands, cooling industrial equipment, floor washing, washing equipment.

After recycling facilities that have passed the biological and chemical treatment stage, another recycled water stream is demineralized by supplying it to the main production, instead of deodorized condensate and hot water. In addition, over 75% of the volume of the stream goes to pulp washing and up to 25% -for washing chips and caustic sludge. The salts contained in this stream are recovered in a chemical recovery system together with spent sulphate liquor and are used in production.

After washing the chips, the water goes through its reverse use cycle for washing, and part of it, together with the chips, enters the digester.

To wash the pulp, chemically purified water from the treatment plants enters the heat exchanger, where it is heated with condensates from the evaporation stations, then it is fed to the accumulator tank of the cooking department, and from there to the washing station. After washing the mass, the washing water, together with the black liquor taken from the mass, enters the evaporation shop.

Part of the water from the accumulator tank is also sent to the washing of sludge from the lime causticization and regeneration workshop, to a quencher classifier in a vacuum filter and to white liquor clarifiers. After that, part of the water is used to prepare white liquor and then to chip production.

Thus, in the course of the above operations, demineralization of recycled water through the regeneration of chemicals occurs.

Salts contained in the treated wastewater (over 90% consisting of sodium sulfate) are washed through chips, pulp, lime and green sludge by evaporation and, together with one stripped off black liquor, are sent to incineration boilers and returned to the production plant with fusion from the boilers cycle for the preparation of white liquors, replenishing the loss of salts. Excess salts arising in the system due to the use of acidic reagents to neutralize the pulp and paperboard and wastewater treatment plants are removed in a dry form after being trapped on electrostatic precipitators of soda recovery boilers. At the same time, the quality of the washed cellulose i.e. permissible concentration of mineral salts in the water used does not exceed 4.8 g / l.

The use of purified total flow, mg / l:

BPKG

COD

weighted

mineral

sulfate

aluminum

phenols

sulfur containing

methanol

oil products

2.4 61 4.0

2.0 g / l 1200 O

0.008 0.2 0.2 0.005

the main production at the stages of washing chips, pulp and caustic sludge does not cause negative

changes in the work of the plant, and the quality of the finished product remains at the existing level,

In addition, when implementing the proposed method, the consumption of sodium sulfate is reduced from 1200 to 40 kg per ton of pulp produced, with the further complete exception of introducing fresh salt into production

Claims (1)

SUMMARY OF THE INVENTION A method for closed circulation of pulp and paperboard production, including collecting recycled water from the stages of preparation of sulfate pulp and the manufacture of cardboard with the formation of a common 0 5 runoff, its chemical and biological treatment and separation into two streams with a concentration of the mineral part of 1.5-4.8 g / l and a content of sulfate ion of 50-65%, one of which is returned to the pulp and paperboard production, distinguishing so that, in order to prevent the discharge of wastewater while sodium sulfate is being recycled from the recycled water, the second stream of purified recycled wastewater is fed to the washing stage of wood chips, cellulose and caustic sludge, and the spent washing liquid is fed to the evaporation and regeneration stage together with spent liquor from sulphate cooking.