CS196645B1 - Sealed pulp bleaching process - Google Patents

Description

Czechoslovak Socialist Republic DESCRIPTION FIXED TO COPYRIGHT CERTIFICATE 196645 (11) (Bl) (22) Enrolled 03 11 76 (21) (PV 7091-76) (51) Int. Cl 3 D 06 L 3/06 (40) Published 31 07 79 OFFICE AND DISCOVERY OFFICE (45) Published 15 11 81 (75)

Author of the invention SCHMIED Jozef ing. CSc., GAJDOS Jan ing., HAVRANEK Jaroslav ing., "KUBELKA Vaclav dr. ing., BÚCHLER Pavol ing., KLANDUCH Jozef ing., Bratislava and NĚMEC Milan ing., Vratimov (54) Close-up bleaching of pulp 1

BACKGROUND OF THE INVENTION The present invention relates to a process for the close bleaching of pulp, wherein the bleaching agent regeneration and the combustion of organics dissolved from the pulp in a bleaching process are addressed. The invention is applicable to all types of unbleached pulps (sulphite, sulphate) and to any of the bleaching steps. However, the condition is the use of chlorine or its compounds in the bleaching process and the use of alkaline extraction.

DoSia! In particular, the pulp pulp bleaching systems are open, that is to say they work with fresh chemicals which are brought to the end of the bleaching process with the extracted organic matter of the effluent while the dissolved organic substances cause the biological and chemical oxygen demand of the effluents, Inorganic chemicals, among which sodium chloride predominates, form a desirable salinity of wastewater. At the same time, the triochemical is a great economic stratagem. S Compared to bleaching, the production of unbleached pulp is much more advanced. Complete regeneration systems allow water circuits to be completely closed. Thus, in a modern cellulose, the open source is the main source of the defective waste water. Whites have the need to build investment and pre-build. expensive biological wastewater treatment plant.

Therefore, new systems are being sought in which the bleacher is integrated into its own production of unbleached pulp so that the wastewater drains are poorly used and the water in washing machines of unbleached pulp is used. somewhere their organic fraction burns. The chlorine compounds are then removed from the recycle by suitable methods. However, these integrated systems are demanding on the construction material due to the corrosion resistance of recirculating chlorides and the large control requirements.

There are also proposals for separately evaporating and burning waste water from the bie-liar. Since they work in addition to chlorine and its compounds also with sodium hydroxide, in particular sodium chloride, considerable difficulties are encountered in the coupling of thickened bleach waters. The main cause of this is the low melting point of the chloride sodium, which is further reduced by rime purity, especially sodium sulphate. This undesirable precipitate is produced by lignin-bound oxidisers in unbleached pulp.

The above mentioned drawbacks have been eliminated by 196643 by the method of closed bleaching of pulp of the invention, which is based on the introduction of a magnesium auxiliary circuit which serves to regenerate ammonia used for the alkali extraction of pulp instead of sodium hydroxide and for the regeneration of chlorine with the disposal of waste organics by incineration.

The magnesium circuit begins with the preparation of magnesium hydroxide, the suspension of which is brought into contact with the hot waste water of the bleacher. In the non-neutralization of these acidic waters, the hydroxide exudes magnesium ammonia from the ammonium salts. The recovered ammonia is returned to the alkaline extraction stages of the bleacher. The magnesium circuit, which now contains magnesium chloride and dissolved organic matter, is condensed to allow solution pyrolysis. Concentration can be converted, for example, in a multi-stage contact vaporizer (multi-flash, or hyperfiltration (reverse-osmosis)) The thickened solution comes into the pyrolysis where the organic substances which dissolve from the pulp during the bleaching process are burned, and the chlorine bound thereto is converted into hydrogen chloride. The thermal pyrolysis deficiency is covered by oil or gas oil, and the magnesium sulphate, which is contained in the concentrated solution due to the oxidation of sulfur bound to the lignin in the pulp, is reduced to sulfur dioxide and magnesium during pyrolysis. closes the magnesium circuit from the pyrolysis to enter the magnesium hydroxide, where it is hydrates at 90 DEG-95 DEG C. The flue gases from the pyrolysis are condensed to form a concentrated solution of soda acid. The undesirable sulfur dioxide does not dissolve the salt acid and leaves the flue gas, e.g., the sulfur dioxide absorption system of the pulp mill. Saline is used for direct manufacturing chemicals. Chlorine dioxide for bleaching is obtained by the known reaction of sodium perchlorate with sodium chlorate. The chlorine ether is produced from hydrogen chloride by catalytic oxidation. Thus, the chlorine ring is closed in the laundry plant.

Small losses of chlorine and magnesium, due to the leakage of the production equipment or absorption to the pulp, can be covered by the hungry waste magnesium chloride at the same time; This substance is fed to the thickened waste leaders prior to the entry of the dopyrolysis.

The solid impurities are separated from the closed system after the neutralization by the waste leader with magnesium hydroxide. Dissolved impurities such as sodium and potassium salts, sulphates, are removed from the circuit by washing magnesium oxide before entering the hydration.

By closing the bleach according to the invention, the suction lube separates into two separate closed cycles. The first cycle consists of the production of non-bleached cellulose with the regeneration of delignification chemicals, the second cycle of bleaching plants with the regeneration of bleaching chemicals. Advantage .tohoto. the way is that the plant does not jeopardize the equipment or the work of the machines in the production of unbleached cellulose and does not complicate the control of the pulp mill. Conversely, the staple fiber dampens the defects in the bleached pulp and destroys the non-wastes from the brewing together with the substances dissolved from the pulp during the bleaching process. Thus, no waste water is removed from the pulp mill which would require biological or chemical cleaning.

Regeneration of the bleaching chemicals of the invention prevents wastage of expensive raw materials and at the same time deprives the pulp mill of the problem of waste management that exists in existing ones. Bleached pulp factories are unsolvable, even if they operate biological and chemical cleaning. The advantage of the method of closed bleaching according to the invention is also the coverage of the chlorine and magnesium losses by the magnesium chloride waste. The high amount of this substance remains as a heavy waste after the production of potassium chloride from the carnality. Dissolved impurities that convert the magnesium chloride waste, the sealed binder system, can easily remove the magnesium oxide scrubber.

In the accompanying drawing, an example of a flow diagram enclosed by the invention is shown. Bleaching is a five-degree blot with grades C E D E D.

The pulp of the unbleached cellulose enters the end of the press 1a from the reactor 2, where it is treated with chlorine gas from the production of chlorine and chlorine dioxide 13. The non-chlorinated cellulose reactor 2 is washed in the press 3 with water coming from 6. The pulp extract extract is separated from the second extraction step E2 in washing machines S to which water enters the extractor 4, where it is treated with ammonium from the ammonia regeneration. The pulp then proceeds to the first chlorine dioxide stage 6 and discharges the filter 7 to other stages of the bleaching process, e.g. j. to the second extraction and second chlorine dioxide stages (not shown in the drawing).

Extraction in the first and second extraction stages is carried out with ammonia. Ammonia regenerates from the combined extract that leaves the scrubber 3 to recover ammonia 8. Regeneration of the ammonia with magnesium hydroxide which is prepared by the hydration of magnesium oxide 13. Magnesium hydroxide is added to the recovery tank 8 in excess to expel the ammonium hydroxide. of the alkali extract was as high as possible. Ammonia-depleted ammonia

Claims (3)

Excess magnesium hydroxide does not neutralize the solids, including the free sulfuric acid. Solid impurities solidify separation of neutralized solution in separator 9. Purified solution from separator 9 arrives at multi-stage contact evaporator 10, where it is concentrated to 30%, and flowed to pyrolysis: 11. The condensate condensate from evaporator 10 is used to wash magnesium oxide, e.g. on the other hand, for washing the pulp from the last bleaching plant (not shown in the drawing). The condensate is already produced in the evaporator system 10, whereby volatile organic substances are released which are fed to the regenerating pulp mill where they are burned. The soluble impurities are extracted from the crude magnesium oxide on the working filter 12, in particular sodium sulfate and sodium chloride and potassium chloride. P R E D Μ E T 1. The bleaching process of the bleaching agent by regenerating bleaching chemicals and slagging dissolved organic matter is characterized in that it comprises an auxiliary magnesium circuit in the bleaching system, consisting of neutralizing waste whitewater and displacing ammonia with magnesium hydroxide at 60-90 ° C , further from the thickening and pyrolysis of neutralized bleaching water, in which dissolved organic substances are burned and the magnesium chloride formed is neutralized by a known reaction to magnesium oxide and hydrogen chloride, whereby the fume gases from pyrolysis 11 go into condensation HCl 14, where a concentrated hydrochloric acid is formed, while the sulfur dioxide-containing flue gases leave the sulfur dioxide uptake in the pulp mill. The hydrochloric acid is boiled into chlorine production and chlorine dioxide. chlorine for reactor 2 by catalytic oxidation of hydrogen chloride. The chlorine dioxide for chlorine dioxide is prepared by reacting the hydrochloric acid with the sodium chlorate solution. Sodium chloride formed by the reaction is re-oxidized to chlorate in electrolysis 16. The ammonia losses are covered by liquid ammonia supplied to the bleach shop in cis- teres. The loss of chlorine and magnesium is covered by the magnesium chloride chloride from the potassium chloride production from the carnality. Magnesium chloride waste comes to the bleach plant in a 30% solution in tanks. The invention, after hydration to magnesium hydroxide, is recycled to neutralize the bleaching water hydrogen chloride is used to produce chlorine and hydrogen chloride by known reactions. 2. The cellulosic whitening method according to claim 1, wherein the loss of chlorine and magnesium is simultaneously covered by the magnesium waste chloride, which is pyrolyzed and decomposed therein to MgO and HCl. 3. The cellulose bleaching process of claim 1, wherein the undesirable accompanying impurities are removed from the magnesium circuit by washing with magnesium oxide from the pyrolysis with water. mtz h 25 81-657