DE2417084A1 - ENVIRONMENTALLY FRIENDLY PROCESS FOR THE PRODUCTION OF WHITE SULPHITE PULP - Google Patents

Description

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O: ■■,; “';: ·.,! S. April 1074

241708 A

Siuko Taavi Paavali

ENVIRONMENTAL PROCESS FOR THE MANUFACTURING OF WHITE SULPHIO PULP

The process is used in the manufacture of bleached sulphite material when using calcium, magnesium or ammonium as a cooking base, both Einais Adapted multiphase process and acidic, neutral or alkaline cooking. The purpose of the process is that caused by the known manufacturing process remove harmful impurities.

In the known manufacturing methods for bleached suIfitzel1.stoff leave three sewage fractions that are significant in terms of environmental pollution, the system. The most common is the so-called Loss of washing, of that part of in the Boiling of dissolved matter consists in the following after the pulp washing Sorting is flushed into the circulation water and that of the pulp washing could not be recovered or which it was not worth recovering. The second main traction consists of the liquor recovered from the incineration evaporation resulting evaporation condensate. With this leaves A significant part of the volatile substances in the waste liquor make up the system, including organic Acids, alcohols, etc. The third waste water fraction, which is highly damaging to the environment, goes

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from the known systems from the waste water of the bleach, i.e. the freezing rate of the Washes between or part of the bleaching stages. Usually this contains Filtrate that follows after the first bleaching stage, usually the chlorination stage Laundry comes out, most of the heavily colored, dissolved in the bleaching process Lignins. But the filtrate of the first alkaline extraction stage, especially in the manufacture of soft fabrics, just as harmful in terms of contamination Have the same effect as the chlorination filtrate, because the latter is relative is low. The pollution effects of the mentioned waste water fractions are usually limited to the following:

chemical ■ biochemical

Oxygen demand Oxygen demand kg KMnO, / t cell st. kg BOD ₅ ct cell st.

Loss of washing 100 ... 600 15 ... 40

Evaporation condensate 150 ... 400 20 ... 60

Bleaching waste 30 ... 100 15 ... 40

Total 280 ... 1100 50 ... 140

At the technical level, there are numerous methods for reducing these Pollution effects. It is characteristic of these methods that the removal or purification of a single waste water fraction is a noticeable investment demands or even exceed the operating costs of the economic potential.

With the method described here, all of the polluting effects mentioned can be achieved can be largely eliminated at low cost. la certain cases can the sugar process bring about a reduction in operating costs and the need for investment to pipeline changes to be carried out as part of normal maintenance limit.

Closing the cellulose manufacturing process and directing all dissolved Substances for the recovery and incineration of the waste liquor by arranging the process flows vegetable based on the countercurrent principle, has been around for a long time among experts known destination. The chlorine compounds used in pulp bleaching Caused risk of corrosion for the equipment, due to the accumulation of chlorine compounds in the chemical circulation and the drop in the melting point of the waste liquor incineration The ashes produced by the action of the sodium used in the alkali extraction have created a number of obstacles that have been described as insurmountable.

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In this process, the system is closed according to the countercurrent principle Removal of the mentioned obstacles achieved as follows:

The washing loss gets into the water by closing the water cycle the "sorting" prevents. Loss of washing is carried along with the pulp to the bleaching plant and, in the case of washing, after the first Bleaching stage, by returning the excess of this filtrate for sorting and on to pulp washing, recovered. The effectiveness of the Laundry is done according to the consumption of bleach and not according to the value of the Waste liquor optimized, as is the case now.

- The polluting effect of the bleaching waste water is eliminated or reduced limited by circulating at least the filtrate after the first bleaching stage following washing for dilution and sorting in such a way that for sorting and further washing of said filtrate the same amount as washing liquid the bleach is passed to this intermediate wash. Wastewater leaving the system In any case, the bleach does not arise from this first intermediate wash and the washing loss from the wash after boiling also decreases with the filtrate for recovery. In most cases, the return is already reduced of the filtrate from the first bleaching stage to the laundry, the wastewater pollution with approx.

■ 75 "L and the share of washing losses disappears completely. Depending on the situation, the countercurrent principle can be extended over the entire bleaching plant, always up to thickening and drainage.

If you want to extend the Oegenstrom principle beyond the chlorination stage, the admission of sodium into the waste liquor during the alkali extraction is prevented, as well as with alkaline oxygen pre-bleaching, if this is used, by replacing the sodium base with another one from the point of view of waste liquor incineration less dangerous base, for which ammonium is mostly suitable. When using magnesium as a cooking base, it is especially useful for oxygen bleaching justified for economic reasons to use magnesium, which here can partly be taken from its own recovery plant.

- The enrichment of the chlorine compounds in the chemical circulation can be simple, by separating off the hydrochloric acid that occurs in the flue gases from the waste incineration Chlorine, before the actual recovery of the sulfur dioxide, using known methods, can be prevented. The hydrochloric acid can i.a. removed so that they can be sucked into the water in an absorption system let, where the great difference between the partial pressure of hydrochloric acid and the Sulfur dioxide the absorption of hydrochloric acid without significant sulfur dioxide losses enables. In the ordinary calcium sulphite process, without sulfur recovery, It is of course not necessary to remove the chlorine, but the hydrochloric acid goes off with the flue gases.

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The occurrence of chlorine corrosion is inherently obvious, especially with evaporation the waste liquor, the pH being always low during evaporation and the temperature usually high, especially in the thick liquor stage. In practice has been noted, particularly in the soda pulp mills on the west coast North America, in whose chemical circulation due to the sea transport of the wood, Chloride is enriched, so that the chloride corrosion per se is not insurmountable Problem when the pH of the liquor is high. With, this procedure the experience mentioned is used and the lye is neutralized before evaporation. The neutralization can, depending on the prevailing temperature, the pH and the chloride strengths, either at one or at several points in the process be carried out and also either all at once or in stages, being particularly the fact that the ammonia remains in the lye makes its own demands on the choice of the neutralization method. In the production of by-products from sulphite waste liquor due to the fermentation process, a slight neutralization is now carried out, which in this process after fermentation in connection with the evaporation can expediently be completed with ammonia and also for Part of the commonly used neutralizing agent, calcium carbonate, with ammonia can also be replaced before fermentation, with the ammonia at the same time also acts as nutrition and the deposition of plaster of paris on the heating surfaces of the Evaporation plant decreases. In all cases, neutralization with Kochbase started and completed with ammonia, or ammonia alone can be used for this.

The polluting effect of the evaporation condensate is caused by the aforementioned. Neutralization significantly reduced. It has long been known that the neutralization of the waste liquor in connection with the evaporation binds the organic acids as salts in the waste liquor, whereby the distillation of the acids mentioned in the evaporated liquor is prevented. In this way, depending on the case, a reduction of 30 ... 70 "L of the biochemical oxygen requirement is achieved for the evaporation condensate. By dividing the condensates in a known manner into different fractions and by separating those fractions into which the other volatile organic compounds such as methanol, furfural, etc. are enriched, and by returning this fraction, which usually also contains a noticeable amount of sulfur dioxide, to the process, preferably for the production of cooking liquor, the polluting effect of the evaporation condensate can be almost completely eliminated belongs that the volatile substances mentioned are removed from the chemical cycle, for example by distillation, from the exhaust gas condensate in which they accumulate naturally.

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Claims (6)

Claims 1. Environmentally friendly manufacturing process for bleached sulphite pulp, characterized, that the preparation of bleached pulp, laundry, sorting, etc. in a closed system where the washing liquid is countercurrent flows, and where wastewater from the bleach is used as washing liquid, is carried out and - that the chlorine compounds are removed from the chemical circulation, in that the chlorine leaving the waste gas as hydrochloric acid from the flue gases using known methods before . Sulfur dioxide recovery is separated. ". 2. The method according to claim 1, characterized in that the caustic effect of the chlorine compounds in the waste liquor is prevented after the neutralization of the waste liquor, at the latest in connection with the evaporation. 3. The method according to claim 1 or 2, characterized in that to include alkali extraction when expanding the countercurrent principle, the sodium base in the extract clay by one from the point of view of the waste liquor incineration harmless other base is replaced, e.g. ammonium, magnesium or a mixture of these two. 4 .. Process according to claims 1, 2 or 3, characterized in that that when alkaline oxygen bleach is used, the usual sodium base is replaced by another base which is harmless from the point of view of the combustion of the fumes e.g. ammonium, magnesium or a mixture of the two. 5. The method according to claims 1, 2, 3 or 4, characterized e t that the production of by-products from sulphite waste liquor with the help of a fermentation process a, by neutralizing the waste liquor even before the fermentation process is made possible, with the ammonium possibly used for neutralization at the same time also acts as nutrition. 6. The method according to claims 1, 2, 3, 4 or 5, characterized η e t that if recovery of the sulfur compounds from the flue gases fails takes place, one can also rely on the separation of the chlorine compounds from the exhaust gases do without and let this go off with the flue gases. A098A3 / 0871
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