FI58169B - FOERFARANDE FOER BEHANDLING AV FIBERSLAM - Google Patents

Description

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-¾¾ (45) Patent meddelat ^ ^ (51) Kv.ik? /Int.a.3 D 21 C 3/02 SUOMI — FINLAND (21) fwentdlwkmw-Newcwweimliif 773928 (22) HRicMnispflvi — Anaekntnf * tf «f 27 * 12.77 ^ ^ (23) AllnipUvt — GiM | h «cadag 27 * 12.77 (41) Tullut (ulkMcal - Bllvlt offumllg 28.06.79

Patent, and registered (44) Nttictvtktipunon j. kuLjullcMun p ™ .-

Patent · och ragltterttyralMn 'Amekan uthgd och utUkriftM puMicund 29 * 08.80 (32) (33) (31) ) (72) Esko Meloni, Helsinki, Finland-Finland (Fl) (7I +) Papula Rein Lahtela Oy (5 * +) Method for treating fibrous sludge - Förfarande för behandling av fiberslam

The invention relates to a process for treating a fibrous slurry containing mainly sulphite cellulose and / or mechanical pulp.

During the mechanical treatment of pulp and paper mill effluents, such as cleaning and clarification, a large amount of fibrous sludge is formed. The fibrous slurry usually contains 0.5 to 3% dry matter with the remainder being water. As such, the fibrous sludge forms a difficult waste problem, which has been solved by separating the dry matter contained in the sludge from the wastewater and by incinerating the sludge. In order to further treat the sludge, its dry matter content usually has to be raised to 20 to 30 pounds and, if the sludge is to be incinerated, even to 30 to 1 + 0) 2. This means that more than 90% of the sludge is dewatered. Filters, presses or centrifuges are used to remove water.

Some of the fibrous sludge is easy to handle mechanically, while some sludges leach very poorly and the dry matter content of the treated sludge remains low. Difficult to handle are especially sulphite mills and mechanical pulp, i.e. sludges containing groundwood and / or millet. Perhaps the most important cause of poor permeability has been found to be the fines contained in the sludge, above all the pa-. regeneration cells and the hemicellulose, pectin and resin contained therein. In addition to poor permeability, the fines contained in the fibrous sludge retain more water than the fibers, which lowers the dry matter content of the sludge achievable in dewatering.

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Several alternative methods are currently known for treating fibrous sludge containing fines that cause processing difficulties. Alternatively, the fines are separated from the rest of the slurry by conventional sorting methods, such as sieves or centrifugal separators. In this case, although the separation is easily feasible, the treatment of the fines-containing fraction constitutes an even more difficult problem.

Furthermore, the fibrous sludge can be burned in the so-called by a wet incineration process in which the organic matter or part of it contained in the sludge is oxidized under elevated pressure and heat. w

In the patient into carbon dioxide and low molecular weight organic compounds. However, this method requires relatively high equipment investments, which makes sludge treatment expensive. ~

A method for chemically treating a fibrous slurry is further known, wherein the slurry is extracted with sodium hydroxide to reduce the hemicellulose and pectin content of the slurry. The method can improve the leachability of the sludge, instead it does not affect the dry matter content of the filtered sludge. This method is also relatively expensive and poses new problems for cleaning and reusing chemicals.

It is an object of the present invention to obviate the above drawbacks and to provide a new method for treating fibrous sludge. The features of the invention are set out in the claims.

According to the invention, the fibrous slurry is boiled by a conventional cooking method, suitably with chips. In cooking, the organic and inorganic fines contained in the fibrous slurry enter the cooking solution and leave the cooking solution with the cooking solution, black liquor, for evaporation, incineration and chemical recovery. At the same time, the fibrous material contained in the fibrous sludge is recovered as the fibrous material enters according to the pulp. In this case, the constituents contained in the fibrous slurry are recovered, the fibrous matter with the pulp and the rest with the black liquor. In particular, the recovery of fibrous matter is of great importance in improving its yield; at present, the amount of fibrous material that has become entrained in the fibrous sludge may be as high as tens of tons per day in some mills, which is mainly recovered using the process according to the invention.

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The process according to the invention can usually be carried out by means of equipment already existing in the pulp mill, te. no special accessories are usually required to implement the method.

Furthermore, the waste problem caused by the fibrous sludge can be eliminated by the method according to the invention in a simple and inexpensive manner. The waste generated in the process, the fines of the fibrous matter dissolved in the black liquor, is recovered in the context of conventional chemical recovery and regeneration.

The process according to the invention is mainly concerned with the treatment of effluents containing sulphite mills, grinders, grinders and newsprint mills and, in general, wood processing mills containing fibrous sludge. Usually, the ✓ fibrous sludge separated from the mill's wastewater contains 0.5 to 3.0% dry matter, in which case the waste must be dewatered before the fibrous sludge is treated. The separation of the fibrous slurry can be carried out, for example, by filtration, compression or centrifugation. , even beyond this.

The method gives the best results when the fibrous slurry contains more than 50% t suitably more than 60% fiber. The suitability of the fibrous slurry for treatment with the process according to the invention also depends on the amount of inorganic substance, such as fillers, contained in the fibrous slurry. The fibrous slurry to be treated may suitably contain 0 to 20% of inorganic material, preferably less than 10%. Of course, more fibrous slurries containing up to 50% inorganic matter can also be treated by the process according to the invention, in which case, however, the increased amount of inorganic dung in the black liquor causes difficulties in the further processing of the liquor. The method can also be advantageously applied to the treatment of mixed sludges which contain not only fibrous material but also bark. The shell can account for up to tens of percent of the dry matter of the sludge to be treated, up to 50%. However, the total amount of crust in the cooking should not exceed 5%, preferably more than 3%.

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When cooking the fibrous slurry by an alkaline cooking method such as the sulfate method, the fibrous slurry is suitably cooked with the chips. The weight ratio of fibrous slurry to wood chips is suitably 1: 100 to 1: 1, preferably 1: 100 to 1: 5. If desired, the amount of fibrous slurry can also be higher up to 75% * up to 100 J5, in the experiment performed the fibrous slurry was boiled by the sulphate method as such.

If desired, the fibrous slurry can, of course, be added to the alkaline soup in any small amounts, e.g. less than 1%.

The percentages given in the specification and claims mean - percentages by weight on a dry matter basis.

The invention is described in detail below by means of exemplary embodiments.

i 1 ·

Example 1.

The compressed waste sludge from the sulfite pulp mill was boiled by an alkaline cooking method in a 15 L digester in the manner of conventional sulfate cooking. No wood chips or other wood was added to the soup. The results are shown in Table 1. It can be seen from the results that the fines and ash contents of the sludge decreased, in addition, the leachability of the sludge improved significantly. The resin content of the slurry decreased to less than 0.3%, the WRV decreased close to the normal WRV value of the sulfate slurry, and the infiltration resistance fell to one-fifth of the original. The fines content was about the same as before cooking, but as the amount of ingredients in the cooking was halved, the amount of fines was reduced in the same proportion.

Since the infiltration resistance of the sludge changed substantially despite the fact that the fines content remained essentially unchanged, it is obvious that the water retention and dewatering properties of the sludge depend above all on the chemical composition, carbohydrate, resin and lignin content of the fines.

Example 2.

The compressed waste sludge from the sulphite pulp mill was boiled by a conventional sulphate method as in Example 1, with pine chips being added to the soup. The amount of fibrous slurry from the total amount of cooked material was 25 Jt, 50%, 75% and 0% in the control sample. The results are shown in Table 2.

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Table 1. Effect of sulphate cooking on sulphite sludge properties.

_Sludge before cooking Boiled sludge

Ash content,% 3.81+ 1 +, 77 SR number (Schopper number) 81+ 29 7

Specific leaching resistance, cm / gx10 270 55 WRV value,% (water retention capacity) 223 '109 (uncertain) DCM extract,% (dichloromethane extract) 7.21 · 0.28 ^ Number of pieces 71 * 3 12.6

Bauer-McNett sorting: - + 10 JC 5.5 '2.8 + 1 * 8% 31.5 38.2 + 100%. . 11.5 1.3 + 200% 10.0 IU, 3-200% H1, 3 1 + 3.1 +

Yield,% 55.7

O

CED viscosity, cnr / g 620

Table 2. Waste sludge cooking with wood chips.

Koe no. Sludge,% Wood chips. % Kappa number Yield. % Ash. % 1,100 0 13.7 55.7 Ml 2 * 75 25 21.6 '1 + 1.7' 1.6 3 50 50 52.0, 1 + 25 75 3l +, 7> 5.3 · 1.1 5,000 1 + 1 +, 8 .1 + 5.3 0.8

The invention is not limited to the embodiments shown, but its applications may vary within the scope of the appended claims.

Claims (6)

58169 6 A method for treating fibrous sludges from sulphite pulp mills, grinders, mills and / or newsprint mills, characterized in that the fibrous sludge is boiled by an alkaline cooking method known per se. Method according to Claim 1, characterized in that the fibrous slurry contains at least 50% of fibrous matter. Process according to Claim 1 or 2, characterized in that the fibrous slurry contains less than 20% of inorganic matter. ~ Method according to one of Claims 1 to 3, characterized in that the fibrous slurry is boiled with the chips. Process according to Claim 4, characterized in that the weight ratio of fibrous slurry to wood chips is 1: 100 to 1: 1, preferably 1:20 to 1: 5. Process according to one of Claims 1 to 5, characterized in that the fibrous slurry is fed to the alkaline cooking at a dry matter content of 5 to 30%, suitably 15 to 25%.