RU2349695C1 - Method of preparing pulp water from carton-paper manufacturing for its repeated use - Google Patents

Abstract

FIELD: chemistry; textiles; paper.

SUBSTANCE: pulp water is sequentially processed with a coagulant - N,N - poly-dimethyl - N¹,N¹ - di-allyl-ammonium chloride and flocculant - anionic polyacrylamide with the subsequent separation of the solid phase from the pulp water by floatation. Processing of pulp water is carried out with the relation of the coagulant to the flocculant from 1.3:1 to 6.7:1, predominantly from 2.6: to 4.0:1. Separation the solid phase from pulp water is carried out with the concentration of suspended materials 1000-2000 mg/dm³.

EFFECT: increase in the degree of purity of pulp water, prepared for its repeated use, decrease in the dry solid content of the cleaned water, removing the need of constantly regulating the pH of the cleaned water.

4 cl, 3 tbl, 3 ex

Description

The invention relates to a technology of partial closed water circulation in paper and cardboard production, in particular to methods for preparing recycled water from paper and cardboard production for its reuse.

A known method of purification of fiber-containing wastewater from suspended solids, including the introduction of aluminum sulfate, flotation agent and polyacrylamide, followed by separation of the sediment by flotation.

According to this method, N, N, N ¹ , N ¹ -tetrakis (2-hydroxyethyl) -1,4-diaminobutin-2 are used as flotation reagent. In this method, polyacrylamide and floreagent are administered at a ratio of 1: (0.5-2.0), respectively (1).

There is also a similar method for purifying fiber-containing wastewater, according to which ammonium salts of monoethanolamine are used as flotation reagent (2).

However, according to these two known cleaning methods described, they can be carried out only in a static mode, while the coagulation and flotation stages in them are separated in time, which is difficult to use under industrial conditions, that is, in a dynamic mode, and the flotation reagents used are unique, since they are obtained in laboratory conditions.

There is also known a method for purifying process waters containing suspended matter and oil, including the introduction of a flocculant, according to which a non-stoichiometric complex of polydimethyl diammonium chloride and the product of the condensation of oleic acid with diethanolamine and sulfuric acid amino ester is introduced as a flocculant, after which the process water is subjected to aeration. According to this method, the amount of flocculant is 0.4-5.0 g per 1 m ^{3 of} process water (3).

The separation of the solid phase from water is carried out in this method by precipitation and aeration, which indicates a relatively low strength of coagulation structures, that is, in a turbulent water flow with a decrease in the efficiency of water purification by suspended solids.

The operation of water purification is assumed in this method also in static mode, that is, with known concentrations of suspended solids and optimal flocculant consumption for a given concentration of suspension. With varying concentrations of suspended solids, it is necessary to constantly change the flow rate of the flocculant, which is difficult to implement in practice. In addition, due to the fact that the reactions of the formation of polyelectrolyte complexes are cooperative in nature, it is rather difficult to organize the synthesis of such complex compounds under industrial conditions while maintaining constant properties. Thus, the efficiency of water purification from suspended solids in this method is an unstable value.

The closest analogue to the proposed method described below is a method for preparing recycled water for paperboard production for reuse, including treating the recycled water sequentially with a coagulant and flocculant - anionic polyacrylamide, followed by separation of the solid phase from the recycled water by flotation (4).

According to this method, aluminum chloride hydroxide is used as a coagulant.

This method is quite effective, however, the process is highly dependent on the pH values of the water to be treated, due to the conditions of hydrolysis of the aluminum salt, which requires constant regulation of pH values. In addition, the hydrolysis of aluminum salts proceeds over time, which leads to the separation of the process into stages of coagulation and flocculation, separated by 30-100 sec. This circumstance complicates the flotation process in a production environment. The use of aluminum salts leads to an increase in the mineralization of the treated water, which reduces the number of water cycles of purified water and, naturally, to a decrease in the degree of water purification.

A disadvantage of the known method is also the difficulties associated with the selection of a selective flocculant that provides wetting hysteresis, that is, firmly fixing the wetting perimeter of polydisperse particles that are heterogeneous in chemical composition.

This leads to a relatively low efficiency of the flotation process, requiring a change in the operating mode of the flotator: the consumption of flotation reagent and / or saturated liquid phase, as well as regulation of the pH values of the treated water.

A new positive result from the use of the present invention is to increase the degree of purification of recycled water prepared for its reuse, to reduce the solids content in the treated water, as well as eliminating the need for constant adjustment of the pH of the purified water.

This positive result is achieved by the fact that in the method of preparing recycled water for paperboard production for reuse, comprising treating the recycled water sequentially with a coagulant and a flocculant — anionic polyacrylamide, followed by separation of the solid phase from the recycled water by flotation, according to the invention, NN- is used as a coagulant polydimethyl N ¹ , N ¹ diallylammonium chloride, and the treatment of the circulating water is carried out at a ratio of coagulant to flocculant from 1.3: 1 to 6.7: 1.

The treatment of recycled water is carried out with a ratio of coagulant to flocculant mainly from 2.6: 1 to 4.0: 1.

The separation of the solid phase from the circulating water is carried out by pressure flotation. The separation of the solid phase from the circulating water is carried out at a concentration of suspended solids 1000-2000 mg / DM ³ .

The authors of the present invention found that a high cationic charge and a relatively low degree of polymerization (10000-1000000), cationic polyelectrolyte (coagulant - N, N polydimethyl N ¹ , N ¹ diallylammonium chloride) increases the likelihood of its direct interaction with the hydrophilic surface of cellulose fiber with its recharge even in the turbulent flow mode of the processed dispersion on the reagent supply line. This, in turn, determines the efficiency of the electrostatic interaction of the anionic flocculant (anionic hydrolyzed polyacrylamide with a degree of polymerization of the order of 5-7 · 10 ⁶ ) with the cellulose fiber surface modified as a result of adsorption of the indicated cationic polyelectrolyte. As a result of this interaction, through the cooperative bonding of polycation segments with polyanions, surface interpolyelectrolyte complexes (IPEC) are formed, which form the surface properties of the fibers.

When the ratios of the starting (beyond the indicated ratios of coagulants to flocculant) polyelectrolytes are changed, when they are mixed, either non-stoichiometric water-soluble or stoichiometric water-insoluble IPEC are obtained. When IPEC nanolayers are fixed on the surface of cellulose fibers, their hydrophilic-hydrophobic characteristics are regulated to a level that provides wetting hysteresis necessary for efficient removal of fibers in the flow of air bubbles, i.e., in pressure flotation mode.

The invention is further illustrated by specific examples of its implementation in laboratory and industrial conditions.

Example 1. In a graduated cylinder with a capacity of 1 dm ³ under laboratory conditions, 1 dm of circulating water with a concentration of suspended solids of 1400-1500 mg / dm ^{3 is} placed. The reverse water is sequentially treated first with a coagulant N, N-polydimethyl N ¹ , N ¹ diallylammonium chloride of the Floquat FL 4540 trademark (Flocate) with a concentration of 4 g / dm ³ , and then the flocculant is hydrolyzed weakly anionic polyacrylamide of the Flopam AN 934SH trademark ( Flops) with a concentration of 1 g / dm ³ . After the introduction of each reagent, the contents are mixed by turning the graduated cylinder.

Then pressure flotation is carried out to create gas bubbles in the suspension, a solution of hydrogen peroxide with the addition of a decomposition catalyst is added, or hydroperite powder is used. The decomposition of the reagent leads to flotation, that is, suspended solids are concentrated in the form of sludge in the upper part of the cylinder, and the circulating water is purified.

The results of the analysis, the costs of the coagulant and flocculant, as well as their ratios are presented in table 1.

Example 2. Preparation of recycled water for cardboard and paper production is carried out analogously to example 1, but using the flotator of the cardboard and printing plant of St. Petersburg "Poseidon Saturn" company "Kandant Lomort" with a productivity of 500-600 m ³ / h.

The reagents indicated in Example 1 (sequentially coagulant and flocculant) are fed to the flotator on the reagent supply line to the feed pipe of the purified circulating water before mixing with the saturated fresh water. The consumption of coagulant is 0.3 kg / t of products, and the consumption of flocculant is 0.09 kg / t of products.

Data on the effectiveness of the treatment of recycled water are presented in table 2.

Example 3. The preparation of recycled water is carried out analogously to example 2 during January-November 2007 in order to assess the reliability and stability of the flotator, statistical data confirming the significance of the proposed method are presented in table 3. In addition, with a decrease in the content of suspended solids, the salt content in the circulating water by an average of 13% (according to the values of electrical conductivity of the treated water).

From tables 1 and 2 it is seen that the proposed method can significantly increase the degree of purification of the purified circulating water and reduce the solids content in the purified water. In addition, it can be seen from the examples that the proposed method eliminates the need for constant regulation of the pH of the purified circulating water.

Information sources

1. SU, 1368266, A1, publ. 01/23/1988

2. SU, 1573004, A1, publ. 06/23/1990

3. RU, 2162445, Cl, publ. 01/27/2001

4. RU, 2158327, Cl, publ. 10.27.2000, the prototype.

Table 1 Way The concentration of suspended solids in the purified circulating water, mg / DM ³ The consumption of reagents, mg / DM ³ Coagulant to Flocculant Ratio The concentration of suspended solids, mg / DM ³ The degree of purification,% Coagulant Flocculant anionic polyacrylamide According to the prototype 1520 thirty 5 6.0 156 87 Proposed 1500 twenty 3 6.7 60 95.9 1500 16 3 5.3 62 95.8 1500 12 3 4.0 52 96.5 1500 8 3 2.6 70 95.2 1500 four 3 1.3 90 93.9 1400 8 5 1,6 45 96.8 1400 8 four 2 65 95.4 1400 8 2 four 60 95.7

table 2 Fiber flotation method Flotator productivity, m ³ / hour Flocculant Coagulant Ratio - Coagulant: Flocculant The concentration of suspended solids, mg / DM ³ The cleaning efficiency,% The degree of purification filter.,% Consumption,
m ³ / hour Conc.
g / dm ³ Consumption,
m ³ / hour Conc.
g / dm ³ Flotator Entrance After flotator After filter After flotator After filter Proposed 566 0.84 2,3 1.37 4.0 2,8 1414 42.5 28.1 97.0 98.0 33.9 560 0.89 2.13 1.39 2.46 1.8 1337 41.2 40.1 97.0 96.9 2.7 536 0.86 2.5 1.40 2.10 1.4 1590 59.8 43,4 96.2 97.3 27.4

Table 3 Months of testing Coagulant consumption, kg / t Flocculant consumption, kg / t Coagulant / Flocculant Ratio Concentrated suspended solids in recycled water,
mg / dm ³ , (average) Concentration of suspended solids after flotation mg / dm ³ , (mean value) The cleaning efficiency,% the pH of the circulating water, (medium values) pH of water after flotation, January 2007 0.24 0,065 3.69 2131 68.8 96.8 7.30 7.24 February 0.23 0.09 2,56 1736 48.3 97.2 7.48 7.45 March 0.25 0.08 3.13 1645 42.5 97.4 7.42 7.41 April 0.30 0,068 4.41 1587 45.0 97.2 7.66 7.48 May 0.28 0,072 3.88 1647 42.1 97.4 7.50 7.32 June 0.25 0,085 2.94 1413 36.6 97.4 7.52 7.27 July 0.25 0,094 2.69 1510 41.7 97.2 7.38 7.25 August 0.27 0,088 3.07 1501 28.3 98.1 7.45 7.43 September 0.24 0,080 3.00 1545 40,2 97.3 7.43 7.49 October 0.3 0,098 3.06 1301 39.7 96.9 7.41 7.52 November 0.3 0.09 3.33 1477 49.5 96.6 7.50 7.51 Average value 0.26 0,083 3.13 1590 43.9 97.2 7.46 7.40

Claims (4)

1. A method of preparing recycled water for paperboard production for reuse, comprising treating the recycled water sequentially with a coagulant and flocculant — anionic polyacrylamide, followed by flotation of the solid phase from the recycled water, characterized in that N, N-polydimethyl- coagulant is used N ¹ , N ¹ -diallylammonium chloride, and the treatment of the circulating water is carried out at a ratio of coagulant to flocculant from 1.3: 1 to 6.7: 1. 2. The method according to claim 1, characterized in that the treatment of circulating water is carried out with a ratio of coagulant to flocculant from 2.6: 1 to 4.0: 1. 3. The method according to claim 1, characterized in that the separation of the solid phase from the circulating water is carried out by pressure flotation. 4. The method according to claim 1, characterized in that the separation of the solid phase from the circulating water is carried out at a concentration of suspended solids 1000-2000 mg / DM ³ .