RU2361026C1 - Method of mortar preparation for polysulfide wood cooking - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: method relates mortar preparation for polysulfide wood cooking and can be used in pulp and paper industry. Method is implemented by oxidation of white liquor by oxygen in saturater in mode of liquor recirculation at 70-90°C in the presence of black liquor in the capacity of catalystic additive. It is used saturater with tangential feed of liquor in it. It is outfitted by porous walls, separating its internal space for two longitudinal hollows. Oxygen is fed at one side of partitions and then into liquor through pores under pressure 0.3-1.4 MPa. Liquor is fed by the other side of partitions pressure for 0.04-0.06 MPa lower oxygen pressure.

EFFECT: oxidation duration reduction of white liquor.

3 cl, 1 dwg, 1 tbl

Description

The invention relates to methods for processing white sulfate liquor in order to obtain a solution for polysulfide cooking of wood and can be used in the pulp and paper industry.

A known method of preparing a solution of sodium polysulfide for cooking cellulose by dissolving elemental sulfur at elevated temperatures in oxidized white liquor (SU, No. 1326692, A1, IPC D21C 3/02, publ. 30.07.87). With a sufficient content of sodium hydroxide in white liquor and the consumption of elemental sulfur in an amount providing a molar ratio of sulfur to sodium hydroxide from 0.4: 1 to 1: 1, you can get a solution with a concentration of polysulfide (g / l in units of sulfur) 58, 3-60.1. The disadvantage of this method is that the addition of elemental sulfur to white liquor disrupts the balance of sulfur and sodium in the cooking solution, increases emissions of gaseous sulfur compounds into the atmosphere.

There is also known a method for producing polysulfide liquor, comprising treating white sulfate liquor with air in the presence of a heterogeneous catalyst. (RU, No. 2217538, C1, IPC D21C 3/02, publ. November 27, 2003) At an oxidation time of 10-15 minutes, the degree of oxidation of sodium sulfide, depending on the types of active component of the catalyst, the amount of catalyst and modifying additive, is 55 , 4-76.9% when the content of polysulfides in the oxidized liquor (g / DM ³ ) from 4.3 to 8.9.

The disadvantages of this technology are the high complexity and multi-stage manufacturing of the catalysts, the high cost of their components and, accordingly, the high cost of the actual process of preparing polysulfide liquor.

The closest in technical essence and purpose is a method for producing polysulfide solutions by oxidizing white sulfate liquor with atmospheric oxygen or pure oxygen using a small amount (0.5%) of black liquor as a catalytic additive (Novikova A.I., Makhover S.S., Butko Yu.G. Oxidation of white liquor with oxygen, Chemistry and technology of fibrous semi-finished products: Proceedings of the LTA named after S.M. Kirov; L., 1985, pp. 5-58). In this method, white liquor for oxidation is supplied from the tank to the saturator column with compressed air or a pump, and oxidation is carried out by bubbling air through a layer of liquor. Liquor at a temperature of 70-90 ° C circulates in the column until a 98-100% degree of oxidation of sodium sulfide is achieved. This value of the oxidation state of sodium sulfide of white liquor of the Svetogorsk PPM was achieved in 160-170 min of liquor treatment and in 90-95 min of liquor treatment of Segezha PPM.

The disadvantage of this method is due to the need for long-term processing of white liquor.

The technical result when using the present invention is to reduce the duration of the oxidation of white liquor.

The specified technical result is achieved by the fact that in the method of preparing a cooking solution for polysulfide cooking of wood by oxidizing white liquor with oxygen in a saturator in the mode of recirculation of liquor at 70-90 ° C in the presence of black liquor as a catalytic additive, according to the invention, use a saturator with a tangential feed lye into it, by porous partitions dividing its internal space into two longitudinal cavities, oxygen is supplied on one side of the partitions and then into the lye through their pores under a pressure of 0.3-1.4 MPa, and this pressure is 0.04-0.06 MPa higher than the pressure of the liquor supplied on the other side of the septum. Before serving in a saturator, a mixture of white and black liquor is subjected to purification by flotation and filtration. The liquor in the recirculation line and before selection for cooking pass through a layer of activated carbon.

Installation for the preparation of a cooking solution for polysulfide cooking includes elements required for any known method of oxidizing white liquor in recirculation mode. This is a supply tank for white liquor to be oxidized, high pressure pumps for feeding liquor to the oxidation and in the liquor recycling system, liquor heater, temperature regulator, saturator reactor, air or oxygen compressor, sampler, piping system and valves, etc. The main part of the installation is a saturator-reactor with internal space divided by porous partitions along the axis into two cavities, white liquor is supplied to one of them and oxygen to the other.

A top view of the cross-section of the saturator is shown in the drawing, where 1 is the saturator body, 2 are porous partitions, 3 are the fastenings of the sides of the partitions to one another, 4 is a cavity for white liquor, 5 is a means for tangential supply of liquor, 6 is a cavity for oxygen , 7 - means for supplying oxygen. The ratio of the scale of the parts in the drawing is not observed.

The saturator reactor can be located horizontally or vertically. The installation may also contain several saturators connected in series with the white liquor stream.

The method is as follows. 0.5% black liquor is added to the white liquor to be oxidized, the mixture is purified from suspended particles by flotation, followed by filtration of the clarified solution. This mixture enters the supply tank. Using the high-pressure screw pump, white liquor is supplied from the tank to the heater, where the temperature of the liquor rises to 70-90 ° С, and then it tangentially enters the outer cavity of the saturator 4.

In the central cavity 6 of the inner space of the saturator, oxygen is supplied by the compressor under a predetermined pressure.

The liquor is pumped into the saturator under a pressure of 0.3-1.4 MPa. This pressure is higher than that required to pump the liquor at the required speed through the entire recirculation system. The oxygen pressure in the saturator should be higher by 0.03-0.06 MPa liquor pressure.

The magnitude of the pressure drops between the cavities in the saturator and the size of the transport pores of the septum provide oxygen through it in the form of tiny bubbles, which are immediately washed off by a rotating stream of liquor, dissolved and react with sodium sulfide. The rotational movement of the liquor stream over the entire height (or length) of the saturator can be maintained by supplying an additional amount of liquor with tangential entry into the general stream through special nozzles. The solubility of oxygen in liquor is proportional to the pressure of the gas supplied to the apparatus, and the higher the liquor pressure is selected, the higher the oxygen pressure must be to ensure its transport through the septum, the higher the oxygen pressure at the outlet of the septum pores and, accordingly, the gas solubility in the liquor. If the above parameters are correctly selected, the speed of the overall process, including the stages of filtering through partitions and dissolving oxygen in the liquor, diffusing it into the volume of the liquor and the actual chemical reactions of oxygen with the components of the liquor, significantly exceeds the speed of a similar process when the liquor is saturated by bubbling oxygen into its volume.

The described process proceeds with the same intensity in the entire volume and along the entire height (length) of the saturator-reactor.

From the saturator, the liquor enters the filter loaded with activated carbon. In the filter, the sulfide oxidation process is accelerated due to the catalytic activity of the carbon material.

At the outlet of the filter, a liquor sample is taken to determine the concentration of sodium sulfide in it. At a concentration of this component above a predetermined value, the liquor passes through the recirculation line and, with the help of a high-pressure screw pump, passes again through the heater to the saturator. The heating of the liquor occurs according to the signal of the thermostat. The oxidation process of the first portion of the liquor proceeds in the recirculation mode of this entire portion until a predetermined degree of sulfide oxidation is achieved, for example, in the range of 75-80%. From this moment, a part of the treated liquor after the filter is continuously discharged to a storage tank of the finished polysulfide liquor continuously and at a certain volume rate and is sent from it to the wood for cooking. From the supply tank with the same volumetric speed, white liquor enters the saturator for processing, and the process is already in continuous mode.

To maintain the oxidation of white liquor with a certain initial concentration of sodium sulfide with optimal intensity in the automatic mode, it is advisable at the start-up stage to evaluate the degree of oxidation of sulfide in each liquor passage through the saturator at a certain volumetric rate, the optimal rate of oxygen into the liquor (without loss of oxidizing agent), the rate of recirculation of liquor to achieve a given degree of oxidation and, accordingly, to assess the acceptable amount of oxide removed from the system lye and fresh white liquor fed into the system.

The data in the table by examples illustrate the effectiveness of the use of the invention. For testing, white liquor was used with an initial concentration of sodium sulfide of 35.6 g / l. The process was carried out at a pilot plant containing 3 sequentially installed laboratory modules of saturator-reactors. At oxidation states in the ranges of 35–40, 55–60, and 75–80%, the selection of treated liquor was started with the simultaneous supply of an equal amount of fresh white liquor to the system. In steady-state conditions, the selection of liquor oxidized to a given degree can reach 20% of the volume of its recycled mass.

The test results of the oxidation of white liquor in the examples No. of examples Processing time, min The degree of oxidation of sodium sulfide,% The content of sodium polysulfide, g / l (in units of S) Oxygen pressure, MPa Differential pressure oxygen / liquor at the inlet to the saturator, MPa The ratio of recirculation, units The selectivity of the oxidation of sodium sulfide,% one 12 35-40 2.6 1.40 0,03 6 76,4 2 eighteen 55-60 4.6 0.85 0.04 9 78,2 3 26 75-80 6.6 0.30 0.05 fourteen 75.8

Claims (3)

1. A method of preparing a solution for polysulfide cooking wood by oxidizing white liquor with oxygen in a saturator in the mode of recirculation of liquor at 70-90 ° C in the presence of black liquor as a catalytic additive, characterized in that they use a saturator with a tangential flow of liquor into it, porous partitions separating its internal space into two longitudinal cavities, oxygen is supplied on one side of the partitions and then into the liquor through their pores under a pressure of 0.3-1.4 MPa, and the liquor is fed on the other side of the partition a pressurized to 0.04-0.06 MPa below the pressure of oxygen. 2. The method according to claim 1, characterized in that before being fed to the saturator, a mixture of white and black liquor is subjected to purification by flotation and filtration. 3. The method according to claim 1, characterized in that the liquor in the recirculation line and before selection for cooking pass through a layer of activated carbon.