RU2244774C1 - Method for production of magnesium-based bisulfite cooking liquor for cellulose manufacturing - Google Patents

Abstract

FIELD: pulp-and-paper industry, in particular cellulose production.

SUBSTANCE: sulfur dioxide is brought into reaction with magnesia raw material (e.g. cake brucite ) with grade of 50-600 mm and initial pH 1.5-2.5. Process is carried out up to pH 2.8-3.5 and content bonded sulfur dioxide 47.0-49.5 % followed by separation of exhaust gas from solution. One-step process is carried out at 70-90⁰C.

EFFECT: method of improved processibility due to decreased number of process steps.

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Description

The invention relates to the field of the pulp and paper industry and can be used in the manufacture of pulp made from fibrous semi-finished products using bisulfite cooking solutions on a magnesium base.

A known method of producing a bisulfite cooking solution on a magnesium base for the production of cellulose, including countercurrent interaction of sulfur dioxide (sulfur dioxide - SO ₂ ) with magnesia raw material - ground brucite in an aqueous medium and separation of the exhaust gas from the solution (SU, 367204, D 21 C 3 / 10, 1973). At the same time, in a known manner, a bisulfite cooking solution is obtained with a content of bound SO _{2 of} 50-55% of the total amount of sulfur dioxide. The known method is carried out in one step in two successively installed devices at pH> 5.0.

To implement the known method, it is necessary to grind brucite, leading to dustiness of the atmosphere. In addition, the method is energy-intensive and is accompanied by severe erosive wear of the equipment, and the sulfur content in the sludge is 12-20%.

There is also known a method for producing a bisulfite solution on a magnesium base, including the interaction of sulfur dioxide with magnesia raw material - lump brucite with a particle size of 50-600 mm at pH = 1.5-2.5 to a proportion of the bound sulfur dioxide content of 40-45%, separation of the processed gas and subsequent processing of the resulting solution to a pH of 3.0-5.0 and a proportion of bound sulfur dioxide of 47-55% (RU, 2149231 C1, D 21 C 3/10, 11/02, 05/20/2000).

The method is carried out in two stages. At the first stage, an acidic solution is obtained with a predetermined content of bound SO ₂ and total SO ₂ exceeding the predetermined value by 0.5-1.5%, with full consumption of brucite. In the second stage, the acidic solution is treated with steam or air to remove excess total SO ₂ in an amount providing a proportion of bound SO _{2 of} 47-55%. The sulfur content in the sludge in this case is 5-7%, since the process is carried out at low pH.

The closest analogue of the present invention is a method for producing a bisulfite cooking solution on a magnesium base for the production of cellulose, comprising reacting sulfur dioxide with magnesia raw material - lump brucite with fraction sizes in the range of 50-600 mm at an initial pH = 1.5-2.5 with subsequent separation exhaust gas from the solution (RU, 2054852, D 21 С 3/10, 02.20.1996).

The known method is carried out in two stages. At the same time, in the first step, an acidic solution is obtained with a given content of total SO ₂ at an initial pH of 1.5-2.5 and a proportion of bound SO _{2 of} 40-45%. Although the temperature of the process of interaction of sulfur dioxide with magnesian raw materials was not specifically indicated in the description of the closest analogue, it is usually about 40 ° C, since the furnace gas is usually cooled to 30-50 ° C. In the second stage, the acidic solution is treated with lump brucite until a final pH of 3-5 is reached and the proportion of bound sulfur dioxide is 47-55%.

In the known method there is no noticeable loss of poorly soluble magnesium sulfite, because the process of obtaining a bisulfite solution is carried out at pH <5, therefore, the sulfur content in the sludge is 5-7%. However, the known method is cumbersome and requires volumetric equipment in both the first and second stages.

In addition, it is necessary to periodically switch the operation of the turms due to the occurrence of surface brucite gypsum casting with calcium and magnesium sulfites and calcium sulfate during the treatment of the acid solution with brucite in the second stage.

A new technical result from the use of the present invention is to increase the manufacturability of the method by reducing the steps of the process. At the same time, the quality of the resulting solution remains at the required level, and the sulfur content in the sludge also does not exceed 5-7%, since the whole process proceeds at a pH of no higher than 3.5.

This result is achieved in that in a method for producing a magnesium sulfide bisulfite cooking solution for cellulose production, comprising reacting sulfur dioxide with magnesian raw material - lump brucite with fraction sizes in the range of 50-600 mm at an initial pH of 1.5-2.5, followed by separating the exhaust gas from the solution, according to the invention, the interaction of sulfur dioxide with magnesia raw material - lump brucite in an aqueous medium is carried out to a final pH of 2.8-3.5 and a proportion of bound sulfur dioxide of 47.0-49.5%. The process is carried out in one step at a temperature of 70-90 ° C.

The elevated temperature is maintained by increasing the temperature of the furnace gas at the entrance to the absorption system. Perhaps the use of steam. As a result, the finished solution leaves the system at an elevated temperature, which, under equilibrium conditions, gives a minimum content of SO ₂ in the form of sulfurous acid and, accordingly, an increased proportion of bound SO _{2 of} 47-49.5% and a pH of 2.8-3.5 (according to the prototype the proportion of bound sulfur dioxide in the first stage was 40-45% and a pH of 2.0-2.5). The purified gas is vented to the atmosphere.

The proposed method is more technologically advanced compared to the prototype, since it is carried out in one step. The finished solution has a high temperature, which allows to reduce the steam consumption during the pulping process and to reduce the boiler revolution by 20-30 minutes. In addition, upon receipt of the bisulfite solution according to the prototype in the second stage, the brucite surface is gypsized over time with calcium and magnesium sulfites and calcium sulfate, as a result of which the interaction of the acid bisulfite solution with brucite is sharply slowed down and there is a need to switch the operation mode of the turm.

The invention is illustrated by the following examples of its implementation.

Example 1. A method of producing a magnesium bisulfite cooking solution is carried out as follows: a turma is filled with lumpy brucite with a piece size of 200-400 mm and furnace gas with a sulfur dioxide content of 13% is passed in terms of dry gas (in terms of real wet gas - 7 , 8%) and with a temperature of 76 ° С. Moreover, due to the heat of the furnace gas, the condensation of water vapor and the heat of reaction of sulfur dioxide with brucite, the temperature of the finished solution at the outlet of the absorption system rises to 80 ° C. The strength of the solution for total SO ₂ support 4.0%. Under equilibrium conditions, at given concentrations of SO ₂ in gas and temperatures in the solution in the form of sulfurous acid, no more than 0.16% SO ₂ will be contained. Thus, in the system receive a bisulfite solution of the following composition:

total SO ₂ - 4.0%;

bound SO ₂ - 1.92%;

the proportion of bound SO ₂ is 48%;

final pH 3.0.

The purified furnace gas is separated from the solution and from the turma enters the atmosphere.

The heat saving compared to the prototype is 0.2 Gcal / t.

Examples 2, 3. Similarly carry out the preparation of bisulfite cooking solutions with the following process parameters (see table). An example reproducing the process by the closest analogue is presented in the table.

Thus, according to the table, the proposed method provides a bisulfite cooking solution of the required quality with a low amount of sulfur loss with sludge at the level of the prototype method. But at the same time, the proposed method is more technologically advanced due to its implementation in one step, eliminates gypsum plastering, and also allows to obtain heat savings of 0.15-0.25 Gcal / t cellulose.

Table Example No. Brucite fraction size, mm Furnace gas Crude bisulfite solution Cooking heat saving, Gcal / t t, ° С Moisture content, g / nm ³ dry gas The concentration of SO ₂ ,% t, ° С SO _{2 total} ,% H ₂ SO ₃ ,% (in units of SO ₂ ) SO _{2 bond} % The proportion of SO _{2 bonds} ,% Final pH In dry gas In wet gas 1 200-400 76 536 13.0 7.8 80 4.0 0.16 1.92 48.0 3.0 0.2 2 100-600 73 440 15.0 9.7 70 4,5 0.26 2.12 47.0 2,8 0.15 3 50-200 82 856 10.0 4.9 90 6.0 0,07 2.97 49.5 3,5 0.25 4 (prot.) 45 45 84 15.0 13.6 40 5,0 0.86 2.07 41,4 2,3 -

For the prototype, the table shows the parameters of only the first stage.

Claims (1)

A method of producing a magnesium-based bisulfite cooking solution for cellulose production, comprising reacting sulfur dioxide with magnesian raw lump brucite with a fraction size in the range of 50-600 mm at an initial pH of 1.5-2.5, followed by separation of the exhaust gas from the solution, characterized the fact that the interaction of sulfur dioxide with magnesian raw materials is carried out to a final pH of 2.8-3.5 and a proportion of bound sulfur dioxide of 47.0-49.5%, while the process is carried out in one step at a temperature of 70-90 ° C.