JPS6364558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the production of cooking liquor in the production of sulfite pulp, and more specifically, the present invention relates to the production of cooking liquor in the production of sulfite pulp, and more specifically, the use of calcium carbonate produced in the process of producing cooking liquor of kraft pulp in place of the raw material limestone or slaked lime. This relates to a method using sludge mainly consisting of:
Sulfite pulp (hereinafter abbreviated as SP) is one of the important methods for producing wood pulp.
With the rapid development of kraft pulp (hereinafter abbreviated as KP), the SP method is gradually being dethroned, but its advantage is that the quality of high brightness and easily bleachable pulp can be varied over a wide range. etc.
The SP method is expected. There are three main types of SP methods: acidic sulfite, bisulfite, and methods that use sulfite as a cooking chemical. Based on these methods, modified methods and two-stage cooking methods have been adopted.
In addition, ions such as Ca, Mg, Na, and NH ₃ are used in cooking chemicals for the purpose of preventing lignin condensation during cooking, and these are called bases.
The SP method uses these cooking chemicals to process wood chips in a digester to achieve the desired quality.
Cooked at 130-150°C, pressure 6-8 Kg/cm ² and appropriate time.

Pulp for various uses can be obtained depending on the degree of cooking, but it is easy to purify and bleach, and pulp for dissolving and paper making can be obtained.

The present invention relates to the production of cooking liquor using the Ca-based acidic sulfite method described above.

Conventional technology and its problems The production of Ca-based acidic sulfite cooking liquor has conventionally been carried out using (1) tower type absorption method, (2) There are three types: () tank absorption method, and (3) pressure absorption tower method.

Each method will be explained below.

(1) Tower-type absorption method A tower filled with limestone is used to absorb SO ₂ , and is currently widely used. The tower is approximately 30 meters high, and is of two-tower type, made of reinforced concrete and lined with liquor-proof bricks. Limestone, the size of a human head, is used as the Ca raw material, and SO ₂ is injected from the bottom of the tower, and water is sprayed from the top of the tower. However, this method has drawbacks such as the complexity of filling the limestone and removing the undissolved components of the limestone, i.e., bad stones.Also, although the concentration of the base Ca compound acid can be adjusted by changing the water temperature, the liquid preparation conditions vary. Easy to do and difficult to adjust.

(2) Tank type absorption method Using lime milk Ca(OH) ₂ as Ca raw material, 3 tanks are used.
The lime milk flows down from the upper tank to the lower tank, and the gas rises from the lower tank to the upper tank.

This method causes a large loss of SO ₂ and uses slaked lime instead of limestone, resulting in high costs and fewer examples.

(3) Pressure absorption tower In the methods (1) and (2), the composition of the raw solution tends to change due to the influence of seasonal water temperature.

To compensate for this drawback, the SO ₂ gas to the absorption tower is pressurized using a blower, and the absorption tower is operated at a pressure of about 1 Kg/cm ² .

As expected, the number of examples is decreasing due to problems such as running costs of blowers and the like.

Based on the above-mentioned current problems regarding the Ca-based acidic sulfite cooking liquor production method, the present inventors have conducted extensive research and have developed a method for producing acidic sulfite cooking liquor using
It has been found that by using the sludge mainly composed of calcium carbonate produced from the KP pharmaceutical process, it is possible to adjust the concentration of the liquid at a stable concentration at a low cost. KP pharmaceutical process is the process of producing KP cooking liquor. The main components of KP's cooking liquor are caustic soda (NaOH) and sodium sulfide (Na ₂ S), but caustic soda is a mixture of sodium carbonate (Na ₂ CO ₃ ) and quicklime (CaO) in the green liquor produced during the recovery process. It is produced by a chemical reaction. At this time, quicklime turns into calcium carbonate (CaCO ₃ ). This calcium carbonate is commonly called sludge,
Usually, it is fired into CaO in a heavy oil-burning furnace and recycled. However, this firing
Due to the presence of water and a small amount of Na in KP sludge, it has the disadvantage that it requires too much firing energy compared to limestone.

Key Points of the Invention If possible, limestone is calcined in a special kiln to produce quicklime, which is used in the causticizing reaction of soda carbonate, and the resulting KP sludge can be used for other purposes as a charcoal raw material as in the present invention. is preferable.

KP sludge is calcium carbonate made by reacting quicklime with carbonate ions in soda soda, and falls into the category of so-called light calcium carbonate.

Light calcium carbonate has better reactivity with SO ₂ than heavy calcium carbonate, which is obtained by directly pulverizing limestone.

The particle size of this sludge is usually about 10μ on average and 63μ
The following accounts for 92% and is relatively detailed.

The chemical composition is 93% _CaCO3 per solid content, Ca
(OH) ₂ 5%, and other components such as hydrochloric acid insoluble components are 2%. The present invention provides a method for producing sulfite pulp cooking liquor, which is characterized in that in the cooking liquor production process in the Ca-based sulfite pulp production process, a sludge containing mainly calcium carbonate produced from the kraft pulp pharmaceutical process is used as a raw material. provided. This sludge is used to produce SP cooking liquor. Various types of absorption equipment can be considered, but generally there are moretana towers, packed towers, etc., which will be described in detail in Examples.

This liquid preparation using sludge is more advantageous when the KP factory and SP factory are adjacent to each other.
Supplied at 4% concentration. The reaction equation between sludge and SO ₂ is as follows.

CaCO ₃ +SO ₂ →CaCO ₃ +CO ₂ ↑PH5-6 (1) CaSO ₃ +SO ₂ +H ₂ O→Ca(HSO ₃ ) ₂ PH3-4 (2) H ₂ O+SO ₂ +Ca(HSO ₃ ) ₂ →H ₂ SO ₃ +Ca
(HSO ₃ ) ₂ PH1-2 (3) The reaction of (1) must be avoided because it tends to cause scaling troubles due to the insolubility of CaSO ₃ .

SO ₂ +H ₂ O→H ₂ SO ₃ PH2～4 (4) 3H ₂ SO ₃ +CaCO ₃ →Ca(HSO ₃ ) ₂ +H ₂ SO ₃ +CO ₂
+H ₂ O PH1-2 (5) Therefore, it becomes necessary to carry out a reaction in a PH range where CaSO ₃ is not produced, as in reaction formulas (4) and (5), for example.

This KP sludge has an overwhelmingly larger specific surface area than ordinary limestone and has good reactivity. Therefore
The reaction rate of (5) becomes considerably faster.

As a result, for example, the tower height for the conventionally used tower absorption method requires 30 m x 2 = 60 m.
It was found that 5m x 2 = 10m is sufficient when using the Moretana tower, etc.

It has been found that the equipment can be made more compact and operating costs can be reduced.

Furthermore, in the case of the conventional tower type, it is very difficult to adjust the concentration of the liquid produced by adjusting the temperature, pressure, amount of packed lime, etc.

Even so, in the summer there is a tendency for the compound acid concentration to increase and the total acid concentration to decrease.In the winter, the compound acid concentration to decrease and the total acid concentration to increase.

However, if KP sludge is used, the compound acid concentration remains constant, and the conditions can be adjusted to keep the total acid concentration constant, making operation relatively easy.

Furthermore, the total acid and synthetic acid concentration can be adjusted to be higher than that of the conventional method.

If a highly concentrated cooking liquor can be prepared, Migita, Yonezawa,
As stated in "Wood Chemistry Volume 2" edited by Kondo, pages 189-190, it is advantageous for the chemical solution to penetrate into the wood chips in the early stage of cooking, which ultimately becomes advantageous for SP cooking.

The SP cooking liquor receives return gas (relief gas) from the wooden pot during cooking into the stock solution adjusted in the pharmaceutical tower, increasing the total acid concentration, but also increasing its variation.

Assuming SP digestibility control, it is preferable to supply a constant total acid concentration.

Therefore, in the present invention, if the concentration of the stock solution is adjusted to be high, it is also possible to alleviate the variation in the total acid concentration at the time of receiving the relief gas by dilution.

Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited by these Examples.

Example 1 SP cooking liquor was prepared using a moretana column and KP sludge as the Ca raw material. The Moretana tower has a liquid production capacity of 20m ³ /hr, total acid 5.7wt%, compound acid 2.3wt%
A cooking liquid was produced.

There are two towers, A tower and B tower, each with an internal diameter of 60 mm.
cm, the height is 5m, and there are 3 shelves.

The SO ₂ gas concentration was 16 vol%, the KP sludge slurry liquid concentration was 3.6 wt%, and the temperature was adjusted to 20°C.

The pH of the liquid at the top of the tower is 1 so that it does not exceed 4.
part of the liquid was circulated.

Example 2 SP cooking liquor was prepared using a static mixer and a packed tower using KP sludge as the Ca raw material. Liquid production capacity is 20m ³ /hr, total acid 5.6wt%, compound acid
A cooking liquor of 2.3wt% was produced. The static mixer in the first stage had a diameter of 20 cm and a length of about 5 m, and the pH of the slurry liquid was 4. The liquid and exhaust gas are applied to a packed tower in the second stage, and the packing is made of magnetic 3
I used the Inchlashig ring. Each packed column has an inner diameter of 1.5 m, a height of 8 m, and a packed bed of 6 m. SO ₂
The gas concentration was 16 vol%, the KP sludge slurry concentration was 3.6 wt%, and the temperature was adjusted to 20°C.

Example 3 SP cooking liquor was produced using a packed tower and KP sludge as the Ca raw material.

Note that a magnetic 3-inch Raschig ring was used as the filling material. The packed tower has a liquid production concentration of 20 m ³ /h and a total acid content of 5.6 wt%.
A cooking liquor containing 2.3wt% of compound acid was produced.

Each packed column has an inner diameter of 1.5 m, a height of 10 m, and a packed bed of 8 m. The SO ₂ gas concentration was 16 wt%, the KP sludge slurry concentration was 3.6 wt%, and the temperature was adjusted to 20°C. One part of the liquid was circulated so that the pH at the top of the column did not exceed 4.

Actions and Effects As a result of producing SP cooking liquor by the method according to the present invention,
There is no need for the complicated work of filling limestone and taking out bad stones as in the conventional method, and the composition of the cooking liquor does not fluctuate due to external conditions such as water temperature, making it possible to obtain a cooking liquor with the desired composition. .

Furthermore, in the case of pharmaceutical equipment, the height of the tower is determined not by the pharmaceutical capacity but by the gas absorption capacity, and is therefore unrelated to the scale of the equipment. Therefore, as can be seen from the examples, the height of the conventional absorption tower, which was 60 m, is extremely low at 10 m or less in the present invention, and the equipment cost can be reduced according to the height, and the equipment is small. It has also become possible to reduce operating costs.

[Brief explanation of drawings]

Figure 1 shows an outline of the SP pharmaceutical flow through the Moretana tower. Figure 2 shows an outline of the SP pharmaceutical flow using a static mixer and packed tower. Figure 3 shows an outline of the SP pharmaceutical flow using a packed column.

Claims (1)

[Claims] 1. A method for producing sulfite pulp cooking liquor, characterized in that in the cooking liquor production process in the Ca-based sulfite pulp production process, a sludge containing mainly calcium carbonate produced from a kraft pulp pharmaceutical process is used as a raw material.