JP5108714B2 - Process for producing calcined lime - Google Patents

Description

  The present invention relates to a method for producing calcined lime, and specifically relates to a method for producing calcined lime by calcining a calcium carbonate-containing object to be fired while suppressing the growth of dam rings in a calcining furnace.

  When manufacturing kraft pulp, when quick lime (calcined lime) is added to causticize the green liquor, lime mud (calcium carbonate-containing material to be calcined) containing calcium carbonate as a main component is generated. This lime mud, after filtering the white liquor, diluting and washing with water, generally contains about 30% by mass or less of water even in powder form. In addition to calcium carbonate, sodium hydroxide or sodium carbonate is added. It is what it contains. The lime mud containing calcium carbonate as a main component is baked in a rotary kiln (calcining furnace) and converted into calcined lime containing calcium oxide as a main component. The calcined lime recovered here is reused by being supplied again to the green liquor causticizing step.

  The rotary kiln used for calcining lime mud is charged with lime mud from the top and heated from below to a maximum of 1200 to 1500 ° C. with a heavy oil burner. It is a device that discharges from. As described above, when a rotary kiln is used in the papermaking process, the rotary kiln is required to operate stably for a long period of time.

  However, when the rotary kiln is operated continuously, the lime mud and the calcined lime adhere to the inner wall, and there is a problem that the dam ring gradually grows. A dam ring is a substance such as sodium hydroxide (melting point 318 ° C.) or sodium carbonate (melting point 851 ° C.), which has a lower melting point than calcium oxide (melting point 2570 ° C.), which is the main component of the product. It is a solid deposit that is generated by viscosifying the material to be fired and bonding the raw materials together in a rotary kiln distributed in the range of from 1 to 1500 ° C. and gradually growing. As the dam ring grows, there are a number of drawbacks, such as failure of the exhaust in the kiln and reduction of the maximum firing rate. In order to remove the dam ring, it is necessary to stop the operation and physically scrape the dam ring, which hinders continuous operation for a long period of time and has a problem in work safety.

  Various techniques have been reported to suppress the growth of dam rings attached to the inner wall of the rotary kiln. For example, in Patent Document 1, glass having a low melting temperature is introduced into a rotary kiln for burning and melting solid waste to produce molten glass, and the molten glass and the slag constituting the dam ring formed are used. A technique for melting and removing a dam ring by reacting is disclosed. In Patent Document 2, when a metal oxide is melted and reduced with a reducing agent in a rotary kiln, the slag basicity of the raw material, the particle size of the reducing agent, It describes that the addition amount and the raw material temperature in the furnace are optimized.

  As a method for preventing dam rings in the production of calcined lime, Patent Document 3 describes that an aqueous dispersion of a spherical silica compound having a particle size of 5 to 150 nm containing a trace amount of sodium or potassium is added to a calcining apparatus. Yes. In addition, in paragraphs [0002] and [0004] of the document, in order to prevent dam ring, a method of mixing magnesium oxide powder with lime mud or spraying it into a high-temperature gas has been tried. It is described that a large amount of use reaching 1 to 5% by mass with respect to lime mud is required, and it is not continuously applied to actual operation due to cost, workability, increase in impurities, and the like.

Further, Non-Patent Document 1 describes that a dam ring is prevented by adding a liquid in which highly reactive magnesium is dispersed using a special surfactant to a kiln that produces calcined lime. Yes.
JP 2001-280613 A JP 2005-126732 A JP 2003-261363 A Masahiro Tsurumi, “KP Kiln Dam Ring Inhibitor”, Japan Paper Association, Paper and Pulp Technology Association, July 2007, Vol. 61, No. 7, p. 806-811

  However, when producing calcined lime, when silica or highly reactive magnesium aqueous dispersion described in Patent Document 3 or Non-Patent Document 1 is added to suppress the growth of dam rings, The water dispersion itself is expensive, and since water is brought into the system, the amount of fuel required for calcination is increased to evaporate water, resulting in the cost required for lime calcination. Has the disadvantage of increasing.

  On the other hand, as mentioned in Patent Document 3, it has been known that the dam ring prevention effect can be obtained by using the powder itself which does not contain water. However, the powder needs to be used in a large amount, and the cost is reduced. In addition, it has been known that it is not suitable for practical operation due to an increase in impurities contained in the product.

  In view of the above situation, the present invention uses a magnesium oxide-containing powder containing magnesium oxide particles in a method for producing a calcined lime by calcining a calcium carbonate-containing object to be calcined, so that the amount used is small. Another object of the present invention is to provide a method for suppressing dam ring growth in a firing furnace efficiently and at low cost.

  The present inventor has made various studies on the dam ring growth inhibitory effect of magnesium oxide powder. By adjusting the median value (median value) of the particle size distribution of the powder, excellent dam ring growth can be achieved even in small amounts. The present inventors have found that a suppressing effect can be achieved and have completed the present invention.

  That is, the present invention is a method for producing a calcined lime by calcining a calcium carbonate-containing object to be calcined in a calcining furnace, wherein the median value of the particle size distribution (median value) is 8 to 20 μm in the calcining furnace. The present invention relates to a method for producing calcined lime, comprising a step of calcining a calcium carbonate-containing material to be fired while introducing a magnesium oxide-containing powder containing particles.

  Preferably, the said calcium carbonate containing to-be-fired thing is a calcium carbonate containing thing produced in the causticizing process of the green liquor in the manufacturing process of a kraft pulp.

  Preferably, the magnesium oxide-containing powder has a magnesium oxide content of 10% by mass or more, and a calcium-containing inorganic content in terms of calcium oxide and a total content of the magnesium oxide content of 30% by mass. That's it.

  Preferably, the input amount of the magnesium oxide-containing powder per day is 0.004% by mass or more and 0.040% by mass or less as the addition amount of the magnesium oxide component with respect to the production amount of the calcined lime per day. It is.

  Preferably, the calcium carbonate-containing material to be fired has a sodium-containing inorganic content of 0.20% by mass or less in terms of absolute dry weight in terms of sodium oxide.

  According to the method for producing calcined lime of the present invention, dam ring growth in a calcining furnace can be efficiently suppressed even when the amount of magnesium oxide-containing powder used is small. Further, since magnesium oxide can be used without being dispersed in water, fuel consumption can be reduced and dam ring growth can be suppressed at low cost.

  In the present invention, when firing the calcium carbonate-containing object to be fired in the firing furnace, the firing furnace contains magnesium oxide particles containing magnesium oxide particles having a median value (median value) of particle size distribution of 8 to 20 μm. Introduce powder.

  The firing furnace used in the present invention is preferably a rotary firing furnace, that is, a rotary kiln because dam ring growth can be effectively suppressed by introducing the magnesium oxide powder. When the rotary kiln is rotated and the object to be fired is peeled off from the rotary kiln and falls, it impacts other dam rings. Can be suppressed. In particular, when the magnesium oxide-containing powder of the present invention is added, it is preferable to use a rotary kiln because the dam ring adhering above the magnesium oxide-containing powder is easily peeled off effectively by the impact described above.

  The calcium carbonate-containing material to be fired generally refers to a substance containing calcium carbonate as a main component, indicates lime mud in the kraft pulp manufacturing process, and the lime mud is at a temperature of 1200 to 1500 ° C. in a firing furnace. By baking, the calcined lime which is a product which has a calcium oxide as a main component is manufactured. As said calcium carbonate containing to-be-fired thing, it is preferable to use the lime mud produced in the causticizing process of the green liquor in the manufacturing process of a kraft pulp. In addition, by supplying the calcined lime obtained by the present invention to the causticizing process of the green liquor, the calcining process in the present invention collects the calcined lime in the manufacturing process of kraft pulp, part of the circulation system by reuse It is preferable to configure. The calcined lime is discharged as lime mud after use in the causticizing process, and then the lime mud is calcined in a calcining furnace to be regenerated into calcined lime and used again in the causticizing process. For this reason, the magnesium oxide particles to be added are easily accumulated in this circulation system, and when the amount of addition increases and the accumulation proceeds, not only the fuel consumption rate deteriorates, but also the concentration of calcined lime decreases, and kraft pulp production There is a problem that the efficiency of the entire process is lowered. In the present invention, as will be described later, since the addition amount is smaller than that of the conventional method, it can be suitably used particularly for the recovery and reuse of the calcined lime in the kraft pulp manufacturing process.

  When water is contained in the material to be fired to be put into the firing furnace, fuel such as heavy oil and oil coke is wasted. Therefore, it is preferable that the moisture content of the material to be fired to be fired into the firing furnace is low. Further, when the moisture content of the object to be fired is low, the amount of sodium hydroxide or sodium carbonate dissolved in water can be reduced, and as a result, formation of dam rings can be suppressed. Specifically, the moisture content of the calcium carbonate-containing material to be fired put into the firing furnace is preferably 25% by mass or less, and most preferably 0% by mass.

  Since sodium components such as sodium hydroxide and sodium carbonate cause the generation and growth of dam rings, it is desirable that they are not included in the calcium carbonate-containing material to be fired that is put into the firing furnace. From this point of view, the calcium carbonate-containing material to be fired preferably has a sodium-containing inorganic substance content of 0.20% by mass or less and 0.08% by mass or less in terms of absolute dry mass in terms of sodium oxide. Further preferred. Here, the absolutely dry mass refers to the mass when dried at a temperature of 200 to 400 ° C. for about 1 hour. The absolute dry mass can be obtained by removing the moisture contained in the substance, but at a temperature of 100 ° C., the moisture contained in the calcium carbonate-containing fired product cannot be sufficiently removed, and if it exceeds 500 ° C. Since calcium carbonate may be changed to calcium oxide, it is preferable to dry within the above temperature range in order to obtain the absolutely dry mass. The content in terms of sodium oxide can be calculated from the content of sodium atoms measured by neutralization titration using hydrochloric acid.

  In order to reduce the water content of the calcium carbonate-containing product to be fired into the firing furnace in advance, in the production method of the present invention, before the calcium carbonate-containing material to be fired is placed in the firing furnace, It is preferable to carry out the drying step using heat. In the causticizing step of the green liquor in the kraft pulp manufacturing process, it is preferable that the resulting calcium carbonate-containing product to be fired (lime mud) is subjected to a drying step and then fired. However, if the water content of the lime mud before the drying step is too high, the fuel required to evaporate the water in the drying step increases, so the water content of the lime mud before the drying step is adjusted low. It is preferable to keep it. Thereby, the basic unit of fuel used per calcined lime can be reduced. Specifically, the moisture content of the lime mud before the drying step is preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 18% by mass or less.

  In the present invention, magnesium oxide-containing powder containing magnesium oxide particles having a median value (median value) of particle size distribution of 8 to 20 μm is introduced in the process of producing calcined lime in a calcining furnace. The introduction of magnesium oxide-containing powder is not intended to introduce the powder in the form of an aqueous dispersion or suspension, but is intended to be introduced into the firing furnace in the form of powder. . In addition, as the magnesium oxide-containing powder of the present invention, it is not necessary to use expensive magnesium oxide that has been surface-treated, and ordinary magnesium oxide particles that have not been surface-treated can be used.

  The introduction of the magnesium oxide-containing powder is preferably not introduced directly into the firing furnace but before the drying step and brought into the firing furnace together with the calcium carbonate-containing article to be fired. When directly charged into the firing furnace, the temperature inside the firing furnace changes abruptly, and the calcium oxide concentration of the resulting calcined lime may fluctuate. It is not preferable for safety.

  The following is assumed as a mechanism by which the growth of the dam ring is suppressed by the introduction of the magnesium oxide-containing powder. That is, by introducing the magnesium oxide-containing powder into the firing furnace, the magnesium oxide concentration in the raw material is increased, and a fragile layer with low bonding strength and easy peeling is formed inside the dam ring. For this reason, the growing dam ring is likely to collapse due to the impact generated by the collision of the object to be fired with the dam ring by the rotation of the rotary kiln during operation. Damping of the dam ring due to the fragile layer is repeated by the rotation of the kiln, and as a result, the growth of the dam ring can be suppressed.

  In the present invention, by limiting the median value of the particle size distribution of the magnesium oxide particles to 8 to 20 μm, the dam ring growth can be effectively suppressed by the magnesium oxide-containing powder. If the median particle size distribution is smaller than 8 μm, an excellent dam ring growth suppression effect cannot be achieved with a small amount of use. When the powder having such a small particle diameter is introduced, the powder is discharged out of the system through an exhaust path connected to the firing furnace, and a sufficient amount is not left in the firing furnace. In particular, in the step (drying step) of drying the object to be fired to the rotary kiln using the exhaust heat of the rotary kiln (drying step), the median particle size distribution is more than 8 μm in the centrifugal powder / exhaust gas separation device (cyclone). Since the small powder is not sent to the powder separation side but is sent to the exhaust gas separation side, it is difficult to mix in the material to be fired. On the contrary, when the median value of the particle size distribution exceeds 20 μm, the dispersibility inside the rotary kiln is lowered, and the dam ring growth suppressing effect is lowered. In particular, the median value of the particle size distribution of the magnesium oxide particles is preferably 10 to 15 μm because an excellent dam ring growth suppressing effect can be exhibited with a small amount of introduction.

  In particular, in a firing furnace for firing a calcium carbonate-containing object to be fired into calcined lime (calcium oxide), a certain amount of exhaust is required to supply oxygen necessary for firing and discharge unnecessary carbon dioxide. Therefore, with the magnesium oxide particles having a median particle size distribution smaller than 8 μm, it is difficult to obtain a sufficient effect in the present invention.

  In the present invention, the median value of the particle size distribution of the magnesium oxide particles is measured by a particle size distribution measuring device (device name: MICROTRAC PARTICLE-SIZE ANALYZER manufacturer: LEEDS & NORTHRUUP INSTRUMENTS).

  The magnesium oxide-containing powder may be composed only of magnesium oxide particles, or may be composed of magnesium oxide particles and other inorganic substances. The magnesium oxide-containing powder content in the magnesium oxide-containing powder is preferably 10% by mass or more because a more excellent dam ring growth suppressing effect can be achieved. Further, in addition to the effect of suppressing dam ring growth, the total weight of the powder to be introduced is small, and the burden of the charging operation can be reduced. Therefore, the higher the magnesium oxide concentration in the magnesium oxide-containing powder, the more preferable, preferably 90 It is at least mass%. Examples of inorganic substances other than magnesium oxide contained in the magnesium oxide-containing powder include calcium oxide, calcium carbonate, calcium hydroxide, and other calcium-containing inorganic substances (hereinafter referred to as calcium-containing inorganic substances) that become calcium oxide by firing at 1200 to 1500 ° C. Examples include silica and kaolin clay.

  In the circulation system such as the production of calcined lime in the kraft pulp production facility, if there are many impurities other than magnesium oxide and calcium-containing inorganic substances, the accumulation of impurities causes deterioration of the fuel consumption rate and the decrease in the concentration of calcined lime, There is a possibility that the manufacturing efficiency of the causticizing process of green liquor in the manufacturing process of kraft pulp is lowered. For this reason, since it is preferable that there are few inorganic substances other than a magnesium oxide and a calcium containing inorganic substance, the content rate in conversion of calcium oxide of the calcium containing inorganic substance in a magnesium oxide containing powder and the total content rate of a magnesium oxide content are 30 mass% or more. It is preferable. More preferably, it is 90 mass% or more, More preferably, it is 98 mass% or more. The content of the calcium-containing inorganic substance in terms of calcium oxide can be calculated from the content of calcium atoms measured by fluorescent X-ray analysis.

  As described above, the magnesium oxide particles in the magnesium oxide-containing powder have a particle size of 8 to 20 μm and a magnesium oxide content of 90% by mass or more, so that a higher concentration of oxidation is performed inside the firing furnace. Magnesium is preferable because it is easy to stay and can suppress the growth of the dam ring more effectively. Further, the total content of magnesium oxide and calcium-containing inorganic substance in terms of calcium oxide is 98% by mass or more, particularly in the circulation system, since accumulation of impurities is small and kraft pulp can be produced efficiently, which is particularly preferable.

  An inexpensive magnesia clinker commercially available as a refractory material can be used as the highly pure magnesium oxide particles not containing a large amount of calcium-containing inorganic material. When the magnesium oxide-containing powder contains a calcium-containing inorganic substance, a mixture of magnesium oxide particles and calcium-containing inorganic powder can be used as the magnesium oxide-containing powder.

  In the present invention, the magnesium oxide-containing powder is continuously fired while being introduced into the firing furnace in a timely manner. The amount of the powder charged per day is sufficient to achieve a sufficient dam ring growth suppressing effect. It is preferable that it is 0.004 mass% or more as an addition amount of a magnesium oxide component with respect to the production amount of the said calcined lime per day. The upper limit of the input amount is not particularly limited, but if it is too large, magnesium oxide will be mixed as an impurity in the calcined lime, especially in the case of a circulating system by recovery and reuse of calcined lime, calcined lime in continuous operation Magnesium oxide accumulates therein, and the deterioration of the basic unit per calcined amount of calcined lime (calcium oxide) of fuels such as heavy oil and oil coke becomes remarkable. In addition, the burden of input work increases. Therefore, it is preferable that the upper limit of the input amount is 0.040% by mass or less as the addition amount of the magnesium oxide component with respect to the production amount of the calcined lime per day. Most preferably, it is 0.013 mass% or more and 0.033 mass% or less as an addition amount of the magnesium oxide component with respect to the production amount of the calcined lime per day.

  The frequency of introducing the magnesium oxide-containing powder is preferably 1 to 3 times a day, more preferably once a day, from the viewpoint of the balance between the dam ring growth suppressing effect and the work load.

  When adding magnesium oxide-containing powder, it is not necessary to gradually add it over a certain period of time (for example, 1 hour). Can do. In addition, by adding magnesium oxide-containing powder at a time, the magnesium oxide concentration in the raw material increases rapidly, and the easily peelable layer formed in the dam ring can be further weakened. The ring tends to collapse.

  As described above, the particle diameter of the magnesium oxide particles is 8 to 20 μm, and the input amount per day is 0.004% by mass as the addition amount of the magnesium oxide component with respect to the production amount of calcined lime per day. More than 0.040 mass%, preferably 0.013 mass% or more and 0.033 mass% or less, a high-concentration magnesium oxide layer can be obtained inside the kiln. Can be suppressed. Furthermore, it is preferable that the content of magnesium oxide particles in the magnesium oxide-containing powder is 90% by mass or more because the effect of suppressing dam ring growth is high. In particular, when the total content of magnesium oxide and calcium-containing inorganic materials in terms of calcium oxide is 90% by mass or more, there are few impurities other than magnesium oxide and calcium-containing inorganic materials, and in particular, the accumulation of impurities is reduced in the circulation system. preferable.

  By introducing magnesium oxide-containing powder containing magnesium oxide particles having a median particle size distribution of 8 to 20 μm into the firing furnace according to the present invention, it is possible to suppress the growth of dam rings in the firing furnace. The frequency of dam ring removal work that needs to be performed while the operation is stopped can be reduced from the conventional once every three months to about once per year. This enables continuous operation over a long period of time. Also, the work time required for one removal work can be reduced to about 30% compared to the case where no magnesium oxide-containing powder is introduced, leading to a reduction in work load.

  In addition, since powder is used instead of an aqueous dispersion or an aqueous suspension, it is not necessary to waste fuel to evaporate water, which is advantageous in terms of cost. Further, it is advantageous not only to use expensive surface activated magnesium but also to obtain magnesium oxide powder which is available at low cost.

  Furthermore, since the magnesium oxide-containing powder containing magnesium oxide particles having a median particle size distribution of 8 to 20 μm can exhibit a dam ring growth suppressing effect even with a small amount of input, a large amount of magnesium oxide is contained in the product. There are few problems which mix and reduce the purity of calcination lime.

  In particular, the kraft pulp manufacturing process is a circulatory system, and when there is a large amount of magnesium oxide to be added, it is easy to accumulate in the system, not only the unit fuel consumption deteriorates, but also the concentration of the obtained calcined lime (calcium oxide) decreases, There is a problem that the efficiency of the causticizing process of green liquor in the kraft pulp manufacturing process is reduced. For this reason, as in the present invention, the amount of magnesium oxide-containing powder containing magnesium oxide particles per day is 0.004 as the amount of magnesium oxide added to the amount of calcined lime produced per day. It is preferable that they are mass% or more and 0.040 mass% or less. If it exceeds 0.040% by mass, the unit fuel consumption is deteriorated and the concentration of calcined lime is likely to be reduced.

  As mentioned above, in addition to the addition amount of magnesium oxide being 0.004 mass% or more and 0.040 mass% or less, the particle diameter of the magnesium oxide particles is 8 to 20 μm, and the magnesium oxide particles in the magnesium oxide-containing powder If the content of is 90% by mass or more, a high-concentration magnesium oxide layer can be obtained, which is preferable because the effect of suppressing dam ring growth is even higher. In particular, when the total content of magnesium oxide and calcium-containing inorganic substances in terms of calcium oxide is 90% by mass or more, accumulation of magnesium oxide in the circulatory system is small. It is preferable because it is difficult.

  The above dam ring growth suppression method requires less magnesium oxide to be added to the calcium carbonate-containing material to be fired, so to suppress the growth of dam rings in the baked lime manufacturing process in the kraft pulp manufacturing process that is a circulation system, Particularly preferably used.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Examples 1-17 and Comparative Examples 1-4
A rotary kiln (short kiln) manufactured by Kawasaki Heavy Industries was used as the firing furnace. A kiln having an inner diameter of 4 m, a length of 75 m, and an inclination angle of 2/100 was used and operated at 60 revolutions per hour. The focal temperature inside the rotary kiln (the highest temperature inside the rotary kiln, the temperature at the tip of the burner flame) was 1300 ° C., and the focal point was set at a point of about 10 to 20 m from the front of the kiln.

  Magnesium oxide-containing powder is a proportion shown in Table 1, and magnesium oxide clinker (model number: UBE98S, manufacturer: Ube Materials Co., Ltd.), calcium-containing inorganic substance (calcium oxide, calcium carbonate, calcium hydroxide) is used as the magnesium oxide particles. (Mixed at a weight ratio of 1: 1) and silicon dioxide (silica) were appropriately mixed. The components contained in the magnesia clinker were roughly as follows by weight.

Magnesium oxide: 98.3%,
Calcium oxide: 0.8%
Silicon dioxide: 0.6%
Iron oxide: 0.2%
Aluminum oxide: 0.1%
The median value of the particle size distribution of the magnesium oxide particles was measured using a particle size distribution measuring device (device name: MICROTRAC PARTIPLE-SIZE ANALYZER manufacturer: LEEDS & NORTHRU INSTRUMENTS).

  Under the addition conditions shown in Table 1, the magnesium oxide-containing powder was added to the calcium carbonate-containing fired product before the drying step provided in the previous step of the rotary kiln. As the calcium carbonate-containing material to be fired, lime mud discharged from the green liquor causticizing process in the kraft pulp manufacturing process was used.

  Lime mud was dehydrated with a lime mud filter, added with a magnesium oxide-containing powder before the drying step, thoroughly mixed with the magnesium oxide-containing powder during the drying step, and then dried to a moisture content of about 0% by mass. . The dried mixture of lime mud and magnesium oxide-containing powder was continuously added from the kiln bottom of the rotary kiln to 720 tons in dry weight per day. The obtained calcined lime had a calcium oxide concentration (purity) of about 80%, and the remaining 20% was a sodium-containing inorganic substance such as calcium carbonate, magnesium oxide, or sodium carbonate.

  In Examples 2 to 4 and Comparative Examples 2 and 3, magnesia clinker (manufactured by Ube Materials Co., Ltd.) having a median particle size distribution adjusted as shown in Table 1 was used as the magnesium oxide particles. In Examples 8 and 9, silicon dioxide (melting point: about 1650 ° C.) is contained in the magnesium oxide-containing powder. In Examples 16 and 17, the sodium lime mud water washing conditions in the lime mud filter are adjusted to obtain sodium oxide equivalent sodium. The content rate of the contained inorganic substance was adjusted, and in Comparative Example 4, instead of the magnesium oxide-containing powder, water-dispersed magnesium oxide (product name: Humeless L, Taiho Kosai Co., Ltd., particle size of several μm) was used.

The content rate of the sodium containing inorganic substance described in Table 1 converted into the sodium oxide in calcined lime was calculated | required by the following.
1) 50 g of calcined lime is dried at a temperature of 200 to 400 ° C. for about 1 hour to determine the moisture content. The determined water content is A (unit: mass%).
2) To 20 g of calcined lime (not dried), add 300 ml of warm water and heat until boiling. After heating, add water to dilute to 500 ml.
3) The supernatant is filtered through filter paper (type: 2 types) specified in JIS P3801, and 100 ml of the filtrate is collected.
4) Add 3 drops of methyl orange specified in JIS K8883 to 100 ml of the filtrate, and titrate with 1/5 normal hydrochloric acid to obtain the drop amount B (unit: ml). The end point is the point at which the filtrate changes from orange to light red.
5) According to the following formula, the content of the sodium-containing inorganic substance converted to sodium oxide in the calcined lime is calculated.
Content (mass%) = 15.5B / (100-A)

The dam ring growth inhibitory effect was evaluated after the rotary kiln was stopped for 3 months and the rotary kiln was stopped.
A: The thickness of the dam ring is less than 0.1 m, and the dam ring growth suppression effect is most excellent.
A: The thickness of the dam ring is 0.1 m or more and less than 0.2 m, and is particularly excellent in the dam ring growth suppressing effect.
(Triangle | delta): The thickness of a dam ring is 0.2 m or more and less than 0.3 m, and is excellent in the growth suppression effect of a dam ring.
X: The thickness of the dam ring is 0.3 m or more, and is inferior in the growth suppression effect of the dam ring.

The basic unit of fuel was the amount of heavy oil used when the rotary kiln was continuously operated for 3 months (heavy oil usage (L) / calcined lime production (t)), and evaluated according to the following criteria.
○: The fuel consumption rate is the same as in Comparative Example 1, and there is no change.
Δ: Fuel basic unit deteriorated by 0.1% or more and less than 0.2% compared to Comparative Example 1. ×: Fuel basic unit deteriorated by 0.2% or more than Comparative Example 1.

  From Table 1, it was excellent when firing was performed while introducing magnesium oxide-containing powder containing magnesium oxide particles having a median particle size distribution (median value) of 8 to 20 μm, despite a small amount of input. It can be seen that the dam ring growth suppression effect was achieved.

Claims (6)

A method for producing a calcined lime by calcining a calcium carbonate-containing material to be calcined in a calcining furnace,
Including a step of firing the calcium carbonate-containing object to be fired while introducing a magnesium oxide-containing powder containing magnesium oxide particles having a median value (median value) of particle size distribution of 8 to 20 μm into the firing furnace. A method for producing calcined lime characterized by the following.   The manufacturing method according to claim 1, wherein the firing furnace is a rotary kiln.   The said calcium carbonate containing to-be-baked material is a manufacturing method of the calcined lime of Claim 1 or 2 which is a calcium carbonate containing thing produced in the causticizing process of the green liquor in the manufacturing process of a kraft pulp.   The magnesium oxide-containing powder has a magnesium oxide content of 10% by mass or more, and a total content of 30% by mass or more of the content of the calcium-containing inorganic substance in terms of calcium oxide and the content of the magnesium oxide. The manufacturing method of the calcined lime in any one of Claims 1-3.   The daily input amount of the magnesium oxide-containing powder is 0.004% by mass or more and 0.040% by mass or less as the addition amount of the magnesium oxide component with respect to the production amount of the calcined lime per day. The manufacturing method of the calcined lime in any one of Claims 1-4.   The said calcium carbonate containing to-be-baked material is a manufacturing method of the calcined lime in any one of Claims 1-5 whose content rate of the sodium containing inorganic substance by sodium oxide conversion is 0.20 mass% or less by an absolute dry mass.