JP7254294B2 - Pre-granulation method for raw materials for sintering - Google Patents

Description

The present invention relates to a method for pre-granulation of raw materials for sintering.

Sintered ore used in steel production is produced by sintering granules obtained by mixing iron ore, which is a raw material, with a coagulant, lime, and the like, and granulating the mixture in a sintering machine. At this time, part of the nitrogen contained in the coagulant becomes nitrogen oxides (hereinafter referred to as "NOx") and mixes into the exhaust gas.
Since NOx is an air pollutant, the concentration and amount of NOx emissions into the atmosphere are regulated, and restrictions such as adjustment of operating conditions occur. Installation of an exhaust gas treatment device for removing NOx is also being carried out, but this requires a large capital investment.

Therefore, in Patent Document 1, the surface of the carbonaceous material (coagulant) is coated with a coating (for example, quicklime or slaked lime) containing 36% by mass or more of Ca derived from a lime-based raw material to reduce NOx during carbonaceous material combustion. Techniques are disclosed.

Although the technique described in Patent Document 1 is an excellent method for reducing NOx, there is a demand for further reduction of NOx. The present inventors have made various studies to reduce NOx generated during sintering. The consolidation medium is granulated with a vibration granulator in a horizontal cylindrical container to form a dense granule (hereinafter sometimes referred to as the "vibration granulation process"), and the coagulant at a low temperature We have found that further reductions in NOx are possible by inhibiting oxidation.

WO2011/129388 Japanese Unexamined Patent Application Publication No. 2015-200007

However, when the inventors of the present invention implemented the technique described in Patent Document 2, it was found that the water content sometimes greatly deviated from the set moisture value, and the granulation properties were remarkably deteriorated. If such a phenomenon occurs, when the above technology is applied to actual operation, NOx will increase at a certain frequency, and sintering production will have to be stopped in order to comply with environmental standards.

The present invention has been made in view of such circumstances, and a pre-granulation method for sintering raw materials that enables stable continuous operation of the vibration granulation process in order to keep NOx generated during sintering at a low level. intended to provide

In order to achieve the above object, the pre-granulation method for sintering raw material according to the present invention includes:
A coagulant and 3% by mass or more (external number) of quicklime and/or slaked lime with respect to the coagulant are charged into a kneader having a single or multiple shaft stirring blade, and charged into the kneader. After kneading to produce a kneaded product with a moisture ratio (internal number) to the total amount of raw materials of 12% by mass or more, the kneaded product is charged into a vibration granulator containing a plurality of consolidation media in a horizontal cylindrical container. The vibrating granules that have been fed and granulated are charged into a granulator that granulates sintering raw materials containing iron ore, or are added to the granules discharged from the granulator. .

A coagulant is a substance that induces a sintering reaction in a sintering machine by oxidation heat generation, and usually contains 70% to 100% carbon.

The present inventors have found that when a raw material mainly composed of a coagulant is granulated with quicklime and/or slaked lime (hereinafter referred to as "quicklime etc.") with a vibration granulator, the ratio of quicklime etc. to the coagulant is 3 % by mass or more, and the ratio of moisture to the total amount of raw materials including coagulant and quicklime (hereinafter referred to as "set moisture") is 12% by mass or more, the horizontal cylindrical container constituting the vibration granulator It was found that deposits adhered to the upper part of the inner peripheral surface and the granulation properties were remarkably deteriorated.
Therefore, the present inventors charged the coagulant and quicklime etc. into a kneader having a stirring blade when the ratio of quicklime etc. to the coagulant is 3% by mass or more and the set moisture ratio is 12% by mass or more. After pre-kneading the mixture, it was charged into a vibration granulator and granulated. When the coagulant, quicklime, etc. are charged into a kneader having stirring blades and kneaded in advance, quicklime etc. and moisture are uniformly dispersed in the raw material by the shearing force of the stirring blades.

In the pre-granulation method for sintering raw material according to the present invention, when the ratio of quicklime etc. to the coagulant is 3% by mass or more and the set moisture ratio is 12% by mass or more, the coagulant and quicklime etc. are mixed with a stirring blade. After being charged into a kneader and kneaded in advance, it is charged into a vibration granulator and granulated, so that the vibration granulation process can be stably and continuously operated. As a result, NOx increases that occur with a certain frequency are suppressed, and a low NOx state can be maintained.

1 is a flow diagram of a sintering plant to which a pre-granulation method for sintering raw material according to an embodiment of the present invention is applied; FIG. FIG. 2 is a schematic diagram for explaining problems in the vibration granulation process;

Next, an embodiment embodying the present invention will be described with reference to the attached drawings for understanding of the present invention.

The present inventors, who have the knowledge described in Patent Document 2, performed vibration granulation of a coagulant together with quicklime or the like in the presence of moisture using a vibration granulator, and faced the following problems. That is, during continuous operation, the water content and the ratio of quicklime sometimes greatly deviate from the set values, and the phenomenon that the granulation properties are remarkably deteriorated occurs with a certain frequency.

When the inside of the vibration granulator 11 was observed at the time of the above trouble, as shown in FIG. rice field. As a result, when vibrating and granulating the coagulant to suppress NOx, NOx will increase at a certain frequency, and sintering production will have to be stopped in order to comply with environmental standards. .

The vibration granulator 11 includes a horizontal cylindrical container 21, a plurality of consolidation media 22 housed in the horizontal cylindrical container 21, and a pair of weight rotation type vibration motors 23 arranged on both sides of the horizontal cylindrical container 21. (See FIG. 2). A cylindrical steel rod is used as the consolidation medium 22, and a pair of weight rotation type vibration motors 23 rotate synchronously in the same direction.

When the pair of weight rotating vibration motors 23 rotates, for example, to the right, the horizontal cylindrical container 21 circularly vibrates in a loop in the vertical plane. As a result, each consolidation medium 22 housed in the horizontal cylindrical container 21 rotates to the right, and when it comes into contact with the horizontal cylindrical container 21, it rotates to the left as a whole. That is, each consolidation medium 22 rotates in the horizontal cylindrical container 21 like a planetary gear. Due to the consolidation action of the consolidation medium 22, the coagulant having low wettability with water can be preferably coated with quicklime or the like.
In order to prevent the vibration of the vibrating granulator 11 from propagating to others, the vibrating granulator 11 is supported on a base 27 via an air spring 26 to prevent vibration.

Under proper operating conditions of the vibration granulator 11, even if deposits adhere to, for example, the lower portion of the inner peripheral surface of the horizontal cylindrical container 21, they are immediately scraped off. Since the medium 22 does not come into contact with the medium 22, deposits 15 are easily formed and grown.

When quicklime or the like is added to the coagulant, the NOx suppressing effect is obtained. However, in the case of low moisture content, there is no problem.
When the coagulant is coated with quicklime or the like, the wettability of the coagulant with water is low (bad). However, as the water content increases, the adhesion of quicklime and the like to the upper portion of the inner peripheral surface of the vibrating granulator 11 increases.

When the ratio (external number) of quicklime or the like to the coagulant is 3% by mass or more and the ratio (inside number) of the set moisture is 12% by mass or more, quicklime etc. having a high affinity for water is added to the horizontal cylindrical container 21. It preferentially adheres to the upper part of the wetted inner peripheral surface. Quicklime or the like adhering to the upper portion of the inner peripheral surface absorbs the raw material moisture, causing the quicklime or the like to further adhere to the upper portion of the inner peripheral surface, thereby facilitating the formation of deposits 15 . Under such circumstances, the amount of quicklime and water that contribute to granulation is extremely reduced, resulting in the deterioration of granulation as described above.

Therefore, in the present invention, the ratio of quicklime etc. to the coagulant (external number) is 3% by mass or more and the set moisture ratio (internal number) is 12% by mass or more, and the coagulant and quicklime etc. are vibrated. Before being charged into the granulator 11, a coagulant, quicklime, etc. are charged into a kneader 10 having a single-shaft or multiple-shaft stirring blades and pre-kneaded (see FIG. 1).

Before vibration granulation, if the coagulant, quicklime, etc. are pre-kneaded in a kneader 10 having a single or multiple shaft stirring blade, the quicklime etc. and water are uniformly dispersed in the coagulant by the shearing force of the stirring blade. can be made
For very sticky powders with high quicklime concentration, high moisture conditions, tumble mixers are not suitable for pre-mixing. Moreover, pre-kneading by the vibration granulator 11 only causes the problems of the present invention and does not solve the problems.

When the kneading treatment by the kneader 10 having the stirring blades is not performed, agglomerates of quicklime or the like are formed in the raw material processed by the vibration granulator 11, and the formation and growth of deposits 15 are promoted. Therefore, the kneading process by the kneader 10 having stirring blades is extremely important.

The blade rotation speed of the kneader 10 is about 15 to 80 rpm, and the residence time is about 30 seconds to 10 minutes.
The kneader 10 may contain other raw materials (for example, iron ore, dust generated in the iron manufacturing process, etc.) in an amount of about 40% or less of the total raw materials in addition to the coagulant, quicklime, and the like. However, if about half or more of the iron ore is included, the amount of quicklime covering the coagulant decreases, making it difficult to obtain the NOx reduction effect.

A kneaded material such as a coagulant and quicklime pre-granulated by a kneader 10 having a single or multiple agitating blade is charged into a vibration granulator 11 and vibration-granulated. The vibration granules produced by the vibration granulator 11 are charged into a drum mixer 12 (an example of a granulator) that granulates sintering raw materials containing iron ore (from either the entrance side or the exit side of the drum mixer 12). ), or added to the granules discharged from the drum mixer 12 , and charged into the sintering machine 13 .

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment. Other possible embodiments and modifications are also included. For example, in the above embodiment, the drum mixer is used as the granulator for granulating the sintering raw material containing iron ore, but other granulators such as a pan pelletizer may be used.

A vibration granulation test of a coagulant that was carried out to verify the effects of the present invention will be described.
(1) Test Conditions The coagulant used generally contains about 15 to 50% by mass of fine powder under 0.25 mm. Therefore, in this test, a coagulant (coke) containing 25% by mass of fine powder under 0.25 mm was used.
In addition, 2 to 20% by mass of quicklime (containing 30% by mass of fine powder under 0.5 mm) is added to the raw material containing 100% by mass of coke powder, which is a coagulant, and the final moisture content is 11 to 25% by mass. After adjusting the amount of water to be added, granulation was performed using a vibration granulator.

The particle size adjustment of the coagulant and quicklime described above is performed by drying each raw material in advance (after absolute drying), and then adjusting the nominal opening described in JIS Z8801-1 (0.25 mm for the coagulant and 0.5 mm for quicklime). The sieve was mechanically sieved with a low tap shaker for 60 seconds (classified), the top and bottom of the sieve were measured, and the particle size was adjusted so that the particle size distribution ratio was calculated by the following formula. rice field.
Particle size distribution ratio (mass%) = (mass under sieve) / (mass above sieve + mass under sieve) x 100
The definitions of the water content and quicklime ratio added to the coagulant are as follows.
Moisture [mass%] is added water amount [kg] / total amount of coagulant granules [kg] (including water, quicklime, etc.) x 100, quicklime ratio [mass%] is added quicklime [kg] / coagulant Amount [kg]×100.

In granulating the coagulant, a vibrating granulator containing 35 steel rods (consolidation medium) with a diameter of 60 mm in a horizontal cylindrical container with an internal volume of 600 L (liter) was used. The continuous granulation treatment was performed at a vibration acceleration of 3 tons/h (gravitational acceleration) and a throughput of 3 tons/h.

A continuous dow mixer equipped with twin-screw blades was used for pre-mixing the coagulant (blade speed 15-80 rpm, residence time 30 seconds-10 minutes). A pre-kneading test was also conducted using a uniaxial pin mixer and a Redige mixer, which are considered to have similar functions (blade rotation speed 15 rpm, residence time 30 seconds, respectively). Further, for comparison, pre-kneading was performed using a continuous drum mixer with a diameter of 1 m (rotational speed: 20 rpm, throughput: 3 tons/h) and a vibrating granulator under the operating conditions described above.

(2) Test results Table 1 shows a list of test results.

In all cases, treatment was performed for 1 hour from the time the granules were first discharged from the vibratory granulator, and testing was performed during the following 2 hours of treatment.
In the test, granules are sampled every 5 minutes, and if the number of times the difference between the set moisture content (% by mass) and the moisture content of the granules (% by mass) exceeds 3% by mass is 1 or less, it passes ( ○), and if it was twice or more, it was regarded as failed (x).

The retention time (h) in the continuous kneader was defined as the amount retained in the machine (ton)÷the amount processed (ton/h).
In the above calculation, the weight including water was used. The value obtained by investigating the following was used as the amount of waste retained in the aircraft (ton).
After the steady operation of the kneader was continued for 30 minutes or longer, the introduction of raw materials into the kneader and the operation were stopped at the same time. Then, the raw material in the kneader was recovered without leaving any residue, and the weight thereof was measured.

As in Reference Examples 1 to 3, when the quicklime concentration is less than 3% by mass or the set moisture content is less than 12% by mass, adhesion trouble does not occur in the vibration granulator, the product moisture is stable, and granulation is easy. was also stable.

When the quicklime concentration was 3% by mass or more and the set moisture content was 12% by mass or more, in Comparative Example 1 in which pre-kneading was not performed, adhesion trouble occurred in the vibration granulator, and the product moisture was significantly reduced. At that time, when the granules were observed, they were completely ungranulated.
In Comparative Example 2, in which a vibrating granulator was used for pre-kneading, adhesion trouble occurred in the vibrating granulator during kneading, and a marked decrease in the water content of the product was observed. On the other hand, no sticking trouble occurred in the vibration granulator after kneading.
In Comparative Example 3, in which a drum mixer was used for pre-kneading, as in Comparative Example 1, adhesion trouble occurred in the vibrating granulator, and a marked decrease in the water content of the product was observed.

Even if the quicklime concentration is 3 to 20% by mass and the set water content is 12 to 25% by mass, as in Examples 1 to 8, a kneader having a single or multiple shaft stirring blade is used, and the blade When pre-kneading is performed under the conditions of a rotation speed of 15 rpm or more and a residence time of 30 seconds or more, there is no sticking problem in the vibration granulator, the moisture content of the granules is stable, and good granulation properties can be maintained. rice field.
In addition, it is considered that there are no particular restrictions on the upper limit of the blade rotation speed and residence time, since the stirring effect can be further enjoyed. For example, favorable results have been obtained even with a blade rotation speed of 80 rpm and a residence time of 600 seconds.

10: kneader, 11: vibration granulator, 12: drum mixer (granulator), 13: sintering machine, 15: deposit, 21: horizontal cylindrical container, 22: consolidation medium, 23: weight rotary vibration motor, 26: air spring, 27: base

Claims (1)

A coagulant and 3% by mass or more (external number) of quicklime and/or slaked lime with respect to the coagulant are charged into a kneader having a single or multiple shaft stirring blade, and charged into the kneader. After kneading to produce a kneaded product with a moisture ratio (internal number) to the total amount of raw materials of 12% by mass or more, the kneaded product is charged into a vibration granulator containing a plurality of consolidation media in a horizontal cylindrical container. The vibrating granules that have been fed and granulated are charged into a granulator that granulates sintering raw materials containing iron ore, or are added to the granules discharged from the granulator. A pre-granulation method for sintering raw materials.

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