JPS62102B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sintering method that hardly causes cracks in the sintered pellets or insufficient sintering when the fly ash granules are loaded on a moving grate and sintered. As a technique for utilizing fly ash generated from coal-fired boilers and the like, there is a technique for using the fly ash as a main raw material and sintering it into lightweight aggregate. In other words, fly ash is used as the main raw material, water is used as a binder, and the raw pellets are kneaded and granulated to form approximately spherical raw pellets, which are loaded onto the moving grate of a sintering machine such as the Dwight Lloyd sintering machine, and heated air is supplied. After drying and igniting, it is allowed to naturalize to produce lightweight aggregate. Figure 1 is an explanatory diagram showing such a sintering procedure.
The product (sintered) aggregate 2 is charged into the hopper 13, and the raw pellets 1 are charged into the hopper 16, and these are stacked on a pallet-shaped movable grate 3 rotating in the direction of the arrow. The product aggregate 2 is supplied as bedding, and the raw pellets 1 are supplied to the hopper 16.
In some cases, it may be charged immediately after granulation. The raw material layer thus formed is sequentially transferred from left to right in the drawing as the grate moves, and is transferred to the drying/preheating furnace 4,
It undergoes sintering through an ignition furnace 5 and a sintering/retention furnace 6, and reaches a cooling zone 7 where it is sufficiently cooled and becomes a product aggregate. A plurality of wind boxes 8 are arranged along the conveyance direction below the upper grate that conveys raw pellets 1, etc., but the lower narrow diameter portion of the boxes 8 is deflected to avoid the return side grate. The exhaust duct 9 is opened and connected to the exhaust duct 9. The interior of the duct 9 is evacuated by a blower 10, and due to the suction airflow, a suction airflow is formed that passes through the raw material layer from top to bottom. Therefore, by connecting a high-temperature air introduction pipe to the upper part of each furnace 4, 5, and 6, high-temperature air is introduced into each furnace, passes between the raw material layers, descends, and enters the wind box 8. It is discharged. Decayed raw pellets, etc. that fall with the discharged air are
The pellets fall through the chute 11 onto the conveyor 12 and are collected, and are generally returned as a raw material for raw pellet granulation for reuse. Note that 14 represents a damper and 18 represents a drive sprocket. However, in the above-mentioned sintering process, defective products that do not meet the specifications for lightweight aggregate (particle size 5 mm to 25 mm, loss on ignition (unburned carbon content) 1% or less, etc.) due to lack of natural materials, etc. are generated. Something happened. The inventors of the present invention conducted various basic experiments to prevent the occurrence of such defective products. First, we investigated which part of the grate most defective products occur.
Figure 2 is a cross-sectional view in the grate width direction at the end of sintering, and the pellets 1a are stacked on the grate 3a and sintering has been completed, but defective pellets 19 have occurred in the lower layer at both ends of the pellet layer. Was. Since these were extinguished while the nature was incomplete, a large amount of loss on ignition remained and the strength was insufficient, and in some cases, the shape of the granules collapsed while remaining unsintered. Therefore, in order to understand the process by which defective pellets are generated, we investigated the progress of sintering from the ignition zone to the heat retention zone and the temperature changes inside the laminated pellets. FIG. 3 shows the cross-sectional state of the grate in the width direction immediately after ignition, and FIG. 4 is an explanatory view showing the same cross-sectional state 5 minutes after ignition. Pellets 1b are stacked on the grate 3b, and air 20 is fed from above so as to penetrate the grate 3b. Immediately after ignition, the ignition layer 21 is at the top layer, but five minutes after ignition, the pellets in the top layer 22 have completed natural sintering, and the ignition layer 21a has moved to the middle layer.
However, as shown in the figure, the migration speed of the ignition layer is faster at the center in the grate width direction and slower at the ends.
On the other hand, a plurality of temperature sensors were buried in the pellet at position 23 indicated by the chain line in the figure, and the temperature distribution at that position immediately after ignition and 5 minutes after ignition was investigated. FIG. 5 shows a width direction temperature distribution graph at the position of the chain line in the pellet layer immediately after ignition, and FIG. 6 shows a width direction temperature distribution graph at the position of the chain line within the pellet layer 5 minutes after ignition. Immediately after ignition, there is no large temperature difference between the center and the edges, and the temperature is almost uniform, but 5 minutes after ignition, the center has risen significantly, but the edges have not risen much, and the temperature distribution graph It has a centrally protruding shape. Incidentally, the portion where the progress of sintering or the temperature rise was delayed was within 500 mm from the side wall of the grate, but it became more noticeable toward the ends. Furthermore, regarding the occurrence of defective pellets, we investigated the factors that cause deviations in the width direction, and investigated whether there might be a difference in air permeability between the edges and the center.
7 and 8 are graphs showing the air permeability of the pellet layer immediately after ignition and 5 minutes after ignition. The air permeability was measured at the point where the supplied air passed through the grate in FIGS. 8 and 4. As shown, the air permeability is large at the ends of the grate and small at the center. The reason why the air permeability in FIG. 8 is high overall is that as sintering progresses, the air permeability improves as water evaporates and decreases. The following findings were found from the above investigation results. In other words, the air permeability at the edges of the heat retention zone is higher than that at the center, so at the edges, the cooling effect due to ventilation is considerably greater than the effect of supplying oxygen and heat to the ignited pellets, and the cooling effect from the side walls is Since the heat dissipation is large, the end pellets are easily cooled, and natural progression is generally expected to be difficult. Moreover, in a normal drying zone, sufficient heated drying air is supplied from above the stacked pellets, so that the upper layer of pellets relatively sufficiently removes the moisture contained therein, but the lower layer of pellets retains the moisture that was taken away in the upper layer. Since it receives a supply of moisture-absorbing air, it tends to be relatively insufficient in releasing the contained moisture. Therefore, it was concluded that a large amount of moisture remained in the pellets at the end of the lower layer, and that the amount of heat was consumed in evaporating the moisture, causing the temperature to rise less and less, resulting in the generation of unsintered pellets or collapsed pellets. The present invention was made in view of these circumstances, and aims to establish a sintering method that can minimize the amount of unsintered pellets and disintegrated pellets generated. be. Therefore, in view of the above considerations, the present invention aims to uniformize the drying of the granules or to send a sufficient amount of heat to the end of the heat retention zone. The gist is that hot air is supplied from the bottom to the top of the grate in half of the preheating zone, or that heated air is supplied particularly intensively to the pellets at both ends in the width direction of the grate in the heat retention zone. be. The present inventors focused on the fact that the drying and preheating in the drying stage was insufficient in the areas where defective pellets frequently occur, that is, the ends in the width direction of the grate, especially the lower ends, as revealed by the above analysis, and developed a drying method. As shown in Figure 9, with the pellets 1c loaded on the grate 3c, hot air 2 is poured from the bottom of the grate.
0a was sent. A temperature sensor was buried in the area indicated by the chain line 23a, and the temperature distribution was investigated.
When a heat amount of m ² ·min was supplied for 1 minute, the temperature distribution at the chain line position was as shown in FIG. The temperature was high at both ends and low at the center, but the difference was significant. In other words, even if the ventilation direction is reversed, the ventilation in the width direction of the grate is better at both ends, and since more hot air penetrates through both ends, the ends dry quickly and the temperature in that area rises. However, since the chain line portion is close to the grate, the upper tendency appears strongly, making the temperature difference between them particularly large. On the other hand, in the conventional drying method, when hot air is supplied from above, the edges cannot be sufficiently dried and preheated because the edges are located close to the bottom of the grate. Since the heated air had already absorbed a considerable amount of moisture and lost its drying power, it seems that the difference between the ends and the center was not greatly amplified. In other words, although it depends on the thickness of the pellets loaded on the grate, the amount of heat held by the drying air, and the ventilation time, if the drying air is only passed from the top to the bottom on one side, the lower layer of the stacked pellets will be dry and preheated over almost the entire area. It was impossible to fully achieve these goals. It is also possible to supply hot air with a large amount of heat to the drying zone for a long time even if the ventilation is only from above, but this requires a large amount of energy and is inefficient, as well as causing rapid drying. This is undesirable as there is a risk of bursting. Furthermore, the hot air blowing in from below is at least
It is preferable to have a heat amount of 250 Kcal/m ² ·min or more, and if it is less than 250 Kcal/m ² ·min, drying will be insufficient and the above effects will not be obtained. The upper limit was set at 7500 Kcal/m ² ·min, taking into account the degree to which bursting would not occur due to rapid drying. Furthermore, when these values are converted into temperature, it is 100 to 500℃.
This corresponds to blowing 10Nm ³ to 50Nm ³ of hot air. By the way, hot air is supplied from below the grate in the above-mentioned drying zone only to half of the drying zone, that is, the first half or the second half of the zone, or the center of the zone, and the remaining half is preheated from above the grate as usual. This is because if ventilation is only from below, the upper part of the pellets will remain wet for the same reason as above, causing bursting (splashing of raw pellets) when ignited, causing the pellets to collapse and fuse, reducing air permeability. This is because as a result of this interference, sintering failure of the entire pellet occurs. In this way, if the lower part of the pellet layer, especially the lower part of both ends, is sufficiently dried, even if there is unbalanced ventilation in the heat retention zone and excess air flows to both ends, the sintering in that part will be prevented. The process progressed in just the right amount, and a lightweight aggregate that was homogeneous and satisfied the specifications was obtained. On the other hand, the temperature distribution map in the heat retention zone (6th
If you carefully examine Figure 2), it is clear that the temperature of the pellets at both ends in the grate width direction has not risen sufficiently, and nature has not progressed sufficiently in these areas. For this reason, we thought that it would be a good idea to supply a particularly large amount of heat to both ends. The occurrence of poor sintering of the pellets was most noticeable in the region up to 150 mm from both ends of the lower layer. Therefore, in order to eliminate this defect, it is recommended to send hot air with a high amount of heat to a range of up to 500 mm from both ends of the upper surface layer. Therefore, as shown in FIG. 11, the heat-retaining air hood that supplies heat-retaining air to the pellets 1d on the grate 3d in the heat-retaining zone has a double structure, and the lower end 24a of the inner hood 24 is 500 mm from the side wall 25. Installed in the following position, the conventional heat amount (1000 to 5000 Kcal/m ² · min) is applied to the inside of the hood 24, and 5000 Kcal/m 2 ·min is applied between the inner hood 24 and outer hood 26.
When a heat amount of ~15000 Kcal/m ² ·min was applied to each, the incidence of sintering defects was drastically reduced even without adding the above-mentioned measures in the drying zone. Afterwards, even more remarkable effects were obtained when heat-retaining air was supplied using the hood. It should be noted that if the heat was less than 5000 Kcal/m ² ·min, the sintering defects at both ends could not be eliminated. There is no basis for setting an upper limit on this, but
The effect of the present invention reaches saturation when the temperature exceeds 15000 Kcal/m ² ·min, and from an energy standpoint, it is uneconomical to use more heat. Note that this corresponds to blowing hot air of 400 to 1000°C at a rate of 20 to 50 Nm ³ /m ² ·min. Regardless of which of the above two methods is used, the entire amount of the grate stacked pellets can be uniformly sintered, and when the two methods are combined, the effect is further improved. By having the structure as described above, the present invention can almost eliminate cracking of sintered pellets and generation of unsintered pellets. Examples of the present invention will be shown below. Comparative Example 1 Pulverized coal was added to flyash containing 3% unresolved carbon to make the carbon content 5%, and water was added to 17%.
and granulated into pellets with a diameter of approximately 12 mm. The pellets were stacked in a Dwight Lloyd sintering machine to a thickness of about 300 mm, dried by applying a heat of 5,000 Kcal/m ² ·min for 2 minutes, and then ignited by applying a heat of 16,000 Kcal/m ² ·min for 2 minutes. did. 2000Kcal/in the surface layer after ignition
Heat was applied for ⁵ minutes to obtain pellets of product. Example 1 A layer of green pellets obtained in the same manner as in Comparative Example 1 was injected from below the grate in the first half of the drying zone using a gas sintering furnace.
300℃ hot air for 1 minute (supplied heat amount approximately 3000Kcal/
^m2・min) from above in the second half.
It was dried and preheated by applying a heat amount of 5000 Kcal/m ² ·min for 1 minute, and then ignited and sintered in the same manner as in the comparative example to obtain product pellets. Table 1 shows the powder ratio, amount of unburned carbon, and crushing strength of the product pellets obtained in Comparative Example 1 and Example 1.

[Table] Example 2 A raw pellet loading layer obtained in the same manner as Comparative Example 1 was heated in a heat retention zone within a range of 200 mm from both ends of the pellet conveying grate inward using the same device as shown in Fig. 11.
Compare the powder ratio, amount of unburned carbon, and crushing strength of product pellets obtained by sintering with a heat amount of 10,000 Kcal/m ²・min for 5 minutes, and a heat amount of 2,000 Kcal/m ²・min for other ranges for 5 minutes. It is shown in Table 2 together with Example 1. In this case, the average temperature of the pellet surface layer at the end of sintering was 350°C at the center and 750°C at the edges.

【table】 [Brief explanation of the drawing]

Figure 1 is a schematic diagram of a sintering device for fly ash granules, Figure 2 is a cross-sectional view in the grate width direction at the end of sintering,
Figure 3 is a cross-sectional view of the pellet layer in the grate width direction immediately after ignition, Figure 4 is the same cross-sectional view 5 minutes after ignition, Figure 5 is a widthwise temperature distribution graph at the chain line position in the pellet layer immediately after ignition, Figure 6 is a graph of the same temperature distribution 5 minutes after ignition, Figure 7 is a graph showing the air permeability in the pellet layer immediately after ignition, Figure 8 is the same graph 5 minutes after ignition, and Figure 9 is the graph of pellets in the drying zone. Fig. 10 is a graph of the temperature distribution in the width direction of the grate indicated by the chain line in Fig. 9, and Fig. 11 is a diagram showing the state of heated air being supplied to the layer (cross-sectional view in the width direction). FIG. 3 is a hot air supply state diagram (cross-sectional view in the grate width direction). 1... Pellet, 3... Grate, 4... Drying zone, 5... Ignition zone, 6... Heat retention zone, 2
0...Hot air, 21...Ignition layer, 23...Temperature sensor installation position.

Claims (1)

[Scope of Claims] 1. Raw pellets made from fly ash as the main raw material and water as a binder are loaded on a moving grate, and while supplying heated air, after drying, preheating and ignition,
In the method of naturally sintering fly ash granules, heated air is supplied so as to pass through the grate from above to below, and at least in the front half of the dry preheating zone, hot air is supplied from below to above the grate. A method for sintering fly ash granules, characterized in that: 2 In claim 1, the hot air supplied from below the grate to the top is 250 to 7500 kcal/ ^m2 .
A method for sintering fly ash granules having a heat capacity of . 3 In a method of sintering fly ash granules, raw pellets made from fly ash as the main raw material and water as a binder are loaded onto a moving grate and sintered by preheating, igniting, and heat retention, the grate is moved from above to below. A method for sintering fly ash granules, which is characterized in that combustion air is supplied so as to penetrate through the pellets, and in the heat retention zone, heated air is supplied particularly intensively to the pellets at both ends in the width direction of the grate. 4 In claim 3, the amount of heat supplied within a range of 500 mm from both ends in the width direction of the grate is 5000 to 500 mm.
A method of sintering fly ash granules at 15000Kcal/ ^m2・min.