JPH0155363B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for reforming fly ash in exhaust gas discharged from a pulverized coal-fired boiler. In recent years, with the rise in the price of heavy oil, energy conversion from heavy oil to coal has progressed rapidly, and boilers in thermal power plants and the like are also being converted from heavy oil-fired to pulverized coal-fired. Coal ash discharged from a boiler is initially taken out in a molten state, but due to surface tension it becomes spheroidized and hardens into so-called fly ash, which has been used in fly ash cement and the like. However, recently, pollution regulations have been tightened, and there is a need to reduce nitrogen oxides (NO _x ) in particular.
Two-stage combustion or exhaust gas recirculation to reduce _NO It was the cause. In other words, when such fly ash containing a large amount of unburned matter is used for fly ash cement, there are problems such as the cement becoming black or having an effect on the strength reduction, making it impossible to use it as it is. It was hot. In addition, it is predicted that the amount of fly ash generated will reach approximately 3.5 million tons by the end of 1985, so a method to dispose of the large amount of fly ash generated will be needed, and it will be used as cement, aggregate, building materials, civil engineering, etc. The use of fly ash is being studied in various fields, but as mentioned above, if the content of unburned matter in fly ash is high, it will have a negative effect on the material, so fly ash with less unburned matter is desired in various fields. It was rare. On the other hand, as a means of removing unburned matter from fly ash, the method of combusting the unburned matter is generally considered, but if all of the fly ash that is generated in large quantities is to be heat treated, then A large amount of fuel must be consumed, resulting in poor combustion efficiency.Furthermore, the unburned content in the fly ash has almost no volatility and is slightly graphitized, so the combustion rate is slow, and as a result the combustion rate inside the reformer is low. The drawback was that the residence time of the liquid had to be increased, making the equipment large and uneconomical. The present invention was developed based on the above-mentioned viewpoint, and it classifies the fly ash discharged from a pulverized coal-fired boiler to significantly reduce the amount of unburned waste to be treated, thereby reducing the amount of unburned fuel for combustion. The purpose of this project is to significantly reduce the amount of waste and make effective use of the fly assembly. The fly ash reforming method according to the present invention classifies fly ash discharged from a coal-fired boiler into coarse particles, medium particles, and fine particles by a known appropriate means. Fine-grained fly ash with a low content of unburned matter is used as an alternative fuel and fine powder, respectively, while medium-sized fly ash is further finely pulverized and classified into fine particles and fine particles. This method is characterized in that the fly ash is re-combusted in a reformer to remove unburned components. The content of unburned matter in the fly ash varies depending on the operating conditions of the boiler, the type and particle size of the pulverized coal, etc., but is generally about 5 to 15%. Among these fly ash, fly ash that can be used for cement generally has an unburned content of 5% or less, and for fly ash that can be used as an alternative fuel, it is advantageous to have a high unburned content. . In consideration of this point, in the examples according to the present invention, flyash was classified into coarse particles, medium particles, and fine particles within the range shown in Table 1.

[Table] According to the results in Table 1, the average particle size of fly ash discharged from a coal-fired boiler is approximately
It has a diameter of 30 μm and contains 7.9% unburned matter. When this is classified at 44μm and 149μm, the particle size is 44μm.
Unburned matter in fine fly ash less than 2.6 m
%, and coarse fly ash with a particle size of 150 μm or more contains 48.2% unburned matter. Therefore, as a fly ash for fly ash cement used with an unburned content of 5% or less,
While those with a diameter of less than 44 μm can be used as is, they contain 48.2% of unburned matter and generate a large amount of heat.
Coarse fly ash of 150 μm or more can be used as an alternative fuel. When classified as 44μm and 149μm in this way, the amount of so-called medium fly ash between 44μm and 149μm is about 1/3 of the total,
Also, the unburned content contained in it is approximately 13.4%, as is clear from Table 1. Next, when we compare the combustion speed of the unburned matter in the medium-grained fly ash classified in this way and the bituminous coal char, we find that the former is generally slower, so the combustion time of the unburned matter is shorter. It will be longer. Therefore,
In order to efficiently burn and remove unburned components, it is necessary to increase the combustion speed of unburned components. Furthermore, it is generally known that when solids are combusted, the combustion rate is linearly proportional to the particle size in the chemical reaction rate-determining stage. In order to confirm the above points, the present inventors finely pulverized fly ash of 44 μm to 149 μm to less than 44 μm, and measured the combustion rate of the pulverized material and the combustion rate of other materials using a thermobalance. As a result, the results shown in Figure 1 were obtained, and it was confirmed that the rate of chemical reaction was limited below 900°C. In Figure 1, the curve indicated by symbol a is for fly ash discharged from a coal-fired boiler, the curve indicated by symbol b is for medium-grained fly ash, and the curve indicated by symbol c is for pulverized fly ash, and the combustion time versus combustion temperature. It expresses the relationship between According to the measurement results, the combustion temperature of the pulverized fly ash was lower than that of other types, and the combustion time was also shorter, confirming the effect of pulverization on the combustion rate. In addition, the ignition temperature of unburned matter is shown in the table below.
As shown in Fig. 2, it decreased in the case of finely pulverized fly ash, indicating that there is an effect of finely pulverized fly ash.

【table】

[Table] In addition, when medium-sized fly ash is crushed, unburned particles are easily crushed and the particle size becomes smaller, so classifying the particles by particle size after crushing is effective in reducing the amount of unburned particles to be processed. It is true. In this example, 44μm to 149μm medium-grain fly ash is used.
Finely pulverize to a fly ash of 10μm or less.
When classified using m as the boundary, as shown in Table 3 below, the unburned content in fine fly ash with a particle size of 10 μm to 44 μm is 3.5%, and the unburned content in fine fly ash with a particle size of less than 10 μm is 3.5%. The fuel content is
It is 18.2%, and if it is classified around this area, the unburned content can be concentrated.

[Table] Therefore, according to the results in Table 3 above, 10μm~
The 44μm fine fly ash has an unburnt content of 5.
% or less, it can be used as a fine powder for fly ash cement and other uses.On the other hand, the final remaining fine fly ash of less than 10 μm is sent to a reformer to burn the concentrated unburned matter. It can be modified by
The amount of fine fly ash of less than 10 μm sent to the reformer is about 1/4 of the total amount of fly ash discharged from the coal-fired boiler. Incidentally, it has been confirmed that the above experimental results have a similar tendency for other types of fly ash, and it is possible to efficiently modify the fly ash. Next, a fly ash reforming apparatus according to the present invention will be explained based on an embodiment shown in the drawings. The reformer shown in FIG. 2 consists of two vertically long airflow furnaces 1 and 2 installed in parallel, one on the upper end outlet side of the primary airflow furnace 1, and the lower end inlet side of the other secondary airflow furnace 2. The main parts are composed of a combustion duct 3 that connects the secondary air flow furnace 2 and a cooler 5 that is connected to the upper end exit side of the secondary air flow furnace 2 via a cyclone 4. Each air flow furnace 1, 2 is
Mixing chambers 6 and 7 whose lower half has an inverted conical shape with a large angle of repose
In addition, the upper half is composed of cylindrical combustion chambers 8 and 9, and a part of the burned flyash is stored in the respective air flow furnaces 1 and 2 in each combustion chamber 8 and 9.
Separation and circulation devices 10 and 11 are respectively arranged for circulation within the chamber. This separation circulation device 10,1
1 is a small circulation cyclone 12, 13, a bunker 14 for temporarily retaining the flyash,
15, and cylindrical chute 16, 17 which guides the flyash falling from the bunkers 14, 15 to the lower part of the combustion chambers 8, 9. It communicates with the combustion duct 3 on the upper end exit side and the secondary air flow furnace exhaust duct 18 on the upper end exit side of the secondary air flow furnace 2, respectively. Further, a jet duct 20 branched from the combustion air supply duct 19 is vertically connected to the lower end of the mixing chamber 6 of the primary air flow furnace 1, and the combustion air supply duct 19 is connected to the combustion air supply duct 19 near this connection point. A swirling flow duct 21 branched from another part of the mixing chamber 6 is spirally connected to the side of the mixing chamber 6. Furthermore, the jet duct 20
A fly ash supply pipe 2 for supplying fine flow fly ash from a hopper 22 is located in the middle.
3 is connected to the mixing chamber 6, and an auxiliary burner 24 is connected to the mixing chamber 6.
is installed. Incidentally, one end of the combustion duct 3 is vertically connected to the lower end of the mixing chamber 7 of the secondary air flow furnace 2 having the same configuration as the above-mentioned primary air flow furnace 1, and the above-mentioned A swirling flow duct 25 constituted by the tip portion of the combustion air supply duct 19 is connected in the same manner as in the case of the primary air flow furnace 1 described above. In addition, the mixing chamber 7 includes a primary air flow furnace 1.
An auxiliary burner 26 is provided as in the case of . In the fly ash reformer configured as described above, high temperature air (e.g. exhaust heat air from a clinker cooling device of a cement firing plant) that has passed through the combustion air supply duct 19 is transferred to the jet duct 20 and the swirl duct. 21 into the lower part of the primary air flow furnace 1 and introduced into the middle part of the jet duct 20 from the fly ash supply pipe 23 while swirling the fine fly ash into the mixing chamber 6.
It squirts inside. In this case, the high-temperature air is sent into the inverted conical mixing chamber 6 with a large angle of repose while being affected by both an upflow flow and a swirling flow, so that the fine fly ash introduced therein is mixed. At the same time, it is possible to give a swirling effect to the fly ash and increase the residence time in the mixing chamber 6. The fine fly ash mixed in this way moves into the combustion chamber 8, where the unburned content in the fly ash is burned, and then introduced into the circulation cyclone 12.
2. Due to this separation effect, a portion (approximately 50%) of the flyash is discharged from the combustion duct 3 together with the combustion air, and
The remaining fly ash is retained in the bunker 14 for a short time and then falls within the chute 16, where it is re-combusted in the combustion chamber 8. As the fly ash is subjected to the circulation action in this way, the unburned parts of the same particles are burned many times, the particle size of the unburned parts gradually becomes smaller, and finally the fly ash is transferred from the circulation cyclone 12 to the combustion duct. It will be introduced within 3. In addition, when a fan for introducing outside air is provided at the tip of the combustion air supply duct 19 and the cold outside air introduced thereby is used as combustion air, the auxiliary burner 2
It is desirable to replenish the heat inside the furnace using 4, and maintain the inside of the furnace at about 700℃. Also, due to the circulation action of the fly ash, unburned matter is not burned,
An unburned matter extraction device (not shown) may be provided at the lower end of the mixing chamber 6 in case unburned matter of large particle size remains. The fly ash discharged from the primary air flow furnace 1 is introduced into the secondary air flow furnace 2 through the combustion duct 3 along with the exhaust gas, and is further mixed with combustion air supplied from the swirling flow duct 25 before entering the combustion chamber 9. and is burned again. Separation circulation device 11
After almost complete combustion of the unburned components due to the action of
The gas is introduced into the cyclone 4 via the cyclone 8 and collected in the cooler 5 after being separated from the exhaust gas. After being cooled by contact heat exchange with the cooling pipe 27, it is discharged outside the system and used for various purposes. Note that the exhaust gas discharged from the cyclone 4 is passed through an exhaust duct 2 connected to the upper part of the cyclone 4.
8 will be introduced. FIG. 3 shows another embodiment of the reformer according to the present invention, in which, like the previous embodiment, two airflow furnaces 1 and 2 installed in parallel are used to process unburned matter in fly ash. However, this embodiment differs from the previous embodiment in that a separation and circulation device 29 is provided between the primary airflow furnace 1 and the secondary airflow furnace 2. That is, the separation/circulation device 29 in this embodiment includes a circulation cyclone 30, a bunker 31, and a distributor 32 having an opening/closing mechanism 33 installed therein, which are connected in series to the upper end exit side of the primary air flow furnace 1, and this distributor. Circulation path 3 extending from the lower end of 32 to the middle of each jet duct 20a, 20b of primary air flow furnace 1 and secondary air flow furnace 2
4 and 35, the fine fly ash that has been combusted in the primary air flow furnace 1 is first separated and collected in a circulation cyclone 30, temporarily retained in a bunker 31, and then distributed by a distributor 32. It can be distributed to both circuits 34, 35 respectively. The fly assembly distributed to one circulation path 34 is
It is returned to the primary air flow furnace 1 again, and after undergoing combustion, is introduced into the circulation device 29 again. In addition, the fly ash distributed to the other circulation path 35 is
Unburned matter is almost completely combusted in the second air flow furnace 2, collected by a cyclone 4, and then cooled by a cooler 5. Note that the exhaust gas from the circulation cyclone 30 and the cyclone 4 is guided into the exhaust gas duct 28. In this embodiment, the primary air flow furnace 1 is
The circulation of the flyash returned to the inside is carried out by the distributor 3.
The amount of circulation is determined by the amount of unburned matter in the reforming flyash discharged from the cooler 5. If the amount is large, complete combustion of the unburned matter can be achieved by increasing the amount of circulation and increasing the chances of combustion. In this embodiment, since the separation circulation device 29 is provided outside the air flow furnaces 1 and 2, the pressure loss inside the air flow furnaces 1 and 2 is smaller than in the previous embodiment, and the primary air flow furnace This has effects such as being able to adjust the amount of circulation of the fly ash to No. 1. The fly ash recovered from the cooler 5 of the reformer in the above embodiment has an unburned content of 0.5.
%, and this can be used for fly-ash cement and other purposes. 4 and 5 show the two types of reformers shown in the above embodiments incorporated into a cement firing plant, in which the combustion air supply duct 19 is connected to the cement clinker cooling device 36, and the cooling device is connected to the cement clinker cooling device 36. The high-temperature air of approximately 700°C extracted from the fly ash is used as unburned combustion air, while the reformer's exhaust duct 28 is connected to an appropriate position of the suspension preheater 37, and the exhaust gas after the fly ash is combusted is The amount of heat it has is used to preheat cement raw materials. In this way, by incorporating a reformer into a cement firing plant, high-temperature combustion air can be used.
In addition to significantly reducing the amount of fuel used in 6, the fly ash contained in the exhaust gas, which has extremely small particle sizes, can be used as part of the raw material for cement. There is no need to generate dust, and the waste heat from the reformer of the present invention can be recovered and used in the suspension preheater 37, so it has great industrial utility value. As explained above, according to the fly ash reforming method of the present invention, by classifying the fly ash discharged from a coal-fired boiler, the amount of unburned matter to be treated can be significantly reduced. In addition to saving fuel for combustion, the combustion furnace can be made smaller. Further, by classifying the flyash in this manner, all the flyash discharged can be effectively used industrially. Further, according to the reformer according to the present invention, since the residence time of unburned matter is increased and the unburned matter can be circulated, the unburned matter is almost completely combusted and the amount contained in the reforming fly ash is increased. The amount of unburned matter produced can be made extremely small.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the combustion temperature and combustion time of unburned components contained in the fly ash, FIG. 2 is an explanatory diagram showing an embodiment of the reformer according to the present invention, and FIG. FIGS. 4 and 5 are explanatory diagrams showing other embodiments of the reforming device. FIGS. 4 and 5 are explanatory diagrams showing an embodiment in which the reforming device according to the present invention is incorporated into a cement firing plant. 1...Primary air flow furnace, 2...Secondary air flow furnace, 6,7
... Mixing chamber, 8, 9 ... Combustion chamber, 10, 11, 2
9...Separation circulation device, 19...Combustion air supply duct, 20...Jet flow duct, 21, 25...Swirling flow duct, 28...Exhaust duct, 36...Cooling device, 37...Suspension preheater.

Claims (1)

[Claims] 1. Fly ash discharged from a coal-fired boiler is classified into coarse, medium, and fine particles, and the coarse fly ash with a high unburned content is used as an alternative fuel.
In addition, while fine-grained fly ash with a low unburned content is used as refined powder, the classified medium-grained fly ash is further finely pulverized and classified into fine particles and fine particles. Granular fly ash is used as fine powder, and the fine fly ash containing a large amount of unburned matter is combusted again in a reformer to remove the unburned matter, and this is used as fine powder. Method for modifying fly atsushi. 2. The fly ash according to claim 1, wherein exhaust heat air from a clinker cooling device of a cement firing plant or outside air is introduced into the reformer as combustion air for the fine fly ash. modification method. 3. The fly ash reforming method according to claim 1, wherein the exhaust gas discharged from the reformer is used for preheating raw materials in a cement firing process. 4. 1 which has a mixing chamber and a combustion chamber, and a jet duct and a swirling duct are connected to the lower end of the mixing chamber for introducing air for combustion of fine fly ash.
A secondary airflow furnace, which has almost the same configuration as the primary airflow furnace, is connected to the outlet side of the primary airflow furnace, and is used to reburn the fine fly ash discharged from the primary airflow furnace. , disposed between the primary airflow furnace and the secondary airflow furnace or inside both airflow furnaces, and transferring a part of the fine fly ash burned in the primary airflow furnace and/or the secondary airflow furnace to the primary airflow furnace. Inside the furnace and 2
1. A fly ash reforming device characterized by comprising a separation and circulation device for circulating within the secondary air flow furnace or within the primary air flow furnace. 5. Claim 4, wherein the jet flow duct and the swirl flow duct are connected to a clinker cooling device of a cement firing plant via a combustion air supply duct.
The fly ash reforming device described in Section 1. 6. The fly ash reforming device according to claim 4, wherein the jet flow duct and the swirl flow duct are connected to an outside air introduction device via a combustion air supply duct. 7. The fly ash reforming device according to claim 4, wherein at least a part of the exhaust duct in the reforming device is connected to an appropriate position of a suspension preheater of a cement firing plant.