JPS5885011A - Modifying method and apparatus for fly ash - Google Patents

Abstract

PURPOSE:To largely reduce the amount of unburnt fly ash to be disposed, by classifying the fly ash discharged from a coal boiler into coarse particles, medium particles and fine particles, and by burning particles which contain a large amount of unburnt content in a modifier unit, so that the unburnt content is nearly completely burnt out. CONSTITUTION:When a modifier unit is brought into operation, first, the air in high temperature, fed from a duct 19, is injected into the lower part of a primary air current furnace 1 through a jet air duct 20 and a swirl air duct 21. While, fly ash having unburnt content, previously classified, is fed into the jet air duct 20 from a hopper 22. The fly ash, swirling, gets into a combustion chamber 8, jetted up through a mixing chamber 6. The unburnt content is burnt out in the combustion chamber 8, but a part of unburnt content is fed into a secondary air current furnace 2, passing through a cyclone 12 and a combustion duct 3, together with the combustion air, and is further burnt in the same manner. The fly ash, of which unburnt content is almost completely burnt out, gets into a cyclone 4, where exhaust gas is separated, and is collected into a cooling unit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reforming fly ash in exhaust gas discharged from a pulverized coal-fired boiler, and a reforming apparatus therefor.

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 it becomes spheroidized due to surface roughness 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, especially regarding nitrogen oxides (N).
Because it is necessary to reduce the
Since an oxidizing means is used, the fly ash contains an equivalent amount of unburned matter for reduction, which causes the properties of the fly ash to deteriorate. In other words, when such fly ash with a high unburned content is used for fly ash cement, it cannot be used as it is because the cement turns black and the strength of the cement decreases. There was a problem □. In addition, the amount of fly ash generated was 350 at the end of the Showa era.
Since it is predicted that the amount of fly ash will reach approximately 10,000 tons, a method for processing the large amount of fly ash generated is required, and studies are underway to find ways to use it in fields such as cement, aggregate, building materials, and civil engineering. As mentioned above, if the unburned content in fly ash is high, it will have a negative effect on the material, so fly ash with less unburned content has been desired in various fields.

On the other hand, as a means of removing unburned matter from fly ash, a method of burning the unburned matter is generally considered.
If all of the fly ash that is generated in large quantities were to be heat-treated, a large amount of fuel would have to be consumed for combustion, resulting in poor combustion efficiency, and the unburned content in fly ash would have little volatility. Because graphitization on the ψ has progressed a little, the combustion rate is slow, which requires a longer residence time in the reformer, which has the disadvantage of increasing the size of the device and making it uneconomical.

The present invention was made based on the above-mentioned viewpoint, and it classifies fly ash discharged from pulverized coal-fired boilers to significantly reduce the amount of unburned waste to be treated, thereby significantly reducing the amount of fuel for unburned combustion. The purpose of this project is to reduce the amount of fly ash and make effective use of fly ash.

The method for reforming 7-litre ash according to the present invention involves classifying fly ash discharged from a coal-fired boiler into coarse particles, medium particles, and fine particles by a known appropriate means, and then classifying the fly ash discharged from a coal-fired boiler into coarse particles, medium particles, and fine particles. and fine-grained 7 litash with low unburned content are used as alternative fuel and fine powder, respectively, while medium-sized fly ash is further finely pulverized and classified into fine particles and fine particles, which contain unburned content. This method is characterized by re-combusting a large amount of fine fly ash using a reformer to remove unburned components.

The content of unburned matter in fly ash varies depending on the operating conditions of the boiler, the type and particle size of pulverized coal, etc., but it is approximately 5.
It is about 15%.

Among these, fly ash that can be used for fly ash cement generally has an unburned content of 5% or less, and although it can be used as an alternative fuel, the one with a higher unburned content is more advantageous. be. In consideration of this point, in the examples according to the present invention, fly ash was classified into coarse particles, medium particles, and fine particles within the range shown in Table 1.

Table 1 According to the results in Table 1, the average particle size of fly ash discharged from a coal-fired boiler is approximately 30 mm.
Contains 7.9% unburned matter.

When this was classified by 44 IIm and 149/Jn, 2.6% of unburned matter was contained in the fine ply ash with a particle size of less than 44I1m, and the coarse ply ash with a particle size of 150#1 or more contained 2.6%. contains 48.2% unburned matter.

Therefore, it is necessary to use 44 tt as fly ash for Ichinori Atsushi cement, which is used with an unburned content of 5% or less.
While less than 150 ean can be used as is, the unburned content is 48.2% and the calorific value is large.
Coarse-grained ply ash can be used as an alternative fuel. When classified as 447in and 149) an f boundaries, the amount of so-called medium-grained fly ash from 441Im to 149Im is about A, and the unburned content contained in it is as shown in Table 1. As is clear, about 1
It is 3.4%.

Next, when we compare the combustion speed of the unburned content in the medium-grained 7-liar sorghum classified in this way and the bituminous coal char, we find that the former is generally slower, so the combustion time of the unburned content is is longer. Therefore, in order to efficiently burn and remove the unburned components, it is necessary to increase the combustion speed of the unburned components. or,
−↓ ζsu.

It is generally known that the combustion rate of a solid combustion chamber is linearly proportional to the particle size in the chemical reaction rate-determining stage. In order to fully address the above points, the inventors have developed 4
447 fly ash from Cape 4 to Cape 149! As a result of pulverizing the pulverized material to less than Il1 and measuring the combustion rate of the pulverized material and the combustion rate of other materials using a thermobalance, the results shown in Figure 1 were obtained: Below 900°C, the chemical reaction is rate-limiting. It was confirmed that there is.

In Figure 1, the curve indicated by symbol a is for fly ash discharged from a coal-fired boiler, the curve already indicated by symbol is for medium-grained fly ash, and the curve indicated by symbol C is for finely pulverized fly ash. According to this measurement result, the combustion temperature of finely pulverized ply ash is lower than that of other types, and the combustion time is also short, so the combustion rate due to pulverization is The effect is M! It was done. In addition, as shown in Table 2 below, the ignition temperature of unburned matter is lower in the case of finely pulverized fly ash, so it was found that pulverization has an effect.

Table 2 In addition, when medium-grained fly ash is crushed, the unburned particles are easily crushed and the particle size becomes small. Effective. In this example, 44 Cape ~ 149IIrn
When medium-grained fly ash is finely pulverized into fly ash of 44 IIm or less, and this is classified using Cape 10 as the boundary,
As shown in Table 3 below, the particle size is 10p to 44#n
The unburned content in the fine-grained fly ash of n is 3.5%, and the unburned content in the fine-grained fly ash below the lO cape is 18.2%. You can concentrate the unused portion.

Table 3 Therefore, according to the results of Table 3 above, 10Ixn~44
Since IMn's fine-grained 7-litre ash has an unburned content of less than 5%, it can be used as fine powder for fly ash cement and other uses, while the final remaining fine-grained fly ash of less than 110l1 can be reformed by sending it to a reformer and burning the concentrated unburned content. Note that the amount of 1Oltn ungrooved fine fly ash sent to the reformer is approximately % of the total amount of fly ash discharged from the coal-fired boiler.

In addition, it has been confirmed that the above experimental results have a similar tendency for other types of fly ash, and fly ash can be efficiently modified.

Next, the fly ash reforming apparatus according to the present invention will be explained based on the embodiment shown in the drawings. The reforming apparatus shown in FIG. , one of the
A combustion duct 3 that connects the upper end exit side of the secondary air flow furnace 1 and the lower end inlet side of the other 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. The main part consists of. Each of the air flow furnaces 1 and 2 has an inverted conical mixing chamber 6, 7 with a large angle of repose in its lower half, and a cylindrical combustion chamber 8, 9 in its upper half. Separation and circulation devices 10 and 11 for circulating part of the burned fly ash within the air flow furnaces 1 and 2, respectively, are arranged within the combustion chamber 8.9. This separation circulation device 10.11Fi, small circulation cyclone 12, 13
and bunker 14 that temporarily retains fly ash.
, 15, and a cylindrical shoe that guides the fly ash falling from the bunkers 14 and 15 downward into the combustion chambers 6 and 1).
The circulation cyclones 12 and 13 are composed of the combustion duct 3 on the upper end outlet side of the primary air flow furnace 1 and the secondary air flow furnace exhaust duct 18 on the upper end exit side of the secondary air flow furnace 2. are connected to each other. Further, a jet duct λ branched off 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 near this connection point, the combustion air supply duct A swirling flow duct 21 branched off from the other part of the mixing chamber 6 is spirally connected to the side of the mixing chamber 6. Further, a fly ash supply pipe n for supplying fine fly ash from a hopper n is connected to a midway portion of the jet duct 20, and an auxiliary burner 24 is installed in the mixing chamber 6. 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 Combustion air supply duct 19
The swirling flow duct core constituted by the tip part of the above-mentioned 1
They are connected in the same way as in the secondary air flow furnace 1. Further, the mixing chamber 7 is provided with an auxiliary nozzle as in the case of the primary air flow furnace 1.

In the fly ash reforming device configured as described above, high-temperature air (for example, exhaust heat air from the tarinka cooling device of a cement firing plant) that has passed through the combustion air supply duct 19 is swirled with the jet duct 20. flow duct 21
The fine fly ash is fed into the lower part of the primary air flow furnace 1 through the ply ash supply pipe n and introduced into the middle part of the jet duct 20. Since the fly ash is fed into the mixing chamber 6, it is possible to promote mixing of the fine particles of fly ash introduced therein, 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.
It is subjected to the separation effect by Due to this separation effect, a part of the fly ash (approximately 50%) is discharged from the combustion duct 3 along with the combustion air, and the remaining fly ash is retained for a short time in the bunker 14 and then falls in the chute 16. Then, it undergoes re-firing in the combustion chamber 8.

As the fly ash is subjected to the circulation action in this way, the unburned particles of the same particles are burned many times, and the particles of the unburned particles gradually become smaller in size. It will be introduced within 3. In addition, a fan for introducing outside air is arranged at the tip of the combustion air supply duct 19,
When the outside cold air introduced by this is used as combustion air, it is desirable to use the auxiliary burner 24 to replenish the amount of heat inside the furnace, and maintain the inside of the furnace at about 700'0. In addition, in case the unburned matter is not combusted even by the circulating action of the fly ash and unburned matter of large particle size remains, an unburned matter extraction device (not shown) is installed at the lower end of the mixing chamber 6. It is also possible to provide one.

The fly ash discharged from the primary airflow furnace 1 passes through the combustion duct 3 together with the exhaust gas and is introduced into the secondary airflow furnace 2.
After being further mixed with the combustion air supplied from the swirling flow duct 3, it moves to the combustion chamber 9 and is combusted again. The fly ash after the unburned content has been almost completely combusted by the action of the separation circulation device 110 is introduced into the cyclone 4 together with the exhaust gas through the secondary air flow furnace exhaust duct 18, and is captured in the cooler 5 after being separated from the exhaust gas. collected. After being cooled by contact heat exchange with the cooling pipe R, it is discharged outside the system and used for various purposes. Incidentally, the exhaust gas discharged from the cyclone 4 is introduced into an exhaust duct 28 connected to the upper part of the cyclone 4.

FIG. 3 shows another embodiment of the reformer according to the present invention, in which, like the previous embodiment, two air flow furnaces 1 are installed in parallel.
．． This embodiment is different from the previous embodiment in that the separation and circulation device 4 is provided between the primary airflow furnace 1 and the secondary airflow furnace 2. It has become.

That is, in this embodiment, the separation circulation system [29] includes a circulation cyclone (equipment) connected in series to the upper end outlet side of the primary air flow furnace 1, a bunker 31, and a distributor 32 equipped with an opening/closing mechanism inside. It is composed of circulation passages 34 and 35 extending from the lower end of this distributor 32 to the middle part of each jet duct 20a, 20b of the primary airflow furnace 1 and the secondary airflow furnace 2, and the primary airflow furnace 1 The fine fly ash that has been combusted is first separated and collected in a circulation cyclone 30, temporarily retained in a bunker 31, and then distributed to both circulation paths (, 35) by a distributor 32. Circulation path 3
The fly ash that has been sorted into 4 is returned to the primary air flow furnace 1, and after being combusted, it is introduced into the circulation device 29 again. Further, the unburned content of the fly ash distributed to the other circulation path is almost completely burned in the secondary air flow furnace 2, and after being collected by the cyclone 4, it is cooled by cooling 115. Note that the exhaust gas from the circulating cyclone and the cyclone 4 is guided into the exhaust gas duct 2B.

In this embodiment, the circulation of the fly ash returned to the primary airflow furnace 1 through the circulation path is carried out by adjusting the opening/closing angle of the opening/closing mechanism in the distributor 32. It is determined by the amount of unburned content in the reformed fly ash discharged from the fly ash. For example, if there is a large amount of unburned content, the amount of circulation should be increased to increase the chances of combustion. Therefore, complete combustion of the unburned content is achieved. can be achieved. In this embodiment, since the separation circulation device 4 is provided outside the air flow furnaces 1 and 2, the pressure loss inside the air flow furnace 1.2 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 fly ash circulated to the 1.

The fly ash recovered from the cooler 5 of the reformer in the above embodiment has an unburned content reduced to 0.5%, and can be used for papermaking, fly ash cement, etc.

Figures 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 The high-temperature air of about 700°C extracted from the device 5 is used as unburned combustion air, while the exhaust duct 28 of the reformer is connected to the suspension preheater 3.
7 and utilizes the heat of the exhaust gas after burning the fly ash to preheat the cement raw material. In this way, by incorporating a reformer into a cement firing plant, high-temperature combustion air can be used, and the fuel for the auxiliary burners 24 and 26 for heating the combustion air installed in the air flow furnace of the reformer can be used. In addition to being able to significantly reduce the amount used, the fly ash contained in the exhaust gas, which has an extremely small particle size, can be used as part of the cement raw material, so it has great utility.

As explained above, according to the fly ash reforming method according to the present invention, by classifying the fly ash discharged from a coal-fired boiler, the amount of unselected partial treatment can be significantly reduced. Therefore, not only can fuel for unburned combustion be saved, but also the combustion furnace can be made smaller. Further, by classifying the fly ash in this manner, all the discharged fly ash can be effectively used industrially.

Furthermore, according to the reformer according to the present invention, since the residence time of unburned substances is increased and the unburned substances can be circulated,
The unburned matter is almost completely combusted, and the amount of unburned matter contained in the modified fly ash can be reduced to an extremely small amount.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the combustion temperature and combustion time of unburned components contained in fly ash, Fig. 2 is an explanatory diagram showing one embodiment of the reformer according to the present invention, and Fig. 3 is an explanatory diagram showing another embodiment of the reforming device, and FIGS. 4 and 5 are 112-illustration 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 chambers 10, 11
, 29...Separation circulation device 19...Combustion air supply duct

Claims (7)

[Claims] (1) The ply ash discharged from coal-fired boilers is classified into coarse, medium, and fine particles, and the coarse 7-liter ash, which has a high unburned content, can be used as an alternative fuel, and the ply ash, which has a low unburned content, can be used as an alternative fuel. While fine-grained ply ash is used as fine powder, classified medium-grained fly ash is further finely pulverized into fine particles and fine particles, and fine-grained ply ash with a low unburned content is refined. It is characterized in that it is used as a powder, and the fine grained 7-lion pulp containing a large amount of unburned matter is burned again in a reformer to remove the unburned matter, and then used as fine powder. Method for modifying fly ash. (2) Exhaust heat air from a talin cooling device of a cement firing plant or outside air is introduced into the reformer as combustion air for fine fly ash. 7. Method for modifying rhinoshu described in Section 7. (3) The method for reforming fly ash according to claim 1, characterized in that the exhaust gas discharged from the reformer is used for preheating raw materials in a cement firing process. (4) A primary air flow furnace having a mixing chamber and a combustion chamber, and a lower end of which a jet flow duct and a swirl flow duct for introducing air for fly ash combustion are constricted, and this primary air flow furnace. It has almost the same configuration as the primary airflow furnace, and is connected to the outlet side of the primary airflow furnace for re-burning the fly ash discharged from the primary airflow furnace, and the primary airflow furnace and the secondary airflow furnace. Reformation of fly ash characterized by having a separation and circulation device disposed inside the airflow furnace both between the furnace and the airflow furnace, and for circulating in the secondary airflow furnace or in the primary airflow furnace. Device. (5) The fly ash reforming device according to claim 4, wherein the jet flow duct and the swirl flow duct are connected to a tarinka cooling device of a cement firing plant via a combustion air supply duct. (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 i 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.