JPH0587757B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for burning municipal waste, industrial waste, coal and other combustible materials in a fluidized bed, and at the same time recovering thermal energy from the fluidized bed. The present invention relates to a heat recovery method and apparatus.

[Conventional technology]

Conventionally, heat recovery from a fluidized bed such as a fluidized bed boiler is carried out by fluidizing gas 33 supplied to an air chamber 34 below a distribution plate 32 provided on the floor surface of a furnace 31, as shown in FIG. 6, for example. A heat transfer tube 36 is disposed within a bed 35 made of a fluidized medium to be fluidized,
The input combustion material 37 is fluidized and combusted, and heat is recovered from the fluidized medium.

By the way, this type of fluidized bed boiler has a bed of 3
The balance between heat generation and heat absorption in the bed 35 greatly depends on the characteristics, especially the calorific value, of the combustion object 37 assumed at the time of design, so when changing the combustion object, it is necessary to change the heat transfer area in the bed 35 according to the characteristics. It was hot. In addition, the boiler load of one bed 35 can only be reduced by about 80% due to the need to maintain the fluidized state and fluidized bed temperature while cooling the fluidized bed, so when a wide turndown ratio is required, The system needs to be of a multi-bed type, making control complicated and expensive. On the other hand, when coal or the like is used as the combustion material, it must be pulverized, and a spreader or the like is required to uniformly disperse the coal into the bed 35. In addition, bed 35
The inner heat transfer tubes 36 have had many problems in that they are susceptible to severe corrosion in a reducing atmosphere due to abrasion and combustion caused by the fluidized medium at a high flow rate.

In order to solve these problems, in a spouted bed circulation type fluidized bed boiler in which heat exchanger tubes 36 are separately placed externally as shown in FIG. It exits the board section 38 and enters the cyclone 39, and is separated into the cyclone 39.
The exhaust gas is collected at the bottom of the pipe and sent to the next equipment via the flue 40. The fluidized medium and the like separated by the cyclone 39 are guided to the heat exchanger chamber 41. A distribution plate 42 is provided on the floor of the heat exchanger chamber 41, and a fluidized bed 45 is formed by the fluidizing gas 33 supplied to an air chamber 44 formed at the bottom of the distribution plate 42. A heat transfer tube 36 is provided in the fluidized bed 45 to recover the heat of the fluidized medium, and the cooled fluidized medium is circulated to the furnace 31 again and heated again. However, this spouted bed circulation type fluidized bed boiler also has the problem that as the equipment increases and becomes larger, troubles tend to increase.

[Problem that the invention seeks to solve]

The present invention solves these problems by dividing the fluidized bed into a combustion part for the combustible material and a heat recovery part for recovering heat from the fluidized medium, and refluxing the fluidized medium from the combustion part through the heat recovery part. A method and device for recovering heat from a fluidized bed that makes the whole body compact by circulating it, has a large tolerance for combustible materials, has a significantly wide turndown ratio, and facilitates maintenance. The purpose is to provide

[Means for solving problems]

As a means for solving the above-mentioned problems, the present invention provides a fluidized bed in which a fluidized medium is fluidized by fluidizing gas blown upward from the bottom, the upper end of which is submerged into the fluidized bed, and a communication port formed at the lower part. A heat recovery section and a combustion section that supplies combustible materials are divided by sharing an upper space by a partition wall, and the flow rate of fluidizing gas blown per unit area at least near the partition wall of the combustion section is set as above. By making the fluidizing gas flow rate larger than the flow rate per unit area of the heat recovery section, the fluidized medium of the combustion section is caused to flow into the heat recovery section over the partition wall, and the flow rate of the fluidized gas blows into the heat recovery section from the lower part of the partition wall. The present invention provides a method for recovering heat from a fluidized bed, characterized in that the fluidized medium of the present invention is returned to a combustion section, and also provides a suitable apparatus for carrying out this method.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings. In the first illustrated example, a fluidized medium made of a fluidized medium is fluidized by a fluidized gas 3 such as air that is blown upward from the bottom in a furnace 1. The layer 5 is divided by a partition wall 7 so that a heat recovery section 8 and a combustion section 9 share a free space. Partition wall 7
The upper end is located below the surface of the fluidized bed 5, that is, the upper end is submerged into the fluidized bed 5, and the communication port 6 is formed at the lower part. For this partition wall 7, a refractory material is used on the side of the combustion section 9 to suppress heat recovery from the combustion section and to withstand the intense movement of the fluidized medium and combustion gas in the combustion section, and the inner wall of the heat recovery section 8 is made of refractory material. It is preferable that the water cooling wall 10 be a part of the heat recovery surface and that the partition wall refractory be protected.

The fluidizing gas 3 is injected into the heat recovery section 8 and the combustion section 9 independently, and in the heat recovery section 8, the fluidizing gas 3 is injected into the air chamber 4 under the distribution plate 2 on the floor for flow adjustment. Fluidizing gas 3 with valve 11
In the combustion section 9, a flow control valve 1 is installed in the air chamber 4' below the distribution plate 2' on the floor.
An inlet pipe for the fluidizing gas 3 having a number 1' is connected and opened.

Further, the heat recovery section 8 is provided with a heat transfer tube 12 through which heat-receiving fluid is passed, and the combustion section 9 is provided with an input port 15 connected to a supply device 14 for a combustible material 13.

In the figure, 16 is an incombustible material discharge port provided at the lowest position of the dispersion plate 2' of the combustion section 9, 17 is an exhaust gas boiler provided in the passage of the combustion exhaust gas 18 and utilizes its exhaust heat, and 19 is the fluidized bed 5. 3 shows bubbles of fluidized gas 3 blown into the interior.

The combustible material 13 fed into the combustion section 9 in the furnace 1 by the feeding device 14 through the inlet 15 is
The fluidizing gas 3 blown from the bottom air chamber 4' through the distribution plate 2' causes the fluidized bed 5 to flow together with the fluidized medium.
It burns and generates heat while forming. At this time, the flow rate regulating valve 11' increases the flow rate of the fluidizing gas per unit area to generate a large number of large bubbles 19 in the fluidized bed 5 in the combustion section 9 to create an intense fluidized state. The surface of the surface is violently rippled, and the average surface level is raised by air bubbles. On the other hand, in the heat recovery section 8, the flow rate control valve 11 reduces the flow rate of fluidizing gas per unit area.
The fluidized bed surface level of the heat recovery section 8 should be set to a fluidized state in which large bubbles do not easily occur, or a weak fluidized state in which the fluidized medium can simply move by the amount of the fluidized medium flowing into the upper part of the bed, and the surface level of the fluidized bed in the heat recovery section 8 should be set to the level of the combustion section 9. It shall be relatively lower than that.

Therefore, due to the surface level difference, the fluidized medium level flows from the combustion section 9 into the heat recovery section 8 over the partition wall 7 as shown by arrow A. In addition, when the bubbles 19 generated in the combustion zone 9 rise within the layer, reach the surface, and burst, a large amount of fluidized medium is ejected from the surface of the fluidized bed 5, but a considerable portion of it remains as it is as shown in the arrow. B
The heat flows into the heat recovery section 8 as shown in FIG. The heat possessed by the fluidized medium flowing into the heat recovery section 8 is recovered by heat exchange with the heat transfer tube 12 in the heat recovery section 8 . Then, at the communication port 6 at the bottom of the partition wall 7, the fluidized medium that has flowed into the upper part of the heat recovery section 8 increases the pressure of the heat recovery section 8 against the combustion section 9, and the differential pressure acts as a force to move the fluidized medium. Working hard,
The fluidized medium whose heat has been recovered and has reached the lower part flows back to the combustion section 9 from the communication port 6 as shown by arrow C. Therefore,
The portion of the communication port 6 is reliably refluxed even without blowing fluidizing gas from the bottom.

As a result, the fluidized medium as a whole moves from bottom to top in the combustion section 9 and from top to bottom in the heat recovery section 8, but the amount greatly depends on the flow rate of fluidized air blown into the combustion section 9 and the height of the fluidized bed. However, according to the experiments conducted by the present inventors, a relationship as shown in FIG. 2 was obtained. From this result, the amount of fluidized air in the combustion section 9 can be minimized if heat is recovered by circulating a fluidized medium such as sand-like incombustibles or crushed limestone or crushed dolomite that also serves as a desulfurization agent in the heat recovery section 8. It can be seen that at least 2 to 3 times the speed (Gmf) is required.
Note that the fluidized bed height (the bed height when the fluidized medium is flowing) is required to reach the top of the partition wall 7, and if it becomes lower than the bed height to the top of the partition wall in the flow state of at least L ₂ , the height of the fluidized bed suddenly increases. There is no problem if the circulation rate decreases and it becomes impossible to actually recover heat from the fluidized bed.

This shows that if the amount of fluidized air is set to about twice the minimum fluidization speed or less, almost no fluidized medium will circulate in the heat recovery section 9, and this means that the surface of the fluidized bed will become quiet, as shown by the arrow This can be explained by the fact that the inflows of A, B, and D all decrease drastically. However, this shows that it is possible to extremely suppress the amount of heat recovery thereby. In addition, when the amount of fluidized air increases and becomes more than three times Gmf, the amount of fluidized medium circulating also increases in proportion to the amount of fluidized air, so the combustion air for the combustion material 13 is also fluidized air at the same time. Therefore, the amount of circulation can be increased almost in proportion to the amount of combustion of the combustible material, and the heat exchange rate between the heat receiving fluid and the fluidizing medium can be changed by adjusting the amount of flowing air blown into the heat recovery section 8 ( (See Figure 3 and its explanation below), the temperature of the fluidized bed will not reach supercooling or overheating, and the combustion material can be increased or decreased according to the demand for recovered heat while maintaining an appropriate air ratio. becomes possible.

Therefore, a large turndown ratio can be achieved, and the amount of heat recovered by the heat transfer tubes 12 in the heat recovery section 8 can be reduced to almost 0, and even the amount of heat recovered including the connected exhaust gas boiler 17, the amount of heat recovered from the fluidized bed is small. By discontinuing recovery, the increase in fluidized bed temperature can be suppressed by air cooling using the amount of fluidized air, and it is possible to maintain the fluidized state and fluidized bed temperature with less fuel, so the increase in fluidized bed temperature can be reduced by 1/
It is possible to reduce the minimum amount of heat to be recovered relative to the maximum amount of heat to be recovered by about 10%. At the same time, in the heat recovery section 8, it is possible to provide fluidized air with only heat transfer in mind, regardless of the air required for combustion, and it is possible to suppress the fluidized state to a weak fluid state of about twice Gmf, so that the fluidized bed boiler It also has the effect of greatly reducing the wear on the heat transfer surface that would otherwise be unavoidable.

That is, it is known that the relationship between the heat transfer coefficient and the amount of flowing air in the heat recovery section 8 is as shown in FIG. 3, and the inventors of the present invention have also confirmed this. According to this, it is unnecessary to set the Gmf to more than twice the Gmf for heat transfer purposes, and it will unnecessarily increase the abrasion caused by the fluidized medium on the heat transfer surface. Since it only needs to be adjusted according to the amount of heat transfer, it is only necessary to change it according to the amount of heat transfer.
It does not need to exceed twice the GMF. This also applies to the combustion section 9 for fluidized medium circulation, as mentioned above.
On the other hand, it is preferable because the amount of flowing air in the heat recovery section 8 needs to be relatively small.

Furthermore, since the combustible material 13 is introduced into the combustion section 9, corrosion caused by the combustion gas on the heat transfer surface and corrosion caused by changes in oxidation-reduction accompanying combustion are reduced, and the flow of the fluidized medium in the heat recovery section 8 is also reduced. Since it is gentle, there is less wear on the heat transfer surface, and the life of the heat transfer surface is significantly improved compared to conventional methods. In addition, the combustion part 9 is in a sufficiently agitated state due to the constant generation of large bubbles 19, and even if the combustion material 13 is concentrated to some extent or is introduced in lumps, the fluidized medium in the bed is Since it is agitated by movement, broken up and dispersed, it is in a weakened fluid state to around 2 to 3 times the Gmf to protect the heat transfer surface, and compared to the conventional one, which keeps the hearth load small. As a result, clinker is less likely to occur and the combustion rate is significantly improved. For example, a combustion rate of 90% or more can be obtained by simply charging coal into the combustion section 9.

Note that if the dispersion plate 2 of the heat recovery section 8 is sloped downward toward the combustion section 9, it is advantageous for discharging the fluidized medium out of the furnace during periodic inspections, etc.
If the dispersion plate 2' is sloped downward toward the incombustible material discharge port 16, it becomes easy to discharge noncombustible materials and a fluid medium for periodic inspection.

Furthermore, the present invention is provided with a reflecting wall 20 above the combustion section 9 and close to the fluidized bed 5 for deflecting the rising gas flow toward the heat recovery section 8 as shown in FIG. Nothing else will change. This reflecting wall 20 can be a part of the furnace wall as in the first illustrated example, but depending on the structure of the furnace 1, it may be formed separately from the furnace wall as in the fourth illustrated example. It can also be taken as a thing.

When this reflecting wall 20 is provided, the fluidized medium ejected from the surface of the fluidized bed 5 collides with the reflecting wall 20, is deflected and guided to the heat recovery section 8 as shown by arrow D, and the circulation of the fluidized medium becomes extremely smooth. be done.

FIG. 4 shows another embodiment of the present invention, in which the first embodiment is arranged in the furnace 1 almost symmetrically with respect to the center line. That is, the combustion section 9 is located in the center of the furnace 1, and the heat recovery section 8 is provided on both sides with a partition wall 7 interposed therebetween. , and in order to smooth the movement of the fluidized medium in the combustion section 9, the air chamber 4' is divided into two air chambers 4'-1 and 4'-2, which are equipped with flow rate control valves 11, 11'-1, and 4'-2, respectively. 11'-2 to adjust the amount of fluidizing gas blown into each air chamber 4, 4'-1, 4'-2, so that the amount of fluidizing gas blown per unit area is lower than that of air chamber 4'-1. The chamber 4'-2 is made larger. Of course, even in this case, the air chamber 4'
Air chamber 4 is made smaller than -1. In order to blow the fluidizing gas 3 into the fluidized bed 5, a diffuser nozzle 21 is used in place of the dispersion plates 2, 2' of the first illustrated example in the fourth illustrated example. Further, when the reflective wall 20 is provided, it is independent from the furnace wall, and an opening is provided in the center for introducing the combustion material 13 into the combustion section 9.

In this fourth illustrated example, the same effect as in the first illustrated example is performed, but the throughput is large, the heat load increases, the calorific value of the combustible material is high,
This is advantageous when large-sized or high-load applications are required that require additional heat transfer area.

In addition, in each of the above examples, when the lower calorific value of the combustible material is relatively low, about 2000 to 4000 kcal/Kg, the amount of heat that must be recovered from the fluidized medium is not very large, so the required fluidized medium circulation amount is It may be less. In that case, the amount of circulation can be covered even if the reflective wall is eliminated.

The height of the partition wall 7 needs to be low to some extent so that the fluidized medium in the combustion section 9 can easily flow into the heat recovery section 8, but it is not preferable that the height is too low for the following reasons. For example, the heat recovery section 8 includes the combustion section 9.
Air bubbles may enter the heat recovery section 8, or the fluidized medium that has flowed into the heat recovery section 8 may not pass through the heat recovery section 8 and may be blocked by the partition wall 7.
This is because the flow state of the heat recovery section 8 is influenced by the combustion section 9, such as when the heat returns to the combustion section 9 on the upper side of the heat transfer section 9, resulting in heat transfer wear and deterioration of heat recovery amount control. In other words, it must be above the partition wall height defining surface 22 (Fig. 1) extending approximately 45 degrees downward toward the combustion section 9 from the highest position of the intralayer heat transfer surface on the combustion section 9 side. is necessary. In addition, the heat recovery section 8 of the combustion material 13
In order to suppress the amount of the combustible material 13 going around, it is desirable to set the input position of the combustible material 13 at a position away from the partition wall 7.

Furthermore, as one form of increasing the size, it is possible to make it as shown in FIG. 5. That is, in the fifth illustrated example, a plurality of heat recovery sections 8 and a plurality of combustion sections 9 are formed,
The combustion material 13 is supplied from the lower part of each combustion section 9 by air transport, etc., and a reflecting wall 20 is provided above each combustion chamber 9, cooling air is passed through the reflecting wall 20, and the outer surface is protected with a refractory material. The operation is the same as that of the previous embodiment. In addition, combustion material 13
Depending on the amount of heat generated, the reflecting wall 20 may be omitted, and the number of heat recovery sections 8 and combustion sections 9 may be further increased when scaled up.

〔Effect of the invention〕

As described above, according to the present invention, the following extremely beneficial effects can be obtained, and the significance of the present invention is extremely large.

The turndown ratio can be made extremely wide.

The heat recovery section and the combustion section are separated and fluidized gas is injected into each section independently, and in the combustion section, the amount of fluidized medium circulating from the combustion section through the heat recovery section is changed approximately in proportion to the amount of combustion material. Furthermore, in the heat recovery section, the heat exchange rate between the heat receiving fluid and the fluidized medium can be changed by adjusting the amount of fluidized gas blown into the fluidized bed, so by stopping heat recovery from the fluidized bed, the amount of fuel used can be drastically reduced. The amount of evaporation can be reduced, the turndown ratio can be set over a wide range, and the followability is good. For this purpose, it is only necessary to adjust the amount of fluidizing gas blown in and the amount of combustible material input, making automation extremely easy. Moreover, the recovery heat adjustment in the heat recovery section is instantaneous, and the change is caused by a change in the sensible heat of a large amount of fluidized medium, that is, the fluidization temperature changes little by little. Characteristically, the response time is within a few minutes, and fluidized bed temperature changes caused by adjustments in the heat recovery section can be kept within a small range. In this way, the fuel and generated heat can be fully utilized.

High tolerance for combustible materials.

Unlike conventional fluidized bed boilers, it may contain coarse noncombustibles, and can accept ordinary municipal waste without crushing it, and can smoothly discharge the noncombustibles. In addition, due to the strong stirring effect in the combustion section, miscellaneous waste can be thrown in without the need for dispersion using a spreader or the like, without fear of burning, etc., and there is no need to adjust the particle size. In addition, it is not necessary to make the particle size of coal particularly fine. Furthermore, any type of coal may be used, and any type of coal containing large incombustible substances may be used, and everything from coal waste to peat can be combustible, regardless of the amount of volatile content. Of course, it can also co-combust municipal waste, industrial waste, coal, sludge, etc., and can be used as a waste combustion furnace.

Maintenance is easy.

Since the heat recovery section and combustion section are separate, the heat transfer surface of the heat recovery section does not come into contact with highly reactive combustion gas, etc., and is not exposed to violently moving fluid media, preventing corrosion of the heat transfer surface. Wear or scaling can be kept to an extremely small level. In addition, the circulation of the fluidizing medium is performed by fluidizing gas,
There is no trouble, heat radiation, dust generation, etc. associated with the circulation of the fluidized medium outside the furnace, and there is no need to deteriorate the surrounding working environment.

The entire device becomes extremely compact.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of a device showing an embodiment of the present invention, Figure 2 is a diagram showing the relationship between the circulation amount of fluidized medium and the amount of fluidized air, and Figure 3 is a diagram showing the relationship between the heat transfer coefficient and the amount of fluidized air. FIGS. 4 and 5 are longitudinal cross-sectional views of devices showing other embodiments of the present invention, and FIGS. 6 and 7 are explanatory cross-sectional views showing conventional examples, respectively. . 1...Furnace, 2, 2'...Distribution plate, 3...Fluidization gas,
4, 4', 4'-1, 4'-2...Air chamber, 5...Fluidized bed, 6...Communication port, 7...Partition wall, 8...Heat recovery section, 9
...Combustion part, 10...Water cooling wall, 11, 11', 11°-1, 11'-2...Flow rate control valve, 12...Heat transfer tube,
13... Combustible material, 14... Supply device, 15... Inlet,
16...Discharge port, 17...Exhaust gas boiler, 18...Combustion exhaust gas, 19...Bubble, 20...Reflecting wall, 21...Diffusion nozzle, 22...Partition wall height regulation surface, 31...Furnace, 32
...Distribution plate, 33...Fluidization gas, 34...Air chamber, 3
5...bed, 36...heat exchanger tube, 37...combustible material, 38
...freeboard section, 39...cyclone, 40...flue duct, 41...heat exchanger chamber, 42...dispersion plate, 44...air chamber, 45...fluidized bed.

Claims (1)

[Claims] 1. A fluidized bed in which a fluidized medium is fluidized by fluidizing gas blown upward from the bottom and discharged from the upper space, the upper end of which is immersed in the fluidized bed, and the lower end of which has a communication port. The combustion section is divided into a heat recovery section and a combustion section to which combustion materials are supplied by a partition wall, and the flow rate of fluidizing gas blown per unit area of the combustion section at least near the partition wall is determined per unit area of the heat recovery section. By setting the flow rate to be larger than the fluidizing gas blowing air volume, the fluidized medium in the combustion section is allowed to flow into the heat recovery section over the partition wall, and the fluidized medium in the heat recovery section is flowed into the combustion section from the lower part of the partition wall. A method for recovering heat from a fluidized bed, characterized by refluxing it. 2. The flow rate of the fluidizing gas blown into the combustion section at least near the partition wall is set to be three times or more the minimum fluidization speed of the fluidized medium, and the flow rate of the fluidized gas blown into the heat recovery section is set to be at least 3 times the minimum fluidization speed of the fluidized medium. A method for recovering heat from a fluidized bed according to claim 1, wherein the heat recovery method is made twice or less. 3 A fluidized bed in which an exhaust gas passage opens in the upper space and fluidizes the fluidized medium by fluidizing gas blown upward from the bottom is formed by a partition wall whose upper end is submerged into the fluidized bed and has a communication port at the lower part. It is divided into a heat recovery section and a combustion section, each of the heat recovery section and the combustion section is provided with an independent fluidizing gas blowing air volume adjustment mechanism, and the heat recovery section is provided with a heat transfer surface through a heat receiving fluid, A combustion material supply device is provided in the combustion section, and a fluidized medium is caused to flow from the combustion section into the upper part of the heat recovery section, and at the same time, a fluidized medium in the lower part of the heat recovery section is made to flow back to the combustion section. Heat recovery device from fluidized bed. 4 A fluidized bed in which an exhaust gas passage opens in the upper space and fluidizes the fluidized medium by fluidizing gas blown upward from the bottom is provided by a partition wall whose upper end is submerged into the fluidized bed and has a communication port at the lower part. The heat recovery section and the combustion section are divided so as to share an upper space, and each of the heat recovery section and the combustion section is provided with an independent fluidizing gas blowing air volume adjustment mechanism, and the heat receiving fluid is passed through the heat recovery section. A heat transfer surface is provided, a combustion material supply device is provided in the combustion section, and a reflecting wall is provided above the combustion section and close to the fluidized bed to deflect the rising gas flow toward the heat recovery section. A heat recovery device from a fluidized bed, characterized in that the fluidized medium is caused to flow from the combustion section to the upper part of the heat recovery section, and at the same time, the fluidized medium in the lower part of the heat recovery section is made to flow back to the combustion section.