JP3913229B2 - Circulating fluid furnace - Google Patents

Description

  The present invention relates to a circulating fluidized furnace that burns an object to be processed while circulating a high-temperature fluidized medium in the furnace body, and more particularly to a circulating fluidized furnace that can smoothly maintain the temperature in the furnace by smoothly circulating the fluidized medium. .

Conventionally, circulating fluidized furnaces have been widely used as facilities for burning industrial waste, municipal waste, sewage sludge, and the like. Circulating fluidized furnaces can be combusted stably even with fluctuations in the properties of the material to be treated, and fluidized media such as fluidized sand circulate and flow in the furnace and burn in contact with the material to be treated. Since no problem occurs and uniform combustion treatment is possible, it is suitable for an object to be treated having a high water content such as sewage sludge.
FIG. 4 shows the configuration of a general circulating fluidized furnace. The circulating flow furnace 60 includes a vertical cylindrical riser 61 that receives and burns an object to be processed, a cyclone 64 that separates a fluid medium from combustion exhaust gas, and a downcomer that drops fly ash collected by the cyclone 64. 65, a seal pot 66 for depositing the fluid medium to prevent the unburned gas in the furnace from being blown into the cyclone 64, and a return pipe 67 for returning fly ash from the seal pot 66 to the riser 61. The

An object to be processed put into the riser 61 is mixed with a fluidized medium while flowing by primary air introduced from the lower part of the riser to form a fluidized bed 63, which is dried, burned and gasified. The gasified object is completely combusted by introducing secondary air in the free board 62, separated from the fluid medium by the cyclone and discharged. On the other hand, the fluid medium is returned to the riser 61 through a seal pot 66.
Such a circulating fluidized furnace is described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-3757), Patent Document 2 (Japanese Patent Laid-Open No. 2001-235128), and the like. In such a furnace structure, the in-furnace gas containing fly ash and fluidized medium circulates at a high speed, so the combustion speed is high and the combustion efficiency is good, but the temperature distribution in the furnace is properly maintained and the combustion efficiency is kept high. It is necessary to have a structure that smoothly circulates the fluid medium.

A seal pot is employed as one of the structures for appropriately maintaining the circulation of the fluid medium, thereby preventing the fluid medium from flowing back to the cyclone. The seal pot structure of Patent Document 1 has a structure in which only one chamber is provided below the downcomer. A fluid medium is deposited on the seal pot to seal the gas in the furnace, and the gas is appropriately blown into the seal pot and accumulated. The returned fluid medium is returned to the furnace.
However, since the pressure fluctuation is large in the fluidized bed lower part of the riser, this pressure fluctuation directly affects the fluidization of the seal pot, so that it is difficult to smoothly circulate the fluid medium.
In order to solve this problem in Patent Document 2, a seal pot structure composed of two flow chambers 66a and 66b communicated as shown in FIG. 4 is adopted, and flow air is blown into these flow chambers independently, The backflow of the gas in the furnace is prevented and the fluid medium is returned smoothly.

  Further, Patent Document 3 (Japanese Patent Laid-Open No. 2002-98313) discloses a configuration that enables a stable combustion state to be maintained by suppressing fluctuations in the combustion state due to disturbance of the fluid medium in the riser. The return pipe has a structure in which the pressure difference between the riser bottom portion and the uppermost portion with respect to the reference pressure difference is set to a height within 20% with respect to the reference pressure difference. Alternatively, the return pipe is installed at a height of 1.2 m or more from the riser bottom, preferably at the top of the secondary air inlet.

JP 2004-3757 A JP 2001-235128 A JP 2002-98313 A

Thus, in order to stabilize the combustion state of the circulating fluidized furnace and maintain high combustion efficiency, it is necessary to smoothly circulate the fluid medium. The seal pot has a structure that allows the fluid medium to circulate properly, but a problem occurs when the riser connection position of the fluid medium return pipe that returns the fluid medium from the seal pot to the riser is not appropriate.
As in Patent Documents 1 and 2, when the height of the fluid medium return pipe is low and the fluid medium is located at a small dense layer height, it will be subject to pressure fluctuations in the dense layer, and will be in the seal pot. Pressure fluctuations occur. As a result, since the seal pot fluid air intermittently flows into the cyclone side and blows up from below the cyclone, the fluid medium scatters from the cyclone, and the fluid medium circulating in the riser decreases, resulting in an appropriate amount of fluid medium circulation. It becomes difficult to maintain. Also, the running cost increases because the fluid medium must be replenished frequently.
Furthermore, when particles having a large particle size accumulate in the lower part of the riser and do not flow, there is a possibility that the fluid medium returned from the seal pot will not enter the riser.

  On the other hand, in Patent Document 3, the height of the return pipe is defined as 1.2 m or more. However, when the height of the fluid medium return pipe is too high, the fluid medium from the seal pot is taken into the rich layer of the riser. Therefore, the lower temperature of the riser is not raised. In particular, when the treatment target is sewage sludge with a high moisture content, the sewage sludge thrown into the riser starts to burn after drying at the lower part of the riser. This is not done and the combustion efficiency deteriorates. In particular, when the return pipe is positioned above the secondary air inlet, the fluid medium returned into the riser is easily wound up by the secondary air and blown up, and the temperature drop below becomes significant. Further, since auxiliary fuel is generally supplied from the lower portion of the riser, there is a risk of poor ignition if the riser lower temperature is too low.

Furthermore, in the structure in which the return pipe position is set based on the pressure difference described in Patent Document 3, in the case of an object to be processed having a high water content, it is difficult to determine a certain position because the pressure fluctuation of the concentrated layer is large.
Therefore, in view of the above-described problems of the prior art, the present invention provides a circulating fluidized furnace capable of avoiding scattering of a fluid medium from a cyclone, smoothly circulating the fluid medium, and performing a stable combustion process. Objective.

Accordingly, in order to solve the above problems, the present invention provides a riser for burning an object to be processed while mixing with a fluid medium, a seal pot for introducing a fluid medium separated and collected from the exhaust gas of the riser by a cyclone, and the seal A return pipe for returning the fluid medium accumulated in the pot to the riser, and the seal pot is formed from two communicating spaces consisting of an inflow chamber and an outflow chamber for the fluid medium, respectively from the lower part of these spaces. In the circulating fluidized furnace configured to introduce fluidized gas,
An object to be processed in which ash is generated such that the particle size of ash generated by combustion of the object to be processed is smaller than the particle diameter of the fluidized medium is selected, and the superficial velocity of the outflow chamber is set to be empty in the inflow chamber. provided with a means for the fluidizing gas respectively controlled to from the tower velocity becomes larger, the connection height of the return pipe and the riser, high Ri by the stationary layer height of the fluidized medium, and the secondary of the riser The position is lower than the height of the air inlet.

In a circulating fluidized furnace, when primary fluidizing air is introduced from the lower part of the riser and the fluid medium is circulated to start the operation, a part of the fluid medium accumulates in the lower part of the riser and forms a thick layer (concentrated layer) of the fluid medium. Form. It has been demonstrated that the height of the dense layer is about one time the static bed height of a stationary fluid medium without introduction of primary air.
The present inventors set the object to be treated as sewage sludge, the riser height is 24 m, and the stationary fluid medium height (static bed height) is 1 m from the diffuser plate (static bed bottom) at the bottom of the riser. As shown in the riser pressure distribution in FIG. 3, the experiment was conducted by using the circulating fluidized furnace installed and operating in the range of 4 to 7 m / s which is the superficial velocity of the general circulating fluidized furnace. It was found that the pressure was high up to a position about 1 times the height of the stationary layer, and the pressure dropped sharply above it. When primary air is introduced, about 30% of the amount of static sand floats and circulates in the upper part of the riser, and the remaining 70% forms a thick layer in the lower part of the riser. This is probably because the surface of the layer approaches the height of the stationary layer.

Since the pressure fluctuation in the dense layer is large, the lower limit of the return position of the fluidized medium is set to one time the stationary layer height, that is, the dense layer as in the present invention, and the fluidized medium is introduced at a higher position. This reduces the back pressure applied to the seal pot and stabilizes the flow of the seal pot. Thereby, it becomes difficult for the air for a flow of a seal pot to flow to the downcomer side, and discharge | emission of the fluid medium from a cyclone can be suppressed. Further, even when a fluid medium having a large particle size accumulates in the lower part of the riser and causes a fluid failure, the fluid medium from the seal pot can be reliably returned to the riser.
In addition, by setting the upper limit of the return position of the fluid medium as the secondary air inlet and introducing the fluid medium at a position lower than this, the hot fluid medium returned to the riser is immediately wound around the secondary air. The high temperature fluid medium falls to the lower portion of the riser and is surely taken into the thick layer without being blown to the free board, so that the temperature of the lower portion of the riser can be maintained at a high temperature. As a result, even an object to be treated such as sewage sludge having a high moisture content is sufficiently dried and efficiently combusted.
The definition of the return position is the lower end position of the return pipe. This is because the back pressure applied to the seal pot depends on the highest pressure part at the lower end of the return pipe, and hot fluidized sand is supplied to the riser through the lower end of the return pipe, confirming the effect of the present invention. This is because it is the most important part to do.

Furthermore, the seal pot is formed from two communicating spaces consisting of an inflow chamber and an outflow chamber for the fluid medium, and is configured to return the fluid medium overflowed from the outflow chamber to the riser via a return pipe. The pressure inside the riser can be reliably maintained, and a fluidized gas is introduced from the lower part of each of these spaces, and (superficial velocity of the outflow chamber)> (superficial velocity of the inflow chamber). Thus, it is possible to reliably prevent the gas in the furnace from being blown into the cyclone.
Therefore, according to the present invention, the combination of these can surely prevent the fluid medium from scattering from the cyclone, and the running cost can be reduced. Moreover, the temperature lowering of the lower part of the riser can be prevented, the temperature of the lower part of the riser can be kept high, and even an object to be treated such as sludge having a high water content can be efficiently dried, burned and gasified.

In addition, it is preferable that the connection height position of the return pipe and the riser is a position higher than about 1 times the stationary bed height of the fluidized medium, and thereby the influence of pressure fluctuation of the dense layer on the seal pot. Can be minimized. Further, when the stationary layer height is H ₀ and the secondary air inlet height is H ₁ , the connection height position of the return pipe and the riser is a position lower than (H ₀ + H ₁ ) / 2. It is preferable to do. Since a turbulent flow due to the introduction of the secondary air is formed in the vicinity of the secondary air inlet, the riser is set by setting an upper limit to (H ₀ + H ₁ ) / 2 located below the secondary air inlet. The fluid medium returned to can be reliably introduced into the lower portion of the riser without being affected by turbulence. The static layer height H ₀ and the secondary air inlet height H ₁ are based on the height of the thick layer bottom.

Furthermore, the object to be processed according to the present invention is an object to be processed in which ash is generated such that the particle size of ash generated by combustion of the object to be processed is smaller than the particle size of the fluidized medium . It is characterized by being. As described above, when the particle size of the ash is very small, the generated ash is not used as a fluid medium and is discharged from the cyclone along with the exhaust gas. As a result, when the fluid medium scatters from the cyclone, it is necessary to newly replenish the fluid medium (sand), leading to an increase in running cost. Therefore, when burning the to-be-processed object with a small ash particle diameter, running cost can be suppressed more effectively by this invention.
Examples of the object to be treated of the present invention include sewage sludge, fuel pellets (RDF), and biomass.
In addition, the gas of each fluidized gas so that the superficial velocity of the outflow chamber is about 0.2 to 0.6 m / s and the superficial velocity of the inflow chamber is less than about 0.2 m / s. A means for controlling the flow rate is provided. Accordingly, the fluid medium can be smoothly returned to the riser, the flowing air can be prevented from flowing into the cyclone side, and the fluid medium can be prevented from being discharged from the cyclone.

  As described above, according to the present invention, the scattering of the fluid medium from the cyclone can be reliably prevented, and the running cost can be reduced. Moreover, the temperature lowering of the lower part of the riser can be prevented, the temperature of the lower part of the riser can be kept high, and even an object to be treated such as sludge having a high water content can be efficiently dried, burned and gasified.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
FIG. 1 is a schematic sectional view of a circulating fluidized furnace according to an embodiment of the present invention, and FIG. 2 is an overall configuration diagram of a sludge treatment system equipped with the circulating fluidized furnace of FIG.
In this embodiment, sewage sludge is used as an object to be treated as an example, but the present invention is not limited to this, and can be applied to municipal waste, industrial waste, and the like. Particularly suitable as a processing target of this embodiment is an object to be processed that generates fly ash having a smaller diameter than a fluid medium by combustion, and examples thereof include sewage sludge, fuel pellets (RDF), and biomass.

With reference to FIG. 2, the sludge treatment system provided with the circulating fluidized furnace according to the present embodiment will be described. This sludge treatment system is a heat recovery / exhaust gas equipped with a sludge 50 supply facility, an incineration facility comprising a circulating fluidized furnace 10, an air preheater 42, a gas cooling tower 43, a bag filter 45, and a chimney 46. And processing equipment.
In the sludge supply facility, the sludge 50 mixed with the limestone powder supplied from the limestone feeder 41 is supplied to the incineration facility by the sludge charging pump 41 by a predetermined amount. The addition of the limestone powder aims to prevent elution of heavy metals and to suppress the generation of harmful gas components such as HCl, SOx, and dioxins.

The sludge supplied from the sludge supply facility is introduced into the circulating fluidized furnace 10 through the sludge inlet 21 and burned while being supplied with the primary air 31 and the secondary air 32 in the riser 11 of the circulating fluidized furnace 10. To do. The exhaust gas generated by the combustion is supplied to the heat recovery / exhaust gas treatment facility after the fluid medium is separated by the cyclone 16.
In the heat recovery / exhaust gas treatment facility, the exhaust gas discharged at a high temperature by the air preheater 42 and the air 52 are subjected to heat exchange, and then the cooled exhaust gas is further sprayed by the cooling water 53 in the gas cooling tower 43. It cools, slaked lime is added with the slaked lime feeder 44, and it introduce | transduces into the bag filter 45, and after separating fly ash in waste gas with this bag filter 45, it discharges | emits out of the system from the chimney 46. The addition of the slaked lime is intended to detoxify acidic components such as HCl and SOx.
On the other hand, the air 52 heated by the air preheater 42 is guided to the circulating fluidized furnace 10, and the primary air 31 introduced from the bottom of the riser 11 and the secondary air introduced from the furnace wall of the riser 11. 32 and flow air 33a and 33b introduced from the bottom of the seal pot 19 of the circulating flow furnace 10.

The incineration facility comprises a circulating fluidized furnace 10 shown in FIG. The circulating fluidized furnace 10 has a vertical cylindrical shape, and a riser 11 that dries, burns, and gasifies the sludge 30 introduced from the sludge inlet 21, and an exhaust gas passage 15 connected to the upper portion of the riser 11. A cyclone 16 that separates the exhaust gas introduced through the exhaust gas passage 15 into a solid gas by centrifugation, a downcomer 18 that is a passage of a fluid medium located below the cyclone 16, and a cyclone of unburned gas in the furnace The seal pot 19 that prevents the blowout to 16 and the return pipe 20 are the main components.
A concentrated layer 12 in which the fluid medium flows densely by the primary air 31 introduced from the primary air inlet 22 is formed below the riser 11, and the lean layer 13 in which the fluid medium is scattered above the dense layer 12. Is formed. Sludge input from the sludge inlet 21 falls on the thick layer 12, where the sludge is dried and burned. Further, in the lean layer 13, combustion and gasification are performed while the sludge is scattered, and the lean layer 13 is conveyed to an updraft formed by the secondary air introduced from the secondary air inlet 23 in the intermediate portion of the riser, The scattered fluid medium, fly ash, and unburned material are conveyed to the free board 14 above the lean layer 13.

In the free board 14, unburned substances in the exhaust gas are completely burned by introducing the secondary air. The exhaust gas containing fly ash and fluid medium is introduced into the cyclone 16 through the exhaust gas passage 15, the fluid medium in the exhaust gas is collected by the cyclone 16, and is sent to the seal pot 19 through the downcomer 18. On the other hand, the exhaust gas from which the fluid medium has been separated is sent from the exhaust gas outlet 17 to the heat recovery / exhaust gas treatment facility.
The seal pot 19 is composed of two communicating spaces. The first space is located below the downcomer 18 and is an inflow chamber 19a into which the fluid medium collected by the cyclone 16 flows. The space is an outflow chamber 19b that communicates with the inflow chamber 19a at the lower part and flows out the fluid medium to the riser 11 through the return pipe 20.
Flowing air inlets 24a and 24b are provided at the bottoms of the inflow chamber 19a and the outflow chamber 19b, respectively, from which flow air 33a and 33b are introduced to flow the fluid medium accumulated in the seal pot 19.

The fluid medium accumulated in the seal pot 19 overflows the outflow chamber 19b toward the return pipe 20 due to the level difference between the inflow chamber 19a and the outflow chamber 19b, and is returned to the riser 11.
In the present embodiment, the gas flow rates of the flow air 33a introduced into the front inflow chamber 19a and the flow air 33b introduced into the outflow chamber 19b are made different from each other, (the outflow chamber superficial velocity)> (the inflow chamber superficial tower) Speed). Preferably, the superficial velocity of the outflow chamber 19b is about 0.2 to 0.6 m / s, and the superficial velocity of the inflow chamber 19a is controlled to be less than about 0.2 m / s. Control of these superficial velocities is preferably performed by the controller 25 shown in FIG. That is, the air 52 heated by the air preheater 42 is branched and introduced into the primary air 31, the secondary air 32, and the flow air 33a and 33b. The air of the flow air 33a and 33b, respectively. A flow rate control valve is provided on the introduction line, and the controller 25 controls the flow rate control valve to open and close so as to achieve the superficial velocity.
With the configuration of the seal pot 19, the pressure in the riser 11 can be maintained, and the blow-in of the furnace gas to the cyclone can be reliably prevented.

Further, in this embodiment, when the height of the stationary bed height A of the fluid medium is H ₀ and the height of the secondary air inlet is H ₁ , the lower limit of the connection height position between the return pipe 20 and the riser 11 Is the height H ₀ of the static bed height A of the fluidized medium.
Furthermore, the upper limit of the connection height position is the secondary air inlet height position C of the riser 11, and is preferably a height position D of (H ₀ + H ₁ ) / 2. At this time, the static layer height H ₀ and the secondary air inlet height H ₁ are based on the height of the thick layer bottom.
The stationary bed height A is the height of a stationary fluid medium in which primary air is not introduced when the furnace is stopped.
The height H ₀ of the stationary layer height A of the fluidized medium, which is the lower limit of the connection height position, substantially coincides with the height of the dense layer 12, and the height position D of (H ₀ + H ₁ ) / 2 is It has been demonstrated that it substantially matches the height of the dilute layer 13.
In this embodiment, when the superficial velocity in the riser 11 is relatively small, the lower limit of the connection height position is set to a position B (higher than the height H ₀ of the stationary layer height A). 0.7H ₀ ).

As in this embodiment, by setting the lower limit of the connection height position and introducing the fluid medium at a position higher than the dense layer, the seal pot 19 has little effect on the pressure fluctuation of the dense layer 12. The back pressure applied to the seal pot 19 is reduced and the flow of the seal pot 19 is stabilized. This makes it difficult for the flow air 33a and 33b of the seal pot 19 to flow to the downcomer 18 side, and the discharge of the flow medium from the cyclone 16 can be suppressed. Further, even when a fluid medium having a large particle size accumulates in the lower portion of the riser 11 and causes a fluid failure, the fluid medium from the seal pot 19 can be reliably returned to the riser 11.
Further, by setting an upper limit of the connection height position and introducing the fluid medium at a position lower than the secondary air introduction port 23, the high-temperature fluid medium returned to the riser 11 immediately becomes the secondary air. Since the hot fluid medium falls to the lower portion of the riser 11 and is surely taken into the concentrated layer 12 without being wound around the free board 14 and wound on the free board 14, the temperature at the lower portion of the riser 11 can be maintained at a high temperature. Thereby, even to-be-processed objects, such as a sewage sludge with a high moisture content, can fully dry and can perform efficient combustion.

It is a schematic sectional drawing of the circulating fluidized furnace which concerns on the Example of this invention. It is a whole block diagram of the sludge processing system which comprised the circulating fluidized furnace of FIG. It is a graph which shows the pressure distribution in a riser. It is a schematic sectional drawing of the conventional circulation flow furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Circulating flow furnace 11 Riser 12 Thick layer 13 Dilute layer 14 Free board 16 Cyclone 18 Downcomer 19 Seal pot 19a, 19b Flow chamber 20 Return pipe 21 Sludge inlet 24a, 24b Flowing air inlet 25 Controller 31 Primary air 32 2 Secondary air 33a, 33b Flowing air

Claims (3)

A riser that combusts the object to be treated while being mixed with a fluid medium, a seal pot that introduces a fluid medium separated and collected from the exhaust gas of the riser by a cyclone, and a return that returns the fluid medium accumulated in the seal pot to the riser A circulating fluidizing furnace having a structure in which the seal pot is formed from two communicating spaces composed of an inflow chamber and an outflow chamber for a fluid medium, and a fluidizing gas is introduced from the lower portion of each space. ,
An object to be processed in which ash is generated such that the particle size of ash generated by combustion of the object to be processed is smaller than the particle diameter of the fluidized medium is selected, and the superficial velocity of the outflow chamber is set to be empty in the inflow chamber. Means for controlling the fluidized gas so as to be larger than the tower speed are provided, and the connection height position between the return pipe and the riser is higher than the stationary bed height of the fluidized medium and the secondary air of the riser A circulating fluidized furnace characterized by being positioned lower than the inlet height. When the height of the stationary layer is H ₀ and the height of the secondary air inlet is H ₁ , the connection height position between the return pipe and the riser is lower than (H ₀ + H ₁ ) / 2. The circulating fluidized furnace according to claim 1. The gas flow rate of each fluidizing gas so that the superficial velocity of the outflow chamber is about 0.2 to 0.6 m / s and the superficial velocity of the inflow chamber is less than about 0.2 m / s. The circulating fluidized furnace according to claim 1 , further comprising means for controlling the temperature .

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