JP3800099B2 - Circulating fluidized bed furnace and circulating fluidized bed boiler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circulating fluidized bed furnace and a circulating fluidized bed boiler.
[0002]
[Prior art]
Circulating fluidized bed furnaces and circulating fluidized bed boilers incinerate by burning or gasifying fuel such as coal and oil coke, municipal waste, waste plastic, waste such as sludge and paper sludge, and RDF (fuel solid waste). Widely used for processing and heat recovery.
[0003]
FIG. 5 is a diagram schematically showing a conventional typical circulating fluidized bed furnace. The circulating fluidized bed furnace shown in FIG. 5 is mainly composed of a riser 1 that incinerates or gasifies a processing object, and a downcomer 2 that collects circulating particles as a fluidized medium and returns them to the riser 1. .
[0004]
The riser 1 is composed of a furnace body 11, and a diffuser tube 12 for blowing primary air into the furnace is provided in the lower part of the furnace body 11. Further, the side wall of the furnace body 11 is provided with a secondary air inlet 13 for injecting secondary air into the furnace and an inlet 15 for injecting a processing object into the furnace in order from below. Yes.
[0005]
In the riser 1, air is blown into the furnace from the air diffuser 12 and the secondary air blowing port 13, and the object to be treated introduced into the furnace through the charging port 15 is raised together with a fluid medium such as sand. In the process, the object to be treated is dried, emits volatile matter, and burns. In addition, when the process target having a high moisture content is exclusively burned or when the ratio of mixed firing is high and it is difficult to self-combust the process target, an auxiliary fuel supply port 14 is provided on the side wall of the furnace body 11, and the auxiliary fuel supply port 14 Auxiliary fuel is supplied into the furnace by oil gun or gas gun.
[0006]
The downcomer 2 includes a collection unit 21 that collects a fluid medium and the like, and a circulating particle return pipe 22 that returns the collected fluid medium and the like to the riser 1. In many cases, the downcomer 2 is provided with a seal portion 23 that prevents the gas from the riser 1 from rising in the collection portion 21.
[0007]
The downcomer 2 is supplied with exhaust gas, unburned material, fluidized medium, and the like generated by the combustion of the processing object from the upper part of the riser 1 through the connection pipe 3. In the collection part 21, they are separated into exhaust gas and fluid medium or ash having a relatively large particle size. The exhaust gas separated by the collection unit 21 is accompanied by ash having a relatively small particle size and sent to the exhaust gas treatment facility, and is discharged from the chimney after dust removal. Further, the fluid medium collected by the collection unit 21 or the ash having a relatively large particle size is returned to the lower portion of the riser 1 through the seal unit 23 and the circulating particle return pipe 22 as circulating particles. Perform re-burning.
[0008]
By the way, in such a circulating fluidized bed furnace, when a wet substance (for example, water content of 30 to 90%) is burned as an object to be treated, an endothermic reaction occurs in the furnace due to evaporation of moisture in the wet substance. Therefore, the combustion state in the furnace tends to become unstable in space and / or time.
[0009]
In order to stabilize the combustion state, the furnace temperature may be stabilized by increasing the amount of the fluid medium (or the particle suspension concentration) present in the riser 1. For this reason, generally, a technique of increasing the amount of the fluid medium existing in the circulating fluidized bed furnace is employed, but this technique has the following problems.
[0010]
That is, when the amount of the fluid medium existing in the circulating fluidized bed furnace is increased to increase the particle suspension concentration, the amount of the fluid medium present in the downcomer 2 is also increased. When the amount of the fluid medium in the downcomer 2 increases, the fluid medium is stored above the seal portion 23, and a longer time is required for the fluid medium to return to the riser 1. As a result, the fluidized medium returns to the riser 1 in an excessively cooled state.
[0011]
Such a decrease in temperature is particularly noticeable when the object to be treated is a wet substance. This is because when the treatment object is a wet substance, the unburnt carbon content present in the downcomer 2 is less than when the treatment object is a substance having a large amount of fixed carbon such as coal. . For these reasons, it is difficult to stabilize the combustion state in the furnace with the technique of increasing the amount of the fluid medium existing in the circulating fluidized bed furnace when the wet substance is burned as the object to be treated. It is.
[0012]
As a method for suppressing the temperature drop of the fluid medium, the amount of fluid medium existing in the downcomer 2 is reduced by increasing the amount of air transported at the seal portion 23 or omitting the seal portion 23. It is possible to make it. However, in this case, there is a possibility that combustion air or exhaust gas flows backward in the downcomer 2 and the concentration of harmful gas in the exhaust gas increases. Moreover, when the amount of carrier air is remarkably increased, the temperature drop of the fluid medium based on the carrier air becomes significant.
[0013]
In addition to the above problems, other problems arise when the amount of fluidized medium present in the circulating fluidized bed furnace is increased to increase the particle suspension concentration. That is, when the amount of the fluid medium present in the circulating fluidized bed furnace is increased to increase the particle suspension concentration, the number of particles that cannot be collected by the collection unit 21 increases. In this case, since the particles flowing through the flue increase with the exhaust gas, the burden on the exhaust gas treatment facility (for example, a dust collector such as a bag filter) increases. Further, since it is necessary to replenish the fluid medium lost from the circulating fluidized bed furnace, the operation cost is also increased.
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and even when the object to be treated is a wet substance, the circulation flow capable of stabilizing the combustion state in the furnace spatially and temporally. An object is to provide a bed furnace and a circulating fluidized bed boiler.
[0015]
Further, the present invention provides a combustion state in a furnace without causing an increase in the concentration of harmful gas in the exhaust gas and an increase in the amount of fluid medium accompanying the exhaust gas even when the object to be treated is a wet substance. An object of the present invention is to provide a circulating fluidized bed furnace and a circulating fluidized bed boiler that can be spatially and temporally stabilized.
[0016]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a riser having a columnar space therein, a connection pipe having one end connected to the upper part of the riser, the other end of the connection pipe, and a lower part of the riser. A downcomer connected to raise the fluid medium from the lower part of the space provided in the riser to the upper part of the space, and the fluid medium reaching the upper part of the space to the connecting pipe and the downcomer. A circulating fluidized bed furnace for performing combustion and / or gasification treatment of a processing object in the space while returning to the lower part of the space, the riser with respect to the upper end of the connection pipe on the riser side top of the space provided within the rather high above 200 mm, the cross-sectional area of the space provided in the riser, the comparison below the open top of the riser side of the connection pipe, the riser side of the connecting pipe Than mouth upper provides a circulating fluidized bed furnace with excellent combustion stability, wherein greater than in the upper.
[0017]
The present invention also provides a circulating fluidized bed boiler comprising a circulating fluidized bed furnace, wherein heat generated by combustion in a space provided in the riser is utilized for fluid evaporation.
[0018]
In the conventional circulating fluidized bed furnace, the gas that reaches the top from the lower part of the space in the riser quickly flows toward the downcomer accompanied by the fluidized medium and unburned particles. On the other hand, in the present invention, since the distance from the top of the riser internal space to the height of the opening upper end of the connection pipe on the riser side is a predetermined value or more, at least a part of the gas that has reached the top from the lower portion of the riser internal space Once stays at the top of the riser space and then flows toward the downcomer. When the gas is retained at the top of the riser internal space in this way, a part of the fluid medium and unburned particles that have reached the top of the riser internal space together with the gas are introduced from the vicinity of the riser side wall where the flow rate is relatively low. Drop toward the bottom of the interior space. Therefore, according to the present invention, the amount of fluid medium and unburned particles entrained in the gas flow flowing from the riser to the downcomer can be reduced and the particle suspension concentration in the riser can be increased.
[0019]
Thus, in the present invention, the particle suspension concentration in the riser can be increased without increasing the amount of fluid medium in the downcomer. In other words, according to the present invention, the particle suspension concentration in the riser can be increased without increasing the amount of fluid medium in the circulating fluidized bed furnace. Therefore, according to the present invention, the above-mentioned problem associated with increasing the amount of fluidized medium in the circulating fluidized bed furnace does not occur.
[0020]
Further, in the present invention, no complicated mechanism or control is required, and the distance from the top of the riser internal space to the height of the opening upper end of the connection pipe on the riser side may be simply set to a predetermined value or more. The production cost of the bed furnace and circulating fluidized bed furnace boiler does not increase significantly. Furthermore, the present invention can be applied to existing circulating fluidized bed furnaces and circulating fluidized bed furnace boilers at a low cost.
[0021]
As described above, in the present invention, the distance d from the top of the space provided in the riser to the height of the opening upper end on the riser side of the connection pipe is 200 mm or more. The reason why the distance d is 200 mm or more is as follows.
[0022]
In the riser internal space top, the fluid medium collides with the top inner wall of the riser and rebounds by its own kinetic energy. When the distance d is short, it is difficult to increase the particle suspension concentration in the riser by dropping the fluid medium that has reached the top of the riser internal space. In a circulating fluidized bed furnace, the gas flow rate in the riser is usually about 2 to 8 m / s. According to the experiments by the present inventors, the particle suspension is performed even when the distance d is 150 mm. Although it is difficult to increase the turbidity, it has been found that the effect of increasing the particle suspension concentration can always be obtained by setting the distance d to 200 mm or more.
[0023]
In the present invention, the distance d is preferably 300 mm or more. In this case, the effect of increasing the particle suspension concentration becomes more remarkable.
[0024]
In the present invention, the distance d is preferably 500 mm or less. When the distance d is long, the particle suspension concentration in the riser can be increased. However, what is important in stabilizing the combustion state in the furnace is not the particle suspension concentration above the connection pipe in the riser space but the particle suspension concentration below the connection pipe in the riser space. According to experiments by the inventors, it has been found that the latter particle suspension concentration does not change greatly when the distance d exceeds 500 mm. From the viewpoint of manufacturing cost, it is not preferable to make the distance d excessively long.
[0025]
In the present invention, the cross-sectional area of the space provided in the riser, as compared to below the open top of the riser side of the connecting pipe, greater in the above the open top of the riser side of the connecting pipe. The “cross-sectional area of the space provided in the riser” means a cross section parallel to the horizontal plane of the space provided in the riser.
[0026]
According to such a structure, it is possible to increase the volume of the portion located above the connection pipe in the riser space, that is, the volume of the space in which the gas stays. Therefore, the flow velocity in the space becomes slower and the above-described effect becomes more remarkable. When the above structure is adopted, in order to prevent the undesired accumulation of the fluid medium falling from the top of the riser inner space, the portion where the cross-sectional area of the riser inner space is changed has a taper of, for example, about 45 °. It is preferable to provide a part.
[0027]
In the present invention, the downcomer can be constituted by a collection part such as a cyclone and a circulating particle return pipe, but preferably further includes a seal part such as a loop seal.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram schematically showing a circulating fluidized bed furnace according to a reference example . The circulating fluidized bed furnace shown in FIG. 1 is mainly composed of a riser 1 and a downcomer 2. The lower portion of the riser 1 and the downcomer 2 are connected to each other, and the upper portions are connected to each other via a connection pipe 3.
[0029]
The riser 1 includes a furnace body 11 in which a columnar space is provided. The cross-sectional shape of the internal space of the furnace body 11 is, for example, a rectangle or a circle. A diffuser tube 12 for blowing primary air into the furnace is provided in the lower part of the furnace body 11. Further, on the side wall of the furnace body 11, an auxiliary fuel supply port 14 for supplying auxiliary fuel into the furnace with an oil gun or a gas gun as necessary, and secondary air for blowing secondary air into the furnace. The inlet 13 and the inlet 15 for introducing the processing object into the furnace are sequentially provided from below. One end of the connection pipe 3 is connected to the riser 1 at a position lower by a distance d (d ≧ 200 mm) from the top of the space provided in the riser 1.
[0030]
The downcomer 2 includes a collection unit 21 such as a cyclone that collects a fluid medium, a circulating particle return pipe 22 that returns the collected fluid medium and the like to the riser 1, and a gas from the riser 1 that collects the gas 21. And a seal portion (loop seal) 23 for preventing back flow. The other end of the connection pipe 3 is connected to the collection unit 21, and the collection unit 21 is connected to the lower portion of the riser 1 through a seal unit 23 and a circulating particle return pipe 22 in order.
[0031]
The process using the circulating fluidized bed furnace shown in FIG. 1 is performed as follows, for example. Here, the case where the distance d is 300 mm and this circulating fluidized bed furnace is used as a circulating fluidized bed sludge incinerator for treating sludge as a wet substance will be described as an example.
[0032]
The sludge that is the object to be treated is charged into the riser 1 from the charging port 15 using, for example, a charging machine. Prior to the introduction of sludge, by supplying primary and secondary air from the air diffuser 12 and the secondary air inlet 13 into the riser 11, respectively, an upward flow of air with a fluid medium such as sand is formed. deep. The furnace temperature is set to a predetermined temperature by supplying auxiliary fuel into the furnace from the auxiliary fuel supply port 14 and burning it.
[0033]
The sludge thrown into the riser 1 rises in temperature, evaporates moisture and ignites. Exhaust gas, unburned components, fluid medium, and the like generated by the combustion of sludge and auxiliary fuel rise in the internal space of the riser 1 and temporarily stay at the top. At this time, part of the fluid medium and unburned particles that have reached the top of the internal space of the riser 1 fall toward the bottom of the internal space of the riser 1. Therefore, the particle suspension concentration in the riser 1 is sufficiently high, and the amount of the fluid medium sent from the riser 1 to the downcomer 2 through the connection pipe 3 together with the exhaust gas is maintained at an appropriate amount.
[0034]
As described above, the exhaust gas, the unburned matter, and the fluid medium supplied to the downcomer 2 are separated into the exhaust gas and the fluid medium, ash having a relatively large particle size, and the like, as described above. The exhaust gas separated by the collection unit 21 is accompanied by ash having a relatively small particle size and sent to the exhaust gas treatment facility, and is discharged from the chimney after dust removal. Further, the fluid medium collected by the collection unit 21 or the ash having a relatively large particle size is returned to the lower portion of the riser 1 through the seal unit 23 and the circulating particle return pipe 22 as circulating particles. Perform re-burning.
[0035]
At this time, in this reference example , as described above, the amount of the fluid medium sent to the downcomer 2 is maintained at an appropriate amount. It will not be done. Therefore, the fluid medium supplied from the riser 1 to the downcomer 2 together with the exhaust gas can return to the riser 1 in a relatively short time. That is, according to this reference example , it is possible to prevent the fluid medium from returning to the riser 1 in an excessively cooled state, and to stabilize the furnace temperature.
[0036]
Moreover, in this reference example , the temperature fall of a fluid medium can be suppressed without increasing the amount of conveyance air in the seal part 23, or omitting the seal part 23. Therefore, there is no possibility that the combustion air or exhaust gas flows backward in the downcomer 2 and the concentration of harmful gas in the exhaust gas increases.
[0037]
Therefore, according to this reference example , in spite of the case where the object to be treated is a wet substance, there is no increase in the concentration of harmful gas in the exhaust gas or increase in the amount of fluid medium accompanying the exhaust gas. It becomes possible to stabilize the combustion state of the space and time.
[0038]
FIG. 2 is a diagram schematically showing a circulating fluidized bed furnace according to an embodiment of the present invention. The circulating fluidized bed furnace shown in FIG. 2 has the same structure as that of the circulating fluidized bed furnace shown in FIG. 1 except that the inner space of the riser 1 is expanded in diameter above the connection pipe 3. According to such a structure, in addition to obtaining the same effect as described in the reference example , the effect of increasing the particle suspension concentration in the riser 1 becomes more remarkable.
[0039]
In the above embodiment , the circulating fluidized bed furnace is described as being used as a circulating fluidized bed sludge incinerator. However, the circulating fluidized bed furnace can be used for other purposes. For example, it can be used to treat other waste such as municipal waste, waste plastic and paper sludge. Moreover, although said embodiment demonstrated using a circulating fluidized-bed furnace for the process of a waste, it can utilize also as a boiler. That is, the heat generated by the combustion in the space provided in the riser 1 can be used for the evaporation of the fluid. In this case, the riser 1 may be charged with fuel such as coal or oil coke, may be charged with the above-mentioned waste, may be charged with RDF, or a mixture thereof. May be. However, the technique described in the above embodiment is particularly useful in the case where a wet substance, particularly a wet substance having a moisture content of 30 to 90%, is exclusively fired or mixed.
[0040]
【Example】
Examples of the present invention will be described below.
[0041]
First, the circulating fluidized bed furnace shown in FIG. 1 was used as a circulating fluidized bed sludge incinerator, and the relationship between the distance d and the pressure difference in the riser 1 (pressure difference in the riser) was examined. The “in-riser differential pressure” is the difference between the pressure at the top of the riser 1 and the pressure at the bottom of the riser 1. The results are shown in FIG.
[0042]
FIG. 3 is a graph showing the relationship between the distance d and the differential pressure in the riser. In the figure, the horizontal axis indicates the distance d, and the vertical axis indicates the pressure difference in the riser. As shown in FIG. 3, the pressure difference in the riser was remarkably increased by setting the distance d to about 200 mm or more. That is, the effect of increasing the particle suspension concentration in the riser 1 by retaining gas at the top of the internal space of the riser 1 was significant when the distance d was about 200 mm or more.
[0043]
Next, the distance d was set to 200 mm, and the change with time of the temperature in the lower part of the internal space of the riser 1 (riser lower part temperature) was examined. For comparison, the distance d was set to 0 mm and the change in the riser temperature with time was examined. The result is shown in FIG.
[0044]
FIG. 4 is a graph showing a change in temperature with time in the lower part of the internal space of the riser 1. In the figure, the horizontal axis indicates the elapsed time, and the vertical axis indicates the riser lower temperature. A curve 51 indicates data obtained when the distance d is set to 200 mm, and a curve 52 indicates data obtained when the distance d is set to 0 mm.
[0045]
As shown by the curve 52, when the distance d was set to 0 mm, the riser lower temperature was unstable, and the combustion state could not be stabilized. On the other hand, as shown by the curve 51, when the distance d was set to 200 mm, the riser lower temperature could be maintained almost constant, and the combustion situation could be stabilized.
[0046]
【The invention's effect】
As described above, in the present invention, since the top of the space provided in the riser is 200 mm or more higher than the opening upper end of the connection pipe on the riser side, the amount of the fluid medium in the downcomer is increased. Without increasing the particle suspension concentration in the riser. Further, in the present invention, since the temperature drop of the fluidized medium can be suppressed without increasing the amount of air transported at the seal part or omitting the seal part, the combustion air or exhaust gas flows backward in the downcomer. There is no risk of increasing the concentration of harmful gases in the exhaust gas.
[0047]
That is, according to the present invention, even if the object to be treated is a wet substance, the combustion state in the furnace does not occur without causing an increase in the concentration of harmful gas in the exhaust gas or an increase in the amount of fluid medium accompanying the exhaust gas. A circulating fluidized bed furnace and a circulating fluidized bed boiler capable of stabilizing the space and time are provided.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a circulating fluidized bed furnace according to a reference example .
FIG. 2 is a diagram schematically showing a circulating fluidized bed furnace according to an embodiment of the present invention.
FIG. 3 is a graph showing a relationship between a distance d and a differential pressure in the riser.
FIG. 4 is a graph showing the change over time of the temperature in the lower part of the internal space of the riser.
FIG. 5 is a diagram schematically showing a conventional typical circulating fluidized bed furnace.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Riser, 2 ... Downcomer, 3 ... Connection piping, 11 ... Furnace main body, 12 ... Aeration pipe, 14 ... Auxiliary fuel supply port, 13 ... Secondary air injection port, 15 ... Input port, 21 ... Collection part, 22 ... circulating particle return pipe, 23 ... seal part, 51, 52 ... curve.

Claims (2)

A fluid medium comprising: a riser provided with a columnar space therein; a connection pipe having one end connected to the upper part of the riser; and a downcomer connected to the other end of the connection pipe and the lower part of the riser While raising the fluid medium reaching the upper part of the space from the lower part of the space provided in the riser to the lower part of the space through the connecting pipe and the downcomer. a circulating fluidized bed reactor for performing the combustion and / or gasification process of the inner with the processing object, the top of the connecting pipe the riser side space provided in the riser with respect to the upper opening end of the rather high than 200mm greater than the cross-sectional area of the space provided in said riser, the comparison also below the open top of the riser side of the connecting pipe, in above the open top of the riser side of the connecting pipe Excellent circulating fluidized bed furnace to a combustion stability characterized by and. A circulating fluidized bed boiler comprising the circulating fluidized bed furnace according to claim 1 , wherein heat generated by combustion in a space provided in the riser is used for fluid evaporation.

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