JP2002372219A - Processing apparatus for waste gas, and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment wherein a waste gas flow passage in a heat exchanger is unlikely to close and produced dust is cleaned with ease. SOLUTION: Waste gas from a melting furnace 5 for melting a waste is flowed through a plurality of stages of indirect heat exchangers 7 to 10 connected in series via waste gas communication passages 70, 71, and 72, and waste heat of waste gas is recovered by dividing the operation into a plurality of steps. Thereupon, the waste gas communication passage 70 connecting at least the uppermost stream heat exchanger 7 and the next stage heat exchanger 8 is formed to include dust capture spaces 70S, 70S where a waste gas flow speed flowing the inside is lower than that in the uppermost stream heat exchanger 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas treatment apparatus and method suitable for hydrated waste such as sewage sludge or garbage which needs to be dried prior to combustion treatment such as incineration or melting treatment.

[0002]

2. Description of the Related Art In recent waste treatment facilities, in response to a demand for energy saving, waste heat generated by incineration and melting is recovered and effectively used as a heat source in the facility or as electric energy by a generator. ing.

[0003] For example, a technique disclosed in Japanese Patent Publication No. 7-24733 discloses an effective use of waste heat in a water-containing waste treatment facility. This conventional technology includes a steam direct dryer that directly contacts steam and water-containing waste to perform drying, and a processing furnace that incinerates or melts the dried waste dried by the dryer, and uses a heat exchanger. The used steam used by the dryer is heated by heat exchange with the exhaust gas from the processing furnace, and is again supplied to the dryer by circulation.

In practice, exhaust heat recovery cannot be sufficiently performed by using only one heat exchanger. Therefore, the exhaust gas of the melting furnace is sequentially passed through a plurality of indirect heat exchangers connected in series via an exhaust gas communication passage. Then, a configuration for recovering the exhaust heat of the exhaust gas in a plurality of stages is adopted.

[0005]

However, in the case of performing such a multi-stage heat exchange, for example, when melting waste, the operating temperature in the melting furnace is about 1300-1500 ° C.
Since the exhaust gas reaches a high temperature, the evaporated metals are mixed into the exhaust gas, and are re-solidified in the process of being sequentially cooled by the heat exchanger to generate dust. The flow path may be blocked. Also,
Periodic cleaning is required, but if dust adheres to all of the heat exchangers in a plurality of stages, the cleaning operation becomes very complicated. In particular, if dust adheres to the heat transfer surface of the heat exchanger, the cleaning operation is not easy. In other combustion treatments, generation and adhesion of dust and cleaning thereof are inevitable.

Accordingly, it is a main object of the present invention to provide an exhaust gas treatment apparatus and a method thereof, in which an exhaust gas passage in a heat exchanger is not easily blocked and generated dust can be easily cleaned.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an exhaust gas from a combustion furnace which is sequentially circulated through a plurality of indirect heat exchangers connected in series via an exhaust gas communication passage. An exhaust gas treatment device for collecting waste gas in a plurality of stages, wherein the exhaust gas communication passage connecting the heat exchangers has a dust trap in which the flow rate of exhaust gas flowing through the exhaust gas communication passage is lower than at least in the upstream heat exchanger. An exhaust gas treatment device, wherein a space is formed.

In the present invention, it is preferable that the flow rate in the dust trapping space is lower than that in all the exhaust gas channels upstream of the dust trapping space. Preferably, the exhaust gas communication passage has a discharge port at a lower end, and substantially the entire lower portion of the inner surface of the passage is continuously downwardly inclined to the discharge port.

On the other hand, in the exhaust gas treatment method of the present invention, the exhaust gas from the combustion furnace is sequentially passed through a plurality of indirect heat exchangers connected in series via an exhaust gas communication passage, and the exhaust heat of the exhaust gas is divided into a plurality of stages. When collecting the dust, the exhaust gas communication passage connecting the heat exchangers captures dust at a flow rate of the exhaust gas at least lower than that in the upstream heat exchanger.

(Function and Effect) In the present invention, the flow rate of the exhaust gas accompanied by the dust is reduced in the dust trapping space in the exhaust gas communication passage connecting the heat exchangers, and the dust contained therein is concentrated in the trapping space. It is captured by descent. Therefore, dust hardly adheres to the heat exchanger after the exhaust gas communication passage, the possibility of blockage of the flow passage is reduced, and the cleaning operation is significantly facilitated.

In particular, if the exhaust gas communication passage has a discharge port at the lower end and substantially the entire lower portion of the inner surface of the passage is continuously downwardly inclined to the discharge port, the flow velocity decreases and the flow rate in the passage decreases. There is an advantage that all the dust that has fallen to the lower surface slides to the discharge port and is collected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to examples of sewage sludge treatment equipment. 1 and 2 show a flow chart of an example of sewage sludge treatment equipment to which the present invention is applied. Reference numeral 1 in FIG. 1 denotes a sludge pit, and the sludge S stored therein is transferred to a hopper (not shown) by a crane or the like (not shown) and supplied to a dryer 3 by a sludge supply pump 2 attached thereto. You.

The sludge is dried in the dryer 3 using heated steam of about 400 ° C. as a drying heat source. As long as the dryer 3 can use a heat medium such as steam as a drying heat source in a circulating manner, it is not a steam direct drying type in which steam and water-containing waste are brought into direct contact to perform drying as in the illustrated example. May be. The circulation heat medium is not limited to steam.

The steam whose temperature has been reduced by the heat exchange with the sludge is supplied to the dust collector 3C at about 150 ° C., where the dried sludge dust is separated and recovered, and then the next step is performed by the steam circulation fan 3F. It is supplied to the steam heater 8 of the eye. In addition, it is preferable to provide a bag filter or a cyclone in multiple stages as the dust collector 3C.

The dried sludge dried and discharged by the dryer 3 and the dried sludge dust collected by the dust collector 3C are then supplied to the melting furnace 5 by pneumatic transport by the dry sludge transport blower 4, where they are burned and melted. The combustion melting furnace 5
Although not particularly limited in the present invention, in the case of the illustrated example, a vertical swirling type preliminary combustion furnace 50, a horizontal main combustion furnace 51 having one end connected to its lower end, and a slag chute 52 connected to the other end are provided. And a vertical mixing cooler 53, which is a natural cooling type.
Is blown into the top of A burner 54 is provided on the upper part of the preliminary combustion furnace 50, and the burner 54 is configured to be supplied with fuel such as city gas, heavy oil, kerosene, and waste oil, and combustion air from a fan 55, The dried sludge blown in the pre-combustion furnace 50 along the swirling direction is burned and melted by the combustion frame by the burner 54 while swirling and descending, and is discharged from the slag chute 52 as molten slag through the main combustion furnace 51. . The discharged molten slag is taken out after being cooled and solidified by the water-cooled slag conveyor 6.

On the other hand, the exhaust gas of the melting furnace 5 is about 1350 to 1
After being cooled to about 850 ° C. through the mixing cooler 53, it is sent to an exhaust heat recovery section including an air preheater 7 and a plurality of stages of steam heaters 8 to 10. In this example, the air preheater 7 and the first-stage steam heater 8 are each composed of a radiant heat exchanger, and the second and third-stage steam heaters 9 and 10 are each composed of a shell-and-tube heat exchanger. However, the present invention is not limited to such types and combinations, and other known heat exchangers may be used.

The air preheater 7 has a heat exchange with exhaust gas of the melting furnace in advance in order to avoid an extreme temperature drop when blowing air of about 20 to 200 ° C. into the main combustion furnace 51 to prevent overheating in the furnace. This is a heat exchanger for preheating. More specifically, as shown in FIG. 3, a vertically disposed cylindrical portion 7T through which the melting furnace exhaust gas flows from an upper supply port 7i to a lower end discharge port 7e (for example, , 1500 ~ 2500mm inside diameter
) And a cylindrical jacket portion 7J provided so as to surround the exhaust gas in the cylindrical portion 7T, and through which the combustion air flows from the upper end supply port 7m to the lower end discharge port 7n. Then, for example, as shown in the figure, the atmosphere is directly supplied to the air preheater 7, and the supplied air flows downward in the jacket portion 7J, and the exhaust gas of the melting furnace flows in the cylindrical portion 7T in parallel. After being preheated to approximately 500 ° C. by indirect heat exchange with the main combustion furnace 51, the temperature inside the furnace is suppressed to an appropriate temperature. This preheated air can also be supplied to the pre-combustion furnace 50. In addition, the preliminary combustion furnace 50
The cooling air of about 200 ° C. taken out from the upper cooling jacket can be supplied alone to the air preheater 7 together with or instead of the atmosphere.

The melting furnace exhaust gas that has passed through the air preheater 7 is:
The temperature becomes approximately 811 ° C. and is supplied to the first-stage steam heater 8 through the exhaust gas communication passage 70. First stage steam heater 8
Has basically the same structure as the air preheater 7. That is, as shown in detail in FIG. 3, the first-stage steam heater 8 includes a vertically arranged tubular portion 8T through which the melting furnace exhaust gas flows from the lower end supply port 8i to the upper discharge port 8e, and a tubular portion. The cylindrical jacket portion 8J is disposed so as to surround the exhaust gas in the 8T, and the steam discharged from the dryer 3 flows from the lower end supply port 8m to the upper end discharge port 8n.
It is composed of About 15 discharged from the dryer 3
The steam at about 0 ° C. is heated to about 181 ° C. by indirect heat exchange with the melting furnace exhaust gas flowing through the cylindrical portion 8T in the process of flowing through the jacket portion 8J. On the other hand, the melting furnace exhaust gas is thereby cooled to about 750 degrees.

Next, in this embodiment, the steam that has passed through the first-stage steam heater 8 is circulated in the order of the second-stage steam heater 9 and the third-stage steam heater 10, and conversely, the exhaust gas from the melting furnace is passed through the third stage The in-situ steam heater 10 and the second-stage steam heater 9 are circulated in this order, and indirect heat exchange is performed in such a manner as to flow back to each other. As shown in detail in FIG. 3, the second and third steam heaters 9 and 10 are provided with shells 9S,
This is a so-called shell-and-tube type heat exchanger having a large number of tubes 9T, 10T in the 10S. The steam is between the inner surfaces of the shells 9S, 10S and the outer surfaces of the tubes 9T, 10T, and the exhaust gas of the melting furnace is the tubes 9T, 10T. The steam is respectively circulated in the 10T, and in the process, the steam is heated by indirect heat exchange with the melting furnace exhaust gas.

More specifically, the steam at about 181 ° C. which has been heated in the first-stage steam heater 8 passes through the steam communication passage 80 to the second-stage steam heater 9. The melting furnace exhaust gas of about 400 ° C. which has completed the heat exchange in the third-stage steam heater 10 is supplied through the exhaust gas communication passage 72. This allows
The steam flowing in the shell 9S is heated to about 232 ° C. by indirect heat exchange with the exhaust gas flowing in the tube 9T. The melting furnace exhaust gas is cooled to about 250 ° C. Next, the steam at about 232 ° C., which has been heated in the second-stage steam heater 9, is supplied to the third-stage steam heater 10 via the steam communication passage 81 and the first-stage steam heater 8. In this case, the melting furnace exhaust gas of about 750 ° C. after the heat exchange is supplied through the exhaust gas communication passage 71, respectively.
As a result, the steam flowing in the shell 10S is reduced by about 3 times by indirect heat exchange with the exhaust gas flowing in the tube 10T.
Heated to about 69 ° C. The melting furnace exhaust gas is about 40
It is cooled to about 0 ° C.

On the other hand, dust contained in the melting furnace exhaust gas is as follows:
The air preheater 7 is deposited and collected at the lower ends of the first to third-stage steam heaters 8 to 10, and after being subjected to processing such as foreign matter removal by a fly ash treatment facility (not shown), is stabilized and externally disposed. Alternatively, it is returned to the inlet side of the dry sludge transport blower 4 and mixed with the dry sludge.

As described above, in this embodiment, of the multistage heat exchangers 7 to 10 for sequentially recovering the exhaust heat of the melting furnace exhaust gas, the former heat exchanger (air) in which dust due to re-solidification of the evaporated metal is likely to be generated. By using the radiant heat exchanger having the above-described configuration as the preheater 7 and the first-stage steam heater 8), even if some dust adheres to the inner peripheral surface of the cylindrical portion, the flow of exhaust gas is obstructed or prevented. It is difficult to reach a situation in which blockage occurs, cleaning is easy, and high temperature resistance is sufficiently ensured. Moreover, simply using such a radiant heat exchanger results in a low heat exchange efficiency, resulting in an excessively large installation space for the exhaust heat recovery unit. As side heat exchangers (second-stage and third-stage steam heaters 9 and 10), a shell-and-tube type heat exchanger having extremely high heat exchange efficiency per unit installation area and sufficiently high temperature resistance is combined. Thereby, the installation space of the exhaust heat recovery unit can be minimized while reducing the possibility of dust blocking the exhaust gas distribution system.

However, even if the above combination is adopted, it is not possible to completely prevent dust from adhering to the inside of the heat exchangers 7 to 10, and regular cleaning is required. However, even if cleaning is necessary, if dust adheres to all of the heat exchangers in a plurality of stages, the cleaning operation becomes very complicated.

Therefore, in this embodiment, as shown in FIG. 4, exhaust gas from the heat exchanger (air preheater 7) on the most upstream side where at least dust due to the evaporated metal is easily generated according to the present invention is used as the heat exchanger in the next stage. In the exhaust gas communication passage 70 to be fed to the (first-stage steam heater 8), for example, the cross-sectional area with respect to the exhaust gas flow direction is set so that the internal exhaust gas flow speed is lower than that of the upstream heat exchanger 7. It is desirable to form dust capture spaces 70S, 70S larger than the heat exchanger 7. Particularly preferably, the dust trapping space 70S, 70S
The flow velocity in the space is determined by the dust trapping space 70S, 7
It is desirable that the exhaust gas flow path be lower than all the exhaust gas flow paths upstream of 0S (that is, in this example, the heat exchanger 7 and the communication passage 72 between the heat exchanger 7 and the mixing cooler 53). The degree of decrease in the flow velocity in the dust trapping spaces 70S, 70S is, for example, about 2 to 5 m.
/ S is desirable. More specifically, the communication path 72
Flow rate in the heat exchanger 7 is 3 to 10 m / sec.
It is desirable to design so as to be 6 m / sec and the flow velocity in the dust trapping space 70S is 2 to 5 m / sec.

As a result, the flow rate of the exhaust gas accompanying the dust generated by cooling in the heat exchanger 7 on the most upstream side is reduced by the dust trapping space 70 in the exhaust gas communication passage 70 to the next stage.
S, 70S, and the dust contained therein is intensively captured in the capturing spaces 70S, 70S. Therefore, some dust may adhere to the heat exchanger 7 on the most upstream side, but it is difficult for the dust to adhere to the heat exchangers 8 to 10 after the exhaust gas communication passage 70, and the flow passage may be blocked. And the cleaning operation becomes remarkably easy. This configuration is particularly suitable when the downstream exhaust gas flow system has a narrow flow path that may be blocked, such as a tube of a shell-and-tube heat exchanger, as in this example.

As shown in the figure, a lateral exhaust gas communication passage (duct) 70 connecting the air preheater 7 and the steam heater 8 is provided.
Is removably connected to a lower end discharge port 7e of the tubular portion of the air preheater 7 at a supply port 70i of the upper wall at one end, and to a tubular section of the steam heater 8 at a discharge port 70e of the upper wall at the other end. When connected to the lower end supply port 8i, there is an advantage that cleaning in the exhaust gas communication passage 70 becomes easy.

In particular, as shown in detail in FIG. 4, the exhaust gas communication passage 70 has a cylindrical upper portion t1 connected in series with a lower end outlet 7e of the air preheater 7 and a conical having a dust outlet x1 at the lower end apex. A conical lower portion having an inlet-side vertical cylindrical portion 70A composed of a lower portion c1 and a cylindrical upper portion t2 connected in series to a lower end supply port 8i of the steam heater 8 and a dust discharge port x2 at the lower end apex. The outlet side vertical cylindrical portion 70B composed of the side portion c2, the inlet side communicates with the side portion of the inlet side vertical cylindrical portion 70A, and the outlet side communicates with the side portion of the outlet vertical cylindrical portion 70B. The horizontal duct in which the lower surface en in the portion is continuously inclined downward to the lower end discharge port x1 of the entrance-side vertical cylindrical portion and the lower surface ex in the output side portion is continuously lowered to the lower end discharge port x2 of the output-side vertical cylindrical portion. The one formed integrally with the portion 70C is preferable. In the exhaust gas communication passage 70, the horizontal duct 70
The entire both sides of the reduced diameter portion ce at the center of the C serve as dust capturing spaces. With this configuration, not only the entire communication path 70 except the reduced diameter portion ce serves as a dust capturing space, but also substantially all of the lower part c1, en, ex, and c2 are formed by downward inclined surfaces. For this reason, there is no horizontal surface over substantially the entire lower surface, and the flow velocity decreases, and substantially all of the dust that has fallen falls down to one of the outlets x1 and x2.
Therefore, the dust trapping ability in the exhaust gas communication passage 70 is further improved, and almost all of the falling dust is discharged from the exhaust port x1,
x2 and can be collected and discharged.

On the other hand, the steam heated by heat exchange with the exhaust gas from the melting furnace is circulated and supplied to the dryer 3. At this time, if necessary, the auxiliary heater 11 (indirect heat exchanger) exchanges heat with the clean exhaust gas from the auxiliary furnace 12 that burns fuel such as city gas, etc., to a predetermined temperature, for example, 400
It is desirable to supply to the dryer 3 after heating to the temperature. For this reason, although not shown, a temperature measuring device for measuring the temperature of the steam returned to the dryer 3 is provided, and based on the measurement result by this temperature measuring device, the amount of the clean exhaust gas blown to the heater 11 and the auxiliary furnace 12 Can be configured to adjust the degree of combustion. Reference numeral 13 denotes an auxiliary furnace fan that feeds combustion air to the auxiliary furnace.

As shown in the figure, it is also preferable to supply a part of the steam returned to the dryer 3 into the melting furnace 5 to prevent overheating. That is, when the steam is directly contacted with the sludge and dried as in this example, the circulating steam increases with time due to evaporation of the water during the drying of the sludge, and it is necessary to discharge this to the outside of the system as necessary. . On the other hand, when the melting furnace 5 is a natural cooling system as described above, a large amount of air must be supplied into the furnace in order to prevent overheating. However, by blowing a part of the circulating steam into the furnace 5 according to the present invention, not only the amount of the circulating steam can be adjusted, but also the specific heat of the steam is about four times that of the air. As a result, the furnace temperature can be adjusted with an extremely small blowing amount. Further, although a large amount of malodorous components are contained in the circulating steam, there is also a secondary advantage that the malodorous components are thermally decomposed when blown into the melting furnace 5. However, the steam blown into the melting furnace 5 has a low temperature (about 370 ° C.) as in this example.
In the case of (1), the temperature inside the furnace drops rapidly, and the temperature control is hindered. In such a case, the preheater 7
It is preferable to mix with the air blown into the melting furnace 5 before blowing into the furnace. In the case of the melting furnace 5 of this example, in order to obtain the above-mentioned advantages, it is desirable to blow the circulating steam into the main combustion furnace 51 and blow the remainder into the mixing cooler 53. Although not shown, a pressure gauge for measuring the internal pressure of the dryer 3 and means for controlling the amount of circulating steam supplied to the melting furnace 5 in accordance with the measurement result of the pressure gauge are provided for adjusting the amount of circulating steam. It is desirable.

On the other hand, the melting furnace exhaust gas cooled to about 250 ° C. by heat exchange with steam is cooled to about 200 ° C. by spraying cooling water and cooling air in the exhaust gas cooler 100.
After cooling to the extent, dust is removed by the bag filter 101. The dust collected by the exhaust gas cooler 100 and the bag filter 101 is also subjected to a treatment such as foreign matter removal by a fly ash treatment facility (not shown) and then stabilized and externally disposed of. And mixed with dry sludge. The exhaust gas that has passed through the bag filter 101 is then supplied to a flue gas treatment tower 102 (scrubber), where the exhaust gas is washed and collected by washing water. After being cooled to about 50 ° C. in the process, the air is introduced into the denitration processing unit 110 by the attraction fan 103.

The denitration processing section 110 preheats the melting furnace exhaust gas to about 250 ° C. in a denitration preheater (indirect heat exchanger) 111 by heat exchange with waste heat, and then heats the furnace 112 using fuel such as city gas. After heating to a reaction tower supply temperature of about 350 ° C., urea water, air, dilution water, and the like are added to perform denitration treatment in the reaction tower 113 by a denitration reaction. In this example, as the exhaust heat medium used in the preheater 111, the clean exhaust gas used in the auxiliary heater 11 of the steam circulation system has an appropriate temperature (about 400 ° C.). Since the subsequent exhaust gas has an appropriate temperature (about 350 ° C.), the entire exhaust gas is used after being mixed and mixed. Of course, either one may be good. This mixed gas is released to the atmosphere from the chimney 114 after heat exchange in the preheater 111. In particular, by mixing the clean exhaust gas used in the auxiliary heater 11 into the exhaust gas after the denitration treatment, there is an advantage that generation of white smoke at the time of release to the atmosphere can be prevented. Reference numeral 115 indicates an air fan that feeds air into the heating furnace.

<Others> (a) In the above example, four stages of heat exchangers using the melting furnace exhaust gas as a heating medium are provided, but the number of stages of the heat exchanger can be determined as appropriate according to the degree of exhaust heat recovery.

(B) The above example is an example of equipment for recovering exhaust heat using circulating steam as a drying heat source. In the present invention, heat recovery is performed from exhaust gas of a melting furnace using a multi-stage heat exchanger. For example, waste heat can be recovered by another heat medium, or the recovered waste heat can be used for other purposes.

(C) The above example is an example of application to a sewage sludge melting treatment facility, but the present invention is not limited to this.
The present invention can be applied to the treatment of other wastes and non-wastes, and can also be applied to combustion treatment equipment such as incineration equipment that does not perform melting.

(D) Although not shown, the entrance lower surface en and the exit lower surface ex are formed at an acute angle at the central reduced diameter portion ce of the exhaust gas communication passage 70 of the above example so that the horizontal surface of the internal lower surface is eliminated. You can also. Thus, the entire lower surface of the communication passage is completely composed of only the downward inclined surface.

[0036]

As described above, according to the present invention, the exhaust gas passage in the heat exchanger is hardly clogged and the generated dust can be easily cleaned.

[Brief description of the drawings]

FIG. 1 is a first-stage flow chart of an example of a sludge treatment facility according to the present invention.

FIG. 2 is a post-stage flow chart.

FIG. 3 is an enlarged view of an exhaust heat recovery unit.

FIG. 4 is an enlarged perspective view of an exhaust gas communication passage.

[Explanation of symbols]

1: Sludge pit, 2: Sludge supply pump, 3: Dryer, 4
... dry sludge transport blower, 5 ... melting furnace, 6 ... water cooled slag conveyor, 7 ... air preheater, 8,9,10 ... steam heater,
11: auxiliary heater, 12: auxiliary furnace, 70, 71, 72 ...
Exhaust gas communication passage, 80, 81: Steam communication passage, 100: Exhaust gas cooler, 101: Bag filter, 102: Smoke exhaust treatment tower, 111: Denitration preheater, 112: Heating furnace, 113: Reaction tower, 114: Chimney.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoji Kojima 2-17-15 Tsukushima, Chuo-ku, Tokyo Tsukishima Machinery Co., Ltd. (72) Inventor Seiichi Bando 2-17-15 Tsukushima, Chuo-ku, Tokyo Machinery Co., Ltd. F-term (reference) 3K065 AB03 AC01 AC02 BA05 BA06 HA03 JA05 JA18 3K070 DA07 DA27 4D059 AA03 AA07 BB01 BB04 BB11 BF02 CA01 CB01

Claims (4)

[Claims] 1. An exhaust gas from a combustion furnace is sequentially passed through a plurality of indirect heat exchangers connected in series via an exhaust gas communication passage,
An exhaust gas treatment device that recovers exhaust heat of exhaust gas in a plurality of stages, wherein the flow rate of exhaust gas flowing inside the exhaust gas communication passage connecting the heat exchangers is lower than at least in the upstream heat exchanger. An exhaust gas treatment device characterized by forming a dust trapping space. 2. The exhaust gas treatment apparatus according to claim 1, wherein a flow velocity in said dust trapping space is lower than in all exhaust gas passages upstream of said dust trapping space. 3. The exhaust gas communication passage according to claim 1, wherein the exhaust gas communication passage has a discharge port at a lower end, and substantially the entire lower portion of the inner surface of the passage is continuously downwardly inclined to the discharge port. Exhaust gas treatment equipment. 4. An exhaust gas from the combustion furnace is sequentially passed through a plurality of indirect heat exchangers connected in series via an exhaust gas communication passage,
In recovering the exhaust heat of the exhaust gas in a plurality of stages, the exhaust gas communication passage connecting the heat exchangers captures dust at a flow rate of the exhaust gas that is at least lower than that in the upstream heat exchanger. An exhaust gas treatment method comprising: