JP6531212B1 - Drying air supply device - Google Patents

Abstract

An object of the present invention is to provide a drying air supply device which has high thermal efficiency and can reduce running cost. A case (12) airtightly and thermally insulated, a combustion furnace (13) disposed at the center of the case, an air supply blower (5) provided below the combustion furnace, and a combustion furnace provided above the combustion furnace The heat radiation pipes 16 and 17 through which the combustion gas from the flow circulates, the secondary heat exchanger 19 provided adjacent to the inner end side of the combustion furnace and to which the heat radiation pipe is connected, and the dry gas formed on the upper surface of the case An exhaust port 27, an air suction port formed on the back of the case, and an air suction duct provided along the back of the case and communicating with the air suction port, the air 59 discharged from the air supply blower is While being discharged from the drying gas outlet through the periphery of the combustion furnace and between the heat radiation pipes, a part of the air flows through the secondary heat exchanger and flows out into the case, and the combustion furnace is cooled and discharged from the combustion furnace Heat absorbed, mixed with air passing between the heat sinks, heated to a predetermined temperature It was constructed as to be discharged from the dry gas outlet. [Selected figure] Figure 2

Description

  The present invention relates to a drying air supply device for supplying drying air to a drying chamber.

  In a drying chamber, for example, a drying chamber for drying after painting, the product after the coating process is carried into the drying chamber, and drying air is supplied to the drying chamber for drying. The drying air usually exchanges heat between the combustion gas after being burned by the combustion burner and the air, and supplies the air whose temperature has been raised to the required temperature as drying air to the drying chamber.

  In recent years, energy savings have been achieved, and running costs have been reduced by saving fuel, and even in the drying air supply device, the thermal energy of the combustion gas can be effectively recovered to reduce the drying air cost. It is desirable to make it available.

JP 2012-117681 A JP, 2013-132607, A JP, 2017-87121, A JP, 2016-211829, A

  SUMMARY OF THE INVENTION The present invention provides a drying air supply device that has high thermal efficiency and can reduce running cost.

  According to the present invention, there is provided an airtightly insulated case, a combustion furnace disposed at the center of the case, an air supply blower provided below the combustion furnace, and the combustion furnace provided above the combustion furnace. A heat release pipe through which the combustion gas from the flow circulates, a secondary heat exchanger provided adjacent to the inner end side of the combustion furnace and connected to the heat release pipe, and a dry gas discharge formed on the upper surface of the case An outlet, an air suction port formed on the back of the case, and an air suction duct provided along the back of the case and in communication with the air suction port, wherein the combustion gas from the combustion furnace is It flows into the secondary heat exchanger through the heat radiation pipe and is exhausted through the exhaust pipe, and the external air is sucked by the air supply blower through the air suction duct and the air discharged from the air supply blower is discharged through the air suction duct. , Around the combustion furnace, through between the heat radiation pipes The air is discharged from the dry gas outlet, and a part of the air is sucked into the secondary heat exchanger, flows through the secondary heat exchanger and flows out into the case, and the air cools the combustion furnace. Heat absorption from the combustion furnace, and heat exchange with the combustion gas through the heat radiation pipe for heating, and a portion of the air is flowed from the heat radiation pipe in the secondary heat exchanger And a portion of the air mixed with the air passing between the heat radiation pipes, and discharged from the drying gas outlet as drying air. It relates to an air supply device.

  Further, according to the present invention, the heat radiation pipe is constituted by two upper and lower stages, the upper heat radiation pipe further extends from the combustion furnace, and the secondary heat exchanger is provided below the extension portion of the heat radiation pipe. The present invention relates to a drying air supply device in which an upper portion of a secondary heat exchanger is in communication with the heat radiation pipe, and a lower portion of the secondary heat exchanger is in communication with the exhaust pipe.

  Furthermore, according to the present invention, an air suction and discharge unit is provided at a lower portion of the secondary heat exchanger, the secondary heat exchanger is unitized, and the air suction and discharge unit sucks a part of the air. The present invention relates to a drying air supply device including a fan, an exhaust fan discharging the combustion gas flowing through the secondary heat exchanger toward the exhaust pipe, or the suction fan and the exhaust fan.

  According to the present invention, a case insulated in a gas-tight manner, a combustion furnace disposed at the center of the case, an air supply blower provided below the combustion furnace, and the above-mentioned combustion furnace are provided. A heat release pipe through which the combustion gas from the combustion furnace flows, a secondary heat exchanger provided adjacent to the inner end side of the combustion furnace and to which the heat release pipe is connected, and a drying formed on the upper surface of the case A gas exhaust port, an air suction port formed on the back surface of the case, and an air suction duct provided along the back surface of the case and communicating with the air suction port, the combustion gas from the combustion furnace is The gas flows into the secondary heat exchanger through the heat radiation pipe and is exhausted through the exhaust pipe, and the external air is sucked by the air supply blower through the air suction duct and discharged from the air supply blower. Air is passed around the combustion furnace and between the heat radiation pipes. The air is discharged from the dry gas outlet, and a part of the air is drawn into the secondary heat exchanger, flows through the secondary heat exchanger and flows out into the case, and the air is discharged from the combustion furnace. Is cooled, heat is absorbed from the combustion furnace, and heat is exchanged with the combustion gas via the heat radiation pipe for heating, and a part of the air flows from the heat radiation pipe in the secondary heat exchanger The heat exchange with the combustion gas is performed, the air is heated to a predetermined temperature, the air passing through the heat radiation pipe and a part of the air are mixed, and the air is discharged as the drying air from the drying gas outlet. Therefore, the air that exchanges heat with the combustion furnace, the heat radiation pipe, etc. flows uniformly from the lower side to the upper side, the installation area decreases, and all the heat generating parts are housed in the case of the heat insulation structure. Heat is recovered to the combustion air without waste, and from the combustion furnace Recovery of contact heat can further heat from the temperature drop combustion gases collected by the secondary heat exchanger, there is exhibited an excellent effect that it is possible to perform efficient heat recovery.

It is a schematic block diagram of the air supply apparatus for drying concerning the Example of this invention. It is a front view which shows the inside of the air supply apparatus for drying which concerns on a present Example. It is a side view showing the inside of the air supply unit for drying. It is a top view which shows the inside of this air supply apparatus for drying. It is the schematic of a secondary heat exchanger used for the said air supply apparatus for drying. It is a perspective view of the heat exchanger main part of this secondary heat exchanger.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the basic configuration of the drying air supply device 1 according to the present embodiment will be described with reference to FIG.

  In FIG. 1, 2 is a burner, 3 is a primary heat exchanger, 4 is a secondary heat exchanger, 5 is an air supply blower, 6 is a drying chamber, 7 is an exhaust gas, and 8 is condensation from combustion gas in the heat exchange process. It is drain water.

  As an example of the operating state in the present drying air supply device 1, the temperature of the combustion gas obtained by the combustion in the burner 2 is 1800 ° C., and the primary heat exchanger 3, the secondary heat exchange The air sucked from the outside of the drying chamber from the air supply blower 5 is fed to the vessel 4, and the primary heating air 9 heated to approximately 80 ° C. is obtained by heat exchange in the primary heat exchanger 3. The secondary heat air 10 heated to 200 ° C. to 300 ° C. is obtained by heat exchange in the secondary heat exchanger 4.

  The primary heating air 9 and the secondary heating air 10 are mixed and supplied to the drying chamber 6, whereby the drying chamber 6 is heated to a maximum temperature of 80 ° C. and provided for drying.

  A specific embodiment of the drying air supply device 1 will be described with reference to FIGS.

  In FIG. 2, reference numeral 12 denotes a case, the case 12 has an airtight structure, a heat insulating material is provided on the inner surface of each surface forming the case 12, and the case 12 has a heat insulating structure .

  The air supply blower 5 is installed on the bottom of the case 12. One or more air supply blowers 5 are provided corresponding to the required air flow of the drying air. In the drawing, two air supply blowers 5 are installed. Furthermore, the air supply blower 5 can adjust the air flow rate according to the drying conditions such as the temperature at which the drying chamber 6 is required.

  A combustion furnace 13 having a horizontal axis at the center of the case 12 and positioned horizontally above the air supply blower 5 is installed.

  The burner 14 is inserted and provided from the outer end side (left end in FIG. 2) of the combustion furnace 13. A combustion gas guide duct 15 is provided at an inner end (right end in the figure) of the combustion furnace 13. The combustion gas guide duct 15 airtightly covers the right end of the combustion furnace 13 and extends upward.

  A required number (three in the present embodiment) of heat radiation pipes 16 are disposed on the upper side of the combustion furnace 13 in parallel with the axis of the combustion furnace 13. The right end of the heat radiation pipe 16 is airtightly connected to the upper extension of the combustion gas guide duct 15.

  A required number (three in the present embodiment) of heat radiation pipes 17 are provided in parallel with the heat radiation pipes 16 above the heat radiation pipes 16, and the left ends of the heat radiation pipes 16 and the heat radiation pipes 17 are ducts 18. It is connected airtightly. The right end of the heat radiation pipe 17 extends horizontally further to the right than the combustion gas guide duct 15. The combustion furnace 13 and the heat radiation pipes 16 and 17 constitute a primary heat exchanger.

  A required number (two sets in the drawing) of secondary heat exchangers 19 is provided below the horizontally extending portion of the heat radiation pipe 17 and adjacent to the side opposite to the burner 14 of the combustion furnace 13. The secondary heat exchanger 19 is located on the downstream side of the heat radiation pipes 16 and 17, and in FIG. 2, the secondary heat exchanger 19 is in the vertical posture with two pairs in the direction perpendicular to the paper surface. It is arranged.

  As shown in FIG. 5, each of the secondary heat exchangers 19 is provided with a hot fluid inlet 44 at the upper right side and a cold fluid outlet 47 at the upper left side. Furthermore, the secondary heat exchangers 19 are respectively provided with a high temperature fluid outlet 45 at the lower right end and a low temperature fluid inlet 46 at the lower left end. The low temperature fluid inlet 46 is provided with a low temperature air induction duct 21, and an upstream end (lower end in the figure) of the low temperature air induction duct 21 is provided with a damper 26 for flow rate adjustment. The damper 26 ascends from below to adjust the flow rate of the air 54 flowing into the cold air induction duct 21, and the cold air induction duct 21 guides the air 54 flowing into the cold fluid inlet 46.

  A communication duct 22 is provided across the right end of the heat radiation pipe 17 and the upper right end of the secondary heat exchanger 19, and the open end of the heat radiation pipe 17 and the high temperature fluid inlet of the secondary heat exchanger 19 It is connected airtightly with 44.

  An exhaust pipe 23 is provided on the outer side of the right side surface of the case 12 in the vertical direction. The lower end of the exhaust pipe 23 is airtightly closed, and an exhaust inlet (not shown) is provided on the side surface of the lower end of the exhaust pipe 23. The exhaust inlet and the high temperature fluid outlet 45 are airtightly connected by an exhaust duct 24. An upstream portion (lower end in the figure) of the exhaust pipe 23 is accommodated in the case 12 and penetrates a ceiling plate of the case 12 to extend to the outside.

  The exhaust pipe 23 is provided with a temperature sensor 30. The temperature sensor 30 detects the temperature of exhaust gas flowing in the exhaust pipe 23, and the detected temperature is input to a control device 35 (described later).

  A drain tank 25 is provided below the secondary heat exchanger 19, and water condensed in the secondary heat exchanger 19 is dropped and stored. The drain tank 25 can be omitted when the present apparatus is operated so that the combustion gas discharged from the secondary heat exchanger 19 does not become 100 ° C. or less.

  The air supply blower 5, the combustion furnace 13, the heat radiation pipe 16, the heat radiation pipe 17, the secondary heat exchanger 19, the exhaust pipe 23, the drain tank 25, etc. It is fixed.

  A drying gas outlet 27 is provided on the upper surface of the case 12 at a position facing the combustion furnace 13. A drying air supply duct 29 for communicating the drying air 28 discharged from the drying gas outlet 27 to the drying chamber 6 (not shown) is in communication with the drying gas outlet 27.

  An air suction duct 31 is provided on the back surface side of the case 12, and an air suction port 32 is formed at a position facing the air supply blower 5 at the lower rear surface of the case 12. The air suction duct 31 communicates with the inside of the case 12 via the air suction port 32.

  An air suction port 33 is provided at the upper end of the air suction duct 31, and a filter 34 is provided below the air suction port 33.

  The drive of the air supply blower 5 and the combustion load control of the burner 14 are controlled by the control device 35, and the air flow control of the air supply blower 5 and the combustion state control of the burner 14 The temperature and air volume of the drying air 28 supplied to the drying chamber 6 are controlled to meet the conditions required for the drying chamber 6. Furthermore, based on the detection result of the temperature sensor 30, the damper 26 is controlled so that the exhaust gas temperature becomes a predetermined temperature, and the flow rate of the air 54 to the secondary heat exchanger 19 is adjusted.

  Next, the secondary heat exchanger 19 will be described with reference to FIG. 6 shows a heat exchanger main body 37 used for the secondary heat exchanger 19. As the heat exchanger main body 37, for example, the one disclosed in Patent Document 1 can be used. .

  Hereinafter, the heat exchanger main body 37 will be briefly described.

  The heat exchanger body 37 is in the form of a hermetically sealed box, and the heat transfer body 42 is accommodated inside the box case 41. The heat transfer body 42 has a structure in which a flat plate of a metal material is folded back in a large number in a zigzag manner, and a high temperature fluid flow passage and a low temperature fluid flow passage are alternately formed by winding the flat plate. The heat transfer body 42 has a large heat transfer area with respect to the flow rate of the heat-exchanged gas, and can perform heat exchange with a high efficiency of 80% or more.

  A hot fluid inlet 44 and a hot fluid outlet 45 are formed on the back of the box case 41 as shown. The hot fluid inlet 44 and the hot fluid outlet 45 communicate with the hot fluid flow path. Further, a cryogenic fluid inlet 46 and a cryogenic fluid outlet 47 are formed on the illustrated front surface of the box case 41, and the cryogenic fluid inlet 46 and the cryogenic fluid outlet 47 communicate with the cryogenic fluid flow channel.

  The combustion gas 57, which is a high temperature fluid, flows through the high temperature fluid flow channel, and the air 54, which is a low temperature fluid, flows through the low temperature fluid flow channel, and the combustion gas 57 passes through the heat transfer body 42 in the process of flowing. Heat is transferred between the air and the air 54.

  Next, the secondary heat exchanger 19 will be described with reference to FIG. In FIG. 5, the heat transfer body 42 is not shown.

  The heat exchanger main body 37 is incorporated in the drying air supply device 1 with the high temperature fluid outlet 45 and the low temperature fluid inlet 46 positioned on the lower side.

  An air suction and discharge unit 51 is provided at the lower end portion of the heat exchanger main body 37, and the air suction and discharge unit 51 is configured of a suction unit 52 and a discharge unit 53.

  The suction unit 52 includes the low temperature air induction duct 21 for inducing the air 54 blown from the air supply blower 5, and the low temperature air induction duct 21 is in communication with the low temperature fluid inlet 46. The discharge portion 53 includes the high temperature fluid outlet 45 of the heat exchanger main body 37 and has the exhaust duct 24 for discharging the combustion gas 57 after heat exchange flowing out from the high temperature fluid outlet 45. The exhaust duct 24 is connected to the exhaust pipe 23.

  A suction fan 55 for sucking the air 54 from the outside through the damper 26 and the low temperature air induction duct 21 and discharging the air 54 from the low temperature fluid inlet 46 is accommodated in the suction portion 52. An exhaust fan 56 is accommodated in the exhaust unit 53, and the exhaust fan 56 sucks the combustion gas 57 from the high temperature fluid outlet 45 and discharges the combustion gas 57 from the exhaust duct 24.

  The suction fan 55 and the discharge fan 56 are integrally rotated by a fan motor 58. The control of the drive of the fan motor 58 and the control of the degree of opening of the damper 26 are executed by the controller 35. The suction fan 55 and the discharge fan 56 may be individually rotated by two motors. Furthermore, either one of the suction fan 55 and the discharge fan 56 may be omitted.

  The combustion gas 57 flows into the heat exchanger body 37 from the high temperature fluid inlet 44 through the communication duct 22, and the combustion gas 57 further flows through the heat exchanger body 37. It is cooled and flows out from the high temperature fluid outlet 45 through the exhaust duct 24. The air 54 flows into the heat exchanger main body 37 from the low temperature fluid inlet 46 through the low temperature air induction duct 21 and is further heated in the process of flowing through the heat exchanger main body 37, It is discharged from the low temperature fluid outlet 47.

  Hereinafter, the operation of the drying air supply device 1 will be described.

  The combustion gas generated by the combustion action of the burner 14 flows into the secondary heat exchanger 19 through the combustion gas guide duct 15, the heat radiation pipe 16, the heat radiation pipe 17, and the connection duct 22, and the secondary heat exchanger 19 The combustion gas flowing through the heat exchanger 19 is exhausted through the exhaust duct 24 and the exhaust pipe 23. The temperature of the combustion gas finally exhausted is cooled to 80 ° C. to 150 ° C.

  The air to be supplied for drying is sucked from the air suction port 33, the flow rate is adjusted by the filter 34, passes through the air suction duct 31 and the air suction port 32, and is sucked by the air supply blower 5 to the upper side. Is discharged.

  The discharged air 59 ascends around the combustion furnace 13 and further passes through between the heat radiation pipes 16 and 17 and flows out from the drying gas outlet 27, and the drying air supply duct 29 It is introduced into a drying chamber (not shown).

  In addition, a part of the air 59 discharged by the air supply blower 5 (the air 54) flows into the secondary heat exchanger 19 through the low temperature air induction duct 21, and the secondary heat exchanger 19 It flows and is discharged into the case 12 from the low temperature fluid outlet 47.

  The air 59 discharged from the air supply blower 5 cools the combustion furnace 13 and absorbs heat generated from the combustion furnace 13 itself in the process of rising around the combustion furnace 13. Accordingly, the outer surface of the combustion furnace 13 functions as a heat transfer surface for heat exchange.

  Furthermore, the air 59 which has risen around the combustion furnace 13 ascends between the heat radiation pipes 16 and 17 and is heated by exchanging heat with combustion gas through the heat radiation pipes 16 and 17 in the process of rising. . The combustion furnace 13 and the heat radiation pipes 16 and 17 function as primary heat exchangers. The temperature of the air (primary heating air) after passing through the heat radiation pipes 16, 17 is approximately 80.degree.

  The air 54 that has flowed into the secondary heat exchanger 19 exchanges heat with the combustion gas 57 in the secondary heat exchanger 19, and the temperature is raised to about 200 ° C. to 300 ° C. The air (secondary heating air) flowing out of the secondary heat exchanger 19 is mixed with the primary heating air, and the drying air is supplied as the drying air 28 at a predetermined temperature (for example, 100 ° C. to 120 ° C.) It is discharged from the device 1.

  Furthermore, the flow rate of the drying air 28 supplied can be adjusted by controlling the driving state of the air supply blower 5 according to the drying state in the drying chamber 6, and the temperature of the drying air 28 can be further adjusted. It can also be adjusted by controlling the combustion state of the combustion furnace 13 and controlling the flow rate of the air 54 sucked via the damper 26 and the fan motor 58.

  The action of heat exchange of the air 59 discharged from the air supply blower 5 between the combustion furnace 13 and the heat radiation pipes 16 and 17 corresponds to the primary heat exchange shown in FIG. 1, and the air The action of heat exchange in the secondary heat exchanger 19 corresponds to the secondary heat exchange shown in FIG.

  In this embodiment, since the combustion furnace 13 is housed in a thermally insulated space, the heat generated from the combustion furnace 13 is not released to the outside, and the combustion furnace 13 is further cooled by the air 59. Since the heat generated by the combustion furnace 13 itself is absorbed by the air 59, the heat generated during the combustion is effectively recovered.

  Further, the combustion gas in the high temperature state exchanges heat with the air 59 which has passed through the combustion furnace 13. However, the heat energy of the combustion gas 57 is finally recovered by the secondary heat exchanger 19, so The radiation pipes 16, 17 may be cooled down to a predetermined temperature of 400 ° C. Further, since the combustion gas flowing through the heat radiation pipes 16 and 17 has a high temperature, and the temperature difference with the air 59 is large, at least the heat transfer area can recover a large amount of heat. Therefore, large diameter tubes are used as the heat transfer tubes 16 and 17, and the heat transfer tubes 16 and 17 can be configured with a smaller number of tubes.

  The temperature of the combustion gas 57 at the time of flowing out from the heat radiation pipe 17 and entering the secondary heat exchanger 19 is as low as about 400 ° C. However, the secondary heat exchanger 19 has high efficiency (80 %) To 85%), and heat recovery from the combustion gas 57 can be effectively performed. Moreover, the flow rate of the combustion gas 57 is reduced to about 1 / number of that at the time of combustion because the temperature of the combustion gas 57 is lowered, and the small secondary heat exchanger 19 can be used. The air supply device 1 can be configured in a small size.

  As described above, since the combustion furnace 13, the heat radiation pipes 16 and 17 (primary heat exchangers), and the secondary heat exchanger 19 are all housed in the heat insulating space defined by the case 12 The heat released to the outside by the heat generated by the combustion is substantially only the exhaust gas discharged from the exhaust pipe 23. Accordingly, heat can be recovered with high efficiency in the drying air supply device 1, and the running cost can be reduced.

  Furthermore, since the combustion furnace 13 and the heat radiation pipes 16 and 17 are disposed above and below, the footprint can be reduced, and the secondary heat exchanger 19 can be further unitized. Installation into the drying air supply device 1 is easy. Further, since the combustion furnace 13 directly exchanges heat with the air 59, there is no need to make the combustion furnace 13 a heat insulation structure, and there is no need for a cooling device. Therefore, the manufacturing cost of the combustion furnace 13 can be reduced.

  Thus, the structure of the drying air supply device 1 can be simplified and downsized, the manufacturing cost can be reduced, and the installation space can be saved. Furthermore, since heat can be recovered with high efficiency, running costs can be reduced.

  In the above embodiment, the heat radiation pipe has two stages, but it may have one or three or more stages. In addition, although three heat radiation pipes are disposed in one stage, two or four or more heat radiation pipes may be provided. Furthermore, although two sets of secondary heat exchangers 19 are provided, three or more sets may be provided.

DESCRIPTION OF SYMBOLS 1 Air supply apparatus for drying 2 Burner 3 Primary heat exchanger 4 Secondary heat exchanger 5 Air supply blower 6 Drying chamber 7 Exhaust 9 Primary heating air 10 Secondary heating air 12 Case 13 Combustion furnace 14 Burner 16, 17 Heat dissipation Pipe 19 Secondary heat exchanger 21 Low temperature air induction duct 23 Exhaust pipe 26 Damper 27 Drying gas outlet 28 Drying air 31 Air suction duct 33 Air suction port 35 Control device 42 Heat transfer body 51 Air suction discharge part 54 Air 55 suction Fan 56 Exhaust fan 57 Combustion gas 59 Air

Claims (3)

An airtightly insulated case, a combustion furnace disposed at the center of the case, an air supply blower provided below the combustion furnace, and combustion gases from the combustion furnace provided above the combustion furnace And a secondary heat exchanger provided adjacent to the inner end side of the combustion furnace and connected to the heat dissipation pipe, a drying gas outlet formed on the upper surface of the case, and An air suction port formed on the back of the case, and an air suction duct provided along the back of the case and in communication with the air suction port;
The combustion gas from the combustion furnace flows into the secondary heat exchanger through the heat radiation pipe, and is further exhausted through the exhaust pipe,
External air is sucked by the air supply blower through the air suction duct,
The air is discharged from the air supply blower as internal air, and the internal air is discharged from the dry gas outlet through the periphery of the combustion furnace and between the heat radiation pipes, and a part of the internal air is the secondary The heat is drawn into the heat exchanger, flows through the secondary heat exchanger and flows out into the case, and the internal air cools the combustion furnace and absorbs heat from the combustion furnace,
Is and heated by heat exchange with the combustion gas through the heat radiation tube,
And a part of the internal air exchanges heat with the combustion gas flowing from the heat radiation pipe in the secondary heat exchanger, is heated to a predetermined temperature, and passes through the space between the heat radiation pipes and the internal air A drying air supply device configured to be mixed with a part and discharged from the drying gas outlet as drying air.   The heat dissipating pipe is constituted by two upper and lower stages, the upper heat dissipating pipe further extends from the combustion furnace, the secondary heat exchanger is provided below the extending portion of the heat dissipating pipe, and the secondary heat exchanger The drying air supply device according to claim 1, wherein an upper portion is in communication with the heat radiation pipe, and a lower portion of the secondary heat exchanger is in communication with the exhaust pipe. An air intake / discharge unit is provided at a lower portion of the secondary heat exchanger, the secondary heat exchanger is unitized, and the air intake / discharge unit is a suction fan for sucking a part of the internal air, the secondary The drying air supply device according to claim 1, further comprising: an exhaust fan discharging the combustion gas flowing through the heat exchanger toward the exhaust pipe, or the suction fan and the exhaust fan.

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