Smoke tube boiler

Abstract

The present subject matter relates to a smoke tube boiler including: a mix chamber, a heat exchanger, a firing rod assembly, a sealing means, and an air-cooled cooling means and a water-cooled cooling means.

Claims

1. A smoke tube boiler comprising: a mix chamber which includes a mixing space in which combustion gas and air are mixed, a mix chamber body having a flat shape, and a flat plate-shaped burner disposed in a horizontal direction above a combustion chamber and positioned over an entire upper area of the combustion chamber; a heat exchanger which includes an outer shell forming an outer wall of a water tank into and from which a heat medium is introduced and discharged and which accommodates the heat medium, an upper plate having an end plate structure that is coupled to the outer shell and configured to form the combustion chamber, a plurality of tubes formed in a flat shape that are configured to allow combustion gas generated in the combustion chamber to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium flowing outside the plurality of tubes, a plurality of turbulators each coupled to an inner side of a corresponding one of the plurality of tubes and configured to induce occurrence of a turbulent flow in the flow of the combustion gas, multi-stage barriers disposed between the outer shell and the plurality of tubes and configured to induce a heat medium flow direction to be alternately changed between a radially inward direction and a radially outward direction, and a lower plate having an end plate structure that is configured to support a lower end portion of the plurality of tubes; a firing rod assembly assembled to pass through one side portion of the mix chamber to one side of the flat plate-shaped burner and configured to extend across an upper portion of the combustion chamber toward a lower side of the flat plate-shaped burner; a sealing means configured to block leakage of mixed gas of the mixing space and exhaust gas of the combustion chamber to the outside through a gap between the mix chamber and the firing rod assembly; and an air-cooled cooling means and a water-cooled cooling means configured to prevent damage caused by degradation of the sealing means by blocking transfer of combustion heat generated in the combustion chamber to the sealing means.

2. The smoke tube boiler of claim 1, wherein: a mix chamber flange and a burner flange are disposed to come in contact with each other at the one side portion of the mix chamber and seal the mixing space; and the sealing means includes a first sealing member disposed at a portion where the mix chamber flange and the burner flange come in contact with each other and configured to prevent leakage of the mixed gas.

3. The smoke tube boiler of claim 2, wherein: the firing rod assembly includes a firing rod and a flame sensing rod; a firing rod coupling plate to which the firing rod is coupled by passing therethrough and a flame sensing rod coupling plate to which the flame sensing rod is coupled by passing therethrough are disposed at an upper portion of the one side portion of the mix chamber; and the sealing means is disposed between the upper portion of the one side portion of the mix chamber and the firing rod coupling plate and between the upper portion of the one side portion of the mix chamber and the flame sensing rod coupling plate.

4. The smoke tube boiler of claim 1, wherein a space between a lower surface of the mix chamber body and an upper surface of the flat plate-shaped burner is formed in a flat disc shape.

5. The smoke tube boiler of claim 1, wherein: a mix chamber flange and a burner flange are disposed to come in contact with each other at the one side portion of the mix chamber and seal the mixing space; the firing rod assembly is assembled to pass through the mix chamber flange and the burner flange; and the air-cooled cooling means allows the mix chamber flange and the burner flange to be cooled by mixed gas introduced into the mixing space.

6. The smoke tube boiler of claim 1, wherein: a mix chamber flange and a burner flange are disposed to come in contact with each other at the one side portion of the mix chamber and seal the mixing space; the firing rod assembly is assembled to pass through the mix chamber flange and the burner flange; and the water-cooled cooling means is disposed to allow an upper plate flange, which is formed at an upper end of the upper plate that comes in contact with the heat medium of the water tank, to come in surface contact with the burner flange so that the burner flange is cooled.

7. The smoke tube boiler of claim 1, wherein a round portion configured to provide support against a water pressure of the heat medium stored in the water tank is formed at an upper portion of the upper plate.

8. The smoke tube boiler of claim 1, wherein a height between a lower surface of the flat plate-shaped burner that is inserted into the upper plate and a bottom surface of the upper plate is set so that an end of a flame generated in the flat plate-shaped burner is spaced a predetermined distance apart from the bottom surface of the upper plate.

9. The smoke tube boiler of claim 1, further comprising a pre-mixing chamber having a space provided therein in which air for combustion and gas which are supplied to the mix chamber are pre-mixed, wherein the space in which the air and gas are pre-mixed is divided in multiple stages by a Venturi structure inside the pre-mixing chamber; and a direction of flow of the gas supplied into the pre-mixing chamber and a direction of flow of the air supplied into the pre-mixing chamber are parallel.

10. The smoke tube boiler of claim 9, further comprising a mixture regulating part configured to open and close flow paths of the air and gas that pass through the pre-mixing chamber and regulate a supply flow rate of the mixture.

11. The smoke tube boiler of claim 10, wherein: the pre-mixing chamber is divided into a first path and a second path by a partition member disposed therebetween; and an air flow path and a gas flow path connected to the first path are in an open state at all times, and an air flow path and a gas flow path connected to the second path are opened and closed by the mixture regulating part.

12. The smoke tube boiler of claim 11, wherein: a first gas distributing member configured to distribute and supply gas supplied from a first gas supply hole to a throat portion of the first path is coupled to the first path; and a second gas distributing member configured to distribute and supply gas supplied from a second gas supply hole to a throat portion of the second path is coupled to the second path.

13. The smoke tube boiler of claim 11, wherein: the mixture regulating part includes a first opening/closing member configured to open and close a flow path of air passing through the second path and a second opening/closing member configured to open and close a flow path of gas that is connected to the second path; and opening/closing operations of the first opening/closing member and the second opening/closing member are simultaneously performed by interlocking.

14. The smoke tube boiler of claim 13, wherein: the first opening/closing member includes a body coupled to a rotating shaft of a driving part and disposed in a transverse direction in the second path and a wing portion formed in a size corresponding to the second path and coupled to oppose an outer side surface of the body; and the second opening/dosing member reciprocates in the transverse direction by interlocking with rotation of the first opening/closing member.

15. The smoke tube boiler of claim 14, wherein: a first sharp edge portion configured to protrude toward the second opening/closing member and a first bottom portion recessed in the opposite direction are alternately formed in the circumferential direction on the body of the first opening/closing member, and a first inclined portion is formed in a section between the first sharp edge portion and the first bottom portion; a second sharp edge portion, a second bottom portion, and a second inclined portion which have shapes corresponding to the first sharp edge portion, the first bottom portion, and the first inclined portion are formed on a body of the second opening/closing member; and the second opening/closing member is elastically supported by an elastic member so as to be pressed toward the first opening/closing member.

16. The smoke tube boiler of claim 15, wherein: the second opening/closing member further includes a guide member configured to guide the body of the second opening/closing member to reciprocate; and a guide groove and a guide rib are formed at corresponding positions in the body of the second opening/closing member and the guide member, respectively.

17. The smoke tube boiler of claim 16, wherein: at the time of contact between the first sharp edge portion of the body of the first opening/closing member and the second bottom portion of the body of the second opening/closing member and contact between the first bottom portion of the body of the first opening/closing member and the second sharp edge portion of the body of the second opening/closing member, while the wing portion of the first opening/closing member is disposed in a direction parallel to a transverse cross-section of the second path so that flow of air to the second path is blocked, the second opening/closing member is moved toward one side and comes in close contact with a communication hole disposed in the gas flow path connected to the second path so that flow of gas to the second path is blocked; and at the time of contact between the first sharp edge portion of the body of the first opening/closing member and the second sharp edge portion of the body of the second opening/closing member, while the wing portion of the first opening/closing member is disposed in a direction perpendicular to the transverse cross-section of the second path so that the second path is opened, the second opening/closing member is moved toward the other side and spaced apart from the communication hole so that the gas flow path connected to the second path is opened.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a view schematically illustrating a configuration of a conventional smoke tube boiler.

(2) FIG. 2 is a perspective view of an exterior of a smoke tube boiler according to the present invention.

(3) FIG. 3 is a perspective view of a mix chamber.

(4) FIG. 4 is a perspective view of a lower surface side of the mix chamber.

(5) FIG. 5 is an exploded perspective view showing a structure in which a firing rod and a flame sensing rod are coupled to the mix chamber.

(6) FIG. 6 is a plan view of the mix chamber and a heat exchanger.

(7) FIG. 7 is a cross-sectional perspective view of a portion taken along line A-A of FIG. 6.

(8) FIG. 8 is a cross-sectional view of a portion taken along line A-A of FIG. 6.

(9) FIG. 9 is a cross-sectional view showing a coupling structure between an upper plate and a burner.

(10) FIG. 10 is a see-through perspective view of the heat exchanger.

(11) FIG. 11 is an exploded perspective view of the heat exchanger.

(12) FIG. 12 is a front view of a state in which a tube assembly and multi-stage barriers are coupled.

(13) FIG. 13A is a plan view of FIG. 12, FIG. 13B is a cross-sectional view taken along line B-B of FIG. 12, and FIG. 13C is a cross-sectional view taken along line C-C of FIG. 12.

(14) FIG. 14 is a plan view of the heat exchanger.

(15) FIG. 15 is a cross-sectional perspective view taken along line D-D of FIG. 14.

(16) FIG. 16 is a see-through perspective view of a tube assembly according to a first embodiment of the present invention.

(17) FIG. 17 is an exploded perspective view of the tube assembly according to the first embodiment of the present invention.

(18) FIG. 18 is a front view of an upper turbulator and a lower turbulator according to the first embodiment of the present invention.

(19) FIG. 19 is an enlarged perspective view of the upper turbulator illustrated in FIG. 17.

(20) FIG. 20 is a plan view of FIG. 19.

(21) FIG. 21A is a cross-sectional view taken along line E-E of FIG. 20, and FIG. 21B is a cross-sectional perspective view taken along line E-E of FIG. 20.

(22) FIG. 22 is a left side view of FIG. 19.

(23) FIG. 23 is a see-through perspective view of a tube assembly according to a second embodiment of the present invention.

(24) FIG. 24 is a front view of a turbulator according to the second embodiment of the present invention.

(25) FIG. 25 is a front view of a turbulator according to a third embodiment of the present invention.

(26) FIG. 26A, FIG. 26B, FIG. 26C and FIG. 26D show cross-sectional views illustrating various embodiments of a support structure of a tube.

(27) FIG. 27 is a see-through perspective view of a smoke tube boiler according to the present invention.

(28) FIG. 28 is an exploded perspective view of the smoke tube boiler according to the present invention.

(29) FIG. 29A is a plan view of a leakage preventing member, and FIG. 29B is an enlarged cross-sectional view taken along line F-F.

(30) FIG. 30 is a cross-sectional view showing a sealing structure and a condensate discharge structure of the smoke tube boiler according to the present invention.

(31) FIG. 31 is a perspective view of a pre-mixing chamber and a mixture regulating part.

(32) FIG. 32 is an exploded perspective view of FIG. 31.

(33) FIG. 33A is a side view of a pre-mixing chamber body, and FIG. 33B is a cross-sectional view of the pre-mixing chamber body taken along line G-G.

(34) FIG. 34A is a plan view of a first mixing chamber guide member and FIG. 34B is a plan view of a second mixing chamber guide member.

(35) FIG. 35 is a plan view of the pre-mixing chamber and the mixture regulating part when a small quantity of heat is used.

(36) FIG. 36 is a cross-sectional view taken along line H-H of FIG. 35.

(37) FIG. 37 is a plan view of the pre-mixing chamber and the mixture regulating part when a large quantity of heat is used.

(38) FIG. 38 is a cross-sectional view taken along line I-I of FIG. 37.

BEST MODE OF THE INVENTION

(39) Hereinafter, configurations and actions relating to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(40) A smoke tube boiler 1 according to the present invention is formed of a compact structure by lowering the overall height of the boiler. To this end, the smoke tube boiler 1 includes: a mix chamber 100 which is disposed above a combustion chamber C and includes a mixing space S in which combustion gas and air are mixed, a mix chamber body 110 having a flat shape, and a flat plate-shaped burner 130; a heat exchanger 200 which includes an outer shell 210 forming an outer wall of a water tank B into and from which a heat medium is introduced and discharged and which accommodates the heat medium, an upper plate 220 having an end plate structure that is configured to form the combustion chamber C and coupled to an inner side of the outer shell 210 so that a heat medium flow path is formed between the upper plate 220 and the outer shell 210, a plurality of tubes 230 formed in a flat shape that are configured to allow combustion gas generated in the combustion chamber C to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium flowing outside the tubes 230, turbulators 240, 250, 280, and 290 coupled to an inner side of the tube 230 and configured to induce occurrence of a turbulent flow in the flow of the combustion gas, multi-stage barriers 261, 262, and 263 disposed between the outer shell 210 and the tube 230 and configured to induce a heat medium flow direction to be alternately changed between a radially inward direction and a radially outward direction, and a lower plate 270 having an end plate structure that is configured to support a lower end portion of the tube 230 and form a bottom surface of the water tank B; and a condensate tray 300 configured to collect condensate CW generated at the lower plate 270, guide the collected condensate CW toward a condensate outlet 310 formed at one side, and guide the combustion gas that passed through the tube 230 toward an exhaust duct 400 which is connected to an upper side of the condensate outlet 310 and disposed at one side of the outer shell 210.

(41) Also, the smoke tube boiler 1 may further include a pre-mixing chamber 500 in which air for combustion and gas which are supplied to the mix chamber 100 are pre-mixed and a mixture regulating part 600 configured to open and close flow paths of the air and gas that pass through the pre-mixing chamber 500 and regulate a supply flow rate of the mixture.

(42) Referring to FIGS. 2 to 8, the mix chamber 100 includes the mix chamber body 110 which is formed in a flat shape that is convex upward, a firing rod assembly 140 assembled to pass through one side portion of the mix chamber body 110 and configured to extend across an upper portion of the combustion chamber C toward a lower side of the flat plate-shaped burner 130, and sealing means 160, 170, and 180 configured to block leakage of mixed gas of the mixing space S and exhaust gas of the combustion chamber C to the outside through a gap between the mix chamber 100 and the firing rod assembly 140.

(43) A burner applied to the present invention is the flat plate-shaped burner 130, wherein the flat plate-shaped burner 130 includes a flat plate-shaped flame hole plate 131 having a plurality of flame holes 131a formed therein and metal fibers 132 coupled to the flame hole plate 131. The mixing space S between a lower surface of the mix chamber body 110 and an upper surface of the flat plate-shaped burner 130 may be formed in a flat disc shape so that the height of the mix chamber 100 is low.

(44) Also, unlike the conventional cylindrical burner, the flat plate-shaped burner 130 is provided across the entire area of the mixing space S, and thus gas and air introduced into the flat plate-shaped burner 130 are supplied to an edge portion of the flat plate-shaped burner 130, i.e., a position in the vicinity of positions where the sealing means 160, 170, and 180 are provided. Therefore, air-cooled cooling of the sealing means 160, 170, and 180 may be performed by the gas and air, and a combustion area may be expanded to decrease a load per unit area so that emission of pollutants such as CO and NOx is reduced and combustion performance is improved.

(45) The firing rod assembly 140 assembled to pass through the one side portion of the mix chamber 100 may include a firing rod 141 and a flame sensing rod 142, and the firing rod 141 may include a first firing rod 141-1 and a second firing rod 141-2. Insulators 141a and 142a formed of an insulating material are coupled to outer side surfaces of the firing rod 141 and the flame sensing rod 142, and bushings 141b and 142b for maintaining airtightness are coupled to outer side surfaces of the insulators 141a and 142a.

(46) The firing rod 141, the insulator 141a, and the bushing 141b are fixed to a firing rod coupling plate 143, and the flame sensing rod 142, the insulator 142a, and the bushing 142b are fixed to a flame sensing rod coupling plate 144. The insulators 141a and 142a are insulating means for preventing occurrence of sparks due to energization during ignition, and the bushings 141b and 142b are configurations for sealing gaps between the outer side surfaces of the insulators 141a and 142a and the firing rod coupling plate 143 and the flame sensing rod coupling plate 144.

(47) Referring to FIG. 5, a firing rod assembly coupling part 150 configured to assemble the firing rod assembly 140 is provided at the one side portion of the mix chamber 100. The firing rod assembly coupling part 150 includes a second sealing member seating portion 151 formed in the shape of a groove so that the firing rod coupling plate 143 and a second sealing member 170 coupled to a lower side thereof are seated and a third sealing member seating portion 152 formed in the shape of a groove so that the flame sensing rod coupling plate 144 and a third sealing member 180 coupled to a lower side thereof are seated. Also, a plurality of heat dissipating fins 153 configured to dissipate combustion heat are provided along a circumference of the firing rod assembly coupling part 150.

(48) Referring to FIGS. 6 to 8, at the one side portion of the mix chamber body 110, a mix chamber flange 111 and a burner flange 133, which is connected to support the edge portion of the flat plate-shaped burner 130, are provided to come in contact and seal the mixing space S, and the firing rod assembly 140 is assembled to pass through the mix chamber flange 111 and the burner flange 133 at a position spaced apart from the mixing space S.

(49) The sealing means include a first sealing member 160 provided at a portion where the mix chamber flange 111 and the burner flange 133 come in contact and configured to prevent leakage of the mixed gas, which is introduced into the mixing space S, to the outside. The first sealing member 160 may be formed of a heat-resistant graphite material.

(50) Also, the sealing means include the second sealing member 170 provided between the mix chamber flange 111 and the firing rod coupling plate 143 and configured to prevent leakage of exhaust gas, which is generated in the combustion chamber C, to the outside and the third sealing member 180 provided between the mix chamber flange 111 and the flame sensing rod coupling plate 144 and configured to prevent leakage of the exhaust gas generated in the combustion chamber C to the outside. The second sealing member 170 and the third sealing member 180 may be formed of a rubber material. The second sealing member 170 and the third sealing member 180 are separately manufactured using separate components and assembled so that deformation of the rubber material due to a high temperature is minimized.

(51) Also, a plurality of close contact protrusions 171 may be formed at predetermined intervals on an outer side surface of the second sealing member 170 and an outer side surface of the third sealing member 180 so as to protrude outward. The close contact protrusions 171 may further improve sealing performance by coming in close contact with a lower surface of the firing rod coupling plate 143 and an upper surface of the second sealing member 170 and coming in close contact with a lower surface of the flame sensing rod coupling plate 144 and an upper surface of the third sealing member 180.

(52) Also, since, as described above, the bushings 141b and 142b are coupled to the outer side surfaces of the insulators 141a and 142a in the firing rod assembly 140, leakage of the mixed gas to the outside of the mix chamber 100 may be more reliably blocked.

(53) Hereinafter, configurations and actions of cooling means for blocking transfer of combustion heat to the sealing means and dissipating heat will be described with reference to FIGS. 7 and 8.

(54) The cooling means is a configuration for blocking transfer of heat to the sealing means configured to prevent leakage of combustion heat generated in the combustion chamber C through a gap between the mix chamber 100 and the firing rod assembly 140. The cooling means may include an air-cooled cooling means and a water-cooled cooling means.

(55) As described above, at the one side portion of the mix chamber 100, the mix chamber flange 111 and the burner flange 133 are provided to come in contact and seal the mixing space S, the firing rod assembly 140 is assembled to pass through the mix chamber flange 111 and the burner flange 133, and the air-cooled cooling means may cause the mix chamber flange 111 and the burner flange 133 to be cooled by convection using the mixed gas introduced into the mixing space S.

(56) Meanwhile, the heat exchanger 200 may be configured as a smoke tube heat exchanger and include the outer shell 210, the upper plate 220 configured to form a bottom surface of the combustion chamber C and an upper surface of the heat exchanger 200, the plurality of tubes 230 along which combustion gas flows and which have an upper end portion configured to pass through and be coupled to a tube insertion hole 221a formed in the upper plate 220, and the water tank B disposed inside the outer shell 210 outside the tubes 230 so as to accommodate a heat medium. The heat medium may be heating water or hot water used for heating or heating water.

(57) The water-cooled cooling means may be provided so that an upper plate flange 223, which comes in contact with a heat medium of the heat exchanger 200 disposed below the combustion chamber C, comes in surface contact with the burner flange 133. The water-cooled cooling means may cause the burner flange 133 and the sealing means 160, 170, and 180 to be cooled by conduction from the heat medium stored in the water tank B.

(58) Also, as described above, the plurality of heat dissipating fins 153 are provided along the circumference of the firing rod assembly 140 at the one side portion of the mix chamber body 110 to which the firing rod assembly 140 is assembled. The heat dissipating fins 153 also serve as a cooling means.

(59) According to the present invention described above, since the mix chamber 100 includes the mix chamber body 110 having a flat shape and the flat plate-shaped burner 130, the height of the mix chamber 100 may be significantly reduced as compared to a structure including the conventional cylindrical burner.

(60) Also, since the sealing means and cooling means are provided in assembling the firing rod assembly 140 to pass through the one side portion of the mix chamber body 110 including the flat plate-shaped burner 130, leakage of the mixed gas and exhaust gas may be blocked, and thermal damage to the sealing means due to combustion heat may be prevented. Therefore, since a heat insulating material is not used in the mix chamber 100 including the flat plate-shaped burner 130, the firing rod assembly 140 may be safely assembled, and thermal damage to the sealing means may be prevented so that leakage of the mixed gas and exhaust gas is blocked.

(61) Meanwhile, referring to FIG. 9, the upper plate 200 includes a bottom portion 221 configured to form the lower surface of the combustion chamber C, a sidewall portion 222 configured to form a sidewall of the combustion chamber C, a round portion 224 which includes the upper plate flange 223, on which the burner flange 133 is seated, and is configured to connect an upper end of the sidewall portion 222 and an inner side end of the upper plate flange 223, and a round portion 225 configured to connect an outer side end of the bottom portion 221 and a lower end of the sidewall portion 222.

(62) Since the upper plate 200 includes the round portions 224 and 225 as described above, a water pressure of the heat medium stored in the water tank B may be distributed and durability of the upper plate 200 may be improved. Preferably, a ratio between an inner diameter d2 of a lower end of the round portion 224 and an outer diameter d1 of the upper plate flange 223 may be 20% or less. When the ratio is 20% or less, the flow rate and temperature of water accommodated in the water tank B may be uniformly controlled.

(63) Also, a height h between the lower surface of the flat plate-shaped burner 130 inserted into the upper plate 220 and the bottom surface of the upper plate 220 may be set so that an end of a flame generated in the flat plate-shaped burner 130 is spaced a predetermined distance apart from the bottom surface of the upper plate 220. Preferably, the height h may be set to be around 80 mm, in consideration of the length of the flame of the flat plate-shaped burner 130. The reason for setting the height h so that the end of the flame is spaced a predetermined distance apart from the bottom surface of the upper plate 220 is that, in order to secure conditions for experimentally minimizing nitrogen oxide (NOx) and carbon monoxide (CO), a predetermined space should be secured between the end of the flame generated by the flat plate-shaped burner 130 and the bottom surface of the upper plate 220.

(64) Also, since the height h of the upper plate 220 is designed to be low, the height of the combustion chamber C is lowered, and thus the overall height of the smoke tube boiler 1 may be lowered. That is, while the height between the lower surface of the burner and the bottom surface of the upper plate is about 190 mm when the conventional cylindrical burner is applied, the height may be reduced to around 180 mm according to the present invention. Thus, there is an advantage in that it is possible to reduce the height by about 40% as compared to the related art.

(65) Meanwhile, in the present embodiment, the electrode rod assembly 140 is formed at a position in the vicinity of one side of a mixture inlet 120 connected to an air blower 700 that allows the mixture to be supplied to the mix chamber 100. In this case, since it is easy for a worker to approach the electrode rod assembly 140 through the mixture inlet 120, convenience in maintenance and repair may be improved.

(66) In another embodiment, the electrode rod assembly 140 may also be disposed at a side opposite the mixture inlet 120. In this case, since the mixture supplied from the air blower 700 is directly supplied to the electrode rod assembly 140, delayed ignition may be prevented.

(67) Referring to FIGS. 10 to 15, the heat exchanger 200 includes tube assemblies 1000-1, 1000-2, and 1000-3, which include the outer shell 210 in which a heat medium inlet 211 and a heat medium outlet 212 are formed to allow introduction and discharge of a heat medium, the upper plate 220 coupled to an inner side of the outer shell 210, so that a heat medium flow path is formed between the upper plate 220 and the outer shell 210, and configured to form a combustion chamber C by the flat plate-shaped burner 130 being seated thereon, the plurality of tubes 230 formed in a flat shape that are configured to allow combustion gas generated in the combustion chamber C to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium, and the turbulators 240, 250, 280, and 290 coupled to an inner side of the tube 230 and configured to induce occurrence of a turbulent flow in the flow of the combustion gas and support the tube 230, and the lower plate 270 configured to support the tube assemblies 1000-1, 1000-2, and 1000-3 and coupled to the condensate tray 300. Configurations and actions relating to embodiments of the tube assemblies 1000-1, 1000-2, and 1000-3 will be described below.

(68) The multi-stage barriers 261, 262, and 263 configured to guide flow of the heat medium so that a heat medium flow direction is alternately changed between a radially inward direction and a radially outward direction may be provided at an outer side surface of the tube 230 so as to be vertically spaced apart from each other. The multi-stage barriers 261, 262, and 263 are fixed and supported by a support 264. The plurality of tubes 230 are installed in the vertical direction so that the combustion gas generated in the combustion chamber C flows downward. The plurality of tubes 230 are spaced apart in the circumferential direction and disposed radially.

(69) In the present embodiment, the multi-stage barriers include the upper barrier 261, the middle barrier 262, and the lower barrier 263 which are formed in the shape of a plate. Referring to FIG. 13A, the upper barrier 261 includes a tube insertion hole 261a through which the tube 230 is inserted and an opening 261b formed at the center and through which the heat medium passes. Referring to FIG. 13B, the middle barrier 262 includes a tube insertion hole 262a formed while a clearance is formed between the tube insertion hole 262a and an outer side surface of the tube 230 so that the heat medium flows through the clearance formed between the tube insertion hole 262a and the tube 230. A central portion 262b of the middle barrier 262 is formed of a structure that is blocked. In one embodiment, the tube insertion hole 262a may be formed of a structure in which two different tubes 230 are inserted while being disposed at both sides so as to be spaced apart. Referring to FIG. 13C, the lower barrier 263 includes a tube insertion hole 263a and an opening 263b disposed at the center which have the same structures as those of the upper barrier 261.

(70) According to the structures of the multi-stage barriers 261, 262, and 263, as indicated by arrows in FIGS. 14 and 15, a heat medium introduced into the outer shell 210 through the heat medium inlet 211 flows radially inward toward the opening 263b formed in the central portion of the lower barrier 263, a heat medium flowing to an upper side of the lower barrier 263 via the opening 263b flows radially outward after being distributed to a clearance space of the tube insertion hole 262a radially formed in the middle barrier 262, a heat medium flowing to an upper side of the middle barrier 262 via the tube insertion hole 262a flows radially inward toward the opening 261b, which is formed in the center of the upper barrier 261, and then passes through the opening 261b so as to be discharged via the heat medium outlet 212 formed at one side of the upper portion of the outer shell 210.

(71) Since the heat medium flow direction is alternately changed between the radially inward direction and the radially outward direction as described above, a distance along which the heat medium flows is increased such that heat exchange efficiency of the heat exchanger 200 is improved. Also, since highly efficient heat exchange performance may be achieved even when the height of the heat exchanger 200 is lowered as compared to conventional heat exchangers, the height of the heat exchanger 200 may be lowered. In addition, since a heat medium flow speed is increased, boiling phenomenon due to localized overheating which may be caused by stagnation of the heat medium may be prevented.

(72) Hereinafter, embodiments of the tube assemblies 1000-1, 1000-2, and 1000-3 will be described with reference to FIGS. 16 to 26.

(73) Referring to FIGS. 16 to 22, the tube assembly 1000-1 according to a first embodiment of the present invention includes the tube 230 formed in a flat shape that is configured to allow combustion gas generated in the combustion chamber C to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium flowing outside the tube 230, an upper turbulator 240 coupled to an upper inner side of the tube 230 in the vicinity of the combustion chamber so as to come in surface contact with the tube 230 so that thermal conductivity is increased and configured to induce occurrence of a turbulent flow in the flow of the combustion gas, and a lower turbulator 240 coupled to the inner side of the tube 230 below the upper turbulator 240 and configured to induce occurrence of a turbulent flow in the flow of the combustion gas.

(74) The upper turbulator 240 includes tube contact surfaces 241 (241a and 241b) configured to come in close contact with the inner side surface of the tube 30 and pressure support parts 242 (242a and 242b) formed to be bent from cut-out portions 243 (243a and 243b) of the tube contact surfaces 241 (241a and 241b).

(75) The tube contact surfaces 241 have a structure in which a first tube contact surface 241a, which comes in surface contact with an inner side surface of one side portion of the tube 230, and a second tube contact surface 241b, which comes in surface contact with an inner side surface of the other side portion of the tube 230, are symmetrical.

(76) The pressure support parts 242 are configurations for preventing deformation and damage of the tube 230 due to the water pressure of the heat medium. The pressure support parts 242 include a first pressure support part 242a configured to protrude so that a portion of a first cut-out portion 243a, which is cut out from the first tube contact surface 241a, is bent toward the second tube contact surface 241b and a second pressure support part 242b configured to protrude so that a portion of a second cut-out portion 243b, which is cut out from the second tube contact surface 241b, is bent toward the first tube contact surface 241a.

(77) A cut-out area of the first cut-out portion 243a is formed to be larger than a cut-out area of the second cut-out portion 243b, a protruding end portion of the first pressure support part 242a comes in contact with the second tube contact surface 241b, and, when the pressure support parts 242 are inserted into the tubes 230, a protruding end portion of the second pressure support part 242b passes through the first cut-out portion 243a and comes in contact with the inner side surface of the tube 230.

(78) According to such a configuration, upon action of the water pressure, the first pressure support part 242a supports the first tube contact surface 241a and the second tube contact surface 241b so that shapes thereof are firmly maintained, and the second pressure support part 242b more firmly supports the tube 230 which is supported by the first tube contact surface 241a and the second tube contact surface 241b.

(79) In addition, as illustrated in FIG. 22, the first pressure support part 242a and the second pressure support part 242b may be provided as a plurality of first pressure support parts 242a and a plurality of second pressure support parts 242b which are spaced apart in a longitudinal direction and a vertical direction. A first pressure support part 242a′ disposed at an upper side and a first pressure support part 242a″ disposed at a lower side may be disposed at positions not overlapping each other in the vertical direction, and a second pressure support part 242b′ disposed at the upper side and a second pressure support part 242b″ disposed at the lower side may be disposed at positions not overlapping each other in the vertical direction. According to such a configuration, the first pressure support parts 242a and the second pressure support parts 242b provided in a zigzag shape across the entire area of the upper turbulator 240 in the longitudinal and vertical directions may allow the water pressure acting on the tubes 230 to be evenly distributed and effectively prevent deformation and damage of the tubes 230.

(80) Also, the first pressure support part 242a and the second pressure support part 242b may be formed in the shape of a plate and have a structure in which both side surfaces thereof having a large area are disposed parallel to a combustion gas flow direction. As indicated by arrows in FIG. 21A, when the combustion gas flows, flow resistance may be minimized in a process in which the combustion gas passes through the first pressure support part 242a and the second pressure support part 242b.

(81) Referring to FIG. 18, the lower turbulator 250 may include a flat surface portion 251 disposed in a longitudinal direction of the tube 230 so as to divide an inner space of the tube 230 into two sides and a plurality of first guide pieces 252 and second guide pieces 253 formed at both side surfaces of the flat surface portion 251 so as to be spaced apart in the longitudinal direction and alternately protrude obliquely.

(82) The first guide piece 252 may be disposed at one side surface of the flat surface portion 251 so as to be inclined toward one side, and the second guide piece 253 may be disposed at the other side surface of the flat surface portion 251 so as to be inclined toward the other side. Accordingly, a heat medium introduced into the first guide piece 252 and a heat medium introduced into the second guide piece 253 may be sequentially passed over to the second guide piece 253 and the first guide piece 252, which are disposed to be adjacent at the opposite side surfaces of the flat surface portion 251, so as to alternately flow in both side spaces of the flat surface portion 251.

(83) A heat medium inlet end of the first guide piece 252 may be connected to one side end of the flat surface portion 251 by a first connecting piece 252a, and a first communication hole 252b through which fluid communication occurs in both side spaces of the flat surface portion 251 may be provided between the one side end of the flat surface portion 251 and the first connecting piece 252a and the first guide piece 252.

(84) A heat medium inlet end of the second guide piece 253 may be connected to the other side end of the flat surface portion 251 by a second connecting piece 253a, and a second communication hole 253b through which fluid communication occurs in both side spaces of the flat surface portion 251 may be provided between the other side end of the flat surface portion 251 and the second connecting piece 253a and the second guide piece 253.

(85) The first guide piece 252 and the second guide piece 253 may have portions cut out from the flat surface portion 251 so as to be bent toward both sides of the flat surface portion 251, and fluid communication may occur in both side spaces of the flat surface portion 251 through the cut-out portions of the flat surface portion 251. Also, supports 253 (253a and 253b) which protrude outward and come in contact with opposite inner side surfaces of the tube 230 are formed on both side surfaces of the lower turbulator 250. Also, a first support part 255 and a second support part 256 which are vertically spaced apart and protrude forward and rearward so as to come in contact with both side surfaces of the tube 230 may be formed at an upper end portion and a lower end portion of the lower turbulator 250.

(86) Referring to FIGS. 23 and 24, the tube assembly 1000-2 according to a second embodiment of the present invention includes the tube 230 formed in a flat shape that is configured to allow combustion gas to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium flowing outside the tube 230, a turbulator 280 coupled to an inner side of the tube 230 and configured to induce occurrence of a turbulent flow in the flow of the combustion gas, and a pressure support part formed at the inner side of the tube 230 and configured to support an external pressure that acts on both opposite side surfaces of the tube 230.

(87) The pressure support part may include a pair of dimples 231 configured to protrude from both side surfaces of the tube 230 toward the inner space of the tube 230 and face each other. The pair of dimples 231 may be provided as a plurality of pairs of dimples 231 which are vertically spaced apart.

(88) The dimple 231 is formed by a process in which the turbulator 280 is inserted into the tube 230 and then the outer side surface of the tube 230 is pressed toward the inner side of the tube 230. Also, a plurality of holes 288 are formed in the turbulator 280 so that, when an external pressure rises, the pair of dimples 231 may come in contact by the holes 288 passing through the dimples 231.

(89) Since the pressure support part is implemented by forming the dimple 231 at the outer side surface of the tube 230 into which the turbulator 280 is inserted, the pressure support part may be implemented without adding a separate component. Therefore, the cost for manufacturing a tube assembly having excellent pressure resistance may be reduced.

(90) Also, first support pieces 286 (286a and 286b) and second support pieces 287 (287a and 287b) which are vertically spaced apart and protrude forward and rearward so as to come in contact with a front surface and a rear surface of the tube 230 may be formed at an upper end portion and a lower end portion of the turbulator 280.

(91) Referring to FIG. 24, although not described herein, reference numeral “281” denotes a flat surface portion, reference numeral “282” denotes a first guide piece, reference numeral “282a” denotes a first connecting piece, reference numeral “282b” denotes a first communication hole, reference numeral “283” denotes a second guide piece, reference numeral “283a” denotes a second connecting piece, reference numeral “283b” denotes a second communication hole, reference numeral “284” denotes a first support part, and reference numeral “285” denotes a second support part. Each element performs the same function as the element referred to by the same name among the elements described above.

(92) Referring to FIG. 25, a turbulator 290 constituting the tube assembly 1000-3 according to a third embodiment of the present invention has a structure in which an upper turbulator 290a disposed at a combustion gas inlet side and a lower turbulator 290b disposed at a combustion gas outlet side are integrally formed. In order to make a flow path between the lower turbulator 290b and the inner side surface of the tube 230 to have a smaller area than a flow path between the upper turbulator 290a and the inner side surface of the tube 230, an area coming in contact with the heat medium inside the tube 230 may be formed to be larger in the lower turbulator 290b than in the upper turbulator 290a.

(93) In one embodiment, an interval L2 at which a plurality of first guide pieces 292 and second guide pieces 293 formed in the lower turbulator 290b are vertically spaced apart may be smaller than an interval L1 at which a plurality of first guide pieces 292 and second guide pieces 293 formed in the upper turbulator 290a are vertically spaced apart.

(94) In this case, the interval at which the plurality of first guide pieces 292 and second guide pieces 293 formed in the turbulator 290 are vertically spaced apart may be formed to gradually decrease from the combustion gas inlet side to the combustion gas outlet side.

(95) According to such a configuration, by making a flow path of combustion gas in a high-temperature state that passes through the upper portion of the tube 230 to have a large area, a sufficient heat exchange may occur while flow resistance of the combustion gas is reduced. By making a flow path of combustion gas in a relatively low temperature state due to the heat exchange that passes through the lower portion of the tube 230 to have a relatively small area, residence time of the combustion gas may be increased. In this way, heat exchange efficiency may be improved.

(96) Referring to FIG. 25, although not described herein, reference numeral “291” denotes a flat surface portion, reference numeral “292a” denotes a first connecting piece, reference numeral “292b” denotes a first communication hole, reference numeral “293a” denotes a second connecting piece, reference numeral “293b” denotes a second communication hole, reference numeral “294” denotes a first support part, reference numeral “295” denotes a second support part, and reference numerals “296” and “297” denote support pieces. Each element performs the same function as the element referred to by the same name among the elements described above.

(97) Referring to FIG. 26A, FIG. 26B, FIG. 26C and FIG. 26D, a support part configured to provide support against the water pressure of the heat medium may be further disposed inside the tube 230.

(98) The support part may include a straight support 232 having both ends fixed to the inner side surface of the tube 230 as illustrated in FIG. 26A and a support 233 having both ends bent and fixed to the inner side surface of the tube 230 as illustrated in FIGS. 26B and 26C.

(99) Regarding the structures illustrated in FIGS. 26A and 26B, during manufacture of the tube 230, one side ends of the supports 232 and 233 are welded to a base material on which the tube 230 will be formed, the base material is rolled and processed in the shape of the tube 230, both side end portions of the base material and the other side ends of the supports 232 and 233 are welded, and the turbulator 290 is inserted into both sides of the supports 232 and 233 and coupled thereto.

(100) Regarding the structure illustrated in FIG. 26C, during manufacture of the tube 230, the support 233 and the turbulator 290 may be coupled first, and then a coupling body consisting of the support 233 and the turbulator 290 may be coupled by being press-fitted into the tube 230.

(101) In another embodiment, as illustrated in FIG. 26D, the support part may include embossments 234 formed to protrude from both side surfaces of the tube 230, which correspond to each other, toward the inner side of the tube 230. According to such a configuration, when a high water pressure acts from outside the tube 230, the embossments 234 formed at corresponding positions may come in contact with each other, and thus deformation of the tube 230 may be prevented.

(102) Since the support parts 232, 233, and 234 are coupled to the inner side of the tube 230 as described above, even when the water pressure of the heat medium acting on the outer side surface of the tube 230 is high, the deformation of the tube 230 may be prevented. Therefore, the tube 230 having the support parts 232, 233, and 234 coupled thereto may be applied not only to boilers or water heaters but also to other combustion devices for various purposes.

(103) Meanwhile, referring to FIGS. 27 to 30, the smoke tube boiler 1 according to the present invention includes a condensate tray 300, which is configured to collect and discharge condensate generated due to condensation of water vapor included in combustion gas that occurs due to the combustion gas passing through the heat exchanger 200, and a leakage preventing member 320 coupled to a connecting portion between the lower plate 270 of the heat exchanger 200 and the condensate tray 300 and configured to prevent leakage of the condensate.

(104) Also referring to FIG. 11, the lower plate 270 is formed of an end plate structure that includes a horizontal portion 271 configured to form the bottom surface of the water tank B and support the lower end portion of the tube 230 by having a plurality of tube insertion holes 271a formed to pass through the lower end portion of the tube 230, a vertical portion 272 coupled to the lower end portion of the outer shell 210, and a round portion 273 configured to connect an outer side end of the horizontal portion 271 and a lower end portion of the vertical portion 272 and formed in a shape convexly bent outward so as to distribute the water pressure of the heat medium.

(105) As described above, the round portion 273 having the shape convexly bent outward is formed at a corner where the horizontal portion 271 and the vertical portion 272 of the lower plate 270 are connected. In this way, since the water pressure of the heat medium may be distributed, water pressure resistance of the lower plate 270 may be improved, deformation of the lower plate 270 may be minimized, and thus durability of the lower plate 270 may be improved.

(106) Hereinafter, a coupling structure between the condensate tray 300 and the leakage preventing member 320 will be described.

(107) Referring to FIGS. 29A, 29B and 30, the leakage preventing member 320 is interposed between an edge portion of the lower plate 270 and an edge portion of the condensate tray 300 so as to prevent leakage of the condensate. A body 321 of the leakage preventing member 320 is provided in a form surrounding lower portions of the round portion 273 and the vertical portion 272 of the lower plate 270. Thus, sideward movement of the condensate CW formed on the horizontal portion 271 of the lower plate 270 may be blocked by a bottom portion 233 formed to extend from a lower portion of the body 321 toward one side, and the condensate CW may drop downward.

(108) Meanwhile, a close contact protrusion 322 may be formed at an inner side surface 321a of the leakage preventing member 320 so as to protrude in a direction toward an outer side surface of the lower plate 270. The close contact protrusion 322 may be provided as a plurality of close contact protrusions 322a, 322b, 322c, 322d. 322e, and 322f which are formed at the inner side surface 321a of the leakage preventing member 320 so as to be vertically spaced apart.

(109) According to the configuration of the close contact protrusion 322, upon action of the water pressure, the close contact protrusion 322 of the leakage preventing member 320 that protrudes in a direction opposite from a direction in which the water pressure acts may come in close contact with the outer side surface of the lower plate 270 and effectively prevent a phenomenon in which the condensate CW penetrates into a gap between the lower plate 270 and the leakage preventing member 320 and leaks. Also, when the close contact protrusion 322 is provided as the plurality of close contact protrusions 322 which are vertically spaced apart, leakage of the condensate CW may be more reliably prevented.

(110) A first flange portion 301 configured to support the leakage preventing member 302 is disposed at the edge portion of the condensate tray 300, and a fastening protrusion 301a and a fastening groove 323a which are fastened to each other are formed at positions corresponding to the leakage preventing member 320 and the first flange portion 301. Also, an extending portion 302 configured to extend upward from an outer side end of the first flange portion 301 and come in close contact with an outer side surface of the leakage preventing member 320 and a second flange portion 303 configured to extend outward from an end of the extending portion 302 are further disposed at the edge portion of the condensate tray 300, and a fitting protrusion 324a and a fitting groove 324b which are fitted to each other are formed at positions corresponding to an upper portion of the leakage preventing member 320 and the second flange portion 303. According to such a configuration, it is possible to simultaneously block leakage of the condensate CW and firmly fix the position of the leakage preventing member 320.

(111) Meanwhile, referring to FIG. 28, an exhaust guide 330 having a plurality of holes 331 (331a and 331b) formed therein is disposed inside the condensate tray 300 so that the combustion gas that passed through the heat exchanger 200 is uniformly distributed and discharged to the entire area of the condensate tray 300. The holes 331 may be formed in different sizes in consideration of a combustion gas flow direction.

(112) Also, a step portion 304 configured to guide the combustion gas that passed through the holes 331 of the exhaust guide 330 to flow toward the condensate outlet 310 formed at a lower portion of one side of the condensate tray 300 is formed on a bottom surface of the condensate tray 300. Thus, as indicated by a dotted-line arrow, which corresponds to a condensate discharge direction, and a solid-line arrow, which corresponds to a combustion gas flow direction, in FIG. 30, the discharge of the condensate and the flow of the combustion gas occur in the same direction inside the condensate tray 300. According to such a configuration, by guiding the condensate in a direction in which exhaust gas flows, corrosion of the lower plate 270 due to stagnation of the condensate may be prevented, and the condensate may be guided toward the condensate outlet 310 and smoothly discharged.

(113) Meanwhile, as illustrated in FIGS. 31 to 38, the smoke tube boiler 1 according to the present invention further includes a pre-mixing chamber 500 having a space provided therein in which air for combustion and gas which are supplied to the mix chamber 100 are pre-mixed and a mixture regulating part 600 configured to open and close flow paths of the air and gas that pass through the pre-mixing chamber 500 and regulate a supply flow rate of the mixture. The space in which the air and gas are pre-mixed is divided in multiple stages by a Venturi structure inside the pre-mixing chamber 500, and a direction of flow of the gas supplied into the pre-mixing chamber 500 and a direction of flow of the air supplied into the pre-mixing chamber may be parallel.

(114) In one embodiment, the pre-mixing chamber 500 is divided into a first path 510 and a second path 520 by a partition member 501 disposed therebetween. An air flow path and a gas flow path connected to the first path 510 may be in an open state at all times, and an air flow path and a gas flow path connected to the second path 520 may be opened and closed by the mixture regulating part 600.

(115) Referring to FIG. 33A and FIG. 33B, a first gas supply hole 530 is provided in an upper portion of one side of the pre-mixing chamber 500, and gas supplied through the first gas supply hole 530 is supplied to the first path 510 via a first space 531 and a first gas discharge hole 532. A second gas supply hole 540 is provided in a lower portion of the one side of the pre-mixing chamber 500, and gas supplied through the second gas supply hole 540 is supplied to the second path 520 via a second space 541, a communication hole 542, a third space 543, and a second gas discharge hole 544. The second space 541 and the third space 543 may be spatially separated and come in communication with each other when the communication hole 542 is open. One side surfaces of the second space 541 and the third space 543 may be sealed by a fixing plate 502. The communication hole 542 may be opened and closed by a second opening/closing member 650 of the mixture regulating part 600 which will be described below.

(116) An air inlet 800 is connected to the first path 510 and the second path 520.

(117) A first gas distributing member 550 configured to distribute and supply gas supplied from the first gas supply hole 530 to a throat portion of the first path 510 may be coupled to the first path 510, and a second gas distributing member 560 configured to distribute and supply gas supplied from the second gas supply hole 540 to a throat portion of the second path 520 may be coupled to the second path 520.

(118) Referring to FIG. 34A and FIG. 34B, a plurality of first distribution holes 551 configured to distribute and supply gas to the first path 510 in a direction parallel to an air flow direction may be formed at a lower portion of the first gas distributing member 550 so as to be spaced apart in the circumferential direction, and a plurality of second distribution holes 561 configured to distribute and supply gas to the second path 520 in the direction parallel to the air flow direction may be formed at a lower portion of the second gas distributing member 560 so as to be spaced apart in the circumferential direction.

(119) Referring to FIGS. 34A to 38, the first gas distributing member 550 is coupled to an inner side surface of the first path 510 while a predetermined first clearance space S1 is formed therebetween, and gas discharged through the first gas discharge hole 532 passes through the first clearance space S1 and then is supplied to the first space 510 via the first distribution hole 551. The second gas distributing member 560 is coupled to an inner side surface of the second path 520 while a predetermined second clearance space S2 is formed therebetween, and gas discharged through the second gas discharge hole 544 passes through the second clearance space S2 and then is supplied to the second space 520 via the second distribution hole 561.

(120) Referring to FIG. 32, the mixture regulating part 600 includes a first opening/closing member 640 configured to open and close a flow path of air passing through the second path 520 and the second opening/closing member 650 configured to open and close the communication hole 542, which is a flow path of gas that is connected to the second path 520, and opening/closing operations of the first opening/closing member 640 and the second opening/closing member 650 may be simultaneously performed by interlocking.

(121) The first opening/closing member 640 includes a body 641 coupled to a rotating shaft 612 of a motor 611, which is a driving part 610, and disposed in a transverse direction in the second path 520 and a wing portion 643 formed in a size corresponding to a transverse cross-sectional area of the second path 520 and coupled to oppose an outer side surface of the body 641. The driving part 610 may be coupled to a first bracket 620 and fixed, and the first opening/closing member 640 may be coupled to a second bracket 630, which is assembled to one side surface of the pre-mixing chamber 500, and fixed.

(122) The body 641 of the first opening/closing member 640 may include a first cam-shaped portion 642 in which a first sharp edge portion 642a configured to protrude toward the second opening/closing member 650 and a first bottom portion 642b recessed in the opposite direction are alternately formed in the circumferential direction, and a first inclined portion 642c is formed in a section between the first sharp edge portion 642a and the first bottom portion 642b. In FIG. 32, for convenience of description, the first opening/closing member 640 and the second opening/closing member 650 which are viewed in different directions are illustrated together.

(123) The second opening/closing member 650 may include a second cam-shaped portion 652 in which a second sharp edge portion 652a, a second bottom portion 652b, and a second inclined portion 652c are formed in shapes corresponding to the first sharp edge portion 642a, the first bottom portion 642b, and the first inclined portion 642c, respectively. A shaft 651 may be coupled to the center of the second cam-shaped portion 652, an airtight member 654 configured to open and close the communication hole 542 may be coupled to one side end of the shaft 651, and one side end of an elastic member 655 may be supported by one side surface of the airtight member 654. The other side end of the elastic member 655 may be supported by an inner side surface of the pre-mixing chamber 500 that is opposite the communication hole 542. Therefore, the second opening/closing member 650 may be elastically supported by the elastic member 655 so as to be pressed toward the first opening/closing member 640.

(124) The second opening/closing member 650 may further include a guide member 653 configured to guide the body, in which the second cam-shaped portion 652 is formed, to reciprocate, and a guide groove 652d and a guide rib 653a may be formed at corresponding positions in the body of the second opening/closing member 650 and the guide member 653.

(125) Hereinafter, actions of the mixture regulating part 600 will be described with reference to FIGS. 35 to 38.

(126) As illustrated in FIGS. 35 to 38, when the load set in the smoke tube boiler 1 is in a low output state, the first sharp edge portion 642a of the first opening/closing member 640 and the second bottom portion 652b of the second opening/closing member 650 come in contact with each other due to driving of the driving part 610, and, simultaneously, the first bottom portion 642b of the first opening/closing member 640 and the second sharp edge portion 652a of the second opening/closing member 650 come in contact with each other. Here, while the wing portion 643 of the first opening/closing member 640 is disposed in a direction parallel to a transverse cross-section of the second path 520 such that the flow of air is blocked in the second path 520, the airtight member 654 of the second opening/closing member 650 is moved toward one side (rightward in FIG. 36) due to an elastic force of the elastic member 655 and comes in close contact with the communication hole 542 such that the flow of gas is blocked in the second path 520. In this way, when the load is in the low output state, air and gas are supplied only through the first path 510.

(127) As illustrated in FIGS. 37 and 38, when the load set in the smoke tube boiler 1 is in a high output state, the first sharp edge portion 642a of the first opening/closing member 640 and the second sharp edge portion 652a of the second opening/closing member 652 come in contact with each other due to driving of the driving part 610. Here, while the wing portion 643 of the first opening/closing member 640 is disposed in a direction perpendicular to the transverse cross-section of the second path 520 such that the second path 520 is opened, the airtight member 654 of the second opening/closing member 650 is moved toward the other side (leftward in FIG. 38) while compressing the elastic member 655 and spaced apart from the communication hole 542 such that the gas flow path connected to the second path 520 is opened. In this way, when the load is in the high output state, air and gas are supplied not only through the first path 510, but also through the second path 520.

(128) Supply flow rates of air and gas introduced into the first path 510 and the second path 520 may be regulated proportional to the set heating or water heating load, according to the number of rotations of the air blower 700 and an opening degree of a gas supply valve (not illustrated).

(129) By making the air flow direction and the gas ejection direction to be the same in the first path 510 and the second path 520 of the pre-mixing chamber 600, gas supplied to the first path 510 and the second path 520 may not be affected by the flow of air, and a mixture containing accurate amounts of air and gas corresponding to a set air-gas ratio may be obtained.

(130) As described above, according to the present invention, the pre-mixing chamber 500 is formed of a double structure including the first path 510 and the second path 520 which have a Venturi structure, and, in consideration of the size of heating or water heating load, when the load is in a relatively low output range, pre-mixing is performed only in the first path 510 and stopped in the second path 520, and, when the load is in a relatively high output range, pre-mixing is performed in both the first path 510 and the second path 520, and thus the turn-down ratio (TDR) may be increased.

(131) Also, according to the present invention, by making the air flow direction and gas flow direction to be the same so that changes in amounts of air and gas being mixed are minimized in the process of opening and closing the second path 520, a combustion state may be stabilized even in a low-load range. Accordingly, combustion efficiency may be improved due to complete combustion and emission of pollutants may be reduced.

(132) The present invention is not limited by the embodiments described above and may be modified by those of ordinary skill in the art to which the invention pertains without departing from the technical idea of the present invention defined by the claims below. Such modifications belong to the scope of the present invention.