Combustion Device

Abstract

[Object] To provide a combustion device capable of suppressing poisoning and deterioration of a CO oxidation catalyst due to adhesion of S (sulfur) to the CO oxidation catalyst, which is provided in the combustion device such as a boiler for the purpose of reducing and removing the CO in the combustion gas. [Solving Means] Provided is a combustion device including at least one can body which has a gas flow passage R allowing passage of a combustion gas G1 generated at a burner 16 and which heats a heat medium through heat exchange with the combustion gas G1 passing through the gas flow passage R, in which, in the gas flow passage R, a CO oxidation catalyst C1 is arranged in a region corresponding to a temperature range at the time of passing of the combustion gas G1 where adhesion of S (sulfur) contained in the combustion gas G1 to the CO oxidation catalyst C1 is suppressed.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a combustion device capable of suppressing deterioration of a CO oxidation catalyst for reducing CO (carbon monoxide) in the combustion gas generated in the combustion device.

[0002] Conventionally, in a combustion device such as a boiler, when reducing to a level below a predetermined value (e.g., a regulation value) the amount of CO contained in the combustion gas generated as a result of combustion at the burner, the combustion gas is passed through a CO oxidation catalyst to thereby remove the CO through oxidation.

[0003] As a technology for thus oxidizing the CO contained in the combustion gas by means of a CO oxidation catalyst, there has been disclosed a construction in which a CO oxidation catalyst is arranged in the exhaust gas passage (e.g., see Patent Document 1).

[0004] [Patent Document 1] JP 2004-69139 A

DISCLOSURE OF THE INVENTION

[Problem to be Solved by the Invention]

[0005] It should be noted, however, that the combustion gas generated through combustion at the burner generally contains SOx derived from S (sulfur) contained in an odorant added to the fuel gas from the viewpoint of safety or contained in the fuel such as heavy oil or derived from the SOx (sulfur oxide) contained in the atmospheric air.

[0006] Thus, there is a problem in that the SOx generated through the combustion at the burner comes into contact with the CO oxidation catalyst or the like, and the S (sulfur) due to the SOx adheres to a catalyst activation material such as a precious metal, resulting in poisoning and deterioration of the catalyst and a reduction in the service life thereof, which leads to an increase in running cost regarding the CO oxidation catalyst or the like.

[0007] The present invention has been made in view of the above-mentioned problem. It is an object of the present invention to provide a combustion device capable of suppressing poisoning and deterioration of a CO oxidation catalyst due to adhesion of S (sulfur) to the CO oxidation catalyst, which is provided in the combustion device such as a boiler for the purpose of reducing and removing the CO in the combustion gas.

[Means for Solving the Problem]

[0008] To solve the above problem, the present invention proposes the following means.

[0009] The invention according to Claim 1 provides a combustion device including at least one can body which has a gas flow passage allowing passage of a combustion gas generated at a burner and which heats a heat medium through heat exchange with the combustion gas passing through the gas flow passage, in which, in the gas flow passage, a CO oxidation catalyst is arranged in a region corresponding to a temperature range at the time of passing of the combustion gas where adhesion of S (sulfur) contained in the combustion gas to the CO oxidation catalyst is suppressed.

[0010] In the combustion device of the present invention, the CO oxidation catalyst is arranged in a region corresponding to a temperature range where the adhesion of S (sulfur) is suppressed, and hence the adhesion of S (sulfur) to the CO oxidation catalyst is suppressed, thereby suppressing deterioration of the CO oxidation catalyst. As a result, it is possible to increase the service life of the CO oxidation catalyst.

[0011] In this specification, the adhesion of S (sulfur) to the CO oxidation catalyst means that S (sulfur) is adsorbed on or reacts with the catalyst activation material constituting the CO oxidation catalyst, to thereby cover or combine with the catalyst activation material.

[0012] The invention according to Claim 2 provides a combustion device according to Claim 1, in which the CO oxidation catalyst is formed by connecting together adjacent water tubes of a water tube group constituting the can body.

[0013] In the combustion device of the present invention, the CO oxidation catalyst is formed through connection of water tubes adjacent to each other, and hence it is possible to arrange the CO oxidation catalyst in a stable manner in a region corresponding to a temperature range where adhesion of S (sulfur) is suppressed in the water tube group.

[0014] Further, by connecting the water tubes adjacent to each other, it is possible to easily arrange a CO oxidation catalyst through which all of the combustion gas to be discharged passes.

[0015] The invention according to Claim 3 provides a combustion device according to Claim 1, in which the CO oxidation catalyst is arranged in a space formed in a water tube group constituting the can body.

[0016] In the combustion device of the present invention, the CO oxidation catalyst is arranged in the space formed in the water tube group constituting the can body, and hence the CO catalyst can be easily arranged in a region corresponding to the temperature range where the adhesion of S (sulfur) is suppressed.

[0017] The invention according to Claim 4 provides a combustion device according to Claim 3, in which the can body has an opening in a side thereof, and in which the CO oxidation catalyst can be inserted into and extracted from the opening.

[0018] In the combustion device of the present invention, the CO oxidation catalyst can be inserted into and extracted from the opening formed in a side of the can body, and hence, when the CO oxidation catalyst has been degenerated and needs replacement, the CO oxidation catalyst can be replaced efficiently in a short time.

[0019] As a result, it is possible to reduce the requisite cost for the replacement of the CO oxidation catalyst and to suppress a reduction in the availability factor of the combustion device, thereby suppressing an increase in production cost.

[0020] The invention according to Claim 5 provides a combustion device according to any one of Claims 1 through 4, in which the CO oxidation catalyst is arranged so as to divide the gas flow passage into an upstream side portion and a downstream side portion, and in which all the combustion gas passing through the gas flow passage passes through the CO oxidation catalyst.

[0021] In the combustion device of the present invention, the CO oxidation catalyst is arranged so as to divide the gas flow passage into the upstream side portion and the downstream side portion, and all the combustion gas passes through the CO oxidation catalyst, and hence it is possible to suppress leakage of CO.

[0022] The invention according to Claim 6 provides a combustion device according to any one of Claims 1 through 5, in which the CO oxidation catalyst is arranged in the gas flow passage in the can body.

[0023] Due to the unevenness in the flame of the burner and the arrangement of the water tube group in the gas flow passage, there maybe generated some unbalance in the temperature, composition, and flow velocity of the combustion gas in the sectional direction of the gas flow passage. However, since the CO oxidation catalyst is arranged in the can body, it is possible to minimize the unbalance in the temperature, composition, and flow velocity of the combustion gas through pressure loss of the CO oxidation catalyst and to reduce the CO efficiently. Further, a uniform heat load can be attained, and hence it is possible to suppress generation of scale adhesion and pitting corrosion of the water tubes, making the deterioration of the CO oxidation catalyst uniform.

[0024] When adhesion or condensation of water occurs in the gap between the base member forming the CO oxidation catalyst and the catalyst activation material, the service life of the CO oxidation catalyst may be shortened. However, since the CO oxidation catalyst is arranged in the can body and maintained at high temperature, the adhesion of water to the CO oxidation catalyst and condensation of water thereon are suppressed, whereby it is possible to increase the service life of the CO oxidation catalyst.

EFFECT OF THE INVENTION

[0025] In the combustion device of the present invention, chemical combination of the CO oxidation catalyst with S (sulfur) is suppressed, and deterioration of the CO oxidation catalyst is suppressed. As a result, it is possible to increase the service life of the CO oxidation catalyst.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] In the following, a first embodiment of the present invention is described with reference to FIG. 1.

[0027] FIG. 1 are diagrams illustrating a small once-through boiler (combustion device) 10 according to the first embodiment, of which FIG. 1(A) is a longitudinal sectional view, and FIG. 1(B) is a cross-sectional view taken along the line I-I of FIG. 1(A).

[0028] The boiler 10 is provided with a fuel supply portion 11, a can body 12, a burner 16, and a combustion gas discharge passage 17, in which the can body 12 is arranged inside a casing 18, and an economizer 19 is provided in the combustion gas discharge passage 17. Further, the boiler 10 has a gas flow passage R through which combustion gas G1 flows from the burner 16 to a discharge port 17A of the combustion gas discharge passage 17 by way of a water tube group 14, and the combustion gas G1 generated at the burner 16 is discharged from the discharge port 17A by way of the gas flow passage R.

[0029] In this embodiment, the fuel of the boiler 10 contains a fuel gas obtained by mixing raw gas with combustion air, and an odorant containing S (sulfur), for example, is added to the raw gas so that any leakage thereof may be discovered at an early stage.

[0030] The fuel supply portion 11 is provided with a blowing fan 11a for supplying combustion air, and a nozzle 11b for supplying raw gas, and the combustion air sent from the blowing fan 11a and the raw gas supplied from the nozzle 11b are mixed with each other in a duct to thereby produce the fuel gas.

[0031] The can body 12 is provided with a lower header 13, a water tube group 14, and an upper header 15, and the water tube group 14 has a plurality of inner water tubes 14A and a plurality of outer water tubes 14B.

[0032] Further, as shown in FIG. 1(A), the inner water tubes 14A and the outer water tubes 14B are arranged vertically between the lower header 13 and the upper header 15, and are connected to the lower header 13 and the upper header 15 so as to allow passage of water.

[0033] Further, as shown in FIG. 1(B), the inner water tubes 14A are arranged on the inner side of the outer water tubes 14B, and the space formed around the inner water tubes 14A constitutes the gas flow passage R.

[0034] The outer water tubes 14B are arranged on the right and left-hand sides of the gas flow passage R and extend from the burner 16 toward the combustion gas discharge passage 17, connection is effected by water tube wall portions 14C between the outer water tubes 14B adjacent to each other, between the outer water tubes 14B and the burner 16 side casing inner wall, and between the outer water tubes 14B and the combustion gas discharge passage 17 side casing inner wall, and the side surface of the casing 18 and the gas flow passage R are separated from each other by the outer water tubes 14B and the water tube wall portions 14C.

[0035] Further, castables (refractories) 18A are arranged on the upper side of the lower header 13 and on the lower side of the upper header 15.

[0036] In this specification, the terms combustion gas G1 implies at least one of the fuel gas that has completed combustion reaction and the fuel gas that is undergoing combustion reaction, and the term combustion gas G1 covers all of the following cases: the case in which there are both the fuel gas that has completed combustion reaction and the fuel gas that is undergoing combustion reaction, the case in which there is only the fuel gas that is undergoing combustion reaction, and the case in which there is only the fuel gas that has completed combustion reaction.

[0037] The burner 16 in the first embodiment has a burner element 16A having on the water tube group 14 side surface thereof a plurality of nozzle holes arranged in a planar fashion along the surface; the fuel gas supplied from the fuel supply portion 11 is burned at the burner element 16A.

[0038] Further, the burner 16 can control the combustion state (e.g., high combustion, low combustion) based, for example, on the pressure of a steam collecting portion (not shown) detected by a pressure sensor.

[0039] In FIG. 1, the portion encircled by the dashed line extending from the burner element 16A toward the water tube group 14 conceptually indicates the flame formed by the burner element 16A.

[0040] The high temperature combustion gas G1 generated through combustion at the burner 16 passes through the gas flow passage R and heats the water in the water tube group 14, heating the water in the economizer 19 after being introduced into the combustion gas discharge passage 17.

[0041] The combustion gas discharge passage 17 is connected to the downstream side of the can body 12 and can discharge the combustion gas G1 to the exterior.

[0042] The economizer 19 is arranged in the combustion gas discharge passage 17 and heats water with the waste heat of the combustion gas G1 passing through the combustion gas discharge passage 17, and supplies the heated water to the lower header 13.

[0043] The casing 18 is formed so as to cover at least the surfaces of the can body 12 on both sides of the boiler 10, the surface thereof on the fuel supply portion 11 side, and the surface thereof on the combustion gas discharge passage 17 side, preventing leakage of the combustion gas G1 and exposure of the heated water tube group 14.

[0044] Further, the casing 18 has, in the water tube group 14, a space P1 for arranging a CO oxidation catalyst C1, and the space P1 is formed, for example, at the center in the longitudinal direction of the can body 12 by arranging the inner water tubes 14A such that a space larger than the thickness of the CO oxidation catalyst C1 is formed linearly in the width direction (a direction orthogonal to the gas flow passage R) of the can body 12 between the inner water tubes 14A adjacent to each other in the direction in which the gas flow passage R extends.

[0045] The space P1 is a region corresponding to a temperature range where adhesion of S (sulfur) contained in the combustion gas G1 to the CO oxidation catalyst C1 is suppressed at least in a state in which the burner 16 performs stable combustion to increase the temperature of the CO oxidation catalyst C1 to a stable level.

[0046] Specifically, the temperature range where adhesion of S (sulfur) to the CO oxidation catalyst C1 is suppressed is, for example, from approximately 400.degree. C. to 1000.degree. C., and, more preferably, from approximately 500.degree. C. to 700.degree. C.

[0047] The stable combustion of the burner 16 refers to a state in which at least one of high combustion and low combustion is being continued, and, in all combustion states, the temperature of the CO oxidation catalyst C1 due to the stable combustion of the burner 16 is preferably in a temperature range in which adhesion of S (sulfur) to the CO oxidation catalyst C1 is suppressed.

[0048] Due to the arrangement of the CO oxidation catalyst C1, the sectional configuration of the gas flow passage R in the space P1 is such that the gas flow passage R is divided into the upstream side portion and the downstream side portion of the CO oxidation catalyst C1, all the combustion gas G1 passes through the CO oxidation catalyst C1, and leakage of any combustion gas G1 not passing through the CO oxidation catalyst C1 to the exterior of the boiler 10 is suppressed.

[0049] As shown in FIG. 2, the CO oxidation catalyst C1 is formed by carrying, for example, platinum, as a catalyst activation material on the surface of a rectangular flat-plate-like base member C10 having a plurality of ventilation holes formed in the thickness direction, and the CO contained in the combustion gas G1 is oxidized into CO.sub.2, thereby removing the CO.

[0050] The base member C10 is formed by alternately superimposing one upon the other first base members C11 formed of strip-like flat plates and second base members C12 formed of corrugated plates and surrounding them by a side plate C13 to fix them in position.

[0051] The first base member C11 and the second base member C12 are formed by stainless-steel plates that have undergone surface treatment in order to enlarge the area with which they come into contact with the exhaust gas and have a multitude of minute protrusions and recesses on their surfaces, with the catalyst activation material being carried by those minute protrusions and recesses.

[0052] There are no particular limitations regarding the structure of the CO oxidation catalyst C1. It is possible, for example, to form instead of the base member C10 a base member allowing ventilation by a metal other than stainless steel or of a ceramic material, with the catalyst activation material being carried by the surface thereof. Further, the ventilation property for the combustion gas G1 may be obtained not by the ventilation holes but by a sponge-like porous structure with ventilation holes whose direction is not fixed, or by a structure in which a large number of pellets carrying a catalyst activation material are accommodated in a container having a flow passage allowing ventilation.

[0053] As the catalyst activation material, it is also possible to use a precious metal other than platinum (Ag, Au, Rh, Ru, Pt, Pd) or a metal oxide (NiOx, CuOx, CoOx, MnOx).

[0054] Further, the CO oxidation catalyst C1 may also have, in addition to the CO oxidation effect, an effect of reducing the NOx contained in the combustion gas G1 as a NOx reduction catalyst. Alternatively, a NOx reduction catalyst may be arranged along with the CO oxidation catalyst C1.

[0055] Next, the operation of the boiler 10 is described.

[0056] 1) The fuel gas supplied from the fuel supply portion 11 to the burner 16 is ejected from the nozzle holes of the burner element 16A and burned to generate a high temperature combustion gas G1.

[0057] 2) While passing through the gas flow passage R, the combustion gas G1 heats the water in the water tube group 14 to vaporize the same. After passing through the water tube group 14, the combustion gas G1 moves toward the discharge port 17A of the combustion gas discharge passage 17.

[0058] The steam generated through heating is supplied to steam consuming equipment by way of the upper header 15.

[0059] 3) When passing through the water tube group 14, the combustion gas G1 passes through the CO oxidation catalyst C1, and the CO contained in the combustion gas G1 is oxidized into CO.sub.2, resulting in a reduction in the concentration of the CO contained in the combustion gas G1.

[0060] 4) The temperature of the CO oxidation catalyst C1 when the combustion gas G1 passes through the CO oxidation catalyst C1 is, for example, from 400.degree. C. to 1000.degree., and reaction of the S (sulfur) contained in the combustion gas G1 with the CO oxidation catalyst Cl is suppressed, thus suppressing adhesion of S (sulfur) to the CO oxidation catalyst C1.

[0061] In the boiler 10 of the first embodiment, the CO oxidation catalyst C1 is arranged in a region corresponding to a temperature range where adhesion of S (sulfur) is suppressed, and hence chemical combination of S (sulfur) with the base member C10 forming the CO oxidation catalyst and the catalyst activation material carried by the base member C10 is suppressed, whereby deterioration of the CO oxidation catalyst C1 is suppressed.

[0062] As a result, it is possible to reduce the running cost of the CO oxidation catalyst C1 and to increase the service life of the CO oxidation catalyst C1.

[0063] Further, the CO oxidation catalyst C1 is arranged in the space P1 formed in the water tube group 14, and hence the CO oxidation catalyst C1 can be easily arranged over the entire section of the gas flow passage R in the can body 12. As a result, discharge of high concentration CO to the exterior of the boiler 10 is suppressed.

[0064] Further, since the CO oxidation catalyst C1 is arranged in the can body 12, the unevenness in the flame of the burner 16 and the unbalance in the temperature, composition, and flow velocity of the combustion gas G1 in the sectional direction of the gas flow passage R generated due to the arrangement of the water tube group 14 can be reduced through pressure loss of the CO oxidation catalyst Cl, and it is possible to efficiently reduce the CO due to the CO oxidation catalyst C1, whereby adhesion of scales to the water tubes 14A, 14B and generation of pitting corrosion are suppressed to make the deterioration of the CO oxidation catalyst C1 uniform, thereby reducing the running cost of the CO oxidation catalyst C1.

[0065] When adhesion and condensation of water occur in the gap between the base member C10 constituting the CO oxidation catalyst C1 and the catalyst activation material, the service life of the CO oxidation catalyst C1 may be reduced. However, the CO oxidation catalyst C1 is arranged within the can body 12 and maintained at high temperature, whereby adhesion and condensation of water to and on the CO oxidation catalyst C1 are suppressed, thereby increasing the service life of the CO oxidation catalyst C1.

[0066] Next, a boiler 20 according to a second embodiment of the present invention is described.

[0067] FIG. 3 is a diagram showing the boiler 20 of the second embodiment.

[0068] The boiler 20 differs from the boiler 10 in the following point. In the boiler 20, there is formed, in the side surface (side) of the boiler 10 indicated by the chain double-dashed line in FIG. 1(A), an opening 18B extending into the interior of the can body 12 from the casing 18 and the water tube wall portions 14C, and a CO oxidation catalyst C2 is arranged in a space P2 of the can body 12 so as to be capable of being inserted into and extracted from the opening 18B.

[0069] The opening 18B is formed, for example, at the center in the longitudinal direction of the boiler 20, and the space P2 is formed in a region corresponding to a temperature range for the arranged CO oxidation catalyst C2 where adhesion of S (sulfur) is suppressed.

[0070] A cover member 18D can be mounted to the opening 18B, and the opening 18B extending through the water tube wall portion 14C and the casing 18 is closed by the cover member 18D. Other components are the same as those of the first embodiment, and hence the same components are indicated by the same reference symbols, and descriptions thereof are omitted.

[0071] In the boiler 20, when the CO oxidation catalyst C1 has been degenerated and needs replacement, it is possible to replace the CO oxidation catalyst C1 efficiently in a short time.

[0072] As a result, it is possible to reduce the cost for the replacement of the CO oxidation catalyst C1, and to suppress a reduction in the availability factor of the boiler 20, thereby suppressing an increase in production cost.

[0073] Next, a boiler 30 according to a third embodiment of the present invention is described.

[0074] FIG. 4 is a diagram showing the boiler 30 of the third embodiment.

[0075] The boiler 30 differs from the boiler 10 of the first embodiment in that, while in the boiler 10 the CO oxidation catalyst C1 formed as a flat plate is arranged in the space P1, in the boiler 30, a CO oxidation catalyst C3 formed by a mesh-shaped stainless steel carrying a catalyst activation material on the surface thereof is mounted, by welding or the like, to water tubes 14A, 14B constituting the water tube group 14 so as to connect the adjacent water tubes 14A, 14B to each other.

[0076] The CO oxidation catalyst C3 is arranged in a region corresponding to a temperature range T (maximum temperature T1, minimum temperature T2), conceptually indicated by the dashed line in FIG. 4, where adhesion of S (sulfur) is suppressed. Other components are the same as those of the first embodiment, and hence the same components are indicated by the same reference symbols, and descriptions thereof are omitted.

[0077] In the boiler 30, in the temperature distribution formed in the gas flow passage R through passage of the combustion gas G1, it is possible to select a position for the arrangement of the CO oxidation catalyst C3 in correspondence with the temperature distribution from a region corresponding to a temperature range (maximum temperature T1, minimum temperature T2) where adhesion of S (sulfur) to the CO oxidation catalyst C3 is suppressed.

[0078] As a result, it is possible to efficiently suppress adhesion of S (sulfur) to the CO oxidation catalyst C3 and to improve the efficiency in the CO oxidation performed by the CO oxidation catalyst C3.

[0079] Next, a boiler 40 according to a fourth embodiment of the present invention is described.

[0080] FIG. 5 are diagrams showing the boiler 40 of the fourth embodiment.

[0081] The boiler 40 differs from the boiler 10 in that, while in the boiler 10 the CO oxidation catalyst C1 is arranged at the center in the longitudinal direction of the can body 12, in the boiler 40, the can body 12 is provided with a first can body 12A and a second can body 12B arranged in series along the combustion gas flow passage R, and that a CO oxidation catalyst C4 is arranged between the first can body 12A and the second can body 12B. The CO oxidation catalyst C4 is arranged in a region corresponding to a temperature range where adhesion of S (sulfur) is suppressed. Other components are the same as those of the boiler 10 of the first embodiment, and hence the same components are indicated by the same reference symbols, and descriptions thereof are omitted.

[0082] In the boiler 40 of the fourth embodiment, the can body 12 is separable, and hence the CO oxidation catalyst C4, which has a large size, can be easily arranged.

[0083] Next, a boiler 50 according to a fifth embodiment of the present invention is described.

[0084] FIGS. 6 and 7 are diagrams illustrating the boiler 50 of the fifth embodiment.

[0085] As shown in FIG. 6, the boiler 50 is provided with a can body 55 having a lower header 51, an upper header 52, an inner water tube group 53 connected to the lower header 51 and the upper header 52 so as to allow circulation, and an outer water tube group 54 connected to the lower header 51 and the upper header 52 so as to allow circulation and arranged on the outer side of the inner water tube group 53 through the intermediation of a combustion gas passage (gas flow passage) 58, and a burner 56 arranged above the central portion of the can body 55, and water in the can body 55 is heated and vaporized until combustion gas G2 generated through combustion at the burner 56 is discharged through a discharge port 57 formed in the upper side surface of the boiler 50.

[0086] As shown in FIG. 7, in the inner water tube group 53, a plurality of inner water tubes 53A are connected in an annular fashion by water tube wall portions 53B, and, in the outer water tube group 54, a plurality of outer water tubes 54A are connected in an annular fashion by water tube wall portions 54B. Further, fins K for absorbing heat are formed on the portions of the inner water tubes 53A and the outer water tubes 54A facing the combustion gas flow passage 58.

[0087] Further, the boiler 50 has, below the water tube wall portions 53B of the inner water tube group 53, a plurality of introduction openings 53D formed in the circumferential direction for introducing the combustion gas G2 into the combustion gas passage 58, and a plurality of discharge openings 54D formed in the circumferential direction of the outer water tube group 54 for discharging the combustion gas G2 in the combustion gas passage 58. Thus, this boiler is formed as a forward flow can body boiler in which the combustion gas G2 introduced into the combustion gas passage 58 flows upwardly.

[0088] A CO oxidation catalyst C5 is formed, for example, by a base member of stainless steel wire shaped into a flat mesh form, with platinum being carried by the base member as the catalyst activation material. As shown in FIG. 7(B), it is arranged in a region corresponding to a temperature range where adhesion of S (sulfur) to the CO oxidation catalyst C5 is suppressed, and it is arranged, for example, such that the surface of the CO oxidation catalyst C5 extends in a direction orthogonal to the longitudinal direction of the combustion gas passage 58, and a plurality of end portions of the CO oxidation catalyst C5 are connected, over the entire periphery of the combustion gas passage 58, to the inner water tube group 53 and the outer water tube group 54 by welding or the like, with the introduction openings 53D and the discharge openings 54D being separated from each other.

[0089] The CO oxidation catalyst C5 may be arranged in a region corresponding to a temperature range where adhesion of S (sulfur) to the CO oxidation catalyst C5 is suppressed and at any position in the gas flow passage from the burner 56 to the discharge port 57. Further, the orientation of the surface of the CO oxidation catalyst C6 can be set freely.

[0090] Instead of the base member formed by shaping stainless steel into a mesh form, it is also possible to adopt a base member formed by a body formed of a metal such as stainless steel or a ceramic material, with the base member carrying a catalyst activation material formed of a precious metal other than platinum (Ag, Au, Rh, Ru, Pt, Pd) or a metal oxide (NiOx, CuOx, CoOx, MnOx). It is also possible for the catalyst activation material to be carried by the fins K by flame spraying or the like.

[0091] Next, a boiler 60 according to a sixth embodiment of the present invention is described.

[0092] FIGS. 8 and 9 are diagrams illustrating the boiler 60 of the sixth embodiment.

[0093] The boiler 60 differs from the boiler 50 of the fifth embodiment in that, instead of the discharge port 57 formed in the upper side surface of the boiler 50, a discharge port 59 is formed substantially at the center in the height direction of the side surface of the boiler 60, an introduction opening 53F for introducing the combustion gas G2 into the combustion gas passage 58 is formed on the circumferetially opposite side of a discharge port 59, and a discharge opening 54F for discharging the combustion gas G2 from the combustion gas passage 58 is formed at a circumferential position corresponding to the discharge port 59, the combustion gas G2 introduced into the combustion gas passage 58 from the introduction opening 53F flows substantially half the circumference through the combustion gas passage 58 and is then discharged from the discharge port 59 by way of the discharge opening 54F, thus, this boiler is formed as a .omega. flow type boiler.

[0094] By removing the water tube wall portions 53B and the water tube wall portions 54B, respectively, the introduction opening 53F and the discharge opening 54F are formed to extend substantially over the entire vertical length of the inner water tubes 53A and the outer water tubes 54A.

[0095] Other components are the same as those of the boiler 50 of the fifth embodiment, and hence the same components are indicated by the same reference symbols, and descriptions thereof are omitted.

[0096] As shown in FIG. 9, a CO oxidation catalyst C6 is arranged in a region corresponding to a temperature range where adhesion of S (sulfur) to the CO oxidation catalyst C6 is suppressed in both the clockwise and counterclockwise routes of the combustion gas passage 58 in plan view, through which the combustion gas G2 heading for the discharge opening 54F from the introduction opening 53F passes, for example, such that the surface of the CO oxidation catalyst C6 extends in the longitudinal direction of the water tubes 53A, 54A and that the introduction opening 53F and the discharge opening 54F are separated from each other through connection of the inner water tube group 53 and the outer water tube group 54 performed by welding or the like.

[0097] The CO oxidation catalyst C6 may be arranged in a region corresponding to a temperature range where adhesion of S (sulfur) to the CO oxidation catalyst C6 is suppressed and at any position in the gas flow passage from the burner 56 to the discharge port 59. Further, the orientation of the CO oxidation catalyst C6 can be set freely.

[0098] The present invention is not restricted to the embodiments described above but allows various modifications without departing from the gist of the present invention.

[0099] For example, while in the above-mentioned embodiments the boilers 10, 20, 30, 40 are small once-through boilers, the boiler 50 is a forward flow can body boiler, and the boiler 60 is a .omega. flow type boiler, the present invention is also applicable to boilers of various other structures, such as a flue and smoke tube boiler and a water heater.

[0100] Further, while in the boiler 20 described above the opening 18B is formed in an side surface of the casing 18, such openings may be formed in both side surfaces of the casing 18.

[0101] Further, while in the boiler 40 described above the can body 12 has two can bodies 12A, 12B, the present invention is also applicable to a boiler having three or more can bodies.

[0102] Further, while in the above-mentioned embodiments the combustion at the burner 16 is controlled to high combustion and low combustion, the present invention is also applicable to a boiler in which the combustion at the burner 16 is controlled based, for example, on the temperature of the combustion gas G1 or the CO oxidation catalyst or the composition of the combustion gas or the like.

[0103] While in the above-mentioned embodiments combustion is effected by supplying the burner 16 with a combustion gas obtained by pre-mixing raw gas and combustion air with each other, it is also possible to use, instead of a fuel gas, a liquid fuel such as heavy oil, or powdered coal.

[0104] Further, while in the above-mentioned embodiments the CO oxidation catalyst C1, C2, C3, C4 is arranged in the gas flow passage R in the can body 12, it is also possible to arrange the CO oxidation catalyst between the burner 16 and the can body 12, between the can body 12 and the combustion gas discharge passage 17, or in the combustion gas discharge passage 17.

BRIEF DESCRIPTION OF THE DRAWINGS

[0105] [FIG. 1] Diagrams showing a boiler according to the first embodiment of the present invention, of which part (A) is a longitudinal sectional view, and part (B) is a cross-sectional view taken along the line I-I of part (A).

[0106] [FIG. 2] A diagram showing an example of the CO oxidation catalyst used in the boiler of the first embodiment.

[0107] [FIG. 3] A cross-sectional view of a boiler according to the second embodiment of the present invention taken along the line I-I of FIG. 1(A).

[0108] [FIG. 4] A cross-sectional view of a boiler according to the third embodiment of the present invention taken along the line I-I of FIG. 1(A).

[0109] [FIG. 5] Diagrams showing a boiler according to the fourth embodiment of the present invention, of which part (A) is a longitudinal sectional view, and part (B) is a cross-sectional view taken along the line II-II of part (A).

[0110] [FIG. 6] A longitudinal sectional view of a boiler according to the fifth embodiment of the present invention.

[0111] [FIG. 7] Cross-sectional views, taken along the line III-III of FIG. 6, of the boiler of fifth embodiment, of which part (A) shows the boiler as a whole, and part (B) shows in detail an example of the CO oxidation catalyst.

[0112] [FIG. 8] A longitudinal sectional view of a boiler according to the sixth embodiment of the present invention.

[0113] [FIG. 9] A cross-sectional view, taken along the line IV-IV of FIG. 8, of the boiler of sixth embodiment.

DESCRIPTION OF REFERENCE SYMBOLS

[0114] G1, G2 combustion gas

[0115] R gas flow passage

[0116] C1, C2, C3, C4, C5, C6 CO oxidation catalyst

[0117] 10, 20, 30, 40, 50, 60 boiler (combustion device)

[0118] 12, 12A, 12B can body

[0119] 14 water tube group

[0120] 16 burner

[0121] 18B opening

[0122] 53 inner water tube group (water tube group)

[0123] 54 outer water tube group (water tube group)

[0124] 55 can body

[0125] 56 burner

[0126] 58 combustion gas passage (gas flow passage)

Claims

1. A combustion device comprising at least one can body which has a gas flow passage allowing passage of a combustion gas generated at a burner and which heats a heat medium through heat exchange with the combustion gas passing through the gas flow passage, wherein, in the gas flow passage, a CO oxidation catalyst is arranged in a region corresponding to a temperature range at the time of passing of the combustion gas where adhesion of S (sulfur) contained in the combustion gas to the CO oxidation catalyst is suppressed.

2. A combustion device according to claim 1, wherein the CO oxidation catalyst is formed by connecting together adjacent water tubes of a water tube group constituting the can body.

3. A combustion device according to claim 1, wherein the CO oxidation catalyst is arranged in a space formed in a water tube group constituting the can body.

4. A combustion device according to claim 3, wherein the can body has an opening in a side thereof, and wherein the CO oxidation catalyst can be inserted into and extracted from the opening.

5. A combustion device according to claim 1, wherein the CO oxidation catalyst is arranged so as to divide the gas flow passage into an upstream side portion and a downstream side portion, and wherein all the combustion gas passing through the gas flow passage passes through the CO oxidation catalyst.

6. A combustion device according to claim 1, wherein the CO oxidation catalyst is arranged in the gas flow passage in the can body.