JPH0791613A - Combustion device - Google Patents

Abstract

PURPOSE:To provide a combustion device which is constituted to suppress the generation of NOx, reduce the generation of CO, and prevent lowering of heat efficiency. CONSTITUTION:A combustion device comprises a heat absorption pipe group consisting of a number of heat absorption pipes 4, 4... arranged in parallel to each other with a given distance therebetween and crossing a combustion flame from a burner means 2. In the heat absorption group, instead of a heat absorption pipe, rod-form members 10 and 10 are arranged in a temp. region where the generation of NOx is suppressed and oxidation of CO is promoted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is suitable for use in water tube boilers such as once-through boilers, natural circulation type water tube boilers, forced circulation type water tube boilers, and the like, and NOx (nitrogen oxide) and CO
The present invention relates to a combustion device that reduces the emission concentration of (carbon monoxide).

[0002]

2. Description of the Related Art In recent years, due to environmental pollution problems and the like, even in boilers, it has been required to further reduce emission concentrations of harmful combustion exhaust substances, particularly NOx and CO. Various measures for reducing the emission concentration of such harmful combustion exhaust gas have been proposed. As one of the measures to reduce the heat, the heat absorption tube is placed as close as possible to the burner, the heat absorption tube group is positioned in the combustion flame, and the heat is exchanged at the same time as cooling the flame.
A technique for suppressing the generation of Ox as much as possible and realizing high load combustion is known from US Pat. No. 5,020,47.
It should be noted that the "combustion flame" used in this specification refers to a high-temperature gas that is currently undergoing a combustion reaction, and is generated in the high-temperature gas by combustible premixed gas that has not completed combustion and combustion. And burned gas. Further, the combustion flame may be paraphrased as combustion gas. However, although the conventional measures can reduce the emission concentration of NOx, CO
There is a problem that the emission concentration is slightly higher. One of the causes is that for CO, the cooling of the combustion flame, which is done to reduce NOx, has a quenching effect, which freezes the reaction, and some of it remains at an equilibrium concentration at high temperature, namely unreacted substances, that is, CO It is thought that it is due to the fact that it is discharged to the outside of the system. In order to solve this problem, the temperature of the flame is 1000 ° C or higher with a cold object placed near or in contact with the flame generated by high-load combustion.
After controlling the temperature below 1500 ° C., the residual CO in the flame is oxidized in the heat insulating space provided on the downstream side of the cold object to cause CO
A technique for converting to ₂ (carbon dioxide) is disclosed in JP-A-60-78.
No. 247 publication.

[0003]

However, this technique is intended to reduce CO emissions, and the N
It is not intended to suppress the generation of Ox. Therefore, the temperature of the adiabatic space of NOx becomes high depending on the position where the adiabatic space is provided, and NOx is generated. Further, there is a problem that the temperature rise of the can body wall defining the heat insulating space becomes large depending on the condition of forming the heat insulating space. In order to prevent this temperature rise, it is necessary to apply a heat insulating material to the inner surface of the can body wall on the heat insulating space side, which leads to an increase in the cost of the apparatus. Further, when the heat insulating material is applied, the heat insulating material may fall due to long-term use, which causes a problem in durability. Furthermore, when the flow velocity of the combustion flame is high, the required CO-to-CO ₂ conversion can be obtained by ensuring a long length in the combustion flame flow direction in the adiabatic space, but this leads to a decrease in thermal efficiency, There is a problem that miniaturization of the can body cannot be realized.

It is an object of the present invention to provide a combustion device capable of suppressing the production of NOx, reducing the produced CO, and preventing a decrease in thermal efficiency.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is substantially parallel to each other and has a predetermined interval and crosses a combustion flame from a burner means. In the heat absorption tube group including a large number of heat absorption tubes, the heat absorption tubes are replaced by a temperature region that suppresses the generation of NOx and promotes the oxidation of CO in the heat absorption tube group. A bar-shaped member is arranged.

[0006]

According to the above-mentioned means, no heat is absorbed in the rod-shaped member located in the heat absorption tube group, the combustion flame is maintained at a relatively high temperature in the vicinity of the rod-shaped member, and unreacted CO and reactive active groups ( Radicals) and / or oxygen atoms (O) and other oxygen are actively contacted, and residual CO undergoes an oxidation reaction to form C
It is converted to O ₂ to reduce CO and suppress the generation of NOx.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing a cross section of a can body of an embodiment in which the combustion method and apparatus according to the present invention are applied to a multi-tube once-through boiler which is a type of water tube boiler. Referring to FIG. 1, a rectangular can body 1 of a multi-tube once-through boiler is a vertical heat absorption pipe arranged along a flow direction (longitudinal direction of the can body) of a combustion flame ejected from a burner means 2 described later. Walls (hereinafter, simply referred to as “tube walls”) 3 and a large number of substantially vertical heats which are arranged substantially parallel to each other and arranged at predetermined intervals so as to intersect with the combustion flame. The burner means 2 for forming a relatively flat flame of the premixing type, which is arranged in one side opening between the absorption tubes 4, 4, ... (Constituting the heat absorption tube group) and the tube walls 3, 3. And the combustion exhaust gas outlet 5 formed in the other side opening between the pipe walls 3 and 3. Pipe wall 3, 3
Defines a combustion / heat exchange zone N. The combustion exhaust gas outlet 5 may be provided at the end of the combustion / heat exchange area N on the side opposite to the burner, and can be formed, for example, by removing a part of the pipe wall 3 and opening it.

In the present embodiment, the pipe walls 3 and 3 are arranged such that a plurality of heat absorption pipes 6 are arranged side by side in the combustion flame flow direction at appropriate intervals.・ ・
Are closed by flat plate-shaped fin members 7, 7 extending along the axial direction of the heat absorbing tubes 6, 6. These pipe walls 3 and 3 are arranged at appropriate intervals so as to be substantially parallel to each other, and cover bodies 8 and 8 are attached to the outer sides of the pipe walls 3 and 3 so as to connect with the pipe walls 3 and 3. Adiabatic spaces 9, 9 are formed between them.

The heat absorbing tubes 4, 4, ... Include three rows of heat absorbing tubes X, Y, Z arranged in the flow direction of the combustion flame. In the following description, the burner means 2 is assigned to each column name X, Y, Z.
Pipe numbers X1, X2 ..., Y1, Y2 ..., Z1, Z2 ... are added by sequentially attaching numbers 1, 2, 3 ... The heat absorbing tubes 6, 6 ... will be described by assigning tube numbers A1, A2 ..., B1, B2. The heat absorption tubes 6, 6 ...
, And the upper and lower ends of the heat absorption tubes 4, 4, ... Arranged between the tube walls 3, 3 are connected to an upper header and a lower header (both not shown), respectively. Then, these both headers are joined to the upper and lower ends of the pipe walls 3 and 3 in a secret manner,
In cooperation with the tube walls 3 and 3, the upper and lower sides and the right and left sides of the combustion / heat exchange area N are divided into confidential parts so that combustion flame and burned gas do not leak to the outside of the can body. And, of the remaining two openings, one is attached with the burner means 2 and the remaining one is
An exhaust stack (not shown) is connected to this opening. In the steam boiler, during normal operation, the entire lower header and the heat absorption pipes 6, 6 ... And the middle of the heat absorption pipes 4, 4 ... are always filled with water, and the heat absorption pipes 6, 6 ,. -And the upper part of the heat absorption tubes 4, 4, ... And the upper header are filled with steam.

As described above, the plurality of heat absorption tubes 4, 4, ... Arranged between the tube walls 3, 3 are arranged in three rows X, Y, Z in parallel in the flow direction of the combustion flame. The heat absorption tubes in the adjacent rows including the heat absorption tubes 6, 6 of the tube walls 3, 3 have a staggered arrangement pattern. Further, the mutual gaps of the heat absorption pipes 6, 6 ..., 4, 4 ... serving as the flow passages of the combustion flame are set to be substantially equal to or smaller than the outer diameter of each heat absorption pipe 6. It is preferable that all of these gaps be the same or different from each other as long as they are within the above-mentioned conditions.

Of the heat absorption tubes 4, 4, ...
The specific temperature range of the temperature range suitable for oxidizing and reducing the generated CO while suppressing the generation of x is previously obtained by an experiment, and the heat absorption tubes X3 and Z3 corresponding to the specific temperature range are thinned (extracted). Instead, heat-resistant non-heat-absorbing tube members (members in which a heat-absorbing heat medium such as water does not flow inside), for example, ceramic rod-shaped members 10 and 10 are attached to this portion.

As the burner means 2, a well-known corrugated type premixing type planar combustion burner is used, but a ceramic plate burner having a large number of small holes for ejecting a premixed gas may be used, or a vaporized combustion oil burner. It is also possible to use various other burners. The gap between the heat absorbing tubes X1 and X2 located immediately in front of the burner means 2 is set to a predetermined distance, for example, equal to or less than three times the outer diameter of the heat absorbing tube 4, and Heat absorption pipes 6, 6 ...
Of the above, the heat absorption tube closest to the burner means 2 is also set on the basis of the above distance.

In the above construction, the combustion flame from the burner means 2 continues to burn in the clearance space between the heat absorption tubes 6, 6, ...
Flow toward each direction, and in the meantime, each heat absorption pipe 6, 6, ...
.., 4, 4 ... Heat is transferred (heat exchange) to the burner means 2 and the immediately preceding heat absorbing tubes 4, 4 and the heat absorbing tubes 6, 6 ,. Since the gaps 4, 4, ... Are set to be narrow as described above, the combustion flame flows toward the combustion exhaust gas outlet 5 while maintaining a high flow velocity, and is cooled with an extremely high contact heat transfer coefficient. .

Since no heat is absorbed in the rod-shaped members 10 and 10, the temperature of the combustion flame in the vicinity of the rod-shaped members 10 and 10 is maintained at about 1000 ° C. to 1200 ° C., and CO generated in the high temperature combustion flame region upstream. The reaction active group (radical) and / or oxygen such as oxygen atom reacts with oxygen to oxidize and reduce CO, and at the same time, generation of NOx is suppressed. In this action, the temperature in the vicinity of the rod-shaped members 10 and 10 is maintained at a high level as compared with the case where the rod-shaped members 10 and 10 are not provided and only a space is provided, and as a result, the CO oxidation reaction is performed in a short distance, and The pressure loss due to abrupt expansion → contraction of the combustion flame (combustion gas) flow path is eliminated, and as a result, a can body without redundant pressure loss is obtained.

Next, another embodiment of the present invention will be described with reference to FIG. 2 is different from the embodiment of FIG. 1 in that in the embodiment of FIG. 1, instead of the heat absorption tubes X3 and Z3,
One rod-shaped member 10 having a circular transverse cross-section was attached, but in the embodiment of FIG. 2, two rod-shaped members each having a diameter smaller than that of the heat absorption pipes 4 are used instead of the heat absorption pipes X3 and Z3. The point is that the members 11 and 11 are mounted and configured to control the flow of combustion flame. Further, in the embodiment of FIG. 2, the heat absorption tube group on the wake side is the fin heat absorption tube 12 and the erofin heat absorption tube 13 so that the heat transfer surface density from the upstream side to the downstream side is made uniform. The other structure is the same as that of the embodiment of FIG. In this embodiment, unburned substances such as CO produced upstream may be frozen by the endothermic tubes 4 and 6 by the control of the flow of the combustion flame by the rod-shaped members 11, 11 ... Is reduced,
Oxidation of unburned substances such as CO is promoted.

The present invention is not limited to the above embodiment. For example, the cross-sectional shape of the rod-shaped members 10 and 11 may be a shape other than a circle, such as a rhombus. Further, in each of the above-described embodiments, the heat absorption tubes 6, 6, ... Are arranged in the tube wall 3 in a plurality of heat absorption tubes 6, 6 ... Although the gap is closed by the fin-shaped members 7, 7 ... Of the flat plate, the structure of the pipe wall may be such that the gap between the heat absorption pipes 6 is made of an appropriate refractory material. The heat absorption tubes 6 may be arranged in close contact with each other.

The number of rows of heat absorption tubes arranged between the tube walls is
The present invention is not limited to the above embodiment. Further, the present invention can be applied to an apparatus in which the burner and the heat absorption tube are arranged not in the vertical direction but in the horizontal direction. Further, the present invention can be applied to water tube boilers other than the once-through type, and can be applied not only to water tube boilers that generate steam but also to water tube boilers that generate hot water. Although the heat medium flowing through the heat absorption tubes 4, 4, ... Is water, it may be a medium other than water, such as oil.

[0018]

As described above, according to the present invention, no heat is absorbed in the rod-shaped member located in the heat absorption tube group, and the combustion flame is maintained at a relatively high temperature in the vicinity of the rod-shaped member. Reactive CO is actively contacted with oxygen such as a reaction active group (radical) and / or oxygen atom (O), and residual CO is oxidized and converted into CO ₂ to reduce CO, and NOx. Generation of NOx is suppressed and NOx And low NOx with low CO emissions A low CO combustion device can be provided.

Further, according to the present invention, the presence of the rod-shaped member can provide a long constant high temperature region without providing a wide heat insulating space as in the conventional case. The temperature rise of the wall can be made small, and it is not necessary to install a heat insulating material on the inner surface of the can body wall to prevent the temperature rise, so that it is possible to provide a device with low cost and excellent durability.

Further, according to the present invention, since it is not necessary to provide a wide heat insulating space as in the conventional case, a can body excellent in space saving and thermal efficiency can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating the schematic structure of a can body according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the schematic structure of a can body according to another embodiment of the present invention.

[Explanation of symbols]

 2 Burner Means 4, 6 Endothermic Tubes 10, 11 Rod-shaped members

Claims (1)

[Claims] Claim: What is claimed is: 1. A heat-absorbing tube group comprising a plurality of heat-absorbing tubes which are substantially parallel to each other and are spaced apart from each other by a predetermined distance so as to intersect with a combustion flame from a burner means. A combustion device, wherein a rod-shaped member is arranged in place of the heat absorption pipe in a temperature region where the generation of NOx is suppressed and the oxidation of CO is promoted in the absorption pipe group.