JP2932956B2 - Waste heat recovery water pipe boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water pipe boiler for recovering exhaust heat of combustion exhaust gas using a surface combustion burner.

[0002]

2. Description of the Related Art In order to reduce the space (compactness) of a boiler, there is a boiler using a surface combustion type burner in which a combustor section is made as small as possible (Japanese Patent Laid-Open No. 6-207707). ).

In order to improve the efficiency of a boiler, there is a method of increasing the thermal efficiency by preheating combustion air by using the heat energy of exhaust gas (JP-A-63-217103). Further, when the boiler is operated at a low load, the combustion exhaust gas is recirculated to the burner outlet to increase the flow rate of the water pipe heat transfer section, thereby increasing the gas flow rate in the water pipe group and increasing the heat transfer efficiency (Japanese Patent Laid-Open Publication No. 1-193503).

[0004]

FIG. 2 shows a boiler adopting the above-mentioned various conventional improvement techniques. Here, reference numeral 11 denotes a water pipe heat transfer section composed of a plurality of water pipes 11a, 12 denotes a combustor section using a surface combustion type burner, and 13 denotes heat for exchanging heat between the high temperature exhaust gas and the premixed gas fuel. An exchanger 14 is a mixer in which a gas fuel 15 and combustion air 16 are previously mixed, 17 is a chimney, 18
Represents a steam header, and 19 represents a part of the combustion exhaust gas.
This is a blower that is fed between the water pipe heat transfer section 11 and the pipe for recirculation.

When the boiler is operated at the maximum load, a premixed gas fuel composed of a rated amount of gas fuel and combustion air having an appropriate excess rate corresponding to the rated amount is supplied to the combustor section 12.
And burned by a surface combustion type burner.
The combustion gas is heat-exchanged in the water pipe heat transfer section 11 and is heated to 200 ° C.
To about 120 ° C through the heat exchanger 13
The temperature is reduced to a low level, and is released from the chimney 17 into the atmosphere.

On the other hand, when the premixed gas fuel is used, the amount of the combustion exhaust gas is reduced under the condition that the heat load of the boiler is low, and the gas flow rate passing through the water pipe group is reduced. Therefore, a part of the combustion exhaust gas is caused to flow to the upstream side of the water pipe heat transfer section 11 by the recirculation blower 19 to increase the gas flow velocity in the water pipe group, thereby preventing a decrease in heat transfer efficiency.

Although the combustion chamber of the boiler has been reduced by using the surface combustion type burner, it is necessary to reduce the heat transfer surface such as a water pipe in order to further reduce the size of the combustion chamber. Further, in order to improve the boiler efficiency, it is necessary to use an exhaust gas heat exchanger, but on the other hand, there is a problem that the compactness is sacrificed. An object of the present invention is to provide an exhaust heat recovery water pipe boiler capable of solving the above-mentioned problems.

[0008]

SUMMARY OF THE INVENTION An exhaust heat recovery water pipe boiler according to the present invention allows heat exchange between flue gas discharged from a combustor section and premixed gas fuel supplied to the combustor section. In a waste heat recovery water pipe boiler provided with an exhaust gas heat exchanger, the exhaust gas heat exchanger flows through a metal fiber sintered mat inside a first region where the fuel premixed gas flows through a partition wall, and the combustion exhaust gas flows through the first region. And a combustor section integrally formed by using a downstream surface layer of the first area as a combustion area; and opposing a combustion area of a downstream surface layer of the first area. And an exhaust gas recirculation means for mixing a part of the combustion exhaust gas with the premixed fuel gas is provided.

[0009]

In the above construction, since the combustor section is integrally formed with the exhaust gas heat exchanger made of the metal fiber sintered mat, the size can be reduced. Further, compactness can be achieved by a configuration in which the water pipe group is arranged to face the combustion area of the combustor section.

[0010] Further, by recirculating a part of the combustion exhaust gas and mixing it with the premixed gas fuel, the oxygen concentration in the premixed gas fuel is reduced, but the excess air ratio can be reduced. Therefore, the amount of surplus air finally exhausted is reduced, and as a result, the thermal efficiency is improved.

On the other hand, although the ignitability generally deteriorates as the oxygen concentration decreases, in the present invention, a premixed gas using an exhaust gas heat exchanger is used instead of the surface combustion method using a metal fiber sintered mat. By using fuel heating together, stable combustion can be ensured even under low oxygen concentration conditions. Furthermore, since the surface combustion method mainly utilizes heat transfer by radiation, it is possible to reduce the temperature of the flame. (Low NO _X combustion is achieved.)

[0012]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a water tube group constituted by a plurality of water tubes 1a; 3, a heat exchanger for recovering thermal energy of boiler exhaust gas and preheating a premixed gas fuel supplied;
And a combustion air 6 are mixed in advance to produce a premixed gas fuel, 7 is a chimney, 8 is a steam header, and 9 is a blower as a means for sending a part of the combustion exhaust gas to the premixed fuel gas and recirculating it. is there.

The heat exchanger 3 is composed of a metal fiber sintered mat 3d, and a combustion zone 2a of the combustor section 2 is integrally formed in a part thereof. Heat exchanger 3 is metal fiber sintered mat 3d
Is divided by a partition 3c into a first region 3a through which the premixed gas fuel flows and a second region 3b through which the combustion exhaust gas flows.

The partition walls 3c are formed so as not to cut the fibers constituting the metal fiber sintered mat. Examples of the method of forming the partition include, for example, a method of impregnating a void portion of the metal fiber sintered mat with a metal or ceramic or the like in the cross section where the partition is formed, or a method of forming the metal fiber sintered mat in the cross section where the partition is formed. There is a method of crushing the steel and attaching a steel strip to the crushing allowance. In this example, the latter method is used.

In this example, the latter method is used, and three rows of the first regions 3b are located between the four rows of the second regions 3b.
It is configured to incorporate the region 3a. The thickness of this mat is 40 mm.

A combustor section 2 having a surface layer as a combustion zone 2a is integrally formed downstream of the first area 3a. When the supplied premixed gas fuel is burned in the combustor section 2, the fiber mat constituting the combustion zone 2a glows red and emits radiant heat. The radiant heat a causes the water tube group 1
Is radiantly heated.

In this case, as shown in FIG. 1, only two water pipes 1a are arranged in opposition to the combustion zone 2a so as to absorb radiant heat in any of the water pipes 1a. In this way, by increasing the number of high-temperature radiant heat transfer portions, the heat transfer surface can be reduced and the size can be reduced.

The high-temperature combustion gas flows in the second region 3 as shown by the arrow b.
b. At this time, heat is applied to the fiber mat in the region, and the fiber mat is discharged as low-temperature exhaust gas. Second area 3
The heat recovered in b is transmitted through the metal fibers of the fiber mat as indicated by arrow c, and is conducted to the first region 3a.

On the other hand, the exhaust gas that has passed through the second region 3b is:
Part of the mixture is mixed into the premixed gas fuel by a blower as exhaust gas recirculation means 9, and the rest is discharged from the chimney 7 to the atmosphere.

The premixed gas fuel mixed with the recirculated exhaust gas passes through the first region 3a of the heat exchanger section as indicated by an arrow d. In this region, thermal energy is transferred from the metal fibers of the fiber mat and the temperature of the premixed gas fuel rises.

The premixed gas fuel having a high temperature burns in the combustion zone 2a on the surface layer downstream of the first zone 3a. here,
Since the amount of fuel to be supplied is limited to the amount required to generate sufficient radiant heat when the surface of the metal fiber sintered mat is red-heated, the flame temperature is lower than that of the conventional burner, for example, 1
It can be suppressed to about 300 ° C and NO in exhaust gas
_X can be suppressed significantly.

In the above embodiment, the thickness of the mat is 40
Although it is mm, it is changed depending on the combustion load and the temperature of the exhaust gas outlet. If more heat is taken, the thickness is increased, and if less heat is taken, the thickness of the mat is reduced.

[0023]

【The invention's effect】

1) The installation area is extremely compact as a facility compared to a conventional water tube boiler. In the conventional water tube boiler, only the first row of the tube group is effective for radiation, and the structure is mainly designed to recover the water by convection heat transfer, whereas in the present invention, the radiant heat is actively By using a burner that is provided in the above-mentioned manner, and by arranging a group of water pipes in the combustion area of the burner, it is possible to reduce the number of water pipes by achieving heat recovery by high-temperature radiant heat transfer.

FIG. 3 shows that the combustion unit can be made compact by integrally forming the combustor section with the exhaust gas heat exchanger. FIG. 3 shows the installation area ratio in comparison with the comparative example.

Comparative Example 1 is a case of a boiler using the surface combustion burner shown in FIG. 2 and recovering heat of combustion exhaust gas by a heat exchanger, and Comparative Example 2 is most commonly used. This is a case of a boiler using a diffusion combustion burner and recovering heat of combustion exhaust gas by a heat exchanger.

2) Boiler efficiency is increased. The first reason is that extra oxygen is not added in excess of the amount of oxygen required for the injected fuel. In conventional boilers, excess air ratio (value of supply air amount divided by theoretical air amount)
Is about 1.10 and discharges 0.1 excess air. In this method, since the fuel gas before combustion is preheated in the heat exchanger section, the excess air ratio can be made closer to 1.0 than before. Actually, since the operation is performed at about 1.02, almost no surplus air is discharged, and accordingly, the amount of exhaust gas is reduced, and the amount of heat that is discarded outside can be reduced.

Second, heat is exchanged in the fiber mat, and the temperature of the exhaust gas at the outlet of the heat exchanger is reduced to 90 ° C. Compared to a temperature of about 120 ° C. in the past, the amount of heat to be discarded to the outside can be reduced, and the steam generated by combustion liquefies to water, so that the heat of solidification can be used effectively. The solidified water is generated in the mat, accumulated in the drain reservoir, and discharged out of the apparatus.

Thus, as shown in FIG. 4, the boiler efficiency of the present invention was considerably improved as compared with the conventional comparative examples 1 and 2. 3) NO _X in the exhaust gas is significantly reduced.

The reason is that the exhaust gas is recirculated in the present invention in comparison with the conventional combustion of a diffusion burner or the combustion of a premix burner burning near a stoichiometric mixture ratio. The maximum temperature of the flame is 1300 ° C
Can be lowered to the extent. This is because it is possible to suppress thermal NO _X generated by combustion at 1400 ° C. or more.

As a result, as shown in FIG.
And compared to 2, it is possible to remarkably low NO _X combustion. 4) Very stable combustion even with lean gas combustion.

In general, in the combustion of a lean gas, a flame is very unstable and easily blows out. However, in the present invention, a surface combustion method using a metal fiber sintered mat is employed, and the metal fiber is exchanged by exhaust gas heat exchange. Since the sintered mat itself and the premixed gas fuel are heated, the base of the flame is difficult to peel off,
Very stable combustion.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a boiler of the present invention.

FIG. 2 shows a comparative example 1 using a surface burning burner;
Explanatory drawing of the boiler which aimed at the heat recovery of the combustion exhaust gas by the heat exchanger.

FIG. 3 is a comparative explanatory view of an installation area.

FIG. 4 is a comparative explanatory diagram of boiler efficiency.

FIG. 5 is a comparative explanatory diagram of NO _X concentration.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Water pipe group, 2 ... Combustor part, 2a ... Combustion area, 3 ... Heat exchanger, 3a ... 1st area, 3b ... 2nd area, 3c ... Partition wall, 3
d: sintered metal fiber mat, 9: exhaust gas recirculation means.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kozo Asano 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Koji Ishiseki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Koji Yamamoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References Jiro 48-32944 (JP, U) (58) Field surveyed (Int .Cl. ⁶ , DB name) F22B 31/08 F23L 15/04

Claims (1)

(57) [Claims] 1. An exhaust heat recovery water pipe boiler provided with an exhaust gas heat exchanger for performing heat exchange between flue gas discharged from a combustor unit and premixed gas fuel supplied to the combustor unit, The exhaust gas heat exchanger, the inside of the metal fiber sintered mat,
A first region through which the premixed gas fuel flows through a partition;
A combustion chamber is integrally formed by dividing the combustion gas into a second region through which the flue gas flows, and a downstream surface layer of the first region as a combustion region. A downstream surface layer of the first region A water pipe group disposed opposite to the combustion zone of the above, and further provided with exhaust gas recirculation means for mixing a part of the combustion exhaust gas into the premixed gas fuel.