JP2972050B2 - heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a general heating furnace such as a heating furnace, a soaking furnace and a heat treatment furnace for heating an object to be heated such as a slab, a billet or a bloom to a predetermined target temperature.

[0002]

2. Description of the Related Art Conventionally, in a heating furnace of this kind, a method is generally used in which an indirect heat exchanger is provided in a flue for energy saving, and air is preheated by sensible heat of combustion exhaust gas for combustion. However, this indirect heat exchange method has the advantage that preheated air at a constant temperature can be obtained over time, but the upper limit temperature of the preheated air is 700 mm from the viewpoint of the material and structure of the heat exchanger.
Since the temperature is limited to about ° C, there is a problem that the exhaust heat recovery efficiency is low and the fuel consumption rate of the heating furnace is high.

On the other hand, a heat storage burner method has recently been put into practical use as a method for recovering high-temperature preheated air.
In this regenerative burner system, a pair of burners having regenerators are alternately burned, the sensible heat of the combustion exhaust gas is stored in the regenerator when the burner is not burning, and the combustion air is heated by the regenerative heat storage during combustion. This method has the advantage of high exhaust heat recovery efficiency because high-temperature air of 1000 ° C or higher is obtained and low fuel consumption rate of the heating furnace, but the flame temperature rises due to the high temperature of the preheated air. As a result, the concentration of nitrogen oxides (NOx) becomes high, and the ratio of the theoretical air amount to the combustion gas amount is about 80 to 90% (for example, 84% for coke oven gas and 87% for natural gas) for ordinary fuel. However, there is a problem that the sensible heat of the combustion exhaust gas becomes excessive in terms of heat balance, and sufficient exhaust heat recovery is not performed.

On the other hand, for example, Japanese Patent Application Laid-Open No. Sho 62-155
No. 922 discloses a method for suppressing nitrogen oxides in a heat storage burner.

The feature of this technique is to suppress nitrogen oxides in the heat storage burner. To achieve this, as shown in FIG. 3, water or steam is injected into the heat storage unit 4 during combustion of the heat storage burner 2. Then, during non-combustion, water or steam is delivered to the combustion chamber 14 of the regenerator 4 via the regenerator bed 13 of the regenerator 4.

However, in the above-described method for suppressing nitrogen oxides, since water or steam is directly injected into the heat accumulator 4,
In addition to the fact that the regenerator 4 increases in size in proportion to the amount of injected steam and that the refractory of the regenerator is damaged by the injection of water, in addition to the problem that excess waste heat cannot be sufficiently recovered in terms of heat balance. there were.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has as its object the purpose of generating steam by utilizing excess exhaust gas sensible heat in terms of heat balance. It is an object of the present invention to provide a heating furnace in which the fuel consumption is reduced and nitrogen oxides are suppressed by directly blowing into a burner or a furnace of the heating furnace.

[0008]

SUMMARY OF THE INVENTION The present invention has the following features.

(1) A pair of burners having a regenerator are alternately burned, sensible heat of combustion exhaust gas is stored in a regenerator when the burner is not burning, and combustion air is heated by the heat storage during combustion. In a heating furnace of the type, a part of the combustion exhaust gas is directly taken out of the furnace through the flue from the heating furnace, and the combustion exhaust gas is indirectly heat-exchanged with cooling water to perform exhaust heat recovery,
The steam generated by the exhaust heat recovery, and none as supplied to the furnace of the burner or furnace.

(2) Condensed water of the combustion exhaust gas generated by the indirect heat exchange is used as cooling water for exhaust heat recovery.

If necessary, (3) the waste heat recovery by the cooling water is performed in the state of the pressurized water, and the steam is generated by reducing the pressure of the pressurized water immediately before supply to the burner or the furnace. .

[0012]

The heating furnace of the present invention generates steam from excess combustion exhaust gas in a thermal balance, and blows the steam directly into the burner or the heating furnace, so that the flame temperature decreases due to an increase in the amount of gas in the heating furnace. To uniformly heat and heat NOx
Can be suppressed, and the partial pressure of steam in the heating furnace increases, so that the amount of heat transferred to the object to be heated increases.

Further, since the condensed water of the combustion exhaust gas is circulated and reused as cooling water for exhaust heat recovery, the amount of cooling water used can be reduced, and the amount of steam generated increases due to an increase in the temperature of the cooling water inlet.

Further, since the exhaust heat recovery and the heat transfer are performed in the state of the pressurized water, the convective heat transfer coefficient is large and the specific volume is small as compared with the steam, so that the heat transfer area of the heat exchanger and the pipe diameter are small. small.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

As shown in FIG. 1, one or more pairs of heat storage burners 2 are attached to a furnace wall of a heating furnace 1 made of a refractory.

This heat storage burner 2 is usually arranged on both sides of the heating furnace 1 as shown in FIG. 2, and a heat storage burner 2a during combustion and a heat storage burner 2b during non-combustion form a pair. The object to be heated 3 is heated by switching and burning alternately.

That is, in the heat storage burner 2a during combustion,
The room temperature air supplied from the lower part of the heat storage unit 4 is heated by the heat storage unit 5 into high temperature preheated air, and the fuel supplied from the fuel nozzle 6 is burned by the high temperature preheated air, and heated by the high temperature combustion gas. The object to be heated 3 in the furnace 1 is heated.

Further, the combustion exhaust gas after heating the object to be heated 3 is sucked into the non-combustion heat storage burner 2b, and the regenerator 5 is heated with the high temperature combustion exhaust gas. Dissipated into the atmosphere.

On the other hand, excess combustion exhaust gas in terms of heat balance is discharged from the furnace bottom of the heating furnace 1 to the flue 7,
The heat is exchanged with the cooling water by the exhaust heat recovery device 8 installed in the air conditioner, and is discharged as low-temperature combustion exhaust gas from the chimney 9 into the atmosphere.

Here, the excess combustion exhaust gas in terms of heat balance means that the specific heat of the combustion exhaust gas and the combustion air can be regarded as substantially the same, and therefore, usually the difference between the combustion exhaust gas amount and the combustion air amount. However, in order to make the effect of steam addition more remarkable, it is of course possible to set the amount of combustion exhaust gas to be equal to or larger than the difference between the amount of combustion exhaust gas and the amount of combustion air.

On the other hand, the cooling water that has exchanged heat with the combustion exhaust gas in the exhaust heat recovery device 8 is heated and becomes steam, and this steam is supplied to the heat storage burner 2 through the steam pipe 10 to add steam to the combustion exhaust gas. Do.

As a result, the high-temperature flame generated by the high-temperature air combustion is diluted with the steam, and the combustion gas temperature becomes suitable for the uniform heating of the article 3 to be heated. Thus, the uniform heating of the article 3 and the generation of nitrogen oxides are suppressed. You.

Further, the partial pressure of the steam of the radioactive gas is increased by the addition of steam, and the heat transfer in the furnace of the heating furnace 1 is promoted.
As a result, the heating furnace can be made compact.

Further, since the generation of steam is performed by using excess combustion exhaust gas and the steam is used by itself in the heating furnace 1, the fuel consumption rate of the heating furnace 1 can be reduced.

The present invention is not limited to the above embodiment. For example, (1) steam generated by the recovery of excess exhaust heat is directly blown into the heating furnace.

(2) Recirculation and reuse of the condensed water of the flue gas generated in the heat exchange section as cooling water for exhaust heat recovery.

(3) Recovering waste heat by cooling water in the state of pressurized water, and reducing the pressure immediately before supply to the burner or the heating furnace to vaporize.

(4) Application to a batch type direct heating furnace, a radiant tube type indirect heating furnace, and the like.

It is needless to say that various changes can be made without departing from the gist of the present invention.

[0031]

According to the heating furnace of the present invention, the following excellent effects can be obtained.

(1) The excess exhaust gas sensible heat is used to generate steam in a heat balance, and this steam is used in the heating furnace system. Therefore, the unit fuel consumption of the heating furnace can be reduced.

(2) The flame temperature is reduced by the blowing of steam, so that uniform heating of the object to be heated and generation of nitrogen oxides can be suppressed.

(3) By blowing steam, the partial pressure of water vapor having gas radioactivity is increased, heat transfer in the furnace is promoted, and the furnace can be made compact.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an embodiment of a heating furnace according to the present invention.

FIG. 2 is a conceptual diagram showing a structure of a heat storage burner and a combustion system.

FIG. 3 is a conceptual diagram showing the structure of a conventional heat storage burner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2, 2a, 2b Heat storage burner 3 Heated object 4 Heat storage 5 Heat storage 6 Fuel nozzle 7 Flue 8 Exhaust heat recovery device 9 Chimney 10 Steam pipe 11 Switching valve 12 Blow nozzle 13 Heat storage floor 14 Combustion chamber

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasumasa Yoshibe 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Machinery & Plant Business Department (72) Inventor Junichi Hayashi Shintomi, Futtsu City, Chiba Prefecture 20-1 Nippon Steel Corporation Technology Development Division (56) References JP-A-6-193862 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21D 1/00 F27D 17/00 101

Claims (3)

(57) [Claims] 1. A regenerative burner system in which a pair of burners having regenerators are alternately burned, sensible heat of combustion exhaust gas is stored in a regenerator when the burner is not burning, and the combustion air is heated by the regenerative heat during combustion. In the heating furnace, a part of the flue gas is directly taken out of the furnace through the flue from the heating furnace, and the flue gas is indirectly heat-exchanged with cooling water to recover waste heat. Is supplied to a burner or a furnace of the heating furnace. 2. The heating furnace according to claim 1, wherein condensed water of the flue gas generated by the indirect heat exchange is used as cooling water for exhaust heat recovery. 3. The method according to claim 1, wherein the waste heat recovery by the cooling water is performed in a state of pressurized water, and steam is generated by reducing the pressure of the pressurized water immediately before supply to a burner or a furnace.
Or the heating furnace according to 2.