JP2013088101A - Method of cooling air preheater in heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of cooling an air preheater in a heating furnace, configured to prevent melting damage of the air preheater by supplying cooling air sufficient for the air preheater, even when an operating state of the heating furnace changes, in the heating furnace including a regenerative burner and a continuous combustion burner.SOLUTION: The air preheater 31 is cooled by discharging a heat-exchanged combustion exhaust gas discharged from the regenerative burner 11, to a flue 30 of an air preheater outlet side 31b, and allowing the combustion air supplied to the continuous combustion burner 12 to pass through the air preheater 31, in the heating furnace 10 including the regenerative burner 11 and the continuous combustion burner 12.In the cooling method, an amount of cooling air A0 necessary for cooling the air preheater 31 to its heatproof temperature or less, is calculated from an amount of combustion exhaust gas passing through the air preheater 31 and a combustion exhaust gas temperature of an air preheater inlet side 31a, and the combustion air preheated by the air preheater 31 is partially diffused to the atmosphere, when an actual measurement value A1 of the amount of combustion air supplied to the continuous combustion burner 12 is less than the amount of cooling air A0.

Description

The present invention relates to a cooling method for an air preheater provided in a heating furnace for heating a steel piece such as a slab, and in particular, air provided in a continuous heating furnace having both a regenerative burner and a continuous combustion burner. The present invention relates to a method for cooling a preheater.

A steel slab such as a slab cast by a continuous casting machine is heated to a target extraction temperature by a continuous heating furnace and then formed into a predetermined shape by a hot rolling mill. An example of a conventional continuous heating furnace for heating a steel piece is shown in FIG. The continuous heating furnace 50 is zoned in the order of the pre-tropical zone, the heating zone, and the soaking zone in order from the loading port of the steel slab S to the extraction port, and a plurality of continuous combustion burners 51 are installed in each zone. The combustion exhaust gas generated in each zone flows through a flue 56 provided at the furnace bottom (inlet side), and is released into the atmosphere from a chimney 57 installed at the end of the flue 56.
An air preheater 54 (air recuperator) that preheats combustion air supplied to the continuous combustion burner 51 using waste heat of combustion exhaust gas flowing through the flue 56 is installed in the middle of the flue 56. Yes. The combustion air is introduced into the combustion air supply system 52 from the combustion air blower 55 installed at the start end of the combustion air supply system 52 and preheated by the air preheater 54, and then each continuous combustion type via the flow control valve 53. It is supplied to the burner 51. In FIG. 4, only a part of the continuous combustion burners shows the combustion air supply system so that the drawn lines are not complicated, but similar combustion air supply systems are also connected to other continuous combustion burners. .

In the continuous heating furnace 50, in order to prevent combustion exhaust gas exceeding the heat resistance temperature (about 800 to 900 ° C.) of the air preheater 54 from flowing into the air preheater 54 and melting the air preheater 54, the air preheater 50 is prevented. A room temperature air supply system 58 for cooling 54 is connected to the flue 56 of the air preheater inlet side 54a. The normal temperature air introduced into the normal temperature air supply system 58 by the cooling air blower 59 is supplied to the air preheater input side via the flow rate adjustment valve 60 that is linked to the output value of the thermometer 61 installed on the air preheater input side 54a. 54a is supplied to the flue 56.
However, in the method of diluting the combustion exhaust gas using such room temperature air, the amount of room temperature air required for diluting the combustion exhaust gas increases as the temperature of the combustion exhaust gas increases. As a result, not only the cooling air blower 59 having a large capacity is required, but also the design of the chimney 57 in consideration of the increase in the amount of exhaust gas due to the increase in the amount of room temperature air is required.

On the other hand, in Patent Document 1, in a heating furnace equipped with a regenerative burner in the pretropical zone, a heating zone and a continuous combustion burner in the soaking zone, the low-temperature combustion exhaust gas after heat exchange discharged from the regenerative burner enters the air preheater. A method of introducing into the side flue gas is disclosed. In this method, low-temperature combustion exhaust gas discharged from a regenerative burner is used instead of room temperature air for diluting combustion exhaust gas. Therefore, the amount of exhaust gas does not increase more than necessary, and the influence on the operating conditions of the heating furnace can be minimized. However, even if the temperature of the flue gas flowing from the furnace to the flue is low and cooling of the flue gas is not required, the total amount of the low-temperature flue gas after heat exchange discharged from the regenerative burner is the flue gas on the inlet side of the air preheater Since it is introduced into the exhaust gas, there is a problem that the temperature of the combustion exhaust gas further decreases and the heat exchange efficiency by the air preheater decreases.

Therefore, in Patent Document 2, in a heating furnace having both a regenerative burner and a continuous combustion burner, a system for introducing low-temperature combustion exhaust gas after heat exchange discharged from the regenerative burner is referred to as an inlet side and an outlet side of an air preheater. The invention is disclosed in which a flow rate adjusting means is provided in each of the two systems and in both systems. In Patent Document 2, as an effect of the present invention, not only is the combustion exhaust gas cooled so that the temperature of the combustion exhaust gas passing through the air preheater does not exceed the heat resistance temperature of the air preheater, but also the combustion exhaust gas is excessively cooled. It is described that it is possible to prevent the heat loss from being reduced.

JP-A-8-199231 JP 2002-81641 A

In a heating furnace having both a regenerative burner and a continuous combustion burner described in Patent Document 1, Patent Document 2, etc., the amount of combustion exhaust gas passing through the air preheater is the combustion exhaust gas generated by the continuous combustion burner. And a part of the combustion exhaust gas generated by the regenerative burner (usually 10 to 20%, since heat exchange by the regenerator was not performed). On the other hand, the combustion air passing through the air preheater is only the amount of air used in the continuous combustion burner. Therefore, the ratio of the amount of combustion exhaust gas passing through the air preheater and the amount of combustion air varies depending on the operating state of the heating furnace. In particular, in the operating state where the combustion amount of the continuous combustion burner is small and the combustion amount of the regenerative burner is large, the amount of combustion air (cooling air amount) having a cooling action is smaller than the amount of combustion exhaust gas passing through the air preheater. Since there are few, cooling of an air preheater becomes inadequate.

Table 1 shows the results of simulation conducted to support the above findings. In this simulation, 30 in 50% load of the combustion amount is rated combustion rate of continuous combustion burner (8,000Nm ³ / h), the amount of combustion regenerative burner rated combustion rate (20,000Nm ³ / h) For each case changed to ˜80%, the ratio of the passing air amount (combustion air amount passing through the air preheater) to the passing exhaust gas amount (combustion exhaust gas amount passing through the air preheater) was calculated. The passing air amount is equal to the combustion air amount of the continuous combustion burner, and the passing exhaust gas amount is obtained by adding 10% (escape rate) of the combustion exhaust gas amount of the regenerative burner to the combustion exhaust gas amount of the continuous combustion burner. is there.

From the table, it can be seen that the ratio of the passing air amount to the passing exhaust gas amount decreases as the combustion load of the regenerative burner increases. That is, in a heating furnace having both a regenerative burner and a continuous combustion burner, when the air preheater is cooled by a conventional method, the air preheater may be insufficiently cooled depending on the operation state of the heating furnace. .

The present invention has been made in view of such circumstances, and in a heating furnace having both a regenerative burner and a continuous combustion burner, sufficient cooling air is supplied to the air preheater even if the operating state of the heating furnace fluctuates. It is an object of the present invention to provide a cooling method for an air preheater in a heating furnace, which can prevent the air preheater from being melted.

In order to achieve the above object, the present invention is a heating furnace having both a regenerative burner and a continuous combustion burner. The flue gas from the bottom of the heating furnace is externally passed through a flue having an air preheater. And the exhaust gas after the heat exchange discharged from the regenerative burner is discharged to the flue on the outlet side of the air preheater, and the combustion air supplied to the continuous combustion burner is further heated to the air preheater. In a method for cooling the air preheater through a vessel,
The amount of cooling air A0 required to cool the air preheater below its heat resistant temperature is calculated from the amount of flue gas passing through the air preheater and the flue gas temperature on the inlet side of the air preheater,
The amount of combustion air supplied to the continuous combustion burner is measured, and when the measured value A1 is less than the cooling air amount A0, part of the combustion air preheated by the air preheater is diffused into the atmosphere. It is characterized by. At that time, it is desirable that the volume A2 of the combustion air dissipating into the atmosphere is (A0-A1) or more.

In the present invention, a part of the preheated combustion air is diffused into the atmosphere, and new combustion air (cooling air) is supplied to the air preheater, thereby increasing the amount of cooling air for cooling the air preheater. Yes. Specifically, based on the amount of combustion exhaust gas passing through the air preheater and the temperature of the combustion exhaust gas, the amount of cooling air A0 required to cool the air preheater to the heat resistant temperature or less is calculated, and the continuous combustion burner is calculated. When the supplied combustion air amount is less than the cooling air amount A0, part of the preheated combustion air is released into the atmosphere. As a result, the pressure of the combustion air supply system decreases, and new combustion air having a cooling action is supplied to the air preheater.

In addition, as for the lower limit of the air preheater temperature at the time of cooling an air preheater, it is desirable to set it as the (heat-resistant temperature -50 degreeC) grade. This is because if the temperature of the air preheater is lower than this, it is disadvantageous for waste heat recovery. In addition, “exhaust gas amount” and “air amount” in this specification are an exhaust gas amount and an air amount per unit time, respectively.

In the method for cooling an air preheater in a heating furnace according to the present invention, when the amount of combustion air supplied to the continuous combustion burner is less than the amount of cooling air required to cool the air preheater to its heat resistant temperature or lower. , Dissipate some of the preheated combustion air to the atmosphere. As a result, new combustion air having a cooling action is supplied to the air preheater, so that the air preheater can be prevented from being melted even if the operating state of the heating furnace fluctuates.

It is a schematic diagram of the heating furnace to which the cooling method of the air preheater in the heating furnace which concerns on one embodiment of this invention is applied. It is a flowchart for demonstrating the procedure of the cooling method of the air preheater. It is an example of the characteristic diagram which shows the relationship between the combustion exhaust gas temperature of an air preheater entrance, and the amount of cooling air required in order to cool an air preheater to the heat resistant temperature or less. It is a schematic diagram of the conventional continuous heating furnace.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.

The schematic diagram of the heating furnace 10 to which the cooling method of the air preheater in the heating furnace which concerns on one embodiment of this invention is applied is shown in FIG. In FIG. 1, only a part of the regenerative burners shows the combustion air supply system so that the drawn lines are not complicated, but the same combustion air supply system is also connected to the other regenerative burners. Although not shown, fuel is supplied to each heat storage burner and each continuous combustion burner via a fuel supply system.

The heating furnace 10 is a continuous heating furnace that is zoned in the order of a pretropical zone, a heating zone, and a soaking zone in order from the loading port of the steel slab S to the extraction port. In this heating furnace 10, a part of the burner installed in the soaking zone is a continuous combustion burner 12, and all the other burners, that is, all the burners installed in the pre-tropical zone and the heating zone, and the soaking zone are used. The remaining burner installed is a heat storage burner 11. The steel piece S charged into the heating furnace 10 from the charging port is heated to the target extraction temperature by the regenerative burner 11 and the continuous combustion burner 12 while being transferred toward the extraction port by a transfer device (not shown). The

Combustion exhaust gas generated in the pre-tropical zone, heating zone, and soaking zone (total amount of combustion exhaust gas generated by the continuous combustion burner 12 and part of the combustion exhaust gas generated by the regenerative burner 11) It flows through the flue 30 provided on the side) and is discharged into the atmosphere from a chimney 32 installed at the end of the flue 30. An air preheater 31 that preheats combustion air supplied to the continuous combustion burner 12 using waste heat of combustion exhaust gas flowing through the flue 30 is installed in the middle of the flue 30. A thermometer 26 for measuring the temperature of the combustion exhaust gas passing through the air preheater 31 is installed in the flue 30 on the air preheater inlet side 31a.

Combustion air is supplied to the continuous combustion burner 12 via a combustion air supply system 14. A combustion air blower 16 that sucks the atmosphere and supplies the sucked air (combustion air) to the continuous combustion burner 12 is installed at the start end of the combustion air supply system 14. The combustion air introduced into the combustion air supply system 14 from the combustion air blower 16 is preheated by the air preheater 31 and then supplied to each continuous combustion burner 12 via the combustion air flow rate control valve 21. The combustion air supply system 14 between the air preheater 31 and the combustion air flow rate control valve 21 is preheated with a diffusion flow rate control valve 23 for releasing the combustion air preheated by the air preheater 31 to the atmosphere. A flow meter 24 for measuring the volume of the combustion air is provided.

The regenerative burner 11 uses two regenerative burners 11 as a set, and heats the steel piece S by an alternating combustion method in which one of the regenerative burner 11 and the other are burned alternately. Each heat storage burner 11 includes a heat storage body (not shown) for storing waste heat of combustion exhaust gas. When the combustion exhaust gas generated by the combustion of one heat storage burner 11 passes through the heat storage body of the other heat storage burner 11, the waste heat of the combustion exhaust gas is stored in the heat storage body. When the other regenerative burner 11 burns, the combustion air is preheated by passing the combustion air through the heat accumulator.

The heat storage burner 11 includes a combustion exhaust gas discharge system 17 in addition to the combustion air supply system 13. The combustion air is introduced into the combustion air supply system 13 from the combustion air blower 15 provided at the starting end of the combustion air supply system 13, and is supplied to the regenerative burner 11 via the combustion air flow rate control valve 22. The combustion air supply system 13 between the combustion air blower 15 and the combustion air flow rate control valve 22 is provided with a flow meter 25 for measuring the amount of combustion air supplied to the regenerative burner 11.

Most of the combustion exhaust gas (about 80 to 90%) generated by the heat storage burner 11 is sucked by the combustion exhaust gas fan 18 installed in the middle of the combustion exhaust gas discharge system 17 and supplies waste heat to the heat storage body. Via the fuel exhaust gas flow rate control valve 20, it is discharged to the flue 30 on the air preheater outlet 31b. In the main heating furnace 10, the entire amount of the low-temperature combustion exhaust gas after heat exchange discharged from the regenerative burner 11 is discharged to the flue 30 on the air preheater outlet 31b, so that the flue 30 on the air preheater inlet 31a is The flowing combustion exhaust gas is not excessively cooled, and a decrease in heat exchange efficiency by the air preheater 31 can be prevented.
On the other hand, the remaining combustion exhaust gas generated by the regenerative burner 11 flows through the flue 30 together with the combustion exhaust gas generated by the continuous combustion burner 12, passes through the air preheater 31, and then is released from the chimney 32 into the atmosphere. Is done.

The present heating furnace 10 is preheated by the air preheater 31 when the amount of combustion air supplied to the continuous combustion burner 12 is less than the amount of cooling air required to cool the air preheater 31 below its heat resistant temperature. A control unit 27 is provided to dissipate a part of the combustion air that has been discharged. The control unit 27 includes a flow meter 24 that measures the amount of combustion air supplied to the continuous combustion burner 12, a flow meter 25 that measures the amount of combustion air supplied to the regenerative burner 11, and an air preheater inlet 31a. Outputs of a thermometer 26 for measuring the temperature of the combustion exhaust gas and a flow meter 25a for measuring the amount of atmospheric emission from the combustion air supply system 14 are input and for controlling the amount of atmospheric emission of the preheated combustion air. A control signal is output to the diffusion flow rate control valve 23.

Next, the cooling method of the air preheater 31 in the heating furnace 10 having the above configuration will be described. In FIG. 2, the flowchart for demonstrating the procedure of the cooling method of the air preheater 31 is shown.
(ST00) Based on the fuel composition of the fuel (for example, coke oven gas) used in the regenerative burner 11 and the continuous combustion burner 12, the theoretical combustion air amount L ₀ and the theoretical wet combustion exhaust gas amount G0 _w are calculated in advance. deep.
(ST10) In the control unit 27, the combustion air amount Air1 supplied to the continuous combustion burner 12 obtained from the flow meter 24 and the continuous combustion burner 12 obtained from a flow meter installed in a fuel supply system (not shown). The combustion exhaust gas amount G1 generated by the continuous combustion burner 12 is calculated from the equation (1) based on the capacity COG1 of the fuel supplied to.
G1 = G0 _w 1 × COG1 (1)
Here, G0 _w 1 is the theoretical wet combustion exhaust gas amount generated by the continuous combustion burner 12, and is given by equation (2).
G0 _w 1 = G0 _w + (Air1 / (COG1 × L ₀ ) −1) × L ₀ (2)

(ST11) In the control unit 27, the combustion air amount Air2 supplied to the regenerative burner 11 obtained from the flow meter 25 and the regenerative burner 11 obtained from a flow meter installed in a fuel supply system (not shown) are supplied. The amount of combustion exhaust gas G2 generated by the regenerative burner 11 is calculated from the equation (3) based on the capacity COG2 of the fuel to be produced.
G2 = G0 _w 2 × COG2 (3)
Here, G0 w ₂ is a theoretical wet flue gas volume generated in the regenerative burner 11 is given by equation (4).
G0 _w 2 = G0 _w + (Air2 / (COG2 × L ₀ ) −1) × L ₀ (4)
(ST12) In the control unit 27, the amount of combustion exhaust gas G passing through the air preheater 31 is calculated from the equation (5). The escape rate in the equation is the ratio (about 10 to 20%) of the amount of combustion exhaust gas flowing through the flue 30 without being sucked into the combustion exhaust gas exhaust system 17 among the combustion exhaust gas generated by the regenerative burner 11. That is.
G = G1 + G2 × escape rate (5)

(ST13) The combustion exhaust gas temperature TG of the air preheater inlet side 31a measured by the thermometer 26 is input to the control unit 27.
(ST14) The amount of combustion exhaust gas G passing through the air preheater 31 using a characteristic diagram showing the relationship between the combustion exhaust gas temperature on the inlet side of the air preheater and the amount of cooling air necessary for cooling the air preheater From the combustion exhaust gas temperature TG on the inlet side 31a of the air preheater, the control unit 27 determines the cooling air amount A0 required to cool the air preheater 31 to the heat resistant temperature or lower.
FIG. 3 shows the amount of combustion exhaust gas passing through the air preheater as a parameter, the combustion exhaust gas temperature on the inlet side of the air preheater as the horizontal axis, and the amount of cooling air necessary for cooling the air preheater to the heat resistant temperature or less. It is an example of the characteristic diagram which took the vertical axis | shaft. When the combustion air amount of the continuous combustion burner 12 is in the upper region of the characteristic line in the figure, the amount of cooling air necessary for cooling the air preheater 31 below its heat resistant temperature is satisfied only by the combustion air. It shows that. On the other hand, when the amount of combustion air of the continuous combustion burner 12 is in the region below the characteristic line in the figure, it is necessary to dissipate a part of the preheated combustion air to the atmosphere to ensure new cooling air.

(ST15) The combustion air amount A1 supplied to the continuous combustion burner 12 is already taken into the control unit 27 as the combustion air amount (actual measurement value) Air1.
(ST16) In the control unit 27, the amount of combustion air A1 supplied to the continuous combustion burner 12 and the amount of cooling air A0 required for cooling the air preheater 31 are compared.
(ST17) When A1 ≧ A0, the current state is maintained. On the other hand, when A1 ≧ A0 is not satisfied, that is, when A0 is larger than A1, the control unit 27 calculates the atmospheric emission amount A2 of the combustion air preheated by the air preheater 31 as (A0−A1).

(ST18) A control signal is output from the control unit 27 toward the diffusion flow rate control valve 23, the diffusion flow rate control valve 23 is opened, and A2 is released into the atmosphere from the preheated combustion air. When a part of the preheated combustion air is diffused into the atmosphere, the pressure in the combustion air supply system 14 decreases, and new cooling air (combustion air having a cooling action) is supplied from the combustion air blower 16 to the combustion air supply system. 14 to cool the air preheater 31.

In the above embodiment, the combustion exhaust gas amount of the regenerative burner 11 is calculated after calculating the combustion exhaust gas amount of the continuous combustion burner 12, but it goes without saying that the reverse may be possible.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of matters described in the claims. Other possible embodiments and modifications are also included. For example, in the above embodiment, the continuous combustion burner is used only for a part of the soaking zone of the heating furnace. However, all the soaking zone burners may be used as the continuous burning burner, or the pre-tropic zone or the heating zone burner. A part of this may be a continuous combustion burner. In short, any heating furnace having both a regenerative burner and a continuous combustion burner may be used, and the arrangement and ratio of the regenerative burner and the continuous combustion burner are not limited.
Moreover, in the said embodiment, although atmospheric emission amount A2 of combustion air was set to (A0-A1), it is good also as (A0-A1) or more. However, at that time, it is desirable that the temperature of the air preheater be equal to or higher than (heat-resistant temperature -50 ° C).

10: heating furnace, 11: regenerative burner, 12: continuous combustion burner, 13, 14: combustion air supply system, 15, 16: combustion air blower, 17: combustion exhaust gas discharge system, 18: combustion exhaust gas fan, 20: Fuel exhaust gas flow rate control valve, 21, 22: Combustion air flow rate control valve, 23: Emission flow rate control valve, 24, 25, 25a: Flow meter, 26: Thermometer, 27: Control unit, 30: Flue, 31: Air Preheater, 31a: Air preheater inlet side, 31b: Air preheater outlet side, 32: Chimney, S: Steel slab

Claims (2)

In a heating furnace that has both a regenerative burner and a continuous combustion burner, flue gas from the bottom of the reheating furnace is discharged outside through a flue with an air preheater, and discharged from the regenerative burner. The exhaust gas after heat exchange is discharged to the flue on the outlet side of the air preheater, and the combustion air supplied to the continuous combustion burner is passed through the air preheater to cool the air preheater. In the method
The amount of cooling air A0 required to cool the air preheater below its heat resistant temperature is calculated from the amount of flue gas passing through the air preheater and the flue gas temperature on the inlet side of the air preheater,
The amount of combustion air supplied to the continuous combustion burner is measured, and when the measured value A1 is less than the cooling air amount A0, part of the combustion air preheated by the air preheater is diffused into the atmosphere. A method for cooling an air preheater in a heating furnace. The method for cooling an air preheater in a heating furnace according to claim 1, wherein the volume A2 of the combustion air that is diffused into the atmosphere is (A0-A1) or more.

Images