JPH08303716A - Recirculating method of waste gas of combustion and device employed for said method - Google Patents

Abstract

PURPOSE: To prevent the deterioration of a catalyst for a denitrating device, corrosion of instruments and useless consumption of ammonia upon low load operation by a method wherein the other end of a gas recirculating duct is connected between the connecting position of the bypass duct of an economizer in a gas discharging pipe and the denitrating device. CONSTITUTION: The waste gas (b) of combustion is mixed into combustion air (a) through a recirculating duct 25 after joining at a connecting position between a gas discharging pipe 13 and the bypass duct 14 of an economizer. Accordingly, when the opening degree of a bypass damper 15b for the bypass duct 14 of the economizer is increased by a controller 23 based on the measuring signal of a temperature measuring device 22, high-temperature waste gas (b) of combustion can be conducted sufficiently into the bypass duct 14 of the economizer even when the load of a boiler has become low and the total amount of waste gas (b) of combustion conducted through the inside of a rear heat transfer unit 3 is reduced whereby the temperature of waste gas (b) of combustion at the inlet port of a denitration device 18 can be retained at a value higher than a predetermined temperature at all times. According to this method, the deterioration of a catalyst for the denitration device 18, the corrosion of instruments and the wasteful consumption of ammonia can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion exhaust gas recirculation method and an apparatus used for the method.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional boiler. The boiler 1 comprises a furnace 2 and a rear heat transfer section 3 provided at the rear of the furnace 2. An air supply pipe 5 for supplying combustion air a to the combustion burner 4 is connected to 2.

Further, in the illustrated case, the rear heat transfer section 3 is divided into a front chamber 7 close to the furnace 2 and a rear chamber 8 remote from the furnace 2 by the partition wall 6 at the upper inside thereof. A reheater 9 is disposed in the chamber 7, and a superheater 10 is disposed in the rear chamber 8.
A control damper 11 for adjusting the flow rate of the combustion exhaust gas b flowing through both the front chamber 7 and the rear chamber 8 is disposed at the lower ends of the front chamber 7 and the rear chamber 8.

There is no partition below the inside of the rear heat transfer section 3 described above, and a economizer 12 is arranged inside. Further, a gas discharge pipe 13 is disposed below the economizer 12 of the rear heat transfer section 3.

Further, there is provided a economizer bypass duct 14 having one end connected between the superheater 10 and the economizer 12 of the rear heat transfer section 3 and the other end connected to the gas discharge pipe 13. Bypassing the economizer 12, the hot exhaust gas b before passing through the economizer 12 is sent to the gas discharge pipe 13.

A midway part of the economizer bypass duct 14 flows in the economizer bypass duct 14 and a shut-off damper 15a for isolating high temperature combustion exhaust gas b flowing in the economizer bypass duct 14. High temperature combustion exhaust gas b
A bypass damper 15b for adjusting the flow rate of the gas is supplied to the gas exhaust pipe 13 through the economizer 12 in the rear heat transfer section 3 on the upstream side of the connection with the economizer bypass duct 14. After that, a damper 16 for adjusting the flow rate of the combustion exhaust gas b flowing in the gas exhaust pipe 13 is provided.

At the connecting portion between the gas exhaust pipe 13 and the economizer bypass duct 14, high temperature combustion exhaust gas b flowing in the economizer bypass duct 14 and combustion exhaust gas b flowing in the gas exhaust pipe 13 are connected. Gas mixer 17 for mixing with
Is provided, and a denitration device 18 for treating nitrogen oxides contained in the combustion exhaust gas b is provided further downstream of the gas mixer 17 of the gas exhaust pipe 13. still,
Reference numeral 24 in the figure denotes an ammonia supply nozzle for supplying ammonia to the inlet of the denitration device 18.

Further, there is provided a gas recirculation duct 19 having one end connected to the air supply pipe 5 and the other end connected to the lower end position of the rear heat transfer section 3, and a midway portion of the gas recirculation duct 19 is provided. Is provided with a circulation fan 20 for taking in the combustion exhaust gas b in the rear heat transfer section 3, and also the air supply pipe 5
A gas mixer 21 for mixing the combustion air a in the air supply pipe 5 and the combustion exhaust gas b taken in from the rear heat transfer section 3 is provided at the connection between the gas recirculation duct 19 and the gas recirculation duct 19. Has been done.

Further, a temperature measuring device 22 for measuring the temperature of the combustion exhaust gas b flowing through the inlet of the denitration device 18 is provided, and the economizer bypass duct 14 based on the signal measured by the temperature measuring device 22. Control device 2 for adjusting the opening / closing opening of the bypass damper 15b of the vehicle and the damper 16 of the gas exhaust pipe 13
3 is provided.

Usually, the gas discharge pipe 13 of the boiler 1 described above
In the denitration device 18 connected to the denitration device, if the temperature of the combustion exhaust gas b on the inlet side of the denitration device 18 is not maintained above a predetermined temperature, even if ammonia is supplied from the ammonia supply nozzle 24 at the inlet part of the denitration device 18, The unreacted ammonia which is not sufficiently used for the reaction reacts with the sulfur content (SO ₃ ) in the combustion exhaust gas b to generate ammonium sulfate, and this ammonium sulfate deteriorates the catalyst of the denitration device 18 or is used in the downstream equipment. Since there is a problem that it adheres and corrodes the equipment, and ammonia is wastefully consumed and becomes uneconomical, it is necessary to reliably maintain the temperature of the combustion exhaust gas b on the inlet side of the denitration device 18 at a predetermined temperature or higher. is there.

Therefore, when the flow rate of the combustion exhaust gas b decreases and the temperature of the combustion exhaust gas b at the inlet side of the denitration device 18 decreases when the boiler 1 has a low load, the signal measured by the temperature measuring device 22 is used as a basis. Further, the controller 23 increases the opening degree of the bypass damper 15b of the economizer bypass duct 14 to increase the high temperature combustion exhaust gas b flowing in the economizer bypass duct 14 that bypasses the economizer 12.
The temperature of the combustion exhaust gas b on the inlet side of the denitration device 18 is increased.

When the boiler 1 has a high load and the flow rate of the combustion exhaust gas b flowing through the rear heat transfer section 3 is sufficient, the temperature of the combustion exhaust gas b decreases much even after passing through the economizer 12. Therefore, it is not necessary to flow the combustion exhaust gas b through the economizer bypass duct 14, and the flow path of the economizer bypass duct 14 is closed by the shut-off damper 15a provided in the economizer bypass duct 14.

On the other hand, in the above-described boiler 1, it is prevented that the amount of NOx (nitrogen oxide) generated increases due to the combustion temperature rising due to the combustion by the combustion air a supplied to the combustion burner 4. In order to achieve this, a part of the combustion exhaust gas b is supplied to the air supply pipe 5 by the gas recirculation duct 19.
To the combustion air a before being supplied to the combustion burner 4 through the gas mixer 21 to mix the combustion exhaust gas b, and reduce the O ₂ concentration of the combustion air a supplied to the combustion burner 4. By doing so, the generation of NOx during combustion is suppressed.

[0014]

However, the conventional boiler 1
In this case, since the combustion exhaust gas b mixed with the combustion air a is taken out from the lower end of the rear heat transfer section 3, when the total amount of the combustion exhaust gas b when the load of the boiler 1 is reduced is small, the bypass damper 15b is operated. Combustion exhaust gas b sent to the economizer bypass duct 14 with a large opening (substantially fully open)
The combustion exhaust gas b flows into the gas recirculation duct 19 even if the flow rate of
4, so that the temperature of the combustion exhaust gas b at the inlet of the denitration device 18 cannot be maintained above a predetermined temperature, ammonium sulphate is generated when the load of the boiler 1 decreases, the catalyst of the denitration device 18 deteriorates, and the downstream side device There were problems such as corrosion and increased consumption of ammonia.

In view of the above situation, the present invention relates to a combustion exhaust gas recirculation method and a method thereof capable of preventing deterioration of the catalyst of the denitration device and corrosion of the equipment even when the load is low, and preventing wasteful consumption of ammonia. The purpose is to provide a device to be used.

[0016]

The method for recirculating flue gas according to the present invention comprises supplying combustion air to a furnace for combustion, and passing the flue gas generated by combustion in the furnace through a economizer. Combustion exhaust gas at the inlet of the denitrification device at the time of low load of the boiler, which is guided to the denitration device through the gas exhaust pipe, and which bypasses the combustion exhaust gas to the gas exhaust pipe from the economizer bypass duct by bypassing the economizer. Is maintained at a predetermined temperature or higher, the combustion exhaust gas downstream of the confluence point of the combustion exhaust gas from the gas exhaust pipe and the economizer bypass duct is mixed with the combustion air.

The flue gas recirculation apparatus of the present invention comprises a furnace to which an air supply pipe for supplying combustion air is connected, a reheater and a superheater provided at the rear of the furnace and above the inside of the furnace. A rear heat transfer section with a economizer in the lower inside,
A gas discharge pipe connected to a lower portion of the rear heat transfer unit and provided with a denitration device, and a carbon economizer in which one end is connected to an upper side of a economizer in the rear heat transfer unit and the other end is connected to the gas discharge pipe. Bypass duct, a bypass damper provided in the middle of the economizer bypass duct, a damper provided upstream of the connection position of the economizer bypass duct in the gas discharge pipe, and one end of the air supply pipe And a gas recirculation duct, the other end of which is connected between the denitrification device and a connection position of the gas discharge pipe with the economizer bypass duct.

[0018]

In the present invention, since the other end of the gas recirculation duct is connected between the connection position with the economizer bypass duct in the gas discharge pipe and the denitration device, the combustion exhaust gas in the rear heat transfer section is Unlike conventional equipment, it is no longer taken into the gas recirculation duct, and even when the boiler has a low load, high-temperature combustion exhaust gas can sufficiently flow through the economizer bypass duct. Can always be maintained above a predetermined temperature.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a combustion exhaust gas recirculation apparatus according to the present invention. Since the structure is substantially the same as that of the boiler 1 shown in FIG. 2, only characteristic parts will be described.

In this embodiment, the gas recirculation duct 2
One end of 5 is connected to the air supply pipe 5 through a gas mixer 21, and the other end of the gas recirculation duct 25 is connected between the gas mixer 17 and the denitration device 18 in the gas discharge pipe 13. is there.

Therefore, in the present embodiment, the combustion exhaust gas b after joining at the connection position of the gas discharge pipe 13 and the economizer bypass duct 14 is mixed with the combustion air a through the gas recirculation duct 25. Even if the boiler 1 is under a low load and the total amount of the combustion exhaust gas b flowing in the rear heat transfer section 3 is reduced, the control device 23 uses the controller 23 based on the signal measured by the temperature measuring device 22. If the opening degree of the bypass damper 15b of 14 is made large, the high temperature combustion exhaust gas b can be made to flow in the economizer bypass duct 14, and therefore the temperature of the combustion exhaust gas b at the inlet of the denitration device 18 is always kept at a predetermined value. By keeping the temperature above the temperature, deterioration of the catalyst of the denitration device 18 and corrosion of the equipment can be prevented, and wasteful consumption of ammonia can be prevented.

It should be noted that the present invention is not limited to the embodiments, and it is needless to say that various changes can be made without departing from the scope of the present invention.

[0024]

According to the present invention, since the other end of the gas recirculation duct is connected between the connection position of the gas exhaust pipe with the economizer bypass duct and the denitration device, when the boiler has a low load. In addition, since the high-temperature combustion exhaust gas can be sufficiently flown through the economizer bypass duct, the temperature of the combustion exhaust gas at the denitration device inlet can always be maintained at a predetermined temperature or higher, and therefore deterioration of the catalyst of the denitration device and corrosion of equipment can be prevented. It is possible to obtain an excellent effect that it is possible to prevent wasteful consumption of ammonia.

[Brief description of drawings]

FIG. 1 is a schematic front view showing an embodiment of a combustion exhaust gas recirculation device of the present invention.

FIG. 2 is a schematic front view showing an example of a conventional boiler.

[Explanation of symbols]

 2 Furnace 3 Rear heat transfer part 5 Air supply pipe 9 Reheater 10 Superheater 12 Cobber 13 Gas exhaust pipe 14 Cobber bypass duct 15b Bypass damper 16 Damper 18 Denitration device 25 Gas recirculation duct a Combustion air

Claims (2)

[Claims] 1. A furnace is supplied with combustion air for combustion.
The combustion exhaust gas generated by the combustion in the furnace is passed through the economizer to be guided to the denitration device via the gas exhaust pipe, and the combustion exhaust gas is bypassed to the economizer to bypass the economizer bypass duct to the gas exhaust pipe. When the combustion exhaust gas at the inlet of the denitrification device is maintained at a predetermined temperature or more at a low load of the boiler being discharged to, the combustion exhaust gas on the downstream side of the confluence of the combustion exhaust gas from the gas exhaust pipe and the economizer bypass duct A method for recirculating flue gas, in which the exhaust gas is mixed with combustion air. 2. A furnace to which an air supply pipe for supplying combustion air is connected, a reheater and a superheater which are provided at the rear of the furnace and are provided above the inside, and a economizer is provided below the inside. A rear heat transfer section, a gas discharge pipe connected to a lower portion of the rear heat transfer section and provided with a denitration device, one end connected to an upper side of the economizer in the rear heat transfer section, and the other end discharged from the gas. A economizer bypass duct connected to the pipe, a bypass damper provided in the middle of the economizer bypass duct, and a damper provided upstream from the connection position of the economizer bypass duct in the gas discharge pipe, Combustion comprising a gas recirculation duct, one end of which is connected to the air supply pipe, and the other end of which is connected between a connection position with the economizer bypass duct in the gas discharge pipe and a denitration device. Exhaust gas recirculation device.