JPH1130405A - Boiler to regulate combustion exhaust gas circulation amount - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform circulation of a proper amount of combustion exhaust gas, in a boiler to effect circulation combustion of combustion exhaust gas. SOLUTION: This boiler comprises a flue 2 through which combustion exhaust gas discharged from a boiler 1 flows, an exhaust gas circulation passage 5 to connect together the flue 2 and a combustion air intake port 4 of a burner 3, and a damper 6 arranged in the middle of the exhaust circulation passage 5 and varying the flow passage area of the exhaust gas circulation passage 5. By feeding combustion exhaust gas through the exhaust gas circulation passage 5 to the burner 3, an amount of NOx generated during combustion is reduced is reduced. The so formed boiler comprises a temperature detecting device 7 to detect temperature in an exhaust gas circulation passage, and an exhaust gas circulation amount regulating device 8 to regulate the opening of the damper 6 based on temperature detected by the temperature detecting device 7. By regulating the opening of a damper 6 according to temperature in the exhaust gas circulation passage 5, a combustion exhaust gas circulation amount is regulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler in which combustion is performed using combustion air having a reduced oxygen concentration by mixing combustion exhaust gas to reduce the amount of NOx generated.

[0002]

2. Description of the Related Art In a boiler, circulating combustion of combustion exhaust gas is performed in which combustion exhaust gas is mixed with combustion air for combustion in order to reduce the amount of NOx generated. When the combustion exhaust gas is mixed with the combustion air, the oxygen concentration of the combustion air decreases, and when combustion is performed with the combustion air having the reduced oxygen concentration, the combustion flame temperature decreases, so that the NOx generation amount decreases. When performing the circulating combustion of the combustion exhaust gas, if the circulation amount of the combustion exhaust gas with respect to the combustion air amount fluctuates, NO
Since the amount of x generation increases and combustion becomes unstable, the circulation rate of the combustion exhaust gas needs to be maintained at a constant value. For example, when the three-position combustion control in which the boiler combustion amount is high combustion, low combustion, and stop is performed, the amount of combustion air used varies depending on the combustion amount, so a damper is provided in the exhaust gas circulation path. Although the amount of circulating flue gas is adjusted, the amount of flue gas flowing through the flue gas circulation path fluctuates due to changes in wind pressure in the flue even if the flow path area of the flue gas circulation path is constant. I couldn't keep it constant.

[0003]

An object of the present invention is to make it possible to circulate an appropriate amount of flue gas in a boiler that circulates combustion flue gas.

[0004]

A flue through which flue gas discharged from a boiler passes, a flue gas circulation path connecting the flue and a combustion air intake of a burner, and a flow path area of the flue gas circulation path in the middle of the flue gas circulation path A temperature detector for detecting the temperature in the exhaust gas circulation path in a boiler in which a damper for changing the amount of NOx is provided, and the combustion exhaust gas is sent to the burner through the exhaust gas circulation path to reduce the amount of NOx generated during combustion. An exhaust gas circulating amount adjusting device that adjusts the degree of opening of the damper based on the temperature detected by the temperature detecting device, and adjusts the degree of opening of the damper according to the temperature in the exhaust gas circulation path to circulate the combustion exhaust gas. Adjust the volume.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart illustrating a part of a case where a plurality of boilers 1 are installed in multiple cans. The boiler 1 is provided with a burner 3 at an upper portion, and is provided with an economizer 10 for recovering heat from combustion exhaust gas discharged from the boiler 1. The flue gas from which heat has been recovered by the economizer 10 is separated into a flue 2 composed of an individual flue section 11 and a collecting flue section 12 in which the flue gas from the individual flue section 11 is collected.
Through to the outside air. An exhaust gas circulation path 5 for extracting a part of the flue gas flowing through the individual flue section 11 is connected to the middle of the individual flue section 11, and the other end of the exhaust gas circulation path 5 is connected to the air intake 4 of the burner 3. I do. A damper 6 for adjusting the flow passage area in the exhaust gas circulation path and a temperature detecting device 7 for detecting the temperature in the exhaust gas circulation path 5 are provided in the middle of the exhaust gas circulation path 5. An exhaust gas circulation amount adjusting device 8 that is electrically connected is provided. Further, an orifice is provided as a flue reducing portion 9 on the downstream side of the connecting portion of the individual flue portion 11 with the exhaust gas circulation path 5.

The boiler 1 generates high-temperature combustion gas in the boiler 1 by burning the burner 3, and heats the water in the boiler 1 by the combustion gas to generate steam. The combustion gas is discharged from the boiler as a combustion exhaust gas after heat exchange in the boiler 1, but since the combustion exhaust gas immediately after being discharged from the boiler has much heat, the economizer 10
It is sent inside to heat the water supply. The flue gas whose temperature has been taken out from the economizer 10 has a reduced temperature.
1. It is discharged into the outside air through the collecting flue section 12. Since the exhaust gas circulation path 5 is connected in the middle of the individual flue section 11, a part of the combustion exhaust gas sent through the individual flue section 11 is sent to the exhaust gas circulation path 5 and reaches the air intake 4 of the burner. The mixture of fresh air and the circulated combustion exhaust gas is sent to the burner 3 as combustion air.

When a plurality of boilers are installed as in this embodiment, the amount and pressure of flue gas sent to the collecting flue section 12 of the flue 2 fluctuate depending on the number of boilers performing combustion. The pressure in the individual flue section 11 fluctuates due to the pressure fluctuation in the flue section 12. If the circulation rate, which is the circulation amount of the flue gas with respect to fresh air, fluctuates, the NOx generation amount increases and combustion becomes unstable. Therefore, the circulation rate of the flue gas needs to be maintained at a predetermined value. Part 1
If the pressure of one part fluctuates, the circulation rate fluctuates because the amount of combustion exhaust gas sent through the exhaust gas circulation path 5 varies even if the flow path area of the exhaust gas circulation path 5 is the same.

[0008] The amount of combustion exhaust gas sent to the burner 3 is adjusted by changing the opening of the damper 6, and the opening of the damper 6 is changed by the amount of combustion of the burner and the temperature detected by the temperature detecting device 7. . When the burner combustion amount is large, the amount of combustion air is large, so the opening degree of the damper 6 is increased. When the burner combustion amount is small, the combustion air amount is small, so that the opening degree of the damper 6 is small. The amount of circulated flue gas is adjusted by performing the above operation. However, if the pressure in the individual flue 11 fluctuates, the amount of circulated flue gas is different even if the opening degree of the damper 6 is the same. Therefore, when the temperature in the exhaust gas circulation path 5 detected by the temperature detection device 7 is low, the opening degree of the damper 6 is increased, and when the temperature in the exhaust gas circulation path 5 increases, the opening degree of the damper 6 is decreased. Combine.

When the pressure of the individual flue section 11 is low, the amount of circulating flue gas becomes small, the amount of heat possessed by the flue gas sent to the exhaust gas circulating path 5 is small, and the speed of moving through the exhaust gas circulating path 5 is low. Then, the temperature of the combustion exhaust gas in the temperature detecting device 7 becomes low. Conversely, if the pressure in the individual flue section 11 is high, the amount of circulation of the combustion gas increases, and the amount of heat held by the combustion exhaust gas sent to the exhaust gas circulation path 5 increases.
The temperature of the combustion exhaust gas at the temperature detecting device 7 becomes high because the speed of moving the inside of the inside is also high. By detecting the temperature of the exhaust gas circulation path 5, the amount of combustion exhaust gas sent through the exhaust gas circulation path 5 can be determined, and the opening of the damper 6 is adjusted according to the temperature detected by the temperature detection device 7. By doing so, the amount of combustion exhaust gas can be adjusted to be an appropriate amount.

Further, by providing the flue reducing portion 9 on the downstream side of the connecting portion of the flue gas circulation path 5 of the individual flue portion 11, the upstream side of the flue reducing portion 9 of the individual flue portion 11 is gathered. Influence of the pressure fluctuation in the flue section 12 makes it less likely to be affected, and even if the pressure in the collecting flue section 12 greatly fluctuates, the fluctuation range of the amount of combustion exhaust gas sent through the exhaust gas circulation path 5 can be reduced.

[0011]

According to the present invention, an appropriate amount of flue gas can be circulated and burned even if the pressure of the flue fluctuates.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Boiler 2 Flue 3 Burner 4 Air intake 5 Exhaust gas circulation path 6 Damper 7 Temperature detection device 8 Exhaust gas circulation amount adjustment device 9 Flue diameter reduction part 10 Economizer 11 Individual flue part 12 Collective flue part

Claims (2)

[Claims] 1. A flue through which flue gas discharged from a boiler passes, a flue gas circulation path connecting the flue and a combustion air intake of a burner, and a flow path area of the flue gas circulation path being changed in the middle of the flue gas circulation path. A temperature detector for detecting a temperature in an exhaust gas circulation path in a boiler in which a damper is provided and a combustion exhaust gas is sent to a burner through an exhaust gas circulation path to reduce the amount of NOx generated during combustion; A boiler for adjusting a combustion exhaust gas circulation amount, comprising: an exhaust gas circulation amount adjusting device that adjusts an opening degree of the damper based on a temperature detected by the device. 2. The boiler according to claim 1, wherein a flue-reducing portion is provided in the middle of the flue downstream of the exhaust-gas-circulation-path connecting portion. A boiler that adjusts the amount of exhaust gas circulation.