JP2003083509A - Boiler for performing recirculation combustion of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize both prevention of generation of photochemical smog and maintenance of high efficiency of a boiler. SOLUTION: The boiler 1 is provided with combustion air amount regulators 8, 9 which regulate a supply amount of combustion air supplied to a combustion device 3 and an exhaust gas circulation passage 5 through which exhaust gas after combustion is circulated to the combustion device. The boiler 1 enables recirculation combustion of the exhaust gas. In the boiler 1, an exhaust gas circulation amount regulator 6 which regulates an amount of the exhaust gas circulating to the combustion chamber is installed and a switch of operation and suspension of recirculation of the exhaust gas is kept possible. In the case that the photochemical smog does not generate, the recirculation combustion of the exhaust gas is not operated and the supply amount of the combustion air is made an amount of air for an EGR suspension state. In the case that the photochemical smog generates, the recirculation combustion of the exhaust gas is operated and the supply amount of the combustion air is made an amount of air for an EGR operation state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler which performs exhaust gas recirculation combustion as required.

[0002]

2. Description of the Related Art When a flame is burned, NOx (nitrogen oxide) which causes photochemical smog is generated. When NOx receives strong ultraviolet rays from the sun, NOx undergoes a photochemical reaction to become a photochemical oxidant such as ozone. During the daytime when the sun is strong, the temperature is high, and the wind is weak, the concentration of the photochemical oxidant increases, and the photochemical oxidant accumulates in a white mist, which is photochemical smog.
Photochemical smog can cause health problems. When the air pollution becomes significant, the prefectural governor will be informed of the situation and ask the smokers and car users to cooperate in reducing the smoke emissions and restricting vehicle operation. Yes (Air Pollution Control Law No. 23
Article). For reference, Figure 3 shows the standards for issuing warnings and measures for emergency cooperation factories and business establishments in Tokyo.

Boilers that burn flames have N
Although Ox is generated, NOx has an adverse effect on the environment as described above, so efforts are being made to reduce the amount of NOx generated. Exhaust gas recirculation combustion is one of the means for reducing the NOx generation amount. When NOx is burned at a high temperature, a large amount of NOx is generated, and when the combustion temperature is low, the generated amount is small. When the exhaust gas is mixed with the combustion air, the oxygen concentration of the exhaust gas is low because the exhaust gas has a small amount of oxygen, and when the combustion air having a low oxygen concentration is used for combustion, the local high temperature region of the flame disappears.
The NOx generation amount decreases as the flame temperature decreases. However, since the amount of oxygen required for combustion does not change, it is necessary to increase the combustion air supply amount as much as the oxygen concentration is low during exhaust gas recirculation combustion.If the combustion air amount is increased, it will be discharged together with the exhaust gas. Since the amount of heat generated is large, the efficiency of the boiler will decrease.

In the case of a boiler having no means for suppressing the NOx generation amount, even if it is necessary to reduce the NOx generation amount due to an increase in the photochemical oxidant concentration, the NOx generation amount can be reduced only by cutting the operation of the boiler. I can't. However, cutting the operation of the boiler means
Since the operation of the entire system using steam is cut, it is not easy to cut the operation to reduce the NOx generation amount.

[0005]

The problem to be solved by the present invention is to prevent the generation of photochemical smog and keep the efficiency of the boiler high.

[0006]

According to a first aspect of the present invention, there is provided a combustion device for supplying fuel and combustion air to perform combustion.
An air blower that supplies combustion air to the combustion device, a combustion air amount adjustment device that adjusts the supply amount of combustion air that is supplied to the combustion device, and an exhaust gas circulation path that circulates the exhaust gas after combustion to the combustion device Exhaust gas circulation amount that adjusts the amount of exhaust gas that circulates to the combustion device in a boiler that enables circulating combustion and that adjusts the combustion air supply amount to supply the oxygen amount that corresponds to the fuel supply amount A control device is provided, and it is possible to switch between execution and stop of exhaust gas recirculation by the exhaust gas circulation amount control device.The above-mentioned combustion air amount control device uses the combustion air supply amount when exhaust gas recirculation is not performed. An EGR stop air flow rate and an EG that is the combustion air supply rate when exhaust gas recirculation is performed
The amount of air for R execution is set, the amount of combustion air is adjusted based on the amount of air for EGR stop when exhaust gas recirculation is stopped, and the amount of combustion air is based on the amount of air for EGR execution during exhaust gas recirculation. It is characterized by performing adjustment of.

According to a second aspect of the present invention, in the boiler that performs the exhaust gas recirculation combustion, the combustion amount during boiler combustion is controlled in two stages of high combustion and low combustion.
For R stop air volume, set high combustion air volume and low combustion air volume when exhaust gas recirculation is stopped, and set EGR implementation air volume for high combustion and low combustion air volume when exhaust gas recirculation is implemented. The set air volume for the EGR stop air volume is set to be smaller than the set air volume for the EGR execution air volume.

According to a third aspect of the present invention, in the boiler for performing the exhaust gas recirculation combustion, the combustion air supply amount adjusting device includes a first damper for setting an EGR stop time air amount,
It consists of a second damper that sets the air flow rate for EGR execution, and when the exhaust gas recirculation is stopped, the second damper is fixed in the open state and the opening of the first damper is adjusted according to the combustion amount to burn the combustion air. Adjust the supply amount, and when recirculating exhaust gas,
The first damper is fixed in the open state and the second damper is used according to the combustion amount.
It is characterized in that the supply amount of combustion air is adjusted by adjusting the opening degree of the damper.

According to a fourth aspect of the present invention, in the boiler for performing the exhaust gas recirculation combustion, exhaust gas recirculation is carried out under weather conditions where photochemical smog is generated, and exhaust gas recirculation is carried out under weather conditions where photochemical smog is not generated. It is characterized by not performing circulation.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of the boiler 1 in one embodiment, and FIG. 2 is its time chart. The boiler 1 is provided with a combustion chamber (not shown) inside, and a combustion device 3 is provided above the combustion chamber. A combustion air supply passage 7 is connected to the combustion device 3, and a blower 10 is connected to the other end of the combustion air supply passage 7. The blower 10 pressurizes the taken-in air and sends it to the combustion device 3 through the combustion air supply passage 7. Boiler 1
An exhaust passage 4 for taking out exhaust gas after combustion from the combustion chamber is provided in the lower part of the exhaust gas, and an exhaust gas circulation passage 5 branched from the exhaust passage 4 is connected in the middle of the exhaust passage 4, and the other end of the exhaust gas circulation passage 5 is The blower 10 is connected to the pipe taking in air. An EGR damper 6 as an exhaust gas circulation amount adjusting device is provided in the middle of the exhaust gas circulation path 5, and a first damper 8 and a second damper 9 as combustion air amount adjusting devices are provided in the middle of the combustion air supply path 7. An air supply control device 2 for controlling the operation of the blower 10, the EGR damper 6, the first damper 8, and the second damper 9 is provided, and the air supply control device 2 is connected to each device by a signal line.

The combustion device 3 of the boiler 1 is supplied with fuel and combustion air to perform combustion. If the amount of combustion during boiler combustion is controlled in two stages, high combustion and low combustion,
The supply amount of high combustion fuel and high combustion air and the supply amount of low combustion fuel and low combustion air are set in advance, and the combustion amount is controlled by controlling the supply amounts of fuel and combustion air. . The amount of combustion air is adjusted by the first damper 8 and the second damper 9 that adjust the flow passage area of the combustion air supply passage 7. When exhaust gas recirculation is not carried out for the first damper 8, an opening for high air volume for combustion and an opening for low air volume for combustion are set, and the exhaust gas recirculation for the second damper 9 is made. In the case where is performed, the opening degree that provides the high combustion air volume and the opening degree that provides the low combustion air volume are set.

The exhaust gas recirculation combustion is carried out by opening the EGR damper 6 which controls the flow passage area of the exhaust gas circulation passage 5 at two points of full opening and full closing. When the EGR damper 6 is fully closed, exhaust gas does not flow to the blower 10,
The air supplied by the blower 10 is only the normal air taken in from the outside of the boiler. When the EGR damper 6 is fully opened,
Since the exhaust gas in the exhaust passage 4 can pass through the exhaust gas circulation passage 5, a flow of the exhaust gas toward the blower 10 is generated, and the air supplied by the blower 10 is supplied from the outside through the normal air and the exhaust passage 4. It becomes air with a low oxygen concentration, which is a mixture of the taken-in exhaust gas. The case where exhaust gas recirculation is performed is when the EGR damper 6 is fully opened.
When the damper 6 is fully closed, the exhaust gas recirculation is stopped.

The EGR damper 6 is operated by the air supply control device 2. The air supply control device 2 adjusts the combustion air supply amount by the first damper 8 when the exhaust gas recirculation is stopped, and when the exhaust gas recirculation is carried out. The amount of combustion air supplied is adjusted by the two dampers 9. Whether or not to carry out exhaust gas recirculation can be switched by an input to the air supply control device 2.

The damper opening set for the first damper 8 corresponds to a low combustion air volume and a high combustion air volume when combustion is performed with air having a normal oxygen concentration without exhaust gas recirculation. Is set to the second damper 9 and the damper opening set to the second damper 9 is set to a low combustion air volume and a high combustion amount in the case of performing combustion with air having a reduced oxygen concentration by performing exhaust gas recirculation. Set the opening for the combustion air volume. The larger the amount of combustion, the larger the amount of oxygen required for combustion, and the smaller the amount of combustion, the smaller the amount of oxygen required for combustion. Therefore, for low and high combustion air volumes, the high combustion air volume is larger. To increase the opening. If the amount of combustion is the same, the amount of oxygen required for combustion is the same, but if the oxygen concentration is low, the amount of oxygen contained in a certain amount of combustion air will decrease, so the amount of combustion air supplied will be increased. Will be needed. Therefore, the low-combustion opening and the high-combustion opening set in the second damper 9 are lower than the low-combustion opening and the high-combustion opening set in the first damper 8. Make sure that the supply is large.

FIG. 2 is a time chart showing an example of air volume adjustment by the EGR damper 6, the first damper 8 and the second damper 9. Initially, the air supply control device 2 is set so that exhaust gas recirculation is not performed, and it starts from the state when exhaust gas recirculation is stopped. When performing combustion without exhaust gas recirculation, the EGR damper 6 is fixed to be fully closed and the second damper 9 is fixed to be fully open, and the opening degree of the first damper 8 is changed according to the combustion amount for combustion. Adjust the air supply. in this case,
Since the EGR damper 6 is closed, the exhaust gas in the exhaust passage 4 does not enter the blower 10, and the blower 10 sends combustion air having a normal oxygen concentration. The second damper 9 is fixed in a fully opened state, and the opening of the first damper 8 is adjusted by the combustion amount. Therefore, the air volume adjusted by the first damper 8 becomes the combustion air supply amount sent to the combustion device 3.

When the exhaust gas recirculation combustion execution is input to the air supply control device 2, the air supply control device 2 moves the EGR damper 6 from fully closed to fully open, the first damper 8 is fully opened, and the second damper 9 is opened. Changes to an opening that matches the amount of combustion. When the EGR damper 6 is opened, the blower 10 sucks the exhaust gas in the exhaust passage 4, so that the oxygen concentration of the combustion air sent from the blower 10 to the combustion device 3 decreases. When performing exhaust gas recirculation combustion, the first damper 8 should be fully open and fixed,
The second damper 9 adjusts the opening according to the amount of combustion. Therefore, the air volume adjusted by the second damper 9 becomes the combustion air supply amount sent to the combustion device 3, and the set opening degree of the second damper 9 has a lower oxygen concentration than the set opening degree of the first damper 8. Since the amount is increased as much as there is, the supply amount of combustion air becomes larger than when the exhaust gas recirculation is stopped.

The purpose of the exhaust gas recirculation combustion is to reduce the NOx generation amount that causes photochemical smog. By reducing the NOx generation amount, it is possible to prevent an increase in the photochemical oxidant concentration. However, since photochemical oxidants are generated by photochemical reactions caused by receiving the strong ultraviolet rays of the sun, the photochemical oxidant concentration does not rise and photochemical smog does not occur unless the weather conditions are high, and NOx emission Does not directly lead to an increase in photochemical oxidant concentration. In other words, even if the efficiency of the boiler is sacrificed, N
Reducing the amount of Ox generated is effective under the weather conditions where photochemical smog occurs, but is not effective under the weather conditions where photochemical smog hardly occurs.

In the case of exhaust gas recirculation combustion, it is necessary to increase the amount of combustion air supplied, so that the amount of exhaust gas increases and the amount of heat discharged together with the exhaust gas increases, so the efficiency of the boiler decreases. Exhaust gas recirculation combustion can obtain the effect of reducing the NOx generation amount, but from the viewpoint of effective use of fuel, it is better not to carry out exhaust gas recirculation combustion. In addition, if the efficiency decreases, the amount of carbon dioxide generated increases because it is necessary to increase the amount of combustion. Although carbon dioxide is not a direct pollutant, it is a greenhouse gas that causes global warming and should be reduced. Therefore, from the perspective of reducing carbon dioxide, it is better not to carry out exhaust gas recirculation combustion. become.

When exhaust gas recirculation combustion is performed, the amount of combustion air to be adjusted in accordance with the combustion amount can be adjusted so that the air flow rate can be adjusted depending on whether exhaust gas recirculation is performed or when exhaust gas recirculation is stopped. Proper combustion can be performed even when it is not performed, and exhaust gas recirculation combustion can be performed only when necessary. If exhaust gas recirculation combustion is performed when the photochemical oxidant concentration increases, the NOx generation amount can be reduced without reducing the boiler operation, and the photochemical smog can be suppressed. On the contrary, when the photochemical oxidant concentration does not increase, by not performing exhaust gas recirculation, the efficiency of the boiler can be kept high, and the fuel consumption is smaller than that of a boiler that constantly performs exhaust gas recirculation combustion. Also, the amount of carbon dioxide generated can be reduced.

It is also known that the blower is provided with an inverter circuit or the like and the rotation speed of the blower is changed to adjust the supply amount of combustion air. May be changed. In this case, the rotation speed is set by the EGR stop air volume when exhaust gas recirculation is not executed and the EGR execution air flow when exhaust gas recirculation is executed, and the rotation speed is set when EGR is stopped. It is set so that the one for use is lower. When the combustion amount is controlled in two stages of high combustion and low combustion as in the embodiment, the high combustion rotation speed and the low combustion rotation speed at the time of exhaust gas recirculation and the exhaust gas recirculation at the time of exhaust gas recirculation are executed. Set the high combustion speed and the low combustion speed.

[0021]

By implementing the present invention, it is possible to reduce the NOx generation amount when the photochemical oxidant concentration is high and to improve the efficiency of the boiler when the photochemical oxidant concentration is low.

[Brief description of drawings]

FIG. 1 is a flow chart of an embodiment of the present invention.

FIG. 2 is a time chart of an embodiment of the present invention.

[Figure 3] Warning issuing standards and measures in Tokyo

[Explanation of symbols]

1 boiler 2 Air supply control device 3 Combustion device 4 exhaust passage 5 Exhaust gas circulation 6 EGR damper 7 Combustion air supply path 8 First damper 9 Second damper 10 blower

Claims (4)

[Claims] 1. A combustion device for supplying fuel and combustion air for combustion, a blower for supplying combustion air to the combustion device, and a combustion air amount adjustment for adjusting the supply amount of combustion air supplied to the combustion device. A boiler that enables exhaust gas recirculation combustion by providing an exhaust gas circulation path that circulates the exhaust gas after combustion to the combustion device, and adjusts the combustion air supply amount to supply the oxygen amount corresponding to the fuel supply amount. In the boiler that is being adjusted, an exhaust gas circulation control device is installed to control the amount of exhaust gas that circulates to the combustion device.The exhaust gas circulation control device enables switching between execution and stop of exhaust gas recirculation. The EGR stop air volume, which is the combustion air supply amount when exhaust gas recirculation is not performed, and the EGR air flow amount when combustion gas is supplied, when the exhaust gas recirculation is performed The air flow rate is set, and when the exhaust gas recirculation is stopped, the combustion air volume is adjusted based on the EGR stop air volume, and when the exhaust gas recirculation is performed, the combustion air volume is adjusted based on the EGR execution air volume. A boiler that performs exhaust gas recirculation combustion characterized by performing. 2. The boiler for performing exhaust gas recirculation combustion according to claim 1, wherein the combustion amount during boiler combustion is controlled in two stages, high combustion and low combustion, and the exhaust gas amount for EGR stop is the exhaust gas. Set the high combustion air volume and low combustion air volume at the time of recirculation stop, and set the high combustion air volume and low combustion air volume at the time of exhaust gas recirculation to EGR execution air volume for EGR stop A boiler for performing exhaust gas recirculation combustion, wherein the set air volume of the air volume is set to be smaller than the set air volume of the EGR implementation air volume. 3. The boiler for performing exhaust gas recirculation combustion according to claim 1, wherein the combustion air supply amount adjusting device includes a first damper for setting an EGR stop air amount and an EG.
It consists of a second damper that sets the air flow rate for R execution, and when the exhaust gas recirculation is stopped, the second damper is fixed in the open state and the opening degree of the first damper is adjusted according to the combustion amount. When the exhaust gas recirculation is carried out by adjusting the supply amount,
A boiler that performs exhaust gas recirculation combustion, wherein the damper is fixed in an open state and the opening amount of the second damper is adjusted according to the combustion amount to adjust the supply amount of combustion air. 4. The boiler for exhaust gas recirculation combustion according to any one of claims 1 to 3, wherein exhaust gas recirculation is performed under weather conditions where photochemical smog occurs, and under weather conditions where photochemical smog does not occur. A method for operating a boiler that performs exhaust gas recirculation combustion, characterized in that exhaust gas recirculation is not performed.