JP2023072285A - Combustion equipment - Google Patents

Abstract

To provide combustion equipment which can receive control optimum for stable combustion and reduction of NOx, regardless of change in fuel property.SOLUTION: Combustion equipment comprises: a gas burner ejecting gaseous fuel to a furnace; an air introduction line for introducing external air for combustion to the gas burner; an air blower disposed in the air introduction line and delivering the external air to the gas burner; an exhaust gas line guiding an exhaust gas of the furnace to the external; an exhaust gas circulation line branched from the exhaust gas line and guiding a part of the exhaust gas to the air introduction line as a circulation gas; a circulation gas adjustment portion disposed in the exhaust gas circulation line and adjusting a flow rate of the circulation gas to the air introduction line; an inlet oxygen concentration detection portion detecting oxygen concentration of mixed gas of the external air and the circulation gas at an inlet of the furnace; and a control device controlling the circulation gas adjustment portion on the basis of the oxygen concentration detected by the inlet oxygen concentration detection portion.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to combustion equipment.

For example, Patent Literature 1 discloses a boiler apparatus capable of achieving stable exhaust gas recirculation combustion and low NOx performance even when the amount of combustion air changes due to changes in furnace pressure. .

Patent Document 1 describes an air supply passage that supplies combustion air to the boiler main body, an air differential pressure sensor that detects the flow rate of combustion air flowing through the air supply passage, and a part of exhaust gas that flows through the exhaust passage. An exhaust gas recirculation path that circulates through the blower provided in the air supply path, a damper that is provided in the exhaust gas recirculation path and serves as an exhaust gas recirculation amount adjustment unit that adjusts the exhaust gas recirculation flow rate, and the damper is detected by an air differential pressure sensor. and a controller for controlling based on a signal corresponding to the calculated combustion air flow rate.

JP 2020-118359 A

As described above, in Patent Document 1, the amount of exhaust gas recirculation is controlled based on a signal corresponding to the combustion air flow rate introduced into the furnace.

However, since there is a lower limit for the oxygen concentration in the combustion air required for stable combustion for each fuel, if the amount of exhaust gas recirculation is controlled based on the detected value of the combustion air flow rate, the fuel property (fuel type of fuel, fuel composition, hydrogen content in the hydrogen-containing gaseous fuel, etc.), there is a risk that an appropriate oxygen concentration will not be supplied to the furnace and the combustion state will become unstable.

Also, part of the exhaust gas is recirculated to the combustion air in order to reduce the NOx generated by combustion, but when the amount of exhaust gas recirculation is increased in order to fully demonstrate the NOx reduction effect from an environmental point of view. Otherwise, the oxygen concentration in the combustion air supplied to the furnace may decrease, and the combustion state may become unstable.

The present disclosure has been made in view of the above problems, and aims to provide a combustion facility capable of optimal control for stable combustion and NOx reduction regardless of changes in fuel properties.

In order to achieve the above object, the combustion equipment according to the present disclosure is provided with a gas burner for ejecting gas fuel into a furnace, an air introduction line for introducing external air for combustion into the gas burner, and the air introduction line, a blower for blowing external air to the gas burner; an exhaust gas line for guiding exhaust gas from the furnace to the outside; an exhaust gas circulation line branched from the exhaust gas line for guiding part of the exhaust gas to the air introduction line; and the exhaust gas circulation. A circulating gas adjusting unit provided in the line for adjusting the flow rate of the circulating gas to the air introduction line, and an inlet oxygen concentration detecting unit for detecting the oxygen concentration of the mixed gas of the external air and the exhaust gas at the inlet of the furnace. and a control device for controlling the circulating gas adjusting section based on the oxygen concentration detected by the inlet oxygen concentration detecting section.

According to the combustion equipment of the present disclosure, by controlling the amount of exhaust gas circulation based on the oxygen concentration at the entrance of the furnace, it is possible to achieve optimum operation control in terms of stable combustion and environmental protection by reducing NOx regardless of changes in fuel properties. become.

BRIEF DESCRIPTION OF THE DRAWINGS It is a system diagram which shows roughly the structure of the combustion equipment which concerns on 1st Embodiment. It is a system diagram which shows roughly the structure of the combustion equipment which concerns on 2nd Embodiment. It is a system diagram which shows roughly the structure of the combustion equipment which concerns on 3rd Embodiment. 8 is a control flowchart of the control device of the second embodiment; FIG. 3 is a relational diagram showing the relationship between the oxygen concentration at the furnace inlet and the combustion speed (combustion limit) when gas fuels are hydrogen and methane. FIG. 4 is a relational diagram showing the relationship between the inlet oxygen concentration at the furnace inlet and the NOx concentration at the furnace outlet.

Combustion equipment according to embodiments of the present disclosure will be described below based on the drawings. This embodiment shows one aspect of the present disclosure, is not limited to this disclosure, and can be arbitrarily changed within the scope of the technical idea of the present disclosure.

<First Embodiment>
(composition)
FIG. 1 is a system diagram schematically showing the configuration of combustion equipment 1 according to the first embodiment. As shown in FIG. 1 , the combustion facility 1 includes a furnace 2 , an air introduction line 4 , a blower 6 , an exhaust gas line 8 and an exhaust gas circulation line 10 . The combustion facility 1 is, for example, a boiler, and generates steam by recovering heat from the exhaust gas G1 generated by the combustion of the gas fuel F.

The furnace 2 is configured to be supplied with and combusted with a gaseous fuel F containing hydrogen. The gas fuel is not limited to gas fuel containing hydrogen, and can be applied to various gas fuels.

"Gas fuels containing hydrogen" include fuels containing hydrogen and other fuels (mixed combustion) and hydrogen only (single-fuel combustion). Even fuels containing hydrogen and other fuels are mainly hydrogen. It can be divided into fuel (50% or more by volume of hydrogen) and other fuel (less than 50% by volume of hydrogen). "Gaseous fuel containing hydrogen" includes all of these cases.

The furnace 2 has a cylindrical shape, and a space for burning the gas fuel F is formed. In the first embodiment, as shown in FIG. 1, the combustion equipment 1 connects a gas burner 3 provided in the furnace 2, a fuel tank 5 in which the gas fuel F is stored, the gas burner 3 and the fuel tank 5, and a fuel supply line 7 for supplying gas fuel F from the fuel tank 5 to the gas burner 3 . The gas burner 3 is also connected to an air introduction line 4, which will be described later, through which external air A is supplied. The gas burner 3 is provided inside the wind box 12 and the air introduction line 4 is also connected to the wind box 12 .

In FIG. 1, the gas burner 3 is provided on the bottom surface of the furnace 2, and is shown so as to eject the gas fuel F vertically upward. The gas fuel F may be jetted horizontally or obliquely upward.

The air introduction line 4 is for introducing external air A into the furnace 2 . In the first embodiment, the air introduction line 4 has one end 4 a open to the atmosphere and the other end 4 b connected to the gas burner 3 . The air introduction line 4 is configured to suck air from the atmosphere at one end 4a and circulate the sucked air as external air A toward the other end 4b (wind box 12). A mixed gas G3 of the external air A and the circulating gas G2 that has flowed into the wind box 12 is mixed with the gas fuel F and ejected (introduced) into the furnace 2 .

The blower 6 is provided in the air introduction line 4 and blows the outside air A to the furnace 2 . Such a blower 6 is, for example, a forced draft blower that blows outside air A into the furnace 2 . Hereinafter, in the direction in which the external air A flows through the air introduction line 4, the portion of the air introduction line 4 on the upstream side of the blower 6 is referred to as the upstream portion 16 of the air introduction line 4, and the air introduction line 4 downstream of the blower 6. The side portion is the downstream portion 18 of the air introduction line 4 .

The exhaust gas line 8 is for guiding the exhaust gas G1 from the furnace 2 to the outside of the combustion equipment 1 . In the first embodiment, the exhaust gas line 8 has one end 8a connected to the furnace 2 and the other end 8b connected to the chimney 20. The exhaust gas is discharged from the one end 8a (furnace 2) toward the other end 8b (chimney 20). G1 is configured to circulate. The chimney 20 discharges the exhaust gas G1 to the outside of the combustion facility 1 . In FIG. 1, one end 8a of the exhaust gas line 8 is connected to the upper side wall of the furnace 2 in the vertical direction.

In the first embodiment, the combustion facility 1 includes an economizer 22 provided in the exhaust gas line 8, as shown in FIG. The economizer 22 is a device for recovering the heat of the exhaust gas G1 flowing through the exhaust gas line 8, and performs heat exchange between exhaust steam discharged from a steam turbine (not shown) and the exhaust gas G1, for example. Hereinafter, in the direction in which the exhaust gas G1 flows through the exhaust gas line 8, the upstream portion of the exhaust gas line 8 from the economizer 22 is referred to as the upstream portion 24 of the exhaust gas line 8, and the downstream portion of the exhaust gas line 8 from the economizer 22. is a downstream portion 26 of the exhaust gas line 8 .

The exhaust gas circulation line 10 is configured to take out part of the exhaust gas G1 from the downstream side of the economizer 22 in the exhaust gas line 8 as a circulation gas G2. In addition, the exhaust gas circulation line 10 includes a circulation fan 28 that guides part of the exhaust gas flowing through the exhaust gas line 8 to the air introduction line 4, and guides the circulation gas G2 to the downstream side of the blower 6 in the air introduction line 4. One end 10 a is connected to the downstream portion 26 of the exhaust gas line 8 and the other end 10 b is connected to the downstream portion 18 of the air introduction line 4 .

By driving the circulation fan 28 , part of the exhaust gas G<b>1 flowing through the downstream portion 26 of the exhaust gas line 8 flows into the exhaust gas circulation line 10 as the circulation gas G<b>2 and is guided to the downstream portion 18 of the air introduction line 4 . Then, the circulating gas G2 guided to the downstream portion 18 of the air introduction line 4 is mixed with the external air A to generate a mixed gas G3 of the circulating gas G2 and the external air A, and the mixed gas G3 is the air introduction line. 4 toward the wind box 12.

Further, as shown in FIG. 1, downstream of the circulation fan 28 in the exhaust gas circulation line 10, a damper 30 is provided as a circulation gas adjustment section for adjusting the flow rate of the circulation gas G2 introduced into the air introduction line 4. there is

At the inlet of the furnace 2, an inlet oxygen concentration detector 32 is installed to detect the oxygen concentration of the mixed gas G3 of the external air A and the circulating gas G2. The oxygen concentration signal is input. The controller 34 has a damper opening controller 36 that controls the opening of the damper 30 based on the oxygen concentration signal.

Each fuel (each hydrogen concentration in gas fuel containing hydrogen) has a lower limit value of oxygen concentration required for stable combustion (combustion limit oxygen concentration). On the other hand, in order to reduce NOx generated by combustion of fuel, the circulating gas G2 is mixed with the external air A and circulated through the furnace 2. However, as the mixed amount of the circulating gas G2 increases, The inlet oxygen concentration of the mixed gas G3 is reduced.

Therefore, the damper opening degree control unit 36 of the control device 34 operates as a circulating gas adjustment unit based on the inlet oxygen concentration detected by the inlet oxygen concentration detection unit 32 so that the oxygen concentration does not fall below the combustion limit of the fuel used. The opening of the damper 30 is controlled to adjust the mixed amount of the circulating gas G2 introduced into the air introduction line 4 . In addition, the damper opening degree control unit 36 of the control device 34 adjusts the mixture amount of the circulating gas G2 introduced into the air introduction line 4 based on the inlet oxygen concentration in order to reduce the concentration of NOx discharged from the furnace 2. do.

(action/effect)
Actions and effects of the combustion facility 1 according to the first embodiment will be described. Based on the oxygen concentration detected by the inlet oxygen concentration detector 32, the controller 34 controls the opening degree of the damper 30 as a circulating gas adjusting unit that adjusts the flow rate of the circulating gas G2 introduced into the air introduction line 4. As a result, it becomes possible to perform optimum operation control in terms of stable combustion and reduction of NOx, regardless of changes in fuel properties.

That is, since each fuel has a lower limit of oxygen concentration required for stable combustion (oxygen concentration of combustion limit), for example, damper By controlling the opening degree of 30, and as in the embodiment described later, by performing fuel cutoff control and alarm generation control using a value added to this lower limit value, regardless of changes in fuel properties By controlling the opening of the damper 30 based on the lower limit value of the oxygen concentration, it is possible to perform optimum operation control in consideration of stable combustion according to each combustion characteristic and environmental aspects due to NOx reduction.

FIG. 5 is a comparative characteristic diagram of the combustion speed (combustion limit) of hydrogen gas fuel and methane gas fuel. The horizontal axis indicates the inlet oxygen concentration (dry base), and the vertical axis indicates the combustion rate. In the case of methane gas, an oxygen concentration of about 12% is the combustion limit. In the case of hydrogen gas (hydrogen only (single combustion)), the oxygen concentration of about 9% is the combustion limit, and combustion is possible even with an oxygen concentration of about 9%. Therefore, the opening degree of the damper 30 can be controlled so that the oxygen concentration does not fall below the combustion limit according to the fuel properties.

Compared to city gas, etc., hydrogen has a higher combustion speed and is superior in combustibility, so the oxygen concentration at the combustion limit is low. Furthermore, the higher the hydrogen content, the lower the lower limit of the oxygen concentration required for stable combustion.

Therefore, when the gas fuel F contains hydrogen, the lower limit of the oxygen concentration required for stable combustion changes according to the hydrogen content. By controlling the opening degree of 30, it is possible to perform more appropriate operational control in terms of stable combustion and environment for gas fuel containing hydrogen.

<Second embodiment>
A combustion facility 1 according to a second embodiment of the present disclosure will be described with reference to FIG. 2 . The combustion facility 1 according to the second embodiment differs from the first embodiment in that a NOx concentration detector is further provided at the outlet of the furnace 2 . In the second embodiment, the same reference numerals are given to the same components as those of the first embodiment, and detailed description thereof will be omitted.

(composition)
FIG. 2 is a system diagram schematically showing the configuration of the combustion facility 1 according to the second embodiment. As shown in FIG. 2, the outlet of the furnace 2 is provided with a NOx concentration detector 40 for detecting the NOx concentration of the exhaust gas G1 at the outlet, and a detection signal is input to the controller 42.

The controller 42 controls the opening of the damper 30 as a circulating gas adjuster so that the NOx concentration detected by the NOx concentration detector 40 does not exceed a predetermined NOx control value K1. When it exceeds, the inlet oxygen concentration detected by the inlet oxygen concentration detection unit 32 becomes the first value obtained by adding a predetermined value to the lower limit of the oxygen concentration required for stable combustion (combustion limit oxygen concentration B). The opening degree of the damper 30 is controlled so that the mixed amount of the circulating gas G2 to the air introduction line 4 increases within a range that does not fall below the threshold value C1 (see FIG. 6).

The predetermined NOx control value K1 is a control value set to reduce NOx in consideration of the environment. Control of the mixing amount of the circulating gas G2 into the air introduction line 4 so as not to exceed the NOx control value K1 is performed based on a master curve M showing the correlation between the inlet oxygen concentration and the NOx concentration in the fuel used (Fig. 6).

The master curve M is prepared in advance by measuring the correlation between the inlet oxygen concentration and the NOx concentration in the fuel used in the furnace 2 during trial operation (usually measured at the maximum load at which NOx is the highest).

Then, in actual operation, the opening degree of the damper 30, which is the circulating gas adjusting section, is controlled so that the NOx concentration detected by the NOx concentration detecting section 40 is equal to or lower than the NOx control value K1.

Note that the O2 control value K2 of the inlet oxygen concentration corresponding to the NOx control value K1 is obtained from the master curve M so that the inlet oxygen concentration detected by the inlet oxygen concentration detection unit 32 is equal to or lower than the O2 control value K2. Alternatively, the opening degree of the damper 30 may be controlled. In this way, if the O2 control value K2 of the inlet oxygen concentration is obtained in advance using the master curve M, the NOx control value K1 set for NOx reduction can be obtained only from the oxygen concentration detection value by the inlet oxygen concentration detection unit 32. It becomes possible to control the damper 30 including When the properties of the fuel used are changed, the NOx concentration deviates from the master curve M created in advance. Therefore, it is preferable to set the O2 control value K2 in accordance with the properties of the fuel.

Then, when the NOx concentration exceeds the set NOx control value K1 due to aging deterioration of the equipment, changes in fuel properties, etc., the inlet oxygen concentration detected by the inlet oxygen concentration detection unit 32 as described above is reduced to the first The opening of the damper 30, which is the circulating gas adjustment unit, is controlled in the opening direction within a range not equal to or less than 1 threshold value C1 to increase the mixed amount of the circulating gas G2 to the air introduction line 4, thereby decreasing the oxygen concentration at the inlet. Let

As shown in FIG. 6, the first threshold value C1 and the second threshold value C2 are set to the oxygen concentration B at the combustion limit of the fuel used (the oxygen concentration at which the combustion rate shown in FIG. 5 is the lower limit value) in the graph of the master curve M. An oxygen concentration value to which a predetermined value is added is set as the first threshold value C1, and an oxygen concentration value that is greater than the combustion limit oxygen concentration B and smaller than the first threshold value C1 is set as the second threshold value C2. be. The predetermined value to be added to the combustion limit oxygen concentration B is a value appropriately set from the viewpoint of stable combustion in the furnace 2 .

The first threshold value C1 is an alarm setting value for issuing an alarm when the inlet oxygen concentration drops below this value, and the second threshold value C2 is set when the inlet oxygen concentration drops below this value. is a fuel limit set value that cuts off the fuel supply or reduces the supply amount.

In some embodiments, as shown in the configuration of the control device 42 in FIG. 2, the control device 42 detects when the inlet oxygen concentration detected by the inlet oxygen concentration detection unit 32 drops below the first threshold value C1. An alarm control unit 44 for issuing an alarm is provided. Then, the alarm means 46 is activated by the alarm controller 44 .

According to such a configuration, by issuing an alarm from the alarm means 46, the operator of the furnace 2 is informed that the fuel is oxygen-deficient, and is urged to take appropriate measures (increase the inlet oxygen concentration). It is possible to prevent the combustion state from becoming unstable due to the shortage and to reduce NOx.

Moreover, in some embodiments, as shown in the configuration of the control device 42 in FIG. A fuel supply control unit 48 is provided to reduce or eliminate the amount of gas fuel F supplied to the furnace 2 in some cases. The fuel supply control unit 48 restricts or cuts off the supply of the gas fuel F from the fuel tank 5 to the gas burner 3 in the wind box 12 .

According to such a configuration, by reducing or setting the supply amount of the gas fuel F to zero, it is possible to reliably prevent the combustion state from becoming unstable due to lack of oxygen and reduce NOx. can.

In some embodiments, the inlet oxygen concentration detection unit 32 is installed in the wind box 12 equipped with the gas burner 3, and the NOx concentration detection unit 40 is installed in the exhaust gas flow direction from the economizer 22 installed in the exhaust gas line 8. is installed on the upstream side of the

According to such a configuration, the inlet oxygen concentration detection unit 32 is installed in the wind box 12, and the NOx concentration detection unit 40 at the furnace exit is installed upstream of the economizer 22 in the exhaust gas line 8. The inlet oxygen concentration in the mixed gas G3 of the external air and the circulating gas introduced into the furnace 2 and the NOx concentration in the exhaust gas G1 discharged from the furnace 2 can be detected with high accuracy.

Since the inlet oxygen concentration detection unit 32 is installed in the wind box 12, the inlet oxygen concentration detection unit 32 is positioned near the gas burner 3 and can accurately acquire information on the oxygen concentration that affects combustion. In addition, since the NOx concentration detection unit 40 is installed upstream of the economizer 22 in the exhaust gas line 8, the closer it is to the exit of the furnace 2, the more quickly the situation can be determined when the boiler conditions change. information can be obtained. In addition, the wind box 12 is easy to secure a space for installing the inlet oxygen concentration detector 32 and is easy to install.

Next, a series of operation control flows by the control device 42 of the second embodiment will be described with reference to the flowchart of FIG.

First, in step S1, an initial value PNOx of NOx concentration (initial value PO2 of inlet oxygen concentration) is set. As shown in FIG. 6, the initial value PNOx of the NOx concentration is a value lower than the NOx control value K1 so as not to exceed the NOx control value K1 set in consideration of the environment. Then, the operation is started with the initial value PO2 of the inlet oxygen concentration corresponding to the initial value PNOx of the NOx concentration as the target value of the inlet oxygen concentration, and the opening degree of the damper 30, which is the circulating gas adjusting section, is controlled.

Since the NOx characteristics of the furnace 2 are unclear at the beginning of operation, the initial value PO2 of the inlet oxygen concentration is set in advance as a preliminary measure so that the NOx concentration does not exceed the NOx control value K1. Operation is started as a target value.

In the next step S2, it is determined whether or not the NOx concentration detected by the NOx concentration detector 40 after the start of operation is equal to or lower than the NOx control value K1. If the determination in step S2 is No, the process proceeds to step S6. In step S6, the opening degree of the damper 30, which is the circulating gas adjustment unit, is controlled in the opening direction so as to increase the mixed amount of the circulating gas. Decrease oxygen concentration.

If the determination in step S2 is Yes, the process proceeds to step S3, in which it is determined whether or not the inlet oxygen concentration exceeds the first threshold value C1. If the determination in step S3 is No, the process proceeds to step S7. In step S7, the alarm control unit 44 activates the alarm means 46 to issue an alarm and to reduce the mixed amount of the circulating gas G2. , the opening of the damper 30, which is a circulating gas adjusting unit, is controlled in the closing direction to increase the oxygen concentration at the inlet.

If the determination in step S3 is Yes, the process proceeds to step S4, in which it is determined whether or not the inlet oxygen concentration exceeds the second threshold value C2. If the determination in step S4 is No, the process proceeds to step S8, where the fuel supply control unit 48 restricts or cuts off the supply of the gas fuel F from the fuel tank 5 to the gas burner 3 in the wind box 12. to reduce or zero the gas fuel amount (fuel cut off).

If the determination in step S4 is Yes, the process proceeds to step S5, where the operation is continued and then terminated.

(action/effect)
Actions and effects of the combustion facility 1 according to the second embodiment will be described. According to the second embodiment, based on the oxygen concentration at the inlet of the furnace 2 and the NOx concentration at the outlet of the furnace 2, the control device 42 controls the NOx concentration at the outlet of the furnace 2 so as not to exceed the NOx control value K1. Furthermore, by controlling the opening degree of the damper 30, which is a circulating gas adjustment unit, and controlling the amount of the circulating gas G2 mixed with the external air A so that the inlet oxygen concentration does not reach the combustion limit oxygen concentration B, Optimal operation control is possible in terms of stable combustion and reduction of NOx, regardless of changes in fuel properties.

<Third Embodiment>
A combustion facility 1 according to a third embodiment of the present disclosure will be described with reference to FIG. 3 . The combustion facility 1 according to the third embodiment further includes a hydrogen concentration detection means 50 for detecting the hydrogen concentration in the gas fuel F containing hydrogen, and a threshold value correction unit 54 in the configuration of the control device 52. different in that it has In the third embodiment, the same reference numerals are given to the same components as those of the first and second embodiments, and detailed description thereof will be omitted.

(composition)
Equipped with hydrogen concentration detection means 50 for detecting the hydrogen concentration of the gas fuel F, the control device 52 has a threshold correction section 54 for correcting the first threshold C1 and the second threshold C2 according to the hydrogen content. The threshold correction unit 54 corrects the first threshold C1 and the second threshold C2 so as to decrease as the hydrogen content increases.

(action/effect)
Actions and effects of the combustion facility 1 according to the third embodiment will be described. According to the third embodiment, the threshold correction unit 54 corrects the first threshold C1 and the second threshold C2 so as to decrease as the hydrogen content increases. That is, as the hydrogen content increases, the combustion limit oxygen concentration B (FIG. 6) decreases, so the first threshold value C1 and the second threshold value C2 are also decreased accordingly.

In this way, by correcting the first threshold value C1 and the second threshold value C2 so as to decrease as the hydrogen content increases, the stabilization of the combustion in the hydrogen-containing gas fuel F is maintained, and the environment is improved. Considered NOx reduction can be effectively realized.

The contents described in each of the above embodiments are understood as follows, for example.

[1] A combustion facility (1) according to the present disclosure includes a gas burner (3) for ejecting gas fuel into a furnace, an air introduction line (4) for introducing external air (A) for combustion into the gas burner, and the A blower (6) provided in the air introduction line for blowing the external air to the gas burner, an exhaust gas line (8) for guiding the exhaust gas (G1) of the furnace to the outside, and a branch from the exhaust gas line to supply the exhaust gas. An exhaust gas circulation line (10) that guides a part of the exhaust gas as a circulating gas (G2) to the air introduction line, and a circulating gas adjustment unit (30) that is provided in the exhaust gas circulation line and adjusts the flow rate of the circulating gas to the air introducing line. ), an inlet oxygen concentration detecting section (32) for detecting the oxygen concentration of the mixed gas of the external air and the circulating gas at the inlet of the furnace, and based on the oxygen concentration detected by the inlet oxygen concentration detecting section and a control device (34, 42, 52) for controlling the circulating gas adjusting unit.

According to the configuration described in [1] above, the control device controls the circulating gas adjusting unit that adjusts the flow rate of the circulating gas introduced into the air introduction line based on the oxygen concentration detected by the inlet oxygen concentration detecting unit. Therefore, it is possible to perform optimum operational control in terms of stable combustion and reduction of NOx in terms of environment regardless of changes in fuel properties.

[2] In some embodiments, the configuration described in [1] above further includes a NOx concentration detection unit (40) that detects the NOx concentration of the exhaust gas at the outlet of the furnace, and the control device (42) and controlling the circulating gas adjustment unit so that the NOx concentration detected by the NOx concentration detection unit does not exceed a predetermined management value.

According to the configuration described in [2] above, the control device controls the circulating gas adjustment unit so that the NOx concentration detected by the NOx concentration detection unit does not exceed a predetermined management value. Reliable control of NOx reduction is possible regardless of the

[3] In some embodiments, in the configuration described in [2] above, when the NOx concentration detected by the NOx concentration detection unit exceeds a predetermined management value, the control device (42) , so that the mixed amount of the circulating gas increases within a range in which the oxygen concentration detected by the inlet oxygen concentration detection unit does not become a first threshold value (C1) obtained by adding a predetermined value to the combustion limit oxygen concentration (B). to control the circulating gas adjustment unit.

According to the configuration described in [3] above, when the NOx concentration detected by the NOx concentration detection unit exceeds a predetermined management value, the oxygen concentration detected by the inlet oxygen concentration detection unit is equal to or lower than the first threshold. Since the circulating gas adjusting unit is controlled so that the amount of circulating gas mixed with the external air increases within a range in which the above does not occur, reliable control can be achieved in terms of stable combustion regardless of changes in fuel properties.

[4] In some embodiments, in the configuration described in [2] or [3] above, the inlet oxygen concentration detection unit is installed in a wind box equipped with the gas burner, and the NOx concentration detection unit It is installed on the upstream side in the exhaust gas flow direction from the economizer provided in the exhaust gas line.

According to the configuration described in [4] above, it is possible to accurately detect the concentration of oxygen introduced into the furnace and the concentration of NOx discharged from the furnace. In other words, the closer to the furnace exit, the more quickly information can be obtained for judging the situation when the boiler conditions change. In addition, since the inlet oxygen concentration detector is installed in the wind box, it is possible to acquire information immediately before the oxygen concentration introduced into the furnace. Also, by installing it in the wind box, it becomes easy to install the inlet oxygen concentration detector at the inlet of the furnace.

[5] In some embodiments, in the configuration described in [3] above, the control device warns when the oxygen concentration detected by the inlet oxygen concentration detection unit drops below the first threshold. It has an alarm control unit that issues

According to the configuration described in [5] above, by issuing an alarm, the operator of the furnace is notified that the fuel is oxygen-deficient, and appropriate measures (increasing the inlet oxygen concentration) are urged to cause oxygen deficiency. Therefore, it is possible to prevent the combustion state from becoming unstable and to reduce NOx.

[6] In some embodiments, in the configuration described in [5] above, the control device controls the oxygen concentration detected by the inlet oxygen concentration detection unit to be equal to or lower than the second threshold, which is lower than the first threshold. A fuel supply controller is provided to reduce or eliminate the supply of gas fuel to the furnace when it is low.

According to the configuration described in [6] above, by reducing or setting the amount of gas fuel supplied to the furnace to zero, it is possible to prevent the combustion state from becoming unstable due to lack of oxygen and reduce NOx. can be done for sure.

[7] In some embodiments, in the configuration described in [6] above, the gas fuel is gas fuel containing hydrogen, hydrogen concentration detection means for detecting the hydrogen concentration of the gas fuel is provided, and the The control device includes a threshold value correction unit that corrects the first threshold value and the second threshold value so as to decrease as the hydrogen content increases.

According to the configuration described in [7] above, by correcting the first threshold value and the second threshold value so as to decrease as the hydrogen content increases, stable combustion in gas fuel containing hydrogen is maintained. In addition, it is possible to effectively realize a reduction in NOx in consideration of the environment.

1 Combustion equipment 2 Furnace 3 Gas burner 4 Air introduction line 5 Fuel tank 6 Blower 7 Fuel supply line 8 Exhaust gas line 10 Exhaust gas circulation line 12 Wind box 16 Upstream part of air introduction line 18 Downstream part of air introduction line 20 Chimney 22 Economizer 24 upstream part of exhaust gas line 26 downstream part of exhaust gas line 28 circulation fan 30 damper (circulation gas adjustment part)
32 inlet oxygen concentration detection units 34, 42, 52 control device 36 damper opening control unit 40 NOx concentration detection unit 44 alarm control unit 46 alarm means 48 fuel supply control unit 50 hydrogen concentration detection unit 54 threshold correction unit A external air B combustion Limit oxygen concentration C1 First threshold C2 Second threshold F Gas fuel G1 Exhaust gas G2 Circulating gas (part of exhaust gas)
G3 Mixed gas of external air and circulating gas K1 NOx control value K2 O2 control value M Master curve PNOx Initial value of NOx concentration PO2 Initial value of inlet oxygen concentration

Claims (7)

a gas burner for ejecting gas fuel into the furnace;
an air introduction line for introducing external air for combustion into the gas burner;
a blower provided in the air introduction line for blowing the external air to the gas burner;
an exhaust gas line for guiding exhaust gas from the furnace to the outside;
an exhaust gas circulation line that branches from the exhaust gas line and guides part of the exhaust gas as a circulation gas to the air introduction line;
a circulating gas adjustment unit that is provided in the exhaust gas circulation line and adjusts the flow rate of the circulating gas to the air introduction line;
an inlet oxygen concentration detection unit that detects the oxygen concentration of a mixed gas of the external air and the circulating gas at the inlet of the furnace;
a control device that controls the circulating gas adjustment unit based on the oxygen concentration detected by the inlet oxygen concentration detection unit;
Combustion equipment. Further comprising a NOx concentration detection unit that detects the NOx concentration of the exhaust gas at the outlet of the furnace,
The control device controls the circulating gas adjustment unit so that the NOx concentration detected by the NOx concentration detection unit does not exceed a predetermined management value.
Combustion equipment according to claim 1 . When the NOx concentration detected by the NOx concentration detection unit exceeds a predetermined management value, the control device adds a predetermined value to the oxygen concentration detected by the inlet oxygen concentration detection unit at the combustion limit. controlling the circulating gas adjustment unit so that the mixed amount of the circulating gas increases within a range that does not fall below the first threshold value;
Combustion equipment according to claim 2. The inlet oxygen concentration detection unit is installed in the wind box equipped with the gas burner, and the NOx concentration detection unit is installed upstream in the exhaust gas flow direction from the economizer provided in the exhaust gas line.
Combustion equipment according to claim 2 or 3. The control device includes an alarm control unit that issues an alarm when the oxygen concentration detected by the inlet oxygen concentration detection unit drops below the first threshold.
Combustion equipment according to claim 3. The control device reduces the amount of gas fuel supplied to the furnace or makes it zero when the oxygen concentration detected by the inlet oxygen concentration detection unit decreases to a second threshold value that is smaller than the first threshold value. comprising a supply control unit;
Combustion equipment according to claim 5. The gas fuel is a gas fuel containing hydrogen, and includes hydrogen concentration detection means for detecting the hydrogen concentration of the gas fuel,
The control device includes a threshold correction unit that corrects the first threshold and the second threshold so as to decrease as the hydrogen content increases.
Combustion equipment according to claim 6.

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