boiler

Abstract

To provide a boiler capable of suppressing fluctuations in the EGR rate. [Solution] According to the present invention, a boiler 1 is provided, comprising a combustion chamber 2, a burner 3 for heating the inside of the combustion chamber 2, a blower 4 for supplying combustion air to the burner 3 via an air intake passage 5, an exhaust gas passage 8 for leading out exhaust gas from the combustion chamber 2, and an exhaust gas recirculation means 9 for circulating a portion of the exhaust gas as recirculated gas to the blower 4, wherein the exhaust gas recirculation means 9 comprises a first recirculation passage 90, a second recirculation passage 91, and a switching means 92, the first recirculation passage 90 connecting a first position P1 of the exhaust gas passage 8 to the suction port 40 of the blower 4, the second recirculation passage 91 connecting a second position P2 of the exhaust gas passage 8 to the suction port 40 of the blower 4, the second position P2 being upstream of the first position P1, and the switching means 92 enabling the flow path of the recirculated gas to be switched between the first recirculation passage 91 and the second recirculation passage 92.

Description

Technical Field

[0001] The present invention relates to a boiler that recirculates and burns a part of exhaust gas.

Background Art

[0002] Conventionally, there is a boiler that reduces the NOx concentration discharged from an exhaust gas passage by circulating a part of the exhaust gas to the intake side, mixing it with fuel gas and combustion air, and ejecting and burning this mixed gas. For example, the boiler described in Patent Document 1 includes an exhaust gas recirculation path that connects an exhaust gas passage (chimney) and the intake port of a blower on the intake side, and thereby recirculates the exhaust gas with a reduced oxygen concentration to the intake side. As a result, the combustion temperature in the burner decreases, and as a result, it is possible to reduce the NOx concentration contained in the exhaust gas.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, due to combustion conditions and the like, the ratio of recirculated gas per unit time (hereinafter referred to as the EGR rate) may vary, and there is a risk that the combustion performance of the burner may become unstable.

[0005] The present invention has been made in view of such circumstances, and provides a boiler capable of suppressing fluctuations in the EGR rate.

Means for Solving the Problems

[0006] According to the present invention, the following inventions are provided. [1] A boiler comprising a combustion chamber, a burner for heating the combustion chamber, a blower for supplying combustion air to the burner via an air intake passage, an exhaust gas passage for discharging exhaust gas from the combustion chamber, and an exhaust gas recirculation means for circulating a portion of the exhaust gas as recirculated gas to the blower, wherein the exhaust gas recirculation means comprises a first recirculation passage, a second recirculation passage, and a switching means, the first recirculation passage connecting a first position of the exhaust gas passage to the intake port of the blower, the second recirculation passage connecting a second position of the exhaust gas passage to the intake port of the blower, the second position being upstream of the first position, and the switching means enabling the flow path of the recirculated gas to be switched between the first recirculation passage and the second recirculation passage. A boiler as described in [2][1], wherein the exhaust gas passage is provided with a pressure loss section that causes a pressure loss due to the flow of the exhaust gas, the first position is located downstream of the pressure loss section, and the second position is located upstream of the pressure loss section. A boiler as described in [3][2], wherein the pressure loss section is an economizer that exchanges heat between the exhaust gas and the feedwater to the boiler. A boiler according to any of [4][1] to [3], further comprising a control means, the control means controlling the burner to burn in at least two combustion states: a high combustion state and a low combustion state in which the amount of combustion is less than that of the high combustion state, and the control means further controlling the switching means to set the flow path of the recirculated gas as the first recirculation path in the high combustion state and the flow path of the recirculated gas as the second recirculation path in the low combustion state. A boiler according to any of [5][1] to [4], wherein the switching means comprises a first damper provided in the first recirculation path and a second damper provided in the second recirculation path, and the flow path of the recirculated gas is switched between the first recirculation path and the second recirculation path by opening and closing the first damper and the second damper. A boiler according to any of [6][1] to [4], wherein the first recirculation path and the second recirculation path share a pipeline on the blower side, and the switching means is a three-way valve positioned at the point where the first recirculation path and the second recirculation path merge, and the three-way valve switches the flow path of the recirculated gas between the first recirculation path and the second recirculation path. [Effects of the Invention]

[0007] According to the present invention, fluctuations in differential pressure can be suppressed by switching the exhaust gas flow path according to the pressure in the exhaust gas passage and the output status of the blower, thereby suppressing fluctuations in the EGR rate. [Brief explanation of the drawing]

[0008] [Figure 1] This is an explanatory diagram showing the schematic configuration of a boiler according to one embodiment of the present invention. [Figure 2] This is an explanatory diagram showing a schematic configuration of a boiler according to a modified example of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention.

[0010] 1. Boiler configuration Boiler 1 according to one embodiment of the present invention is a steam boiler (once-through boiler) that generates steam by heating water in water tubes (not shown) and supplies steam to load equipment (not shown).

[0011] As shown in Figure 1, the boiler 1 of this embodiment comprises a combustion chamber 2, a burner 3, a blower 4, an air intake passage 5, a gas supply passage 6, a water supply passage 7, an exhaust gas passage 8, an exhaust gas recirculation means 9, and a control means 10. The steam generated by the boiler 1 is supplied to the load equipment via a steam-water separator (not shown) and a steam passage 11. Each component will be described in detail below.

[0012] The combustion chamber 2 is a boiler body in which numerous water tubes (not shown) are arranged inside.

[0013] Burner 3 heats the water in the water tube by heating the inside of the combustion chamber 2. In this embodiment, burner 3 is a pre-mixing type burner, in which the combustion air supplied from the air intake passage 5 and the fuel gas supplied from the gas supply passage 6 are mixed before combustion. However, burner 3 may also be a pre-mixing type.

[0014] The blower 4 is configured to supply combustion air to the burner 3 via the air intake passage 5. The blower 4 in this embodiment includes a fan and a motor that rotates the fan, and the amount of combustion air supplied can be adjusted by controlling the rotation speed of the motor through the control means 10. In addition, the blower 4 in this embodiment has an air intake passage 41 that draws in outside air and a recirculation shared passage 94 (described later) of the exhaust gas recirculation means 9 connected to its intake port 40, so that recirculated gas from the exhaust gas passage 8 is taken in at the same time as the outside air.

[0015] The air intake passage 5 is a conduit connecting the blower 4 and the burner 3. A damper 50 is provided in the air intake passage 5.

[0016] The gas supply passage 6 supplies fuel gas to the burner 3. The gas supply passage 6 is equipped with a fuel gas control valve 60, and the amount of fuel gas burned can be adjusted by changing the opening degree of the fuel gas control valve 60 through the control means 10.

[0017] The water supply channel 7 connects the water source (not shown) to the water pipe of the combustion chamber 2 and supplies water to maintain the water level in the water pipe.

[0018] The exhaust gas passage 8 is a pipeline that guides the combustion gas, which has exchanged heat with the water in the water pipe in the combustion chamber 2, from the combustion chamber 2 as exhaust gas. In the present embodiment, an economizer 80 as a pressure loss portion that causes a pressure loss due to the flow of the exhaust gas is provided in the exhaust gas passage 8. The economizer 80 recovers the heat in the exhaust gas by exchanging heat between the exhaust gas flowing through the exhaust gas passage 8 and the feed water flowing through the feed water passage 7, and preheats the feed water with the waste heat of the exhaust gas.

[0019] The exhaust gas recirculation means 9 is a pipeline that connects the exhaust gas passage 8 and the suction port 40 of the blower 4 and circulates a part of the exhaust gas flowing through the exhaust gas passage 8 to the blower 4 as recirculation gas. By recirculating the exhaust gas with a reduced oxygen concentration as combustion air by the exhaust gas recirculation means 9, the combustion temperature in the burner 3 is lowered, and as a result, the NOx concentration contained in the exhaust gas can be reduced.

[0020] Here, the exhaust gas recirculation means 9 of the present embodiment includes a first recirculation path 90, a second recirculation path 91, and a switching means 92. In the present embodiment, the switching means 92 includes a first damper 92a and a second damper 92b.

[0021] The first recirculation path 90 connects a first position P1, which is a position on the downstream side (exit side) of the economizer 80 in the flow path of the exhaust gas passage 8, and the suction port 40 of the blower 4. The second recirculation path 91 connects a second position P2, which is a position on the upstream side (combustion chamber 2 side) of the economizer 80 in the flow path of the exhaust gas passage 8, and the suction port 40 of the blower 4. The first damper 92a of the switching means 92 is provided in the first recirculation path 90, and the second damper 92b is provided in the second recirculation path 91.

[0022] The first damper 92a opens and closes under the control of the control means 10 to control the flow of the recirculation gas through the first recirculation path 90. The second damper 92b opens and closes under the control of the control means 10 to control the flow of the recirculation gas through the second recirculation path 91. The switching means 92 of the present embodiment is configured to switch the flow path of the recirculation gas between the first recirculation path 90 and the second recirculation path 91 by opening and closing the first damper 92a and the second damper 92b.

[0023] Furthermore, in this embodiment, the first recirculation path 90 and the second recirculation path 91 share a pipeline on the downstream side of the recirculated gas flow path, i.e., on the blower 4 side. The shared portion, the recirculation shared passage 94, is provided with a recirculation adjustment damper 95 for adjusting the flow rate of the recirculated gas.

[0024] The control means 10 is configured as a control unit. The control means 10 controls various parts of the boiler 1, such as controlling the amount of combustion air supplied by the blower 4, controlling the amount of combustion gas supplied by the fuel gas adjustment valve 60 of the gas supply passage 6, and controlling the amount of recirculated gas supplied by the recirculation adjustment damper 95 of the exhaust gas recirculation means 9. In addition, the control means 10 in this embodiment controls each part to burn the burner 3 in at least two combustion states: a high combustion state and a low combustion state with a lower combustion amount than the high combustion state. The specific operation of the boiler 1 under the control of the control means 10 will be described later.

[0025] Specifically, the control means 10 can be configured as an information processing device equipped with a CPU, memory (e.g., flash memory), an input unit, and an output unit. The processing performed by the control means 10 configured as an information processing device is carried out by the CPU reading and executing a program stored in memory. Examples of information processing devices include personal computers, PLCs (programmable logic controllers), or microcontrollers. However, some functions of the control means 10 may be configured to be executed on a cloud connected by any communication means.

[0026] 2. Operation of Boiler 1 Next, the operation of the boiler 1 of this embodiment will be described. As described above, the boiler 1 of this embodiment is configured to be controlled in two combustion modes, a high combustion state and a low combustion state, by controlling each part by the control means 10. The low combustion state is a combustion state in which the amount of combustion is lower than the amount of combustion in the high combustion state. If the amount of fuel gas supplied in the high combustion state is set to 100%, the amount supplied in the low combustion state is set to, for example, 50%. The amount of fuel gas supplied is adjusted by changing the opening degree of the fuel gas control valve 60. In addition, in either combustion mode, the combustion air supplied to the burner 3 is controlled so that the ratio of combustion air to fuel gas is set to a set ratio by, for example, the rotation speed of the motor of the blower 4 or the opening degree control of the recirculation adjustment damper 95.

[0027] In a high-combustion state, the control means 10 increases the opening of the fuel gas control valve 60 in the gas supply passage 6 to supply fuel gas to the burner 3, and controls the rotation speed of the motor of the blower 4 so that fuel air is supplied in proportion to the amount of fuel gas supplied. Also in a high-combustion state, the control means 10 opens the first damper 92a of the first recirculation passage 90 and closes the second damper 92b of the second recirculation passage 91, thereby making the recirculated gas flow path the first recirculation passage 90. As a result, the exhaust gas flowing through the exhaust gas passage 8 exchanges heat with the feedwater in the feedwater passage 7 by the economizer 80, and then flows as recirculated gas from the first position P1 through the first recirculation passage 90 and is drawn into the blower 4. Then, in the blower 4, the recirculated gas (for example, with an oxygen concentration of 4%) and the outside air from the air supply passage 41 (with an oxygen concentration of 21%) are mixed to achieve an oxygen concentration of, for example, 19%, and the mixed combustion air is supplied to the burner 3 by the blower 4.

[0028] On the other hand, in a low combustion state, the control means 10 adjusts the fuel gas adjustment valve 60 of the gas supply passage 6 to supply a smaller amount of fuel gas to the burner 3 than in a high combustion state, and controls the rotation speed of the motor of the blower 4 so that fuel air is supplied in proportion to the amount of fuel gas supplied. Also in a low combustion state, the control means 10 closes the first damper 92a of the first recirculation passage 90 and opens the second damper 92b of the second recirculation passage 91, thereby switching the flow path of the recirculated gas to the second recirculation passage 91. As a result, the exhaust gas flowing through the exhaust gas passage 8 flows through the second recirculation passage 91 from the second position P2 as recirculated gas and is drawn into the blower 4 before heat exchange by the economizer 80. Then, in the blower 4, similar to the high-combustion state, the recirculated gas (for example, with an oxygen concentration of 4%) and outside air from the air supply passage 41 (with an oxygen concentration of 21%) are mixed to achieve an oxygen concentration of, for example, 19%, and the mixed combustion air is supplied to the burner 3 by the blower 4.

[0029] 3. Effects In the boiler 1 according to this embodiment, the exhaust gas recirculation means 9 is equipped with two recirculation paths, a first recirculation path 90 and a second recirculation path 91. The second recirculation path 91 is connected to the exhaust gas path 8 at a second position P2, which is upstream of the first position P1. More specifically, the first position P1, where the first recirculation path 90 is connected to the exhaust gas path 8, is downstream of the economizer 80, while the second position P2, where the second recirculation path 91 is connected to the exhaust gas path 8, is upstream of the economizer 80. As the exhaust gas flows through the economizer 80, pressure loss occurs, so the pressure at the second position P2 is higher than the pressure at the first position P1. Therefore, by switching the flow path of the recirculated gas between the first recirculation path 90 and the second recirculation path 91 according to the pressure in the exhaust gas path 8 and the rotation speed of the motor of the blower 4, the flow path can be adjusted to suppress fluctuations in differential pressure, thereby suppressing fluctuations in the EGR rate.

[0030] More specifically, in the boiler 1 according to this embodiment, the control means 10 opens the first damper 92a of the first recirculation passage 90 and closes the second damper 92b of the second recirculation passage 91 when in a high combustion state, so that the recirculated gas flows through the first recirculation passage 90. Here, in a high combustion state, the exhaust gas flowing through the exhaust gas passage 8 is at high pressure, so if the recirculated gas were to be taken in from the second recirculation passage 91 (i.e., the second position P2) in a high combustion state, the differential pressure with the intake port 40 of the blower 4 would become excessive, and the flow rate of the recirculated gas (i.e., the EGR rate) would become excessive. This point becomes more pronounced when soot or the like adheres to the economizer 80, increasing the pressure loss and raising the pressure at the second position P2.

[0031] However, in a high combustion state, by taking in recirculated gas from the first recirculation path 90, that is, from the first position P1, it is possible to use exhaust gas whose pressure has decreased due to pressure loss by the economizer 80 as recirculated gas and maintain the flow rate of the recirculated gas (i.e., the EGR rate) at an appropriate level.

[0032] On the other hand, in the boiler 1 according to this embodiment, the control means 10 closes the first damper 92a of the first recirculation passage 90 and opens the second damper 92b of the second recirculation passage 91 when in a low combustion state, so that the recirculated gas flows through the second recirculation passage 91. Here, in a low combustion state, the exhaust gas flowing through the exhaust gas passage 8 is at a lower pressure compared to a high combustion state. Therefore, if the recirculated gas were to be taken in from the first recirculation passage 90 (i.e., the first position P1) in a low combustion state, the pressure at the first position P1 would decrease further due to the pressure loss by the economizer 80, causing a decrease in the differential pressure with respect to the suction port 40 of the blower 4, and potentially resulting in insufficient flow rate of recirculated gas (i.e., EGR rate).

[0033] However, in low-combustion conditions, by taking in recirculated gas from the second recirculation path 91, that is, from the second position P2 upstream of the economizer 80, it is possible to suppress the decrease in differential pressure even in low-combustion conditions, secure the necessary flow rate of recirculated gas, and maintain an appropriate EGR rate. And by maintaining an appropriate EGR rate, it is possible to suppress the rise in NOx concentration.

[0034] Furthermore, in low-combustion conditions, closing the first damper 92a of the first recirculation path 90 prevents the recirculated gas that has flowed through the second recirculation path 91 from returning to the exhaust gas path 8 from the first recirculation path 90 without being taken into the blower 4 (short-passing).

[0035] 4. Variations Furthermore, the present invention can also be implemented in the following embodiments.

[0036] In the above embodiment, the first recirculation path 90 is equipped with a first damper 92a, and the second recirculation path 91 is equipped with a second damper 92b. The first damper 92a and the second damper 92b constitute a switching means 92 that switches the flow path of the recirculated gas between the first recirculation path 90 and the second recirculation path 91. However, as shown in Figure 2, it is also possible to use a three-way valve 92c as the switching means 92. By providing a three-way valve 92c at the position where the first recirculation path 90 and the second recirculation path 91 merge, it is also possible to switch the flow path of the recirculated gas between the first recirculation path 90 and the second recirculation path 91. By using a three-way valve 92c, the switching means can be easily configured, and control by the control means 10 is also easy.

[0037] In the above embodiment, the exhaust gas passage 8 was provided with an economizer 80 as a pressure loss section that generates pressure loss due to the flow of exhaust gas. However, in the present invention, the exhaust gas passage 8 of the boiler 1 does not need to be equipped with an economizer 80. For example, an orifice provided in the exhaust gas passage 8 or a bent pipe (elbow, vent, etc.) constituting the exhaust gas passage 8 can be used as a pressure loss section. Even with such a configuration, by connecting the first recirculation passage 90 to the exhaust gas passage 8 at a position downstream of the pressure loss section (first position P1) and connecting the second recirculation passage 91 to the exhaust gas passage 8 at a position upstream of the pressure loss section (second position P2), and switching the flow path of the recirculated gas between the first recirculation passage 90 and the second recirculation passage 91 according to the pressure in the exhaust gas passage 8 and the rotation speed of the motor of the blower 4, the flow path can be adjusted so as to suppress fluctuations in differential pressure, thereby suppressing fluctuations in the EGR rate.

[0038] In the above embodiment, the amount of combustion air supplied to the burner 3 was controlled by controlling the rotation speed of the motor. However, instead of this, or in addition to this, the flow rate of combustion air may be controlled by adjusting the opening degree of the damper 50 provided in the air intake passage 5.

[0039] In the above embodiment, the control means 10 controlled the first damper 92a and the second damper 92b according to the combustion state of the burner 3 (high combustion state or low combustion state) and switched the flow path of the recirculated gas. However, instead of switching the flow path according to the combustion state, it is also possible to configure the system to switch the flow path of the recirculated gas according to the pressure in the exhaust gas passage 8 (specifically, the pressure near the first position P1). Specifically, for example, it is preferable to install a pressure gauge near the first position P1, that is, downstream of the economizer 80, and set the flow path of the recirculated gas to the first recirculation passage 90 when the pressure detected by the pressure gauge is above a predetermined pressure, and to set the flow path of the recirculated gas to the second recirculation passage 91 when the pressure is below the predetermined pressure. With such a configuration, it is possible to adjust the flow path in a way that suppresses fluctuations in differential pressure, thereby suppressing fluctuations in the EGR rate.

[0040] In the above embodiment, the boiler 1 was configured to be controlled in two combustion modes: a high combustion state and a low combustion state. However, the present invention can also be applied to a multi-stage value-controlled boiler controlled in three or more combustion modes, or to a proportional boiler that can continuously control the combustion rate. In these cases, for example, it is preferable to set the recirculation gas flow path as the first recirculation path 90 when the combustion rate is above a predetermined amount, and to set the recirculation gas flow path as the second recirculation path 91 when the combustion rate is below a predetermined amount.

[0041] The first damper 92a, the second damper 92b, and the recirculation adjustment damper 95 used in the above embodiment may each be solenoid valves or other valves.

[0042] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] This disclosure also includes matters that contribute to achieving Sustainable Development Goals (SDGs) Goal 12, "Responsible Consumption and Production," and Goal 13, "Take urgent action to combat climate change." [Explanation of symbols]

[0043] 1: Boiler 2: Combustion chamber 3: Burner 4: Blower 5: Air supply path 6: Gas supply lines 7: Water supply channel 8: Exhaust gas passage 9: Exhaust gas recirculation means 10: Control means 11: Steamway 40: Inlet 41:Air supply path 50: Damper 60: Fuel gas control valve 80: Economizer 90: 1st recirculation path 91:Second recirculation path 92: Switching means 92a: First Damper 92b: Second Damper 92c: Three-way valve 94: Recycled Common Path 95: Recirculation Adjustment Damp P1: Position 1 P2: Position 2

Claims

1. The combustion chamber and A burner that heats the combustion chamber, A blower that supplies combustion air to the burner via an air intake passage, An exhaust gas passage for discharging exhaust gas from the combustion chamber, A boiler comprising an exhaust gas recirculation means for circulating a portion of the exhaust gas as recirculated gas to the blower, The exhaust gas recirculation means comprises a first recirculation path, a second recirculation path, and a switching means. The first recirculation path connects the first position of the exhaust gas path to the intake port of the blower, The second recirculation path connects the second position of the exhaust gas path to the intake port of the blower. The second position is upstream of the first position, The switching means is a boiler that can switch the flow path of the recirculated gas between the first recirculation path and the second recirculation path.

2. A boiler according to claim 1, The exhaust gas passage is provided with a pressure loss section that generates pressure loss due to the flow of the exhaust gas. A boiler in which the first position is located downstream of the pressure loss section, and the second position is located upstream of the pressure loss section.

3. A boiler according to claim 2, The pressure loss section is an economizer that exchanges heat between the exhaust gas and the feedwater to the boiler, and the boiler.

4. A boiler according to claim 1 or claim 2, Further equipped with control means, The control means controls the burner to burn in at least two combustion states: a high combustion state and a low combustion state in which the amount of combustion is less than that of the high combustion state. A boiler in which the control means further controls the switching means so that the flow path of the recirculated gas becomes the first recirculation path in the high combustion state and the flow path of the recirculated gas becomes the second recirculation path in the low combustion state.

5. A boiler according to claim 1 or claim 2, The switching means comprises a first damper provided in the first recirculation path and a second damper provided in the second recirculation path, and the flow path of the recirculated gas is switched between the first recirculation path and the second recirculation path by opening and closing the first damper and the second damper, in a boiler.

6. A boiler according to claim 1 or claim 2, The first recirculation path and the second recirculation path share a pipeline on the blower side. The switching means is a three-way valve positioned at the point where the first recirculation path and the second recirculation path merge, and the three-way valve switches the flow path of the recirculated gas between the first recirculation path and the second recirculation path in the boiler.

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