Boiler

Abstract

To provide a boiler capable of reducing a back-fire risk in mixed combustion with fuel having a fast combustion speed.SOLUTION: A boiler (1) includes: a first fuel supply passage (51) for supplying to a combustion chamber as fuel, mixed gas obtained by mixing a first kind of gas and a second kind of gas having a combustion speed faster than that of the first kind of gas; a second fuel supply passage (52) connected to the first fuel supply passage (51), and supplying gas having a combustion speed slower than that of the second kind of gas to the first fuel supply passage (51) to mix with the mixed gas; a first adjusting valve (15) provided in the second fuel supply passage (52); specific means (16, 6) for specifying a mixture ratio of the second kind of gas from the mixed gas; and control means (6) for controlling the first adjusting valve (15) when a mixture ratio of the second kind of gas specified by the specific means (16, 6) becomes equal to or more than a predetermined value, and supplying gas of the second fuel supply passage (52) to the first fuel supply passage (51).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a boiler. [Background technology]

[0002] In recent years, there has been a demand for reducing CO2 (carbon dioxide) emissions in order to prevent global warming. For this reason, attempts have been made to reduce carbon dioxide emissions by co-firing natural gas with a gaseous fuel other than natural gas. For example, there is a boiler that uses ammonia as part of the fuel in addition to natural gas and co-firing it (for example, Patent Document 1). Co-firing of natural gas with hydrogen has also been attempted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-032391 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, hydrogen burns faster than natural gas, so a higher hydrogen mixture ratio increases the burning speed in the combustion chamber, which can increase the risk of flashback.

[0005] The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a boiler that reduces the risk of flashback when co-firing with gas having a high combustion speed. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, a boiler according to one aspect of the present invention includes a first fuel supply passage for supplying a mixed gas, which is a mixture of a first type of gas and a second type of gas having a faster combustion speed than the first type of gas, to a combustion chamber as fuel; a second fuel supply passage connected to the first fuel supply passage for supplying a gas having a slower combustion speed than the second type of gas to the first fuel supply passage for mixing it with the mixed gas; a first adjusting valve provided in the second fuel supply passage; an identification means for identifying a mixing ratio of the second type of gas from the mixed gas; and a control means for controlling the first adjusting valve to supply gas from the second fuel supply passage to the first fuel supply passage when the mixing ratio of the second type of gas identified by the identification means becomes equal to or greater than a predetermined value.

[0007] According to the above configuration, when the mixture ratio of the second type of gas having a faster combustion speed among the mixed gases supplied to the first fuel supply passage reaches or exceeds a predetermined value, the gas having a slower combustion speed than the second type of gas is supplied to the first fuel supply passage, thereby reducing the risk of flashback in the combustion chamber.

[0008] Preferably, the fuel supply system includes a pilot burner, a second regulating valve provided in the first fuel supply passage, and a third fuel supply passage for branching a portion of the mixed gas in the first fuel supply passage from the upstream side of the second regulating valve and supplying it to the pilot burner, and the identification means is provided in the third fuel supply passage.

[0009] According to the above configuration, the identification means for identifying the mixing ratio of the second type of gas is provided in the third fuel supply passage for supplying the mixed gas to the pilot burner. Therefore, for example, there is no need to provide a new fuel passage for identifying the mixing ratio, and further, the mixed gas used for identifying the mixing ratio can be utilized for combustion in the pilot burner.

[0010] Preferably, the control means controls the aperture of the first adjustment valve so that a mixing ratio of the second type of gas identified by the identification means becomes equal to or greater than a predetermined value while the gas of the second fuel supply passage is being supplied to the first fuel supply passage.

[0011] According to the above configuration, it is possible to suppress a decrease in combustion efficiency caused by an excessively large proportion of gas having a slow combustion rate among the gases supplied to the combustion chamber. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram illustrating a schematic configuration of a boiler. [Diagram 2] 11 is a flowchart illustrating an example of an MFC-related process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The boiler according to the present disclosure will be described with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included in the present invention.

[0014] <Overview of the configuration> A boiler 1 equipped with a combustion device according to an embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a diagram showing a schematic configuration of a boiler 1 equipped with a combustion device according to an embodiment of the present invention.

[0015] The boiler 1 comprises a boiler body 2 that burns fuel to generate steam, a blower 3 that sends air into the boiler body 2 through an air supply passage 30, a flue 4 that guides exhaust gases and the like from the boiler body 2, a fuel supply passage that supplies fuel to the boiler body 2, a control unit 6 that controls the operation of the boiler 1, a pilot burner (an example of a burner) 8, an ignition device 9, and a main burner 20.

[0016] The main burner 20 is provided at the connection between the boiler body 2 and the air supply passage 30, and combustion air is supplied from the blower 3 via the air supply passage 30. The pilot burner 8 has a tip close to the main burner 20 and is provided so as to be able to ignite the main burner 20.

[0017] The ignition device 9 is an ignition device (igniter) that generates a spark for igniting the pilot burner 8, and is provided in the air supply passage 30. The pilot burner 8 is ignited by the spark generated by the ignition device 9 to generate a flame, and this flame ignites the main burner 20, causing the fuel to burn in the boiler body 2.

[0018] The fuel supply passage includes a first fuel supply passage 51 to which the mixed gas is supplied, a second fuel supply passage 52 connected to the first fuel supply passage and supplying gas to the first fuel supply passage 51, and a third fuel supply passage 53 branched from the first fuel supply passage 51. The first fuel supply passage 51 is connected to the air supply passage 30. The fuel supplied from the first fuel supply passage 51 to the air supply passage 30 is mixed with air blown from the blower 3 and supplied to the main burner 20 in the boiler body 2. A part of the mixed gas supplied to the first fuel supply passage 51 is branched to the third fuel supply passage 53 and supplied to the pilot burner 8. A part of the mixed gas supplied to the first fuel supply passage 51 is branched to the third fuel supply passage 53 and supplied to the pilot burner 8. The fuel supplied from the third fuel supply passage 53 to the pilot burner 8 is mixed with the supplied air.

[0019] The first fuel supply passage 51 is provided with on-off valves (solenoid valves) 11 and 12 for opening and closing the passage, a fuel supply amount adjustment valve 13, and an orifice 14 downstream of a branch point to the third fuel supply passage (hereinafter, collectively referred to as on-off valves, etc.). The fuel supply amount adjustment valve 13 functions as a pressure adjustment valve capable of adjusting the flow rate of fuel supplied to the boiler body 2, and also has a shutoff function. The fuel supply amount adjustment valve 13 is provided downstream of the on-off valves 11 and 12, and is a motor valve whose opening is adjusted by the control unit 6. Note that the fuel supply amount adjustment valve 13 is not limited to a motor valve as long as it adjusts the flow rate of fuel, and may be, for example, an air-type control valve.

[0020] A mixed gas obtained by mixing a first type of gas with a second type of gas having a faster combustion speed than the first type of gas is supplied to the first fuel supply passage 51. The first type of gas may be, for example, a hydrocarbon gas, such as natural gas or 13A city gas mainly composed of natural gas, or may be gas supplied from an LPG (liquefied petroleum gas) cylinder. The second type of gas is, for example, hydrogen. The mixed gas supplied to the first fuel supply passage 51 is mixed so that different types of gases are mixed to have a certain mixing ratio (hereinafter also referred to as a reference ratio). For example, the natural gas and hydrogen are mixed in advance to have a ratio of 90% to 80% and 10% to 20%, respectively. The reference ratio is also, for example, a mixing ratio appropriate for operation that allows the boiler to be operated safely and efficiently.

[0021] A gas having a slower combustion speed than hydrogen, which is the second type of gas, is supplied to the second fuel supply passage 52. The flow rate of the gas supplied to the second fuel supply passage 52 is adjusted by a flow rate regulator provided on the second fuel supply passage 52. In this embodiment, an example will be described in which the flow rate regulator is an MFC (mass flow controller) 15 equipped with a mass flow measurement sensor and a flow rate adjustment function. However, the flow rate regulator is not limited to a mass flow controller, and may be any device that has the function of a flow rate adjustment valve (valve) that can adjust the fuel flow rate by the control unit 6 (control signal).

[0022] The gas (hereinafter also referred to as adjustment gas) supplied to the second fuel supply passage 52 may be, for example, a hydrocarbon gas, such as natural gas or 13A city gas mainly composed of natural gas, or may be a gas supplied from an LPG (liquefied petroleum gas) cylinder. The adjustment gas may be the same gas as the first type of gas supplied to the first fuel supply passage 51, or may be a different gas, so long as the adjustment gas has a slower combustion speed than hydrogen, which is the second type of gas. For example, 13A city gas (first type of gas) and hydrogen (second type of gas) may be supplied to the first fuel supply passage 51, and 13A city gas may be supplied to the second fuel supply passage as the adjustment gas. Alternatively, the first fuel supply passage 51 may be supplied with city gas 13A (first type of gas) and hydrogen (second type of gas), and the second fuel supply passage may be supplied with gas from an LPG cylinder as the adjustment gas, or the first fuel supply passage 51 may be supplied with a mixed gas of gas (first type of gas) supplied from an LPG cylinder and hydrogen (second type of gas), and the second fuel supply passage may be supplied with city gas 13A or gas supplied from an LPG cylinder as the adjustment gas. The adjustment gas supplied to the second fuel supply passage 52 is supplied to the first fuel supply passage 51 when the MFC 15 is in the open state, and is mixed with the mixed gas flowing through the first fuel supply passage 51.

[0023] The third fuel supply passage 53 is provided with a densitometer 16 for measuring the density of combustible gas, and measures the density of a portion of the mixed gas branched off from the first fuel supply passage 51. The control unit 6 specifies the hydrogen mixture ratio of the mixed gas in accordance with the variation in density, for example, based on a density range (hereinafter also referred to as a safe density range) when the mixture ratio of gas supplied from the upstream of the first fuel supply passage is a predetermined ratio of 90% to 80% natural gas and 10% to 20% hydrogen. For example, when the hydrogen mixture ratio increases, the density measured by the densitometer 16 decreases, and when the hydrogen mixture ratio decreases, the density measured by the densitometer 16 increases.

[0024] Conventionally, if the ratio of hydrogen, which has a high combustion speed, to the fuel supplied to the combustion chamber of a boiler becomes high, the ejection speed of the mixed gas from the burner becomes slower than the combustion speed of the flame in the combustion chamber, and there is a risk of the flame flowing back into the burner, resulting in a backfire. In particular, in the case of a premixed combustion method in which air and fuel are mixed in advance, the risk of backfire tends to increase as the hydrogen mixture ratio increases. Hereinafter, the lower limit of the ratio at which the risk increases is also referred to as the dangerous mixture ratio.

[0025] Therefore, in this embodiment, when the gas density measured by density meter 16 falls below the lower limit of the safe density range, it is determined that the hydrogen ratio in the mixed gas has reached a predetermined value or higher, so MFC 15 is opened and a gas (adjustment gas) having a slower combustion speed than hydrogen is supplied from second fuel supply path 52 to first fuel supply path 51.

[0026] The predetermined value is, for example, a ratio higher than the upper limit of the reference ratio of the mixed gas (e.g., 20%) and lower than a dangerous mixture ratio of hydrogen (e.g., 40%) that may cause flashback in the combustion chamber of the boiler (e.g., 30% with a little margin before reaching 40%, or 21%). This makes it possible to reduce the ratio of hydrogen even if the mixture ratio of the mixed gas supplied from the upstream side of the first fuel supply passage 51 fluctuates due to some influence and the mixture ratio of hydrogen becomes high. This makes it possible to reduce the risk of flashback.

[0027] Furthermore, in this embodiment, the density meter 16 is provided on the third fuel supply passage 53 branched off from the first fuel supply passage 51 in order to supply gas to the pilot burner 8. Therefore, it is not necessary to add a new fuel line for the mixture ratio measurement. Also, the sample gas used for the measurement can be supplied to the boiler body 2 and reused for combustion, eliminating the waste of fuel.

[0028] Also, after opening MFC15, the opening degree of MFC15 is controlled according to the variation of the mixing ratio. For example, the hydrogen mixing ratio is controlled to be in the range of 10% to 20% of the reference ratio, for example. In this way, while controlling the hydrogen mixing ratio to be lower than a predetermined value, the opening degree of MFC15 is controlled so that the hydrogen mixing ratio is equal to or higher than a predetermined value (for example, 10% which is the lower limit of the appropriate hydrogen mixing ratio). For example, when the hydrogen mixing ratio becomes less than a predetermined value (for example, less than 10%), MFC15 may be closed. Thereby, even when the hydrogen mixing ratio has decreased too much, the hydrogen mixing ratio can be increased and maintained at an appropriate mixing ratio, so that a decrease in combustion efficiency can be suppressed.

[0029] The control unit 6 is realized by a computer including a memory, a timer, and an arithmetic processing unit inside. The control unit 6 controls the opening and closing of various valves and the operation of the ignition means 9, and controls the combustion state of the boiler 1. The control unit 6 adjusts the supply flow rate of the fuel supplied from the first fuel supply path 51 to the air supply path 30 (and thus to the main burner 20) based on the supply flow rate of the combustion air to the boiler body 2 according to the combustion stage. That is, if the flow rate of the combustion air increases, the opening degree of the fuel supply amount adjustment valve 13 is increased to increase the fuel flow rate. On the other hand, if the flow rate of the combustion air decreases, the opening degree of the fuel supply amount adjustment valve 13 is decreased to decrease the fuel flow rate.

[0030] Also, the control unit 6 identifies the hydrogen mixing ratio of the mixed gas supplied to the first fuel supply path 51 based on the gas density measured by the density meter 16, and controls the opening degree of MFC15 according to the identified hydrogen mixing ratio.

[0031] <Regarding MFC-related processing> The MFC-related processing performed by the control unit 6 will be described with reference to FIG. 2. FIG. 2 is a flow chart for explaining an example of the MFC-related processing. The MFC-related processing is repeatedly executed by the control unit 6 at predetermined time intervals (for example, every second) during the operation of the boiler 1. In step S01, the hydrogen mixing ratio of the mixed gas branched off from the first fuel supply line 51 is identified based on information measured by the density meter 16 provided in the third fuel supply line 53. For example, if the detected density is lower than the lower limit density of the safe density range, it can be assumed that the hydrogen mixing ratio of the mixed gas is higher than the reference ratio. Therefore, the hydrogen mixing ratio is identified according to the density decrease rate (detected value).

[0032] In step S02, it is determined whether the hydrogen mixture ratio identified in step S01 is equal to or greater than a predetermined value. The predetermined value is, for example, a predetermined ratio (e.g., 21% or 25%) that is lower than a dangerous hydrogen mixture ratio that may cause flashback in the combustion chamber of the boiler. If it is not determined in step S02 that the hydrogen mixture ratio is equal to or greater than the predetermined value, the process ends because it can be assumed that the hydrogen mixture ratio is within a range in which combustion can be continued safely.

[0033] On the other hand, when it is determined in step S02 that the hydrogen mixture ratio is equal to or greater than the predetermined value, the process proceeds to step S03, where the MFC 15 is opened and the opening degree is controlled according to the hydrogen mixture ratio, and the process ends. For example, when it is determined in step S01 that the hydrogen mixture ratio specified according to the density of the mixed gas measured is equal to or greater than the predetermined value, the risk of backfire in the combustion chamber is increased. Therefore, the MFC 15 provided in the second fuel supply passage 52 is opened, and an adjustment gas (e.g., natural gas, LPG, etc.) having a slower combustion speed than hydrogen is supplied to the first fuel supply passage 51 and mixed. The opening degree of the MFC 15 is controlled so that the hydrogen mixture ratio is within a range of, for example, 10% to 20% of the reference ratio. The mixture ratio controlled in step S03 is not limited to being the same as the standard mixture ratio, but may be set to a range wider than the standard mixture ratio (e.g., a hydrogen mixture ratio of 8% to 25%) or may be controlled to a range narrower than the standard mixture ratio (e.g., a hydrogen mixture ratio of 13% to 17%) as long as it is within a range in which combustion efficiency of the boiler can be maintained and combustion can be continued safely.

[0034] When the hydrogen mixture ratio has decreased based on the information measured by the density meter 16 and it is no longer necessary to supply fuel from the second fuel supply passage 52 (for example, when the hydrogen mixture ratio becomes less than 10% when the MFC 15 is opened), the MFC 15 is controlled to the closed state. Alternatively, the MFC 15 may be closed by an operator who closes the MFC 15 after confirming safety. In addition, since the mixture ratio of hydrogen gas supplied to the first fuel supply passage 51 may temporarily increase to a predetermined value or higher, the MFC 15 may be controlled to the closed state when a predetermined time (for example, one minute) has elapsed since the start of the process in step S03.

[0035] As described above, in the boiler 1 according to the present embodiment, a mixed gas obtained by mixing a first type of gas (e.g., natural gas of a hydrocarbon system, LPG, etc.) with a second type of gas (e.g., hydrogen, etc.) having a faster combustion speed than the first type of gas is supplied to the combustion chamber as fuel. Also, when it is determined in step S02 of FIG. 2 that the mixture ratio of hydrogen having a faster combustion speed is equal to or greater than a predetermined value based on the density of the mixed gas measured by the density meter 16, the MFC 15 is opened, and an adjustment gas (e.g., natural gas, LPG, etc.) having a slower combustion speed than hydrogen is mixed from the second fuel supply passage 52 into the mixed gas supplied to the first fuel supply passage 51. This reduces the risk of backfire in the combustion chamber.

[0036] In addition, the density meter 16 is provided on a third fuel supply passage for branching a part of the mixed gas supplied to the first fuel supply passage 51 from an upstream side of an on-off valve or the like and supplying it to the pilot burner 8. This makes it unnecessary to provide a new fuel passage for identifying the mixture ratio, for example, and allows the sample gas used for measurement by the density meter 16 to be reused for combustion in the pilot burner 8.

[0037] Furthermore, in a state in which the adjustment gas is being supplied from the second fuel supply passage 52 to the first fuel supply passage 51, the control unit 6 controls the opening degree of the MFC 15 so that the mixture ratio of hydrogen in the mixed gas specified based on the density measured by the density meter 16 is equal to or higher than a predetermined value (for example, equal to or higher than 10% hydrogen, which is the lower limit of the reference ratio). This makes it possible to prevent the ratio of the adjustment gas from becoming too high, thereby preventing the combustion efficiency from decreasing.

[0038] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Modifications of the above-described embodiment that can be applied to the present invention will be described below.

[0039] In the above embodiment, an example has been described in which the density meter 16 is provided on the third fuel supply passage 53, which is a supply passage for supplying fuel to the pilot burner 8. However, this is not limiting, and in cases where the density meter 16 cannot be provided on the third fuel supply passage 53 for some reason, a measurement fuel supply passage branched from the upstream of the opening / closing valve of the first fuel supply passage 51 may be provided separately to measure the density of a part of the mixed gas. In addition, the sample gas used for measurement may be supplied to the first fuel supply passage 51, the third fuel supply passage, or directly to the pilot burner 8 or the main burner 20, and reused.

[0040] In the above embodiment, an example has been described in which a density meter 16 for measuring the density of gas is used to specify the hydrogen mixture ratio in the mixed gas. However, the present invention is not limited to this as long as the hydrogen ratio in the mixed gas can be specified. For example, instead of the density meter 16, a calorimeter may be used to specify the hydrogen mixture ratio according to the amount of heat detected by the calorimeter. For example, if the hydrogen mixture ratio is specified to be equal to or greater than a predetermined value in response to the amount of heat detected by the calorimeter increasing above the amount of heat corresponding to the upper limit of a reference ratio (for example, a hydrogen mixture ratio of 10% to 20%), the MFC 15 is controlled to an open state.

[0041] In the above embodiment, the fuel supplied to the first fuel supply passage 51 is supplied in advance within a range of 10% to 20% hydrogen, which is a mixture ratio appropriate for operation, and when there is a fluctuation due to some factor and the hydrogen mixture ratio increases, an example has been described in which the MFC 15 is opened to control the mixture ratio. However, this is not limited to the case where the hydrogen mixture ratio increases, and the MFC 15 may be opened in advance and the mixed gas supplied to the first fuel supply passage 51 and the adjustment gas supplied by the second fuel supply passage may be mixed to control the hydrogen ratio to 10% to 20%.

[0042] Alternatively, natural gas may be supplied to the first fuel supply passage 51, and hydrogen may be supplied to the second fuel supply passage 52 to form a mixed gas on the first fuel supply passage 51, and the mixture ratio of hydrogen may be controlled to be within an appropriate range (e.g., 10% to 20%) according to the density measured by the density meter 16.

[0043] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0044] 1. Boiler 2 Boiler body 3. Blower 4 Flue 51 1st fuel supply path 52 2nd fuel supply path 53 3rd fuel supply path 6. Control Unit 8 Pilot Burner 9 Ignition device 11. On-off valve 12. On-off valve 13 Fuel supply adjustment valve 14 Orifice 15 MFC 16 Density meter 20 Main burner 30 Air supply line

Claims

1. a first fuel supply passage for supplying a mixed gas obtained by mixing a first type of gas with a second type of gas having a faster combustion speed than the first type of gas to a combustion chamber as fuel; a second fuel supply passage connected to the first fuel supply passage for supplying a gas having a combustion speed slower than that of the second type of gas to the first fuel supply passage and mixing the gas with the mixed gas; a first adjusting valve provided in the second fuel supply passage; An identification means for identifying a mixture ratio of the second type of gas from the mixed gas; a control means for controlling the first adjusting valve to supply gas in the second fuel supply passage to the first fuel supply passage when the mixing ratio of the second type of gas identified by the identification means becomes equal to or greater than a predetermined value.

2. A pilot burner and a second adjusting valve provided in the first fuel supply passage; a third fuel supply passage for branching a part of the mixed gas in the first fuel supply passage from an upstream side of the second adjusting valve and supplying the part to the pilot burner, The boiler according to claim 1 , wherein the identifying means is provided in the third fuel supply passage.

3. 2. The boiler according to claim 1, wherein the control means controls an aperture of the first adjusting valve so that a mixing ratio of the second type of gas identified by the identification means is equal to or greater than a predetermined value in a state in which the gas in the second fuel supply passage is supplied to the first fuel supply passage.

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