JP7811151B2 - Combustion System - Google Patents

Description

The present invention relates to combustion systems such as industrial heating furnaces, boilers, and water heaters and coolers.

In recent years, there has been a demand to reduce CO ₂ (carbon dioxide) emissions in order to prevent global warming, and as a result, technology for burning hydrogen in addition to or instead of fossil fuels has been attracting attention.

In burners that use hydrogen as fuel, there is a risk of flashback occurring before and after operation is started due to the generation of a combustible mixture containing hydrogen and air in the fuel pipes.

As a result, technology has been developed to install a flame arrestor in the fuel pipe (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2018-200166

However, the technology in Patent Document 1 above has the problem of the high cost required for the flame arrestor.

In light of these issues, the present invention aims to provide a combustion system that can prevent flashback at low cost.

In order to solve the above problems, the combustion system of the present invention includes a burner, a fuel gas supply passage connecting a fuel gas supply source and the burner, an oxidant gas supply passage connecting a blower and the burner, an inert gas supply passage connecting an inert gas supply source and the fuel gas supply passage, and a flow rate control unit that controls one or more of the flow rate of the fuel gas supplied to the burner through the fuel gas supply passage, the flow rate of the oxidant gas supplied to the burner through the oxidant gas supply passage, and the flow rate of the inert gas supplied to the fuel gas supply passage through the inert gas supply passage, and the flow rate control unit performs pre-purge control to supply inert gas to the fuel gas supply passage through the inert gas supply passage, The control system includes: operation start control, which is a control performed after the pre-purge control, in which the supply of fuel gas to the burner is started to start the operation of the burner; operation in progress control, which is a control performed after the operation start control, in which the supply of fuel gas to the burner is started for at least a predetermined period; operation stop control, which is a control performed after the operation in progress control, in which the supply of fuel gas to the burner is stopped to stop the operation of the burner; and post-purge control, which is a control performed after the operation stop control, in which inert gas is supplied to the fuel gas supply path through the inert gas supply path for a predetermined period of time , and the supply of inert gas to the fuel gas supply path through the inert gas supply path is maintained from the pre-purge control to the post-purge control .

Furthermore, during in-operation control, the flow rate control unit may control the flow rate of fuel gas supplied to the burner according to the required heat quantity, and may control the flow rate of oxidant gas supplied to the burner so that the air ratio is maintained within a predetermined range.

Furthermore, during in-operation control, the flow rate control unit may control the flow rate of the inert gas based on the concentration of NOx contained in the exhaust gas generated by burning the fuel gas.

Furthermore, when the flow rate control unit reduces the flow rate of fuel gas supplied to the burner during operation control, it may increase the flow rate of inert gas supplied to the fuel gas supply path.

Furthermore, the flow control unit may maintain the supply of inert gas to the fuel gas supply path even when the flow rate of fuel gas supplied to the burner is set to zero during in-operation control.

This invention makes it possible to prevent flashbacks at low cost.

1 is a diagram illustrating a combustion system according to a first embodiment. FIG. FIG. 2 is a functional block diagram of a control device according to the first embodiment. FIG. 2 is a diagram illustrating a gas supply unit according to the first embodiment. 5A and 5B are diagrams illustrating control by a flow rate control unit according to the first embodiment. FIG. 4 is a diagram illustrating the relationship between the flow rate of hydrogen and the concentration of NOx contained in exhaust gas. 10A and 10B are diagrams illustrating control by a flow rate control unit according to a first modified example. 10A and 10B are diagrams illustrating control by a flow rate control unit according to a second modified example. 10A and 10B are diagrams illustrating control by a flow rate control unit according to a third modified example. FIG. 10 is a diagram illustrating control by a flow rate control unit according to a fourth modified example. FIG. 13 is a diagram illustrating control by a flow rate control unit according to a fifth modified example. FIG. 13 is a diagram illustrating control by a flow rate control unit according to a sixth modified example. FIG. 13 is a diagram illustrating control by a flow rate control unit according to a seventh modified example. FIG. 4 is a diagram illustrating a combustion system according to a second embodiment. FIG. 10 is a functional block diagram of a control device according to a second embodiment.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Dimensions, materials, and other specific values shown in these embodiments are merely examples intended to facilitate understanding of the invention and, unless otherwise specified, do not limit the present invention. Furthermore, in this specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

First Embodiment: Combustion System 100
Fig. 1 is a diagram illustrating a combustion system 100 according to a first embodiment. In Fig. 1, dashed arrows indicate the flow of signals. As shown in Fig. 1, the combustion system 100 includes a combustion facility 110, a gas supply unit 120, and a control device 130.

The combustion equipment 110 is a furnace that burns fuel gas. Examples of the combustion equipment 110 include an industrial heating furnace, a furnace that constitutes a boiler, or a water heater/chiller. The combustion equipment 110 is equipped with one or more burners 112.

The gas supply unit 120 supplies one or more of fuel gas, oxidant gas, and inert gas to the burner 112. In this embodiment, a gas supply unit 120 is provided for each burner 112. A fuel gas supply source 122 is connected to the gas supply unit 120. A main shutoff valve 124 is provided between the fuel gas supply source 122 and the gas supply unit 120. The main shutoff valve 124 opens and closes the flow path formed between the fuel gas supply source 122 and the gas supply unit 120. During operation of the combustion system 100, the main shutoff valve 124 is maintained in an open state. Details of the gas supply unit 120 will be described later.

The fuel gas is either or both of a gas with a high burning rate and a high adiabatic flame temperature. The fuel gas contains, for example, at least one of hydrogen and acetylene. The burning rate of hydrogen is approximately seven times that of hydrocarbon fuel gas (e.g., city gas 13A). The adiabatic flame temperature of hydrogen is approximately 200°C higher than that of methane or city gas 13A. In this embodiment, hydrogen is used as an example of fuel gas.

The oxidant gas includes one or more of air, oxygen, and oxygen-enriched gas. In this embodiment, air is used as an example of the oxidant gas.

The inert gas may include one or more of nitrogen, carbon dioxide, helium, argon, and combustion exhaust gas. In this embodiment, nitrogen is used as an example of the inert gas.

Figure 2 is a functional block diagram of the control device 130 according to the first embodiment. As shown in Figure 2, the control device 130 includes a central control unit 132 and a memory 134.

The central control unit 132 is composed of a semiconductor integrated circuit that includes a CPU (central processing unit). The central control unit 132 reads programs and parameters for operating the CPU from ROM. The central control unit 132 manages and controls the entire combustion system 100 in cooperation with RAM as a work area and other electronic circuits.

In this embodiment, the central control unit 132 functions as a flow rate control unit 140. The flow rate control unit 140 controls the gas supply unit 120. Details of the flow rate control unit 140 will be described later.

Memory 134 is composed of ROM, RAM, flash memory, HDD, etc. Memory 134 stores programs and various data used by central control unit 132. For example, memory 134 holds NOx information, etc. NOx information is information that associates the flow rate of hydrogen being burned with the nitrogen flow rate at which the concentration of NOx (nitrogen oxides) contained in exhaust gas produced by the combustion of that hydrogen becomes a predetermined value. NOx information is created in advance through experiments, simulations, etc., and is held in memory 134.

[Gas supply unit 120]
3 is a diagram illustrating the gas supply unit 120 according to the first embodiment. As shown in FIG. 3, the gas supply unit 120 includes an oxidizing agent supply unit 210, a fuel supply unit 230, and an inert gas supply unit 250.

[Oxidizing agent supply unit 210]
The oxidant supply unit 210 supplies air to the burner 112. In this embodiment, the oxidant supply unit 210 includes an oxidant gas supply passage 212, a blower 214, a flow control valve 216, and a flow adjustment valve 218.

The oxidant gas supply channel 212 is a flow path connecting the blower 214 and the burner 112. The intake side of the blower 214 is open to the atmosphere. The discharge side of the blower 214 is connected to the oxidant gas supply channel 212. The blower 214 supplies air to the burner 112 through the oxidant gas supply channel 212.

The flow control valve 216 is provided in the oxidant gas supply path 212. The opening of the flow control valve 216 is adjusted by the flow control unit 140. The flow control valve 216 is, for example, a butterfly valve with a control motor.

The flow rate adjustment valve 218 is provided in the oxidant gas supply path 212 between the flow rate control valve 216 and the burner 112. The flow rate adjustment valve 218 is, for example, a butterfly valve.

[Fuel supply section 230]
The fuel supply unit 230 supplies hydrogen to the burner 112. In this embodiment, the fuel supply unit 230 includes a fuel gas supply passage 232, a pressure regulating valve 234, shutoff valves 236a and 236b, a pressure equalizing valve 238, and a flow rate regulating valve 240.

The fuel gas supply path 232 is a flow path that connects the fuel gas (hydrogen) supply source 122 (main shutoff valve 124) and the burner 112.

The pressure regulating valve 234 is provided in the fuel gas supply path 232. The pressure regulating valve 234 regulates the pressure of the hydrogen supplied downstream to a preset pressure.

Shut-off valves 236a and 236b are provided downstream of the pressure regulating valve 234 in the fuel gas supply path 232. The shut-off valves 236a and 236b open and close the fuel gas supply path 232.

The pressure equalizing valve 238 is provided downstream of the shutoff valve 236b in the fuel gas supply path 232. The pressure equalizing valve 238 equalizes the pressure between the oxidant gas supply path 212 and the fuel gas supply path 232. By providing the pressure equalizing valve 238, the pressure downstream of the flow control valve 216 in the oxidant gas supply path 212 (between the flow control valve 216 and the burner 112) and the pressure downstream of the pressure equalizing valve 238 in the fuel gas supply path 232 (between the pressure equalizing valve 238 and the burner 112) can be made substantially equal (e.g., 2 kPaG). Furthermore, by controlling the air flow rate using the flow control valve 216 through the action of the pressure equalizing valve 238, the hydrogen flow rate can be controlled while maintaining a constant ratio of the air flow rate to the hydrogen flow rate (air ratio).

The flow rate control valve 240 is provided in the fuel gas supply line 232 between the pressure equalizing valve 238 and the burner 112. The flow rate control valve 240 is, for example, a butterfly valve.

[Inert gas supply unit 250]
The inert gas supply unit 250 supplies nitrogen to the fuel gas supply path 232. In this embodiment, the inert gas supply unit 250 includes an inert gas (nitrogen) supply source 252, an inert gas supply path 254, a pressure regulating valve 256, a pressure switch 258, a shutoff valve 260, a flow rate regulating valve 262, and a check valve 264.

The nitrogen supply source 252 is, for example, a nitrogen cylinder that stores nitrogen, or a nitrogen production device. The nitrogen production device is equipped with, for example, a nitrogen separation membrane and separates nitrogen from compressed air. By using a nitrogen production device as the nitrogen supply source 252, the cost required for nitrogen can be reduced.

The inert gas supply path 254 is a flow path that connects the nitrogen supply source 252 and the fuel gas supply path 232. In this embodiment, the inert gas supply path 254 connects the nitrogen supply source 252 with the shutoff valve 236b and the pressure equalizing valve 238 in the fuel gas supply path 232.

The pressure regulation valve 256 is provided in the inert gas supply line 254. The pressure regulation valve 256 regulates the pressure of the nitrogen supplied downstream to a preset pressure.

The pressure switch 258 is provided downstream of the pressure adjustment valve 256 in the inert gas supply path 254. The pressure switch 258 detects when the pressure of the nitrogen supply source 252 falls below a predetermined value. For example, if the nitrogen supply source 252 is a nitrogen cylinder, the pressure switch 258 detects when the pressure of the nitrogen cylinder falls below a predetermined value. The provision of the pressure switch 258 makes it possible to determine when the nitrogen cylinder needs to be replaced.

Shut-off valve 260 is provided downstream of pressure switch 258 in inert gas supply line 254. Shut-off valve 260 opens and closes inert gas supply line 254.

The flow rate adjustment valve 262 is provided downstream of the shutoff valve 260 in the inert gas supply path 254. The opening of the flow rate adjustment valve 262 is adjusted by the flow rate control unit 140. The flow rate adjustment valve 262 is, for example, a butterfly valve.

The check valve 264 is provided downstream of the flow rate adjustment valve 262 in the inert gas supply path 254. The check valve 264 prevents hydrogen from entering the inert gas supply path 254 from the fuel gas supply path 232.

[Control by flow rate control unit 140]
Next, the control of the gas supply unit 120 by the flow rate control unit 140 will be described.

The flow rate control unit 140 controls one or more of the flow rate of hydrogen supplied to the burner 112 through the fuel gas supply line 232, the flow rate of nitrogen supplied to the fuel gas supply line 232 through the inert gas supply line 254, and the flow rate of air supplied to the burner 112 through the oxidant gas supply line 212, to perform pre-purge control, operation start control, operation control, operation stop control, and post-purge control.

Start-up control is control that starts the supply of hydrogen to the burner 112 and starts operation of the burner 112 (combustion equipment 110). In-operation control is performed while the burner 112 (combustion equipment 110) is in operation. In-operation control is control that is performed to operate the burner 112 (combustion equipment 110) efficiently. Shutdown control is control that stops the supply of hydrogen to the burner 112 and stops operation of the burner 112 (combustion equipment 110). Pre-purge control is control that is performed before start-up control. Post-purge control is control that is performed after shutdown control.

In this embodiment, the flow control unit 140 controls the shutoff valves 236a, 236b and the flow control valve 216 to control the flow rates of air and hydrogen supplied to the burner 112. The flow control unit 140 also controls the shutoff valve 260 and the flow adjustment valve 262 to control the flow rate of nitrogen supplied to the fuel gas supply path 232.

Figure 4 is a diagram illustrating the control of the flow rate control unit 140 according to the first embodiment. In Figure 4, the vertical axis represents flow rate. In Figure 4, the horizontal axis represents time. Note that at time T0, the blower 214 is stopped, the main shutoff valve 124 is open, and the shutoff valves 236a, 236b, and 260 are closed.

As shown in FIG. 4, the flow control unit 140 performs pre-purge control from time T1 to time T2. The flow control unit 140 also performs operation start control at time T2. The flow control unit 140 then performs operation stop control at time T7. Therefore, the flow control unit 140 performs operation control after time T2 until before time T7. The flow control unit 140 also performs post-purge control from time T7 to time T8. Each control is described in detail below.

[Pre-purge control, operation start control]
At time T1, the flow rate control unit 140 starts pre-purge control by opening the shutoff valve 260 and starting the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254. The flow rate control unit 140 adjusts the opening of the flow rate adjustment valve 262 to control the nitrogen supplied to the fuel gas supply line 232 to a flow rate Fa.

In addition, at time T1, the flow control unit 140 starts operation of the blower 214 to purge the combustion equipment 110 with air.

Then, at time T2, a predetermined time after time T1, the flow rate control unit 140 performs operation start control, which opens the shut-off valves 236a and 236b, begins supplying hydrogen to the burner 112 through the fuel gas supply line 232, ignites the gas, and starts operation of the burner 112. Also, as shown in FIG. 4, the flow rate control unit 140 performs operation start control while maintaining the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254. During operation start control, the flow rate control unit 140 adjusts the aperture of the flow rate control valve 216 to control the air flow rate to the required flow rate and to control the hydrogen supplied to the burner 112 to flow rate F1. Flow rate F1 is the minimum flow rate required for ignition.

In this way, the flow rate control unit 140 performs pre-purge control, supplying nitrogen to the fuel gas supply line 232 through the inert gas supply line 254 from time T1 to time T2. The time from time T1 to time T2 is set to the longer of the time during which the combustion equipment 110 is purged with air and the time during which the fuel gas supply line 232 is purged with nitrogen. The time during which the combustion equipment 110 is purged with air is the time from the start of air supply until approximately five times the volume of the combustion equipment 110 is supplied. The time during which the fuel gas supply line 232 is purged with nitrogen is, for example, the time from the start of nitrogen supply until approximately five times the volume of the fuel gas supply line 232 is supplied. Generally, the time during which the combustion equipment 110 is purged with air is longer than the time during which the fuel gas supply line 232 is purged with nitrogen.

[Control during operation]
Then, after time T2, the flow control unit 140 performs in-operation control to control the flow rates of air and hydrogen supplied to the burner 112 in accordance with the required heat quantity (required temperature) of the combustion equipment 110, while maintaining the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254.

For example, once ignition is complete (time T3), the flow control unit 140 increases the opening of the flow control valve 216 to increase the air flow rate and control the hydrogen supplied to the burner 112 to flow rate F2. Flow rate F2 is a flow rate greater than flow rate F1. Flow rate F2 is the flow rate required for rated combustion.

Then, once the flow rate F2 is reached (time T4), the flow rate control unit 140 maintains the flow rate F2 and performs rated combustion until time T5.

After rated combustion, that is, from time T5 to time T6, the flow control unit 140 adjusts the aperture of the flow control valve 216 based on the heat quantity required by the combustion equipment 110, and controls the flow rate of air supplied to the burner 112 to control the hydrogen flow rate within the range of flow rate F1 or more and flow rate F2 or less while maintaining a constant air ratio. Furthermore, from time T5 to time T6, the flow control unit 140 references the NOx information stored in memory 134 and controls the aperture of the flow adjustment valve 262 to control the nitrogen supplied to the fuel gas supply path 232 within the range of flow rate Fa or more and flow rate Fb or less so that the concentration of NOx contained in the exhaust gas is below a predetermined value.

Figure 5 illustrates the relationship between the volume fraction of nitrogen in the mixed gas and the concentration of NOx contained in the exhaust gas. In Figure 5, the vertical axis represents the concentration of NOx contained in the exhaust gas, and the horizontal axis represents the volume percent (vol%) of nitrogen contained in the mixed gas (hydrogen and nitrogen) supplied from the fuel gas supply line 232 to the burner 112. Also, in Figure 5, circles represent a case where the flow rate of the mixed gas supplied from the fuel gas supply line 232 to the burner 112 is relatively low (low flow rate). Also, in Figure 5, triangles represent a case where the flow rate of the mixed gas supplied from the fuel gas supply line 232 to the burner 112 is relatively high (high flow rate). Also, in Figure 5, when the mixed gas supplied from the fuel gas supply line 232 to the burner 112 contains 0% nitrogen (i.e., only hydrogen is supplied), the NOx concentration at a low flow rate is set to 100.

As shown in Figure 5, regardless of the flow rate of the mixed gas, as the nitrogen concentration in the mixed gas increases, the concentration of NOx contained in the exhaust gas decreases.

In the example shown in Figure 5, the NOx concentration in the exhaust gas tends to be lower when the flow rate of the mixed gas is high compared to when the flow rate is low. This is because the flow velocity of the mixed gas and air ejected from the burner 112 is higher when the flow rate of the mixed gas is high than when the flow rate is low. Therefore, near the burner 112 in the combustion equipment 110, the amount of exhaust gas in the combustion chamber that is entrained by the jet of mixed gas and air increases. As a result, the oxygen concentration in the combustion area decreases, which lowers the flame temperature and suppresses the amount of NOx generated (low NOx effect due to self-exhaust gas recirculation).

Therefore, as shown in FIG. 4, when the flow rate control unit 140 reduces the flow rate of hydrogen supplied to the burner 112 in accordance with the required heat quantity between time T5 and time T6, it increases the flow rate of nitrogen supplied to the fuel gas supply path 232. This allows the flow rate control unit 140 to reduce the concentration of NOx contained in the exhaust gas.

The nitrogen flow rate Fa is the larger of the flow rate at which the NOx concentration reaches a predetermined value when the hydrogen flow rate is F2, and the flow rate at which nitrogen can replace the fuel gas supply path 232 in a time equal to or shorter than the time it takes for air to replace the inside of the combustion equipment 110 during pre-purge control. The nitrogen flow rate Fb is a flow rate greater than the flow rate Fa, and is the flow rate at which the NOx concentration reaches a predetermined value when the hydrogen flow rate is F1.

Then, at time T6, the flow control unit 140 adjusts the aperture of the flow control valve 216 to control the air flow rate, setting the hydrogen flow rate to flow rate F2 and maintaining it at flow rate F2 to perform rated combustion. During rated combustion, the flow control unit 140 adjusts the aperture of the flow control valve 262 to maintain the nitrogen supplied to the fuel gas supply path 232 at flow rate Fa.

[Shutdown control, post-purge control]
Then, at time T7, the flow control unit 140 performs operation shutdown control to stop the operation of the burner 112 by stopping the supply of hydrogen to the burner 112 while maintaining the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254.

Specifically, at time T7, the flow control unit 140 closes the shut-off valves 236a and 236b, stops the supply of hydrogen to the burner 112 through the fuel gas supply path 232, and performs operation shutdown control to stop the operation of the burner 112.

Then, at time T8, a predetermined time after time T7 when the operation shutdown control was performed, the flow control unit 140 closes the shutoff valve 260 and stops the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254, thereby performing post-purge control. The flow control unit 140 also stops the operation of the blower 214 at time T8.

In this way, the flow rate control unit 140 performs post-purge control, supplying nitrogen to the fuel gas supply line 232 through the inert gas supply line 254, from time T7 to time T8. The time from time T7 to time T8 is set to the time during which the fuel gas supply line 232 is replaced with nitrogen. Note that the time from time T7 to time T8 may be the same as the time from time T1 to time T2.

As described above, the combustion system 100 according to this embodiment performs pre-purge control and post-purge control. Therefore, the combustion system 100 can prevent a combustible mixture of hydrogen and air from forming in the fuel gas supply path 232. Fuel gases such as hydrogen, which have a fast combustion rate, have a high incidence of flashback, but by performing pre-purge control and post-purge control, the combustion system 100 can prevent flashback.

Furthermore, the combustion system 100 has a simple configuration in which nitrogen is supplied to the fuel gas supply line 232, minimizing the risk of equipment damage due to flashback without the need to install a flashback prevention device such as a flame arrester in the fuel gas supply line 232. This makes it possible for the combustion system 100 to prevent flashback at low cost.

In addition to pre-purge control and post-purge control, the combustion system 100 also supplies nitrogen to the fuel gas supply line 232 during in-operation control. This allows the combustion system 100 to dilute hydrogen with nitrogen, thereby lowering the flame temperature. As a result, the combustion system 100 can reduce the NOx concentration in the exhaust gas of fuel gases with high flame temperatures, such as hydrogen.

Furthermore, the combustion system 100 can increase the flow rate of the mixed gas (hydrogen and nitrogen) injected from the fuel injection port of the burner 112, thereby promoting self-exhaust gas recirculation. This allows the combustion system 100 to lower the flame temperature, further reducing the NOx concentration in the exhaust gas.

In addition, during operation control, the combustion system 100 controls the flow rate of nitrogen so that the NOx concentration is below a predetermined value. This allows the NOx concentration in the exhaust gas to be reduced to below the predetermined value.

In addition, the combustion system 100 supplies nitrogen to the fuel gas supply path 232 during operation control, which allows the nozzle of the burner 112 and other components to be cooled, thereby improving the durability of the burner 112.

Furthermore, as described above, during operation control, the flow rate control unit 140 controls the flow rate of hydrogen supplied to the burner 112 in accordance with the required heat quantity while maintaining a constant air ratio. As a result, during operation control, the flow rate control unit 140 can improve the thermal efficiency of heating operation by burning hydrogen.

[First Modification]
In the first embodiment described above, the flow control unit 140 refers to the NOx information stored in the memory 134 and controls the opening degree of the flow rate adjustment valve 262 so that the concentration of NOx contained in the exhaust gas becomes equal to or less than a predetermined value during the in-operation control from time T5 to time T6. However, the flow rate control unit 140 may supply nitrogen to the fuel gas supply path 232 through the inert gas supply path 254 during the in-operation control.

Figure 6 is a diagram illustrating the control of the flow rate control unit 140 according to the first modified example. In Figure 6, the vertical axis represents flow rate. In Figure 6, the horizontal axis represents time.

As shown in FIG. 6, the flow rate control unit 140 of the first modified example adjusts the opening of the flow rate adjustment valve 262 during the in-operation control period from time T5 to time T6, and maintains the flow rate Fa of nitrogen supplied to the fuel gas supply path 232.

In other words, the flow rate control unit 140 of the first modified example maintains the opening degree of the flow rate adjustment valve 262 so that the nitrogen supplied to the fuel gas supply path 232 is at a flow rate Fa from time T1 to time T8.

As described above, the flow rate control unit 140 of the first modified example supplies nitrogen to the fuel gas supply path 232 during in-operation control. This allows the flow rate control unit 140 of the first modified example to lower the flame temperature and reduce the concentration of NOx in the exhaust gas.

Furthermore, the flow rate control unit 140 of the first modified example supplies nitrogen to the fuel gas supply path 232 during operation control, thereby cooling the nozzle of the burner 112, etc., and improving the durability of the burner 112.

[Second Modification]
7 is a diagram illustrating the control of the flow rate control unit 140 according to the second modified example. In FIG. 7, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 7, the flow rate control unit 140 of the second modified example controls the flow rate adjustment valve 262 during operation control so as to supply a constant ratio of nitrogen to the flow rate of hydrogen supplied to the burner 112.

For example, in the second modified example, when hydrogen is supplied to the burner 112 at a flow rate F1, the flow rate control unit 140 controls the flow rate adjustment valve 262 so that nitrogen is supplied at a flow rate Fc. The nitrogen flow rate Fc is equal to or greater than the flow rate Fa, for example, 20% by volume of the hydrogen flow rate F1. Furthermore, in the second modified example, when hydrogen is supplied to the burner 112 at a flow rate F2, the flow rate control unit 140 controls the flow rate adjustment valve 262 so that nitrogen is supplied at a flow rate Fd. The nitrogen flow rate Fd is, for example, 20% by volume of the hydrogen flow rate F2.

As explained above, the flow rate control unit 140 of the second modified example sets the flow rate of nitrogen to a predetermined volume ratio (e.g., 20% by volume) relative to the flow rate of hydrogen. As a result, in the second modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see Figure 5). Therefore, in the second modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned (combustion conditions).

Furthermore, the flow rate control unit 140 of the second modified example supplies nitrogen to the fuel gas supply path 232 during in-operation control. This allows the flow rate control unit 140 of the second modified example to lower the flame temperature and reduce the concentration of NOx in the exhaust gas.

Furthermore, the flow rate control unit 140 of the second modified example supplies nitrogen to the fuel gas supply path 232 during operation control, thereby cooling the nozzle of the burner 112, etc., and improving the durability of the burner 112.

[Third Modification]
8 is a diagram illustrating the control of the flow rate control unit 140 according to the third modified example. In FIG. 8, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 8 , the flow control unit 140 of the third modified example closes the shutoff valves 236a and 236b (the hydrogen flow rate is zero) during the period from time T5 to time T6 during the in-operation control, based on the required heat quantity of the combustion equipment 110. The flow control unit 140 of the third modified example maintains the supply of nitrogen to the fuel gas supply path 232 even during this period during which the hydrogen flow rate is zero during the in-operation control.

In one comparative example, when the supply of hydrogen is stopped during in-operation control, the supply of nitrogen to the fuel gas supply line 232 is stopped. In such a comparative example, if the fuel gas supply line 232 is not purged with nitrogen before the supply of hydrogen is resumed, there is a risk of backfire. In other words, in this comparative example, it is necessary to purge the fuel gas supply line 232 with nitrogen before resuming the supply of hydrogen. As a result, this comparative example has the problem of reduced responsiveness in stopping and resuming the supply of hydrogen during in-operation control, which reduces the accuracy of temperature control of the combustion equipment 110.

On the other hand, the flow rate control unit 140 of the third modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. As a result, the flow rate control unit 140 of the third modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, making it possible to improve the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the third modified example can control the temperature of the combustion equipment 110 with high precision.

Furthermore, the flow rate control unit 140 of the third modified example sets the flow rate of nitrogen to a predetermined volume ratio (e.g., 20% by volume) relative to the flow rate of hydrogen. As a result, in the third modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see Figure 5). Therefore, in the third modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

[Fourth Modification]
9 is a diagram illustrating the control of the flow rate control unit 140 according to the fourth modification. In FIG. 9, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 9, the flow rate control unit 140 of the fourth modified example opens and closes the shut-off valves 236a and 236b so that the flow rate of hydrogen supplied to the burner 112 is zero or a flow rate F2. For example, the fourth modified example 140 opens the shut-off valves 236a and 236b from time T2 to time T5, and supplies hydrogen to the burner 112 at a constant flow rate of F2.

Furthermore, the flow rate control unit 140 of the fourth modified example opens and closes the shut-off valves 236a and 236b so that the flow rate of hydrogen supplied to the burner 112 is zero (supply stopped) or flow rate F2 (supply resumed) based on the heat quantity required by the combustion equipment 110 between time T5 and time T6.

Then, from time T6 to time T7, the flow rate control unit 140 of the fourth modified example maintains the shut-off valves 236a and 236b in an open state so that the hydrogen supplied to the burner 112 is at a flow rate F2.

Furthermore, as in the first modification, the flow control unit 140 of the fourth modification maintains the opening degree of the flow adjustment valve 262 so that the nitrogen supplied to the fuel gas supply path 232 is at a flow rate Fa from time T1 to time T8.

As described above, the flow rate control unit 140 of the fourth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the fourth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, making it possible to improve the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the fourth modified example can perform temperature control of the combustion equipment 110 with high precision.

[Fifth Modification]
10 is a diagram illustrating the control of the flow rate control unit 140 according to the fifth modified example. In FIG. 10, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 10, the hydrogen flow rate control (opening/closing control of shut-off valves 236a, 236b) by the flow rate control unit 140 in the fifth modified example is the same as in the fourth modified example.

On the other hand, in the fifth variant, the flow control unit 140 controls the flow adjustment valve 262 during operation control so that a constant ratio of nitrogen is supplied to the flow rate of hydrogen supplied to the burner 112.

For example, in the fifth modified example, when the flow rate of hydrogen supplied to the burner 112 is F2, the flow rate control unit 140 controls the flow rate adjustment valve 262 so that the flow rate of nitrogen is Fe. The flow rate of nitrogen Fe is, for example, 20% by volume of the flow rate of hydrogen F2. Furthermore, in the fifth modified example, when the flow rate of hydrogen supplied to the burner 112 is zero, the flow rate control unit 140 controls the flow rate adjustment valve 262 so that the flow rate of nitrogen is Fa.

As described above, the flow rate control unit 140 of the fifth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the fifth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, making it possible to improve the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the fifth modified example can perform temperature control of the combustion equipment 110 with high precision.

Furthermore, the flow rate control unit 140 of the fifth modified example sets the flow rate of nitrogen to a predetermined volume ratio (e.g., 20% by volume) relative to the flow rate of hydrogen. As a result, in the fifth modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see Figure 5). Therefore, in the fifth modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

[Sixth Modification]
11 is a diagram illustrating the control of the flow rate control unit 140 according to the sixth modified example. In FIG. 11, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 11, the nitrogen flow rate control (control of the flow rate adjustment valve 262) by the flow rate control unit 140 in the sixth modified example is the same as in the first modified example.

On the other hand, the flow rate control unit 140 of the sixth modified example controls the flow rate of hydrogen supplied to the burner 112 to either zero (supply stopped), flow rate F1 (supply resumed), or flow rate F2 (supply resumed) during in-operation control. As shown in FIG. 11 , the flow rate control unit 140 of the sixth modified example adjusts the aperture of the flow rate control valve 216 during operation start control (time T2) so that the hydrogen flow rate is F1, and controls the air flow rate and hydrogen flow rate. Furthermore, at time T3 during in-operation control, the flow rate control unit 140 of the sixth modified example increases the aperture of the flow rate control valve 216 to increase the air flow rate and increase the hydrogen flow rate so that the hydrogen flow rate is F2, thereby performing rated combustion.

Then, the flow rate control unit 140 of the sixth variant adjusts the opening of the flow rate control valve 216 and controls the air flow rate and hydrogen flow rate so that the flow rate of hydrogen supplied to the burner 112 is either zero, flow rate F1, or flow rate F2 based on the heat quantity required by the combustion equipment 110 during the period from time T5 to time T6 during operation control.

Furthermore, the flow control unit 140 of the sixth modified example performs rated combustion by adjusting the opening of the flow control valve 216 so that the hydrogen flow rate becomes F2 during the in-operation control period from time T6 to time T7.

As described above, the flow rate control unit 140 of the sixth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the sixth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, making it possible to improve the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the sixth modified example can perform temperature control of the combustion equipment 110 with high precision.

[Seventh Modification]
12 is a diagram illustrating the control of the flow rate control unit 140 according to the seventh modification. In FIG. 12, the vertical axis represents the flow rate, and the horizontal axis represents time.

As shown in FIG. 12, the hydrogen flow rate control (control of the flow rate control valve 216) by the flow rate control unit 140 in the seventh modified example is the same as in the sixth modified example.

On the other hand, the flow rate control unit 140 of the seventh variant controls the flow rate adjustment valve 262 during operation control so that a fixed ratio of nitrogen is supplied to the flow rate of hydrogen supplied to the burner 112.

For example, when hydrogen is supplied to the burner 112 at a flow rate F1, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 so that nitrogen reaches a flow rate Ff. The nitrogen flow rate Ff exceeds the flow rate Fa, for example, 20% by volume of the hydrogen flow rate F1. Furthermore, when hydrogen is supplied to the burner 112 at a flow rate F2, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 so that nitrogen reaches a flow rate Fg. The nitrogen flow rate Fg is, for example, 20% by volume of the hydrogen flow rate F2.

Furthermore, in the seventh modified example, the flow rate control unit 140 controls the flow rate adjustment valve 262 during operation control so that the nitrogen flow rate becomes Fa, even when the flow rate of hydrogen supplied to the burner 112 is zero.

As described above, the flow rate control unit 140 of the seventh modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the seventh modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, making it possible to improve the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the seventh modified example can perform temperature control of the combustion equipment 110 with high precision.

Furthermore, the flow rate control unit 140 of the seventh modified example sets the flow rate of nitrogen to a predetermined volume ratio (e.g., 20% by volume) relative to the flow rate of hydrogen. As a result, in the seventh modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see Figure 5). Therefore, in the seventh modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

Second Embodiment
Fig. 13 is a diagram illustrating a combustion system 300 according to the second embodiment. Fig. 14 is a functional block diagram of a control device 330 according to the second embodiment. In Fig. 13, dashed arrows indicate signal flows.

As shown in FIG. 13, the combustion system 300 includes a combustion facility 110, a gas supply unit 120, a concentration sensor 310, and a control device 330. Components that are substantially the same as those in the combustion system 100 described above are designated by the same reference numerals and will not be described again.

The concentration sensor 310 detects the concentration of NOx contained in the exhaust gas produced by burning hydrogen within the combustion equipment 110.

As shown in FIG. 14, the control device 330 includes a central control unit 332 and a memory 334.

The central control unit 332 is composed of a semiconductor integrated circuit that includes a CPU (central processing unit). The central control unit 332 reads programs and parameters for operating the CPU from ROM. The central control unit 332 works in cooperation with RAM as a work area and other electronic circuits to manage and control the entire combustion system 300.

Memory 334 is composed of ROM, RAM, flash memory, HDD, etc. Memory 334 stores programs and various data used by the central control unit 332.

In this embodiment, the central control unit 332 functions as a signal acquisition unit 340 and a flow rate control unit 342.

The signal acquisition unit 340 acquires the detection results of the concentration sensor 310.

As in the first embodiment described above, the flow rate control unit 342 controls one or more of the flow rate of hydrogen supplied to the burner 112 through the fuel gas supply path 232, the flow rate of nitrogen supplied to the fuel gas supply path 232 through the inert gas supply path 254, and the flow rate of air supplied to the burner 112 through the oxidant gas supply path 212, thereby performing pre-purge control, operation start control, operation stop control, and post-purge control.

In this embodiment, after rated combustion during in-operation control, that is, from time T5 to time T6, the flow control unit 342 adjusts the aperture of the flow control valve 216 to control the air flow rate based on the heat quantity required by the combustion equipment 110, thereby controlling the hydrogen supplied to the burner 112 to a range of not less than flow rate F1 but not more than flow rate F2. Furthermore, from time T5 to time T6, the flow control unit 140 controls the aperture of the flow adjustment valve 262 based on the detection results of the concentration sensor 310 acquired by the signal acquisition unit 340, thereby controlling the nitrogen supplied to the fuel gas supply path 232 to a range of not less than flow rate Fa but not more than flow rate Fb, so that the concentration of NOx contained in the exhaust gas is below a predetermined value.

As described above, the combustion system 300 according to this embodiment controls the flow rate of nitrogen during in-operation control so that the NOx concentration is below a predetermined value. This allows the NOx concentration in the exhaust gas to be reduced to below the predetermined value.

While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that a person skilled in the art could conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

For example, in the first embodiment described above, the fuel supply unit 230 includes a pressure equalizing valve 238. However, the fuel supply unit 230 may include a flow control valve instead of the pressure equalizing valve 238. The flow control valve may be, for example, a butterfly valve with a control motor.

Furthermore, in the first embodiment described above, the fuel supply unit 230 is configured to include both the shut-off valve 236a and the shut-off valve 236b. However, it is sufficient for the fuel supply unit 230 to include either the shut-off valve 236a or the shut-off valve 236b.

Furthermore, in the above first embodiment and the first to seventh modified examples, the flow rate control unit 140 performs pre-purge control. However, it is sufficient for the flow rate control unit 140 to perform at least operation start control, operation control, operation stop control, and post-purge control.

Furthermore, the combustion system 300 of the second embodiment may perform the control of the first to seventh variants.

Furthermore, in the above first and second embodiments, the gas supply unit 120 is equipped with a pressure equalizing valve 238, and the air ratio is kept constant. However, the flow control unit may control the flow rate of fuel gas supplied to the burner 112 in accordance with the required heat quantity, and control the flow rate of oxidant gas supplied to the burner 112, so that the air ratio is maintained within a predetermined air ratio range, at least during control during operation.

100 Combustion system 112 Burner 140 Flow rate control section 212 Oxidant gas supply channel 232 Fuel gas supply channel 254 Inert gas supply channel 300 Combustion system 342 Flow rate control section

Claims (5)

Burner and
a fuel gas supply line connecting a fuel gas supply source and the burner;
an oxidant gas supply passage connecting the blower and the burner;
an inert gas supply channel connecting an inert gas supply source and the fuel gas supply channel;
a flow rate control unit that controls one or more of the flow rate of the fuel gas supplied to the burner through the fuel gas supply path, the flow rate of the oxidant gas supplied to the burner through the oxidant gas supply path, and the flow rate of the inert gas supplied to the fuel gas supply path through the inert gas supply path;
Equipped with
The flow rate control unit
pre-purge control for supplying the inert gas to the fuel gas supply line through the inert gas supply line;
an operation start control that is performed after the pre-purge control and starts supplying the fuel gas to the burner to start operation of the burner;
an in-operation control that is a control performed after the operation start control and that supplies the fuel gas to the burner for at least a predetermined period of time;
an operation stop control that is a control performed after the operation control, and stops the supply of the fuel gas to the burner to stop the operation of the burner;
a post-purge control that is a control that is performed after the operation shutdown control, and that supplies the inert gas to the fuel gas supply line through the inert gas supply line for a predetermined time;
and
The combustion system maintains the supply of the inert gas to the fuel gas supply line through the inert gas supply line during the period from the pre-purge control to the post-purge control . The combustion system described in claim 1, wherein, during the in-operation control, the flow rate control unit controls the flow rate of the fuel gas supplied to the burner in accordance with the required heat quantity, and controls the flow rate of the oxidizer gas supplied to the burner so as to maintain the air ratio within a predetermined range. The combustion system described in claim 1 or 2, wherein the flow rate control unit controls the flow rate of the inert gas based on the concentration of NOx contained in exhaust gas generated by burning the fuel gas during the in-operation control. The combustion system described in claim 1 or 2, wherein the flow rate control unit increases the flow rate of the inert gas supplied to the fuel gas supply line when the flow rate of the fuel gas supplied to the burner is reduced during the in-operation control. The combustion system described in claim 1 or 2, wherein the flow control unit maintains the supply of the inert gas to the fuel gas supply path even when the flow rate of the fuel gas supplied to the burner is set to zero during the in-operation control.