JP2011247554A - Combustion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve more stable combustion in a combustion device that uses biogas.SOLUTION: The combustion device 1 in which standard fuel and biogas are mixed for combustion includes: a standard fuel line 10 for supplying standard fuel as main fuel; a biogas line 30 configured to supply the biogas as sub-fuel, and having biogas supply valves 31, 32 for regulating the supply of the biogas; and a controller 50 for controlling the opening/closing of the biogas supply valve 31 to regulate the mixing quantity of the biogas with respect to the standard fuel.

Description

  The present invention relates to a combustion apparatus that burns fuel in a boiler or the like, and more particularly to a combustion apparatus that uses biogas as fuel.

  In recent years, due to increasing awareness of environmental issues, there has been an increasing tendency to effectively use biogas obtained by fermenting sewage sludge and organic factory wastewater as an energy source. For example, Patent Documents 1 to 4 listed below disclose combustion apparatuses that use biogas as fuel.

  By the way, normally, since the generation amount and components of biogas are not stable, if biogas is used alone as a fuel, combustion may become unstable or a desired output may not be stably obtained. . For this reason, the following Patent Documents 1 to 4 disclose that a fuel that can be stably supplied, such as city gas, is supplementarily mixed with biogas and used.

JP 2002-226878 A JP 2003-065083 A JP 2003-065084 A JP 2003-222324 A

  However, if a biogas having an unstable component is used as a fuel, it is inevitable that it becomes an obstacle to stable combustion, and incomplete combustion is likely to occur by using biogas as a fuel. Further, when biogas is used as a fuel when the combustion state such as ignition is not stable, not only incomplete combustion is promoted but also the fire is extinguished.

  This invention is made | formed in view of such a subject, and aims at implement | achieving more stable combustion in the combustion apparatus which uses biogas.

  In order to solve the above-described problems, a combustion apparatus according to the present invention includes a standard fuel line that supplies standard fuel as a main fuel and a secondary fuel as a secondary fuel in a combustion apparatus that mixes and burns standard fuel and biogas. A biogas line having a biogas supply valve for supplying biogas and adjusting a supply of biogas, and a control for controlling opening and closing of the biogas supply valve to adjust a mixing amount of the biogas with respect to the standard fuel And a vessel. The biogas supply valve includes not only a single valve but also a plurality of valves such as a combination of a shutoff valve and a flow control valve.

  According to the present invention, it is possible to prevent the occurrence of incomplete combustion and the extinction of fire due to mixing of biogas.

FIG. 1 is a schematic diagram schematically showing the configuration of a combustion apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the biogas mixing timing in the present embodiment in comparison with the combustion mode. FIG. 3 is a view for explaining stable combustion according to the present embodiment.

  Hereinafter, a combustion apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a combustion apparatus mounted on a boiler will be described as an example. FIG. 1 is a schematic diagram schematically showing the configuration of the combustion apparatus according to the present embodiment. As shown in the figure, a combustion apparatus 1 is a combustion apparatus mounted on a boiler 5, and a controller for controlling the boiler 5 including a main burner 6, a pilot burner 7, a fuel supply line 10, and the combustion apparatus 1. 50.

  The fuel supply line 10 includes a standard fuel supply line 20, a biogas supply line 30, a main supply line 40, and a pilot supply line 45. The standard fuel supply line 20 is a line that supplies city gas that is the main fuel of the combustion apparatus 1. The standard fuel supply line 20 includes a flow rate control valve 22 for adjusting the flow rate of the standard gas flowing through the line. As standard fuel, gas fuel such as propane gas or liquid fuel such as kerosene or light oil may be supplied.

  The biogas supply line 30 is a line for supplying biogas, which is a secondary fuel of the combustion apparatus 1, and includes a buffer tank 35, an electromagnetic valve 31, and a flow control valve 32. The buffer tank 35 is provided with a sensor 36 for detecting the biogas content in the buffer tank 35. For example, a pressure sensor or a differential pressure sensor is used as the sensor 36.

  The solenoid valve 31 and the sensor 36 are connected to the controller 50. The output of the sensor 36 is transmitted to the controller 50, and the controller 50 controls the opening and closing of the electromagnetic valve 31. When the controller 50 determines from the output of the sensor 36 that the remaining amount of biogas in the buffer tank 35 is less than a predetermined value, the controller 50 closes the solenoid valve 31 to stop the supply of biogas and burns only with the standard fuel. The apparatus 1 is operated. Thereby, even when the biogas in the buffer tank 35 is emptied, it is possible to prevent the biogas supply equipment from being damaged by continuing the supply of the biogas.

  A mixer (mixer) 15 is installed at a junction of the standard fuel supply line 20 and the biogas supply line 30 of the fuel supply line 10, and the standard fuel supply line 20 and the biogas supply line 30 are input to the mixer 15. Connected to the side.

  Therefore, the city gas and the biogas are mixed in the mixer 15, and this mixed fuel (mixed gas) is supplied to the downstream side of the line. In addition, the mixing amount of the biogas with respect to the standard fuel (city gas) in the present embodiment is adjusted by the mixer 15 and the flow control valve 32 so that the volume ratio is 10%.

  The fuel supply line 10 is branched downstream of the mixer 15 into a main supply line 40 that supplies fuel to the main burner 6 and a pilot supply line 45 that supplies fuel to the pilot burner 7. Biogas mixed fuel or standard fuel is supplied to both the main supply line 40 and the pilot supply line 45.

  The main supply line 40 is provided with a main flow rate control unit 12 including a pressure sensor, a solenoid valve, a flow rate control valve, and the like. The fuel flowing into the main supply line 40 is supplied by the main flow rate control unit 12. The flow rate is appropriately adjusted according to the amount of combustion in the main burner 6.

  In the present embodiment, the fuel supply amount is controlled by proportional valve control, that is, the fuel supply amount is controlled according to the supply amount of combustion air from the blower. Of course, other control methods may be adopted. For example, the fuel supply amount may be controlled by a shut-off valve type that independently controls the supply amount of combustion air and the fuel supply amount. In this case, the fuel supply amount is controlled by opening and closing the fuel supply valve for high fuel that is controlled to open only in the high combustion mode.

  Note that the boiler 5 according to the present embodiment has three combustion modes of high combustion, low combustion (for example, 50% of high combustion), and stop while repeatedly controlling the pre-purge, combustion, and post-purge stages. It is a boiler that is controlled by position, that is, has a multi-stage combustion mode.

  Next, biogas mixing timing in this embodiment will be described. FIG. 2 is a diagram showing the mixing timing of the biogas in the present embodiment in comparison with the combustion mode. FIG. 2A shows the mixing timing according to the first embodiment, and FIG. 2B shows the mixing timing according to the second embodiment. ing.

  In the figure, a circle indicates that the fuel is supplied, and a cross indicates that the supply of the fuel is stopped. In addition, mixing of the following biogas and stop of mixing are realized by the controller 50 controlling the opening and closing of the electromagnetic valve 31.

  As shown in FIG. 2 (a), in the first embodiment, after the initial ignition of the combustion apparatus 1, biogas mixing is not performed until a predetermined time has elapsed, and only standard fuel is supplied to the burners 6 and 7. . The predetermined time is a time until the combustion with only the standard fuel is stabilized, and in the present embodiment, is a time until shifting to the low combustion mode.

  When shifting to low combustion (L) and becoming a stable combustion state, the supply of biogas is started, the standard fuel and the biogas are mixed, and the mixed fuel is combusted. Thereafter, when the transition from low combustion to high combustion (H) is started, the supply of biogas is stopped and combustion using only the standard fuel is performed.

  Thereafter, when the combustion shifts to a high combustion state and a stable combustion state is reached, the supply of biogas is started again, and the combustion with the mixed fuel is resumed. When the transition from high combustion to low combustion is started, the supply of biogas is stopped, and when the transition to low combustion is started, the supply of biogas is resumed.

  Thereafter, when the transition to the pilot combustion (P) in which the combustion of the main burner 6 is stopped and only the pilot burner 7 is started is started, the supply of biogas is stopped again. When shifting to pilot combustion and entering a standby state, pilot combustion using only standard fuel is continued.

  As described above, in the first embodiment, the combustion with the mixed fuel of the biogas is limited to the combustion mode of the low combustion and the high combustion, and during the transition of the combustion mode and at the time of pilot combustion until a predetermined time elapses after ignition. The biogas is controlled not to be supplied. This is to prevent instability of combustion caused by mixing biogas having unstable components.

  Here, stable combustion will be described with reference to FIG. FIG. 3 is a diagram for explaining stable combustion according to the present embodiment, where the vertical axis represents the oxygen concentration in the combustion gas, and the horizontal axis represents the calorific value.

  The stable combustion range is a range in which the fuel can be combusted stably, and if the stable combustion range is deviated, incomplete combustion occurs or the flame disappears. In the present embodiment, the stable combustion range is defined by the calorific value and the oxygen concentration. In the figure, the range surrounded by the solid line A and the solid line B which are bold lines is the stable combustion range.

Moreover, in the figure, the solid line C shows the combustion state in the low combustion mode (L), and the solid line D shows the combustion state in the high combustion mode (H). In solid lines C and D, points L ₀ and H ₀ indicated by circles indicate the combustion state using only the standard fuel, and points L ₁ and H ₁ indicated by triangles indicate a volume ratio of 10 to the standard fuel (city gas). % combustion state by mixing fuel by mixing the biogas, point L _2, H ₂ indicated by square marks represents the combustion state by standard fuel mixed fuel prepared by mixing 30% of biogas volume ratio (city gas) ing.

Also, in the figure, the two-dot chain line connecting the points L ₀ → H ₀ and H ₀ → L ₀ is the combustion at the time of transition from low combustion to high combustion and from high combustion to low combustion under the combustion of only the standard fuel It shows the transition of the state. On the other hand, the alternate long and short dash line connecting the points of L ₀ → H ₁ shows the transition of the combustion state during the transition from low combustion (standard fuel only) to high combustion (standard fuel + 10% biogas), and the point of H ₁ → L ₀ The alternate long and short dash line connecting the two indicates the transition of the combustion state at the time of transition from high combustion (standard fuel + 10% biogas) to low combustion (standard fuel only).

  As shown in the figure, in both cases of low combustion and high combustion, in the case of only standard fuel and in the case of standard fuel + 10% biogas, the combustion state is within the range of stable combustion. In the case of fuel + 30% biogas, it is outside the range of stable combustion. Therefore, in order to ensure stable combustion when mixing biogas, it is desirable that the amount of biogas mixed be 25% or less by volume ratio (when the standard fuel is gas).

In addition, when the combustion mode is shifted from low combustion to high combustion and from high combustion to low combustion, the combustion state once oscillates in an unstable direction, as indicated by the alternate long and short dash line. In particular, in the transition from low combustion to high combustion, the oxygen concentration greatly fluctuates in the direction of increasing, and the transition from L _{0 to} H ₁ indicated by the alternate long and short dash line is out of the stable combustion range. .

  Thus, since the combustion state tends to become unstable during the transition to the combustion mode as compared with that during the combustion mode, as shown in FIG. 2, in the present embodiment, during the transition to the combustion mode. Stops supplying biogas and burns only with standard fuel.

  Here, the combustion state becomes unstable when the mode is changed. In general, the combustion apparatus is controlled so as to keep the balance between the fuel and the combustion air amount constant, but if the fuel property changes when the combustion mode is changed. This is because the balance between the fuel and the amount of combustion air is temporarily lost.

  The range of stable combustion at the time of low combustion shown in FIG. 3 indicates that the oxygen concentration is in the range of approximately 2 to 6%. Generally, if the oxygen concentration of the combustion gas is within this range, Although it becomes stable combustion, it is more preferable that it is in the range of 3 to 5%.

  Next, Example 2 will be described. As shown in FIG. 2B, the second embodiment is characterized in that biogas is not mixed in the high combustion mode as compared with the first embodiment, and other mixing timing is the same as that of the first embodiment. The same.

  As shown in FIG. 3, the supply of biogas was stopped in the high combustion mode, as shown in FIG. 3, in the high combustion mode with a large calorific value, the stable combustion range of the oxygen concentration was narrowed compared to the low combustion mode, leading to unstable combustion. This is because it is easy. Therefore, according to the second embodiment, the biogas consumption is reduced, but in addition to the operational effects of the first embodiment, stable combustion can be ensured even at higher combustion.

  As described above, the present embodiment has been described in detail. In the present embodiment, control is performed so that mixed combustion using standard fuel and biogas is performed at a timing at which stable combustion can be maintained even if biogas is mixed. It is possible to prevent the occurrence of incomplete combustion and the extinction of fire due to the mixing of biogas. Thereby, biogas can be effectively utilized by the stable combustion.

  Furthermore, in the present embodiment, even when the remaining amount of biogas in the buffer tank installed in the biogas supply line is less than a predetermined value, control is performed so as not to mix biogas, which is insufficient. Unstable combustion due to the supply of biogas and damage to the biogas supply equipment can also be prevented.

  The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the combustion apparatus installed in the boiler has been described. However, the present invention can also be applied to a combustion apparatus installed in equipment other than the boiler, such as an incinerator, a combustion furnace, and an absorption refrigerator. Needless to say.

  In the above embodiment, the combustion apparatus having the two combustion modes of low combustion and high combustion has been described. However, the present invention includes three combustion modes such as a combustion apparatus having three combustion modes of low combustion, medium combustion, and high combustion. The present invention can also be applied to a combustion apparatus having two or more multi-stage combustion modes.

  Furthermore, the present invention can also be applied to a single combustion mode combustion apparatus. Also in this case, stable combustion can be ensured in the combustion apparatus using the biogas mixed fuel by stopping the mixing of the biogas during the period until the combustion becomes stable after ignition or during pilot combustion.

  Moreover, in the said embodiment, although it has comprised so that the mixing amount of biogas may be switched by volume ratio 0% (at the time of mixing stop) or 10% (at the time of mixing) with respect to standard fuel (city gas), The mixing amount may be adjusted in multiple stages. Specifically, the mixing amount may be adjusted continuously by a proportional control valve, or the mixing amount may be adjusted stepwise by opening and closing shut-off valves arranged in parallel. However, in any case, it is desirable to mix within a range of 0 to 25% by volume ratio.

DESCRIPTION OF SYMBOLS 1 Combustion device 5 Boiler 6 Main burner 7 Pilot burner 10 Fuel supply line 15 Mixer 20 Standard fuel supply line 30 Biogas supply line 31 Solenoid valve 32 Flow control valve 35 Buffer tank 36 Sensor 40 Main supply line 45 Pilot supply line 50 Control vessel

Claims (5)

In a combustion device that mixes and burns standard fuel and biogas,
A standard fuel line for supplying standard fuel as the main fuel;
A biogas line having a biogas supply valve for adjusting the supply of biogas, supplying biogas as an auxiliary fuel;
And a controller for controlling opening and closing of the biogas supply valve in order to adjust a mixing amount of the biogas with respect to the standard fuel.   2. The combustion apparatus according to claim 1, wherein the controller controls opening and closing of the biogas supply valve so that stable combustion is achieved even when the biogas is mixed with the standard fuel.   The controller controls the biogas supply valve to be closed when the combustion apparatus is ignited and to open the biogas supply valve after a predetermined time has elapsed after ignition with the standard fuel. Or the combustion apparatus of 2. The combustion device is a combustion device installed in a boiler having a multi-stage combustion mode,
The combustion apparatus according to any one of claims 1 to 3, wherein the controller controls the biogas supply valve to be closed during the transition to the combustion mode. The combustion device is a combustion device installed in a boiler having a multi-stage combustion mode,
The combustion apparatus according to any one of claims 1 to 3, wherein the controller controls the biogas supply valve to close during high combustion.

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