JP2016006356A - Boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler 1 capable of easily and rapidly detecting a valve-over leakage of a shutoff valve 14 for changing-over a presence or non-presence of gas supply for a burner 4 when the shutoff valve is closed, showing a superior load following characteristic while assuring its safety characteristic and reducing radiation loss as well.SOLUTION: A leakage detection means 16 determines presence or non-presence of a gas valve-over leakage exceeding a set flow rate during closed-state of a shutoff valve 14. While the burner 4 is stopped, when leakage exceeding the set flow rate is detected by the leakage detection means 16, operation transfer to an igniting operation is prohibited, and in turn when a leakage exceeding the set flow rate is not detected, an operation transfer to an igniting operation without any purge can be carried out if it is within a safe waiting time form completion of purging after closing of the shutoff valve 14. The safe waiting time is set within a time in which gas concentration within a furnace reaches an explosion lower limit concentration. Since the operation transfer to the igniting operation can be carried out without any pre-purge, it shows a superior load following characteristic and a heat radiation loss can also be reduced.

Description

  The present invention relates to a gas-fired boiler.

  In a gas-fired boiler, a shut-off valve that switches whether gas is supplied to the burner is provided in a gas supply path to the burner. As a method for controlling the boiler by monitoring the presence and amount of over-leakage (gas leakage due to poor closing) when the shut-off valve is closed, for example, a technique disclosed in Patent Document 1 below is known.

  In this prior art, during post purge, based on the pressure change between the double shutoff valves, the presence or absence of leakage through each shutoff valve is determined. It is determined whether or not the amount is less than or equal to an allowable value. If no leak is detected, the pre-purge can be skipped and the ignition operation can be performed.On the other hand, if the leak is detected, if the leak amount is less than the allowable value, the pre-purge can be shifted to the ignition operation. If the amount is larger than the allowable value, the post purge is continued to prevent the shift to the ignition operation. In other words, in the prior art, the presence / absence and amount of leakage is determined, and pre-purge is omitted only when there is no leakage. If there is leakage below the allowable value, pre-purge is performed, and if there is leakage exceeding the allowable value, post-purging is performed. Continue purging.

Japanese Patent No. 3931619

  For detection of over-leakage when the shut-off valve is closed, it is simple and quick to check whether there is a leak exceeding the set flow rate. However, in this case, even if it is determined that there is no leakage, it must be considered that there is a possibility of leakage of the set flow rate as a worst case. There is a risk that a small amount of leaked gas may accumulate in the furnace, and safety measures in that case are required.

  Considering this point, it can be said that in the prior art, pre-purge is performed before the shift to the ignition operation even if the leakage amount is less than the allowable value. However, ignition is delayed by the amount of pre-purge execution, and load followability (responsiveness to fluctuations in steam pressure in the case of a steam boiler) is poor. Moreover, since the heat in the furnace is released to the outside by the pre-purge, the heat dissipation loss increases.

  Therefore, the problem to be solved by the present invention is to provide a boiler that can easily and quickly detect leakage through a valve and has excellent load followability and reduced heat dissipation loss while ensuring safety.

  The present invention has been made to solve the above-mentioned problems. The invention according to claim 1 is directed to a shutoff valve for switching the presence / absence of gas supply to a burner, and a gas exceeding a set flow rate while the shutoff valve is closed. The leakage detection means for determining the presence or absence of over-valve leakage, and when the leakage detection means detects leakage exceeding the set flow rate during combustion stop of the burner, it is impossible to shift to the ignition operation, while the set flow rate If the leakage exceeding the above is not detected, the boiler includes an operation control means capable of shifting to an ignition operation without pre-purge within a safety waiting time from the end of the purge after the shutoff valve is closed.

  According to the first aspect of the present invention, it is possible to determine whether or not there is a gas leaking over the set flow rate while the shutoff valve is closed. And when the leak exceeding a setting flow volume is detected, since it cannot make transfer to ignition operation, safety | security can be ensured. On the other hand, if no leakage exceeding the set flow rate is detected, it is possible to shift to ignition operation without pre-purge within the specified safety standby time after purging. Loss can also be reduced.

  The invention according to claim 2 assumes that there may be a leak of the set flow rate at the maximum, even if a leak exceeding the set flow rate is not detected, and the furnace volume, the gas lower explosive limit concentration, and the set flow rate. 2. The boiler according to claim 1, wherein the safety standby time is set within a time until the gas concentration in the furnace reaches the lower explosion limit concentration.

  According to the second aspect of the present invention, when a leak exceeding the set flow rate is not detected, the safety standby time is set within the time until the gas concentration in the furnace reaches the lower explosion limit concentration, and the safety standby time is set. If it is within, it is possible to shift to the ignition operation without pre-purge, so that it is excellent in load followability and heat dissipation loss can be reduced while ensuring safety.

  According to a third aspect of the present invention, when the leakage exceeding the set flow rate is not detected, the inside of the furnace is purged every safety waiting time during the standby due to the combustion stop of the burner. Item 3. The boiler according to Item 2.

  According to the third aspect of the present invention, when the leakage exceeding the set flow rate is not detected, the gas concentration in the furnace is reduced to the lower explosion limit concentration by purging the inside of the furnace every safety waiting time during the standby of the boiler. Since it does not exceed, safety can be ensured.

  According to a fourth aspect of the present invention, in the boiler according to the third aspect, if there is a load request during standby between the purges, the operation shifts to an ignition operation without pre-purge.

  According to the fourth aspect of the present invention, when the leakage exceeding the set flow rate is not detected, the gas concentration in the furnace is reduced to the lower explosion limit concentration by purging the inside of the furnace every safety waiting time during the standby of the boiler. Since it does not exceed, it is safe to shift to the ignition operation without pre-purge. Moreover, since it is possible to shift to the ignition operation without pre-purge, the load followability is excellent.

  According to a fifth aspect of the present invention, a post-purge is performed immediately after the shut-off valve is closed, and a purge that is being executed is performed during a purge other than the post-purge during the purge after the shut-off valve is closed. The boiler according to claim 3 or 4, wherein the boiler is stopped in the middle and shifted to an ignition operation.

  According to the fifth aspect of the present invention, when the leakage exceeding the set flow rate is not detected, the gas concentration in the furnace is reduced to the lower explosion limit concentration by purging the inside of the furnace every safety waiting time during the standby of the boiler. Therefore, it is safe to stop the purge during the purge and shift to the ignition operation without pre-purge. Moreover, since it is possible to shift to the ignition operation without pre-purge, the load followability is excellent.

  In the invention according to claim 6, even if a pair of the shutoff valves are provided in series in the gas supply path to the burner, and no leakage exceeding the set flow rate is detected while the shutoff valve is closed, The boiler according to any one of claims 1 to 5, wherein it is constantly monitored that the pressure between the shut-off valves closed with the pressure between the shut-off valves being open does not exceed a predetermined pressure. It is.

  According to the sixth aspect of the present invention, even when no leakage exceeding the set flow rate is detected, a small amount of gas over a relatively long period of time can be monitored by constantly monitoring that the pressure between the shutoff valves does not exceed the predetermined pressure. The presence or absence of leakage can be monitored.

Furthermore, the invention described in claim 7 sets the predetermined pressure to P _in × α, and monitors whether the leakage flow rate through the valve during closing of the shutoff valve does not exceed Q _max × √α (however, , Q _max is the set flow rate, the P _in a boiler according to claim 6, wherein the gas supply pressure, alpha numeric less than 1).

According to the seventh aspect of the present invention, even when a leak exceeding the set flow rate is not detected, by constantly monitoring that the pressure between the shutoff valves does not exceed P _in × α, the leak rate through the valve is Q _max. It can be ensured that x√α is not exceeded.

  According to the boiler of the present invention, leakage through a valve can be detected easily and quickly, and it is excellent in load followability and can reduce heat dissipation loss while ensuring safety.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the boiler of one Example of this invention, and shows a part in cross section.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing a boiler 1 according to an embodiment of the present invention, and a part thereof is shown in cross section.

  The boiler 1 of this embodiment is a gas-fired multi-tube once-through boiler, a can body 3 provided with a large number of water pipes 2, a burner 4 for heating the water pipe 2 of the can body 3, and the burner 4 combusting. A blower 5 for supplying working air, a gas supply path 6 for supplying fuel gas to the burner 4, and an exhaust gas path 7 for discharging exhaust gas from the can 3 are provided.

  The can body 3 is configured by connecting the upper header 8 and the lower header 9 with a number of water pipes 2 and is covered with a can cover (not shown). The shape of the can 3 is not particularly limited, but is a square in this embodiment. The can body 3 is appropriately supplied with water from the lower header 9 into the water pipe 2 through the water supply passage 10, and the water level in the water pipe 2 is maintained as desired. The can 3 is provided with a burner 4 at one end and an exhaust gas path 7 at the other end. The exhaust gas path 7 is provided with an economizer as desired. The combustion gas from the burner 4 (including the flame at the beginning) is exchanged with the water in each water pipe 2 and then led out from the exhaust gas passage 7 as exhaust gas. The water in each water pipe 2 is heated by the combustion gas from the burner 4 and is led out as steam from the upper header 8 to the steam path 11 via a steam separator (not shown). The steam is sent to various steam-using facilities via a steam header or the like as desired.

  The burner 4 is a premix burner in this embodiment, but may be a premix burner in some cases. In the illustrated example, the burner is a completely premixed burner having a flat combustion surface (premixed gas ejection surface). The burner 4 may be switched on or off for the presence or absence of combustion, and the amount of combustion may be adjusted stepwise or continuously. For example, the burner 4 can switch the combustion amount at three positions: high combustion (100% combustion), low combustion (for example, 50% combustion), and stop. Alternatively, the burner 4 can switch the combustion amount at four positions of high combustion, medium combustion, low combustion, and stop. Alternatively, the burner 4 is continuously adjusted in combustion amount in proportion to the increase / decrease in load demand. In any case, the burner 4 is supplied with combustion air and gas in an amount corresponding to the combustion amount.

  The combustion air is supplied to the burner 4 by feeding the air from the blower 5 through the combustion air passage 12. For adjusting the flow rate of the combustion air, a damper (a plate material whose inclination angle can be changed) 13 is provided in the combustion air passage 12 to adjust the position of the damper 13, but instead of or in addition to this, an inverter May be used to change the rotational speed of the motor of the blower 5.

  In this embodiment, the gas is supplied to the burner 4 by feeding the gas from the gas supply path 6 through the combustion air path 12. When the damper 13 is provided in the combustion air passage 12, gas is supplied from the gas supply passage 6 to the combustion air passage 12 downstream from the damper 13. The gas from the gas supply path 6 is ejected in the combustion air path 12, mixed with the air from the blower 5, and sent to the burner 4.

  The gas supply path 6 is provided with a shutoff valve 14 for switching the presence or absence of gas supply. In the present embodiment, the gas supply path 6 is provided with a pair of shut-off valves (upstream shut-off valve 14A and downstream shut-off valve 14B) arranged in series and an orifice 15 in this order. When the gas supply to the burner 4 is executed, each shut-off valve 14 is opened, and when the gas supply to the burner 4 is stopped, each shut-off valve 14 is closed. In this embodiment, the downstream shut-off valve 14B has a function of maintaining the gas pressure on the outlet side at a desired pressure when opened. Further, the gas supply path 6 may be provided with a flow rate adjustment valve (not shown) downstream from each shutoff valve 14. It is possible to adjust the air ratio according to the combustion amount by changing the opening degree of the flow rate adjusting valve according to the combustion amount.

  When the burner 4 is ignited using a pilot burner, the boiler 1 further includes a pilot burner (not shown) in addition to the main burner 4 as the burner. The pilot burner is provided close to the main burner 4 and is ignited by an ignition device. During the combustion of the pilot burner, combustion air and gas are supplied to the pilot burner. The blower for supplying combustion air to the pilot burner may be configured identically or integrally with the blower 5 for supplying combustion air to the main burner 4, or may be provided separately from the blower 5 for the main burner 4. Good. In any case, it is preferable that the presence / absence and amount of combustion air supplied to each burner can be individually changed by using a damper as desired.

  In the boiler 1 of this embodiment, the gas leakage over the set flow rate (gas leakage due to poor closing under the condition to be closed) of one or both of the shut-off valves 14 during the shut-off of each shut-off valve 14 is further performed. Leak detection means 16 for determining presence or absence is provided. The specific configuration of the leak detection means 16 is not particularly limited, but typically, the pressure between the shutoff valves 14 is monitored to determine the presence or absence of leakage through the valve. In this case, the leak detection means 16 includes pressure detection means (pressure switch or pressure sensor) between the shutoff valves 14. Then, the controller determines whether or not there is a valve leakage exceeding the set flow rate, based on the detection signal from the pressure detection means, while controlling the opening and closing of each shut-off valve 14 as necessary. This controller may be configured integrally with a controller of operation control means (not shown) described later. Alternatively, the pressure detection means and the controller of the leak detection means 16 may be unitized as a valve probing system (VPS) 16A. In that case, the controller of the operation control means, which will be described later, controls the boiler 1 by acquiring a result of determining whether the valve 14 leaks through the valve probing system 16A.

  The leak detection means 16 of the present embodiment determines whether or not each shut-off valve 14 has leaked through the valve as follows, but only a part of the judgment functions (for example, the judgment function of the downstream-side shut-off valve 14B) depending on the case. You may have. Alternatively, even when determining the over-leakage for both shut-off valves 14, only one of the determination results of the over-leakage determination results for both shut-off valves 14 is used in the control by the operation control means described later. May be.

  The determination of over-leakage of the upstream shut-off valve 14A is made by the following (A1) or (A2).

  (A1) After closing the pair of shut-off valves 14, the space between the shut-off valves 14 is opened to atmospheric pressure via a predetermined mechanism of the leak detection means 16 (in other words, not via the downstream shut-off valve 14B). . And the pressure between the cutoff valves 14 is monitored in the state which closed the open part. If there is a predetermined pressure rise between the shutoff valves 14 (for example, if the first set pressure is exceeded within the first set time), it is determined that there is a leak exceeding the set flow rate in the upstream shutoff valve 14A. On the other hand, if there is no such pressure increase, it is determined that there is no leakage exceeding the set flow rate in the upstream shutoff valve 14A.

  (A2) With the pair of shutoff valves 14 closed, the downstream shutoff valve 14B is once opened and then closed. Alternatively, when closing the shutoff valve 14 when the combustion of the burner 4 is stopped, the upstream shutoff valve 14A is first closed, and then the downstream shutoff valve 14B is closed with a delay. In any case, the pressure between the shutoff valves 14 can be reduced to a predetermined value (in-furnace pressure in this embodiment), and then the pressure between the shutoff valves 14 is monitored. If there is a predetermined pressure rise between the shutoff valves 14 (for example, if the second set pressure is exceeded within the second set time), it is determined that the upstream shutoff valve 14A has a leak exceeding the set flow rate. On the other hand, if there is no such pressure increase, it is determined that there is no leakage exceeding the set flow rate in the upstream shutoff valve 14A.

  The determination of over-leakage of the downstream shut-off valve 14B is made by the following (B1) or (B2).

  (B1) After closing the pair of shut-off valves 14, the gap between the shut-off valves 14 is supplied from the gas supply source via a predetermined mechanism of the leak detection means 16 (in other words, not via the upstream shut-off valve 14A). Gas can be supplied. For example, after the pressure between the shutoff valves 14 is released, the gas supply pressure is applied between the shutoff valves 14 in a state where the open portion is closed. If the pressure between the closed shut-off valves 14 cannot be increased to a predetermined level (for example, boosted to the third set pressure within the third set time), it is determined that the downstream shut-off valve 14B has a leak exceeding the set flow rate. On the other hand, if the pressure can be increased to a predetermined level, it is determined that there is no leakage exceeding the set flow rate in the downstream cutoff valve 14B.

  (B2) With the pair of shutoff valves 14 closed, the upstream shutoff valve 14A is once opened and then closed. Alternatively, when closing the shutoff valve 14 when combustion of the burner 4 is stopped, the downstream shutoff valve 14B is first closed, and then the upstream shutoff valve 14A is closed with a delay. In either case, the gas supply pressure can be applied between the shutoff valves 14, and then the pressure between the shutoff valves 14 is monitored. If there is a predetermined pressure drop between the shutoff valves 14 (for example, if the pressure drops below the fourth set pressure within the fourth set time), it is determined that the downstream shutoff valve 14B has a leak exceeding the set flow rate. On the other hand, if there is no such pressure drop, it is determined that there is no leakage exceeding the set flow rate in the downstream shutoff valve 14B.

  Here, based on whether the pressure between the shutoff valves 14 exceeds (or falls below) the set pressure within the set time, the presence / absence of leakage through the valve exceeding the set flow rate is determined. Alternatively, the pressure drop rate) may be monitored to determine whether there is leakage through the valve exceeding the set flow rate.

  The boiler 1 is controlled by a controller (not shown) as operation control means. In particular, the controller is connected to the motor of the blower 5, the position adjusting device of the damper 13, each shut-off valve 14, the leak detection means 16, and the like, and controls the combustion of the burner 4 based on the load request.

  In the case of a steam boiler, the load requirement is a load for use of steam, and can be monitored based on the steam pressure (steam pressure at or within the can 3 where steam is supplied). When the load requirement is large, the vapor pressure decreases, while when the load requirement is small, the vapor pressure increases. Therefore, the vapor pressure is monitored by a pressure detector (pressure sensor or pressure switch). The controller determines that there is no load request when the vapor pressure exceeds the upper limit pressure, and determines that there is a load request when the vapor pressure falls below the lower limit pressure. When there is no load request, combustion of the burner 4 is stopped, while when there is a load request, the burner 4 is burned. During the combustion of the burner 4, as described above, the combustion amount of the burner 4 may be adjusted stepwise or continuously in accordance with the increase or decrease of the load demand.

  In order to burn the gas in the burner 4, the blower 5 is operated and each shut-off valve 14 is opened, and ignition is performed by a pilot burner (or an ignition device). On the other hand, in order to stop the combustion in the burner 4, each shut-off valve 14 may be closed. While waiting for the combustion of the burner 4 to stop, the blower 5 is stopped. Instead of or in addition to this, a damper is provided on the inlet side or the outlet side of the blower 5 and the damper is closed, or a damper is provided in the exhaust gas passage. The damper may be closed.

  The combustion amount of the burner 4 is adjusted by adjusting the flow rates of combustion air and gas supplied to the burner 4. The adjustment of the flow rate of the combustion air is performed by adjusting the position of the damper 13 or changing the rotational speed of the motor of the blower 5 using an inverter instead of or in addition to this. On the other hand, the gas flow rate may be adjusted by changing the opening of a flow rate adjusting valve (not shown) provided in the gas supply path 6.

  While each shut-off valve 14 is closed (that is, when combustion of the burner 4 is stopped), at the set timing, the leak detection means 16 determines whether one or both shut-off valves 14 have a gas exceeding the set flow rate through the valve. . If a leak through the valve exceeding the set flow rate is detected, the controller will not allow subsequent ignition. For example, 5 [L / hr] is set as the set flow rate, and the pressure change necessary for the determination (for example, the pressure drop during the inspection of the downstream side shutoff valve 14B) is, for example, about 150 [Pa / s], which is sufficient Safety is ensured.

  If the controller does not detect over-valve leakage exceeding the set flow rate, it will pre-purge if there is a load request within a predetermined safe waiting time after post-purging (and intermittent intermittent purging, which will be described later). Shift to ignition operation without The post-purge is furnace ventilation performed immediately after the combustion of the burner 4 is stopped, and the pre-purge is furnace ventilation performed immediately before the combustion of the burner 4 is started. After the post-purge, the boiler 1 is in a standby state waiting for a load request. If there is a load request during this standby, the boiler 1 is conventionally ignited after the pre-purge. However, in the case of the boiler 1 of this embodiment, within the safe standby time. Since there is no possibility of explosion, pre-purge can be omitted.

  The safety standby time is set as the standby time that can be safely ignited without ventilation within the time until the inside of the furnace reaches the lower explosion limit concentration. In other words, even if the leak detection means 16 does not detect a leak exceeding the set flow rate, there may be a leak of the set flow rate at the maximum, and this is taken into consideration based on the furnace volume, the gas lower explosive limit concentration and the set flow rate. The safety standby time is set within the time until the gas concentration in the furnace reaches the lower explosion limit concentration. For example, when the furnace volume in the can 3 is 181 [L] and the fuel gas is propane (lower explosion limit concentration 2.2%), a leak of 5 [L / hr] occurs as the set flow rate. If the gas diffuses uniformly with respect to the furnace volume, the time to reach the lower explosion limit concentration is about 48 minutes according to the following equation.

  Time to reach the lower explosion limit concentration [min] = {furnace volume [L] × (lower explosion limit concentration [%] / 100)} / {set flow rate [L / hr] / 60}

  Then, the safety standby time is set within the time required to reach the lower explosion limit concentration. Specifically, the safety standby time may be set by taking a predetermined safety factor in the time until reaching the lower explosion limit concentration. If the safety factor is 2, in the case of the above example, the safety standby time is 24 minutes, which is half of 48 minutes.

  More specifically, the control method of the boiler 1 of the present embodiment is as follows.

  (A) When the burner 4 burns the gas, when there is no load demand and the shutoff valve 14 is closed and the combustion is stopped, the leak detection means 16 determines whether or not there is a leak through the valve exceeding the set flow rate. At the same time, the inside of the furnace is ventilated by the air blower 5 as a post purge. For example, the inside of the furnace is ventilated by ventilating the inside of the furnace with an air volume four times the furnace volume. Thereafter, the blower 5 is stopped, and a transition is made to a standby state (waiting for the next load request).

  (B) When a leak exceeding the set flow rate is detected by the leak detection means 16, even if there is a load request, the ignition operation is not shifted. When a leak exceeding the set flow rate is detected, it is desirable to notify the user and to continue the furnace ventilation (post-purge). When leakage exceeding the set flow rate is detected, it is impossible to shift to the ignition operation, so that safety can be ensured.

  (C) If the leak detection means 16 does not detect a leak that exceeds the set flow rate, it shifts to a standby state after the end of the post purge, but if there is a load request during this standby, the standby time (from the end of the post purge) If the (elapsed time) is within the safety standby time, the operation immediately shifts to the ignition operation without pre-purge (that is, returns to the burner combustion state). For example, in the case of the pilot ignition system, if there is a load request, the pilot burner may be immediately ignited, the main burner 4 may be ignited by the pilot burner, and the combustion of the pilot burner may be stopped. In that case, while operating the air blower 5, each cutoff valve 14 is open | released. In this case, the post-purge can be regarded as a substantially pre-purge.

  If no leakage exceeding the set flow rate is detected, the safety standby time is set in advance until the gas concentration in the furnace reaches the lower explosion limit concentration, and if it is within the safety standby time, ignition is performed without pre-purge. Since it is possible to shift to the operation, the load followability is excellent and the heat dissipation loss can be reduced while ensuring the safety.

  (D) Although leakage exceeding the set flow rate is not detected by the leakage detection means 16, if there is a load request after elapse of the safety standby time after the end of the post purge, the pre-purge may be shifted to the ignition operation. In order to prevent inferior load followability due to the implementation of the above, it is preferable to perform the same purge as the post-purge during the standby time during standby. In other words, during standby, it is preferable to purge the inside of the furnace every time the safety standby time elapses and maintain the standby state.

  (E) In (d), if there is a load request during standby between purges, the process immediately proceeds to the ignition operation without pre-purge as in (c). In this case, the latest purge can be substantially regarded as a pre-purge.

  By purging the inside of the furnace every safety waiting time during standby of the boiler 1, the gas concentration in the furnace does not exceed the lower explosion limit concentration, so it is safe to shift to the ignition operation without pre-purge. Moreover, since it is possible to shift to the ignition operation without pre-purge, the load followability is excellent.

  (F) In (d), if there is a load request during a purge other than post-purge, the purge being executed is stopped halfway, and immediately, as in (e), the operation proceeds to the ignition operation without pre-purge. It is good to do. Specifically, if there is a load request during the purge, the rotational speed of the blower 5 is reduced and / or the position of the damper 13 is adjusted to move to the ignition operation as soon as the air flow is reduced to a level suitable for ignition. To do. In this case, the previous purge can be substantially regarded as a pre-purge.

  If a leak exceeding the set flow rate is not detected, the gas concentration in the furnace does not exceed the lower explosive limit concentration by purging the inside of the furnace at the safety standby time while the boiler 1 is on standby. It is safe to stop the purge and shift to the ignition operation without pre-purge. Moreover, since it is possible to shift to the ignition operation without pre-purge, the load followability is excellent.

  Conventionally, there is known a continuous pilot control that improves the load followability by omitting pre-purge by continuously burning the pilot burner. However, if the gas supply pressure is relatively low, It may not be used due to the pressure inside the furnace. In addition, it is possible to omit the pre-purge unless a valve leakage is detected using a valve leakage detector, but if there is a small amount of valve leakage, if the standby time becomes long, Gas accumulates and it is dangerous to ignite without pre-purge. However, according to the boiler 1 of this embodiment, the purge timing is set in consideration of the leakage flow rate that can be detected by the leakage detection means 16 and the standby time during which leakage continues, so that when a load request is made Can safely shift to the ignition operation without purging again. As a result, the load followability is excellent, and an operation with significantly reduced loss can be achieved as compared with continuous pilot control involving heat dissipation loss due to ventilation.

  By the way, you may add the following trace leak determination functions to the boiler 1 of a present Example further. This minute leak determination function can be used for various gas-fired combustion apparatuses independently of the combustion control based on the determination result of leakage exceeding the set flow rate described above (control using the safety standby time). . That is, while the shut-off valves 14 are closed, it is monitored by checking the pressure change between the shut-off valves 14 that the over-leakage of each shut-off valve 14 is less than or equal to the set flow rate (typically A1 or A2 and B1 or B2). Therefore, the present invention can be widely applied to systems that can confirm that no leakage exceeding the set flow rate occurs when the gas supply pressure is applied to the shutoff valve 14. If a leak through the valve is detected, it is impossible to shift to the ignition operation. On the other hand, even if a leak through the valve is not detected, the following monitoring is performed while the shut-off valve is closed (especially during standby). Just do it.

  That is, while the shutoff valve 14 is closed, even if the leak detection means 16 does not detect a leak exceeding the set flow rate, the pressure between the shutoff valves 14 may be monitored by the leak detection means (pressure detection means). Specifically, even when the leak detection means 16 does not detect a leak exceeding the set flow rate, the pressure between the shut-off valves 14 closed with the pressure between the shut-off valves 14 open while the shut-off valve 14 is closed is predetermined. Monitor constantly that pressure is not exceeded.

  For example, with the pair of shutoff valves 14 closed, the downstream shutoff valve 14B is once opened and then closed to lower the pressure between the shutoff valves 14 to the furnace pressure (substantially atmospheric pressure). Alternatively, the space between the shutoff valves 14 is temporarily opened to atmospheric pressure via a predetermined mechanism of the leak detection means 16. In this way, it is constantly monitored that the pressure between the shut-off valves 14 closed with the pressure between the shut-off valves 14 open does not exceed a predetermined pressure. Note that the operation for releasing the pressure between the shutoff valves 14 may be the operation performed when determining the leakage exceeding the set flow rate described above, and need not be performed again.

The set flow rate (standard flow past the valve leak determination of the cutoff valve 14) Q _max, the gas supply pressure (the pressure upstream of the upstream-side shut-off valve 14A) and P _in, value of less than 1 alpha. In general, the flow rate through the valve is proportional to the square root of the pressure. Therefore, if the predetermined pressure is P _in × α, the gas flow rate that may leak from the shutoff valve 14 does not exceed Q _max × √α unless the predetermined pressure is exceeded.

  For example, even when the set flow rate as a reference for leak determination by the leak detection means 16 is set to 50 [L / hr] due to various restrictions, the pressure between the shutoff valves 14 in the standby pressure monitoring is the gas supply pressure. For example, by constantly monitoring that α = 1/25 or less, it can be ensured that there is no gas leakage exceeding 10 [L / hr].

  As described above, even when the leak detection unit 16 does not detect a leak exceeding the set flow rate, the pressure between the shut-off valves 14 does not always exceed a predetermined pressure even after the leak determination (while the shut-off valve 14 is closed). By monitoring, it is possible to monitor the presence or absence of a small amount of gas leakage over a relatively long time. If the controller determines a leak, the controller should notify the user and start or continue the purge.

  The boiler 1 of the present invention is not limited to the configuration of the above embodiment, and can be changed as appropriate. In particular, when the shut-off valve 14 is closed, it is judged whether there is a gas leaking over the set flow rate, and if a leak exceeding the set flow rate is detected, it is impossible to shift to the ignition operation, but a leak exceeding the set flow rate is detected. If not, if the transition to the ignition operation can be performed without pre-purge within the safe waiting time after the end of the purge after closing the shutoff valve 14, the other configuration can be changed as appropriate.

  For example, the can body 3 of the boiler 1 is not limited to a rectangular shape, and may be a cylindrical shape. In that case, the burner 4 is preferably installed on the upper portion of the can body 3 so as to face downward. Further, the configuration of the burner 4 is appropriately changed accordingly. The gas leak detection method of the present invention can be applied to any gas burner. The burner 4 may be ignited by an ignition device instead of ignition by a pilot burner. Further, although the boiler 1 is a steam boiler in the above-described embodiment, a hot water boiler or the like may be used in some cases.

  Furthermore, in the said Example, although mixing of the gas to the combustion air supplied to the burner 4 was performed in the downstream from the air blower 5, you may carry out in the upstream from the air blower 5 depending on the case. In that case, the suction port of the blower 5 may be provided with a gas suction mechanism that sucks gas as air is sucked into the suction port and sends the gas together with air to the suction port. The gas suction mechanism typically includes a venturi tube, and a gas supply path 6 is connected to the throat portion thereof. When the blower 5 is operated with the shutoff valve 14 of the gas supply path 6 opened, the gas from the gas supply path 6 is mixed into the air to the blower 5. When the gas is sucked through the venturi pipe, the downstream shut-off valve 14B functions as a zero governor when opened, and the outlet pressure is preferably adjusted to atmospheric pressure. When the outlet side of the downstream shut-off valve 14B is set to atmospheric pressure, gas does not flow unless air flows through the venturi, so that gas leakage when the blower 5 is stopped can be reliably prevented.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Water pipe 3 Can body 4 Burner 5 Blower 6 Gas supply path 7 Exhaust gas path 8 Upper header 9 Lower header 10 Water supply path 11 Steam path 12 Combustion air path 13 Damper 14 Shut-off valve (14A: upstream side shut-off valve, 14B: downstream shut-off valve)
15 Orifice 16 Leakage detection means (16A: Valve Probing System (VPS))

Claims (7)

A shut-off valve for switching the presence or absence of gas supply to the burner;
Leak detection means for determining the presence or absence of leaking gas exceeding the set flow rate during closing of the shutoff valve,
When leakage exceeding the set flow rate is detected by the leak detection means while combustion of the burner is stopped, it is impossible to shift to ignition operation, while when leakage exceeding the set flow rate is not detected, after the shutoff valve is closed A boiler comprising: an operation control unit that enables a transition to an ignition operation without pre-purge if the purge is within a safety standby time. Even if a leak exceeding the set flow rate is not detected, assuming that there may be a leak of the set flow rate at the maximum, the gas concentration in the furnace is based on the furnace volume, the lower gas explosion limit concentration, and the set flow rate. The boiler according to claim 1, wherein the safety standby time is set within a time until reaching a lower explosion limit concentration. 3. The boiler according to claim 1, wherein when no leakage exceeding the set flow rate is detected, the inside of the furnace is purged every safety waiting time during standby due to the combustion stop of the burner. 4. The boiler according to claim 3, wherein if there is a load request during standby between the purges, the boiler shifts to an ignition operation without pre-purge. Immediately after closing the shutoff valve, perform a post purge,
4. The purge after the shut-off valve is closed, and if there is a load request during a purge other than the post-purge, the purge that is being executed is stopped halfway and the operation proceeds to the ignition operation. Item 4. The boiler according to item 4. A pair of the shutoff valves are provided in series in the gas supply path to the burner,
Even when the leakage exceeding the set flow rate is not detected during closing of the shutoff valve, it is constantly monitored that the pressure between the shutoff valves closed with the pressure between the shutoff valves open does not exceed a predetermined pressure. The boiler of any one of Claims 1-5 characterized by the above-mentioned. The predetermined pressure is set to P _in × α, and it is monitored that the leakage flow rate through the valve during closing of the shut-off valve does not exceed Q _max × √α (where Q _max is the set flow rate and P _in is Gas supply pressure, α is a value less than 1)
The boiler according to claim 6.

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