boiler

Abstract

To provide a boiler capable of converging an air ratio upon transition of a combustion quantity into an appropriate range.SOLUTION: A boiler includes on-off valves 11, 12 for opening and closing channels of a fuel supply passage 5, fuel flow regulating valves 13 which are provided on a downstream side of the on-off valves 11, 12 on the fuel supply passage 5 and regulate a flow rate of fuel to be supplied to a boiler, a pressure detection part 15 which detects a pressure of a primary side of the fuel flow regulating valves 13 on the fuel supply passage 5 and a control part 6 which controls an opening of the fuel flow regulating valves 13 and shifts a combustion amount to any of multiple combustion amounts. The control part 6 includes pressure specifying means which specifies a pressure of the primary side of the fuel flow regulating valves 13 on the combustion amount after the transition on the basis of, pressure losses on the on-off valves 11, 12 of each of the combustion amount before the transition and the combustion amount after the transition and a pressure detected by the pressure detection part 15 and, in a transition term for shifting to a different combustion amount, controls the opening of the fuel flow rate adjusting valve 13 in accordance with the pressure specified by the pressure specifying means, in the transition term for the different combustion amount.SELECTED DRAWING: Figure 2

Description

Technical Field

[0006]

[0001] The present invention relates to a boiler.

Background Art

[0002] Conventionally, there is a boiler that adjusts the fuel flow rate by a flow rate adjustment valve without using a governor that keeps the pressure of the supplied fuel constant in a fuel supply pipe (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a boiler, when the combustion amount is shifted and the fuel flow rate supplied to the boiler changes, the pressure loss when passing through the primary side (upstream side, for example, a shut-off valve, etc.) of the flow rate adjustment valve in the fuel supply pipe changes, so the pressure of the fuel reaching the flow rate adjustment valve also fluctuates. Therefore, if the opening degree of the flow rate adjustment valve is uniformly controlled considering only the combustion amount after the shift, when the pressure of the fuel reaching the flow rate adjustment valve is low, the supplied fuel decreases and the air ratio becomes high, and when the pressure of the fuel reaching the flow rate adjustment valve is high, the supplied fuel increases and the air ratio becomes low. As a result, the air ratio cannot be converged within an appropriate range, and there is a risk of occurrence of combustion abnormalities such as misfire and an increase in the carbon monoxide concentration due to incomplete combustion.

[0005] The present invention has been conceived in view of such a situation, and an object thereof is to provide a boiler capable of converging the air ratio at the time of shifting the combustion amount within an appropriate range.

Means for Solving the Problems

[0006] To achieve the above objective, the boiler of the present invention includes an on-off valve for opening and closing the flow path of a fuel supply passage, a fuel flow control valve provided downstream of the on-off valve in the fuel supply passage for adjusting the flow rate of fuel supplied to the boiler, and in the fuel supply passage It is provided between the aforementioned on-off valve and the aforementioned fuel flow control valve, The aforementioned fuel The system includes a pressure detection unit that detects the pressure on the primary side of a flow control valve, and a control unit that transitions to one of a plurality of combustion amounts and controls the opening degree of the fuel flow control valve. The control unit includes a pressure identification means that, when transitioning to a different combustion amount, identifies the pressure on the primary side of the fuel flow control valve at the combustion amount after the transition, based on the pressure loss at the on-off valve for each of the combustion amounts before and after the transition, and the pressure detected by the pressure detection unit. During the transition period when transitioning to a different combustion amount, the system controls the opening degree of the fuel flow control valve according to the pressure identified by the pressure identification means.

[0007] According to the above configuration, during the transition period when switching to a different combustion rate, the pressure on the primary side of the fuel flow control valve at the new combustion rate is identified, and the opening degree of the fuel flow control valve is controlled according to the identified pressure. This allows the opening degree of the fuel flow control valve to be controlled according to the pressure of the fuel reaching the fuel flow control valve, even when the combustion rate is switched and the flow rate of fuel supplied to the boiler changes. As a result, the air-fuel ratio can be brought within an appropriate range, suppressing the occurrence of combustion abnormalities such as misfires and the increase in carbon monoxide concentration caused by incomplete combustion.

[0008] Preferably, the control unit includes a supply means for supplying combustion air at a flow rate corresponding to the transitioning combustion rate, and an air flow rate detection unit for detecting the flow rate of the supplied combustion air. The control unit includes a flow rate corresponding value identification means for identifying a flow rate corresponding to the fuel flow rate corresponding to the combustion air flow rate detected by the air flow rate detection unit, and an adjustment value identification means for identifying an adjustment value for adjusting the fuel flow rate supplied to the boiler during a transition period when transitioning to a different combustion rate. During the transition period, the control unit controls the opening degree of the fuel flow rate adjustment valve according to the pressure identified by the pressure identification means and a value obtained by adding or subtracting the adjustment value identified by the adjustment value identification means to the flow rate corresponding value identified by the flow rate corresponding value identification means.

[0009] According to the above configuration, during the transition period when switching to a different combustion rate, the opening of the fuel flow control valve is controlled according to a value obtained by adding or subtracting a specific value to a flow rate correspondence value that corresponds to the detected combustion air flow rate, and to a specific adjustment value, based on a specified pressure on the primary side of the fuel flow control valve at the combustion rate after the transition. This prevents the air-fuel ratio from temporarily changing due to the fuel flow rate changing with a certain time delay following the change in the amount of combustion air supplied during the transition period when switching to a different combustion rate. As a result, fluctuations in the air-fuel ratio during the transition of combustion rates can be controlled to be as stable as possible, combustion abnormalities such as misfires can be suppressed, and the increase in carbon monoxide concentration due to incomplete combustion can also be suppressed.

[0010] Preferably, even during a transition period to a different combustion rate, the control unit does not control the opening degree of the fuel flow control valve according to the pressure identified by the pressure identification means if the difference between the combustion rate before the transition and the combustion rate after the transition is within a predetermined range.

[0011] With the above configuration, unless the difference in combustion amount exceeds a predetermined range, the opening degree of the fuel flow control valve is not controlled according to the pressure determined by the pressure determination means. This prevents the opening degree of the fuel flow control valve from being controlled in response to small changes in combustion amount. As a result, it is possible to suppress hunting, which occurs when the opening degree of the fuel flow control valve becomes unstable. [Brief explanation of the drawing]

[0012] [Figure 1] This is a diagram illustrating the general configuration of a boiler. [Figure 2] This is a flowchart illustrating an example of boiler control. [Figure 3] This is an example of a table for specifying the corrected opening angle according to this embodiment. [Modes for carrying out the invention]

[0013] <Outline of the structure> A boiler 1 according to an embodiment of the present invention will be described below with reference to Figure 1. Figure 1 is a schematic diagram showing the configuration of a boiler 1 according to an embodiment of the present invention.

[0014] The boiler 1 comprises a boiler body 2 that burns fuel to generate steam, a blower 3 that supplies air into the boiler body 2 via an air supply passage 30, a flue 4 that discharges exhaust gas from the boiler body 2, a fuel supply passage 5 (fuel supply line) that supplies fuel to the boiler body 2, and a control device 6. While the explanation describes an example where the fuel is gas, it is not limited to gases; it may also be a liquid such as oil.

[0015] The fuel supply line 5 is connected to the air supply line 30. The fuel (gas) supplied from the fuel supply line 5 is mixed with the air blown from the blower 3 in the air supply line 30 and supplied to the burner 20 inside the boiler body 2.

[0016] The air supplied from the blower 3 is supplied as combustion air to the burner 20 in the boiler body 2 via the air supply passage 30. The flow rate of the combustion air is adjusted by installing a damper 7 in the air supply passage 30 and adjusting the position (opening) of the damper 7, or, in addition to or alternatively, by changing the rotation speed of the fan of the blower 3 using an inverter. In this embodiment, the flow rate of the combustion air is adjusted by controlling the opening of the damper 7 and controlling the blower 3 with an inverter.

[0017] The fuel supply passage 5 is equipped with on-off valves (solenoid valves) 11 and 12 for opening and closing the flow path, a fuel flow rate control valve 13, and a pressure sensor 15 (pressure detection unit). The on-off valves 11 and 12 are collectively called a double shut-off valve. The fuel flow rate control valve 13 functions as a pressure regulating valve capable of adjusting the flow rate of fuel supplied to the boiler body 2, and also has a shut-off function. The fuel flow rate control valve 13 is located downstream of the on-off valves 11 and 12 and is a motor valve whose opening degree is adjusted by the control device 6. Note that the fuel flow rate control valve 13 is not limited to a motor valve as long as it adjusts the flow rate of fuel; for example, it may be a pneumatic control valve.

[0018] The pressure sensor 15 is located downstream of the on-off valves 11 and 12 and detects the pressure of the fuel flowing upstream (primary) of the fuel flow control valve 13. The pressure sensor 15 transmits a detection signal to the control device 6 to determine the pressure on the primary side of the fuel flow control valve 13. This allows the detection signal from the pressure sensor 15 to be input to the control device 6. The analog signal output from the pressure sensor 15 is converted to a digital signal and input to the control device 6.

[0019] The control device 6 is implemented by a computer that includes internal memory, a timer, and an arithmetic processing unit, and controls the fuel flow control valve 13 and the blower 3 based on signals from various sensors, including the electrically connected pressure sensor 15. The control device 6 also controls the combustion rate (burnup rate) in the boiler body 2 to one of several combustion states with progressively different rates, according to the set target steam pressure and the steam pressure of the steam header. The control device 6 controls the opening degree of the flow control valve 13 and the amount of air supplied by the blower 3 according to the controlled combustion state. The multiple combustion states include a high combustion state, a medium combustion state, and a low combustion state. The combustion rate in the boiler body 2 decreases in the order of high combustion state, medium combustion state, and low combustion state.

[0020] In the air supply passage 30, a combustion air pressure reducing member 8 such as a perforated metal is provided downstream of the damper 7. The air flow rate detection unit 9 detects the differential pressure before and after the combustion air pressure reducing member 8 and outputs differential pressure information. The air flow rate detection unit 9 is electrically connected to the control device 6. Thereby, the differential pressure information from the air flow rate detection unit 9 can be input to the control device 6. Note that the analog signal output from the air flow rate detection unit 9 is converted into a digital signal and input to the control device 6.

[0021] The control device 6 controls the blower 3 so as to have a mode (for example, rotational speed, frequency) corresponding to the combustion amount being controlled, and supplies a combustion air amount corresponding to the combustion amount. The flow rate of the combustion air corresponding to the combustion amount is predetermined for each of a plurality of combustion states (combustion amounts). The control device 6 calculates (detects) the flow rate of the combustion air actually supplied to the boiler body 2 based on the differential pressure information before and after the combustion air pressure reducing member 8 detected by the air flow rate detection unit 9.

[0022] The control device 6 adjusts the opening degree of the fuel flow rate adjustment valve 13 based on a flow rate corresponding value for specifying the opening degree of the fuel flow rate adjustment valve 13 corresponding to the calculated flow rate of the combustion air, a correction opening degree for correcting the opening degree of the fuel flow rate adjustment valve 13 according to the operating condition, and a flow rate adjustment value. The flow rate corresponding value is a value for specifying the opening degree of the fuel flow rate adjustment valve 13 that can supply a fuel flow rate at which the air ratio becomes a predetermined value within an appropriate range in relation to the calculated flow rate of the combustion air when the fuel supply pressure is constant. Thereby, for example, if the flow rate of the combustion air increases, the opening degree of the fuel flow rate adjustment valve 13 is increased to increase the fuel flow rate, while if the flow rate of the combustion air decreases, the opening degree of the fuel flow rate adjustment valve 13 is decreased to decrease the fuel flow rate. As a result, it is possible to supply a flow rate (design value) that is the flow rate required from the boiler according to the combustion amount and at which the air ratio is within an appropriate range. Note that the correction opening degree and the flow rate adjustment value are values for correcting the opening degree specified from the flow rate corresponding value, and details thereof will be described later.

[0023] The control device 6 comprises a control unit 61 and a storage unit 62. The storage unit 62 stores various information related to the boiler 1, such as information for identifying the mode of the blower 3 according to the combustion amount (e.g., rotation speed, frequency) and opening adjustment information for identifying the opening degree of the fuel flow control valve 13. The opening adjustment information includes information such as tables and calculation formulas for identifying flow rate corresponding values, corrected opening degrees, and flow rate adjustment values.

[0024] The control unit 61 transmits an opening degree identification signal to the fuel flow control valve 13 to specify the opening degree based on the opening degree adjustment information stored in the memory unit 62. As a result, the fuel flow control valve 13 is controlled to an opening degree corresponding to the differential pressure before and after the combustion air pressure reducing member 8, thereby adjusting the flow rate of fuel supplied to the boiler body 2. The information for specifying the flow rate corresponding value among the opening degree adjustment information may be a table that can specify the opening degree of the fuel flow control valve 13 according to the differential pressure (or the flow rate of combustion air calculated from the differential pressure), or it may be a calculation formula that can specify the opening degree of the fuel flow control valve 13 according to the differential pressure (or the flow rate of combustion air calculated from the differential pressure). Similarly, the information for specifying the correction opening degree and flow rate adjustment value among the opening degree adjustment information may also be a table that can specify the correction opening degree and flow rate adjustment value, or it may be a calculation formula.

[0025] In this embodiment, the fuel supply passage 5 does not have a governor-equipped shut-off valve or the like that supplies fuel at a constant pressure, thus reducing manufacturing costs. However, in this case, the pressure loss in the double shut-off valve varies depending on the flow rate of fuel (which is also the fuel supplied to the boiler 1) flowing through the double shut-off valve, causing the fuel pressure reaching the fuel flow control valve 13 to fluctuate. In particular, when the combustion state is transitioned and the flow rate of fuel supplied to the boiler changes, the pressure loss when passing through the double shut-off valve in the fuel supply passage 5 changes significantly, causing the fuel pressure reaching the fuel flow control valve 13 to fluctuate greatly. For example, if the opening of the fuel flow control valve 13 is controlled based only on a flow rate corresponding value calculated according to the flow rate of combustion air, and the flow rate of fuel supplied to the boiler 1 is high (for example, when transitioning to a high combustion state), the pressure loss increases, the pressure downstream of the double shut-off valve decreases, and the supplied fuel tends to be less than the design value, resulting in a high air-fuel ratio. Conversely, when the fuel flow rate supplied to boiler 1 is low (for example, when transitioning to a low combustion state), the pressure loss decreases, causing the pressure downstream of the double shut-off valve to increase, and the supplied fuel tends to exceed the design value, resulting in a low air ratio.

[0026] To solve these problems, we focused on the fact that the pressure loss when passing through the double shut-off valve in the fuel supply line 5 is proportional to the square of the flow rate of the circulating fuel and the square of the combustion state (combustion amount, combustion rate). When starting control to transition (change) the combustion state (combustion amount) to a different combustion state, we calculate an estimated value of the fuel pressure reaching the primary side of the flow control valve 13 after the transition (estimated destination fuel supply pressure Pg2') based on the pressure loss value ΔP corresponding to the combustion state before the transition and the combustion state after the transition, and the pressure detected by the pressure sensor 15 (current fuel supply pressure value Pg2). Then, we identify the corrected opening degree of the fuel flow control valve 13 from the calculated estimated destination fuel supply pressure Pg2', and correct and control the opening degree of the fuel flow control valve 13, which is identified based on the flow rate corresponding value, based on the corrected opening degree. In other words, the opening degree of the fuel flow control valve 13 is corrected and controlled taking into account the estimated value of the fuel pressure reaching the primary side of the fuel flow control valve 13 after the transition. This makes it possible to bring the air-fuel ratio within an appropriate range even when the pressure of the fuel reaching the primary side of the fuel flow control valve 13 fluctuates due to the transition in combustion state.

[0027] The memory unit 62 stores in advance pressure loss values ​​ΔP corresponding to each combustion state (combustion amount), as well as information corresponding to the following formula for calculating the estimated transition fuel supply pressure Pg2'. For example, when a transition from combustion state a to combustion state b with a different combustion amount (for example, a transition from a low combustion state to a medium combustion state) begins, the estimated transition fuel supply pressure Pg2' is calculated based on the following formula using the stored pressure loss value ΔP and the current fuel supply pressure value Pg2 detected by the pressure sensor 15. Note that the pressure loss value corresponding to combustion state a is ΔPa, and the pressure loss value corresponding to combustion state b is ΔPb.

[0028] (Formula) Pg2´=Pg2-(ΔPb-ΔPa) Furthermore, the memory unit 62 stores a table, as shown in Figure 3, which defines the corrected opening degree (%) of the fuel flow control valve 13 according to the estimated destination fuel supply pressure Pg2' after the transition in combustion state (combustion amount). The relationship between the estimated destination fuel supply pressure Pg2' and the corrected opening degree can be determined in advance through experiments or other means. The opening degree of the fuel flow control valve 13 is corrected and controlled by adding (summing) the opening degree, which is determined by multiplying the opening degree, which is determined from the flow rate corresponding value, by the specified corrected opening degree. For example, if the estimated destination fuel supply pressure Pg2' is 30kPa, the corrected opening degree is calculated to be 17% from the table shown in Figure 3, and the valve is corrected and controlled by adding 17% of the opening degree, which is determined from the flow rate corresponding value, to that opening degree. As shown in Figure 3, the corrected opening degree is set to be larger the smaller the estimated destination fuel supply pressure Pg2' is, so the added opening degree is also larger. Note that in the table shown in Figure 3, the correction opening for the estimated transition fuel supply pressure Pg2' is only shown in units of 10 kPa; however, in reality, the correction opening is stored in corresponding units, for example, every 1 kPa.

[0029] The control device 6 calculates the estimated destination fuel supply pressure Pg2' using the above formula, based on the current fuel supply pressure Pg2 and the pressure loss values ​​ΔP for the combustion rate before the transition (current combustion rate) and the combustion rate after the transition (target combustion rate). It then determines the corrected opening degree of the fuel flow control valve 13 by referring to the table shown in Figure 3. The process of determining the corrected opening degree is performed at the start of the transition of the combustion state. Note that the values ​​shown in Figure 3 are examples and may vary depending on the boiler.

[0030] In boiler 1, in addition to the corrective control by the corrected opening described above, the following corrective control is also performed. Boiler 1 prioritizes changes in the flow rate of combustion air and adjusts the fuel flow rate according to the actual flow rate of combustion air supplied, with the fuel flow rate adjustment being a follow-up control based on feedback of the combustion air flow rate. Therefore, when the combustion state transitions to another combustion state, it becomes a transient state and the air ratio fluctuates greatly, which may make it difficult to maintain a combustion state with an appropriate air ratio. For example, when transitioning from a low combustion state to a medium combustion state, the increase in fuel supply lags behind the increase in the flow rate of combustion air, which tends to result in a period of high air ratio. To solve this, the control device 6, when transitioning combustion states, corrects the opening of the fuel flow control valve 13, which is determined based on the flow rate corresponding value, in addition to the corrected opening of the fuel flow control valve 13, which is determined according to the estimated fuel supply pressure of the transition destination Pg2', based on the flow rate adjustment value described later.

[0031] The memory unit 62 stores various information about the boiler 1, including the transition time Δt required for transitioning from one combustion state to a different combustion state, and information for identifying the theoretical opening degree of the fuel flow control valve 13, which is uniquely determined according to the combustion state (combustion amount). The transition time Δt is determined for each boiler by the inverter frequency of the blower 3, acceleration / deceleration time, damper 7 opening degree, damper 7 opening / closing speed, etc. When transitioning combustion states, the airflow rate is changed by changing, for example, the inverter frequency of the blower 3 or the opening degree of the damper 7. However, because there are limitations on the inverter frequency that can be changed per unit time, it takes a predetermined amount of time to reach the airflow rate corresponding to the combustion state after the transition. Also, since the opening degree of the damper 7 does not change instantaneously but changes at a constant speed, it takes a predetermined amount of time to reach the target opening degree. Due to these factors, if the fuel supply amount is changed immediately to correspond to the target air ratio according to the combustion state after the transition, it may not be possible to converge the air ratio to an appropriate range.

[0032] When a transition in the combustion state is detected during operation, the timer of the control device 6 starts measuring, for example, the elapsed time t0 since the start of the transition. Based on the measured elapsed time t0, the theoretical opening of the fuel flow control valve 13 which is predetermined according to the combustion state, and the transition time Δt, the control device 6 calculates, for example, a flow rate adjustment value during the transition period. The flow rate adjustment value is a value that identifies the value used to add or subtract (correct) the opening of the flow control valve 13 based on the flow rate corresponding value. The control device 6 repeatedly performs the process of calculating the flow rate adjustment value during the transition period in operation.

[0033] Furthermore, the memory unit 62 stores a flow rate corresponding value, which is the opening degree of the flow control valve 13 determined based on the flow rate of combustion air, and information corresponding to the following formula for calculating the flow rate adjustment value mentioned above. For example, when a transition from combustion state a to a different combustion state b is initiated, the transition time Δt is determined and the elapsed time t0 is started to be measured, and the flow rate adjustment value is calculated based on the following formula at the elapsed time t0. The theoretical opening degree corresponding to combustion state a is denoted as theoretical opening degree A, and the theoretical opening degree corresponding to combustion state b is denoted as theoretical opening degree B. Here, in a boiler that performs control in which the change in the flow rate of combustion air precedes and the adjustment of the fuel flow rate follows through feedback, when the process for initiating the transition of combustion states is started, the process for changing the flow rate of combustion air is started, and then, after a certain delay of time until the flow rate of combustion air is determined, the process for changing the flow rate of fuel is started, and this delay time is denoted as T.

[0034] (Formula) Flow rate adjustment value = {(BA) / Δt}·t However, the value of t is determined as follows, depending on the elapsed time t0.

[0035] 0≦t0 <T : t=t0 T≦t0<Δt : t=T Δt≦t0<Δt+T : t=(T+Δt)-t0 In the boiler 1 of this embodiment, the opening degree of the fuel flow control valve 13, which is determined based on a flow rate corresponding value corresponding to the calculated flow rate of combustion air, is corrected and controlled based on the flow rate adjustment value calculated by the above formula, in addition to the corrected opening degree of the fuel flow control valve 13, which is determined according to the estimated transition fuel supply pressure Pg2'. This process is repeated during the combustion state transition period until the flow rate of combustion air detected by the flow rate detection unit 9 becomes the flow rate corresponding to the combustion state after the transition.

[0036] This allows for the stable control of air-fuel ratio fluctuations during transitions in combustion states (combustion rate) in boilers that employ so-called feedback control, where changes in combustion air flow rate precede changes in combustion air flow rate. It prevents temporary changes in the air-fuel ratio caused by a delay in the change in combustion air flow rate following a change in fuel supply when the combustion rate changes (transitions). As a result, air-fuel ratio fluctuations during combustion rate transitions can be stabilized as much as possible, suppressing combustion abnormalities such as misfires and reducing the increase in carbon monoxide concentration caused by incomplete combustion. The following sections will explain this control in more detail.

[0037] <About boiler control processing> Figure 2 is a flowchart illustrating an example of boiler control according to the present invention. The control device 6 performs this control at regular intervals (e.g., every second) and continues to perform this control while the boiler 1 is in operation.

[0038] In step S01, it is determined whether a change (transition) in the combustion rate is necessary based on the detected vapor pressure in the vapor header and the target vapor pressure. If it is not determined in step S01 that a change in the combustion rate is necessary, this control is terminated. On the other hand, if it is determined in step S01 that a change in the combustion rate is necessary, the process proceeds to step S02.

[0039] In step S02, the combustion amount is changed from a to a different combustion amount b. In step S03, the blower 3 is controlled in a manner corresponding to the combustion amount b changed in step S02.

[0040] In step S04, the theoretical opening A corresponding to the combustion amount a (current combustion amount), the theoretical opening B corresponding to the combustion amount b (target combustion amount), and the transition time Δt are determined. The transition time Δt is a predetermined transition time required until combustion air at a flow rate corresponding to the combustion amount b (combustion amount after transition) is supplied by the supply means (blower 3, etc.). In step S05, the elapsed time t0 from the start of the transition is started to be measured.

[0041] In step S06, the pressure loss value ΔPa corresponding to combustion amount a and the pressure loss value ΔPb corresponding to combustion amount b are identified from the pressure loss value ΔP stored in the memory unit 62, and the current fuel supply pressure value Pg2 is identified based on the detection signal from the pressure sensor 15.

[0042] In step S07, the value obtained by subtracting ΔPa from ΔPb identified in step S06 is subtracted from the current fuel supply pressure value Pg2 to calculate the estimated transition fuel supply pressure Pg2'.

[0043] In step S08, the corrected opening degree of the fuel flow control valve 13 is determined by referring to the table shown in Figure 3 and based on the estimated transition fuel supply pressure Pg2' calculated in step S07.

[0044] In step S09, the airflow rate of the combustion air is detected (calculated) based on the differential pressure detected by the airflow rate detection unit 9.

[0045] In step S10, based on the air flow rate detected in step S09, a flow rate correspondence value is identified to determine the fuel flow rate corresponding to the combustion air flow rate.

[0046] In step S11, the value obtained by subtracting the theoretical opening A corresponding to the combustion amount a from the theoretical opening B corresponding to the combustion amount b is divided by the transition required time Δt, and then multiplied by a value t specified according to the time t0 elapsed since the transition from the combustion amount a (the combustion amount before the transition) to the combustion amount b (the combustion amount after the transition) started, to calculate the flow rate adjustment value at the elapsed time t0. When the value of t0 is 0 ≦ t0 < T, t = t0. When the value of t0 is T ≦ t0 < Δt, t = T. When the value of t0 is Δt ≦ t0 < Δt + T, t = (T + Δt) - t0. Here, when the process for starting the transition of the combustion amount is started, after the process for changing the flow rate of the combustion air is started, the process for changing the flow rate of the fuel is started with a delay of a fixed time until the flow rate of the combustion air is specified as described above. Let that delay time be T.

[0047] In step S12, based on the correction opening specified in step S08, the flow rate corresponding value specified in step S10, and the flow rate adjustment value calculated in step S11, the opening of the fuel flow rate adjustment valve 13 is controlled. As a result, the opening of the fuel flow rate adjustment valve 13 is controlled to an opening corrected based on the opening specified based on the flow rate corresponding value specified in step S10, the correction opening specified in step S08, and the flow rate adjustment value calculated in step S11. For example, the fuel flow rate adjustment valve 13 is controlled to an opening that is increased or decreased by the opening specified based on the flow rate adjustment value calculated in step S11 from the opening specified based on the flow rate corresponding value specified in step S10, and then increased by the opening multiplied by the ratio (%) of the correction opening specified in step S08. Note that the fuel flow rate adjustment valve 13 may be controlled to an opening that is first increased by the opening multiplied by the ratio (%) of the correction opening specified in step S08, and then increased or decreased by the opening specified based on the flow rate adjustment value calculated in step S11 from the opening specified based on the flow rate corresponding value specified in step S10.

[0048] In step S13, it is determined whether the airflow rate detected in step S09 is the combustion air flow rate corresponding to the combustion amount b. If, in step S13, it is determined that the airflow rate detected in step S09 is not the combustion air flow rate corresponding to the combustion amount b, the process proceeds to step S09. On the other hand, if, in step S13, it is determined that the airflow rate detected in step S09 is the combustion air flow rate corresponding to the combustion amount b, the process ends.

[0049] As described above, in this embodiment, in a boiler that adjusts the fuel flow rate by controlling the opening degree of a fuel flow control valve without using a governor to keep the supply pressure constant, even if there is a fluctuation in the fuel pressure (supply amount) reaching the primary side of the fuel flow control valve 13 due to pressure loss in the double shut-off valve that occurs when the combustion state (combustion amount) is transitioned, in step S07 the fuel pressure reaching the fuel flow control valve 13 at the combustion amount after the transition (estimated transition destination fuel supply pressure Pg2') is calculated, the corrected opening degree of the fuel flow control valve 13 is identified, and the opening degree of the fuel flow control valve 13 can be corrected and controlled using the identified corrected opening degree. As a result, the air ratio can be brought into an appropriate range, and the occurrence of combustion abnormalities such as misfires and the increase in carbon monoxide concentration due to incomplete combustion can be suppressed.

[0050] Furthermore, the process for calculating the flow rate adjustment value is carried out until the detected air flow rate reaches the combustion air flow rate corresponding to the combustion amount b (steps S09 to S13). This allows the fuel flow rate to be changed immediately after the combustion amount transitions from one to a different amount (immediately after the combustion air flow rate changes), thereby adjusting the air-fuel ratio during the transition period to an appropriate air-fuel ratio. This prevents the air-fuel ratio from temporarily changing due to the fuel flow rate changing a certain time after the change in the amount of combustion air supplied when the combustion amount transitions. As a result, the fluctuation in the air-fuel ratio during the transition of combustion amount can be controlled to be as stable as possible, combustion abnormalities such as misfires can be suppressed, and the increase in carbon monoxide concentration due to incomplete combustion can also be suppressed.

[0051] The present invention is not limited to the embodiments described above, and various modifications and applications are possible. Below, we will describe some modifications of the above embodiments that are applicable to the present invention.

[0052] In the above embodiment, steps S06 to S08 in Figure 2 and the correction processing in S12 based on S06 to S08 may be omitted if the difference in combustion amount before and after the transition is within, for example, 10% of 100% of the combustion amount, even if the combustion amount is transitioning, but may be performed only if it exceeds 10%. This prevents steps S06 to S08 in Figure 2 and the correction processing in S12 based on S06 to S08 from being performed when there are small changes in the combustion amount that make it difficult to distinguish whether or not a transition is occurring. As a result, it is possible to suppress hunting caused by unstable opening of the fuel flow control valve 13.

[0053] In the above embodiment, an example was described in which the transition time Δt for transitioning to a different combustion state is stored in the storage unit 62 as one of the pieces of information related to the boiler 1. However, the invention is not limited to this, and the transition time Δt may be calculated each time at the start of the transition based on the amount of combustion before and after the transition.

[0054] In the above embodiment, an example was described in which a formula is used to calculate the estimated destination fuel supply pressure Pg2'. However, the invention is not limited to this, and the pressure may be determined by a table pre-stored in the storage unit 62. For example, a table capable of identifying the estimated destination fuel supply pressure Pg2' for each current fuel supply pressure Pg2 based on the relationship between the current combustion amount and the destination combustion amount may be pre-stored in the storage unit 62. When transitioning the combustion amount, the table corresponding to the current fuel supply pressure Pg2 is referenced, and the estimated destination fuel supply pressure Pg2' corresponding to the current combustion amount and the destination combustion amount is read and identified.

[0055] In the above embodiment, when determining the corrected opening of the fuel flow control valve 13, a table is used which defines the corrected opening of the fuel flow control valve 13 according to the estimated destination fuel supply pressure Pg2' after the transition in combustion amount, as shown in Figure 3. However, the invention is not limited to this, and the corrected opening may be calculated each time using, for example, a pre-stored formula, according to the estimated destination fuel supply pressure Pg2'.

[0056] In the above embodiment, an example of application to a boiler in which the flow rate change of combustion air precedes the adjustment of the fuel flow rate through feedback was described. However, the invention is not limited to this, and may be applied to any boiler in which the flow rate change of fuel precedes the adjustment of the combustion air flow rate through feedback. Furthermore, it may also be applied to a boiler that does not perform such so-called feedback control. For example, it may be a boiler in which the fuel flow rate change and the combustion air flow rate change are immediately controlled to predetermined openings and airflow rates according to the combustion state.

[0057] In the above embodiment, an example was described in which the opening degree specified from the fuel flow rate corresponding value specified in step S10 is corrected and controlled using the corrected opening degree specified in step S08 and the flow rate adjustment value calculated in step S11 (step S12). However, the invention is not limited to this, and it is also possible to correct and control the opening degree specified from the flow rate corresponding value using only the corrected opening degree specified in step S08. Furthermore, in boilers where the fuel flow rate change precedes the control, or in boilers that do not perform such feedback control, it is also possible to correct and control the theoretical opening degree of the fuel flow control valve 13, which is uniquely determined according to the combustion state (for example, the theoretical opening degree according to the target combustion state), using only the corrected opening degree specified in step S08.

[0058] In the above embodiment, an example was described in which the process of identifying a corrected opening degree to correct the opening degree determined from the fuel flow rate corresponding value corresponding to the combustion air flow rate is performed at the start of the transition to a new combustion state. However, the process is not limited to this, and may be performed during steady-state operation. For example, at predetermined intervals, the pressure loss value ΔP corresponding to the controlled combustion state and the current fuel supply pressure value Pg2 may be identified, and the value obtained by subtracting the pressure loss value ΔP corresponding to the controlled combustion state from the identified current fuel supply pressure value Pg2 may be applied to the estimated transition fuel supply pressure Pg2' in the table in Figure 3 to identify the corrected opening degree of the fuel flow control valve 13, thereby correcting the opening degree determined from the fuel flow rate corresponding value corresponding to the combustion air flow rate. Furthermore, in boilers where the fuel flow rate change precedes the operation, or in boilers that do not perform such feedback control, the corrected opening degree of the fuel flow control valve 13 may be identified by a similar process, and the theoretical opening degree of the fuel flow control valve 13, which is uniquely determined according to the combustion state, may be corrected and controlled. As a result, even when controlled to a low combustion state, the air-fuel ratio can be brought to an appropriate range even if there are fluctuations in the fuel pressure reaching the primary side of the fuel flow control valve 13 due to factors other than changes in the combustion state, such as fluctuations in the pressure upstream of the double shut-off valve. In steady state, the corrected opening of the fuel flow control valve 13 is not limited to being determined based on Pg2' calculated using the pressure loss value ΔP as described above. Instead, the corrected opening of the fuel flow control valve 13 may be determined based on the current fuel supply pressure value Pg2 detected at predetermined intervals without using the pressure loss value ΔP, and the valve may be controlled by correcting the opening determined from the fuel flow rate corresponding to the combustion air flow rate, or by correcting the theoretical opening of the fuel flow control valve 13 which is uniquely determined according to the combustion state. In other words, the method for determining the corrected opening of the fuel flow control valve 13 may be switched between transition and steady state.

[0059] In the above embodiment, an example was described in which the pressure of the fuel flowing on the primary side of the fuel flow control valve 13 is detected using a pressure sensor 15. However, the embodiment is not limited to this, and for example, multiple orifices or the like may be provided in the fuel supply passage 5 to detect differential pressure, and the fuel supply flow rate may be detected based on the differential pressure.

[0060] In the above embodiment, an example was described in which the pressure loss value ΔP (ΔPa, ΔPb) used to calculate the estimated transition fuel supply pressure Pg2' is the pressure loss when passing through the double shut-off valve in the fuel supply line 5. However, the pressure loss is not limited to the pressure loss in the double shut-off valve; instead, or in addition, the pressure loss when passing through other equipment installed on the fuel supply line 5 may be used. When calculating the estimated transition fuel supply pressure Pg2', for example, if an orifice is provided in the fuel supply line 5 as described above, the pressure loss when passing through the orifice provided upstream or downstream of the on-off valves 11 and 12 in the fuel supply line 5 may be used. Alternatively, a strainer for capturing foreign matter in the fuel may be provided upstream of the on-off valves 11 and 12, and the pressure loss when passing through the strainer may be used. In other words, a pressure identification means for identifying the pressure on the primary side of the fuel flow control valve at the combustion rate after the transition can be said to include, at a minimum, a means for identifying the estimated transition fuel supply pressure Pg2', which is the pressure on the primary side of the fuel flow control valve, based on, for example, the current fuel supply pressure value Pg2 and the pressure loss values ​​ΔP for the combustion rate before the transition (current combustion rate) and the combustion rate after the transition (target combustion rate). In the case where other equipment is provided on the fuel supply path 5 as described above, it can be said that a means for identifying the estimated transition fuel supply pressure Pg2', which is the pressure on the primary side of the fuel flow control valve, can also be said to include a means for identifying the estimated transition fuel supply pressure Pg2', which is the pressure on the primary side of the fuel flow control valve, by also using (taking into account) the pressure loss when passing through said other equipment.

[0061] In the above embodiment, we have described a case where the boiler is controlled to one of several combustion states with progressively different combustion rates. However, the method is not limited to this, and can also be applied to so-called proportionally controlled boilers that can finely control the combustion rate. In that case, although we have described a case where the pressure loss value ΔP corresponding to the combustion rate specified in step S06 is stored in advance in the above embodiment, it is also possible to calculate the pressure loss value ΔP corresponding to the combustion rate after each change in the combustion rate. For example, the pressure loss values ​​ΔP corresponding to 100%, 60%, and 20% combustion rates may be stored, and the pressure loss value ΔP for 80% combustion rate may be calculated by adding half of the difference between the pressure loss values ​​ΔP for 100% and 60% combustion rate to the pressure loss value ΔP for 60% combustion rate.

[0062] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0063] 1 Boiler 2. Boiler body 3. Blower 4 Flue 5 Fuel supply path 6 Control device 61 Control Unit 62 Storage section 7 Damper 8 Combustion air pressure reduction member 9. Air flow detection unit 11. Shut-off valves 12. Shut-off valves 13 Fuel flow control valve 15. Pressure sensor (pressure detection unit) 20 burners 30 Air supply path

Claims

1. A shut-off valve for opening and closing the flow path of the fuel supply line, A fuel flow control valve is provided downstream of the on-off valve in the fuel supply passage and adjusts the flow rate of fuel supplied to the boiler, A pressure detection unit is provided between the on-off valve and the fuel flow control valve in the fuel supply passage, and detects the pressure on the primary side of the fuel flow control valve, The system includes a control unit that switches to one of several combustion levels and controls the opening degree of the fuel flow control valve, The control unit, When transitioning to a different combustion rate, the system includes pressure identification means that identifies the pressure on the primary side of the fuel flow control valve at the transitioned combustion rate, based on the pressure loss in the on-off valve at the combustion rate before and after the transition, and the pressure detected by the pressure detection unit. A boiler that, during a transition period to a different combustion rate, controls the opening degree of the fuel flow control valve according to the pressure identified by the pressure identification means.

2. A supply means that supplies combustion air at a flow rate corresponding to the amount of combustion being transferred, It includes an air flow rate detection unit that detects the flow rate of the supplied combustion air, The control unit, A flow rate correspondence value identification means for identifying a flow rate correspondence value to determine the fuel flow rate corresponding to the flow rate of combustion air detected by the air flow rate detection unit, Includes means for identifying adjustment values ​​to identify adjustment values ​​for adjusting the flow rate of fuel supplied to the boiler during a transition period to a different combustion rate, The boiler according to claim 1, wherein during the transition period, the opening degree of the fuel flow control valve is controlled according to the pressure identified by the pressure identification means and the value obtained by adding or subtracting the addition or subtraction value identified by the addition or subtraction value identification means to the flow rate corresponding value identified by the flow rate corresponding value identification means.

3. The boiler according to claim 1 or 2, wherein the control unit does not control the opening degree of the fuel flow control valve according to the pressure identified by the pressure identification means, even during a transition period to a different combustion rate, if the difference between the combustion rate before the transition and the combustion rate after the transition is within a predetermined range.

Images