Method and device for controlling rotation speed of boiler water supply pump in power generation facility

Abstract

To achieve excellent energy-saving performance by minimizing energy loss and stabilize operation through the use of a boiler water supply flow regulation valve, even when a combustion condition in a waste treatment power generation facility fluctuates significantly and no pressure loss element, such as a high-pressure water supply heater, is present.SOLUTION: In a power generation facility where water is supplied to a boiler (10) via a boiler water supply flow regulation valve 22, the boiler water supply flow regulation valve 22 is controlled to stabilize a water level (L) in a boiler drum 10. Additionally, a rotation speed of a boiler water supply pump 14 is controlled to adjust differential pressure Pi-PO between an inlet and an outlet of the boiler water supply flow regulation valve 22 to a target value ΔP using an inverter (46).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method and device for controlling the rotation speed of a boiler feedwater pump in a power generation facility, and in particular to a method and device for controlling the rotation speed of a boiler feedwater pump in a power generation facility which suppresses energy loss and is energy-efficient, and which maintains controllability using a boiler feedwater flow control valve and enables stable operation even in cases where the combustion state fluctuates greatly and there is no pressure loss element such as a high-pressure feedwater heater, such as in a waste treatment power generation facility. [Background technology]

[0002] 2. Description of the Related Art In a power generation facility having a function of generating electricity using steam from a boiler by a steam turbine generator or the like, a feedwater flow rate control device is known for a boiler feedwater system that returns condensate or the like to the boiler.

[0003] Such a power generating facility has a boiler feedwater system that controls the water level in the boiler drum to a constant level. As shown in Fig. 1 for one boiler, the boiler feedwater system for a boiler drum 10 is mainly composed of a boiler feedwater pump 14 that is driven at a constant speed by a boiler feedwater pump driving motor 12, a boiler feedwater pump outlet side piping 16, a boiler feedwater piping 18, a boiler feedwater flowmeter 20, a boiler feedwater flow control valve 22, a boiler drum water level meter 24, a boiler generated steam transport piping 26, a boiler generated steam flowmeter 28, and a boiler feedwater flow control device 30, and controls to keep the water level in the boiler drum 10 constant.

[0004] The boiler feedwater flow control device 30 mainly receives a signal L of the boiler drum water level (also called drum level) from the boiler drum water level gauge 24, and controls the opening of the boiler feedwater flow control valve 22 so that the water level is constant. s and the boiler feedwater flow rate signal F from the boiler feedwater flow meter 20 w The difference between the above values ​​is fed back to the opening of the boiler feedwater flow rate control valve 22 to further stabilize the drum water level. w and the generated steam flow rate signal Fs The so-called three-element control is carried out.

[0005] The boiler feedwater pump 14 is always operated at a constant speed at which maximum capacity can be achieved, and the water level in the boiler drum 10 is controlled by the boiler feedwater flow control device 30 through the opening of the boiler feedwater flow control valve 22, regardless of the operating state of the boiler.

[0006] As shown in Figure 2 as an example of a case where there are multiple boilers, even in a configuration in which all boiler feedwater pumps 14 are shared by connecting a shared boiler feedwater pump outlet side piping 17 including a header, etc. to two or more boilers, when the water level in one boiler drum 10 is high and the other is low, different opening degrees are required for the boiler feedwater flow control valve 22. However, since the boiler feedwater flow control device 30 is independent for each boiler, there is no problem.

[0007] In particular, in waste treatment power generation facilities, a single boiler may not be able to ensure a sufficient amount of waste combustion, so multiple boilers are often used to optimize the design of the entire facility.

[0008] Furthermore, when a desuperheater 32 is installed on the boiler-generated steam transport piping 26 and a portion of the boiler feedwater is sprayed onto the steam to control the steam temperature so that it does not exceed a set value, the boiler feedwater pump 14 is always operated at a constant speed at which it can exert its maximum capacity, ensuring a sufficient head for supplying water to the desuperheater 32. Furthermore, since the desuperheater feedwater piping 34 to the desuperheater 32 branches off upstream of the boiler feedwater flow rate control valve 22, the high-pressure feedwater before being reduced in pressure by the boiler feedwater flow rate control valve 22 reaches the desuperheater 32 directly, ensuring sufficient pressure.

[0009] However, conventionally, the boiler feedwater pump 14 is designed to have the maximum capacity and rotates at a constant speed, and the flow rate is controlled by applying a pressure difference by throttling the boiler feedwater flow control valve 22 to compensate for the surplus pump head and flow rate, resulting in energy loss. This is a problem because the boiler feedwater pump 14 is one of the largest in the power generation facility.

[0010] On the other hand, as a technique similar to the present invention, Patent Document 1 describes controlling the rotation speed of a turbine for driving a feedwater pump so that the differential pressure across a flow control valve is constant.

[0011] Furthermore, Patent Document 2 describes that in order to ensure an appropriate amount of water injection into the boiler-generated steam desuperheater, the necessary differential pressure is applied to the feedwater flow control valve, and the control signal is corrected by a signal based on the mixed-combustion ratio of gas fuel and oil fuel in the boiler.

[0012] Furthermore, Patent Document 3 describes that in a plant having a common feedwater system for multiple boiler equipment, a circuit is added to one feedwater flow control valve to cause it to follow the opening degree of the other feedwater flow control valves, and feedwater pump rotation speed control is performed based on a deviation signal between the differential pressure before and after the feedwater flow control valve on the control valve side that controls the feedwater flow control valve using drum level control only and the set value. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 5-79605 [Patent Document 2] Japanese Patent Application Publication No. 6-180102 [Patent Document 3] JP 2000-274603 A Summary of the Invention [Problem to be solved by the invention]

[0014] However, compared to commercial power generation facilities that use coal or LNG as fuel and have small fluctuations in generated steam flow rate within ±3% (JIS B8102), waste treatment power generation facilities use a wide variety of waste as fuel, resulting in unstable combustion conditions and fluctuations in generated steam flow rate of ±10%, making it difficult to remove the boiler feedwater flow control valve and control only the boiler feedwater pump speed. This is because waste treatment power generation facilities do not have a high-pressure feedwater heater installed between the boiler drum 10 and the boiler feedwater pump 14, making it difficult to fine-tune the flow rate by adjusting the speed alone, and also because it is difficult to adjust the flow rate by adjusting the speed alone when the boiler pressure is low or the feedwater flow rate is low, such as during startup and shutdown.

[0015] In this regard, Patent Document 1 intends to control the rotation speed to a constant value to prevent erosion of the flow control valve due to the high pump head at the time of boiler startup, while the present invention intends to control energy loss and stable operation during constant speed operation. Also, Patent Document 1 is premised on rotation speed control by a turbine, but the present invention assumes an inverter.

[0016] Moreover, Patent Document 2 aims to ensure the amount of water injected into the desuperheater.

[0017] Moreover, in Patent Document 3, the feedwater flow rate is controlled only by drum level control, and is not a three-element control that also includes control of the feedwater flow rate and the generated steam flow rate.

[0018] Furthermore, none of Patent Documents 1 to 3 specifically considers power generation by burning waste, and no inverter is used to control the rotation speed of the boiler feed water pump.

[0019] Therefore, the inventor considered installing a boiler feedwater pump rotation speed control device to solve the energy loss problem. In particular, in waste treatment power generation facilities, the combustion state is not stable compared to commercial power generation facilities that use coal or LNG as fuel, so it is difficult to remove the boiler feedwater flow control valve and control only the boiler feedwater pump rotation speed, so a boiler feedwater flow control valve that controls the boiler water level is used in combination. In addition, it is necessary to determine whether to give priority to the boiler feedwater flow control valve or the boiler feedwater pump rotation speed in response to the feedwater request signal from the boiler drum, and how to control the one that is not given priority, and thereby minimize and optimize the pump rotation speed.

[0020] Furthermore, as shown in the example of Figure 2, in a configuration in which the boiler feed pump outlet piping is connected to two or more boilers so that all of the boiler feed pumps are shared and operate at the same rotation speed, it is necessary to determine how to process the multiple different feedwater request signals from each boiler drum and give priority to either each boiler feedwater flow control valve or the boiler feedwater pump rotation speed shared by multiple boilers, and thereby minimize and optimize the pump rotation speed.

[0021] In addition, when a desuperheater is installed on the boiler generated steam piping and some of the boiler feedwater is sprayed with steam to control the steam temperature so that it does not exceed a set value, if the required feedwater pressure to the desuperheater is greater than the required feedwater pressure to the boiler drum, controlling the boiler feedwater pump speed solely based on the boiler drum water level will not provide enough pressure to the desuperheater, so it is necessary to consider a control method for how to reflect this shortage in the boiler feedwater pump speed.

[0022] The present invention has been developed through research to solve the above-mentioned conventional problems, and has as its objective to suppress energy loss and achieve excellent energy saving performance, while maintaining controllability using a boiler feedwater flow control valve and enabling stable operation even in cases where there are large fluctuations in the combustion state of waste treatment power generation equipment and there is no pressure loss element such as a high-pressure feedwater heater. [Means for solving the problem]

[0023] In the present invention, each boiler is supplied with water via a boiler feedwater flow control valve, and the conventional boiler feedwater flow control valve is combined with the boiler feedwater pump rotation speed control of the present invention. In this case, the pressure at the inlet and outlet of the boiler feedwater flow control valve installed for each boiler is measured to determine the boiler feedwater pump rotation speed, and the differential pressure is taken in as a signal. A target value (set value) for the differential pressure is determined in advance, and the boiler feedwater pump rotation speed is controlled to achieve the target value.

[0024] In addition, when all boiler feedwater pumps are shared, the minimum value of the differential pressure signals of the boiler feedwater flow control valves sent from multiple boilers is selected. The target value (set value) of the differential pressure is determined in advance, and the boiler feedwater pump rotation speed is controlled so that the selected differential pressure achieves the target value.

[0025] Furthermore, when a desuperheater is installed, the target value (set value) of the differential pressure is set in advance as a target value that includes a value that is predicted to be insufficient as the desuperheater required pressure so that the desuperheater required pressure is higher than the boiler drum required pressure, and the boiler feed water pump rotation speed is controlled to achieve this target value.

[0026] The present invention was made based on the above-mentioned study results, and solves the above-mentioned problem in a power generation facility in which water is supplied to a boiler via a boiler feedwater flow control valve, by controlling the boiler feedwater flow control valve so that the water level in the boiler drum is constant, and by controlling the rotation speed of the boiler feedwater pump so that the differential pressure between the inlet and outlet of the boiler feedwater flow control valve becomes a target value.

[0027] The present invention also provides a boiler feedwater pump rotation speed control device for power generation equipment, in which water is supplied to a boiler via a boiler feedwater flow control valve, characterized in comprising: means for controlling the boiler feedwater flow control valve so that the water level in the boiler drum is constant; and means for controlling the boiler feedwater pump rotation speed so that the differential pressure between the inlet and outlet of the boiler feedwater flow control valve becomes a target value.

[0028] Here, the rotation speed of the boiler feed water pump can be controlled by using an inverter.

[0029] The power generation facility may be a waste treatment power generation facility that burns waste in a boiler to generate power.

[0030] In addition, in a power generation facility with multiple boilers, when all the boiler feedwater pumps are operated at the same rotational speed, the rotational speed of the boiler feedwater pumps can be controlled so that the minimum pressure difference between the inlet and outlet of the boiler feedwater flow control valves of all boilers becomes a target value.

[0031] In addition, in a power generation facility in which a desuperheater is provided on the boiler generated steam piping on the boiler outlet side to prevent the steam temperature from exceeding a set value, the target value of the differential pressure between the inlet and outlet of the boiler feedwater flow control valve can be set to a target value that includes a value that is expected to be insufficient as the desuperheater required pressure so that the desuperheater required pressure is higher than the boiler drum required pressure, and the boiler feedwater pump rotation speed can be controlled. Effect of the Invention

[0032] According to the present invention, a rotation speed control device is provided on the boiler feedwater pump, and a boiler feedwater flow control valve is provided that performs constant control of the boiler drum water level. By using both in combination, energy loss can be suppressed, and excellent energy-saving effects can be achieved.

[0033] Therefore, energy loss is suppressed and energy saving is achieved, and even in cases where the combustion state fluctuates greatly and there is no pressure loss element such as a high-pressure feedwater heater, such as in waste treatment power generation equipment, controllability by the boiler feedwater flow control valve is maintained and stable operation can be obtained. [Brief description of the drawings]

[0034] [Figure 1] A piping diagram showing an example of a conventional boiler feedwater system with one boiler [Diagram 2]A piping diagram showing an example of a conventional boiler feedwater system with multiple boilers. [Diagram 3] A piping diagram showing the configuration of a first embodiment of the present invention applied to a boiler feedwater system with one boiler. [Figure 4] A diagram showing how to control the boiler feed pump speed. [Diagram 5] A piping diagram showing the configuration of a second embodiment of the present invention applied to a boiler feedwater system having multiple boilers. [Figure 6] A diagram showing how to control the boiler feed pump speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the contents described in the following embodiments. Furthermore, the components in the embodiments described below include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the embodiments described below may be appropriately combined or appropriately selected for use.

[0036] In the first embodiment of the present invention, in a boiler feedwater system with one boiler similar to the conventional example shown in FIG. 1, as shown in FIG. 3, a boiler feedwater flow control valve inlet side pressure gauge 40 and a boiler feedwater flow control valve outlet side pressure gauge 42 are provided on the inlet side and outlet side of a boiler feedwater flow control valve 22 of a boiler feedwater piping 18, and as shown in FIG. 4, the inlet side pressure P i and the outlet pressure P detected by the outlet pressure gauge 42 O Differential pressure signal P i -P O The rotation speed of the boiler feedwater pump driving motor 12 is controlled by a boiler feedwater pump rotation speed control device 48 using a rotation speed controller 46 formed of, for example, an inverter INV so that the rotation speed of the boiler feedwater pump driving motor 12 becomes the target value ΔP. The other configuration is the same as in Fig. 1, so the same reference numerals are used and the description will be omitted.

[0037] Here, the differential pressure signal P i-P O In this embodiment, the measured value P of the inlet pressure gauge 40 is i and the measured value P of the outlet pressure gauge 42 O Alternatively, a differential pressure gauge that directly measures the differential pressure between the inlet and outlet sides of the boiler feedwater flow rate control valve 22 may be used.

[0038] As a result, the boiler feedwater flow rate control valve 22 is operated in a state where the opening degree is larger than before, and the differential pressure signal P i -P O Since it is possible to reduce the rotation speed of the boiler feed water pump 14, energy loss can be suppressed.

[0039] In addition, as a result of adjusting the boiler feed water pump rotation speed, the flow control valve pressure fluctuates, and there is a feedback effect that brings the differential pressure closer to the target value.

[0040] In this way, while performing the conventional constant boiler drum water level control using the boiler feedwater flow control valve 22, in parallel, the boiler feedwater pump rotation speed is determined so as to keep the inlet / outlet differential pressure constant using the boiler feedwater flow control valve 22, making it possible to automatically control the rotation speed of the boiler feedwater pump 14 to a minimum value.

[0041] Next, a second embodiment of the present invention applied to a boiler feedwater system having a plurality of boilers will be described.

[0042] In the second embodiment, as shown in FIG. 5, in a boiler feedwater system having a plurality of boilers similar to the conventional example shown in FIG. 2, a boiler feedwater flow control valve inlet side pressure gauge 40 and a boiler feedwater flow control valve outlet side pressure gauge 42 similar to those in the first embodiment are provided in each of the boilers, such as the No. 1 boiler, the No. 2 boiler, etc., as in the first embodiment, and a differential pressure signal P i -P O6, a minimum value selection circuit 50 is provided for selecting the minimum value of the multiple flow control valve differential pressures input from the boilers, and the minimum value selected by the minimum value selection circuit 50 is input to the boiler feedwater pump rotation speed control device 48, and the rotation speed of the boiler feedwater pump drive motor 12 is controlled using a rotation speed controller 46 formed of, for example, an inverter INV, so that the minimum value becomes a predetermined target value (set value). The other configuration is the same as in Fig. 2, so the same reference numerals are used and the description will be omitted.

[0043] Here, the differential pressure signal P i -P O In this embodiment, the measured value P of the inlet pressure gauge 40 is i and the measured value P of the outlet pressure gauge 42 O Alternatively, a differential pressure gauge that directly measures the differential pressure between the inlet and outlet sides of the boiler feedwater flow rate control valve 22 may be used.

[0044] In this embodiment as well, as a result of adjusting the boiler feedwater pump rotation speed, the flow rate control valve pressure fluctuates, and there is a feedback effect of bringing the differential pressure closer to the target value.

[0045] In this way, the rotation speed of the boiler feedwater pump is automatically controlled to the minimum value while matching the boiler with the greatest feedwater flow requirement so that the feedwater flow rate is not insufficient for any boiler, thereby reducing energy loss.

[0046] Furthermore, when a desuperheater 32 is provided as in the above embodiment, by setting the target differential pressure value to a value that includes the pressure attenuator 32, it becomes possible to automatically perform control that always satisfies not only the boiler drum water level but also the pressure requirements of the desuperheater 32.

[0047] In all of the above embodiments, an inverter INV is used as the rotation speed controller 46 to reduce the rotation speed of the drive motor 12 of the boiler feedwater pump 14 so as to provide the necessary differential pressure to the boiler feedwater flow rate control valve 22, so that in the case of small to medium-sized facilities such as waste treatment power generation facilities (with a power generation capacity of less than 50 MW as a guideline), the initial cost can be reduced compared to turbines and fluid couplings, and sufficient conversion efficiency can be obtained. Furthermore, since the inverter is driven by a motor, it can be operated stably even before boiler pressure is established, compared to turbine drive. The type of rotation speed controller 46 is not limited to this.

[0048] The scope of application is not limited to waste treatment power generation facilities, but can also be applied to other power generation facilities in general, such as commercial power generation facilities. [Explanation of symbols]

[0049] 10...Boiler drum 12...Boiler feed pump drive motor 14…Boiler feed pump 16...Boiler feed pump outlet piping 17…Boiler feed pump outlet shared piping 18...Boiler feed water piping 20...Boiler feedwater flow meter F w …Boiler feed water flow rate signal 22...Boiler feedwater flow control valve 24...Boiler drum water level gauge L…Boiler drum water level signal 26…Boiler generated steam transport piping 28...Boiler generated steam flow meter F s …Boiler generated steam flow signal 30...Boiler feedwater flow control device 32...Desuperheater 34…Desuperheater water supply piping 40...Boiler feedwater flow control valve inlet pressure gauge P i …Boiler feedwater flow control valve inlet pressure 42...Boiler feedwater flow control valve outlet pressure gauge P O…Boiler feedwater flow control valve outlet pressure 46... Revolution speed controller (INV) 48...Boiler feed pump speed control device 50…Minimum value selection circuit P i -P O …Differential pressure signal ΔP: Differential pressure target value

Claims

1. In a power generation facility where water is supplied to a boiler via a boiler feedwater flow control valve, Controlling the boiler feedwater flow rate control valve so that the water level in the boiler drum is constant; A method for controlling the rotation speed of a boiler feedwater pump in a power generation facility, comprising controlling the rotation speed of the boiler feedwater pump so that the differential pressure between the inlet and outlet of the boiler feedwater flow control valve becomes a target value.

2. 2. The method for controlling the rotation speed of a boiler feed pump in a power generating facility according to claim 1, wherein the rotation speed of the boiler feed pump is controlled by using an inverter.

3. 3. The method for controlling the rotational speed of a boiler feed pump in a power generating facility according to claim 1, wherein the power generating facility is a waste treatment power generating facility which generates power by burning waste in a boiler.

4. The boiler feedwater pump rotation speed control method for a power generation facility as described in claim 1, characterized in that when all of the boiler feedwater pumps in a power generation facility having multiple boilers are operated at the same rotation speed, the boiler feedwater pump rotation speed is controlled so that the minimum value of the differential pressure between the inlet and outlet of the boiler feedwater flow control valve of all the boilers becomes a target value.

5. In a power generation facility where a desuperheater is installed on the boiler generated steam piping on the boiler outlet side to prevent the steam temperature from exceeding a set value, 2. The method for controlling the rotation speed of a boiler feedwater pump in a power generation facility according to claim 1, wherein the target value of the differential pressure between the inlet and outlet of the boiler feedwater flow control valve is set to a target value including a value that is expected to be insufficient as the attemperator required pressure so that the attemperator required pressure is higher than the boiler drum required pressure, thereby controlling the rotation speed of the boiler feedwater pump.

6. In a power generation facility in which water is supplied to a boiler via a boiler feedwater flow control valve, a means for controlling the boiler feedwater flow rate control valve so as to keep the water level in the boiler drum constant; a means for controlling the rotation speed of the boiler feedwater pump so that the pressure difference between the inlet and the outlet of the boiler feedwater flow control valve becomes a target value; A boiler feed pump rotation speed control device for a power generation facility, comprising:

7. 7. The boiler feed pump revolution speed control device for a power generating facility according to claim 6, wherein the revolution speed of the boiler feed pump is controlled by using an inverter.

8. 8. The boiler feed pump rotation speed control device for a power generating facility according to claim 6, wherein the power generating facility is a waste treatment power generating facility that generates power by burning waste in a boiler.

9. 7. A boiler feedwater pump rotation speed control device for a power generation facility as described in claim 6, characterized in that, when all of the boiler feedwater pumps in a power generation facility having a plurality of boilers are operated at the same rotation speed, a means for controlling the rotation speed of the boiler feedwater pumps so that the minimum value of the differential pressure between the inlet and outlet of the boiler feedwater flow control valve of all the boilers becomes a target value.

10. In a power generation facility where a desuperheater is installed on the boiler generated steam piping on the boiler outlet side to prevent the steam temperature from exceeding a set value, 7. A boiler feedwater pump rotation speed control device for a power generation facility as described in claim 6, further comprising a means for controlling the rotation speed of the boiler feedwater pump by setting a target value of the differential pressure between the inlet and outlet of the boiler feedwater flow control valve to a target value including a value that is expected to be insufficient as the attemperator required pressure so that the attemperator required pressure is higher than the boiler drum required pressure.

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