A system and method for steady state operation of an electric boiler at very low power

Abstract

The application discloses a kind of steady operation system and method of electric boiler at very low power, including the following steps: electric boiler at very low power, using the joint control mode of electric boiler pressure signal and electric boiler inner cylinder water level signal to control electric boiler, in the case where the water conductivity in the inner cylinder of electric boiler is stable, first buffer control pressure and second buffer control pressure are set in the range from electric boiler power-on starting pressure to tripping shutdown pressure, wherein, first buffer control pressure is used as the pressure signal of initial drainage of the inner cylinder of electric boiler, and second buffer control pressure is used as the pressure signal of initial water supply of the inner cylinder of electric boiler, at the same time, three-phase electrode is kept in continuous power-on state, and the power of electric boiler is stabilized and the pressure is adjusted according to the water level of the inner cylinder of electric boiler, which can avoid the problem of frequent start and stop of electric boiler during steady operation at very low load, and the problem of pressure overshoot is not easy to occur.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nuclear power plant electric boiler control, and relates to a steady-state operation system and method of an electric boiler at an extremely low power. BACKGROUND

[0002] The power control system of the electric boiler of a nuclear power plant is relatively complex, and involves temperature control, pressure control, chemical control, electrical control and various influencing factors. In the existing technology of the electric boiler used in a nuclear power plant, when the electric boiler is operated at an extremely low load (lower than 10% of the rated full load), a pressure control mode is usually adopted, that is, a certain pressure set value is set for the electric boiler, when the pressure reaches the set value, the power supply of the electric boiler is disconnected, and the electric boiler stops heating; when the pressure is lower than a certain value, the power supply of the electric boiler is closed, and the electric boiler continues to increase the temperature and pressure. Due to the large thermal inertia of the electric boiler, the control range of the load fluctuation of the electric boiler at an extremely low load is small, and this pressure regulation mode causes the electric power rate of the boiler to rise and fall in a pulse mode, the power supply command is frequent, the electrical switch is repeatedly closed and opened, and the loss of the electrical switch is increased. At the same time, the pressure lags behind the electric power, and the pressure rises and falls in a steep slope mode, which easily causes pressure overshoot, causes large control deviation, and the large pressure fluctuation in the short term also causes stress fatigue, which reduces the service life of the thermal equipment. SUMMARY

[0003] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a steady-state operation system and method of an electric boiler at an extremely low power, which can avoid the problem of frequent start and stop of the electric boiler during steady-state operation at an extremely low load, and is not prone to pressure overshoot.

[0004] To achieve the above-mentioned purpose, the steady-state operation method of the electric boiler at an extremely low power includes the following steps:

[0005] At an extremely low power of the electric boiler, a combined control mode of the pressure signal of the electric boiler and the water level signal in the inner cylinder of the electric boiler is adopted to control the electric boiler, a first buffer control pressure and a second buffer control pressure are set in the range from the start-up pressure to the stop operating pressure of the electric boiler under the condition that the water conductivity in the inner cylinder of the electric boiler is stable, the first buffer control pressure is used as the pressure signal for initial drainage of the inner cylinder of the electric boiler, the second buffer control pressure is used as the pressure signal for initial water supply of the inner cylinder of the electric boiler, and at the same time, the three-phase electrode is kept in a continuous power-on state, and the power of the electric boiler is stabilized and the pressure is adjusted according to the water level in the inner cylinder of the electric boiler.

[0006] The steady-state operation system of the electric boiler at an extremely low power includes an inner cylinder of the electric boiler, an outer cylinder of the electric boiler, a feed water pump, a circulating pump, a circulating regulating valve, a steam pressure sensor, a steam regulating valve and a steam output pipeline.

[0007] The electric boiler inner cylinder is located in the electric boiler outer cylinder, the outlet of the feed water pump is communicated with the water inlet on the top side of the electric boiler outer cylinder, the outlet at the bottom of the electric boiler outer cylinder is divided into two routes after passing through the circulating pump, one of the two routes is communicated with the water inlet on the side of the bottom of the electric boiler outer cylinder, and the other route is communicated with the water inlet on the side of the electric boiler inner cylinder through the circulating regulating valve, and the steam outlet at the top of the electric boiler inner cylinder is communicated with the steam output pipeline through the steam pressure sensor and the steam regulating valve.

[0008] The pH meter, the inner cylinder water level sensor and the three-phase electrode are arranged in the electric boiler inner cylinder.

[0009] The outlet of the feed water pump is communicated with the water inlet on the top side of the electric boiler outer cylinder through the feed water regulating valve.

[0010] The circulating pump is communicated with the water inlet on the side of the bottom of the electric boiler outer cylinder through the recirculation orifice plate.

[0011] The inner cylinder drain valve is arranged at the drain outlet of the bottom of the electric boiler inner cylinder.

[0012] The pipeline between the circulating regulating valve and the water inlet on the side of the electric boiler inner cylinder is provided with a chemical dosing system.

[0013] The chemical dosing system is interlocked with the pH meter.

[0014] The steady-state operation method of the electric boiler at an extremely low power includes the following steps:

[0015] 1) When the electric boiler operates at an extremely low power, the electric conductivity of the water in the electric boiler inner cylinder is kept stable through the pH meter and the chemical dosing system; the electric boiler inner cylinder is supplied with make-up water through the circulating pump, the recirculation orifice plate and the circulating regulating valve; the electric boiler inner cylinder is drained through the inner cylinder drain valve; the water level of the electric boiler inner cylinder is measured through the inner cylinder water level sensor; the electric boiler outer cylinder is supplied with water through the feed water pump and the feed water regulating valve; the three-phase electrode is in an energized state; the steam pressure signal of the electric boiler inner cylinder is measured through the steam pressure sensor, and the steam regulating valve keeps a set opening degree to supply steam to downstream users;

[0016] 2) the average value of the start pressure and the stop pressure of the electric boiler is set as P, the difference between the start pressure and the stop pressure of the electric boiler is 2*ΔP, the energized start pressure of the electric boiler is (P-ΔP), and the pressure of the electric boiler at the time of tripping is (P+ΔP);

[0017] 3) in the range from the energized start pressure (P-ΔP) of the electric boiler to the pressure (P+ΔP) at the time of tripping, the buffer control pressure P+α*ΔP and P-α*ΔP are set, wherein P+α*ΔP is taken as the pressure signal of the initial drainage of the electric boiler inner cylinder, and P-α*ΔP is taken as the pressure signal of the initial make-up water of the electric boiler inner cylinder;

[0018] 4) when the conductivity of the water in the inner cylinder of the electric boiler is stable, the power of the electric boiler is proportional to the water level of the inner cylinder of the electric boiler;

[0019] 5) when the steam pressure of the inner cylinder of the electric boiler rises to P+α*ΔP, the inner cylinder drain valve is opened until the steam pressure of the inner cylinder of the electric boiler decreases to P, and then the inner cylinder drain valve is closed;

[0020] 6) when the steam pressure of the inner cylinder of the electric boiler decreases to P-α*ΔP, the water flow to the inner cylinder of the electric boiler is increased by the combined adjustment of the circulating pump, the recirculation orifice plate and the circulating regulating valve, and when the steam pressure of the inner cylinder of the electric boiler rises to P, the water flow is restored to the original flow by the combined adjustment of the circulating pump, the recirculation orifice plate and the circulating regulating valve;

[0021] 7) when the steam pressure of the inner cylinder of the electric boiler rises to P+ΔP, the three-phase electrode is de-energized, the electric boiler stops running, the inner cylinder drain valve is closed, the circulating regulating valve is closed, and the water in the outer cylinder of the electric boiler is recirculated by the circulating pump and the recirculation orifice plate until the steam pressure of the inner cylinder of the electric boiler decreases to P-ΔP, at which time the three-phase electrode is energized, the electric boiler is restarted, and the water flow is restored to the original water flow by the combined adjustment of the circulating pump, the recirculation orifice plate and the circulating regulating valve.

[0022] The electric boiler has the following beneficial effects:

[0023] The steady-state operation system and method of the electric boiler at an extremely low power have the following beneficial effects: when the first buffer control pressure and the second buffer control pressure are set in the range from the startup pressure to the tripping shutdown pressure of the electric boiler during the operation of the electric boiler, the first buffer control pressure is used as the pressure signal for the initial drainage of the inner cylinder of the electric boiler, the second buffer control pressure is used as the pressure signal for the initial water supply of the inner cylinder of the electric boiler, the buffer control pressure is used as the input of the control signal, the electric boiler is not frequently started and stopped during the steady-state operation at an extremely low load, the service life of the electrical switch and other electrical equipment is prolonged, the power of the electric boiler changes more stably, the corresponding pressure changes more gently, the control deviation is small, the pressure overshoot is not easy to cause, the stress fatigue is obviously reduced, and the service life of the thermal equipment is prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 FIG. 1 is a structural schematic diagram of the electric boiler;

[0025] Figure 2 FIG. 2 is a schematic diagram of the power change and power on-off of the electric boiler at an extremely low power before optimization during operation;

[0026] Figure 3 FIG. 3 is a schematic diagram of the power and pressure change of the electric boiler at an extremely low power after optimization during steady-state operation.

[0027] Wherein, 1 is a feed water pump, 2 is a feed water regulating valve, 3 is an inner cylinder water level sensor, 4 is a three-phase electrode, 5 is a steam pressure sensor, 6 is a steam regulating valve, 7 is a pH meter, 8 is a chemical dosing system, 9 is an inner cylinder of an electric boiler, 10 is an outer cylinder of an electric boiler, 11 is an inner cylinder drain valve, 12 is a circulating pump, 13 is a recirculation orifice plate, and 14 is a circulating regulating valve. DETAILED DESCRIPTION

[0028] In order to make the personnel in the technical field better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments, and are not intended to limit the scope of the present application. In addition, in the following description, the description of the known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts should belong to the scope of protection of the present application.

[0029] The structural schematic diagrams according to the disclosed embodiments of the present application are shown in the drawings. These drawings are not drawn to scale, in which some details are enlarged for the purpose of clear expression, and some details can be omitted. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are only exemplary, and in actuality, there can be deviations due to manufacturing tolerances or technical limitations, and regions / layers with different shapes, sizes and relative positions can be additionally designed by those skilled in the art according to actual needs.

[0030] Embodiment one

[0031] The steady-state operation method of the electric boiler at an extremely low power includes the following steps:

[0032] The electric boiler is controlled by a combined control mode of the electric boiler pressure signal and the inner cylinder 9 water level signal at an extremely low power, in which the first buffer control pressure P+α*ΔP and the second buffer control pressure P-α*ΔP are set in the range from the electric boiler power-on start pressure (P-ΔP) to the electric boiler tripping stop pressure (P+ΔP) while maintaining the water electrical conductivity in the inner cylinder 9 of the electric boiler stable, wherein P+α*ΔP is used as the pressure signal for initial drainage of the inner cylinder 9 of the electric boiler, P-α*ΔP is used as the pressure signal for initial water replenishment of the inner cylinder 9 of the electric boiler, and the three-phase electrode 4 is kept in a continuous power-on state, and the electric boiler power is stabilized and the pressure is adjusted according to the water level of the inner cylinder 9 of the electric boiler.

[0033] Embodiment two

[0034] Reference Figure 1The steady-state operation system of the electric boiler under extremely low power according to the present invention includes a water pump 1, a water regulating valve 2, an inner cylinder water level sensor 3, a three-phase electrode 4, a steam pressure sensor 5, a steam regulating valve 6, a pH meter 7, a chemical dosing system 8, an inner cylinder of the electric boiler 9, an outer cylinder of the electric boiler 10, an inner cylinder drain valve 11, a circulation pump 12, a recirculation orifice plate 13, and a circulation regulating valve 14.

[0035] The inner cylinder 9 of the electric boiler is located inside the outer cylinder 10 of the electric boiler. The outlet of the water pump 1 is connected to the water inlet on the top side of the outer cylinder 10 of the electric boiler via the water regulating valve 2. The outlet at the bottom of the outer cylinder 10 of the electric boiler is divided into two paths after passing through the circulation pump 12. One path is connected to the water inlet on the bottom side of the outer cylinder 10 of the electric boiler via the recirculation orifice plate 13, and the other path is connected to the water inlet on the side of the inner cylinder 9 of the electric boiler via the circulation regulating valve 14. An inner cylinder drain valve 11 is provided at the drain outlet at the bottom of the inner cylinder 9 of the electric boiler. The steam outlet at the top of the inner cylinder 9 of the electric boiler is connected to the steam output pipeline via the steam pressure sensor 5 and the steam regulating valve 6.

[0036] The inner cylinder 9 of the electric boiler is equipped with a pH meter 7, an inner cylinder water level sensor 3 and a three-phase electrode 4; a chemical dosing system 8 is installed on the pipe between the circulation regulating valve 14 and the water inlet on the side of the inner cylinder 9 of the electric boiler, and the chemical dosing system 8 is interlocked with the pH meter 7.

[0037] Example 3

[0038] The steady-state operation method of the electric boiler under extremely low power according to the present invention includes the following steps:

[0039] 1) When the electric boiler operates at extremely low power (below 10% of rated full load, typically below 3MW), the conductivity of the water inside the inner cylinder 9 is kept stable via pH meter 7 and chemical dosing system 8. Makeup water is supplied to the inner cylinder 9 via circulation pump 12, recirculation orifice plate 13, and circulation regulating valve 14; drainage is performed on the inner cylinder 9 via inner cylinder drain valve 11. The water level in the inner cylinder 9 is measured by inner cylinder water level sensor 3. Water is supplied to the outer cylinder 10 via feedwater pump 1 and feedwater regulating valve 2. With three-phase electrode 4 energized, the steam pressure signal in the inner cylinder 9 is measured by steam pressure sensor 5, and steam regulating valve 6 maintains a set opening to supply steam to downstream users.

[0040] 2) The average pressure of the electric boiler starting and stopping is P, and the difference between the two is 2*ΔP. Therefore, the starting pressure of the electric boiler is (P-ΔP), and the shut-off pressure of the electric boiler is (P+ΔP).

[0041] 3) In the range of the electric boiler power-on starting pressure (P-ΔP) to the tripping off operating pressure (P+ΔP), the buffer control pressure P+α*ΔP and P-α*ΔP are set, wherein P+α*ΔP is used as the pressure signal for the initial drainage of the electric boiler inner cylinder 9, and P-α*ΔP is used as the pressure signal for the initial water supply of the electric boiler inner cylinder 9, wherein α is 0.5-0.8;

[0042] 4) When the electric conductivity of the water in the electric boiler inner cylinder 9 is stable, the power of the electric boiler is proportional to the water level of the electric boiler inner cylinder 9;

[0043] 5) When the steam pressure of the electric boiler inner cylinder 9 rises to P+α*ΔP, the inner cylinder drainage valve 11 is opened to reduce the water level of the electric boiler inner cylinder 9, and then the power of the electric boiler is reduced until the steam pressure of the electric boiler inner cylinder 9 is reduced to P, at which time the inner cylinder drainage valve 11 is closed;

[0044] 6) When the steam pressure of the electric boiler inner cylinder 9 is reduced to P-α*ΔP, the water flow is increased to the electric boiler inner cylinder 9 through the combined adjustment of the circulating pump 12, the recirculation orifice plate 13 and the circulating regulating valve 14 to increase the power of the electric boiler, and when the steam pressure of the electric boiler inner cylinder 9 rises to P, the water flow is restored to the original flow through the combined adjustment of the circulating pump 12, the recirculation orifice plate 13 and the circulating regulating valve 14;

[0045] 7) When the steam pressure of the electric boiler inner cylinder 9 rises to P+ΔP, the three-phase electrode 4 is powered off, the electric boiler stops running, the inner cylinder drainage valve 11 is closed, the circulating regulating valve 14 is closed, and the water in the electric boiler outer cylinder 10 is recirculated through the circulating pump 12 and the recirculation orifice plate 13 until the steam pressure of the electric boiler inner cylinder 9 is reduced to P-ΔP, the three-phase electrode 4 is powered on, the electric boiler is restarted, and the water flow is restored to the original water flow through the combined adjustment of the circulating pump 12, the recirculation orifice plate 13 and the circulating regulating valve 14.

[0046] Example Four

[0047] The average downstream steam load of an electric boiler is about 1.1 MW, P is 1.2 MPa, the power fluctuation range before optimization is 0-2.9 MW, and the pressure fluctuation range is 0.99-1.25 MPa.

[0048] Referring to Figure 2 and Figure 3 , after the application is adopted: ΔP is 0.1 MPa, α is 0.7, the power-on / power-off frequency of the electric boiler power supply is reduced to 10% of the original, the power fluctuation range is 0.55-1.73 MW, and the pressure fluctuation range is 1.01-1.22 MPa. The ranges of power and pressure fluctuations are significantly reduced, and the mean square deviation is significantly decreased, and the system stability and economy are significantly improved.

[0049] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or equivalent replacement should be covered in the protection scope of the claims of the present application.

Claims

1. A method for steady state operation of an electric boiler at very low power, characterized in that, The application discloses a stable operation system of an electric boiler at an extremely low power, which comprises an electric boiler inner cylinder, an electric boiler outer cylinder, a feed water pump, a circulating pump, a circulating regulating valve, a steam pressure sensor, a steam regulating valve and a steam output pipeline. The electric boiler inner cylinder is located in the electric boiler outer cylinder, the outlet of the feed water pump is communicated with a water inlet on the top side of the electric boiler outer cylinder, the outlet at the bottom of the electric boiler outer cylinder is divided into two routes after the circulating pump, one of the two routes is communicated with a water inlet on the side of the bottom of the electric boiler outer cylinder, and the other route is communicated with a water inlet on the side of the electric boiler inner cylinder through the circulating regulating valve, and the steam outlet at the top of the electric boiler inner cylinder is communicated with the steam output pipeline through the steam pressure sensor and the steam regulating valve. A pH meter, an inner cylinder water level sensor and three-phase electrodes are arranged in the electric boiler inner cylinder. The circulating pump is communicated with the water inlet on the side of the bottom of the electric boiler outer cylinder through a recirculation orifice plate. An inner cylinder drain valve is arranged at the drain outlet at the bottom of the electric boiler inner cylinder. A chemical dosing system is arranged on the pipeline between the circulating regulating valve and the water inlet on the side of the electric boiler inner cylinder. The application further discloses a method for operating the stable operation system of the electric boiler at the extremely low power. 1) When the electric boiler is operated at an extremely low power, the electric conductivity of water in the electric boiler inner cylinder is kept stable through the pH meter and the chemical dosing system; the electric boiler inner cylinder is supplied with water through the circulating pump, the recirculation orifice plate and the circulating regulating valve; the electric boiler inner cylinder is drained through the inner cylinder drain valve; the water level of the electric boiler inner cylinder is measured through the inner cylinder water level sensor; the electric boiler outer cylinder is supplied with water through the feed water pump and the feed water regulating valve; the three-phase electrodes are in an energized state; the steam pressure signal of the electric boiler inner cylinder is measured through the steam pressure sensor; and the steam regulating valve keeps a set opening degree to supply steam to downstream users. 2) The average value of the starting pressure and the stopping pressure of the electric boiler is set as P, the difference between the starting pressure and the stopping pressure of the electric boiler is 2*ΔP, the energized starting pressure of the electric boiler is P-ΔP, and the pressure of the electric boiler at the time of tripping is P+ΔP. 3) In the range from the energized starting pressure P-ΔP to the pressure P+ΔP at the time of tripping, the buffer control pressure P+α*ΔP and P-α*ΔP are set, wherein P+α*ΔP is taken as the pressure signal of the initial drainage of the electric boiler inner cylinder, and P-α*ΔP is taken as the pressure signal of the initial water supply of the electric boiler inner cylinder. 4) When the electric conductivity of water in the electric boiler inner cylinder is stable, the power of the electric boiler is proportional to the water level of the electric boiler inner cylinder. 5) When the steam pressure of the electric boiler inner cylinder rises to P+α*ΔP, the inner cylinder drain valve is opened until the steam pressure of the electric boiler inner cylinder reduces to P, and then the inner cylinder drain valve is closed. 6) When the steam pressure of the electric boiler inner cylinder reduces to P-α*ΔP, the water flow is increased to supply water to the electric boiler inner cylinder through the combined adjustment of the circulating pump, the recirculation orifice plate and the circulating regulating valve, and when the steam pressure of the electric boiler inner cylinder rises to P, the water flow is restored to the original flow through the combined adjustment of the circulating pump, the recirculation orifice plate and the circulating regulating valve. 7) When the steam pressure of the inner cylinder of the electric boiler rises to P+ΔP, the three-phase electrode is de-energized, the electric boiler stops running, the inner cylinder drain valve is closed, the circulation regulating valve is closed, the water in the outer cylinder of the electric boiler is recirculated through the circulation pump and the recirculation orifice plate until the steam pressure of the inner cylinder of the electric boiler decreases to P-ΔP, at this time the three-phase electrode is energized, the electric boiler is restarted, and the water flow is restored to the original water flow through the joint adjustment of the circulation pump, the recirculation orifice plate and the circulation regulating valve.

2. The method for steady state operation of an electric boiler at very low power according to claim 1, characterized in that, The outlet of the feed water pump is connected to the water inlet on the top side of the outer cylinder of the electric boiler through the feed water regulating valve.

3. The method for steady state operation of an electric boiler at very low power according to claim 1, characterized in that, The chemical dosing system is interlocked with the pH meter.

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