Electric heating system for ultra-supercritical boiler steam-water separator

Abstract

The invention relates to the technical field of ultra-supercritical coal-fired boilers, in particular to an electric heating system for a steam-water separator of an ultra-supercritical boiler, which comprises an upper monitoring part, a lower control part, a field acquisition control part and an electric heating device which are electrically connected in sequence, the electric heating device is used for heating a steam-water separator of the ultra-supercritical boiler, the electric heating device is arranged on the surface of a main body of the steam-water separator and the surfaces of six nozzles of the main body of the steam-water separator, and the field acquisition control part is used for controlling working parameters of the electric heating device based on acquired temperature data of the steam-water separator. According to the technical scheme, the temperature of the outer wall and the inner wall of the steam-water separator is increased through heating of the external power source, the overall temperature of thick-wall components of the steam-water separator is gradually increased in a heat conduction mode, and fatigue life damage caused by additional thermal stress due to temperature difference in the water feeding process is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-supercritical coal-fired boilers, in particular to an electric heating system for an ultra-supercritical boiler steam-water separator. Background Art

[0002] Coal-fired power will shift from the past "main power source, basic status, and supporting role" to "equal emphasis on base load power source and regulating power source" in the near and medium term (2021-2030). Coal-fired power will play a fundamental role in coal conversion, electric heat supply, and system peak regulation. In the long term (2031-2050), coal-fired power will become a pure "regulating power source" to ensure the safety of power supply and to fully absorb clean energy peak regulation. As the annual utilization hours of coal-fired power gradually decrease, the flexible operation of coal-fired power will become normalized. However, the design life of the main pressure-bearing components of coal-fired units is generally 30 years. Taking the design of a supercritical boiler as an example, during the entire life cycle, the cold start and stop times are >500 times, the warm start and stop times are >1200 times, the hot start times are >5000 times, and the extremely hot start times are >500 times. As the flexible operation requirements of coal-fired units become more and more frequent, the rapid load changes and the number of cold, warm, hot and extremely hot starts of coal-fired units will increase significantly. How to ensure the safety of thick-walled components under flexible operation has become a focus of attention.

[0003] The steam-water separator of an ultra-supercritical boiler is a thick-walled pressure-bearing component. During the cold start and hot start processes, changes in thermal stress affect the safe operation of the steam-water separator. Therefore, during the cold start process, in order to ensure that the feed water from the deaerator or auxiliary steam header does not cause excessive thermal stress shock to the thick-walled pressure-bearing components, the method of increasing the water supply time and reducing the feed water flow rate is generally adopted to slowly heat the steam-water separator, reduce the increase in additional thermal stress caused by excessive temperature rise, and avoid fatigue damage caused by increased stress amplitude in the nozzle part of the steam-water separator, which affects the safe operation of the steam-water separator. Summary of the invention

[0004] The present invention proposes an electric heating system for an ultra-supercritical boiler steam-water separator, which can increase the overall temperature of thick-walled components of the steam-water separator and reduce fatigue life damage caused by additional thermal stress due to temperature difference during water supply.

[0005] The present invention provides an electric heating system for an ultra-supercritical boiler steam-water separator, comprising an upper monitoring part, a lower control part, a field acquisition control part and an electric heating device which are electrically connected in sequence, wherein the electric heating device is used to heat the steam-water separator of the ultra-supercritical boiler, and the electric heating device is arranged on the surface of the main body of the steam-water separator and its six nozzles, and the field acquisition control part is used to control the working parameters of the electric heating device based on the collected temperature data of the steam-water separator.

[0006] Compared with the prior art, the present invention has the following beneficial effects: an external power source is used to heat and increase the temperature of the outer wall and the inner wall of the steam-water separator, and the overall temperature of the thick-walled parts of the steam-water separator is gradually increased through heat conduction, thereby reducing fatigue life damage caused by additional thermal stress caused by temperature difference during water supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0008] Figure 1 It is a hardware principle diagram of an electric heating system for an ultra-supercritical boiler steam-water separator provided by an embodiment of the present invention;

[0009] Figure 2 It is a schematic diagram of the layout of the partitions of the electric heating device provided by an embodiment of the present invention;

[0010] Figure 3 is a system architecture diagram of an electric heating system for an ultra-supercritical boiler steam-water separator provided by an embodiment of the present invention;

[0011] Figure 4 is a schematic diagram of an electric heating device provided by an embodiment of the present invention;

[0012] Figure 5 is a logic operation principle diagram of the electric heating device provided by an embodiment of the present invention;

[0013] Figure 6 It is a system structure diagram of the steam-water separator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0015] Please refer to Figure 1An embodiment of the present invention provides an electric heating system for a steam-water separator of an ultra-supercritical boiler, comprising an upper monitoring part, a lower control part, a field acquisition control part and an electric heating device electrically connected in sequence, the electric heating device being used to heat the steam-water separator of the ultra-supercritical boiler, the electric heating device being arranged on the surface of the main body of the steam-water separator and its six nozzles, the field acquisition control part being used to control the working parameters of the electric heating device based on the collected temperature data of the steam-water separator.

[0016] An external power source is used to heat the outer and inner walls of the steam-water separator to increase the temperature. Through heat conduction, the overall temperature of the thick-walled parts of the steam-water separator is gradually increased to reduce fatigue life damage caused by additional thermal stress caused by temperature difference during water supply.

[0017] In one embodiment of the present invention, the heating method of the electric heating device includes electric induction heating and far infrared heating.

[0018] The present invention performs electric heating control on the thick wall temperature of an ultra-supercritical steam-water separator, and mainly adopts not limited to far infrared but also electric induction heating method to heat the thick-walled pressure-bearing parts of the wall surface of the steam-water separator. By monitoring the load, flow rate and the inner and outer wall temperatures of the steam-water separator of the boiler, the wall temperature of the steam-water separator of the power station boiler in cold, warm and hot start-up, as well as variable load operation is effectively controlled, thereby reducing the stress amplitude of these processes.

[0019] The present invention takes the steam-water separator of an ultra-supercritical boiler as an object. For the steam-water separator, a ceramic far-infrared electric heating sheet is used to cover the surface of the steam-water separator body and six nozzles, and about 48 pieces of 500*480 or special-shaped ceramic heating sheets are used for wrapping. The temperature control cabinet is divided into 12 output circuits, each circuit is connected to 4 pieces of resistance heaters for heating. The 12 output circuits of the control cabinet are divided into two groups into one partition, and the steam-water separator is divided into 6 partitions for partition heating. The partitions are as follows Figure 2 shown.

[0020] like Figure 2 and Figure 3 As shown, in one embodiment of the present invention, the upper monitoring part is an industrial computer, the lower control part is a PLC system, the field acquisition control part includes a temperature transmitter, a temperature sensor and a single-phase thyristor power regulator, the output end of the temperature transmitter is electrically connected to the PLC system, the temperature sensor is electrically connected to the electric heating device and the temperature transmitter, and the single-phase thyristor power regulator is electrically connected to the PLC system and the electric heating device.

[0021] like Figure 4As shown, in one embodiment of the present invention, the electric heating device includes an electric heating temperature control cabinet, a heater connecting wire, a flexible ceramic heater and a temperature measuring thermocouple, and the electric heating temperature control cabinet includes a PLC control unit, a two-phase thyristor module and a thyristor phase shift module.

[0022] In one embodiment of the present invention, the PLC control unit uses PLC to control power output, the temperature transmitter converts the signal of the temperature measuring thermocouple into an output current of 4-20mA, and the PLC control unit uses the deviation between the temperature feedback value and the set value as the input quantity for calculation, and the generated control signal is used to adjust the power supply voltage output by the thyristor module and control the start and stop of the electric heating system at the same time. The temperature control is set according to the target temperature and the time required for heating. The electric heating temperature control cabinet adopts a 380V three-phase four-wire power supply, and is equipped with 12 output circuits, 12 temperature measurement points, and 6 power control circuits, wherein each power control circuit corresponds to 2 output circuits and 2 temperature measurement points, and the output voltage of the two output circuits is controlled according to the highest temperature fed back between the two temperature measurement points to achieve the purpose of controlling power.

[0023] like Figure 5 As shown, in one embodiment of the present invention, the temperature control program of the PLC control unit includes a temperature curve compilation program, a temperature curve operation calculation program, a temperature collection and comparison program, a PID analog output calculation program and an alarm program. The temperature curve operation calculation program is used to calculate the program-given temperature value, the temperature collection and comparison program compares the maximum collected temperature value, and the PID analog output calculation program is used to calculate the output analog value according to the given temperature value and the maximum collected temperature value to control the power supply voltage output by the thyristor module. Specific embodiment:

[0025] The main body of this scheme is the steam-water separator of the power station boiler, and its outer wall is heated to 120℃ by an induction electric heating device. The steam-water separator is a vertical cylinder, with a total of two, and its outer diameter is The wall thickness is 105mm, the height is 3600mm, the material is SA-336F12, the density is 7820kg / m3, and the specific heat capacity is 0.5024kJ / kg. The mass of a single separator is:

[0026] m=ρV=7750kg

[0027] 1. Electric heating device and electric heating control part

[0028] 1.1 Electric heating device

[0029] The electric heating device adopts electric induction heating, covering the surface of the steam-water separator body and six nozzles. The power of the electric heater can ensure the heat dissipation inside the steam-water separator, ensuring that the metal temperature of the steam-water separator body can be heated from ambient temperature to 120 degrees within 1 hour.

[0030] The electric heater is covered on the separator body, and the wall temperature detection points are arranged at the same time. The temperature detection points are arranged according to the actual situation on site (10 points are expected) to control the output power of the electric heater. The insulation material is arranged outside the heater, and the thickness of the insulation material should ensure that the insulation surface temperature meets the insulation surface temperature requirements of the power equipment.

[0031] 1.2 Electric heating control cabinet

[0032] The electric heating control cabinet is mainly composed of thyristor power regulator, temperature sensor, temperature transmitter, etc. The electric heating output power is controlled by the thyristor power regulator through the temperature sensor and temperature transmitter, and changes the electric heating power output according to the temperature setting of the PLC system to achieve the purpose of regulating the temperature field of the steam-water separator.

[0033] 2. Control functions include

[0034] 2.1 Electric heating control

[0035] Electric heating automatic program control function: including automatic heating program, automatic power adjustment program, automatic start and stop program, etc.;

[0036] External / internal interlock protection function: including safe operation interlock protection, power failure protection, steam-water separator over-temperature protection, etc.;

[0037] Heating control: can realize continuous proportional adjustment; and can accept PLC load control signal.

[0038] 2.2 Contact with PLC system

[0039] The electric heating system and PLC system use communication, and some important signals are connected by hard wiring.

[0040] 2.3PLC control part

[0041] The PLC system is responsible for monitoring and controlling the steam-water separator and its electric heating system, and is responsible for system debugging and configuration and adjustment of the operating software. Appropriate isolation measures should be taken for all analog signals entering the PLC system.

[0042] Each steam-water separator is equipped with an online temperature monitoring system to monitor the temperature in real time and continuously, and connect with the PLC system through communication.

[0043] The start and stop of the electric heating of the steam-water separator should be related to the start and stop of the power station boiler, and the DCS signal is required as a reference for operation.

[0044] 3. Host computer monitoring

[0045] The thermal parameters of the electric heating signal of the steam-water separator, the equipment status, the temperature measuring instrument data, etc. are uploaded to the upper computer monitoring system through the communication network. After data integration and deep mining, the information system technology is used to realize data display, statistics, and analysis, so as to provide information and tools for the formulation of rapid start and stop and variable load control strategies for thick-walled components of power station boilers, ensure safe production under the flexible operation of power station boilers, and monitor the life loss of thick-walled pressure-bearing components under rapid start and stop and variable load processes.

[0046] 3.1 Data collection and processing

[0047] The host computer system can continuously collect and process all measurement signals and equipment status signals related to the operation of the steam-water separator and the electric heating system, and provide relevant operation information to the operator in a timely manner to achieve safe operation of the system. Its basic functions are:

[0048] (1) Collection and processing of process variables: data from all temperature measurement points of all steam-water separators, and display of the data.

[0049] (2) Alarm processing: Alarms are issued for process variables exceeding their limits and important events, and incorrect alarms can be automatically locked and eliminated.

[0050] (3) Screen display: alarm display; graphic display (analog diagram, bar graph, trend curve, group parameters, soft manual operation screen); fault status display, etc.

[0051] (4) Record and print reports: variable trend records; parameter limit-exceeding and alarm records; accident sequence records; equipment operation cumulative records; equipment status records; equipment performance records; periodic records; screen copies, etc.

[0052] (5) Storage of historical data.

[0053] 3.2 Thermal protection and alarm

[0054] (1) Sound and light alarm

[0055] LCD alarm is the main alarm method. All input, output and intermediate variable calculation values ​​of the PLC system can be used as alarm sources of the data acquisition system. All alarm items can be displayed on the host computer and PLC, and sound signals will be issued to remind operators to deal with them in time. False alarm signals should be suppressed during the start-stop process.

[0056] When the following parameters exceed or fall below the specified value, an audible and visual alarm will be issued:

[0057] 1) The temperature of the steam-water separator exceeds the set value

[0058] 2) Abnormality of electric heating equipment

[0059] (2) Thermal protection

[0060] When the temperature of the steam-water separator exceeds the set value or other equipment fails, a stop heating signal is given to the electric heating control cabinet.

[0061] 3.3 The host computer monitoring system communicates and controls with the PLC system.

[0062] Through the MODBUS interface, a dedicated communication protocol is used to complete the data format communication between the host computer and the PLC system.

[0063] 3.4 Description of the system architecture

[0064] like Figure 6 As shown in the figure, the system communicates with the thermal control parameters of the boiler through the DCS, obtains the real-time state parameters of the steam-water separator in an external form, obtains the specific state parameters of the steam-water separator operation through DCS real-time communication, and sends the data to the lower PLC control communication unit through optical fiber communication and relying on the field bus communication module of the DCS system. During the operation of the system, according to the thermal parameters obtained by the DCS, combined with the PLC for electronic control, the far-infrared electric heating of the startup process is carried out according to the state of the boiler. In advance, the outer wall of the steam-water separator is electrically heated, thereby reducing the temperature difference between the inner wall and the outside during the startup process, achieving the goal of reducing the additional thermal stress during the startup process. The PLC and ceramic far-infrared electric heating system use the MODBUS communication protocol for data exchange, realize the electric heating of the outer wall of the steam-water separator according to the state of the unit steam-water separator, install multiple temperature measurement points on the steam-water separator as the measurement points for the control of the electric heating heating plate, and perform closed-loop control through 6 loops to realize the electric heating of the steam-water separator. This system is operated as an external plug-in. In the future, the system will not be limited to the steam-water separator. This heating method can be used for the boiler high-temperature superheater outlet header, high-temperature reheater outlet header and economizer inlet header to reduce the additional thermal stress of the pipe seat and pipeline caused by the temperature difference under start-stop and variable load, and realize the effective regulation of the additional thermal stress of start-stop and variable load.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electric heating system for an ultra-supercritical boiler steam-water separator, characterized in that: It includes an upper monitoring part, a lower control part, a field acquisition control part and an electric heating device which are electrically connected in sequence. The electric heating device is used to heat the steam-water separator of the ultra-supercritical boiler. The electric heating device is arranged on the main body of the steam-water separator and the surface of its six nozzles. The field acquisition control part is used to control the working parameters of the electric heating device based on the collected temperature data of the steam-water separator.

2. The electric heating system for an ultra-supercritical boiler steam-water separator according to claim 1, characterized in that: The heating methods of the electric heating device include electric induction heating and far infrared heating.

3. The electric heating system for an ultra-supercritical boiler steam-water separator according to claim 1, characterized in that: The upper monitoring part is an industrial computer, the lower control part is a PLC system, the field acquisition control part includes a temperature transmitter, a temperature sensor and a single-phase thyristor power regulator, the output end of the temperature transmitter is electrically connected to the PLC system, the temperature sensor is electrically connected to the electric heating device and the temperature transmitter respectively, and the single-phase thyristor power regulator is electrically connected to the PLC system and the electric heating device respectively.

4. The electric heating system for an ultra-supercritical boiler steam-water separator according to claim 1, characterized in that: The electric heating device comprises an electric heating temperature control cabinet, a heater connecting wire, a flexible ceramic heater and a temperature measuring thermocouple. The electric heating temperature control cabinet comprises a PLC control unit, a two-phase thyristor module and a thyristor phase shift module.

5. The electric heating system for an ultra-supercritical boiler steam-water separator according to claim 4, characterized in that: The PLC control unit uses PLC to control power output. The temperature transmitter converts the signal of the temperature measuring thermocouple into an output current of 4 to 20 mA. The PLC control unit uses the deviation between the temperature feedback value and the set value as input and performs calculations. The generated control signal is used to adjust the power supply voltage output by the thyristor module and simultaneously control the start and stop of the electric heating system.

6. The electric heating system for an ultra-supercritical boiler steam-water separator according to claim 5, characterized in that: The temperature control program of the PLC control unit includes a temperature curve compilation program, a temperature curve operation calculation program, a temperature collection and comparison program, a PID analog output calculation program and an alarm program. The temperature curve operation calculation program is used to calculate the program-given temperature value, the temperature collection and comparison program compares the maximum value of the collected temperature, and the PID analog output calculation program is used to calculate the output analog value according to the given temperature value and the maximum value of the collected temperature to control the power supply voltage output by the thyristor module.

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