A drainage system applied to flexible operation of a supercritical coal-fired boiler

Abstract

The application discloses a drainage system applied to flexible operation of a supercritical coal-fired boiler. The application is characterized in that a temperature sensor group and a drainage pipe are arranged on a lateral wall inlet header of a horizontal flue, and an electric regulating valve on the drainage pipe is controlled according to a first temperature signal and a second temperature signal measured by the temperature sensor group and a main steam pressure signal and a main steam flow signal taken from a boiler automatic control system, so that the condensed accumulated water in the header is discharged to a boiler drainage expander through the drainage pipe, and the condensed accumulated water in the inlet header of the superheater is prevented from causing water blockage in the header, thereby ensuring normal use of the pipeline and safe operation of the boiler.

Description

Technical Field

[0001] This invention relates to the field of safe operation design technology, and in particular to a drainage system for flexible operation of supercritical coal-fired boilers. Background Technology

[0002] Due to the volatility, intermittency, and unpredictability of renewable energy generation, the high proportion of renewable energy connected to the grid increases the pressure on grid peak shaving and frequency regulation, posing challenges to the safe operation of the grid. Therefore, as a flexible and adjustable mainstay of power sources, large thermal power units, especially supercritical thermal power units, participate in wide-load and deep peak shaving, which is an important guarantee for energy security. Their rapid load change and start-up and shutdown capabilities are particularly important. However, during boiler start-up, shutdown, and low-load operation, steam condensate is usually generated in the heating surfaces and headers. If this steam condensate generated due to low-load boiler operation is not discharged in time, it will block the superheater and reheater pipes and headers, leading to water blockage or rapid cooling of the inner surface of the headers. This damages the surface materials of the pipes and headers, causing cracks in the materials of the superheater, reheater, and headers, resulting in material failure.

[0003] Figure 1 This describes the steam-water system flow chart for a once-through boiler. The boiler mainly consists of two parts: a combustion system and a steam-water system. The boiler's steam-water system comprises an economizer, water-cooled walls, a start-up separator, a superheater, and a reheater. Its primary function is to fully absorb the heat released by the fuel, causing the water inside the boiler tubes to evaporate and form superheated steam with a certain temperature and pressure. Figure 1 Water from the feedwater pump enters the economizer, where it is heated and its temperature rises. It then flows through the economizer outlet header, and via the outlet feedwater downcomer, into the boiler's front and rear spiral water-cooled wall inlet headers, the front, rear, and side spiral water-cooled walls and intermediate headers, the vertical water-cooled wall, the vertical water-cooled wall outlet header, the flame deflector inlet header, the horizontal flue side wall inlet header, the flame deflector, the horizontal flue side wall outlet header, and finally to the steam-water separator. From there, the water enters each stage of superheaters and is transformed into steam with qualified pressure, temperature, and flow rate. Finally, it flows through the main steam pipeline into the turbine's high-pressure cylinder to perform work.

[0004] According to the steam-water flow path during normal boiler operation, the steam flowing from the steam-water separator first flows into the horizontal flue side wall superheater and the tail wall superheater, then into the low-temperature superheater in the tail flue, then into the screen superheater and the high-temperature superheater, and finally into the high-pressure cylinder of the turbine through the steam header. The low-temperature reheater at the tail end flows into the high-temperature reheater in the horizontal flue, and then into the intermediate-pressure cylinder of the turbine through the steam header. When the boiler is shut down, the flue gas temperature in the furnace continuously decreases, causing the residual steam inside the superheaters and reheaters to condense, and the steam inside the headers also cools and produces condensate. When the pressure difference in the superheater and reheater tubes is insufficient to allow all the steam to flow into the headers, condensate will form at the vertical pipe bends of the superheaters and reheaters, blocking the pipeline flow; a small amount of condensate will also form in the headers of the horizontal flue side wall superheater and the screen superheater. This condensate poses a significant safety hazard to the rapid start-up and shutdown of the unit and is crucial for the safe operation of these devices.

[0005] Furthermore, to ensure flexible boiler operation, boiler units typically operate under low-load conditions. In areas unheated, such as headers, heat loss exceeds the heat carried in by the fluid, causing the steam temperature inside the headers to gradually decrease. When the steam temperature drops to saturation temperature, condensation begins within the headers, forming a small amount of condensate. Whether the water accumulates in the headers or flows into the headers from the pipes, if it is not drained promptly, it can cause water blockages and rapid cooling of the header surface, jeopardizing the safe operation of the boiler equipment. While large boilers currently have drainage systems, according to operating procedures, these drainage systems only open at pressures below 5 atmospheres. This is insufficient to meet the requirements of deep peak shaving and long-term low-load operation of current supercritical boilers. Therefore, specialized monitoring equipment must be added to handle water accumulation caused by shutdowns, deep peak shaving, and low-load conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a drainage system for flexible operation of supercritical coal-fired boilers, so as to treat the accumulated water generated during shutdown, deep peak shaving and low load.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a drainage system for flexible operation of a supercritical coal-fired boiler, the drainage system comprising: a drainage pipe, a boiler drainage expansion tank, a temperature sensor group, and a control component;

[0009] One end of the drain pipe is connected to the superheated collector tube at the inlet header of the supercritical coal-fired boiler; the other end of the drain pipe is connected to the boiler drain expansion tank; and a drain regulating electric door is provided on the drain pipe.

[0010] The temperature sensor group is connected to the control component. The temperature sensor group includes a first temperature sensor and a second temperature sensor. The first temperature sensor and the second temperature sensor are respectively disposed on the upper wall and the lower wall of the superheated heat collector tube.

[0011] The control component is connected to the boiler automatic control system of the supercritical coal-fired boiler and the control terminal of the drain regulating electric valve, respectively. The control component is used to control the state of the drain regulating electric valve according to the first temperature signal, the second temperature signal, the main steam pressure signal, and the main steam flow signal. The first temperature signal and the second temperature signal are measured by the first temperature sensor and the second temperature sensor, respectively. The main steam pressure signal and the main steam flow signal are obtained from the boiler automatic control system.

[0012] Optionally, the control component includes a first controller and a second controller;

[0013] The first controller is connected to the temperature sensor group and the second controller respectively. The first controller is used to compare the first temperature signal and the second temperature signal to obtain a temperature difference signal, and when the temperature difference signal is greater than a first temperature difference threshold, the temperature difference signal is output to the second controller.

[0014] The second controller is connected to the control terminal of the boiler automatic control system and the control terminal of the drain regulating electric valve. The second controller is used to output an electric valve opening signal to control the drain regulating electric valve to open when the temperature difference signal, the main steam pressure signal and the main steam flow signal do not meet the preset conditions, and output an electric valve closing signal to control the drain regulating electric valve to close after a preset time since the drain regulating electric valve has been opened.

[0015] Optionally, there are multiple temperature sensor groups, and each of the multiple temperature sensor groups is respectively set at multiple first preset positions on the hydrophobic pipe.

[0016] The first preset position is the position between two adjacent manifolds.

[0017] Optionally, the control component includes a plurality of first controllers and second controllers;

[0018] Each of the first controllers is connected to one of the temperature sensor groups in a corresponding manner, and the first controllers are also connected to the second controller.

[0019] The first controller is used to compare the first temperature signal and the second temperature signal to obtain a temperature difference signal, and when the temperature difference signal is greater than a first temperature difference threshold, output the temperature difference signal to the second controller;

[0020] The second controller is connected to the control terminal of the boiler automatic control system and the control terminal of the drain regulating electric valve. The second controller is used to output an electric valve opening signal to control the drain regulating electric valve to open when the temperature difference signal, the main steam pressure signal and the main steam flow signal do not meet the preset conditions, and output an electric valve closing signal to control the drain regulating electric valve to close after a preset time since the drain regulating electric valve has been opened.

[0021] Optionally, the preset condition is:

[0022] The temperature difference signal is less than the second temperature difference threshold, the main steam pressure signal is greater than the pressure threshold, and the main steam flow signal is greater than the flow threshold.

[0023] Optionally, the preset time is 5 seconds.

[0024] Optionally, the drainage system further includes a pressure reducing valve, which is disposed at a second preset position on the drainage pipe, the second preset position being located between one end of the drainage pipe and the drainage regulating electric gate.

[0025] A control component for a drainage system used in the flexible operation of a supercritical coal-fired boiler, as described above.

[0026] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] This invention provides a condensate drainage system for the flexible operation of a supercritical coal-fired boiler. The invention involves arranging a temperature sensor array and adding a condensate drain pipe on the inlet header of the horizontal flue side wall. Based on the first and second temperature signals measured by the temperature sensor array, and the main steam pressure and main steam flow signals from the boiler's automatic control system, the invention controls an electrically operated regulating valve on the condensate drain pipe to discharge condensate from the header to the boiler's condensate expansion tank. This ensures that condensate in the superheater inlet header does not cause blockages, thereby ensuring the normal operation of the pipeline and the safe operation of the boiler. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the steam-water process of a once-through boiler in the background art of this invention;

[0030] Figure 2 This is a schematic diagram of a drainage system applied to the flexible operation of a supercritical coal-fired boiler in an embodiment of the present invention.

[0031] Figure 3 This is an example diagram of a drainage system applied to the flexible operation of a supercritical coal-fired boiler in an embodiment of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide a drainage system for flexible operation of supercritical coal-fired boilers, so as to treat the accumulated water generated during shutdown, deep peak shaving and low load.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] This invention provides a drainage system for the flexible operation of a supercritical coal-fired boiler. The drainage system includes: a drainage pipe, a boiler drainage expansion tank, a temperature sensor group, and a control component. One end of the drainage pipe is connected to the superheated collector tube at the inlet header of the supercritical coal-fired boiler; the other end of the drainage pipe is connected to the boiler drainage expansion tank; a drainage regulating electric valve is installed on the drainage pipe; the temperature sensor group is connected to the control component, and the temperature sensor group includes a first temperature sensor and a second temperature sensor, which are respectively installed on the upper and lower walls of the superheated collector tube; the control component is connected to the boiler automatic control system of the supercritical coal-fired boiler and the control terminal of the drainage regulating electric valve, and the control component is used to control the state of the drainage regulating electric valve according to a first temperature signal, a second temperature signal, a main steam pressure signal, and a main steam flow signal; the first temperature signal and the second temperature signal are measured by the first temperature sensor and the second temperature sensor, respectively, and the main steam pressure signal and the main steam flow signal are obtained from the boiler automatic control system.

[0036] In one implementation, the control component includes a first controller and a second controller. The first controller is connected to both the temperature sensor group and the second controller. The first controller compares the first temperature signal and the second temperature signal to obtain a temperature difference signal, and outputs the temperature difference signal to the second controller when the temperature difference signal is greater than a first temperature difference threshold. The second controller is connected to both the boiler automatic control system and the control terminal of the drain regulating electric valve. The second controller outputs an electric valve opening signal to control the drain regulating electric valve to open when the temperature difference signal, the main steam pressure signal, and the main steam flow signal do not meet preset conditions, and outputs an electric valve closing signal to control the drain regulating electric valve to close after a preset time since the valve has been opened. For example, in this embodiment of the invention, the first controller and the second controller can be implemented using a first-stage comparator and a second-stage comparator, respectively.

[0037] As another implementation, in this embodiment of the invention, the number of temperature sensor groups can be set to multiple, and the multiple temperature sensor groups are respectively set at multiple first preset positions on the drainage pipe; the first preset position is the position between two adjacent manifolds.

[0038] At this time, the control component includes multiple first controllers and second controllers; the multiple first controllers are respectively connected to multiple temperature sensor groups one-to-one, and the multiple first controllers are also connected to the second controllers; the first controllers are used to compare the first temperature signal and the second temperature signal to obtain a temperature difference signal, and when the temperature difference signal is greater than a first temperature difference threshold, output the temperature difference signal to the second controller; the second controllers are respectively connected to the control terminals of the boiler automatic control system and the drain regulating electric valve, and the second controllers are used to output an electric valve opening signal to control the drain regulating electric valve to open when the temperature difference signal, the main steam pressure signal, and the main steam flow signal do not meet preset conditions, and output an electric valve closing signal to control the drain regulating electric valve to close after a preset time since the drain regulating electric valve has been opened.

[0039] In this embodiment, the first controller and the second controller can also be implemented using a first-stage comparator and a second-stage comparator, respectively, such as... Figure 2 and Figure 3 As shown.

[0040] The first-stage comparator includes a subtractor, a comparator, and a controllable switch. The two inputs of the subtractor are connected to the first temperature sensor and the second temperature sensor, respectively. The output of the subtractor is connected to the first input of the comparator. The second input of the comparator is used to input a reference voltage, which is used to characterize the first temperature difference threshold. The output of the comparator is connected to the control terminal of the controllable switch. The input of the controllable switch is connected to the output of the subtractor. The output of the controllable switch is connected to the input of the second-stage comparator.

[0041] The second-stage comparator can be implemented using three comparators and a three-input AND gate.

[0042] The preset conditions in the above two embodiments are: the temperature difference signal is less than the second temperature difference threshold, the main steam pressure signal is greater than the pressure threshold, and the main steam flow rate signal is greater than the flow rate threshold. The preset time in the above two embodiments is 5 seconds. For example, the condensate drain system also includes a pressure reducing valve, which is located at a second preset position on the condensate drain pipe, between one end of the condensate drain pipe and the condensate drain regulating electric valve.

[0043] This invention provides a condensate drainage system for flexible operation of supercritical coal-fired boilers. It is mainly applied at the inlet header of the superheater on the side wall of the horizontal flue. By monitoring the inlet header and adding a condensate drain pipe, the condensate regulating electric valve on the drain pipe is controlled to guide the condensate in the pipe to the boiler condensate expansion tank. At the same time, a pressure reducing valve should also be installed on the drain pipe to reduce the pressure of the water flowing out of the header before introducing it into the boiler condensate expansion tank.

[0044] like Figure 2 As shown, in this embodiment of the invention, a temperature sensor group and a drain pipe are installed on the inlet header of the superheater on the horizontal flue side wall, leading to the boiler drain expansion tank. The temperature sensor group is arranged in two groups, one above and one below the superheater collector tubes, and is respectively installed between the branch pipes of the header, simultaneously monitoring the temperature above and below the tube walls of the superheater collector tubes. A drain pipe is also added to the header, equipped with a pressure reducing valve and a drain regulating electric valve. By opening the electric regulating valve, the condensate in the superheater tubes is discharged to the drain expansion tank.

[0045] Because the boiler is in operation throughout the entire control process, and the steam-water mixture inside the pipes is constantly flowing, it is necessary to set the valve opening interval and frequency. To ensure the operating pressure of the entire pipeline, the opening time of the electric regulating valve should not be too long; it is generally set to close after 5 seconds of opening. After the condensate is reduced in pressure by the pressure reducing valve, it flows into the boiler condensate expansion tank through the pressure difference in the drain pipe.

[0046] In terms of signal control, such as Figure 3As shown, the temperature sensor installed on the superheater inlet header on the side wall of the horizontal flue is mainly responsible for monitoring the temperature of the upper and lower walls of the superheater tubes and transmitting the measured wall temperatures (first temperature signal and second temperature signal) to the first-stage comparator. When the operating pressure inside the boiler tubes is constant, the saturation temperature of the steam is a constant value. When the steam temperature drops to the saturation temperature during low-load boiler operation, condensation begins. Therefore, the first-stage comparator mainly monitors the temperature difference between the upper and lower walls of the tubes, and the reference value can be set as the steam saturation temperature. When the monitored temperature difference (temperature difference signal) is greater than the reference value (first temperature difference threshold), the temperature difference signal from the first-stage comparator and the pressure and flow signals (main steam pressure signal and main steam flow signal) from the boiler automatic control system are transmitted together to the second-stage comparator. The second-stage comparator also sets reference values ​​for three parameters. When the measured value of any parameter reaches the upper or lower limit of the reference value, the second-stage comparator outputs a command to open the regulating valve, opening the electric regulating valve on the drain pipe to discharge condensate.

[0047] The workflow of a condensate drainage system for flexible operation of a supercritical coal-fired boiler, as provided in this embodiment of the invention, is as follows:

[0048] A reference value (first temperature difference threshold) for monitoring wall temperature is set for the temperature sensors installed at the top and bottom of the header. The upper and lower wall temperatures of the header are monitored at any time, and the temperature signals are transmitted to the first-stage comparator. The first-stage comparator compares the temperature signals. When the difference is greater than the set allowable value for condensate discharge, the temperature difference signal calculated by the first comparator is sent to the second-stage comparator.

[0049] In the second-stage comparator, in addition to the temperature difference signal from the real-time monitoring header, there are also the main steam pressure signal and the main steam flow signal from the boiler automatic control system DCS. Through real-time monitoring and comparative analysis of these three signals, the second-stage comparator finally sends a command to the electric regulating valve installed on the drain pipe to open the valve and discharge the condensate in the header.

[0050] Because the entire boiler system needs to maintain a stable pressure, the opening time of the electric regulating valves cannot be too long. They are generally set to automatically close after 5 seconds of opening. A small amount of condensate in the header is sent to the condensate expansion tank for treatment and utilization through the pressure difference in the pipes.

[0051] After one round of condensate discharge is completed, the sensor continues to monitor the wall temperature at the top and bottom of the header, monitors temperature changes in real time and transmits temperature signals to the first-stage comparator, and then controls the opening and closing of the electric regulating valve through the second-stage comparator to discharge the condensate in the header in a timely manner and ensure the safety of the entire boiler operation.

[0052] The beneficial effects of the technical solution of the present invention based on the above embodiments are as follows:

[0053] This invention utilizes a temperature sensor and a drain pipe installed on the inlet header of the horizontal flue wall. The temperature difference signal from the sensor, along with the pressure and flow signals from the boiler's automatic control system, are transmitted to a comparator device. This device controls an electrically operated regulating valve on the drain pipe, discharging condensate from the header to the boiler's condensate expansion tank. This ensures that condensate in the superheater inlet header does not cause blockages, thus preventing issues that could affect the normal operation of the pipeline and the safe operation of the boiler.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A drainage system for flexible operation of a supercritical coal-fired boiler, characterized in that, The drainage system includes: a drainage pipe, a boiler drainage expansion tank, a temperature sensor group, and a control component; One end of the drain pipe is connected to the superheated collector tube at the inlet header of the supercritical coal-fired boiler; the other end of the drain pipe is connected to the boiler drain expansion tank; and a drain regulating electric door is provided on the drain pipe. The temperature sensor group is connected to the control component. The temperature sensor group includes a first temperature sensor and a second temperature sensor. The first temperature sensor and the second temperature sensor are respectively disposed on the upper wall and the lower wall of the superheated heat collector tube. The control component is connected to the boiler automatic control system of the supercritical coal-fired boiler and the control terminal of the drain regulating electric valve, respectively. The control component is used to control the state of the drain regulating electric valve according to the first temperature signal, the second temperature signal, the main steam pressure signal, and the main steam flow signal. The first temperature signal and the second temperature signal are measured by the first temperature sensor and the second temperature sensor, respectively. The main steam pressure signal and the main steam flow signal are obtained from the boiler automatic control system. The control component includes a first controller and a second controller; The first controller is connected to the temperature sensor group and the second controller respectively. The first controller is used to compare the first temperature signal and the second temperature signal to obtain a temperature difference signal, and when the temperature difference signal is greater than a first temperature difference threshold, the temperature difference signal is output to the second controller. The second controller is connected to the control terminal of the boiler automatic control system and the drain regulating electric door respectively. The second controller is used to output an electric door opening signal to control the drain regulating electric door to open when the temperature difference signal, the main steam pressure signal and the main steam flow signal do not meet the preset conditions, and output an electric door closing signal to control the drain regulating electric door to close after a preset time since the drain regulating electric door has been opened. The preset conditions are: The temperature difference signal is less than the second temperature difference threshold, the main steam pressure signal is greater than the pressure threshold, and the main steam flow signal is greater than the flow threshold. The first controller and the second controller are implemented using a first-stage comparator and a second-stage comparator, respectively. The first-stage comparator includes a subtractor, a comparator, and a controllable switch. The two inputs of the subtractor are connected to the first temperature sensor and the second temperature sensor, respectively. The output of the subtractor is connected to the first input of the comparator. The second input of the comparator is used to input a reference voltage, which is used to characterize the first temperature difference threshold. The output of the comparator is connected to the control terminal of the controllable switch. The input of the controllable switch is connected to the output of the subtractor. The output of the controllable switch is connected to the input of the second-stage comparator. The second-stage comparator consists of three comparators and a three-input AND gate.

2. The drainage system for flexible operation of a supercritical coal-fired boiler according to claim 1, characterized in that, The number of temperature sensor groups is multiple, and the multiple temperature sensor groups are respectively set at multiple first preset positions on the hydrophobic pipe; The first preset position is the position between two adjacent manifolds.

3. The drainage system for flexible operation of a supercritical coal-fired boiler according to claim 2, characterized in that, The control component includes multiple first controllers and second controllers; Each of the first controllers is connected to one of the temperature sensor groups in a corresponding manner, and the first controllers are also connected to the second controller. The first controller is used to compare the first temperature signal and the second temperature signal to obtain a temperature difference signal, and when the temperature difference signal is greater than a first temperature difference threshold, output the temperature difference signal to the second controller; The second controller is connected to the control terminal of the boiler automatic control system and the control terminal of the drain regulating electric valve. The second controller is used to output an electric valve opening signal to control the drain regulating electric valve to open when the temperature difference signal, the main steam pressure signal and the main steam flow signal do not meet the preset conditions, and output an electric valve closing signal to control the drain regulating electric valve to close after a preset time since the drain regulating electric valve has been opened.

4. The drainage system for flexible operation of a supercritical coal-fired boiler according to claim 1 or 3, characterized in that, The preset time is 5 seconds.

5. The drainage system for flexible operation of a supercritical coal-fired boiler according to claim 1, characterized in that, The drainage system also includes a pressure reducing valve, which is set at a second preset position on the drainage pipe. The second preset position is located between one end of the drainage pipe and the drainage regulating electric gate.

6. A control component according to any one of claims 1-5 for use in a condensate drainage system for flexible operation of a supercritical coal-fired boiler.

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