A pulverizing system and method capable of operating flexibly under low load

Abstract

The present invention provides a pulverizing system and method that can operate flexibly under low load. Taking three coal mills as an example, the pulverizing system includes a boiler, an air preheater, three coal mills, a coal mixing chamber, a regenerator, and a burner. The air preheater is installed below the tail flue of the boiler. The first output end of the air preheater is connected to the three coal mills through a first pipeline. A first control valve M1, a second control valve M2, and a third control valve M3 are respectively arranged in the middle of the first pipeline. The three coal mills are all equipped with a first monitoring device; the second output end of the air preheater is connected to the regenerator, and the regenerators are arranged in series. The first output end of the regenerator is connected to the coal mixing chamber. The outlet of the coal mixing chamber is connected to the burners on each layer through a second pipeline. A second monitoring device is installed in the second pipeline. The three coal mixing chambers are interconnected through a fourth control valve K1 and a fifth control valve K2.

Description

Technical Field

[0001] The present invention relates to the technical field of boiler pulverizing technology, and in particular to a pulverizing system and method that can operate flexibly under low load. Background Art

[0002] To improve the grid's ability to absorb renewable energy and compensate for the instability of renewable energy sources like photovoltaic and wind power, thermal power plants are beginning to shoulder the heavy responsibility of peak and frequency regulation. This necessitates the flexible operation of thermal power units. Simultaneously, faced with the overwhelming impact of renewable energy and the demands of relevant national policies, how thermal power plants can transition to a safer, more environmentally friendly, and more economical operating model has become a critical issue that the industry urgently needs to address. The pulverizing system, primarily responsible for producing sufficient quantities of qualified pulverized coal for boiler combustion, is a crucial component of thermal power units and is closely linked to boiler load and efficiency. In the context of deep peak shaving, the flexible, economical, and safe operation of the pulverizing system is crucial for variable-load operation.

[0003] Currently, technical solutions for flexible operation transformation of pulverizing systems mainly focus on the start-up and shutdown decisions and operating status adjustment of coal mills under variable loads. For example, Patent 1, an artificial intelligence-based intelligent operation optimization method for coal mill startup and shutdown (CN113843039B), uses artificial intelligence and big data technologies, combined with historical operating data to construct a coal mill operation control model. The real-time operating data of the coal mill and the real-time status data of the water-cooled wall are input into the control model. After optimization in the startup and shutdown module, optimization in the coal feed module, and operation simulation module, the optimal recommended instructions are output. Patent 2, a coal mill combination operation control method, device, equipment, and storage medium (CN111389575B), aims to optimize the coal mill operation combination. It proposes to determine the operating characteristics of each coal mill based on historical data, further screen the key characteristics of the coal mill, determine the operating ranking of each coal mill, and output a coal mill operation combination plan based on constraints and load changes.

[0004] Existing technical solutions primarily focus on determining the start and stop conditions for a single coal mill, aiming to reduce pulverizing energy consumption under low loads. However, in existing pulverizing systems, a single coal mill is connected to only one row of burners. A mill shutdown causes the entire row of burners to cease operation, shifting the distribution of pulverized coal airflow within the furnace and causing the center of the flame to shift, exacerbating uneven heating of the water-cooled walls. Frequent load fluctuations cause the water-cooled walls to experience fluctuating flame heat transfer, generating alternating thermal stresses that shorten the service life of the pipes and endanger safe boiler operation. Furthermore, when increased load necessitates starting the coal mill, the inertia of restarting prevents the boiler from responding promptly to the load change, extending system latency. Summary of the Invention

[0005] The object of the present invention is to provide a pulverizing system and method that can operate flexibly under low load, so as to solve the problems raised in the above background technology.

[0006] The present invention is achieved through the following technical solutions:

[0007] On the one hand, the present invention provides a pulverizing system that can operate flexibly under low load. Taking three coal mills as an example, the pulverizing system includes a boiler, an air preheater, three coal mills, a coal mixing chamber, a regenerator, and a burner. The air preheater is installed below the tail flue of the boiler. The first output end of the air preheater is connected to the three coal mills through a first pipeline. A first control valve M1, a second control valve M2, and a third control valve M3 are respectively provided in the middle of the first pipeline. The three coal mills are each equipped with a first monitoring device, which is used to collect coal mill energy consumption information and outlet coal powder fineness.

[0008] The second output end of the air preheater is connected to the regenerator, and the regenerators are arranged in series. The first output end of the regenerator is connected to the coal mixing chamber. The outlet of the coal mixing chamber is connected to the burners on each layer through a second pipeline. A second monitoring device is installed in the second pipeline to collect the coal powder concentration, air-powder mixture flow and temperature entering the burners on each layer. The three coal mixing chambers are interconnected through the fourth control valve K1 and the fifth control valve K2 respectively.

[0009] Preferably, the second output end of the regenerator is connected to an exhaust gas treatment device.

[0010] Preferably, the fourth control valve K1 and the fifth control valve K2 are respectively installed at the interface between the branch line and the coal mixing chamber.

[0011] Preferably, the coal mixing chamber is hemispherical.

[0012] On the other hand, the present invention also provides a milling method that can be flexibly operated under low load, the milling method comprising the following steps:

[0013] Step 1: Determine the energy consumption of each coal mill based on the coal mill operation history data, and determine the upper and lower limits of the pulverizing output. Divide the output ratio according to the coal mill energy consumption. Under the premise of ensuring the normal operation of the coal mill, the coal mill with low energy consumption is given more output, thereby reducing the energy consumption of pulverizing.

[0014] Step 2: According to the pulverizing output ratio determined in step 1, the openings of the first control valve M1, the second control valve M2, and the third control valve M3 are controlled to ensure the air-coal ratio of the coal mill;

[0015] In step 3, the air preheater uses the flue gas from the boiler to heat the cold air into primary air and secondary air. The primary air output from the air preheater enters the coal mill for drying and carries qualified pulverized coal into the regenerator. The first monitoring device installed at the coal mill outlet monitors and records the pulverized coal fineness and pulverizing energy consumption in real time.

[0016] Step 4: The pulverized coal is further dried using the waste heat of the flue gas through a regenerator. The pulverized coal airflow dried by the regenerator enters the coal mixing chamber, and the flue gas at its outlet enters the exhaust gas treatment device for harmless treatment;

[0017] Step 5: Evenly mix the pulverized coal airflows of the main and branch routes through the coal mixing chamber, and then adjust the coal feed rate of each layer of burners through the opening of the fourth control valve K1 and the fifth control valve K2 to achieve regulation of the operating load of each layer of burners.

[0018] Preferably, the milling method further comprises:

[0019] The information collected by the first monitoring device and the second monitoring device is transmitted to the control center in real time to detect whether the fineness of the coal powder at the outlet of each coal mill meets the operating requirements. If not, the operating parameters of the corresponding coal mill are adjusted, and the energy consumption of the adjusted coal mill is re-evaluated. The results are returned to the control center, and steps 2 and 5 are repeated;

[0020] If the pulverized coal fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If not, readjust the opening of the first control valve K1 and the second control valve K2, and readjust the coal feed to each layer of burners. If it is reasonable, the control is completed.

[0021] Prioritize, when the boiler load is reduced and cutting and grinding operation is required or a coal mill fails, it can be directly shut down, and the pulverizing output ratio can be redistributed according to the boiler load and the operating energy consumption of the remaining coal mills, and the coal feed amount of each layer burner can be reasonably configured by adjusting the opening of the fourth control valve K1 and the fifth control valve K2.

[0022] Prioritize, when the boiler load increases and the coal mill needs to be restarted, the working coal mill is first gradually adjusted to the maximum output to achieve a stable increase in the boiler load during the coal mill restart phase, accelerate the boiler load response speed, and after the coal mill is restarted, the pulverizing ratio can be redistributed according to the current load and resume normal operation.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a pulverizing system and method that can operate flexibly under low load, which connects the coal mills of the pulverizing system into a whole, breaking the isolated state of independent operation of the coal mills. When the boiler is running at low load or the coal mill suddenly fails, the coal powder can be redistributed by regulating the valve to ensure the operation of the burners in each layer, thereby enhancing the flexibility of the pulverizing system operation, helping to optimize the combustion of the boiler under low load, preventing the furnace flame from exhibiting obvious flame deviation due to the cessation of the operation of the entire row of burners, and thus preventing the water-cooled wall temperature distribution from changing drastically due to the obvious flame deviation. This helps to extend the fatigue service life of the water-cooled wall pipes.

[0025] At the same time, when the boiler load increases and the coal mill is restarted, the load response speed of the boiler can be accelerated by adjusting the output of the working coal mill during the restart phase, thereby enhancing the flexibility and reliability of the pulverizing system operation.

[0026] Furthermore, comprehensive consideration is given to pulverized coal fineness and the heat loss from mechanical incomplete combustion in the boiler. By controlling valves and adjusting mill operating parameters, both pulverizing energy consumption and mechanical incomplete combustion heat loss are minimized. Furthermore, waste heat from the flue gas at the air preheater outlet is utilized to further dry the pulverized coal, facilitating its ignition and combustion, thereby improving the thermal efficiency of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only preferred embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a structural diagram of a pulverizing system that operates flexibly under low load provided by the present invention.

[0029] Figure 2 The present invention provides a flow chart of a pulverizing method that operates flexibly under low load. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more apparent, exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0031] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art are not described to avoid confusion with the present invention.

[0032] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0033] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present invention. When used herein, the singular forms "a", "an", and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0034] In order to fully understand the present invention, a detailed structure will be provided in the following description to illustrate the technical solution proposed by the present invention. Optional embodiments of the present invention are described in detail below. However, in addition to these detailed descriptions, the present invention may also have other implementations.

[0035] On the one hand, if Figure 1 As shown, the present invention provides a pulverizing system that can be flexibly operated under low load, the pulverizing system comprising a boiler, an air preheater, three coal mills, a coal mixing chamber, a regenerator, and a burner. The air preheater is installed below the flue at the rear of the boiler, and utilizes the flue gas at the rear of the boiler to heat cold air into primary air and secondary air. The function of the primary air is to provide oxygen for the combustion of the pulverized coal in the initial stage, and the function of the secondary air is to provide oxygen for the complete combustion of the pulverized coal in the furnace. The first output end of the air preheater is connected to the three coal mills through a first pipeline. A first control valve M1, a second control valve M2, and a third control valve M3 are respectively provided in the middle of the first pipeline. The three coal mills are all equipped with a first monitoring device, which is used to collect energy consumption information of the coal mill and the fineness of the outlet coal powder.

[0036] The second output end of the air preheater is connected to the regenerator, and the regenerators are arranged in series. The first output end of the regenerator is connected to the coal mixing chamber. The outlet of the coal mixing chamber is connected to the burners on each layer through a second pipeline. A second monitoring device is installed in the second pipeline to collect the coal powder concentration, air-powder mixture flow and temperature entering the burners on each layer. The three coal mixing chambers are interconnected through the fourth control valve K1 and the fifth control valve K2 respectively.

[0037] Preferably, the second output end of the regenerator is connected to an exhaust gas treatment device.

[0038] Specifically, the exhaust gas at the outlet of the regenerator is treated harmlessly to reduce environmental pollution.

[0039] Preferably, the fourth control valve K1 and the fifth control valve K2 are respectively installed at the interface between the branch line and the coal mixing chamber to prevent coal powder from being retained in the second pipeline.

[0040] Preferably, the coal mixing chamber is hemispherical in shape, which can reduce the dead zone in the coal powder mixing process.

[0041] For example, taking three coal mills as an example, the coal mills of the pulverizing system are connected as a whole to break the isolated state of independent operation of the coal mills. When the boiler is running at low load or the coal mill suddenly fails, the coal powder can be redistributed by adjusting the fourth control valve K1 and the fifth control valve K2 to ensure the operation of each layer of burners, enhance the flexibility of the operation of the pulverizing system, help optimize the combustion of the boiler under low load, prevent the furnace flame from showing obvious flame deviation due to the cessation of the operation of the entire row of burners, and thus prevent the drastic change in the temperature distribution of the water-cooled wall, which helps to extend the fatigue service life of the water-cooled wall pipes. When an accident occurs in a coal mill, the remaining coal mills can quickly take over to ensure the operation of all burners and enhance the reliability of the operation of the pulverizing system.

[0042] On the other hand, see Figure 1 and Figure 2 In the figure, the valve opening 0-1 represents the valve from fully closed to fully open, thereby controlling the flow rate and flow direction of the fluid. The present invention also provides a milling method that can be flexibly operated under low load, and the milling method includes the following steps:

[0043] Step 1: Determine the energy consumption of each coal mill based on the coal mill operation history data, and determine the upper and lower limits of the pulverizing output. Divide the output ratio according to the coal mill energy consumption. Under the premise of ensuring the normal operation of the coal mill, the coal mill with low energy consumption is given more output, thereby reducing the energy consumption of pulverizing.

[0044] Step 2: According to the pulverizing output ratio determined in step 1, the openings of the first control valve M1, the second control valve M2, and the third control valve M3 are controlled to ensure the air-coal ratio of the coal mill;

[0045] In step 3, the air preheater uses the flue gas from the boiler to heat the cold air into primary air and secondary air. The primary air output from the air preheater enters the coal mill for drying and carries qualified pulverized coal into the regenerator. The first monitoring device installed at the coal mill outlet monitors and records the pulverized coal fineness and pulverizing energy consumption in real time.

[0046] Step 4: The pulverized coal is further dried using the waste heat from the flue gas through a regenerator. This not only recovers the waste heat from the flue gas but also facilitates the transportation and combustion of the pulverized coal. The pulverized coal airflow dried by the regenerator enters the coal mixing chamber, and the flue gas at its outlet enters the exhaust gas treatment device for harmless treatment.

[0047] Step 5: Mix the pulverized coal airflows of the main and branch routes evenly through the coal mixing chamber to prevent uneven pulverized coal airflow from affecting the working condition of the burner. Then, adjust the coal feed amount of each layer of burners through the opening of the fourth control valve K1 and the fifth control valve K2 to realize the regulation of the working condition of each layer of burners.

[0048] Preferably, the milling method further comprises:

[0049] The information collected by the first monitoring device and the second monitoring device is transmitted to the control center in real time to detect whether the coal fineness at the outlet of each coal mill meets the operating requirements. If not, the operating parameters of the corresponding coal mill, such as the speed, separator damper opening, grinding roller pressure, etc., are adjusted. The energy consumption of the adjusted coal mill is re-evaluated and the results are returned to the control center (steps 2 and 5);

[0050] If the pulverized coal fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If not, readjust the opening of the fourth control valve K1 and the fifth control valve K2, and readjust the coal feed to each layer of burners. If it is reasonable, the control is completed.

[0051] Prioritize, when the boiler load is reduced and cutting grinding operation is required or a coal mill fails, it can be directly shut down, and the pulverizing output ratio can be redistributed according to the boiler load and the operating energy consumption of the remaining coal mills. By adjusting the opening of the fourth control valve K1 and the fifth control valve K2, the coal feed amount of each layer burner can be reasonably configured, which can optimize combustion, reduce the flame center offset distance, prevent drastic changes in flame position, reduce the thermal stress of the water-cooled wall, and enhance the stability of the pulverizing system.

[0052] Prioritize, when the boiler load increases and the coal mill needs to be restarted, the working coal mill is first gradually adjusted to the maximum output to achieve a stable increase in the boiler load during the coal mill restart stage, accelerate the boiler load response speed, and after the coal mill is restarted, the pulverizing ratio can be redistributed according to the current load and restored to normal operation to enhance the flexibility of the pulverizing system.

[0053] For example, when the pulverizer restarts due to increased boiler load, the output of the working pulverizer can be adjusted during the restart phase to accelerate the boiler's load response, enhancing the flexibility and reliability of the pulverizing system. Taking into account the fineness of the pulverized coal and the heat loss from mechanical incomplete combustion in the boiler, valves and pulverizer operating parameters are adjusted to minimize pulverizing energy consumption and mechanical incomplete combustion heat loss. Furthermore, waste heat from the flue gas at the air preheater outlet is used to further dry the pulverized coal, facilitating its ignition and combustion, thereby improving the thermal efficiency of the power plant.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pulverizing system that operates flexibly under low load, characterized in that: The pulverizing system includes a boiler, an air preheater, three coal mills, three coal mixing chambers, three regenerators, and three-layer burners. The air preheater is installed below the tail flue of the boiler. The first output end of the air preheater is connected to the three coal mills in parallel through a first pipeline. A first control valve M1, a second control valve M2, and a third control valve M3 are respectively installed in the middle of the first pipeline. The three coal mills are each equipped with a first monitoring device, which is used to collect coal mill energy consumption information and outlet coal powder fineness; The second output end of the air preheater is connected to a regenerator, and the three regenerators are arranged in series in sequence. The outlets of the three coal mills are connected one-to-one with the inlets of the three regenerators, and the outlets of the three regenerators are connected one-to-one with the inlets of three coal mixing chambers. The outlets of the three coal mixing chambers are connected one-to-one with the three layers of burners through second pipelines. The second pipelines are each equipped with a second monitoring device for collecting the coal powder concentration, air-powder mixture flow and temperature entering each layer of burners. The three coal mixing chambers are arranged in series in sequence, wherein a fourth control valve K1 is provided on the connecting pipeline between the first coal mixing chamber and the second coal mixing chamber, and a fifth control valve K2 is provided on the connecting pipeline between the second coal mixing chamber and the third coal mixing chamber.

2. A milling system capable of flexible operation under low load according to claim 1, characterized in that: The second output end of the regenerator is connected to an exhaust gas treatment device.

3. A pulverizing system capable of flexible operation under low load according to claim 2, characterized in that: The coal mixing chamber is hemispherical.

4. A milling method that operates flexibly under low load, characterized in that: The method is applied to the pulverizing system according to any one of claims 1 to 3, and the pulverizing method comprises the following steps: Step 1, determining the energy consumption of each pulverizer based on historical operation data of the pulverizer, and determining the upper and lower limits of the pulverizing output, dividing the output ratio according to the energy consumption of the pulverizer, and making the pulverizer with low energy consumption bear more output while ensuring the normal operation of the pulverizer, thereby reducing the energy consumption of pulverizing; Step 2: According to the pulverizing output ratio determined in step 1, the openings of the first control valve M1, the second control valve M2, and the third control valve M3 are controlled to ensure the air-coal ratio of the coal mill; In step 3, the air preheater uses the flue gas from the boiler to heat the cold air into primary air and secondary air. The primary air output from the air preheater enters the coal mill for drying and carries qualified pulverized coal into the regenerator. The first monitoring device installed at the coal mill outlet monitors and records the pulverized coal fineness and pulverizing energy consumption in real time. Step 4: The pulverized coal is further dried using the waste heat of the flue gas through a regenerator. The pulverized coal airflow dried by the regenerator enters the coal mixing chamber, and the flue gas at its outlet enters the exhaust gas treatment device for harmless treatment; Step 5: Evenly mix the pulverized coal airflows of the main and branch routes through the coal mixing chamber, and then adjust the coal feed rate of each layer of burners through the opening of the fourth control valve K1 and the fifth control valve K2 to achieve regulation of the operating load of each layer of burners.

5. The method for producing flour with flexible operation under low load according to claim 4, characterized in that: The flour making method further comprises: The information collected by the first monitoring device and the second monitoring device is transmitted to the control center in real time to detect whether the fineness of the coal powder at the outlet of each coal mill meets the operating requirements. If not, the operating parameters of the corresponding coal mill are adjusted, and the energy consumption of the adjusted coal mill is re-evaluated. The results are returned to the control center, and steps 2 and 5 are repeated; If the pulverized coal fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If not, readjust the opening of the first control valve K1 and the second control valve K2, and readjust the coal feed to each layer of burners. If it is reasonable, the control is completed.

6. A milling method with flexible operation under low load according to claim 5, characterized in that: It also includes the following: when the boiler load is reduced and cutting and grinding operation is required or a coal mill fails, it can be directly shut down, the pulverizing output ratio can be redistributed according to the boiler load and the operating energy consumption of the remaining coal mills, and the coal feed amount of each layer burner can be reasonably configured by adjusting the opening of the fourth control valve K1 and the fifth control valve K2.

7. A milling method with flexible operation under low load according to claim 6, characterized in that: It also includes when the boiler load increases and the coal mill needs to be restarted, first gradually adjusting the working coal mill to the maximum output, so as to achieve a stable increase in the boiler load during the coal mill restart phase, accelerate the boiler load response speed, and after the coal mill is restarted, the pulverizing ratio can be redistributed according to the current load and the normal operating state can be restored.

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