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

Abstract

The invention provides a coal pulverizing system and method capable of flexibly operating under low load, taking three coal mills as an example, the coal pulverizing system comprises a boiler, an air pre-heater, the three coal mills, a coal mixing chamber, a heat regenerator and a combustor, the air pre-heater is arranged below a tail flue of the boiler, a first output end of the air pre-heater is connected with the three coal mills through a first pipeline, and a second output end of the air pre-heater is connected with the three coal mills through a second 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, and the three coal mills are respectively provided with a first monitoring device; the second output end of the air pre-heater is connected with heat regenerators, the heat regenerators are arranged in series, the first output ends of the heat regenerators are connected with the coal mixing chamber, an outlet of the coal mixing chamber is connected into all layers of combustors through a second pipeline, and a second monitoring device is arranged in the second pipeline. The three coal mixing chambers are mutually connected through a fourth control valve K1 and a fifth control valve K2 respectively.

Description

Technical Field

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

[0002] In order to improve the grid's ability to absorb new energy power and make up for the instability of new energy power such as photovoltaic and wind power, thermal power plants have begun to take on the heavy task of peak load regulation and frequency regulation, and the flexible operation and transformation of thermal power units is imperative. At the same time, facing the strong impact of new energy and the requirements of relevant national policies, how thermal power plants can shift to a safer, more environmentally friendly and economical operation mode has become a key issue that the industry urgently needs to solve. The pulverizing system is mainly responsible for producing qualified and sufficient pulverized coal for boiler combustion. It is an important part of thermal power units and is closely related to boiler load and boiler efficiency. Under the background of deep peak load regulation of boilers, the flexible, economical and safe operation of the pulverizing system is an important guarantee for variable load operation of boilers.

[0003] At present, the technical solutions for the flexible operation transformation of the pulverizing system mainly focus on the start-stop decision and operation status adjustment of the coal mill under variable load. For example, Patent 1 - A coal mill start-up and shutdown intelligent operation optimization method based on artificial intelligence (CN113843039B) uses artificial intelligence technology and big data technology to build a coal mill operation control model in combination with historical operation data, and inputs the real-time operation data of the coal mill and the real-time status data of the water-cooled wall into the control model. After the optimization of the start-up and shutdown module, the optimization of the coal feeding module and the operation simulation module, the optimal recommended instruction is output. Patent 2 - Coal mill combination operation control method, device, equipment and storage medium (CN111389575B) proposes to determine the operating characteristics of each coal mill based on historical data for the optimization of coal mill operation combination, and further screen out the key characteristics of the coal mill, determine the operation ranking of each coal mill, and output the coal mill operation combination plan in combination with constraints and load changes.

[0004] The existing technical solutions mainly focus on the judgment of the start and stop conditions of a single coal mill in order to reduce the energy consumption of pulverizing under low load. However, in the existing pulverizing system, a coal mill is only connected to a row of burners. The shutdown of the coal mill will cause the entire row of burners connected to it to stop working, causing the distribution of coal powder airflow inside the furnace to change, causing the flame center to shift, and aggravating the uneven heating of the water-cooled wall. When the load changes frequently, the water-cooled wall will be affected by the fluctuation of the flame heat transfer and will produce alternating thermal stress, resulting in a shortened service life of the pipe and endangering the safe operation of the boiler. In addition, when the load increases and the coal mill needs to be started, the inertia of restarting makes it difficult for the boiler to respond to the load change in time, which prolongs the lag time of the system. Summary of the invention

[0005] The object of the present invention is to provide a powder making system and method which can operate flexibly under low load, so as to solve the problems raised in the above-mentioned 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 be flexibly operated 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 flue at the tail end of the boiler. The first output end of the air preheater is connected to the three coal mills through a first pipeline. The first control valve M1, the second control valve M2, and the 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, which is used to collect energy consumption information of the coal mill and the fineness of the outlet coal powder.

[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 of 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 rate and temperature entering the burners of 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 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, and the milling method comprises the following steps:

[0013] Step 1: determine the energy consumption of each coal mill according to 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, and make the low-energy-consuming coal mill bear more output under the premise of ensuring the normal operation of the coal mill, thereby reducing the pulverizing energy consumption;

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

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

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

[0017] Step 5, the pulverized coal airflows of each main route and branch route are mixed evenly through the coal mixing chamber, and then the coal feed amount of each layer of burners is adjusted by 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 operation requirements. If not, the operation 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 coal powder fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If it is unreasonable, readjust the opening of the first control valve K1 and the second control valve K2, and readjust the coal supply to each layer of burners. If it is reasonable, the control is completed.

[0021] Preferably, when the boiler load is reduced and grinding operation is required or a coal mill fails, it can be shut down directly, and the pulverizing output ratio can be redistributed according to the boiler load and the operating energy consumption of the remaining coal mills. The coal feed to each layer of burners 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 coal mill in working state is first gradually adjusted to the maximum output, so as to achieve a stable increase in the boiler load during the coal mill restart phase, accelerate the load response speed of the boiler, 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 operated at low load or the coal mill fails suddenly, the coal powder can be redistributed by adjusting the valve to ensure the operation of the burners on 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 showing obvious flame deviation due to the cessation of the operation of the entire row of burners, and thus preventing 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.

[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] In addition, the fineness of the pulverized coal and the heat loss of the mechanical incomplete combustion of the boiler are comprehensively considered. The energy consumption of pulverizing and the heat loss of the mechanical incomplete combustion are minimized by controlling the valve and the operating parameters of the coal mill. At the same time, the waste heat of the flue gas at the outlet of the air preheater is used to further dry the pulverized coal, which is conducive to the ignition and combustion of the pulverized coal and improves 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 drawings required for use in the description of the embodiments will be briefly introduced below. 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 A structural diagram of a milling system that operates flexibly under low load provided by the present invention.

[0029] Figure 2 A flow chart of a milling method that operates flexibly under low load provided by the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present invention more obvious, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only 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 protection scope of the present invention.

[0031] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0032] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the 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 be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" 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 proposed in the following description to illustrate the technical solution proposed by the present invention. The optional embodiments of the present invention are described in detail as follows, but 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 uses the flue gas at the rear of the boiler to heat the cold air into primary air and secondary air. The function of the primary air is to provide oxygen for the combustion of the coal powder in the initial stage, and the function of the secondary air is to provide oxygen for the complete combustion of the coal powder in the furnace. The first output end of the air preheater is connected to the three coal mills through a first pipeline, and the first control valve M1, the second control valve M2, and the 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, and the first monitoring device 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 of 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 rate and temperature entering the burners of 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 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 fails suddenly, 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, thereby enhancing the flexibility of the operation of the pulverizing system and helping to optimize the combustion of the boiler under low load. It prevents the furnace flame from exhibiting obvious flame deviation due to the cessation of the operation of the entire row of burners, which in turn causes drastic changes in the temperature distribution of the water-cooled wall, helping 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 indicates that the valve is 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 comprises the following steps:

[0043] Step 1: determine the energy consumption of each coal mill according to 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, and make the low-energy-consuming coal mill bear more output under the premise of ensuring the normal operation of the coal mill, thereby reducing the pulverizing energy consumption;

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

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

[0046] Step 4: The pulverized coal is further dried by using the waste heat of the flue gas through a regenerator, which not only recovers the waste heat of the flue gas, but also facilitates the transportation and ignition 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 tail gas treatment device for harmless treatment;

[0047] Step 5, mix the pulverized coal airflows of each main route and branch route evenly through the coal mixing chamber to prevent uneven pulverized coal airflow from affecting the working condition of the burner, and 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 fineness of the coal powder at the outlet of each coal mill meets the operation requirements. If not, the operation parameters of the corresponding coal mill are adjusted, such as the rotation speed, the opening of the separator baffle, the grinding roller pressure, etc., and the energy consumption of the adjusted coal mill is re-evaluated, and the results are returned to the control center, step 2 and step 5;

[0050] If the coal powder fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If it is unreasonable, readjust the opening of the fourth control valve K1 and the fifth control valve K2, and readjust the coal supply to each layer of burners. If it is reasonable, the control is completed.

[0051] Preferably, when the boiler load is reduced and grinding operation is required or a coal mill fails, it can be shut down directly, 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 of burners 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 coal mill in working state is first gradually adjusted to the maximum output, so as to achieve a stable increase in the boiler load during the restarting stage of the coal mill, accelerate the load response speed of the boiler, and after the coal mill is restarted, the pulverizing ratio can be redistributed according to the current load and the normal operation state can be restored to enhance the flexibility of the pulverizing system.

[0053] For example, 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. Taking into account the fineness of the coal powder and the mechanical incomplete combustion heat loss of the boiler, the pulverizing energy consumption and the mechanical incomplete combustion heat loss are minimized by adjusting the valve and coal mill operating parameters. At the same time, the waste heat of the flue gas at the outlet of the air preheater is used to further dry the coal powder, which is conducive to the ignition and combustion of the coal powder and improves 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 milling system that operates flexibly under low load, characterized in that: The pulverizing system comprises 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 tail end of the boiler. The first output end of the air preheater is connected to the three coal mills through a first pipeline. The first control valve M1, the second control valve M2, and the 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, 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 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 of 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 rate and temperature entering the burners of each layer. The three coal mixing chambers are interconnected through the fourth control valve K1 and the fifth control valve K2 respectively.

2. A milling system that can be flexibly operated under low load according to claim 1, characterized in that: The second output end of the regenerator is connected to a tail gas treatment device.

3. A milling system that can be flexibly operated under low load according to claim 2, characterized in that: The fourth control valve K1 and the fifth control valve K2 are respectively installed at the interface between the branch and the coal mixing chamber.

4. A milling system that can be flexibly operated under low load according to claim 3, characterized in that: The coal mixing chamber is hemispherical.

5. A milling method with flexible operation under low load, characterized in that: The method is applied to the flour milling system according to any one of claims 1 to 4, and the flour milling method comprises the following steps: Step 1: determine the energy consumption of each coal mill according to 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, and make the low-energy-consuming coal mill bear more output under the premise of ensuring the normal operation of the coal mill, thereby reducing the pulverizing energy consumption; Step 2, according to the pulverizing output ratio determined in step 1, control the openings of the first control valve M1, the second control valve M2 and the third control valve M3 to ensure the air-coal ratio of the coal mill; Step 3: The air preheater uses the flue gas at the tail of the boiler to heat the cold air into primary air and secondary air. The primary air output by the air preheater enters the coal mill for drying and carries qualified coal powder into the regenerator. The first monitoring device installed at the outlet of the coal mill monitors and records the coal powder fineness and pulverizing energy consumption in real time. Step 4, using the waste heat of flue gas to further dry the pulverized coal through a regenerator, and the pulverized coal airflow dried by the regenerator enters the coal mixing chamber, and the flue gas at its outlet enters the tail gas treatment device for harmless treatment; Step 5, the pulverized coal airflows of each main route and branch route are mixed evenly through the coal mixing chamber, and then the coal feed amount of each layer of burners is adjusted by 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.

6. A milling method for flexible operation under low load according to claim 5, 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 operation requirements. If not, the operation 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 coal powder fineness meets the requirements, check whether the mechanical incomplete combustion heat loss of the boiler is reasonable. If it is unreasonable, readjust the opening of the first control valve K1 and the second control valve K2, and readjust the coal supply to each layer of burners. If it is reasonable, the control is completed.

7. A milling method for flexible operation under low load according to claim 6, characterized in that: It also includes the following: when the boiler load is reduced 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 to each layer of burners can be reasonably configured by adjusting the opening of the fourth control valve K1 and the fifth control valve K2.

8. A milling method for flexible operation under low load according to claim 7, 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, achieving a stable increase in the boiler load during the coal mill restart phase, accelerating the boiler load response speed, and after the coal mill is restarted, the pulverizing ratio can be reallocated according to the current load and normal operation can be restored.

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