A Peak-Shaving Method Based on Online Monitoring and Control of a Fan Mill Coal-Fired Boiler

Abstract

This invention relates to a peak-shaving method for a coal-fired boiler based on online monitoring and control of a fan-operated coal mill. By adjusting the pulverized coal flow regulating valve of the lowest primary air pulverized coal pipeline of a single coal mill, the pulverized coal flow rate in the lowest primary air pulverized coal pipeline is reduced. When the primary air velocity in the lowest primary air pulverized coal pipeline falls below a specified value, the pipeline is closed using a shut-off valve. Then, a pulverized coal balancing system is used to control the pulverized coal concentration, velocity, and flow rate balance in the remaining two primary air pulverized coal pipelines. After one coal mill is adjusted, the remaining two are adjusted similarly. The advantages of this invention are: by closing the lower primary air pulverized coal pipelines of the three operating coal mills, the minimum load period is further reduced while ensuring concentrated combustion flame. Furthermore, it can increase the reheat steam temperature during the low-load stage of the boiler, reduce the NOx content at the furnace outlet during the low-load stage, and improve the degree of pulverized coal burnout, reducing the content of flyback combustibles.

Description

Technical Field

[0001] This invention relates to the field of deep peak shaving technology for coal-fired power units, specifically to a peak shaving method based on online monitoring and control of a fan mill coal-fired boiler. Background Technology

[0002] In a new power system dominated by new energy sources, as the proportion of renewable energy gradually increases, thermal power units need to adapt to more flexible dispatching requirements. Improving the deep peak-shaving capacity of coal-fired units has become an urgent task.

[0003] Currently, coal-fired power units using fan mills typically employ six mills arranged in a hexagonal configuration to supply pulverized coal. To avoid unplanned shutdowns, at least three mills must operate during the lowest load period. However, when the coal supply decreases excessively, the pulverized coal concentration in the primary air duct decreases. Furthermore, due to the design characteristics of the primary air duct at the fan mill outlet, there is a problem of concentrated pulverized coal concentration at the bottom and diluted concentration at the top. The pulverized coal concentration in the upper primary air duct is the average of all ducts, which severely affects the boiler combustion stability during low load periods and impacts the unit's deep peak-shaving capability.

[0004] Excessive primary air rate during low-load periods leads to increased NOx emissions at the furnace outlet, resulting in increased SCR ammonia injection, increased ammonia escape, increased air preheater blockage of the air box, and impacts unit operation safety and economy. Excessive primary air rate during low-load periods can also delay pulverized coal combustion, affecting the degree of pulverized coal burnout and reducing boiler efficiency.

[0005] The existing coal mill includes: a fan-type coal mill body, an impeller installed inside the body, and three primary air and pulverized coal pipes corresponding to the combustion chamber of the coal-fired unit. The primary air pipes are arranged in a "glove-type" manner, and the pulverized coal in the coal-fired boiler is burned evenly by using the three primary air and pulverized coal pipes.

[0006] Currently, coal-fired power units using fan mills have a deep peak load of around 50%, which cannot meet the grid dispatching needs, affects the grid peak shaving efficiency, and makes the units almost unprofitable during the deep peak shaving phase. Summary of the Invention

[0007] In view of the above problems, the purpose of this invention is to provide a peak-shaving method based on online monitoring and control of a fan-driven coal mill-fired boiler, which is used to ensure the coal powder concentration in the primary air duct of the coal mill and reduce the output of the coal mill without reducing the number of operating coal mills, thereby achieving deep peak shaving of coal powder during low-load stages, so as to overcome the shortcomings of the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler includes the following steps:

[0010] Step S1: Install coal powder flow regulating valves on the upper, middle and lower primary air coal powder pipelines of the coal mill, and use the coal powder flow regulating valves to control the coal powder flow of the primary air coal powder pipelines.

[0011] Step S2: Install a pulverized coal flow monitoring sensor at the middle position of the upper, middle and lower primary air pulverized coal pipes of the coal mill, and use the pulverized coal flow monitoring sensor to monitor the pulverized coal concentration, wind speed and flow rate in the primary air pulverized coal pipes;

[0012] Step S3: Install a shut-off gate in the middle of the primary air pulverized coal pipeline in the lower layer of the coal mill and behind the pulverized coal flow monitoring sensor. Use the shut-off gate to control the opening and closing of the primary air pulverized coal pipeline.

[0013] Step S4: Install a backflush pipe in the middle of the primary air pulverized coal pipeline in the lower layer of the coal mill and in front of the shut-off gate. Use the backflush pipe to blow air into the primary air pulverized coal pipeline. The backflush pipe is used to blow away residual powder from the shut-off gate to the burner nozzle section to prevent spontaneous combustion of powder in the primary air pulverized coal pipeline.

[0014] Step S5: When the fan pulverizer coal-fired boiler receives a low load command, the fan pulverizer coal-fired boiler's air-coal balance regulation system will switch from full operation mode to low load operation mode, that is, from the operation of six pulverizers in full operation mode to the operation of three pulverizers in odd or even arrangement, and then from the operation of three pulverizers to the operation of three pulverizers in peak shaving mode.

[0015] Step S6: In the peak shaving mode of the coal mill, the coal powder flow regulating valve of the lowest primary air coal powder pipeline of a single coal mill is adjusted using the air-coal powder balance adjustment system to reduce the coal powder flow of the lowest primary air coal powder pipeline. When the primary air velocity of the lowest primary air coal powder pipeline is lower than the specified value, the lowest primary air coal powder pipeline is closed using the shut-off gate. Then, the coal powder concentration, velocity, and flow rate in the remaining two primary air coal powder pipelines are controlled by the air-coal powder balance adjustment system. After one coal mill is adjusted, the other two coal mills are adjusted in the same way.

[0016] As a preferred embodiment of the invention, in step S6, the control of the air-powder balance adjustment system includes the following steps:

[0017] Step S61: Use the air-coal balancing adjustment system to control the coal powder flow regulating valve to gradually reduce the opening and closing of the primary air coal powder pipeline in the lower layer to 0%, and at the same time use the coal powder flow monitoring sensor on the primary air coal powder pipeline in the lower layer to measure the internal coal powder concentration, wind speed and flow rate.

[0018] Step S62: Use the air-coal balancing adjustment system to control the opening and closing of the coal powder flow regulating valves in the primary air coal powder pipelines of the middle and upper layers, and under the monitoring of the coal powder flow monitoring sensor, balance the coal powder concentration, air velocity, and flow rate in the primary air coal powder pipelines of the middle and upper layers.

[0019] Step S63: After the coal powder flow regulating valve of the primary air coal powder pipeline in step S61 is closed to 0%, the primary air coal powder pipeline is closed by controlling the shut-off gate through the air-coal powder balance regulating system.

[0020] Step S64: After the primary air pulverized coal pipeline is closed, use the backflush pipeline to purge the residual pulverized coal in the primary air pulverized coal pipeline;

[0021] Step S65: After one coal mill has been adjusted, repeat steps S61-S64 to complete the adjustment of the remaining two coal mills.

[0022] As a preferred embodiment of the invention, in step S64, a quick-closing valve for duct purging is installed on the backflush pipeline, and the quick-closing valve for duct purging is used to control the opening and closing of the backflush pipeline.

[0023] As a preferred embodiment of the invention, an interlocking mechanism is installed between the duct purge quick-shut-off valve and the shut-off gate to prevent simultaneous opening.

[0024] As a preferred embodiment of the invention, the interlocking mechanism is provided with a circuit breaker.

[0025] As a preferred embodiment of the invention, the pulverized coal flow monitoring sensor comprises: five electrostatic ion strength measuring rings and two pulverized coal flow rate measuring rings interspersed between the five electrostatic ion strength measuring rings.

[0026] As a preferred embodiment of the invention, the pulverized coal flow rate measuring ring is used to measure the pulverized coal flow rate.

[0027] As a preferred embodiment of the invention, the electrostatic ion strength measuring ring calculates the coal powder concentration by the coal powder flow frequency. The intensity of electrostatic ions is positively correlated with the coal powder concentration. The current coal powder concentration is measured in real time by the change in the electrostatic ion strength between the measured electrostatic ion strength and the standard coal powder concentration.

[0028] As a preferred embodiment of the invention, the pulverized coal flow monitoring sensor further includes an insulating ring disposed between an adjacent electrostatic ion strength measuring ring and a pulverized coal flow rate measuring ring.

[0029] As a preferred embodiment of the invention, the pulverized coal flow monitoring sensor further includes a signal loading dyeing ring and a signal balancing ring, wherein the signal loading dyeing ring and the signal balancing ring are respectively positioned at both ends, and an insulating ring is provided between the signal loading dyeing ring and the signal balancing ring and the adjacent electrostatic ion strength measuring ring.

[0030] As a preferred embodiment of the invention, the signal loading staining ring is used to uniformly collect signals and transmit them to the signal amplification processor.

[0031] As a preferred embodiment of the invention, the signal balancing ring is used to balance and differentiate the signals between the five electrostatic ion strength measuring rings and the two pulverized coal flow rate measuring rings.

[0032] The advantages and positive effects of this invention are:

[0033] 1. This invention addresses the requirement that at least three coal mills must be operating in the lowest load section of a coal-fired unit. If fewer than three coal mills are used, it will be impossible to guarantee the formation of a tangential circle. Currently, the lowest load section using three coal mills is also higher than the usage requirements. This application further reduces the lowest load section by closing the primary air and pulverized coal pipeline at the bottom of the three operating coal mills, thereby ensuring the concentration of the combustion flame.

[0034] 2. This invention enables the shut-off of the bottom primary air pulverized coal pipeline without shutting down the machine, and after shutting down, the bottom primary air pulverized coal pipeline is backflushed to prevent spontaneous combustion of accumulated pulverized coal in the pipeline section.

[0035] 3. This invention can improve the reheat steam temperature during the low-load stage of the boiler. The main reason is that after the bottom primary air pulverized coal pipeline (burner) is closed, the center of the boiler flame moves upward, the heat exchange of the corresponding convective heating surface increases, and the reheat steam temperature increases.

[0036] 4. This invention can reduce the NOx content at the furnace outlet during low-load stages. The main reason is that this method reduces the primary air rate of the boiler compared to the original combustion method, thereby reducing the NOx content at the furnace outlet.

[0037] 5. This invention can improve the degree of pulverized coal combustion and reduce the combustible content of fly ash. The main reason is that this method increases the pulverized coal concentration in the pulverized coal pipe, thus ensuring complete combustion. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0039] Figure 2 This is a schematic diagram showing the installation positions of the six coal mills in this invention.

[0040] Attached reference numerals: 3. Upper primary air pulverized coal pipeline; 2. Middle primary air pulverized coal pipeline; 1. Lower primary air pulverized coal pipeline; 4. Pulverized coal flow regulating valve; 5. Pulverized coal flow regulating valve; 6. Pulverized coal flow monitoring sensor; 7. Pulverized coal flow monitoring sensor; 8. Pulverized coal flow monitoring sensor; 9. Shut-off gate; 10. Backflush pipeline; 11. Quick shut-off gate; 12. Detailed Implementation

[0041] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for ease of description of one or more embodiments.

[0042] Example 1

[0043] See Figure 1-2 This embodiment provides a peak-shaving method based on online monitoring and control of a fan mill coal-fired boiler, including the following steps:

[0044] Step S1: Install a pulverized coal flow regulating valve 4 on the upper primary air pulverized coal pipeline 3 of the coal mill, a pulverized coal flow regulating valve 5 on the middle primary air pulverized coal pipeline 2, and a pulverized coal flow regulating valve 6 on the lower primary air pulverized coal pipeline 1. Use the pulverized coal flow regulating valves 4, 5, and 6 to control the pulverized coal flow of the primary air pulverized coal pipeline. In this embodiment, the pulverized coal flow regulating valves 4, 5, and 6 are pulverized coal flow regulating valves for boiler air pulverized coal pipelines manufactured by Changchun Huilintong Technology Co., Ltd., with patent number 2020222936946.

[0045] Step S2: Install a pulverized coal flow monitoring sensor 7 at the middle position of the upper primary air pulverized coal pipe 3 of the coal mill, a pulverized coal flow monitoring sensor 8 at the middle position of the middle primary air pulverized coal pipe 2 of the coal mill, and a pulverized coal flow monitoring sensor 9 at the middle position of the lower primary air pulverized coal pipe 1 of the coal mill. Use the pulverized coal flow monitoring sensors 7, 8, and 9 to monitor the pulverized coal concentration, wind speed, and flow rate in the primary air pulverized coal pipes. In this embodiment, the pulverized coal flow monitoring sensors 7, 8, and 9 are a pulverized coal flow monitoring device and control method for deep peak-shaving coal-fired boilers produced by Changchun Huilintong Technology Co., Ltd., patent number 2023102773234. In this embodiment, the pulverized coal flow monitoring sensor uses four speed sensors, that is, two speed sensors are added on the basis of the above patent. Since four speed sensors can further improve the monitoring accuracy of the pulverized coal flow monitoring sensor.

[0046] Step S3: Install a shut-off gate 10 in the middle of the primary air pulverized coal pipeline 1 at the bottom of the coal mill and behind the pulverized coal flow monitoring sensor 9. Use the shut-off gate 10 to control the opening and closing of the primary air pulverized coal pipeline. The shut-off gate 10 is a pneumatic or electric fast shut-off gate. The shut-off gate 10 is used to quickly close the pipeline during system adjustments to prevent a large amount of pulverized coal from staying in the pipeline.

[0047] Step S4: Install a backflush pipe 11 at the middle position of the lower primary air pulverized coal pipe 1 of the coal mill, in front of the shut-off gate 10. Use the backflush pipe 11 to blow air into the lower primary air pulverized coal pipe 1. The backflush pipe 11 is used to purge residual pulverized coal from the shut-off gate to the burner nozzle section, preventing spontaneous combustion of pulverized coal in the primary air pulverized coal pipe. A pneumatic or electric quick-closing gate 12 is installed on the backflush pipe 11, using a rapid on / off mode. The air source for the backflush pipe 11 can be selected from two sources: one is the secondary air box corresponding to the burner area, and the other is the flue gas from the induced draft fan outlet.

[0048] Step S5: When the fan pulverizer coal-fired boiler receives a low load command, the fan pulverizer coal-fired boiler's air-coal balance regulation system will switch from full operation mode to low load operation mode, that is, from the operation of six pulverizers in full operation mode to the operation of three pulverizers in positions one, three, and five, and then from the operation of three pulverizers to the operation of three pulverizers in peak shaving mode.

[0049] Step S6: In the peak-shaving mode of the coal mill, the coal powder flow regulating valve 6 of the lower primary air coal powder pipeline 1 of a single coal mill is adjusted using the air-coal powder balance regulation system to reduce the coal powder flow of the lower primary air coal powder pipeline 1. When the primary air velocity of the lower primary air coal powder pipeline 1 is lower than the specified value (the opening degree of the coal powder flow regulating valve 6), the lower primary air coal powder pipeline 1 is closed using the shut-off gate 10. Then, the coal powder concentration, velocity, and flow in the upper primary air coal powder pipeline 3 and the middle primary air coal powder pipeline 2 are balanced using the air-coal powder balance regulation system. After one coal mill is adjusted, the other two coal mills are adjusted in the same way. After all three coal mills are adjusted, the unit load is reduced proportionally while the coal powder concentration remains unchanged, and the boiler combustion remains unchanged.

[0050] Step S61: Use the air-coal balance adjustment system to control the coal powder flow regulating valve 6 to gradually reduce the opening and closing of the lower primary air coal powder pipeline 1 to 0% (10% each time), and at the same time use the coal powder flow monitoring sensor 6 on the lower primary air coal powder pipeline 1 to measure the internal coal powder concentration, wind speed and flow rate.

[0051] Step S62: Use the air-coal pulverized coal balance adjustment system to control the opening and closing of the coal powder flow regulating valves 4 and 5 in the upper primary air coal powder pipeline 3 and the middle primary air coal powder pipeline 2, and under the monitoring of the coal powder flow monitoring sensor 7 and the coal powder flow monitoring sensor 8, balance the coal powder concentration, wind speed and flow rate in the upper primary air coal powder pipeline 3 and the middle primary air coal powder pipeline 2.

[0052] Step S63: After the coal powder flow regulating valve 6 of the lower primary air coal powder pipeline 1 is closed to 0% in step S61, the air-coal powder balance regulating system is used to control the shut-off gate 10 to close the lower primary air coal powder pipeline 1 as a whole.

[0053] Step S64: After the lower primary air pulverized coal pipeline 1 is closed, the residual powder is purged by using the backflush pipeline 11 to clean the residual powder between the shut-off gate 10 and the outlet of the lower primary air pulverized coal pipeline 1.

[0054] Step S65: After one coal mill has been adjusted, repeat steps S61-S64 to complete the adjustment of the remaining two coal mills.

[0055] In this embodiment, an interlocking mechanism is installed between the duct purge quick shut-off valve 12 and the shut-off gate 10 to prevent them from being opened simultaneously.

[0056] In this embodiment, by using the coal mill peak-shaving mode, the coal powder concentration in the lower primary air duct of the fan mill is reduced and the coal powder concentration in the upper primary air duct is increased, which can achieve balanced combustion, improve boiler combustion efficiency, increase the boiler flame center temperature, and raise the reheat steam temperature of the boiler under low load conditions.

[0057] In this embodiment, the coal mill peak-shaving mode is used to adjust the pulverized coal flow rate in the lower pulverized coal pipe to the minimum flow rate under the premise that the air duct is not blocked, under the minimum load condition of the three mills. The lower shut-off gate is then closed, and the coal feed rate of the coal mill is reduced to the flow rate of the pulverized coal in the middle and upper pulverized coal pipes before the lower shut-off gate is closed. By applying this mode, without reducing the thermal power of individual burners, the lowest primary air duct of each coal mill can be closed, reducing the load rate by 33% under the original load condition, thereby improving the deep peak-shaving capacity of the unit.

[0058] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler, characterized in that: Includes the following steps: Step S1: Install coal powder flow regulating valves on the upper, middle and lower primary air coal powder pipelines of the coal mill, and use the coal powder flow regulating valves to control the coal powder flow of the primary air coal powder pipelines. Step S2: Install a pulverized coal flow monitoring sensor at the middle position of the upper, middle and lower primary air pulverized coal pipes of the coal mill, and use the pulverized coal flow monitoring sensor to monitor the pulverized coal concentration, wind speed and flow rate in the primary air pulverized coal pipes; Step S3: Install a shut-off gate in the middle of the primary air pulverized coal pipeline in the lower layer of the coal mill and behind the pulverized coal flow monitoring sensor. Use the shut-off gate to control the opening and closing of the primary air pulverized coal pipeline. Step S4: Install a backflush pipe in the middle of the primary air pulverized coal pipeline in the lower layer of the coal mill and in front of the shut-off gate. Use the backflush pipe to blow air into the primary air pulverized coal pipeline. The backflush pipe is used to blow away residual powder from the shut-off gate to the burner nozzle section to prevent spontaneous combustion of powder in the primary air pulverized coal pipeline. Step S5: When the fan pulverizer coal-fired boiler receives a low load command, the fan pulverizer coal-fired boiler's air-coal balance regulation system will switch from full operation mode to low load operation mode, that is, from the operation of six pulverizers in full operation mode to the operation of three pulverizers in odd or even arrangement, and then from the operation of three pulverizers to the operation of three pulverizers in peak shaving mode. Step S6: In the peak shaving mode of the coal mill, the coal powder flow regulating valve of the lowest primary air coal powder pipeline of a single coal mill is adjusted using the air-coal powder balance adjustment system to reduce the coal powder flow of the lowest primary air coal powder pipeline. When the primary air velocity of the lowest primary air coal powder pipeline is lower than the specified value, the lowest primary air coal powder pipeline is closed using the shut-off gate. Then, the coal powder concentration, velocity, and flow rate in the remaining two primary air coal powder pipelines are controlled by the air-coal powder balance adjustment system. After one coal mill is adjusted, the other two coal mills are adjusted in the same way.

2. The peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 1, characterized in that, In step S6, the control of the air-powder balance adjustment system includes the following steps: Step S61: Use the air-coal balancing adjustment system to control the coal powder flow regulating valve to gradually reduce the opening and closing of the primary air coal powder pipeline in the lower layer to 0%, and at the same time use the coal powder flow monitoring sensor on the primary air coal powder pipeline in the lower layer to measure the internal coal powder concentration, wind speed and flow rate. Step S62: Use the air-coal balancing adjustment system to control the opening and closing of the coal powder flow regulating valves in the primary air coal powder pipelines of the middle and upper layers, and under the monitoring of the coal powder flow monitoring sensor, balance the coal powder concentration, air velocity, and flow rate in the primary air coal powder pipelines of the middle and upper layers. Step S63: After the coal powder flow regulating valve of the primary air coal powder pipeline in step S61 is closed to 0%, the primary air coal powder pipeline is closed by controlling the shut-off gate through the air-coal powder balance regulating system. Step S64: After the primary air pulverized coal pipeline is closed, use the backflush pipeline to purge the residual pulverized coal in the primary air pulverized coal pipeline; Step S65: After one coal mill has been adjusted, repeat steps S61-S64 to complete the adjustment of the remaining two coal mills.

3. The peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 1, characterized in that, In step S64, a quick shut-off valve for duct purging is installed on the backflush pipeline. The quick shut-off valve for duct purging is used to control the opening and closing of the backflush pipeline.

4. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 3, characterized in that, An interlocking mechanism is installed between the duct purge quick-shut-off valve and the shut-off gate to prevent them from being opened simultaneously.

5. The peak-shaving method based on online monitoring and control of a fan mill coal-fired boiler according to claim 4, wherein the interlocking mechanism is equipped with a circuit breaker.

6. A peak-shaving method based on online monitoring and control of a fan mill coal-fired boiler according to claim 1, characterized in that, The pulverized coal flow monitoring sensor includes: five electrostatic ion intensity measuring rings and two pulverized coal flow velocity measuring rings interspersed between the five electrostatic ion intensity measuring rings.

7. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 6, characterized in that, The coal powder flow rate measuring ring is used to measure the coal powder flow rate.

8. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 6, characterized in that, The electrostatic ion strength measuring ring calculates the coal powder concentration based on the coal powder flow frequency. The electrostatic ion strength is positively correlated with the coal powder concentration. The current coal powder concentration is measured in real time by the change in electrostatic ion strength between the measured electrostatic ion strength and the standard coal powder concentration.

9. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 6, characterized in that, The pulverized coal flow monitoring sensor also includes an insulating ring, which is disposed between an adjacent electrostatic ion strength measuring ring and a pulverized coal flow rate measuring ring.

10. A peak-shaving method based on online monitoring and control of a fan-mill coal-fired boiler according to claim 6, characterized in that, The pulverized coal flow monitoring sensor also includes a signal loading dyeing ring and a signal balancing ring, which are respectively set at both ends. An insulating ring is provided between the signal loading dyeing ring and the signal balancing ring and the adjacent electrostatic ion strength measuring ring.

11. A peak-shaving method based on online monitoring and control of a fan mill coal-fired boiler according to claim 10, characterized in that, The signal loading staining ring is used to collect signals uniformly and transmit them to the signal amplification processor.

12. A peak-shaving method based on online monitoring and control of a fan mill coal-fired boiler according to claim 10, characterized in that, The signal balancing loop is used to balance and distinguish the signals between the five electrostatic ion strength measurement loops and the two pulverized coal flow rate measurement loops.

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