Novel combustor system for increasing low-load stable combustion threshold value of coal-fired boiler and control method

Abstract

The invention belongs to the field of power generation, and discloses a novel combustor system for increasing the low-load stable combustion threshold value of a coal-fired boiler and a control method.The system comprises a coal pulverizing machine, a middle storage type powder bin, a powder feeder, a common layer combustor, a stable combustion layer combustor, a combustor auxiliary pipeline, a primary air valve, a primary air recirculation valve and a secondary air baffle. The method that the main combustors are matched with the stable combustion combustors to form the stable combustion combustor layer is adopted, when the boiler operates at low load, the operation load of the single main combustor in the layer is increased by stopping the main combustors without the stable combustion combustors, and therefore the purpose of increasing the low-load stable combustion threshold value of the coal-fired boiler is achieved.

Description

Technical Field

[0001] The present invention belongs to, but is not limited to, the field of power generation technology, and in particular relates to a novel burner system and control method for improving the low-load stable combustion threshold of a coal-fired boiler. Background Art

[0002] With the rapid increase in the proportion of renewable energy in the power system, thermal power units are being required to provide more and more flexible supply. To address the problems of wind and solar power curtailment, deep peak shaving has become the norm for coal-fired power plants. During deep peak shaving, the boiler load drops to a lower level. To ensure safe boiler operation, at least two pulverizing systems and their corresponding burners are in operation. At this minimum, if the depth of the boiler's peak shaving is to be increased, the operating load of the burner must be further reduced. However, existing burner systems are often designed for high boiler load requirements and ensure uniform heat distribution in the furnace during operation. At low boiler loads, existing burner designs result in local heat loads at the burner that are significantly lower than at high boiler loads, resulting in combustion instability in the boiler.

[0003] Other existing technical solutions, such as patent 202411033077.9, use the addition of pulverized coal gasification device to improve the combustion stability of the burner. Patents with application numbers 201410467276.0 and 201010244692.6 respectively reveal the innovative design of fuel oil and gas ignition and combustion stabilization systems; and patents with application numbers 201710109787.9, 201721294248.9, 201810192558.2, 201810867626.0, 201820453959.4, 201710 Patents 931919.6, 201210083504.5, 201710661801.6, 201710483595.4, 201910584293.5, 201920008532.8 and 201920454263.8 focus on burners, air inlet methods, coal inlet methods, pulverized coal concentration and thin separation, preheating pulverized coal, increasing primary air temperature, increasing pulverizer outlet temperature and optimizing pulverized coal fineness, etc., aiming to improve the combustion effect of pulverized coal and other technical improvements to improve the combustion efficiency of boilers.

[0004] The above technologies have improved the low-load stable combustion capability of the boiler to a certain extent, but they focus more on the overall transformation of the entire layer of burners. At present, there are almost no transformation plans for changing the internal operation mode of each layer of burners under low load. Considering that flame instability always begins to occur in the local area where the temperature is insufficient, it is necessary to propose a technology that, under the premise of reducing the overall combustion load in the layer, shuts down some burners and increases the local heat load of some burners. Compared with the existing technology of improving the stable combustion capability of the entire layer of burners, exploring the internal operation mode of each layer of burners under low load and proposing targeted burner improvement plans are of great significance for improving the deep peak-shaving capability of thermal power units and ensuring the stable operation of my country's power system.

[0005] In view of the above analysis, the technical problems that need to be solved urgently in the existing technology are:

[0006] (1) Fire is easily extinguished at low load. Since the heat load of the burner is evenly distributed during low load operation, the local heat load drops quickly, making fire extinguishing more likely to occur.

[0007] (2) The cost of stable combustion adjustment is high. When the burner is running below the stable combustion threshold, it is necessary to frequently add oil, operate plasma heating, and add complex pyrolysis and gasification equipment to assist combustion;

[0008] (3) The system is difficult to stabilize. Under low load, a large number of manual adjustments are required to ensure stable combustion of the unit. The interlocking control of the entire burner layer cannot isolate the root cause of instability, making it difficult to adjust the system to be stable. Summary of the Invention

[0009] In response to the problems existing in the prior art, the present invention provides a new burner system and control method for improving the low-load stable combustion threshold of a coal-fired boiler.

[0010] The present invention is implemented as follows: a new burner system for improving the low-load stable combustion threshold of a coal-fired boiler is characterized in that the new burner system for improving the low-load stable combustion threshold of a coal-fired boiler includes a powder making machine, a central storage powder bin, a powder feeder, a common layer burner, a stable combustion layer burner, burner auxiliary pipelines, a primary air valve, a primary air recirculation valve, and a secondary air baffle.

[0011] Furthermore, the furnace burners in this system are divided into a common burner layer and a stabilizing burner layer. The common burner layer can adopt the original pulverizing combustion system configuration and operation mode, while the stabilizing burner layer adopts a central storage pulverizing system. The two lowest burner layers in the boiler are modified to use the central storage pulverizing system, and are referred to as stabilizing burner layers. When the unit is performing deep peak regulation, the stabilizing burners are put into operation, and then the two independently operating main burners are removed. This allows the coordinated main burners and stabilizing burners to operate together, increasing the local furnace heat load of the boiler and raising the low-load stabilizing combustion threshold of the coal-fired boiler. The ordinary burner layer retains the original coal-fired boiler layout, and the stable combustion burner layer is configured by combining the main burner with the stable combustion burner. Under ultra-low load, the stable combustion burner can be put into operation and some of the main burners can be shut down to achieve centralized configuration of the furnace heat load and improve the low-load stable combustion threshold of the coal-fired boiler; for the pulverizing system of the stable combustion burner layer, the pulverized coal bin is used to realize intermediate storage-type pulverized coal processing, ensuring that the stable combustion burner layer can still stably supply pulverized coal when the operating mode is adjusted under ultra-low load; for the stable combustion burner layer, the main burner and the secondary air box of the stable combustion burner are configured in parallel, and the baffle of the secondary air box of the stable combustion burner can be completely closed to ensure that the stable combustion layer can operate stably under different load conditions.

[0012] Furthermore, the coal mill outlet is connected to the first wind box through the first valve, and the merging moisture absorption pipe is connected to the fine powder separator; the upper end of the fine powder separator is provided with a first explosion-proof door, the lower end of the fine powder separator is connected to the coal powder bin, the coal powder bin has a moisture absorption pipe connected to the fine powder separator inlet pipe, the upper end outlet of the fine powder separator is connected to the powder exhaust fan, and the fan outlet is divided into two routes: one route is to the coal mill inlet powder drop pipe, which is a recycling pipe, and the baffle on the pipe is a hot air recycling damper; the other route is distributed by the second wind box and then connected to the burner through the third valve and the coal powder mixer, the lower end of the coal powder bin is connected to the powder feeder, and the powder feeder is connected to the coal powder mixer; the primary air is connected to the third valve and the middle pipe of the coal powder mixer through the fourth valve.

[0013] Each pulverized coal mixer is connected to a primary air valve via an air duct and to a pulverized coal feeder via a pulverized coal pipe. The primary air valve is connected to the unit's inherent primary air system, and the pulverized coal feeder is connected to the unit's inherent pulverized coal silo system.

[0014] Furthermore, the overall workflow of the system is as follows: When the boiler load is above 40%, the A and D stabilizing burner layers operate normally, and only the six main burners on the front and rear walls are put into operation, while the stabilizing burners remain off. When the boiler load is below 40%, and deep peaking below 20% load is estimated to be required, four stabilizing burners on the front and rear walls are put into operation, and then the two main burners on the front and rear walls that are not equipped with stabilizing burners are reduced in load until they are shut down. When the unit operates below 20% load, the stabilizing burners operate at a fixed load, and the main burners are responsible for load regulation.

[0015] Furthermore, the overall control principle of the system is as follows: the total fuel amount is divided into the main fuel amount and the stabilizing fuel amount, which are controlled separately; the primary air volume is controlled by the opening of the hot air recirculation valve to match the change in the burner powder amount; the secondary air of the stabilizing burner is separately controlled by the secondary air damper, and can be completely closed when the stabilizing burner is shut down.

[0016] Furthermore, the main burners 1, 3, 4, 6 on each floor are interlocked and controlled with the main burners 2, 5 respectively, and the stable combustion burners on each floor correspond to the main burners 1, 3, 4, 6 and are interlocked and controlled.

[0017] Furthermore, the interlocked burner fuel quantity instructions are consistent. The difference between the boiler master fuel command and the stabilizing burner fuel command on each floor is the main burner fuel command. The ratio of the main burner fuel command to the number of main burners in operation on that floor is the main burner powder feeder powder quantity instruction. The difference between the powder feeder powder quantity instruction and the powder feeder powder quantity measurement is used as the input of the PID controller to provide the main burner powder feeder speed instruction. The powder feeder powder quantity measurement value is calculated by the function unit to provide the main burner primary air volume instruction. The difference between the primary air volume instruction and the primary air volume measurement is used as the input of the PID controller to provide the primary air recirculation valve opening instruction.

[0018] Furthermore, the fuel quantity instructions for the main burners 1, 3, 4, and 6 adopt the main burner fuel instructions, and the fuel quantity instructions for the main burners 2 and 5 are switched and controlled by the stable combustion burner input instruction. When the stable combustion burner input instruction is 1, the fuel quantity instructions for the main burners 2 and 5 slowly change to the main burner fuel instructions. When the stable combustion burner input instruction is 0, the fuel quantity instructions for the main burners 2 and 5 slowly change to 0.

[0019] Furthermore, the fuel instruction of the stable combustion burner is used to generate the primary and secondary air ratios of the stable combustion burners 1, 3, 4, and 6 through the function generator. The quotient of the 30s measurement value of the primary air volume and the 30s measurement value of the secondary air volume of the stable combustion burners 1, 3, 4, and 6 is used as the primary and secondary air ratio measurement value. The difference between the primary and secondary air ratios of the stable combustion burners 1, 3, 4, and 6 and the primary and secondary air ratio measurement values ​​is used as the input of the PID controller to give the secondary air damper openings of the stable combustion burners 1, 3, 4, and 6. The secondary air damper openings of the stable combustion burners 1, 3, 4, and 6 are summed with the secondary air volume bias instructions of the stable combustion burners 1, 3, 4, and 6 to give the secondary air damper opening instructions of the stable combustion burners 1, 3, 4, and 6.

[0020] Furthermore, the operation of the stabilizing burner is not restricted by the main burner. During startup, the stabilizing burner can be used for ignition instead of the main burner to reduce the energy consumption of boiler startup.

[0021] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0022] The present invention employs a method of combining a main burner with a stabilizing burner to form a stabilizing burner layer. When the boiler is operating at low load, the operating load of a single main burner within the layer is increased by shutting down the main burner without the stabilizing burner, thereby improving burner stability at the same low load. The load of the shut-down main burner is transferred to the stabilizing burner operating with the main burner, further increasing the local heat load of the operating burner, significantly improving combustion stability during low-load operation and raising the low-load stabilizing burner threshold of the coal-fired boiler.

[0023] This invention improves the regulation performance of coal-fired boilers in low-load ranges. When only two burners are in operation, the main burners and the stabilizing burners in the stabilizing burner layer operate simultaneously, allowing the boiler to withstand higher loads without having to operate the next burner layer. This reduces the need to switch the pulverizing system in the coal-fired boiler, making the operation of the coal-fired boiler more flexible.

[0024] The present invention can be used to expand the peak-shaving margin of coal-fired boilers, reduce the minimum operating load of coal-fired boilers, and help power plants better cut valleys and fill peaks.

[0025] The present invention can reduce the startup cost of the boiler. When the boiler is started, the operation time of oil injection or plasma-assisted ignition can be reduced by putting the stable combustion burner into operation, thereby achieving the effect of saving fuel.

[0026] Taking a 660MW coal-fired boiler as an example, its current minimum stable combustion load is approximately 20%-30%. The implementation of this invention can significantly improve the boiler's low-load stable combustion capability, with an expected 5% reduction in the minimum stable combustion load. Peak-shaving capacity revenue, calculated at 80 yuan / MW, can increase by 2,640 yuan. With electricity compensation at 0.6 yuan / kWh and a 9-hour peak-shaving period, this can increase by 178,200 yuan. Based solely on peak-shaving compensation, the implementation of this invention can generate up to 180,840 yuan in additional peak-shaving revenue per day.

[0027] This invention proposes a technical solution for coal-fired power plant combustion system transformation. This solution involves shutting down some burners while reducing the overall combustion load within a layer during deep peak load regulation. This solution increases the local heat load of the burners by combining main and stabilizing burners. The proposed combustion system utilizes a pulverized powder silo to ensure flexibility in start-up, shutdown, and operating condition adjustment. This combination addresses the current need for comprehensive transformation of burners within a layer of boilers to stabilize combustion at low loads, which has limited the ability to address the issue of reduced local heat loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of a new burner system for improving the low-load stable combustion threshold of a coal-fired boiler provided by an embodiment of the present invention;

[0029] Figure 2This is a logic diagram of the stable combustion layer fuel control of a novel burner system provided by an embodiment of the present invention;

[0030] Figure 3 This is a logic diagram of secondary air control for a stable combustion layer of a novel burner system provided by an embodiment of the present invention;

[0031] Figure 4 is the average volume temperature of typical areas under different adjustment measures: (a) typical area of ​​the main combustion zone of the boiler; (b) typical area behind the burner nozzle;

[0032] Figure 5 It is the power of a single burner of the boiler under different adjustment measures;

[0033] In the figure: 1. Disposable recirculation valve; 2. Pulverized coal mixer; 3. Pulverized coal feeder; 4. Primary air valve; 5. Primary air recirculation valve; 6. Main burner; 7. Stable combustion burner; 8. Upper burner; 9. Stable combustion layer burner. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] Taking the coal-fired boiler of a 660MW ultra-supercritical unit as an example, at 20% load, for safety reasons, it is necessary to keep the two pulverizing systems on the bottom layer running, so that the load of a single burner in the boiler is approximately 50% of the burner's full load, and the combustion stability is significantly reduced. To improve the stability and economy of the unit's ultra-low load operation, the present invention adopts a method of combining a main burner with a stabilizing burner to form a stabilizing burner layer. When the boiler is running at low load, by shutting down the main burner without the stabilizing burner, the operating load of the single main burner in the layer is increased, thereby achieving the purpose of raising the low-load stabilizing burner threshold of the coal-fired boiler.

[0036] like Figure 1 As shown, an embodiment of the present invention provides a novel burner system for improving the low-load stable combustion threshold of a coal-fired boiler. The burner system includes a pulverizer, an intermediate pulverizer storage bin, a pulverizer feeder, a conventional layer burner, a stable combustion layer burner, burner auxiliary piping, a primary air valve, and a primary air recirculation valve. Furthermore, the burner system includes a secondary air box and a secondary air damper.

[0037] The stabilizing burner layer includes a main burner system and a stabilizing burner system. The new burner system is located on two floors, A and D, at the bottom of the boiler. Each stabilizing burner system includes six main burners, each connected to six pulverized coal mixers. Each stabilizing burner system includes four stabilizing burners, arranged to coordinate with the main burner systems on both sides and in the center of the furnace, each connected to four pulverized coal mixers. Each main burner is located on the same secondary air box, and each burner is equipped with an independently adjustable secondary air damper. Each stabilizing burner is located on the same secondary air box. The stabilizing burners and air boxes are located below the main burners and connected in parallel with the main burner air boxes. Each burner is equipped with an independently adjustable secondary air damper. Each pulverized coal mixer is connected to a primary air valve via an air duct and to a pulverized coal feeder via a pulverized coal pipe. The primary air valve is connected to the unit's inherent primary air system, and the pulverized coal feeder is connected to the unit's inherent pulverized coal silo system.

[0038] The present invention is mainly used to improve the operational stability of coal-fired boilers under load conditions below 30%. The overall workflow is as follows: when the boiler load is higher than 40%, the A and D stabilizing burner layers operate normally, and only 6 main burners on the front and rear walls are put into operation, and the stabilizing burners remain closed. When the boiler load is lower than 40%, and it is estimated that deep peak regulation below 20% load is required, 4 stabilizing burners on the front and rear walls are put into operation, and then the 2 main burners on the front and rear walls that are not equipped with stabilizing burners reduce their load until they are shut down. When the unit operates below 20% load, the stabilizing burners operate at a fixed load, and the main burners are responsible for load regulation.

[0039] The general control principle is: the total fuel amount is divided into the main fuel amount and the stable combustion fuel amount, which are controlled separately; the primary air volume is controlled by the opening of the hot air recirculation valve to match the change of the burner powder amount; the secondary air of the stable combustion burner is separately controlled by the secondary air damper, and can be completely closed when the stable combustion burner is shut down.

[0040] The main burners 1, 3, 4, and 6 on each floor are interlocked and controlled with the main burners 2 and 5 respectively, and the stable combustion burners on each floor correspond to the main burners 1, 3, 4, and 6 for interlocked control.

[0041] The fuel quantity instructions for interlocked burners are consistent. The difference between the boiler master fuel instruction and the stabilizing burner fuel instruction on each floor is the main burner fuel instruction. The ratio of the main burner fuel instruction to the number of main burners in operation on that floor is the main burner pulverizer feed quantity instruction. The difference between the pulverizer feed quantity instruction and the measured pulverizer feed quantity is used as the input of the PID controller, which provides the main burner pulverizer feed speed instruction. The measured pulverizer feed quantity value is calculated by the function unit to provide the main burner primary air volume instruction. The difference between the primary air volume instruction and the measured primary air volume is used as the input of the PID controller, which provides the primary air recirculation valve opening instruction.

[0042] The fuel quantity instructions for main burners 1, 3, 4, and 6 adopt the main burner fuel instruction, and the fuel quantity instructions for main burners 2 and 5 are switched and controlled by the stable combustion burner input instruction. When the stable combustion burner input instruction is 1, the fuel quantity instructions for main burners 2 and 5 slowly change to the main burner fuel instruction. When the stable combustion burner input instruction is 0, the fuel quantity instructions for main burners 2 and 5 slowly change to 0.

[0043] The fuel instructions for the stable combustion burners are used to generate the primary and secondary air ratios of the stable combustion burners 1, 3, 4, and 6 through the function generator. The quotient of the 30s measurement value of the primary air volume and the 30s measurement value of the secondary air volume of the stable combustion burners 1, 3, 4, and 6 is used as the primary and secondary air ratio measurement value. The difference between the primary and secondary air ratios and the primary and secondary air ratio measurement values ​​of the stable combustion burners 1, 3, 4, and 6 is used as the input of the PID controller to give the secondary air damper openings of the stable combustion burners 1, 3, 4, and 6. The secondary air damper openings of the stable combustion burners 1, 3, 4, and 6 are summed with the secondary air volume offset instructions of the stable combustion burners 1, 3, 4, and 6 to give the secondary air damper opening instructions of the stable combustion burners 1, 3, 4, and 6.

[0044] The operation of the stabilizing burner is not restricted by the main burner. During startup, the stabilizing burner can be used for ignition instead of the main burner to reduce the energy consumption of boiler startup.

[0045] The following are two specific embodiments and implementation schemes:

[0046] Example 1: Pure stable combustion burner

[0047] (1) System configuration:

[0048] The combustion stabilizing burners on the front and rear walls are respectively connected to the A and D pulverizing systems on both sides. A single combustion stabilizing burner can bear up to 30% of the load of a single main burner.

[0049] (2) Implementation plan:

[0050] When the boiler load drops below 35%, the main burners on both sides operate at full capacity. At this time, burners 2 and 5 on both sides are deactivated, and the stable combustion burner is put into operation. The control strategy is as follows:

[0051] According to the total fuel quantity instruction of the boiler master control, the fuel quantity instruction of the stable combustion burner and the actual fuel quantity signal, the speed control instruction of the main burner and the stable combustion burner powder feeder is given.

[0052] The speed control instruction of the pulverizer feeder of the stabilizing burner is given by the PID controller based on the difference between the fuel quantity instruction of the stabilizing burner and the actual fuel quantity.

[0053] The difference between the total fuel quantity instruction and the stable combustion burner fuel quantity instruction is used as the main burner fuel instruction. The difference between the main burner fuel instruction and the actual fuel quantity is used to give the speed control instruction of the main burner powder feeder through the PID controller.

[0054] The air volume is adjusted by adjusting the primary air powder concentration and the primary and secondary air ratio to ensure fine control of the burner air distribution under low load and to ensure the stable operation of the stable combustion burner.

[0055] The ratio of the real-time fuel amount to the primary air volume of the burner is used as the primary air powder concentration. By setting the difference between the primary air powder concentration and the actual primary air powder concentration, the PID controller gives the burner primary air damper instruction.

[0056] The ratio of the burner's real-time secondary air volume to the primary air volume is used as the primary and secondary air ratio. By setting the difference between the primary and secondary air ratio and the actual primary and secondary air ratio, the PID controller gives the burner's secondary air damper instruction.

[0057] Different function generators are used for the stable combustion burner and the main burner to generate the primary air powder concentration set value and the primary and secondary air ratio set value respectively according to the boiler load.

[0058] The PID controller adopts dead zone control to reduce the frequent adjustment of the primary and secondary air dampers.

[0059] Example 2: Deep-adjustable stable combustion burner

[0060] (1) System configuration:

[0061] The combustion stabilizing burners on the front and rear walls are connected to the A and D pulverizing systems on both sides respectively. A single combustion stabilizing burner can bear a maximum of 15% of the load of a single main burner.

[0062] (2) Implementation plan:

[0063] When the boiler load drops below 30%, the main burners on both sides operate at full capacity. At this time, the burners 2 and 5 on both sides are deactivated, and the stabilizing burner is put into operation. The control strategy is the same as that in Example 1.

[0064] The two examples select different stabilizing burner sizes based on the degree of deep adjustment required for the unit. Example 1 improves the furnace heat load, with the stabilizing burner bearing a load equivalent to 60% of the maximum load of the shut-down main burner, maintaining the original minimum load without shutting down more main burners. Example 2 uses a smaller burner size, resulting in a lower minimum load for maintaining stable operation.

[0065] The combustion stabilizing burner used in Example 1 is larger in scale and has a better combustion stabilizing effect, but its deep adjustment capability is smaller due to its large power reduction; the combustion stabilizing burner used in Example 2 is smaller in scale and has a slightly worse combustion stabilizing effect, but it can perform deep adjustment with relatively lower output.

[0066] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware portion can be implemented using dedicated logic; the software portion can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. Those skilled in the art will appreciate that the above-mentioned devices and methods can be implemented using computer-executable instructions and / or contained in processor control code, for example, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0067] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

[0068] In order to explore the strategy for optimizing the ultra-low load stable combustion operation of coal-fired boilers, through CFD simulation calculation, decibel adopted the method of reducing the number of burners in operation, increasing the operating power of a single burner, increasing the pulverized coal concentration, reducing the ignition heat of the pulverized coal airflow, and accelerating the ignition process of the pulverized coal; and adopted the method of increasing the fineness of the pulverized coal to reduce the ignition heat of the pulverized coal airflow. These two different methods enhance the heat release of the pulverized coal. According to the actual situation, numerical tests were conducted on different working conditions such as four burners, a single mill, eight burners, increasing the fineness of the pulverized coal, and increasing the power of the burner on the wall, as shown in Table 1. After processing, the average volume temperature of the typical area under different adjustment measures and the power of a single burner of the boiler under different adjustment measures were obtained, as shown in Table 1. Figure 4 、 Figure 5 shown.

[0069] Depend on Figure 4 It can be seen that under ultra-low load, the method of reducing the number of burners in operation and increasing the power of a single burner can significantly improve the local heat load behind the burner nozzle, indicating that the adjustment method of increasing the power of a single burner can achieve a significant stabilizing effect. At the same time, the method of increasing the fineness of coal powder and increasing the power of the burner on the wall can achieve a good stabilizing effect under 20% load, but the effect is not obvious under lower load. Figure 5It can be found that when only the power of a single burner is changed, when the power of a single burner is higher than or close to 60% of the power of a single burner at full load, the boiler as a whole will not experience burner instability. When the power of a single burner is lower than this level, burner instability will occur. Based on the above analysis, when the power of a single burner is higher than 60% of the full load power, the boiler can achieve stable combustion.

[0070] Table 1 Setting of stable combustion operation adjustment conditions under ultra-low load

[0071]

Claims

1. A burner system for improving the low-load stable combustion threshold of a coal-fired boiler, comprising a pulverizer, a pulverized coal bin, a pulverized coal feeder, a common burner, a stable combustion burner, a primary air system, a secondary air system, and auxiliary air ducts, characterized in that: The system is provided with at least one combustion stabilizing burner layer, which is arranged at the lower part of the furnace and is used to replace the original front and rear wall burners; the layer includes multiple main burners and multiple combustion stabilizing burners, wherein the combustion stabilizing burners are arranged at positions corresponding to specific main burners; The pulverized coal bin is arranged in the pulverized coal supply path of the stable combustion burner layer and is supplied with pulverized coal by an independent pulverized coal feeder; the primary air system and the secondary air system are respectively connected to each burner through an adjustable baffle to form independently controllable primary air and secondary air supply circuits; The system has the function of redistributing heat load among burners. Under low-load conditions of the boiler, some main burners are shut down to keep the stable combustion burners running continuously to increase the minimum stable combustion load threshold of the boiler.

2. The burner system according to claim 1, wherein The combustion stabilizing burner is connected to the main burner through a secondary air box arranged in parallel. The combustion stabilizing burner secondary air box is equipped with a full-close baffle, which can keep the combustion stabilizing burner running independently when the main burner is closed.

3. The burner system according to claim 1, wherein: The pulverizing system includes a fine powder separator, a recycling channel, a moisture absorption pipe and a powder exhaust fan; the upper end of the fine powder separator is provided with an explosion-proof door, and the lower end is connected to the pulverized coal bin, and the lower part of the pulverized coal bin is connected to an independent powder feeder to ensure a stable supply of pulverized coal in low-load mode.

4. The burner system according to claim 1, wherein: There are a total of ten main burners and stabilizing burners in the burner layer. The stabilizing burners are fixed at the corresponding positions of the main burners numbered 1, 3, 4, and 6. The remaining main burners can be completely shut down during low-load operation, and the heat load is concentrated on the stabilizing burners and auxiliary main burners.

5. A control method for the burner system according to claim 1, characterized in that: The following steps are involved: The total fuel quantity instruction and actual fuel quantity signal are obtained through the boiler main control system, and the PID controller is used to adjust the speed of the main burner powder feeder and the stable combustion burner powder feeder respectively; The control method supports the independent control of the main burner and the stabilizing burner in different zones, so that the stabilizing burner can operate continuously and stably in the low-load mode and realize the dynamic optimization of the overall fuel distribution of the system.

6. The control method according to claim 5, wherein: The difference between the fuel setting value and the actual fuel quantity of the stable combustion burner is used as input to generate a speed instruction of the powder feeder of the stable combustion burner through the first PID controller; The difference between the total fuel instruction and the steady combustion burner fuel instruction is used as the main burner fuel instruction. The deviation between the main burner fuel instruction and the actual fuel quantity is calculated, and the main burner powder feeder speed instruction is generated through the second PID controller.

7. The control method according to claim 5, wherein: The real-time primary air powder concentration is used as the reference parameter for primary air regulation. The position of the primary air baffle is controlled by the third PID controller through the difference between the set value and the measured value to achieve precise air supply for the stable combustion burner.

8. The control method according to claim 5, wherein: The ratio of secondary air to primary air flow is used as the basis for the primary and secondary air ratio. The difference between the set value and the measured value is used to adjust the position of the secondary air baffle through the fourth PID controller to optimize the local wind field structure of the stable combustion burner.

9. The control method according to claim 5, wherein: In the control system, function controllers are set for the main burner and the stable combustion burner respectively, and the target air-powder concentration and air ratio parameters are dynamically generated according to the boiler load to realize the intelligent air distribution adjustment of the zoned burner.

10. The control method according to claim 5, wherein: During the boiler startup phase, the stable combustion burner is put into operation first and set to a constant load operation mode to reduce dependence on oil guns or plasma ignition, shorten the startup time and improve the initial combustion stability.

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