Coal Pulverizing and Combustion System Based on Direct-Fired Pulverized Coal Boiler

Abstract

The present invention discloses a coal pulverizing and combustion system based on a direct-fired pulverized coal boiler, which includes a large-capacity coal pulverizing group, a small-capacity coal pulverizing group, a high-power burner group, and a low-power burner group; the large-capacity coal pulverizing group includes multiple sets of matched first raw coal bins, first coal feeders, and large-capacity coal pulverizers; the small-capacity coal pulverizing group includes multiple sets of matched second raw coal bins, second coal feeders, and small-capacity coal pulverizers; the high-power burner group includes a first air box and multiple high-power burners, and the multiple high-power burners are arranged in the first air box; the low-power burner group includes a second air box and multiple low-power burners, and the multiple low-power burners are arranged in the second air box; the large-capacity coal pulverizers and the high-power burners are arranged in one-to-one correspondence, and the small-capacity coal pulverizers and the low-power burners are arranged in one-to-one correspondence. Applying this solution can meet the reliability requirements for ultra-low load operation on the basis of expanding the boiler load operation range.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired boilers, and particularly to a coal pulverizing and combustion system for realizing ultra-low load operation based on a direct-fired pulverized coal boiler. Background Art

[0002] In the prior art, in order to adapt to the construction of a new power system with new energy as the main body, it is necessary for the coal-fired boilers of thermal power units to be able to operate in a relatively wide load range. In particular, in order to absorb the power generation of new energy, the coal-fired boilers need to have the ability to operate at ultra-low loads (such as below 30% of the rated load).

[0003] As is well known, the coal pulverizing and combustion system is a key factor affecting the ultra-low load operation of boilers. Most of the coal-fired boilers of coal-fired power units are equipped with direct-fired coal pulverizing systems. The gas-solid two-phase fluid carrying qualified fineness pulverized coal led out from the coal mill through the coarse powder separator is directly blown into the furnace through the burner. However, the air-powder characteristics of the direct-fired coal pulverizing system will affect the ignition performance of the burner and the combustion state organization in the furnace, thus restricting the level of low-load operation of the boiler.

[0004] In view of this, there is an urgent need to provide a solution for realizing ultra-low load operation for the existing coal pulverizing and combustion system to overcome the above defects. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a coal pulverizing and combustion system based on a direct-fired pulverized coal boiler, which meets the reliability requirements of ultra-low load operation on the basis of expanding the boiler load operation range.

[0006] The present invention provides a coal pulverizing and combustion system based on a direct-fired pulverized coal boiler, including a large-capacity coal grinding group, a small-capacity coal grinding group, a high-power burner group, and a low-power burner group; the large-capacity coal grinding group includes multiple sets of matched first raw coal bins, first coal feeders, and large-capacity coal mills; the small-capacity coal grinding group includes multiple sets of matched second raw coal bins, second coal feeders, and small-capacity coal mills; the high-power burner group includes a first air box and multiple high-power burners, and the multiple high-power burners are arranged in the first air box; the low-power burner group includes a second air box and multiple low-power burners, and the multiple low-power burners are arranged in the second air box; the large-capacity coal mills are arranged in one-to-one correspondence with the high-power burners and are connected by large mill outlet powder pipes, and the small-capacity coal mills are arranged in one-to-one correspondence with the low-power burners and are connected by small mill outlet powder pipes.

[0007] Optionally, the coal pulverizing and combustion system further includes a forced draft fan, a primary air fan, and an air preheater. The forced draft fan is connected to the first air box and the second air box respectively through the air preheater and the secondary hot air main pipe; the primary air fan is connected to the hot air sub-pipes of each large-capacity coal pulverizer and each small-capacity coal pulverizer respectively through the air preheater and the primary hot air main pipe.

[0008] Optionally, an air inlet regulating valve is provided on each of the hot air sub-pipes.

[0009] Optionally, on-line air and powder monitoring devices are respectively provided on the large coal mill outlet powder pipe and the large coal mill outlet powder pipe, which are used to monitor the coal powder data in the corresponding powder pipes in real time and output an adjustment control signal according to the coal powder data.

[0010] Optionally, outputting the adjustment control signal according to the coal powder data includes: outputting an adjustment control signal to the coal feeder, the primary air fan or the forced draft fan according to the calorific value, volatile matter, and moisture of the coal in the coal powder data.

[0011] Optionally, outputting the adjustment control signal according to the coal powder data further includes: outputting an adjustment control signal to the separator of the coal pulverizer according to the fineness of the coal powder in the coal powder data.

[0012] Optionally, outputting the adjustment control signal according to the coal powder data further includes: outputting an adjustment control signal to the air inlet regulating valve according to the coal powder concentration in the coal powder data.

[0013] Optionally, both the first air box and the second air box are arranged on the boiler, and the first air box is located below the second air box.

[0014] Optionally, the air preheater is arranged on the flue of the boiler.

[0015] Compared with the prior art, this solution provides a novel coal pulverizing and combustion system based on a direct-fired pulverized coal boiler. Specifically, through the coupled matching design of the large-capacity coal pulverizing group, small-capacity coal pulverizing group, high-power burner group, and low-power burner group, the coal pulverizer and burner can be put into operation according to the actual operation needs, greatly expanding the ultra-low load operation range of the boiler and meeting the reliability requirements of ultra-low load operation.

[0016] In an alternative embodiment of the present invention, on the large mill outlet powder pipe and the large mill outlet powder pipe, there are respectively installed on-line air-powder monitoring devices for monitoring the pulverized coal data in the corresponding powder pipes in real time, and outputting adjustment control signals according to the pulverized coal data, so as to systematically adjust the coal pulverizing and combustion characteristics on-line. In a specific implementation, according to the calorific value, volatile matter, and moisture of the pulverized coal in the pulverized coal data, adjustment control signals can be output to the coal feeder, primary air fan, or secondary air fan, so as to calculate and adjust the coal feeding amount of the boiler coal feeder, the air supply volume of the primary air fan, and the air supply volume of the secondary air fan on-line according to the boiler load, realizing more precise control. At the same time, according to the fineness of the pulverized coal in the pulverized coal data, adjustment control signals can be output to the separator of the coal mill to adjust the rotation speed of the separator of the coal mill on-line, so that the fineness of the pulverized coal is within a reasonable control range. In addition, according to the concentration of the pulverized coal in the pulverized coal data, adjustment control signals can be output to the air inlet adjustment valve to adjust the primary air volume of each coal mill on-line and reasonably control the air-coal ratio.

[0017] Applying this coal pulverizing and combustion system solution, the boiler can ensure good air-powder characteristics entering the burner in the full load range. When the boiler is at low load, the air-coal ratio and pulverized coal fineness of the coal pulverizing system can be effectively reduced, and the low load stable combustion performance of the burner is improved, and a lower boiler stable combustion load rate can be achieved without using auxiliary combustion. In addition, during ultra-low load operation, it can meet a lower primary air rate of the boiler, improving the combustion efficiency and low NOx combustion level. Brief Description of the Drawings

[0018] Figure 1 It is a flowchart of the coal pulverizing and combustion system based on a direct-fired pulverized coal boiler provided by an embodiment of the present application.

[0019] In the figure:

[0020] Boiler 1, air preheater 2, secondary air fan 3, primary air fan 4, high-power burner 5, low-power burner 6, first air box 7, second air box 8, first on-line air-powder monitoring device 9, first raw coal bunker 10, first coal feeder 11, large-capacity coal mill 12, second raw coal bunker 13, second coal feeder 14, small-capacity coal mill 15, large mill air inlet adjustment valve 16, small mill air inlet adjustment valve 17, large mill outlet powder pipe 18, small mill outlet powder pipe 19, primary hot air main pipe 20, secondary hot air main pipe 21, second on-line air-powder monitoring device 22. Detailed Embodiment

[0021] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0022] For a coal-fired power unit with a direct-fired coal pulverizing system configured for a coal-fired boiler, the air-powder characteristics of the direct-fired coal pulverizing system will affect the ignition performance of the burner and the combustion state organized in the furnace, thereby restricting the low-load operation level of the boiler.

[0023] The existing method of using a variable-frequency coal mill to reduce the minimum output has the following deficiencies:

[0024] 1) Driven by a traditional main motor, the minimum coal feeding output of a medium-speed coal mill can generally reach about 25% of the maximum output. If the coal feeding output is further reduced, jitter will occur during the grinding of the grinding rollers due to less coal stored on the grinding table, affecting the normal operation of the coal mill.

[0025] 2) However, the minimum ventilation volume of the coal mill remains unchanged, which may lead to too high a primary air rate in the boiler and make it difficult for the boiler to achieve stable combustion.

[0026] 3) In addition, the coal mill frequency converter is a high-voltage frequency converter, which will increase the cost of the coal mill by a large amount.

[0027] The existing method of achieving the lowest load operation by running a single coal mill has the following deficiencies: Under ultra-low loads, the coal-fired unit requires the boiler to achieve stable combustion without using combustion support measures. There may be risks of a single coal mill tripping due to an accident and the burner extinguishing, and even trigger a Main Fuel Trip (MFT) of the boiler, with relatively high operation risks.

[0028] The existing method of increasing the number of coal mills and the number of boiler burner layers to achieve a lower stable combustion load for the boiler has the following deficiencies:

[0029] 1) The increase in the number of coal mills and the number of burner layers increases the investment cost of the coal pulverizing system and the boiler body;

[0030] 2) Affected by the layout space, the increased quantity is limited, and overall, the effect of reducing the boiler load is not obvious.

[0031] Based on this, the embodiment of the present application provides a coal pulverizing and combustion system for realizing ultra-low load operation based on a direct-fired pulverized coal boiler. Through the good matching of the coal pulverizing system and the boiler combustion system, it provides technical guarantee for obtaining good characteristics of the coal pulverizing and combustion system when the boiler load changes between high and low. Please refer to Figure 1 , which is a flowchart of the coal pulverizing and combustion system based on a direct-fired pulverized coal boiler provided by the embodiment of the present application.

[0032] As Figure 1 shown, the coal pulverizing and combustion system based on the direct-fired pulverized coal boiler is mainly composed of four parts, namely coal pulverizing, air distribution, coal powder feeding, and combustion.

[0033] Among them, the coal pulverizing section includes a large-capacity coal grinding group S1 and a small-capacity coal grinding group S2. Among them, the large-capacity coal grinding group S1 includes multiple sets of first raw coal bins 10, first coal feeders 11, and large-capacity coal grinders 12 with matching capacities; the small-capacity coal grinding group S2 includes multiple sets of second raw coal bins 13, second coal feeders 14, and small-capacity coal grinders 15 with matching capacities. Here, "large capacity" and "small capacity" mean that the coal grinders have different coal output amounts per unit time. One of the two groups of coal grinders is a relatively large-capacity coal grinder, and the other is a relatively small-capacity coal grinder. It should be understood that "large capacity" and "small capacity" are used to characterize the relative coal output capacity, rather than specifically referring to a specific coal output amount.

[0034] In specific implementation, both the large-capacity coal grinder 12 and the small-capacity coal grinder 15 are equipped with dynamic separators to dynamically adjust the fineness of the pulverized coal to meet the use and adjustment requirements under different working conditions. During the coal pulverizing process, the raw coal stored in the raw coal bin first enters the coal feeder, and the coal feeder is used to quantitatively feed coal to the coal grinder. Specifically, the raw coal in the first raw coal bin 10 enters the large-capacity coal grinder 12 through the first coal feeder 11, and the raw coal in the second raw coal bin 13 enters the small-capacity coal grinder 15 through the second coal feeder 14. After entering the coal grinder, qualified pulverized coal required for boiler combustion is ground out.

[0035] Among them, the air distribution section includes a forced draft fan 3, a primary air fan 4, and an air preheater 2. The primary air output by the primary air fan 4 serves as the conveying medium for the pulverized coal in the coal grinder. In specific implementation, the primary cold air enters the air preheater 2 under the action of the primary air fan 4 to be heated to form primary hot air. The primary hot air enters the primary hot air main pipe 20, and then respectively passes through the hot air sub-pipes of the large-capacity coal grinder 12 and the small-capacity coal grinder 15 to convey the qualified air-powder mixture ground out by the corresponding coal grinder. Among them, the primary air volume of the corresponding coal grinder can be adjusted respectively through the large grinder air inlet regulating valve 16 and the small grinder air inlet regulating valve 17.

[0036] The secondary air output by the forced draft fan 3 mainly plays a role in assisting combustion. The secondary cold air enters the air preheater 2 under the action of the forced draft fan 3 to be heated to form secondary hot air. The secondary hot air enters the secondary hot air main pipe 21 and can be respectively conveyed to the first air box 7 and the second air box 8 until the secondary nozzles of each burner.

[0037] In this implementation scheme, the air preheater 2 is arranged on the flue of the boiler 1 to make full use of the flue gas heat to heat the primary air and the secondary air, having good energy-saving effects. In other possible implementation schemes, other heating and air supply methods can also be adopted. The embodiments of this application do not make limitations.

[0038] Among them, the powder feeding part includes a large mill inlet air regulating door 16, a small mill inlet air regulating door 17, a large mill outlet powder pipe 18, a small mill outlet powder pipe 19, a first on-line air-powder monitoring device 9 and a second on-line air-powder monitoring device 22. The large mill inlet air regulating door 16 is arranged on the hot air sub-pipe of the high-output coal mill 12, and the small mill inlet air regulating door 17 is arranged on the hot air sub-pipe of the low-output coal mill 15. The first on-line air-powder monitoring device 9 is arranged on the conveying path established by the large mill outlet powder pipe 18, and the second on-line air-powder monitoring device 22 is arranged on the conveying path established by the small mill outlet powder pipe 19.

[0039] In this way, the primary hot air respectively controls the air volume through the corresponding inlet air regulating doors. After entering the corresponding coal mills, while drying the pulverized coal, the pulverized coal that has been ground qualified is sent into the corresponding powder feeding pipelines, and after passing through the on-line pulverized coal monitoring device, it is conveyed to the burner. Specifically, the air-powder mixture in the high-output coal mill 12 enters the large mill outlet powder pipe 18. After the air-powder mixture in the powder pipe passes through the first on-line air-powder monitoring device 9, it enters the high-power burner 5; the air-powder mixture in the low-output coal mill 15 enters the small mill outlet powder pipe 19. After the air-powder mixture in the powder pipe passes through the second on-line air-powder monitoring device 22, it enters the low-power burner 6.

[0040] Among them, the combustion part includes a high-power burner group T1 and a low-power burner group T2. The high-power burner group T1 includes a first air box 7 and a plurality of high-power burners 5. The first air box 7 is arranged on the boiler 1, and the plurality of high-power burners 5 are arranged in the first air box 7. The low-power burner group T2 includes a second air box 8 and a plurality of low-power burners 6. The second air box 8 is arranged on the boiler 1, and the plurality of low-power burners 6 are arranged in the second air box 8. Optionally, the first air box 7 is arranged below the second air box 8.

[0041] The power of the burner, that is, the heat output power. The higher the heat power means that the burner can provide more heat energy. Here, "high power" and "low power" mean that one of the two groups of coal mills is a high-power burner with a relatively high heat output power, and the other is a low-power burner with a relatively low heat output power. It should be understood that "high power" and "low power" are used to characterize the relative heat output ability, rather than referring to a specific power value.

[0042] To meet the performance requirements of organizing combustion, the high-power burner group T1 is correspondingly arranged with the high-output coal mill 12, and the low-power burner group T2 is correspondingly arranged with the low-output coal mill 15. During ultra-low load operation, only two low-power burners 6 in the low-power burner group T2 need to be put into operation. During the operation of other loads, the corresponding burner combinations can be put into operation according to the organization of combustion; for example, but not limited to, putting into operation some high-power burners 5, or putting into operation the high-power burners 5 and the low-power burners 6 in combination. The embodiments of the present application are not limited.

[0043] In this embodiment, the large-output coal mill 12 and the high-power burner 5 are arranged in one-to-one correspondence and are respectively connected through the large mill outlet powder pipe 18. The small-output coal mill 15 and the low-power burner 6 are arranged in one-to-one correspondence and are respectively connected through the small mill outlet powder pipe 19. To simplify the illustration, only the connection relationship between a set of the large-output coal mill 12 and the high-power burner 5 and the small-output coal mill 15 and the low-power burner 6 is shown in the figure.

[0044] In addition, in the system shown in the figure, three coal mills are taken as examples in the large-output coal mill group S1 and the small-output coal mill group S2 respectively, and three burners are taken as examples in the high-power burner group T1 and the large-output coal mill 12 respectively. In specific implementation, the coal mills in the large-output coal mill group S1 and the small-output coal mill group S2 and the burners in the high-power burner group T1 and the large-output coal mill 12 can be set to other numbers as long as they can effectively increase the boiler load operation range, and all are within the scope claimed in this application.

[0045] It should be noted that in specific implementation, the number and capacity configuration of the large- and small-output coal mills and the large- and small-power burners are determined by the coupling calculation of the coal pulverizing system and the combustion system. The coupling calculation principle is as follows: One coal mill is reserved for operation when the boiler is at full load, and two small-output coal mills are maintained for operation at the lowest stable combustion load. An initial coal mill capacity distribution ratio is set according to the coal consumption of the boiler, and the coal mill type is selected; then the boiler combustion system checks and calculates the heat load data in the burner area according to the capacity and air-coal ratio parameters of the coal mill. The heat load deviation and air-coal ratio in the burner area can meet the performance requirements such as stable combustion and coking control under different loads of the boiler. Otherwise, the distribution ratio of the coal mill capacity will be adjusted until the iteration is completed.

[0046] In order to better realize the air-powder characteristics in each burner under different loads of the boiler, especially under low-load operation, and ensure the combustion characteristics of the boiler, the coal pulverizing and combustion system based on the direct-fired pulverized coal boiler provided in the embodiment of this application is provided with an air-powder on-line monitoring and regulating device. Among them, the first air-powder on-line monitoring device 9 is arranged on the conveying path established by the large mill outlet powder pipe 18, and the second air-powder on-line monitoring device 22 is arranged on the conveying path established by the small mill outlet powder pipe 19.

[0047] Based on the setting of the on-line monitoring and adjustment device for wind and pulverized coal, it is possible to monitor in real time data such as the calorific value, volatile matter, and moisture of the coal in the corresponding pulverized coal pipe, and calculate and adjust the coal feeding amount of the boiler coal feeder, the air supply amount of the primary air fan 4, and the air supply amount of the induced draft fan 3 according to the boiler load online, so as to achieve more accurate control. In addition, by monitoring the pulverized coal fineness data in the corresponding pulverized coal pipe in real time, the separator speed of the coal mill can be adjusted online to keep the pulverized coal fineness within a reasonable control range. In addition, based on the pulverized coal concentration data collected in real time, the primary air volume of each coal mill can be adjusted online to reasonably control the air-coal ratio.

[0048] In specific implementation, by putting into operation two sets of second raw coal bins 13, second coal feeders 14, and small-output coal mills 15 in the small-output coal mill group S2, and two sets of small-power burners 6 in the small-power burner group T2, stable ultra-low load operation can be achieved.

[0049] It should be understood that the specific implementation of the functional components such as the air preheater, induced draft fan, primary air fan, burner, on-line monitoring device for wind and pulverized coal, raw coal bin, coal feeder, and coal mill described in this embodiment is not the core inventive point of this application. Those skilled in the art can implement it based on the prior art, so it will not be elaborated here.

[0050] In addition, the ordinal numbers "first" and "second" used herein are only used to describe the components or structures with the same function in the technical solution. It can be understood that the use of the above ordinal numbers does not constitute a limitation to the understanding of the technical solution claimed in this application.

[0051] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A pulverizing and combustion system based on a direct-fired pulverized coal boiler, characterized in that: The pulverizing and combustion system comprises a high-output coal grinding group, a low-output coal grinding group, a high-power burner group and a low-power burner group; The high-output coal grinding group includes multiple sets of matching first raw coal bins, first coal feeders and high-output coal grinding mills; the low-output coal grinding group includes multiple sets of matching second raw coal bins, second coal feeders and low-output coal grinding mills; The high-power burner group includes a first wind box and a plurality of high-power burners, and the plurality of high-power burners are arranged in the first wind box; the low-power burner group includes a second wind box and a plurality of low-power burners, and the plurality of low-power burners are arranged in the second wind box; The high-output coal mill is arranged in one-to-one correspondence with the high-power burner and is connected through the powder pipe at the large mill outlet; the low-output coal mill is arranged in one-to-one correspondence with the low-power burner and is connected through the powder pipe at the small mill outlet; During ultra-low load operation, the low-power burners in the low-power burner group are put into operation. During remaining load operation, some of the high-power burners are put into operation according to the organized combustion, or the high-power burners and the low-power burners are put into operation in combination.

2. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 1 is characterized in that: The pulverizing and combustion system also includes an air supply fan, a primary air fan and an air preheater. The air supply fan is connected to the first wind box and the second wind box respectively through the air preheater and the secondary hot air main pipe; the primary air fan is connected to the hot air sub-pipes of each of the large-output coal mills and each of the small-output coal mills respectively through the air preheater and the primary hot air main pipe.

3. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 2 is characterized in that: Each of the hot air sub-tubes is provided with an air inlet regulating door.

4. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 3 is characterized in that: The large mill outlet powder pipe and the large mill outlet powder pipe are respectively provided with air-powder online monitoring devices for monitoring the coal powder data in the corresponding powder pipes in real time and outputting adjustment control signals according to the coal powder data.

5. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 4 is characterized in that: The step of outputting a regulating control signal according to the pulverized coal data comprises: According to the calorific value, volatile matter and moisture of the coal in the pulverized coal data, an adjustment control signal is output to the coal feeder, the primary fan or the blower.

6. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 4 or 5, characterized in that: The step of outputting a regulating control signal according to the pulverized coal data further comprises: According to the coal powder fineness in the coal powder data, an adjustment control signal is output to the separator of the coal mill.

7. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 6 is characterized in that: The step of outputting a regulating control signal according to the pulverized coal data further comprises: According to the coal powder concentration in the coal powder data, an adjustment control signal is output to the air inlet adjustment door.

8. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 2 or 3, characterized in that: The first wind box and the second wind box are both arranged on the boiler, and the first wind box is located below the second wind box.

9. The pulverizing and combustion system based on a direct-fired pulverized coal boiler according to claim 2 or 3, characterized in that: The air preheater is arranged on the flue of the boiler.

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