Multi-stage pulverized coal concentrator and pulverized coal combustion system

Abstract

The invention discloses a multi-stage pulverized coal concentrator and a pulverized coal combustion system, and relates to the technical field of pulverized coal combustion. The multistage pulverized coal concentrator comprises a main pulverized coal pipe, a first separation pipe, a second separation pipe and a concentrated phase pipe, the main pulverized coal pipe comprises an elbow section, and an enrichment zone used for enriching pulverized coal is limited on the inner wall of the outer side of the elbow section; the first separation pipe and the second separation pipe are connected to the elbow section corresponding to the enrichment zone and are arranged at an interval along the extension direction of the elbow section, and the other ends of the first separation pipe and the second separation pipe are respectively connected with the concentrated phase pipe; and the first separation pipe and the second separation pipe are used for separating the pulverized coal in the enrichment zone and conveying the pulverized coal to the concentrated phase pipe. According to the multi-stage pulverized coal concentrator, the separation efficiency of concentrated-phase pulverized coal can be guaranteed, the concentration of the separated concentrated-phase pulverized coal is guaranteed, and the ignition stability of the concentrated-phase pulverized coal is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of pulverized coal combustion, and in particular, to a multi-stage pulverized coal concentrator and a pulverized coal combustion system. Background Art

[0002] The flexible peak shaving of coal-fired power units is the basis for solving the problem of the increasing consumption of renewable energy power and ensuring the stable power supply in China. In the related art, during the low-load operation of coal-fired power units, auxiliary combustion methods such as micro-oil and plasma are mostly used, resulting in a significant increase in operating costs and maintenance costs. To address this problem, in the related art, a method is proposed to divide the main pulverized coal airflow into a high-concentration thick phase and a low-concentration lean phase, and through the characteristics of high calorific value and flammability of the thick-phase pulverized coal, the low-load stable self-ignition is achieved by using pulverized coal to ignite pulverized coal, reducing the dependence on external auxiliary combustion methods.

[0003] However, in the related art, during the separation of the thick and lean phases of pulverized coal, there is a low separation efficiency of the thick and lean phases of pulverized coal, and the concentration of the thick-phase pulverized coal cannot be controlled, which may lead to the inability of the combustible components in the thick-phase pulverized coal to fully aggregate, seriously affecting its ignition stability. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to some extent.

[0005] To this end, an embodiment of the present invention provides a multi-stage pulverized coal concentrator, which can ensure the separation efficiency of the thick-phase pulverized coal and ensure the concentration of the thick-phase pulverized coal after separation to ensure the ignition stability of the thick-phase pulverized coal.

[0006] An embodiment of the present invention also provides a pulverized coal combustion system.

[0007] The multi-stage pulverized coal concentrator according to the embodiment of the present invention includes:

[0008] A main pulverized coal pipe, the main pulverized coal pipe includes an elbow section, and an enrichment zone for enriching pulverized coal is defined by the inner wall of the outer side of the elbow section;

[0009] A first separation pipe, a second separation pipe and a thick-phase pipe, the first separation pipe and the second separation pipe are connected to the elbow section corresponding to the enrichment zone and are arranged at intervals along the extending direction of the elbow section, the other ends of the first separation pipe and the second separation pipe are respectively connected to the thick-phase pipe, and the first separation pipe and the second separation pipe are used to separate the pulverized coal in the enrichment zone and convey it to the thick-phase pipe.

[0010] The multi-stage pulverized coal concentrator according to the embodiment of the present invention can ensure the separation efficiency of the thick-phase pulverized coal and the concentration of the thick-phase pulverized coal after separation to ensure the ignition stability of the thick-phase pulverized coal.

[0011] In some embodiments, the axis of the first separation pipe is arranged at a first included angle with the tangent line of the elbow section at the connection position of the first separation pipe and the elbow section, the axis of the second separation pipe is arranged at a second included angle with the tangent line of the elbow section at the connection position of the second separation pipe and the elbow section, both the first included angle and the second included angle are acute angles, and the first included angle is greater than the second included angle.

[0012] In some embodiments, the first included angle is not less than 25° and not greater than 35°, and / or the second included angle is not less than 20° and not greater than 30°.

[0013] In some embodiments, the cross-sectional diameter of the first separation pipe is not greater than one-tenth of the cross-sectional diameter of the elbow section, and the cross-sectional diameter of the second separation pipe is not greater than one-tenth of the cross-sectional diameter of the elbow section.

[0014] In some embodiments, the elbow section includes an inlet and an outlet. In the extending direction of the elbow section, the distance between the connection position of the first separation pipe and the elbow section and the inlet is not greater than one-half of the distance between the inlet and the outlet, and the distance between the connection position of the second separation pipe and the elbow section and the inlet is not greater than seven-ninths of the distance between the inlet and the outlet.

[0015] In some embodiments, a controller is included. A first valve is provided on the first separation pipe, a second valve is provided on the second separation pipe, and a concentration detector is provided on the dense-phase pipe. The first valve, the second valve, and the concentration detector are respectively electrically connected to the controller. The concentration detector is used to measure the pulverized coal concentration in the dense-phase pipe and transmit it to the controller when the first valve or the second valve is opened, and the controller is used to open the second valve or the first valve when the measured pulverized coal concentration is less than the set pulverized coal concentration.

[0016] In some embodiments, the first separation pipe includes a first pipe section and a second pipe section. A Venturi tube is provided between the first pipe section and the second pipe section. The Venturi tube includes a throat section, and an air draft pipe is connected to the throat section.

[0017] In some embodiments, a third separation pipe is included. The third separation pipe is provided between the first separation pipe and the second separation pipe and there is at least one, and both ends of the third separation pipe are respectively connected to the elbow section and the dense-phase pipe.

[0018] In some embodiments, the axis of the third separation pipe is arranged at a third included angle with the tangent line of the elbow section at the connection position of the third separation pipe and the elbow section, and the third included angle is less than the first included angle and greater than the second included angle.

[0019] The pulverized coal combustion system according to an embodiment of the present invention includes the multi-stage pulverized coal concentrator of any one of the above embodiments. Description of the Drawings

[0020] Figure 1 is a schematic structural view of the multi-stage pulverized coal concentrator according to an embodiment of the present invention.

[0021] Figure 2 is a schematic structural view of the elbow section in the multi-stage pulverized coal concentrator according to an embodiment of the present invention.

[0022] Figure 3 is a schematic connection view of the Venturi tube and the induced air pipe in the multi-stage pulverized coal concentrator according to an embodiment of the present invention.

[0023] Reference Signs:

[0024] Main pulverized coal pipe 1; elbow section 11; inlet 111; outlet 112; enrichment zone 12;

[0025] First separation pipe 2; first valve 21; first pipe section 22; second pipe section 23;

[0026] Second separation pipe 3; second valve 31;

[0027] Dense-phase pipe 4;

[0028] Venturi tube 5; throat section 51;

[0029] Induced air pipe 6. Detailed Embodiment

[0030] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0031] As Figure 1 and Figure 2 shown, the multi-stage pulverized coal concentrator according to an embodiment of the present invention includes a main pulverized coal pipe 1, a first separation pipe 2, a second separation pipe 3, and a dense-phase pipe 4. A main pulverized coal air flow is transported in the main pulverized coal pipe 1. The main pulverized coal pipe 1 includes an elbow section 11. An inner wall of an outer side portion of the elbow section 11 defines an enrichment zone 12 for enriching pulverized coal. The first separation pipe 2 and the second separation pipe 3 are correspondingly connected to the elbow section 11 and are spaced apart along the extending direction of the elbow section 11. The other ends of the first separation pipe 2 and the second separation pipe 3 are respectively connected to the dense-phase pipe 4. The first separation pipe 2 and the second separation pipe 3 are used to separately separate the pulverized coal in the enrichment zone 12 and transport it to the dense-phase pipe 4.

[0032] When the multi-stage pulverized coal concentrator according to the embodiment of the present invention is in use, after the main pulverized coal air flow enters the elbow section 11, due to the centrifugal force and inertia, the pulverized coal will move towards the inner wall of the outer side of the elbow section 11, resulting in an increase in the concentration of pulverized coal particles at this position and thus forming an enrichment zone 12. And along the extension direction of the elbow section 11, the concentration of pulverized coal particles in the enrichment zone 12 increases successively. At the position of the first separation pipe 2, part of the pulverized coal in the enrichment zone 12 is discharged from the elbow section 11 through the first separation pipe 2 and enters the dense-phase pipe 4, realizing the preliminary separation of the pulverized coal in the enrichment zone 12, reducing the amount of pulverized coal to be processed subsequently. At the position of the second separation pipe 3, the concentration of pulverized coal particles in the enrichment zone 12 is further increased. Part of the pulverized coal in the enrichment zone 12 is discharged from the elbow section 11 through the second separation pipe 3 and enters the dense-phase pipe 4, realizing the re-separation of the pulverized coal in the enrichment zone 12, further extracting the dense-phase pulverized coal, and thus obtaining the separated dense-phase pulverized coal in the dense-phase pipe 4 and outputting the lean-phase pulverized coal at the discharge port of the main pulverized coal pipe 1, ensuring the maximization of the pulverized coal separation effect.

[0033] The multi-stage pulverized coal concentrator according to the embodiment of the present invention realizes the two-stage separation of the main pulverized coal air flow through the first separation pipe 2, the second separation pipe 3 and the elbow section 11, can realize more refined classification of pulverized coal particles, improves the separation efficiency of the dense-phase pulverized coal, and ensures the concentration of the dense-phase pulverized coal particles in the dense-phase pipe 4 to ensure the ignition stability of the dense-phase pulverized coal.

[0034] Optionally, the axis of the first separation pipe 2 is parallel to the axis of the elbow section 11, and the axis of the second separation pipe 3 is parallel to the axis of the elbow section 11, so as to reduce the power consumption after the pulverized coal in the elbow section 11 enters the first separation pipe 2 and the second separation pipe 3, and ensure the conveying power of the pulverized coal in the first separation pipe 2, the second separation pipe 3 and the dense-phase pipe 4.

[0035] In some embodiments, as Figure 1 and Figure 2 shown, the axis of the first separation pipe 2 forms a first included angle with the tangent line of the elbow section 11 at the connection position of the first separation pipe 2 and the elbow section 11, and the axis of the second separation pipe 3 forms a second included angle with the tangent line of the elbow section 11 at the connection position of the second separation pipe 3 and the elbow section 11. Both the first included angle and the second included angle are acute angles, and the first included angle is greater than the second included angle.

[0036] By restricting the angles of the first separation pipe 2 and the second separation pipe 3 relative to the elbow section 11, the resistance loss when the pulverized coal in the enrichment zone 12 of the elbow section 11 enters the first separation pipe 2 and the second separation pipe 3 respectively is reduced, that is, excessive kinetic energy loss is avoided, the conveying power of the dense-phase pulverized coal in the first separation pipe 2, the second separation pipe 3 and the dense-phase pipe 4 is ensured, and the first included angle and the second included angle decrease step by step, which conforms to the movement law of pulverized coal particles and is beneficial to improving the pulverized coal separation accuracy.

[0037] In some embodiments, the first included angle is not less than 25° and not greater than 35°, so as to ensure the efficient separation of larger pulverized coal particles and avoid excessive resistance loss.

[0038] Optionally, the angle of the first included angle can be 25°, 28°, 30°, 32° or 35°.

[0039] In some embodiments, the second included angle is not less than 20° and not greater than 30°, which is convenient for separating fine particles in the pulverized coal, further improving the concentration of the dense-phase pulverized coal collected in the dense-phase pipe 4, enhancing the separation efficiency of the dense-phase pulverized coal, and achieving a more refined classification.

[0040] Optionally, the angle of the second included angle can be 20°, 22°, 25°, 28° or 30°.

[0041] In some embodiments, the cross-sectional diameter of the first separation pipe 2 is not greater than one-tenth of the cross-sectional diameter of the elbow section 11, and the cross-sectional diameter of the second separation pipe 3 is not greater than one-tenth of the cross-sectional diameter of the elbow section 11. By restricting the pipe diameters of the first separation pipe 2 and the second separation pipe 3, the consumption of the conveying wind force of the main pulverized coal pipe 1 at the positions of the first separation pipe 2 and the second separation pipe 3 is reduced. While ensuring the concentration of the dense-phase pulverized coal in the first separation pipe 2 and the second separation pipe 3, it is ensured that the lean-phase pulverized coal obtained after the separation of the main pulverized coal air flow is normally conveyed in the main pulverized coal pipe 1.

[0042] In some embodiments, as Figure 1 and Figure 2 shown, the elbow section 11 includes an inlet 111 and an outlet 112. In the extending direction of the elbow section 11, the distance between the position where the first separation pipe 2 is connected to the elbow section 11 and the inlet 111 is not greater than one-half of the distance between the inlet 111 and the outlet 112, and the distance between the position where the second separation pipe 3 is connected to the elbow section 11 and the inlet 111 is not greater than seven-ninths of the distance between the inlet 111 and the outlet 112.

[0043] Specifically, at the first half section position of the elbow section 11, the pulverized coal particles just start to be affected by the centrifugal force and move towards the outer side wall, but have not been fully enriched yet, and the particle concentration is relatively low at this time. In the second half section of the elbow section 11, due to the centrifugal force, the pulverized coal particles are most enriched in the lower region of the outer side wall.

[0044] The first separation tube 2 is arranged at the first half position of the elbow section 11, that is, in the extending direction of the elbow section 11, the distance between the connection position of the first separation tube 2 and the elbow section 11 and the inlet 111 is not greater than half of the distance between the inlet 111 and the outlet 112. This can extract part of the dense-phase pulverized coal in advance, reduce the pulverized coal concentration in the subsequent air flow, and avoid the pulverized coal particle concentration at the position of the second separation tube 3 exceeding the maximum separation efficiency of the second separation tube 3, creating better conditions for the separation of the second separation tube 3;

[0045] The second separation tube 3 is arranged at the second half position of the elbow section 11, that is, in the extending direction of the elbow section 11, the distance between the connection position of the second separation tube 3 and the elbow section 11 and the inlet 111 is not less than half of the distance between the inlet 111 and the outlet 112. Since the axis of the second separation tube 3 forms a second included angle with the tangent line of the elbow section 11 at the connection position of the second separation tube 3 and the elbow section 11, for the convenience of installation, the distance between the connection position of the second separation tube 3 and the elbow section 11 and the inlet 111 is not greater than seven-ninths of the distance between the inlet 111 and the outlet 112. The elbow section 11 is a 90° elbow, that is, the included angle formed by the connection line between the inlet 111 of the elbow section 11 and the axis of the circle corresponding to the outer part of the elbow section 11 and the connection line between the connection position of the second separation tube 3 and the elbow section 11 and the axis of the circle corresponding to the outer part of the elbow section 11 is not greater than 70°. Arranging the second separation tube 3 at this position can efficiently capture the enriched pulverized coal particles and achieve the deep separation of the pulverized coal particles to ensure the pulverized coal particle concentration in the dense-phase pipe 4.

[0046] In some embodiments, it includes a controller, such as Figure 1 As shown, the first separation tube 2 is provided with a first valve 21, the second separation tube 3 is provided with a second valve 31, and the dense-phase pipe 4 is provided with a concentration detector. The first valve 21, the second valve 31, and the concentration detector are respectively electrically connected to the controller. The concentration detector is used to measure the pulverized coal concentration in the dense-phase pipe 4 when the first valve 21 or the second valve 31 is opened and transmit it to the controller. The controller is used to open the second valve 31 or the first valve 21 when the measured pulverized coal concentration is less than the set pulverized coal concentration.

[0047] Specifically, during operation, one of the first separation pipe 2 and the second separation pipe 3 is in a connected state. The pulverized coal in the elbow section 11 enters the dense-phase pipe 4 through the first separation pipe 2 or the second separation pipe 3. The concentration monitor on the dense-phase pipe 4 detects the concentration of the pulverized coal. For example, when the concentration of the pulverized coal in the dense-phase pipe 4 is lower than the set concentration of 0.8 kg / kg, that is, when the stable ignition condition of the dense phase cannot be satisfied, the second valve 31 or the first valve 21 is adjusted to open through the controller. At this time, the second separation pipe 3 or the first separation pipe 2 is connected, further increasing the concentration of the pulverized coal entering the dense-phase pipe 4. That is, during the operation process, according to the load level of the coal-fired power unit, three operation states can be correspondingly selected: the first separation pipe 2 is separately connected, the second separation pipe 3 is separately connected, and both the third separation pipe and the second separation pipe 3 are connected, so as to realize the multi-level precise control of the pulverized coal concentration in the dense-phase pipe 4, ensure the efficient separation of the dense-phase pulverized coal, ensure the combustion efficiency and stability of the separated dense-phase pulverized coal, further ensure the operation stability of the coal-fired power unit under various load operation states, and then improve the load regulation ability of the coal-fired power unit.

[0048] In some embodiments, such as Figure 1 and Figure 3 shown, the first separation pipe 2 includes a first pipe section 22 and a second pipe section 23. A Venturi tube 5 is provided between the first pipe section 22 and the second pipe section 23. The Venturi tube 5 includes a throat section 51, and an air guiding pipe 6 is connected to the throat section 51.

[0049] Specifically, the first separation pipe 2 includes a first pipe section 22 and a second pipe section 23. The other end of the first pipe section 22 is connected to the elbow section 11, and the other end of the second pipe section 23 is connected to the dense-phase pipe 4. The first valve 21 is correspondingly arranged at one end of the first pipe section 22 close to the elbow section 11. As Figure 3 shown, the Venturi tube 5 includes an inlet section, a contraction section, a throat section 51 and a diffuser section arranged in sequence. The inlet section is connected to the first pipe section 22, the diffuser section is connected to the second pipe section 23, and the throat section 51 is communicated with an air inlet annular pipe. The air guiding pipe 6 is provided on the air inlet annular pipe. When the dense-phase pulverized coal separated in the first separation pipe 2 enters the contraction section, the flow rate of the dense-phase pulverized coal increases and the pressure decreases, forming a negative pressure area at the throat section (the smallest pipe diameter section). This low-pressure area will generate a suction force on the external gas, sucking the gas into the pipeline through the air guiding pipe 6 and the air inlet annular pipe. The sucked gas is fully mixed with the dense-phase pulverized coal at the throat and the diffuser section and flows together with the fluid, realizing the transportation or mixing of the gas. The high-efficiency suction and uniform mixing of the pulverized coal are realized through the negative pressure area generated by the Venturi tube 5, ensuring the efficient and stable transportation of the dense-phase pulverized coal, and further ensuring the stable ignition property of the dense-phase pulverized coal.

[0050] Optionally, a Venturi tube 5 is also provided on the second separation pipe 3, and the corresponding structure and setting method are the same as those of the Venturi tube 5 provided on the first separation pipe 2, and will not be elaborated here.

[0051] In some embodiments, a third separation pipe is included. The third separation pipe is disposed between the first separation pipe 2 and the second separation pipe 3 and there is at least one of them. Both ends of the third separation pipe are respectively connected to the elbow section 11 and the dense-phase pipe 4.

[0052] By providing the third separation pipe, a path for separating pulverized coal can be added between the first separation pipe 2 and the second separation pipe 3, further enhancing the separation effect of pulverized coal particles at the position of the enrichment zone 12 in the elbow section 11 and ensuring the concentration of pulverized coal in the dense-phase pipe 4.

[0053] Optionally, there is one, two or three third separation pipes.

[0054] In some embodiments, the axis of the third separation pipe is arranged at a third included angle with the tangent line at the connection position of the third separation pipe and the elbow section 11. The third included angle is less than the first included angle and greater than the second included angle. By restricting the inclination angle of the third separation pipe relative to the elbow section 11, the separation effect of the third separation pipe on pulverized coal is ensured, and the resistance loss when pulverized coal enters the third separation pipe in the enrichment zone 12 of the elbow section 11 is reduced, that is, excessive kinetic energy loss is avoided, and the conveying power of dense-phase pulverized coal in the third separation pipe and the dense-phase pipe 4 is ensured.

[0055] The multi-stage pulverized coal concentration enhancer according to the embodiments of the present invention has the following advantages: efficient separation of thick and thin pulverized coal is achieved through the first separation pipe and the second separation pipe, and further, the pulverized coal concentration of the separated dense-phase pulverized coal is ensured, the combustion efficiency and stability of the dense-phase pulverized coal are improved, the load regulation ability of the coal-fired power unit is significantly improved, and its peak shaving flexibility is enhanced.

[0056] The pulverized coal combustion system according to the embodiments of the present invention will be described below.

[0057] The pulverized coal combustion system according to the embodiments of the present invention includes the multi-stage pulverized coal concentration enhancer according to any one of the above embodiments.

[0058] The pulverized coal combustion system according to the embodiments of the present invention can ensure the efficient separation of thick and thin pulverized coal, ensure the concentration of the separated dense-phase pulverized coal, thereby ensuring the stable ignition and combustion efficiency of the dense-phase pulverized coal, significantly improving the load regulation ability of the coal-fired power unit, enhancing its peak shaving flexibility, and ensuring the operation reliability and stability of the coal-fired power unit under low-load operation conditions.

[0059] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0060] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0061] In the present invention, unless otherwise clearly specified and defined, the terms such as "mounted", "connected", "connected to", "fixed" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or communicable with each other; it may be directly connected, or indirectly connected through an intermediate medium, and may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0062] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0063] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0064] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A multi-stage pulverized coal concentrator, characterized in that Comprising: A main pulverized coal pipe, the main pulverized coal pipe including an elbow section, and an inner wall of an outer side portion of the elbow section defining an enrichment zone for enriching pulverized coal; A first separation pipe, a second separation pipe and a dense-phase pipe, the first separation pipe and the second separation pipe being connected to the elbow section corresponding to the enrichment zone and being spaced apart along an extending direction of the elbow section, and the other ends of the first separation pipe and the second separation pipe being respectively connected to the dense-phase pipe, the first separation pipe and the second separation pipe being configured to respectively separate the pulverized coal in the enrichment zone and convey it to the dense-phase pipe.

2. The multi-stage pulverized coal concentrator according to claim 1, wherein, An axis of the first separation pipe forms a first included angle with a tangent line of the elbow section at a connection position between the first separation pipe and the elbow section, an axis of the second separation pipe forms a second included angle with a tangent line of the elbow section at a connection position between the second separation pipe and the elbow section, both the first included angle and the second included angle are acute angles, and the first included angle is greater than the second included angle.

3. The multi-stage pulverized coal concentrator according to claim 2, wherein, The first included angle is not less than 25° and not greater than 35°, and / or, the second included angle is not less than 20° and not greater than 30°.

4. The multi-stage pulverized coal concentrator according to claim 1, wherein, A cross-sectional diameter of the first separation pipe is not greater than one tenth of a cross-sectional diameter of the elbow section, and a cross-sectional diameter of the second separation pipe is not greater than one tenth of the cross-sectional diameter of the elbow section.

5. The multi-stage pulverized coal concentrator according to claim 1, characterized in that, The elbow section includes an inlet and an outlet. In an extending direction of the elbow section, a distance between a position where the first separation pipe is connected to the elbow section and the inlet is not greater than one half of a distance between the inlet and the outlet, and a distance between a position where the second separation pipe is connected to the elbow section and the inlet is not greater than seven ninths of the distance between the inlet and the outlet.

6. The multi-stage pulverized coal concentrator according to claim 1, wherein Comprising a controller, a first valve is provided on the first separation pipe, a second valve is provided on the second separation pipe, a concentration detector is provided on the dense-phase pipe, the first valve, the second valve and the concentration detector are respectively electrically connected to the controller, the concentration detector is configured to measure a pulverized coal concentration in the dense-phase pipe and convey it to the controller when the first valve or the second valve is opened, and the controller is configured to open the second valve or the first valve when the measured pulverized coal concentration is less than a set pulverized coal concentration.

7. The multi-stage pulverized coal concentrator according to claim 1, characterized in that, The first separation pipe includes a first pipe section and a second pipe section, a Venturi tube is provided between the first pipe section and the second pipe section, the Venturi tube includes a throat section, and an induced air pipe is connected to the throat section.

8. The multi-stage pulverized coal concentrator according to claim 2, wherein, Comprising a third separation pipe, the third separation pipe is provided between the first separation pipe and the second separation pipe and at least one is provided, and both ends of the third separation pipe are respectively connected to the elbow section and the dense-phase pipe.

9. The multi-stage pulverized coal concentrator according to claim 8, wherein, An axis of the third separation pipe forms a third included angle with a tangent line of the elbow section at a connection position between the third separation pipe and the elbow section, the third included angle is less than the first included angle and greater than the second included angle.

10. A pulverized coal combustion system, characterized in that, Comprising the multi-stage pulverized coal concentrator according to any one of claims 1-9.

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