A pulverized coal graded flameless combustion device coupled with thick-lean separation

Abstract

The present invention discloses a pulverized coal graded flameless combustion device coupled with dense-lean separation, comprising: a primary air nozzle for conveying pulverized coal and primary air into a combustion chamber; a secondary air nozzle and a tertiary air nozzle for conveying secondary air and tertiary air into the combustion chamber, respectively, wherein the secondary air and the tertiary air are high-speed oxidant airflow and high-temperature oxidant airflow, respectively; the secondary air nozzle is coaxially arranged inside the tertiary air nozzle, the primary air nozzle is evenly distributed around the tertiary air nozzle, and a separation mechanism is provided inside the primary air nozzle for separating the pulverized coal airflow into a dense pulverized coal airflow and a lean pulverized coal airflow, wherein the dense pulverized coal airflow is closer to the oxidant airflow. On the one hand, the present invention reduces the energy consumption and cost of the flameless combustion technology through an oxidant injection method that cooperates with external preheating and internal speed increase, and on the other hand, promotes pulverized coal ignition by dense-lean separation of the pulverized coal airflow, shortening the ignition delay and the flame floating distance.

Description

Technical Field

[0001] The invention belongs to the technical field of coal combustion, and in particular relates to a pulverized coal graded flameless combustion device coupled with thick-lean separation. Background Art

[0002] As the emission requirements for nitrogen oxides become increasingly stringent, controlling NOx emissions has become a research focus in the field of environmental protection. 3 To meet the ultra-low emission limit requirements, the development of new low-nitrogen combustion technology and burner design is imminent.

[0003] MILD combustion, as an advanced combustion technology, has attracted widespread attention for its stable combustion process and low NOx emissions. This technology uses high-speed jets to entrain high-temperature flue gases, creating intense flue gas circulation within the furnace. This significantly dilutes the fuel and oxidizer, expands the combustion zone, and reduces peak temperatures and oxygen concentrations, thereby suppressing NOx formation. However, MILD combustion presents two major challenges in its application: 1) The oxidizer requires high-temperature preheating and high-velocity injection, increasing energy consumption and costs; and 2) the non-premixed combustion method prevents the fuel and oxidizer jets from forming a stable flame before they converge. Consequently, significant flame lift occurs near the burner outlet, impacting combustion stability. Summary of the Invention

[0004] Purpose of the invention: In order to solve the above problems, the present invention provides a pulverized coal graded flameless combustion device coupled with thick and thin separation. On the one hand, the oxidant injection method with coordinated external preheating and internal speed increase is used to reduce the energy consumption and cost of the flameless combustion technology. On the other hand, the pulverized coal airflow is separated into thick and thin parts to promote the ignition of the pulverized coal, shorten the ignition delay and the flame floating distance.

[0005] Summary of the invention: To achieve the above-mentioned objectives, the present invention provides a pulverized coal graded flameless combustion device coupled with thick-lean separation, comprising a combustion chamber, a primary air nozzle, a secondary air nozzle, and a tertiary air nozzle, wherein the primary air nozzle is used to convey pulverized coal and primary air into the combustion chamber, and the secondary air nozzle and the tertiary air nozzle are used to convey secondary air and tertiary air into the combustion chamber, respectively, wherein the secondary air and the tertiary air are respectively a high-speed oxidant airflow and a high-temperature oxidant airflow;

[0006] The secondary air nozzle is coaxially arranged inside the tertiary air nozzle, and the primary air nozzle is evenly distributed around the tertiary air nozzle. A separation mechanism is provided in the primary air nozzle for separating the initial pulverized coal airflow (primary air carrying pulverized coal) into a concentrated pulverized coal airflow and a lean pulverized coal airflow, wherein the concentrated pulverized coal airflow is closer to the middle oxidant airflow (secondary air and tertiary air).

[0007] Specifically, the separation mechanism includes a first separation block, which is laterally arranged on the inner wall of the primary air nozzle away from the tertiary air nozzle, and axially located in the middle of the primary air nozzle or closer to the outlet end of the primary air nozzle, thereby dividing the initial coal powder airflow into two streams of thick and thin coal powder airflows.

[0008] Furthermore, the cross-section of the first separation block is triangular, having an upper slope θ1 and a lower slope θ2 relative to the inner wall of the primary air nozzle, wherein the upper slope θ1 is closer to the inlet end of the primary air nozzle, θ1 is 120°~150°, and θ2 is 135°~160°.

[0009] Specifically, the separation mechanism further includes a second separation stopper, which is laterally arranged in the middle of the primary air nozzle and axially closer to the outlet of the primary air nozzle than the first separation stopper, thereby further enhancing the degree of separation.

[0010] Furthermore, the cross section of the second separation block is rectangular, and its slope θ3 relative to the cross section of the primary air nozzle is 5° to 25°.

[0011] Specifically, the secondary air nozzle adopts a converging nozzle structure, comprising an inlet section, a contracting section, and an outlet section that are sequentially connected, with the diameter ratio of the outlet section to the inlet section being 1 / 3 to 1 / 2. The internal high-speed jet generates a strong internal circulation and entrainment of high-temperature flue gas within the combustion chamber, thereby diluting the oxidant and preheating the pulverized coal particles to achieve flameless combustion.

[0012] Furthermore, the tertiary air nozzle is equipped with a swirler, which includes an inner swirl ring, guide vanes, and an outer swirl ring. The guide vanes are installed between the inner and outer swirl rings and have a blade inclination angle of 15° to 25°. The addition of the swirler enhances the mixing of pulverized coal and oxidant at the burner outlet, alleviates the problem of flame lift caused by slow preheating of pulverized coal particles, and promotes flame propagation.

[0013] Furthermore, a quaternary air nozzle is installed on the downstream sidewall of the combustion chamber to deliver quaternary air into the combustion chamber. Located upstream of the flue gas recirculation area, the quaternary air nozzle, as part of the air staging technology, helps reduce NOx emissions. It also increases airflow momentum in the downstream recirculation area, further expanding the recirculation area and promoting faster flameless combustion.

[0014] Specifically, the distribution positions of the four secondary air nozzles correspond to the primary air nozzles, and their inclination angles α relative to the combustion chamber wall are 30° to 45°.

[0015] Specifically, the primary air accounts for 5% to 10%, the secondary air accounts for 60% to 70%, the tertiary air accounts for 5% to 10%, and the quaternary air accounts for 20% to 25%. Under multi-layer staged combustion, a weakly reducing atmosphere is created in the main reaction zone, suppressing the oxidation of fuel nitrogen (Fuel-N). More coke particles remain in the main reaction zone, promoting heterogeneous NOx reduction and further reducing NOx emissions.

[0016] Beneficial effects:

[0017] 1. This invention utilizes a pulverized coal DC burner as a dense-lean separation burner equipped with a blunt body. This separates the pulverized coal particles before entering the furnace into two streams of varying density. The dense pulverized coal stream is closer to the high-temperature oxidant jet (tertiary air), ensuring that more pulverized coal is drawn into the high-temperature zone for combustion. This promotes contact between the pulverized coal particles and the oxidant, reduces the preheating time of the pulverized coal particles, facilitates the formation of a stable flame at the burner outlet, and shortens the flame's floating distance. This configuration improves ignition and combustion of low-quality, low-volatile coal and has a wide range of applications.

[0018] 2. This invention utilizes a composite nozzle with a high-temperature, high-speed oxidizer jet, consisting of a normal-temperature, high-speed jet on the inside and a high-temperature, low-speed jet on the outside. This allows the pulverized coal to initially contact the high-temperature oxidizer on the outside, promoting ignition and flame propagation. The high-speed jet on the inside then entrains the high-temperature flue gas, diluting the oxidizer and preheating the coal particles to achieve flameless combustion. Compared to traditional methods of preheating the entire oxidizer and injecting it at high speed, this invention only requires partial oxidizer preheating and acceleration, reducing process energy consumption and costs during flameless combustion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the pulverized coal graded flameless combustion device in an embodiment of the present invention;

[0020] Figure 2 2. A top view of a pulverized coal graded flameless combustion device according to an embodiment of the present invention;

[0021] Figure 3 a to 3c are schematic structural diagrams of the primary air nozzle, the first separation block and the second separation block in the embodiment of the present invention respectively;

[0022] Figure 4 Schematic diagram of the structure of the secondary air nozzle and the tertiary air nozzle in an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the structure of the four-secondary air nozzle in an embodiment of the present invention;

[0024] Figure 6Schematic diagram of flue gas circulation in a pulverized coal graded flameless combustion device according to an embodiment of the present invention;

[0025] The figure includes: 1. primary air nozzle, 2. secondary air nozzle, 3. tertiary air nozzle, 4. quaternary air nozzle, 5. combustion chamber, 11. first separation block, 12. second separation block, 31. swirler. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0027] Reference Figure 1 This embodiment provides a pulverized coal graded flameless combustion device coupled with thick-lean separation, which mainly includes a combustion chamber 5 and a primary air nozzle 1, a secondary air nozzle 2, a tertiary air nozzle 3, and a quaternary air nozzle 4 connected to the combustion chamber 5, wherein the primary air nozzle 1 is used to transport pulverized coal and primary air into the combustion chamber 5, and the secondary air nozzle 2, the tertiary air nozzle 3, and the quaternary air nozzle 4 are used to transport secondary air, tertiary air, and quaternary air into the combustion chamber 5, respectively.

[0028] Specifically, the primary air nozzle 1, secondary air nozzle 2, and tertiary air nozzle 3 are all positioned upstream of the combustion chamber 5. The secondary air nozzle 2 is coaxially positioned within the tertiary air nozzle 3, the primary air nozzle 1 is evenly distributed around the tertiary air nozzle 3, and the quaternary air nozzle 4 is positioned on the downstream sidewall of the combustion chamber 5. Furthermore, a separation mechanism is provided within the primary air nozzle 1 for separating the initial pulverized coal airflow into a high-speed, concentrated pulverized coal airflow and a low-speed, lean pulverized coal airflow, with the high-speed, concentrated pulverized coal airflow being closer to the central oxidant jet. The initial pulverized coal airflow here refers to the primary air carrying the pulverized coal, and the high and low speeds, and the concentrated and lean pulverized coal airflows after separation are all relative to the initial pulverized coal airflow.

[0029] For example, referring to Figure 2 、 Figure 3a. There are four primary air nozzles 1, symmetrically arranged around the tertiary air nozzle 3. Two separation blocks are installed inside the primary air nozzles 1. After the initial pulverized coal airflow encounters the first separation block 11, it is split into two pulverized coal airflows due to the presence of a blunt body. After passing through the second separation block 12, the separation between the two airflows is further strengthened. As a result, a high-speed concentrated pulverized coal airflow (towards the inside) and a low-speed lean pulverized coal airflow (towards the outside) are formed at the burner (i.e., the primary air nozzle 1) outlet. The high-speed concentrated pulverized coal airflow is closer to the central oxidant jet (secondary and tertiary air), making it easier to be drawn into the main reaction zone and react with the oxidant, promoting pulverized coal ignition and shortening ignition delay. For low-volatile pulverized coal, pulverized coal particles are difficult to ignite. The concentrated-lean separation method ensures that more pulverized coal enters the high-temperature zone, promoting contact between pulverized coal particles and oxygen, thereby improving combustion stability.

[0030] Reference Figure 3 a. The first separation block 11 is arranged on the inner wall of the primary air nozzle 1 away from the tertiary air nozzle 3 in the horizontal direction, and is located in the middle of the primary air nozzle 1 or closer to the outlet end of the primary air nozzle 1 in the axial direction; the second separation block 12 is arranged in the middle of the primary air nozzle 1 in the horizontal direction, and is closer to the outlet end of the primary air nozzle 1 than the first separation block 11 in the axial direction, thereby further strengthening the separation degree. Figure 3 b. Figure 3 c. The first separation block 11 has a triangular cross-section with an upper slope θ1 and a lower slope θ2 relative to the inner wall of the primary air nozzle 1. The upper slope θ1 is closer to the inlet of the primary air nozzle 1 and is 120° to 150°, while θ2 is 135° to 160°. The second separation block 12 has a rectangular cross-section with a slope θ3 of 5° to 25° relative to the cross-section of the primary air nozzle 1. Other bluff structures can also be used to achieve concentrated and diluted separation of the pulverized coal airflow, thereby promoting pulverized coal ignition and shortening ignition delay.

[0031] Specifically, the middle oxidant nozzle is divided into two nozzles, the inner and outer nozzles, namely the secondary air nozzle 2 and the tertiary air nozzle 3, wherein the secondary air nozzle 2 is used to transport a normal temperature high-speed oxidant jet (normal temperature is about 303K, and the injection speed is greater than 100m / s), and the tertiary air nozzle 3 is used to transport a preheated low-speed oxidant airflow (preheating temperature is greater than 1000K, and the injection speed is about 26m / s). The reason for this arrangement is that the preheated oxidant airflow on the outer side first comes into contact with the high-speed concentrated coal powder airflow, promoting the ignition and flame propagation of the coal powder particles, and then the high-speed jet on the inner side generates a strong internal circulation in the combustion chamber 5 to entrain high-temperature flue gas, thereby diluting the oxidant and preheating the coal powder particles to achieve a flameless combustion state. Compared with the traditional oxidant jet that is fully preheated and injected at high speed, only part of the oxidant is accelerated and preheated here, which greatly reduces energy consumption and cost.

[0032] Reference Figure 4 The secondary air nozzle 2 adopts a convergent nozzle structure, comprising an inlet section, a contracting section, and an outlet section, which are sequentially connected. The diameter ratio of the outlet section to the inlet section is 1 / 3 to 1 / 2. Furthermore, a swirler 31 is provided within the tertiary air nozzle 3. The swirler 31 comprises an inner swirl ring, guide vanes, and an outer swirl ring. The outer swirl ring is fixedly mounted on the inner wall of the tertiary air nozzle 3, and the middle of the inner swirl ring passes through the secondary air nozzle 2. This arrangement is due to the fact that after the high-temperature oxidant gas flows through the turbine guide vanes, a strong recirculation zone is generated near the burner outlet. This ensures sufficient mixing of the pulverized coal and the high-temperature oxidant, promotes contact between the pulverized coal particles and the oxidant, and facilitates ignition and flame propagation of the pulverized coal particles. Simultaneously, the circulating flue gas within the recirculation zone dilutes the oxidant concentration, which helps suppress NOx generation. For example, there are six guide vanes, each approximately 1 mm thick and 20 mm high, with a blade inclination angle of 15° to 25°.

[0033] Compared to the traditional flameless combustion process in which all the oxidants are directly preheated and injected at high speed (preheating temperature is about 1573K, injection speed is about 65m / s), the present invention only needs to preheat and accelerate part of the oxidant to achieve flameless combustion. Specifically, the oxidant is divided into two parts and injected into the furnace: one part goes through the secondary air nozzle 2 to achieve high-speed injection (injection speed>100m / s), and the other part goes through the tertiary air nozzle 3 to achieve high-temperature injection (preheating temperature>1000K) and is combined with a swirler to ensure that a stable flame is formed at the burner outlet. The high-speed injection of the secondary air is to promote the formation of strong flue gas circulation in the furnace and promote flameless combustion; the high temperature + swirl of the tertiary air is to promote flame propagation, shorten the flame floating distance, and improve combustion stability.

[0034] Specifically, refer to Figure 6 The quaternary air nozzle 4 is arranged on the downstream side wall of the combustion chamber 5 and is used to deliver the quaternary air to the recirculation area in the middle and downstream of the combustion chamber 5. By injecting the oxidant jet, the momentum of the recirculated flue gas jet is increased, which is conducive to promoting the continuous expansion of the flue gas recirculation area and ensuring that the unburned coal char particles upstream of the furnace are fully burned. For example, referring to Figure 2 、 Figure 5 There are four secondary air nozzles 4, each corresponding to a burner (ie, a primary air nozzle 1), and an inclination angle α relative to the side wall of the combustion chamber 5 is 30° to 45°.

[0035] Specifically, the primary, secondary, tertiary, and quaternary air constitute all the oxidants, and the gas components are all air, of which the primary air accounts for 5% to 10%, the secondary air accounts for 60% to 70%, the tertiary air accounts for 5% to 10%, and the quaternary air accounts for 20% to 25%. The proportion here can be the ratio of mass flow or volume flow, and the primary and quaternary air are both injected at room temperature and low speed (temperature of about 303K, injection speed of about 26m / s). Figure 6 Under multi-layer staged combustion, a weak reducing atmosphere is present in the main reaction zone, the oxidation process of fuel nitrogen (Fuel-N) is suppressed, and more coke particles remain in the main reaction zone, which is conducive to promoting the heterogeneous reduction of NOx, thereby further reducing NOx emissions.

[0036] In summary, the present invention configures the pulverized coal direct current burner as a double-blunt thick-lean separation burner to promote pulverized coal ignition and improve combustion uniformity; configures the high-temperature, high-speed oxidizer nozzle as a composite nozzle with normal-temperature, high-speed injection on the inner side and high-temperature, low-speed injection on the outer side to reduce energy consumption and cost; at the same time, a swirler 31 is provided in the outer oxidizer nozzle to increase the swirl intensity of the oxidizer, enhance the flame stability at the burner outlet, and further alleviate the flame floating problem; in addition, a fourth air nozzle 4 is installed on the downstream side wall of the combustion chamber 5 to further reduce NOx emissions.

[0037] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A pulverized coal graded flameless combustion device coupled with thick and thin separation, characterized in that: It includes a combustion chamber, a primary air nozzle, a secondary air nozzle and a tertiary air nozzle, wherein the primary air nozzle is used to transport pulverized coal and primary air into the combustion chamber, and the secondary air nozzle and the tertiary air nozzle are used to transport secondary air and tertiary air into the combustion chamber, respectively, wherein the secondary air and the tertiary air are respectively a high-speed oxidant airflow and a high-temperature oxidant airflow; The secondary air nozzle is coaxially arranged inside the tertiary air nozzle, and the primary air nozzle is evenly distributed around the tertiary air nozzle. A separation mechanism is provided in the primary air nozzle for separating the initial pulverized coal airflow into a concentrated pulverized coal airflow and a lean pulverized coal airflow, wherein the concentrated pulverized coal airflow is closer to the middle oxidant airflow.

2. The pulverized coal graded flameless combustion device according to claim 1, characterized in that: The separation mechanism includes a first separation block, which is laterally arranged on the inner wall of the primary air nozzle away from the tertiary air nozzle, and axially located in the middle of the primary air nozzle or closer to the outlet end of the primary air nozzle.

3. The pulverized coal graded flameless combustion device according to claim 2, characterized in that: The cross-section of the first separation block is triangular, and has an upper slope θ1 and a lower slope θ2 relative to the inner wall of the primary air nozzle, wherein the upper slope θ1 is closer to the inlet end of the primary air nozzle, θ1 is 120°~150°, and θ2 is 135°~160°.

4. The pulverized coal graded flameless combustion device according to claim 2, characterized in that: The separation mechanism further includes a second separation stopper, which is laterally arranged in the middle of the primary air nozzle and axially closer to the outlet end of the primary air nozzle than the first separation stopper.

5. The pulverized coal graded flameless combustion device according to claim 4, characterized in that: The cross section of the second separation block is rectangular, and its slope θ3 relative to the cross section of the primary air nozzle is 5° to 25°.

6. The pulverized coal graded flameless combustion device according to claim 1, characterized in that: The secondary air nozzle adopts a convergent nozzle structure, which includes an inlet section, a contraction section and an outlet section connected in sequence, wherein the diameter ratio of the outlet section to the inlet section is 1 / 3 to 1 / 2.

7. The pulverized coal graded flameless combustion device according to claim 1, characterized in that: A swirler is provided in the tertiary air nozzle, which includes a swirling inner ring, guide vanes and a swirling outer ring. The guide vanes are installed between the swirling inner ring and the swirling outer ring, and the blade inclination angle is 15° to 25°.

8. The pulverized coal graded flameless combustion device according to claim 1, characterized in that: A quaternary air nozzle is provided on the downstream side wall of the combustion chamber for conveying quaternary air into the combustion chamber.

9. The pulverized coal graded flameless combustion device according to claim 8, characterized in that: The distribution positions of the four secondary air nozzles correspond to those of the primary air nozzles, and their inclination angles α relative to the combustion chamber wall are 30° to 45°.

10. The pulverized coal graded flameless combustion device according to claim 8, characterized in that: The primary air accounts for 5% to 10%, the secondary air accounts for 60% to 70%, the tertiary air accounts for 5% to 10%, and the quaternary air accounts for 20% to 25%.

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