Pulverized coal grading flameless combustion device coupled with rich-lean separation

Abstract

The invention discloses a coal powder grading flameless combustion device coupled with rich-lean separation, which comprises a primary air spray pipe, a secondary air spray pipe, a secondary air spray pipe and a combustion chamber, the secondary air spray pipe and the tertiary air spray pipe are respectively used for conveying secondary air and tertiary air into the combustion chamber, and the secondary air and the tertiary air are respectively high-speed oxidant airflow and high-temperature oxidant airflow; the secondary air spray pipe is coaxially arranged in the tertiary air spray pipe, the primary air spray pipes are uniformly distributed around the tertiary air spray pipe, a separation mechanism is arranged in each primary air spray pipe and is used for separating pulverized coal airflow into thick pulverized coal airflow and thin pulverized coal airflow, and the thick pulverized coal airflow is closer to oxidant airflow. On one hand, the energy consumption and the cost of a flameless combustion technology are reduced through an oxidizing agent injection mode of cooperative cooperation of outer side preheating and inner side speed increasing, and on the other hand, pulverized coal ignition is promoted and the ignition delay and the flame floating distance are shortened through dense-thin separation of pulverized coal airflow.

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 requirements for nitrogen oxide emissions 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] As an advanced combustion technology, MILD combustion is favored for its stable combustion process and low NOx emissions. This technology uses high-speed jets to entrain high-temperature flue gas, forming a strong flue gas internal circulation in the furnace, greatly diluting the fuel and oxidant, expanding the combustion area, reducing the peak temperature and oxygen concentration, and thus inhibiting NOx generation. However, there are two main problems with flameless combustion in its application: 1) The oxidant needs to be preheated at high temperature and injected at high speed, which increases additional energy consumption and cost; 2) The non-premixed combustion method causes the fuel jet and the oxidant jet to be unable to form a stable flame propagation before the two meet, so there is obvious flame floating near the burner outlet, affecting the combustion stability. Summary of the invention

[0004] Purpose of the invention: In order to solve the above-mentioned 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 pulverized coal and shorten the ignition delay and the flame floating distance.

[0005] Invention content: To achieve the above-mentioned purpose, the present invention provides a pulverized coal graded flameless combustion device coupled with thick-thin 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 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 a high-speed oxidant airflow and a high-temperature oxidant airflow, respectively;

[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 inside 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 also includes a second separation stopper, which is arranged in the middle of the primary air nozzle in the transverse direction and is closer to the outlet of the primary air nozzle in the axial direction than the first separation stopper, so as to further enhance 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, 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. The inner high-speed jet generates a strong internal circulation entrainment of high-temperature flue gas in the combustion chamber, thereby diluting the oxidant and preheating the coal powder particles to achieve a flameless combustion state.

[0012] Furthermore, a swirler is provided in the tertiary air nozzle, which includes a swirling inner ring, a guide vane and a swirling outer ring, and the guide vane is installed between the swirling inner ring and the swirling outer ring, and the blade inclination angle is 15° to 25°. By adding a swirler, the mixing of coal powder and oxidant at the burner outlet is enhanced, the flame floating problem caused by slow preheating of coal powder particles is alleviated, and flame propagation is promoted.

[0013] Furthermore, a quaternary air nozzle is provided on the downstream side wall of the combustion chamber for conveying quaternary air into the combustion chamber. The quaternary air nozzle is located upstream of the flue gas internal circulation area. On the one hand, as part of the air classification technology, it is beneficial to reduce NOx emissions. On the other hand, it can increase the airflow momentum in the downstream recirculation area, further expand the recirculation area, and promote faster realization of the flameless combustion state.

[0014] Specifically, 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°.

[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 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 heterogeneous reduction of NOx, thereby further reducing NOx emissions.

[0016] Beneficial effects:

[0017] 1. The present invention sets the coal powder DC burner as a thick and thin separation burner equipped with a blunt body to separate the coal powder particles before entering the furnace into two coal powder flows with different thick and thin, wherein the thick coal powder side is closer to the high-temperature oxidant jet (tertiary air), ensuring that more coal powder is concentrated and sucked into the high-temperature area for combustion, promoting the contact between coal powder particles and oxidant, reducing the preheating time of coal powder particles, facilitating the formation of a stable flame at the burner outlet, and shortening the flame floating distance. For low-quality coal with low volatile matter, this setting can improve its ignition and combustion, and has a wide range of applications.

[0018] 2. The present invention sets the high-temperature and high-speed oxidant nozzle as a composite nozzle with normal-temperature high-speed injection inside and high-temperature low-speed injection outside, so that the coal powder first contacts the high-temperature oxidant outside, thereby promoting the ignition and flame propagation of the coal powder particles, and then the high-speed flue gas is entrained by the high-speed jet inside to dilute the oxidant and preheat the coal powder particles to achieve a flameless combustion state. Compared with the traditional method of preheating all and injecting the oxidant at high speed, the present invention only needs to preheat and accelerate part of the oxidant to reduce the process energy consumption and cost in the flameless combustion process. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 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 the embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the structure of the four-air nozzle in the 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 The present embodiment provides a pulverized coal graded flameless combustion device coupled with thick-thin 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, the secondary air nozzle 2, and the tertiary air nozzle 3 are all arranged upstream of the combustion chamber 5, wherein the secondary air nozzle 2 is coaxially arranged inside 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 arranged on the downstream side wall of the combustion chamber 5. Furthermore, a separation mechanism is provided in the primary air nozzle 1, which is used to separate the initial pulverized coal airflow into a high-speed concentrated pulverized coal airflow and a low-speed light pulverized coal airflow, wherein the high-speed concentrated pulverized coal airflow is closer to the middle oxidant jet. The initial pulverized coal airflow here refers to the primary air carrying pulverized coal, and the high speed and low speed, concentrated and light after separation are all relative to the initial pulverized coal airflow.

[0029] For example, refer to Figure 2 , Figure 3a. There are four primary air nozzles 1, which are symmetrically arranged around the tertiary air nozzle 3. At the same time, two separation blocks are installed inside the primary air nozzle 1. After the initial coal powder airflow encounters the first separation block 11, it is divided into two coal powder airflows due to the presence of the blunt body. After the two airflows pass through the second separation block 12, the degree of separation is further strengthened. Therefore, a high-speed concentrated coal powder airflow (inside) and a low-speed light coal powder airflow (outside) will be formed at the outlet of the burner (i.e., the primary air nozzle 1). The high-speed concentrated coal powder airflow is closer to the middle oxidant jet (secondary air and tertiary air), and is easily sucked into the main reaction zone and then reacts with the oxidant, promoting coal powder ignition and shortening ignition delay. For low-volatile coal powder, coal powder particles are difficult to ignite. The concentrated and light separation method can ensure that more coal powder enters the high-temperature zone, promotes the contact of coal powder particles with more oxygen, and improves combustion stability.

[0030] Reference Figure 3 a. The first separation block 11 is disposed on the inner wall of the primary air nozzle 1 away from the tertiary air nozzle 3 in the transverse 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 disposed in the middle of the primary air nozzle 1 in the transverse 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 enhancing the degree of separation. Figure 3 b. Figure 3 c. The cross section of the first separation block 11 is triangular, and has an upper slope θ1 and a lower slope θ2 relative to the inner wall of the primary air nozzle 1, wherein the upper slope θ1 is closer to the inlet end of the primary air nozzle 1, θ1 is 120° to 150°, and θ2 is 135° to 160°; the cross section of the second separation block 12 is rectangular, and its slope θ3 relative to the cross section of the primary air nozzle 1 is 5° to 25°. In addition, other blunt body structures can also be used to achieve the separation of the thick and thin coal powder airflow to promote the ignition of coal powder and shorten the 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 convey the normal temperature high-speed oxidant jet (normal temperature is about 303K, the injection speed is>100m / s), and the tertiary air nozzle 3 is used to convey the preheated low-speed oxidant airflow (preheating temperature>1000K, injection speed is about 26m / s). The reason for this arrangement is that the preheated oxidant airflow on the outer side first contacts with the high-speed concentrated coal powder airflow, promoting the ignition and flame propagation of the coal powder particles, and then through the high-speed jet on the inner side, a strong internal circulation is generated in the combustion chamber 5 to entrain the high-temperature flue gas, thereby diluting the oxidant and preheating the coal powder particles to achieve a flameless combustion state. Compared with the traditional full preheating and high-speed injection of the oxidant jet, 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 converging 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. Further, a swirler 31 is provided in the tertiary air nozzle 3, and the swirler 31 is composed of a swirl inner ring, a guide vane and a swirl outer ring. The swirl outer ring is fixedly assembled on the inner wall of the tertiary air nozzle 3, and the middle of the swirl inner ring passes through the secondary air nozzle 2. The reason for this arrangement is that after the high-temperature oxidant airflow passes through the turbine guide vane, a strong recirculation zone is generated near the burner outlet, which ensures the full mixing of coal powder and high-temperature oxidant, promotes the contact between coal powder particles and oxidant, promotes the ignition of coal powder particles and flame propagation, and at the same time, the circulating flue gas in the recirculation zone dilutes the oxidant concentration, which is beneficial to suppressing the generation of NOx. Exemplarily, the number of guide vanes is six, the blade thickness is about 1 mm, the height is about 20 mm, and the blade inclination angle is 15° to 25°.

[0033] Compared with 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 injected into the furnace in two parts: 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 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 smoke 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 jet momentum of the recirculated flue gas is increased, which is conducive to promoting the continuous expansion of the flue gas recirculation area, while 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, primary air nozzle 1), and the 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 winds constitute all the oxidants, and the gas components are all air, of which the primary wind accounts for 5% to 10%, the secondary wind accounts for 60% to 70%, the tertiary wind accounts for 5% to 10%, and the quaternary wind accounts for 20% to 25%. The proportion here can be the ratio of mass flow or volume flow, and the primary and quaternary winds are both injected at normal temperature and low speed (the temperature is about 303K, and the injection speed is 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-thin separation burner to promote pulverized coal ignition and improve combustion uniformity; configures the high-temperature and high-speed oxidant nozzle as a composite nozzle with normal-temperature and high-speed injection on the inner side and high-temperature and low-speed injection on the outer side to reduce energy consumption and cost; at the same time, a swirler 31 is arranged in the outer oxidant nozzle to increase the swirl intensity of the oxidant, 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 above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pulverized coal graded flameless combustion device coupled with thick-thin separation, characterized in that: It comprises 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 high-speed oxidant airflow and high-temperature oxidant airflow, respectively; 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 inside 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 oxidant airflow in the middle.

2. The pulverized coal graded flameless combustion device according to claim 1, characterized in that: The separation mechanism includes a first separation stopper, 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 also includes a second separation stopper, which is arranged in the middle of the primary air nozzle in the transverse direction and is closer to the outlet end of the primary air nozzle in the axial direction 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 tapered nozzle structure, which includes an inlet section, a contraction section and an outlet section that are 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 arranged in the tertiary air nozzle, which comprises 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 fourth air nozzle is arranged on the downstream side wall of the combustion chamber for conveying the fourth air into the combustion chamber.

9. The pulverized coal graded flameless combustion device according to claim 8, characterized in that: The distribution position of the four secondary air nozzles corresponds to that of the primary air nozzles, and the inclination angle α thereof relative to the combustion chamber wall is 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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