WO2010083638A1 - Method for igniting pulverized coal in coal-fired boiler and burner thereof - Google Patents

Abstract

A method for igniting the pulverized coal in a coal-fired boiler and a burner thereof are provided, both of which belong to the technical field of the ignition of coal-fired boilers. The burner for igniting pulverized coal includes a primary air nozzle (1), through which a mixture of pulverized coal and air is blown into the furnace of the boiler, and an opposite fire outlet (9). The primary air nozzle (1) connects with a flow passage (2, 3). The flow passage (2, 3) is a passage having a step-shaped cross-section thereby the flow passage (2, 3) expands sharply. The mixture of pulverized coal and air can form circumfluence (B, C) in the flow passage (2, 3). An ignition component (8) is equipped on the wall of the circumfluence zone. The ignition component (8) firstly ignites the circumfluence (B, C) and then ignites the main current (A) by the ignited circumfluence (B, C), thus realize the ignition of all the pulverized coal current.

Description

 BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an ignition technique in a coal-fired boiler, and particularly to a method for igniting pulverized coal with low manufacturing cost, simple structure and simple operation. A burner and a method of igniting pulverized coal using the burner. BACKGROUND OF THE INVENTION In a coal-fired power plant, coal is ground into fine powder by a coal mill, and then blown into the furnace by air. Since the coal is difficult to catch fire, the furnace temperature is very low when the boiler is started, and the coal powder cannot be ignited. The furnace is heated to a considerable extent by oil or natural gas or artificial gas to inject the pulverized coal for combustion. In addition, the furnace temperature is also low under the low load of the boiler, and the combustion instability is also supported by oil or combustible gas. Due to the cyclical changes in the electrical load, the boiler starts and stops frequently, so that a large amount of oil is consumed in the start-up and low-load operation of the unit. Therefore, technologies that do not use oil or use less oil have been used in some power plants.

 The plasma igniter currently used uses a two-pole breakdown air with a voltage to generate a very high temperature plasma to ignite the pulverized coal, and can realize the startup of the power station boiler without using the oil completely, but because of its complicated structure and high investment cost, A 300MW boiler needs an investment of 4.5 million yuan. In addition, its operation is complicated, its service life is short, and there are many mechanical failures. Therefore, the maintenance cost is also quite large. Although it can save 100% oil, it can only save 75%. cost. In addition, its coal type has poor adaptability and cannot ignite coal that is difficult to catch fire. Plasma igniters have been used in more than 200 boilers.

 There is also a micro-oil igniter which uses compressed air to efficiently atomize the oil, and first ignites the coal powder in the coal-rich pulverized coal-air mixture (hereinafter referred to as the mixture) with a small amount of high-temperature gas generated by a high burning rate ( Primary ignition), then igniting the leaner mixture (secondary ignition) with the ignited mixture, and then igniting more of the mixture with the ignited "secondary" mixture (third stage ignition). This achieves the function of using a small amount of oil to a large amount of pulverized coal, which can save 95% of boiler start-up and low-load combustion-supporting oil. Although the micro-oil ignition technology is simpler than the plasma igniter, the system is still complicated. The number of control monitoring points is the same as that of the plasma igniter. Although the investment is only one-third of the plasma, there are still 130~ The huge 1.8 million yuan. It has been applied to 100 to 600 MW units.

In addition to the above-mentioned micro-oil igniter, there is also a high-temperature air oil-free igniter which uses an electromagnetic induction technique to apply an alternating magnetic field having a high magnetic flux density to a metal tube, causing eddy currents in the tube wall to generate heat, and then The air is heated through the tube, and the pulverized coal is heated by the heated air to ignite the pulverized coal. This technology investment cost is as high as that of plasma igniters and is currently used in a few power plants. In addition to the above three technologies that have been put into practical use, ignition technology such as resistance heating ignition, electric induction heating ignition and laser ignition are still in the laboratory stage. However, the aforementioned ignition techniques that do not use oil or use less oil have in common that the heating of all the mixtures to be ignited to the ignition point of the coal particles is the basic means, that is, the heating method, that is, the ignition thereof. The source acts directly on all the mixture to be ignited, so it needs to be ignited at a higher temperature (much higher than the ignition point of the coal particles), and more NOx pollution will be generated during the ignition process, and the supporting equipment will be complicated, and the cost will be complicated. High, therefore, there are disadvantages such as high investment cost, complicated structure, and poor adaptability of coal types to varying degrees. SUMMARY OF THE INVENTION An object of the present invention is to provide a burner for igniting pulverized coal for a coal-fired boiler which is low in manufacturing cost, simple in structure, simple in operation, and reduces NOx pollution.

 In order to achieve the above object, the specific content of the present invention is:

 The burner for igniting pulverized coal for a coal-fired boiler according to the present invention comprises: blowing a pulverized coal-air mixture into a primary air vent of the boiler furnace and an outlet of the opposite end, wherein the primary air vent is connected to a flow passage, and in the flow passage The pulverized coal-air can form a reflow, and an ignition element is mounted on the wall surface of the recirculation zone.

 Specifically, the first design structure is as follows: The burner for igniting the pulverized coal is a stepped passage as a whole, one end is a primary air nozzle, the other end is a fire outlet, and the other walls of the passage are closed; the stepped passage is provided a first flow path connected to the primary air outlet, a third flow path connected to the fire exit, and a second flow path between the first flow path and the third flow path, wherein the second flow path is larger than the first flow path The area suddenly expands, and the third-flow channel has a larger cross-sectional area than the first flow channel, but is smaller than the second flow channel cross-sectional area, between the first flow path and the second flow path, and between the second flow path and the third flow path. Connected by the wall of the head; the igniter element is disposed in whole or in sections on the inner wall of the top of the second flow path or on the inner wall surface of the third flow path adjacent to the second flow path.

 The first flow channel and the second flow channel are connected between the second flow channel and the third flow channel by a head wall.

 Wherein, the ignition element is disposed in whole or in sections on the inner wall surface of the third flow path adjacent to the second flow path.

 Wherein, the second flow channel is expanded on one side of the first flow channel.

 Wherein, the second flow channel suddenly expands in a vertical direction or a horizontal direction.

 Wherein, the second flow channel is enlarged on both sides of the first flow channel.

 Wherein, the second flow channel suddenly expands in a vertical direction or a horizontal direction.

The invention also provides a burner for multi-stage igniting pulverized coal, which is formed by connecting the burners of the first designed pulverized coal powder in series, and the burners are connected to each other. The multi-stage burner for igniting pulverized coal, the lower-stage burner is in communication with the fire exit of the first-stage burner through its upper wall surface or lower wall surface position. Specifically, the second design structure is: the burner for igniting the pulverized coal has a flow passage connected to the primary air nozzle as a transition tube with a gradually increasing cross section, and an opening angle formed by the wall of the transition tube and the axis of the flow passage α is greater than 12° and less than 90°.

 Specifically, the third design structure is as follows: The burner for igniting pulverized coal for the coal-fired boiler has a straight pipe connected to the primary air nozzle, and a bluff body is placed in the straight pipe or at the outlet.

 Another object of the present invention is to provide a method for igniting coal powder in a coal-fired boiler. The burner of any of the above structures is installed in the original burner position of the coal-fired boiler or other suitable position to the furnace, and the pulverized coal-air mixture is fed through the primary air nozzle, and the recirculation zone in the burner is first ignited by the ignition element. The pulverized coal-air mixture is further ignited by the ignited reflux, and a flame is injected into the boiler furnace from the outlet.

 Wherein, the ignition element adopts various ignition forms such as chemical energy, thermal energy, electric energy, and light energy.

 The method of generating reflux in a coal-fired boiler burner is also an important aspect of the present invention. Is to design the cross section of the burner flow passage in the form of the first type of step described above, or the second type of transition duct section of a sufficiently short cross section, or a third type of bluff body placed in or at the outlet of the burner Form, so that the gas entering from the primary air vent can produce backflow in the flow channel.

 Compared with the prior art, the features and effects of the present invention are:

1, the invention is based on the theory of flame stability (first ignited reflux) and design, which is _before: all ignition technology has substantial differences.

 2. Since the burner and the ignition method of the present invention are designed based on the theory of flame stability, since it has self-stabilizing ability, the supply of the external heat source can be stopped once the mixture gas is ignited, and the flame can be self-stabilized, that is, enter The mixture of burners will steadily ignite continuously. This self-stabilizing capability is not available in all existing ignition technologies, and this burner is essentially different from all ignition techniques in the prior art.

 3. Since the present invention only needs to ignite the reflux mixture, and because of the self-stabilizing ability, the external heat source is supplied for about 40 minutes, so that it can achieve 100% without oil ignition, and the energy consumption is also the lowest.

 4. The burner of the present invention expands in cross section to generate reflow, which can realize the mainstream of the ignition mixture at a lower temperature (<1000 ° C), has a simple structure and does not require the use of expensive heat-resistant steel, and thus has the lowest cost. That's about 1/10 of the micro-oil ignition technology.

 5. With the present invention, the mixture can be ignited at a lower temperature (&lt; 1000 °C), and thus NOx generation is also the lowest.

6. The primary ignition of the present invention is to ignite coal powder adjacent to the hot wall in the recirculation zone. Due to the low flow rate in the recirculation zone (1/10 of the main gas flow, 1/100 of the secondary recirculation) and due to turbulent eddy currents, The pulverized coal stays in the vicinity of the hot wall for a long time. Their ignition process is a "turbulent fluidized bed"; and only one pulverized coal in the recirculation zone is ignited. Due to the low reflux velocity, the velocity gradient at the boundary is also extremely low. The flame can quickly spread throughout the recirculation zone, which in turn ignites the main gas stream. Therefore, it can be reasonably inferred that all coals that can be burned on a fluidized bed can be stably burned on the burner. This function is also not available in all of the above ignition technologies.

 7. The present invention ignites the mixture at a lower temperature (<100 (TC) without a cooling system, and there is a portion higher than the ash melting point and a portion lower than the ash melting point at the same time in the burner, so its slagging probability BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a perspective view showing the structure of a burner for igniting pulverized coal according to the present invention.

Fig. 1B is a schematic view showing the internal section and working principle of the pulverized coal burner shown in Fig. 1A.

Fig. 2A is a schematic view showing the relationship between the position of the re-contact point and the airflow characteristic in the sudden expansion of one side of the present invention.

Fig. 2B is a schematic view showing the relationship between the position of the re-contact point and the airflow characteristic in the sudden expansion of both sides of the present invention.

Fig. 3A is a perspective view showing the combined structure of the secondary burner of the present invention.

Fig. 3B is a schematic view showing the profile and working principle of the pulverized coal burner A-A shown in Fig. 3A.

Figure 4 is a schematic perspective view showing the two-dimensional expansion of the burner for igniting pulverized coal according to the present invention.

Figure 5A: Schematic diagram of the opening angle of the wall of the transition section at 12-15°.

Fig. 5B: Schematic diagram of the opening angle formed by the walls of the transition pipe section being greater than 12-15°.

Figure 5C: Schematic diagram of the angle formed by the walls of the transition section at 90° or 180°.

Figure 6: Schematic diagram of the structure and working principle of the multi-stage burner of the present invention.

Fig. 7 is a schematic view showing the structure of a sudden expansion of both sides in the vertical and horizontal directions in the multi-stage burner of the present invention.

Fig. 8A is a schematic view showing the structure of placing a bluff body in the existing burner DC channel.

Fig. 8B is a schematic view showing the structure of placing a bluff body at the outlet of the existing burner DC channel. DETAILED DESCRIPTION OF THE INVENTION The present invention treats a pulverized coal-air mixture as a "premixed combustible gas" and applies a theory of stability with respect to a premixed combustible gas flame to a pulverized coal-air mixture. The invention blows the mixture into the primary air nozzle of the furnace as a Bunsen burner. (Bunsen burner is the basic device for studying the phenomenon of premixed combustible gas flame. According to the theory, the flame of a mixture is stabilized and the mixture is ignited. The mechanism of physics (fluid mechanics, heat transfer) is the same, the mechanism by which the flame is blown out is due to the large velocity at the boundary of the flame root. The gradient causes a large loss of tangential heat loss from the combustion wave. To stabilize or ignite a gas stream, sufficient heat is supplied outside the root of the burner outlet. The essential mechanism for igniting a gas stream is to allow the combustion wave to propagate across the entire gas stream across the flame root boundary layer where heat loss is significant.

 The solution to this concept is to allow the mixture to flow out of a primary air vent to an abruptly enlarged flow path to form a reflux, which is ignited to provide the desired heat to the primary gas stream.

 5A to 5C illustrate the meaning and configuration of the flow path in which the area is suddenly enlarged, and the formation of the reflow. In engineering applications, when a fluid flows from a pipe of smaller cross section into a pipe 3' having the same or different cross-section, the transition pipe section 2 is gradually changed in size and shape in order to reduce the pressure loss. ' (commonly known as "horn" "wedge tube" "day round place", etc.) to join, as shown in Figure 5A, at this time, the opening angle of the transition tube section 2' and the axis of the pipe section α is equal to or less than 12-15 °, the fluid will flow close to the pipe wall; and when the opening angle α is greater than 12-15°, the fluid begins to leave the transition 1 = wall surface, and in the larger section pipe 3 ' somewhere in contact with the pipe wall, called The contact point (point F shown in Fig. 5A) is such that a reflow can be formed between the main fluid and the exiting wall. At this time, if the fluid is a premixed combustible gas, igniting the reflux can ignite the main gas stream. When the opening angle of the transition tube 2' is as large as 90° (− side enlargement) or 180° (both sides are enlarged), or the length of the transition duct 2′ is as small as zero, a step on one side or both sides is suddenly expanded (Fig. 5c) As shown), the wall of the transition tube is actually a head wall which is perpendicular to the small section tube wall and the large section wall 3', and the two tubes are joined together, which is the step The wall forms a flow path in which the area suddenly expands or the step shape suddenly expands.

 The sudden expansion of the step shape can form a large recirculation zone within a small pipe length, so the burner adopts a step-shaped sudden expansion design, and a rectangular shape is adopted for the general case of the power plant boiler.

 In combination with the above principles, the following is a detailed description of the structural composition and the efficacies of the pulverized coal igniting burner of the present invention as follows:

 1A and FIG. 1B, a schematic view of a basic embodiment of a burner for igniting pulverized coal according to the present invention, which is a flow passage having two stages which are stepped abruptly in only one direction, wherein the primary air vent 1 (wall 5) The wall 7 of the flow passage 3 having a large cross section is coupled with the head wall (step wall) 12 to form a flow passage 3 in which the section of the section is suddenly enlarged, and the flow passage 3 is parallel to the flow passage of the other section. The flow path 2 (which is surrounded by the wall 6) which is small but smaller than the primary air vent is connected by the head wall 13, and the other step in the opposite direction is suddenly enlarged. The wall 5 of the spout 1, the head wall 12, the wall 7 of the flow channel 3, the head wall 13 and the wall 6 of the flow channel 2 constitute the body of the burner, recirculating in the inner wall surface of the flow channel 3 and in the flow channel 2. The inner wall surface is provided with the ignition element 8 (see Fig. 1B) in whole or in sections, and the outlet 2 of the flow path 2 is used to eject a burning flame. The function of the burner body is to generate two backflows and to provide support for the ignition element 8.

In operation, as shown in FIG. 1B, when the mixture flows from the primary air nozzle 1 into the burner body, As the section suddenly expands, the airflow leaves the wall and spreads. At the downstream of the flow channel 2, the re-contact point P re-contacts the wall of the flow channel 2, which is called the main airflow A, and its boundary is D (imaginary boundary line). Between the main airflow A and the stepped wall surface that is separated (i.e., below the wall of the head wall 12 and the flow channel 3 and below the head wall 13 and above the boundary line D), a recirculation zone is formed for the recirculation zone, wherein one reflow B and The main air flow flows back to the step surface. On the way, the second step is enlarged to expand the flow path 3, and a secondary reflow is formed at the top of the flow path 3 (: the inner wall surface disposed on the flow path 3 and the ignition element 8 of the inner wall surface of the flow path 2 ignite the reflow B and C The main air stream A is then ignited.

 The igniter element 8 is an electric group heating coil or a molybdenum disilicide heating element made of heat-resistant stainless steel, or may be heated by any other heating method to heat the recirculation zone or directly heated to reflow (including introducing a high-temperature gas in the recirculation zone). Reflux ignition. The igniting element can be placed in a high-temperature resistant thin-walled interlayer (using a Λ1Λ material) to be isolated from the high-temperature flue gas. The support structure of the igniter element 8 can also be made withdrawable, and the burner can be extracted after the pulverized coal is ignited. Its service life

 When the heating element 8 is heated, the mixture flows into the burner body from the primary air nozzle 1, and the heated wall can cause the mixture in the secondary recirculation C in the vicinity to ignite. Since the secondary reflow has a low velocity gradient at the wall surface, the heat is generated. The heat provided by element 8 and the hot wall allows the flame to cross the boundary layer between the reflow and the hot wall; and passes to the entire recirculation zone at reflux B and C. After the recirculation zone is ignited, its temperature rises rapidly through reflow. The boundary layer D of the main gas stream provides sufficient heat to the main gas stream A, thereby passing the flame to the center of the main gas stream A, and the entire gas stream is ignited, ejecting fire from the burner outlet 9 to the furnace. After the main gas stream is ignited, the recirculation zone B is no longer an unignited low temperature mixture but a burned and burning high temperature mixture, which continuously supplies heat to the boundary layer of the main gas stream, so that the primary air outlet is continuously discharged. The 'unburned mixture' of the (Benson nozzle) is ignited, at which point the supply of electricity to the heating element can be stopped and the flame can stabilize itself.

 The heating element 8 can be disposed on the inner wall surface of the recirculation zone (including the secondary recirculation zone), and its power density should be not less than 120 kw/m2, so that the heating element and the wall surface temperature reach 950 °C. The layout area and distribution can be appropriately reduced depending on the coal type. The best position for the layout is near the "re-contact point" and the secondary recirculation area.

 The length L3 of the flow path 3 should be less than 1/2 re-contact distance, and its height h3 should be smaller than the height h of the flow path 2.

 2A and 2B show the characteristic relationship when the airflow enters the one-side or double-sided section to suddenly enlarge the flow path, wherein the broken line represents the imaginary boundary line of the main airflow and the recirculation; H is the unilateral inlet height, and h is the step of sudden expansion. Height (the difference between the height of the single-sided large-area runner and the height of the one-sided inlet), f is the distance from the starting point of the wall of the large-flow head to the point of re-contact.

As shown in Fig. 2A and Fig. 2B, when the mixture flows into a flow area where the cross section is suddenly enlarged, the gas flow can be caused to flow back. Sudden expansion can be a sudden expansion on one side or a sudden expansion on both sides. In order to prevent external cold air from entering the recirculation zone, the length of the burner should be greater than the distance 1 from the contact point to the wall of the head. The distance 1 has the following approximate relationship with h/H.

 One-sided stepped enlargement

 ― 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0

 H

 丄 1.0 1.2 3.0 4.0 4.8 6.4 8 12 16

 H

 Double stepped enlargement

 ― 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0

 H

 ― 1.8 2.5 3.0 4.0 5.6 9.5 13.0 22.5 29

 H

 When the two-sided step is enlarged and the positions of the re-contact points on both sides are different, as shown in Fig. 2Β, <1, the above relationship is used for the distance of the larger re-contact point.

 Larger h/H can have a larger recirculation volume, which is conducive to the stability of the main airflow flame, but requires a larger burner length. Currently, h/H=1.0, visible on-site space and flame Stability requirements (primary wind speed change) Adjust according to the above data.

 In order to obtain a larger recirculation volume at the same h/H, thereby increasing its heat capacity and combustion rate, thereby improving the flame stability (adaptability to different primary wind speeds and coal types), downstream of the recirculation zone, That is, immediately adjacent to the step portion, a sudden expansion portion of the return passage, that is, a secondary recirculation portion (i.e., a portion above the flow passage 3 in Figs. 1A and 1B) is established. The second recirculation zone has a lower speed, and the coal particles stay longer and are more easily ignited.

 The sudden expansion of the main airflow can be expanded in the horizontal direction (z-axis) or the vertical direction (y-axis) (one-dimensional expansion, see Fig. 1A) or simultaneously in two directions (z-axis direction and y-axis direction are two-dimensionally expanded, See Figure 4). When expanding in a certain direction, it can be enlarged on one side or enlarged on both sides. The two-dimensional expansion can refer to the above-mentioned one-dimensional expansion.

3A and 3B, which is a second embodiment of the present invention, the utility of the same ignition energy and apparatus is used to increase the ignition capacity (burning amount/hour) of the burner. It consists of a burner that suddenly expands on one side (or both sides) in one basic embodiment (as a primary burner) and another burner that is enlarged on both sides (or one side) (as a secondary burner) in series to make. There is a primary air vent 1 and a secondary air vent 4 respectively, and the outlet of the primary burner is connected to the recirculation zone of the secondary burner. Like the primary burner, the secondary burner body is also composed of a plurality of wall faces and a plurality of seals. The head wall encloses a plurality of internal flow paths. It can produce primary and secondary reflow. The high temperature gas stream of the ignited primary burner and the reflux of the secondary mixture to be ignited, in the recirculation zone of the secondary burner, are mixed with each other at a relatively slow rate. The secondary mixed reflux is ignited by radiation and convection heat exchange to further ignite the primary gas stream of the secondary mixture as in the case of the primary burner, thereby achieving the purpose of improving the ignition capacity of the burner. Finally, the burned secondary mixture flows into the furnace through the secondary burner outlet 9. In this embodiment, the burner has a two-stage burner, but the process of being ignited is actually four-stage ignition: Reflux, primary primary flow, secondary reflux, and secondary primary flow.

 In Figure 3B, E11 is the mixture flowing into the primary burner, E12 is the primary mixture being ignited, and E13 is the ignited mixture flowing out of the primary burner and flowing into the secondary burner recirculation zone. E21 is the mixture flowing into the secondary burner, E22 is the ignited secondary mixture, and E23 is the ignited mixture flowing out of the secondary burner and flowing into the furnace. B1 is the recirculation zone of the primary burner. B2 is the recirculation zone of the secondary burner. P is the re-contact point of the primary burner, and P' is the re-contact point of the secondary burner.

 The cross-sectional size of the secondary burner depends on the amount of coal required. The length of the secondary burner at this time is determined by the following principles.

 The secondary burner has only one side that expands toward the primary airflow.

 Imagine the M line as a sudden expansion of the wall surface of the flow channel. Then, according to the above method, the re-contact point P1 of the flow path is suddenly enlarged in the imaginary area after the primary main airflow flows out, and the N-line is suddenly enlarged as the flow path. The wall surface, and then the above-mentioned method is used to determine the secondary main air flow. This imaginary area suddenly expands the re-contact point P2 of the flow path. At this time, the boundary of the primary airflow has an intersection point S (as shown in Fig. 3B), and the distance from the secondary primary airflow inlet is is, and the length of the secondary burner should not be less than fs.

 When the secondary burner is expanded in the other direction, the large value in the subsequent sum is determined as the minimum value of the burner length.

 If the actual space is allowed to be preferably in the direction opposite to the primary airflow or in the adjacent direction, abrupt expansion is performed and a secondary recirculation zone is added to improve flame stability.

According to the same principle, the outlet of the secondary burner can be connected to the recirculation zone of the lower (third stage) burner (see Figure 6), so that the combusted high temperature gas flowing from the secondary burner ignites the tertiary burner. The reflux causes further ignition of the primary gas stream of the tertiary burner. In Figure 6, Al, A2, A3 are the mixture of the first, second and third burners respectively, Pl, P2, P3, the re-contact point of the mixture of the first, second and third burners, Bl, B2, B3 For the recirculation zone of the first, second and third burners, S12 is one, the intersection S23 of the secondary mixture is two, the intersection of the three-stage mixture, and so on, and more burners are connected in this way. In this way, on the one hand, the ignition capacity of the burner series is improved, on the other hand, the number of burners with self-stabilizing capacity of the boiler is increased, and the flame stability of the entire furnace is improved, and the boiler is arranged on the four corners of the burner as long as the site permits. It is possible to connect all the primary air vents on one corner in this way. In this way, the entire furnace has an absolute flame holding capacity. It will be beneficial to the burning of inferior coal. The primary, secondary and tertiary burners are connected from bottom to top. If the flow passages of the secondary and tertiary burners cannot be suddenly expanded upward due to space constraints, abrupt expansion on both sides in the horizontal direction (already suddenly expanded downward) is performed to design the secondary and tertiary burners. As shown in Fig. 7, a secondary burner which suddenly expands to both sides in the horizontal direction, wherein the primary burner has a primary air nozzle 1, the secondary burner has a secondary air outlet 4, and the secondary burner has a third flow. The track 43 is expanded not only in the vertical direction (y-axis) but also in the horizontal direction ( _Z- axis).

 In general, the above two different structural embodiments are such that the mixture flows from a smaller cross-section passage primary air vent to a channel-shaped abruptly enlarged passage, resulting in a hydrodynamically known internal separation flow, thereby Part of the recirculation is formed (see Figure 1B). Since the flow rate in the recirculation zone is only 1/10 of the main gas flow and is easily ignited, the flow rate through the secondary recirculation zone is only 1/100 of the main gas flow (see Figure 1B). Therefore, its velocity gradient at the boundary is only 1/100 of the mainstream. In the present invention, another burner which is identical in principle can be referred to the structure of Fig. 5B. In contrast to the burner of the stepped abruptly enlarged passage, the cross section of the burner flow passage is designed to be sufficiently short in cross section. The form of the transition pipe section, wherein the wall angle α formed by the wall of the transition pipe section 2' and the pipe section axis is greater than 12° less than 90°, and the length of the transition pipe section 2′ is sufficiently short. In this configuration, the air flow forms a recirculation zone between the transition pipe and the re-contact point of the larger section pipe 3', and the ignition element is mounted in the return zone. However, this design structurally lengthens the burner and has a small volume in the recirculation zone. The burner is abruptly expanded compared to the stepped shape described above, and the flame stability is inferior and it is inconvenient to install the ignition element. Therefore it is technically an alternative but may not be the best solution.

 In the present invention, another type of burner which can form a recirculation can be modified for the existing burner, mainly in the DC channel of the primary air nozzle 21 of the existing burner (see Fig. 8A) or at the exit (see Fig. 8B). The bluff body (non-streamline body) 22 is placed, and the pulverized coal-air mixture blown from the primary air nozzle is recirculated in the rear region S of the bluff body 22 to form a recirculation zone, and the ignition element is installed in the recirculation zone. . However, there are bluff body wear problems and inconvenient placement of ignition components in this design, so it is technically an alternative but may not be the best solution.

The above describes various forms of burners designed based on the principles of the present invention. The following describes the ignition operation of a coal-fired boiler by the present invention. The basic point is that the ignition element is first used to heat and ignite the pulverized coal in the recirculation zone of the burner. The primary air stream is further ignited by the ignited reflux. The following operations can be carried out: In principle, the burner designed according to the invention is installed in the same manner as the ordinary pulverized coal burner and the furnace, in the original burner position of the boiler or other suitable position to the furnace, from the primary air vent of the burner. Drum into the pulverized coal-air mixture, the wall position of the recirculation zone is connected to the ignition element, and the ignition element can be selected Using an ignition device that utilizes chemical energy (such as flammable fuel oil or combustible gas), using an ignition device that uses thermal energy (such as a heat transfer layer or a heat medium input port) to utilize electrical energy (such as resistance heating or electromagnetic induction heating and arcing, etc.) The ignition device of the electrothermal conversion device, or the ignition device using light energy (such as laser), and then the primary ignition is performed. After the pulverized coal-air mixture in the primary burner is ignited, the heating rate of the boiler can be sawed to the second. The third stage is fed into the pulverized coal-air mixture, the combustion power of the burner is gradually increased, and the boiler furnace temperature is gradually increased. The ordinary burner can be put into the boiler equipment to start. The ignition element can be turned off after about 20-30 minutes or less after the pulverized coal-air mixture in the primary burner is ignited.

According to the above working principle and method, an industrial scale full-scale verification test device is designed. The primary air nozzle (ie, the mixture inlet) of the test device has a 210 mm X 70 mm distance section, and the mixture enters a 210 hidden X. A rectangular cross section of one step of 150 m/n is arranged with a common electric resistance wire on the wall surface of the recirculation zone. After heating for about 20 minutes, the temperature of the resistance wire is 950 ° C, and the heat output density of the heated wall is 120 KW. /m ² . Immediately after being fed into the mixture, the mixture was ignited. The power supply was stopped 20 minutes after the ignition, and the flame was still stable. The flow rate of the mixture was 17.8 m/s, and the amount of coal burned was about 400 kg/h. This test shows that the present invention has industrial applicability.

 As can be appreciated from the above description, the technical information further suggested by the present invention is that recirculation is generated in the coal-fired boiler burner, and the main airflow can be supplied with the required heat by igniting the recirculation to ignite the main airflow. As for the method of generating the reflux, one is to design the burner flow passage section into the above-mentioned stepped abruptly enlarged passage form, but there may be other forms: for example, the burner flow passage section may be designed to have a larger section. In the form of a sufficiently short transition section (see Figure 5B), the flow is removed from the transition duct section to create a return flow; or a bluff body (Figures 8A and 8B) is placed in the existing burner runner or at the outlet to create a recirculation . As long as reflow can be generated, the main gas flow can be easily ignited by igniting the recirculation through the ignition element in the recirculation zone, achieving the object of the present invention, in principle achieving the same technical effect as the burner of the stepped abruptly enlarged passage (but not the optimal method and Effect). Therefore, the relevant examples will not be repeated. Industrial applicability

 The invention is based on the flame stability theory design of a burner for igniting pulverized coal for a coal-fired boiler, which uses a sudden enlargement of the cross section to generate a reflux, and ignites the mixture at a lower temperature (<1000 ° C) by first igniting the reflux. Stable ability, low energy consumption, low cost, low NOx formation, low slagging rate, suitable for use in various coal-fired boilers, low investment, simple structure, completely oil-free and highly adaptable to coal Ignition technology, industrial applicability.

 The present invention has been described by the foregoing embodiments, but its specific structure can be changed without being made without departing from the basic structure (establishing reflow) and working principle (first igniting reflow) of the present invention. The foregoing is the most reasonable method of use of the present invention, and is only one of the modes that can be specifically implemented by the present invention, but is not limited thereto.

Claims

Rights request  A burner for igniting pulverized coal for a coal-fired boiler, comprising: blowing a pulverized coal-air mixture into a primary air vent of the boiler furnace and an outlet of the opposite end, wherein the primary air vent is connected to a flow passage, And in the flow channel, the pulverized coal-air can form a reflow, and an ignition element is disposed on the wall surface of the recirculation zone.  2. The burner for igniting pulverized coal for a coal-fired boiler according to claim 1, wherein the whole is a stepped passage, one end is a primary air vent, and the other end is a fire outlet, and the other walls of the passage are closed; a stepped passage, a first flow passage connected to the primary air nozzle, a third flow passage connected to the fire outlet, and a second flow passage between the first flow passage and the third flow passage, wherein the second flow passage Compared with the cross-sectional area of the first flow passage, the third flow passage has a larger cross-sectional area than the first flow passage, but is smaller than the cross-sectional area of the second flow passage, between the first flow passage and the second flow passage, and between the second flow passage and the third flow passage. The channels are connected by a head wall; the ignition elements are disposed in whole or in sections on the inner wall of the top of the second flow path or on the inner wall of the third flow path adjacent to the second flow path.  3. A burner for igniting pulverized coal according to claim 2, wherein the second flow passage is expanded on one side or both sides of the first flow passage.  A burner for igniting pulverized coal according to claim 3, wherein said second flow passage abruptly expands in a vertical direction or a horizontal direction.  A burner for igniting pulverized coal for a coal-fired boiler according to claim 2 or 3 or 4, wherein the multi-stage burner is formed by connecting at least two burners of said structure in series, and The primary burner is in communication with the fire exit of the first stage burner through its upper or lower wall surface.  6. The burner for igniting pulverized coal for a coal-fired boiler according to claim 1, wherein the flow passage connected to the primary air nozzle is a transition tube having a gradually larger cross section, and the wall and the flow axis of the transition tube The resulting opening angle α is greater than 12° and less than 90°.  7. The burner for igniting pulverized coal for a coal-fired boiler according to claim 1, wherein the flow passage to which the primary air nozzle is connected is a straight pipe, and a bluff body is placed in the straight pipe or at the outlet.  8. A method for igniting pulverized coal by a coal-fired boiler, wherein the burner for igniting pulverized coal according to any one of claims 1 to 7 is installed at a position of a primary burner of a coal-fired boiler or other suitable position to the furnace, once through The air vent is fed into the pulverized coal-air mixture. The pulverized coal-air mixture in the recirculation zone of the burner is first ignited by the igniter element, the main gas stream is further ignited by the ignited reflux, and the flame is injected into the boiler furnace from the outlet.  9. The method of igniting pulverized coal in a coal-fired boiler according to claim 7, wherein the igniting element uses a plurality of ignition forms such as chemical energy, thermal energy, electric energy, and light energy. u 10. A method of producing a recirculation in a burner by designing a section of the burner flow passage to be in the form of a step according to any one of claims 2 to 5, or a sufficiently short transition section of the section according to claim 6 Or in the form of a bluff body placed in or at the outlet of the burner, as described in claim 7, such that gas entering from the primary air vent can produce backflow in the flow path.