WO2018036566A1

WO2018036566A1 - System and method for burning pulverized coal

Info

Publication number: WO2018036566A1
Application number: PCT/CN2017/099187
Authority: WO
Inventors: Zheng Shi; Kaining WEI
Original assignee: Zheng Shi
Priority date: 2016-08-25
Filing date: 2017-08-25
Publication date: 2018-03-01

Abstract

A system and a method for burning pulverized coal are provided. The system includes a pulverized coal dense dilute separator, an ignition Blowpipe (6), a first deflection device (8) and a flame generation device (9). The primary air/pulverized coal mixture is separated into dense phase and dilute phase by the separator, before the primary air/pulverized coal mixture enters the boiler combustion chamber. The dense phase mixture enters an inlet of the ignition blowpipe (6), and then it is deflected by the first deflection device (8) to flow back. A portion of the dilute phase mixture outside of the ignition blowpipe (6) mixes with a reflux of the dense phase mixture, and a turbulent region is made.

Description

SYSTEM AND METHOD FOR BURNING PULVERIZED COAL

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Patent Application CN201610724403X, entitled “System for Burning Pulverized Coal” , filed on August 25, 2016. The entire disclosure of the above application is incorporated herein by reference.

This application also claims priority of Patent Application CN2017102956371, entitled “System for Burning Pulverized Coal” , filed on April 28, 2017. The entire disclosure of the above application is incorporated herein by reference.

This application also claims priority of Patent Application CN2017102951768, entitled “System for Burning Pulverized Coal” , filed on April 28, 2017. The entire disclosure of the above application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to ignition and stable combustion under low loads for large-scale pulverized coal-fired boilers.

BACKGROUND

Large-scale pulverized coal power plants, especially those designed with tangentially-fired boilers, traditionally use oil-fired guns for ignition. This allows for the combustion chamber’s temperature to become high enough so that the pulverized coal can ignite by itself once it is delivered inside. Unfortunately, this means that large amounts of fuel oil needs to be burnt before achieving stable combustion conditions, which also means increased startup costs.

During the past several years, two new forms of technologies have gradually developed to resolve the abovementioned issue: one being the tiny-oil ignition technology that uses oil-fired guns mounted inside the pulverized coal burner and enables reduced amount of fuel during the ignition process, and the other technology makes use of a plasma generator mounted inside the pulverized coal burner and ignites the pulverized coal ignition with a plasma torch.

These two types of technologies both have major drawbacks. Although the tiny-oil ignition does manage to reduce fuel-oil consumption by 80 ～ 90％, due to its large base, the consumption levels of fuel-oil are still significant. Similarly, although plasma ignition does not consume fuel-oil, the cost of the equipment, its installation as well as the level of electricity consumption is high. Furthermore, the lifecycle of the plasma anode and cathode are short, and the price of the parts is high, requiring frequent replacements.

No matter which technology is used, the pulverized coal is initially ignited inside the combustion chamber by either an oil-fired flame or a plasma flame, causing the amount of time the pulverized coal spends within the flame to be limited and thus the coal not being sufficiently heated and burnt. Therefore, for the case of low loads, since the temperature of the combustion chamber is low, large-scale pulverized coal boilers cannot maintain stable combustion of pulverized coal and need additional ignition source to maintain stable combustion.

Thus, there exist a need in the prior art for a solution that can allow for notable savings in ignition fuel, decrease the amount of regulated pollutant emissions, and through a simple design allow for cheap installation and maintenance.

SUMMARY OF INVENTION

At present, the diameter of the primary air blowpipes is typically about 0.5 meters. Ignition device such as tiny-oil ignition and plasma ignition is installed in the primary air blowpipe. Traditionally, primary air is used to deliver the pulverized coal particles into the boiler. Unfortunately, the volumes of primary air are usually relatively large and, since the pulverized coal particles do not require so much air during the ignition phase, the excess air needs additional heat in order to be consumed. The flame temperature is therefore reduced, and thus the pulverized coal’s complete combustion is delayed.

Aiming to solve the problems above, the present invention discloses a system for burning pulverized coal for new or operating large-scale pulverized coal-fired boilers, at a primary air blowpipe. The system includes a pulverized coal dense dilute separator, an ignition blowpipe, a first deflection device, and a flame generation device. The ignition blowpipe is inserted along the central axis of a primary air blowpipe and that has a diameter substantially smaller than that of the primary air blowpipe. The first deflection device is connected to the outlet of the ignition blowpipe and is capable of substantially reversing the flow direction of the air and pulverized coal mixture coming into the boiler combustion chamber through the ignition blowpipe.

In accordance with one embodiment of the present invention, the pulverized coal and a small amount of ignition air is delivered inside an ignition blowpipe located inside an existing primary air blowpipe and with a diameter substantially smaller than that of the primary air blowpipe. Since, during the pulverized coal ignition phase, there is no need for extra heat to heat up the excess air, the flame temperature is higher and the pulverized coal is combusted faster. The direction of the pulverized coal is reversed by the first deflection device located at the outlet of the ignition blowpipe. Under the influence of the primary air, the pulverized coal slows down gradually, and then the pulverized coal accelerates in the direction of the primary air and finally enters the combustion furnace along with the flame. The abovementioned process significantly increases the amount of time the pulverized coal spends within the flame.

In accordance with one embodiment of the present invention, the system comprises a pulverized coal dense dilute separator. During the boiler ignition period, before the primary air and pulverized coal mixture enters the boiler combustion chamber, the primary air and pulverized coal mixture is separated into dense phase and dilute phase by the pulverized coal dense dilute separator. The dense phase primary air and pulverized coal mixture enters the inlet of the ignition blowpipe, then is deflected by the first deflection device to flow back. A portion of the dilute phase primary air and pulverized coal mixture flows outside the ignition blowpipe, meets with a portion of the dense phase primary air and pulverized coal mixture of reflux, and forms a turbulent region. The pulverized coal in the turbulent region is ignited by the flame generation device.

With the design of the present invention, stable flame can be generated from the pulverized coal in the boilers, without using auxiliary fuels to preheat. After injecting the pulverized coal, the pulverized coal can be ignited within a short time period.

In accordance with one embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, enters the flame of pulverized coal, and is preheated and ignited by the flame. The dense phase primary air and pulverized coal mixture stays in the flame for longer time, and can be preheated sufficiently, leading to stable combustion.

In accordance with one embodiment of the present invention, the pulverized coal dense dilute separator is an annular blunt body located on the interior wall of the primary air blowpipe, and the orientation of the pulverized coal dense dilute separator is perpendicular to the central axis of the primary air blowpipe. The annular blunt body is triangular along the tangent plane of the primary air blowpipe, for the dense phase primary air and pulverized coal mixture to be easily imported into the ignition blowpipe that is inserted along the central axis of the primary air blowpipe, and the dilute phase primary air and pulverized coal mixture flows in the gap between the ignition blowpipe and the primary air blowpipe. The experiments showed that the distribution of the blunt body in this way can help achieve dense dilute separation. The concentration of the pulverized coal contained in the dilute phase primary air and pulverized coal mixture is so low that the dilute phase primary air and pulverized coal mixture is nearly transparent under macroscopic observation.

In accordance with one embodiment of the present invention, the pulverized coal dense dilute separator is a cyclone separator, and the inlet of the cyclone separator is connected to the primary air blowpipe. Many types of commercial cyclone separators can be used, depending on specific situations. In accordance with one embodiment of the present invention, the cyclone separator is distributed in the place far away from the boiler combustion chamber.

It is important to point out that the pulverized coal dense dilute separator described above is an embodiment of the present invention. People skilled in the art can understand that many other pulverized coal dense dilute separators can be used, which are within the spirit and scope of invention.

In accordance with one embodiment of the present invention, the outlet of the ignition blowpipe extends beyond the interior wall of the boiler combustion chamber. The conventional pipe diameter of the primary air blowpipe is about 500 millimeters. In the primary air blowpipe, the flow field of ignition and stable combustion is not the best. After the outlet of the ignition blowpipe extends beyond the interior wall of the boiler combustion chamber, the region between the outlet of ignition blowpipe and the outlet of primary air blowpipe is an open space and can achieve the flow field of ignition and stable combustion reasonably.

In accordance with one embodiment of the present invention, the system further includes a rotary blade cascade that is affixed between the primary air blowpipe and the ignition blowpipe to exert rotational force upon the primary air. For the purpose of improving the speed of the flame, the rotary blade cascade can be omitted, and this does not affect the implementation of the present invention.

In accordance with one embodiment of the present invention, before the dilute phase primary air and pulverized coal mixture meets with the dense phase primary air and pulverized coal mixture of reflux, the dilute phase primary air and pulverized coal mixture passes through an air-diversion device, to enable a portion of the dilute phase primary air and pulverized coal mixture to bypass the turbulent region and substantially avoid a direct collision of the dense phase with the dilute phase of the primary air and pulverized coal mixture. Shunting part of the dilute phase primary air and pulverized coal mixture can improve the stability of the flame.

In accordance with one embodiment of the present invention, the interior diameter of the inlet of the ignition blowpipe is bigger than that of the middle section of the ignition blowpipe. The diameter of the ignition blowpipe is not fixed. Bigger inlet is convenient for the entrance of the entrance of the dense the primary air and pulverized coal mixture.

In accordance with one embodiment of the present invention, the system further includes a retraction mechanism. After the pulverized coal has been ignited, the retraction mechanism is activated to retract the ignition blowpipe from the primary air blowpipe to a place far away from the boiler combustion chamber.

In accordance with one embodiment of the present invention, the deflection device is a deflection cap. The deflection cap and the exterior wall of the ignition blowpipe form an annular passage through which the ignition air and pulverized coal mixture enters into combustion.

It is important to point out that the deflection cap described above is an embodiment of the present invention. People skilled in the art can understand that many other deflection devices can be used, which are within the spirit and scope of invention.

In accordance with one embodiment of the present invention, the system further includes an annular deflection device that is located on the ignition blowpipe and between the first deflection device and the pulverized coal dense dilute separator. In the process of the portion of dense phase primary air and pulverized coal mixture flowing back, a portion of the dense phase primary air and pulverized coal mixture is deflected towards the central axis of the primary air blowpipe under the action of the annular deflection device. When the dense phase primary air and pulverized coal mixture ejects from the first deflection device located at the outlet of the ignition blowpipe, a backflow is formed and diffuses at a certain angle. The annular deflection device can restrict the diffusion, force a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe, and thus enhance the penetrability of the portion of dense phase primary air and pulverized coal mixture flowing back, and dramatically increase the distance of pulverized coal flowing back in the flame, extend residence time of pulverized coal in the flame, make pulverized coal get better preheating and ignition, and improve ignition property and stable combustion performance of pulverized coal.

In accordance with one embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back. A portion of the dense phase primary air and pulverized coal mixture is deflected towards the central axis of the primary air blowpipe under the action of the annular deflection device in the process of flowing back, enters the flame of pulverized coal, and is preheated and ignited by the flame. Therefore, the pulverized coal spends longer time in the flame, and thus is better preheated to achieve more stable combustion later.

In accordance with one embodiment of the present invention, the annular deflection device is a pipe. The interior diameter of the pipe gradually decreases in the direction of the dense phase primary air and pulverized coal mixture flowing back. Because the dense phase primary air and pulverized coal mixture of reflux will diffuse at a certain angle, the energy of the primary air and pulverized coal mixture after diffusing is dispersive, the distance of flowing back in the flame is short, and the preheating is not sufficient. The annular deflection device can restrict the diffusion of the dense phase primary air and pulverized coal mixture, force a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe, enhance the penetration of the portion of dense phase primary air and pulverized coal mixture flowing back, and dramatically increase the distance of pulverized coal flowing back in the flame.

It is important to point out that the annular deflection device described above is an embodiment of the present invention. People skilled in the art can understand that many other annular deflection devices can be used, which are within the spirit and scope of invention.

In accordance with one embodiment of the present invention, a second annular deflection device is arranged between the first deflection device and the pulverized coal dense dilute separator, to increase the distance of pulverized coal flowing back, and increase the stability of the flame.

In accordance with one embodiment of the present invention, the system further includes a second deflection device that is located between the first deflection device and the pulverized coal dense dilute separator. In the process of the portion of the dense phase primary air and pulverized coal mixture flowing back, the direction of a portion of the dense phase primary air and pulverized coal mixture that flows back is reversed again under the action of the second deflection device.

In accordance with one embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back and enters the flame of pulverized coal, and a portion of the dense phase primary air and pulverized coal mixture is deflected by the second deflection device to flow back again, and then is preheated and ignited by the flame. As a result, the pulverized coal spends longer time in the flame, and is better preheated to achieve stable combustion later.

In accordance with one embodiment of the present invention, the second deflection device is a cone with the diameter gradually increasing in the direction of the primary air. One side of the cone is connected to the exterior wall of the ignition blowpipe, and the other side of the cone and the interior wall of the primary air blowpipe form an annular passage. The second deflection device is capable of reversing again the flow direction of a portion of the pulverized coal after the first reversion, and a portion of the dilute phase air and pulverized coal mixture flows through the annular passage, meets with the portion the dense phase primary air and pulverized coal mixture that is reversed again, and forms a turbulent region. The experiment showed that, compared to the dense phase primary air and pulverized coal mixture crashing into the dilute phase primary air and pulverized coal mixture to reverse its direction, using the second deflection device to reverse again the flow direction of a portion of the pulverized coal after the first reversion can increase the distance of pulverized coal flowing back in the flame, extend residence time of pulverized coal in the flame, and improve stable combustion performance of pulverized coal.

It is important to point out that the second deflection device described above is an embodiment of the present invention. People skilled in the art can understand that many other deflection devices and methods can be used, which are within the spirit and scope of invention.

In accordance with one embodiment of the present invention, the cone of the second deflection device has one or more annular slits. A portion of the dilute phase air and pulverized coal mixture enters the second deflection device through the annular slit to supply combustion oxygen and to prevent deposition of pulverized coal in the second deflection device.

In accordance with one embodiment of the present invention, the present invention proposes a method for burning pulverized coal, for new or operating large-scale pulverized coal-fired boilers, in the following steps:

- separating, by a pulverized coal dense dilute separator, the primary air and pulverized coal mixture into dense phase and dilute phase, before the primary air and pulverized coal mixture enters the boiler combustion chamber；

- directing the dense phase primary air and pulverized coal mixture into the inlet of an ignition blowpipe, wherein the ignition blowpipe is inserted along the central axis of the primary air blowpipe and has a diameter substantially smaller than the diameter of the primary air blowpipe；

- deflecting the dense phase primary air and pulverized coal mixture that is exiting the ignition blowpipe by a first deflection device to flow back, wherein the first deflection device is connected to the outlet of the ignition blowpipe and is capable of substantially reversing the flow direction of the air and pulverized coal mixture coming into the boiler combustion chamber through the ignition blowpipe；

- meeting, by a portion of the dilute phase primary air and pulverized coal mixture flows outside the ignition blowpipe with a portion of the dense phase primary air and pulverized coal mixture that flows back, and forming a turbulent region；

- igniting the pulverized coal in the turbulent region by a flame generation device.

BRIEF DESCRIPTION OF THE DRAWINGS

To better illustrate the technical features of the embodiments of the present invention, various embodiments of the present invention will be briefly described in conjunction with the accompanying drawings. It should be obvious that the drawings are only for exemplary embodiments of the present invention, and that a person of ordinary skill in the art may derive additional drawings without deviating from the principles of the present invention.

FIG. 1 is a cross-sectional view of a conventional power plant’s boiler in accordance with one embodiment of the invention.

FIG. 2 illustrates a primary air blowpipe installed with an annular blunt body in accordance with one embodiment of the invention.

FIG. 3 is a schematic diagram illustrating installation of an air-diversion blowpipe at the outlet of the primary air blowpipe in accordance with one embodiment of the invention.

FIG. 4 is a schematic diagram illustrating installation of rotary blade cascades on the inside and the outside the air-diversion blowpipe in accordance with one embodiment of the invention.

FIG. 5 is a schematic diagram illustrating a primary air blowpipe installed with an annular deflection device in accordance with one embodiment of the invention.

FIG. 6 is a schematic diagram illustrating a primary air blowpipe installed with two annular deflection devices in accordance with one embodiment of the invention.

FIG. 7 is a schematic diagram illustrating a primary air blowpipe installed with the second deflection device in accordance with one embodiment of the invention.

FIG. 8 is a schematic diagram illustrating the second deflection device with one annular slit in accordance with one embodiment of the invention.

FIG. 9 is a schematic diagram illustrating the second deflection device with two annular slits in accordance with one embodiment of the invention.

FIG. 10 is a schematic diagram illustrating the process flow for burning pulverized coal in accordance with one embodiment of the invention.

FIG. 11 is a schematic diagram illustrating the process flow for burning pulverized coal, when an annular deflection device is installed in the primary air blowpipe, in accordance with one embodiment of the invention.

FIG. 12 is a schematic diagram illustrating the process flow for burning pulverized coal, when a second deflection device is installed in the primary air blowpipe, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of the invention illustrated in the accompanying drawings. While the invention will be described in conjunction with the embodiments, it will be understood that this is not intended to limit the scope of the invention to these specific embodiments. The invention is intended to cover all alternatives, modifications and equivalents within the spirit and scope of invention, which is defined by the apprehended claims.

Furthermore, in the detailed description of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, and components are not described in details to avoid unnecessarily obscuring a clear understanding of the present invention.

FIG. 1 is a cross-sectional view of a conventional power plant’s boiler in accordance with one embodiment of the invention. As shown in FIG. 1, conventional power plant’s boiler uses the primary air to deliver the pulverized coal. The primary air blowpipes 5 are arranged by layers at the middle and lower parts of the boiler combustion chamber. The primary air blowpipes 5 are connected to the boiler combustion chamber through the pulverized coal combustor 1. The secondary air blowpipes 2 are arranged above and under the pulverized coal combustor 1. The tertiary air blowpipe 3 is arranged on top of the boiler combustion chamber. Oil-fired guns are arranged in the secondary air blowpipes 2 located at the middle and the bottom of the boiler combustion chamber. The inlet of the primary air blowpipe 5 is connected to the pulverized coal feeding machine 4.

Tiny-oil ignition and plasma ignition usually replace the pulverized coal combustors 1 located on the first floor or the second floor from the bottom with tiny-oil combustor of plasma combustor. The pulverized coal enters the primary air blowpipe 5 through pulverized coal feeding machine 4, then is ignited by oil flame or plasma flame in the combustor 1, and then is injected into the boiler combustion chamber.

As shown in FIG. 2, the pulverized coal dense dilute separator is an annular blunt body. The system for burning pulverized coal includes an ignition blowpipe 6 that is inserted along the central axis of the primary air blowpipe 5 and that has a diameter substantially smaller than that of the primary air blowpipe 5, an annular blunt body 7 located on the interior wall of the primary air blowpipe 5 and with the orientation perpendicular to the central axis of the primary air blowpipe 5, a first deflection device 8 that is connected to the outlet of the ignition blowpipe 6 and is capable of substantially reversing the flow direction of the air and pulverized coal mixture coming into the boiler combustion chamber through the ignition blowpipe 6, and a flame generation device 9. The first deflection device 8 can be blunt body, bend or trepanning with special angle.

The annular blunt body 7 is triangular along the tangent plane of the primary air blowpipe, for the dense phase primary air and pulverized coal mixture to be easily imported into the ignition blowpipe that is inserted along the central axis of the primary air blowpipe, and the dilute phase primary air and pulverized coal mixture flows in the gap between the ignition blowpipe and the primary air blowpipe. The experiments showed that the distribution of the blunt body in this way can help achieve dense dilute separation. The concentration of the pulverized coal contained in the dilute phase primary air and pulverized coal mixture is so low that the dilute phase primary air and pulverized coal mixture is nearly transparent under macroscopic observation. The annular blunt body 7 is directly arranged on the primary air blowpipe. The structure doesn’ t need other wind powder separator and pulverized coal storage device, and can significantly change the pulverized coal supply system of existing pulverized coal-fired boilers and simplify the system, and thus reduce the equipment investment.

In accordance with one embodiment of the present invention, the pulverized coal dense dilute separator is a cyclone separator, and the inlet of the cyclone separator is connected to the primary air blowpipe. Many types of commercial cyclone separators can be used, depending on specific situations.

As shown in FIG. 3, the air-diversion device is an air-diversion blowpipe. An air-diversion blowpipe 10 is installed at the inside of the outlet of the primary air blowpipe 5 and the outside of the ignition blowpipe 6. The inner diameter of the air-diversion blowpipe 10 gradually increases along the flow direction of the primary air. The air-diversion blowpipe 10 divides the dilute phase primary air and pulverized coal mixture into two parts, i.e., the dilute phase primary air and pulverized coal mixture outside the air-diversion blowpipe and spread out to keep away from the dense phase primary air and pulverized coal mixture of reflux, and the dilute phase primary air and pulverized coal mixture inside the air-diversion blowpipe and blown into the dense phase primary air and pulverized coal mixture of reflux. Reducing the amount of the dilute phase primary air and pulverized coal mixture entering the dense phase primary air and pulverized coal mixture of reflux can make the reflux path of the dense phase primary air and pulverized coal mixture longer, and thus achieve more stable combustion.

Besides air-diversion blowpipe, the air-diversion device can also be in other structures. Before the dilute phase primary air and pulverized coal mixture meets with the dense phase primary air and pulverized coal mixture of reflux, the dilute phase primary air and pulverized coal mixture passes through an air-diversion device, to enable a portion of the dilute phase primary air and pulverized coal mixture to bypass the turbulent region and substantially avoid a direct collision of the dense phase with the dilute phase of the primary air and pulverized coal mixture. Shunting part of the dilute phase primary air and pulverized coal mixture can improve the stability of the flame.

The system further includes a rotary blade cascade 11 that is affixed between the primary air blowpipe 5 and the ignition blowpipe 6 to exert rotational force upon the primary air. Rotational force caused by the rotary blade cascade 11 adds another dimension (for example, centrifugal force) to the existing turbulent region. Thus, the pulverized coal is mixed more evenly, after being ignited by the flame generation device, and thus more stable flame is generated. In addition, since the pulverized coal spends more time in the turbulent region, the proportion of pulverized coal burning increases before the pulverized coal leaves the modified primary air blowpipe 5. For the purpose of improving the speed of the flame, the rotary blade cascade can be omitted, and this does not affect the implementation of the present invention.

The conventional pipe diameter of the primary air blowpipe 6 is about 500 millimeter. In the primary air blowpipe 6, the flow field of ignition and stable combustion is not the best. In another embodiment of the present invention, after the outlet of the ignition blowpipe 6 extends beyond the interior wall of the boiler combustion chamber, the region between the outlet of ignition blowpipe 6 and the outlet of primary air blowpipe 5 is an open space and can achieve the flow field of ignition and stable combustion reasonably.

In another embodiment of the present invention, the interior diameter of the inlet of the ignition blowpipe 6 is bigger than that of the middle section of the ignition blowpipe 6. The diameter of the ignition blowpipe is not fixed. Bigger inlet is convenient for the entrance of the entrance of the dense the primary air and pulverized coal mixture.

In another embodiment of the present invention, the ignition blowpipe 6 is connected to an electric actuator. After the pulverized coal has been ignited, if the ignition blowpipe 6 needs to stop supplying pulverized coal, the electric actuator can be started to retract the ignition blowpipe 6 from the primary air blowpipe 5. In this way, the system doesn’ t need additional cooling device.

In another embodiment of the present invention, the first deflection device 8 is a deflection cap. The deflection cap 8 and the exterior wall of the ignition blowpipe 6 forms an annular passage through which the ignition air and pulverized coal mixture enters into combustion. The first deflection device 8 can be other structures, as long as the first deflection device 8 can substantially reverse the flow direction of the air and pulverized coal mixture. People skilled in the art can understand that many other first deflection devices can be used, which are within the spirit and scope of invention.

As shown in FIG. 5, the annular deflection device 12 is a pipe. The interior diameter of the pipe gradually decreases in the direction of the dense phase primary air and pulverized coal mixture flowing back. The annular deflection device 12 is located on the ignition blowpipe 6 and between the first deflection device 8 and the annular blunt body 7.

FIG. 6 is a schematic diagram illustrating a primary air blowpipe installed with two annular deflection devices in accordance with one embodiment of the invention. As shown in FIG. 6, a second deflection device 12 is located between the first deflection device 8 and the annular blunt body 7.

The annular deflection device 12 is a pipe and located on the ignition blowpipe 6. The interior diameter of the pipe gradually decreases in the direction of the dense phase primary air and pulverized coal mixture flowing back. The annular deflection device 12 can restrict the diffusion of the dense phase primary air and pulverized coal mixture, force a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe, enhance the penetration of the portion of dense phase primary air and pulverized coal mixture flowing back, and dramatically increase the distance of pulverized coal flowing back in the flame.

It is important to point out that the annular deflection device described above is an embodiment of the present invention. People skilled in the art can understand that many other annular deflection devices that aim to tuck a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe and accordingly increase the distance of the pulverize coal flowing back can be used. These annular deflection devices are within the spirit and scope of invention.

As shown in FIG. 7, the second deflection device is a cone. The second deflection device 13 is located between the first deflection device 8 and annular blunt body 7 and is capable of reversing again the flow direction of a portion of the pulverized coal after the first reversion.

The second deflection device 13 is a cone with the diameter gradually increasing in the direction of the primary air. One side of the cone is connected to the exterior wall of the ignition blowpipe 6, the other side of the cone and the interior wall of the primary air blowpipe 5 form an annular passage. The second deflection device 13 is capable of reversing again the flow direction of a portion of the pulverized coal after the first reversion, and a portion of the dilute phase air and pulverized coal mixture flows through the annular passage, meets with the portion the dense phase primary air and pulverized coal mixture that is reversed again, and forms a turbulent region. The experiment showed that, compared to the dense phase primary air and pulverized coal mixture crashing into the dilute phase primary air and pulverized coal mixture to reverse its direction, using the second deflection device to reverse again the flow direction of a portion of the pulverized coal after the first reversion can increase the distance of pulverized coal flowing back in the flame, extend residence time of pulverized coal in the flame, and improve stable combustion performance of pulverized coal.

As shown in FIG. 8, the cone of the second deflection device has one annular slit. A portion of the dilute phase air and pulverized coal mixture enters the second deflection device through the annular slit to supply combustion oxygen and to prevent deposition of pulverized coal in the second deflection device.

As shown in FIG. 9, the cone of the second deflection device has two annular slits. When the fuel is highly volatile coal that has high calorific values, the two annular slits can supply oxygen to the combustion further.

It is important to point out that the second deflection device described above is an embodiment of the present invention. People skilled in the art can understand that many other deflection devices that aim to reduce the backflow drag of dense phase primary air and pulverized coal mixture flowing back and accordingly increase the distance of the pulverize coal flowing back can be used. All the second deflection devices are within the spirit and scope of invention.

As shown in FIG. 10, the present invention provides a method f for burning pulverized coal, for new or operating large-scale pulverized coal-fired boilers, in the following steps:

In another embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, enters the flame of pulverized coal, and is preheated and ignited by the flame. The dense phase primary air and pulverized coal mixture stays in the flame for longer time, and can be preheated sufficiently, leading to stable combustion.

FIG. 11 illustrates the process flow for burning pulverized coal, when an annular deflection device is installed in the primary air blowpipe, in accordance with one embodiment of the invention, in the following steps:

- in the process of the portion of dense phase primary air and pulverized coal mixture flowing back, deflecting a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe under the action of an annular deflection device, wherein the annular deflection device is located on the ignition blowpipe and between the first deflection device and the pulverized coal dense dilute separator.

In another embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, and a portion of the dense phase primary air and pulverized coal mixture is further deflected towards the central axis of the primary air blowpipe by the annular deflection device in the process of flowing back, enters the flame of pulverized coal, and is preheated and ignited by the flame.

FIG. 12 illustrates the process flow for burning pulverized coal, when a second deflection device is installed in the primary air blowpipe, in accordance with one embodiment of the invention, in the following steps:

- in the process of the portion of the dense phase primary air and pulverized coal mixture flowing back, reversing again the direction of a portion of the dense phase primary air and pulverized coal mixture that flows back under the action of a second deflection device, wherein the second deflection device is located between the first deflection device and pulverized coal dense dilute separator；

In another embodiment of the present invention, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back and enters the flame of pulverized coal, and a portion of the dense phase primary air and pulverized coal mixture is deflected by the second deflection device to flow back again, and is preheated and ignited by the flame.

Compared with other technologies, the present invention offers a number of advantages: stable combustion is automatically achieved, no need for oil-fired or plasma-generated flames during prolonged periods； the primary air and pulverized coal mixture is separated into dense phase and dilute phase by the pulverized coal dense dilute separator, forms a turbulent region, and the pulverized coal in the turbulent region is ignited, significant reduction in the consumption of fuel oil or electricity； the range of coal quality variety is expanded and comprises pulverized coal that contains less volatiles.

Installing an annular deflection device in the system for burning pulverized coal, offers a number of advantages: in the process of a portion of dense phase primary air and pulverized coal mixture flowing back, using the annular deflection device to tuck a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe, can enhance the penetrability of a portion of dense phase primary air and pulverized coal mixture flowing back, dramatically increase the distance of pulverized coal flowing back in the flame, extend residence time of pulverized coal in the flame, make pulverized coal get better preheating and ignition, and improve ignition property and stable combustion performance of pulverized coal.

Installing a second deflection device in the system for burning pulverized coal, offers a number of advantages: using the second deflection device to lead the dilute phase primary air and pulverized coal mixture towards the direction of interior wall of the primary air blowpipe, to prevent a portion of the dense phase primary air and pulverized coal mixture flowing back and a portion of the dilute phase primary air and pulverized coal mixture from crashing into each other, decrease resistance of pulverized coal flowing back in the flame, increase the distance of pulverized coal flowing back in the flame, extend residence time of pulverized coal in the flame, delay the mixture of pulverized coal flame and combustion air, and improve ignition property and stable combustion performance of pulverized coal.

Claims

A system for burning pulverized coal, for new or operating large-scale pulverized coal-fired boilers, at a primary air blowpipe, comprising:

a pulverized coal dense dilute separator；

an ignition blowpipe inserted along the central axis of a primary air blowpipe, wherein the ignition blowpipe has a diameter substantially smaller than the diameter of the primary air blowpipe；

a first deflection device that is connected to the outlet of the ignition blowpipe and is capable of substantially reversing the flow direction of the air and pulverized coal mixture coming into the boiler combustion chamber through the ignition blowpipe；

a flame generation device；

wherein, during boiler ignition period, before the primary air and pulverized coal mixture enters the boiler combustion chamber, the primary air and pulverized coal mixture is separated into dense phase and dilute phase by the pulverized coal dense dilute separator； the dense phase primary air and pulverized coal mixture enters the inlet of the ignition blowpipe, then is deflected by the first deflection device to flow back； a portion of the dilute phase primary air and pulverized coal mixture flows outside the ignition blowpipe, meets with a portion of the dense phase primary air and pulverized coal mixture that flows back, and forms a turbulent region； the pulverized coal in the turbulent region is ignited by the flame generation device.
The system of claim 1, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, enters the flame of pulverized coal, and is preheated and ignited by the flame.
The system of claim 1, wherein the pulverized coal dense dilute separator is an annular blunt body, and is located on the interior wall of the primary air blowpipe, and wherein the orientation of the pulverized coal dense dilute separator is perpendicular to the central axis of the primary air blowpipe.
The system of claim 1, wherein the pulverized coal dense dilute separator is a cyclone separator, and wherein the inlet of the cyclone separator is connected to the primary air blowpipe.
The system of claim 1, wherein the outlet of the ignition blowpipe extends beyond the interior wall of the boiler combustion chamber.
The system of claim 1, further comprising a rotary blade cascade that is affixed between the primary air blowpipe and the ignition blowpipe to exert rotational force upon the primary air.
The system of claim 1, wherein before the dilute phase primary air and pulverized coal mixture meets with the dense phase primary air and pulverized coal mixture of reflux, the dilute phase primary air and pulverized coal mixture passes through an air-diversion device to substantially avoid a direct collision of the dense phase and the dilute phase of the primary air and pulverized coal mixture.
The system of claim 1, wherein the interior diameter of the inlet of the ignition blowpipe is bigger than the interior diameter of the middle section of the ignition blowpipe.
The system of claim 1, further comprising a retraction mechanism, wherein, after the pulverized coal has been ignited, the retraction mechanism is activated to retract the ignition blowpipe from the primary air blowpipe.
The system of claim 1, wherein the first deflection device is a deflection cap, and the deflection cap and the exterior wall of the ignition blowpipe form an annular passage, and wherein the ignition air and pulverized coal mixture enters into combustion through the annular passage.
The system of claim 1, further comprising an annular deflection device that is located on the ignition blowpipe and between the first deflection device and the pulverized coal dense dilute separator, wherein, in the process of the portion of dense phase primary air and pulverized coal mixture flowing back, a portion of dense phase primary air and pulverized coal mixture that flows back is further deflected towards the central axis of the primary air blowpipe under the action of the annular deflection device.
The system of claim 11, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, and wherein a portion of the dense phase primary air and pulverized coal mixture is further deflected towards the central axis of the primary air blowpipe by the annular deflection device in the process of flowing back, enters the flame of pulverized coal, and is preheated and ignited by the flame.
The system of claim 11, further comprising a second annular deflection device that is affixed between the first deflection device and the pulverized coal dense dilute separator.
The system of claim 11, wherein the annular deflection device is a pipe, and wherein the interior diameter of the pipe gradually decreases in the direction of the dense phase primary air and pulverized coal mixture that flows back.
The system of claim 1, further comprising a second deflection device that is located between the first deflection device and the pulverized coal dense dilute separator, wherein, in the process of the portion of the dense phase primary air and pulverized coal mixture flowing back, the direction of a portion of the dense phase primary air and pulverized coal mixture that flows back is reversed again under the action of the second deflection device.
The system of claim 15, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back and enters the flame of pulverized coal, and wherein a portion of the dense phase primary air and pulverized coal mixture is deflected by the second deflection device to flow back again, and is preheated and ignited by the flame.
The system of claim 15, wherein, the second deflection device is a cone with the diameter gradually increasing in the direction of the primary air, one side of the cone is connected to the exterior wall of the ignition blowpipe, and the other side of the cone and the interior wall of the primary air blowpipe form an annular passage, and wherein the flow direction of a portion of the air and pulverized coal mixture reversed by the first deflection device is reversed again by the second deflection device, and a portion of the dilute phase air and pulverized coal mixture flows through the annular passage, meets with the portion the dense phase primary air and pulverized coal mixture that is reversed again, and forms a turbulent region.
The system of claim 15, wherein the cone of the second deflection device has one or more annular slits, wherein a portion of the dilute phase air and pulverized coal mixture enters the second deflection device through the annular slit to supply combustion oxygen and to prevent deposition of pulverized coal in the second deflection device.
A method for burning pulverized coal, for new or operating large-scale pulverized coal-fired boilers, at a primary air blowpipe, comprising:

separating, by a pulverized coal dense dilute separator, the primary air and pulverized coal mixture into dense phase and dilute phase, before the primary air and pulverized coal mixture enters the boiler combustion chamber；

directing the dense phase primary air and pulverized coal mixture into the inlet of an ignition blowpipe, wherein the ignition blowpipe is inserted along the central axis of the primary air blowpipe and has a diameter substantially smaller than the diameter of the primary air blowpipe；

deflecting the dense phase primary air and pulverized coal mixture that is exiting the ignition blowpipe by a first deflection device to flow back, wherein the first deflection device is connected to the outlet of the ignition blowpipe and is capable of substantially reversing the flow direction of the air and pulverized coal mixture coming into the boiler combustion chamber through the ignition blowpipe；

meeting, by a portion of the dilute phase primary air and pulverized coal mixture flows outside the ignition blowpipe with a portion of the dense phase primary air and pulverized coal mixture that flows back, and forming a turbulent region；

igniting the pulverized coal in the turbulent region by a flame generation device.
The method of claim 19, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, and enters the flame of pulverized coal, and is preheated and ignited by the flame.
The method of claim 19, further comprising, in the process of the portion of dense phase primary air and pulverized coal mixture flowing back, deflecting a portion of dense phase primary air and pulverized coal mixture towards the central axis of the primary air blowpipe under the action of an annular deflection device, wherein, the annular deflection device is located on the ignition blowpipe and between the first deflection device and the pulverized coal dense dilute separator.
The method of claim 21, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back, and wherein a portion of the dense phase primary air and pulverized coal mixture is further deflected towards the central axis of the primary air blowpipe by the annular deflection device in the process of flowing back, enters the flame of pulverized coal, and is preheated and ignited by the flame.
The method of claim 19, further comprising, in the process of the portion of the dense phase primary air and pulverized coal mixture flowing back, reversing again the direction of a portion of the dense phase primary air and pulverized coal mixture that flows back under the action of a second deflection device, wherein the second deflection device is located between the first deflection device and pulverized coal dense dilute separator.
The method of claim 23, wherein, after boiler ignition, the dense phase primary air and pulverized coal mixture is deflected by the first deflection device to flow back and enters the flame of pulverized coal, and wherein a portion of the dense phase primary air and pulverized coal mixture is deflected by the second deflection device to flow back again, and is preheated and ignited by the flame.