An annular hot and cold primary air mixing device at the inlet of a coal mill

Abstract

The present invention discloses an annular hot and cold primary air mixing device at the inlet of a coal mill. The present invention includes a hot primary air pipeline, a cold primary air pipeline, a cold primary air interface expansion pipe, a cold primary air annular air duct, and a cold primary air uniform grid; the cold primary air sequentially enters the hot primary air pipeline through the cold primary air pipeline, the cold primary air interface expansion pipe, the cold primary air annular air duct, and the cold primary air uniform grid, and the hot and cold primary air are mixed and then enter the coal mill. By designing the cold primary air interface expansion pipe, the cold primary air annular air duct, and the cold primary air uniform grid, and adopting a scheme of arranging grid holes at equal distances and equal widths or in a gradually expanding manner, and designing applicable and preferred structures for square, rectangular, and circular shapes, the present invention realizes distributed and uniform air inlet, enables the hot and cold primary air to be quickly and uniformly mixed within a limited distance, improves the uniformity of the velocity field and temperature field of the mixed air, enhances the accuracy and stability of the air volume and temperature measurement at the inlet of the coal mill, and realizes more precise and stable control of the coal mill.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mill in coal-fired power plants, in particular to an annular cold and hot primary air mixing device at the inlet of a coal mill. Background Art

[0002] In large coal-fired power plants, the mixing method of cold primary air and hot primary air at the inlet of the coal mill generally adopts a direct impact entry, which makes it difficult for the cold primary air to penetrate the hot primary air flow field in the vertical direction. Moreover, in the subsequent mixing pipe section, the mixing distance between the cold primary air and the hot primary air is short, and the cold and hot primary airs cannot be effectively mixed. The flow field of the mixed air before entering the mill, including the velocity and temperature distribution, is seriously uneven, resulting in large deviations and fluctuations between the measured data of the air volume and air temperature at the inlet of the coal mill during the actual operation of the power plant. Further, it leads to problems such as poor accuracy and stability of the air volume control, frequent actions of the air dampers, etc., which have an adverse impact on the air volume control of the coal mill, the automatic regulation of the coal mill, and the stable operation of the coal mill. This phenomenon is more common when the layout of the primary air pipeline in the coal pulverizing system of coal-fired power plants is becoming increasingly compact. Therefore, it is necessary to improve the structure at the mixing point of the cold and hot primary airs at the inlet of the coal mill, so that the cold and hot primary airs can be quickly and evenly mixed within a limited distance, improve the flow field of the mixed air entering the mill, and improve the accuracy and stability of the air volume and air temperature measuring devices at the inlet of the coal mill, and achieve precise control of the ventilation volume of the coal mill and the temperature before and after the coal mill. Summary of the Invention

[0003] In order to solve the problem that the cold and hot primary airs at the inlet of the coal mill in coal-fired power plants cannot be mixed in time and effectively, the present invention provides an annular cold and hot primary air mixing device at the inlet of a coal mill.

[0004] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0005] Taking a rectangular or square primary air pipeline with a relatively small aspect ratio as an example, the present invention includes a hot primary air pipeline, a cold primary air pipeline, a cold primary air interface expansion pipe, a cold primary air annular air duct, a cold primary air uniform grid, and a guide baffle.

[0006] The cold primary air enters the hot primary air pipeline through the cold primary air pipeline, the cold primary air interface expansion pipe, the cold primary air annular air duct, and the cold primary air uniform grid, and the cold and hot primary airs are mixed and then enter the coal mill.

[0007] The hot primary air pipeline and the cold primary air pipeline are the hot primary air pipeline and the cold primary air pipeline designed conventionally for the coal mill in the power plant.

[0008] The described cold primary air interface expansion pipe includes two flow guiding baffles that divide the cold primary air into three paths, which respectively enter the cold primary air annular air ducts on the front side and both sides of the hot primary air pipe, achieving air intake from all around in a circular shape. The opening flow areas of the three channels formed by the flow guiding baffles should be consistent with the air volume distribution ratio of the three channels. Generally, the proportion of the flow area of the middle opening inlet in the total flow area is less than or equal to the proportion of the air intake in the front side in the total air volume, so as to achieve uniform air volume distribution and effectively reduce the flow resistance in the pipe.

[0009] In the described cold primary air annular air duct, the cold primary air flows in the cold primary air annular air duct and enters the cold primary air uniform grilles on the peripheral pipe walls of the hot primary air pipe. Generally, the flow areas on both sides of the cold primary air annular air duct are not less than the inlet areas on both sides of the cold primary air interface expansion pipe.

[0010] The described cold primary air uniform grilles are arranged on the four sides of the wall surface of the hot primary air pipe. A plurality of grille holes are arranged along the flowing direction of the cold primary air. The cold primary air enters the hot primary air pipe evenly through the grille holes, achieving uniform mixing in all directions. The flow areas and quantities of the grille holes should ensure the uniformity of air flow distribution. According to the actual pipe size, two or more equally divided grille holes are arranged on each side of the hot primary air pipe. Generally, the grille holes on the two facing sides are arranged in a counter-flow manner. Generally, the total flow area of all the grille holes of the cold primary air uniform grilles is not less than the flow area of the cold primary air pipe, so as to reduce the local resistance loss.

[0011] For a rectangular hot primary air pipe with a relatively large aspect ratio and short-side air intake, the above-mentioned all-around circular air intake device can still be selected. Preferably, it can be simplified to a two-side air intake mode. The two flow guiding baffles in the cold primary air interface expansion pipe divide the cold primary air into two paths, and the cold primary air uniform grilles are arranged on the long side of the hot primary air pipe to achieve two-side air intake, which can basically meet the requirement of uniform mixing of cold and hot primary air.

[0012] For a circular hot primary air pipe, a circular cold and hot primary air mixing device can be designed. Just arrange the cold primary air uniform grilles around the circumference of the hot primary air pipe to achieve circumferential air intake.

[0013] The beneficial effects of the present invention are as follows:

[0014] The annular cold and hot primary air mixing device for the mill inlet provided by the present invention for hot primary air pipes of various shapes adopts an equal-area annular air intake mode, which can achieve distributed air intake, enabling the cold and hot air flows to be mixed evenly in a shorter distance and faster time, and basically can effectively improve the uniformity of the temperature field and velocity field distribution of the primary air in the pipe and at the mill inlet. If considering that the change of the flow rate and resistance along the cold primary air annular air duct will cause the air volume entering each grille hole along the way to be not uniform enough, a layout scheme with the grille hole area gradually expanding along the flowing direction can be further preferably adopted to make the air volume entering each grille hole equal.

[0015] The present invention designs an extended pipe for the cold primary air interface, a cold primary air annular duct, and a cold primary air evenly distributed grille, and adopts a scheme of arranging grille holes with equal distance and equal width or gradually expanding. For three types of primary air ducts, namely square, rectangular, and circular, applicable and optimal structures are designed. Distributed and uniform air inlet is achieved, enabling the hot and cold primary air to be quickly and evenly mixed within a limited distance, improving the uniformity of the velocity field and temperature field of the mixed air, enhancing the accuracy and stability of the air volume and temperature measurement at the mill inlet, and achieving more precise and stable control of the mill. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the overall structure of the annular hot and cold primary air mixing device at the mill inlet applicable to rectangular or square pipes with a relatively small aspect ratio in the present invention. The grille holes of the cold primary air evenly distributed grille are arranged with equal flow area.

[0017] Figure 2 It is a schematic diagram of the overall structure of the annular hot and cold primary air mixing device at the mill inlet applicable to rectangular pipes with a relatively large aspect ratio in the present invention. The grille holes of the cold primary air evenly distributed grille are arranged with equal flow area.

[0018] Figure 3 It is a schematic diagram of the overall structure of the annular hot and cold primary air mixing device at the mill inlet applicable to circular pipes in the present invention. The cold primary air evenly distributed grille is arranged with equal flow area.

[0019] Figure 4 It is a schematic diagram of the overall structure of the annular hot and cold primary air mixing device at the mill inlet applicable to the gradually expanding arrangement of grille holes in the present invention. The area of the grille holes of the cold primary air evenly distributed grille gradually expands along the flow direction.

[0020] In the figure: 1. Hot primary air duct; 2. Cold primary air duct; 3. Extended pipe for cold primary air interface; 4. Cold primary air annular duct; 5. Cold primary air evenly distributed grille; 6. Deflector baffle. Detailed Description of the Embodiment

[0021] The implementation of the present invention will be described in detail below with reference to the drawings.

[0022] Embodiment 1:

[0023] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the overall structure of the annular hot and cold primary air mixing device at the mill inlet applicable to rectangular or square pipes with an aspect ratio less than a specified ratio in the present invention, including a hot primary air duct 1, a cold primary air duct 2, an extended pipe 3 for the cold primary air interface, a cold primary air annular duct 4, a cold primary air evenly distributed grille 5, and a deflector baffle 6.

[0024] The cold primary air passes through the cold primary air duct 2, the cold primary air interface expansion pipe 3, the cold primary air annular air duct 4, and the cold primary air distribution grille 5 in sequence and enters the hot primary air duct 1. After the cold and hot primary air are mixed, they enter the coal mill.

[0025] The cold primary air interface expansion pipe 3 includes two flow guiding baffles 6, which divide the cold primary air into three paths and enter the cold primary air annular air ducts 4 on the front side and the left and right sides of the hot primary air duct 1 respectively, realizing air intake from all around in a circular shape. The size of the opening flow area of the three channels formed by the flow guiding baffles 6 is consistent with the air volume distribution ratio of the three channels. The proportion of the flow area of the middle opening on the front side entering the hot primary air duct 1 in the total flow area is less than or equal to the proportion of the air intake on the front side in the total air volume, so as to achieve uniform air volume distribution and effectively reduce the flow resistance in the pipeline.

[0026] In the cold primary air annular air duct 4, the cold primary air flows in the cold primary air annular air duct 4 and enters the cold primary air distribution grille 5 on the peripheral wall of the hot primary air duct 1. The flow areas on both sides of the cold primary air annular air duct 4 are not less than the inlet areas on both sides of the cold primary air interface expansion pipe 3.

[0027] The cold primary air distribution grille 5 is arranged on the peripheral walls of the hot primary air duct 1, and a plurality of grille holes are arranged along the flowing direction of the cold primary air. The cold primary air enters the hot primary air duct 1 evenly through the grille holes, realizing uniform mixing in all directions. The flow area and quantity of the grille holes should ensure the uniformity of air flow distribution. According to the actual pipeline size, two or more equally divided grille holes are arranged on each surface of the hot primary air duct 1, and the grille holes arranged on the corresponding surfaces are arranged in a counter-flush manner. The total flow area of all the grille holes of the cold primary air distribution grille 5 is greater than or equal to the flow area of the cold primary air duct 2, so as to reduce the local resistance loss.

[0028] Embodiment 2:

[0029] For the rectangular hot primary air duct 1 with an aspect ratio greater than a specified ratio and short-side air intake, the above-mentioned all-around annular air intake device can still be selected. Preferably, as Figure 2 , it can be simplified to a two-side air intake mode. The two flow guiding baffles 6 in the cold primary air interface expansion pipe 3 divide the cold primary air into two paths, and the cold primary air distribution grille 5 is arranged on the long side of the hot primary air duct 1, realizing two-side long-side air intake, which can basically meet the requirement of uniform mixing of cold and hot primary air.

[0030] Embodiment 3:

[0031] For the circular hot primary air duct 1, a circular-ring cold and hot primary air mixing device can be designed. As Figure 3 , it is only necessary to arrange the cold primary air distribution grille 5 on the circumference of the hot primary air duct 1 to realize circumferential air intake.

[0032] As described above, the annular hot and cold primary air mixing device for the mill inlet provided by the present invention for the primary hot air ducts 1 of various shapes adopts an equal-area annular air inlet mode, which can achieve distributed air inlet, enabling the hot and cold airflows to be mixed evenly in a shorter distance and a faster time, and basically effectively improving the distribution uniformity of the temperature field and velocity field of the primary air in the duct and at the mill inlet. If it is considered that the change in the flow rate and resistance along the cold primary air annular duct 4 will cause the air volume entering each grille hole along the way to be not uniform enough, a layout scheme with the grille hole area gradually expanding along the flow direction can be further preferably adopted to make the air volume entering each grille hole equal, such as Figure 4 .

[0033] The annular hot and cold primary air mixing device for the mill inlet provided by the present invention, on the basis of the original hot and cold primary air mixing duct at the mill inlet of a coal-fired power plant, realizes distributed uniform air inlet through the designed cold primary air interface expansion pipe, cold primary air annular duct and cold primary air uniform grille, enabling the hot and cold airflows to be mixed evenly in a shorter distance and a faster time, improving the uniformity of the velocity field and temperature field of the mixed air, thereby improving the accuracy of the measurement of the primary air volume and temperature, and precisely regulating the operating state of the mill and the pulverizing system. For newly designed units, the device of the present invention can also be adopted.

[0034] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. A ring-shaped hot and cold primary air mixing device at the inlet of a coal mill, characterized in that it includes a hot primary air pipeline, a cold primary air pipeline, a cold primary air interface expansion pipe, a cold primary air annular air duct, and a cold primary air uniform grille. Among them: the cold primary air sequentially enters the hot primary air pipeline through the cold primary air pipeline, the cold primary air interface expansion pipe, the cold primary air annular air duct, and the cold primary air uniform grille, and the hot and cold primary air are mixed and then enter the coal mill; the device also includes two guiding baffles, which divide the cold primary air into three paths: one path enters the front side of the hot primary air pipeline, and the other two paths respectively enter the cold primary air annular air ducts on the left and right sides and the rear side, realizing air intake from all around in a ring shape; the opening flow areas of the three channels formed by the guiding baffles are consistent with the air volume distribution ratio of the three channels, and the proportion of the flow area of the middle opening entering the front side of the hot primary air pipeline in the total flow area is less than or equal to the proportion of the air intake on the front side in the total air volume, so as to achieve uniform air volume distribution; the cold primary air flows in the cold primary air annular air duct and enters the cold primary air uniform grille on the surrounding pipe walls of the hot primary air pipeline; the flow areas on both sides of the cold primary air annular air duct are greater than or equal to the inlet areas on both sides of the cold primary air interface expansion pipe; the cold primary air uniform grille is arranged on the wall surface where the hot primary air pipeline is located all around, and a plurality of grille holes of the same size are evenly arranged; the cold primary air enters the hot primary air pipeline evenly through the grille holes, and uniform mixing is achieved in all directions; on the surface of the hot primary air pipeline where the cold primary air uniform grille is arranged, there are two or more grille holes, and the grille holes on the opposite two surfaces are arranged in a counter-flush manner; and the total flow area of all the grille holes is greater than or equal to the flow area of the cold primary air pipeline; for the cold primary air uniform grille, the areas of the grille holes are equal; for the cold primary air uniform grille, the areas of the grille holes are designed to gradually expand along the flow direction of the cold primary air.

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