A medium-speed coal mill for coal-fired boiler with inner cone heat recovery

Abstract

The invention discloses a medium-speed coal mill for a coal-fired boiler with inner cone heat recovery, comprising a coal mill shell and a coarse powder separator, the coarse powder separator comprising a cone shell, and also comprising a heating medium inlet pipe and a heating medium outlet pipe; a hollow interlayer arranged along the circumferential direction is provided on the side wall of the cone shell; one end of the heating medium inlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell to connect to a heat medium source; one end of the heating medium outlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell; during the coarse powder separation process, a heating medium with a temperature of 100-240°C is introduced into the hollow interlayer of the side wall of the cone shell through the heating medium inlet pipe. The invention realizes the control of the outlet temperature of the coal mill, thereby realizing the decoupling control of the air-coal ratio and temperature of the coal mill outlet, and the introduction of the heating medium is also conducive to rapid warm grinding, thereby improving the load response capability of the boiler.

Description

Technical Field

[0001] The invention relates to a medium-speed coal mill for a coal-fired boiler with inner cone heat recovery, belonging to the technical field of coal mills for coal-fired power plants. Background Art

[0002] The coal mill is one of the most important auxiliary machines in a coal-fired power plant. Its operating conditions directly affect the safe and economical operation of the boiler. At the same time, it is also one of the auxiliary machines with the largest power consumption in a power plant. According to the working speed of the coal mill, the coal mills in power plants can be roughly divided into the following three types: high-speed coal mills, such as fan coal mills; medium-speed coal mills, such as flat disc coal mills, ball coal mills, bowl coal mills, etc.; low-speed coal mills, such as drum steel ball coal mills. Generally, drum steel ball coal mills are mostly used in intermediate storage silo type pulverizing systems, and other types of coal mills are mostly used in direct blowing type pulverizing systems.

[0003] Most modern large-scale power station boilers use direct-blowing pulverizing systems. Due to the advantages of medium-speed coal mills, such as light weight, small footprint, low investment, low power consumption, low metal wear and low noise, most of the large domestic thermal power plants currently use medium-speed coal mills.

[0004] The medium-speed coal mill consists of at least three parts: a driving device, a grinding device and a coarse powder separator. The grinding device is usually composed of a rotating grinding ring driven by a driving device and three fixed and self-rotating grinding rollers rolling along the grinding ring; the coarse powder separator is composed of a coarse powder separation baffle and a cone shell, and is arranged above the grinding ring. The raw coal falls onto the grinding ring from the coal drop pipe, and is thrown onto the grinding raceway by the centrifugal force of the rotating grinding ring, and is ground by the grinding roller. The grinding and drying of the raw coal are carried out simultaneously. The high-temperature primary air enters the grinding ring evenly through the nozzle ring, dries the coal powder mixture tangentially thrown out from the grinding ring after grinding, and transports it to the coarse powder separator above the grinding ring. The pebble coal falls into the pebble coal box through the nozzle ring. The coal powder mixture is separated from the coarse powder by the coarse powder separation baffle. The qualified fine powder is carried into the furnace for combustion by the primary air, and the coarse powder returns to the grinding ring from the bottom of the cone shell under its own gravity for re-grinding.

[0005] During the operation of the above-mentioned coal mill, the coarse powder returned to the grinding ring from the bottom of the cone shell contains not only large particles of coal powder, but also a large amount of impurities such as quartz sand and pyrite. Since the density of impurities is several times that of coal, only particles finer than qualified coal powder can be carried into the furnace by primary air. However, the hardness of impurities is significantly higher than the density of coal, and it takes multiple cycles of separation and grinding to be ground fine enough. The circulation rate of impurities in the coal mill is generally greater than 10, and is mixed with large particles of coal powder. The average circulation rate of coarse powder is generally about 8, and the residence time in the coal mill is generally 2 to 5 seconds.

[0006] In order to ensure the combustion efficiency and stability of the boiler, when the coal mill is running, it is generally necessary to ensure that the air-coal ratio of the air-powder mixture at the outlet of the coarse powder separator is between 1.6-2.5 and the temperature is between 60-100℃. The control of these two important target parameters is achieved by mixing the cold and hot primary air at the inlet of the coal mill. However, due to factors such as low temperature of low-load hot primary air and high moisture content of raw coal, the temperature of the air-powder mixture is lower than the target value under the premise of ensuring that the air-coal ratio is within the appropriate range, that is, the air-coal ratio and temperature cannot be decoupled for control. In addition, the temperature of the air-powder mixture at the outlet of the coal mill should not be too high, which is easy to cause the volatile matter of the raw coal to precipitate, causing safety hazards; generally, considering that the air temperature at the inlet of the coal mill is higher than the precipitation temperature of the volatile matter of the raw coal, the set temperature of the air-powder mixture at the outlet of the coal mill needs to be significantly lower than the precipitation temperature of the volatile matter of the raw coal to prevent the problem of local overheating during the drying process of the raw coal, thereby ensuring the safe and reliable operation of the pulverizing system, but this will lead to a decrease in boiler efficiency. Summary of the invention

[0007] In order to achieve decoupling control of the air-coal ratio and temperature at the coal mill outlet, shorten the warm-up time, increase the temperature of the air-powder mixture at the coal mill outlet, and ensure its operation safety, the present invention provides a medium-speed coal mill for a coal-fired boiler with inner cone heat recovery.

[0008] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0009] A medium-speed coal mill for a coal-fired boiler with inner cone heat recovery comprises a coal mill shell and a coarse powder separator, wherein the coarse powder separator is arranged on the inner side of the coal mill shell, and the coarse powder separator comprises a cone shell, and also comprises a heating medium inlet pipe and a heating medium outlet pipe; a hollow interlayer arranged along the circumferential direction is provided on the side wall of the cone shell; one end of the heating medium inlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell to connect to a heat medium source; one end of the heating medium outlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell; in the process of coarse powder separation, a heating medium with a temperature of 100-240°C is introduced into the hollow interlayer of the side wall of the cone shell through the heating medium inlet pipe, and the temperature of the heating medium is not higher than the precipitation temperature of volatile matter of the ground raw coal.

[0010] The medium flowing out of the heating medium outlet pipe can be cyclically heated and then sent into the hollow interlayer of the cone shell side wall through the heating medium inlet pipe for recycling, or can be used for other purposes.

[0011] The present application has a hollow interlayer, that is, a double-layer structure, and a gap is left between the double layers for the circulation of heating medium.

[0012] The applicant has found through research that by adopting the above technical solution, the air-coal ratio can be precisely controlled by precisely controlling the air volume at the coal mill inlet. As for the coal mill outlet temperature, the decoupling control of the air-coal ratio and temperature at the coal mill outlet can be achieved by introducing a heating medium. During the raw coal grinding process, the heating medium in the hollow interlayer of the side wall of the cone shell can heat the coarse powder that falls back into the cone shell by heat conduction, and at the same time, it can radiate heat to the entire internal components of the coal mill and the coal powder or coal particles, thereby significantly increasing the temperature of the air-powder mixture at the coal mill outlet; and the introduction of the heating medium is also conducive to rapid warm grinding, thereby improving the load response capability of the boiler. The temperature of the heating medium is not higher than the precipitation temperature of the raw coal volatile matter. This heating method is different from using high-temperature hot primary air to dry the coal powder (the temperature of the hot primary air is generally higher than the precipitation temperature of the raw coal volatile matter). It has a higher operating safety and allows the temperature of the air-powder mixture at the coal mill outlet to be significantly increased, thereby improving the boiler efficiency.

[0013] During operation, the outlet temperature of the coal mill can be used to adjust the temperature and amount of the heating medium, thereby achieving precise control of the outlet temperature of the coal mill, thereby realizing decoupling control of the air-coal ratio and temperature at the outlet of the coal mill.

[0014] In order to improve the heating efficiency, preferably, the cone shell includes an outer cone shell and an inner cone shell, both of which are cone-shaped structures, the inner cone shell is arranged inside the outer cone shell, and a 5-20 cm interval is left between the inner cone shell and the outer cone shell, so that most of the coarse powder can pass through the two cone shells; the side wall of the outer cone shell and the side wall of the inner cone shell are both provided with a hollow interlayer arranged along the circumferential direction; the heating medium inlet pipe is connected to the hollow interlayer on the side wall of the outer cone shell and the side wall of the inner cone shell at the same time, and the heating medium outlet pipe is connected to the hollow interlayer on the side wall of the outer cone shell and the side wall of the inner cone shell at the same time, that is, the heating medium can enter the hollow interlayer of the side wall of the outer cone shell and the side wall of the inner cone shell at the same time through the same heating medium inlet pipe, and can flow out through the same heating medium outlet pipe. That is, the cone shell is formed by the nested combination of the inner and outer cone shells, and a interval is left between the inner and outer cone shells. With this design, most of the coarse powder passes between the two cone shells, resulting in a better heating effect.

[0015] It should be noted that there are gaps between the bottom of the outer cone shell, the bottom of the inner cone shell and the coal drop pipe for the coarse powder to fall.

[0016] In order to further improve the heat utilization rate and heating uniformity, 60-80% of the coarse powder passes between the inner cone shell and the outer cone shell, and the remaining coarse powder passes through the inner side of the inner cone shell. The coarse powder passing between the inner cone shell and the outer cone shell and passing through the inner side of the inner cone shell returns to the grinding ring for re-grinding.

[0017] In order to improve the efficiency and reliability of the operation of the hollow interlayer, such as to facilitate water drainage or removal of impurities, preferably, the heating medium inlet pipe and the heating medium outlet pipe are distributed on both sides of the cone shell, the heating medium inlet pipe is connected to the top of the hollow interlayer, and the heating medium outlet pipe is connected to the bottom of the hollow interlayer.

[0018] In order to increase the service life of the cone shell, the surface of the cone shell is sprayed with a wear-resistant coating or affixed with a wear-resistant sheet.

[0019] In order to avoid the wear of the heating medium inlet pipe and the heating medium outlet pipe, the airflow surface of the heating medium inlet pipe and the heating medium outlet pipe are installed with anti-wear angle steel or anti-wear ceramic sheets. Since the airflow in the coal mill is from top to bottom, the above-mentioned airflow surface generally refers to the bottom of the heating medium inlet pipe and the heating medium outlet pipe.

[0020] The above-mentioned heating medium is water vapor or hot water.

[0021] In order to improve the heat utilization rate, a coil or a coil is arranged in the hollow interlayer, the inlet of the coil or the coil is connected to the heating medium inlet pipe, and the outlet of the coil or the coil is connected to the heating medium outlet pipe.

[0022] In this application, directional terms such as top and bottom refer to relative positions shown in the drawings or when the device is in normal use.

[0023] The technologies not mentioned in the present invention are all referred to the prior art.

[0024] The medium-speed coal mill for a coal-fired boiler with inner cone heat recovery of the present invention is provided with a hollow interlayer on the side wall of the cone shell. The outlet temperature of the coal mill is controlled by the introduction of heat medium, thereby realizing decoupling control of the air-coal ratio and temperature at the outlet of the coal mill. The introduction of heating medium is also conducive to rapid warming of the mill, thereby improving the load responsiveness of the boiler. Furthermore, the design of a double-layer heating cone shell further improves the heating effect and the load responsiveness of the boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a coal mill to which the present invention is applicable.

[0026] Figure 2 It is a schematic structural diagram of the inner cone heat recovery device of the medium-speed coal mill in Example 1 of the present invention.

[0027] Figure 3 It is a schematic structural diagram of the inner cone heat recovery device of the medium-speed coal mill in Example 2 of the present invention.

[0028] In the figure, 1 is a cone shell, 11 is a hollow interlayer, 12 is a heating medium inlet pipe, 13 is a heating medium outlet pipe, 14 is an inner cone shell, 15 is an outer cone shell, 2 is a coal mill outer shell, 3 is a coal drop pipe, 4 is fine powder, 5 is coarse powder, and 6 is primary air. DETAILED DESCRIPTION

[0029] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] like Figure 2 As shown, a medium-speed coal mill for a coal-fired boiler with inner cone heat recovery includes a coal mill shell and a coarse powder separator, the coarse powder separator is arranged on the inner side of the coal mill shell, and the coarse powder separator includes a cone shell, which is characterized in that it also includes a heating medium inlet pipe and a heating medium outlet pipe; a hollow interlayer arranged along the circumferential direction is provided on the side wall of the cone shell; one end of the heating medium inlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell to connect to a heat medium source; one end of the heating medium outlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the medium-speed coal mill shell; during the coarse powder separation process, water vapor (from auxiliary steam) with a temperature of 170°C is introduced into the hollow interlayer of the side wall of the cone shell through the heating medium inlet pipe; because the precipitation temperature of the volatile matter of the ground raw coal is above 180°C, the safety of this heating method can be guaranteed.

[0032] Engineering practice has verified that during the raw coal grinding process, the heating medium in the hollow interlayer of the cone shell side wall can heat the coarse powder that falls back into the cone shell through heat conduction, and at the same time can radiate heat to the entire internal components of the coal mill and the coal powder or coal particles, thereby significantly increasing the temperature of the air-powder mixture at the coal mill outlet from about 65°C before commissioning to about 85°C; and the introduction of the heating medium is also conducive to rapid warming of the mill, thereby improving the load response capability of the boiler. The above technical solution can ensure accurate control of the air-coal ratio by accurately controlling the coal mill inlet air volume, and the coal mill outlet temperature can be accurately increased by the introduction of the heating medium, thereby realizing the decoupling control of the coal mill outlet air-coal ratio and temperature.

[0033] Example 2

[0034] On the basis of Example 1, the following improvements were made: Figure 3As shown, in order to improve the heating efficiency, the cone shell includes an outer cone shell and an inner cone shell, both of which are cone-shaped structures, and the inner cone shell is arranged inside the outer cone shell, and a 5-20cm interval is left between the inner cone shell and the outer cone shell, so that most of the coarse powder can pass through the two cone shells; the side wall of the outer cone shell and the side wall of the inner cone shell are both provided with a hollow interlayer arranged along the circumferential direction; the heating medium inlet pipe is connected to the hollow interlayer on the side wall of the outer cone shell and the side wall of the inner cone shell at the same time, and the heating medium outlet pipe is connected to the hollow interlayer on the side wall of the outer cone shell and the side wall of the inner cone shell at the same time, that is, the heating medium can enter the hollow interlayer of the side wall of the outer cone shell and the side wall of the inner cone shell at the same time through the same heating medium inlet pipe, and can flow out through the same heating medium outlet pipe. That is, the cone shell is formed by the nested combination of the inner and outer cone shells, and a interval is left between the inner and outer cone shells. With this design, most of the coarse powder passes between the two conical shells, resulting in better heating effect and a greater increase in the temperature of the air-powder mixture at the pulverizer outlet.

[0035] Example 3

[0036] Based on Example 2, the following improvements were made: a 15 cm gap was left between the inner cone shell and the outer cone shell, so that about 75% of the coarse powder passed through the two cone shells, and the rest passed through the inner side of the inner cone shell, which can maximize the heat utilization rate and heating uniformity. The temperature of the air-powder mixture at the outlet of the coal mill was increased from about 65°C before commissioning to about 120°C.

[0037] Example 4

[0038] On the basis of Example 1 or 3, the following improvements were further made: in order to improve the reliability of the operation of the hollow interlayer, such as to facilitate water drainage or removal of impurities, the heating medium inlet pipe and the heating medium outlet pipe are distributed on both sides of the cone shell, the heating medium inlet pipe is connected to the top of the hollow interlayer, and the heating medium outlet pipe is connected to the bottom of the hollow interlayer.

[0039] Example 5

[0040] On the basis of Example 4, the following improvements are further made: in order to increase the service life of the cone shell, the surface of the cone shell is sprayed with a wear-resistant coating or affixed with a wear-resistant sheet. In order to avoid wear of the heating medium inlet pipe and the heating medium outlet pipe, the heating medium inlet pipe and the heating medium outlet pipe are both installed with anti-wear angle steel or anti-wear ceramic sheets on the airflow surface.

[0041] Example 6

[0042] On the basis of Example 5, the following improvements were further made: in order to improve the heat utilization rate, a coil or a serpentine pipe is arranged in the hollow interlayer, the inlet of the coil or the serpentine pipe is connected to the heating medium inlet pipe, and the outlet of the coil or the serpentine pipe is connected to the heating medium outlet pipe.

Claims

1. A medium-speed coal mill for a coal-fired boiler with inner cone heat recovery, comprising a coal mill housing and a coarse powder separator, wherein the coarse powder separator is arranged inside the coal mill housing, and the coarse powder separator comprises a cone shell, and is characterized in that: It also includes a heating medium inlet pipe and a heating medium outlet pipe; a hollow interlayer arranged along the circumferential direction is provided on the side wall of the cone shell; One end of the heating medium inlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the shell of the medium-speed coal mill and is connected to the heat medium source; One end of the heating medium outlet pipe is connected to the side wall of the cone shell and communicated with the hollow interlayer of the side wall of the cone shell, and the other end passes through the shell of the high-speed coal mill; During the coarse powder separation process, a heating medium with a temperature of 100-240°C is introduced into the hollow interlayer of the cone shell side wall through the heating medium inlet pipe, and the heating medium temperature is not higher than the precipitation temperature of the volatile matter of the ground raw coal; The outlet temperature of the coal mill is used to adjust the temperature and amount of the heating medium, so as to achieve precise control of the outlet temperature of the coal mill, thereby achieving decoupling control of the air-coal ratio and temperature at the outlet of the coal mill; The cone shell includes an outer cone shell and an inner cone shell, both of which are cone-shaped structures, the inner cone shell is arranged inside the outer cone shell, and a 5-20 cm interval is left between the inner cone shell and the outer cone shell; the side walls of the outer cone shell and the inner cone shell are both provided with hollow interlayers arranged along the circumferential direction; the heating medium inlet pipe is connected to the hollow interlayers on the side walls of the outer cone shell and the inner cone shell at the same time, and the heating medium outlet pipe is connected to the hollow interlayers on the side walls of the outer cone shell and the inner cone shell at the same time; 60-80% of the coarse powder passes between the inner cone shell and the outer cone shell, and the remaining coarse powder passes through the inner side of the inner cone shell.

2. The medium-speed coal mill for coal-fired boiler with inner cone heat recovery as claimed in claim 1, characterized in that: The heating medium inlet pipe and the heating medium outlet pipe are distributed on both sides of the cone shell. The heating medium inlet pipe is connected with the top of the hollow interlayer, and the heating medium outlet pipe is connected with the bottom of the hollow interlayer.

3. The medium-speed coal mill for coal-fired boiler with inner cone heat recovery as claimed in claim 1 or 2, characterized in that: The surface of the cone shell is sprayed with a wear-resistant coating or affixed with a wear-resistant sheet.

4. The medium-speed coal mill for coal-fired boiler with inner cone heat recovery as claimed in claim 1 or 2, characterized in that: Anti-wear angle steel or anti-wear ceramic sheets are installed on the airflow facing surfaces of the heating medium inlet pipe and the heating medium outlet pipe.

5. The medium-speed coal mill for coal-fired boiler with inner cone heat recovery as claimed in claim 1 or 2, characterized in that: The heating medium is steam or hot water.

6. The medium-speed coal mill for coal-fired boiler with inner cone heat regeneration according to claim 1 or 2, characterized in that: A coil or a coil is arranged in the hollow interlayer, the inlet of the coil or the coil is connected to the heating medium inlet pipeline, and the outlet of the coil or the coil is connected to the heating medium outlet pipeline.

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