Transformation method for reducing pebble coal emission rate of medium-speed coal mill

Abstract

The invention provides a transformation method for reducing pebble coal emission rate of a medium-speed coal mill, which comprises the following steps: acquiring coal quality data, and determining operation parameters of the coal mill; wherein the operation parameters of the coal mill comprise the air density at an air ring and the design area at an air ring outlet; the primary air volume of the coal mill is calculated according to the operation parameters of the coal mill; acquiring a target primary wind speed according to the coal quality data; according to the primary air volume of the coal mill, the target primary air speed and the air density at the air ring, the air ring flow area is calculated; and transforming the design area of the air ring outlet of the coal mill according to the through-flow area of the air ring to obtain the actual area of the air ring outlet of the coal mill. The air ring has the technical effects that the design is reasonable, the primary air speed is ensured to be within a reasonable interval by improving the through-flow area of the air ring, and the coal mill is better ensured to operate under a good working condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal-fired power plant power generation, and particularly relates to a transformation method for reducing the stone coal discharge rate of a medium-speed coal mill. BACKGROUND

[0002] As a core equipment of the coal pulverizing system of a boiler in a coal-fired power plant, the medium-speed coal mill has been widely applied in the domestic power industry, and the stone coal discharge rate is an important parameter affecting the safe and economic operation of the medium-speed coal mill. In the operation of the coal mill, the stone coal falls from top to bottom to the stone coal chamber through the wind ring, and the primary air enters the grinding area from bottom to top through the wind ring. At the throat of the wind ring, the hot air flowing in the opposite direction collides with the stone coal, separates the fine coal mixed in the stone coal, and returns to the grinding bowl to prevent the fine coal from being discharged from the coal mill. Only the stone coal that cannot be ground falls into the stone coal chamber and is discharged from the coal mill, so the air speed at the wind ring of the coal mill is a key parameter related to the stone coal discharge amount of the coal mill. When the coal mill is operated at low load, the air speed at the wind ring is lower, and the lower air speed causes a large amount of stone coal discharge, especially when poor coal is encountered, the amount of stone coal discharge is larger.

[0003] Therefore, the low air speed at the wind ring is the main reason for the large amount of stone coal discharge, and a transformation method for reducing the stone coal discharge rate of the medium-speed coal mill is urgently needed to solve the problem of large amount of stone coal discharge. SUMMARY

[0004] The application aims to at least solve one of the technical problems in the prior art, and provides a new technical solution of a transformation method for reducing the stone coal discharge rate of a medium-speed coal mill.

[0005] According to one aspect of the application, a transformation method for reducing the stone coal discharge rate of a medium-speed coal mill is provided, including the following steps: Step S1, obtaining coal quality data and determining the operating parameters of the coal mill; wherein the operating parameters of the coal mill include the air density at the wind ring and the design area at the outlet of the wind ring; Step S2, calculating the primary air flow of the coal mill according to the operating parameters of the coal mill; Step S3, obtaining a target primary air speed according to the coal quality data; Step S4, calculating the flow area of the wind ring according to the primary air flow of the coal mill, the target primary air speed, and the air density at the wind ring; Step S5, transforming the design area at the outlet of the wind ring of the coal mill to obtain the actual area at the outlet of the wind ring of the coal mill according to the flow area of the wind ring.

[0006] Optionally, transforming the design area at the outlet of the wind ring of the coal mill includes setting a throttling unit at the outlet of the wind ring of the coal mill.

[0007] Optionally, the throttling unit comprises a throttling ring or a throttling plate.

[0008] Optionally, when the throttling unit is a throttling ring, the throttling ring is arranged outside and / or inside the outlet of the wind ring.

[0009] Optionally, the throttling ring is a 16Mn arc-shaped steel plate, and the thickness is 10mm.

[0010] Optionally, when the throttling unit is a throttling plate, a plurality of throttling plates are arranged along the circumference of the outlet of the wind ring.

[0011] Optionally, after the actual area of the outlet of the wind ring of the coal mill is obtained by modifying the design area of the outlet of the wind ring of the coal mill according to the flow area of the wind ring, the method further comprises: Step S6, verifying and optimizing the actual area of the outlet of the wind ring of the coal mill.

[0012] Optionally, verifying and optimizing the actual area of the outlet of the wind ring of the coal mill comprises: determining whether the stone coal amount and composition, the current of the coal mill, the pressure difference between the inlet and outlet of the coal mill, the fineness of the coal powder, the display of the primary air volume / air speed, and the outlet temperature of the coal mill meet the requirements, to determine the operation feedback of the coal mill; According to the operation feedback of the coal mill, iteratively adjusting the actual area of the outlet of the wind ring until the optimal area is obtained.

[0013] Optionally, the calculation method of the flow area A of the wind ring is as follows: ; In the above formula, Q is the primary air volume of the coal mill, V is the target primary air speed, p is the air density at the wind ring, and K is the flow coefficient.

[0014] Optionally, the value range of K is 0.70-0.75.

[0015] One technical effect of the present application is: In the embodiments of the present application, the actual area of the outlet of the wind ring of the coal mill is obtained by modifying the design area of the outlet of the wind ring of the coal mill according to the flow area of the wind ring, and the actual area of the outlet of the wind ring is the flow area of the wind ring, so that the primary air is distributed more evenly when flowing through the wind ring, and the resistance loss is appropriately reduced, thereby the output of the coal mill is significantly improved after the stone coal discharge amount of the coal mill is reduced, the service life of the scraper and other components of the coal mill is increased, the fire phenomenon of the primary air chamber and the stone coal bucket is basically eliminated, and the work load of the stone coal discharge workers is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1A flowchart of a retrofit method for reducing the stone coal emission rate of a medium-speed coal mill according to an embodiment of the present application; Figure 2 A structural schematic diagram of a medium-speed coal mill after retrofit according to an embodiment of the present application; Figure 3 A structural schematic diagram of a throttle ring according to a first embodiment of the present application; Figure 4 A structural schematic diagram of a throttle ring according to a second embodiment of the present application; Figure 5 A structural schematic diagram of a throttle ring according to a third embodiment of the present application; Figure 6 A structural schematic diagram of a throttle plate according to an embodiment of the present application.

[0017] In the figure: 1, mill bowl; 2, air ring; 21, air ring outlet; 3, throttle unit; 31, throttle ring; 32, throttle plate; 4, dynamic-static gap. DETAILED DESCRIPTION

[0018] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. Note that the relative arrangement, numerical expressions, and numerical values of components and steps set forth in these embodiments are not limiting to the scope of the present application unless otherwise specifically stated.

[0019] Embodiments of the present application will be described in detail below, examples of which are shown in the accompanying drawings, in which the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are for the purpose of explanation only, and are not to be understood as limiting the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0020] The terms "first", "second" in the specification and claims of the present application can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise stated. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / ", generally represents a "or" relationship between the front and rear associated objects.

[0021] According to one aspect of the present application, referring to Figure 1 , a retrofit method for reducing the stone coal emission rate of a medium-speed coal mill is provided, which improves the air speed at the air ring by changing the flow area of the air ring of the coal mill, and aims to improve the air speed at the air ring to reduce the lighter stone coal and coal particles falling into the stone coal emission system, thereby reducing the stone coal emission rate of the medium-speed coal mill.

[0022] Specifically, the transformation method for reducing the stone coal emission rate of the medium-speed coal mill comprises the following steps: In step S1, coal quality data is obtained, and operation parameters of the coal mill are determined; wherein the operation parameters of the coal mill comprise air density at the air ring and design area at the outlet of the air ring of the coal mill; In step S2, the primary air flow of the coal mill is calculated according to the operation parameters of the coal mill; In step S3, a target primary air speed is obtained according to the coal quality data; In step S4, the air ring flow area is calculated according to the primary air flow of the coal mill, the target primary air speed and the air density at the air ring; In step S5, the design area at the outlet of the air ring of the coal mill is transformed according to the air ring flow area, so as to obtain the actual area at the outlet of the air ring of the coal mill.

[0023] In the embodiments of the present application, the design area at the outlet of the air ring of the coal mill is transformed according to the air ring flow area, so as to obtain the actual area at the outlet of the air ring of the coal mill, that is, the air ring flow area, so that the primary air is distributed more uniformly when flowing through the air ring, and the resistance loss is appropriately reduced, thereby obviously improving the output of the coal mill after reducing the stone coal emission of the coal mill, increasing the service life of the scraper and other components of the coal mill, basically eliminating the fire phenomenon of the primary air chamber and the stone coal bucket, and greatly reducing the work load of the stone coal emission workers.

[0024] It should be noted that, referring to Figure 2 The primary air enters from below the grinding bowl 1, flows through the outer diameter of the rotating grinding bowl 1 through the air ring 2 with a fixed area around the grinding bowl 1 (making the airflow tend to be vertical), and the smaller and lighter coal particles at the outer diameter of the grinding bowl 1 are carried upward by the airflow, while the heavy and hard-to-grind foreign matter falls into the side body area through the airflow. Due to the low wind speed at the throat of the air ring 2 (i.e., at the outlet 21 of the air ring), the amount of stone coal is large, so a throttling unit is arranged at the outlet of the air ring of the coal mill, which changes the air ring flow area and forms a streamlined nozzle with the air ring 2, so that the primary air is distributed more uniformly when flowing through the air ring 2, and the resistance loss is appropriately reduced.

[0025] Optionally, the design area at the outlet of the air ring of the coal mill is transformed, comprising arranging a throttling unit 3 at the outlet of the air ring of the coal mill.

[0026] Optionally, the throttling unit 3 comprises a throttling ring 31 or a throttling plate 32. This helps to effectively transform the design area at the outlet of the air ring of the coal mill, and the operation mode is relatively simple.

[0027] Optionally, referring to Figures 3 to 5In the throttling unit 3 is a throttling ring 31, the throttling ring 31 is arranged outside and / or inside of the outlet of the wind ring. The design of the throttling ring 31 is reasonable, which helps to obtain a smaller wind ring flow area at the outlet of the wind ring of the coal mill.

[0028] Optionally, the throttling ring 31 is a 16Mn arc-shaped steel plate with a thickness of 10mm. The design of the throttling ring is reasonable and has high strength.

[0029] Optionally, when the throttling unit 3 is a throttling plate 32, a plurality of throttling plates 32 are arranged along the circumference of the outlet of the wind ring. This can effectively transform the design area of the outlet of the wind ring of the coal mill to obtain a reasonable wind ring flow area, and the operation mode is relatively simple.

[0030] Optionally, after transforming the design area of the outlet of the wind ring of the coal mill according to the wind ring flow area to obtain the actual area of the outlet of the wind ring of the coal mill, the method further comprises: Step S6, verifying and optimizing the actual area of the outlet of the wind ring of the coal mill.

[0031] Optionally, verifying and optimizing the actual area of the outlet of the wind ring of the coal mill comprises: determining whether the stone coal amount and composition, the mill current, the mill inlet and outlet pressure difference, the coal fineness, the primary air volume / air speed display, and the mill outlet temperature meet the requirements to determine the running feedback of the coal mill; According to the running feedback of the coal mill, iteratively adjusting the actual area of the outlet of the wind ring until the optimal area is obtained.

[0032] In the above embodiment, for the stone coal amount and composition, the target is significantly reduced and the composition is mainly gangue / pyrite; (core index) (target <0.05%BM); for the mill current, it reflects the load of the grinding disc, and too large may cause coal blockage and too small may cause the grinding roller not to be effectively loaded; for the mill inlet and outlet pressure difference (ΔPmill), it reflects the material level in the mill and the ventilation resistance, and is strongly related to the primary air speed and the coal fineness; for the coal fineness (R 90 , R 200 ), it is ensured to be within the qualified range. Too high air speed may increase the amount of coarse powder, and too low air speed may cause the fineness to be too fine but the output to decrease; for the primary air volume / air speed display, it verifies whether the target value is reached; for the mill outlet temperature, it ensures sufficient drying.

[0033] Finally, according to the running feedback of the coal mill (especially the stone coal amount and the mill running stability), iteratively adjusting the wind ring flow area until the optimal area is obtained. For the optimal air speed determination: the stone coal amount <5kg / t of coal and mainly mineral matter.

[0034] Optionally, the wind ring flow area A is calculated as follows: ; In the above formula, Q is the primary air flow of the coal mill, V is the target primary air speed, p is the air density at the wind ring, and K is the flow coefficient.

[0035] In the above embodiment, the wind ring flow area A is accurately calculated, thereby accurately modifying the design area at the outlet of the wind ring of the coal mill, and good working conditions of the coal mill are better ensured.

[0036] In the embodiment of the present application, for a reasonable primary air speed, the typical range is 18-35 m / s; bituminous coal is recommended to be 25-35 m / s; and anthracite / high-density coal is recommended to be 18-25 m / s (to reduce the amount of stone coal).

[0037] For the primary air flow Q (kg / s or m³ / s) of the coal mill, the larger of the following two values is taken: lQ dry = the air flow required for drying (calculated according to the moisture of the coal and the heat balance); Q trans = BM x air-coal ratio (BM is the grinding output, and the air-coal ratio is 1.6-2.2 kg / kg).

[0038] For the target primary air speed V (m / s), the selection principle is: high volatile coal (bituminous coal): 25-35 m / s; high ash / high pyrite coal: 18-25 m / s (to reduce stone coal); or, the recommended value of the manufacturer or the operation data of the similar unit is referred to.

[0039] The air density p (kg / m³) at the wind ring is calculated by the following formula: ; In the above formula, P is the absolute pressure (Pa) at the wind ring ≈ inlet pressure + 0.5 x grinding bowl pressure difference; R is the gas constant = 287 J / (kg·K); and T is the temperature (K) at the wind ring ≈ inlet temperature - (40-80°C).

[0040] For example, p is estimated as (inlet pressure + 0.5 x ΔP mill ) / (287 x (inlet temperature - 60 + 273)).

[0041] For the flow coefficient K, the manufacturer of the coal mill usually provides the K value or the equivalent effective area according to the design of the wind ring (blade angle, shape, number), and the given value of the manufacturer is preferred. When there is no accurate data, for a typical medium-speed mill wind ring design, 0.65-0.85 is usually taken (the recommended initial value is 0.70-0.75, and the final value is determined by combining field test calibration and reverse deduction).

[0042] Exemplarily, the coal quality data further include Hardgrove Grindability Index (HGI), Moisture in the air-dried basis (Mad), Volatile matter on a dry ash-free basis (Vdaf), Ash content on as-received basis (Aar), Total sulfur on air-dried basis (St.ad), etc. The mill parameters further include model, maximum output BM, grinding disc diameter, base wind ring area, mill manufacturer recommended wind speed range, etc.

[0043] In determining the target primary air speed V, the recommended values of different coal types by the manufacturer can be referred to; the coal quality characteristics (especially for high-ash, high- pyrite coal, the lower limit value is inclined to be selected) can be combined; the successful operation experience of similar units burning similar coal types can be referred to; of course, the intermediate low value (for example, 22-25 m / s) can be initially selected conservatively, and optimized after running.

[0044] Optionally, the value range of K is 0.70-0.75. This helps to quickly and accurately calculate the wind ring flow area A.

[0045] In the embodiment of the present application, the transformation method for reducing the stone coal emission rate of the medium-speed coal mill can reduce the stone coal emission rate of the medium-speed coal mill. In order to make the medium-speed coal mill run normally, the wind speed at the throat of the wind ring 2 should be 70-90 m / s. If the wind speed is too low, the primary air cannot effectively carry the coal powder, which will cause the output of the coal mill to decrease and the amount of stone coal to increase. If the wind speed is too high, a large amount of unqualified coal powder will be input into the boiler by the primary air, causing combustion difficulty. In addition, due to the high wind speed, the wind-coal coexistence zone in the "boiling" state at the throat of the moving ring becomes thicker, increasing the ventilation resistance of the coal mill, and also making the coal layer in the grinding area thinner, causing the vibration of the coal mill to intensify. The excessively high wind speed will also intensify the abnormal wear of the moving and stationary wind rings (i.e., the gap 4 between the moving and stationary rings, i.e., the gap formed between the moving and stationary rings), shortening the service life thereof. Therefore, the technical route of reducing the wind ring flow area to increase the primary air speed to reduce the stone coal emission rate of the medium-speed coal mill needs to consider the reasonable flow area of the wind ring 2 in combination with the actual coal type operation condition of the power plant, to ensure that the primary air speed is located in a reasonable range and to ensure the good operation of the coal mill.

[0046] For example, the late period can also be modified to the way of discharging stone coal, the current non-closed stone coal discharging device is modified to the environment-friendly closed negative pressure pumping stone coal discharging device, which can greatly reduce dust pollution, improve the working environment of discharging workers, and further reduce the labor intensity of discharging workers.

[0047] It can be understood that the above embodiments are only exemplary embodiments for illustrating the principles of the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered as the protection scope of the present application.

Claims

1. A retrofit method for reducing the rate of stone coal discharge from a medium speed coal mill, characterized in that, The method comprises the following steps: Step S1, obtaining coal quality data and determining operation parameters of the coal mill; wherein the operation parameters of the coal mill comprise air density at the air ring and design area at the outlet of the air ring; Step S2, calculating primary air volume of the coal mill according to the operation parameters of the coal mill; Step S3, obtaining target primary air speed according to the coal quality data; Step S4, calculating air ring flow area according to the primary air volume of the coal mill, the target primary air speed and the air density at the air ring; Step S5, modifying the design area at the outlet of the air ring of the coal mill according to the air ring flow area, so as to obtain actual area at the outlet of the air ring of the coal mill.

2. The retrofit method of reducing the shot out rate of a medium speed mill of claim 1, wherein, The modification of the design area at the outlet of the air ring of the coal mill comprises setting a throttling unit at the outlet of the air ring of the coal mill.

3. The retrofit method of reducing the shot out rate of a medium speed mill of claim 2, wherein, The throttling unit comprises a throttling ring or a throttling plate.

4. The retrofit method of reducing the shot out rate of a medium speed mill of claim 3, wherein, When the throttling unit is a throttling ring, the throttling ring is arranged outside and / or inside the outlet of the air ring.

5. The retrofit method of reducing the shot out rate of a medium speed mill of claim 4, wherein, The throttling ring is a 16Mn arc-shaped steel plate with a thickness of 10mm.

6. The retrofit method of reducing the shot out rate of a medium speed mill of claim 3, wherein, When the throttling unit is a throttling plate, a plurality of throttling plates are arranged along the circumference of the outlet of the air ring.

7. The retrofit method of reducing the shot out rate of a medium speed mill of claim 1, wherein, After the modification of the design area at the outlet of the air ring of the coal mill according to the air ring flow area, so as to obtain actual area at the outlet of the air ring of the coal mill, the method further comprises: Step S6, verifying and optimizing the actual area at the outlet of the air ring of the coal mill.

8. The retrofit method of reducing the shot out rate of a medium speed mill of claim 1, wherein, The verification and optimization of the actual area at the outlet of the air ring of the coal mill comprises: determining whether the amount and composition of stone coal, the current of the coal mill, the pressure difference between the inlet and outlet of the coal mill, the fineness of the pulverized coal, the display of the primary air volume / air speed and the outlet temperature of the coal mill meet the requirements, so as to determine the operation feedback of the coal mill; iteratively adjusting the actual area at the outlet of the air ring according to the operation feedback of the coal mill, until the optimal area is obtained.

9. The retrofit method of reducing the shot out rate of a medium speed mill of claim 1, wherein, The calculation method of the air ring flow area A is as follows: ； In the above formula, Q is the primary air volume of the coal mill, V is the target primary air speed, p is the air density at the air ring, and K is the flow coefficient.

10. The retrofit method of reducing the shot out rate of a medium speed mill of claim 9, wherein, The value range of K is 0.70-0.75.

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