JP2002370044A - Vertical roller mill - Google Patents

Abstract

(57) [Summary] [Problem] To expand the operation range on the mill low load side. SOLUTION: A primary air supply duct 10 introduces primary air A into a primary air chamber 11 formed at a lower position of a crushing table 7, and the mill casing 1 passes through a blowing port 12 located on an outer peripheral portion of the crushing table 7. Crushing chamber 2
In a vertical roller mill configured to supply primary air A to a primary air supply duct, a bypass duct 21 is connected between the primary air supply duct 10 and the crushing chamber 2. Bypass duct 21
Is provided in the middle of the primary air supply duct 1 according to the mill load.
0 to the grinding chamber 2 through a bypass duct 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical roller mill used to supply pulverized coal to a pulverized coal burner provided in a coal-fired boiler.

[0002]

2. Description of the Related Art Among such vertical roller mills, there is a type as shown in FIG. 2 as an example of a type which can obtain a relatively high pulverizing efficiency. That is, raw coal is introduced into the vertical center of the cylindrical mill casing 1 so as to form the crushing chamber 2 so that the raw coal 3 can be introduced toward the center of the mill casing 1. A pipe 4 is provided downward, and a pulverizing table 7 arranged at a bottom position in the mill casing 1 so as to be rotated at a low speed by a drive motor 5 via a speed reducer 6 is provided. Is equipped with a plurality of crushing rollers 9 that can be pressed onto the crushing table 7 by the above operation.
Is pulverized between the pulverizing table 7 and the pulverizing roller 9 to obtain pulverized coal 3a.

In addition, an annular primary air A is introduced into a lower region of the milling table 7 in a lower end portion of the mill casing 1 through a primary air supply duct 10 connected to a lower end side wall of the mill casing 1. In order to form the primary air chamber 11 and blow out the primary air A in the primary air chamber 11 into the crushing chamber 2, a plurality of fixed or rotary blowing ports ( A mill air port) 12 is provided, and a classifier 16 is provided at an upper position surrounding the raw coal input pipe 4 in the mill casing 1 so as to be rotationally driven by a classifying motor 15 on the mill casing 1. Pulverized coal pulverized in 2 3
a is conveyed upward by the primary air A blown into the pulverizing chamber 2 from the blowing port 12 and supplied to the pulverized coal burner through a pulverized coal pipe connected to a pulverized coal outlet 17 at the top of the mill casing 1. At this time, the pulverized coal 3a having a predetermined diameter or more is classified by a classifier 16 and returned to the center of the pulverizing table 7, and is then put together with the raw coal 3 fed from the raw coal input pipe 4. To be crushed again. 18
Is a foreign matter discharge pipe connected to the bottom of the primary air chamber 11 for discharging foreign matter such as pyrite mixed in with the raw coal 3, 13 is a flow rate adjusting damper of the primary air supply duct 10, and 19 is a shutoff damper. Is shown.

In the above-mentioned vertical roller mill, since the area of the blowing port 12 is fixed, it is necessary to secure a minimum flow rate of the primary air A blown from the blowing port 12 in order to prevent ash fall. Similarly, the air flow rate in the pulverized coal pipe from the mill casing 1 to the pulverized coal burner must be kept at a minimum,
Is dominant, and therefore, the air flow rate at the blow-out port 12 determines the minimum primary air amount of the mill and, consequently, the minimum load of the mill.

[0005]

However, when the flow rate of the air blown into the pulverizing chamber 2 from the blowing port 12 decreases, not only foreign matter such as pyrite but also the raw coal 3 falls into the primary air chamber 11. Therefore, there is a problem that the minimum primary air flow rate is restricted, and as a result, the mill operation range is sandwiched.

That is, in the case of pulverized coal burner combustion, the mixing ratio (A / C) of primary air and coal (pulverized coal) greatly affects the combustibility, so that the primary air flow rate is larger than that of coal (A / C). C is high), it is difficult for the burner to continuously maintain combustion due to the self-flame, and the ignition burner needs to support combustion. Therefore, the only way to reduce the boiler load below the minimum load on the mill is to stop the mill. During that stop time, the boiler also needs to maintain a constant load.
The same applies to the mill start time at the next boiler load increase. Therefore, this time is one of the bottlenecks in securing the boiler high load change rate and reducing the boiler startup time.

Therefore, the present invention is intended to expand the operation range on the low load side of the mill.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a crushing table rotatable on a lower portion in a mill casing and a crushing roller pressed against the crushing table. Is arranged, a pulverizing chamber for pulverizing the raw coal charged on the pulverizing table into pulverized coal is formed in the mill casing, and further, a primary air chamber is provided at a lower position of the pulverizing table. The primary air introduced into the primary air chamber through the primary air supply duct is blown into the grinding chamber from a blowing port provided at a position around the grinding table, and the pulverized coal is milled. In a vertical roller mill that is to be discharged from the pulverized coal outlet at the top of the above, a bypass duct is communicatively connected between the required position of the primary air supply duct and the pulverizing chamber, and A structure in which a bypass flow rate control damper in the middle of the bypass duct.

According to the load of the mill, part of the primary air introduced into the primary air chamber through the primary air supply duct can be supplied to the grinding chamber through the bypass duct.
It is possible to reduce only the amount of air passing through the outlet port without changing the total primary air flow rate, and it is possible to expand the operation range of the mill while securing the outlet port flow rate.

[0010] Further, the bypass flow rate adjusting damper is provided with an opening degree transmitter, and the bypass flow rate adjusting damper is feedback-controlled based on a command from a controller according to the mill load. The opening degree of the flow control damper can be feedback controlled.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In a configuration similar to that of the vertical roller mill shown in FIG. 2, a required portion of a primary air supply duct 10 is supplied to a pulverizing chamber 2 in a mill casing 1. The primary air supply duct 10 and the mill casing 1 are connected so that a part of the primary air A passing through the primary air supply duct 10 can be bypassed and supplied to a level directly above the blow-out port 12 opening into the grinding chamber 2.
The bypass duct 21 is connected to the lower position of the actuator, and the actuator 2 is provided in the middle of the bypass duct 21.
2 is equipped with a bypass flow rate adjustment damper 23 which is to be operated by, and the position transmitter 19 of the analog is placed in the bypass flow rate control damper 23, further, the signals S ₁ of the open degree transmitter 19 A controller 20 is provided for comparing and calculating a mill load signal S ₀ based on a mill differential pressure, a total primary air flow rate and the like, and sending a feedback control signal S ₂ to the actuator 22 of the bypass flow rate adjusting damper 23.

The load at which the bypass flow rate adjusting damper 23 of the bypass duct 21 starts to be opened is determined by the condition for calculating the area of the blow-out port 12 of the mill.
The area of the outlet port 12 is set smaller than the conventional one shown in FIG. 2 so that the same flow rate can be obtained even if the flow rate of the primary air A passing through the outlet port 12 is reduced.

Low mill load (low primary air flow)
Sometimes, the bypass flow rate regulating damper 23 of the bypass duct 21 by the control signal S ₂ from the controller 20 based on the mill load signal S ₀ at this time is caused to fully closed or in slightly open, thereby, the primary air A and the conventional Similarly, all are introduced into the primary air chamber 11 and then blown into the pulverizing chamber 2 through the blowout port 12.

On the other hand, when the mill load rises, the bypass
Slowly adjust the bypass flow rate adjustment damper 23 in the duct 21
Open, if the mill load exceeds a certain value, the mill load at that time
Load signal S₀Control signal S from the controller 20 based on₂By
The bypass flow rate adjusting damper 23 is opened, and the primary air
A part of the primary air A passing through the supply duct 10 is
To be supplied to the crushing chamber 2 through the branch 21.
You. In this case, increase of primary air flow rate with increase of mill load
Is supplied to the grinding chamber 2 through the bypass duct 21.
The opening of the bypass flow control damper 23 is controlled so that
However, the opening of the bypass flow rate adjusting damper 23 is
Is detected by the transmitter 19 and the signal S ₁Is the controller 2
0, the bypass flow rate adjustment damper 23
Is feedback-controlled, so that
The primary air flow supplied to the grinding chamber 2 without
It will be controlled accurately according to the situation.

As described above, according to the mill load, it is possible to reduce only the air flow rate passing through the blow-out port 12 while securing the total primary air flow rate necessary for transporting the pulverized coal at that time. As a result, the operating range on the low-load side of the mill can be expanded while ensuring the minimum primary air flow velocity.
Therefore, in the past, the operation of the mill had to be stopped due to the decrease in the mill load, but since the operation of the mill does not have to be stopped, the minimum boiler load obtained without stopping the mill can be obtained. Can be expanded, and it becomes possible to cope with a high load change of the boiler. Further, from this, the prescribed coal supply amount at the start and stop of the mill can be reduced, the impact on the boiler can be reduced, and the margin of the fuel ratio at the time of fuel switching (fuel oil or coal switching) increases. Therefore, the restriction on the burner number control can be relaxed.

[0017]

As described above, according to the vertical roller mill of the present invention, the crushing table rotatably driven at the lower portion in the mill casing and the crushing roller pressed against the crushing table are provided. Arranged, a pulverizing chamber for pulverizing raw coal put on the pulverizing table into pulverized coal is formed in the mill casing, and further, a primary air chamber is provided at a lower position of the pulverizing table. The primary air introduced into the primary air chamber through the primary air supply duct is blown into the pulverizing chamber from a blowing port provided at a position around the pulverizing table, and the pulverized coal is
In a vertical roller mill configured to discharge from a pulverized coal outlet at the top of a mill casing, a bypass duct is connected and connected between a required position of the primary air supply duct and a pulverizing chamber, and a bypass is provided in the middle of the bypass duct. Since the flow rate adjustment damper is provided, a part of the primary air passing through the primary air supply duct can be directly supplied to the pulverization chamber through the bypass duct according to the mill operation condition, which is necessary for the transport of pulverized coal. It is possible to reduce only the air flow passing through the blow-out port without changing the total primary air flow, thereby expanding the operation range of the mill while securing the air flow velocity to prevent carbon loss. Boiler load operation width without starting and stopping can be expanded, plant startup time can be shortened, and it is possible to respond to high load changes. The bypass flow rate adjustment damper is provided with an opening degree transmitter, and the bypass flow rate adjustment damper is feedback-controlled based on a command from a controller according to the mill load. An excellent effect that the primary air flow rate supplied to the crushing chamber can be accurately controlled according to the mill load condition is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a vertical roller mill of the present invention.

FIG. 2 is a schematic view showing an example of a vertical roller mill.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mill casing 2 Crushing chamber 3 Raw coal 3a Pulverized coal 7 Pulverizing table 9 Crushing roller 10 Primary air supply duct 11 Primary air chamber 12 Blow-out port 17 Pulverized coal outlet 19 Opening transmitter 20 Controller 21 Bypass duct 23 Bypass flow rate Adjustment damper A Primary air

Claims (2)

[Claims] A crushing table rotatably driven and a crushing roller pressed against the crushing table are arranged at a lower portion in a mill casing, and raw coal charged on the crushing table is arranged. A pulverizing chamber for pulverizing coal into pulverized coal is formed in the mill casing, a primary air chamber is formed at a lower position of the pulverizing table, and introduced into the primary air chamber through a primary air supply duct. A vertical roller mill in which the primary air thus obtained is blown into a pulverizing chamber from a blowing port provided at a position around the pulverizing table, and the pulverized coal is discharged from a pulverized coal outlet at the top of the mill casing. In the above, a bypass duct is communicatively connected between a required position of the primary air supply duct and the crushing chamber, and a bypass flow rate adjusting damper is provided in the middle of the bypass duct. A vertical roller mill characterized by having a configuration as described above. 2. The vertical type according to claim 1, wherein an opening degree transmitter is provided in the bypass flow rate adjusting damper, and the bypass flow rate adjusting damper is feedback-controlled based on a command from a controller according to the mill load. Roller mill.