JP2002005703A - Primary air flow measuring device for mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the primary air flow measuring device for a mill, capable of accurately measuring a pressure difference and obtaining the accurate measured flow value of the primary air flow, without receiving any influence from a dynamic pressure or a vortex flow even if a stream lining distance at the upstream side of a venturi is not secured because of a restriction on the layout of a primary air supply duct. SOLUTION: A perforated panel 60 for stream lining, on which many holes 59 are bored, is disposed in the primary air supply duct 38 at the further downstream side of a primary air flow control damper 41 and the further upstream side of the detecting point of a pressure P1 at the entrance part of a venturi 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary air flow measuring device for a mill.

[0002]

2. Description of the Related Art Generally, a mill 1 as shown in FIG. 6 has been used to pulverize a granular material such as coal supplied to a coal-fired boiler to obtain fine powder such as pulverized coal.

[0003] A table 5 which is rotationally driven by a driving device 3 such as a motor via a speed reducer 4 is disposed in a lower portion of the inside of a casing 2 of the mill 1. The bracket 6 is the casing 2
The pivot bracket 6 is provided with a roller 8 that rotates about an axis O extending in a direction substantially perpendicular to the horizontal shaft 7 at the tip of the pivot bracket 6. A fluid pressure cylinder 9 using a fluid such as oil is attached to the journal cover 2 a of the casing 2, and a rod 9 a of the fluid pressure cylinder 9 is extended to fit into the plunger housing 10. By pressing the pressing portion 6a of the pivot bracket 6 via the plunger 11, the roller 8 is pressed against the upper surface of the horizontally rotating table 5, and the roller 8 and the table 5 cooperate, and the coal or the like on the table 5 Can be crushed.

In the casing 2, a primary air chamber 37 is formed below the table 5, and an annular body 12 is arranged so as to surround the table 5. From the air supply duct 38 to the primary air chamber 3
An air port 14 is provided so that the primary air 13 introduced into 7 can be blown into the upper part of the casing 2.

A head frame 15 is provided outside the upper portion of the casing 2 so as to communicate with the inside of the casing 2, and a bearing tube 16 is fixed in the head frame 15 so as to extend vertically. Bearings 17 and 18 are fitted into the bearing cylinder 16 at a required interval vertically.
A fine powder supply pipe 19 for supplying fine powder such as pulverized coal to a burner (not shown) of the boiler is connected to a side portion of the head frame 15.

A hollow cylindrical rotary shaft 20 extending vertically is fitted into the bearings 17 and 18, and a rotary classifier 21 is mounted on a portion of the rotary shaft 20 extending into the casing 2.
A pulley 22 is fitted to a portion of the rotary shaft 20 extending above the bearing tube 16.
A pulley 25 is fitted to an output shaft 24 of a driving device 23 such as a vertical motor installed outside the upper portion of the casing 2. The pulley 25 is fitted to the pulley 22 fitted to the rotary shaft 20. An endless belt 26 is looped between them.

In the rotary classifier 21, a rotary plate 27 is fitted to the lower end of the rotary shaft 20, and an outer peripheral portion of the rotary plate 27 is
It has a configuration in which a number of flat blades 28 extending upward are arranged.

A rotary classifier 2 is provided in the casing 2.
1, a truncated inverted conical reject chute 31 is provided.
A slit 32 extending along the inclined surface is formed in the first inclined surface so that a powder obtained by pulverizing a granular material such as coal blown up by the primary air 13 can pass through.

A chute 3 of a coal feeder 34 driven by a driving device 33 such as a motor is provided inside the rotary shaft 20.
A chute tube 30 whose upper end is connected to 5 is arranged so that its lower end is opened slightly above the roller 8 in the casing 2.

In FIG. 6, reference numeral 36 denotes a coal bunker for storing coal.

In the mill 1 shown in FIG. 6, the granular material such as coal cut out from the coal bunker 36 to the coal feeder 34 is driven by the driving device 33 of the coal feeder 34 from the chute 35 through the chute pipe 30. The table 5 which is thrown into the casing 2 and falls on the table 5 and is driven by the drive unit 3 via the speed reducer 4 to rotate in the horizontal direction, and the roller which is in contact with the table 5 and rotates. The powder such as coal, which has been pulverized by the cooperative operation with the secondary air 8, rises in the casing 2 as shown by an arrow, accompanied by the primary air 13 blown out from the air port 14, and passes through the slit 32 of the reject chute 31. Then, it is blown up above the reject chute 31 and the drive unit 23
The coarse powder is classified by the rotary classifier 21 which is driven by the rotary shaft 20 and rotates together with the rotating shaft 20, and the fine powder such as the pulverized coal which has been classified into the coarse powder enters the head frame 15 through the rotary classifier 21. The coarse powder that has been sent from the head frame 15 to the fine powder feed pipe 19 and sent to a burner (not shown) of the boiler and that has been classified by the rotary classifier 21 slides down the reject chute 31. To be returned to the table 5.

Meanwhile, in a primary air supply duct 38 connected to the primary air chamber 37 of the mill 1, hot air preheated by an air preheater (not shown) and cold air not preheated are respectively supplied. The primary air 13 is mixed by adjusting the opening degree of the hot air damper 39 and the cold air damper 40 so that the required temperature of the primary air 13 flows therethrough. And a primary air flow measurement venturi 42 and a primary air cutoff damper 43 are sequentially provided. The primary air flow rate 44 measured by the venturi 42 is a primary air flow rate command value 46 based on the coal supply command 45 so that a primary air flow rate command value 46 is obtained. The opening degree of the air flow control damper 41 is adjusted.

The control system for controlling the flow rate of the primary air 13 includes a differential pressure detector 47 for detecting a differential pressure ΔP between the pressure P1 at the inlet of the venturi 42 and the pressure P2 at the throat 42a of the venturi 42; A first function generator 49 for obtaining and outputting a primary air flow rate 48 based on the differential pressure ΔP detected by the detector 47; a temperature detector 50 for detecting the temperature T of the primary air 13; A second function generator 52 for calculating and outputting a specific weight correction coefficient 51 based on the temperature T detected in the step (a), and a second function generator 52 for the primary air flow rate 48 output from the first function generator 49. A multiplier 53 for multiplying the output specific weight correction coefficient 51 to obtain and output an actual primary air flow rate 44, and a third function generator 54 for obtaining and outputting a primary air flow rate command value 46 based on a coal supply command 45 And the third function A subtractor 56 for calculating a difference between the primary air flow command value 46 output from the generator 54 and the primary air flow 44 output from the multiplier 53 and outputting a primary air flow deviation 55, A proportional-integral adjuster 58 that performs a proportional integration process on the output primary air flow deviation 55 and outputs an opening command 57 of the primary air flow control damper 41 for eliminating the primary air flow deviation 55. Have.

As shown in FIG. 7, a function for obtaining and outputting a primary air flow rate 48 from a calculation formula based on Bernoulli's theorem with respect to a change in the differential pressure ΔP is set and input to the first function generator 49 as shown in FIG. ing.

As shown in FIG. 8, a function for outputting the specific weight correction coefficient 51 as a predetermined value with respect to a change in the temperature T is input to the second function generator 52 as shown in FIG.

For example, as shown in FIG. 9, a function for outputting a primary air flow rate command value 46 as a predetermined value in response to a change in the coal supply command 45 is input to the third function generator 54. I have.

When the mill 1 is operated, the pressure P at the inlet of the venturi 42 is detected by the differential pressure detector 47.
1 and the pressure difference ΔP between the pressure P2 of the throat portion 42a of the venturi 42 is detected and output to the first function generator 49,
In the first function generator 49, the primary air flow rate 48 is obtained based on the differential pressure ΔP detected by the differential pressure detector 47 and output to the multiplier 53, and the primary air 13 is detected by the temperature detector 50. The temperature T is detected and output to a second function generator 52, which calculates a specific weight correction coefficient 51 based on the temperature T detected by the temperature detector 50, and 53, and the multiplier 53 multiplies the primary air flow rate 48 output from the first function generator 49 by the specific weight correction coefficient 51 output from the second function generator 52 to obtain an actual primary The air flow rate 44 is obtained and output to the subtractor 56.

On the other hand, in the third function generator 54, a primary air flow rate command value 46 is obtained based on the coal supply command 45 and is output to the subtractor 56. The difference between the primary air flow command value 46 output from the generator 54 and the primary air flow 44 output from the multiplier 53 is determined, and the primary air flow deviation 55 is output to the proportional integral controller 58, Integral controller 58
, The primary air flow deviation 55 output from the subtractor 56 is proportionally integrated, and the primary air flow deviation 55
The opening command 57 of the primary air flow control damper 41 is output to eliminate the primary air flow control damper 41, the opening of the primary air flow control damper 41 is adjusted, and the primary air flow 44 becomes the primary air flow command The control is performed so as to be 46.

[0019]

However, in the conventional mill 1 as described above, particularly in the case of a large mill,
Due to the restrictions on the layout of the primary air supply duct 38, the rectification distance upstream of the venturi 42 (the straight pipe distance between the primary air flow control damper 41 and the venturi 42) often cannot be sufficiently ensured, and the primary pressure That is, the pressure P1 at the inlet of the venturi 42 is affected by the dynamic pressure or the eddy current, so that the differential pressure ΔP cannot be measured stably, and the accurate measurement value of the flow rate of the primary air 13 cannot be obtained. .

In view of such circumstances, the present invention provides a method for controlling a differential pressure without being affected by a dynamic pressure or a vortex even when a rectification distance on the upstream side of a venturi cannot be secured due to restrictions on the layout of a primary air supply duct. The primary purpose of the present invention is to provide a primary air flow measuring device for a mill capable of stably measuring the primary air flow and obtaining an accurate primary air flow measurement value.

[0021]

According to the present invention, a primary air supply duct in which a primary air flow control damper and a primary air flow measurement venturi are sequentially provided on the way is connected to a primary air chamber. A primary air flow measuring device for a mill, which obtains a primary air flow rate based on a pressure difference between an inlet pressure and a pressure of a venturi throat portion, wherein the primary air flow rate measurement device is located downstream of a primary air flow control damper and at a Venturi pressure. A primary air flow measuring device for a mill, characterized in that a rectifying perforated plate having a large number of holes is arranged in a primary air supply duct upstream of a pressure detection point at an inlet. is there.

According to the above means, the following effects can be obtained.

As described above, a rectifying perforated plate having a number of holes formed in the primary air supply duct downstream of the primary air flow control damper and upstream of the pressure detection point at the inlet of the venturi. Is arranged, a drift occurs in the primary air after passing through the primary air flow control damper, but the flow is rectified when passing through the perforated plate.

As a result, due to restrictions on the layout of the primary air supply duct, even if the straightening distance upstream of the venturi (the straight pipe distance between the primary air flow control damper and the venturi) cannot be sufficiently ensured, the primary The pressure, that is, the pressure at the inlet of the venturi is not affected by the dynamic pressure or the vortex, the differential pressure can be measured stably, and an accurate measurement value of the primary air flow rate can be obtained.

[0025]

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

FIGS. 1 to 3 show an embodiment of the present invention. In the drawings, the portions denoted by the same reference numerals as those in FIGS. 6 to 9 represent the same components. This embodiment is similar to the conventional one shown in FIGS. 6 to 9, but is characterized in that, as shown in FIGS. 1 to 3, the inlet of the venturi 42 is located downstream of the primary air flow control damper 41. In the primary air supply duct 38 on the upstream side of the detection point of the pressure P1 of the section, the rectifying perforated plate 6 provided with a number of holes 59 is provided.
0 is provided.

The perforated plate 60 has a thickness of about 5 [m].
m], the diameter D is about 6 as shown in FIG.
The hole 59 of [mm] has a center-to-center distance p of about 9 [m].
m], and the distance L from the end of the duct casing of the primary air flow control damper 41 is approximately 150 [m], as shown in FIG.
m] in the primary air supply duct 38.

In the illustrated example, the venturi 4 is connected to the end of the primary air flow control damper 41 from the end of the duct casing.
The straight pipe distance H of the primary air supply duct 38 to the start of the throttle 2 is approximately 1500 [mm], and the primary air supply duct 3
The width W and depth of 8 are approximately 850 × 2128 [mm].

Next, the operation of the illustrated example will be described.

As described above, the primary air flow control damper 41
If a rectifying perforated plate 60 having a large number of holes 59 is provided in the primary air supply duct 38 further downstream and upstream of the pressure P1 detection point at the inlet of the venturi 42, the primary air Although a drift occurs in the primary air 13 after passing through the flow control damper 41, the primary air 13 is rectified when passing through the perforated plate 60.

A comparison between the simulation results of the primary air flow in the case where the perforated plate 60 is provided as in the illustrated example and the case where the perforated plate 60 is not provided as in the conventional example is shown below. As shown in FIGS. 4A and 4B, when the perforated plate 60 is provided, the primary air 13 after passing through the primary air flow rate control damper 41 is supplied to the perforated plate 60.
When the perforated plate 60 is not provided, the primary air 13 after passing through the primary air flow control damper 41 has a drift.

FIG. 5 shows a comparison of the differential pressure ΔP measured when the perforated plate 60 is provided as in the illustrated example and when the perforated plate 60 is not provided as in the conventional example.
When the perforated plate 60 is provided and the opening degree of the primary air flow control damper 41 is about 17% or more, the differential pressure ΔP becomes a positive (+) value, While the flow rate of the air 13 can be measured, when the perforated plate 60 is not provided, the differential pressure ΔP becomes positive unless the opening degree of the primary air flow rate control damper 41 is about 25% or more. Since the value of (+) is not obtained, the flow rate measurement of the primary air 13 becomes impossible, and the width of the flow rate measurement of the primary air 13 is wider when the perforated plate 60 is provided as in the illustrated example. I understand.

As a result, due to the restrictions on the layout of the primary air supply duct 38, the straightening distance upstream of the venturi 42 (the straight pipe distance between the primary air flow control damper 41 and the venturi 42) cannot be sufficiently ensured. Also, the primary pressure, that is, the pressure P1 at the inlet of the venturi 42 is not affected by the dynamic pressure or the vortex, and the differential pressure ΔP can be measured stably.
An accurate flow measurement value of the primary air 13 will be obtained.

In this way, even when the rectification distance on the upstream side of the venturi 42 cannot be ensured due to restrictions on the layout of the primary air supply duct 38, the differential pressure ΔP is stably measured without being affected by dynamic pressure or eddy current. Yes, primary air 1
3 accurate flow measurements can be obtained.

It should be noted that the primary air flow measuring device of the present invention is not limited to the illustrated example described above, and various changes can be made without departing from the scope of the present invention. .

[0036]

As described above, according to the primary air flow measuring device of the present invention, even if the straightening distance on the upstream side of the venturi cannot be ensured due to the restriction on the layout of the primary air supply duct, it is not possible to operate the mill. The differential pressure can be stably measured without being affected by the pressure or the vortex, and an excellent effect that an accurate measured value of the primary air flow rate can be obtained can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of an example of an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of an example of an embodiment of the present invention.

FIG. 3 is a plan view of a perforated plate according to an example of an embodiment of the present invention.

FIG. 4 is a diagram comparing a simulation result of a primary air flow of an example (when a perforated plate is provided) of the embodiment of the present invention and a conventional example (when a perforated plate is not provided).

FIG. 5 is a diagram comparing measured differential pressures in an example of the embodiment of the present invention (when a perforated plate is provided) and a conventional example (when a perforated plate is not provided).

FIG. 6 is an overall schematic configuration diagram of a conventional example.

FIG. 7 is a diagram showing a function set and input to a first function generator shown in FIGS. 1 and 6;

FIG. 8 is a diagram showing a function set and input to the second function generator shown in FIGS. 1 and 6;

9 is a diagram showing a function set and input to the third function generator shown in FIGS. 1 and 6. FIG.

[Explanation of symbols]

 1 Mill 13 Primary Air 37 Primary Air Chamber 38 Primary Air Supply Duct 41 Primary Air Flow Control Damper 42 Venturi 42a Throat 44 Primary Air Flow 47 Differential Pressure Detector 59 Hole 60 Perforated Plate P1 Pressure P2 Pressure ΔP Differential Pressure

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01F 1/88 G01F 1/88 15/04 15/04

Claims (1)

[Claims] A primary air supply duct in which a primary air flow control damper and a primary air flow measurement venturi are sequentially provided on the way is connected to a primary air chamber, and a pressure at an inlet of the venturi and a throat of the venturi are provided. A primary air flow measuring device for a mill, which obtains a flow rate of primary air based on a pressure difference between the primary air flow rate and a pressure of a venturi upstream of a pressure detection point at an inlet of a venturi. A rectifying perforated plate having a number of holes formed therein is disposed in a primary air supply duct on a side of the mill.