JP2927469B2 - Vertical mill - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vertical mill having a classifier therein, and more particularly to a vertical mill having an improved pulverizing function.

[Prior art] In coal-fired boilers, low-pollution combustion (low NOx, reduction of unburned fuel) and rapid load fluctuation operation (coal supply change) have been implemented, and along with that, the performance of fine mills has been improved. Now required.

A vertical roller mill equipped with a grinding table and a plurality of rollers has been used as one type of pulverizer for finely pulverizing lump materials such as coal, cement raw materials or new raw materials, and has recently become one of the representative models. Is hardening.

As shown in FIG. 11, this type of pulverizer is a disc-shaped rotary machine that is driven by a motor having a speed reducer (not shown) at a lower portion of a cylindrical mill housing 114 and that rotates at a low speed on a horizontal plane. The table 103 is provided with a plurality of crushing rollers 111 which rotate by being pressed down by a hydraulic pressure or a spring or the like to a position where the outer peripheral portion of the upper surface thereof is equally divided in the circumferential direction. The raw material to be crushed 101 supplied from the raw material supply pipe 102 to the center of the rotary table 103 moves to the outer peripheral part in a spiral locus on the rotary table 103 due to the rotation of the rotary table 103 and the centrifugal force. It is crushed between the crushing race 105 surface of the table 103 and the crushing roller 111 and crushed. A hot air 110 sent through a duct (not shown) is guided to the base of the mill housing 114, and the hot air 110 flows between an outer peripheral portion of the rotary table 103 and an inner peripheral portion of the mill housing 114. It is blowing up from the air throat 108. The crushed powder is dried while rising in the mill housing 114 by hot air 110 blown up from the air throat 108. The powder and granules transported to the upper part of the mill housing 114 are classified by a cyclone separator or a rotary classifier provided on the upper part of the mill housing 114, and fine powder having a predetermined particle size or less is conveyed by hot air 110, not shown. In the boiler, it is sent to a pulverized coal burner or a pulverized storage bin. Coarse powder having a predetermined particle size or more that does not pass through the classifier falls onto the rotary table 103 and is pulverized again together with the raw material 101 just supplied into the mill. In this way,
The crushing is repeated by the crushing roller 111.

For such a purpose, in order to enhance the crushing ability, a structure of an optimal roller or a groove-shaped crushing race 105 formed on the upper surface of the rotary table has been proposed. On the other hand, irrespective of the shape of the roller or the crushing race, that is, even if it is a conventional type, it is considered that controlling the movement of the powder layer on the table is effective for increasing the crushing force.

[Problems to be solved by the invention]

In a conventional vertical roller mill whose structure is shown in cross-sectional view in FIG. 11, in a high-load operation, the powder, which is the raw material to be pulverized, is placed in a pulverizing section, particularly in a space sandwiched by three pulverizing rollers 111. If the body stays too much, it becomes a resistance to the rolling of the crushing roller 111, and there is a problem that the useless power that is not directly involved in the crushing increases, and as a result, the crushing efficiency decreases.

FIG. 7 shows the experimental results of the pilot mill,
The thickness of the powder layer under the crushing roller is summarized as a change with respect to power consumption. Both the vertical and horizontal axes are rendered dimensionless using the values under standard grinding conditions. When the thickness of the powder layer below the grinding roller reaches a predetermined value, the power consumption increases sharply. There is a limit to the amount of coal that can be held as a compaction bed between the grinding roller and the grinding race. Therefore, in this case, as schematically shown in FIG. 8-1, the powder 120, which is the raw material to be crushed, overflows from between the crushing rollers 111, and this becomes the rolling resistance of the crushing rollers 111. it is conceivable that. Between the crushing rollers 111, the powder 120 becomes supersaturated, and
Overflows, the powder layer becomes as shown in FIG. 8-2.
The shear resistance between the crushing surfaces of the adjacent crushing rollers 111A and 111B rotating in the opposite direction. This behavior is predicted to be one of the main causes of the power consumption surge phenomenon shown in FIG. In addition, when the powder 120 overflows between the crushing rollers 111A and 111B, the crushing roller bites and resistance to pneumatic transport occurs after the generation of fine powder. Also have various adverse effects.

FIG. 9 and FIG. 10 show the basic experimental results of the batch mill, and show the fine powder generation rate w (200 mesh pass g / min) and the effective pulverization rate for the coal load rate in the mill, respectively.
It is a summary of the change in S / μeMwD (a value obtained by dividing the increase in surface area of the generated fine powder ΔS by the effective grinding energy rate μeMwD, which is the net grinding power consumption, which is substantially equivalent to the grinding efficiency). A comparison is made using rollers A and B having different structures (A type: a roller having a substantially arc-shaped crushing surface, B type: a two-step roller having a step in which the diameter of the crushing portion is changed). From the results in FIG. 9, it can be seen that the B type roller has a high crushing ability under the condition of a high load factor. However, when the B type roller is used as shown in FIG.
Efficiency is lower than A type. This characteristic indicates that the structure of the roller has a strong influence on the flow resistance of the roller which is trying to rotate by rotating the group of particles. That is, it is estimated that the space between the rollers is small in the B type roller, and the non-pulverized particles overflow in the biting portion and the fine powder generating portion of the roller, and the rolling resistance of the roller is increased.

As an example of the prior art relating to a method of controlling the supply of the granular material to the roller pulverizing section, as shown in FIG.
There is a proposal to supply the crushing roller 212 to the biting portion by providing the crushing roller 212. This method is considered to be effective for promoting biting and preventing the vibration of the mill under the condition of low load where the number of rollers is as small as 2 and the raw material is small in the pulverizing section. It does not meet the demand for improved grinding efficiency during operation.

In the prior art shown in FIG. 13, a container provided with a combination of a raw material supplied from a chute 1350 and a frustoconical portion 1347 for guiding return particles from a secondary classification portion and a small-diameter cylindrical portion 1346 is provided in a mill. Things. In this technique, particles which are recirculated from the primary (gravity) classifying section to the pulverizing section or, when a rotary classifier is used, particles which are repelled to the mill housing 1340 side and fall to the pulverizing section, are formed by rollers 1343. The gap between the roller 1343 and the small-diameter cylindrical portion 1346, the gap between the roller 1343 and the truncated cone 1347, or the gap between the roller 1343 and the leveling member 1348 may overflow the roller 1343. In particular, in the case of increasing the amount of recirculation in the mill in order to increase the particle size under a high load, the particle layer accumulated between the series of container members (1346, 1347, 1348) and the roller 1343 is formed by the roller 1343. Rolling resistance of the mill, resulting in an increase in power of the mill. By the way, high C / A (C, A) to reduce NOx and increase efficiency of pulverized coal combustion including mills
(Coal and primary (mill) air mass flow rates) are recent trends. Therefore, there is a tendency to reduce the air for milling as much as possible.
The return rate from the next (gravity) classifier is considerably higher than in the previous operation.

An object of the present invention is to solve the above-mentioned problems and solve the problem.
It is an object of the present invention to provide a mill that does not reduce the grinding efficiency even under operating conditions where the amount of recirculation from the next classification section is large and under high load operation.

[Means for solving the problem]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a rotary table that rotates on a horizontal plane around a vertical rotation axis below a casing, and a plurality of rotary tables arranged on the rotary table. Crushing roller, a raw material supply pipe for supplying raw material to be crushed to a crushing section formed by the rotary table and the crushing roller, and an annular space for blowing up airflow provided between the rotary table and the casing, In a vertical mill having a primary classifier for primary classifying the granules that have been pulverized in the pulverizing unit and transported upward from the annular space by the airflow blown from the annular space, in the space between the pulverizing rollers, An upper end is located at a position higher than an upper end of the crushing roller, and is connected to the upper part of a truncated cone opening toward the primary classifier above the mill,
This is achieved by a vertical mill provided with a powder layer holder having a cylindrical lower portion whose bottom is open toward the rotary table.

In the present invention, at the lower end of the cylindrical lower portion of the powder layer holder, a supply guide for supplying the powder particles received by the powder layer holder to a pulverizing unit formed by a rotary table and a pulverizing roller may be provided. preferable. Preferably, the supply guide is divided in accordance with the number of the crushing rollers, and the lower end of the divided supply guide is extended between the crushing rollers.

[Action]

The raw material supplied into the mill and the powder particles returned from the classifying section to the pulverizing section in the mill enter the above-described substantially cylindrical powder particle holder, so that the ratio of direct contact with the roller is small, and the contact rate is small. The waste of power caused by the resistance is avoided. Further, since the granular material is supplied to the pulverizing portion of the pulverizing roller on the pulverizing race via the above-described plate-shaped pulverulent material supply guide, the pulverulent material overflows between the pulverizing rollers, and the pulverizing roller is rotated. The problem of a sudden increase in dynamic resistance is solved. Therefore, according to the present invention, it is possible to minimize the decrease in crushing efficiency even under high-load operation, which is a condition in which the crushing section is supersaturated and power is wasted. In addition, since the powder does not overflow into the fine powder generation / air flow blow-up portion of the crushing roller, the pressure loss in the crushing portion can be reduced. Further, particularly under a high load condition, the grinding roller bites and grinds an appropriate amount of the raw material with a high load, so that the particle size of the fine powder is improved.

〔Example〕

1 and 2 show the structure of a vertical mill according to the present invention. Figure 1 is a longitudinal section through the center axis of the mill,
On the other hand, FIG. 2 is a view of the pulverizing section viewed from above from the line II-II in FIG.

The raw material 1 to be pulverized is supplied into the mill from a raw material supply pipe 2 provided on the central axis of the upper part of the mill, and a cylindrical powder layer holder 15 installed in a space between three pulverizing rollers 8 is provided.
, Falls on the rotary table 3 rotating at a low speed below the mill. The raw material to be pulverized on the rotary table 3 is sent by a centrifugal force to a pulverizing race 7 having a substantially arc-shaped cross section formed on the upper surface of an annular pulverizing ring 6 provided on the outer peripheral side of the rotary table 3. Be paid. The raw material to be pulverized on the pulverizing race 7 is pulverized by a pulverizing roller 8 which rolls while being pressed on the pulverizing race 7. The granular powder generated by the pulverization in this manner is transported to the upper side of the mill by hot air 13 blown from an air throat 11 provided outside the rotary table 3. Of the transported powders, the coarse ones fall to the pulverizing part by gravity (primary classification) and are re-pulverized. The relatively coarse particles among the powders and granules that have passed through the primary classifier are centrifugally applied to the mill housing 14 by a rotary classifier.
Is repelled to the inner wall (secondary classification), and finally returns to the crushing section by gravity and is crushed again. The fine particles that have passed through the secondary classification area by the rotary classifier are conveyed to the outside of the mill from the product fine powder collection duct 21 and collected as a product. In the case of a mill for a pulverized coal-fired boiler, the mill is directly transported to a pulverized coal burner (not shown) and burned, or stored in a pulverized coal bin (not shown). In the rotary classifier according to the present embodiment, a rotary cylinder 17 around a raw material supply pipe (center chute) 2 serves as a rotation axis, and a plurality of plate-like blades 19 are arranged below the rotary cylinder at equal intervals in a circumferential direction. A rotary classifier rotor 18 is provided. In the vertical mill, the rotation directions of the rotary classifier and the rotary table 3 are the same.

A feature of the present invention is that a powder layer holder 15 is provided in a space between the crushing rollers 8 to receive a group of crushed raw material particles accumulated on the rotary table 3. This powder layer holder 15
Is substantially cylindrical, the upper end of which is located higher than the upper end of the crushing roller 8, and has a frustoconical inlet portion 15A that opens upward from the mill. At the entrance,
Container 15 having a cylindrical shape and opening at the bottom above rotating table 3
B is connected to the lower end of this container, as shown in FIG. 3, a plate-shaped powdery material supply guide which is widened between the biting portion of the crushing roller 8 and the fine powder generating portion. 16 are provided. Note that the powder layer holder 15 is held by a plurality of supports 22 having a fixing portion in the mill housing 14. 14A and 14B are perspective views of the powder layer holder.
Shown in the figure. In the pulverizing operation, the granular material accumulates on the pulverizing portion of the mill, that is, on the rotary table 3. In particular, when the mill is operated under a high load (conditions that increase the supply amount), or when the circulation amount in the mill is increased by changing the operating conditions of the classifier or the air amount, a large amount of granular powder accumulates. The crushing roller 8 is buried. The powder layer holder 15 according to the present embodiment receives the bulk raw material 1 supplied from the raw material supply pipe (center chute) 2 and the powder returned from the primary or secondary classification unit, and rotates the powder. To prevent direct contact with the pulverizing roller 8 and resistance. In addition, the powder supply guide 16 prevents the powder from overflowing into the pulverizing portion (biting portion and fine powder generation portion) of the pulverizing roller 8 and causes the pulverizing roller 8 to pulverize an appropriate amount of the pulverulent material. Has a role. When the coal hold-up in the mill increases, the inside of the powder layer holder 15 is filled with the granular material, and in an extreme case, the powder layer holder 15 may overflow from above. However, as compared with the case where no countermeasure is taken as in the conventional vertical mill, the effect of improving the particle size (improving the pulverizing efficiency) or reducing the pressure loss by the powder layer holder 15 is remarkable. This will be described later.

Regarding the operation method of the mill, increase the coal supply beyond the standard coal supply (the limit that satisfies the specified particle size), or use the mill for the coal hold-up reference value (the coal seam differential pressure in the mill). (Determined from the threshold value), the grinding load of the mill is increased to 1.3 times.

FIG. 3 schematically shows the state of the granular material in the pulverizing section of the mill according to the present invention. In the pulverizing section, most of the granular material (feed, circulating particles from the primary (gravity) classification and secondary (rotation) classification) 23 as the raw material to be pulverized is received in the powder layer holder 15 according to the present invention. Then, the powder is supplied from below the powder supply guide 16 attached to the lower portion of the powder layer holder 15 to the position where the grinding roller 8 is engaged. In this way, except for the biting portion of the crushing roller 8, the powder 23 is prevented from coming into contact with the crushing roller 8 and having a large resistance. Therefore, most of the power consumed in the pulverizing section is used for actual pulverization, and the pulverization efficiency is finally improved. Further, since the amount of the granular material overflowing to the upper portion of the air throat 11 is reduced, the pressure loss in the pulverizing section is reduced.

Fig. 4-1 shows the dimensionless power consumption of pulverization (consumption power under standard coal supply conditions is 100%) with respect to coal supply load ratio (standard coal supply amount is 100%) under a constant load condition. Dimensionless), which is a comparison between the mill according to the present invention and the conventional mill. Generally, the power increases with an increase in the coal feed load factor, but the rate of increase in the power of the mill according to the present invention is lower than that of the conventional type, and the difference increases as the load increases. As shown in FIG. 3, even in a high load condition, the mill according to the present invention allows a more appropriate amount of the raw material to be pulverized for the pulverization by the action of the powder layer holder 15 and the powder supply guide 16. It is considered that the powder was fed to the biting portion of the roller 8 and was efficiently pulverized. In a mill without measures, the amount of raw material in the biting portion of the crushing roller is too large, causing poor biting, or the powder layer under the crushing roller becomes too thick and the load pressure of the crushing roller is diffused. Could be.

FIG. 4-2 shows the change of the dimensionless fine powder particle size (based on the particle size of 200 mesh pass; dimensionless based on the standard condition particle size of 100%) with respect to the coal supply load factor. However, in this experiment, the pulverization load was increased under conditions that were larger than the standard coal supply. At low load, there is not much difference in the particle size between the present invention example and the conventional example. However, at high loads, the reduction in particle size of the mill according to the invention is small, and the difference from the particle size of the conventional mill, which is greatly reduced, is significantly increased. This is because, in the mill according to the present invention, the roller has an improved pulverizing ability so that the rollers can efficiently bite in a proper amount of the raw material with a high load. The mill according to the present invention has a so-called wide-range function with little change in particle size under such a wide range of load. As described above, when the capacity of the pulverizing unit is increased, the amount of coarse particles penetrating to the air throat is reduced, so that the pressure loss of the mill is also reduced.

Fig. 5 shows the dimensionless coal seam pressure difference (the dimension of the total pressure loss in the mill due to the contribution of coal, which is dimensionless based on the coal seam pressure difference under the standard coal feed conditions of the conventional mill).
Are summarized as changes with respect to the coal load factor. As described above, in the mill according to the present invention, since the amount of the granular material that overflows onto the air throat 11 without being sufficiently pulverized is reduced, the effect of reducing the pressure loss is particularly remarkable particularly under high load conditions. I understand. Such a reduction in pressure loss also produces an effect that the power of the primary blower can be reduced.

FIG. 6 shows the combustion test results of the pulverized coal produced by the mill according to the present invention as a map of the NOx concentration in the exhaust gas and the unburned portion in the ash. It can be seen that the pulverized coal produced by the mill according to the present invention reduces both the NOx concentration and the unburned content in the ash. First, the decrease in unburned ash content is due to the fact that the ignition / flame holding state in the vicinity of the burner is improved due to the improvement in the particle size, and the combustion zone is greatly expanded, so that the burning out is greatly accelerated. On the other hand, such improvement in ignition and flame holding properties also produces an effect of reducing NOx concentration. That is, in the flame in a self denitration burner, the flame center of the burner near stable low air ratio combustion zone at a high temperature is formed by a larger scale, a reducing agent for reducing the once generated NO to N ₂ Are actively generated. Therefore, as a result, NOx
The concentration is reduced.

As described above, the use of the vertical mill embodying the present invention not only improves the performance of the mill, but also enables low-pollution operation of the coal-fired power plant.

The vertical mill according to the present invention is not limited to a pulverized coal-fired boiler, or a mill for a solid fuel-fired boiler such as petroleum coke, which has been described as an example so far, but a cement finishing mill or a steel slag crushing mill, or It can be applied almost directly to the blast furnace blowing fine grinding mill. Particularly in the field of cement, the vertical mill according to the present invention is considered to be particularly effective because recently strict quality control and energy saving operation are being promoted recently.

〔The invention's effect〕

According to the present invention, since extra particles to be crushed do not enter between the crushing rollers, the rolling resistance of the rollers is small, and the crushing power can be reduced. In addition, since the supply of the particles to be ground is appropriately performed, the milling ability of the mill is improved, and the particle size of the fine powder of the product is improved.

[Brief description of the drawings]

FIGS. 1, 2, 14A and 14B are views showing the structure of the vertical mill according to the present invention, FIG. 3 is a diagram for explaining the functions of the mill according to the present invention, and FIG. 6 to 6 are explanatory diagrams of experimental results by the present invention mill, FIGS. 7 to 10 are explanatory diagrams of problems in the conventional vertical mill, FIG. 11 is a structural diagram of the conventional vertical mill, FIG. FIG. 13 and FIG. 13 are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1 ... Raw material to be ground, 2 ... Raw material supply pipe, 3 ... Rotary table, 4 ... Rotary table shaft, 5 ... Rotary table rotating shaft, 6 ... Grinding ring, 7 ... Grinding race, 8 ...
... Pulverizing roller, 9 ... Roller shaft, 11 ... Air throat, 13 ... Hot air, 14 ... Mill housing, 15 ... Powder layer holder, 16 ... Powder supply guide, 21 ... Product fine powder collection duct , 22 ... Powder layer holder support.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Kanemoto 6-9 Takaracho, Kure City, Hiroshima Prefecture Inside the Kure Factory of Babcock Corporation (72) Inventor Yoshinori Taoka 6-9 Takaracho Kure City, Hiroshima Prefecture Babcock Day (72) Inventor Tadashi Hasegawa 6-9 Takara-cho, Kure-shi, Hiroshima Babcock In-house Kure Factory (56) References JP-A-62-149353 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) B02C 15/04

Claims (3)

(57) [Claims] 1. A rotary table that rotates on a horizontal plane about a vertical rotation axis below a casing, a plurality of crushing rollers disposed on the rotary table, and crushing formed by the rotary table and the crushing roller. A raw material supply pipe for supplying the raw material to be ground to the part, an annular space part for airflow blowing provided between the rotary table and the casing, and an airflow pulverized in the grinding part and blown from the annular space part. In a vertical mill having a primary classifier for primary classifying the powder and granules transported above the mill, in a space between the grinding rollers, an upper end is located at a position higher than an upper end of the grinding roller, A powder bed holder having a frusto-conical upper portion opening toward the primary classifier above the mill, and a cylindrical lower portion connected to the upper portion and having a bottom opening toward the rotary table. Vertical mill, characterized in that the provided. 2. A supply guide for supplying a powdery material received by the powder layer holder to a pulverizing section formed by the rotary table and the pulverizing roller, at a lower end of a cylindrical lower portion of the powder layer holder. The vertical mill according to claim 1, wherein the vertical mill is provided. 3. The supply guide is divided according to the number of the crushing rollers, and the lower end of the divided supply guide is extended between the crushing rollers.
Vertical mill according to 1.