Biomass mill

The invention provides a biomass mill, comprising a rotatable pulverizing table 5, a recessed groove 6 which is provided in form of ring on an upper surface of the pulverizing table and has an arcuate cross-section, a pressure roller 9 pressed into the recessed groove, a blowout hole 16 for blowing out the air from around the pulverizing table, and a chute 18 for supplying a wooden biomass toward a center of the pulverizing table, wherein the wooden biomass is supplied via the chute, the wooden biomass is pulverized between the pulverizing table and the pressure roller, and the pulverized wooden biomass is carried by blowing the air through the blowout hole, wherein a surface from an outer peripheral of the recessed groove to the blowout hole is flat surface.

BACKGROUND OF THE INVENTION

The present invention relates to a biomass mill for pulverizing a wooden (ligneous) biomass such as wooden chips, wooden pallets, etc. to be used as a fuel for boilers.

In the boilers currently in operation, a coal is primarily used as a solid fuel. For the purpose of reducing discharge of CO2, it is now studied and attempted to use a wooden biomass as a type of fuel, which has little burden on the environment.

When the wooden biomass is used as the fuel for boilers, the wooden biomass such as wooden chips, wooden pellets, etc. must be pulverized so that the wooden biomass will be combustible by burners.

When the wooden biomass is mixed in coal and is used as fuel, and if a mixing quantity of the wooden biomass is not much, it can be mixed and pulverized by using an existing type of coal mill. However, if the quantity of the wooden biomass used is increased, it is necessary to pulverize the wooden biomass by itself.

When a device for pulverizing the wooden biomass is manufactured, if it is designed as the device for pulverizing based on a coal roller mill for pulverizing coal, it would be possible to manufacture the device at low cost without extensively improving and without substantially changing manufacturing facility.

First, referring toFIG. 4, description will be given on a vertical mill1for pulverizing coal.

A closed space is formed by a casing3, which is erected on a base2, and a pulverizing table5is mounted in a lower portion of the space via a table drive unit4. The pulverizing table5is rotated at constant speed by the table drive unit4. On an upper surface of the pulverizing table5, a table segment7is provided, which has a recessed groove6with a cross-section in arcuate form.

The necessary sets, e.g. 3 sets, of pressure roller units8are arranged in radial direction from a rotation center of the pulverizing table5. The pressure roller unit8has a pressure roller9, which can be tilted freely with a horizontal support shaft11as a center. In a lower portion of the casing3, 3 sets of roller pressure devices12are disposed so that the roller pressure devices penetrate the casing3in radial direction. Each pressure roller9is pressed into the recessed groove6by the roller pressure device12.

Under the pulverizing table5, a primary air chamber13is provided. Above the pulverizing table5inside the casing3, a classifier chamber14is arranged.

In the lower portion of the casing3, a primary air supply port15is mounted, and the primary air supply port15is communicated with the primary air chamber13. Around the pulverizing table5, a gap is formed, and the gap fulfills a function as a primary air blowout hole16.

In an upper part of the casing3, a coal supply and discharge unit17is disposed. A chute18in form of pipe is provided so that the chute18penetrates a central portion of the coal supply and discharge unit17, and the chute18is extended to inner space of the casing3. The coal is supplied to the chute18, and the supplied coal is to fall down to the pulverizing table5.

A classifier19is rotatably mounted at the middle of the chute18. The classifier19has a strip-type blade21, which is disposed with a predetermined pitch in circumferential direction, and the classifier19is rotated by a rotary drive unit22.

A pulverized coal feeding pipe23for feeding the pulverized coal to the boiler burner is connected to the coal supply and discharge unit17.

Now, description will be given on pulverizing operation of coal at the vertical mill1.

Under a condition that the pulverizing table5is rotated and the primary air is introduced via the primary air supply port15, the coal in form of lump is sent through the chute18. The coal in form of lump fall toward a center of the pulverizing table5from a lower end of the chute18, and the coal is supplied onto the pulverizing table5.

The coal on the pulverizing table5is moved in outer peripheral direction by centrifugal force. The coal is then caught by the pressure roller9, is pulverized and is turned to powder state. Further, the coal is filled up in outer peripheral region by the centrifugal force from the table segment7. The pulverized coal thus filled up is moved upward by the primary air, which is blown upward via the blowout hole16.

On a peripheral region of the table segment7, a dumb-ring24or an inner edge26ais disposed in order to hold the coal on the table segment7for a required time period and to increase a pulverizing efficiency, and a coal layer with a thickness as required is formed on an upper surface of the table segment7.

When the wooden biomass such as wooden chips, wooden pellets, etc. (hereinafter referred as “wooden biomass”) is supplied to the vertical mill1or to a mill with an equivalent structure and is pulverized, it is found that the biomass exhibits behavior different from behavior of the coal described as follows, and that the pulverizing efficiency cannot be attained sufficiently.

Because the coal has no caking property and has high specific gravity, when the coal is pulverized, the coal is moved smoothly by the centrifugal force caused by the rotation of the pulverizing table5, and the pulverizing efficiency as desired can be attained. Similarly, sufficient pulverizing efficiency can be accomplished when a mixing ratio of the wooden biomass is 5% or less.

However, when the mixing ratio of the wooden biomass is increased or when the wooden biomass is pulverized by itself, the wooden biomass moves less smoothly on the table compared with a case of the coal because the wooden biomass is light in weight and is made of fibers. Therefore, a frequency of an engagement of the wooden biomass with the pressure roller9is low, and the pulverizing operation is not carried out effectively.

Further, when the wooden biomass is not moved smoothly toward outer periphery of the pulverizing table5, the powder after pulverizing is not efficiently discharged out of the mill and the powder after pulverizing is stagnated in the mill. This causes an increase of differential pressure within the mill and an increase of the power of the table drive unit4. Thereby, pulverizing capacity will be limited.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a biomass mill, by which it is possible to ensure smooth moving of a wooden biomass on a pulverizing table, to promote discharge of powder from the mill and to increase a pulverizing capacity.

To attain the above object, the present invention provides a biomass mill, comprising a rotatable pulverizing table, a recessed groove which is provided in form of ring on an upper surface of the pulverizing table and has an arcuate cross-section, a pressure roller pressed into the recessed groove, a blowout hole for blowing out the air from around the pulverizing table, and a chute for supplying a wooden biomass toward a center of the pulverizing table, wherein the wooden biomass is supplied via the chute, the wooden biomass is pulverized between the pulverizing table and the pressure roller, and the pulverized wooden biomass is carried by blowing the air through the blowout hole, wherein a surface from an outer peripheral of the recessed groove to the blowout hole is flat surface.

Also, the present invention provides the biomass mill as described above, wherein at least an outer peripheral groove width angle of the recessed groove is set from 0° to 35°, and also provides the biomass mill as described above, wherein the outer peripheral groove width angle of the recessed groove is set to a value smaller than the inner peripheral groove width angle.

The present invention provides a biomass mill, comprising a rotatable pulverizing table, a recessed groove which is provided in form of ring on an upper surface of the pulverizing table and has an arcuate cross-section, a pressure roller pressed into the recessed groove, a blowout hole for blowing out the air from around the pulverizing table, and a chute for supplying a wooden biomass toward a center of the pulverizing table, wherein the wooden biomass is supplied via the chute, the wooden biomass is pulverized between the pulverizing table and the pressure roller, and the pulverized wooden biomass is carried by blowing the air through the blowout hole, wherein a surface from an outer peripheral of the recessed groove to the blowout hole is flat surface. As a result, the wooden biomass is easily moved in outer peripheral direction, and the pulverizing capacity can be increased. Because the outer peripheral groove width angle of the recessed groove is designed smaller than the inner peripheral groove width angle, the wooden biomass is moved in outer peripheral direction more easily, and this contributes to the increase of the pulverizing capacity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Description will be given below on the best aspect for carrying out the present invention by referring to the attached drawings.

First, in order to explain the present embodiment more accurately, description will be given on a relation between a conventional type table segment7and a pressure roller9by referring toFIG. 2.

An air port ring26is disposed on outer periphery of the table segment7. A blowout hole16is formed on the air port ring26at a predetermined distance so that a primary air is blown upward via the blowout hole16. An inner edge26aof the air port ring26is designed so that an inner edge26aof the air port ring26is tapered and inclined downward toward a center, and the inner edge26ais inclined in approximately similar manner to a tangential line on an outer edge end of a recessed groove6. The inner edge26ais designed in such manner that a pulverized coal can be moved smoothly from the recessed groove6to the inner edge26a.

On an upper surface and on inner periphery of the air port ring26, a dumb-ring24and the inner edge26aare provided. The dumb-ring24is positioned between the outer peripheral edge of the inner edge26aand the blowout hole16. An inner peripheral surface of the dumb-ring24runs in vertical direction, and is a surface bent discontinuously with the inner edge26a.

InFIG. 2, reference numeral27denotes a layer of the pulverized coal where the coal is pulverized, and an arrow mark28indicates a flow of the pulverized coal layer27.

The dumb-ring24is disposed on a periphery of the table segment7so that the flow of the pulverized coal layer27is blocked and a thickness of the pulverized coal layer27is maintained. After passing beyond the dumb-ring24or the inner edge26a, the pulverized coal is blown upward by the primary air blown via the blowout hole16.

As described above, the coal has no caking property and has high specific gravity. Thus, the pulverized coal layer27is moved smoothly by the centrifugal force caused by the rotation of the pulverizing table5. In this respect, in order to maintain the time to apply pressure by the pressure roller9and to attain the pulverizing efficiency as desired, the dumb-ring24or the inner edge26ais needed, which can suppress the flow of the pulverized coal layer27.

In contrast, the wooden biomass is made of light-weight fibers and the wooden biomass moves on the table not very smoothly compared with the coal. Accordingly, when the dumb-ring24or the inner edge26ais disposed, the movement of the pulverizing table5is hindered more.

Therefore, in case of the wooden biomass, the frequency of the engagement with the pressure roller9is low, and the pulverizing is not carried out effectively. After the pulverizing, the powder (hereinafter referred as “biomass powder”) is not easily discharged out of the mill. As a result, the pulverizing capacity is limited because of the increase of differential pressure within the mill and the increase of moving power of the table drive unit4.

If a combustion is taken into account in case of the coal, it is necessary to pulverize the coal so that an average particle diameter of the pulverized coal will be about 40 μm. In case of the wooden biomass, a quantity of volatile components is large and the combustion proceeds fairly well. Accordingly, pulverizing may be carried out to have the maximum particle size of less than 1 mm.

In the present embodiment, special consideration is given on the movement of the biomass powder and on the particle diameter of the biomass powder.

Now, referring toFIG. 1, description will be given on the present embodiment by comparing with the example in the prior art as shown inFIG. 2.

In the example of the prior art, when the dumb-ring24is disposed, the recessed groove6is designed symmetrically to a line, which runs perpendicularly to the center of the groove (left-to-right symmetry in the figure). Here, it is supposed that a radius of curvature of the recessed groove6is set to “r” and angle of groove width (i.e. an angle from the centerline to a groove edge; hereinafter referred as “groove width angle”) is θ2. Then, depth D2of the recessed groove6is given as: (r−r cos θ2). To calculate the depth from a deepest position of the recessed groove6to an upper surface of the dumb-ring24, a height of the inner edge26aand a height of the dumb-ring24must be added. In the prior art, the groove width angle θ2is 40° or more.

In the present embodiment, the dumb-ring24and the inner edge26aare not used. A portion from outer peripheral edge of the recessed groove6to the blowout hole16is designed as a horizontal flat surface. Further, a groove width angle on inner peripheral side from the center of the groove (hereinafter referred as “inner peripheral groove width angle θ2”) and a groove width angle on outer peripheral side (hereinafter referred as “outer peripheral groove width angle θ1”) are set up separately. Then, the inner peripheral groove width angle θ2is set so as to be equal to the outer peripheral groove width angle θ1(θ1=θ2), or the outer peripheral groove width angle θ1is set to a value smaller than the inner peripheral groove width angle θ2 (θ1<θ2).

Also, it is set as: θ2=45° to 30°, andθ1=35° to 0°.

The flat surface may be horizontal or may be inclined upward to outside or may be inclined downward with respect to a horizontal plane. To design the flat surface horizontally or with ascending inclination or descending inclination, it is determined according to the pulverized condition of the wooden biomass or to the moving condition in radial direction.

A depth D1on outer peripheral side of the recessed groove6in the present embodiment is: (r−r cos θ1) (<D2). Compared with the prior art, the depth of the groove is shallower by an extent of h2. Further, the depth of the groove is shallower by an extent of h1, i.e. shallower by the height of the inner edge26aand the height of the dumb-ring24.

Therefore, according to the present embodiment, the depth of the groove on outer peripheral side is shallower by (h1+h2) than the prior art. As a result, the biomass powder is more easily moved toward outer peripheral side of the pulverizing table5. Further, because the dumb-ring24is not used, a stagnation of the biomass powder in the recessed groove6can be eliminated, and the biomass powder moves more quickly toward outer peripheral side.

In case where the outer peripheral groove angle θ1=0, the depth of the groove on outer peripheral side is 0, and the groove will be shallower by an extent of “h1+D2”.

Then, the width of the recessed groove6is “2r sin θ2” in the prior art, while it is “r sin θ1+r sin θ2” (where θ1<θ2; r sin θ1<r sin θ2). Thus, the region where pressure is applied by the pressure roller9will be smaller, and the pulverized particle diameter will be larger than the pulverized particle diameter in the past.

In the present embodiment, if the maximum particle diameter of the biomass powder is set to about 1 mm, and further, the dumb-ring24and the inner edge26aare not used, and also, if the depth and the width of the recessed groove6are decreased, the pulverizing capacity can be extensively increased.

Next, description will be given below on a more concrete example. In the example given below, the inner peripheral groove width angle θ2is set to be equal to the outer peripheral groove width angle θ1(θ1=θ2).

The turning radius (radium of gyration) R at the center of the recessed groove6is set to 675 mm, and the radius of curvature “r” of the recessed groove6is set to 189 mm. Then, according to the present embodiment, the outer peripheral groove width angle is set to: θ1=31°, and the depth of the groove on outer peripheral side is: D=27 mm when the outer peripheral groove width angle θ1=31°. When this is compared with the example in the prior art where the groove width angle θ1=40° and where the dumb-ring24and the inner edge26aare provided, the depth in the present embodiment will be shallower by 38 mm compared with the example in the prior art.

FIG. 3shows the results of comparison between a case where a conventional type coal mill is used as a biomass mill and the wooden chips and the wooden pellets are pulverized by themselves and a case where the wooden chips and the wooden pellets are pulverized by a biomass mill according to the present embodiment.

As shown inFIG. 3, when mill motor power (driving force) is approximately the same, a supply quantity is increased from 200 kg/h to 300 kg/h in case of the wooden chips, and from 400 kg/h to 500 kg/h in case of the wooden pellets. As a result, better effects by the present embodiment can be confirmed.

The biomass powder can be moved toward the outer peripheral side easier by simply making the outer peripheral groove width angle θ1be smaller than the inner peripheral groove width angle θ2. Further, if it is supposed that the outer peripheral groove width angle θ1=0° or ≈0, i.e. the groove width on the outer peripheral side is supposed to be 0 or to be approximately 0, the moving of the biomass powder toward the outer periphery side can be more positively promoted. Therefore, by selecting the outer peripheral groove width angle θ1in the range of θ1=35° to 0° and/or by selecting tilt angle of the flat surface, it is possible to accomplish the pulverizing operation of the biomass powder in optimal condition.