Screw press apparatus

Details Screw press apparatus Screw press apparatus

2001-07-09

2003-09-09

Ostrager, Allen (Department: 3725)

Presses

With drain means for expressed liquid

Drainage through or along pressure surface

C100S099000, C100S048000, C100S112000, C100S147000, C100S148000

Reexamination Certificate

active

06615710

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an improvement of a screw press apparatus to be used for dehydration such as of sludge, and particularly, it relates to a structure for enhancing a filtering function of a screw press and a structure for eliminating blocking of a screen.
BACKGROUND ART
A typical screw press apparatus has an outside tube and a screw shaft disposed in the outside tube. Raw liquid is fed between the outside tube and the screw shaft, ad is dehydrated and compressed by rotation of the screw shaft, to be separated into solid and liquid.
As the raw liquid is concentrated, getting sludgy, and is further dehydrated, forming a cake, the load of a driving device for rotating the screw shaft increases, so that the cake may not be compressed sufficiently.
The outside tube is covered with a metallic screen low of pressure resistance. In the case where adhesive foul water or the like is dehydrated, high pressure resistance is required, and thus the metallic screen is reinforced with a ring, a flange or the like. Moreover, since the mesh of the metallic screen, which processes adhesive slurry, is generally fine, the screen tends to be clogged and thus it is necessary to clean the screen.
The clogged screen is cleaned by a brushing or by a blowing with compressed air. However, as it is difficult to uniformly apply a brush and a blow of compress air to the screen due to the presence of reinforcing flange or the like, and as the screen has uniformly fine meshes, there is a possibility that the screen may not be cleaned sufficiently.
DISCLOSURE OF THE INVENTION
A principal object of the present invention is to provide a screw press apparatus in which the structure for supplying raw liquid and the structure of a screen are improved, so that a dehydrating process exhibits an enhanced performance, and the screen has a reduced load thereon in a dehydration process for sludge, effecting a facilitated sufficient elimination of a blocking of the screen.
Another object of the invention is to provide a control device implemented for load reduction to be effected on a rotary drive for a screw shaft in a dehydration process for slurry.
To achieve the object, a screw press apparatus according to a first aspect of the invention comprises a first and a second frame (
3
,
4
) in opposition to each other, an outside tube (
5
) having a screen (
8
) on its peripheral surface, a screw shaft (
6
) having a spiral screw blade (
13
), a supply pipe (
16
) for supplying raw liquid in the screwshaft (
6
), and a cleaning pipe (
34
) for ejecting cleaning water to the screen (
8
). The outside tube (
5
) is supported on the frames (
3
,
4
). The screw shaft (
6
) is inserted through the outside tube (
5
) and is supported rotatably on the frames (
3
,
4
). The supply pipe (
16
) is fixed to one end (
6
a
) of the screw shaft (
6
) supported on the first frame (
3
). The screen (
8
) is disposed between the frames (
3
,
4
) and has a plurality of fine holes (
74
). The screw shaft (
6
) and the screen (
8
) define a cylindrical space (
70
) continuously extending from an upstream region (
71
) at a side of the first frame (
3
) to a downstream region (
72
) at a side of the second frame (
4
). The screw blade (
13
) is projected from the screw shaft (
6
) into the cylindrical space (
70
) and continuously extends from the upstream region (
71
) to the downstream region (
72
). An opening (
73
) for supplying the raw liquid from the supply pipe (
16
) to the upstream region (
71
) of the cylindrical space (
70
) is formed in the screw shaft (
6
). An outer peripheral surface of the screw shaft (
6
) and an inner peripheral surface of the screen (
8
) have a relative distance therebetween, which decreases from the upstream region (
71
) towards the downstream region (
72
). Raw liquid fed from the opening (
73
) to the upstream region (
71
) is pressurized and carried towards the downstream region (
72
) by the screw blade (
13
), while being separated into filtrate allowed to flows through the fine holes (
74
) out of the screen (
8
) and a cake allowed to move in the cylindrical space (
7
), to be discharged from the downstream region (
72
). Sizes of the fine holes (
74
) of the screen (
8
) decrease gradually from the upstream region (
71
) towards the downstream region (
72
).
According to the above arrangement, the raw liquid fed from the opening (
73
) of the screw shaft (
6
) to the upstream region (
71
) of the cylindrical space (
70
) is carried towards the downstream region (
72
) by the screw blade (
13
). The relative distance between the outer peripheral surface of the screw shaft (
6
) and the inner peripheral surface of the screen (
8
) corresponds to a radial width of the cylindrical space (
70
). As the width decreases from the upstream region (
71
) towards the downstream region (
72
), the raw liquid is carried and simultaneously pressurized gradually, and the filtrate flows through the fine holes (
74
) out of the screen (
8
), to be concentrated. R raw liquid in the cylindrical space (
70
) becomes sludge in an intermediate stage, and is further concentrated to form the cake, to be finally discharged from the downstream region (
72
). Namely, raw liquid is separated into the filtrate which flows out of the fine holes (
74
) and the cake which is discharged from the downstream region (
72
).
Since the opening (
73
) for supplying raw liquid is formed in the screw shaft (
6
), the raw liquid is fed in free of influences from the screw blade (
13
). Therefore, even if soft flocs cohered by a cohesive agent is mixed in the raw liquid, the flocs are hardly broken, assuring a dehydration performance free of damages.
The sizes of the fine holes (
74
) of the screen (
8
) decrease gradually from the upstream region (
71
) towards the downstream region (
72
). On the contrary, the pressure acting on the raw liquid in the cylindrical space (
70
) rises gradually from the upstream region (
71
) where the radial width is large towards the downstream region (
72
) where the radial width is small. For this reason, in the upstream region (
71
) low of pressure, the filtrate flows out of the large fine holes (
74
) satisfactorily. Moreover, since the fine holes (
74
) become smaller gradually towards the downstream region (
72
) high of pressure, where sludge is changed to a cake, the sludge hardly flows out of the fine holes (
74
) and thus only the filtrate outflows satisfactorily. Therefore, raw liquid is separated into the filtrate and the cake satisfactorily, and thus the filtering performance is improved.
In the case where the screen (
8
) is blocked, cleaning water is ejected from the cleaning pipe (
34
) to the screen (
8
), and thus the screen (
8
) is reusable.
A second aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a scraper (
14
) fixed to the screw blade (
13
). The scraper (
14
) is continuously extends from the upstream region (
71
) to the downstream region (
72
) and contacts elastically on the screen (
8
).
According to this arrangement, since sludge is scrapped off from the fine holes (
74
) of the screen (
8
) periodically by the scraper (
14
), the blocking of the screen (
14
) is prevented previously in a whole region covering from the upstream region (
71
) to the downstream region (
72
).
The scraper (
14
) extends continuously from the upstream region (
71
) to the downstream region (
72
), and in comparison to a case where a scraper is disposed partially, the positioning is facilitated, with a reduced tendency to have positional deviation.
A third aspect of the invention provides a screw press apparatus depending from the first aspect, which further comprises a claw (
28
) fixed to the supply pipe (
16
), a first movable claw (
31
) provided on the outside tube (
5
) in correspondence to the claw (
28
), a first spring (
30
) for biasing the first movable claw (
31
), a first guide surface (
75
) provided on at least one of the claw (
28
) and the first movable claw (
31
), to work when th

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