Imperforate bowl: centrifugal separators – Rotatable bowl – Including driven material-moving means therein
Reexamination Certificate
2002-08-08
2004-08-24
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Including driven material-moving means therein
Reexamination Certificate
active
06780148
ABSTRACT:
TECHNICAL FIELD
This invention relates to a centrifugal separator for concentrating, dewatering, as well as for recovering heavy sedimentation components and separated water from sewage sludge, industrial wastewater, and several products in chemical and food industries by centrifugal force.
BACKGROUND ART
In solid/liquid separation of sludge, decanter type centrifugal separators have generally been used in the past. As indicated in
FIG. 7
, this separator is comprised of a bowl
1
, (outer rotating cylinder) that is formed by connecting a cone
31
, at the tip of a horizontally elongated straight drum section
30
, and in which an inner cylinder
11
(inner rotating cylinder) is equipped with a spiral blade
12
and a screw conveyor
10
is provided to rotate at a relative speed difference with respect to the bowl
1
, so that sludge processing liquid, a, is fed into bowl
1
from inner cylinder
11
to achieve solid/liquid separation by centrifugal force. Dewatered cake b, which is a heavy component separated by the sedimentation process, is scraped toward the front end of the bowl by spiral blade
12
, receives further compaction and dewatering treatments in cone
31
before it is discharged out of the separator from sludge discharge holes
7
, provided at the front end of the separator. The separated liquid c is discharged through the overflow process out of the separator through a discharge opening
32
, provided at a rear end wall
3
of bowl
1
which is located at the opposite side. (Hereafter in this description the direction in which the centrifugal force is exerted, or the direction along which the bowl radius increases, is referred to as the “down” direction; while the direction along which the bowl radius decreases is referred to the “up” direction)
This decanter type centrifugal separator, which stores filtered liquid in bowl
1
, is characterized by a feature requiring that the cone
31
whose front end is squeezed to a small diameter up to the same level (water level) of the discharge hole
32
for the separated liquid, in order to prevent filtered liquid from being discharged through the sludge discharge hole
7
that is designed to discharge the cake, and in order to improve the dewatering effect by elevating the dewatered cake above the water level in the bowl by a cone section, called the “beach”.
Although conventional centrifugal separators have been developed to concentrate or dewater crystals in the liquid phase, if the same separators are applied for the concentration or dewatering of processing items such as sludge, which has different characteristics from the former, it is necessary to provide a strong compaction effect in order to squeeze water out so that the dewatering efficiency can be improved, because the sedimentation layer of the sludge is pasty and is strongly hydrophilic. In the conventional decanter type centrifugal separators mentioned, the processing liquid, a, supplied to the center section of bowl
1
undergoes solid/liquid separation under the strong centrifugal force field (approximately 2,000 to 3,0000G) in the straight drum section
30
immediately after being supplied. Yet, in cone section
31
where the dewatered cake b is discharged, the centrifugal force is weak resulting in an increase in the moisture content, because its distance from the center of rotation (radius) is short. In fact, in the system depicted in
FIG. 7
, it has been observed that the moisture content becomes minimum in the d section, which is around the boundary between the straight drum section and the cone section. Moreover, it is necessary to elevate the cone section against the strong centrifugal force in order for the sedimentation layer to be discharged. Even if an attempt is made to move the sedimentation layer by the screw conveyor, the so-called co-rotation phenomenon due to friction resistance occurs when the moisture content is low, resulting in the cake becoming stagnant and unable to be discharged. Conversely, there is a tendency that only the cake having relatively high moisture content near the center of rotation of straight drum section
30
can be discharged.
Also since the dewatered cake b passes through a cone having a long slope in order to be discharged over the water level in the bowl, there is a disadvantage in that a slip is produced at this section impairing the discharge process, resulting in sludge being discharged together with separated liquid through a separated liquid discharge opening
32
, and contaminating the separated liquid. In addition, since the dewatered cake to be discharged has a relatively high moisture content in the vicinity of the rotational center of straight drum section
31
, in order to decrease the moisture content of the cake to be discharged, the current practice is to increase the rotational speed of bowl
1
beyond what is actually needed (approximately at 2,000 to 3,000 rpm), which requires a large amount of power.
In order to discharge the pasty sedimentation layer, which is difficult to transport by a screw conveyor, an operating condition called the “negative dam” or the “upside overflow” is used, in which the discharge opening position of the separated liquid is higher than the discharge opening of the sedimentation layer. One of such systems, for example, is the Ambler type system (U.S. Pat. No. 3,172,851, and Japanese Patent Application Kokai H6-190302), which uses the head press of the processing liquid in the bowl to assist in the discharge of the sedimentation layer.
Nevertheless, since the liquid level in the bowl is high, the sedimentation layer is still below the liquid surface even in the “beach” section, there has been a problem in that the moisture content increases since the “beach” having a low head press due to the centrifugal force is elevated as it is. (A strong centrifugal force is applied in the bowl, and some layer in the bowl receives a strong pressure due to the centrifugal force applied to the liquid layer or the sedimentation layer above. In this description, this pressure is called the head press.)
In addition, for the Lee type centrifugal separator, a separation plate having a slight gap with the bowl wall is provided in the vicinity of the boundary between the straight drum section and the cone section. An attempt is made to extract only the bottom sections of the sedimentation layer through this gap between the bowl wall and the separation plate.
Yet, as mentioned above, it is difficult to transport the pasty sedimentation layer having low moisture content by the screw conveyor. Since the usable head press is limited to the water level in the bowl, a special construction including a scraping-up device (Japanese Patent Application Kokai H4-59065) is needed for discharging such a layer.
One of these types is designed to supply the processing liquid through a rotating shaft of the bowl so that the separated liquid and sedimentation layer can be discharged through the rotating shaft (Japanese Patent Publication S63-31261). Although this system has an outstanding performance as a separator, there are cases in which difficulties have been encountered in discharging a dewatered cake having low moisture content.
All centrifugal separators mentioned above have their sedimentation layer discharge opening at essentially the same or higher level than the liquid level in the bowl. Even when the head press in the bowl is used for discharge, the head press of the processing liquid in the bowl is lower than the head press of the heavy solid layer; thus it is theoretically impossible to discharge the heavy solid layer only by the head press, thus it requires some type of discharging mechanism.
DISCLOSURE OF INVENTION
This invention is to solve the problems mentioned above for the decanter type centrifugal separator, in order for the conventional centrifugal separator to be able to achieve direct discharge of the sludge from the d section in which the moisture content is the lowest. With this invention, the separation process is expedited and its efficiency is improved, while the bowl speed r
Matsui Hiroyuki
Mizukami Hiroyoshi
Ohinata Tetsuo
Suzuki Noboru
Uchikawa Takashi
Cooley Charles E.
Kotobuki Engineering & Manufacturing Co., Ltd.
LandOfFree
Decanter type centrifugal separator with restriction... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Decanter type centrifugal separator with restriction..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Decanter type centrifugal separator with restriction... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3341237