Generally recognized systems referred to as gas-liquid separators for defoaming and degassing include container type devices that are filled with liquid and then heated or decompressed, systems that employ a gas permeation membrane which only the gas can pass, and systems employing centrifugation.
Of the above systems, the heating and decompressing types are mainly for batch processing, and are unsuitable for continuous processing, and they have the further disadvantage of larger space requirements. In the permeation membrane type system, clogging of the membrane occurs easily as a result of particles or solids in the liquid, and this entails increased replacement costs.
In contrast, the centrifugation system is suitable for continuous processing, having the advantage of not being impaired by particles and solids. However, the following problems still remain unsolved.
Firstly, there remains the problem of insufficient gas-liquid separation performance when the system is applied to advanced defoaming or degassing operations.
In the centrifugation system, since the separation is performed using only the mass difference between the gas and liquid, if a powerful vacuum device is installed then the centrifugal separation performance may be overwhelmed by the suction power of the vacuum device, which may cause liquid penetration into the vacuum device. Therefore, with the centrifugation system, it is no easy task to achieve powerful removal of the gas only. For advanced defoaming and degassing performance, a powerful vacuum device is required. However this also means that the pumped liquid may become mixed with the gas and be drawn easily into the vacuum device. This can become a constraint when applying the system to advanced defoaming or degassing operations, causing insufficient gas-liquid separation performance.
Secondly, in applications for treatment of food materials and ultra-pure liquids, there is the problem of insufficient cleanability, both for CIP (Cleaning In Place: internal cleaning without disassembly) cleaning and disassembly cleaning.
Normally, the apparatus used for the above purposes requires, as “sanitary specifications”, not only a flat and smooth liquid contact surface, but also a structure in which easy CIP cleaning, disassembly cleaning, and reassembly can be performed. However, the structure of the centrifugation system is complicated due to its rotating parts, which means disassembly is difficult. CIP cleaning of liquid contact parts without leaving any shadows is also difficult due to the complicated passages.
International Publication WO2001/02732 (Patent Document 1) is an invention which focuses on solving the first of the aforementioned problems, that is, the gas-liquid separation performance. (This invention will be hereinafter called “Original Invention 1”.)
As exemplified in FIG. 27, the structure of the apparatus according to Original Invention 1 includes a gas-liquid separator installed in the passage of a liquid-feed main pump 31, and a gas-liquid separating impeller 33 which rotates by means of a motor 34 and is installed in the gas-liquid separator container 32 that is provided with an inlet 32a and an outlet 32b. A cavity holder 35 is also installed, and holds the tail bottom of a tornado-shaped cavity s caused by the rotation, preventing it from extending and being suctioned by the main pump 31. Clearance t between the cavity holder 35 and the inner wall of the container 32 is narrowed to a passage area which passes only the pumped liquid, which is pressed against the inner wall of the container 32 by the centrifugal force produced by rotation of the gas-liquid separating impeller 33. An exhaust pipe 36 opens near the center of the tornado-shaped cavity s to draw out the cavity gas by means of a vacuum device 37 via the exhaust pipe 36 and an exhaust passage r.
Also, a protection means 38 is installed in the exhaust passage r. This device only allows the gas to pass to the vacuum device 37, preventing the pumped liquid from passing in case the pumped liquid is mixed into the exhaust gas. In addition, a gas return passage u and a boosting means 39 are also employed for the special purpose of remixing the exhausted gas into the pumped liquid after the liquid is sent by the main pump 31, returning the pumped liquid to its original condition.
In Original Invention 1, gas bubbles in the pumped liquid are forcibly separated by the centrifugal force produced by the rotation of the gas-liquid separating impeller 33, and the cavity holder 35 prevents the tail bottom of the tornado-shaped cavity s from extending and passing through to the downstream side. Furthermore, since the rotating liquid that is pushed against the inner wall of the container 32 takes priority for the flow through the clearance t, there is little possibility of gas bubbles passing through the clearance t. Therefore, gas can be collected effectively and drawn out by the vacuum device 37. This largely resolves the aforementioned first problem, that is the gas-liquid separation performance.
In Original Invention 1, however, the aforementioned second problem, that is the insufficient cleanability of the system, has not been resolved in any way. There is, instead, the occurrence of new shadows or bottlenecks which create cleaning problems such as on the back side of the cavity holder 35 or in the exhaust pipe 36 installation part. This is due to the presence of the cavity holder 35 and the clearance t which are employed to improve the gas-liquid separation performance. The system cannot be used with various kinds of liquids because there is the possibility of clogging due to the bottleneck in the case of liquids such as food materials that contain particles or lumps. Further problems also occur. For example, because the cavity is simply drawn into the exhaust pipe 36 opening, if the formed cavity becomes unstable, then the entry of pumped liquid into the exhaust passage cannot be prevented. This makes it necessary to depend on a separately installed protection means 38 to remove the intruding liquid.
International Publication WO2004/058380 (Patent Document 2) is an invention proposed to simultaneously solve the first of the aforementioned problems, that is, the gas-liquid separation performance, and also the second problem, that is, the insufficient cleanability. (This invention will be hereinafter called “Original Invention 2”.)
As exemplified in FIG. 28 and FIG. 29, the structure of the apparatus according to Original Invention 2 includes a casing which can be separated into 1a and 1b and forms one cylindrical chamber when connected, and an impeller 2 rotated by a motor. The impeller 2 is provided with a separation impeller part 2s which performs gas-liquid separation in all areas around the rotating peripheral area, and a discharge impeller part 2d which is formed by expanding the diameter near the one axial end 2r so as to provide discharge pressure to the pumping liquid. Also, a discharge outlet b is formed in the casing 1a at a position opposite the discharge impeller part 2d. 
At the same time, the other axial end 2f of the impeller 2 is formed to slide along the inner wall of the casing 1a while maintaining the smallest possible predetermined clearance. Also, an exhaust outlet e is formed near the center of the casing 1a opposite the sliding impeller part for discharging the cavity gas generated from the gas-liquid separation, and the exhaust outlet e is connected to a vacuum device. A suction inlet a is formed in the casing 1a at a position between the discharge outlet b and the exhaust outlet e.
Also, a cleaning fluid inlet c for cleaning inside of the apparatus is provided at a position near a shaft sealing part 4 of a rotating shaft 3.
When this apparatus is operated, the pumped liquid flows in from the suction inlet a after being throttled by a throttle means 7. Gas bubbles in the pumped liquid are forced into centrifugal separation by the rotation of the separation impeller part 2s, and the liquid flows toward the discharge outlet b while forming a thin layer on the inner peripheral wall of the casing 1a. At the same time, the gas gathers near the center of the impeller 2 to form a cavity. The cavity gas is drawn out by the vacuum device from the exhaust outlet e located near the center of rotation.
Even if the pumped liquid is mixed into the gas flowing toward the exhaust outlet e, because the mass of the liquid is larger than that of the gas, the liquid is shaken off by the centrifugal force of the separation impeller part 2s. In addition, because the sliding clearance between the axial end 2f and the casing 1a is small, the liquid cannot penetrate from this area either. Therefore, the pumped liquid does not flow into the vacuum device during operation, the vacuum device is safe, and enhanced gas-liquid separation can be performed using the powerful vacuum device.
When performing CIP cleaning of this apparatus, liquid contact parts can be cleaned without leaving any shadows by pouring cleaning fluid into the apparatus from the suction inlet a or the cleaning fluid inlet c, and discharging it from the discharge outlet b, the exhaust outlet e or the drain d while the apparatus is in operation. Also, when performing disassembly cleaning of this apparatus, cleaning of liquid contact parts and reassembly is easy because the casing can be easily separated into parts 1a and 1b. The impeller 2 is exposed completely after the separation, and can be easily pulled out from the rotating shaft 3.
Thus, the apparatus according to Original Invention 2 enables gas-liquid separation functions such as advanced defoaming or degassing operations. It also has sufficient cleanability, and allows both CIP cleaning and disassembly cleaning in order to meet sanitary specifications. Therefore it is extremely practical and useful, however the following problems still remain unsolved in some applications.
That is, due to the configuration of this apparatus that the centrifugal separation is forcibly carried out by the rotation of the impeller 2, excessive agitation, fracture or shear of the pumped liquid may be caused by friction with the edge of the impeller 2 and the inner periphery of the casing 1a if the operation is continued at a high rotation speed. In the gas-liquid separation for liquids such as food materials, particle-containing liquids, highly viscous liquids and foaming liquids, there are cases where excess foaming due to excessive agitation of the pumped liquid, destruction of particles due to excessive fracture or shear, and property change of the pumped liquid due to temperature rise by stirring heat or frictional heat are undesirable. In order to deal with these applications, it is required to satisfy the high gas-liquid separation performance while carrying out gentle gas-liquid separation without excessive stress on the pumped liquid.
A typical method for gentle gas-liquid separation without excessive stress on the pumped liquid is to reduce the rotation speed of the impeller 2. However, this method can also cause the deterioration of the gas-liquid separation performance, creating a trade-off relationship between these two requirements. In order to enable the apparatus to handle various kinds of liquids, the new method that solves the above trade-off and maintain/enhance the defoaming/degassing performance even under the condition of the reduced rotation speed is required.