Fluid handling – Systems – Closed circulating system
Reexamination Certificate
1999-03-15
2002-01-22
Rivell, John (Department: 3753)
Fluid handling
Systems
Closed circulating system
C366S136000, C239S127000, C222S318000
Reexamination Certificate
active
06340033
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to high solids concentration slurries showing shear-thinning visco-plastic Theological properties and, more specifically, to a process and apparatus which allows for improved transfer of such thick, high solids content slurries or mud from a reservoir to a conduit or any other transportation device.
A large number of industrial processes generate solids residues which normally have to be washed and transported to disposal sites or to other recycling processes. The most common method used in industry to transport these solids residues is to slurry them in a carrying medium, water being the most commonly used medium, and to pump them to the desired destination. If the slurry is sufficiently concentrated, other means of transfer, such as belt conveyors, can also be used. It is important and most desirable, from an economical point of view, to operate with slurries of the highest solids concentration possible. This keeps the total amount of material to be handled, and eventually to be disposed of, to a minimum. When washing is necessary, a high solids content allows a maximum washing efficiency in the minimum number of washing stages. Finally, maximizing the solids content of a slurry has a favorable impact on the environment by reducing the total amount of material at the disposal site and reduces the risk of spillage and leakage of liquid effluents.
Achieving a high solids concentration from a dilute slurry can be done in numerous ways, the most common ones being by means of filtration, hydrocyclone, centrifuge, flotation, magnetic separation or gravity settler also called decanter or thickener. Each of these methods is capable of producing, to various degrees, a slurry of sufficiently high concentration that the thickened slurry or resulting mud will behave as a paste or a compacted cake. If the solids concentration achieved is very high and a relatively dry cake is formed, conventional dry transportation systems, such as belt or screw conveyors can be used. This is the case, for example, when a high efficiency vacuum filter or a pressure filter, such as a plate and frame type filter, is used. The high capital, operating and maintenance cost of these filters constitute, on the other hand, a major drawback.
The introduction of synthetic flocculants for the improvement of the performance of settlers/thickeners (Chandler, U.S. Pat. No. 4,040,954) and the development of high efficiency thickeners, such as the ones described by Bagatto et al. (U.S. Pat. Nos. 4,830,507 and 5,080,803) and by Farmery et al. (U.S. Pat. No. 5,718,510) have led to a generation of equipment capable of producing, directly in a gravity thickener, very high solids content slurries or muds which exhibit paste-like behavior.
These new settlers are limited, however, in performance by the need to maintain an underflow solids concentration which is low enough to ensure evacuation of the mud or thick slurry from the equipment. This underflow solids concentration is normally continuously monitored in order to avoid situations which would result in a severe blockage and, in many instances, the necessity to empty the reservoir by external means.
The use of positive displacement pumps to transport the material away from the thickening equipment to an appropriate disposal site can also be a limitation to the maximum solids concentration which can be tolerated in use. Although such pumps have, in principle, the capacity to transport very high solids slurries from the pressure side of the pump, the mud must be sufficiently fluid to be introduced continuously into the pump on the suction side.
Khan et al. (U.S. Pat. Nos. 5,188,739 and 5,188,740) have described a process by which a sanitary sewage sludge mixed with carbonaceous material is fed at a relatively high solids concentration into a reactor. This is achieved, as Khan et al. describe it in their patents, by the action of a pump which reduces the viscosity of the sludge by its shearing effect. In the Khan et al. patents, the material is fed directly from a centrifuge to a pump and is sufficiently fluid to be evacuated from the thickening equipment. Khan et al.'s objective is to have a material fluid enough to enter into a subsequent reactor. However, the Khan patents do not address the problem of getting the slurry into the pump in the first place.
In summary, therefore, the difficulty of handling and transferring high viscosity slurries has limited the attempts to maximize the solids contents of such slurries, and has therefore limited the advantages that the formation of such slurries could offer.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to make it possible to transfer high viscosity slurries from containers with reliability and consistency.
Another object of the invention is to facilitate transfer of high viscosity slurries, thus allowing thickening equipment to be used more efficiently and effectively.
Yet another object of the present invention, at least in its preferred forms, is to provide a method of, and apparatus for, moving slurries out of reservoirs or equipment such as, but not exclusively, deep thickeners and high efficiency settlers, so that such slurries may be transferred from the equipment in which they are formed or held to destinations where they may be used, treated or discarded. Such movement may be possible when the slurries are very thick, and have paste-like consistency exhibiting shear thinning visco-plastic rheological properties (non-Newtonian fluids).
According to one aspect of the invention, there is provided a method of removing a slurry having shear-thinning visco-plastic properties from a reservoir holding a body of the slurry, the slurry having a viscosity so high that direct withdrawal of a flow of the slurry from the reservoir is difficult, the method comprising: creating a submerged region of shear-thinned slurry of reduced viscosityin the body of slurry for entraining adjacent slurry of the high viscosity; and removing from the reservoir a portion of the slurry of reduced viscosity containing entrained slurry of high viscosity. The stream of shear-thinned slurry is preferably created by withdrawing slurry temporarily from the submerged region via an outlet to form a flow of withdrawn slurry, subjecting the withdrawn slurry to shear to produce a flow of shear-thinned slurry of reduced viscosity, and returning the shear-thinned slurry of reduced viscosity to the submerged region of the body via an inlet spaced from the outlet, thereby creating a flow of slurry between the inlet and the outlet. This withdrawal, shear application and return is preferably carried out continuously, at least during the period when slurry is to be transferred from the reservoir.
According to another aspect of the invention, there is provided apparatus for holding and delivering a slurry having a viscosity so high that direct withdrawal of a flow of the slurry from a reservoir holding a body of the slurry is difficult, the apparatus comprising: a reservoir for holding a body of the slurry; means for creating a submerged region of slurry of reduced viscosity in the body to entrain adjacent slurry of the high viscosity; and means for removing from the reservoir a portion of the slurry of reduced viscosity containing entrained slurry of high viscosity. The apparatus preferably comprises a first conduit having an inlet in the reservoir for withdrawing slurry from the submerged region, shear generating means communicating with the first conduit for subjecting withdrawn slurry from the first conduit to shear, a second conduit communicating with the shear generating means, having an outlet in the reservoir, for returning shear-thinned slurry of reduced viscosity from the shear generating means to the submerged region of the body, the inlet and the outlet being spaced from each other in the region, thereby creating the stream between the inlet and the outlet.
The invention may be used with any slurry having the required shear-thinning visco-plastic Theological properties. Slurries derive
Paradis Ronald
Puxley Donald L.
Alcan International Limited
Cooper & Dunham LLP
Rivell John
LandOfFree
Transfer of shear-thinning slurries does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transfer of shear-thinning slurries, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transfer of shear-thinning slurries will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2854086