Rotary kinetic fluid motors or pumps – Plural runners having different type flow paths
Reexamination Certificate
1998-11-27
2001-04-03
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Plural runners having different type flow paths
C415S169100, C415S062000, C415S121100, C415S066000
Reexamination Certificate
active
06210105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
A flow directing device assists the feed of a medium to high consistency slurry through a pump by conditioning the slurry prior to pumping the slurry.
2. Description of Related Art
Pulp and paper mills universally have a major problem moving medium consistency stock (8% to 12% cellulose fibers mixed in water) and high density stock (12% to 18% cellulose fibers mixed in water) from one area of the mill to another. There are several advantages to maintaining the highest possible transport consistency. First, the end product of such mills is paper, not water. Second, mills maintain a stored inventory of stock (e.g. pulp) to run a paper machine when the pulp mill is down and stored water takes up valuable space. Third, the total tonnage of pulp that can be transferred is increased at higher pulp concentrations.
Several basic types of pumps have been used to deliver pulp through piping systems: 1) positive displacement pumps such as rotary lobe and intermeshing screw types, 2) high speed centrifugal pumps, and 3) rotary disc pumps. All of these have advantages and disadvantages.
Positive displacement pumps literally suck the pulp into the suction end and spit it out the other end. These pumps have very close tolerances that must be maintained in order for the pump to operate properly. Pulp must be clean as a small tramp solid, such as a metal staple, can jam the rotating parts, wrecking the pump. Maintenance is very high and expensive. This type of pump has the lowest power cost of operation and the highest maintenance cost of operation.
Centrifugal pumps have poor suction characteristics and depend on an inducer device, attached to the front of the impeller, to drag the medium into the impeller. This inducer creates a vortex in the suction to the pump, leading to the formation of large air bubbles that often block all flow of medium into the pump. These air bubbles must be continuously sucked out of the pump eye by a vacuum system. These pumps are popular because they greatly reduce the high maintenance costs of the positive displacement pumps. However, the unpredictable nature of vacuum systems makes reliable operation of these pumps virtually impossible. Centrifugal pumps are limited to about 12½% pulp consistency without frequent problems with bridging and clogging.
Rotary disk pumps are relatively new and have many advantages over positive displacement and centrifugal pumps. Rotary disk pumps can pass large tramp solids (up to 3″ in diameter), produce no fiber damage, can pump up to 16% consistency, and have very low maintenance requirements. With adequate flow of material, such pumps are capable of handling 18+% consistency stock. However, these still have problems of their own. The major disadvantage is the lack of suction capability. That is, rotary disk pumps can only pump the material that flows into, or is pushed into, the pump. Since pulp has very little gravity flow at consistencies above 10%, this type of pump has serious problems in pumping any higher consistency. Another problem with rotary disk pumps is the “bridging” of stock above the pump suction, effectively blocking all flow into the pump. Vacuum systems have been tested on the backside of rotary disk pumps in an effort to “suck” pulp into the pump. However, this has proven to be unsuccessful.
Several devices have been produced to assist such pumps. Most are various types of inducers (Archimedes screws, beaters, augers, impellers, etc.) attached to the pump impeller shaft. These are commonly in use today to “fluidize” the stock and pull the pulp into the pump suction. However, existing devices are associated with many problems, such as mixing air into the pulp fibers, shearing the pulp fibers, and creating a pump suction vortex.
There is a need for an improved flow directing device that: 1) eliminates bridging of stock, 2) creates a non-vortexing flow, 3) is totally independent from pump operation, 4) focuses flow into the pump suction, 5) minimizes “slip/stick”, 6) does not require dilution water, 7) does not mix air into the pulp fibers, 8) significantly improves the flow into the pump suction, and 9) handles entrained air up to 30%, by volume, without problems.
SUMMARY OF THE INVENTION
The invention overcomes the above and other problems by providing a low-speed, mechanical device designed for facilitating the flow of medium to high consistency pulp stock slurry into pumps. More particularly, the invention provides a flow directing device including a flow director with a two-stage turbine, a turbine shaft, a turbine mounting adapter, a gear reducer and an electric motor. The device is used with a dropleg that preferably includes a sloped bottom wall and a drain and may be retrofit to existing droplegs. The flow directing device is adapted to assist flow of medium to high consistency pulp suspensions to a pump, preferably a rotary disc pump. The flow directing device is independently operated, separate from operation of the pump. That is, startup, shutdown, rotating speed and control of the flow directing device are independent from the pump. Thus, the flow directing device's speed can be optimized to assist flow and break up bridging, which is the agglomeration of solids that can become trapped in the pumping system. The flow directing device and pump work in concert with each other to form a unique stock pumping system capable of handling paper stock consistencies from 8-18% without problems associated with other types of pumping systems.
Regardless of its physical appearance, paper stock is by definition, a slurry. Accordingly, paper stock inherently exhibits properties that consistently are associated with slurries. The total content of medium to high paper stock slurry is comprised of 8-18% pulp fibers, by weight, and 82-92% water, by weight. The normal physical characteristics and appearance of paper stock are created when water droplets are entrapped in voids and pockets within the entangled fibers. This phenomenon, also known by the technical term “freeness,” pertains to the ability of stock to hold enormous quantities of water within the fiber mat. In its normal state, as the stock consistency increases, the material tends to form a semi-solid, non-flowing mass extremely difficult to pump. In order to pump paper stock slurry, the physical nature of the material must be altered by liberating a significant amount of entrapped water from the fiber mat to radically modify the nature of the material.
The first turbine (farthest from the pump) of the flow directing device is designed to condition the stock by liberating entrapped water from the fiber mat, thereby modifying its rheology. That is, the physical characteristics of the material are altered. The specific design of the first turbine, in terms of blade diameter and blade pitch, provides a localized shear stress to accomplish this change in rheology. The second turbine (closest to the pump) has a special and different diameter and blade pitch to impart shear stress to the stock. This transforms the slurry to a non Neutonian, Bingham-plastic fluid. Inherent to the transition of this state is the decrease in the apparent viscosity of the paper stock by a factor of 50%, or even greater.
Each paper stock slurry differs in consistency, fiber length, temperature, freeness, Kappa number, and other variables. Each has a specific transformation point in terms of shear stress at which it transforms to the Bingham-plastic state. The flow directing device and the pump operate in concert to accomplish and maintain this transitional, change-of-state paper stock slurry. This is achieved through precise combination of type, size, blade pitch, spacing and rotational speed of the flow directing device turbines, as well as the pump speed.
When paper stock slurry is in the modified, shear-thinned state, the flow directing device has the unique capability of delivering paper stock slurry to the suction port of the pump in required quantities and consistencies. The operating speeds of both the fl
Irish & Asssociates
Look Edward K.
Oliff & Berridg,e PLC
Woo Richard
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