DFD Technology Overview

Section 1: The Rotary Disc Pump

Overview:  The rotary disc pump is unique among all pump technologies. Only the rotary disc pump uses the principles of boundary layer and viscous drag to generate a powerful molecular force field that pulls, rather than pushes, fluid through the pump. For the reasons listed below, the rotary disc pump is excellent for all types of stock at consistencies from 8% to 18+%.

Features and Benefits: The rotary disc pump offers many advantages over conventional centrifugal and positive displacement pumps for handling thick or high-density stock.

1. Non-impingement device: There are no vanes, cutwater or any close clearances in the rotary disc pump to produce impingement. Fluid is moved by the discpack - two or more rotating parallel discs – and moves in laminar flow bands parallel to the discs, and therefore does not impinge on the moving parts of the pump.
2. Non-pulsing: All pumping action is produced across rotating discs. Therefore, there is nothing in the pumping action to produce pulses.
3. Non-vortexing in pump suction: This is a major difference between the rotary disc pump and high-speed centrifugal pumps. There are no impeller vanes or intimate flow inducer to create pre-rotation or vortexing of the fluid in the pump suction. Inlet flow into the the rotary disc pump is laminar and straight. This inherent factor eliminates the buildup of an air bubble in the suction eye that requires continuous removal in centrifugal pumps.
4. Handles entrained air: The rotary disc pump passes entrained air, 50% or more, with no change in size of distribution of individual air bubbles. Bubbles migrate to the area of lowest pressure, midway between discs, and pass through the discpack without imploding.
5. Low-shear: Non-impingement operation and no close tolerances in the rotary disc pump design combine to eliminate the problem of shear, stress and degradation of delicate fibers.
6. Hydraulic and volumetric efficiency proportional to increase in viscosity: An increasing thickness of the boundary layer increases the efficiency of transferring energy from the boundary layer to successive layers of fluid. Pumping efficiency increases with increasing viscosity. With centrifugal pumps, flow, efficiency and discharge pressure are inversely proportional to viscosity - precisely the opposite of the rotary disc pump.
7. Handles solids and slurries with little wear: The boundary layer establishes a buffer zone between the discpack and the side bands of fluid pulled through the pump. This insulates the discpack against wear associated with pumping solids and slurries, resulting in gradual wear. Spacing between the discs can be designed to pass tramp solids as large as 6" O.D. or 8" in length.
8. Low NPSH requirements: The rotary disc pump is superior to other pump technologies in NPSH requirements, operating with about 50% of the NPSH required by centrifugal pumps.
9. Run-dry capability: Only the rotary disc pump, of all the available technologies, can run dry or against blocked suction or blocked discharge with no damage to the pump or pumping system
10. High reliability and low maintenance: The rotary disc pump is non-impinging, has no close clearances, has heavy-duty construction, and is not subject to catastrophic failures. Maintenance can be scheduled at the customer’s convenience. It is common for the wet-end parts of  the rotary disc pump to last from 5 to 10 times as long as the comparable parts in centrifugal and positive displacement pumps.
11. Life cycle costs: In viscous and abrasive services, the rotary disc pump has the lowest life cycle cost in the industry as calculated on the basis of original cost of pump, cost of repair parts, maintenance labor, lost production time and loss of product.
12. Low bearing loading: Due to its operating principles, the rotary disc pump pump has no radial loading and very low axial loading, meaning long life and low maintenance of seals and bearings

Overview: The FloDirector is a unique, low-speed, mechanical device that facilitates flow of medium- to high-consistency paper stock slurry into a pump. It enables a pump to handle higher consistencies than the pump could handle without the FloDirector. The FloDirector and the rotary disc pump operate independent of each other in terms of startup and shutdown, speed and overall control. The two devices work in concert to comprise a unique paper stock pumping system capable of handling consistencies from 8% to 18+%, with none of the problems usually associated with other available types of heavy stock pumping systems.

Paper Stock: Regardless of its physical appearance, paper stock is, by definition, a slurry. Accordingly, paper stock inherently exhibits properties that consistently are associated with slurries. Medium to high consistency paper stock slurries are comprised, by weight, of 8% to 18% pulp fibers, and 82% - 92% water. Different types of pulp (hardwood/soft wood), fiber length, Kappa number, etc., all effect the slurry. The 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 its 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 reduce the difficulty of pumping paper stock slurry, the physical nature of the material must be altered radically by liberating a significant amount of entrapped water from the fiber mat. This is the basis of the design of the FloDirector device.

FloDirector Function: The FloDirector first turbine (farthest from the pump) pre-conditions the stock by liberating entrapped water from the fiber mat to modify its rheology (i.e. physical characteristics of the material). The specific design of this turbine (in terms of diameter and blade pitch) provides a localized shear stress to accomplish this change in rheology. The second turbine (nearest to the pump) has a special and different diameter and blade pitch that imparts a high shear stress to the stock. This transforms the slurry to a non-Neutonian, Bingham-plastic fluid. Inherent to the transition to this state is the decrease in the apparent viscosity of the paper stock by a factor of up to 90%.

Paper Stock Slurries: These can differ in % consistency, fiber length, temperature, freeness, Kappa number, and other physical characteristics. Each stock has a specific transition point in terms of shear stress at which it transforms to the Bingham-plastic state. The FloDirector and the pump operate in concert to accomplish and maintain this transitional, change-of-state of the paper stock slurry. This is controlled by the precise combination of type, size, blade pitch, spacing and rotational speed of the FloDirector turbines, and the pump speed.

FloDirector/Pump Relationship: The FloDirector has the inherent and unique capability of delivering paper stock slurry in the modified, shear-thinned state to the suction port of the pump in the required quantities and consistencies. Operating speeds of the pump and FloDirector are adjusted independently to maintain indefinitely the Bingham-plastic state at a pumping rate several times higher than stock not in this transitional state. This increases overall pump efficiency and reduces the power output of motors and drives. As paper stock slurry is removed from the zone of influence of the FloDirector, it gradually reverts to its original form and state with no apparent negative effects. This transitory state induced by the FloDirector changes the physical properties and nature of the media exposed to the FloDirector. This is the essence and function of the FloDirector.

Uniqueness of FloDirector Design: The FloDirector transforming paper stock to the Bingham-plastic state to lower its apparent viscosity, making it easier to pump. It operates at low speeds to minimize any deleterious effects on pulp fibers. It has no close clearances subject to jamming with tramp solids. It requires little maintenance, as there are no areas of wear that effect performance. The FloDirector acts as a first-stage, axial-flow pump to increase suction pressure and the available NPSH.

SECTION III: THE DROPLEG:

The special dropleg developed for the system is a geometric design that accommodates the installation angle of the FloDirector and enhances the flow of stock into the pump suction. There are no pockets or areas of induced turbulence in the design that would trap stock or reduce the operating efficiency of the system. Its standard construction is 316SS, and it is available in any weldable metallurgy. All interior surfaces of the dropleg are polished to a cottonball finish.

SECTION IV: DFD THICK STOCK PUMPING SYSTEM

The FloDirector device emerged from an extensive engineering and R&D program. The rotary disc pump differs from all other pump technologies. The combination of the unique FloDirector and the rotary disc pump comprise an advanced pumping system that produces the benefits listed below.

1. Water dilution: This system requires no water dilution system to handle paper stock consistencies from 8% to 18+%.
2. Entrained air: This system requires no entrained air or gas removal system to pump paper stock slurries at consistencies from 8% to 18+%.
3. Air bubbles: The FloDirector’s unique pushing action has no effect on the distribution and size of entrained gas or air bubbles in the paper stock slurry. It does not intimately mix air with pulp fibers, or attach insulating, microscopic air bubbles to the fibers, as is the case with other technologies. This is an important consideration when pulp fibers are chemically treated downstream of the pump.
4. Changed rheology: FloDirector produces a physical change in paper stock slurry, transforming the slurry to a Bingham-plastic state, with as much as 90% reduction in the apparent viscosity, and producing a modified stock slurry easily pumped by the rotary disc pump.
5. Air-lubricated plug flow: At some point downstream of the pump, the paper stock gradually reverts to "plug flow" in the discharge pipe. Pulp fiber matting and the higher density of the stock squeeze pockets of entrained air to the outside of the plug and against the pipe wall. This air layer becomes a lubricating film, or air bearing, to the stock plug, reducing pipe friction and horsepower required to move the stock through the piping system.
6. Improved NPSH: The FloDirector enhances the pump suction conditions by improving the pulp rheology and increasing the NPSH (net positive suction head) available to the pump. These factors reduce the tendency of the pump to cavitate at reduced static suction head. As little as 48" of static suction head above the pump centerline is sufficient NPSH to operate the system.
7. No fiber damage: The FloDirector’s slow operational speed delivers stock to the pump suction with a gentle pushing action. This minimizes any pulp fiber damage.
8. Handles tramp solids: This system can handle entrained tramp solids up to 6" O.D. or 8" long. These include undigested knots, wood chips, rocks, bullets and nails, pieces of wire, metal or plastic strapping, and bolts and nuts, to mention a few items, commonly associated with paper stock slurry produced from trees or recycled waste products.
9. Special Turbine design: The two FloDirector turbines are of different design but combine to reduce any bridging tendency of the stock, regardless of consistency, and change the rheology of the pulp, without fiber damage, to a state that is easily pumped by the rotary disc pump.
10. Required BHP: The FloDirector improves the overall stock pumping characteristics, reducing the BHP required to deliver paper stock slurry through the discharge piping.
11. Stock transformation state: The FloDirector continually delivers stock in the required quantities and in a Bingham-plastic state that is easily pumped by the rotary disc pump.
12. No Slip-stick or pulsation: Pulp is discharged by the rotary disc pump free of slip-stick and pulsation and is discharged in the desired flow rates and at the required discharge pressure.