positive displacement pump choices for wastewater applicationshandling+&+reduction+cho… ·...

Positive Displacement Pump Choices

for Wastewater Applications

Positive Displacement Pump Choices | Wastewater Applications

Summary of Presentation

1. Why do you need Positive Displacement Pumps in Wastewater?

2. What types of Positive Displacement Pumps are available for Wastewater Sludge?

3. Which type of Positive Displacement Pumps should I use?

4. What Applications for Positive Displacement Pumps do you have?


Although many applications can be handled by Centrifugal Pumps, there are several reasons why you should use a Positive Displacement Pump in wastewater applications. Positive Displacement Pumps are specially designed to handle a variety of different sludges found in wastewater due to:

•Viscosity

•High Solids Content

•High Pressure

•Metering

•Truck Loading

•Truck Offloading

•Air Entrainment

•Suction Lift

Reversibility

•Size

•Portability

•Much, Much More!

Why do we need Positive Displacement Pumps in Wastewater?

Viscosity & High Solids Content are two of the major reasons to install Positive Displacement Pumps. They are designed specifically to pump thick and viscous material. A Positive Displacement Pump moves liquid through rotating cavities from one side of the pump to another. All Positive Displacement Pumps work with a very similar principal.




Suction Lift - Most of the wastewater applications have a flooded suction, or the liquid level above the pump suction, however this is not always the best case scenario. Positive Displacement Pumps have distinct features that allow them to pull a suction lift as shown:

• Up to 25’ (8 m)

• Self Priming without Vacuum Assist

• Able to Pass Air Through the Pump



Metering & Compact Size – Positive Displacement Pumps are commonly used for their metering abilities, as they provide a very smooth and even flow rate for process equipment. They can also be very compact in size.

• Belt Filter Press Feed

• Centrifuge Feed

• Gravity Belt Thickener Transfer

• Screw Press Feed



Loading & Reversibility –Positive Displacement Pumps are commonly used due to their ability to reverse. These are very useful in many applications found in wastewater such as:

• MBR Permeate

• Truck Loading & Offloading

• Plugged Lines


How do they work? Designed specifically to pump thick and viscous materials, a Positive Displacement Pump moves liquid through rotating cavities from one side of the pump to another. As the fluid moves through the pump, it is discharged out the other side of the pump. All Positive Displacement Pumps work with a very similar principal, just a different design, and most feature reversible flow directions. Below are the most two common designs. In addition, we will discuss how others work as well.



Rotary LobePump

Progressing CavityPump


What types of Positive Displacement Pumps are available for Wastewater Sludge?

There are many different styles of Positive Displacement Pumps in the marketplace with vast differences and advantages. We will discuss each of these common units, however, there are two that are much more common in the industry over others.

Some of the Positive Displacement Pumps found in wastewater are:

• Air Operated Diaphragm

• Rotary Lobe Pumps

• Progressive Cavity Pumps (PC)

• Double Disc

• Peristaltic (Hose) Pumps


Air Operated Diaphragm


Progressive Cavity

Rotary Lobe

Peristaltic (Hose)

Double Disc

Air Operated Diaphragm Pumps

• Up to 200 GPM Maximum

• Up to 125 PSI Maximum

• Slurries up to 75% Solids by Volume

• Air controlled & Spring Controlled

• 25’ (8 m) Suction Lift Capable



Disadvantages:

• Air Operated (High Cost)

• Spring Loaded (Safety Concerns)

• Heavy Pulsation (Even with Pulsation Dampeners)

• Loud

• Frequent Replacement of Ball Checks

• Time consuming & Difficult Repairs

• Not Reversible

Advantages:

• Highly Abrasive Resistant

• No Mechanical Seals or Packing

Suction

Discharge



Double Disc Pumps

• Up to 700 GPM with Single Pump

• Up to 110 PSI Stall (60 PSI Operating)

• Electric Controlled




Disadvantages:

• Can not Handle High Pressures

• Low Solids Percentage (Up to 6-7% by Weight)

• Medium Pulsation (Even with Dampeners)

• Frequent Replacement of Flap Valves

• Difficult Repair from Under Pump

• Not Reversible

Advantages:


• No Seals

Suction

Discharge



Peristaltic (Hose) Pumps





• Reversible



Disadvantages:

• Low Solids Percentage

• Medium Pulsation (Even with Pulsation Dampeners)

• Frequent Replacement of Hose Based on Hours

• Difficult to Repair in Small Places

• Consumes a lot of Space

Advantages:


• No Seals

• Reversible Suction

Discharge



Progressive Cavity Pumps (PC)






Disadvantages:

• Cannot Run Dry

• Takes up a lot of Space

• Expensive & Difficult Rebuilds

• Gear & Pin Joints in Wetted Section of the Pump

• Slight Pulsation

Advantages:

• Can add Multiple Stages for High Pressure Applications

• Can Pmp very High Solids Content with Hopper Designs

• Good at Low flow High Pressure

• Reversible




Designs with Combined with Screw Hopper Feeder




With the many different designs that are available, and their unique features, this can make maintenance a little easier. Many parts are used to build the pump, but just assembled in a little different configuration.



Rotary Lobe Pumps




• PTO Drive

• Hydraulic Operation



Disadvantages:

• Low Pressures (Up to 232 PSI)

• Low Solids Percentage, up to 18% by weight

• Not Good for Low Flow High Pressure

Advantages:

• Can Run Dry without Damage

• Small and Compact

• Can be Mounted in any Direction

• Easy In-Line Repairs

• No Joints

• No Pulsation

• Reversible



Rotary Lobe Pumps

There are many different design features in Rotary Lobe Pumps depending on the model:

• Radial Wear Plates

• Cartridge Mechanical Seals

• Adjustable Casings

• Dynamic Injection



Lobes & Stators

Lobes and Stators come in a variety of in both rubber coating, and in metal for the longest possible life in multiple applications. Rotary Lobe Pumps also have a multitude of designs available, with different features over one another. Some of the material options are:

• Buna-N

• EPDM

• Viton

• Polyurethane

• CSM

• Steel / Stainless

• Steel / Stainless Tungsten Carbide



Positive Displacement Pump Choices| Wastewater Applications

Positive Displacement Pump Control Panels

One of the major advantages of Positive Displacement Pumps is their ability to control flow through a VFD.

Positive Displacement Pumps require the use of Constant Torque VFD’s, as they require constant torque through their entire operating range.

The slower you run the pump, the lower the GPM output is on the pump.



Applications for Positive Displacement Pumps

In wastewater treatment plant applications, Positive Displacement Pumps can be used in several applications. Some of these applications include:

• Primary Sludge

• Scum

• Return Activated Sludge (RAS)

• Grease

• FOG

• Thickened Waste Activated Sludge

• Membrane Bioreactor (MBR)

• Digested Sludge

• Gravity Belt Thickeners

• Centrifuge Feed

• Belt Filter Press Feed

• Screw Press Feed

What Applications for Positive Displacement Pumps do you have?



Rotary Lobe Pumps are designed with operation and maintenance in mind. In-line pumps are simple to install in any pipeline. Some applications have hair & rags that do not effect these pumps as much as centrifugal pumps.


Digested Sludge Waste Activated Sludge



When feeding digesters, the sludge can sometimes be thick and difficult to flow through when using centrifugal pumps. Positive Displacement Pumps can take up to 18% solids by weight, which is thick and very difficult to move. Thus, using these types of pumps are widely preferred.


Thickened Sludge Waste Activated Sludge



Some applications require specific flow rates to feed to process equipment like Belt Presses, Centrifuges, Gravity Belt Thickeners, or Screw Presses. Positive Displacement Pumps provide a smooth and steady flow so that polymer can be metered in slowly.


Screw Press Feed Belt Press Feed



Due to their ability to pull a suction lift, Positive Displacement Pumps are often in applications requiring high vertical lift. Unlike Self-Priming Centrifugal Pumps, not only can they pull a suction lift, but they can also pump viscous sludges without an issue.


Polymer Feed Primary Sludge

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