Have You Tried A Peristaltic Pump For That Petrochemical Application?

By Chuck Treutel, Marketing Manager, Watson-Marlow Bredel

If you have not tried one yet…maybe it is time. These unique pumps have been building a reputation throughout the petrochemical industry as the "pumps for tough applications." Peristaltic pumps (commonly referred to as hose pumps or tube pumps) have been solving pumping problems for decades in a variety industries, ranging from petrochemical, pulp & paper, food processing, mining, paints, pigments and coatings to water and wastewater treatment. Many features of peristaltic pumps are truly unique in comparison with other pumping technologies. These pumps have no valves, seals or glands, and the fluid only comes in contact with the inside of a hose or tube. Because they are simple to install, easy to operate and quick to maintain, they are the world's fastest-growing pump type. In fact, many engineers have come to regard peristaltic pumping technology as a problem solver for difficult, even previously "unpumpable" fluids. Peristaltic pumps combine precise positive displacement and low maintenance requirements with the ability to handle abrasive and aggressive fluids, such as hydrocarbons and oil products which, wear out many other pump types. This unique combination of features often proves to be a cost-effective alternative for difficult pumping applications.

Principle of Operation

The basic principle of a peristaltic pump is a mechanical application of "peristalsis," a physiological term referring to the alternating contraction and relaxation of muscles around a tube (throat or intestines for example) to force the tube's contents through it. Understandably, the functionality of this basic peristaltic principle as a method of mechanical fluid transfer was developed in medical and biotechnology applications. A smooth wall flexible tube or hose is squeezed along its length, positively displacing the fluid contained within the tube. The tube's restitution after the squeeze creates a vacuum, which draws more fluid into the tube, causing a gentle pumping action with minimal damage to the media inside the tube, particularly when compared to other methods of mechanical transfer. Also, because the fluid is contained completely within the tube, the opportunity for contamination of the fluid is minimal. These attributes have made peristaltic pump technology attractive for many industrial applications, shaping its evolution into one of the most sought after pump types on the market, thus making them capable of handling flow rates and pressures unthinkable thirty years ago.

The Hose is the Heart

Historically, the fundamental challenge in applying peristaltic technology to petrochemical applications was the development of a hose element, which could accommodate the high pressures and flow rates demanded by the industry along with the capacity to handle the highly viscous, abrasive and chemically aggressive fluids. The traditional hose design is triple-layered with an extruded inner layer surrounded by a reinforcement cord matrix, and a durable, machined outer layer. This hose element is the "heart" of the pump. It dictates the suction lift capabilities, discharge pressure capabilities, metering accuracy and repeatability, as well as life of the pump. With new hose materials, construction and manufacturing technology, today's hose pumps are capable of over 350gpm, 230psi and metering accuracy to +/- 1%…and that is while pumping the most abrasive, viscous and corrosive products imaginable!

Petrochemicals

Hydrocarbons and oil products - petrochemicals - are problematic and difficult to handle using rubber materials. NBR and CSM could be used if only traces of petrochemical product are present; however, the hose is still likely to be attacked by the chemicals.

Over the past decade or so more and more items made from rubber have been replaced by thermoplastic elastomers (TPEs). These materials exhibit a similar elastic behavior to rubber, but also can be processed like thermoplastics. As it turns out, TPE was found to be oil resistant and possessed the right properties to perform as a peristaltic hose.

Applications

Many companies use organic solvents to make aerosol spray paints, wall paints, lacquers, paint strippers, adhesives, printing ink, spot removers, cosmetics, perfumes and antifreeze products. The ability to handle oil, polymers, fats, fuel oils and cleaning chemicals means that these pumps can be used in many sectors, such as printing, pulp and paper, packaging, construction and manufacturing. The pump can also run dry, so it is ideal for skimming oil film from water.

Hose pumps have been successful in replacing traditional pump types in corrosive, viscous and abrasive handling applications. A traditional pump typically operates with the rotor and stator in the product zone. Abrasive particles in the product quickly open up critical tolerances between the rotor and stator, causing a drop-off in pumping efficiency and eventual failure. Traditional positive displacement pumps require tight tolerances in order to function.

A hose pump rotor is located out of the pumped-product zone and never touches the pumped media. The hose is the only part to touch the product, keeping abrasive pump wear to a minimum. A properly selected heavy-duty pump hose does not fail due to abrasive wear; it fails from fatigue, and number of compressions. Regardless of the product, whether it is abrasive lime slurry or nonabrasive polymer, the hose life is the same.

Chemical metering is another area in which hose pumps have become an exceptional alternative to traditional pumping and metering methods. Many process streams, controlled by a combination of pumps and flowmeters, can be served just as well with a well-designed hose pump and tachometer, a considerable savings in equipment costs. High concentrations of caustic materials or particulate matter can attack the wetted parts of the flowmeter and affect the reliability of the measurement. Viscous media can coat flow sensors, affecting their measurement, and many slurries have also proven difficult to measure with a flowmeter. Utilizing a hose pump, the chemically compatible hose material can be checked and selected prior to installation, and fluid characteristics or process pressure will not affect the metering accuracy of the pump. Hose pumps have been successfully employed in a wide variety of highly automated metering applications, with accurate control of flow rate and total flow through the regulation of pump speed. Another nice feature of the peristaltic design, when integrated into more complex systems, is that the pump can act as its own check valve. Some portion of the hose or tube is always occluded, so when the pump stops, that point stays squeezed shut. This feature removes the need for an additional valve to prevent over-dosing or backflow.

SOURCE: Watson-Marlow Bredel