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Pumping aggressive fluids

Challenge for pumps: the 6 most difficult media

Acids, solids, pollutants—when it’s necessary to pump difficult media, the system must withstand enormous burdens. Here we cover  the top 6 critical fluids and how they can be pumped safely and carefully using special pumps for aggressive media.

sulfuric acid is one of the difficult fluids to pump
Picture: Wikipedia - Alexander Savin


Pumping critical media can cause severe damage to the system. Aggressive media pose a danger especially for pumps, since continuous contact can damage the pump material and quickly destroy the unit. Which media do operators need to handle with particular care? What solutions are available for the safe transport of sulfuric acid, contaminated chemicals, or cryogenic liquids? The overview of six particularly difficult media provides this information.


1. Sulfuric acid

Sulfuric acid is one of the most powerful of all acids and has extremely corrosive properties. This makes it one of the most difficult liquids to pump. How corrosive it actually is on plant components varies with the concentration. For example, a standard material such as 1.4408 (AISI 316) is resistant in weak, cold acid, but completely unstable in the range of 10 to 85 percent, yet again resistant if the concentration exceeds this amount. An additional problem: The corrosive behavior of metallic materials is heavily dependent on the temperature of the sulfuric acid. As a result, hardly any metallic alloy is resistant to corrosion at fluctuating concentrations and temperatures.

The solution: In contrast to metal alloys, fluoroplastics such as PFA or PTFE cover the entire concentration range of sulfuric acid. Horizontal plastic pumps made of these materials can easily withstand operating temperatures of up to 180 degrees Celsius—for example the horizontal centrifugal pump CM on PFA solid material with magnetic coupling from MUNSCH.


2. Cryogenic media

Chemical resistance is crucial for critical media. But the temperature can also cause problems. Cryogenic liquids such as liquefied petroleum gas or liquefied natural gas (LNG) are a challenge. These are stored at temperatures as low as -161 degrees Celsius and have to be transported at temperatures just as cold. Under such extreme conditions, leaks quickly occur. In addition, the severe cold is dangerous for engine and bearings.

The solution: Cryogenic pumps are specially designed for pumping cryogenic liquids. Cryogenic pumps are equipped with submersible motors resistant to low temperatures and can achieve a long service life even at extreme temperatures. The NIKKISO cryogenic pump from LEWA is adapted to many applications and industries. It is used both in condensate containers and in fixed installations.


3. Wash solutions with solid content

Plastics compete with metallic materials not only in the field of highly concentrated acids, especially when it comes to thick-walled solid materials. Even in liquids considered to be rather harmless, chlorides, fluorides or a temporary fluctuation of the pH-value can afflict metallic pumps by continually wearing away pump material through erosion corrosion. Solids present in the medium destroy the protective oxide layer on the metal surface and accelerate corrosion. Many operators try to condition the liquids by means of elaborate measures, for example by adding caustic soda solution—but often with only moderate success.

The solution: Horizontal centrifugal pumps like the NPC from MUNSCH made of the wear-resistant solid plastic UHMW-PE prevent erosion corrosion. Their solids-tested mechanical seal makes them even more robust.


4. Contaminated chemicals

These dirty fluids occupy the top three positions on the list of hard-to-pump media. In many chemical production processes, toxic, aggressive liquids are pumped. Often, the media also contain impurities such as fibers, agglomerates, or crystals. The hazard class of the liquids often requires aggregates that are hermetically sealed, for example magnetic coupling pumps. However, these pumps alone are quickly overtaxed by the presence of massive impurities—they damage the pumps considerably, making them fail at the end.

The solution: Magnetically coupled centrifugal pumps with external flushing, such as the CM-FA from MUNSCH, provide one remedy. The conveying chamber and magnetic drive chamber are strictly separated from each other in this series. Sensitive drive elements are supplied with clean fluid from outside.


5. Shear-sensitive media with high viscosity

Yogurt as a critical medium? Sounds strange to laymen, but this is very familiar to food experts. The dairy product is shear-sensitive, highly viscous and often loaded with solids, and being foodstuff, it also has high hygiene requirements. During the production process, it is important to protect the valuable bacterial cultures and to avoid separation of the phases of different viscosity. For yogurt varieties containing pieces of fruit, the shape and consistency of the fruit should also be retained. Centrifugal pumps are not a good match here: they would damage the fruit content, and their efficiency decreases sharply at high viscosity.

The solution: Eccentric screw pumps such as the NEMO from NETZSCH convey low to extremely high-viscosity media with low shear, continuously and at stable pressures. In the hygienic version, all parts in contact with the media are FDA-compliant and thus ideally suited for use with sensitive foodstuffs. CIP cleaning is also no problem thanks to the bypass line and flushing connection.


6. Fertilizers

First place among the critical media is reserved for aggressive acids with high corrosion potential. Sulfuric acid is used in the production of fertilizer, which in itself places high demands on all components of the production plant. In addition to phosphorous pentoxide as the actual fertilizer component, a large quantity of calcium sulfate (gypsum) is also produced during the breakdown of phosphate rock. Pumps used in this area therefore convey a highly corrosive and abrasive slurry, which often shortens the life cycle of the unit considerably. The combination of abrasion and corrosion plays an important role here.

The solution: Plastic pumps like the vertical cantilever pump TPC from MUNSCH do not have the word corrosion in their dictionary. When handling aggressive media, solid plastics such as polyethylene have a significantly longer service life than most metallic alloys.



The right pumping solution for every medium

Every system operator has a different view on what media in fluid conveyance are particularly difficult. The good news: for every liquid, no matter how aggressive, sensitive or critical, there is a pump that is up to the challenge. Regardless of the medium to be pumped: with the PUMPselector, any operator can find the right pump for his applications with just a few clicks.


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