Pumps & Valves How to Handle Aggressive Media: Centrifugal Pumps Could Do More

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AZO GmbH + Co. KG

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Richter Chemie-Technik GmbH

The requirements for pumps are clear: A safe, efficient and reliable performance — An yet, corrosive media provides a tough challenge for the versatile machines. Can engineers only choose between wear and energy loss? Lined magnetic drive pumps could change the way we handle fluidics.

Fluidic keeps the world running: Thus, pumps are the heart of almost every production process and plant. Hardly any industry would be possible without the aid of these versatile machines  — not even electromobility: Hydrofluoric acid is used in the production of electrolytes for batteries — a corrosive and volatile product with a pungent odor that needs to be pumped safely and reliably.

Safety remains a key requirement for pump and flow systems: Not least after devastating accidents such as those in Tianjin, China, in 2015, the explosion in Ludwigshafen, Germany, in 2016, or at the Leverkusen Chemical Park in 2021, authorities and operators have once again increased the requirements for the systems used. Thus, every pump must be robust and leak-free if it is to safely convey corrosive or environmentally hazardous substances.

Magnetically coupled pumps without a continuous shaft are tailor made for demanding applications like these. But of course, aggressive pumping media also takes its toll away on these flow machines. Components such as the impeller corrode, which reduces the efficiency and results in expensive replacements. Plastic-lined solenoid pumps, in which the parts in contact with the medium are made of or lined with PFA or PTFE, provide an alternative. Pumps with such “inner values” can be used instead of components made from “exotic” and thus expensive metal materials such as Hastelloy, Monel or Tantalum, as well as for solids-laden (up to 30 percent according to the manufacturer Richter Chemie-Technik), crystallizing, toxic, hot or otherwise critical media.

Not Just Pumps: What Can Lined Valves Do?

When refrigerants contribute to global warming: According to the UN Environment Program, harmful refrigerants equivalent to at least 240 million metric tons of CO₂ entered the atmosphere in 2020, thus intensifying climate change. But of course not a single air conditioning system in the world functions without a refrigerant. Accordingly, a major air conditioning manufacturer from the United States has launched an ambitious project aimed at reducing the climate impact of its refrigerants.

Because of their corrosion resistance and reliability, lined Richter KN Series ball valves were selected for the first production plant. Thick-walled lined valves provide the optimum combination of operational reliability and value for money when used in corrosive processes. A special design trick of the Richter designers is the use of a one-piece ball shaft, which avoids the typical weak point of the transition from the ball to the selector shaft.

You Can’t Have Everything … Can You?

Unfortunately, these benfits in stability and safety come at the price of slightly lower efficiencies and less favorable NPSH values: Plastic-lined pumps require larger internal gaps to provide room for material expansion. In addition, the maximum head is often limited as the load capacity of lined impellers is difficult to calculate. This is not only a theoretical problem: If a pump is operated outside the specified operating range for too long or at too high media temperatures and densities, the impeller may break and the pump may be totally lost. In practice, at least with aggressive media, it often comes down to a trade-off: Simple and proven technology with a risk of failure, or compromise on performance? Having both hardly seemed to be an option.

And yet things could be different: After intensive analysis of data on known impeller failures, the engineers and developers at Richter Chemie-Technik have a deep understanding of the mechanisms by which such component failures occur. Using CFD, it was possible to determine exactly how the flow forces are distributed in the pump. This made it possible to couple the CFD results with an FEM component calculation, which led to the determination of the stress distribution in the impeller. And not only that: The engineers were able to set up a calculation tool with which they could reliably make a statement about the impeller stability with just a few operating and device parameters.

Smart & Digital Pumps

Smart Pumps: The Future is Digital and Connected

With the knowledge gained in this way, it was possible to design a completely new impeller geometry: Here, intermediate blades (splitter blades) distribute the mechanical load evenly over several impeller blades. In the same breath, optimization of the geometry ensures improved flow characteristics and more even hydraulic loads; in addition, a specially designed trailing edge significantly reduces pressure surges. This is complemented by a “heavy duty” design in which the metallic support extends from the wheel disc through the blades into the cover disc. Furthermore, the developers were able to benefit from their experience with compressor designs: Here, measures to reduce secondary flows in the housing have long been part of everyday life — after all, gap height and efficiency loss are roughly proportional. With a clever design, the gap dimension can be optimized to such an extent that the overall efficiency approaches the level of all-metal pumps.

The Best of Two Pump Worlds

Does this make the contrast between metallic centrifugal pumps and lined magnetic pumps obsolete? At least the performance and safety gap seems to have become much smaller. In other words, the best of both worlds is now within reach for users — at least in fluidics. Efficiency, head or NPSH value need not be at odds with reliability, long service life and operational safety, the developers are certain.

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In this way, pumps today are helping to build the world of tomorrow — sometimes literally. One example is the most important building material: concrete. The artificial stone is produced worldwide on a billion-ton scale. Tragically, its most important ingredient, cement, is a secret climate killer with enormous CO₂ emissions. Nearly 2.8 billion tons, or between six and nine percent of man-made carbon dioxide emissions, are attributable to cement plants. The industry is aware of the problem: German manufacturers have announced that they want to become emissions-neutral by 2050. To this end, well-known cement companies in Germany and the USA are working on a process in which CO₂ is captured and recycled (Carbon Capture and Utilization, CCU). The developers are confident that around 60 percent of emissions could be avoided in this way. What does all this have to do with pumps? The substances used, such as sodium hydroxide or potassium hydroxide, are not simple pumping media — no wonder that lined pumps and fittings from Richter Chemie-Technik are also firmly planned in the corresponding production processes of the future. (dst)

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