Technical article, published in: Schüttgut (4/2019)

Adverse ambient conditions for switchgear: the flotation Emergency pull-wire switches systems used in potassium chloride extraction at the K+S Machine safety potash works in Neuhof-Ellers in extreme environments

At its Neuhof-Ellers site near Fulda, the company K+S Kali mines raw potash and magnesium salts at depths of down to 800 metres. The atmosphere in the flotation plants which separate the potassium chloride from the rock salt and other mineral salt constituent parts is extremely corrosive. Trust is therefore placed in "Extreme" emergency pull-wire switches which have been thoroughly tested and which allow the plants to be switched off very fast should a dangerous situation occur.

ar below the surface of the earth, at a Potash does not play a direct role in F depth of 540 to 780 metres, Upper human nutrition, but its indirect impor- Permian deposits are to be found in the tance is all the greater for it. Without eastern parts of Hesse and Thuringia: raw potash, basic plant products such as grain potash and magnesium salts which K+S would be almost impossible to farm Kali has been mining for decades.

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economically, and the resulting yield would be considerably lower. In the Neuhof-Ellers mine, around 20 km west of Fulda, there is also a third, much rarer salt: here kieserite is mined – a mineral containing magnesium and sulphurous material (magnesium sul- phate), which is ideally suited as a fertiliser for certain crops because it not only generally strengthens the plants, but also prevents chlorosis, a deficiency disease.

Fertiliser extraction from a depth of 700 m K+S is thus making an important The flotation systems are safeguarded using contribution to feeding the growing world emergency pull-wire switches population. The company is one of the largest potash producers and is a leading measures include multiple emergency salt supplier worldwide. Products sold pull-wire switches, each one installed ® ® ® include Korn-Kali , 60er Kali , ESTA alongside the basin and spanning a ® kieserite and Magnesia-Kainit . distance of about 10 metres. They enable In Neuhof-Ellers, the mined raw salt is the staff on site to stop a dangerous first separated electrostatically into its machine movement immediately, without kieserite and residual mineral components having to walk to an emergency-stop using the patented energy-saving and dry button installed in an operating panel. In an ® ESTA process. This process is performed emergency, this can save precious on a huge scale: with a daily capacity of seconds. 12,500 tonnes. Every year the potash plant Originally, K+S used one-sided generates up to 1.4 million tonnes of emergency pull-wire switches from various standard and specialised fertilisers. manufacturers in its plants. Regular safety In a second step, potassium chloride is checks repeatedly revealed failures. One of ® extracted from the residue of the ESTA the responsibilities of Christoph Hachfeld, plant by means of flotation. The precursor Operational Engineer for Electrotech- is a salt suspension in a saturated saline nology, is electrical maintenance and solution, into which air is blown. Special repair of the flotation systems: "The reason flotation agents cause the air bubbles to why the emergency switches failed was attach themselves only to the potassium usually corrosion of the plunger: pulling chloride for separation purposes, and then the wire then has no effect." to swim to the surface as foam. This foam The reason for this is obvious: the saline is then removed and, in a further step, solution in the flotation basins has a dried. temperature of around 40 °C and is K+S operates a total of six two-stage extremely corrosive. It is unavoidable that flotation systems in Neuhof-Ellers. Safety salty splashes or at least minute drops of this saline solution fall onto the emergency

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stop switch. The constantly high humidity in die-cast aluminium housing is hard- the flotation plants exacerbates the coated, and an additional sealing cuff corrosive atmosphere, as confirmed by prevents dirt from penetrating. The Hachfeld: "The condi- exterior metal components tions here are even »The conditions here are even and accessories, such as the more unfavourable more unfavourable than in a pull-wire unit, screws, than in a typical salt- typical saltwater environment. thimble and wire, are made water environment. Even V2A stainless steels out of V2A and V4A stainless Even V2A stainless corrode here very fast.« steel. steels corrode here very fast. The salty, Christoph Hachfeld, K+S Kali Refit after 1-year test phase foggy, fluid droplets K+S started by ordering a also attack the interior of e.g. switches if single ZS 73 in the "Extreme" version they are not effectively sealed." described above and testing it for one year. When Hachfeld assumed responsibility The result: the emergency pull-wire switch for maintenance of the production plants functioned in these extreme conditions with about three years ago, he looked up the no problems for the entire 12 months. The relevant providers and researched surface operations maintenance team in emergency pull-wire switches for extreme Neuhof then refitted all its flotation ambient conditions. This led him to the systems with the ZS 73. Since then, they steute "Extreme" range. have been working hard in the name of This range includes several series of machine safety without any malfunctioning emergency pull-wire switches for extreme at all - even though the adverse ambient environments, one of which is the ZS 73. Its conditions are clearly in evidence.

Tip for bulk goods and solids!

Compact and safe design At the POWTECH 2019, the new Machine operators are thus In addition, the new device can steute solenoid interlock for gas reliably prevented from opening be used in applications with a and dust explosive zones was the guard door before all high switching frequency and in presented for the first time ever. dangerous movements have adverse environments up to The features of this Ex STM 298- stopped. IP67. 3 GD safety switch include a very The new solenoid interlock is The Ex STM 298-3GDG is ATEX compact, slim design, making it also very versatile because it is approved for gas Ex zone 2 and well suited to mounting on available with different dust Ex zone 22. Typical appli- machine profile systems and in actuators (straight, angled and cations for the dust Ex approved narrow installation locations. sliding) and because the variant, presented at the Inside the die-cast aluminium actuator head can be adjusted in POWTECH for the first time, housing there is a robust 90° steps. Users also have a include the safeguarding of switching system which guaran- choice of switching inserts: the doors on manufacturing, filling tees locking of the guard door. range includes a variety of and packaging machines hand- Here high locking forces are normally open and normally ling dust-raising products or achieved (up to 3000 N for closed contacts. powdery goods. straight and sliding actuators).

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Author:

Rainer Lumme Product Manager Extreme steute Technologies

Images: steute Technologies GmbH & Co. KG

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steute Schaltgeräte Brückenstr. 91 Phone: + 49 (0) 5731 745 0 [email protected] GmbH & Co. KG 32584 Löhne, Germany Fax: + 49 (0) 5731 745 200 www.steute.com