Magnetically Coupled Sealless Pump Pumping Acid from the Depths

From Dominik Stephan

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Pumping oleum is challenging enough — add a submersion depth of 11 meters, and things get really interesting. But a magnetically coupled sealless pump is up to the challenge, providing safe and reliable handling of hazardous liquids.

The compact design of the GVSO pump enables a simple and easy process for pump replacement.
The compact design of the GVSO pump enables a simple and easy process for pump replacement.
(Source: Rheinhütte )

Oleum is an important byproduct and intermediate in the production of sulfuric acid. The colorless liquid is such a strong dehydrating agent that it draws water from the air, creating a characteristic fine mist that has led to its common name of fuming sulfuric acid. Its main ingredient, sulfuric acid, is in high demand for the production of fertilizers: Roughly 270 million tons were produced in 2017. Yet, the production process is extremely demanding, since sulfuric acid is highly corrosive, requires high temperatures and often includes abrasive byproducts.

Oleum itself, consisting of 100 percent sulfuric acid plus sulfur trioxide, is highly acidic and will react will most organic substances, even drawing hydrogen from carbohydrates (hydrolysis). Apart from that, it also releases the highly acidic and aggressive SO3 gas.

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Oleum producers often face challenges like failing seals or corroding materials, leading to frequent shutdowns of key equipment like pumps. Most importantly, any damage to pump seals can lead to the release of toxic sulfur trioxide, endangering operators on site.

Magnetically Coupled Sealless Pump for Oleum

With these problems in mind, a major sulfuric acid producer approached pump specialist Rheinhütte Pumpen. The German firm is well versed in supplying pump solutions for the sulfuric acid value chain, from production to recycling processes. Their solution: A magnet drive sealing system on a vertical centrifugal pump (type GVSO), which completely seals off the pump from the motor. That is not only safer but also more reliable and economical compared to a pressurized double mechanical seal with its gas panel and monitoring systems, the pump experts state.

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An additional challenge is the submersion depth of the pump with a total length of 11 meters, the Rheinhütte engineers explain. But GVSO pumps are up to the task, since their compact design allows for individual depth adjustment from a mere 0.5 m to up 17.5 m, using one or more intermediate bearings. The Rheinhütte test field capability (with a pit depth of 20 m) confirmed the expectations and proved the concept.

If constant temperatures and viscosities are required, for example during the production of molten sulfur, the pumps are also available in a heated version. Here, the manufacturer offers a tailor-made heating jacket system that can be used with steam or other heat transfer media. In this case, only two additional connections are required for the inlet and outlet. GVSO pumps can handle volume flow rates of up to 4,000 m3/h.

Intelligence Inside: Keep Track of Vibration and Temperature

The proposed material (Rheinhütte’s proprietary 1.4136 S, a high alloyed ferritic cast steel with 30 percent chrome and 2.5 percent molybdenum, but no nickel) offers high resistance against erosion, corrosion and abrasion. It is fully resistant in highly concentrated H2SO4 service as well in oleum.

The cooperation between the pump experts and the sulfuric acid plant operator dates back to 2016, when ITT Rheinhütte received a first order for a single pump unit, followed by two additional units in 2017 and three further pumps in 2019. A single additional GVSO pump in 2021 completed the modernization of oleum transfer on the site.

Rheinhütte equips its GVSO pumps with an innovative I-Alert sensor for vibration and temperature to provide additional safety assurance for plant operators. The device can be configured with preset thresholds that trigger an optical alarm, and provides full data transparency via an app or cloud platform. In this way, any necessary action can be taken in good time before a potential pump failure occurs. (dst)

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