Plastic-lined magnetic drive pumps deliver a high level of safety and reliability when conveying corrosive, toxic or ultrapure media. However, this unique feature has so far come at the expense of some noticeable disadvantages with respect to pump performance; in addition, plastic as a material limits the robustness of the impeller and thus the head that can be achieved by the pump. By adapting the technologies used in the compressor industry, it has now been possible to develop a new generation of pumps that are closing the performance gap between mechanical seal pumps and metallic magnetic drive pumps.
Richter Chemie-Technik’s MNK portfolio of seal-less magnetic drive pumps is designed for the conveyance of corrosive, hazardous, and pure media in the chemical, pharmaceutical, and petrochemical industries, semiconductor production, water treatment, pulp, metal processing and waste disposal/recycling.
The product range is rated for everything from average to the most difficult operating conditions, for media where stainless steel, iron silicon alloy and others do not have sufficient corrosion resistance. As an alternative to pumps made of expensive exotic metals like Hastelloy, Monel and tantalum, MNK pumps can handle solids-laden, crystallising, toxic, hot or otherwise critical media.
The company’s continual technological improvements and advances led to a recently introduced feature for the MNK 200-150-315. Said to be the world’s largest fluoropolymer-lined, magnetically-driven centrifugal pump, it achieves flow rates up to 600 m3/h and delivery heights up to 60 m. High-quality external corrosion protection is assured through epoxy coating of the pump, while the screws and drive shaft are made from stainless steel.
The impeller assembly, with radial plain bearings made of sintered silicon carbide (SSiC) or hard carbon, rotates about an SSiC shaft. Axial thrust rings made of SSiC or carbon-reinforced PTFE absorb the axial thrust. The plain bearing system can also be made completely of SSiC components: brief dry-running is possible with Richter’s optional, time-tested SAFEGLIDE® Plus plain bearing system.
Another optional extra is SAFESEALTM, an innovative secondary seal developed for greater protection, which reduces the medium leaking from the pump to 0,1%. For this purpose, an additional barrier comprising a PTFE seal is installed in the rolling bearing chamber.
These capabilities were extended yet further to satisfy end users who demanded more in terms of the density of the conveyed product, temperature, and flexible delivery rates from the partial load range to the overload range. The result was an impeller with five main blades and five additional ‘splitter blades’. Now standard on the MNK 200-150-315, this technology (dubbed ‘Impeller Hydraulics III’) can also be retrofitted to older models sold prior to its introduction.
The latest advance comes courtesy of a new generation of plastic-lined magnetic drive pumps that have closed the gap between mechanical seals pumps and metallics magnetic drive pumps when it comes to efficiency, head and NPSH value (net positive suction head). This was impressively demonstrated in heavy-duty continuous operation over a period of six months by an MNK 125-100-315 pump installed at a customer in the chemistry industry.
Monitoring the flow
For continuous monitoring of its magnetic pumps, Richter offers the SAFERUN® Pump Monitoring System. With sophisticated sensors that are strategically placed between the CFR can and the PTFE/PFA can insert, critical operating data is collected and analysed. The sensors are shielded from the media in the process to ensure absolutely no contact, and therefore no interference, with the process.
SAFERUN® consists of two components, the CMS-T transducer and the CMS-S can system. The sensors integrated in the can measure torque, power, speed and temperature during operation. They are protected inside the double can, making it unnecessary to select a special probe tip material in the presence of aggressive fluids.
The current operating point is displayed by the SAFERUN® transducer with integrated traffic-light LEDs. Metering and operating data are also saved in a data memory (history log) for later analysis. Other pump-specific data, such as the operating-hour counter, can be displayed on a tablet PC.
Changes in process parameters are collected, analysed and displayed in easy-to-understand symbols and colours. The icons and signalling on the display were chosen with simplicity in mind, to ensure that the information is understood at a glance, and to allow untrained personnel to quickly assess a possibly critical situation. All data is stored in a history log and can be downloaded at any time for evaluation.
Important process parameters such as flow, density and viscosity changes can be retrieved and/or stored. Operating conditions that could lead to pump failure are also monitored, including torque changes, coupling failure, dry-running, lubrication shortage, gas build-up and others. In addition, the temperature is measured directly and continuously on the containment shell to allow for detection of possible ignition hazards according to ATEX directives, and so that any changes in process temperature can be detected and signalled at an early stage. SAFERUN® meets SIL 1 and is approved according to ATEX for Ex Zones 1 and 2, or Zones 21 and 22.
SAFERUN® data can be read out easily through an RFID interface with a tablet PC, while direct monitoring can be carried out via HART or analog (4-20 mA) interface. This monitoring option has been adopted by several pump operators, where it has delivered significant cost reductions and extended plant availability. All the operating data is also stored in the history log by the transducer, and is available even when the system in unpowered.
SAFERUN® is completely assembled and parameterised for the respective pump at the Richter factory, with the net result being speed-independent performance monitoring by speed-dependent factory parametrisation. The advantage of this for the end user, as opposed to a conventional motor load monitor, is that the specific pump performance curve and the fluid data are saved in SAFERUN®. Consequently, an assessment can be made of the pump’s performance range independently of the speed.
Two operating modes are provided: In conti mode (constant density), the power consumption of centrifugal pumps is proportional to the density. The pump monitoring runs based on the water performance curve under consideration, and is compared against the SAFERUN®-stored density references.
In batch mode (variable density and viscosity), the pump is repeatedly run through the whole batch during start-up. Stored operating points are plotted in the SAFERUN® app. The user adjusts the operating limits to the speed-torque characteristic of the batch process for optimal pump protection. In this mode, the system works for different speeds.
For additional information about this addition to the Valve & Automation stable, visit https://valve.co.za/product/richter-mnk-magnetic-drive-pump/
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