Key points
When it comes to processing highly toxic or corrosive fluids, managing and preventing leaks is an essential prerequisite. Hannah Verrall of HMD Kontro Sealless Pumps looks at the enhanced safety offered by sealless pumps and considers the options for secondary control and containment systems, which are recommended for particularly hazardous applications.
For the chemical industry and other processing applications, especially those involving the pumping of highly toxic or corrosive materials around a plant, managing risk is an exceptionally important operational issue.Â
The release of toxic chemicals to the atmosphere risks not only the safety of employees but also can lead to structural damage and equipment degradation, not to mention environmental impacts where leakages are not contained.
Building in safety
While establishing clear contingency plans to minimise the spread of chemicals should a spill occur, choosing the right pumps is also a key consideration. This includes not only the materials used for pump casings but also the sealing system itself.
Almost 85% of premature pump failures can be attributed to mechanical seals. By contrast, sealless magnetic drive pumps provide a leak-free solution that does not rely on mechanical seals and eradicates the need for associated seal support systems.
In a magnetic drive pump, the impeller is connected to an inner magnet ring via a shaft and rotated by an outer magnet ring driven by an electric motor. The shaft, bearing holder and inner magnet ring are enclosed within a can or containment shell that contains the process liquid and is rated for the same conditions as the main pump casing, which is where the impeller is located.
The containment shell forms part of the primary pressure boundary, and although its breach is an extremely rare occurrence, the possibility of such an event can lead to environmental and safety issues which should be considered.
One concern with traditional magnetic drive pumps is the eddy currents that are induced within the wall of the metallic containment shell when the driving magnetic field rotates around it.
Some magnetic drive pump products, such as HMD Kontro’s CSA/CSI ASME and ISO ranges, have the option of a non-metallic shell, where eddy currents and the resulting overheating is eliminated, along with induction losses, saving energy and offering efficiency and reliability benefits. With a superior fire, erosion and impact tolerance, these pumps are very much suited for chemicals which are toxic, pungent, corrosive, hot/cold or hazardous.
Risk Mitigation
The latest magnetic drive pump technology provides complete containment of the pumped liquid as standard. However, some situations and increasingly stringent regulations demand an even higher level of protection.
With highly hazardous process applications, particularly flammable, highly explosive or highly toxic liquids, HSE guidance (among others) calls for a secondary level of protection as a further line of defence for preventing, controlling or mitigating major hazard events.
These next generation pumps, such as HMD Kontro’s CSA and CSI ranges of ASME and ISO sealless pumps, now offer secondary protection as an option to either control or contain any leakage in the unlikely event of a breach in the primary containment shell. HMD Kontro offer these secondary protection options for both new pump units and as an upgrade feature for existing installations.
There are two methods of secondary protection, both of which feature secondary sealing devices that are independent of the primary sealing system, maximising reliability and providing an enhanced level of safety.
Secondary Control
Secondary Control features a sealing device located at the rear of the magnetic coupling housing that restricts product release to atmosphere following primary containment breach.
The system includes leak detection instrumentation (either a pressure or liquid sensor) within the secondary area to stop the pump and alert the user and allows for the removal of the process fluid via the secondary housing vent or drain connections in the unlikely event of containment shell breach.
Secondary Containment
Secondary Containment is a system that fully contains any leaked fluid following a containment shell leak. It features a dry-running mechanical seal at the rear of the magnetic coupling housing, which completes the sealing of the secondary pressure boundary, along with leak detection instrumentation within the secondary containment area.
During normal operation, the non-contacting gas seal rotor and stator parts are separated by a thin air gap. If primary containment leakage is detected, the pump is immediately shut down by the leak detection instrument and the dry-running seal closes, sealing the secondary pressure boundary and providing complete containment. Any leaked fluid can then be safely removed via the secondary drain and vent connections.
Monitoring and Control
In both options, leak detection instrumentation is a key part of the system design to shut down the pump should a containment shell breach occur. The instrumentation can consist of a pressure sensor and/or a liquid sensor fitted to the magnetic coupling housing. For low vapour liquids, a liquid level sensing probe is used, and for high vapour liquids, a pressure sensor. These are set to stop the pump immediately if any leaked fluid is detected within the secondary pressure area.
Additionally, other recommended instrumentation devices such as RTD temperature monitoring and power control provide additional pump protection against upset conditions, further enhancing reliability and safety.
The Benefits of Secondary Control / Containment in Sealles Pumps
Secondary Control and Containment systems which conform to the applicable standards and regulations, allow for a high degree of protection and safety. While total product containment is intrinsic to sealless pumps, the addition of Secondary Control or Containment creates an even higher integrity pump solution providing extra peace of mind for particularly hazardous applications.
