The demand for aluminium has been on a relentless growth track, driven by the needs of many and diverse industries in established and rapidly developing regions of the world. The introduction of point feeding in the aluminium processing and production industry back in the 1970s helped provide a welcome improvement in equipment and pot life as well as reducing maintenance costs and downtime.
An additional important benefit has been a significant advancement in the controllability of alumina feeding. A regular repeatable small alumina dose is critical to the control of reduction pots, providing the operator with control over the pot, optimising its performance and reducing a generation of global warming gases.
Controlling alumina feeding enables the cells to run at an optimum level and prevents the build-up of undissolved alumina in the bath, leading to a “mucky” pot. Point feeding the pot correctly requires the feed hole in the crust to be open at the time of alumina discharge.
The quest for open feeder holes has led to crust breaker technology advancements and the introduction of bath sensing systems. The bath sensing system controls the operation of a pneumatic crust breaker cylinder to break the crust and retract as soon as the contact with the bath is detected. The decision to pursue advanced crust breaker technology was based on the compressed air consumption and its associated costs. Generally, over 80 percent of compressed air consumption is for breaker/feeder devices. Thus, it important to target performance improvements by adopting an evolutionary crust breaker technology on potlines.
Crust breaker technology has evolved and improved, and this along with data-driven process control enhancements have helped maximise the benefits of point feeding. In simple terms, pneumatic cylinders are used to break the crust. The fact that the crust to penetrate may vary from strong to weak, or indeed may not have formed at all, raised the need for intelligent crust breaking (ICB) technology developed by Parker.
The operating principle in ICB differs from that of a standard actuator with the air supply being fed to the piston via flow restrictions to reduce the air feed to the actual driving sides of the piston. The resultant effect of the air restrictions is that low piston loads are applied to more than 90 percent of crust breaker strokes – effectively apply the force required as opposed to a repeated high force.
The ICB has served the industry well, but additional gains are possible if, rather than sensing the ICB end of stroke, the ICB reverses on contact with the bath - Parker’s Bath Sensing Modules (BSMs) enable this. A signal to the Pot Control System from the BSM indicates that the ICB has sensed the liquid bath. The sensing of the bath effectively means that there is an open hole in the crust and that alumina can be properly fed.
Parker’s electronic BSM is able to operate in the harsh environments of a pot room in magnetic fields and at high temperatures. BSMs currently installed have proven to be 100 percent reliable with zero defects over a five-year period. The units are optimised for ease of deployment and use and are plug-and-play with a ‚self-teach’ routine, tuning the modules internal electronic component parameters to suit environmental and pot conditions.
If you would like to find out more about Parker's Intelligent Crust Breaking cylinder and Bath Sensing Technology for the metal industry contact us.
Article contributed by:
Madhu Gaste, application manager, global primary aluminium smelters, Parker Pneumatic Division Europe.
Alex Moerel, senior electronic engineer, Parker Pneumatic Division Europe.
Goran Kling, gobal marketing manager, primary aluminium, Parker Pneumatic Division Europe
Soumen Mitra, business development manager, Parker India