Case Studies

Anode Rodding Case Studies

Rod Shop Spent Anode (Butt) Stripping Press/Crusher
Problem
The butt stripping press could not strip and break-up a butt over a certain thickness. Up to 10% of the butts had to be routed to a manual crusher to strip a large spent anode.

The manual crusher was very labor intensive and consumed man-hours that were not available. The alternatives were to increase manning to increase the through put of the manual crusher or to replace the stripping press via a capital project of over $1 MM.

Action Taken
EFI worked with a team of production and maintenance employees and identified the root cause of the problem as the guillotine crusher blades stalling on thick anode butts.

EFI designed blades using surface hardened steel with serrations to increase the crushing pressure. The first iteration tested solved the stalling problem and reduced hydraulic pressure but produced large pieces that the downstream crushers could not process.

The team designed and tested a second iteration that produced more fracture lines & smaller pieces.

Benefit
The solution provided reduced the hydraulic pressure of the crusher which reduced the amount of breakdowns of the crusher. Also, larger butts were able to be processed which relieved the need for increased manning on the manual crusher.

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Dust Containment at Chain Flail Butt Cleaner
Problem
The seal between an oscillating conveyor and the discharge hopper from a chain flail butt cleaning machine failed excessively.

A failed seal caused an unacceptable dusty atmosphere in the Rod Shop and an unacceptable buildup of material in the conveyor pits which clogged the conveyor and resulted in conveyor and butt cleaning machine outages.

Action Taken
The seal materials that were used were fabric and/or elastomer. Working with the Carbon Area Maintenance team, EFI prototyped a labyrinth metal seal that successfully survived a 6 month trial. EFI also performed air flow measurements on the Butt Crushing Material Handling Dust collector.

Benefit
EFI completed a design drawing package for a complete retrofit of the seal. The airflow measurement work did result in increasing the fan speed and resultant air flow by 15% at no capital cost. The atmosphere in the rod shop became significantly better.

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Green Mill Case Studies

Green Mill Dry Scrubber
Problem
Industrial Hygiene standards required that the scrubber be certified as satisfying the design guidelines in the Industrial Ventilation Handbook.

Action Taken
EFI performed measurements, sketched changes for numerous pick-up locations, and identified fouled ducts. After cleaning and duct modifications were completed, EFI certified compliance with the Industrial Ventilation Handbook.

Benefit
Implementation of all changes recommended by EFI resulting in significantly improved fume collection and a certifiable system.

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Material Handling Case Studies

Improve Reliability of Ore Delivery to Pots
Problem
Anode effect rates were high due to upsets in the alumina delivery to the pot. Alumina is delivered to the pot through a series of level air slides directly to the pot feeder.

Actions Taken
EFI worked with process engineers, operators, and maintenance personnel in the potline and fume control departments and determined that there were multiple issues that kept alumina from getting to the pot feeder.

• EFI determined that many of the air slides at the pots are fouled on the clean air side.
• Established that the pot air slide blowers have been “slowed down” starving the air slides for volume and pressure.
• EFI established that the venting and lack of air space for the main supply air slides caused the slide to be operated at high pressures which causes cracking of the welds in the slides.
• EFI worked with process engineers and pot operators, established that the ore delivery valve behaves differently for “excessively fine ore”, i.e. less ore is delivered per “shot”. EFI performed a study and proved that the pot feeders were sensitive to angle of repose of the alumina which made the feeder shot weight less and variable when an excessive amount of fines are in the alumina.
• Working with potline mechanics and electricians, EFI prototyped level control for the large main supply air slides.
• EFI demonstrated the effect of “grit” on the pot air slide by setting up an offline air slide with Plexiglas cutouts.

Benefits

• As a result of the work from EFI, a routine daily sampling and testing system for alumina in various locations in the alumina transport was established. The alumina was tested with a flow funnel. The data was used as additional information to adjust base feed rates to the pots to reduce the number of anode effects and not over feed the pots.
• Air pressure to the main supply air slides was reduced which reduced the amount of leaks in the slides from crack welds.
• A means to control compressed air purge of the clean air side of the air slide was prototyped.
• The dust collector at the rail car unload station was being investigated to the capture the superfines and remove them from the good alumina stream.

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Anode Cover Material Delivery
Problem
Anode crust was delivered from the crushing system to potlines through a dense phase system. The dense phase system had a very poor history of reliability with excessive down time. This resulted in a very poor plant bath balance.

The pots had a deficit of bath which required a lot of manual labor to crust. The % alumina in the anode cover material was roughly 80 – 90%.

At times the crust silos became too full due to the lack of crust transport, so that material had to be taken out of the silos.

Actions Taken:

• EFI with process engineers performed a mass balance of anode cover and crushed bath to establish what alumina percentage is possible in the anode cover material with the current dense phase system at various operational availability levels.
• Performed empirical measurements on cover establishing actual practice.
• Established the existing transport rate for the crust dense phase conveying system.
• EFI applied the Failure Mode and Effects Analysis to the dense phase conveying system for crust and established a future transport rate.
• EFI performed a reliability analysis with operators and maintenance personnel and established a direction to solve the various problems in order of priority of impact on uptime.

Benefits

• As a result of the work from EFI, a much better understanding of the crust delivery problem developed. The studies showed that the dense phase, even at 100% uptime was not capable of delivering the amount of material required to attain a 50%/50% crust to alumina composition for anode material needed to improve the plant bath balance.
• EFI established that a supplemental means for crust transport was required.
• EFI developed concept sketches and budget costs for the supplemental crust transport. The solution was less than $70K.

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Potline Case Studies

Prototype Improved Butt Reference Anode Setting Method
Problem
Anode setting to an even horizontal plane was done by referencing the butt removed from the pot. This was done by an operator transferring a chalk mark from the rod of the butt to the rod of the new anode. This method can not be audited for correct position in the pot. Also the variation of the amperage traveling through all of the anodes was great. This variation is expressed by the coefficient of variation of the anode loads.

Actions Taken

• Established inaccuracy of current method using a manual chalk mark transfer.
• Developed the concept of using the anode setting mast on the PTM as the reference to set anodes .
• Developed concept of using an encoder mounted on the anode mast that measures the travel of the mast. 1 PTM was modified for test. A computer stored all of the various positions of the mast during anode setting.
• Performed testing over 9 pots for 2 anode cycles.

Benefits
The concept was successfully tested by the prototype. Measurements of anode current loading for the 9 test pots were compared to 9 control pots show a 10 point reduction in the coefficient of variation. The measurements stored in the computer enabled an audit of each anode setting. Also, the measurements enabled a butt thickness of every anode set.

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Improve Metal Tapping
Problem
An excessive amount of bath is drawn into the hot metal tapping ladle which causes the ladle to be cleaned more often and also clogs various equipment in the casting facility.

Action taken
EFI identified that vortexing of the liquids were the critical issue. EFI developed concepts and procedures to reduce that vortexing during metal tapping including:

• Control the tapping rate by controlling rate of compressed air to the venturi.
• Redesign the tapping tube to increase open area of the tube intake thereby reducing velocity.
• Accurately control the height of the tapping tube below the metal/bath interface.
• Working with the pot operators, EFI performed baseline testing that established a lower limit to the amount of bath tapped per pound of metal tapped.

Benefit
Successfully proved concept for further plant trials and implementation.

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Improve Pot Scoop
Problem
The Scoop didn’t “reach” far enough into the pot and wasn’t able to thoroughly clean the anode hole and retrieve all the dropped carbon pieces. Also, the pneumatic cylinder rod routinely fails.

Action taken
EFI redesigned the Scoop utilizing many of the existing components.

Benefit
One scoop was modified and put into service and performing as expected and improved the anode hole cleaning process. All scoops were modified with EFI’s recommended changes.

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Improve Pot Scoop Stand
Problem
When stored in its stand, the Scoop has twice fallen “back into the PTM cab” resulting in one serious injury.

Action taken
EFI redesigned the Stand so that the scoop will always fall away from the PTM

Benefit
One redesigned Scoop Stand was put into service and performing as expected. All scoop stands were modified with EFI’s recommended changes.

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Anode Hauler
Problem
Rear brakes failed to release quickly resulting in damaging tires. Also the bed showed fatigue failure.
Actions taken

• EFI troubleshot the brake circuit and tested design change using an adjustable sequence valve.
• EFI also examined the fatigue failures and altered design drawings.

Benefit

• One anode hauler brake circuit was modified and placed into service and performed as expected. Orders were placed for materials to modify the other anode haulers.
• EFI completed detailed fabrication drawings for the anode hauler bed.

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Miscellaneous PTM Cab Improvements 1
Problem
Existing windows foul/scratch easily and caused poor visibility for the crane operators.

Actions Taken
EFI located a hard coated polycarbonate material. With a team of production and maintenance personnel, EFI tested the material. The team feels the improvement is significant.

Benefit
All PTM front windows were replaced with the new material.

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Miscellaneous PTM Cab Improvements 2
Problem
The fixed steps/ladder damage the removable pot hoods during anode changing.

Actions Taken
Working with the Pot Operators, EFI designed a folding ladder.

Benefit
Design was accepted by plant for implementation.

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Miscellaneous PTM Cab Improvements 3
Problem
The PTM cab ventilation system ingests excessive pot fumes due to the location of the fresh air inlet.
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Actions Taken
EFI worked with the Pot Operators and the Maintenance HVAC crews. EFI prototyped a concept to alter the location of the ventilation pick-up to a point closer to the louvers on building sidewall.

Benefit
Concept and prototype was successful and ready for plant implementation.

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Transport Ladle Handling
Problem
New hot metal transport ladles could not be turned with the existing turning device so that the ladle can be cleaned.

Action Taken
EFI worked with the Potline Services Crew and determined what modifications were required.

Benefits
EFI modified the fixture design & certified the structural design drawings.
The solution was implemented quickly and minimized the disruption of the process of cleaning transport ladles.

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Cast House Case Studies

Continuous Homogenizing Oven Cooling Rate
Problem
The time required to cool down the homogenizing oven was a Cast House production constraint.

Action taken
EFI engaged the OEM (Hertwich) and established that it is possible to “force feed ambient air” into the oven significantly reducing cool down time.

Benefits
Supplemental fans on order. When implemented the Cast House homogenized billet cooling time can be reduced from more than 24 hours to12 hours.

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Casting Pits Fall Protection
Problem
Several previous fall protection design concepts at casting pits were not successful.

Action taken
With a team of Casting Operators, EFI sorted out the issues.

Benefits
The team accepted the Concept sketches for implementation in the plant.