Article submitted for the “ALSCO Magazine”
The Richmond Virginia ALSCO Metals plant expects to save $157,000 in the current year with improvements made to the batch anneal operation. We were all amassed to find so much money in a batch.
The Richmond facility was looking for ways to eliminate a manufacturing bottleneck in the batch anneal process and found so much more. The Manufacturing process at the Richmond facility is unique in the world and is explained in the accompanying sidebar.
As Richmond continually made improvements in each production, area it became apparent that the batch anneal operation was fast becoming a significant bottleneck to future production increases. The overall time required to anneal the coils was reduced in two ways. First, the annealing schedule was modified to reduce the time required to anneal the coils. This reduced the time by several hours. The second process improvement involved changing algorithm that controlled the way the temperature was regulated. This reduced the time required to bring the coils up to temperature and reduced processing time. The total process improvement almost doubled the capacity of the batch anneal process with no capital expenditures.
During these changes to the batch, anneal process it was noticed that the nitrogen usage seemed high. Nitrogen is used in the batch ovens to prevent oxidation of the aluminum and prevent the oil remaining on the coils from burning. The Richmond engineering group looked into the nitrogen usage and found, that the steady flow was almost double the setpoint and could be lowered significantly and still maintain the oxygen level needed for the process.
Several contributing factors were found and had to be corrected and several process changes were made to reduce the overall nitrogen usage.
· The nitrogen control valve setpoint had to be reset to allow the valve to close properly
· The control algorithm was modified and tuned to provide smooth nitrogen flow
· Air flow restrictions were reduced to improve the cooling time and reduce nitrogen usage
· Nitrogen distribution in the oven was redirected to improve temperature control and reduce nitrogen usage
· Air infiltration paths in the batch anneal oven were found and reduced
· The oxygen setpoint was raised cooling, after the heating process removed the oil that could cause a fire hazard
Process time reduction and nitrogen were the focus of our improvements and several coasts were identified as areas of savings. The two areas of improvement allowed cost savings in three utility costs.
· Annealing process changes to reduce process run time:
o Reduced nitrogen costs
o Reduced natural gas costs
o Reduced electrical power costs
· Nitrogen usage reduction
o Reduced nitrogen costs
o Reduced natural gas costs – Because the nitrogen does not have to be heated
Continual Improvement – It is important not to relay on “That is the way we’ve always done it”. Although great improvements have been made, potential savings have been identified. These savings will be incorporated as manufacturing operations allow. Due to the reduced flow of nitrogen, on-site generation can now be considered for a significant savings over liquid nitrogen delivery used now. A plan has been set in place to monitor the batch anneal process and look for changes that would allow waste. Continual improvement requires continual vigilance.
There is no perfect process. Everyone should be looking for ways to improve the process that you work with. An operator identified the high nitrogen usage. Maintenance and engineering need to be sensitive to this type of comment to find the savings that are in every process.
Richmond Operation Sidebar
The ALSCO Metals plant in Richmond, Virginia produces aluminum sheet using a unique process.
Recycled aluminum is melted in one of three furnaces. The molten metal is cleaned and alloyed and cast by a spinning pot with small holes that produce tear shaped pellets that are stored in silos ready for the hot mill.
The pellets are taken from the silos and heated as they fall through a process furnace to be compacted by the rollers of the mill to form a continuous sheet that is coiled and cooled in preparation for the cold mill.
Coils from the hot mill are reduced in thickness by several passes through the mill. Once the final thickness (gage) is reached the coils are headed to the batch anneal operation.
The coils are loaded onto carts and rolled into the batch anneal oven, heated to soften the aluminum by a stress relief treatment to meet customer specifications.
The softened coils are levelled (remove curl and cross width bow), slit to the correct width, cut into coil sizes needed for the customer to handle and sent to shipping.
The coils are packed, prepared for shipment and loaded onto trucks.