Best Practices in Aluminum Scrap Recycling Systems

Understanding and applying best practices in aluminum scrap recycling systems is key to realizing the full potential of your recovery system. Recognizing that a 1% deviation in contaminant levels can translate to more than a 2% move in metals recovery, highlights the value in investing in the latest recovery technologies. By focusing on properly sizing and configuring the thermal oxidizer early in the design process, operators will be able to realize the full potential of the metals recovery system and avoid wasted melt furnace capacity. 

At the scale of many captive recycling operations, recovering waste heat from the process can produce a significant annual cost savings and overall reduction in facility greenhouse gas emissions.


Benefits of Secondary Heat Recovery

A perfect example of the cost savings benefits of secondary heat recovery in aluminum scrap recycling can be found in an installation at a merchant metals recycling operation in Arkansas. The existing system was an early design pre-treatment system with rudimentary drying technology. The custom engineered system upgrade included an innovative design of a thermal oxidizer for this application equipped with a quad down flow inlet plenum, axial mounted down-fired burner as well as primary and secondary heat exchangers. This configuration maximized turbulence in the combustion chamber, resulting in excellent destruction efficiency and protected the burner from potential particulate carryover.

The energy saved from the introduction of primary and secondary heat recovery resulted in a payback for the new thermal energy system (oxidizer and dryer heat source) of less than 1.5 years! This exceptional payback was achieved at a still relevant fuel value of $3.85/MMBtu.

Fast forward to today and we are seeing advances in aluminum scrap pre-treatment drying technology that not only results in reduced particulate carryover but also a combined increase in VOC loading, a reduction in permits table emissions levels, as well as demands for even higher uptime and serviceability of the systems.

In response to these changes thermal oxidizer designs have evolved along with the advances in pre-treatment drying technology. Understanding and projecting loading and sizing remains a critical part of the system configuration. The latest systems being deployed incorporate multi-pass modular heat exchangers to maximize system energy efficiency as well as serviceability. Additionally, large diameter stainless steel shell and tube heat exchangers provide exceptional balance of wear resistance, life expectancy, maintainability as well as initial procurement cost. 


The rendering highlights the latest design of a recuperative thermal oxidizer for a global Tier 1 aluminum parts producer. This system is part of an integrated melt system being provided by an industry leading metals recovery systems provider. The system is sized to support pre-treatment of 3 tones/hour of aluminum chips through a jet drying system and includes primary heat recovery to minimize energy consumption. This unit incorporates innovative packaging features to minimize the overall system footprint while at the same time insuring ease of maintenance and service.

The unit’s modular 2-pass secondary shell and tube heat exchanger configuration provides for ease of maintenance with strategically placed access doors and large diameter stainless steel tubes for maximum service life. In addition, the modular design simplifies installation and allows for quick change out in the future when the heat exchanger is no longer serviceable.

Another key design element, shown in the insulated stack. At 65’ tall and with a diameter of 42”, the design and materials of construction were critical to meeting the customer’s performance requirements as well as capital budget. An insulated design allowed the team to optimize the materials selection and reduce the overall project capital cost.

CONCLUSION 

The capacity through the system can only be as great as the emissions limits permit. Whether for a new system or retro-fit of an existing plant, focusing on addressing emissions performance rate limiting factors will insure overall project success.

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