Multiple Prime and Finishing Ovens with Air Handling System for Metal Coating Application
Recuperative Thermal Oxidizer & Multistage Heat Recovery for Aluminum Parts Producer
A global Tier 1 aluminum parts producer needed the latest design recuperative thermal oxidizer. This system was part of an integrated melt system being provided by a metals-recovery systems provider. The system is sized to support pretreatment of 3 tons per hour of aluminum chips through a jet-drying system.
Dealing with particulate matter on the inlet, avoiding formation of hazardous air pollutants (HAPs) at the discharge of the unit, and withstanding the abrasive atmosphere within the system were all challenges that needed to be overcome successfully. In spite these system application improvements, even the most efficient drying system will produce some level of particulate-matter emissions. The challenge was choosing a design that limits the potential for emissions will reduce the demand on the downstream particulate-matter removal system. It also will reduce any subsequent loading on the downstream thermal oxidizer. Within the thermal oxidizer itself, burner placemen-t and orientation, the combustion chamber configuration and the design of primary and secondary heat exchangers all contributed to a system design that can operate in the face of the particulate-matter loading one can realistically expect to see during standard operation.
Innovation in aluminum-scrap pretreatment drying technology not only results in reduced particulate carryover but also a combined increase in VOC loading, a reduction in permittable emissions levels, and an uptick in demands for even higher system uptime and serviceability. 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 a good balance of wear resistance, life expectancy, maintainability, and initial procurement cost.
The thermal oxidizer system includes primary heat recovery to minimize energy consumption. Also, packaging features minimize the overall system footprint while at the same time easing maintenance and service. The unit’s modular, two-pass secondary shell-and-tube heat exchanger configuration eases maintenance. Strategically placed access doors and large-diameter stainless steel tubes help maximum service life. In addition, the modular design simplifies installation and allows for a quick changeout in the future when the heat exchanger is no longer serviceable.
A key design element is the insulated stack. At 65 feet tall and with a diameter of 42 inches, 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 designers to optimize materials selection and reduce the overall project capital cost.
At the scale of many captive recycling operations, recovering waste heat from the process can produce a significant annual cost savings and an overall reduction in facility greenhouse gas emissions.
Understanding and applying best practices in aluminum scrap-recycling systems is key to realizing the full potential of the recovery system. Recognizing that a 1 percent deviation in contaminant levels can translate to more than a 2 percent change in metals recovery highlights the value in investing in modern 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. The capacity through the system can only be as great as the emissions limits permit.