Recuperative Thermal Oxidizer and Heat Recovery System for Aluminum Recycling Operation

The Challenge

An Aluminum Recycling Plant utilized a very inefficient gas-fired Afterburner and gas-fired Rotary Kiln that was consuming 32 million BTUs per hour. They wanted an air pollution control system that was able to save them on their exorbitant fuel cost.

The Solution

Evaluating the appropriate oxidation system for a specific process stream is more challenging and requires in depth analysis of the specific process gas and operating parameters, as there are many configurations to choose from. For this application , an 18,000 SCFM Recuperative Thermal Oxidizer with Primary and Secondary Heat Exchanger was installed.  This eliminated the need for the natural gas burner in the Rotary Kiln all together.

Recuperative systems, also known as shell and tube-type heat exchangers are  the most common systems generally used for thermal oxidizers with low to medium process flow rate and can provide up to 80% thermal energy recovery efficiency. They are generally air-to-air exchange systems, in which the hot, clean air passes over a series of stainless steel tubes transferring heat energy, via convection to the incoming colder air passing through the tubes.   Shell and tube-type of heat exchangers are further divided on the basis of their functionality and configuration, including parallel, counter-type, and series type heat exchangers.

For this design, both Primary and Secondary Heat Exchangers were incorporated into a unique system application. In these combination units, the gas leaving the oxidizer will generally heat a primary or pre-heat exchanger, then it will continue on to the secondary heat exchanger. Secondary heat exchange systems use the waste heat from the combustion process to run other parallel production processes throughout the manufacturing facility, such as ovens, furnaces, and general comfort heating.

The Results

The newly installed system now consumes only 10 million BTUs per hour due to the heat recovery generated by the primary and secondary Heat Exchangers. This resulted in a savings of over 22 million BTUs per hour.