Air-To-Air Heat Exchanger Delivers Significant Savings To Food Processing Facility

A new Regenerative Thermal Oxidizer (RTO) was installed by a food processing facility to control odor from the roasting operation. The oxidizer delivered a thermal rate of efficiency of 95% and contained supplemental fuel injection (SFI) which is utilized during low VOC loading conditions to reduce fuel cost. The customer was exploring other options to further reduce its operating costs. Figure 1 shows the reported values with RTO.

Waste Heat Recovery
One of the most effective ways of reducing operating cost is to recover metal heat exchanger as preheated combustion air, process air, or plant comfort heat.

In any energy recovery product, the key design factors is the temperature of the air stream, airflow rate, the desired heat to be transferred to the heat exchanger, and permissible pressure drop of the application.

Anguil examined the application data with a Heat Exchanger Performance Modeling Programwhich models flow rates and temperatures from ambient to 1,800°F. The program conducts a boundary layer analysis for the particular application and alters the plate thickness and spacing of the heat exchanger to improve performance.

Plate Type Heat Exchanger
For this application, a secondary plate type heat exchanger was selected due to its versatility, robust, and cleanable plates. The plate style heat exchanger is compact and has a low pressure drop and low capital cost, thus making it suitable for this application.

The RTO exhaust heat was utilized to preheat 7,000 SCFM of air to about 190°F. This hot air combines with external air to deliver 30,000 SCFM of heated air to the makeup air unit. About 1.5 MMBTU/hr of heat is transferred by the secondary heat exchanger from the RTO exhaust to the air going back to the makeup air unit. The expected annual savings for the project was pegged at about $45,000.00. Figure 2 shows the projected values with energy recovery system.

Conclusion
The principle design factors in any energy recovery product are temperature of the air stream, airflow rate, permissible pressure drop of the application, and the required heat to be transferred to the heat exchanger. Air-to-air heat exchanger offered significant savings to the food processing facility. The plate style heat exchanger is compact, has low pressure drop, and entails low capital cost, thus making it a low-cost option for odor control.