Case study - Air-to-air heat exchanger provides plant heat and big savings

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Courtesy of Anguil Environmental Systems, Inc.

OVERVIEW

A food processing facility installed a new Regenerative Thermal Oxidizer (RTO) for odor control from its roasting operation.  The oxidizer was designed for 95% thermal rate of efficiency and included supplemental fuel injection (SFI) which is used during low VOC loading conditions, to help save fuel cost.  The customer was looking at additional ways  to further reduce their operating cost.

ACTION

Recovering waste heat is one of the easiest and most effective means of reducing operating cost.  Exhaust heat from energy consuming processes and exhaust stacks is returned through a metal heat exchanger  it as process air, preheated combustion air or plant comfort heat.

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

Anguil analyzed the application data with a Heat Exchanger Performance Modeling Program which models temperatures from ambient to 1,800°F and flow rates.  The program performs a boundary layer analysis for the specific application and adjusted the plate thickness and spacing of the heat exchanger to maximize performance.

SOLUTION

A secondary plate type heat exchanger was chosen for this application because of its' ,  versatility and rugged , yet cleanable plates.  The plate style heat exchanger has a low pressure drop, small foot print and  low capital cost , making it the best economical option for this application.

The RTO exhaust heat was used to preheat 7,000 SCFM of air to approximately 190°F. This hot air mixes with outside air to provide 30,000 SCFM of heated air to the makeup air unit. The secondary heat exchanger transfers approximately 1.5 MMBTU/hr of heat from the RTO exhaust to the air going back to the makeup air unit and the estimated yearly savings for the project was approximately $45,000.00.

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