Honors Theses

Date of Defense

4-15-2008

Dr. Andrew Klin

Dr. Peter E. Parker

Dr. Betsy M. Aller

Abstract

Baking ovens consume huge amounts of energy in an inefficient manner. An Excel model can be used to track the energy distribution through an oven, identifying the largest energy loss areas. This project entails developing a model based on collected data from an operating oven, validating the model's accuracy, and then analyzing the oven for areas of improvement.

All the energy entering the oven was from the combustion of natural gas, and the energy exited the oven through the surfaces, band, exhaust and product. Data, such as temperatures, dimensions, pressures, humidity, and band speed, were gathered from an operating oven, and were used to test the model. Information related to the natural gas consumption of the oven was collected for validation of the model. Using basic heat transfer equations and concepts, a model was developed that quantified the energy losses from the surfaces, through the exhaust and band, and though baking the product. A change to any input is immediately reflected in the model results, thus the effects of changes in inputs such as temperatures can be seen instantly. Using the model, energy losses were calculated to be 8.4 million BTU per hour.

Next the model required validation. Using the natural gas data, the energy entering the oven was calculated to be 4.6 million BTU per hour. Since the model had been checked for calculation errors, the difference between energy entering and energy exiting was accounted for from an inoperable gas meter.

The product received 24% of the entering energy, and over 50% was being lost through the oven band and exhaust. The energy needed to evaporate the water from the product is exiting in the exhaust, meaning that it can be recovered from the exhaust. When the latent heat of vaporization is accounted for in the exhaust, almost 50% of the energy is in the exhaust, and nearly 75% is lost through the band and exhaust combined. Based on the cost of energy, the oven costs \$640,000 annually from natural gas consumption.

Based on the major areas of loss from the oven, it is recommended that the reducing the temperature loss of the band as it returns to the front of the oven. This could be accomplished by better insulating the return path of the band, as it is currently losing 40 °F. By reducing the temperature loss by 25 °F, a savings of \$22,000 annually could be expected. In addition, by recovering energy through the exhaust by installing a stack heat exchanger or by reducing exhaust energy loss by venting less exhaust, greater savings could be expected. For a 10% reduction in energy loss from the exhaust, a savings of \$30,000 annually could be expected.