Heat Recovery from Stack Emissions at Kellogg's Co.
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Heat Recovery from Stack Emissions at Kellogg's Co. |
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Kellogg's Co. produces their Nutrigrain and Pop Tarts at their Muncy, PA
plant. During the baking process, heat is lost through the oven stacks,
costing the plant thousands of dollars annually. The purpose of this
project is to quantify the amount of heat lost in the plant, determine where
the greatest heat sink is located, and design a system of recovering heat from the major heat sink.
Identification of Heat Sources: The major heat sources found in the plant were:
Temperature measurements showed the overall temperature of the plant to be roughly 20 degrees C, on a 10C day in February. Measurements in the stack of the ovens read measurements ranging from 100C to 250C. It was determined that this source of heat would be highly suitable for a heat exchanger design. It was calculated that the plant loses 405.5 kW, which is 35035200 KJ/day.
Heat Exchanger Design:
A finned-cross flow heat exchanger was used to
recover the lost heat of the exhaust oven stacks. The design involves
combining the exhuast from the three ovens into one pipe. Attached to this
pipe is the heat exchanger. There will be 19 tubes flowing with 2 rows, across a
2 ft
wide pipe, with a total area of 8ft2. The working fluid for
this design will be water, which will have to be piped up to the heat exchanger
then circulated back down to where it will be used in the plant.
| Medium | Heat Transfer Coefficient |
| Exhaust from ovens | 221 W/m^2 K |
| Air in tubes | 135 W/m^2 K |
| Water in tubes | 20044 W/m^2 K |
| Overall for air to air | 78 W/m^2 K |
| Overall for water to air | 196 W/m^2 K |
A second type of heat exchanger design was attempted using the oven stacks. The only modification from the previous finned-cross flow heat exchanger was the removal of the fins and the use of air as the working fluid. This drastically reduced the amount of components needed for the system to run, but is limited to only winter use in the plant. The heat transfer coefficient was reduced by roughly a third to 78 W/m^2 K, with a pressure drop less than 800 PA. There will be 4 rows and 19 columns to this design.
There are several advantages and disadvantages to both systems. The air to water system has a much greater heat transfer coefficient, so it will transfer the greatest amount of heat from the stacks. However, this system will require the greatest amount of additional components.
The air to air system is the easiest to implement, only requiring a fan to blow the cool air into the exchanger. The heated air can be ventilated throughout the plant. The major disadvantage of this system however is the drastically reduced heat transfer coefficient, and the reality that this system will be unusable during the summer months because of the need to cool the plant instead of heating it further.
The scope of this project was limited to the initial measurements and the design of the heat exchanger for the plant. Additional research is needed in the following areas:
Updated April 22, 2004