Process Energy Efficiency Improvement in Wisconsin Cheese Plants

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Date
1997Author
Zehr, Stephen
Publisher
University of Wisconsin-Madison
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Show full item recordAbstract
Wisconsin continues to lead the nation in the production of cheese, providing
about 30% of the national supply. The industry is less secure than it once was,
however, due to narrowing profit margins and competition from large plants in
California and elsewhere. In 1994, the production of cheese consumed 87.7% of
the milk produced in Wisconsin. Thus the success of the Wisconsin cheese
industry is closely linked to the success of the Wisconsin dairy industry at large,
which provides about three billion dollars per year in gross income.
In this study, the utility use of two representative cheese plants is examined.
Utility costs generally represent about 11% of the total manufacturing cost of
cheese. Utility use is one of the few variables that a plant manager can influence
to improve plant profitability.
The largest fraction of the energy used at a typical plant is devoted to processing
whey, a byproduct of significant food value. Two types of equipment are
commonly used to process or remove moisture from whey: evaporation systems
and spray dryers. Through the course of this research project, models for both
evaporation and spray drying equipment were developed. Pinch analysis has
been applied to investigate heat recovery options such as open cycle heat
pumps and heat exchange units.
Significant opportunities for reduction of utility use have been identified for
both the evaporation system and the spray drying system examined. Making
use of the low temperature vapor rejected from the evaporation system by
preheating raw milk provides two simultaneous benefits. Steam use by the
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pasteurizer is decreased, and the cooling rejection load on the cooling tower
(equipped with a 60 hp motor) is eliminated. Cost savings associated with these
benefits are estimated to exceed $70,000 per year.
In the spray dryer system studied, outdoor air is heated to 240�F before being
introduced into the drying chamber. Exhaust air leaves the chamber at 155�F.
The use of either direct or indirect heat exchange between the supply air before
it reaches the burner and the exhaust air is explored. Energy cost savings in the
range of $40,000 to $70,000 are predicted for this opportunity.
In addition to the heat recovery analysis just described, this study explores an
alternative control strategy to reduce electricity costs related to maintaining a
cold storage warehouse through demand shifting. By sub-cooling the stored
cheese during the off-peak period, it is possible to meet all or most of the
cooling load in the warehouse as the sub-cooled cheese returns to its normal
storage temperature. In this way, operation of the cooling equipment during
peak-time can be avoided or reduced significantly. This control strategy has
been examined using a finite difference model of the warehouse. The model has
demonstrated the approach to be feasible. It has been estimated to result in
reduced annual electric costs of about $15,000.
Subject
Thesis (M.S.)--University of Wisconsin--Madison, 1997.
Dissertations Academic Mechanical Engineering.
University of Wisconsin--Madison. College of Engineering.
Permanent Link
http://digital.library.wisc.edu/1793/7763Description
Under the supervision of Professors Sanford Klein, Douglas Reindl, and Doug
Reinemann; 106pp.
Citation
Zehr, S. (1997). Process Energy Efficiency Improvement in Wisconsin Cheese Plants. Master's Thesis, University of Wisconsin-Madison.