Exergetic Analysis and Exergy Loss Reduction in the Milk Pasteurization for Italian Cheese Production

Dario Friso,Federica Tono,Lucia Bortolini

doi:10.3390/en13030750

Abstract

The cheese industry has high energy consumption, and improvements to plant efficiency may lead to a reduction of its environmental impact. A survey on a sample of small-medium Italian cheese factories was carried out in order to assess the efficiency of heat recovery of the milk pasteurization equipment for the cheese production. Then, an exergetic analysis to calculate the related exergy loss was carried out together with a cost-benefit analysis to identify the optimized value of the heat efficiency. The exergy loss reduction was determined throughout an exergy analysis that takes into account this last value and the comparison with the previous exergy losses. Finally, the feasibility and the consequent additional reduction of exergy losses were verified, if a cogeneration heat and power (CHP) combined to the pasteurization equipment is assumed. Results show a current heat recovery efficiency of 93.2% in the Italian cheese factories; a close connection between the exergetic losses and the efficiency of the heat recovery exchanger; the optimized recovery efficiency equal to 97.3% obtained from the cost-benefit analysis; a related important exergetic loss reduction of −45% in the heat exchangers, as a second result of the exergetic analysis; a similar reduction of the exergy loss (−42%) of the whole system, as a third result of the exergetic analysis; a total exergy loss reduction of 22.9 kJ kg−1milk, which corresponds to a lower environmental impact due to CO2 reduction; a further reduction of the exergy loss of −10% when the cogeneration heat and power CHP are used.

Highlights

The Italian annual production of cow’s milk is more than 12 million ton y−1 ; of this amount, about 2.5 million ton y−1 are used as food without transformation, while the remaining production is transformed in Italian cheese [1]
In all the factories the high temperature/short time (HTST) milk pasteurization occurred by operating the milk in three plate heat exchangers (PHEs) [25] at a temperature Tmpo
The exergetic analysis carried out on the PHEs used for HTST milk pasteurization in the Italian cheese factories allowed to highlight a close connection between the exergetic losses and the efficiency of the heat recovery exchanger

Summary

Introduction

The Italian annual production of cow’s milk is more than 12 million ton y−1 ; of this amount, about 2.5 million ton y−1 are used as food without transformation, while the remaining production is transformed in Italian cheese [1]. The other half of milk production is transformed into cheese by most cheese factories [1], which are connoted to be mainly like a partially craft activity, but with a high regional diversification of dairy products highly appreciated by consumers that stimulates food and wine tourism and increases the positive effects on local economy. At the time, these small factories have a reduced inclination to invest in equipment leading to higher production costs, related to the low energetic efficiency of the plants. In France there are about 700 factories with an average per capita production about 22,000 ton y−1 , in Germany

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