Abstract:
Dairy processing is regarded as being one of the most energy intensive industries in countries where primary production dominates the economy. In the New Zealand economy, dairy processing energy consumption typically accounts for about 15 % of the total energy consumption of the industrial sector. An annual spend of NZ$2 – 3 million on energy is typical for a medium to large dairy processing (milk powder) site and these energy costs are a significant incentive to reduce total energy usage. This paper proposes the use of the thermodynamic concept exergy as a potential tool for improving the energy efficiency of the dairy industry. Although exergy analysis has been proposed for process optimisation in other industries, applications are rare in dairy processing. Therefore exergy analysis was applied as a case study to a milk powder production plant typical of New Zealand. The aim was to show that the concept of exergy has a great potential to be used as a useful diagnostic tool for analysing and optimising dairy processes in terms of exergy or energy efficiency. It was found that the exergy efficiency for dairy processing (i.e. milk powder plant) unit operations ranges from 36 – 99 % with higher exergy losses observed in the evaporators and drier than in other unit operations, and opportunities for exergy efficiency were subsequently identified.