Thermal pollution mitigation and energy harnessing of the condensation process of an olive oil extraction refinery: A case study

Abstract

This paper presents a model to assess strategies for bettering a hexane condensation system from an olive oil extraction refinery in Portugal’s mountainous north. The water used as a cooling fluid is discharged with a higher temperature than the mountain river, provoking the deterioration of the aquatic flora and fauna, leading to high environmental impact. The model allowed the comparison of solutions for different temperatures of discharge for summer and winter and possible heat recovery back to the factory. The current condensation system power is 1.838 MW and consists of a four-walled pond of 115.3 m3 that cools down the submerged hexane pipes. Nudging in the pond’s structure leads to the introduction of internal channels to increase the turbulence, thus increasing the hexane–water heat exchange rate. Heat recovery of 19.38 kW is possible for the water coming from the pond in the drying bagasse process inside the factory, before discharge into the river. However, the model demonstrates that the decrease in temperature after the heat recovery process falls short of avoiding thermal pollution, leading to complementary actions such as shading the channel or changing the discharge velocity or angle to mitigate the thermal pollution locally.