Water Sludge Drying: modelling of solar thermal plant for solar vacuum dryer
Abstract
The use of dryers that operate at pressures below atmospheric can be a smart technological solution to allow better matching between commercial solar collectors and solar drying applications. At atmospheric pressure, water boils at 100°C, while at 500 mbar, 200 mbar, and 100 mbar water boils at 81.5°C, 60.5°C, and 45.6 °C, respectively. For instance, for Evacuated Tube Collectors (ETC) it is challenging to provide a constant heat at temperatures higher than 90°C. Furthermore, the tuning of the boiling temperature allows a better adaptation of the solar heat provided by a solar plant to the heat required for water sludge drying. To understand the technical feasibility of a Vacuum Solar dryer for water sludge, two solar plants with two types of solar collectors with water as the working fluid were modelled: i) ETC ii) parabolic trough collector (PTC). The modelling and design of a vacuum dryer for the drying of water sludges is presented. The results reveal that a light vacuum can improve the performance in terms of the solar fraction of the solar dryer for both ETC and PTC solar fields.