Effect of regeneration heat and energy storage on thermal drying performance in a hardwood solar kiln

Abstract

The use of energy efficiency tools and solar energy in wood drying can help reduce the often heavy energy consumption of industrial dryers. The rational management of energy in terms of drying has attracted a lot of attention and the main objective of this work is to adapt the techniques of renewable energy and energy saving in solar kilns. The present work is therefore a contribution to the improvement of energy efficiency and the modeling of a solar wood kiln with thermal storage and heat regeneration. The drying system consists of five main units, a drying chamber, a multi-pass solar air collector, a cylindrical parabolic solar collector, a thermal storage tank and a Closed Feed Air Heater. The investigation carried out in this work is based on the establishment of mass and energy conservation equations in different components of the drying system. The governing equations of heat and mass transfer are solved using the implicit finite difference method. The discrepancies between the experimental and numerical results do not exceed 5%. The results show that the drying time is shorter in June and longer in December. The drying time decreases as the collector area increases and the boards thickness decreases. By incorporating a Closed Feed Air Heater with an effectiveness of 0.75, in the solar dryer, the collector and drying efficiency values are increased from 0.48 to 0.56 and 0.43 to 0.88, in June, respectively. The integration of the thermal storage unit in the solar kiln has the effect of reducing the drying time up to 40 and 60%, in June and December, respectively. Moreover, the combined use of thermal storage and regeneration heat is efficient in reducing the energy consumption ratio (kWh.m−3) up to 50% and 54%, in June and December, respectively. The proposed solution can significantly improve thermal drying performance and thus overcoming the problem of longer drying time, especially in winter.