Cold air ventilation for cooling and drying of poplar wood chips from short rotation coppice in outdoor storage piles in Germany

Highlights: • The controlled cold air ventilation (CAV) enables low-loss drying of wood chips in the early springtime. • Using CAV, the rise of temperature in the storage pile was avoided with very low energy consumption of 79 MJ t⁻¹ (DM). • Within just one month of drying, the moisture content of the wood chips could be reduced from 52% to 12%. • The dry matter loss could be limited to 11% in the storage period March/April. • The thermal energy gain due to the fast drying makes up for more than 6 times the electric energy for the blower operation. The storage and natural drying of wood chips from short rotation coppices (SRC) in open-air piles can be related to high dry matter losses (DML) of more than 20%. Thus it should be researched, whether such loss can energy efficiently be reduced using cold air ventilation (CAV). Respectively, a dedicated channel system for sensor controlled ventilation and drying of wood chips was developed and tested in the drying process of two storage piles of poplar chips (2 × 90 m³). The ventilation of the storage piles was facilitated in two consecutive program phases: a cooling program, subsequent to the harvest in the month of March, and a drying program under more favorable weather conditions in the month of April. The characteristically high temperature rise typical for wood chip storage immediately subsequent to storage intake could be limited to an average storage pile temperature of 6.3 °C with just 41 blower operation hours due to the cooling program in the month of March. Due to the subsequent drying process in April, the storage pile could be dried further from 51.5% to 11.9% in 196 blower operation hours. The required energy input for the process of CAV, consisting of cooling and drying, amounted to 456 MJ t⁻¹ (dry matter). At a total demand of electric energy of 5332 MJ per storage pile, a more than six times higher thermal energy advantage of 35,233 MJ was achieved. DML of 11% were measured at the end of wood chip drying using CAV.