Hybrid heat pipe screw dryer: A novel, continuous and highly energy-efficient drying technology

We report on a novel type of screw conveyor dryer (SCD) with passive heating by an annular heat pipe, 'Heat Pipe Screw Dryer' (HPSD). It was firstly optimised, with its best performance corresponding to the lowest thermal resistances of 0.08-0.18 °C/W achieved at 11% filling ratio and in horizontal orientation. It was applied in the drying of a ceramic raw material slurry (initial moisture 33 wt. %). The highest moisture reduction of 46% (final moisture 18 wt. %) was achieved at 200 °C and 260 s. The specific moisture extraction rate (SMER) was 2.04 kg/kWh, more energy efficient than conventional dryers. Moreover, overall heat transfer coefficients were measured to be 35% higher than in a conventional steam jacketed-SCD due to the excellent thermal conductivity of the annular heat pipe. Solids build up on the surfaces increased from 3-62%, as moisture reduction increased from 10- 46%, respectively. Non-stick coating on the screw conveyor resulted in 10% fouling remediation on average. Significant potentials for even greater fouling reduction have been identified for this particular application of ceramic processing. Overall, the HPSD offers the opportunity for excellent energy recovery and space saving in drying processes, but more suitable for less fouling materials.