Reducing fossil energy consumption of a belt dryer for medicinal and aromatic plants by using biogas waste heat

摘要

Conventional multi-belt dryers have a high energy consumption mainly covered by fossil fuel energy resources. The aim of this study was to harness the waste heat from a combined heat and power unit (CHP) of a biogas plant for drying flat parsley (Petroselinum crispum) and artichoke (Cynara cardunculus) on a belt dryer. The leaves were dried by hot air partially heated by light fuel oil burners and waste heat from the CHP. The belt dryer consists of a single-belt pre-dryer and a five-belt dryer including three temperature zones with a total drying area of 316 m ~2. High temperatures were applied for drying parsley with a temperature profile of 90/80/70°C for the three zones. The waste heat of the CHP was capable of heating the drying air for the pre-dryer to 75°C. The energy consumption of the light fuel oil and the thermal energy from the biogas CHP were measured. The specific energy consumption for drying flat parsley was 6,753 kJ per kg of evaporated water, with a share of 38.6% of the thermal energy being provided by the CHP. The capacity was 186 kg/h of dry material.