Study of a downdraft gasifier and externally fired gas turbine for olive industry wastes

Olive mill technology generates a variety of biomass wastes: olive pits/stones and remaining pomace resultant from olive oil extraction. Solid wastes are also generated during the pruning of olive trees (leaves and small branches). This renewable biomass could be a feasible option in gasification technology. Thermodynamic calculations evaluate the optimum operating parameters of a small scale gasification system. The product gas obtained from the downdraft gasifier has low calorific values: 4.35 MJ kg− 1for exhausted pomace, and around 5.20 MJ kg− 1for olive pits and leaves and prunings. The power system provides 70 kWe and 150 kWth with a biomass consumption of 80–85 kg h− 1. Simulation results show the most important operating parameters are turbine inlet temperature (TIT), pressure ratio (Π) and hot side temperature difference of the heat exchanger (HTHE). High electric efficiency (20%) and overall efficiency (65%) are achievable with such a system.