This research work presents a techno-economic analysis of a biomass gasification plant fueled with residues from the olive oil and almond industries for combined heat and power generation in the agrifood sector. The experimental plant consists of a downdraft fixed bed gasifier, a producer gas cleaning and cooling system and a spark-ignition engine–generator set as a power generation unit, which generates about 10–12 kW of rated electric power. With an average consumption between 13–14 kg/h of exhausted olive pomace pellets as feedstock, the producer gas volumetric flow rate was 31 Nm3/h (vol. %: 19.2 H2, 12.9 CO, 1.9 CH4, 19.2 CO2, 46.7 N2). The average cold gas efficiency was nearly 63%. This work also addresses the characterization and potential application of the carbonaceous solid residue (biochar), discharged from the gasifier at 1.7 kg/h. Finally, an economic feasibility analysis was developed, wherein the payback period ranges between 5–9 years.
This research work proposes an integrated gasification plant for simultaneous generation of renewable electricity and drying of olive pomace, a thick sludge with a moisture content close to 60–70% (wet basis), which constitutes by far the most abundant by-product in the Spanish olive oil industry. Due to its massive rate of production and increasing associated transportation costs, olive pomace management currently represents a substantial expense for oil mills. The integrated gasification plant, which can be installed directly at oil mills, consists of a pelletizer, a downdraft gasifier under autothermal operation fueled with dried olive pomace pellets, a producer gas cooling and cleaning unit and a microturbine as power generation unit. The wet olive pomace continuously produced in oil mills is eventually dried in a co-current flow rotary drum dryer with the hot exhaust gases leaving the microturbine at temperatures close to 300 °C, allowing a self-sufficient operation of the integrated gasification plant. The integrated gasification plant was modeled using Aspen Plus® process simulator. The developed model was validated against experimental and simulation results of relevant works. Under optimum operating conditions, the electrical efficiency of the proposed plant is 18.8%, while the additional drying stage allows achieving an overall efficiency of 51.0%. Electricity consumption by the pelletizer and ancillary equipment represents 10–20% of the net electric power generation from the microturbine. However, since the integrated gasification plant is fueled with an inexpensive by-product of olive oil production that is massively produced on-site, the plant performance parameters are remarkably satisfactory.
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