Abstract
Abstract 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.
Highlights
The cultivation of olive trees (Olea europaea L.) for the production of olive oil is an established practice in the Mediterranean basin for millennia
The proposed plant consists of a pelletizing machine or pelletizer, a downdraft fixed bed gasifier fueled with dried olive pomace pellets, a producer gas cooling and cleaning unit, a microturbine for electric power generation and a co-current flow rotary drum dryer for drying wet olive pomace with the hot exhaust gases leaving the microturbine
The savings in the transportation costs of wet olive pomace are estimated at 6 €/t, considering an average distance between the olive oil mill and the olive pomace oil extraction plant of about 50 km
Summary
The cultivation of olive trees (Olea europaea L.) for the production of olive oil is an established practice in the Mediterranean basin for millennia. The performance of downdraft gasifiers coupled to microturbines has already been addressed in a number of works [13,14,15,16,17,18,19,20,21,22,23,24], and allows the generation of electric power for selfconsumption on a distributed scale It is not known of a previous work aimed at developing an integrated gasification process for simultaneously generating electric power and drying wet olive pomace at an olive oil mill. Despite their lower net electrical efficiency, microturbines were chosen over spark-ignition engines as power generation unit due to their greater availability of thermal energy in the exhaust gases [25,26,27]. The emissions of air pollutants such as carbon monoxide, unburned hydrocarbons and nitrogen oxides in the exhaust gases from microturbines are considerably lower than those of a gas engine of similar size, operating on the same mass flow rate of producer gas [16]
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