Determination of Optimized Parameters for the Flexible Operation of a Biomass-Fueled, Microscale Externally Fired Gas Turbine (EFGT)
Biomass as a source of renewable energy is a promising solution for current problems in energy supply. Olive waste is considered as an interesting option, especially for Mediterranean countries. Within this paper, a microscale externally fired gas turbine (EFGT) technology is presented as a decentralized power plant, within the range of 15 kW th , based on olive residues. It was modeled by Aspen Plus 8.6 software to provide a sufficient technical study for such a plant. Optimized parameters for
... ized parameters for pressure ratio and turbine air-mass flow have been mapped for several loads to provide information for process control. For all cases, mechanical output, efficiency curves, and back-work ratio have been calculated. Using this information, typical plant sizes and an example of power production are discussed. Additionally, achievable energy production from olive waste is estimated on the basis of this data. The results of this study show that such a plant has an electrical efficiency of 5%-17%. This variation is due to the examination being performed under several combustion temperatures, actual load, heat exchanger temperatures, and heat transfer efficiency. A cost estimation of the discussed system showed an estimated capital cost of 33,800 to 65,300 € for a 15 kW th system. Energies 2016, 9, 856 2 of 15 two-or three-phase schemes [1, 5] . Solid residues (rich in water) are approximately 40% from pressing, and 30%-50% and 60%-70% for three and two phases, respectively [6, 7] . Each olive tree can produce an average of 10-30 kg/year of pruning residues; these are mostly burned in the field with a small portion used for animals feeding  . The produced water contains organic acids, lipids, alcohols, and phytotoxic materials that are dangerous for the environment; however, its organic matter and nutrients make it valuable for fertilizing soil  . Roughly, solid dry residues can be estimated at 25% of the mass of the processed olive , thus it can be estimated that 685,625 tons is available worldwide for 2015/2016, with 97% in Mediterranean countries. The chemical composition of olive waste generally differs from one sample to another because it depends on several factors like olive mill processing pressure and temperature, but also olive type, soil, and growing conditions. When the process is handled in normal conditions, the fat percentage is between 8% and 16%; the nucleus presence is approximately 40%, which is rich in minerals like calcium and copper, and has a high percentage (up to 40%) of fibers  . The variability in the chemical composition of olive waste for two prototype samples, a Spanish and a Jordanian sample, is shown in Table 1 . However, the effect of sample composition on electrical efficiency and plant operation will be investigated in a future study. For the present study, the Aspen modeling calculations were performed with the Jordanian sample. A noticeable difference is clear in fixed carbon and ash contents, in addition to the relatively high values for higher heating value (HHV).