Abstract
This paper presents the theoretical model and the simulation of a cutting edge hybrid power system composed of an externally-fired gas turbine (EFGT) coupled with an organic Rankine cycle (ORC) as a bottoming unit for the maximization of electrical power. The power plant is fed with different biomass sources from olive industry wastes (pruning, dry pomace, stones, leaves and twigs), providing more than 550 kW of electric power and a net electrical efficiency of 26.0%. These wastes were burnt directly at atmospheric pressure in an EFGT, producing 400 kW of electric power and exhaust gases at 300 °C. Ten suitable ORC working fluids have been studied to maximize the electric power generation: cyclohexane, isohexane, pentane, isopentane, neopentane, R113, R245fa, R365mfc, R1233zd and methanol. The best fluid was R1233zd, reaching 152.4 kW and 22.1% of ORC thermal efficiency; as drawback, however, R1233zd was not suitable for Combined Heat and Power CHP applications due its lower condensation temperature. Thus, despite R113 gave minor electricity production (137.5 kW) this allowed to generate additional thermal power (506.8 kW) in the way of hot water at 45 °C.
Highlights
The olive tree (Olea europaea L.) is one of the best well known crops of the Mediterranean region
Despite this work studied a similar approach (EFGT-organic Rankine cycle (ORC)), it is important to highlight that the present study proposes a different biomass conversion technology, the study of ten suitable ORC working fluids and it has been calculated the optimum operating conditions for each olive oil industry waste: stones, dry pomace, pruning, leaves and twigs
It can be seen as the ηeEFGT increases with the compressor pressure reaching a maximum: e.g., the optimum Pc for turbine inlet temperature (TIT) = 800 ◦ C is around 4.0 bar reaching an electrical efficiency of 15.6%; while for TIT = 950 ◦ C the optimum Pc is around 6.0 bar, reaching an electrical efficiency of 21.2%
Summary
The olive tree (Olea europaea L.) is one of the best well known crops of the Mediterranean region. Its cultivation and the production of olive oil have been anchored deeply in the history of the Mediterranean countries for more than 7000 years. The olive oil sector is nowadays facing several obstacles that push towards the need of a new approach, to cultivation, production, logistics and consumption and to by-product and waste management and, in the final analysis, to enhance sustainability. Thereby, it is crucial to adopt a holistic vision to manage the olive oil sector as a whole, and here is where the value chain management plays a crucial role. The amount and physico-chemical properties of the wastes produced depend on the olive oil extraction method. One of the most abundant sources of wastes in the olive oil value chain is the pruning of the olive trees. It is estimated that one hectare of olive grove produces 2–3 tons of prunings per year [3]
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