Study of a downdraft gasifier and externally fired gas turbine for olive industry wastes D. Vera a , F. Jurado a, ⁎, J. Carpio b a Department of Electrical Engineering, University of Jaén, 23700 EPS Linares, Spain b Department of Electrical and Computer Engineering, UNED, 28040 Madrid, Spain abstract article info Article history: Received 2 February 2011 Received in revised form 17 May 2011 Accepted 18 May 2011 Available online 8 June 2011 Keywords: Olive wastes Gasifier Externally fired gas turbine Product gas 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 -1 for exhausted pomace, and around 5.20 MJ kg -1 for olive pits and leaves and prunings. The power system provides 70 kW e and 150 kW th 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Approximately 2.9 million tons of olive oil were produced worldwide in 2009 [1]. Spain is the first producer of olive oil in the world, with a 41.6% of total production (last year, the olive oil production in Spain was roughly 1.2 million tons). Olive mill technology generates a variety of biomass wastes (Fig. 1): olives pits and the remaining pomace resultant from olive oil extraction (virgin pomace). Solid wastes are also generated in the olive groves during pruning of olive trees: leaves and small branches. Leaves can be used as animal feed, fertilizer or in the production of compost. Olive tree prunings, small branches, pits and exhausted pomace can be used for energy production via thermo-chemical applications: combustion, gasification (producer gas) or anaerobic digestion process (biogas) [2]. Manual pruning of olive trees takes place twice a year, once after harvesting the olives and again at the end of spring [3,4]. The residues are autochthonous and an important renewable source that farmers burn uncontrollably. Three types of olive oil biomass have been tested in Resolive Project: small prunings and leaves, olive pits or stones, and dried olive pomace or exhausted pomace (“orujillo”). Table 1 provides the calorific value, and proximate and ultimate analyses (dry basis) of these wastes. In terms of thermodynamic performance, cycles featuring gas turbines offer the greatest potential for high efficiencies compared to conventional steam–Rankine systems [5]. Probably, the Inte- grated Gasification Combined Cycle (IGCC) is the most well known emerging technology for integrating solid biomass fuels with gas turbines. However, the use of biomass as fuel in conventional (internally fired) gas turbine engines enclose various problems [6]. Firstly, the gas turbines are sensitive machines that require extremely clean gas to avoid damage to the turbine blades (such as erosion, incrustation and corrosion) and blockage of filters and fuel injectors. This requires installa- tion of an expensive gas clean up system, consisting of scrubbers, ceramic filters, cyclones, tar removal systems…, which takes place after the gasifier outlet. Secondly, the low calorific value of the product gas (4–6 MJ Nm - 3 ) [2], obtained from biomass gasification, necessitates a high fuel flow. This requires a design modification in the combustor and the turbine inlet guide vanes [8]. As an alternative to steam–Rankine and IGCC technologies, the Externally Fired Gas Turbine (EFGT) system offers a number of advantages [7,8]. This paper presents the results from a performance evaluation of a CHP system based on a biomass gasifier with an externally fired gas turbine (EFGT). This system is capable of producing 70 kW e and 150 kW of thermal energy (sanitary hot water, SHW). The gasification system is modeled using an equilibrium model based on minimization of the Gibbs free energy [9–11]. The gasifier modeled is a fixed bed type, downdraft, stratified and with an open top. These gasifiers allow biomass with moisture contents less than 20% and operate at atmospheric pressure with a reaction temperature around 800 °C [12,13]. In the specific gasifier, biomass consumption circles around 80 kg h -1 . The average LHV of fuel gas Fuel Processing Technology 92 (2011) 1970–1979 ⁎ Corresponding author. Tel.: + 34 953 648518; fax: + 34 953 648605. E-mail address: fjurado@ujaen.es (F. Jurado). 0378-3820/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2011.05.017 Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc