Evaluation of ashes produced from fluidized bed combustion of residues from oranges' plantations and processing Despina Vamvuka * , Marios Trikouvertis, Despina Pentari, George Alevizos Department of Mineral Resources Engineering, Technical University of Crete, 73100 Crete, Greece article info Article history: Received 5 July 2013 Accepted 16 July 2014 Available online Keywords: Residues from oranges' plantations and processing Fluidized bed Combustion Ashes abstract Residues from oranges' plantations and processing may play an important role as biofuels for heat and power production in Mediterranean countries. The management of ashes produced during combustion is a great issue for the energy sector. Ash quality from lab-scale fluidized bed tests of these residues was evaluated in terms of operational parameters, environmental impact and potential uses with respect to legislative restrictions. Bottom and fly ashes were characterized by mineralogical, chemical, particle size distribution and thermal analyses, at different excess air ratios, fuel feed rates and fuel mixing ratios. The results showed that fly ashes were rich in Ca, K, P and Sr minerals. Slagging/fouling potential of pruning was very low, however that of peels and leaves was significant. The effect of excess air ratio or fuel feed rate on the quality of ashes was small. In the case of blends, the composition of the ashes varied between those of the blend components. Fly ashes of orange tree residues could be utilized as soil amendment agents, secondary building materials, or for road construction. Their environmental impact upon land recycling or management strategies is expected to be very low. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction EU directive on renewable energy sets the target for all member states to obtain 20% of its energy needs from renewable sources by 2020 [1]. Market needs for fuel diversification, as a result of high degree of dependence from fossil fuel imports and price fluctua- tions, as well as for policies aiming at the reduction of greenhouse emissions and financial incentives, such as feed-in tariffs and green certificates, contribute to the increased exploitation of biomass in the heating/electricity sector. Residues from agricultural production and processing industries are readily available in large quantities, especially in Mediterranean countries, and solid wastes are generated by every social activity, the disposal of which is no longer viable due to the high cost and the environmental regulations. Combustion of these residues either alone, or in mixtures with other fuels, can reduce the volume of wastes, allowing for energy recovery. Among dedicated combustion technologies applied, fluidized bed has been proven as the most versatile, due to its inherent ad- vantages of simple design and scale-up, fuel flexibility, good mixing and temperature control, high efficiency and low pollutant emissions [2e4]. During combustion, ash-forming species may either leave the process as bottom ash, or become released as fly ash and flue dust. The fate of these species is dependent on their physical characteristics, chemistry, boiler design and combustion conditions [5]. Slagging, fouling and corrosion of surfaces, mainly created by the presence of alkali metals, alkaline earth metals, sil- icon, chlorine and sulphur, are all problems related to these ash constituents, which can reduce the efficiency and availability of the facilities, thereby increasing the power cost [6e9]. Also, heavy metals contained in the ashes may pose a significant risk to the environment, if irrationally managed and disposed [9e11]. There- fore, the management of ashes is a great issue for the energy gen- eration industry and alternative ways of recycling or utilization of such waste products are becoming increasingly important [4,5,12,13]. There is a lot of information in literature on the characteristics, or the slagging/fouling tendency of ashes from combustion or co- combustion of biomass fuels in fluidized beds. Raw materials used were mainly woody agricultural wastes. Silicate and calcium minerals were predominant in these ashes [13e15] and differing sintering mechanisms were found out [16,17] for the biomass fuels tested, depending on the relative proportions of problematic ele- ments. Also, trace element partitioning in fluidized beds has been the focus of several investigations and the importance of ash ma- trix, particle size, bed material, combustion system and operating * Corresponding author. Tel.: þ30 28210 37603; fax: þ30 28210 69554. E-mail address: vamvuka@mred.tuc.gr (D. Vamvuka). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene http://dx.doi.org/10.1016/j.renene.2014.07.029 0960-1481/© 2014 Elsevier Ltd. All rights reserved. Renewable Energy 72 (2014) 336e343