refractories WORLDFORUM 6 (2014) [1] 95 1 Introduction Olivine is an interesting raw material for re- fractory application due to its abundance and its chemico-physical properties. Natural olivine (Mg 0,92 ,Fe 0,08 )SiO 4 is an orthosilicate resulting from the complete solid solution between forsterite (Mg 2 SiO 4 ) and in few content fayalite (Fe 2 SiO 4 ). The structure con- sists of isolated SiO 4 4– tetrahedra, where each of the tetrahedra oxygen atoms is shared by three octahedral cations [1]. Olivine is widely used in different industrial fields such as a catalyst in thermal processes [2], as tundish refractory lining for steel- making [3], and as material for renewable energies [4]. In the field of energy produc- tion, olivine is used as raw material in bubb- ling fluidized bed (BFB) for biomass gasifica- tion technologies. It is also used after cal- cination at high temperature to enhance the mechanical strength and its catalytic aspect [5]. Basically, the fluidized bed reactor tech- nology allows a good distribution of the pro- duced heat (750–900 °C) and a good mixing of fuel, resulting in a homogeneous temperature field. However, the fluidized bed aggregates due to the interaction between the molten biomass ashes, forming new compounds with low melting points (500–1000 °C). The solid particles form ag- glomerates ensuing from sticking and sinter- ing at high temperature. Then the flow gas upwards becomes insufficient which is a major technical and economical problem for industrial BFB reactors.Therefore, agglomer- ation is mainly dependent on the bed mater- ial and the process temperature, where the high temperature greatly affects the agglom- eration processes [6]. There is extensive literature on the enhance- ment of olivine in terms of chemico-physical and mechanical aspects, for example, cal- cination treatment [5], metal doping [7], and use of additives [8]. Nevertheless, although the striking feature of olivine was demon- strated, the microscopic mechanisms are not well understood. The academic and industri- Behaviour of Olivine Refractories at High Temperature: Agglomeration in a Fluidized Bed Reactor Rudy Michel, Mohamed Ramzi Ammar, Patrick Simon, Emmanuel de Bilbao, Jacques Poirier Rudy Michel, Mohamed Ramzi Ammar, Patrick Simon, Emmanuel de Bilbao, Jacques Poirier CNRS, CEMHTI UPR3079, Univ. Orléans 45071 Orléans France Corresponding author: Rudy Michel E-mail: rudy.michel@cnrs-orleans.fr Keywords: olivine refractory, fluidized bed, Raman spectrometry, in situ XRD Received: 31.05.2013 Accepted: 24.09.2013 Natural olivine is an important refractory raw material because of its abundance in the earth’s crust. It is composed of solid solution of mag- nesium silicate with forsterite Mg 2 SiO 4 configuration and iron silicate in a small amount of fayalite Fe 2 SiO 4 . This raw material is mainly used in different refractory applications. For instance, it is used in fluidized bed reactors to produce a high calorific fuel-rich synthesis gas (CO + H 2 ) from biomass. However, in gasification/combustion reactor, the ag- glomeration of the fluidized bed may occur due to the reactions be- tween olivine and biomass ashes. Additionally, olivine undergoes phase transformations (dehydration and oxidation) during calcination at high temperature, which significantly affect the chemical processes. Among these phase transformations, magnetite is produced and con- tributes to the reactivity of refractories as well as to the particle ag- glomeration with biomass ashes. al objectives of this research are to develop an original laboratory reactor to emulate the agglomeration at high temperature in BFB, to study olivine materials using powerful and complementary techniques (XRD and Raman spectroscopy), to clarify the physicochemical mechanism of the interaction with molten ashes and to give practical recommenda- tions to limit the bed defluidization of the re- newable energy reactor. 2 Characterization of olivine refractory Fig. 1 illustrates the in situ high tempera- ture-XRD data of olivine. The hydrated ser- pentine phase disappears at about 600 °C. Consequently, both forsterite and enstatite phases are expected to be formed after the heat treatment of olivine in air according to the following chemical equation (eq. 1): 2Mg 3 Si 2 O 5 (OH) 4 → 2Mg 2 SiO 4 + 2MgSiO 3 + 4H 2 O (1) New phases are formed as seen by the 2θ = 23,8° and 32,7° peaks between EIRICH AWARD 2013