Biomass gasification in a fluidized bed reactor: effect of temperature on properties and oxidative reactivity of chars

Conference Dates

June 19-24, 2016



Biomass gasification is a promising alternative to fossil fuels for the synthesis of highly energetic products via Fischer-Tropsch or methanation processes. It is a thermochemical conversion occurring at high temperatures with many simultaneous reactions. For temperatures above 350°C, biomass undergoes a thermal decomposition called pyrolysis which leads to the formation of volatile products either condensable (steam and tars) or incondensable (H2, CO, CO2, CH4 and C2Hx) and a solid residue called char [1]. Then, the char reacts with steam and carbon dioxide at temperatures greater than 700°C to produce syngas.

These transformations are endothermic. Therefore, a contribution of energy is required to maintain the temperature and the different reactions. One of the most encouraging and advanced technology is dual fluidized beds [2]. Its principle relies on the circulation of a media (sand, olivine or catalyst particles) which acts as a heat carrier between an endothermic reactor, where biomass gasification produces syngas, and an exothermic reactor where combustion of a part of the char from the gasification of biomass produces heat. Therefore, it is of importance to carefully understand the effect of operating conditions on char structure and composition which are directly related to its reactivity in combustion and steam gasification.

During pyrolysis of biomass, many changes occur in the solid structure including (1) the loss of functional groups on the carbon surface, (2) ordering of the carbon microstructure to tend to a graphitic crystalline form, (3) the formation of pores which directly influence the surface area, (4) the modification in ash content and its distribution that affect the catalytic activity of chars. Together, these changes are responsible for the steam gasification and combustion reactivity of the chars.

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