Publication | Peer Reviewed Scientific Journals | Thermische Vergasung und Gasreinigung

Thermal Stability of Bed Particle Layers on Naturally Occurring Minerals from Dual Fluid Bed Gasification of Woody Biomass

Kuba M, He H, Kirnbauer F, Skoglund N, Boström D, Öhman M, Hofbauer H

Published 20 October 2016

Citation: Kuba M, He H, Kirnbauer F, Skoglund N, Boström D, Öhman M, Hofbauer H. Thermal Stability of Bed Particle Layers on Naturally Occurring Minerals from Dual Fluid Bed Gasification of Woody Biomass. Energy & Fuels. 20 October 2016;30(10): 8277-8285.

Abstract

The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However as olivine contains heavy metals such as nickel and chromium no further usage of the nutrient-rich ash is possible and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz and K-feldspar in terms of agglomeration and fractionation at typical temperatures. To this end samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar which become mixed into the fluidized bed during operation. Using experimental analysis and thermochemical it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fractionation of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However quartz may be less active during the build-up of the layers due to lower amounts of Ca in the initial layer formation.
 

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