Title:
Influence of Pre-Treatment of Herbaceous Biomass Feedstocks on Ash-Related Issues in Chemical Looping Gasification
Author(s):
Lebendig, F., Müller, M.
Document(s):
Paper
Poster
Abstract:
Different ash-related issues, such as agglomeration, fouling and slagging, high temperature corrosion or poisoning of oxygen carrier materials can cause significant economic and ecologic challenges for reliable implementation of chemical looping gasification. Herbaceous biomass feedstocks show in general a higher ash content than woody feedstocks, and are therefore usually more associated with potential risks. The most problematic inorganic species originating from biomass ashes are alkali metals, chlorine and sulphur. Fuel optimization in form of torrefaction or/and leaching feedstock, but also blending with additives may be needed to avoid difficulties. Therefore, the influence of different or combined pre-treatment methods was investigated. Wheat straw was selected as sample material and pre-treated (torrefied, water-leached, and, additionally both steps were combined). A multiple step model was developed to analyze ash-related difficulties: First, all samples were chemically characterized by means of elemental (CHNOS) analysis, ICP-OES/MS and ion chromatography. Thermodynamic modelling with thermochemical software FactSageTM and corresponding data bases was implemented for determining condensed and gas phase formation. In accordance with an appropriate gasification temperature, ternary phase diagrams (SiO2-K2O-CaO system) were constructed to predict the ash-correlated state of matter (solid, liquid-slag or mixed phase): the raw feedstock was compared with pre-treated varieties. Experimental studies on gas phase chemistry under gasification-like conditions at 950 °C were conducted by molecular beam mass spectrometry (MBMS) for understanding interactions between inorganic species. Both, devolatilization reaction as well as the ash/char reaction were analyzed in detail. Feedstock samples were ashed under gasification-like conditions at 950 °C, and mineral compounds were examined by X-ray-diffraction analysis. Hot stage microscopy was performed, which allowed for the determination of the melting behavior of feedstock ashes. Noticeable differences in terms of release and ash melting behavior were observed between the raw materials and the leached ones. Thermodynamic predictions and experimental investigations showed concordant and plausible results.
Keywords:
biomass, gasification, straw, torrefaction, pretreatment, slag, ash-related issues, water-leaching
Topic:
Biomass Conversion for Bioenergy
Subtopic:
Gasification for Synthesis Gas Production
Event:
29th European Biomass Conference and Exhibition
Session:
2AV.4.6
Pages:
530 - 536
ISBN:
978-88-89407-21-9
Paper DOI:
10.5071/29thEUBCE2021-2AV.4.6
Price:
FREE
