Investigation of the Formation of Coherent Ash Residues during Fluidized Bed Gasification of Wheat Straw Lignin

Juraj Priscak,Florian Benedikt,Nils Skoglund,Hermann Hofbauer,Matthias Kuba,Katharina Fürsatz

doi:10.3390/en13153935

Juraj Priscak, Florian Benedikt + Show 4 more

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https://doi.org/10.3390/en13153935

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Abstract

Thermal conversion of ash-rich fuels in fluidized bed systems is often associated with extensive operation problems caused by the high amount of reactive inorganics. This paper investigates the behavior of wheat straw lignin—a potential renewable fuel for dual fluidized bed gasification. The formation of coherent ash residues and its impact on the operation performance has been investigated and was supported by thermochemical equilibrium calculations in FactSage 7.3. The formation of those ash residues, and their subsequent accumulation on the surface of the fluidized bed, causes temperature and pressure fluctuations, which negatively influence the steady-state operation of the fluidized bed process. This paper presents a detailed characterization of the coherent ash residues, which consists mostly of silica and partially molten alkali silicates. Furthermore, the paper gives insights into the formation of these ash residues, dependent on the fuel pretreatment (pelletizing) of the wheat straw lignin, which increases their stability compared to the utilization of non-pelletized fuel.

Highlights

As at 2015 in Paris, at the 21st session of the Conference of the Parties (COP21), 195 countries had signed the Paris agreement, which aims to keep a global temperature rise at the end of the century below 2 ◦ C compared to the pre-industrial levels
Gasification of wheat straw lignin resulted in an overall promising performance regarding the conversion into product gas of similar quality as when softwood is used as fuel
Locations of the temperature and pressure measurement points (GR1, GR6 and GR15) in the gasification reactor are shown in the schematic display of the gasification reactor next to the diagram

Summary

Introduction

As at 2015 in Paris, at the 21st session of the Conference of the Parties (COP21), 195 countries had signed the Paris agreement, which aims to keep a global temperature rise at the end of the century below 2 ◦ C compared to the pre-industrial levels. Panel on Climate Change (October 2018, Korea) states that even with current policies, we are possibly on a pathway to increase the average global temperature by 3 ◦ C [1]. The increase of global temperature is directly linked to the release and concentrating of CO2 and other greenhouse gases in the atmosphere. Fossil fuels used in combustion are one major producer of greenhouse gases. The most widespread technology used today using biomass is combustion, which converts the chemical energy stored in biomass into heat and possibly electricity. Another thermochemical conversion process, gasification, offers the possibility to convert biomass into a gaseous secondary energy carrier—product gas, with high calorific value and nearly free of nitrogen. The Energies 2020, 13, 3935; doi:10.3390/en13153935 www.mdpi.com/journal/energies

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