Effectiveness of bed additives in abating agglomeration during biomass air/oxy combustion in a fluidised bed combustor

Hetian Chi,Miguel A Pans,Chenggong Sun,Hao Liu

doi:10.1016/j.renene.2021.12.072

Hetian Chi, Miguel A Pans + Show 2 more

Open Access

https://doi.org/10.1016/j.renene.2021.12.072

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Abstract

In this study, molochite (calcined kaolin) and dolomite with particle sizes (ca.1 mm) similar to those of the sand bed materials of industrial-scale fluidised beds, rather than powders which were normally used by previous studies, were investigated as the bed additives to counter agglomeration with the combustion of wheat straw and miscanthus pellets in a 20 kWth bubbling fluidised bed combustor under both conventional air combustion and oxy-fuel combustion conditions. The performance of the additives in abating agglomeration was compared to that achieved with another agglomeration countermeasure, lime addition to fuel. Dolomite was found to be superior to molochite in terms of prolonging defluidisation time when firing wheat straw. When firing miscanthus, similar effects of these two bed additives on defluidisation time were observed. The most significant improvement to the combustion performance was achieved by lime addition to fuel for both fuels. Moreover, the oxy-fuel combustion atmosphere showed a great impact on the effectiveness of dolomite but little influence on the effectiveness of molochite. The agglomeration samples were analysed by CAMSIZER, XRD and SEM/EDX and the results were used to derive the possible anti-agglomeration mechanisms of the additives under both air and oxy combustion conditions.

Highlights

Fluidised bed combustion technologies have been widely acknowledged as a superior choice to utilise low quality fuels such as biomass and waste to produce heat and power due to their excellent fuel flexibility and high combustion efficiency [1]
When using molochite as the bed additive, it was effective for MC combustion (T#9 MC-Air-5%Molochite) and prolonged the defluidisation time to 118 min which was more than two times the value without the bed additive (T#7 MC-Air) (52 min)
The anti-agglomeration ability of molochite and dolomite as the bed additive has been experimentally investigated with two types of biomass under both air combustion and oxy-fuel combustion conditions in a 20 kWth fluidised bed combustor

Summary

Introduction

Fluidised bed combustion technologies have been widely acknowledged as a superior choice to utilise low quality fuels such as biomass and waste to produce heat and power due to their excellent fuel flexibility and high combustion efficiency [1]. One of the most effective approaches to counter agglomeration is to use bed additives during biomass fluidised bed combustion [8,9]. Through chemical reactions, these additives such as calcite, lime, kaolin and etc. Previous investigations [20e22] demonstrated that as an additive kaolin could react with the ash-derived alkali chlorides and sulphates forming refractory alkali aluminium silicates mitigating the ash-related agglomeration

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