Cogasification of Australian Brown Coal with Algae in a Fluidized Bed Reactor

Abstract

Recently the use of algae for CO 2 abatement, wastewater treatment and energy production has increasingly gained attention worldwide. In order to explore the potential of using algae as an alternative fuel as well as the possible challenges related to the algae gasification process, two species of macroalgae, Derbesia tenuissima and Oedogonium sp., and one type of microalgae, Scenedesmus sp. were studied in this research. In this work, Oedogonium sp. was cultivated with two protocols: producing biomass with both high and low levels of nitrogen content. Cogasification of 10 wt% algae with an Australian brown coal were performed in a fluidized bed reactor and the effects of algae addition on syngas yield, ash composition and bed agglomeration were investigated. It was found that CO and H 2 yield increased and CO 2 yield decreased after adding three types of macroalgae in the coal, with a slight increase of carbon conversion rate, compared to the coal alone experiment. In the case of coal/Scenedesmus sp, the carbon conversion rate decreased with lower CO/CO 2 /H 2 yield as compared to coal alone. Samples of fly ash, bed ash, and bed material agglomerates were analysed using scanning electron microscopy combined with an energy dispersive X-ray detector (SEM-EDX) and X-ray diffraction (XRD). It was observed that both the fly ash and bed ash samples from all coal/macroalgae tests contained more Na and K as compared to the coal test. High Ca and Fe contents were also found in the fly ash and bed ash from the coal/Scenedesmus sp test.Significant differences in the characteristics and compositions of the ash layer on the bed particles were observed from the different tests. Agglomerates were found in the bed material samples after the co-gasification tests of coal/ Oedogonium N+ and coal/ Oedogonium N-. The formation of liquid alkali-silicates on the sand particles was considered to be the main reason of agglomeration for the coal/ Oedogonium N+ and coal/ Oedogonium N-tests. Agglomerates of fused ash and tiny silica sand particles were also found in the coal/ Scenedesmus sp test. In this case, however, the formation of a Fe-Al silicate eutectic mixture was proposed to be the main reason of agglomeration. Debersia was suggested to be a potential alternative fuel which can be co-gasified with brown coal without any significant operating problems under the current experimental conditions. However, for the other algae types, appropriate countermeasures are needed to avoid agglomeration and defluidization in the co-gasification process.

The industrial ecology of freshwater macroalgae for biomass applications

“…Cultivation conditions Temperature (°C) 5.8 32.1 [9,11,12,[14][15][16]42,57,58] Water flow rate (volumes day −1 ) 0 (batch culture) 5.0 [9,11,12,[14][15][16][17]35 [11,12,[39][40][41][42]48,58] respectively) with high energy potential (HHV of 33.7 and 33.5 MJ kg −1 respectively) when processed using hydrothermal liquefaction [13,39]. Furthermore, the quality of the biocrude can be improved through selective post-harvest processing to reduce the quantities of heteroatoms (N + S) [31].…”

“…For example, Spirogyra has been converted to bioethanol through fermentation [46]. Freshwater macroalgae biomass can be used as a combustible fuel [47] and is also suitable for co-combustion with coal [48,49]. Freshwater macroalgae can also be converted to energy using biological processing through anaerobic digestion to methane and subsequent conversion to energy, most commonly through combustion.…”

Increasing Porosity of Molded Calcium‐Based Sorbents by Glucose Templating for Cyclic CO2 Capture

“…Combining the aims of preparing anti‐attrition molded sorbents and enhancing their porosities, this work adopted an extrusion‐spheronization technology to obtain novel spherical tough calcium‐based sorbents with glucose templating. Due to the pyrolysis and decomposition of the fine glucose powder at high temperatures and release of a large amount of gases , such as CO, CO 2 , H 2 , CH 4 , and C 2 H 6 , if the Ca‐based sorbents and glucose were mixed uniformly, well‐developed pores and cavities will be left inside the tough spherical sorbents. Besides, it was assumed that a well‐developed porosity structure will improve the gas‐solid reaction for the CO 2 capture process .…”

“…Due to the pyrolysis and decomposition of the fine glucose powder at high temperatures and release of a large amount of gases , such as CO, CO 2 , H 2 , CH 4 , and C 2 H 6 , if the Ca‐based sorbents and glucose were mixed uniformly, well‐developed pores and cavities will be left inside the tough spherical sorbents. Besides, it was assumed that a well‐developed porosity structure will improve the gas‐solid reaction for the CO 2 capture process . In addition, the enhancing effect of pure carbohydrate on the mechanical strength of mold pellets was not clear.…”

Influence of Coal Blending on Ash Fusibility in Reducing Atmosphere

“…The mechanism of how coal blending affects ash fusibility requires further research. Moreover, the additive blending or coal blending can lower ash fusion temperature because a low-temperature eutectic mixture is generated [11,22,23,33]. On the contrary, the ash fusion temperature is expected to increase if a low-temperature eutectic mixture is not generated.…”