400 / 2018-07-27 16:52:59

Hydrothermal carbonization of natural microalgae for solid fuel: influence of pre-deashing

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Ashes are the major obstacle in the utilization of biomass. Ashes seriously influence biomass processing due to inhibit reaction, decrease products yields, reduce products quality and damage the equipment. It is necessary to conduct deashing pre-treatment before biomass processing. The natural Scenedesmus was used in this study. It has high ash content (44.66%) and low lipids content (1.4%) compared to the cultivated microalgae. Due to the high moisture content, the hydrothermal carbonization (HTC) is a promising technology to obtain the solid fuel without pre-drying. HCl pre-deashing treatment was applied before the HTC. The results show that the ash content significantly reduced from 44.66% for natural microalgae to 14.45% for acid-washing microalgae. The X Ray Fluorescence (XRF) results showed that the major ash elements of natural microalgae were Na, Al, Si, P, S, Cl, K, Ca, Fe, while the acid-washing microalgae were Si. After HTC process, the contents of carbon and hydrogen increased, resulting in the higher heating values (HHVs) increased. The fixed carbon contents increased. Higher carbonization temperature promoted the carbonization process. The combustion behaviour was evaluated by thermogravimetric analysis. The maximum combustion rate temperature (Tm) increased. According to the trends of activation energy (E) and pre-exponential factor (A) values, HC-260 was a good substitute for solid fuels on the basis of easy and stable combustion.