Enhancing hydrogen-rich syngas production and energy recovery efficiency by integrating hydrothermal carbonization pretreatment with steam gasification

Abstract

Steam gasification behavior and kinetics of hydrothermally treated low-lipid microalgae Nannochloropsis sp. were probed in this work. The roles of hydrothermal carbonization (HTC) parameters (HTC temperature, HTC reaction time) as well as gasification conditions (gasification temperature, S/B mass ratio) in modulating the properties of hydrothermal carbons (HCs) as well as gasification performance were elucidated. Experimental results indicated that the aromaticity of the HCs derived from Nannochloropsis sp. was promoted, whereas the polarity was lowered by the increased HTC temperature and reaction time. At optimum HTC conditions (HTC temperature of 180 °C, residence time of 12 h) and gasification conditions (gasification temperature of 900 °C, S/B mass ratio of 2), the total maximum energy recovery efficiency was as high as 1.59. Kinetic parameters for the major gaseous products during the steam gasification of raw microalgae and the two typical HCs (HC–180C-12 h and HC-220C-12 h) were further determined. Kinetic results verified that the gasification reactivity of HC-180C-12 h was greatly higher than other two feedstock, and H2 formation was greatly promoted compared to the other two gaseous products. Overall, combining hydrothermal pretreatment and steam gasification in one step is a promising technology that could greatly promote hydrogen-rich syngas production and energy recovery efficiency from low-lipid microalgae.