Fuel characteristics and combustion behavior of seaweed-derived hydrochars

Abstract

In this study, conversion of seaweeds into hydrochars was investigated with the aim of obtaining a renewableenergy feedstock. The seaweeds Fucus serratus and Alaria esculenta, and a mixture of seaweeds, mainly consisting ofCystoseria sp. and Laurencia sp., were subjected to hydrothermal carbonization (HTC) in subcritical water at threedifferent temperatures: 200, 225, and 250 °C. Fuel characteristics and chemical properties of the derived hydrocharswere determined using the standard fuel analysis and spectroscopic methods. The combustion behavior of seaweeds andhydrochars was examined via nonisothermal thermogravimetric analysis under air atmosphere. The seaweed-derivedhydrochar yields were lower than those of the lignocellulosic-derived hydrochar yields in the literature. Hydrocharsderived from Fucus serratus and Alaria esculenta became increasingly similar to lignite with higher process temperature.Fucus serratus-derived hydrochars had the highest calorific value due to their higher carbon content and significantlylower ash content. HTC converted the seaweeds to hydrochars with improved combustion characteristics observed bylower burnout temperature and higher reactivity during combustion. The slagging index values of hydrochars impliedmedium or high slagging potential during combustion. On the other hand, HTC resulted in hydrochars with reducedfouling index implying medium fouling potential during their combustion due to the significant removal of alkali metals.