Fate of inorganic material during hydrothermal carbonisation of biomass: Influence of feedstock on combustion behaviour of hydrochar

Abstract

A series of high moisture content biomass have been processed by hydrothermal carbonisation (HTC) in a batch reactor at two temperatures (200 °C and 250 °C). The feedstocks processed include food waste, secondary sewage sludge, AD press cake, microalgae, macroalgae and a fibre derived from municipal derived wastes. In addition, three lignocellulosic biomass including miscanthus, willow and oak wood have been processed under identical conditions. The yields and properties of the resulting hydrochars including their HHV, CHNS, mineral content and ash fusibility properties have been determined and compared with their starting biomass. Typical char yields for lignocellulosic material range between 58-70 wt% at 200 °C and reduce to 40-46 wt% at 250 °C. The behaviour and mass balance is however very feedstock dependent and the higher lignin biomass produce higher yields of hydrochar. There is a significant upgrading of the energy density of the hydrochars with calculated HHV ranging from typically 24 MJkg -1 at 200 °C to 28-31 MJkg -1 at 250 °C for lignocellulosic material. The exception is for sewage sludge and AD press cake which result in a significant solubilisation of organic matter. A significant removal of alkali metals is observed and this in turn changes the ash chemistry upon combustion. This change in ash chemistry has been shown to change the ash melting behaviour and the hemisphere temperatures (oxidizing conditions) were seen to increase substantially. A number of predictive slagging and fouling indices have been used to evaluate the influence of the ash chemistry on the fuel combustion behaviour and this combined with the ash fusion testing has shown that HTC reduces the potential fouling and slagging in some of the resulting hydochars if combusted.

HTC of Wet Residues of the Brewing Process: Comprehensive Characterization of Produced Beer, Spent Grain and Valorized Residues

“…This indicates that a part of inorganic fraction of the original spent grain is lost. This is well in line with generally accepted consensus for hydrothermal carbonization and has been confirmed by a multitude of results from different studies, performed with different types of biomass [27,31,78,79]. Most certainly it is the case of HTC of BSG, even though a part of inorganic substance susceptible to precipitation into liquids is washed out from the malt, during the brewing process, which can be confirmed by a high content of macronutrients in various beers [80].…”

Influence of the parameters of the hydrothermal carbonization of the biomass on the biocoal obtained from peat

“…In the case of hydrothermal carbonization, unlike other thermal methods, mineral components are washed into the water and there is a noticeable decrease. The similar trend for inorganics removing from biomass in water during HTC is described in [8]. This is due to the destruction of lignocellulose, in which there is a large amount of mineral components.…”

Gasification characteristics of hydrochar and pyrochar derived from sewage sludge

“…Escala et al [11] reported that conducting HTC and drying the hydrochar have energetic advantages compared with drying the sewage sludge for thermal disposal treatment. In addition, the HTC-pretreated sewage sludge is reported to have improved combustion properties compared to the pyrochar and raw sludge [6,9,12,13]. In terms of gasification of the biochar, Alvarez-Murillo et al [5] studied the steam gasification characteristics of the hydrochar derived from olive stone as a representative of lignocellulosic biomass.…”