Prediction of Hydrothermal Carbonization with Respect to the Biomass Components and Severity Factor

Abstract

In recent years, hydrothermal carbonization (HTC) has been introduced as an attractive method for converting biomass into value-added products. The complex reaction chemistry and variable composition of biomass have, however, been barriers to find general equations for describing the HTC process. The goal of this study is to establish a link between the composition of biomass and the expected hydrochar from HTC. Based on the experimental design found from response surface methodology, the biomass components, namely pure cellulose, hemicellulose, and lignin, were submitted in different combinations into 39 HTC experiments with severity factors (SFs) of 3.83, 5.01, and 6.19. Using the experimental data, an attempt was then made to predict the mass yield, higher heating value (HHV), carbon content (C%), and energy recovery factor of the hydrochars according to the biomass composition and the process severity. The results revealed that the interactions between the biomass components do not have a major effect on the hydrochar characteristics, whereas the interaction between cellulose and SF is the most significant. Moreover, it was shown that, after the lignin content, the hemicellulose content has the highest positive impact on HHV and C% of the hydrochar. An optimization study showed that, with a focus on minimizing the SF while the HHV is maximized, biomass with a cellulose content of 40%, hemicellulose of 35%, and lignin of 25%, under the severity of 4.41 will be the most suitable case for HTC treatment. Finally, a comparison between the predictions and the experimental data in the literature suggests that the proposed equations can provide a good evaluation on the HTC of several biomass feedstocks, especially when the amount of ash and extractives are low.

Hydrothermal Carbonization of Organic Waste and Biomass: A Review on Process, Reactor, and Plant Modeling

“…The design of experiment-response surface methodology (DoE-RSM) is a statistical approach used to investigate the interaction between independent and response variables of a process. The concept implies the usage of a set of designed experiments to obtain an optimal response (the output) [80]. This approach aims to identify the optimal conditions that lead to the optimal response so to optimize the experimental activity.…”

“…(13): Hoekman et al [79] used the severity factor to compare products from fast HTC (reaction time of 20-30 s) of loblolly pine with those of typical HTC batch reactors. Starting from experimental data (relevant to 39 HTC tests), Heidari et al [80] made an attempt to predict the effect of several severity factor values (3.83, 5.01, and 6.19) on the hydrochar mass yield, higher heating value (HHV), and carbon content. With the same aim, in a work dealing with the water recycling effect during the HTC of sawdust, Heidari et al [81] used severity factors between 4.3 and 5.3.…”

Numerical Comparison of a Combined Hydrothermal Carbonization and Anaerobic Digestion System with Direct Combustion of Biomass for Power Production

“…This can be an indication that direct combustion can be a better option when the heating content of the biomass in its raw form is relatively high. For instance, when the lignin content of the biomass is higher [29]. Figure 4a illustrates that, with an increase in the HHV of the biomass from 12 to 23 MJ/kg, the net power that was produced by both scenarios increases.…”

“…HHV can be considered to be a specific property of each biomass, as its value is different from one biomass to another. The HHV of the hydrochar not only depends on the severity of the HTC process, but it is also highly dependent on the fiber structure and chemical composition of the biomass [29]. Figure 4a,b show the effects of changes in the HHV of the raw biomass in the net power and efficiency, respectively.…”

“…This can be an indication that direct combustion can be a better option when the heating content of the biomass in its raw form is relatively high. For instance, when the lignin content of the biomass is higher [29].…”