|LIBRA, JUDY - Leibniz Institute|
|ALVAREZ-MURILLO, ANDES - University Of Extremadura|
Submitted to: Energies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2020
Publication Date: 11/2/2020
Citation: Ro, K.S., Libra, J.A., Alvarez-Murillo, A. 2020. Comparative studies on water- and vapor-based hydrothermal carbonization: Process analysis. Energies [MDPI]. https://doi.org/10.3390/en13215733.
Interpretive Summary: Hydrothermal carbonization (HTC) reactor systems reported in the literature to convert wet organic wastes into value-added hydrochar can be generally classified as liquid water-based (HTC) or vapor-based (VTC). We can expect that different processes and reactions may take place depending on how water is distributed in the reactor, leading to potentially different characteristics of the hydrochars produced. In order to systemically analyze process conditions, we theoretically developed models for predicting reactor pressure, the distribution between water phases, and the liquid water volume fractions with respect to reactor temperatures. We also demonstrated that the theoretical pressure model could be used to predict reactor pressure and the importance of predicting reactor pressure to prevent potential danger of explosion. We defined a new solid content parameter based on the liquid water in physical contact with feedstock. Using these tools, we now can analyze and compare process conditions.
Technical Abstract: Hydrothermal carbonization (HTC) reactor systems reported in the literature to convert wet organic wastes into value-added hydrochar are generally classified as liquid water-based (HTC) or vapor-based (VTC). However, the distinction between the two is often ambiguous. In this paper we present a methodological approach to analyze process conditions for hydrothermal systems. We first theoretically developed models for predicting reactor pressure, volume fraction of liquid water and water distribution between phases as a function of temperature. The reactor pressure model predicted the measured pressure reasonably well. We also demonstrated the importance of predicting the condition at which the reactor system enters the subcooled compression liquid region to avoid the danger of explosion. To help understand water-feedstock interactions, we defined a new solid content parameter %S(T) based on the liquid water in physical contact with feedstock, which changes with temperature due to changes in the water distribution. Using these models, we then compared the process conditions of 7 different HTC/VTC cases reported in the literature. This study illustrates that a large range of conditions need to be considered before applying the label VTC or HTC. These tools can help in designing experiments to compare systems and understand results in future HTC research.