Numerisk modellering og validering av den hydrotermiske prosessen som gjør lignin flytende

Rukshan Madhawa Jayathilake fra Fakultet for teknologi og realfag ved UiA disputerer for ph.d.-graden med avhandlingen «Numerical modelling and validation of Hydrothermal liquefaction of Lignin» tirsdag 3. mai 2022.

Han har fulgt doktorgradsprogrammet ved Fakultet for teknologi og realfag ved UiA, med spesialisering i ingeniørvitenskap, forskningsområde fornybar energi.

Slik oppsummerer Rukshan Madhawa Jayathilake selv avhandlingen:

Numerical modelling and validation of Hydrothermal liquefaction of Lignin:

Shrinking core approach on particle decomposition and a comparative analysis of biocrude and HTL char

For hundreds of years, petroleum crude oil has been used for energy generation. Due to environmental impact and the depletion of petroleum crude oil, biocrude came up as a renewable alternative.

Hydrothermal liquefaction (HTL) is a method that mainly produces a liquid biocrude. In the HTL process, initially, the biomass is decomposed into smaller molecules through hydrolysis.

Newer concepts of liquefaction models and appropriate feedstocks

To improve the HTL process and to make better predictions different models are used. Different models provide different advantages and disadvantages.

In this study, an improved biomass decomposition model is proposed using the shrinking core concept.

The shrinking core concept provides a relatively less complex, nonetheless effective way to model liquefaction at the particle level.

Several relevant cases with different operating conditions were tested on the applied models to see how they worked. Some weaknesses were found. These were related to heat transfer, initial kinetic data, and other kinetic parameters such as rate constants.

Lignin as feedstock

A wide range of feedstock is used for the HTL process.

Lignin is found to be a useful feedstock to be used in the HTL process. Nevertheless, still, there are many aspects to be investigated related to lignin liquefaction such as char formation and co-liquefaction behavior.

Therefore, the liquefaction performances of lignin and its behavior are investigated in different aspects.

In this PhD research, the developed model is evaluated in different stages for its limitations as well as for its reliability.

Further, the behavior of lignin liquefaction is investigated to uncover its true liquefaction potential.

The research study is mainly divided into four stages:

• A more basic version of the model is used to model the liquefaction of a wood particle where the wood liquefaction is considered the cumulative liquefaction effect of the wood model compounds (cellulose, hemicellulose, and lignin). The basic model guided the study toward more appealing modifications and improvements such as the oily film and ash layer formation during the liquefaction process. The main takeaway from the basic version of the model was the null hypothesis of the equality of cumulative liquefaction effect of model compounds to the wood liquefaction in the same operating conditions.
• The next step of the study was to develop a more robust and comprehensive version of the model. The formation of oily film and an inorganic layer around the lignin particle and their behavior is modeled considering water transport through layers, diffusion of products, and dissolution of products in water. Moreover, the particle's surface and center point temperatures are measured using a layer model through mass transfer. The model proved to be both quick and robust.
• The evolution of char production and behavior is then studied in this study. The char is produced at different operating temperatures and residence times. Then they are tested chemically, thermally, and morphologically to understand its characteristics. Finally, a possible formation pathway for HTL char is proposed during the investigation.
• At the next phase, the synergistic effect of co-liquefaction of lignin with laminaria saccharina (sugar kelp) is explored to see the possibility of lignin being used as a co-liquefaction feedstock.

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