An Evaluation of Influential Variables on the Energy Efficiency of Hydrothermal Liquefaction

Authors: Amanda Wetmore; Emma Bennett; Jenna Hirshfeld

Advisor: Michael Timko

Category: Undergraduate

The need for clean, renewable energy is becoming increasingly crucial due to the negative environmental impacts associated with burning fossil fuels and the depleting supply of nonrenewable energy sources. Hydrothermal liquefaction (HTL) is an energy producing process that has the potential to replace nonrenewable energy sources. HTL is a thermochemical conversion process that converts biomass such as algae, wood, and sewage sludge into liquid biocrude. HTL, compared to other thermochemical conversion methods, is especially attractive because it allows for a wet feedstock. Sewage sludge is a cheap and abundant waste that can be used as feedstock for HTL due to its high water content. Although HTL is a promising source of clean, renewable energy, more information is needed on its energy efficiency and factors that contribute to the efficiency of the process.

In this study, we used energy return on investment (EROI) to measure the energy efficiency of HTL and determined which factors in the process were most impactful on EROI. We then included the energy required for biocrude upgrading into the study as a correction factor for EROI and projected EROI values for literature studies based on their specific process conditions. Our study revealed that biocrude yield, feedstock solids loading, and biocrude higher heating value have the most influence on the EROI of HTL. When determining EROI we varied biocrude yield from 10-60%, feedstock solids loading from 0.075-0.325 wt fraction, and biocrude higher heating value from 35.6-43.5 MJ/kg. The resulting EROI values ranged from 0.91 to 20.81 and the trends demonstrated that EROI increases with increasing biocrude yield, solids loading, and heating value. Including the upgrading process as a correction factor drastically decreases the EROI, making the new range 0.64-3.43.


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