(721f) Challenges of Designing a Short Residence Time Hydrothermal Continuous Reactor for Algae Processing

Growing demands for renewable energy and fuels have led to a search for economical and efficient biomass pretreatment methods. We have extensively studied the continuous Flash Hydrolysis (FH) laboratory-scale reactor as an environmentally-benign method for fractionating microalgae components. Several of our recent studies showed promising results for lipid and protein by-product recovery with FH of microalgae at 280^oC for 9 s in continuous process. The short residence time of the order of seconds, in a continuous process is crucial for fractionating algae components without their degradation to undesired products. However, heating algae slurry at a desired heating rate of 50 - 100ºC under hydrothermal conditions to bring up to the reaction temperature and quenching the products bring several engineering challenges such as dealing with rapid heat transfer and multiphase flow.

The current study presents the experiences of designing, testing, and operating one of its kind pilot-scale mobile flash hydrolysis unit for processing microalgae slurry. For the rapid heating of the algae slurry, two different mechanism were reviewed. They were: mixing of room-temperature concentrated algae slurry with high-pressure clear hot water, and direct heating of the room-temperature diluted algae slurry. For the direct heating, after evaluating different techniques, induction heating was chosen. Both heating mechanisms have their advantages and disadvantages related with their sizing and will be discussed in this study. Regarding the quenching of the products, similar challenges were found. The best option was found to be passing the products in a constantly stirred chill water pool.