Dewatering Method for an Electromechanical Algae Oil Extraction Process

Photo of Natasha Siu, Derrick Turk, Matthew Tuttle,
and Michael VanOverloop Students: Natasha Siu, Derrick Turk, Matthew Tuttle, and Michael VanOverloop

Sponsor: UT Center for Electromechanics

Date: Summer 2008

Requirements:

The dewatering system must have a positive impact on the overall process economics. The team calculated that if the dewatering cost exceeds $14.70 per gallon of algae oil produced, it will be more cost-effective to send the unconcentrated solution through the extraction process. Based on a baseline scenario of a one-acre pond, the system must handle at least 23.75 gpm of inflow. The system should be compatible with various types of algae, ranging in size from 3 to 10 microns. The sponsor also requested that the system concentrate the solution to at least 2% by weight. Other desirable requirements include minimal power consumption, minimal exposure of algae to air, minimal conductivity increase of the solution, minimal water loss, and maximum uptime.

Problem:

The goal of the project is to identify a commercially viable algae dewatering process that produces a slurry with 2-5% algae density by weight and is compatible with the electromechanical algae oil extraction process developed by the Center for Electromechanics (CEM). This will greatly improve the economic viability of the oil extraction process.

Solution:

The team conducted research and concept generation to develop a set of possible dewatering methods. This included investigation of related fields such as wastewater management, as well as patent searches. Among the concepts generated was a rotary drum filter concept, shown in the image above, designed by the team as a novel solution to the problem. The viability of the solutions in the large initial set of concepts was evaluated. This narrowed the set down to four feasible solutions: continuous centrifugation, dissolved air flotation, electroflotation, and the team's rotary drum filter.

Economic analysis was performed to determine the costs associated with purchasing and operating each of these systems over a five-year period. This included obtaining quotes from vendors, estimating power consumption, and—in the case of the rotary drum filter—estimating the cost to manufacture the solution. The concepts were evaluated against each other on the basis of cost as well as other criteria. The team's rotary drum filter fared best in evaluation, followed somewhat closely by dissolved air flotation and electroflotation.

Due to the conceptual nature of the rotary drum filter, and the fact that other concepts also evaluated highly, the team recommends a sequence of tests be performed to determine the method that the sponsor should pursue. The rotary drum filter can be inexpensively prototyped and evaluated. Should this concept fail, conductivity tests should be performed to validate or discard dissolved air flotation. Similar tests are recommended for electroflotation should dissolved air flotation prove inviable. Finally, centrifugation provides a significantly more expensive but proven last resort option.

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