Alternative Energy Production Challenges
Putting algae to use as an energy source requires efficient harvesting/extraction and dewatering of sufficient biomass. Due to the high water content of many species, it takes a large amount of raw material to create even a small amount of oil or carbohydrates for further processing into fuel. Large-scale production is even more challenging, considering the resulting biofuels need to be competitive with petroleum prices to gain popularity and widespread use.
One way to accomplish this involves using a series of decanter centrifuges and disk stack separator centrifuges, which can handle a large inflow volume but may not be able to achieve necessary G-forces to separate and compact fine particles. Microalgae particles typically range between two and 10 microns, where many centrifuges are designed to separate particles larger than 10 microns.
What’s more, separators can operate at sufficiently high G-forces to separate these fine particles, about 10,000 g, but only at lower concentrations than typical in algae dewatering applications. The result is a process requiring several pieces of equipment, a large physical footprint, and considerable energy (and expense) to run.
Another method is a two-stage separation process where the microalgae is pre-concentrated through flotation or flocculation, then run through a special type of decanter centrifuge (Flottweg Sedicanter®) designed to handle large volumes of material with high concentrations of these tiny particles. This technology combines aspects of a traditional decanter centrifuge and disk stack separator, such as:
- G-forces up to 10,000 (as opposed to a maximum of 6,000 g for traditional models)
- Inflow capacity up to 7,000 gallons per minute
- Functionality for materials with up to 25-35 percent solids
The result is higher percentage of dry solids with less energy used. For example, a sample of 120 m3 of algae at a 3 g/l concentration yielded 360 kg of dry solids using both methods. However, the two-stage process (with Sedianter®) achieved 24 percent dry solids instead of 17 percent from the series of decanters. Further drying of the resulting biomass would also require less energy because of this.
In just about any application there is often more than one way to accomplish a goal. In the case of microalgae processing, engineering and separation expertise are the keys to saving energy costs and moving closer to viable alternative fuels.