Machine Design
Algae Automation

Algae Automation

Producers are now taking baby steps toward mechanized bioreactors in the hope of producing mass quantities of fuel based on algae.

Authored by:
Leland Teschler

Key points
Algae-oil production is at the experimental stage but firms working in this area hope to field production ready equipment later on this year.

Biofuel Review,
Do-it-yourself algae biodiesel,
OriginOil Inc.,
Wikipedia page on algae oil

You could call it the great green hope of the environmental movement. Some look upon algae today as both a cure for dependence on foreign oil and as a way to soak up the greenhouse gas, CO2.

The allure of algae is that certain strains of it can produce an oil that can be refined into fuel. Moreover, the process can be more efficient than making ethanol from crops. One biofuels company says algae can produce more oil in an area the size of a two-car garage than can a football field of soybeans.

The catch, though, is that it would still take a lot of pond scum to replace a meaningful amount of gasoline. The U.S. Dept. of Energy figures an algae-bearing area of 15,000 square miles would be needed to produce the amount of oil needed to take over for current U.S. petroleum demands. That’s a few thousand square miles larger than Maryland, or about the size of 1.3 Belgiums.

There’s also the question of getting waste CO2 to the algae. In a perfect world, the CO2 generated by power plants would get recycled as algae food. But, “You are not going to put a 20,000-acre pond next to a power plant,” says OriginOil Inc. CEO Riggs Eckelberry. OriginOil in Los Angeles is one of the companies trying to automate the process of growing and harvesting algae oil. It has patented technologies that let algae grow more quickly and will promote the efficient extraction of its oil.

To avoid the need for ponds spanning thousands of acres, OriginOil grows algae in a bioreactor. Bioreactors have an advantage over Mother Nature in that they can stimulate growth of algae 24/7, not just when the sun shines. Moreover, it’s possible to mix up the algae in a bioreactor so all of it gets hit with light, nutrients, and CO2. That’s not the case on a pond surface where only the top half-inch of algae can grow.

A properly nurtured algae mass can divide up to 16 times within a period of 24 to 48 hr. The problem with producing algae, though, is one of getting a reliable, high volume process in place. Firms such as OriginOil have devised ways of growing, harvesting, and processing algae, but their efforts could be termed working prototypes at best. They are now translating their technology into production methods.

Fracture mechanics
One way OriginOil promotes the growth of algae is through a technique it calls Quantum Fracturing. The idea is based on a method devised some years ago for wastewater treatment. It aerates the algae with supersmall, micron-sized bubbles of CO2 that are easy for the algae to absorb. The technique is said to be better for algae growth than conventional aeration which uses much larger gas bubbles.

“The problem with normal aeration is that the algae doesn’t have enough time to attach to the CO2 bubbles passing through. Plus the bigger bubbles just vent to the atmosphere. You have to recapture and reintroduce them. That is an extremely wasteful process,” says Eckelberry.

Another means of boosting algae production is through a bioreactor that is specially designed to be scaled up for making mass quantities of algae. Called the Helix BioReactor, it is basically a tank that contains a rotating vertical shaft studded with low-energy lights. The lights are arranged in a helix pattern to uniformly illuminate layers of algae in the tank without any overlap in coverage. Built-in spot chillers and heaters keep the tank contents at an optimum growing temperature. An “algae life-support” computer monitors tank conditions and takes action as needed. Besides keeping an eye on temperature, OriginOil monitors the algae feeding process by gaging the pH of the mix.

The lights are a cold-cathode fluorescent type that emit red and blue light frequencies known to stimulate algae growth. They mount on a column that rotates at a slow rate of about once every 5 or 6 sec. The slow rotation is designed to accommodate the algae’s natural flashing interval: Algae looks for photons only every few seconds. The rest of the time it spends absorbing the light. Ignoring this cycle risks overwhelming the algae. There is a similar risk with CO2, so exposure to the gas is carefully managed as well.

Lights are spaced about a half-inch apart on the column to correspond with the algae growth layer in a typical pond. This keeps the algae thriving throughout the tank instead of just in the top half inch. In all, there are 24 vertical layers of algae growth per vertical foot in the tank. “We have done a lot of work to automate the feeding and respiration cycle,” says Eckelberry. “In our system there is no nocturnal recovery period as you would have with a pond. But the holy grail is to get the process to the point of a daily harvest and daily algae bloom because at that point, you have an algae production machine.”

OriginOil has an experimental 200-gallon version of its BioReactor up and running. But that’s really not big enough to make a dent in the nation’s petroleum demands. The company is now building one that holds 2,500 gallons which it aims to commercialize. It envisions a “starter kit” for commercial algae production that uses four of the reactors.

The process of scaling up the BioReactor is nontrivial, says Eckelberry. The critical dimensions and various aspects of delivering light, CO2, and nutrients to the algae may not translate linearly from the experimental tank to the 2,500-gallon version, he explains. So there will be some research and experimentation involved before the new system is considered ready for prime time. OriginOil’s target date for launch is next year.

Once the BioReactors are up and running, the algae they produce will go to a special oil-extraction process which OriginOil says is economical compared to conventional methods. “Algae has a husk which you have to crack to extract oil,” says Eckelberry. “You can’t squeeze it because that is energy inefficient. The hard part really is in the cracking of the cell walls to release the oil while not using much energy.”

OriginOil’s extraction method employs microwaves tuned to the frequency of the lipids in the algae, along with ultrasound, to separate the oil from the biomass. The microwaves break the cell walls while the ultrasound is used to induce a cavitation in the algae mass. Algae oil and biomass have different specific gravities so they tend to separate under the influence of ultrasound-induced heat and pressure.

Eckelberry says the company is still perfecting its extraction process and continues to make discoveries in this area. Still, he says, “It is relatively easy to turn algae biomass into fuel. It is not like cellulosic sources as used for ethanol where you have to break down lignins. Algae has no lignins.”

Nevertheless, growing algae in bioreactors makes no sense unless it uses less energy than skimming scum from ponds. “BioReactors start with a handicap in that open ponds benefit directly from the sun. Indoors, you have pumps and motors and chillers, all of which incur an energy penalty. You have to overcome that penalty with a high-productivity system,” says Eckelberry. “You could also neutralize some of the penalty by using solar arrays to power your equipment and combust the biomass that is produced along with the harvested oil.”

In addition, algae automation needs to get production costs down to levels comparable with fossil fuels. “We know the price point for algae ail today is not viable,” says Eckelberry. “It is about $8/gallon and that is at least an order of magnitude too high. Our task in coming years is to work on reducing that figure.”

Interestingly enough, the first real applications for algae oil probably won’t be as a vehicle fuel. “The commercial road map for algae will likely start in unsung areas like waste energy or energy for gas-fired furnaces which are friendly to algae that doesn’t produce oil,” explains Eckelberry. “Out of the 3,000 commercial varieties of algae only 300 are oil bearing. One way you can use this stuff is to choose a fast-growing nonoil-bearing algae and gasify it for use in, say, a gas-fired kiln. You can also process algae in a way that gives methane and a by-product of fertilizer.”

TAGS: Energy
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