Algae and other aquatic biomass hold significant promise for our country’s ability to produce renewable energy domestically. At Genifuel we have developed efficient growth and harvesting techniques for the aquatic biomass. With this gasification process, we can convert the biomass to a clean fuel that is almost completely carbon-neutral.

—Genifuel President Jim Oyler

PNNL originally developed the catalytic gasification process to clean up industrial and food processing waste as an alternative to incineration. Over the past 10 years, PNNL scientists advanced the technology to include a more stable catalyst that enables it to also convert wet biomass, such as algae. PNNL has tested the gasifier with terrestrial plants, kelp and water hyacinths. It works especially well for aquatic biomass such as algae, because the feedstock doesn't require drying before fuel production.

More than 99% of the biomass is gasified to yield both a product gas and steam, which contains the carbon dioxide produced during gasification. After condensation, the water enriched with dissolved carbon dioxide is recycled to the growth ponds to accelerate growth of the next generation of biomass while reducing emissions to nearly zero.

The PNNL gasifier runs at relatively low temperatures—350 °C compared with 700 °C or more for other systems—in a small stainless steel reactor. Compared with other methods of gasifying biomass, such as anaerobic digestion, PNNL’s process works 400 times faster and gives higher yields.

According to Doug Elliott, the PNNL scientist who invented the gasification process, “It is simple—we put wet biomass like algae in the gasifier, where it is catalytically converted, and we collect fuel gas and byproducts. It’s serendipity that our system creates carbon dioxide as a byproduct that Genifuel needs naturally to grow the algae. It’s a completely green process.”

The technology behind the gasification process has been under development for a number of years. PNNL scientists have achieved significant advances in the chemistry of catalysts and the selection of the optimum temperatures and pressures for the process, as well as improving the systems to protect the catalyst from impurities in the biomass.

Genifuel grows aquatic biomass, such as algae, in shallow ponds or troughs, then harvests and processes the biomass for conversion using the PNNL technology. Water used in the growth ponds doesn’t have to be high-quality fresh water, and can be treated wastewater, brackish or alkaline water, or even salt water, Oyler said. Non-crop land can be used, so the process doesn’t compete with food production.

The company has been working with PNNL for nearly two years to demonstrate low-cost production of renewable natural gas from this feedstock. In addition to the license from Battelle, Genifuel also has a number of patents pending for its growth and production technologies using aquatic biomass.

Genifuel says it has no current plans to produce natural gas for motor fuel. The company points out, however, that the methane in the renewable natural gas can be made dimethyl ether (DME) for use as a diesel engine fuel.

Resources

• Elliott, DC (2008) Catalytic Hydrothermal Gasification of Biomass. Biofuels, Bioproducts & Biorefining 2, (3,):254-265. doi: 10.1002/bbb.74

• Hydrothermal Gasification of Biomass (Elliott presentation, 2006)

• DC Elliott, LJ Sealock, Jr (1996) Chemical Processing in High-Pressure Aqueous Environments: Low-Temperature Catalytic Gasification. Trans IChemE, Vol 74. Part A, pp 563-566