Gasifying walnut shells for heat and electricity in California

Gasifying walnut shells for heat and electricity in California

Dixon Ridge Farms, based in California, grows, processes and sells organic walnuts.

In the past, most of the walnut shell was sold to a nearby large commercial biomass plant.

Now, the shell is converted to electricity and heat onsite.

“We estimate that the walnut shell that we would normally sell for $20/ton are worth $150/ton when gasified and used to offset our onsite heat and electricity costs”, says Russ Lester, owner of Dixon Ridge Farms.

In 2007, the Lester family set a goal of being energy self-sufficient and carbon negative. They looked for a solution that would use the shell as an onsite feedstock for generating power, heat and, eventually, synthetic diesel fuel.

They worked with Community Power Corporation to install a BioMax® 50 System that could convert the walnut shell into electricity and heat.

The system produces about 4400 ft3 of syngas from about 45 kg of shell/hour. The syngas operates an engine generator that produces up to 50 kW of electricity.

During the harvest season, some of the syngas is diverted to four modified axial fan dryers to displace propane (LPG) and dry the walnut crop. It displaces propane in the drying process, reducing costs significantly.

In 2012 a BioMax® 100 System was added, increasing the farm’s renewable electric energy production by 100 kW.