National Raisin Co. to use Omnitek generator for biogas project

By Katie Fletcher | July 22, 2014

Omnitek Engineering Corp. has received an order from National Raisin Co. Inc., based in Fowler, California, for a 250 kW diesel to biogas converted power generator to operate as a combined-heat-and-power (CHP) unit, also called cogeneration or distributed generation, to simultaneously produce heat and electricity from biogas.

The National Raisin Co. is a privately owned and vertically integrated dried fruit product manufacturer in North America. The biogas to power the company’s electric generator will be derived from an anaerobic digester (AD) process capable of producing an estimated 100,000 cubic feet of renewable natural gas (RNG) per day from the farm's liquid waste, which is currently diverted to a municipal water treatment facility. “AD was the logical choice because it would not only reduce the biochemical oxygen demand (BOD) and suspended solids by at least 85 percent, it would also produce the needed energy to make the system almost energy independent,” said Russell Murray, president and founder of Russell J. Murray & Associates Inc. “In addition, the treated water can be reused to irrigate the surrounding vineyards that are owned by National Raisin.”

Water isn’t the only resource used on the vineyards. The solids generated by the system will be retained in the digester, and removed periodically for use in the vineyards as an organic fertilizer. With both the water and solids being used on the vineyards, “there will be nearly total reuse of a resource that was once an expensive disposal problem,” Murray said.

Besides reducing water treatment costs by at least 80 percent, the AD process will also reduce CO2 and other greenhouse gas emissions in the surrounding area.

Murray’s company is a waste water consulting firm that specializes in design, construction and operation of systems for food processors. He approached National Raisin owners about 6 years ago with the design and financial justification for an AD system to treat their waste water flow. The initial decision to use Omnitek technology resulted after Werner Funk, Omnitek president, said he could meet the emission requirements of the San Joaquin Valley Air Quality Control Board.

“With the technology that Werner was suggesting, I was able to get an Authority to Construct from the Air Board for the use of his engine on the project,” Murray said.

The permit for the project required NOx and CO emission levels of 0.15 grams per brake horsepower per hour (g/bhp-hr) and 5.15 g/bhp-hr respectively—representing some of the lowest levels for such an installation. “The California Air Resource Board permit limits the use of the engine to 2,000 hours per year,” Murray said. “Once the project has had one year of operation and has successfully met the air board emission limits, we plan to apply for more hours of operation.” The project will be eligible for greenhouse gas and carbon credits, which could be used to offset extending hours of engine operation, Murray added.

“We are gratified by the adoption of our technology by the National Raisin Co. and look forward to additional opportunities in the region,” Funk said in a statement. “Combining Omnitek's technology with the abundance of biogas derived through this innovative anaerobic process offers significant economic and environmental benefits to the agricultural industry.”

The digester is an in ground, double lined lagoon that will be continuously stirred and heated to 95 F. The mixing will be done by proprietary agitators that have no moving parts and require no maintenance, according to Murray. “The electrical demand of these agitators is a fraction of that required by traditional methods used to accomplish this task,” Murray said. “The operation of the entire AD will use very little outside energy as compared to similar ADs and far less than an aerobic treatment would require.”

The budget for the project is estimated to be less than $2 million. The excavation of the lagoon started on May 12, 2014, with a projected startup date of the digester in mid to late October this year. “It should be producing good quantities of useable gas by Dec. 1, 2014,” Murray said. “The system should be running in a stable state and completely treating all of National Raisins waste water by the end of December 2014.”