November 2005

California city to generate electricity from kitchen grease

Millbrae, CA— The City of Millbrae, California, and Chevron Energy Solutions, a unit of Chevron announced they are starting construction of facilities at Millbrae’s Water Pollution Control Plant (WPCP) that will generate on-site electricity from restaurant kitchen grease and other organic matter. The upgrades to the WPCP will make it one of the first wastewater treatment plants in the United States to receive and process inedible grease in a comprehensive system specifically designed to control odors, generate reliable power, reduce energy costs and provide a new municipal revenue stream.

The new system will efficiently create and use a free biofuel — digester gas produced from grease — and will increase the amount of “green power” now generated by the facility’s cogeneration plant by 40 percent. Because the system will generate electricity on-site, the city will avoid having to purchase about 1.5 million kilowatt-hours from the local utility each year. This lower demand translates to 1,178,000 fewer pounds of carbon dioxide emissions annually, equivalent to planting 166 acres of trees.

The upgraded system — the latest Chevron ES project to develop an alternative energy source — will produce about $264,000 in combined energy savings and revenues from its grease receiving facility each year. This will effectively pay for the $5.5 million facility improvements — as well as maintenance — at no new cost to the city’s ratepayers. The project may be awarded a rebate through Pacific Gas & Electric Co.’s (PG&E) Self-Generation Incentive Program, which would reduce the total project cost by about $200,000.

The innovative new system is a culmination of nine months of collaborative planning by the City of Millbrae and Chevron ES, which is engineering and managing the installation as prime contractor. Designed as a cost-effective way to renovate the City’s aging wastewater treatment infrastructure, the system’s equipment is enclosed to minimize odors and will include:

-A new 250-kilowatt microturbine cogeneration system, fueled by natural and digester gas, to power the WPCP’s wastewater treatment facilities - a compressed natural gas tank to store fuel on site.

-An innovative facility that will receive inedible kitchen grease — produced mostly by local restaurants and collected by hauling companies.

-“Chopper pumps” that reduce grease particle size and help process and move the grease to two anaerobic “digester tanks.” The tanks house microbes that digest organic matter from wastewater and produce methane (natural gas) as a byproduct, which is used to fuel the microturbine.

Excess heat produced by the microturbine will warm the digester tanks to their optimum temperature. This beneficial use of otherwise wasted energy while generating electricity is known as “cogeneration.”

The new system will provide a revenue stream for the City and a source of methane for on-site power generation. The facility will be easily accessible, operate 24 hours a day, and provide deodorizing washes for grease hauling trucks.


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