East Bay Municipal Utility District - 11-MW CHP System - Case Study
LOCATION: Oakland, California
MARKET SECTOR: Wastewater Treatment Facility (WWTF)
FACILITY SIZE: 65 million gallons per day
FACILITY PEAK LOAD: 10 megawatts (MW)
EQUIPMENT: 4.6-MW Solar Turbines Mercury 50™ gas turbine and 3 x 2.1-MW Enterprise engines
FUEL: Digester gas
USE OF THERMAL ENERGY: Digester heating
CHP TOTAL EFFICIENCY: 80%
ENVIRONMENTAL BENEFITS: Methane destruction reduces GHG emissions
TOTAL PROJECT COST: $19 million (includes turbine and related equipment modifications made in 2011)
ANNUAL ENERGY SAVINGS: $1.2 million
PAYBACK: 15 years
CHP IN OPERATION SINCE: 1985 (modified in 2011)
The East Bay Municipal Utility District (EBMUD)’s wastewater treatment facility supplies wastewater treatment service for 650,000 customers in an 88 square-mile (228 km2) area along the eastern shore of San Francisco Bay. Approximately 75 million gallons per day of wastewater is treated to meet stringent state and federal standards before recycling it or releasing it to the Bay. EBMUD has received many honors and awards for its efforts to protect public health and keep pollutants from reaching the Bay, and partners with residents and businesses to help them keep contaminants out of sewers and the Bay.
Reasons for CHP
Since 1985, EBMUD has been generating electrical power in Oakland from digester gas using three 2.1-MW combustion engines manufactured by the former Enterprise Engine Machinery Company. The facility began accepting high-strength wastes in 2002 that are trucked in from food processing operations, including wastes from wineries, animal processing and food scraps. Digester gas production doubled and then exceeded the maximum engine gas feed rate. To avoid flaring excess digester gas, a 4.6-MW Solar Turbines gas turbine was added in 2011 to convert the gas to electricity. In doing so, EBMUD became the first wastewater treatment facility in North America to become a net energy producer, with excess electricity sold back to the grid.
CHP Equipment & Configuration
The 4.6-MW gas turbine is utilized as the lead equipment for electricity generation and kept at 100% capacity. Due to parasitic load elements like gas conditioning and compression, net electricity generation is 3.8 MW. In addition to the turbine, one or two of the older combustion engines are kept running depending on the amount of additional digester gas available. The overall system produces an average of 6 MW of renewable electricity, with a peak facility demand of 10 MW. All recoverable waste heat from the turbine and engines is captured and utilized to provide thermal heat to the digesters.