Central Energy Facility (CEF) - Cardinal Cogen
Stanford's Central Energy Facility is a combined heat and power plant comprised of four facilities:
- Boiler Plant
- Chilled Water Plant
- Cogeneration Plant
- Ice Plant
- Four 125 psig, 80,000 lb/hr boilers
- Operates on Natural Gas or #2 fuel oil
- Constructed in 1957, Renovated 1996
- Three 1,000 ton steam absorption chillers
- One 4,000 ton steam turbine driven centrifugal chiller
- Four 1,000 to 1,400 ton electrical centrifugal chillers
- Natural gas powered turbine driving a 42 MW generator
- Waste Heat Recovery Steam Generator (HRSG)
- Steam powered turbine driving a 14 MW generator
- Five 2,500 ton electric rotary screw chillers
- 120,000 ton hours of ice storage coils located in a 4 million gallon tank under the Jordan Quad parking lot
The current plant location was chosen for its proximity to the main academic campus and the initial phase of the current Stanford Hospital. Originally only producing steam, chilled water production for cooling was added in the 1970s electrical production in the 1980s, and Ice Storage in the late 1990s. Ice Storage helps manage peak electrical demand and further optimize steam and electrical production.
What’s a combined Heat and Power Plant?
A facility that produces both electrical power and thermal energy for local heating loads. Academic campuses are often great locations for this technology. CHP efficiencies can exceed 70%, making them the most efficient method available today for converting carbon based fuels into usable energy.
What’s a combined cycle power plant?
A plant that produces electrical power from the primary combustion source (in our case a gas turbine), and then uses the waste heat to produce power in a secondary process (in our case a heat recovery steam generator and steam turbine driving an second electrical generator). When thermal heat is extracted from the process for heating loads, the plant is also a combined heat and power plant.
What’s a PURPA Qualifying Facility?
An electrical generation facility that meets minimum combined heat and power efficiencies as established by the Public Utility Regulatory Policies Act of 1978. This designation entitles the facility to sell excess power to the local utility at the utility’s avoided cost of power generation.
The first facility constructed at this location was the Boiler Plant - the third steam plant in Stanford's over 100 year long history of centralized steam production for heating buildings.
Stanford stores on site enough fuel oil for three days operation. The Boiler Plant is now primarily a back up for the cogeneration facility, although it is also used to generate supplemental steam during peak demand. The boilers were renovated in 1996 for low NOx operation. Modifications include low NOx burners, flue gas re-circulation, new instrumentation and electronic controls.
Stanford's Chilled Water Plant was constructed in 1972 and has undergone several major renovations, the most recent in 2006.
The plant has a total nameplate capacity of 11,600 tons and consists of:
The steam-powered chillers capture for productive use the excess steam generated by the cogeneration plant during the summer when campus steam loads are low and electrical rates are high. The electric chillers provide off peak and winter capacity when there is not enough steam to operate the steam powered chillers.
The Cogeneration Plant was commissioned in 1987 and is owned and operated by Cardinal Cogen, a subsidiary of General Electric. The Plant is a combined-cycle power plant consisting of:
Stanford uses about 60% of the electrical power (the balance is sold to PG&E) and 80% of the low-grade waste heat generated by the plant. This qualifies the plant as a Qualifying Facility under the Public Utility Regulatory Policies Act of 1978 (PURPA).
The waste heat in the form of low-pressure steam is distributed to campus and hospital buildings for comfort and domestic water heating, and to Stanford's Chilled Water Plant for steam powered chillers. Should the gas turbine not be operable, steam from Stanford's Boiler Plant can be used to produce about 5 MW of emergency power from the steam turbine.
Why Ice Matters
Our Ice Plant reduces peak electrical demand by 8 MW and saves Stanford about $500,000 annually! Additionally, ice storage allows us to reduce the chilled water supply temperature from 44° F to 40° F during peak demand, effectively increasing distribution capacity by 25% with existing piping.
Stanford's Ice Plant was constructed in 1999 and provides additional summer cooling capacity without having to operate electric chillers during periods of high electrical rates.
Using ice storage or a combination of ice storage and chillers, the Ice Plant can produce 20,000 tons of cooling using its:
Except under extreme cooling load conditions, the Ice Plant chillers operate only at night when electrical rates are low, “building” ice in the tank. The ice is “burned” the following day when electrical rates are high in lieu of operating electrical chillers.