NOTE: Restrictions are in place to limit access to one or more of the files associated with this item. Authorized users must log in to gain access. Non-authorized users do not have access to these files.
Visit the Energy Systems Laboratory Homepage.
Cheng Cycle Brings Flexibility to Steam Plant
MetadataShow full item record
In 1983 Frito-Lay embarked on building a new 160,000 sq. ft. manufacturing facility in Kern County California. Based upon an estimated steam load between 5,000 and 50,000 lb/hr and an electrical load of approximately 1500 KW, the Engineering Department examined several energy optimization systems for this site. It was determined that a modified gas turbine cogeneration system was the best overall option. This system is unique in that it injects superheated steam from the waste heat boiler back into the gas turbine. When steam is injected into the turbine combustor, electrical output increases due to the increased mass flow and specific heat of the steam/air mixture. Electrical output ranges from 3.5 KW without injection to a theoretical 6.0 KW at maximum injection. Despite the volatility of nuclear power in California, project risk was low because the implementation of nuclear power would increase retail rates whereas the avoidance of nuclear power would increase avoided costs (buyback rates). When Frito-Lay decided, in 1983, to build a new snack food plant in Kern County, Calif., its main concern was to minimize the plant's total energy costs. The company therefore evaluated the various cogeneration options available and, for each option, conducted an energy-cost analysis. However, plant performance was not to be sacrificed in order to reduce the overall energy costs. After technical and economic analysis had been completed, Frito-Lay chose a cogeneration system using the Cheng Cycle---a gas-turbine system using steam injection that allows for efficient thermal tracking and simultaneous electrical generation. The company began construction of the Kern County plant to produce corn, tortilla, and potato chips in October 1984. Preliminary operation began in April 1986. The plant encompasses 160,000 ft, and is located just outside the city of Bakersfield. Steam is used for space heating as well as process applications. Total steam demand is expected to vary between 5000 and 55,000 lb/hr, depending on production and seasonal variations. The electrical usage of the plant is anticipated to fall between 1000 and 2500 kW, again depending on plant operations. Current utility energy costs are on the order of 50¢/therm for natural gas and 9¢/kWh for electricity. Cogeneration technology involves the simultaneous production of thermal and electrical energy. In Frito-Lay's case, the cogeneration system supplies steam for plant process needs and generates electricity for plant consumption and sale to the local utility. The modified gas turbine used in the plant is a Cheng Cycle Series Seven, Figure 1. It is a product of International Power Technology (IPT) of Palo Alto, Calif., which has patented the steam injection and control systems. The system is unique in that it injects superheated steam from the waste heat boiler back into the gas turbine. This steam injection process increases the electrical output of the turbine and improves cycle performance compared to traditional gas turbine systems.
Keller, D. C.; Bynum, D.; Kosla, L. (1987). Cheng Cycle Brings Flexibility to Steam Plant. Energy Systems Laboratory (http://esl.eslwin.tamu.edu). Available electronically from