The term “combined cycle” refers to a gas turbine generator producing electricity while the waste heat is then used to generate steam (and additional electricity) via a steam turbine. This is an extremely efficient process for large industrial plants and especially in the food industry. Adding the steam cycle to the gas turbine cycle increases the amount of electricity generated from a given amount of natural gas. Subsequently, there is greater fuel efficiency and fewer emissions produced, per unit of electricity generated, than would be produced by the gas turbine on its own.
Spotlight: Combined Cycle Projects
Proctor & Gamble
Proctor & Gamble and the Sacramento CoGeneration Authority upgraded the capacity of three combustion turbines and one steam turbine at the P&G facility in Sacramento. Combustion turbine #1 along with the steam turbine comprise a combined cycle unit. Prior to upgrade, this system provided 164MW of electricity to the grid and process steam for the manufacturing facility. The existing facility consisted of two 42.5MW gas-fired combustion turbines, two heat recovery steam generators and a 35MW steam turbine generator in two combined cycle systems. There was additionally an existing natural gas-fired 45MW combustion turbine simple cycle peaker unit. This upgrade was three fold: increase output by 22MW, raise thermal efficiency and decrease combustion turbine pollutant emissions. EETS engineers were asked to review all electrical facilities, upgraded turbines and related generator step-up transformers to insure all equipment ratings were sufficient to carry the increased output. This detailed analysis included generator step-up transformer loading, all aspects of steam turbine upgrades (generator, switchgear, bus duct, voltage variation, temperature, loss of life calculations).
Sacramento Municipal Utility District and Campbell Soup asked EETS to work on this co-generation project. This co-generation facility replaces large boilers. The Siemens gas turbines produce 146MW of electricity plus recycled water from the soup plant produce steam. The steam was used in the processing of soup.