The Vulnerability of Attemperators

2018-05-18_16-01-29.jpgBecause of the severe thermal and differential-pressure environments desuperheaters (also called attemperators) of combined cycle units operate in, routine inspection is a necessity to avoiding costly damage. Even well-designed hardware requires routine inspection to identify and replace worn or broken components before they damage steam pipes, headers, tubes, or worse yet, make their way to the steam turbine. Attemperators prevent thermal damage to superheater and reheater tubes, and to outlet steam piping and downstream equipment. The attemperators in combined cycle power plants operate in a manner similar to that of standard desuperheaters used in conventional coal-fired power plants for the past 40 years. High-pressure feedwater is extracted from the feedwater discharge line and directed to a valve control station, which regulates feedwater sprayed directly into path of the high-temperature steam. This process reduces the temperature and pressure of the primary steam systems so that it can be recaptured without doing harm to the downstream components. The desuperheater components in combined cycle units were originally designed to operate for short periods of time during startup to reduce the temperature of steam entering the condenser or to maintain low-temperature steam flow through the HRSG until adequate steam flow and temperature are achieved for steam turbine operation. However, several conditions exist within the combined cycle design and operation that lend to a more vulnerable environment for the attemperators.