Join us in either Dubai or Karachi this fall for HRSG & Waste Heat Boiler training!
Peter Jackson, President of Tetra Engineering Group was invited to present Tetra's experience on Purge Credit implementations at the 501F User Conference this February (2019). Combined cycle power plants use fuels and other materials that can cause fires or explosions in the combustion turbine, ducting, or heat recovery steam generator. Purging that equipment with ambient air to displace residual combustible gases before starting is a normal safety practice. But when plants are cycled, the disadvantages of purging often outweigh the advantages.
How low can you go? That’s the question owners of gas turbine combined cycle plants are asking these days as they are being called upon to operate those units for rapid response in markets where load following is becoming the norm. The resulting cyclic operation introduces challenges that can result in damage to steam cycle components if you aren’t careful.
Tetra Engineering provides a full-scope service for the modelling and operation analysis of all types of natural or forced circulation Power Boiler and HRSGs, including supercritical and once-through designs. This can be integrated into a full plant model to incorporate the steam turbine and steam cycle balance of plant.
The level of detail can be adapted to focus on local effects (e.g. row-to-row temperature differences) and can be steady-state or time-dependent, the latter to model transients such as startups. The state-of-the-art Power Plant Simulator and Designer™ (PPSD) software package developed by KED software is the primary tool for this work. Frequent applications at Tetra Engineering include:
Many combined cycle power plants have experienced thermal shock damage to bypass power piping, especially in the HP steam and Hot Reheat systems. Severe shocks occur when inadequate drainage exists and liquid water accumulates in bypass piping, for example during periods of operation when the bypass is closed or during shutdowns. Startups where the bypass is opened then allows the accumulated liquid to be picked up and carried at high velocity downstream where it impacts on the internal surface at a change in piping direction, imparting a significant load and associated stress. Low load operation is another means by which very high attemperator spray can fail to be absorbed by the steam and consequently come in contact (in liquid form) with the pipe wall.