Once Through Steam Generators

Onshore, where there is less focus on saving weight and reducing footprint, the conventional approach to implementing a combined cycle solution is a drum-based horizontal Heat Recovery Steam Generator (HRSG)

once through steam generators

For offshore applications BIH can offer a once through steam generation (OTSG) solution in which high pressure, high purity steam is generated from the turbine exhaust gases and despatched to a steam turbine.

OTSGs are lighter and more compact than conventional HRSGS and are a drum-less solution that is perfectly suited to the constraints of offshore installation. Without the thermal mass of the steam drum the start-up and shut-down times are much shorter compared with those of drum -based HRSGs and therefore more suited to the frequent cycling that may be encountered in offshore applications.

  • Fast response time due to inherent low thermal mass of OTSGs
  • High operating flexibility – cold start-up in conjunction with GT start or hot start-up with GT already in operation
  • High metallurgy coils contributing to reduced weight, high corrosion resistance and greater resistance to the fatigue effects associated with thermal cycling and continuous dry-run capability
  • No boiler blowdown required
  • Simplified control scheme compared with conventional HRSGs
Heat Recovery Steam Generator
  • Flow stabilisation measures to minimise the risk of flow instability occurring
  • Integral exhaust gas bypass system enables greater capacity control and increases operating flexibility
  • Possibility to design with multiple pressure levels and/or utility heating
  • Vertical exhaust gas flow arrangement reducing the footprint of the unit.
  • OTSG essentially maintenance free with operating runtimes dictated by Gas Turbine maintenance schedule
  • Shorter construction time due to modular design and no need for interconnecting boiler piping

OTSGs can be offered for onshore applications but the more stringent water quality needed compared to drum-based HRSGs mean that they are better suited for heat recovery where higher steam parameters and reduced footprint is required.


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