Use of steam jet booster as an integration strategy to operate a natural gas combined cycle with post-combustion CO2 capture at part-load

Highlights: • Use of a steam ejector in a natural gas combined cycle with CO₂ capture at part-load operation. • Fixed pressure, sliding pressure and the use of steam jet booster were analysed and compared. • The ejector reduces the amount of steam extracted from the crossover to the capture plant. • Ejector avoids severe damage in the blades of the low pressure steam turbine. This paper aims to evaluate the integration of the steam jet booster in a natural gas combined cycle with CO₂ capture at low part-load operation. The steam ejector takes a high pressure motive steam flows in a supersonic nozzle while dragging a low pressure steam which comes from the crossover. Both flows mix into one at fixed pressure of 3.5 bar and sent to the reboiler. The results are compared with two integration alternatives: uncontrolled and controlled steam extraction control. Uncontrolled steam extraction provides better part-load performance than controlled. However, with sliding pressure, at 42.3% gas turbine load the low pressure steam turbine operates at 27% of its capacity compared with 66% when the energy plant operates without capture, this imposes a potential risk to the integrity of the turbine. When the steam ejector is integrated, there is no significant improvement in the efficiency compared with sliding pressure strategy. However, the used capacity of the low pressure steam turbine increases from 27% to 42.8%. Therefore, the use of the steam ejector represents a solution to avoid severe damage to the low pressure steam turbine, thus bringing more flexibility, and ensure that steam extraction will not impose any constraint to the energy plant with CO₂ capture at part-load.