The Top Cycle gas turbine

The Top Cycle gas turbine is a novel gas turbine cycle where the excess air in the gas turbine is replaced with high pressure steam, creating an ultra-wet environment for combustion with 50% + steam in the combustion chamber. Excess air is air that is not used for combustion but for volume and cooling.

Replacing the excess air with high pressure, hot, steam reduces the need for compressed air in the gas turbine. The reduction in compression energy can instead be used for driving the generator to generate power. This increase represents 4-6% points in electrical efficiency.

The high level of steam in combustion leads to a very stable combustion with a very slow flame speed and evenly distributed thermal profile. These characteristics result in ultra-low emissions from combustion, especially for when Hydrogen is used as fuel, but also for fossil gas and biomass emissions levels are very low compared to traditional gas turbine combustion.

Replacing the excess air with steam also means that the gas turbine is not symmetric in the volume flow, the compressor is smaller than the turbine (expander). This results in an imbalance of the gas turbine that needs to be addressed, like the pushing- and pulling forces generated. Typically, the pushing- and pulling forces from these cancel each other out, but in the Top Cycle, new thrust barings to handle this imbalance are needed. Additionally, the rotation speeds of the compressors and turbines can differ more than a traditional gas turbine, requiring new design for the gearbox.