Hydrogen in the Power-to-Gas concept
Hydrogen is extremely suitable as a storage medium for renewable energies when they produce excess power (e.g. strong wind on a public holiday). This is called the Power-to-Gas concept. Using the excess electricity provided by wind turbines and solar panels to generate H2 through electrolysis enables you to store the energy in the hydrogen temporarily. When the electricity demand increases, the gas can be burned in a gas turbine to produce electricity and heat.
Gas turbine: General overview
A gas turbine is a type of internal combustion engine. Air is sucked into the inlet and compressed by the compressor stage. Energy is then added by introducing fuel (in our case: hydrogen) in with the air in a combustion chamber and igniting it so the combustion generates a high temperature flow. This high-temperature high-pressure gas enters a turbine, where it expands, producing a shaft work output in the process.
However, due to the high combustion temperature of hydrogen, the turbine outlet gasses (at a temperature of about 900 °C) can be used to pre-heat the air entring the combustion chamber by the use of a recuperator. This increases the efficiency of the overall system significantly. Even after the recuperator, the exhaust gasses are still hot enough to be used in a CHP (Combined Heat and Power) system. The hot gasses can be used for any industrial process heating, to produce steam to drive a steam turbine or to heat up water for use in a domestic heating application.
And all this is achieved without any carbon dioxide emissions.
Gas turbine: Compressor stage
The compressor stage in our gas turbine will be a 1-stage centrifugal type that will bring the air up to a pressure of 4.5 bar. The rotor will be 3D-printed in Titanium, a strong yet lightweight material. We have already done extensive CFD testing of the entire compressor stage.
Gas turbine: Combustor
Conventional gas turbine combustion chambers cannot burn pure hydrogen; the combustion properties of hydrogen di ffer greatly from conventional fuels such as natural gas or kerosine. Compared to these conventional carbon-based fuels, hydrogen has a much higher adiabatic flame temperature and a higher laminar burning velocity. Because of this, the combustion of pure hydrogen brings with it a higher risk of problems like flame flashback, which can cause catastrophic damage to the fuel nozzles. All of this means that you cannot simply modify an existing conventional burner. A new design, from scratch, has to be made for a gas turbine combustion chamber that burns pure hydrogen.
The preliminary test geometry for the combustor is a partially-premixed single swirl nozzle design. This geometry is used for the CFD simulations, both RANS and LES, to validate the turbulence and combustion models. This test geometry already yields good temperature homogeneity at the outlet, with an average value of 1300°C.
Gas turbine: Turbine stage
The turbine section will be a single stage radial design. To keep the geometry simple, no complicated internal cooling channels will be present in the rotor. However, because of the high inlet temperature (1300°C), a highly heat-resistant yet strong technical ceramic material will be used for the radial turbine rotor; Silicon Nitride.