Safety Challenges Related to the Use of Hydrogen-Natural Gas Blends in Gas Turbines

In a context of the decarbonization of the power sector, the gas turbine manufacturers are expected tohandle and burn hydrogen or hydrogen/natural gas mixtures. This evolution is conceptually simple in order to displace CO2 emissions by H2O in the combustion exhaust but raises potential engineering andsafety related questions. Concerning the safety aspect, the flammability domain is wider and the laminar flame speed is higher for hydrogen than for natural gas. As a result, handling fuels with increased hydrogen concentration should a priori lead to an increased the risk of flammable cloud formation with air and also increase the potential explosion violence.
A central topic for the gas turbine manufacturer is the quantification of the hydrogen fuel content from which the explosion risk increases significantly when compared with the use of natural gas. This work will be focused on a risk study of the fuel supply piping of a gas turbine in a scenario where mixing between fuel and air would occur. The pipes are a few dozens of meters long and show singularities: elbows, connections with other lines … They are operated at high temperature and atmospheric or high pressure.
The paper will first highlight through CFD modelling the impact of increasing hydrogen content in the fuel on the explosion risk, based on a geometry representative of a realistic system. Second, the quantification of the explosion effects will be addressed. Some elements of the bibliography relative to flame propagation in pipes will be recalled and put in sight of the characteristics of the industrial case. Finally, a CFD model proposed recently for accounting for methane or hydrogen flames propagating in long open steel tubes was used to assess a hydrogen fuel content from which the flame can strongly accelerate and generate significative pressure effects, for a flammable mixture initially at atmospheric conditions.