Session: 03-11 Energy Transition

Paper Number: 123189

123189 - Innovative H2-O2 Burner Utilizing Water-Cooled Combustion for Superheated Steam Generation 

Hydrogen, as a carbon-free energy carrier, plays a pivotal role in the transition towards cleaner energy sources. Its potential to replace fossil fuels offers a substantial opportunity for mitigating carbon dioxide emissions. When hydrogen is burned stoichiometrically with oxygen, emission-free use is possible, since pure superheated steam is produced as exhaust. However, the combustion of hydrogen and oxygen is technically very challenging, since the adiabatic flame temperature is about 3400 K and the laminar flame speed is almost 100 times faster compared to methane-air combustion. Consequently, conventional burners struggle to operate with hydrogen and oxygen within a limited range, or not at all.

In order to master the technological requirements, a novel burner concept has been devised, employing liquid water for flame cooling. Liquid water proves remarkably effective in cooling the flame due to its high enthalpy of vaporization. The introduction of water is facilitated by a two-component nozzle seamlessly integrated into the burner. This arrangement ensures the pre-mixing of oxygen and water before their entry into the combustion chamber. The premixing yields a very fine water spray with a homogeneous droplet distribution. Since the droplet or vaporized water is present in the main reaction zone as a result of the premixing with the oxygen flow, there is a significant temperature reduction everywhere in the flame. It has already been demonstrated that the flame at the hottest zones is more than 1000 K cooler compared to pure hydrogen-oxygen combustion. The quantity of added water plays a pivotal role in achieving this temperature reduction.

Experiments were conducted to assess varying water admixture rates. The objective is to introduce the maximum feasible amount of water for cooling purposes, with the aim of diminishing the thermal load on the components, while simultaneously avoiding the occurrence of quenching. Quenching arises when an excessive amount of energy is extracted from the reaction, leading to its premature termination. Within the framework of this burner concept, this issue can be attributed to an oversupply of water, inadequate droplet dispersion, or excessively large droplets. However, it strongly depends on the operating parameters and the design of the burner geometry and can be avoided.

The burner's design was guided by Computational Fluid Dynamics (CFD) investigations, employing the Fluent software with the realizable-k-ε model. Detailed chemistry calculations were conducted using a comprehensive reaction mechanism. To validate the numerical findings, experimental data will be employed. To this end, a dual-pronged approach is taken. Firstly, a cold, non-reactive flow field is analyzed using a Particle Image Velocimetry (PIV) system, wherein helium acts as a surrogate for hydrogen. Concurrently, an experimental examination of combustion takes place on a separate test setup. A new test rig was specially constructed for this purpose, comprising the primary burner and a quartz glass tube. This setup serves to isolate combustion from the ambient air while still enabling optical access. It allows for the measurement of OH distribution and temperatures at various positions on the test rig.

Utilizing the experimental data, we have demonstrated that the numerical results provide a solid foundation for burner design. A refinement of the spray model and the droplet characterization will be necessary, however, to regard the droplet size more accurate. With the such refined numerical model the basis for future scaling of this interesting new burner concept will be given.

Presenting Author: Lars Eichhorn Institute of Technical Combustion, Leibniz University Hannover

Presenting Author Biography: Lars Eichhorn is a research assistant at the Institute of Technical Combustion in Hannover, Germany.

Authors:

Dennis Sanders Institute of Sustainable Energy Supply, Jade University of Applied Sciences
Lars Eichhorn Institute of Technical Combustion, Leibniz University Hannover
Niklas Siwczak Institute of Power Plant Engineering and Heat Transfer, Leibniz University Hannover
Roland Scharf Institute of Power Plant Engineering and Heat Transfer, Leibniz University Hannover
Friedrich Dinkelacker Institute of Technical Combustion, Leibniz University Hannover
Karsten Oehlert Institute of Sustainable Energy Supply, Jade University of Applied Sciences