Abstract
Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply, e.g., as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system, burner design and other boundary conditions, these changes may cause higher combustion temperatures and laminar combustion velocities, while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas, these effects may cause risk of flashback, reduced operational safety, material deterioration, higher nitrogen oxides emissions (NOx), and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems, but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.
Highlights
Publisher’s Note: MDPI stays neutralClimate change and the resulting need to reduce the emission of greenhouse gases (GHG) while still providing energy for a growing world population is one of the major challenges of the 21st century, affecting all sectors of society and economy
In the residential and commercial sector, natural gas is exclusively used as a fuel to provide low-temperature heat, which is used for space heating, food preparation or to produce warm water, to name the most common applications
The changing fuel properties due to the admixture of hydrogen into natural gas must be considered when assessing how residential and commercial gas appliances may respond to higher levels of H2 in natural gas
Summary
Publisher’s Note: MDPI stays neutralClimate change and the resulting need to reduce the emission of greenhouse gases (GHG) while still providing energy for a growing world population is one of the major challenges of the 21st century, affecting all sectors of society and economy. While the widespread use of electricity from renewable sources is one option to reduce energy-related greenhouse gas emissions, the use of hydrogen as a carbon-free fuel is considered a promising decarbonisation option, in hard-to-abate applications, e.g., aviation, heavy duty road and ship transport or some industrial high temperature processes. The European gas industry considers hydrogen (H2 ) to be essential for the decarbonisation of their business model. They support the creation of dedicated hydrogen infrastructures supplying hydrogen to end-users [2], and prepare for the injection of hydrogen into existing natural gas pipelines in order to reduce CO2 emissions quickly and ramp up demand for hydrogen. In Germany, for example, the German association for gas and water (DVGW) plans to increase permissible hydrogen concentrations in natural gas with regard to jurisdictional claims in published maps and institutional affiliations
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