Although hydrogen combustion does not generate carbon dioxide, soot or sulphur compounds, burning hydrogen in air can still produce nitrogen oxides, or NOx, at high temperatures. These gases contribute to smog, acid rain and respiratory irritation.

Scientists from Gdańsk University of Technology and the University of Gdańsk investigated whether UV radiation could help purify exhaust gases from hydrogen burners, potentially improving the environmental performance of hydrogen-powered heating systems.

The study, published in Scientific Reports, was conducted by Dominik Kreft and Konrad Marszałkowski from Gdańsk University of Technology and Karol Szczodrowski from the University of Gdańsk.

Hydrogen is widely viewed as a potential low-emission fuel because its combustion primarily produces water vapour. It is considered particularly promising in sectors where replacing fossil fuels with electricity is difficult.

Researchers noted, however, that hydrogen combustion usually occurs in ordinary air rather than pure oxygen. Because air contains large amounts of nitrogen, the intense heat generated during combustion can trigger reactions between nitrogen and oxygen molecules, forming nitrogen oxides.

To address this problem, the researchers tested a method known as direct photolysis, in which ultraviolet photons break chemical bonds within gas molecules.

The team constructed a laboratory system consisting of a hydrogen-oxygen burner, a vertical reactor, a UV lamp and an exhaust gas analyser.

Scientists measured changes in concentrations of nitric oxide (NO), nitrogen dioxide (NO2) and total nitrogen oxides under different gas flow conditions, burner pressures and UV lamp power levels.

The researchers found that ultraviolet radiation significantly reduced nitric oxide concentrations, in some cases lowering them to zero. However, part of the NO was simultaneously converted into nitrogen dioxide, another harmful nitrogen oxide.

As a result, the researchers said effective purification must be evaluated based on total NOx reduction rather than reductions in individual compounds alone.

The best performance was recorded at a gas flow rate of 2.6 cubic decimetres per second, a supply pressure of 100 kilopascals and a 160-watt UV lamp.

Under those conditions, NOx concentrations fell from 20.84 parts per million to 18.59 ppm, representing a 12.1% reduction.

In a separate analysis based on specific energy density, the researchers reported a maximum treatment efficiency of 10.8%.

The study also found that the initial concentration of pollutants played a critical role. When NOx concentrations fell below roughly 17 to 18 ppm, ultraviolet treatment no longer improved exhaust gas quality and in some cases increased measured NOx levels.

The researchers said the results demonstrate the technology’s potential but also show it remains far from industrial deployment.

Further work is needed to optimize radiation wavelengths, improve UV source efficiency, lower energy consumption and test the process under higher pollution loads and larger-scale operating conditions.

The authors also noted that UV radiation poses safety risks to skin and eyes, requiring appropriate protective measures.

The study highlights the broader challenge of evaluating emerging low-emission technologies beyond carbon dioxide emissions alone.

Researchers said hydrogen may reduce greenhouse gas emissions, but its use in boilers, engines and industrial systems will still require methods to control other forms of pollution before it can be considered fully environmentally friendly. (PAP)

kmp/ zan/

tr. RL