Applicability of Optical Emission Spectroscopy for Industrial Flame Analysis with Hydrogen and Natural Gas Mixtures Based on Laboratory Study

• Mixing small amounts of hydrogen into a natural gas flame increases thermal radiation due to increased soot formation. • High shares of hydrogen radically decrease the thermal radiation of the flame (less soot formation), leading to higher convective heat transfer. • The temperature of the flame can be measured from spectra by using grey body radiation from soot. • In furnaces, higher convective heat transfer must be taken into account when using hydrogen. However, thermal radiation from furnace walls reduces the difference between natural gas and hydrogen in furnaces. This study investigates optical emission spectroscopy as an analysis method for hydrogen and natural gas burner flames relevant to industrial use. The equipment used was a low-cost industrial spectrometer, which measures light in the wavelength range of 500–1000 nm. Measurements were conducted with an open flame burner and a burner-heated furnace, with different mixture ratios of natural gas and hydrogen. Based on the results, it can be concluded that the relative amount of thermal radiation and soot particles from an open flame can be approximated using optical spectra. When adding hydrogen to a natural gas flame, the solid angle of soot particles rises by the first 5-16% of hydrogen, leading to higher thermal radiation. With higher shares of hydrogen, the solid angle of soot particles decreases radically, leading to lower thermal radiation. The temperatures that were measured from the optical spectra based on radiation from soot particles show that the flame's temperature could be measured up to 46% share of hydrogen. In the burner-heated furnace, the intensive thermal radiation from the inner walls gets mixed with the radiation from the flame, making it easier to determine the temperature of the wall rather than the flame itself. The study also presents the spectroscopic differences between different gas mixtures. In addition, the background phenomena and practical effects of these differences are discussed.