RE:RE:RE:As long a plasma torches put out NOXious fumes...From Sweden Report on Plasma Torch
2.5.3 NOx emissions from plasma torches
One of the major technical issues with the use of thermal plasma torches is the nitrogen
oxides that can be generated in the high temperature plasma which may limit the plasma
torch in its various applications. An electric arc operating in an oxidizing gas atmosphere,
in combination with high plasma temperatures, leads to formation of NOx. The plasma
bulk temperature is normally 5000 - 6000 K, while the maximum temperature in the
plasma jet can be up to 10 000 K [39].
The NOx formation in plasma torches has not been studied extensively since most research
has focused on NOx emissions from conventional fuel combustion, where temperatures
usually are below 2000 °C. One study has been made on plasma torches applied to an
electric arc furnace [40]. These trials did not confirm any influence of the electric parameters
of the plasma torch on the formation of NOx. The influence was not detectable due to
other more dominant parameters, including the composition of the furnace atmosphere.
Two common methods for industrial NOx reduction are flue gas recirculation (FGR) and
staged combustion. FGR involves extracting flue gases and mixing it with combustion air
in order to lower the oxygen content of the combustion air as well lowering the combustion
temperature. Staged combustion is a reduction strategy that works by injecting additional
fuel in a secondary combustion zone. This creates a fuel rich reburning zone where
NOx is destroyed through reactions with hydrocarbon radicals. These two reduction
strategies could probably also be applied to plasma torches with some modifications. For
example, a study by Uhm et al. [39] showed that NOx generated by a plasma torch can
be disintegrated in a fuel-burning atmosphere with an exponential decrease in terms of
methane flow rate