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Hitachi has been issued a patent for a low NOx gas turbine combustor for hydrogen combustion, especially in IGCC applications. Below is comments on the technology from Jeff Phillips of EPRI:
"I looked at the brief description of the Hitachi patent and it is different from nitrogen dilution. They are trying an approach called rich/lean combustion to try to stay away from the high NOx production
region (which occurs right around stoichiometric combustion where you have just enough oxygen to react with all of the fuel).
Most so-called dry low NOx combustors avoid the stoichiometric region by running very lean (lots of excess air) and thoroughly mixing the air with the fuel before it reaches the combustion chamber. The problem with doing that with hydrogen fuel is that H2 has a very wide flammability zone and it is difficult to prevent the fuel from burning as soon as it is mixed with air.
Hitachi apparently feels they can get around this by starting with a fuel-rich mixture of H2 and air in the first part of the combustor, then injecting more fuel into the combustion products and then finally bringing excess air and burning away all of the fuel in the second part (lean zone) of the combustion chamber."