NOx reduction of city gas/hydrogen mixed combustion by two-stage combustion

抄録

Increasing attention has been focused on hydrogen as a boiler fuel due to the carbon-free fuels. On the hydrogen combustion as the boiler fuel, the hydrogen burner should be applied the diffusion combustion to avoid the flashback because of the high burning velocity of hydrogen. Thus, the NOx reduction is important for hydrogen burner. This study investigated the NOx reduction by two-stage combustion of city gas and hydrogen mixed combustion. The lean premixed tubular flame of city gas / air mixture is formed on the first stage combustion. Combustion rate and air ratio of the first stage are 4 kW and 1.8. Downstream of the first stage combustor, hydrogen was injected at 7.4 m/s from three nozzles located around the combustion chamber. The stable diffusion flame of hydrogen was achieved in the swirling flow at the 3 kW of combustion rate. The NOx emission was suppressed to only 21.4 ppm because of the slow combustion reaction and the mild temperature rise. In the case of the single stage hydrogen diffusion combustion, the NOx emission increased to 289 ppm. The NOx reduction by using the two-stage combustion is effective for the hydrogen combustion.