Performances and emission characteristics of NH3–air and NH3[sbnd]CH4–air combustion gas-turbine power generations

Abstract

For the first time, NH3–air combustion power generation has been successfully realized using a 50kW class micro gas turbine system at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. Based on the global demand for carbon-free power generation as well as recent advances involving gas-turbine technologies, such as heat-regenerative cycles, rapid fuel mixing using strong swirling flows, and NOx reduction using selective catalytic reduction (SCR), allow us to realize NH3–air combustion gas-turbine system, which was abandoned in the 1960′s. In the present system, the combustor adopted gaseous NH3 fuel and diffusion combustion to enhance flame stability. The NH3 pre-cracking apparatus for combustion enhancement using generated H2 was not employed. The NH3–air combustion gas-turbine power generation system can be operated over a wide range of power and rotational speeds, i.e., 18.4kW to 44.4kW and 70,000rpm to 80,000rpm, respectively. The combustion efficiency of the NH3–air gas turbine ranged from 89% to 96% at 80,000rpm. The emission of NO and unburnt NH3 depends on the combustor inlet temperature. Emission data indicates that there are NH3 fuel-rich and fuel-lean regions in the primary combustion zone. It is presumed that unburnt NH3 is released from the fuel-rich region, while NO is released from the fuel-lean region. When diluted air enters the secondary combustion zone, unburnt NH3 is expected to react with NO through selective non-catalytic reduction (SNCR). NH3CH4–air combustion operation tests were also performed and the results show that the increase of the NH3 fuel ratio significantly increases the NO emission, whereas it decreases the NO conversion ratio. To achieve low NOx combustion in NH3–air combustion gas turbines, it is suggested to burn large quantities of NH3 fuel and produce both rich and lean fuel mixtures in the primary combustion zone.