Low Fuel-NOx Combustion of Synthetic LCV Gas

Abstract

Fuel NOx is one of the main issues related to the combustion of biomass derived Low Calorific Value (LCV) Gas. The high NOx emissions accompanying the combustion of that fuel in gas turbines or gas engines are compromising the CO2 neutral character of biomass and are a barrier towards the introduction of this green energy source in the market. The reduction of NOx emissions has been one of the main preoccupations of researchers in the LCV gas combustion field. Although, much has been achieved for thermal NOx which is caused mainly by the conversion of the nitrogen of the air in high temperature regions, less work has been devoted to the reduction of fuel NOx, which has as a main source the fuel bound nitrogen FBN, namely ammonia in case of biomass. Reducing the conversion of the FBN to NOx has been the main issue in recent research work. However, fuel NOx could be reduced significantly applying methods; like washing the gas in a scrubber prior its entrance to the combustor, and SNCR or SCR methods applied at the exhaust. But those solutions stay very expensive in terms of polluted waste water and catalyst cost. In this paper, the approach is to reduce the conversion of FBN to NOx inside a newly designed combustor. The idea is to optimize the combustion process ending up with the lowest possible conversion of FBN to NOx. The LCV gas used in the experiments described in this paper is made by mixing CO, CO2, H2, natural gas and N2 with proportions comparable to those of the real LCV gas. This gas is then doped with NH3 to simulate the FBN. In this paper the conversion ratio of FBN to NOx versus the FBN concentration is presented. Furthermore, the system is investigated in terms of the effect of CH4 concentration on the conversion of FBN to NOx. And measurements along the combustor axis were performed with a traversing probe where temperature and important emissions along the axis were measured. In all the experiments described in the paper, The LCV gas has an HHV (High Calorific Value) ranging from 4 to 7Mj/nm3. The newly designed combustor contains an embedded inner cylinder. In these experiments presented are without that embedded cylinder. The purpose of the current experiments is to be compared to the later experiments with the insert in order to define clearly the effect of the inner cylinder. Furthermore, this arrangement, i.e. without the insert, gave us the opportunity to traverse the combustor by a probe and to measure temperature and species profiles, which is of a great importance in defining the key parameter controlling the conversion of NH3 to NOx.