Multi-stream FPV-LES modeling of ammonia/coal co-firing on a semi-industrial scale complex burner with pre-heated secondary, tertiary, and staged combustion air

Abstract

The study investigates ammonia/coal co-firing using a non-adiabatic multi-stream flamelet/progress variable (FPV) approach on a 760 kWth semi-industrial test furnace of Central Research Institute of Electric Power Industry (CRIEPI). The furnace features an advanced low NO_x CI-α burner with preheated secondary, tertiary, and staged combustion air streams, closely resembling conditions in commercial-scale power plant burners. Two ammonia injection cases are investigated, one where ammonia is injected through the burner and the other where it is injected through a measurement port positioned 1.0 m downstream, both at a fixed ammonia co-firing ratio of 20 % based on LHV. To address varying oxidizer stream temperatures for primary, secondary, tertiary, and staged air streams, an additional dimension is introduced to the flamelet chemtable. The thermochemical space has seven dimensions, three for fuel mixture fractions (volatile matter, char off-gases, and ammonia), and dimensions for the mixture fraction variance, reaction progress variable, total enthalpy, and oxidizer temperature. The seven-dimensional non-adiabatic (7D-NA) FPV-LES model's accuracy is assessed by comparing its predictions with measured data as well as with previous modelling results that had certain limitations, such as six- dimensional non-adiabatic (6D-NA) FPV-LES model that ignored difference in oxidizer temperature and five-dimensional adiabatic (5D-AD) FPV-LES model that ignored both difference in oxidizer temperature and heat loss in flamelet chemtable. In both cases of ammonia injection, 7D NA-FPV-LES model improved over previous model's predictions by accurately capturing the burner exit flow field. It successfully identified trend between the two cases, predicting a slightly higher peak temperature near burner exit in case injecting ammonia through downstream due to development of stronger internal recirculation zone. Results showed peak NO notably higher and closer to burner when ammonia injected through downstream, consistent with measured data due to prevalence of NO reduction for ammonia injected through burner in proximity of burner.

Novelty and significance statement

The novelty of this research is that it introduces an approach that can be accurately applied to the FPV-LES modeling of actual commercial power plant burners with highly complex oxidizer streams at varying temperatures. This approach has been validated on the complex CI-α burner of the CRIEPI test furnace of semi-industrial scale, which has preheated secondary, tertiary, and staged air streams, resembling actual conditions encountered in commercial power plant burners. The proposed approach can consider multiple oxidizer streams and it can also consider variation in oxidizer composition (although oxidizer composition is fixed in this study). This research will be significant in adoption of multi-mixture fraction FPV-LES approach to complex burners of commercial power plants. Additionally, the study provides valuable insights into ammonia/coal co-firing in a semi-industrial scale furnace with complex burner, aligning with global decarbonization goals, emphasizing the utilization of zero-carbon fuels like ammonia in actual scale commercial power plants.