Experimental and numerical investigations on oxy-coal combustion in a 35 MW large pilot boiler

- A compatible operation of oxy- and air-combustion is achieved in a large pilot boiler.
- The predicted results using the improved sub-models agree well with the experimental.
- The average temperature and heat flux distribution are similar to air-combustion.
- The heat transfer increases by 9% and 6% under wet and dry recycle oxy-combustion.
- An increase of 2% in the recycle ratio decreases the heat transfer by about 6%.

This paper reports on the recent experimental and numerical results from a 35 MW front wall-fired large pilot boiler. The boiler features a first-of-its-kind compatible design of oxy-fuel combustion and conventional air combustion (air-combustion). A sub-bituminous coal is used as fuel in the experiment. Wet and dry flue gas recycle oxy-fuel conditions are investigated, while air-combustion is also examined for reference.Measured in-furnace temperature, species concentration, exhaust emission, and transferred heat to membrane-wall and superheater are compared between oxy-fuel and air-combustion. Detailed numerical studies of combustion and heat transfer are performed using in-house developed sub-models for oxy-fuel condition, including a radiative property model and a global reaction mechanism. The predicted results agree well with the experimental data. The experimental and numerical results show that stable oxy-fuel combustion is achieved in the 35 MW large pilot boiler. Importantly, the oxy-fuel combustion and air-combustion can operate well with the especially designed burner system at similar heat loads in the experiment. Moreover, similar average temperatures and heat flux distributions are achieved under wet and dry flue gas recycle oxy-fuel conditions with an initial O2 concentration of 28% in the oxidant. Transferred heat to membrane-wall and superheater in oxy-fuel combustion is slightly greater than in air-combustion. Furthermore, the flue gas recycle ratio significantly influences the heat transfer in oxy-fuel combustion. Increasing the recycle ratio from 0.71 to 0.73 reduces the transferred heat to membrane-wall by approximately 6%, while that of superheaters increases by approximately 4%. The selection of the optimized recycle ratio is a trade-off between boiler performance and flame stability of the burner system.