Combustion in oxy-fuel technology takes place in the O_2/CO_2/H_2O mixture created with a flue gas recirculation into the combustion chamber. Although a lot of scientific and engineering efforts have been done to prove the feasibility of PC boiler retrofit, there are still some challenges left in the field of optimization of pulverized coal combustion. The main interest in presented research was focused on comprehensive study of the influence of O_2/CO_2/H_2O atmosphere as well as pulverized coal preparation on combustion behaviour. So far, the main effort in retrofit studies has been focused on the achieving of similar heat fluxes, comparable unburned carbon content in the fly ash and the similar exit furnace gas temperature in regards to the values found in the air mode. It was usually achieved by proper adjustment of the flue gas recirculation rate, an oxidizer staging and burners modifications. This work additionally investigates the effect of the coal grinding which is also an important factor that should be taken into account in oxy-combustion optimization. Both oxygen enriched atmosphere as well as gasification reaction with CO_2 and H_2O are responsible for higher coal reactivity which results in much lower UBC then in air atmosphere. It was found that coarse grinding has positive impact on combustion behaviour, thus enabling the realization of the process with a smaller recirculation rate. The benefits of these observation lead to less energy demand for coal preparation and flue gas pumping and hence result in higher efficiency of the oxy-combustion process. The experiments were carried out in two laboratory rigs: one for single particles investigation and second one for semi- industrial pulverized coal combustion. The first setup consisted of electrically heated horizontal tube operated at 1223 K. The combustion tests were performed with particles of the size less than 2 mm and were focused on the influence of the particles size and O_2 concentration in atmosphere on particle temperature and time of combustion. The second setup consisted of 15 meters long horizontal combustion furnace with one front burner with thermal output of 0.5 MW. The furnace was equipped with several ports for oxidizer staging and suction pyrometers for gas analysis. The combustion tests were focused on the influence of coal grinding and flue gas recirculation on unburned coal in ash, profiles on combustion temperature, NO_x emission and heat fluxes. Results of experiments were supported by CFD modelling with the use of Ansys Fluent software. Finally results of the study provided an estimation of the possible energy savings that can be gained by a proper optimisation of coal grinding and flue gas recirculation rate.
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