Numerical Simulation And Optimization On An Oxy-fuel Swirl Burner

CO2 is generally considered as the main source of greenhouse gas. As global warming becomes more severe, more and more countries and regions begin to pay attention and participate in the CO2 reduction projects. Coal-fired power plants are one of the main source of CO2 emissions, and due to the large quantity of emission,it is desperate to develop the technology of CO2 reduction and capture. Oxy-fuel combustion has become one of the most active and promising topics in CO2 capture technology due to its high efficiency of reduction and economy. Meanwhile, the development of oxy-fuel combustion burners is always the key issue to which can make the technology industrialize in large scale.This research focuses on the 12 MW O2 pre-mixing swirling oxy-fuel combustion burner, which was applied to a pilot-scale testing boiler. There are three parts in this paper. Firstly, the combustion characteristics of oxy-fuel combustion was investigated and the kinetic parameters of combustion reaction was calculated. Then the combustion performances of single burner were studied and optimized through numerical simulation. Finally cold air flow experiments were performed and numerical simulation of combustion was carried out in the boiler.Based on the coal combustion characteristics experiments in different atmosphere, it seemed that the coal devolatilization and ignition temperature increased and the maximum weight losing rate decreased, resulting the increasing of coal burn out time. Further research was carried out in the single burner numerical simulation to confirm the influence of atmosphere on coal combustion. Methods of optimizing recirculation region distribution and increasing combustion oxygen concentration were proposed to improve the performance of burner in oxy-fuel combustion.After researches on the change of swirl number, air distribution ratio and primary air oxygen concentration of the swirl burners, it was found to be helpful to the improving of coal combustion characteristics to optimize the swirl number and air distribution ratio of the burner. Nevertheless, change of primary air oxygen concentration had little impact on the improving of coal characteristics, if average oxygen concentration of combustion remained the same. It was also confirmed to be effective to the optimization of flow field and improvement of coal combustion characteristics to equip the burner with dense sparse devices. Besides, a new type of dense sparse burner together with central secondary air was also developed according to the feature of oxy-fuel combustion. Results showed that this structure was a feasible optimization proposal which can improve the combustion characteristics and reduce the burning distance of pulverized coal in oxy-fuel atmosphere.Finally, based on the cold air flow experiments in the boiler, simulation on the prototype operating condition, parameter-optimization operating condition and structure-optimization operating condition in the boiler was conducted. Under the normal operating condition and the overfire air operating condition, results showed that the delay of coal ignition in the oxyfuel atmosphere was improved after optimization. And the coal burning and burn out rate was increased. Moreover, the possibility of coking around the ter wall in the boiler was reduced.