Experimental Studies And Simulation Of Coal Water Slurry Reburning To Decrease NOx Emission In Large Scale Station Boiler

Reduction performance and influence factors of coal water slurry (CWS) reburning technology applied in large scale station boiler were studied in this paper through experiments and numerical simulation.The influences of temperature, coal water slurry concentration and particle size on release of CmHn, CO, H₂ were studied through a fixed bed reactor. At the same time, volatile amount and surface area of char are improved with temperature and concentration increasing. Experiment results show the major reasons of CWS reburning achieving higher NOx reduction efficiency are the increment of reductive matter such as CH_i, CO, H₂ and improvement of surface areas of char.To study the characteristic of coal water slurry when used as reburning fuel, its fuel NOx formation mechanics were studied. The influences of reaction temperature, excess air ratio, coal water slurry concentration and particle size on fuel NOx formation of CWS and volatile of CWS were studied through a fixed bed reactor. The relative contribution of volatile NOx and char NOx formation of CWS was also studied.The homogeneous reduction reaction of volatile is important for coal water slurry reburning technology. So the influence of temperature, excess air ratio in reburning zone, concentration and particle size on volatile, char and coal water slurry reburning were studied through a fixed bed reactor. The relative contribution of homogeneous reduction reactions and heterogeneous reduction reactions to reduction efficiency of coal water slurry reburning were also studied.Burner which can apply reburning technolgoy was designed for a 670t/h boiler the biggest coal water slurry-fired boiler in the world. To review the operational aspect of boiler and burner, the cold and hot tests were successfully conducted. The experiment results show oil-fired and coal water slurry-fired conditions both reach the design standard. To study the NOx reduction efficiency and influence factors on coal water slurry reburning technology applied in large scale station boiler, the reburning experiments were conducted. Experiments include the influence of reburning fuel fraction, excess air ratio in reburning zone, excess air ratio in primary combustion zone, temperature in reburning zone, and flue residence time in over fire zone and mixing condition on NOx reduction efficiency of coal water slurry reburning. The experiment results show compared with 788 mg/Nm³ NOx emission under base experiment condition, Among experiments rage, when reburning fuel fraction is 16%, the escess air ratio in primary combustion zone is 1.13, the reburning zone excess air ratio is 0.95 and the excess air ratio in over fire zone is 1.2, NOx emission reach 454 mg/Nm³ and the reduction efficiency is up to 42.5%. At the same time the carton content of fly ash and slag condition of boiler were almost not influenced by coal water slurry technology applied. These show coal water slurry rebuing technology applied in large scale station boiler is a prospect method and offer instruct for the practical utilization of coal water slurry reburning.The last, combustion and reburning conditions in a 670 t/h coal water slurry-fired boiler were simulated. The numerical simulation results are consistent with the experiment results. NOx formation rule and coal water slurry reburning technology reduction efficiency in large scale station boiler were obtained from simulating results. The flow field, temperature field and species field were compared before and after the reburning condition were operated. That gives a preview for coal water slurry reburning technology utilization.