NO_x Formation Modeling Of Pressurized Oxy-fuel Fluidized Bed Combustion

Pressurized oxy-fuel fluidized bed combustion technology, which combinedoxy-fuel combustion with pressurized fluidized bed, has obvious advantages on systemefficiency and pollutant emission control. As gas at high pressure can no longer beregarded as an ideal gas, NOxformation mechanism of pressurized oxy-fuel fluidized bedcombustion is quite different from atmospheric conditions. In the paper, thehydrodynamic characteristics of pressurized oxy-fuel fluidized bed and pollutantemissions were carried out and conclusions are as follows:1) A two-dimensional hydrodynamic model of pressurized oxy-fuel CFB isdeveloped. In the modeling the CFB riser is divided into two regions: the bottom zoneand the upper zone. Model results at temperatures from20to1000℃and pressures from0.1to6.0MPa show that: with the increase of system pressure, the annular zone thicknessgets thinner, bed voidage decreases and solid volume fraction increase simultaneously.As the pressure increases, a noticeable decline of Umfis observed. However, for a fixedpressure, Umfincreases firstly and reduces afterward with the increase of temperature,and the corresponding temperature of Umfpeak becomes higher with increasing pressure.2) NOxformation model under atmospheric oxy-fuel fluidized bed combustion wasfirst established. Effects of temperature and atmosphere on NOxgeneration are analyzed.Results show that with the increase of furnace temperature and oxygen concentration,NO concentration increases gradually; compared with air combustion, NO production ofoxy-fuel combustion at the same O2concentration is lower. Based on the NOxformationmodel of atmospheric oxy-fuel fluidized bed combustion, NOxformation model atpressurized condition was then created. Calculation results show the similar NO trend asexperiment values of a small pressurized bubbling bed oxy-fuel system. As the pressureincreases, NO concentration under air and21O2/79CO2atmosphere decreased slightly;while NO content increased under30O2/70CO2and40O2/60CO2atmosphere, elevatedpressure did not change the fact that NO production increases with oxygen fraction.