Mechanisms Of In-Furnace Desulfurization In O₂/CO₂ Coal Combustion And Flow Fields Of Sorbent Nozzles

It's well known that there's still much difficulty in promoting the in-furnace desulfurization rate of Calcium-based sorbent during coal combustion at high temperature, which limits the spread of this technology. And now, with the emergence of In-furnace Desulfurization in O2/CO2 Coal Combustion, the situation may be changed. O2/CO2 Coal Combustion is an economical and effective method to control the CO2 produced during combustion. It is possible that it will become a popular technology in controlling the emission of green house gases. Although studies have showed that there is some difference in the reaction characteristics between this technology and the traditional one, we still don't know its mechanisms. This study mainly focuses on the theoretical analysis of this method and its mechanisms. Besides, the sorbent particles do not stay for a long time in the furnace, and reaction time and concentration of SO2 play an important role in the desulfurization efficiency, so different kinds of sorbent nozzles are designed and experiments are carried to improve the weakness. Then numerical simulation is conducted to compare the results and direct the experiments.Firstly, through the analysis of desulfurization reaction process of CaCO3 in O2/CO2 the effect of CO2 to the calcination of CaCO3 is studied. What is different from the traditional methods is that the method of chemical thermodynamics analysis is applied, and a relatively accurate formula of chemical reaction equilibrium is acquired. The kinetic character of the reaction in different conditions is studied with TGA. After that, the kinetic controlling mechanism of the calcination reaction in different conditions is probed. What's more, the pore structure of resultant resulted from different conditions is got by mercury porosimetry.This report shows that two different mechanisms of chemical reactions are studied by using chemical thermodynamic analysis in terms of the fact that desulfurization can be greatly affected by the equilibrium condition of sulfur-retention reaction when the temperature is high in the furnace. Through study, the relationship between temperature and concentrations of SO2, O2, CO2 under equilibrium condition is showed. By comparing the mechanisms of two chemical reactions, it is suggested that the factor controlling the mechanisms of the reactions is the velocity difference between calcination and sulfation reaction. This conclusion is further confirmed by experiments in a drop tube furnace.Finally, on the basis of turbulent jet theory, different figures and sizes of sorbent nozzles are designed and experiments on the free injection flow fields are performed. By comparison, the best type of nozzle is determined. Then, numerical simulation with turbulence model is conducted, results from which accord with the experiment results. This suggests that numerical simulation can be used as guidance with the design and experiment of sorbent nozzles.