Investigation On Calcined Decomposition And Sulfation Characteristic For Modified Calcite Under O₂/CO₂ Atmosphere

The static characteristic of calcined decomposition, sintering and sulfation for limestone,scallop and modified limestone were carried out on the fix-bed reacter and the vertical thermal balance system . And then we use the drop tuber furnac(eDTF)investigate the dynamic characteristic of sulfuraization for limestone and Na-Treated. Through the systematic investigatement, the main conclusions are as follows:Firstly, the characteristic of calcined decomposition, sintering for modified limestone and scallop has been analyzed. Based on the exprimental and simulations studies, CO₂ partial pressure is one of a main factors to CaCO₃ decomposition.When CO₂ concentration is low, the intial decomposition temperature is more dependent on the CO₂ partial pressure. The effect of partial pressure to the calcined reaction weakened when the CO₂ partial pressure is greater than 0.5. With the CO₂ partial pressure increased, the intial decomposition temperature and activation energy are both increased. The calcined activation energy decreased obviously with Na2CO₃ added. Based on SEM, XRD testing analysis, it is founded that the calcined pore size distribution and grain are both small and easier to plug the hole with glue sintering for limestone. Compared to the O₂/CO₂ atmosphere, the calcined sintering is more serious, which is aslo the main reason for lower desulfurization in the O₂/N₂ atmosphere. As to modified limestone and Scallop, it has big pore size distribution and the grain size is amlost not change with the temperature increase. BET and PV change are relatively flat with calcined time, the BET is four times higher as the limestone after 1800s calcination.Sescondly, the static characteristic of desulfurization and Ca conversion were both investigated in O₂/CO₂ atmosphere based on fix-reactor using simulated flug gas. The result shows that the mechanism was main controlled by direct CaCO₃-SO₂ sulfation under higher CO₂ concentration, which is different from the indirect CaO-SO₂ sulfation process for O₂/N₂ atmosphere when the sulfation temperature below 950℃. It is an important reason for the higher efficiency at O₂/CO₂ atmosphere. The sulfation effciency at O₂/CO₂ is higher than the O₂/N₂ at the same experimental condition for limestone. Compared to Limestone, modified limestone and Scallop both have higher sulfation efficiency and the sulfation efficiency can be improved significantly and less affected by temperature with Na2CO₃ added. The Ca conversion results get in our experiment at 850℃and 1000℃for limestone, modified limestone and scallop is 35.92% and 30.07%, 67.03% and 72.65%, 36.43% and 54.7% seperately.Finally,in order to get more realistic injection desulfurization process, the influence of temperature, atmosphere and Ca/S mole rate to desulfurization efficiency has been discussed based on DTF. The result shows that: compared to conventional indirect desulfurization, the O₂/CO₂ atmosphere enabled higher sulfation degree and desulfurization efficiency. what's more, it has a higher optimum and wider range of sulfation temperature. The optimum sulfation temperature in our dicussed is 1000℃and the temperature range is 1000-1100℃for limestone. The Alkaline Earth Metal Na would inhabit the decomposition of sulfate and improve the optimum sulfation temperature and desulfurization significantly. In our study, the best temperature for Na-Treated and Scallop is nearly 1050℃. The desulfurization efficiency for limestone, Na-Treated and Scallop is 58.93%, 64.17% and 71.45% seperately at 1100℃. With the result dicussed above, modified by additive methods(added Na2CO₃) can significantly prompt the desulfurization efficiency and Ca utilization.