Development of the Next Generation CaO-Sorbent for Sulfur- and Nitrogen-Compound Removal

石灰石和石灰是去除硝氮化合物的重要吸附剂。然而，它们的孔隙率通常很低，容量也很低。为了解决这一问题，除了开发一种适合去除孔隙度的多孔石灰的制备方法外，澄清反应机理和澄清孔径分布对反应性的影响是非常重要的。提出了用乙酸、水和乙酸与水的混合物制备大孔氧化钙的新方法。通过这些方法，我们可以从天然石灰中制备出不同孔径分布的样品。采用系列样品研究了CaO-和CaCO_3-吸附剂的孔径分布对SO_x脱除的影响。结果表明，如果能制备出大孔、中孔和微孔数量充足，且不同孔径的孔之间串联良好的石灰，就能更好地保证反应物（SO_2和O_2）的渗透性，防止硫化过程中的孔堵塞，将大大提高石灰的反应性和利用率。从CaCO_3-吸附剂的研究结果还表明，如果CaCO_3样品中的大孔发育到足以去除SO_2，则CaCO_3样品的反应活性与CaO样品相同。当CaO用于去除H_2S时，由于ca与水的反应释放出H_2S， CaO-吸附剂形成的CaS必须在处置前转化为CaSO_4。为了寻找一种将CaS完美转化为CaSO_4和CaO的方法，采用试剂级CaS在H_2O存在下进行了CaS氧化分解的基本特性研究，因为通常采用含湿的热燃烧气体进行CaS的分解。结果表明，H_2O的存在对CaS转化为CaO和SO_2的影响较大：H_2O直接与CaS反应，生成H_2与O_2立即反应。阐明了石灰同时脱除SOx和NOx的机理，提出了该反应的反应方案：SO_2与H_2O反应生成SO_3 <2->，此时NO和NO_2可以一步参与反应，另一步加速SO_3 <2->向SO_4 <2->的转化。在h2o的存在下，NO_2的主体部分转化为硝酸盐。吸附形成的SO_3 <2->对NO的脱除有重要作用，而NO对SO_2的脱除作用可归因于SO_3 <2->氧化为SO_4 <2->的催化作用。少

Limestone and lime are very important materials as sorbents for S-and N-compound removal. However their porosities are usually low, and their capacity are low. To solute this problem, the clarifications of the reaction mechanisms and the clarification of the effect of pore size distribution on the reactivity are very important in addition to the development of a preparation method of a porous lime which porosityis suitable for the removal. We present new preparation methods of macro-porous CaO using acetic acid, water and a mixture of acetic acid and water. By using these methods, we could prepare the samples, which pore size distributions were different each other, from a natural lime. The effects of pore size distribution of the CaO- and CaCO_3- sorbent on the removal of SO_x using the serial samples were studied. It was concluded that if we can prepared a lime that has an adequate number of macropore, mesopore and micropore, and good serial connection of these different size pore to … More ensure the permeability of reactant(SO_2 and O_2) and prevent pore plugging during sulfation, the reactivity and utility of the lime will be drastically improved. From the results of study on the CaCO_3-sorbent, it was also suggested that if the macropores in the CaCO_3 sample are developed enough to SO_2 removal, the reactivity of the CaCO_3 sample is same as that of CaOWhen CaO is used for H_2S removal, CaS formed from the CaO-absorbent has to be converted to CaSO_4 before disposal because H_2S is released from the reaction between CaS and water. To find out a method for the perfect conversion of CaS to CaSO_4 and CaO, the basic characters of the oxidative decomposition of CaS were examined using reagent grade CaS in the presence of H_2O because hot combustion gas contained moisture is usually used for the decomposition of CaS. It was found that the presence of H_2O affected drastically to the conversion of CaS to CaO and SO_2 : H_2O directly reacted with CaS and formed H_2 reacted immediately with O_2.The mechanism of the simultaneous removal of SOx and NOx by slaked lime was clarified : A reaction scheme of this reaction was proposed : SO_2 reacted with H_2O and formed SO_3^<2->, then NO and NO_2 might participate the reaction in one step and the other hand, accelerated the conversion of SO_3^<2-> to SO_4^<2->. The main part of NO_2 was converted to nitrate salts in the presence of H_2O. SO_3^<2-> formed from the adsorption is supposed to be significant for the removal of NO, and the enhancement of NO to the SO_2 was ascribed to its catalytic effect in the oxidation of SO_3^<2-> to SO_4^<2->. Less