| The expeditious development of national economy increases the consumption of fossil energy, leading the increase of emission of carbon dioxide. It is general accepted that CO2 is one of the most important culprit of greenhouse effect. The technological treatment on CO2 reduction must be emphasized under the enormous international and environmental pressure. As we all know, power plant is one of the most important CO2 emission source, however it exists serious energy loss, equivalence 13～37 percent of overall energy output, caused by the CO2 reduction and recovery technology which is employed on the power plants. The exploitation of high temperature compliant CO2 adsorbent, hence, is the key technology of energy saving.In the thesis, CaO-based CO2 high temperature adsorbent had been doped with the elements of Mg, Al, Ce, Zr, La and modified by the high tempereture solide state method, the citric acid combustion method and the coprecipitation method. The adsorbent's capacity and the cycle performance are evaluated by the thermogravimetry analysis(TGA). In connection with different preparation methods, the precursors (only in the high temperature solide state method), doping elements and doping proportions were analyzed respectively. As a result, in conjunction with the simulation flue gas of 30 percent CO2 the optimal adsorption condition for doped adsorbents is 700℃. In general, the introduction of doped elements has an adverse effect on the single-time adsorption capacity for most of the investigated adsorbents, the positive improvement is observed only on a small minority of the adsorbents. At the same time the capacity of CaO various with different precursors doped with the same element. Various doped elements have different influence on the adsorption capacity adsorbent. The capacity of CaO doped by La and Mg has a slight decrease, and the capacity of CaO is decreased seriously with doped element Ce. With the increasing percentage of the doped element, the capacity of CaO adsorption decreased.The investigation of the adsorbent's recycle stability shows that the adsorption stability of most adsorbents is improved after modification. In the case of CaC2O4-CaO-La(8:2) prepared with high tempereture solide state method, the recycle stability is improved 12.69% after 10 times recycle compared with that of blank CaO, and after 20 times recycle the improvement of recycle stability is 8.4%; the recycle stability of NMS-CaO-La(8:2), prepared with the citric acid combustion method, has an enhancement of 9.2% after 10 times recycle, and 17.6% after 20 times recycle. Moreover the single-time adsorption capacity stands remain at 140wt%. In addition, the adsorbent's performance is characterized by X-ray diffraction (XRD), N2-adsorption/desorption and SEM, and the reason behind the performance improvement after doping is discussed respectively. It is confirmed that element-doping has changed the channel structure of the adsorbents. La can enrich the channel structure, restrain the interaction sintering of CaO particles, increase the sintering temperature and prevent the collapse of the pore during the adsorption/desorption process. The recycle stability is improved consequently.In this contribution, various experiments are also conducted with fixed-bed adsorption. The different influence factors, such as doping element, preparation methods and particle size, on adsorption curve (penetration curve) and the adsorption rate curve are investigated. It is found that adsorbents with large particle size have slower adsorption rate and lower adsorption capacity than that of the adsorbents with small particle size. The result of fixed-bed adsorption has an excellent agreement with that of TGA experiment. The fixed-bed, which approaches to industrial adsorption equipment, can be therefore considered as scale up of TGA experiment. The result of this investigation has hence implication on practical application. |
PDF Full Text Request