Choice Of Molten Salt Circulating Heat Carrier Smokeless Combustion Of Iron-based Oxygen Carriers (exergy) Analysis,

Since industry revolution, with increasing of population and developing of science and technology, the consuming of fossil fuels by traffic , industry and other branch is also increasing . Now we all know that combustion of fossil fuels leads to emission of CO₂, NOx and SO_x into the atmosphere, which are believed to contribute to air pollution and greenhouse effect. Now every country has learnt that it is important to protect environment. In resent years, scientists are studying how to make use of wind energy , water power and terrestrial heat more efficiency . They want to find a kind of combustion technology to use fossil fuels with high efficiency and low pollution. Now, some scientists are studying catalytic combustion and clean coal technology which can combust fossil fuels more efficiently and reduce pollution gas to emit into the air than technologies by used now . However it is impossible for all over the present combustion technologies to eliminate CO₂ emission fundamentally in combustion process. So we develop a new combustion called nonflame combustion technique with a thermal cyclic carrier of molten salt (NFCT), which was based on the knowledge of energy chemistry, fuel cell and combustion technology. In our technology, oxygen is separated from air and then burned with fuels in a molten bath to produce a high concentration of CO2 which is favorable for subsequent capture and storage.In our research, the fuel by used was CH₄, the molten salt by used was 1:1 weight ratio of Na₂O₃ and K₂CO₃ and the oxygen carrier by used was Fe₂O₃-based oxygen carrier. In the system, Δ_rG, Δ_rH and logK in some most possible reactions are calculated and HSC chemistry 5.1 software is used to analyze productions of the reactions .The Fe₂O₃-based oxygen carriers were characterized by means of., XRD, SEM, BET, TG, O₂-TPD, CH₄-TPR, GC, etc.. Though analyzing in theory and experiment, we discover the mechanism of the reaction between Fe₂O₃ and CH₄. The results show that iron oxide will undergo statechanging step as follows : Fe₂O₃â†' Fe₃O₄â†' FeO â†' Fe. In the research, we found that the Fe₂O₃-based oxygen carriers were acted after one cycle reaction. Fe80Al-M (means a carrier composed of 80 wt% of Fe₂O₃ and 20 wt% of Al₂O₃ and prepared by mechanical mixing) has the best reaction capability in pure Fe₂O₃ Fe90Al-M, Fe80Al-M and Fe70Al-M . Outlet gas products of the fixed-bed reactor were analyzed by a gas analyzer. It is found that at the beginning reaction stage CH₄ is mainly converted into CO₂ when CH₄ was introduced into the Fe₂O₃.The exergy efficiency of a CH₄ fired conventional combustion-GT (gas turbine) and a NFCT-GT system were calculated and compared. Moreover, the Grassmann Diagram of exergy flow for the two systems was made. In this paper, NFCT utilizes methane as a fuel, Fe₂O₃ as oxygen carrier and 1:1 weight ratio of Na₂CO₃ and K₂CO₃ mixture as molten salt. Nonflame combustion technology using thermal cyclic carrier of molten salt gas turbine (GT) was compared with the conventional combustion of methane gas turbine (GT). The net power efficiency of the NFCT is higher than for the corresponding GT systems with conventional combustion. If we could utilize the physical exergy remaining in the exhaust in an efficient way, the net power efficiency of NFCT systems could be even further increased.In conclusion, the NFCT system has a bright prospect in increasing the efficiency of energy conversion process, as well as in reducing green house gas emission.