Study On The Use Of Calcium Sulfate As Oxygen Carrier In Unmixed Combustion

The combustion of fossil energy releases much of CO₂ into the atmosphere, which makes the global problem "greenhouse effect" being paid more and more attention to by the governments all over the world. Unmixed combustion (UMC) introduced a kind of material named "oxygen carrier" for transferring oxygen between fuel and air, and releases the energy stored in the fuel instead of mixing the fuel and air directly in the conventional combustion. At the same time, the separation of CO₂ is achieved and a high concentration of CO₂ could be captured in the vent gas. Aiming at the problems of the oxygen carrier in unmixed combustion, calcium sulfate (CaSO₄) is used as a new kind of material for applying in the unmixed combustion. The possibilities of using CaSO₄ as oxygen carrier in UMC, the improvements of CaSO₄ reactivities, the cycle performances as well as some simulation work on hydrogen production based on unmixed combustion were studied.Using the thermodynamic data for calculating the Gibbs free energy and equilibrium constant, the feasibility of utilizing CaSO₄ as oxygen carrier in UMC was analyzed, and the conditions of temperature and pressure for the reactions between CaSO₄ and gaseous fuel was also analyzed.The experimental research was carried out on the thermogravinietric apparatus and the fixed bed reactor, testing the reactions between gaseous fuel and oxygen carriers, which were made by mixing CaSO₄ with inert and active materials through different methods. The results showed, when CaSO₄ reacted with fuel only, the initiative temperature was too high to satisfy the UMC process. However, the initiative reacting temperature could be decreased by adding both inert and active materials into CaSO₄. The inert material played a role of supporting and transferring heat while mixing with CaSO₄, and it was not involved in the reaction. The active material not only took part in the reactions itself, but it also improved the activity of CaSO₄ to large extent and increased the reaction speed between CaSO₄ and gaseous fuel. Furthermore, the configurations of CaSO₄ and the modified CaSO₄ reacting with gaseous fuel were characterized by X-ray diffusion and specific surface area measurement. The components of reduced CaSO₄ and the reasons for the improvements of oxygen carrier's reactivity were analyzed by the characterization results.The process of autothermal hydrogen production from coke oven gas based on unmixed combustion was proposed. Part of the primary thermodynamic problems and the chemical equilibrium characters were studied. The system was simulated and evaluated by considering the total efficiency.