Theoretical And Experimental Study On Oxygen-enriched Combustion Technology In Circulating Fluidized Bed

World warming is due to the worse of Greenhouse effect mainly by massive CO₂ emission. Among many Greenhouse gases, CO₂ contributes the biggest to Greenhouse Effect due to its long lifetime and massive emission. CO₂ mainly comes from the combustion of fossil fuels. The amount of CO₂ emission becomes larger, as the development of economics and the demand for energy. In the case of controlling CO₂ emission, various advanced methods should be combined together to fit different cases.The effect of CO₂ could be debated by way of controlling CO₂ production or disposing recovered CO₂. Up to now, many methods have been developed to controlling CO₂ production, such as adjusting energy structure, improving power generation efficiency, advocating energy saving, utilizing renewable energy and exploring new energy. CO₂ could be recovered from combustion exhausts or from atmosphere. At present, it is feasible to recover and utilize CO₂ directly in the combustion process of fossil fuels. Recovered CO₂ could be stored underground, seabed or obsolete oil wells, even could be injected into low yield oil wells for enhancing oil production.Direct separation of CO₂ from flue gas will lead to a reduction of power generation efficiency and an increase of power generation cost. The content of CO₂ in flue gas is only about 3-15%, which will lead to complicated separation process and high cost. This is because CO₂ separation is very difficult from common flue gas, which has low CO₂ concentration and high N₂ concentration at normal pressure. Therefore, if CO₂ concentration is increased during combustion process, the cost on separation will be reduced markedly. The oxygen-enriched combustion technology has been proposed to increase CO₂ concentration, where mixed gases of O₂ and recycled flue gas substituting for air. In this case, most N₂ is separated before combustion, and flue gas will have a high CO₂ concentration up to 95%. Flue gas will be directly liquefied and recovered without separation. Part of flue gas will be circulated and mixed with oxygen to be loaded into furnace. Oxygen-enriched combustion is also called as O₂/CO₂ combustion, or air separation and flue gas recycle. CO₂ Separation and SO₂ treatment become easier, NO_x emission is reduced in oxygen-enriched combustion technology. Oxygen-enriched combustion technology is one of the new clean coal combustion technologies that can control pollutant emission. Oxygen-enrichedcombustion technology embodies better tech-economic advantages among many CO₂ emission control technologies from coal-fired power station. Oxygen-enriched combustion technology in circulating fluidized bed combined the advantages of oxygen-enriched combustion and circulating fluidized bed may have promising application foreground.Coal-char pyrolysis, firing, burnt and limestone calcination under O₂/N₂ orO₂/CO₂ atmosphere were carried on a thermobalance. Limestone calcination and sulfurationunder O₂/CO₂ atmosphere were tested on a bench scale fluidized bed facility. The characteristics of coal combustion and pollutant emission under O₂/N₂ or O₂/CO₂ atmosphere were experimented on a circulating fluidized bed multi-function test-facility.Reaction parameters under kinetic control of coal-char pyrolysis and limestone calcination under O₂/N₂ and O₂/CO₂ atmosphere on the thermobalance were obtained. The effect of different ratio of O₂ and CO₂ (N₂) to coal-char reaction was also discussed. Simulated calculation was just consistent with the thermogravimetric test results.Reaction of limestone calcination and sulfuration under O₂/CO₂ atmosphere were experimented on a bench scale fluidized bed facility and analyzed by thermodynamic analysis. Limestone samples were analyzed by Press Mercury Apparatus and Scanning Electron Microscope. Mechanism for limestone calcination and sulfuration under O₂/CO₂ atmosphere was raised and discussed.A circulating f...