Carbon capture technology in combustion—oxygen-enriched (pure oxygen) combustion

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Carbon capture technology in combustion — Oxygen-enriched (pure oxygen) combustion. Oxygen-enriched combustion involves using a mixture of oxygen-enriched gas (with an O2 concentration >20.947%) and some of the exhaust gas drawn back as a substitute for air in the combustion process; this increases the CO2 concentration in the exhaust gas, facilitating its compression and separation. The separated CO2 can then be directly processed and stored； Oxygen-enriched combustion is applied in industries such as steel, glass, and cement ； Advantages: Relatively simple to modify, easy to scale up, suitable for upgrading existing units ； Theoretically, the CO2 concentration can be as high as over 80% ； Disadvantages: Oxygen generation equipment requires high investment, consumes a lot of energy, and has high costs. Significant advantages of pure oxygen combustion (100% oxygen enrichment): energy savings + environmental protection + integrated carbon capture. ● Energy savings: Taking natural gas combustion as an example, with air as the oxidizing agent: CH4+2O2+7.5N2→CO+2H2O+7.5N2. In pure oxygen combustion: CH4+2O2→CO2+2H2O. Nitrogen makes up about 78% of air; during normal combustion, a large amount of nitrogen does not participate in the combustion process and is released after unnecessary heating, carrying away a lot of heat and thus increasing energy consumption significantly ； In pure oxygen combustion, the oxidizing gas is pure oxygen, with almost no nitrogen present; as a result, there is no unnecessary heating, which means that pure oxygen combustion offers higher thermal efficiency and lower energy consumption ； Widely used in the steelmaking industry for ladle drying, saving 10%-50% energy compared to conventional methods ； ●Environmental protection: 95% of the pollutants in flue gas, namely nitrogen oxides, are thermal NOX (with raw material-derived and fuel-derived NOX accounting for only about 5%). This phenomenon occurs as a result of the reaction between N2 and O2 that has not fully participated in the combustion process at high temperatures; the higher the temperature, the higher the concentration of NOX ； When pure oxygen is used as the combustion aid gas, very little nitrogen enters the reactor (due to poor sealing; theoretically, it is zero), which significantly reduces the generation of thermally induced NOx, thereby greatly lowering the cost of nitrogen oxide removal ； ●Increased production: With pure oxygen combustion, the burning is complete, the flame temperature is high; the main products are CO2 and H2O. The radiation capacity is strong, and the flame radiation temperature can increase by about 100 ℃, which facilitates rapid heating of the heated object ； ●Carbon capture: The CO2 concentration in the flue gas resulting from the combustion of natural gas with pure oxygen can reach up to 90%-95%. For a pure-oxygen combustion case at a steel plant, the technical and economic parameters are as follows: the price of oxygen is 0.36 yuan/Nm3, the price of converter gas is 0.2 yuan/Nm3, the calorific value of converter gas is 1150 kcal, and the oxygen coefficient is 0.22. Compared to the original level, 30 Nm3 of converter gas per ton of steel, the savings amount to >55%. Original cost: 30×0.2=6 yuan/ton. Current cost: Fuel cost: 30×0.45×0.2=2.7 yuan; Oxygen cost: 30×0.45×0.21×0.36=1.02 yuan. Total cost: 2.7+1.02=3.72 yuan. Cost savings rate: (6-3.72)/6=38%. By increasing the baking temperature and reducing the baking time, fuel savings exceed 55%, while cost savings exceed 38%.