- Oxy-fuel combustion is an advanced combustion technology in which fuel is burned using pure oxygen (O₂) or an oxygen-rich mixture instead of regular air. Traditional combustion uses atmospheric air, which contains about 78% nitrogen and only 21% oxygen. In oxy-fuel combustion, nitrogen is largely eliminated from the process, resulting in a flue gas primarily composed of carbon dioxide (CO₂) and water vapor (H₂O). This streamlined gas composition significantly simplifies CO₂ capture and storage (CCS), making oxy-fuel combustion a powerful tool for reducing greenhouse gas emissions from industries and power plants.
- The primary goal of oxy-fuel combustion is to enhance the efficiency of carbon capture. In standard combustion, the nitrogen in air absorbs heat and contributes to the formation of pollutants like nitrogen oxides (NOₓ). By removing nitrogen from the combustion environment, oxy-fuel systems not only reduce NOₓ emissions but also produce a concentrated stream of CO₂ that can be easily separated and compressed for sequestration or utilization. This makes the process particularly attractive for industries seeking to comply with strict environmental regulations and decarbonize their operations.
- Because pure oxygen produces much higher flame temperatures than air, oxy-fuel combustion systems typically recycle a portion of the flue gas back into the combustion chamber. This recycled flue gas, primarily consisting of CO₂ and water vapor, acts as a thermal ballast, helping control the flame temperature and maintain operational safety and equipment integrity. This process is known as flue gas recirculation (FGR) and is crucial for adapting oxy-fuel combustion to existing boilers and furnaces.
- Oxy-fuel combustion can be applied in various sectors, including coal-fired power generation, cement production, glass manufacturing, and steelmaking—all of which are major sources of CO₂ emissions. For example, in a coal-fired power plant retrofitted for oxy-fuel combustion, the coal is burned in a mixture of oxygen and recycled flue gas, resulting in a flue stream from which CO₂ can be readily separated, purified, and either stored underground (geological sequestration) or utilized in processes like enhanced oil recovery or synthetic fuel production.
- Despite its advantages, oxy-fuel combustion faces several challenges. The most significant is the cost and energy demand of oxygen production, which typically involves cryogenic air separation units (ASUs). These systems are capital-intensive and consume substantial energy, potentially reducing the overall efficiency of the power plant or industrial process. Researchers are exploring more efficient oxygen production methods, such as membrane separation or chemical looping, to make oxy-fuel combustion more economically viable.
