Benefits and Optimizations of Oxyfuel Combustion

Oxyfuel combustion provides an attractive alternative for decarbonization of fired process heaters used in steam cracking units. In Oxyfuel, fuel is combusted with high purity oxygen from an air separation unit (ASU) rather than combustion air to significantly reduce inert nitrogen in the resultant flue gas. In Oxyfuel combustion, a portion of the flue gas is recycled back to the fired heater to reduce the oxygen concentration and obtain combustion and heat transfer characteristics similar to conventional combustion air to minimize the impact on furnace design. The significant reduction of nitrogen in flue gas from Oxyfuel increases the CO₂ concentration approximately ten times and reduces the volume of flue gas product by an order of magnitude. The higher concentration of CO₂ in the flue gas requires purification to remove water, excess oxygen required for efficient combustion, and trace inert nitrogen with a CO₂ purification unit. Within the CO₂ purification unit, either gaseous CO₂ or liquid CO₂ can be produced. With liquid CO₂, pumping to supercritical pressures can be achieved with lower overall power requirements compared to CO₂ compression. In this paper the application of Oxyfuel combustion for steam cracking unit heaters, oxygen requirements from the ASU, and considerations for the CO₂ purification unit will be discussed