Process Evaluation of Oxy-fuel Combustion with Flue Gas Recycle in a Conventional Utility Boiler

Abstract

In recent years, extensive studies were conducted to understand the potential implementation of oxy-fuel combustion with flue gas recycle in conventional boilers as an effort of mitigating CO2 emissions. The benefits of the technology include reduction of NOx and CO emissions by recycling more than 60% of the flue gas back into the boiler; generation of a flue gas stream with CO2 concentration higher than 90% on a dry basis, which can be easily recovered and stored; and utilization of the conventional boiler with minimum modifications. However, a practical implementation of the technology needs a thorough analysis of the mass and energy balance and their impacts on boiler thermal performance. This paper conducts a detailed process analysis on the oxy-fuel combustion with flue gas recycle in a conventional boiler. Key parameters such as the flue gas recycle ratio, boiler exit oxygen, and flue gas velocity and temperature distributions are investigated. Computational fluid dynamics (CFD) simulations are performed to help the understanding of the oxy-fuel combustion characteristics in a conventional boiler and in a single coal fired low NOx burner. The study shows that the ideal flue gas recycle ratio depends on boiler exit O2 and fuel properties and is generally around 0.7−0.75. Dry flue gas recycle helps to maintain the furnace temperature.