Reducing the recycle flue gas rate of an oxy-fuel utility power boiler Haining Gao ⇑ , Allan Runstedtler, Adrian Majeski, Robert Yandon, Kourosh Zanganeh, Ahmed Shafeen CanmetENERGY, Natural Resources of Canada, 1 Haanel Drive, Ottawa K1A 1M1, Canada highlights  Studied concepts to manage temperature at reduced recycle flue gas rate.  Acceptable temperature could be achieved with 55% flue gas recycling.  Used additional heat transfer surfaces, reduced inlet gas temperature.  Also used novel firing strategies to manage furnace temperature.  The heat transfer through the radiant areas is increased at reduced flue gas rate.  The heat flux on the furnace walls is higher at reduced recycle flue gas rate. article info Article history: Received 9 May 2014 Received in revised form 12 September 2014 Accepted 19 September 2014 Available online 16 October 2014 Keywords: Oxy-fuel Recycle flue gas CFD Utility boiler abstract Oxy-fuel combustion is a technology for capturing CO 2 from coal fired power plants. One drawback of this technology is the need for a large quantity of recycled flue gas (RFG) to avoid excessively high tempera- tures inside the furnace. Instead of only using RFG to manage flue gas temperature, this paper presents and evaluates the concept of using additional heat transfer surfaces in the boiler furnace, reduced incom- ing gas temperature and combustion control technologies to manage the flue gas temperature in an oxy- fuel boiler with reduced RFG rate. A 1000 MW e ultra-supercritical coal fired utility power boiler was modified using these concepts and studied using a computational fluid dynamics (CFD) model. The com- bustion, temperature, and heat transfer characteristics of the boiler were compared for three cases: (i) standard air combustion mode, (ii) conventional oxy-fuel combustion mode recycling 72% of the exhaust flue gas, and (iii) the novel oxy-fuel boiler concept recycling 55% of the exhaust flue gas. It is shown by the CFD results that the modified 1000 MW e boiler could achieve an acceptable temperature level in its fur- nace while recycling 55% of total exhaust flue gas in spite of an increase in predicted temperature level. The predicted heat transfer through the radiant heat transfer areas of the modified boiler, including the furnace walls and platen super heater is significantly increased. Some heat transfer surfaces traditionally arranged in the convective heat transfer sections would need to be arranged inside furnace as radiant heat transfer surfaces for operation at oxy-fuel combustion mode with reduced RFG rate. The predicted heat flux on the furnace walls of this boiler is higher than that of a commercial air-fired boiler and of a conventional oxy-fuel boiler, although not higher than that of oil-fired utility power boilers. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Oxy-fuel combustion is one of the promising technologies for CO 2 capture in the utility power industry. During oxy-fuel combus- tion, pulverized coal is burned in a mixture of nearly pure O 2 and the recycled flue gas (RFG, mainly CO 2 ), leading to an exhaust gas with very high CO 2 concentration, ready for storage after conditioning. Burning coal in pure O 2 would result in an extreme temperature in a boiler furnace, which would cause tube failures of the furnace walls and serious slagging problems on the furnace walls when burning low ash fusion temperature coals. Burning coal in pure O 2 would also lead to an increase in furnace outlet temperature (FOT) at the entrance of the close-spaced convective heat transfer surfaces, which may cause excessive ash accumulations on the sur- faces. Many researchers have been trying to achieve similar tem- peratures and heat transfer distributions in oxy-fuel combustion utility power boilers compared to commercial air combustion units [1–6], where the idea is to utilize the existing technologies and designs of conventional air combustion boilers and make the unit workable at both air combustion mode and oxy-fuel combustion http://dx.doi.org/10.1016/j.fuel.2014.09.065 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Fuel 140 (2015) 578–589 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel