Characterization of Oxy-combustion Impacts in Existing Coal-fired Boilers

Abstract

This report summarizes Year 1 results of a research program designed to use multi-scale experimental studies and fundamental theoretical models to characterize and predict the impacts of retrofit of existing coal-fired utility boilers for oxy-combustion. Through the course of Year 1 activities, great progress was made toward understanding the issues associated with oxy-combustion retrofit of coal-fired boilers. All four Year 1 milestones and objectives have been, or will be, completed on schedule and within budget. Progress in the four milestone areas may be summarized as follows: • University of Utah has performed size segregated ash composition measurements in the Oxy-Fuel Combustor (OFC). These experiments indicate that oxy-combustion retrofit may impact ash aerosol mineral matter composition. Both flame temperature and flue gas composition have been observed to influence the concentration of calcium, magnesium and iron in the fine particulate. This could in turn impact boiler fouling and slagging. • Sandia National Labs has shown that char oxidation rate is dependent on particle size (for sizes between 60 and 100 microns) by performing fundamental simulations of reacting char particles. These predictions will be verified by making time-resolved optical measurements of char particle temperature, velocity and size in bench-scale experiments before the end of Year 1. • REI and Siemens have completed the design of an oxy-research burner that will be mounted on University of Utah’s pilot-scale furnace, the L1500. This burner will accommodate a wide range of O2, FGR and mixing strategies under conditions relevant for utility boiler operation. Through CFD modeling of the different burner designs, it was determined that the key factor influencing flame stabilization location is particle heat-up rate. The new oxy-research burner and associated equipment is scheduled for delivery before the end of Year 1. • REI has completed a literature survey of slagging and fouling mechanisms in coal-fired power plants to understand key issues influencing these deposition regimes and infer their behavior under oxy-fired conditions. Based on the results of this survey, an algorithm for integrating slagging predictions into CFD models was outlined. This method accounts for ash formation, particle impaction and sticking, deposit growth and physical properties and impact of the deposit on system flow and heat transfer. A model for fouling in the back pass has also been identified which includes vaporization of sodium, deposition of sodium sulfate on fly ash particles and tube surfaces, and deposit growth rate on tubes. In Year 1, REI has also performed a review of the literature describing corrosion in order to understand the behavior of oxidation, sulfidation, chloridation, and carburization mechanisms in air-fired and oxy-combustion systems. REI and Vattenfall have met and exchanged information concerning oxy-coal combustion mechanisms for CFD simulations currently used by Vattenfall. In preparation for Year 2 of this program, two coals (North Antelope PRB, Western bituminous) have been ordered, pulverized and delivered to the University of Utah and Sandia National Labs. Materials for the corrosion experiments have been identified, suppliers located, and a schedule for equipment fabrication and shakedown has been established. Finally, a flue gas recycle system has been designed and is being constructed for the OFC.