Topics in Oxy-Coal Retrofit of Utility Boilers - Burner Principles and Fire-Side Corrosion

摘要

Application of oxy-firing to existing power plants presents unquantified challenges as the characteristics of oxy-firing compared to air-firing have not yet been fully determined. Among the outstanding issues are the operation of oxy-coal burners and firing system within an air-fired utility boiler and fireside corrosion of waterwall and superheat tube metal surfaces. Results are presented from an experimental program where a 1.2 MW oxy-coal research burner was fired under air and oxy conditions in a pilot-scale furnace. The dependence of flame characteristics on primary velocity, O2 concentration and mixing strategy are evaluated by evaluating flame shape and stabilization location. Ignition delay in oxy-coal flames was overcome by a 13% reduction in primary velocity. A stable and attached flame was achieved with no oxygen enrichment of the coal carrying gas. Oxygen injection at the burner face was most effective when introduced on the boundary between the primary and inner secondary gas streams. The corrosion rates of materials typical of coal-fired US utility boilers have been measured through implementation of a real-time electrochemical noise sensing technique for both air- and oxy-fired conditions. Materials chosen for this investigation include SA210 for the waterwalls and T22, P91 and 347H for the superheater. Waterwall corrosion rates decreased when converting from air to oxy-firing for all coals. Superheater corrosion rates increased when converting from air- to oxy-firing for most conditions tested. Corrosion rates for the lower alloyed materials (SA210 and T22) were shown to increase drastically during transients from reducing to oxidizing conditions when air-firing and from oxidizing to reducing conditions when oxy-firing. The presence of trisulphates strongly increases the corrosion rate of the 347H material under high sulfur and low temperature conditions.