1、STP-PT-066DESIGN GUIDELINES FOR CORROSION, EROSION AND STEAM OXIDATION OF BOILER TUBES IN PULVERIZED COAL-FIRED BOILERSSTP-PT-066 DESIGN GUIDELINES FOR CORROSION, EROSION AND STEAM OXIDATION OF BOILER TUBES IN PULVERIZED COAL-FIRED BOILERS Prepared by: W. R. Livingston Doosan Babcock Ltd. Colin Davi
2、s E.ON New Build Also Shown Are Plant Data From the Literature 127 Figure 4-17: Comparison of the Predicted Values of Inner Oxide Thickness for Alloys T22, T23, T91, T91 and T122 at 725, 1,450, and 2,120 psi at 1022F (50, 100, and 146 bar at 550C) 128 Figure 4-18: Comparison of the Predicted Values
3、of Inner Oxide Thickness for Alloys T22, T23, T91, T91 and T122 at 725, 1,450, and 2,120 psi for 1112F (50, 100 and 146 bar for 600C) . 129 Figure 4-19: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for Alloy T23 at 192 Bar Over a Range of Temperatures. Also Shown, As Indivi
4、dual Points, Are Plant Data from the Literature 37 . 130 Figure 4-20: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for T91 at 3,630 psi (250 bar) Over a Range of Temperatures. Also shown, As Individual Points, Are Plant Data from the Literature 38 131 Figure 4-21: A Compari
5、son of the Predicted Values of Inner Oxide Thickness (Curves) for T92 2,800 psi (192 Bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Literature 39 . 131 Figure 4-22: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) For E911 at 2,700
6、psi (186 Bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Literature 40 132 Figure 4-23: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for HCM9M at 2,785 psi (192 Bar) Over a Range of Temperatures. Also Shown, As Individual Points,
7、 Are Plant Data from the Literature 37 132 Figure 4-24: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for HCM12 at 2,785 psi (192 Bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Literature 37 133 STP-PT-066: Design Guidelines for
8、Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal-Fired Boilers vii Figure 4-25: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for T122 at 2,785 psi (192 Bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Lite
9、rature 37 133 Figure 4-26: A Comparison of the Predicted Values of Inner Oxide Thickness (Curves) for 1714CuMo at 4,496 psi (310 bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Literature 41 134 Figure 4-27: A Comparison of the Predicted Values of Inner O
10、xide Thickness (Curves) for X3CrNiMoBN 17-13-3 at 2,700 psi (186 Bar) Over a Range of Temperatures. Also Shown, As Individual Points, Are Plant Data from the Literature 40 . 134 Figure 4-28: Contour Plot Example for Alloy T22 at 1022F (550C) Showing the Predicted Inner Oxide Thickness as a Function
11、of Time and Pressure . 135 STP-PT-066: Design Guidelines for Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal-Fired Boilers 1 FOREWORD This report provides a development of design rules for advanced power plant boilers that pertain to fireside corrosion, erosion and steam ox
12、idation of boiler tubes. These boilers will operate at advanced steam conditions, include discussion of CO2 capture and contain co-firing of biomass or waste materials. The authors acknowledge, with deep appreciation, the activities of ASME ST-LLC and ASME staff and volunteers who have provided valu
13、able technical input, advice and assistance with review of, commenting on, and editing of, this document. Established in 1880, the American Society of Mechanical Engineers (ASME) is a professional not-for-profit organization with more than 135000 members and volunteers promoting the art, science and
14、 practice of mechanical and multidisciplinary engineering and allied sciences. ASME develops codes and standards that enhance public safety, and provides lifelong learning and technical exchange opportunities benefiting the engineering and technology community. Visit www.asme.org for more informatio
15、n. The ASME Standards Technology, LLC (ASME ST-LLC) is a not-for-profit Limited Liability Company, with ASME as the sole member, formed in 2004 to carry out work related to new and developing technology. The ASME ST-LLC mission includes meeting the needs of industry and government by providing new s
16、tandards-related products and services, which advance the application of emerging and newly commercialized science and technology and providing the research and technology development needed to establish and maintain the technical relevance of codes and standards. Visit www.stllc.asme.org for more i
17、nformation. STP-PT-066: Design Guidelines for Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal-Fired Boilers 2 PART ONE - DESIGN GUIDELINES FOR PULVERIZED COAL BOILERS STP-PT-066: Design Guidelines for Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal
18、-Fired Boilers 3 1 GENERAL OVERVIEW The purpose of this document is to provide a set of Design Guidelines for boiler design engineers and others aimed at the minimization of the effects of fireside corrosion, particle impact erosion and steam-side oxidation on boiler tubing and other components of l
19、arge, pulverized coal-fired boilers. Particular emphasis is placed on the boiler components considered to be at highest risk in advanced supercritical and ultra-supercritical boilers, i.e. the superheater and reheater tubing operating at metal surface temperatures up to approximately 1350F (730C). M
20、odern coal-fired steam power plants are required to incorporate the relevant advances in technology to improve efficiency and maximize power generated per unit of coal burned, and hence reduce the overall emissions of CO2. They should also be fitted with advanced combustion technologies and environm
21、ental control equipment to comply with mandated limits on the release levels of the prescribed pollutant species to air, land and water. The pressure part materials are required to have the relevant high-temperature strength capabilities, and the heat transfer surfaces are exposed to increasingly ag
22、gressive hot flue gases. The available alloys are increasingly required to operate near to the limits of their capabilities. The boilers are also expected to have the capability of cyclic operation, and pressure parts are required to have the minimum possible wall thickness, to minimize thermal fati
23、gue. It is increasingly important, therefore, that the minimum tube dimensions, calculated according to the ASME Boiler dfw = metal thickness loss due to furnace wall corrosion; dsh = metal thickness loss due to superheater/reheater corrosion; der = metal thickness loss due to erosive wear. STP-PT-0
24、66: Design Guidelines for Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal-Fired Boilers 5 2 CORROSION - FIRESIDE OF BOILER TUBES 2.1 Technical Background The incidence of significant metal wastage due to accelerated fireside corrosion of boiler tubes has been a practical is
25、sue of some importance in coal-fired utility boilers for many years. The boiler design rules and design features that were introduced in the 1950s and 1960s, in response to corrosion problems associated with increases in boiler capacity and final steam temperatures at that time, have proved to be re
26、asonably successful in containing the incidence of excessive corrosion losses. However, a number of current and future developments, associated principally with improvement of the environmental performance of coal-fired power plants, and the imperative to reduce the CO2 emission levels, are changing
27、 this position somewhat, viz: The introduction of primary NOx emission control technologies to large coal-fired boilers, which has involved the installation of air-staged, low-NOx burners and the operation of a portion of the furnace volume under reducing conditions, has led to an increase in the in
28、cidence of excessive rates of furnace wall tube wastage. This has been associated with increases in the incidence of flame impingement and the presence of the gaseous and solid products of sub-stoichiometric coal combustion local to the furnace walls. The operation of boilers at minimum excess air l
29、evels for NOx emission control also tends to increase the flue gas temperatures at the furnace exit and hence to increase the superheater metal temperatures, and can alter the balance of heat absorption through the boiler. The interest within the industry in the design of coal-fired utility boiler p
30、lants capable of producing steam at increasingly-higher temperatures and pressures, and hence generating electricity at higher efficiency levels, has led to an interest in new materials for high-temperature components that can operate at these advanced conditions. The co-firing of non-conventional f
31、uels in boilers designed for coal firing has resulted in significant changes in the chemistry of the ash deposits on the heat exchanger surfaces in the furnace and the convective section, commonly with increased levels of alkali metal sulfates and chlorides. This has led to a number of instances whe
32、re excessive corrosion rates have been reported. Current developments in the oxy-fuel firing of coal-fired boilers, to facilitate CO2 capture and sequestration, has resulted in an increasing interest in the operation of boiler plants with advanced steam conditions, and with relatively high flue gas
33、concentrations of CO2 and H2O and of the more important acid gas species, principally SO2/SO3 and HCl. These flue gas compositions are significantly outside the ranges for which there is relevant plant experience, and there are risks of excessive corrosion rates. 2.2 Furnace Wall Corrosion Extensive
34、 plant experience over many decades has indicated that good combustion control and the maintenance of oxidizing conditions at the furnace walls tend to promote the growth of a thin, protective oxide scale on the fireside surface of furnace wall tubing that will tend to limit further corrosion. On th
35、e other hand, poor combustion conditions, i.e. reducing conditions and fluctuating oxidizing-reducing atmospheres local to the walls, have been implicated in the incidence of accelerated furnace wall tube corrosion, particularly when firing coals with high sulfur contents. In general terms, it has b
36、een found that operation with localized CO concentrations at the furnace wall in excess of 2-3% is considered to be undesirable. The effects of the furnace soot blowers and water cannons in removing ash deposits and exposing the furnace surfaces to higher temperatures and to particle impact erosion,
37、 in addition to the corrosive attack, also may act to increase the metal wastage rates. STP-PT-066: Design Guidelines for Corrosion, Erosion and Steam Oxidation of Boiler Tubes in Pulverized Coal-Fired Boilers 6 At the boiler design stage, it is clear that ensuring that the furnace has sufficient vo
38、lume to contain the flames or the fireball, and that the wing burner-side wall clearances in wall-fired plants are sufficient, will help prevent flame impingement. The use of curtain air supplies to protect certain vulnerable areas of the furnace wall surface in the burner region is also considered
39、by some designers to be of benefit, but this inevitably involves the introduction of additional air to the furnace, and this may be incompatible with the optimization of low-NOx firing systems. There is no evidence to date to suggest that furnace wall wastage rates are higher under oxy-fuel firing c
40、onditions which are, in some cases, associated with significantly higher levels of acid gases in the recirculated flue gas streams, than are present from air firing. It should be noted, however, that plant experience of oxy-fuel firing is limited. 2.2.1 Predictive Methods for Furnace Wall Corrosion
41、A number of methods for the prediction of the rates of corrosion of furnace wall tubes have been proposed. These are based principally on the results of laboratory corrosion experiments or of measurements of metal loss rates on plant. While satisfactory predictions of corrosion rates for combustion
42、conditions where low-NOx firing is not practiced have been made, models for corrosion under low-NOx firing conditions commonly incorporate parameters that are not readily available, such as the CO or H2S levels in the combustion gas near the furnace walls. As a result, it is fair to say that, at the
43、 present time, there is no general consensus within the industry as to which of the available models provides the most reliable approach. A number of corrosion models have been incorporated into Computation Fluid Dynamics (CFD) codes in an attempt to provide predictions of the localized metal wastag
44、e rates. EPRI, for instance, has made use of both pyrite deposition and chloride corrosion models with CFD models to provide predictions of the metal wastage distributions within several power plant boilers burning coals containing a range of sulfur and chlorine concentrations. Models of this type d
45、iffer principally in the way that they attempt to quantify heat flux variations in the boiler and the severity of reducing conditions that apply at the furnace walls. Clearly, there are important differences in the technical basis of the available predictive models of the corrosion process, and in t
46、he approach to validation of the models. It is difficult at the present time to recommend a preferred predictive method with any confidence. 2.2.2 Remedial Measures for Furnace Wall Corrosion The remedial measures available for the control of furnace wall corrosion are based either on operational ch
47、anges or on materials solutions. The implementation of remedial measures based on operational changes may include the following activities: There may, in some cases, be scope for the improvement of the coal mill performance, of the pulverized coal and air distributions to the burners, or for the mod
48、ification of the burner settings to alter the flame conditions. These actions may help to move the flames away from the furnace side or rear walls, and reduce the impact of flame impingement on the furnace surfaces. Diagnostic techniques, such as the use of sniffer ports to permit sampling and analy
49、sis of the combustion gases (including CO, O2, H2S, etc.) local to the walls, or the use of corrosion probes inserted through the furnace wall membrane to provide an estimate of the corrosion rates at the conditions that apply at the walls, can be of assistance in this context. In some cases, where there is localized corrosion of furnace wall surfaces due to reducing conditions, it may also be appropriate to retrofit the boiler with a curtain air supply, which is injected local to the furnace wall, and which can be effective in reducing the extent
