Ash-related issues during biomass combustion: Alkali-induced slagging, silicate melt-induced slagging (ash fusion), agglomeration, corrosion, ash utilization, and related countermeasures

Corrosion in biomass combustion: A materials selection analysis and its interaction with corrosion mechanisms and mitigation strategies

Externally fired gas turbine technology: A review

The fate of chlorine during MSW incineration: Vaporization, transformation, deposition, corrosion and remedies

Under CO2 exposure at an intermediate temperature, typically 550 °C, 9Cr–1Mo steel forms a duplex oxide scale made of an outer magnetite layer and an almost-as-thick inner Fe–Cr rich spinel oxide layer It is proposed that the inner Fe–Cr spinel layer grows according to a mechanism involving void formation at the oxide/metal interface The driving force for pore formation is the outward magnetite growth: iron vacancies are injected at the oxide/metal interface then condense into voids The fresh metallic surface made available is then oxidized by CO2, which diffuses fast through the scale The physical aspects, the integrity and the nature of the scale are shown to be very dependent on the oxygen potential existing in the environment

Corrosion of 9Cr steel in CO 2 at intermediate temperature I: Mechanism of void-induced duplex oxide formation

Metallic and intermetallic coatings are widely used in jet engines and land-based gas turbines for oxidation and corrosion protection in the hotter parts of the engines. However there is a significant number of industrial processes where the use of protective coatings at high temperatures could contribute to a significant extension of life-time or an increase in operation temperature and thus efficiency. Examples of such industries are incineration and gasification of waste, biomass and coal, chemical process industries and petrochemical plants where highly aggressive environments are encountered containing species of e.g. carbon, chlorine, sulphur, vanadium or alcalines. Since most of these process environments contain only very low oxygen partial pressures or exhibit high concentrations of extremely aggressive compounds, the conventional, uncoated materials come to their limits. In recent years in laboratory work a number of new types of coatings have been developed for high-temperature applications which include diffusion coatings, overlay coatings and nanotechnological approaches for sealing porosity. In the paper the background of this development and the thermodynamic fundamentals are discussed together with some more recent solutions based on synergistic effects of multi-element coatings. Some results of performance tests of these coatings in sulfidizing, carburizing, chloridizing and vanadate environments will be presented. At the end conclusions can be drawn on the suitability of the different types of coatings for their specific applications.

Development of coatings for protection in specific high temperature environments

Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 °C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic-martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe 2 Al 5 or FeAl phases were thus developed for deposition temperatures between 650 and 715 °C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe 2 Al 5 coatings at 550 °C. Furthermore, Si or codiffusion Al-Si coatings were developed at temperatures as low as 550 °C.

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

The reduction of emissions from power generation plants is a key part of the Kyoto Protocol Reduced emissions per unit of power produced can be achieved via increased thermal efficiency and this can be achieved by increasing steam parameters (ie temperature and pressure) Increased steam parameters in turn leads to accelerated corrosion of boiler components Biomass and solid waste fuels introduce a number of aggressive species into process environments that result in enhanced rates of boiler degradation This paper reports on studies, both theoretical and experimental, of the corrosion behaviour of high-alloy steels and Ni-base alloys as well as coatings for use in high efficiency coal and/or biomass- and waste-fired power plants



Coatings produced within the SUNASPO project have been laboratory tested in gaseous atmospheres representative of coal combustion, biomass combustion and waste incineration Laboratory tests were carried out mainly in the temperature range 500 °C to 800 °C Initial results showed the poor performance of traditional uncoated low-alloy boiler steels P91 (9% Cr) and HCM12A (12% Cr), as well as the higher alloy steel, 17Cr/13Ni Results show the beneficial effects of coatings containing Al, Si, Al + Si, Al + Ti and Al + B in reducing the rate of corrosive attack In a combustion product gas containing 100 ppm HCl and 1000 ppm SO2, aluminizing affords corrosion resistance of low-alloy steels such as HCM12A and P91 similar to that of Alloy 800 over 1000 h of test The presence of Al inhibits internal, sometimes localized corrosion by promoting the formation of a protective surface oxide layer even at relatively low temperatures The results of experiments in simulated coal; biomass and waste atmospheres are presented and discussed in terms of both corrosion kinetics and mechanisms of degradation

Gaseous corrosion of alloys and novel coatings in simulated environments for coal, waste and biomass boilers

There is a need to develop cleaner electric power systems, with reduced emission of pollutants. This implies an increase in the maximum temperature of heat exchanger tubes, which is now, 600°C in modern power plants. For conventionally used ferritic steels, this increase is limited by the steels' mechanical properties and their corrosion resistance in coal, waste or biomass fired environments. Austenitic steels and nickel based alloys are potential candidates for increasing performance at higher temperature (700°C. Nonetheless, the corrosion resistance of these materials could be improved even further by applying a coating. Pack cementation is one of the easiest and cheapest coating processes. However, it requires a heating step which is presently performed at a minimum temperature of 750–800°C. The microstructure of the material may be significantly changed at these temperatures during the coating process, especially for ferritic–martensitic steels. Since the microstructure dictates the mechanica...

Diffusion coatings for heat exchanger materials

The oxidation behaviour of several commercial alloys in simulated steam was investigated and compared with that of model alloys with systematic variations of selected alloying elements in the temperature range of 550' C to 650 °C Also, creep tests of specimens pre-oxidized in steam or in flue gas were carried out in order to study the interaction between creep and corrosion The corrosion products were characterised by optical microscopy, XRD, SEM/ EDX and Raman spectroscopy It was found that the oxidation resistance of the materials increased with increasing chromium content High chromium materials exhibited the best oxidation behaviour, whereas the low chromium materials formed thick, multilayered oxide scales, prone to spallation Anomalous temperature dependences were found in materials with intermediate chromium contents Creep tests showed a significant reduction in the creep strength of both alloys was caused by a 1000 h thermal exposure treatment at 650 °C for P92 and at 800 °C for Alloy 800 An additional, though much smaller reduction in strength was observed for the specimens that had been oxidized for 1000 h at 650 or 800 °C prior to testing Further testing is required for confirmation of this effect

V. Rohr

Papers

Development of coatings for protection in specific high temperature environments

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

Gaseous corrosion of alloys and novel coatings in simulated environments for coal, waste and biomass boilers

Diffusion coatings for heat exchanger materials

Steam oxidation and its potential effects on creep strength of power station materials