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Supercritical power generation boilers often corrode in 650 °C water vapor. A study on chemical pre-oxidation protection of boiler steel surfaces was conducted to address this problem. Firstly, the TP347H boiler steel was placed in a tubular furnace with a flow rate of 20 mm/s of oxygen and oxidized for 2 h at 300 ℃. The protective effect of the oxide layer on the boiler steel was studied using the gravimetric method. Scanning electron microscope (SEM) was used to observe the surface morphology of the material. Combined with the product composition analysis, the following conclusions were obtained: after 2 h of oxidation at 300 ℃, the thickness of the oxidation layer of TP347H boiler steel could reach 0.2 μm. This oxide layer reduced the corrosion rate of the material in 650 ℃ water vapor by 87.5% compared to the material without pre-oxidation. The corrosion products of the TP347H boiler steel without oxidation after corroded in high temperature water vapor could be divided into two layers: the surface layer was mainly the oxide of Fe, and the bottom layer was the oxide of Fe, Cr, and Ni. The bonding strength between the two layers was poor, and the outer layer products were easy to fall off. After the surface oxidation treatment, the corrosion products of the sample were only a monolayer. The corrosion products were mainly oxides of Fe, Cr and Ni. The bonding strength between the coating and the substrate was good, and the corrosion products were not easy to fall off.

Corrosion in oil-fired boilers is accelerated in the presence of V, Cl and S which derive from low-grade fuels or the environment. 10CrMo9-10 steel is commonly used in such boilers. In order to evaluate the salts corrosion behavior of such low Cr steels, samples were immersed in several vanadate salt combinations of Cl, S, Na and Ca in air at 600 °C. Even during short-term exposure, different dominant corrosion mechanisms could be identified such as active oxidation, sulfidation and acidic or basic fluxing, depending on the exact salt composition. The aggressiveness of the different salt mixtures was ranked with regard to the metal loss. It is also demonstrated that corrosion can be reduced by the addition of a calcium-containing inhibitor. [ABSTRACT FROM AUTHOR]

As superheater header is exposed to high pressure and temperature in power plant boilers, it is one of the most sensitive parts in a power plant.Cracks may form where tubes and main steam outlet (nozzle) are connected to reservoir. This article examines a quarter-circle crack at the corner of a nozzle junction and its propagation steps under the influence of simultaneous interaction of creep and fatigue. Header loading in each cycle includes transient steps (increase and decrease in temperature and pressure) at the beginning and at the end of a cycle and intermediate steady state (fixed pressure and temperature) during operation. For crack growth calculations, stress distribution in a track-free part was calculated. Fatigue–creep crack growth was achieved using crack growth rules and the remaining lifetime was obtained. Research result shows that creep phenomenon is responsible for maximum crack growth. [ABSTRACT FROM AUTHOR]

A failure analysis investigation was carried out on the secondary Superheater tubes of a boiler unit in a steam power plant. The tubes, made of DIN-16CrMo4 steel, failed by bulging and rupture only after about three years of operation. Metallurgical investigations revealed that microstructural degradation had mainly occurred at the external (fireside) tube surface. Long-term overheating was identified as the root cause of the premature failure. [ABSTRACT FROM AUTHOR]

The article analyzes conditions, causes of breakdown, and the main types of corrosion of elements exposed to the greatest wear, and also the classification of breakdowns using oil with different composition in the boilers of the most common designs. Recommendations are made aimed at improving operational reliability and data are provided optimizing planned and preventive boiler maintenance. [ABSTRACT FROM AUTHOR]

Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low grade fuels. In order to avoid vanadate-induced corrosion several ceramic inhibitors and intermetallic coatings and their interaction were studied. Inhibitor ceramics such as CaO and MgO tend to react strongly with vanadium oxides forming vanadates with higher melting temperatures whereas Cr 2 O 3 , Al 2 O 3 , and SiO 2 are the most protective oxides for alloys at high temperatures even in the presence of vanadium pentoxide. Three potential inhibitors were tested on uncoated as well as on Cr, Al, and AlSi diffusion coated 10CrMo9-10 steel by immersion in 60 mol% V 2 O 5 –40 mol% Na 2 SO 4 salt at 650 °C. Materials performance was analyzed by calculating substrate recession rates and by metallographic characterization of the corrosion scales and of the metal subsurface zones so that the mechanism and extent of corrosion could be characterized. In the end different materials combinations (coatings and inhibitors) could be ranked with regard to the detrimental or beneficial role of the different approaches. The present results thus provide a much deeper insight into materials resistance in vanadium-containing environments at boiler simulating conditions than previous studies. [ABSTRACT FROM AUTHOR]

A novel probe has been developed to characterize particles in boilers of waste incineration plants, which are under suspicion to essentially drive the corrosion processes. The probe collects larger particles on impaction plates and smaller particles on membranes, whose deposition characteristics have been studied by computational fluid dynamics. Artifacts by condensation of salt vapors are largely suppressed. The size distribution, morphology and chemical properties of the particles can be investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The probe has been employed for measurements in a waste incineration plant to characterize the aerosol on its way through the boiler. [ABSTRACT FROM AUTHOR]

Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low grade fuels. Several iron-based alloys and a nickel-based alloy were studied in order to verify the effect of different Cr and Al contents under conditions typical for the partial oxidation process. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Samples were exposed to HS-containing syngas atmosphere in order to simulate boiler operating conditions without ash deposition. The prevailing corrosion mechanism under this reducing atmosphere was sulfidation. In order to simulate boiler conditions with oil ash deposits, samples were immersed in 60 mol% VO-40 NaSO salt in the same syngas atmosphere. The prevailing corrosion mechanism in this case was sulfidation under a reducing atmosphere and dissolution of iron or chromium from the substrate. The nickel-based substrate showed the best performance under these experimental conditions. In order to simulate air inlet due to shutdowns, samples were immersed in the same salt during exposure in air. The prevailing corrosion mechanism was still sulfidation in the oxidizing atmosphere accelerated by the presence of vanadate salt. This corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of oxides in the molten deposit, and their precipitation near the outer surface of the deposit. [ABSTRACT FROM AUTHOR]

One way of reducing the furnace wall corrosion is to lower the temperature of the wall by reducing the boiler pressure. To test this, four coupons of 16Mo3 were exposed in the furnace wall of a waste wood fired boiler for 1075 h. The temperatures of the samples were individually controlled in the range 280-410°C. The corrosion rates and corrosion mechanism were investigated. The deposits were analysed by XRD and SEM/EDS. The corrosion fronts were studied by focused ion beam milling (FIB)/EDS. The environment was modelled by Thermo-Calc. The amount of potassium and chlorine in the deposit decreased with decreasing temperature. The FIB sections showed a distinctive iron chloride layer at the corrosion front, with an outer layer of iron oxide. The corrosion rate decreased with decreasing metal temperature, but the boiler pressure needs to be reduced to a low level to achieve this, which is not beneficial for the electrical efficiency and therefore not a viable way of reducing corrosion. [ABSTRACT FROM AUTHOR]

Due to the high-temperature boiler corrosion induced by chloride-rich fly ash deposits, steam generation in today's Waste-to-Energy (WtE) plants is typically designed only for 40 bar/400 °C as an economic compromise between acceptable corrosion rate and maximum power generation. The high-corrosive metal chlorides in the fly ash can react with SO forming low-corrosive sulfates. The sulfation efficiency is enhanced by high SO levels and sufficient residence time of the flue gas at high-temperatures (700-900 °C). The fly ash sulfation was tested in full scale in a Swedish WtE plant by applying the economic sulfur recirculation method. Probes of several alloys (16Mo3, Inconel 625, Sanicro 28) were exposed for 1000 h at controlled material temperatures in the superheater position, at normal and during sulfating operation respectively. Analyses of the fly ash showed that the molar Cl/S was decreased to values well below 1 and the corresponding corrosion rates of the individual material samples were less than half when sulfur recirculation was in operation. These positive findings demonstrate that the sulfur recirculation process has high potential for low-corrosive high-temperature steam generation (T ≈ 500 °C) and improved electricity production. Further steam superheating can be realized by staged superheating using small amounts of secondary fuel. [ABSTRACT FROM AUTHOR]

Highlights: [•] WtE plants are to be optimized beyond current acceptance levels. [•] Emission and consumption data before and after 5 technical improvements are discussed. [•] Plant performance can be increased without introduction of new techniques or re-design. [•] Diagnostic skills and a thorough understanding of processes and operation are essential. [ABSTRACT FROM AUTHOR]

Biomass plants, apart from producing energy, help to reduce CO2(g) emissions. One of the biggest problems for their development is superheater corrosion due to fuel corrosivity, especially of the straw. This limits both the temperature of the vapour and also the effectiveness of the plant. In order to know more about the reactions which happen inside the boiler of biomass, thermodynamic calculations using software (HSC Chemistry) have been carried out. Field tests have been carried out in the Sanguesa Biomass Plant in Navarra (Spain): determination of the types of oxides and the deposits formed on the superheaters tubes as well as a program to measure temperatures. Finally, the global results are discussed. [ABSTRACT FROM AUTHOR]

In an attempt to look at means for reduction of corrosion in boilers, combustion experiments are performed on demolition wood with kaolin as additive. The experiments were performed in a multi-fuel reactor with continuous feed of pellets and by applying staged air combustion. A total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of kaolin addition and other combustion-related parameters. In particular chlorine and potassium distribution between the gas phase, the bottom ash and the fly ash is reported as a function of increased kaolin addition, reactor temperature and air staging. Kaolin addition of 5 and 10% were found to give the least aerosol load in the fly ash. In addition, the chlorine concentration in aerosol particles was at its lowest levels for the same addition of kaolin, although the difference between 5 and 10% addition was minimal. The reactor temperature was found to have a minimal effect on both the fly ash and bottom ash properties. [ABSTRACT FROM AUTHOR]

Improvement of the energy efficiency of waste to energy (WtE) plants demands closer attention to detail in order plant integrity is not compromised. Availability for operation of WtE plants of >90% is a basic requirement to ensure the continuous supply of waste can be managed without the need for excessive storage or unnecessary transport. The drive to increase energy efficiency comes from the need of plant operators to maximise economic income, but also from European targets to meet the challenges of climate change and security of energy supply. Energy efficiency in WtE plants is reviewed based on experiences in Europe. While in the 1990s the emphasis for WtE operators was reducing emissions, more recently major efforts have been made to increase the export of energy. In the main, this has been approached by increasing steam temperature. However, the subsequent rate of corrosion can be catastrophically high and there is thus a need to improve corrosion resistance of heat exchange components to achieve acceptable service lifetimes. Trials have been conducted using more corrosion resistant boiler steels, but the preference is now for use of corrosion resistant coatings and claddings (e.g. alloy 625) to ensure plant reliability. Spray coating and weld cladding techniques are described. Other energy efficiency improvement methods described include online boiler cleaning, inhibiting fouling, achieving complete combustion and optimising flue gas cleaning (to reduce plant internal energy consumption). From what was until recently considered a good net efficiency of electricity production of 18%, measures being taken aim to achieve 30% in the most optimistic case. [ABSTRACT FROM AUTHOR]

Abstract: Failures of industrial boilers have been reported to be mainly due to water side corrosion and scaling. Boiler corrosion is due to highly alkaline or acidic conditions of the boiler water. The present work has been aimed at investigating the corrosion behaviour of T22 (2.25 Cr–1 Mo) boiler steel TIG weldments in neutral and alkaline media. The parent metal and weld root regions are chosen as regions of exposure for the study made at room temperature and at 100°C. Electrochemical polarization technique such as Tafel line extrapolation (Tafel) was used to measure the corrosion current. Corrosion inhibition using thiourea at 100ppm concentration was studied in these experiments. Micro-structural observation and surface characterization using SEM and XRD studies have been made on samples exposed at 100°C. The results show that parent metal experiences higher corrosion rate than weld metal and thiourea as inhibitor is found unsuitable in NaOH medium. [Copyright &y& Elsevier]

When SL Dolly was recovered from Ullswater after being submerged for 67 years, the wrought iron boiler was found to have surprisingly little corrosion. This article describes the results of a project to investigate the reasons for this behaviour and determine whether it was a property of the wrought iron or a consequence of the lakebed environment. Weight loss measurements and electrochemical impedance spectroscopy were used to compare the corrosion rates of wrought iron and modern boiler steel exposed to tap water and samples of lake water and lakebed sediment. A corrosion probe was used to make in situ linear polarisation resistance measurements at the spot where Dolly sank. The corrosion rate of wrought iron on the lakebed was estimated to be in the range 0·018–0·030 mm year-1, which corresponds to a metal loss of 1·2–2·0 mm over the 67 year period; this metal loss is consistent with the condition of the boiler. The effects of microstructure, material composition and water chemistry are considered in detail, and it is concluded that the low oxygen content and the low concentration of dissolved solids in the lake water were the underlying causes of the observed corrosion behaviour. [ABSTRACT FROM AUTHOR]

For the requirements of performance assessment of the thermal power plant control process, the combustion control system of a 330 MW generator unit in a power plant is studied. Firstly, the five variables that affect the process control performance are determined by the mechanism analysis method. Then, a data-driven performance assessment method based on the operational data collection from the supervisory information system was proposed. Using principal component analysis technique, we found that five different variables have different degrees of effect on the performance of the combustion process. By means of qualitative and quantitative analysis, five contribution rates of different variables affecting the performance index of the system were obtained. After that, the data is normalized to the non-dimensional variable, the performance assessment index of the boiler combustion process is defined, and the classification and assessment criterion of it are given. Through using the proposed method on the operation data of the 1# boiler and 2# boiler within 1 day, the performance indexes are calculated and achieved during different time periods. Analysis of the results shows that this method will not generate additional disturbance to the normal operation of the system, and it can achieve a simple, reliable, accurate and rapid qualitative and quantitative analysis of the performance of the boiler combustion control system, and also it can be extended and applied to other multivariable control systems. [ABSTRACT FROM AUTHOR]