Corrosion behavior of 15CrMo steel for water-wall tubes in thermal power plants in the presence of urea and its byproducts

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Zhiping Zhu ◽  
Xianzhi Song ◽  
Youwei Song ◽  
Pan Zhou ◽  
Mingpeng He
Keyword(s):  
Corrosion Behavior ◽  
Power Plants ◽  
Thermal Power ◽  
Electrochemical Analysis ◽  
Urea Concentration ◽  
Localized Corrosion ◽  
Urea Solution ◽  
X Ray Diffraction ◽  
Water Wall ◽  
Urea Decomposition

AbstractThe corrosion behavior of 15CrMo used for water-wall tubes was studied in various urea-containing solution to determine the corrosion problem of water-wall tubes caused by urea in a coal-fired power plant. Urea decomposition tests, together with corrosion experiments, were carried out. The temperature was 320 °C, and the concentrations of urea were 70, 140, 280, 560 and 840 mg/L. Weight loss experiments and surface analysis indicated that the corrosion of 15CrMo steel is mainly manifested as localized corrosion. The corrosion rate of 15CrMo steel increased with the increase of urea concentration, and the maximum value reached 0.686 mm/y (mm per year) when the urea concentration was 840 mg/L. Electrochemical analysis suggested that the corrosion rates of 15CrMo were enhanced substantially by urea decomposition products. The results of UPLC-ESI-MS, infrared spectroscopy and X-ray diffraction showed that urea solution produced corrosive ions NH2COO− during the decomposition process, which caused the corrosion of 15CrMo. Results provided evidence as relevant explanation for the corrosion behavior of 15CrMo in urea solution.

scholarly journals The issue of improving the efficiency of nitrogen oxide neutralization systems in diesel internal combustion engines

2021 ◽  
Vol 1 (2) ◽  
pp. 101-112
Author(s):  
A.V. Shabanov ◽  
◽  
D.V. Kondratiev ◽  
V.K. Vanin ◽  
A.Yu. Dunin ◽  
...  
Keyword(s):  
Nitrogen Oxides ◽  
Internal Combustion Engine ◽  
Power Plants ◽  
Internal Combustion Engines ◽  
High Efficiency ◽  
Combustion Engine ◽  
Thermal Power ◽  
Internal Combustion ◽  
Urea Solution ◽  
Exhaust Gas

The most effective method of reducing nitrogen oxides in diesel exhaust gas is selective purifica-tion by the SCR-NH3 method. The method uses ammonia released during thermolysis and hydroly-sis of a urea solution when it is injected through a nozzle into a neutralizer. This method has a rela-tively low efficiency of cleaning the exhaust gas from nitrogen oxides. The main factor hindering the achievement of high efficiency of the NOx neutralization system is the insufficiently high tem-perature during the implementation of this process. The article analyzes various ways to increase the efficiency of the neutralization process and proposes a new method for neutralizing NOx by using urea injection into the cylinders of the inter-nal combustion engine at the expansion stroke in a diesel internal combustion engine. Efficiency can be achieved due to a higher exhaust gas temperature in the cylinder of the internal combustion engine and an increase in the time of the process of thermolysis and hydrolysis of urea. The kinetics of the decomposition of nitrogen oxides, the process of NH3 oxidation, and the cal-culation of temperature conditions in the cylinder of a diesel internal combustion engine at the ex-haust cycle are considered. The experience of neutralization of NOx contained in the flue gases of thermal power plants, where NOx purification takes place at high temperatures without the use of a catalyst, is analyzed. It is shown that the modernization of the SCR-NH3 process, due to the injection of urea at the exhaust stroke in a diesel internal combustion engine, will simplify the existing method of NOx neutralization and at the same time obtain additional advantages for a modern high-speed engine

Experimental Analysis of Hot Corrosion Behaviour of some Composite Coatings on Boiler Steel at Elevated Temperature

2021 ◽  
Vol 41 ◽  
pp. 43-54
Author(s):  
Prince Puri ◽  
Khushdeep Goyal ◽  
Rakesh Goyal ◽  
Bal Krishan
Keyword(s):  
Hot Corrosion ◽  
Power Plants ◽  
Corrosion Behaviour ◽  
Composite Coatings ◽  
Thermal Power ◽  
Tube Steel ◽  
X Ray Diffraction ◽  
Boiler Steel ◽  
Boiler Tube Steel ◽  
Silicon Tube

Hot corrosion is the main reason of failure of boiler tubes used at high temperature in thermal power plants. This paper is an attempt to investigate the effect of different composite coatings on boiler tube steel in corrosive environment of Na2SO4 – 60%V2O5 at 900°C for 50 cycles. The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with weight change statistics, X-ray diffraction, and scanning electron microscopy. It is found that 100Cr3C2 composite coatings provided the higher resistance to corrosion as compared to other types of coatings. Cr carbide layer was formed on the surface and these layers provided the protection from hot corrosion.

scholarly journals Mössbauer and X-ray Studies of Phase Composition of Fly Ashes Formed after Combustion of Ekibastuz Coal (Kazakhstan)

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 929
Author(s):  
Adilkhan Shokanov ◽  
Mikhail Vereshchak ◽  
Irina Manakova
Keyword(s):  
Phase Composition ◽  
Power Plants ◽  
Thermal Power ◽  
Hyperfine Interactions ◽  
Mixed Valence ◽  
X Ray Diffraction ◽  
Fly Ashes ◽  
Environment Effect ◽  
X Ray ◽  
Magnetite Fe3o4

Mössbauer spectroscopy and X-ray diffraction have been used to study samples of fly ashes formed after combustion of coal from the Ekibastuz basin at the thermal power plants TPP-2 and TPP-3 in Almaty (Kazakhstan). It has been established that the fractions of fly ashes contain iron in the form of magnetite Fe3O4 and hematite α-Fe2O3. The mixed valence of iron Fe3+ ↔ Fe2+ in the octahedral sublattice of magnetite is destroyed by isostructural substitution impurities. Maghemite γ-Fe2O3 is additionally present in the fly ash of TPP-3 as a product of magnetite slow oxidation. It was shown that at T ≥ 1400 °C the proportion of magnetite in fly ashes increases due to decomposition of hematite, maghemite, hercynite and the drop of iron content in mullite. It was concluded that the amount of iron in magnetite is a temperature indicator of fly ashes formation. The parameters of hyperfine interactions have been determined in the iron-containing minerals of fly ashes. It was identified that formation of the fly ashes structure occurs in oxidizing atmosphere, since no traces were revealed of reducing environment effect on the phase composition.

scholarly journals Economizer water-wall damages initiated by feedwater impurities

2014 ◽  
Vol 68 (5) ◽  
pp. 559-563 ◽  
Author(s):  
Sonja Vidojkovic ◽  
Antonije Onjia ◽  
Aleksandar Devecerski ◽  
Nebojsa Grahovac ◽  
Aleksandra Nastasovic
Keyword(s):  
Power Plants ◽  
Thermal Power ◽  
Plant Stress ◽  
Electric Energy ◽  
X Ray Diffraction ◽  
Reliable Operation ◽  
Water Steam ◽  
Magnetite Layer ◽  
The Cost

The main causes of efficiency loss in thermal power plants are boiler tube failures that diminish unit reliability and availability, and raise the cost of the electric energy. For that reason, regular examination of boiler tubes is indispensable measure for prevention future malfunctions of power units. Microscopic examination of economizer inner wall microstructure, analysis of chemical composition of deposit using x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) has been performed in a subcritical power plant. Stress corrosion cracking, pitting corrosion, destroyed protective magnetite layer, presence of magnetite and hematite in deposit and corrosive impurities within the cracks were indicated the effect of inadequate quality of feedwater that can not entirely ensure reliable operation of the boiler. It may be stated that maintenance of present boiler does not provide its reliable operation. Extensive chemical control of water/steam cycle was recommended.

scholarly journals Effect of Manganese on Microstructure and Corrosion Behavior of the Mg-3Al Alloys

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 460 ◽  
Author(s):  
Yao ◽  
Liu ◽  
Zeng ◽  
Li ◽  
Lei ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Corrosion Behavior ◽  
Galvanic Corrosion ◽  
Intermetallic Phase ◽  
Localized Corrosion ◽  
Experimental Investigations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electrochemical Tests ◽  
Microstructure Observation

Microstructure and corrosion behavior of the Mg-3Al-xMn (x = 0, 0.12, 0.21, 0.36, 0.45) (hereafter in wt.%) alloys were experimentally investigated by electron probe microanalysis (EPMA), scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electrochemical, and hydrogen evolution tests. A new self-constructed Mg-Al-Mn-Fe thermodynamic database was used to predict the solidification paths of the alloys. The addition of Mn showed no grain refinement in the cast Mg-3Al alloys. According to the microstructure observation, Al-Fe phases were observed in the non-Mn-added alloy, while Al8Mn5(LT) (Al8Mn5 in low temperature) became the main intermetallic phase in the Mn-added alloys, and the amount increased gradually with the Mn addition. The τ–Al0.89Mn1.11 phase with lower Al/(Fe + Mn) ratio was observed in the alloys with 0.36 and 0.45 wt.% Mn content. According to the electrochemical tests, all five alloys showed localized corrosion characteristics in 3.5 wt.% NaCl solution. Compared with the Mg-3Al alloy, the corrosion resistance of Mn-added alloys were significantly improved and increased gradually with the Mn addition, which was due to the variation of Al-containing intermetallic compounds. The present experimental investigations and thermodynamic calculations confirmed the mechanism that the increasing amount of Al8Mn5(LT) with Mn addition could encapsulate the B2-Al(Mn,Fe) phase with higher Fe. Therefore, it could prevent this detrimental phase from contacting magnesium matrix, thus suppressing micro-galvanic corrosion and improving corrosion resistance gradually.

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