Unusual Application of Plasma Sprayed Coating for Boiler Tubes in Oil-Fired Boilers

1998 ◽  
Author(s):  
K. Tani ◽  
Y. Harada ◽  
Y. Kobayashi
Keyword(s):  
Heat Exchanger ◽  
Hot Corrosion ◽  
Heat Load ◽  
Chemical Cleaning ◽  
Boiler Water ◽  
Combustion Gas ◽  
Water Side ◽  
Boiler Tubes ◽  
Sprayed Coating ◽  
Plasma Sprayed

Abstract The unusual effects of plasma sprayed coating on the fire-side of evaporator tubes located in an oil-fired steam generating boiler are discussed. The main heat transfer surfaces are constructed by heat exchanger tubes, evaporator tubes and superheaters. Maintenance to prevent of the boiler failure or the preserve heat exchanger effectiveness is a very important factor in the operation of boiler facilities. In a boiler which employs heavy gravity oil as a fuel, plasma sprayed Ni-Cr alloy has often been applied to boiler tubes for the relief of hot corrosion by combustion gas. However, the circulation of boiler water causes an internal deposit to form on the inner wall of evaporator tubes. The internal deposit generates excess heat load against the tubes. As the overheating of the tubes often causes the evaporator tubes to fail, they are chemically cleaned periodically. In this paper, the influence of Ni-Cr plasma sprayed coating for the heat flux, which dominates the formation of the internal deposit, is investigated. Ni-Cr plasma sprayed coating is substitutionally hot corrosion resistant and is a composite coating into which the fuel ash containing a vanadium or sulfur compound are interstitially penetrated and solidified. It is derived that the existence of the coating on the fire-side of the evaporator tubes normalizes the heat load in their inner walls. Moreover, the suppression of internal deposit formation decreases the frequency of chemical cleaning for tubes. The dual effects of plasma sprayed coating for hot corrosion resistance in the fire side and the suppression of internal deposit on the water side of the tubes are reported.

scholarly journals Effects of Selective Laser Modification and Al Deposition on the Hot Corrosion Resistance of Ceria and Yttria-Stabilized Zirconia Thermal Barrier Coatings

Coatings ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 353 ◽  
Author(s):  
Panpan Zhang ◽  
Xiaofeng Zhang ◽  
Fuhai Li ◽  
Zhihui Zhang ◽  
Hong Li ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Hot Corrosion ◽  
Molten Salts ◽  
Yttria Stabilized Zirconia ◽  
Air Plasma ◽  
Laser Remelting ◽  
Stabilized Zirconia ◽  
Α Al2o3 ◽  
Sprayed Coating ◽  
Plasma Sprayed

The air-plasma-sprayed ceria and yttria-stabilized zirconia (CYSZ) coating was modified by selective laser remelting and Al deposition to enhance hot corrosion resistance. The dotted coating was obtained after selective laser remelting. Magnetron sputtering was used to deposit an Al film on the dotted coating, and a vacuum heat treatment was subsequently performed to produce a dense α-Al2O3 overlay. Hot corrosion behavior of the following three types of coatings was investigated: plasma-sprayed, dotted, and dotted coatings combined with Al deposition (DA). Hot corrosion behaviors were evaluated in a mixture of 55 wt % V2O5 and 45 wt % Na2SO4 molten salts at 1000 °C for 30 h. The hot corrosion reaction between molten salts and zirconia stabilizers (Y2O3 and CeO2) led to the generation of monoclinic zirconia, YVO4, and CeVO4 plate-shaped crystals, and the mineralization of CeO2. The results indicated that the hot corrosion resistance of the DA coating was the best, and the dotted coating had superior hot corrosion resistance in comparison with the plasma-sprayed coating. The minimal surface roughness and dense dotted units improved the hot corrosion resistance of the dotted coating. The dense α-Al2O3 overlay with chemical inertness effectively inhibited the infiltration of molten salts, which led to the optimal hot corrosion resistance of the DA coating.

HOT CORROSION OF CERIA-YTTRIA STABILIZED ZIRCONIA PLASMA SPRAYED THERMAL BARRIER COATING BY EUTECTIC VANDIUM PENTAOXIDE-SODIUM SULFATE

2018 ◽  
Vol 18 (1) ◽  
pp. 182-192 ◽  
Author(s):  
Mohammed J Kadhim ◽  
Mohammed H Hafiz ◽  
Maryam A Ali Bash
Keyword(s):  
Thermal Barrier Coating ◽  
Hot Corrosion ◽  
Monoclinic Phase ◽  
Volume Fraction ◽  
High Volume ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Plan View ◽  
Barrier Coating ◽  
Plasma Sprayed

The high temperature corrosion behavior of thermal barrier coating (TBC) systemconsisting of IN-738 LC superalloy substrate, air plasma sprayed Ni24.5Cr6Al0.4Y (wt%)bond coat and air plasma sprayed ZrO2-20 wt% ceria-3.6 wt% yttria (CYSZ) ceramic coatwere characterized. The upper surfaces of CYSZ covered with 30 mg/cm2 , mixed 45 wt%Na2SO4-55 wt% V2O5 salt were exposed at different temperatures from 800 to 1000 oC andinteraction times from 1 up to 8 h. The upper surface plan view of the coatings wereidentified for topography, roughness, chemical composition, phases and reaction productsusing scanning electron microscopy, energy dispersive spectroscopy, talysurf, and X-raydiffraction. XRD analyses of the plasma sprayed coatings after hot corrosion confirmed thephase transformation of nontransformable tetragonal (t') into monoclinic phase, presence ofYVO4 and CeVO4 products. Analysis of the hot corrosion CYSZ coating confirmed theformation of high volume fraction of YVO4, with low volume fractions of CeOV4 and CeO2.The formation of these compounds were combined with formation of monoclinic phase (m)from transformation of nontransformable tetragonal phase (t').

Thermodynamic Estimate of Minimal Dissipation for Heat Exchange System

2008 ◽  
Author(s):  
Andrei A. Akhremenkov ◽  
Anatoliy M. Tsirlin ◽  
Vladimir Kazakov
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Heat Load ◽  
Point Of View ◽  
Exchange System ◽  
Heat Exchange System ◽  
Heat Exchange Surface ◽  
Minimal Dissipation ◽  
The Difference ◽  
Exchange Surface

In this paper we consider heat exchange system from point of view of Finite-time thermodynamics. At first time the novel estimate of the minimal entropy production in a general-type heat exchange system with given heat load and fixed heat exchange surface is derived. The corresponding optimal distribution of heat exchange surface and optimal contact temperatures are also obtained. It is proven that if a heat flow is proportional to the difference of contacting flows’ temperatures then dissipation in a multi-flow heat exchanger is minimal only if the ratio of contact temperatures of any two flows at any point inside heat exchanger is the same and the temperatures of all heating flows leaving exchanger are also the same. Our result based on those assumptions: 1. heat transfer law is linear (17); 2. summary exchange surface is given; 3. heat load is given; 4. input tempretures for all flows are given; 5. water equivalents for all flows are given.

Corrosion of Boiler Tubes

1943 ◽  
Vol 149 (1) ◽  
pp. 74-88 ◽  
Author(s):  
T. Henry Turner
Keyword(s):  
Great Britain ◽  
Research Laboratory ◽  
General Corrosion ◽  
Boiler Tube ◽  
Shot Blasting ◽  
Chemical Research ◽  
Boiler Water ◽  
National Importance ◽  
Boiler Tubes ◽  
Chemical Research Laboratory

The reduction of the number of boiler tube failures to a minimum is now a matter of national importance. Revolutionary improvement is not expected in the nature of the tubes. Tubes fail rapidly by local, and less rapidly by general, corrosion. The removal of scale by shot blasting before use will reduce the extent of losses due to pitting, and so will additions of 0·2–0·5 per cent of copper. Metallurgical data regarding tubes, and chemical data regarding feed waters are summarized in the paper, from the author's extensive records. After discussing how corrosion occurs at cracks in oxide, scale, or paint, suggestions are made for preventing corrosion in locomotive, marine, and stationary boilers. Recommendations include simplification and standardization of boiler water tests by a suitable British Standards Committee, and the suggested Specification is sketched in outline. The paper is concluded by Appendixes comprising (i) a questionnaire (with answers) on the present-day practice as regards the manufacture of boiler tubes in Great Britain; (ii) a list of reports published by the American Railroad Engineering Association; and (iii) a bibliography of selected items on corrosion, for the index prepared and maintained at the Chemical Research Laboratory, Teddington.

Investigations of the Fracture of Composites Matrix-Coating Under Tension

1998 ◽  
Author(s):  
V.E. Panin ◽  
V.A. Klimenov ◽  
S.V. Panin
Keyword(s):  
Steel Matrix ◽  
Matrix Composites ◽  
Coating Quality ◽  
Deformation Stages ◽  
The Matrix ◽  
Sprayed Coating ◽  
Plasma Sprayed

Abstract Deformation stages and specific features were studied by mesomechanical methods under tension of plasma sprayed coating-steel matrix composites. The effect of coating quality on the deformation of the matrix at the mesolevel was revealed. The results obtained make it possible to predict reliability and durability of this kind of coating and of the entire composite.

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