Coupling mechanism of dew point corrosion and viscous ash deposits

Liang, Zhiyuan; Zhao, Qinxin; Wang, Y. G.; Li, Y. X.; Zhang, Zhicheng

doi:10.1002/maco.201307042

Cited by 19 publications

(3 citation statements)

References 8 publications

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“…As investigated for the 316L and ND steels in the conditions of a gas deep cooling device operation, the metal surface was covered by an ash deposit layer, coupling layer, and corrosion layer. Layered structure of the deposits leads to the accumulation of the acids in the resurface layer, and the corrosion rate rises significantly, especially when the wall temperature is lower than the dew point [36,37]. Such mechanism is not relevant to the corrosion in fluids; however, the formation of a nonuniform scale layer may lead to the localization of corrosion.…”

Section: Resultsmentioning

confidence: 99%

Anticorrosion Behaviour of Calcareous Deposits Formed on Steel Heat‐Exchange Surfaces

Vorobyova

2020

Advances in Materials Science and Engineering

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A new electrode to study both scaling and corrosion processes of mild steel in tap water was developed. Two identical steel rings are placed on the outside of a glass tube which is heated from inside with an electric spiral; the rings are connected to a corrometer to form a two-electrode corrosion probe. The corrosion rate variations with scale thickness, scale deposition time, and solution composition are measured using the linear polarization resistance technique. The deposited scale was formed of calcite crystals of 50–100 μm as established with SEM and XRD. The scale layer of 0.2 mm formed in tap water within 90 hours reduces the steel corrosion rate from 0.8 to 0.1 mm/year and serves as a barrier layer to prevent further corrosion.

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Section: Resultsmentioning

confidence: 99%

Anticorrosion Behaviour of Calcareous Deposits Formed on Steel Heat‐Exchange Surfaces

Vorobyova

2020

Advances in Materials Science and Engineering

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“…As the temperature of the flue gas decreases, the acid gas in the flue gas, such as sulfur trioxide, will condense and form acid on heat-transfer surfaces. This may lead to dew point corrosion, destruction of the surfaces, ash deposition, and blockage. − Previous studies indicated that the ash deposition was mainly composed of ash and acid reaction products, iron sulfate and iron oxide. At present, there are few studies on ash deposition of the flue gas cooler caused by ammonium slip.…”

Section: Introductionmentioning

confidence: 99%

Study on Deposits Containing Rich Fluorine, Boron, and Ammonium on the Heating Surface of a Flue Gas Cooler in a 300 MW Coal-Fired Boiler

Wang

Zhao

et al. 2017

Energy Fuels

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To understand deposit formation in the flue gas cooler, which is used to recover the exhaust heat from a 300 MW coal-fired boiler in China, a mineralogical study was carried out. Several deposit samples on the surface of the flue gas cooler were collected. Then, the samples were examined by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). Mineralogical analysis showed that the deposits could be divided into three layers. The high concentrations of O, Si, and Al in the outer layer were indicative of the formation of ash particles in the flue gas, and the high contents of Fe, O, Cl, and S in the inner layer were indicative of the formation of iron corrosion products, in comparison to the interlayer. In addition, the relatively higher contents of F and N in outer layer and interlayer were interpreted as the formation of ammonium fluoroborate (NH4BF4) and its intermediates [NH4F, HBF4, (NH4)2SiF6, and H3BO3], which were further proven by XRD and XPS analyses. The inner layer defined as the corrosion layer was caused by condensed acid on the surface of the flue gas cooler when the heating surface temperature was below the HF dew point. The formation of NH4BF4 was due to the enrichment of fluorine and boron in the coal as well as the escape of ammonia from selective catalytic reduction (SCR).

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“…However, most of the work focused on the ash deposition at high temperatures. − Fewer studies have been performed on the deposit characteristic under low temperatures. Some researchers have examined the deposit formation of air preheaters in coal-fired power plants. , Several experiments have been performed on low-temperature ash deposition with test probes in coal-fired power plants. − However, the deposit formation of a real LPE has seldom been discussed in recent years, and the deposition mechanism is still unclear. Besides, the formation and deposition of NH 4 HSO 4 in air preheaters have been explored by a number of investigators, , but little literature has been reported concerning the effect of NH 4 HSO 4 on PLEs in coal-fired power plants.…”

Section: Introductionmentioning

confidence: 99%

Deposit Formation of the Low-Pressure Economizer in a Coal-Fired Thermal Power Plant

et al. 2017

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A field study was conducted to investigate the deposit formation of the low-pressure economizer (LPE) in a 330 MW thermal power plant. The deposits on the LPE were inspected visually, and eight deposit samples were collected at the inlet and outlet of the LPE according to the site conditions. The samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and particle size analysis. The results showed that the thick deposits on the supporting tubes at the LPE inlet were mainly due to the ash particles that had absorbed the H2SO4 condensate in the flue gas before the LPE inlet. NH4HSO4 began to form on the heat-exchange tubes at the LPE inlet. Both the H2SO4 condensation and NH4HSO4 formation stimulated the deposit formation on the heat-exchange tubes at the LPE inlet. The plugging of the heat-exchange tubes at the LPE outlet was primarily induced by the condensation of much more H2SO4. H2SO4 and NH4HSO4 could also react with the fly ash to form sulfates. The LPE deposition mechanism was discussed, and the coupling model of the H2SO4, NH4HSO4, and fly ash behaviors during the deposit formation under different temperature conditions was proposed.

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Coupling mechanism of dew point corrosion and viscous ash deposits

Cited by 19 publications

References 8 publications

Anticorrosion Behaviour of Calcareous Deposits Formed on Steel Heat‐Exchange Surfaces

Anticorrosion Behaviour of Calcareous Deposits Formed on Steel Heat‐Exchange Surfaces

Study on Deposits Containing Rich Fluorine, Boron, and Ammonium on the Heating Surface of a Flue Gas Cooler in a 300 MW Coal-Fired Boiler

Deposit Formation of the Low-Pressure Economizer in a Coal-Fired Thermal Power Plant

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