Thermal resistance by slagging and its relationship with ash properties for six coal blends in a commercial coal-fired boiler

Park, Ho-Young; Lee, Jeong Eun; Kim, Hyun Hee; Park, Sangbin; Baek, Se Hyun; Ye, Insoo; Ryu, Changkook

doi:10.1016/j.fuel.2018.08.134

Cited by 24 publications

(7 citation statements)

References 24 publications

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“…The fouling factors of #1 and #2 are finally stable at 8.5 and 4.5 m 2 ·°C/kW. The result of #1 is close to the study of Park et al 32 He studied the relationship between thermal resistance, which called “foul factor” in our paper, and slagging on the heating surface by burning blended coal in a 500‐MW “Tower”‐type boiler. With the progress of the test, the thermal resistance of the primary superheater, in Figure 4 of this paper, reached 7–10 m 2 ·°C/kW within a few hours…”

Section: Resultssupporting

confidence: 85%

“…Many scholars attribute severe ash deposition to high content of alkali metals and alkaline earth metals (AAEMs) in Zhundong coal ash. Up to now, in Wucaiwan region, one of the highest yield mines in Zhundong, there are nearly 20 units fueled by calciumrich Wucaiwan coal, including Tianchi energy coal, Yihua coal, and Shenhua coal, which usually contain Ca (27)(28)(29)(30)(31)(32)(33)(34)(35) wt %) and Na (3.5-8.2 wt %) in ash. 4 The sublimation and condensation of Ca/Na compounds and their effects on ash deposition under 750-1200 C have been widely studied.…”

Section: Introductionmentioning

confidence: 99%

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Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility

Jin

Yang

et al. 2022

Asia-Pacific J Chem Eng

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Thermal power plants in Zhundong area of Xinjiang equip Π-typed boiler widely in recent years. With the increasing ratio of Zhundong coal in blended fuels, the slagging is strengthened. And the boiler shutdown was caused by ash deposition on the convective heating surface frequently. In order to study the mechanism of this problem, a 0.4-MW th pilot-scale facility was built and expected to study ash deposition and heat transfer characteristics on the convective heating surface of 100% burning calcium-rich Zhundong coal.Thermodynamic model calculation was implemented on the heat transfer characteristics of two groups of tube panels, on which ash samples were collected after experiments. Then, simulation calculation was applied by software for verification. The ash samples were characterized by X-ray diffraction spectroscopy (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray detector (EDX). FactSage 7.3 thermochemical software package and a high-temperature viscometer were also used to figure out the viscosity-temperature characteristics. Results showed that a "step change" of heat transfer characteristics occurred when the flue gas temperature of inlet tube panel #2 approached to 1000 C. After the "step change," the heat transfer characteristics became stable. The ash deposition mainly consisted of siliconcalcium compounds of tube panel #1, while in contrast, that of tube panel #2 consisted of gehlenite, CaSO 4 , and Na 2 SO 4 . The ratio of liquid phase in raw coal ash samples increased sharply when the flue gas temperature exceeded 1030 C. With the increase of surface temperature of fouling tube panel, the CaSO 4 would be decomposed to release CaO, which reacted with gehlenite or other compounds to form low temperature eutectics. The fouling of ash would transfer to slagging and lead to the deterioration of ash deposition, which induced the formation of "step change" during the experiment.

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Section: Resultssupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility

Jin

Yang

et al. 2022

Asia-Pacific J Chem Eng

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“…Torrefaction is known to improve the grindability of biomass owing to the degradation of the fibrous structure. , Figure shows the grindability determined by the TTBGI tests versus the weight loss for TWP from different processing conditions. For comparison purposes, the HGI values of 10 commercial coals from a domestic 500 MWe power plant were also plotted, which ranged between 39 and 62 . The TTBGI of the raw wood pellets was only 16, which is known to increase the power consumption and also deteriorate the coal grindability when comilled.…”

Section: Results and Discussionmentioning

confidence: 99%

Improving Energy Density and Grindability of Wood Pellets by Dry Torrefaction

Park

Kim

et al. 2019

Energy Fuels

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In dedicated wood pellet combustion and cofiring with coal in large pulverized fuel furnaces, poor grindability and low bulk density of biomass are important issues for lowering the unburned carbon in ash and achieving high cofiring ratios with coal for pulverized fuel combustion furnaces. In this study, the torrefaction of wood pellets was investigated for improvement of energy density and grindability. The torrefaction tests were performed using a fixed bed reactor for a temperature range of 210–310 °C and holding time of 15–60 min. The mass yield varied from 86.18 to 39.46% accompanied by an increase in the carbon content and heating value. The properties of torrefied wood pellets (TWP) were correlated with the mass yield for use with different time–temperature histories. The bulk density decreased by the mass yield rose to a power of 0.538. The energy density of TWP was higher in the initial torrefaction stage with a peak of 10.41 GJ/m3 but was below that for the original pellets when the mass yield was approximately ≤60%. The grindability of TWP increased almost linearly with the degree of torrefaction, and the mass yield of 80% attained the lower range of the grindability of coal.

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“…In the boundary condition, the entire furnace wall (evaporator) was set to have the average water/steam temperature of 652.15 K with an overall heat transfer coefficient of 250 W/m 2 K and inner wall emissivity of 0.7. The heat transfer coefficient was taken as the average of measured values 3.51-4.37 m 2 K/kW of thermal resistance equivalent to 229-285 W/m 2 K depending on the coal types [29]. The tube bundles from primary SH to the economizer were simplified as porous zones, with local source terms calculated for flow resistance, convection, and radiation based on the detailed geometry and steam conditions [30].…”

Section: Cfd Modelingmentioning

confidence: 99%

Optimization of Air Distribution to Reduce NOx Emission and Unburned Carbon for the Retrofit of a 500 MWe Tangential-Firing Coal Boiler

Kang

Park

et al. 2019

Energies

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The use of separated overfire air (SOFA) has become a standard technique of air staging for NOx reduction in the coal-fired boiler and can also be applied to existing boilers by retrofit. This study was to optimize the air distribution for the proposed SOFA installation in a 500 MWe tangential-firing boiler that has 20 identical units in Korea. Using computational fluid dynamics (CFD) incorporating advanced coal combustion submodels, the reference case was established in good agreement with the design data, and different flow ratios of burner secondary air, close-coupled OFA (CCOFA), and SOFA were evaluated. Increasing the total OFA ratio effectively suppressed NO formation within the burner zone but had a negative impact on the boiler performance. With moderate air staging, NO reduction became active between the CCOFA and SOFA levels and, therefore, the OFA distribution could be optimized for the overall boiler performance. For total OFA ratios of 25% and 30% with respective burner zone stoichiometric ratios of 0.847 and 0.791, increasing the SOFA ratio to 15% and 20%, respectively, was ideal for decreasing the unburned carbon release and ash slagging as well as NO emission. Too high or low SOFA ratios rapidly increased the unburned carbon because of inefficient mixing between the strong air jets and char particles. Based on these ideal cases, the actual air distribution can be adjusted depending on the coal properties such as the ash slagging propensity.

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Thermal resistance by slagging and its relationship with ash properties for six coal blends in a commercial coal-fired boiler

Cited by 24 publications

References 24 publications

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility

Improving Energy Density and Grindability of Wood Pellets by Dry Torrefaction

Optimization of Air Distribution to Reduce NOx Emission and Unburned Carbon for the Retrofit of a 500 MWe Tangential-Firing Coal Boiler

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Thermal resistance by slagging and its relationship with ash properties for six coal blends in a commercial coal-fired boiler

Cited by 24 publications

References 24 publications

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MWth facility

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MWth facility

Improving Energy Density and Grindability of Wood Pellets by Dry Torrefaction

Optimization of Air Distribution to Reduce NOx Emission and Unburned Carbon for the Retrofit of a 500 MWe Tangential-Firing Coal Boiler

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Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility

Ash deposition and heat transfer characteristics on the convective heating surface of calcium‐rich Zhundong coal combustion in a 0.4‐MW_th facility