Coal Ash Fusion Temperature Research Articles

Regulation Mechanism of Ash Fusion of Iron‐Rich Coal in Xinjiang with Different Additives

AbstractTo realize the high‐efficiency utilization of iron‐rich coal (ZC), it is necessary to conduct in‐depth research on its ash fusion characteristics and regulation mechanism. In this paper, the fusion temperature test of ZC coal ash was first carried out in a weak reducing atmosphere, and diatomite (GZT) and Naomaohu high‐calcium coal (NMH) were selected as additives. The results show that the four characteristic temperatures of ZC coal ash are all low under weak reducing conditions. The addition of NMH ash lowered the fusion temperature of ZC coal ash, while the GZT ash increased the fusion temperature to varying degrees. When the addition ratio of NMH ash is less than 40 %, the effect of increasing the difference between the deformation temperature and flow temperature of ZC coal ash is still positive. The addition of NMH ash made the slag system generate a high content of calcium‐magnesium feldspar and calcium‐iron feldspar, decreasing the fusion temperature of the blended coal ash. The addition of GZT ash increased the content of SiO2 in the slag system and promoted the increase of the iron‐pyroxene content, and the formation of the iron‐aluminum pyroxene and cordierite mineral phases, thereby increasing the coal ash fusion temperature.

Effecting mechanisms of iron-rich sludge on ash fusion characteristics of coal with high ash fusion temperature under reducing atmosphere

Co-gasification is crucial for large-scale clean conversion of coal and sludge. In this study, the effects of municipal sewage sludge (MSS, Fe2O3:48.11 %) and pharmaceutical sewage sludge (PSS, Fe2O3: 67.80 %) on ash fusion temperature (AFT) of high AFT Xiangyuan coal (XY) were explored using an AFT analysis, X-ray fluorescence spectrometry, X-ray diffraction, scanning electronic microscopy, and thermodynamics FactSage calculation. The results showed that when MSS or PSS ash mass ratios reached 20 % or 16 % (for XY mixtures, the mass ratio of MSS or PSS should be >5.81 wt% or 5.07 wt%), respectively, the AFT met the requirement of liquid-slag discharge for entrained-flow bed gasification. Under a reducing atmosphere (6:4, CO/CO2, volume ratio), Fe2+ destroyed the bridging-oxygen bonds in the network structure and generated low melting-point (MP) hercynite (FeAl2O4). This resulted in the AFT decreases in the XY mixtures with the additions of PSS or MSS. Meanwhile, the high calcium content (CaO: 13.40 %) easily reacted with Al2O3 and SiO2 and formed anorthite (CaAl2SiO8), which inhibited high-MP mullite formation and decreased the mixed XY AFT. With the increasing SS mass ratio, the surface of the ash sample and thermodynamic FactSage calculation were in good agreement with the experimental results.

Ash fusion characteristics of iron‐rich coal in Xinjiang under different atmospheres and the influence mechanism of adding red mud and pipeline scale

AbstractTo realize the high‐efficiency utilization of iron‐rich coal, it is necessary to conduct in‐depth research on the ash fusion characteristics and regulation mechanism. In this paper, the ash fusion temperature test of iron‐rich coal in Xinjiang (ZC) under different atmospheres was first carried out. Then, red mud (HJ) from Huajin Aluminum Industry and black water pipe scale (GDG) were selected as the additives. After the same ashing procedure, the two additives were mixed with iron‐rich coal ash in different proportions to realize the regulation of the chemical composition of the coal ash to improve the ash fusion characteristic. The ash fusion temperature (AFT) experiment was carried out in the automatic ash melting point analyzer, and high‐temperature ash melting slags at different temperatures were prepared. The mineral phases of coal ash and slag were characterized by XRD and compared with the Factsage simulation calculation results to reveal the influence mechanism of coal ash fusion temperature. The result shows that the fusion temperature of ZC iron‐rich coal ash is significantly different between oxidizing atmosphere and weak reducing atmosphere. Compared with the oxidizing atmosphere, the four characteristic temperatures of ZC iron‐rich coal ash are significantly lower under weak reducing conditions, and the difference is about 150°C. The addition of red mud and pipeline scale increased the fusion temperature of ZC coal ash to varying degrees. The addition of HJ ash has little effect on the deformation temperature of ZC coal ash, while the addition of different proportions of HJ ash significantly increases the flow temperature of ZC coal ash. When the addition ratio of HJ ash is 40%, the flow temperature FT of ZC coal ash increases most obviously, which is about 50°C. The addition of HJ ash and GDG ash will lead to an increase in the content of iron‐containing spinel, thereby increasing the ash flow temperature.

Effects of Proximate Analysis on Coal Ash Fusion Temperatures: An Application of Artificial Neural Network.

The temperature at which coal ash melts has a significant impact on the operation of a coal-fired boiler. The coal ash fusion temperature (AFT) is determined by its chemical composition, although the relationship between the two varies. Therefore, it is important to have mathematical models that can reliably predict the coal AFTs when designing coal-based processes based on their coal ash chemistry and proximate analysis. A computational intelligence model based on the interrelationships between coal properties and AFTs was used to predict the AFTs of the coal investigated. A model that integrates the ash, volatile matter, fixed carbon contents, and ash chemistry as input and the AFT [softening temperature, deformation temperature, hemispherical temperature, and flow temperature] as an output provided the best indicators to predict AFTs. The findings from the models indicate (a) a method for determining the AFTs from the coal properties; (b) a reliable technique to calculate the AFTs by varying the proximate analysis; and (c) a better understanding of the impact, significance, and interactions of coal properties regarding the thermal properties of coal ash. This study creates a predictive model that is easy to use, computer-efficient, and highly accurate in predicting coal AFTs based on their ash chemistry and proximate analysis data.

Increased Coal Slagging Index by Using Zeolite Synthetic

The use of coal as fuel has experienced several obstacles, one of which is the formation of Slagging (crust). Slagging is formed by the melting point of coal ash or low ash fusion temperature, caused by low levels of Al2O3 ­in coal ash. The addition of synthetic zeolite to coal before use is intended to increase the level of Al2O3, so that it will increase the ash fusion temperature of coal ash. The increase in ash fusion temperature also causes an increase in the slagging index of coal. With the high increase in the slagging index obtained, the lower the potential for the formation of slagging. The smaller the potential of Slagging formed, the use of coal also decreases. This study aims to determine the effect of adding waste-based synthetic zeolite to coal ash on increasing coal slagging index. Research uses a type of experimental research. Itis collected by conducting laboratory tests, namely making observations and direct testing of samples with variations in the addition of synthetic zeolite to coal by 5%, 10%, and 15%. The results showed that synthetic zeolite added to coal was able to reduce the potential for slagging formation. Slagging index from the results of research for oxidation conditions is a standard sample of 1,246oC, SBZ5 by 1,242oC, SBZ10 by 1,250oC, and SBZ15 by 1,274oC. Reduction conditions i.e. standard sample of 1,130oC, SBZ5 by 1,116oC, SBZ10 by 1,136oC, and SBZ15 by 1,168oC. SBZ15 sample is a variation that has a good slagging index, which is for oxidation conditions which is 1,274oC, and for reduction conditions that is 1,168oC

Effect of Coal Blending on Ash Fusibility and Slurryability of Xinjiang Low-Rank Coal

This work investigated the effect of coal blending on ash fusibility and slurryability of Xinjiang low-rank coal. The results showed that Xinjiang low-rank coals were characterized by high internal water content, high volatile content, high ash fusing point, and poor slurryability, which can not be directly used in coal water slurry gasification. The blending method not only reduced the ash fusibility but also improved the slurryability of these low-rank coals. When the coals with low calcium and high silicon contents (KG and YK) were blended with coal with high calcium content (SH), the ash fusion temperatures of the blended coal were significantly reduced. Moreover, the SH coal showed the worst slurryability performance with a concentration of 48.56%. The slurryability of HS coal can be dramatically improved by blending with KG. When the mass fraction of KG coal reached 70%, the concentration of coal water slurry increased by 11%. For the blended coal of KG and YK, the concentration and stability of coal water slurry gradually increase with the increasing mass ratio of KG. The coal blending method can effectively improve the concentration of coal water slurry for the low-rank coals, which were difficult-to-prepare slurry.

Co-combustion behavior, kinetic and ash melting characteristics analysis of clean coal and biomass pellet

In this study, the co-combustion characteristics and ash fusion temperatures of clean coal, biomass pellet and their blends were investigated by thermal analyzer and ash-melting point analyzer, respectively. Kinetic parameters were calculated by using the multistage reaction random pore model, which could be very consistent with the combustion law of the samples. The results show that the combustion characteristics of biomass pellet are better than those of clean coal, mainly influenced by the chemical structure. After mixing the two fuels, the flammability and comprehensive combustion performance were gradually improved, and there was an obvious synergistic effect. The best effect was when the biomass pellet mixing ratio was 60%. The increase of heating rate could promote synergy. The various activation energies of the solid carbon combustion stage decreased with the increase of biomass pellet ratio, and the change rule was similar to the synergistic effect. By detecting the shrinkage rate of ash and analyzing the phase composition and transformation, it is determined that the biomass blending ratio of 40–60% was most conducive to efficient utilization of the two fuels.

Predict coal ash fusion temperature based on liquid-phase content and its variation trend using FactSage software

Predict coal ash fusion temperature based on liquid-phase content and its variation trend using FactSage software

Influence of coal ash characteristics on the pretreatment process of fluidized bed cement calcination

A new two-process Portland cement clinker manufacturing equipment was utilized to substitute traditional rotary kilns for emission reduction. Cement raw meal became an intermediate product after calcination in the pretreatment process, and the intermediate product turned into a clinker after the final calcination process. During the pretreatment process, the cement raw meal granulated and CaCO3 decomposition and C2S formation occurred simultaneously. Compositions of coal ash differed with cement raw meal and influenced mineral formation and granulation in the first process. Clinker quality and equipment feasibility were influenced accordingly. Therefore, the influence of coal ash component, content and ash fusion temperature on mineral formation and granulation was investigated. Results showed that high-SiO2/Al2O3 coal ash decreased C2AS formation in the intermediate product. Minor component MgO and alkali oxides had no contribution to C2S formation. SO3 promoted C2S formation and suppressed C2AS formation. Mineral types remained unchanged and mass fraction of granules over 1 mm in intermediate products fluctuated slightly as coal ash content increased. Ash fusion temperatures of coal ash were not directly related to granulation. The pretreatment process was feasible and suggestions for fuel selection were provided from the view of coal ash.

Morphological changes and ash fusibility of coal, rice straw and their mixture during CO2 gasification

The gasification behavior of single particle of coal, rice straw, and coal-rice straw mixture were investigated by in-situ heating stage microscope, X-ray diffraction, and scanning electron microscopy. The gasification process of coal particle can be divided into three stages consisting of swelling stage, shrinkage stage, and ash fusion stage, while the swelling stage is not observed for the gasification of rice straw particle. The presence of rice straw particle facilitates the shrinkage of coal particle during the co-gasification process due to the migration and catalytic effect of alkaline components which are abundant in biomass. Further, it was found that the average melting temperature of particles is close to the deformation temperature (DT) of ash sample, implying that the DT may reflect the melting properties of particles in a real gasifier. Finally, the ash fusion mechanisms were explored. It was identified that the formation of high-melting points mullite, quartz and anorthite are responsible for the high ash fusion temperatures of coal (with flow temperature over 1500 °C). The addition of 20 wt% rice straw (with flow temperature of 1133 °C) to coal improves the formation of lower-melting points minerals containing alkaline and alkaline-earth elements, and sulphur in the mixture that facilitates the ash fusion process and induces the slag formation. Thus, the flow temperature of the mixture decreases to 1369 °C. The ash fusion behavior of coal follows the “softening-melting” mechanism, while this behavior of rice straw shows a typical “melting-dissolution” mechanism. The ash fusion behavior of coal-rice straw mixture reveals both mechanisms; however, the “melting-dissolution” mechanism seems to be more characteristic for this mixture.

Slagging Characteristics and Optimization of Operating Temperature on High-Alkali Coal Gasification

In order to mitigate the slagging risks of high-alkali coal (HAC) gasification while optimizing the operating temperatures for practical application, the experimental and calculational works were performed on the horizontal tubular furnace system and the FactSage 7.2 software, respectively. The slagging tendencies of three HACs were anticipated by applying different indexes of ash chemistry characteristics prior to experiments, but the determined results were found inconsistent. The relationship between Na retained ratio (RNa) and the ash fusion temperatures (AFTs) of gasification residues demonstrated that the AFTs of coal with high RNa are low, while AFTs of coal with low RNa are high. Nevertheless, when the residues contained a large number of calcium-containing silicates and aluminosilicates, the ATFs were reduced significantly even if its RNa stayed at a low level. Furthermore, the operating temperatures of the three coals (in order of Mulei coal, Shaerhu coal, and Tietou coal) were suggested to be controlled below 1150°C, 1100°C, and 950°C, respectively.

Laser-induced breakdown spectroscopy for quantitative and qualitative analysis of the ash fusion temperatures of coal in power plants

Prediction of coal ash fusion temperatures by LIBS with generalized spectral variables using coal rather than coal ash.

Effect of sodium and calcium on the ash fusion temperatures of Zhundong coal

The effect of sodium and calcium on the ash fusion temperatures (AFTs) of Zhundong coal was investigated in this study using an ash fusibility tester combined with X-ray diffraction technology. The results indicate that the AFTs of Zhundong coal are closely related to the content of sodium and calcium in coal ash compounds. The pretreatment of the raw coal with water leaching and hydrochloric acid leaching can remarkably enhance the AFTs, which is attributed to the removal of inherent alkali metal species in coal. The AFTs decrease first and then increase not only with the increment of Na2CO3 loading but also with the increment of CaO addition, and the minimum AFTs were, respectively, reached at 15 mass% Na2CO3 loading and 10 mass% CaO addition. The transformation of hematite during ashing of Zhundong coal with different Na2CO3 loadings gives much contribution to the reduction of the AFTs. Meanwhile, the formation of KSi3AlO8 and muscovite accounts for the rising AFTs beyond the loading amount of 15 mass% Na2CO3. For Zhundong coal-added CaO, the drop of AFTs maybe results from the formation of low-melting iron species and eutectic salts, whereas the growing AFTs may be ascribed to the overdosed lime with high melting point and the formation of Ca2SiO4 during ashing.

Investigation on regulation mechanism of red mud on the ash fusion characteristics of high ash-fusion-temperature coal

Red mud (RM) used as a flux to decrease coal ash fusion temperature (AFT) has great economic and environmental attractions. The effects of Bayer RM (BRM) and Sintering RM (SRM) on the AFTs of high silicon-aluminum coal (Jiaozuo coal (ZJ)) or high aluminum coal (Pingsuo coal (PS)) were investigated by X-ray fluorescence analysis, X-ray diffraction, and FactSage calculation. With increasing BRM/SRM mass ratio, the AFTs of JZ or PS mixture firstly decreased quickly and then slowly. When ash flow temperatures were decreased to <1400 °C, for ZJ mixtures, the mass ratio of BRM or SRM should not be <1.38% or 0.65%; while for PS, BRM or SRM should not be <2.76% or 1.81%, respectively. SRM lower AFT’s of two coals compared to the addition of BRM resulted from that SRM higher CaO content (20.12 wt%) than that of BRM (8.87 wt%), and its lower A/B value (1.15) than BRM (1.53). The increasing contents of Na2O, Fe2O3, and CaO inhibited high melting-point (MP) mullite formation and prompted the formations of low MP albite, hercynite, and anorthite with increasing RM mass ratio. This caused the respective decrease in the AFTs. The mineral evolution based on FactSage calculation could explain the AFT changing trend with increasing BRM or SRM mass ratio.

Ash fusion temperature regulation mechanism of Xiangyang coal by coal blending

The modifications in the low ash fusion temperature (AFT) of Xiangyang coal (XY) were investigated by blending it with three high AFT coals [Jincheng coal (JC), Sunjiahao coal (SJH), and Shajuzi coal (SJZ)], respectively. These three coals all improved XY AFT effectively. With the JC mass ratio varying from 0 to 50%, the AFT of XY/JC gradually increased. The AFT of XY/SJH increased significantly (0–30%), slowly (30–40%), and rapidly (40–50%) with increasing SJH content. For SJZ, the AFT of XY/SJZ increased quickly (0–30%) and very slowly (30–50%). For XY entrained-flow gasification, the appropriate blending ratios of JC, SJH, and SJZ were 40–50%, 30–40%, and 20–40%, respectively. X-ray diffraction, scanning electron microscopy, and FactSage thermodynamic calculation were applied to investigate the effects of mineral transformation on AFT. Quartz (SiO2), anorthite (CaAl2Si2O8), diopside (CaMgSi2O6), and hedenbergite (CaFeSi2O6) were detected in XY ash at 1100 °C. As the mass ratios of high AFT coals increased, the obvious increase in anorthite content led to the rise in the AFT of XY/JC; mullite (Al6Si2O13); and corundum (Al2O3) with a high melt point formed in ashes causing the increase in the AFTs of XY/SJH and XY/SJZ, respectively.

Investigation on improve ash fusion temperature (AFT) of low-AFT coal by biomass addition

The co-gasification of coal and biomass is of importance for coal clean conversion and biomass utilization on a large scale. To investigate the effecting behaviors of biomass on ash fusion characteristics of low ash-fusion-temperature (AFT) coal, the ash chemical properties of three materials (Shenmu coal (SM), chestnut shell (CS), and rice husk (RH)), the variations in SM mixed AFT with increasing CS or RH mass ratio and their mechanisms were explored through silicate-network structure theory, X-ray powder diffractometry, and FactSage software. The formations of anorthite, gehlenite and their eutectics caused SM with low AFT. An increased CS mass ratio led to the increasing contents of high melting-point (MP) kalsilite, lime and magnesia and the decreasing contents of low MP nepheline, olivine, and gehlenite, this made SM mixed AFTs increased gradually. Increasing high MP tridymite content led to SM mixed AFT mostly increased with increasing RH mass ratio. The temperature that all minerals changed into liquid phase based on FactSage calculation could reflect the AFT variation of samples.

Failure Analysis of Secondary Superheater Tube in a 600-MW Coal Power Plant

A failure analysis was carried out on an A213 T91 secondary superheater tube after 4 months of overhaul. The failure caused the 600-MW coal power plant was shut down. The investigation consisted of visual inspections, microstructure analysis, Vickers hardness test, x-ray diffraction, and ash fusion temperature test and ash content analysis. The failed tube had a thin-lip rupture with sharp edges and experienced a decrease in hardness in the area of lip rupture. The microstructure analysis shows the coarse carbide and some isolated voids. Corrosion products were detected in slag deposits, and nonuniform thin oxide layer in the inner wall of the tube was observed. It is concluded that the main failure of the failed tube was due to the formation of slag deposits on the outer surface of the tube wall. This formation has resulted in simultaneously occurring phenomena, which was the localized flue gas erosion followed by the rapid overheating of the tube. The formation of slag deposits was in consequence of the use of coal with lower ash fusion temperature than required coal ash fusion temperature for the power plant.

Ash deposit characteristics of blended coal in coal combustion process

Coal combustion process often occurs the problems in the reactor which is caused by fouling and slagging. One of the procedures to reduce the risk of fouling and slagging by blending the coal of Pendopo, Palangkaraya, Muara Enim and Samarinda, with the ratio of 25:75, 50:50, and 75:25. The ash deposit tendency is known by analyzing the composition and ash fusion temperature of coal, determining the ash type and calculating of the fouling and slagging. The results showed that the Pendopo and Palangkaraya coal with a ratio of 25:75 and 50:50 were classified as lignite with fouling and the slagging index was classified as a high and medium tendency. While the other blended coal was classified as a low and low-medium tendency.

Prediction of coal ash fusion temperatures using computational intelligence based models

In the coal-based combustion and gasification processes, the mineral matter contained in the coal (predominantly oxides), is left as an incombustible residue, termed ash. Commonly, ash deposits are formed on the heat absorbing surfaces of the exposed equipment of the combustion/gasification processes. These deposits lead to the occurrence of slagging or fouling and, consequently, reduced process efficiency. The ash fusion temperatures (AFTs) signify the temperature range over which the ash deposits are formed on the heat absorbing surfaces of the process equipment. Thus, for designing and operating the coal-based processes, it is important to have mathematical models predicting accurately the four types of AFTs namely initial deformation temperature, softening temperature, hemispherical temperature, and flow temperature. Several linear/nonlinear models with varying prediction accuracies and complexities are available for the AFT prediction. Their principal drawback is their applicability to the coals originating from a limited number of geographical regions. Accordingly, this study presents computational intelligence (CI) based nonlinear models to predict the four AFTs using the oxide composition of the coal ash as the model input. The CI methods used in the modeling are genetic programming (GP), artificial neural networks, and support vector regression. The notable features of this study are that the models with a better AFT prediction and generalization performance, a wider application potential, and reduced complexity, have been developed. Among the CI-based models, GP and MLP based models have yielded overall improved performance in predicting all four AFTs.

Effects of leaching and additives on the ash fusion characteristics of high-Na/Ca Zhundong coal

Considering the intensive application of Zhundong coal and its serious slagging during combustion in pulverized coal fired boilers, the effects of water leaching and different dosages of additives (Na2CO3, CaO, SiO2, and kaolin) into the leached coal on ash fusion characteristics were studied using sintering tester, X-ray Fluorescence, and X Ray Powder Diffraction. After leaching, the contents of Na2O, K2O, CaO, MgO, SO3, and Cl decreased, whereas the contents of SiO2 and Fe2O3 increased. As a result, the slagging and fouling index of Basic/Acid ratio decreased from 1.6 in the raw coal ash to 1.1 in the leached coal ash, and alkali-induced slagging was reduced. However, the decreased ash fusion temperatures (AFTs) of the leached coal worsen the melt-induced slagging. Detailed analysis on the effects of ash compositions on the AFTs by additions of Na2CO3, CaO, SiO2, and kaolin additives into the leached coal showed that Na2CO3 and SiO2 improved the formation of low-melting Na2SO4 and Na2SiO3, and thus decreased the AFTs; However, overdosed Na2CO3 (for instance 9 wt%) improved the formation of relative high-melting Na4Al2Si2O9 and thus increased the AFTs. Overdosed SiO2 as a high-melting contaminant also increased the AFTs. Similar with the function of overdosed SiO2, CaO in the ash of leached coal was excess, and the AFTs increased with increased CaO dosage. Kaolin, which decomposed as high-melting mullite and cristobalite, caused an elevation of the AFTs. Therefore, water leaching decreased the AFTs of Zhundong coal and consequently worsen melt-induced slagging, lime and kaolin additives increased the AFTs effectively, but Na2CO3 and SiO2 additives showed ‘V’ shaped functions on the AFTs. These general results are useful for the pretreatment of Zhundong coal during combustion and alleviating slagging.