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Lingxue Kong - One of the best experts on this subject based on the ideXlab platform.
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Viscosity temperature property of coal ash Slag at the condition of entrained flow gasification a review
Fuel Processing Technology, 2021Co-Authors: Lingxue Kong, Jin BaiAbstract:Abstract Viscosity-temperature property of coal ash Slag plays the key role for stable and long term operation of entrained flow gasifiers, which is the quantitative parameter for Slag tapping process. It is described by a curve of Slag Viscosity as a function of temperature, which includes three aspects: Viscosity value dependence on temperature, temperature of critical Viscosity (TCV), and pattern of Slag Viscosity-temperature curve. A clear and comprehensive understanding of Viscosity-temperature property of coal ash Slag and its influencing factors is really important for Slag tapping, operation and design of a gasifier. This review begins with essence of Slag Viscosity-temperature property and requirement for Slag tapping, and then focused on utilization of basic oxides to adjust Slag Viscosity-temperature property. It was found that TCV of a crystalline Slag is vitally dependent on crystallization behavior of Slag, and crystallization kinetics of Slag needs further to be investigated in the future. In addition, residual char in Slag, water vapor in syngas, and temperature program in Viscosity measurement significantly affect the Slag Viscosity-temperature property and Slag tapping process. Finally, based on results reported in the literatures, several perspectives were proposed for future studies on Slag Viscosity-temperature property of coal ash Slag.
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structure and flow properties of coal ash Slag using ring statistics and molecular dynamics simulation role of cao na2o in sio2 al2o3 cao na2o
Chemical Engineering Science, 2020Co-Authors: Longfei Gao, Lingxue Kong, Jin Bai, Xingchen Liu, Zongqing BaiAbstract:Abstract Molecular dynamics simulation was applied to investigate the microstructure of Slag in SiO2-Al2O3-CaO-Na2O system. A new structure model for Slag was established through ring-statistics by MD simulation. The network structure was simplified into crosslinked rings divided into three types based on the ring size. The change of amorphous structure was well described by ring distribution. The destruction of Slag structure by Ca2+ is more significant than Na+, and high CaO/Na2O resulted in low content of medium and large rings and low Viscosity. The ring distribution coefficient (Rdc) was defined to establish the relationship between structure and Viscosity: ŋ=26.7Rdc-10.2. When CaO/Na2O ratio increases, the ring distribution transforms from medium or high-order to low-order, leading to the decreasing of Rdc and Slag Viscosity. Moreover, CaO/Na2O ratio also changes the diffusivity of Slag and thus the melting behavior. Finally, a linear relationship between the empirical liquidus temperature (Tliq) and atomic diffusivity from the MD simulations was obtained.
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flow properties of ash and Slag under co gasification of coal and extract residue of direct coal liquefaction residue
Fuel, 2020Co-Authors: Xi Cao, Lingxue Kong, Baozi Peng, Zhen Liu, Ziyang Feng, Andrzej SzlekAbstract:Abstract Efficient utilization of the extraction residue (ER) of direct coal liquefaction residue is a bottle neck for the efficiency of direct coal liquefaction process. The co-gasification of the ER and coal is a promising way for large-scale utilization of ER. Flow properties of the feedstock including ash fusibility and Slag Viscosity are important parameters for the gasification process. To optimize co-gasification of the ER and coal, the ash fusibility and Slag Viscosity behavior of ER and coal under gasification conditions were studied. The results show that the ash fusion temperatures (AFTs) of the blending were lowered with the increasing blending ratio of ER due to the high content of calcium and iron in ER. The content of quartz and anorthite in the blended ashes decreased with the increasing ER blending ratio. The Slag viscosities at high temperatures also decreased as the blending ratio of ER increased. The high content of calcium and iron in ER resulted in the decrease in the Slag polymerization degree because of the break of Si-O structure and transformation from [AlO4]5− to [AlO6]9−. Besides, the Slag presented the behavior of a crystalline Slag when the ER blending ratio was increased up to 25% for the formation of anorthite during cooling. For the entrained flow gasification, the ER addition can effectively lower the operation temperature of the gasifiers, improve the gasification efficiency and avoid the Slag tapping problems. The optimal ER addition should be in the range of 10–20%, and the corresponding tapping temperature was 1258–1575 °C.
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improved prediction of critical Viscosity temperature by fusion behavior of coal ash
Fuel, 2019Co-Authors: Tinggui Yan, Lingxue Kong, Jin Bai, Zongqing Bai, Zhigang Wang, Huiling ZhaoAbstract:Abstract Coal ash Slag Viscosity is critical for Slag tapping in entrained-flow coal gasifiers, so the accurate prediction of Slag Viscosity and the critical temperature of Viscosity (Tcv) will help the coal selection, flux addition and gasifier operation. Many empirical correlation models based on ash fusion temperature have been proposed to calculate Tcv. In order to correlate the Viscosity with the fusion behavior and then improve the prediction of Tcv, we measured the Viscosity of several synthetic coal ash Slags with a high-temperature rotary viscometer and studied their ash fusion behavior through thermomechanical analysis. X-ray diffraction was used to compare the mineral transformation before and after Tcv combined with the FactSage calculation. The Viscosity measurement shows that the Viscosity above Tcv of glassy Slags is higher than that of the crystalline type. The mineral transformation from FactSage also demonstrates that the precipitation rate of solid phase is lower for glassy Slags. The fusion behavior for the glassy and the crystalline Slag is also distinctly different. The fusion range from deformation temperature (DT) to flow temperature (FT) of the ash for the glassy Slag was larger than that of the crystalline one, and the shrinkage above FT in TMA trace slopes gently. The correlation between the fusion behavior and Viscosity-temperature behavior for the glassy Slag is reasonable, because the large temperature range from DT to FT and the low shrinking rate of the stage III indicate the high Viscosity of the liquid phase formed and the slow melting of the remained solid phase respectively, which are also the correlative condition prefer for the formation of glass as mentioned above. For the crystalline Slag, the small fusion range from DT to FT means the rapid melting of the solid phase and the high flowability of the liquid phase which are indicative for the rapid precipitation during cooling. The slow rate of the stage III indicates the slow melting of the remained solid which can be the crystal nucleus. When the Viscosity of the liquid phase is low, it also benefit for the formation of crystalline Slags. The characteristic in fusion behavior for different type of Slag also suggested that the predicting Tcv by applying one method to all the crystalline Slags and non-crystalline Slags is not appropriate.
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experimental and theoretical investigation on relationship between structures of coal ash and its fusibility for al2o3 sio2 cao feo system
Journal of Fuel Chemistry and Technology, 2019Co-Authors: Xin Dai, Lingxue Kong, Jin Bai, L I Dongtao, Ping Yuan, Tinggui Yan, Li WenAbstract:Abstract The molecular dynamics simulation, thermal dynamic calculation and experimental investigation were combined to illustrate ash Slag Viscosity variation mechanism for Al 2 O 3 -SiO 2 -CaO-FeO system. The Viscosity declines and the Viscosity curve are transformed from crystalline Slag to glassy Slag with increasing mass ratio (C/F) of calcium to ferrous oxide in Al 2 O 3 -SiO 2 -CaO-FeO system. There is an inflexion point when the C/F is equal to 2. When the C/F is below 2, there are mainly crystalline minerals in the system. While the C/F is above 2, there are mainly amorphous minerals in the system. With the increase of C/F, six-coordinated Al ([AlO 6 ] 9− ) is transformed to four coordinated Al ([AlO 4 ] 5− ) microscopically. Besides, the content of bridging oxygen decreases while that of non-bridging oxygen increases. Quantified function between base composition and Viscosity are constructed based on the stability coefficients defined by oxygen bond species.
Huaizhu Li - One of the best experts on this subject based on the ideXlab platform.
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the internal and external factor on coal ash Slag Viscosity at high temperatures part 3 effect of cao on the pattern of Viscosity temperature curves of Slag
Fuel, 2016Co-Authors: Wen Li, Xiaoming Li, Huaizhu LiAbstract:Abstract Limestone is widely used in entrained flow gasifiers to improve Slag Viscosity properties, while Viscosity–temperature curve of Slag is typical of a crystalline Slag when CaO content is above a certain level, of which the Viscosity sharply increases when the temperature is lowered below temperature of critical Viscosity ( T CV ). Experiments were conducted on selected Slags at about 5 wt% Fe 2 O 3 level to investigate effect of CaO on the pattern of Viscosity–temperature curve (PVTC) of Slag. The results showed that the higher CaO content at which the Viscosity of Slag exhibited the behavior of a crystalline Slag increased as silica/alumina ratio (S/A) of Slag increased. PVTC of Slag was essentially depended on the increase of solid amount with decreasing temperature. Although solid amount at high temperatures was lowered due to addition of CaCO 3 , its average increase rate (Rs) increased with increasing CaO content. When anorthite and melilite were the dominant solid formed in Slag, the Viscosity of Slag will exhibite the behavior of a crystalline Slag once Rs exceeded 0.250 wt%/°C. However, effect of CaO content on Rs diminished with increasing S/A when Rs was less than 0.250 wt%/°C. Rs is able to be used as the indication for using limestone as flux for Slag tapping.
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the internal and external factor on coal ash Slag Viscosity at high temperatures part 2 effect of residual carbon on Slag Viscosity
Fuel, 2015Co-Authors: Lingxue Kong, Xiaoming Li, Wen Li, Huaizhu LiAbstract:Abstract As an important and inevitable component of gasification Slag, residual carbon is an internal factor that influences the flow properties of Slag. In this study, the effect of residual carbon on Slag Viscosity was investigated. Viscosity of Slag containing graphite was measured at 1350–1680 °C under an argon (Ar) atmosphere. The fusibility of ash was examined with thermomechanical analyzer (TMA). X-ray diffraction (XRD) was used to investigate the mineral composition of ash processed at high temperatures and that of the Slag after Viscosity measurement. FactSage was employed to calculate the free energy (ΔG) of the reactions within ash and Slag at high temperatures. The Slag Viscosity increased with increasing the mass fraction of residual carbon, and a sharp increase of Viscosity with decreasing temperature was observed for Slags containing residual carbon. The presence of residual carbon led to the formation of crystalline phases, and it had a significant effect on Slag Viscosity when the mass fraction exceeded 5%. Quartz and mullite was the two main crystalline phases for Slags with less than 5% residual carbon. However, when the mass fraction of residual carbon was more than 5%, moissanite as well as quartz and mullite were formed in Slags. Ash fusibility increased with increasing the mass fraction of residual carbon for the same reason. Thus, less than 5% of residual carbon within Slag is desirable in order to prevent the above problems. FactSage calculation revealed that SiO2 preferred to react with CaO and Al2O3 to form anorthite and mullite at high temperatures. Moissanite was produced by carbothermic reaction among anorthite, mullite, free SiO2 and residual carbon. Furthermore, SiO2 became difficult to react with graphite as it was chemically combined with CaO and Al2O3. Due to the low ΔG of carbothermic reaction between SiO2 and residual carbon, coals with high S/A ratios are favorable to the carbothermic reaction due to the abundant free SiO2 in the ash and Slag.
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the internal and external factor on coal ash Slag Viscosity at high temperatures part 1 effect of cooling rate on Slag Viscosity measured continuously
Fuel, 2015Co-Authors: Lingxue Kong, Xiaoming Li, Wen Li, Huaizhu LiAbstract:Abstract Entrained flow gasification employs a high temperature, high pressure Slagging gasifier, in which Slag Viscosity plays a key role in determining operating conditions. The effect of cooling rate on Viscosity properties were investigated by high temperature rotational viscometer. Viscosities of two Slag, which exhibited glassy and crystalline Slag behavior, were determined under continuous measurement conditions. The results showed that viscosities of two Slag both decreased with increasing cooling rate. When the temperature was above the liquidus temperature (TLiquidus), the difference between Slag viscosities was small. However, it showed a large difference below TLiquidus, and a more obviously effect was observed on crystalline Slag. Above TLiquidus, Slag Viscosity only depended on the bulk composition of Slag which was little affected by cooling rate, resulting in the small difference between viscosities measured at different cooling rates. Below TLiquidus, Slag Viscosity was closely related to the amount of solid phase that was greatly affected by cooling rate. For glassy Slag, mullite was not crystalized in Slag during cooling, and Slag Viscosity depended on the compositions of Slag. However, for crystalline Slag, anorthite was crystalized in Slag, and its amount significantly decreased with increasing cooling rate, leading to the large difference between viscosities measured at different cooling rates. Meanwhile, temperature of critical Viscosity (TCV) decreased with increasing cooling rate, and a good linear relationship existed between TCV and cooling rate. Furthermore, TCV measured under equilibrium conditions was able to be predicted by the linear regression formula of the “continuous measurement” experiments data.
Jin Bai - One of the best experts on this subject based on the ideXlab platform.
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thermochemical and analytical approach to describe secondary Slag phase formation and local process conditions in a full scale bgl gasifier
Fuel Processing Technology, 2021Co-Authors: Daniel Schwitalla, Bernd Meyer, Jin Bai, Stefan Guhl, Marcel Laabs, Markus ReinmollerAbstract:Abstract This study aims to directly analyze untreated process samples from a full-scale BGL gasifier. It assesses as well as categorizes the findings to identify the most important effects governing the behavior of Slags under gasifier conditions. A process Slag sample from the Schwarze Pumpe BGL-type waste gasifier is thoroughly analyzed via X-ray diffraction (XRD), X-ray fluorescence (XRF), and using a scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX). The results are interpreted with the aid of thermodynamic equilibrium calculations using the FactSage™ software package to yield the main influence factors on Slag Viscosity and -structure. Since these are derived from full scale process samples, the severity of the impact to these processes can be assessed. Especially the effect of secondary phases apart from the main Slag phase is evaluated. The differences between laboratory measurements and full-scale processes are identified. The composition of the gas atmosphere above the Slag bath cannot easily be determined. This study uses a method to determine and include this gas atmosphere into the process Slag analysis through thermodynamic equilibrium calculations. The temperature of the Slag bath and the gas atmosphere around the Slag is backtracked via analytically validated thermodynamic equilibrium calculations.
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Viscosity temperature property of coal ash Slag at the condition of entrained flow gasification a review
Fuel Processing Technology, 2021Co-Authors: Lingxue Kong, Jin BaiAbstract:Abstract Viscosity-temperature property of coal ash Slag plays the key role for stable and long term operation of entrained flow gasifiers, which is the quantitative parameter for Slag tapping process. It is described by a curve of Slag Viscosity as a function of temperature, which includes three aspects: Viscosity value dependence on temperature, temperature of critical Viscosity (TCV), and pattern of Slag Viscosity-temperature curve. A clear and comprehensive understanding of Viscosity-temperature property of coal ash Slag and its influencing factors is really important for Slag tapping, operation and design of a gasifier. This review begins with essence of Slag Viscosity-temperature property and requirement for Slag tapping, and then focused on utilization of basic oxides to adjust Slag Viscosity-temperature property. It was found that TCV of a crystalline Slag is vitally dependent on crystallization behavior of Slag, and crystallization kinetics of Slag needs further to be investigated in the future. In addition, residual char in Slag, water vapor in syngas, and temperature program in Viscosity measurement significantly affect the Slag Viscosity-temperature property and Slag tapping process. Finally, based on results reported in the literatures, several perspectives were proposed for future studies on Slag Viscosity-temperature property of coal ash Slag.
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structure and flow properties of coal ash Slag using ring statistics and molecular dynamics simulation role of cao na2o in sio2 al2o3 cao na2o
Chemical Engineering Science, 2020Co-Authors: Longfei Gao, Lingxue Kong, Jin Bai, Xingchen Liu, Zongqing BaiAbstract:Abstract Molecular dynamics simulation was applied to investigate the microstructure of Slag in SiO2-Al2O3-CaO-Na2O system. A new structure model for Slag was established through ring-statistics by MD simulation. The network structure was simplified into crosslinked rings divided into three types based on the ring size. The change of amorphous structure was well described by ring distribution. The destruction of Slag structure by Ca2+ is more significant than Na+, and high CaO/Na2O resulted in low content of medium and large rings and low Viscosity. The ring distribution coefficient (Rdc) was defined to establish the relationship between structure and Viscosity: ŋ=26.7Rdc-10.2. When CaO/Na2O ratio increases, the ring distribution transforms from medium or high-order to low-order, leading to the decreasing of Rdc and Slag Viscosity. Moreover, CaO/Na2O ratio also changes the diffusivity of Slag and thus the melting behavior. Finally, a linear relationship between the empirical liquidus temperature (Tliq) and atomic diffusivity from the MD simulations was obtained.
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improved prediction of critical Viscosity temperature by fusion behavior of coal ash
Fuel, 2019Co-Authors: Tinggui Yan, Lingxue Kong, Jin Bai, Zongqing Bai, Zhigang Wang, Huiling ZhaoAbstract:Abstract Coal ash Slag Viscosity is critical for Slag tapping in entrained-flow coal gasifiers, so the accurate prediction of Slag Viscosity and the critical temperature of Viscosity (Tcv) will help the coal selection, flux addition and gasifier operation. Many empirical correlation models based on ash fusion temperature have been proposed to calculate Tcv. In order to correlate the Viscosity with the fusion behavior and then improve the prediction of Tcv, we measured the Viscosity of several synthetic coal ash Slags with a high-temperature rotary viscometer and studied their ash fusion behavior through thermomechanical analysis. X-ray diffraction was used to compare the mineral transformation before and after Tcv combined with the FactSage calculation. The Viscosity measurement shows that the Viscosity above Tcv of glassy Slags is higher than that of the crystalline type. The mineral transformation from FactSage also demonstrates that the precipitation rate of solid phase is lower for glassy Slags. The fusion behavior for the glassy and the crystalline Slag is also distinctly different. The fusion range from deformation temperature (DT) to flow temperature (FT) of the ash for the glassy Slag was larger than that of the crystalline one, and the shrinkage above FT in TMA trace slopes gently. The correlation between the fusion behavior and Viscosity-temperature behavior for the glassy Slag is reasonable, because the large temperature range from DT to FT and the low shrinking rate of the stage III indicate the high Viscosity of the liquid phase formed and the slow melting of the remained solid phase respectively, which are also the correlative condition prefer for the formation of glass as mentioned above. For the crystalline Slag, the small fusion range from DT to FT means the rapid melting of the solid phase and the high flowability of the liquid phase which are indicative for the rapid precipitation during cooling. The slow rate of the stage III indicates the slow melting of the remained solid which can be the crystal nucleus. When the Viscosity of the liquid phase is low, it also benefit for the formation of crystalline Slags. The characteristic in fusion behavior for different type of Slag also suggested that the predicting Tcv by applying one method to all the crystalline Slags and non-crystalline Slags is not appropriate.
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experimental and theoretical investigation on relationship between structures of coal ash and its fusibility for al2o3 sio2 cao feo system
Journal of Fuel Chemistry and Technology, 2019Co-Authors: Xin Dai, Lingxue Kong, Jin Bai, L I Dongtao, Ping Yuan, Tinggui Yan, Li WenAbstract:Abstract The molecular dynamics simulation, thermal dynamic calculation and experimental investigation were combined to illustrate ash Slag Viscosity variation mechanism for Al 2 O 3 -SiO 2 -CaO-FeO system. The Viscosity declines and the Viscosity curve are transformed from crystalline Slag to glassy Slag with increasing mass ratio (C/F) of calcium to ferrous oxide in Al 2 O 3 -SiO 2 -CaO-FeO system. There is an inflexion point when the C/F is equal to 2. When the C/F is below 2, there are mainly crystalline minerals in the system. While the C/F is above 2, there are mainly amorphous minerals in the system. With the increase of C/F, six-coordinated Al ([AlO 6 ] 9− ) is transformed to four coordinated Al ([AlO 4 ] 5− ) microscopically. Besides, the content of bridging oxygen decreases while that of non-bridging oxygen increases. Quantified function between base composition and Viscosity are constructed based on the stability coefficients defined by oxygen bond species.
Lian Zhang - One of the best experts on this subject based on the ideXlab platform.
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xinjiang lignite ash Slagging and flow under the weak reducing environment at high temperatures Slag Viscosity and its variation with ash type and addition of clay
Fuel, 2019Co-Authors: Baiqian Dai, Jie Zhao, Lian ZhangAbstract:Abstract In this study, five different ashes derived from Xinjiang lignite were tested for Slagging at 1300–1400 °C in a weak reducing environment (1% CO in nitrogen), at different exposure time from 10 min to 2 h. The apparent viscosities for different Slags were determined by using a modified inclined plane (M-IP) method with an inclination of 25° based on the Slag travel length per unit mass. In particular, the variation on Slag Viscosity upon the blending of additives including clay and MgO was examined in detail. As have been confirmed, the Slags derived from the original basic and neutral ashes start to flow from 1400 °C onwards. The viscosities calculated based on the M-IP method at 1400 °C are in the range from ∼1 Pa·s for neutral ash to ∼5 Pa·s for the basic ash Slags. For both neutral and acidic Slags, their viscosities calculated by the M-IP method show a good agreement with some of the existing empirical models that have been validated for high-rank coal Slags. Upon the addition of 10 wt% clay, the Viscosity of basic ash at 1300 °C was reduced to 1.53–1.71 Pa·s, demonstrating a comparable flow-ability and Viscosity to that of the original ash at 1400 °C. The addition of MgO promotes the Slag flow-ability and reduces the Slag Viscosity to a relatively small extent in comparison to clay. Instead of melting with other elements in the ash matrix to form Slag, the discrete Mg grains are observed in the Slag matrix. It could even partially react with the alumina plate. The precipitation of Mg may promote the Slag flow-ability by alleviating the Slag penetration into the alumina plane and the resultant friction between them. Additionally, the viscosities for both the original Slags and those blended with clay decrease quickly upon the increase of the exposure time, substantiating a non-linear Slagging propensity and hence, probably non-Newtonian property. A minimum exposure time of 40 min is essential to ensure these Slags to settle down and reach their equilibrium viscosities in the M-IP method.
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xinjiang lignite ash Slagging and flowability under the weak reducing environment at 1300 c a new method to quantify Slag flow velocity and its correlation with Slag properties
Fuel Processing Technology, 2018Co-Authors: Baiqian Dai, Lian ZhangAbstract:Abstract In this study, a novel measurement method for the direct visualisation and quantification of lignite Slag flowability has been established. The ash Slagging was tested under a weak reducing environment (1% CO 2 in nitrogen) at temperature range from 1000 to 1300 °C to mimic a cyclone combustion furnace for the Chinese Xinjiang lignite. Five different ash samples with a broad variation on the basicity, i.e. base/acid ratio from 1.98 to 0.27, and their blends with up to 40 wt% clay were loaded on a 25°–inclined corundum substrate and exposed to the above-mentioned reducing gases in a pre-heated horizontal furnace. The thermodynamic equilibrium software, FactSage 6.4 and typical Viscosity equations were also employed to quantify the liquid fraction in each Slag and its Viscosity, respectively. Efforts were further made to correlate the calculated liquid fraction and Viscosity of a Slag and its flow velocity. As has been found, the neutral ash with the lowest ash fusion temperature is the only original ash sample that can melt and flow at 1300 °C without the use of clay additive, although its flow velocity is quite marginal. The addition of clay into basic ashes, at 8–10 wt% is able to improve the Slag flow velocity by 6–7 times at 1300 °C. Both ash basicity and liquid fraction within an ash are critical in determining the Slag flow velocity. However, neither has proven to be a sole and sufficient factor affecting the Slag flowability. The Slag Viscosity is believed to be a key factor counter balancing the liquid fraction within a Slag. This hypothesis was proven by the addition of 5–10 wt% MgO into a basic ash that decreased both the liquidus fraction and Slag Viscosity. Since the decrease on the Slag Viscosity (based on the calculation) was more remarkable than the liquidus fraction, the Slag flow velocity was improved consequently. Apart from providing a new method to quantify Slag flowability, this study also paved a direction for the future study focusing on lignite ash Slag Viscosity and modelling approach to correlate lignite Slag properties and its flow velocity. A universal method has yet to be established for either of them.
Haifeng Liu - One of the best experts on this subject based on the ideXlab platform.
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a new prediction method for the Viscosity of the molten coal Slag part 1 the effect of particle morphology on the suspension Viscosity
Fuel, 2018Co-Authors: Jie Zhou, Zhongjie Shen, Qinfeng Liang, Haifeng LiuAbstract:Abstract Viscosity is the key factor affecting the flowability of molten coal Slag in the entrained flow gasifier. The volume fraction and morphology of solid phase in Slag are important factors affecting the Slag Viscosity. In this study, the malt syrup and the particles with different sizes and morphologies were chosen as the simulation medium to study the effect of particle morphology on the suspension Viscosity. The influences of size, shape and aspect ratio of solid particles on the suspension Viscosity were considered. It was concluded that the suspension Viscosity increased with the decrease of the particle size. The suspension Viscosity increased with the increase of the aspect ratio of the particles. This phenomenon was more obvious under the high volume fraction of solid phase. With the same size and aspect ratio, the non-spherical particles had greater effect on the suspension Viscosity than spherical particles. A correction factor was used to modify the Viscosity model with the consideration of particle size, shape and aspect ratio. The prediction results of new modified Viscosity model of the suspension finally showed good agreement with the measured experimental data.
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modeling study of residence time of molten Slag on the wall in an entrained flow gasifier
Fuel, 2018Co-Authors: Binbin Zhang, Qinfeng Liang, Zhongjie Shen, Haifeng LiuAbstract:Abstract In an entrained flow coal gasifier, the Slag Viscosity property is of great importance to the Slagging process. The Slag Viscosity is affected by the crystal mineral and the crystallization process has a time effect. The molten Slag residence time in gasifier was calculated by Slag flow model to estimate the isothermal time or crystal growth time during the cooling process. The residence times of tracer Slag unit were calculated by the Slag velocity. The residence time distribution (RTD) curve was obtained and the mean residence time was about 100–500 s in this study. Moreover, the molten Slag mean residence time decreases significantly with increasing ash contents in coal, decreases slightly with increasing operating temperatures, and increases with increasing Slag critical viscosities and temperatures. In addition, a plug flow reactor (PFR) series a similar laminar flow tubular reactor model was used to analysis the RTD curves of molten Slag with different operating conditions.
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Viscosity fluctuation behaviors of coal ash Slags with high content of calcium and low content of silicon
Fuel Processing Technology, 2017Co-Authors: Xia Liu, Qinfeng Liang, Haifeng LiuAbstract:This work aims to study the ash Slagging behaviors of two specific coals, on account of a blocking problem of the Slag discharge encountered when these coals were used in an industrial entrained-flow gasifier. Through the measurements of the ash fusion temperatures (AFTs) and the Slag viscosities of the two coal samples, it was found that while the coal ashes had sufficiently low AFTs, they exhibited a strong Viscosity fluctuation as well as a Slag foaming and expansion. By comparing to the Slagging behaviors of some artificial ash mixtures, it was ascertained that while the enrichment of sulfate in the coals ashes was responsible for the Slag foaming and expansion, the Viscosity fluctuation was attributed to a high content of calcium together with a low content of silicon in the coal ashes. With the help of X-ray diffraction (XRD) analysis and FactSage thermochemical modeling, it was found that the presence of a crystalline gehlenite phase during the Slagging process for the two coal ashes was closely related to the Slag Viscosity fluctuation. The addition of silica to the coal ashes could virtually eliminate the Slag Viscosity fluctuation. The sand (a silica rich mineral) addition method had also been successfully used in the industrial gasifier.