Ash Fusion Temperatures Research Articles

Kinetics of steam and CO2 gasification with high ash fusion temperature coal char under elevated pressure

ABSTRACTA high ash fusion temperature (AFT) coal char was gasified with steam and CO2 under elevated pressure in a modified pressurized thermogravimetric analyzer. The ambient pressure varied from 0.5 MPa to 3 MPa. It was found that activation energy Ea (char-CO2 reaction) was from 214.19 kJ/mol to 240.35 kJ/mol, and activation energy Ea (char-steam reaction) was from 170.02 kJ/mol to 174.02 kJ/mol by using shrinking core model. The factor of partial pressure influence (n) was 0.44 and 0.54 for CO2 and steam gasification, respectively. The results proved that the high AFT coal (LJ coal) has poor gasification reactivity by comparing with other research and provided complete kinetic data for developing the entrained flow gasification technology using high AFT coal.

Sodium transformation characteristic of high sodium coal in circulating fluidized bed at different air equivalence ratios

Reacting atmosphere has great influence on sodium migration during high sodium coal thermal conversion, and influence the slagging and deposition characteristics further. The effect of different air equivalence ratios (ERs) on sodium migration and transformation during thermal conversion of high sodium Zhundong coal in circulating fluidized bed was investigated. The effect of ERs on the sodium content in circulating ash and bottom ash was similar. As the decrease of ER, the sodium content in the ashes increased due to the effect of carbon inhibition. Sodium in the bottom ash exists mainly as NaAlSiO4 and NaAlSi3O8, namely insoluble sodium. As to the fly ash, the sodium content decreased with the ER increase under reducing atmosphere, whereas the sodium content increased with the ER increase under oxidizing atmosphere. Sodium mainly exists as NaCl under reducing atmosphere and Na2SO4 was the main sodium existence under oxidizing atmosphere. The variety of sodium content in the ashes with the flue gas temperature was different under different reacting atmospheres. The ash fusion temperatures were also influenced by the atmosphere to a great extent. The fly ash fusion temperature was higher than that of bottom ash at the same ER. With lower ERs under reducing atmosphere and higher ERs under oxidizing atmosphere, the risk of slagging in the furnace and fouling in tail heating surface should be paid attention during the thermal conversion of high sodium coal.

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

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% CO2 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 40wt% 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 8–10wt% 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 5–10wt% 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.

Inhibition of sodium release from Zhundong coal via the addition of mineral additives: A combination of online multi-point LIBS and offline experimental measurements

The retention performance of 5 different sorbent additives, including 2 pure additives, i.e., silica and alumina, and 3 typical natural mineral additives, i.e., kaolin, mica and pyrophyllite, on the release of sodium during the combustion of Zhundong coal is investigated via a combination of online multi-point Laser-Induced Breakdown Spectroscopy (LIBS) technique and offline measurements including inductively coupled plasma atomic emission spectrometer (ICP-AES), X-ray diffraction, and ash fusion temperatures (AFTs). The online and offline measurement results for the sodium release of Zhundong coal/additives mixtures are compared and verified with each other. Ternary phase diagram simulations are performed to further substantiate the impact of different additives on liquidus temperatures of Zhundong coal ash. All the five sorbent additives show a significant sodium retention effect, while alumina and kaolin are better additives considering the effects on AFTs.

The mineral evolution during coal washing and its effect on ash fusion characteristics of Shanxi high ash coals

Gasification has been deemed as the most promising method for the thermochemical conversion of Shanxi high ash coals, although the use of these high ash coals leads to high consumption of coal and oxygen, low syngas yield and cold gas efficiency. In order to improve gasification efficiency, it is necessary to reduce the ash content of these Shanxi high ash coals. In this work, three representative Shanxi high ash coals were floated with ZnCl2 flotation agent to obtain floated coal samples with different ash contents. The mineral evolution during coal washing and its effect on ash fusion characteristics were thoroughly investigated. A radio frequency oxygen plasma furnace, X-ray diffraction (XRD) and SIROQUANT were used to analyze the variation of mineral compositions of the floated coals. Quartz (SiO2), kaolinite (Al2(Si2O5)(OH)4), calcite (CaCO3), and tobelite (NH4Al3Si3O10(OH)2) were main mineral which were found in Shanxi high ash coals, and the high contents of quartz and kaolinite led to high AFTs (ash fusion temperatures) of these coals. As mineral content decreased, the contents of quarts, kaolinite, and calcite in the floated coals were obviously lowered, and this resulted in the decrease of S/A (mass ratio of SiO2/Al2O3) of the coal ashes. The ash fusion temperatures of Shanxi high ash coals were therefore significantly influenced by the extent of coal washing. Furthermore, the content of amorphous material in coals increased obviously with the decrease of ash content. These results have important implication in the selection of the appropriate coal washing procedure prior to gasification of these coals.

Investigating a high vanadium petroleum coke ash fusibility and its modification

Petroleum coke (petcoke), especially high vanadium (V) petcoke, has been produced increasingly because of the growing consumption of petroleum oil. Petcoke ash fusibility is closely related to ash slagging, which has an important impact on the clean and efficient utilization of petcoke. This study investigates a high V petcoke ash fusibility and its modification by coal blending and flux addition at reducing atmosphere. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to determine the crystalline minerals and surface morphology of high-temperature ash slag, respectively. The ash fusion process was predicted by thermodynamic equilibrium calculations. The results show that Shengli Oilfield petcoke (SL) has a high ash fusion temperature (AFT), whereas coal blending and flux addition can effectively decrease the AFT of SL, which may be ascribed to the mineral transformations during ash fusion process. The synergistic effects of high-melting vanadium trioxide (V2O3) and coulsonite (FeV2O4) result in the high AFT of SL. When SL blends with Shenmu (SM) coal and Qi coal (QC), the formation of low-melting andradite (Ca3Fe2Si3O12) and the decrease of V2O3 contribute to the progressive decline of AFT. When the addition of flux calcium oxide (CaO) reaches 10%, the low-melting calcium orthovanadate (Ca3V2O8) formed under reducing atmosphere decreases the AFT. With increasing CaO content, the content of V2O3 and FeV2O4 decreases while that of Ca3V2O8 and Ca3Fe2Si3O12 increases gradually, which further leads to a decrease in the AFT.

Correlations of chemical properties of high-alkali solid fuels: A comparative study between Zhundong coal and biomass

The utilization of Zhundong coal has given rise to serious ash-related issues mainly because of its high-alkali characteristic, partly similar to biomass with high-potassium content. The chemical properties of such coals and biomass may have marked impacts on reactivity and ash fouling. However, the correlations of different chemical properties of high-alkali solid fuels have been seldom investigated, and then only on a few samples. Here, a comparative study of chemical properties of Zhundong coal and biomass was conducted based on a large database. Correlations between carbon content and ash yield and carbon content and fixed carbon were noted. The fuel ratios of nearly all types of agricultural biomass lay within a range of 0.15–0.30, approximately an order of magnitude lower than those of Zhundong coals, much lower than those of Zhundong coals. There were no significant associations between chemical property and wheat-growing region. In most cases, the ash composition, even for a single biomass type, showed considerable variation, with the K2O content of wheat and corn straw ash being particularly variable. Most Zhundong coals had medium and similar ash fusion temperatures regardless of the changing ash compositions. Contrary to biomass, the Na2O content in Zhundong coal ash was an order of magnitude higher than K2O content. The ash composition of a particular biomass type usually fell in a small region of the ternary diagram of acidic-alkali metal-alkaline earth metal oxide components.

Regulation of high temperature flow properties of ash containing V and Ni

Three ashes containing V and Ni were preparation for the study. CaO addition and coal ash blending were chosen for regulation of high temperature flow properties. The regulation mechanism was explored by XRD, SEM-EDX and ternary phase diagram analysis. The results show that karelianite and Ni are main refractory matters in petroleum coke ash at high temperature. CaO addition and coal ash blending decrease the liquid temperatures of ash components except V and Ni, which reduces the ash fusion temperatures. When the contents of V and Ni are fewer than 30% in ash, CaO can obviously decrease the fusion temperature of ash, and the viscosity-temperature property becomes crystal type. When the contents of V and Ni are higher than 30% in ash, coal ash blending is an effective method to decrease the fusion temperature. In this condition, 5% of coal ash blending ratio is required, and its viscosity-temperature property is suitable for slag tapping, but when the coal ash proportion is 10% the viscosity-temperature property of ash becomes crystal type for the precipitation of vanadium-rich spinel, which cannot meet the requirement of slag tapping.

Physico-chemical characterization of slag waste from coal gasification syngas plants: Effect of the gasification temperature on slag waste as construction material

Abstract The ash fusion temperature determines the suitability of coal for the entrained flow gasification/combustion process. For this purpose, Indonesian KPU coal samples and their ash and slag contents were comprehensibly characterized via X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and inductively coupled plasma optical emission spectrometry (ICP-OES) methods. To assess their environmental impacts, leachate solutions were prepared from the discharged slag for ICP-OES analyses. The experimental data were comprehensively explained in terms of ash fusion temperatures and fluidity properties of the coal ashes. More specifically, the coal slagging behavior inside of coal gasifier/combustors necessitated optimization of the operational conditions for subsequent mild slagging. The currently used coal gasification operation temperature ranges favored mild slagging at 1200 to 1300 °C (19.9 to 20.1 bar) and incomplete slagging at 1100...

Investigation on Blended Ash Fusibility Characteristics of Biomass and Coal with High Silica–Alumina

The blended ash fusibility characteristics and its variation mechanism of biomass (peanut hull (PH), bean straw (BS), and corn cob (CC)) and Changzhi coal (CZ) with high silica–alumina were investigated using an ash fusion temperature (AFT) detector, thermogravimetric differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and FactSage software. The results showed that the AFT of CZ mixed ash decreased with the addition of PH ash, and the AFT of CZ mixed ash decreased rapidly (0–30%) and then changed slowly (30–50%) with an increasing BS ash mass ratio; however, the AFT of CZ mixed ash decreased first (0–20%) and then increased (20–50%) with an increasing CC ash mass ratio. The different AFT variations mainly depend on the ash chemical compositions and their existing form. Biomass ash with high contents of fluxing oxides promotes the transformations of high melting point (MP) mullite and quartz into low-MP minerals and their eutectics, resulting in a decrease in the AFT. At high temperature, ...

Optimization of leaching conditions for removing sodium from sodium-rich coals by orthogonal experiments

The leaching pretreatment has been adopted to mitigate the ash-related problems encountered during gasification and combustion of sodium-rich coals. However, the wide-spread applications of this technology are limited to produce the ultra clean coal through remove all the ash by some aggressive agents. In the present study, some mild agents, such as deionized water, ammonium acetate solution and diluted hydrochloric acid, were employed to selectively remove troublesome sodium rather than all the ash. The primary leaching conditions such as particle size, temperature, residence time and concentration of agents were optimized by orthogonal experiments for the first time to achieve maximum removal efficiency of sodium (RES). Based on the range analysis, it was found that the significant factor was leaching temperature in the water-leaching (W-leaching) treatment and the RES showed a positive correlation with temperature. However, in both ammonium acetate-leaching (A-leaching) and diluted hydrochloric acid-leaching (H-leaching) treatments, the concentration of agents were found to play the dominant role and RES presented a volcanic relationship with it. Under optimal conditions, the leaching treatments were less time-consuming with improved RES (47.6% for W-leaching, 97.9% for A-leaching and 96.8% for H-leaching). Besides, the properties of coal samples after leaching were determined by a series of analysis methods. The results showed that the leaching treatments could significantly decrease the content of AAEMs and coal ash. Due to the removal of AAEMs, the ash fusion temperatures increased, while both gasification and combustion reactivity decreased obviously. The application to other three sodium-rich coals confirmed that the optimal leaching conditions had a good universality.

Prediction of correlation between ash fusion temperature of ASTM and Thermo-Mechanical Analysis

Ash problems, such as slagging and fouling, are important because of their negative effect of reducing the heat transfer on the furnace wall and tube in pulverized coal boilers and decreasing the boiler safety. However, slagging has positive effect on gasifier. Slagging is protecting furnace wall and reducing heat loss in gasifier. Slagging and fouling are related to ash deposition, which is determined by the coal-ash fusion temperature, chemical composition of coal ash, and boiler operating conditions et al. The coal-ash fusion temperature is a particularly important factor in slagging and fouling. To measure the ash fusion temperature, the ASTM D1857 test is used, not only by thermal power plants and steelmaking companies in South Korea but all over the world. In this study, the fluid temperature (FT) of ASTM D1857 was predicted by Thermo-Mechanical Analysis (TMA). Three bituminous coals (Glencore, Trafigura, Moolarben) and four sub-bituminous coals (KPU, Berau, Jembayan, PRB) were selected for the TMA tests, wherein T25, T50, T75, and T90 were measured. These four temperatures corresponded to shrinkage levels of 25%, 50%, 75%, and 90%, respectively. The T90 of the bituminous coals and T50 of the sub-bituminous coals were similar to the initial deformation temperature (IDT) of ASTM. The T90 of the bituminous coals was greater than 1300°C, and the T90 of the sub-bituminous coals was ∼1250°C. Two FT-prediction equations—for bituminous coal and sub-bituminous coal—were established according to the T25, T50, T75, and T90 relationships of each coal. The FT-prediction equations indicated an average gap of 71°C in the sub-bituminous coals. For the sub-bituminous coals, the average difference was quite low: ∼23°C. The FT-prediction equations matched the FT of ASTM and are useful for determining the ash fusion temperature in a short time.

Physicochemical properties and gasification reactivity of the ultrafine semi-char derived from a bench-scale fluidized bed gasifier

Zhundong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization. The purpose of this study is to investigate the physicochemical properties and gasification reactivity of the ultrafine semi-char, derived from a bench-scale fluidized bed gasifier, using Zhundong coal as fuel. The results obtained are as follows. In comparison to the raw coal, the carbon and ash content of the semi-char increase after partial gasification, but the ash fusion temperatures of them show no significant difference. Particularly, 76.53% of the sodium in the feed coal has released to the gas phase after fluidized bed gasification. The chemical compositions of the semi-char are closely related to its particle size, attributable to the distinctly different natures of diverse elements. The semi-char exhibits a higher graphitization degree, higher BET surface area, and richer meso- and macropores, which results in superior gasification reactivity than the coal char. The chemical reactivity of the semi-char is significantly improved by an increased gasification temperature, which suggests the necessity of regasification of the semi-char at a higher temperature. Consequently, it will be considered feasible that these carbons in the semi-char from fluidized bed gasifiers are reclaimed and reused for the gasification process.

Effect of Ash Composition (Ca, Fe, and Ni) on Petroleum Coke Ash Fusibility

Ash fusion behavior is closely associated with ash-related problems including fouling, sintering, and slagging, which results in a negative effect on the utilization of petroleum coke (petcoke). Petcoke ash contains high levels of vanadium (V), nickel (Ni), iron (Fe), and calcium (Ca). The chemical composition of ash plays an intrinsic role in determining ash fusibility. To better understand the modification mechanism of the ash fusion temperatures (AFTs), this study investigates the influences of ash composition (CaO, Fe2O3, and NiO) on the synthetic petcoke ash fusibility from the perspectives of ash composition change and temperature rising. The AFTs of synthetic ash samples were identified by the ash fusibility tester. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were applied to explore the relationships between the experimental AFTs and the variation of mineral composition and microstructure of high-temperature ash slag. Moreover, the ash melting process was predicted by the SiO2–...

Effect of Chemical Compositions on Ash Fusibility Characterization of a Jincheng Anthracite during Combustion and Gasification

The ash melting temperature of coal ash has an important effect during the fluidized bed combustion and gasification process, which affects the slagging and deposition characteristics of the boiler. Experiments on the effects of chemical components on the ash fusion behaviors have been completed on the ash fusion temperatures (AFTs) analyzer under typical gasification and combustion atmospheres. Meanwhile, calculations on the variation of minerals in ash with ash composition were conducted using the FactSage software. The results indicated that the AFTs under gasification were a little higher than those under the combustion atmosphere. On increasing the Fe2O3, CaO, and Na2O contents under the combustion and gasification atmospheres, the four temperatures deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT), and flow temperature (FT) decreased dramatically and the generation and transformation of minerals occurred. The iron-containing minerals, such as hercynite and fayalite, formed with increase in the content of Fe2O3; the Ca-bearing feldspar minerals, like gehlenite and anorthite, started appearing on increasing the CaO content, and the Na-containing feldspar minerals, like carnegieite, were detected as the Na2O was increased. These three minerals can form low-temperature eutectics, decreasing the fusion temperature.

Regulation of ash-fusion behaviors for high ash-fusion-temperature coal by coal blending

Blending is a promising method to modify the ash-fusion characteristics of coal to meet gasification requirements. To investigate the variation in ash-fusion behavior for high ash-fusion-temperature (AFT) coal through coal blending and its regulating mechanism, the ash-chemistry characteristics of four coals (Nantun, Pengzhuang, Biaodian, and Xiangyuan) were analyzed. Mineral-transformation behaviors in the mixed ashes were investigated by X-ray powder diffractometry using normalized reference intensity ratio software, scanning electron microscopy analyzer equipped with energy-dispersive X-ray spectrometry, and FactSage software. Pengzhuang and Biaodian coals, AFTs meet entrained-flow gasifier requirements when the Xiangyuan mass ratio reaches 20%. The Nantun requires a Xiangyuan mass ratio of XY >30% because of its high aluminum oxide content. The required Xiangyuan optimal blending mass ratio is 40%–70% for the three high AFT coals to meet gasification requirements in the entrained-flow gasifier. An increased Xiangyuan mass ratio leads to decreasing contents of high melting-point mullite and silica and increasing contents of low melting-point anorthite, hercynite, gehlenite, and hedenbergite. Amorphous matter in three mixed ash types resulted in a decrease in their AFTs. The variation in liquid phase under certain conditions reflects the change in AFT.

Influence of phosphorous based additives on ash melting characteristics during combustion of biomass briquette fuel

To solve the ash related problems during biomass combustion, the combustion process, potassium fixation and ash fusion temperatures of two agricultural biomass briquettes (maize straws and cotton stalks) with phosphorus-based additives (NH4H2PO4 and Ca(H2PO4)2) were investigated. The briquetting process were performed in a lab-scale densification system. Results showed that the ash of maize straw briquette extends to agglomeration at 900 °C, and fully melted at 1000 °C and 1100 °C. The melted products were dark solid glaze shape, adhered to the porcelain boat. Additives enhanced potassium fixed ratios by different levels. At 1100 °C, the potassium fixed ratio changing rate of NH4H2PO4 was 52.87%–64.89%, while that of Ca(H2PO4)2 was 35.90%–41.74%. So the influence of NH4H2PO4 on potassium fixation ability was better than that of Ca(H2PO4)2. High melting point calcium potassium phosphates were produced by adding additives from XRD. SEM-EDS showed that the additives attached on fibers physically, reacting with potassium chemically, preventing the shrinkage and melt. Both NH4H2PO4 and Ca(H2PO4)2 increased ash fusion temperature of biomass briquettes by 55–277 °C.

Mineral phase transformation of biomass ashes – Experimental and thermochemical calculations

Abstract The paper is focused on the thermal characterisation of biomass ashes especially of mineral phase transformation. Ash generated during combustion (with high alkali metal concentration) can deposit and consequently cause serious operating problems such as slagging, fouling and corrosion of metal surface limiting heat transfer. Four biomass ashes with different origin were investigated. The chemical composition of the mineral matter of ashes varied between the samples, but CaO, SiO 2 , K 2 O, MgO, P 2 O 5 and Al 2 O 3 are the main compounds of the ashes. The thermal behaviour of ashes was studied using TG-DSC and Ash Fusion Temperatures (AFTs) techniques. In order to describe and understand the mineral matter transformation at high temperatures the FactSage Thermodynamics Model was used. FactSage calculations allowed to predict chemical composition in equilibrium, showed amount of liquid slag and solid phases, and gave information about slagging properties of ashes. A corrosion study of the metal surface used for heat transfer biomass ashes was undertaken. The corrosion behaviour of steel X10CrMoVNb9-1 in the present of biomass ash at 650 °C in 1000 h in furnace. The degradation of the metal surface was investigated by observation of surface morphology using the SEM method. The presence of potassium and chlorine in deposits causes the acceleration of oxidation. They break and peel off the surface easily, thus evidently accelerating corrosion.

The fusion characteristics of ashes from anthracite and biomass blends

Fusion characteristics of ashes from anthracite and biomass (pine sawdust and corn stalk) blends were investigated. These ashes were prepared in a muffle furnace (MF) and a drop tube furnace (DTF) at the temperatures of 815 °C and 1200 °C respectively. The fusion temperatures of ashes were measured in an ash fusion temperature analyzer, the morphological characteristics and element component of ashes were analyzed by means of SEM (Scanning Electron Microscope) fitted with EDS (Energy Disperse Spectroscopy). The minerals species and transformation characteristics were also detected using XRD (X-ray diffraction). The fusion temperatures of MF blends ashes were lower than those of DTF blends ashes because of the difference of ash preparation temperatures. The structures of ashes made in MF were dispersed and loose, but the ashes made in DTF were denser and larger resulting in obvious agglomeration. The fusion temperatures decreased with biomass addition ratio increasing due to large amounts of alkali and alkali-earth species in pine sawdust/corn stalk ash regardless the ash preparation method. K and Ca-bearing compounds can react with aluminosilicates in anthracite to create low temperature eutectics which can decrease the fusion temperatures of anthracite and biomass blends.

The Impact of Bark Content in Wood Pellets on Emission Production During Combustion in Small Heat Source

The combustion of biomass is relatively complicated. To minimize the emission production it is necessary to ensure the optimal setting of combustion process. The article deals with the impact of bark content in wood biomass on performance and emission parameters of a small heat source. The increasing content of bark in wood biomass changes its chemical composition and parameters, namely its net calorific value, ash content, ash fusion temperature and others. During experiments samples of wood pellets made from spruce having 1, 2, 5 and 10 percent bark content together with a reference sample without any bark content were burned. The samples were burned in a hot water boiler with a rated output of 18 kW. It was found out that with the increasing bark content, the thermal output of the heat source decreases and the emission production increases, particularly the production of both carbon monoxide (CO) and particulate matter (PM). At the same time it was confirmed that with the increasing bark content the amount of ash also increases. Results showed that the burning of wood pellets with higher bark content has a more negative impact on the environment.