Synthetic Ash Research Articles

Slagging inhibition through co-firing of coal gangue and high sodium coal: An experimental and modelling study

This study delves into the intractable slagging issues encountered in the combustion of high-sodium coal (HSC), with a particular focus on assessing the mitigating effects of co-combusting HSC with two types of coal gangue (CGs). Through detailed examination of the mineralogy and fusion temperatures (AFTs) of the ashes, alongside meticulous experimentation and theoretical analysis with synthetic ashes (SAs), the key factors affecting AFTs were identified. The results show that co-combustion of HSC with just 10% CGs notably raised AFTs, reducing slagging and fouling risks, thus enhancing safe use of HSC in industrial boilers. These improvements stem from compositional changes in the major components of ashes through co-combustion. AFTs were found to decrease with increased alkali oxides (Na2O, K2O) and iron oxide (Fe2O3) content, exhibiting a non-linear response to SiO2/Al2O3 ratio with a minimum at 2. The elevation in AFTs results from introducing acidic components and concurrently reducing alkali oxides and Fe2O3 through co-combustion. Optimal CGs for co-combustion with HSC features low alkali oxides content, high combined SiO2 and Al2O3 levels, a balanced SiO2/Al2O3 ratio, and reduced Fe2O3 content. Such selections not only mitigate ash-related issues but also promote eco-friendly waste utilization. In summary, this work provides a strategic framework for selecting CGs to co-fire with HSC in industrial boilers, targeting slagging and fouling mitigation, and integrating sustainable waste management practices into energy production. The findings underline the potential of co-combustion strategies for mitigating ash-related problems and advancing towards greener energy solutions.

ASSESSMENT OF THE CORROSION-MECHANICAL PROPERTIES OF THE LEFT MATERIALS AND FORECASTING THE SAFETY OF GAS TURBINE PARTS

Purpose. Determination of the possibility of using the temperature-time parametric dependences of Miller-Larson, Manson-Haferd, and Sherby-Dorn for long-term prediction of the strength characteristics of parts subjected to oxidation and high-temperature sulfide-oxidation effects. Research methods. Long-term strength studies were performed on samples of ВЖЛ-12У and ЗМІ-3У alloys in synthetic ash (66.2 % Na2SO4, 20.4 % Fe2O3, 8.3 % NiO, 3.3 % CaO, 1.8 % V2O5) and an oxidizing environment at temperatures of 800 °C and 850 °C. The Miller-Larson, Manson-Haferd, and Sherby-Dorn temperature-time parametric dependences were used to predict the tensile strength of materials in an oxidizing and corrosive environment. The microstructure of the samples was studied using an optical microscope MIM-8M. Results. The results obtained indicate a high level of corrosion resistance of ЗМІ-3У samples at 800 °C and 850 °C and the possibility of determining the tensile strength of the material for a period of 1000, 5000, and 10000 hours by the calculation method. Tests of ВЖЛ-12У alloy samples in synthetic ash showed a discrepancy between the experimental time to fracture and the calculated value, regardless of the parametric method, which indicates a direct dependence of long-term strength on the degree of corrosion damage to the surface of the samples. Scientific novelty. The possibility of using the Miller-Larson, Manson-Haferd, and Sherby-Dorn temperature-time parametric dependences for long-term prediction of the strength characteristics of parts in an oxidizing environment has been confirmed. In a sulfide-oxide environment, the use of parametric methods to determine strength characteristics for up to 10,000 hours is possible only for corrosion-resistant alloys. Intensive corrosion damage to ВЖЛ-12У alloy leads to accelerated deformation, which limits the use of temperature and time dependencies for effective prediction of the time of failure of parts made of this material. Practical value. Determining a reliable method for predicting the strength characteristics of heat-resistant alloys in an oxidizing and corrosive environment allows reducing the time and financial costs of conducting lengthy field studies.

Understanding adhesion induced by calcium compounds at 900 °C using model particles

In waste and biomass combustion plants, ash adheres to the inside of the combustors and surfaces of air heaters, etc., accumulating over time and causing operational problems due to the deposited ash layer. Here, we evaluated the adhesion properties of calcium-rich ash using synthetic ash. Specifically, we investigated the role of Ca-Al in ashes. The adhesion of Ca-Al synthetic ash and mixed ash of Ca-Al and SiO2, which is included in ash and utilized as a bed material in fluidized-bed combustion systems, was investigated. Adhesion was found to increase when three conditions were met: Ca/Al molar ratio >1, SiO2 coexistence, and 900 °C. The increase in tensile strength of the powder bed corresponded to shrinkages in volume, specific surface area, and total pore volume, suggesting solid phase sintering as the cause of increased adhesion. Adding alumina nanoparticles to the highly adherent sample successfully suppressed the adhesion increase.

Effects of phosphorus on the fusion characteristics of synthetic ashes with different Al2O3/CaO ratios

In this paper, five series of synthetic ashes with different Al2O3/CaO ratio mass ratios were prepared, and the ash fusion temperatures (AFTs) of the samples with different percentages (5–20 wt%) of phosphorus pentoxide (P2O5) added were measured under a mild reducing atmosphere to study the effect of phosphorus on the fusion characteristics of the ashes in different compositions. X-ray diffraction (XRD), thermodynamic equilibrium calculations, and high-temperature heating stage microscopy (HHSM) were used to investigate the mechanism of phosphorus in changing the fusion characteristics of the ash. The results showed that the addition of P2O5 produced the least effect on AFTs of samples with an Al2O3/CaO ratio of 6:4. For lower Al2O3/CaO ratios (classified as peralkaline), the addition of P2O5 caused a decrease-increase-decrease trend in AFTs, while for higher Al2O3/CaO ratios (classified as peraluminous), the AFTs of samples were decreased by phosphorus. The stronger affinity of P2O5 for CaO and Al2O3, compared to that of SiO2, was noticed and led to a shift of main minerals in the slag from silicates to phosphates and to the isolation of SiO2. In addition, the phosphorus-bearing samples followed the same “melt-dissolution mechanism” as the phosphorus-free samples.

Correlation between Flow Temperature and Average Molar Ionic Potential of Ash during Gasification of Coal and Phosphorus-Rich Biomass

The co-gasification of biomass and coal is helpful for achieving the clean and efficient utilization of phosphorus-rich biomass. A large number of alkali and alkaline earth metals (AAEMs) present in the ash system of coal (or biomass) cause varying degrees of ash, slagging, and corrosion problems in the entrained flow gasifier. Meanwhile, phosphorus is present in the slag in the form of PO43−, which has a strong affinity for AAEMs (especially for Ca2+) to produce minerals dominated by calcium phosphates or alkaline Ca-phosphate, effectively mitigating the aforementioned problems. To investigate the changing behavior of the slag flow temperature (FT) under different CaO/P2O5 ratios, 72 synthetic ashes with varying CaO/P2O5 ratios at different Si/Al contents and compositions were prepared, and their ash fusion temperatures were tested. The effects of different CaO/P2O5 ratios on the FT were analyzed using FactSage thermodynamic simulation. A model for predicting slag FT at different CaO/P2O5 ratios was constructed on the basis of the average molar ionic potential (Ia) method and used to predict data reported from 19 mixed ashes in the literature. The results showed that Ia and FT gradually increased with a decreasing CaO/P2O5 ratio, and the main mineral types shifted from anorthite → mullite → berlinite, which reasonably explained the decrease in ash fusion temperatures in the mixed ash. The established model showed good adaptability to the prediction of 19 actual coal ash FTs in the literature; the deviation of the prediction was in the range of 40 °C. The model proposed between FT and Ia based on the different CaO/P2O5 ratios can be used to predict the low-rank coal and phosphorus-rich biomass and their mixed ashes.

Superheater ash deposit ageing – Impact of melt fraction on morphology and chemistry

The initial melting behaviour of synthetic ash deposits, with a focus on how the amount of melt formed, affects the final deposit morphology, was studied. Binary and ternary reciprocal deposits were exposed to a temperature gradient with varying exposure time, steel temperature, and furnace temperature. Two different archetype deposit morphologies emerged. The final deposit morphology was identified to depend on the amount of melt formed during the experiment. A skeletal deposit morphology developed in systems with less than 30 wt-% melt. Short-term experiments proved that the formation of the skeletal structure is accelerated by the presence of melt, accumulating at contact points of distinct particles. If melt fractions exceeded 30 wt-%, a molten morphology developed, as the amount of melt present was sufficient to fill the pores within the deposit. For molten deposits of ternary reciprocal systems, enrichment of K in the formed melt and concurrent movement toward the steel was observed. The results confirmed a deposit ageing mechanism that has been proposed earlier, based on full-scale superheater deposit samples. The experiments showed that deposit melting and ageing behaviour are strongly connected, as the two identified morphologies differed in their ageing behaviour. The presented results improve the understanding of the initial melting behaviour of deposits and illustrate the connection between deposit morphology and deposit ageing. The results can be utilised as input data for deposition models and help in predicting the final deposit morphology and its associated ageing behaviour, aiding boiler operators and manufacturers dealing with deposit-related issues.

Investigations on Single Minerals and Synthetic Ash Components for the Enrichment of Copper from Waste Incineration Bottom Ashes by Flotation

Currently, MSWI (municipal solid waste incineration) ashes are predominantly landfilled, although they can have copper contents comparable to those of low-grade ores. Based on a previously published characterization of MSWI-BA, this paper presents investigations on the identification of potential collectors for copper recovery from MSWI-BA by flotation. The studies were conducted with single minerals (mainly copper oxide and sulfide) and synthetic slag components. Collector screening included thiourea-, thiophosphate-, and thiocarbamate-based collectors. In addition to commercial collector mixtures, pure ureas were also examined. At least one representative from each collector group was selected for the more in-depth studies: the thiourea S-n-dodecyle-iso-thiourea hydrochloride, the thiophosphate Danaflot 245, AERO 3473, and AERO MX-5160 as a mixture of a thiocarbamate and thiophosphates. Studies of the influence of collector concentration and pH were carried out with these. In addition, the contact angles of various metal oxides and the matrix composition with and without collector treatment were determined. Subsequently, flotation tests were carried out with mixtures of copper oxide and the individual matrix components (quartz, glass, cement, gypsum). AERO MX-5160 proved to be the most suitable collector, although alginic acid was added as a depressant due to a lack of selectivity towards gypsum.

Impact of potassium on bio-ash slagging and resultant slag flowing characteristics under mild reducing environment

This study aims to clarify the role of potassium (K) on the flowability of bio-slag in the reducing gas environment at 900-1400 °C. Through the use of an inclined plate method, a number of approaches were attempted to clarify the flow rate of bio-slags as a function of basic-to-acid ratio, as well as the comparison with a reference coal ash and synthetic ashes made by the blending of bio-ash with CaO, Al2O3 and K2O. At the same base-to-acid ratio (B/A) and 1400 °C, coal slag has a flow rate that is nearly four times larger than that of bio-slag. This is due to the co-existence of abundant K2O and Al2O3 in bio-slag that is in favour of the formation of solid KAlSi2O6. In contrast, the co-existence of abundant CaO and Al2O3 in coal slag is in favour of the formation of molten species. In addition, the inherent K in bio-ash underwent considerable mass loss due to both vaporisation and its interaction with the corundum plate. Upon the increase in the inclination angle of the plate, the extent of K penetrating within the corundum plate was mitigated considerably, which in turn minimised the plate corrosion. Simultaneously, the bio-slag formed readily spread out along the plate. The addition of extra K into bio-ash is beneficial in promoting the flow rate. However, even with an increased base-to-acid ratio to 1.2, the flow rate of bio-slag is still less than that of coal slag at the base-to-acid ratio of 0.72, due to the superiority of Ca2+ over K+ in promoting the bio-slag flow. For practical application, the use of CaO as a flux additive is beneficial in discharging the bio-slag out of the furnace. Moreover, the flow rates of bio-slag in the locations with low angles to the ground within the furnace should be monitored to minimise the accumulation of bio-slag as well as its corrosion against the refractory wall.

Effect of iron on crystallization and flow properties of coal ash slag: A combined computational-experimental study

The crystallization and viscosity behavior of coal ash slag play a decisive role in the stable slagging of industrial gasifiers. However, the influence of iron on the crystallization and flow properties of slag is still poorly understood for its heterovalent component. Therefore, the influence of iron on the melting and crystallinity of slag was studied by preparing synthetic ashes with different iron contents, in this work. The results demonstrated that the ash fusion temperature (AFTs) could be significantly lowered with the increase of Fe content. This was because of the low-temperature eutectic reaction in slag caused by the increased iron content, which led to the transformation of the sub-liquid phase in slag from high-melting mullite to low-melting anorthite and spinel. At high temperature, iron was mainly presented in slag as Fe2+. At the same time, Fe2+ as an alkaline component could terminate the interconnection between [SiO4]4- and [AlO4]5- tetrahedral by replacing Si4+ and Al3+ in slag. This consequence destroyed the slag network structure and lowered the polymerization degree. Slag with lower polymerization degree exhibited lower viscosity and stronger ionic transport capacity, which was favorable for crystal growth. Meanwhile, thermodynamic and quantum chemical calculations revealed that anorthite was a crystalline mineral during slag cooling.

Influence of MgO content on bio-ash slagging propensity and flowability under mild reducing environment

In this work, an inclined plate technique was used to investigate the slagging propensity of bio-ashes and the flowability of the resulting bio-slags in a reducing gas environment at 1300 °C. A number of different approaches were trialled to visualise and measure the slagging propensity of bio-ash as a function of MgO content, as well as their comparison with reference coal ashes and several synthetic ashes generated by blending bio-ash with CaO, Al2O3, SiO2 and K2O individually and/or collectively. As has been found, the presence of 6–16 wt% MgO in bio-ash and coal ash exerted little influence on the ash fusion temperature. However, the slag flowability is slow for a relatively high viscosity of the bio-slags. In contrast, the coal slags flew much faster, although the formation of spinel crystals was confirmed in the high MgO content. Among the major basic oxides within bio-ash and coal ash, CaO is most influential in depolymerising ash matrix to promote its flowability. In contrast, the presence of Fe2O3 is subtle, a small increase of whose content can cause the interaction with MgO for the formation of crystallised spinel. The co-presence of K2O and Al2O3 is the most negative, causing a significant decrease in the slag flowability. Finally, regarding the traditional methodologies for ash study, the base/acid (B/A) ratio for an overall balance between basic and acid oxides is unable to differentiate the discrepancy between coal ash and bio-ash. Likewise, the thermodynamic equilibrium prediction on liquidus amount and viscosity should be deemed as the empirical index that overlooks the kinetic control and formation of crystalline for the Mg-rich ash samples.

Controlling particle adhesion of synthetic and sewage sludge ashes in high temperature combustion using metal oxide nanoparticles

During combustion, ash particles can adhere to the internal walls of the plant due to partial melting and generate a liquid bridge force at the high operating temperatures. The adhered ashes inhibit energy recovery and stable operation of the plant. To achieve highly efficient energy recovery during combustion, it is necessary to investigate suitable methods to control adhesiveness according to each operational case. Herein, the ability of small amount (1–3 wt%) of nanoparticles (NPs: SiO2 NPs, Al2O3 NPs, and Fe3O4 NPs) as additives to control the adhesiveness at high temperatures was investigated. The controllability of each type of NP with respect to the adhesiveness of various synthetic ashes, which served as model compounds, was evaluated to clarify the role played by the different NPs. To demonstrate the practical utility of the NPs as additives, ash samples derived from the incineration of sewage sludge were investigated. Given the chemical complexity of the ash systems, it was discovered that a chemical effect and an increase in the porosity of the powder bed can effectively decrease the adhesiveness of ash particles produced at high temperatures.

Shear Strength Testing of Synthetic Ash: The Role of Surface vs Interparticle Adhesions

In thermal power plants, deposition of fly ash on the surfaces of the heat exchanger causes a significant drop in the heat-transfer efficiency and this inhibits effective fuel utilization. It is widely accepted that alkali metals such as sodium and potassium are the trigger for fly ash deposition given that the alkali metals potentially form low-melting-point materials which have adhesive properties and can be deposited on the surface of the exchanger. However, detailed mechanistic studies of this process are challenging due to the chemical complexity and diversity of fly ash samples collected from commercial thermal plants. Herein, it is demonstrated that fly ash deposition triggered by alkali metals can have different mechanisms due to the effects of interparticle and/or surface adhesions. A key enabler for facilitating detailed mechanistic studies is the combined use of tensile and shear strength testers linked to a synthetic ash strategy that utilizes chemically synthesized inorganic particles.

Migration behavior of potassium under condition of steam gasification of Yulin coal

A fixed bed reactor and atomic absorption spectroscopy were used to investigate potassium recovery efficiency of Yulin coal loaded with potassium carbonate (ZA-K), Yulin demineralized coal loaded with potassium carbonate (ZA-THK) and synthetic ash (Configurations of four oxides: SiO2, Al2O3, CaO, Fe2O3) loaded with potassium carbonate after reaction. Fourier infrared spectroscopy and Raman spectroscopy were used to study influence of structural evolution of ZA-K and ZA-THK on migration of potassium during pyrolysis. The results show that the yield of water-soluble potassium decreases with increasing temperature. Three times water washing could recover 94.06%−98.80% of the total water-soluble potassium. Formation of insoluble potassium is due to the phase of potassium aluminosilicate formed by potassium, silicon and aluminum in the coal ash. Potassium is easier to volatilize from ZA-THK than that from ZA-K. At 700−850 °C potassium in ZA-THK is volatilized 10.28%−44.92% higher than that of ZA-K, resulting from that the ash in ZA-K would fix the loaded potassium in coal ash. Another reason may be caused by decrease in the degree of aromatic polymerization of ZA-THK through demineralization process, leading to more small-ring aromatic structures (2−8 rings) appearing in the coal.

Role of Phosphorus and Iron in Particle Adhesiveness at High Temperatures Using Synthetic Ashes

During sewage treatment, phosphorus (P) is concentrated in sewage sludge, and the sludge is incinerated to produce P-concentrated ash particles. The P-containing ash particles possess high adhesive...

Effect of the MCM-41 mesoporous silica on the microstructure and performance of cement matrix

The paper describes the results of research on the influence of the MCM-41 mesoporous silica on the selected properties of cement matrix. The MCM-41 used in the study was produced from waste solution after production of synthetic ash zeolites, which made the material much cheaper than its commercial counterparts. Mechano-physical properties were evaluated and the microstructure was analyzed by XRF, XRD, SEM-EDS, and nitrogen adsorption/desorption tests. The most beneficial content of the MCM-41 was found to be between 0.5 and 1%. It was noticed that the excess of active silica causes disturbances in the proper hydration process, which was schematically modeled. No studies have been reported in the literature so far which would be devoted to the assessment of the influence of the MCM-41 on the properties of the cement matrix, and the research conducted indicated a very high application potential of this additive.

Influence of water vapor on continuous cooling crystallization characteristics of coal ash slag

The influence of water vapor on crystallization characteristics and kinetics of two synthetic ashes during continuous cooling were investigated by the single hot thermocouple technique (SHTT) and differential scanning calorimetry (DSC) under Ar with 0%, 10%, 20% and 30% H2O. Anorthite (CaAl2Si2O8) and gehlenite (Ca2Al2SiO7) were the major crystalline phases for the slag with 75.44% (YL) and 29.72% (YZ) silicon-aluminum levels, respectively. As the water vapor content increased, the initial crystallization temperature (Ton) and the maximum crystal ratio (Xmax) of the YL slag increased, while it decreased for the YZ slag. The continuous cooling crystallization kinetics was determined based on DSC data. The effect of water vapor proportion on crystallization temperature of the slag showed a similar trend with that on the TCV. As the water vapor proportion increased, the obtained values of crystallization activation energy (Ec) of the YL slag decreased, while it increased for the YZ slag. The influence of water vapor on crystallization kinetics of coal ash slag showed its dependence on nucleation and crystal growth style during continuous cooling. The results well explained the influence of water vapor on crystallization behavior of anorthite and gehlenite crystalline phases as well as its effects on slag viscosity and TCV in our previous studies.

Superheater deposits and corrosion in temperature gradient – Laboratory studies into effects of flue gas composition, initial deposit structure, and exposure time

The heterogeneous nature of the ash chemistry of biomass fuels gives rise to challenges in predicting the deposit melting, sintering, and enrichment of corrosive ash species. An experimental method has been developed to study the evolution of ash deposit chemistry and morphology in temperature gradients simulating the conditions of real superheater deposits. The method is based on applying synthetic ash mixtures on an air-cooled corrosion probe, which is inserted into a tube furnace. The focus has been on how the melting behavior of alkali salt-rich deposits, i.e., KCl–K2SO4–NaCl–Na2SO4 mixtures, affects the chemistry and morphology. Intradeposit vaporization-condensation of alkali chlorides has been of interest. The interaction of reactive gas components (H2O + SO2), with the deposits, was also studied. The vaporization-condensation mechanism leads to enrichment of alkali chlorides in crevices and voids within deposits, leading also to build-up of chlorides on the steel surface, which causes accelerated corrosion, due to the formation of low-melting FeCl2 mixtures. Liquid phase sintering and temperature gradient zone melting (TGZM) were the main mechanisms for the supersolidus sintering of the deposits. Iron and nickel oxides were found within the deposits and at the outer edge of deposits, due to the TGZM mechanism.

A FactsSage Simulation Study on the Interaction of Synthetic Petcoke Slags with Alumina Crucibles

In entrained flow gasifiers, inorganic species in solid fuels are converted to slag, which flows continuously along the gasifier’s refractory lining. Slag viscosity is critical for its continuous flow and, consequently, reliable operation of the gasifier. Viscosity of synthetic petcoke ash was measured in a high temperature viscometer (up to 1500 °C) using high alumina crucibles. Crucible material was found to dissolve in slag, causing thinning and leading to formation of holes on the walls. To explain this dissolution, thermodynamic equilibrium calculations were performed in FactSage™ (Thermfact/CRCT, Montreal, QC, Canada and GTT-Technologies, Aachen, Germany) using different synthetic petcoke ash compositions in 100% H2, 5% H2/ 95% N2, 69.5% CO/30.5% CO2, and 100% O2 atmospheres. An inverse correlation was found between crucible dissolution and alumina content in the slag. Rates of dissolution of alumina from crucible into slag varied significantly in the different atmospheres. The correlation was validated experimentally by heating six synthetic slags with varying compositions to 1500 °C in 5% H2/N2 (to simulate viscometer’s atmosphere) gas. SEM-EDS analysis of the samples confirmed that the sample with lower initial content of alumina in the slag showed higher amounts of aluminum at the slag–crucible interface. Additions of alumina in the synthetic petcoke ash (containing up to 49.74% V2O5) mitigated crucible dissolution.

Mechanistic Determination of the Role of Aluminum in Particle Adhesiveness at High Temperatures Induced by Sodium and Potassium Using a Synthetic Ash Strategy

Energy recovery from various fuels with high efficiency is an important objective to realize sustainable energy conversion systems. During the combustion process, ash particles are produced that can form aggregates inside of combustion plants, which inhibit stable and effective plant operation. This is a serious problem for plant operation, and the control of ash particle aggregation under high-temperature conditions is an important objective. In this research, a method to effectively suppress the adhesiveness of particles at high temperatures is proposed based on a synthetic ash strategy. Synthetic ashes were prepared from a base material with sodium (Na) or potassium (K) as target elements to induce adhesiveness. The base material included both silicon (Si) and aluminum (Al). The tensile strengths of powder beds of the prepared synthetic ash with various alkali concentrations were measured at high temperatures, by which it was confirmed that Na could induce higher adhesiveness than K at low alkali concentrations. This difference was ascribed to the presence of Al. The role of Al in particle adhesiveness was clarified by control of the Al concentration through the addition of aluminum oxide (Al₂O₃) nanoparticles, and the ratio of alkali to Al (Na/Al or K/Al) had an effect on particle adhesiveness at high temperatures, that is, the particle adhesiveness could be suppressed by a decrease of these ratios.

Comparison of Natural and Synthetic Petroleum Coke Slag Viscosities under Reducing Conditions: Applicability of Predictive Models Using Factsage and Modified Urbain Model

The viscosity of slag from an operating integrated gasification combined cycle (IGCC) plant utilising petroleum coke and a synthetic petcoke slag with the same composition made from chemical grade oxides in a reducing environment for gasification application were investigated in this study. A high temperature rotating bob-type viscometer was used to measure viscosity between temperatures of 1250–1375 °C. Natural and synthetic ash had similar viscosities above 1300 °C in this study. The viscosity was predicted by using FactSage, a thermodynamic modelling software, in conjunction with different viscosity models, available in the open literature. Percentage deviations of predicted viscosities from different models with experimentally measured values ranged from about 41 to 151%. Crystallisation of the slag was noted in SEM-EDS (scanning electron microscopy– energy dispersive spectroscopy) and FactSage results. Solid phases from FactSage predictions were used to modify the Kalmanovitch–Frank model with the Roscoe method. It predicted the viscosity of the slag accurately between 1250 and 1375 °C. Average percentage deviation from measured natural ash viscosity was about 11%.