Ash Fusion Test Research Articles

Quantum and experimental study on coal ash fusion with borax fluxing agent

Borax fluxing agent was added to four kinds of coal ash in terms of different quality ratios. The ash fusion test (AFT) of the mixtures of coal ash plus borax fluxing agent was carried out and the reactivity of mullite in coal ash was calculated by the density functional theory (DFT). The space group of the mullite is Pbam, belonging to the orthorhombic system. The results suggest that mullite is likely to combine with electron acceptor rather than with electron donor. The activity of Si is higher than that of Al when mullite combines with the electron donor. When borax is added into mullite, Na + as the electron acceptor easily enters into the lattice of mullite, causing a transition from mullite to nepheline. The calculation results agreed well with the AFT results under reducing atmosphere.

Behaviour of calcium-containing minerals in the mechanism towards in situ CO 2 capture during gasification

Mineral matter transformation and the behavior of mineral matter in the coal during gasification, provide more information on the suitability of a specific coal source for combustion or gasification purposes. Therefore, the chemistry and mineral interactions have to be understood in order to determine the suitability for fixed bed gasification purposes with regards to mineral matter transformations and slagging properties. Although a suite of minerals important for the gasification process were identified [Van Dyk JC, Melzer S, Sobiecki A. Mineral matter transformations during Sasol-Lurgi fixed bed dry bottom gasification – utilization of HT-XRD and FactSage modelling. Minerals Engineering 2006; 19: 1126–35], some of the minerals, i.e. anorthite and calcite, with a specific behavior at different concentrations in the mineral structure and the transformation thereof was not studied and highlighted in detail. A number of other researchers [Reifenstein AP, Kahraman H, Coin CDA, Calos NJ, Miller G, Uwins P. Behavior of selected minerals in an improved ash fusion test: quartz, potassium feldspar, sodium feldspar, kaolinite, illite, calcite, dolomite, siderite, pyrite and apatite. Fuel 1999; 78: 1449–61], [Kondratiev A, Jaks E. Predicting coal ash slag flow characteristics (viscosity model for the Al 2O 3–CaO–‘FeO’–SiO 2 system). Fuel 2001; 80: 1989–2000] and [Kondratiev A, Jak E. Applications of the coal ash slag viscosity model for the slagging gasification technologies (viscosity model in the Al 2O 3–CaO–‘FeO’–SiO 2 system), 18th Pittsburgh Coal Conference, Newcastle, Australia, December 2001]) also did not investigate these gasification changes and mineralogical deformation during specific gasification conditions in detail. The principle aim of this paper is to identify the role of Ca-containing mineral species towards the in situ capture of CO 2 during gasification, as well as understanding the chemistry and interpret the mechanism of CO 2 capture by means of high temperature X-ray diffraction (HT-XRD), in combination with FactSage modeling. The CaO content of a South African and another coal source investigated in the present study, were 6 mass% and 30 mass% respectively. The basic components present in the coal, or specifically CaO, only act as a fluxing component up to a specific percentage, where after the ash fusion temperature starts to increase again. At this turning point the (Si+Al):Ca molar mass ratio is 2.75, which implies that after the turning point, the formation of anorthite is maximized and can thereafter only remain at the same level. The anorthite formation, when the Ca content increases, follows the inverse trend of the ash flow temperature prediction curve with the coal containing 6% CaO. The decrease in anorthite formation, with increasing Ca content, after the turning point in the graph, can be explained by the fact that more of the crystalline phase becomes a liquid (slag), and thus also the increase in the amount CaO in the slag will be observed. At the turning point, it is also interesting to note the stabilisation of the amount of other Ca-containing species. These are the minerals that are responsible and available for the mechanism where CO 2 can be captured on Ca to form CaCO 3. The formation of CaCO 3 can also be observed from the turning point where the (Si+Al):Ca molar mass ratio is <2.75, which corresponds with the formation of other Ca-containing species. Thermodynamic modeling with FactSage results indicated that anorthite can only form to the point where the (Si+Al):Ca molar mass ratio is >2.75. Anorthite (CaSi 2Al 2O 8) forms within the gasification zone and all non-reacted Ca react with CO 2 to form CaCO 3 further down in the combustion zone.

ESTUDO DA FUSIBILIDADE DAS CINZAS DE CARVÕES EM FUNÇÃO DA COMPOSIÇÃO QUÍMICA E MINERALÓGICA

Due to the great use of coal in the ironmaking plants and powerstations, it is very important to have a deeper knowledge of inorganic matter of this raw material. This study aims to identify the mineral phases responsible for the fluidity behavior of the coal ashes. Three differents types of coal were selected for this study. At first an identification of the mineral matter of the coals was done through the XRD. The ashes from the coals combustion were characterized through XRF chemical analysis and XRD. The rheologic properties were studied by the ash fusion tests in oxidant atmosphere. As an auxiliary tool in the fusibility tests, SEM was also used. The presence of different crystaline phases among the samples via XRD was also observed. The fusibility tests showed the different behaviour of the ashes in their respective temperatures of softening and fusibility. Concerning the studied coals, the illite and quartz phases tend to decrease the softening temperature. The phases rich in aluminium tend to increase the fusion temperature of the samples, whereas the presence of K, Na, Ca e Mg oxides in the formed phases contribute to the ashes fusibility.

00/00159 Correlation of ash behaviour in power stations using the improved ash fusion test

00/00159 Correlation of ash behaviour in power stations using the improved ash fusion test

Behaviour of selected minerals in an improved ash fusion test: quartz, potassium feldspar, sodium feldspar, kaolinite, illite, calcite, dolomite, siderite, pyrite and apatite

A suite of minerals found in coals were analysed using an improved ash fusion test. These minerals were quartz, potassium feldspar, sodium feldspar, calcite, dolomite, siderite, pyrite, kaolinite, illite and apatite. Each specimen was also analysed by XRD as an “as-received” specimen, an 800°C product and a 1600°C product. These results allowed evaluation of the applicability of the improved ash fusion test for determination of chemical changes occurring in the ash fusion furnace. Phase changes were observed in the improved ash fusion test for the Na feldspar, siderite and pyrite specimens. K feldspar movement could, in part, be related to phase changes. The complex reactions occurring in the illite and kaolinite specimens limited the interpretation. The calcite and dolomite specimens movement was dominated by reactions of calcite, lime and portlandite. The quartz and apatite specimens were relatively inert. These results indicate that the improved ash fusion test can provide a link between the various standard ash fusion tests and analytical tools such as XRD to provide enhanced understanding of the processes occurring in the ash fusion furnace.

Correlation of ash behaviour in power stations using the improved ash fusion test

The improved ash fusion test has been found to be a useful tool for correlation with ash behaviour in power stations. The improved ash fusion test monitors the ash behaviour in the standard ash fusion test furnace and allows some interpretations on the ash fusion temperatures and ash stickiness. The results of a survey sent to nine Australian power stations on general slagging experience of the main feed coals were compared with the results of the improved ash fusion test. Comparison showed that improved ash fusion test indexes reasonably correlated with perceived performance of the coals in the power stations.

Predicting Bed Agglomeration Tendencies for Biomass Fuels Fired in FBC Boilers: A Comparison of Three Different Prediction Methods

In this paper a comparison between three different types of techniques to predict the bed agglomeration tendency of a FBC (fluidized-bed combustor) was performed. The three techniques were the standard ASTM ash fusion test, a compression strength based sintering test and a lab-scale combustion test. The tests were performed on 10 different types of biomasses. The results showed significant differences in the predicted bed agglomeration temperatures depending on which technique was used. The ASTM standard ash fusion test generally showed 50−500 °C higher temperatures than the sintering tests or the lab-scale FBC combustion tests. The sintering test showed, in five cases, 20−40 °C lower sintering temperatures than what was detected as the bed agglomeration temperature with the lab-scale FBC. In two cases, a significantly lower sintering temperature than the bed agglomeration temperature was detected, and in three cases, a significantly higher sintering temperature was detected than the bed agglomeration tem...

Quantification of fusion in ashes from solid fuel combustion

The fusion of ashes produced during solid fuel combustion greatly affects the tendency of these ashes to cause operational problems in utility boilers. In this paper, a new and quantitative laboratory method for assessing the fusion of ashes based on simultaneous thermal analysis, STA, is described. Using STA, melting is detected as an endothermic reaction involving no change in mass. The measurement signals are transferred into a fusion curve showing the melt fraction in the ash as a function of temperature. This is done either by a simple comparison of the energies used for melting in different temperature ranges or by accounting for the relevant melting enthalpies. The method repeatability is good, melting onset determinations and completions generally within 10°C, and melt fractions at given temperatures generally within 10% melt. Results are presented for simple binary salt mixtures, for which the agreement with fusion as determined by phase diagrams is very good, and for straw (salt-rich) and coal (silicate-rich) ashes. Comparing ash fusion curves to index points of current standard ash fusion tests showed initial melting at temperatures typically between 50° and 100°C – but in extreme cases as low as 260°C – below the melting onset as found by the standard fusion tests. Characterizing the fusion by STA provides a more detailed description of the ash fusion as compared to conventional methods, and the onset of ash fusion is more precisely determined. Furthermore, in combination with, e.g. computer-controlled scanning electron microscopy, the method enables identification of the chemical species melting in different temperature ranges. Since ash melting has a major impact on the deposit formation tendency, the presented detailed ash fusion determination improves the prediction of problems related to ash deposition in boilers.

Experimental determination of bed agglomeration tendencies of some common agricultural residues in fluidized bed combustion and gasification

Ever increasing energy demand and the polluting nature of existing fossil fuel energy sources demonstrate the need for other non-polluting and renewable sources of energy. The agricultural residues available in abundance in many countries can be used for power generation. The fluidized bed technology seems to be suitable for converting a wide range of agricultural residues into energy, due to its inherent advantages of fuel flexibility, low operating temperature and isothermal operating condition. The major ash-related problem encountered in fluidized beds is bed agglomeration which, in the worst case, may result in total defluidization and unscheduled downtime. The initial agglomeration temperature for some common tropical agricultural residues were experimentally determined by using a newly developed method based on the controlled fluidized bed agglomeration test. The agricultural residues chosen for the study were rice husk, bagasse, cane trash and olive flesh. The results showed that the initial agglomeration temperatures were less than the initial deformation temperature predicted by the ASTM standard ash fusion tests for all fuels considered. The initial agglomeration temperatures of rice husk and bagasse were more than 1000°C. The agglomeration of cane trash and olive flesh was encountered at relatively low temperatures and their initial agglomeration temperatures in gasification were lower than those in combustion with both bed materials. The use of lime as bed material instead of quartz improved the agglomeration temperature of cane trash and olive flesh in combustion and decreased the same in gasification. The results indicate that rice husk and bagasse can be used in the fluidized bed for energy generation since their agglomeration temperatures are sufficiently high.

Application of a new ash fusion test to Theodore coals

The standard ash fusion test is criticised widely due to its subjective nature. Interlaboratory exercises showed that operators could differ up to 400°C in initial deformation temperature determination in the standard ash fusion test. The improved ash fusion test proved to be a useful tool to resolve ambiguous results from the standard ash fusion test. Good correlations were found between the ash chemistry and major movement temperatures in the new ash fusion test for this data set. Moreover, initial deformation as well as spherical and flow temperatures from the standard ash fusion test showed good correlations with major movement and 85% movement temperatures from the new ash fusion test for this data set. A coal washing exercise showed that ash fusion temperatures in the new test improved significantly. Further, ply blending was found to alter the ash fusion characteristics. Major movement temperatures from the improved ash fusion test were found to be additive in ply blending.

Investigation of slagging in pulverized fuel co-combustion of biomass and coal at a pilot-scale test facility

One option to reduce the CO 2 emissions is biomass used for energy production. Co-combustion of biomass in existing coal-fired power stations offers a great potential. In pulverized coal combustion facilities, one implementation problem is the tendency of slagging and fouling of biomass. At the IVD, experiments were carried out to obtain information about biomass deposit characteristics in pulverized fuel (pf) co-combustion. This paper presents results from the IVD 0.5 MW pf combustion experimental facility obtained from different tests with coal–biomass mixtures ranging from small biomass shares up to a pure biomass firing. Samples of fuels, the fly ash path, deposition and slagging probes, and slags on furnace walls were taken. The amounts of deposits found on probes inserted into the combustion chamber, their macroscopic characteristics, elemental composition and fusion temperatures were analyzed and compared. Generally, the deposits from the co-combustion experiments softened in ash fusion tests like the main component (coal ash) rather than like a mixture. When co-firing biomass with 25% of thermal input, no slagging was detected on cooled probes with 650°C in the flue gas with 1050°C. Most deposit samples from the probes softened at higher temperatures compared to the laboratory-made ash and as expected for a mixture, but melted as mixtures are expected to. Slagging occurred on uncooled refractory samples, at higher biomass shares, and when the biomass particles were not completely burnt out and sticky when reaching the probes.

Statistical Analysis of Automated Coal-Ash Fusion Temperatures for West Virginia Coals: ABSTRACT

During 1984-1986, the West Virginia Geological and Economic Survey dramatically expanded its coal-ash fusion data base, and conducted statistical studies of the new data. More, better distributed data were obtained for the Survey's computerized data base, which is used in (1) the coal-quality exploration program, (2) mapping, and (3) estimating ash fusion temperature based on ash and sulfur in coal. The new data, obtained using an automated ash fusion analyzer, were subjected to extensive analysis. Along with realizing the major goals of the study, they have three additional findings. (1) Interpolating between reducing-atmosphere softening temperature and reducing-atmosphere fluid temperature has yielded a reliable equation to predict the reducing-atmosphere hemispherical temperature of West Virginia coals. This parameter is missing from many older analyses. (2) Regardless of the care taken, human factors figure heavily in the accuracy of all ash fusion tests performed in nonautomated ash fusion analyses. (3) They have developed improved estimation equations using machine-generated ash fusion analyses that will be more reliable than earlier equations that used a combination of human operator and machine analyses.

Technique to measure the temperature of agglomeration of coal ash

Examination of deposits from gasification pilot units indicates that agglomerates of fused ash appear to form at temperatures below the initial deformation temperature as defined by the ASTM ash fusion test. A simple method was developed to estimate the temperature at which coal ash will begin to fuse or agglomerate in process equipment. This test confirms that fusion of ash occurs at temperatures below those of the ASTM ash fusion test. The test also offers a method to compare the fusion properties of ashes for several coals.

Evaluation of Additives for Prevention of High Temperature Corrosion of Superalloys in Gas Turbines

A number of commercially available chemical additives for utilization in modern high temperature gas turbines were evaluated for their corrosion and deposit inhibiting characteristics. The evaluation was made in pressurized passages which simulate conditions of operating gas turbines. Initial screening tests of 10 hr each were made with a contaminant level of 50 ppm vanadium, and promising additives were further tested for times up to 300 hr at the more realistic contaminant level of a No. 3 GT fuel. Characteristics of the deposits were studied with x-ray diffraction and ash fusion tests. Corrosion rates for various alloys tested with treated fuel were measured and compared to test results obtained with untreated fuel. Conclusions were drawn as to the type of elements most effective in reducing corrosion caused by combinations of vanadium and sodium. The role of elements in preventing deposit buildup is also assessed.