Initial Deformation Temperature Research Articles

Characteristics and composition of lignites and boiler ashes and their relation to slagging: The case of Mae Moh PCC boilers

In order to examine the cause of occasional slagging problems, a dedicated 7-day sampling and data collection were carried out on two 300-MWe units of Mae Moh power plant owned by the Electricity Generating Authority of Thailand. The properties of feed lignite varied from low (∼11% in ash) to medium (∼18% in ash) CaO content during the sampling period. The elemental content was measured for collected fly ashes, bottom ashes and slags, and compared with those of the feed lignite. The analysis and operational data obtained during the 7-day sampling period were compared with those obtained from the additional laboratory-scale investigation of high Ca lignites and those obtained from one of the units during another period when slagging problem was experienced. The study found that, apart from Ca, the concentration of three other elements and their compounds – Fe, Al and Si, plays a very important role in slag formation and its control while these lignites are used in large utility units. The flue exit gas temperatures (FEGT) of the unit experiencing slagging were also found to approach the initial deformation temperatures (IT) of the lignite ash. The solution appears to be the monitoring of the concentration of four elements, i.e. oxides of Ca, Fe, Al and Si in the feed lignite, and in ensuring through proper mining or blending that concentration of CaO, Fe 2O 3 and Al 2O 3 is kept <20%, ∼15% and >15%, respectively, at all times. Also, it is important that the FEGT during operation is kept sufficiently below the IT of the ash of feed lignite at all times.

Viscosity predictions of the slag composition of gasified coal, utilizing FactSage equilibrium modelling

Agglomeration of ash particles provides the desired porosity of the ash bed for adequate agent (steam and oxygen) flow and distribution, whereas excessive slagging inside the gasifier can cause channel burning, pressure drop problems or unstable operation, resulting in cut backs on gasifier load, which implies a direct loss in gas production. The ash flow temperature (AFT) is one property that specifically gives more information on the suitability of a coal source for combustion or gasification purposes. However, normal AFT analyses give an average flow property and do not indicate exactly at what temperature the first melt/slag is occurring or what the properties of the slag is at a specific temperature. Operating experience indicates that even when the gasifiers are operated at temperatures above the flow temperature as given by AFT analysis, a low percentage of slag is formed. In this study, the focus will be on the application of viscosity determinations together with FactSage modelling. Conventional AFT analyses take the bulk chemical composition of the mineral phase into account, and does not differentiate between the composition in the slag–liquid phase and the composition of the crystalline phase. It is therefore important to describe the viscosity of not only the completely molten phase, but also the partly crystallised slag and liquid portion. The combination of viscosity predictions together with FactSage modelling will result in viscosity predictions of the actual liquid component, rather than just an average or pseudo-viscosity prediction of the total mineral system at a specific temperature. Based on the fact that the Urbain model assumes the composition as 100% liquid or molten, which is not the case for example during fixed bed gasification where the mineral structure is of a heterogeneous nature with partial melting and crystalline material, viscosity predictions of the slag or molten portion can be more accurately determined by using the FactSage results. The viscosities, as determined from specific slag compositions at specific temperatures between 1000 °C and 1250 °C, differ from the average viscosity prediction and is highly likely to be a more accurate prediction of the slag viscosity than just based on the average mineral composition. The viscosity of the actual slag composition also remains fairly constant up to temperatures >1200 °C. This can also be related back to the initial deformation temperature onset of the coal, where the slag properties are cumulative enough for the onset of deformation to start. The specific decrease of the viscosity at the temperature between 1200 °C and 1250 °C correlates with the slag formation trend as obtained with FactSage modelling. During the gasification process the viscosity of the slag portion decreases to ±3.5 cp, which is on the border between a weak deposit and strong deposit. With increasing temperature above 1250 °C, for this specific coal source the viscosity moved into the strong deposit region. After the gasification zone, the viscosity increased again as the material crystallised in the combustion process. For a specific coal source, the viscosity of the slag portion can thus be calculated. The major source of glass is derived from included minerals in carbon rich particles. It is clear that a focus on the modification of the unclassified/amorphous phase, to increase the viscosity (decrease slag formation or have a higher concentration of crystalline phases) at a certain temperature, is important. An AFT analyses only supplies information on the temperature where a mass of material, enough to deform the structure of the cone, starts to slag and does not give information on the properties of the slag below that point. The use of viscosity predictions together with FactSage modelling supplies a better understanding of slag and ash properties at specific temperatures.

Martensitic Transformation during Simultaneous High Temperature Forming and Cooling Experiments

The main target of hot stamping is to combine accurate forming, low forming forces and high material strength in complex steel components. In the present study, the hot stamping process is simulated by means of simultaneous forming and quenching experiments. This is performed by uniaxial compression tests at high temperatures using a dilatometer. The effects of process parameters like strain, strain rate, initial deformation temperature, austenization time and applied forces on the martensitic transformation of the boron steel 27MnCrB5 are investigated. It is concluded that with increasing strain rate and initial deformation temperature, martensite content, hardness and martensite start temperature (Ms) are increased. On the contrary, when applying larger deformations, the above mentioned properties are decreased. It is also concluded that, regardless of the process parameters, higher applied forces retard the successful martensitic transformation during hot stamping.

The effects of non-isothermal deformation on martensitic transformation in 22MnB5 steel

In the present paper, the effects of process parameters on phase transformations during non-isothermal deformations are described and discussed. Non-isothermal high temperature compressive deformations were conducted on 22MnB5 boron steel by using deformation dilatometry. Cylindrical samples were uniaxially deformed at different strain rates ranging from 0.05 to 1.0 s −1 to a maximum compressive strain of 50%. Qualitative and quantitative investigations were carried out using surface hardness mapping data as well as dilatation curves. It was observed that a higher initial deformation temperatures resulted in a higher martensite fraction of the microstructure, while a variation in the martensite start temperature was negligible. Another conclusion was that by applying larger amounts of strain as well as higher force levels, not only the martensite start temperature, but also the amount of martensite was reduced. Moreover, it was concluded that using surface hardness mapping technique and dilatometry experiments were very reliable methods to quantify and qualify the coexisting phases.

Influence of the rolling parameters in high-temperature thermomechanical treatment on the structure and mechanical properties of steel

The enhancement of the mechanical properties of rolled steel depends on the deformational parameters of high-temperature thermomechanical treatment, including the number of deformational passes n and the distribution of the total reduction over the individual passes k e [1‐3]. In laboratory conditions, the thermomechanical treatment of initial 30icae steel billet of dimensions 8.5 × 70 × 150 mm is investigated in a planned experiment based on a second-order orthogonal plan. The treatment conditions are characterized by the following parameters: initial deformation temperature t id = 880 ° C; holding time between passes and before final quenching in water τ h1 = 5 s and τ h2 = 10 s, respectively; tempering time t tem = 250 ° C, 2 h [3, 4]. The variation and coding of the deformational parameters for 30icae steel are as follows:

Effects of texture, temperature and strain on the deformation modes of zirconium

Clock-rolled, high-purity, textured polycrystalline zirconium exhibits significant plastic anisotropy for compression along the through-thickness and in-plane directions and strong temperature dependence of flow stress for both orientations. Orientation imaging microscopy in a scanning electron microscope and defect analysis via transmission electron microscopy are used to characterize the defect microstructures as a function of initial texture, deformation temperature and plastic strain. The observed deformation mechanisms are correlated with the measured mechanical response.

Thermomechanical response of an Ni–Ti–Cr shape-memory alloy at low and high strain rates

The thermomechanical response of an Ni–Ti–Cr shape-memory alloy is investigated at various initial temperatures, over a wide range of strain rates, using an Instron hydraulic testing machine and one of the modified split-Hopkinson-bar systems at the Center of Excellence for Advanced Materials, University of California, San Diego. The transition stress for the stress-induced martensite formation is observed to be quite sensitive to the initial deformation temperature, but the yield stress of the resulting martensite is not. The linear transition stress–temperature relation with a slope of 8.5 MPa K−1, obtained in a quasistatic loading regime, seems to remain valid for strain rates up to 500–700 s−1. The transition stress and the yield stress of the stress-induced martensite show strain-rate sensitivity, increasing monotonically with increasing strain rate. There exists a certain critical strain rate at which the transition stress equals the yield stress of the material. This critical strain rate determines the material's deformation behaviour; the material deforms by the formation of stress-induced martensites and their subsequent yielding, when the strain rate is less than this critical value, and through dislocation-induced plastic slip of the parent austenite, when the strain rate exceeds the critical value. It appears that the critical strain rate increases slightly with decreasing initial temperature.

The relationship between the tendency of lignites to agglomerate and their fusion characteristics in a fluidized bed combustor

Agglomeration temperatures of six lignite ashes were measured in a laboratory scale fluidized bed of quartz sand. The results were compared with the characteristic temperatures of the lignite ashes. The agglomeration temperatures of the burning lignites were determined by measuring the active bed temperature and pressure drop across the bed. The results show that, in such a fluidized bed, agglomeration can begin at temperatures well below the ash fusion temperature. For the six lignites tested, agglomeration started at 860–1060 °C, which is about 125–200 °C lower than their initial ash deformation temperatures and 300–400 °C lower than their ash fusion temperatures. Considering the fact that burning particles in a fluidized bed are 150–200 °C hotter than the bed, the results suggest that lignite ashes can agglomerate at temperature levels about the initial deformation temperature. Although the agglomeration tendency appears to decrease with increasing ash initial deformation or fusion temperatures, no meaningful correlation was found, at least for the lignite ashes tested, between the agglomeration and characteristic ash temperatures. In the fluidized bed combustor burning lignites, agglomeration temperature of ashes decreases with Na 2O content and increases with Al 2O 3 content. Fluidized bed combustor, on the other hand, becomes more vulnerable to agglomeration as the total basic oxide content of bed inventory increases.

パイロット試験で採取されたセラミックフィルター集塵灰の物性評価

To understand agglomeration phenomena of ash particles in a hot gas ceramic filter system, actual tests were carried out on candle filters with a 4MWth pressurized internally circulating fluidized bed boiler (PICFB) pilot plant. Coal ashes build up on the ceramic filters were analyzed by computer controlled scanning electron microscopy (CCSEM) and thermo- mechanical analyzer (TMA). The dust cake taken at 800°C did not show any sign of bridging or cleaning difficulty, while those at 950°C showed some difficulty in cleaning because of ash bridging between the adjacent ceramic filters. The initial deformation temperatures of the non-bridge dust were about 800°C. The index of R2O/ (Al2O3+SiO2) (R2O=Na2O or K2O) for the non-bridge dust cake showed in the range of 1 to 25wt%, and the particle size of the potassium rich particles was in the range of 0.5 to 2.2m. However, the index for the bridge cake approached to below 5% and the particle size of the potassium rich particles shifted to the larger range of 2.2 to 10m. It was observed that weak sintering takes place by the reaction of potassium rich particles and the ash particles that adjoins the particles. Ther-modynamic equilibrium has been also examined for this system.

Recovery of vanadium from a previously burned heavy oil fly ash

The recovery of vanadium from heavy oil fly ash having a high carbon content was performed using a four-step process consisting of a preliminary burning in order to reduce the carbonaceous fraction, followed by an acid leaching and an oxidative precipitation of vanadium pentoxide. The preliminary burning was conducted in the temperature range 650 to 1150 °C, below the initial deformation temperature (IDT) of the fly ash. The temperature of the preliminary burning step was revealed to be a significant parameter. Above 950 °C various phenomena (fusion, volatilisation of V, formation of V–Ni refractory compounds) occurred that adversely affected the recovery of vanadium. The burning temperature of 850 °C was found to be the best as a result of the trade-off between the overall vanadium recovery yield (83%) and the V 2O 5 weight percentage in the precipitate (84.8%).

00/02320 Interactions between vapor-phase mercury compounds and coal char in synthetic flue gas

The high-temperature behaviour of ashes from a suite of coals exhibiting a wide range of mineralogies has been investigated. Phase analysis of ash samples quenched from various temperatures under either a reducing (60% CO/40% CO2) or an oxidizing (air) atmosphere was performed by Mössbauer spectroscopy, scanning electron microscopy (SEM)/automatic image analysis (AIA), and X-ray diffraction (XRD). It was found that significant partial melting of the ashes occurred at temperatures as low as 200–400 °C below the initial deformation temperature (IDT) defined by the ASTM ash cone fusion test. Melting was greatly accelerated under reducing conditions, for which the percentage of melted ash increased rapidly between 900 and 1100 °C, saturating at temperatures above ≈ 1200 °C. The observation of such phases as wustite (FeO), fayalite (Fe2SiO4), hercynite (FeAl2O4), and ferrous glass in samples quenched from 900 to 1200 °C indicates that ash melting in a reducing atmosphere is usually controlled by the iron-rich corner of the FeO-Al2O3-SiO2 phase diagram. Ashes rich in CaS are an exception to this rule, for large quantities of iron sulphide are formed and the melting behaviour is controlled in part by the FeO-FeS phase diagram. Under oxidizing conditions, potassium appears to be the most important low-temperature fluxing element, as the percentage of glass in samples quenched from temperatures below 1100 to 1200 °C was proportional to the amount of the potassium-bearing mineral illite contained in the coal. Above 1200 °C in air, calcium and, to a lesser extent, iron became effective as fluxing elements; melting accelerated between 1200 and 1400 °C, and was near completion between 1400 and 1500 °C for most ashes. To retard ash melting, it is generally concluded that aluminium is the most desirable constituent of ash, whereas the most undesirable constituents are iron, calcium, and potassium.

99/04019 Robust automatic generation control: Azzam, M. et al. Energy Converse. Manage., 1999, 40, (13), 1413–1421

Results are given on the mineralogy, morphology, geochemistry and physical characteristics of fly ash from the Megalopolis lignite fields, Peloponnese (S. Greece). The main mineral species present are quartz, anhydrite, plagioclase, haematite, gehlenite and calcite. Also present, in minor and trace amounts, are lime, alkali feldspars, bassanite, gypsum, mica and unburnt lignite. Morphologically, fly ash consists of irregularly shaped, oval and spherical particles, of widely varying sizes. Chemically, the fly ash samples examined fall in the pozzolan field in the triangular diagram CaOSiO2Al2O3. The trace elements As, Cd, Mo and Se, and Ni, V and Zn, of great and moderate environmental concern respectively, occur in concentrations higher than the respective Clarke values. Ash fusion temperatures vary within the range 1257°C (initial deformation temperature) to 1339°C (flow temperature) on average. Fouling and slagging parameters of the ash are within the preferred ranges of empirical practice. The chemistry of the fly ash reveals properties of concern to the construction industry, to the prediction of lignite-fired boiler performance and to health and environment.

The influences of mineral behaviour on blended coal ash fusion characteristics

The ash fusion characteristics and mineral behaviour of three kinds of individual coal ash and a series of two-component blended ashes were studied. The ash fusibility and chemical composition were measured and analysed. The samples were heated progressively from 800°C to the initial deformation temperature (IT) at 100°C intervals in reducing atmosphere. Mineral composition and type at each temperature interval were determined by X-ray diffraction (XRD) analysis. The results show that blended ash softening temperatures do not change linearly with blending ratios. It can lie between or lower or higher than that of the individual parent coals. Some combinations of component coal’s mineral produce low-melting eutectic minerals at high temperature and this is the main reason causing the non-arithmetic averaging of softening temperature of blended ash. It is consistent with the results from the ternary system phase diagram.

Mineral transformation during combustion of coal blends

Mineral behaviour for two individual coals (I, J) and their two-component coal blends and 800°C ash blends heating were studied. Ash samples were heated progressively from 800°C to IT (initial deformation temperature) at 100°C intervals under different conditions. Coal samples were heated from room temperature to the corresponding temperature. Mineral transformation at each temperature was determined by X-ray diffraction and SEM measurements. The results show that Si, Al, Fe and Ca compounds have a great form variation during heating. Their forms at different temperatures depend on the chemical composition of the ash, the blending ratio and the atmosphere. For different coal ashes, the main mineral matters at 800°C were quartz, anhydrite, hematite, calcite and feldspar. As the temperature increased, oxidation, thermal decomposition, transformation and reaction occurred between the components. Comparing a 40% I + 60% J ash blend with individual ashes, fayalite was formed at 1100°C for the blend; the reaction product existed in a glassy phase at 1300°C. For a coal blend having the same ash ratio as the ash blend, FeO reacted with amorphous SiO 2 or Al 2 O 3 to form fayalite and hercynite at 1000°C. As the temperature increased to 1100°C, fayalite and hercynite increased obviously. At 1200°C, some iron inclusion compounds melted to become glassy phase matter. Compared with the ash blend, iron species undergo a different change during coal blend heating: fayalite and hercynite formed earlier, iron compounds melted to form a glassy phase at lower temperature. This may be caused by early combustion of the more reactive coal (J coal) in the blend inducing local variation in oxygen concentration gradients around the less reactive coal and consequently affecting the reaction atmosphere and Fe mineral behaviour and interaction. That is to say, for coal blends, the mineral transformation was affected by both the mineral species interaction and the combustion behaviour. The calculations were performed to examine the fate of mineral matter under different combustion conditions using a thermodynamic chemical equilibrium calculation program. Calculations from coal blends were comparable with experiments from ash blends, this is because the calculation program only considers the interaction among the mineral species but does not consider the combustion reaction. It indicates that combustion and the relative volatiles also affected the mineral behaviour and slagging during coal blend combustion. Meanwhile, the mineral species evaporations were measured at high temperature: the main evaporated species were Na, K pure species and compounds, Fe, FeO, SiO and SiO 2 . The evaporation of Fe has an important effect on initial deposition. Calculations were comparable with the experiments.

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.

Harvest of grass for combustion in late summer and in spring

Swedish studies concerning the production of grass for combustion during the 1980s demonstrated that it was impossible to produce fuel guaranteed to be of acceptable hygienic quality at a reasonable cost. In those studies, the grass was harvested during summer using conventional haymaking methods. To avoid the problems involved with a summer harvest, it was proposed in 1989 that the grass be harvested during the winter or spring following the growing season. Since then, a system based on this delayed-harvest concept has been evaluated with regard to biological yield, losses during winter, harvesting technology, losses during harvesting and fuel characteristics. The crop used has been reed canary grass ( Phaláris arundinácea L.). In contrast to harvest in late summer, a spring harvest was found to be of practical value. It provides a usable fuel of higher quality than that of grass from summer harvesting. The delay in the harvest leads to reduced concentrations of most elements that are undesirable in combustion, e.g. nitrogen, sulphur, chlorine or potassium. An exception is silica, the concentration of which increases during winter. A valuable effect of spring harvesting is that the initial ash deformation temperature is increased. Furthermore, the need for fertilizer with delayed harvest is low owing to the low content of nutrients in the harvested material. The main disadvantage is that there are major losses of material during the autumn and winter.

Mineralogy, geochemistry and physical properties of fly ash from the Megalopolis lignite fields, Peloponnese, Southern Greece

Results are given on the mineralogy, morphology, geochemistry and physical characteristics of fly ash from the Megalopolis lignite fields, Peloponnese (S. Greece). The main mineral species present are quartz, anhydrite, plagioclase, haematite, gehlenite and calcite. Also present, in minor and trace amounts, are lime, alkali feldspars, bassanite, gypsum, mica and unburnt lignite. Morphologically, fly ash consists of irregularly shaped, oval and spherical particles, of widely varying sizes. Chemically, the fly ash samples examined fall in the pozzolan field in the triangular diagram CaOSiO 2Al 2O 3. The trace elements As, Cd, Mo and Se, and Ni, V and Zn, of great and moderate environmental concern respectively, occur in concentrations higher than the respective Clarke values. Ash fusion temperatures vary within the range 1257°C (initial deformation temperature) to 1339°C (flow temperature) on average. Fouling and slagging parameters of the ash are within the preferred ranges of empirical practice. The chemistry of the fly ash reveals properties of concern to the construction industry, to the prediction of lignite-fired boiler performance and to health and environment.

Practical Design of Ni3Al with High Hot Workability

ABSTRACTFrom our previous work, Ni3Al polycrystals with combined addition of magnesium and silicon kept high values of compressive strain at rupture (CSR) when the strain rate rose. In order to further improve hot workability of Ni3Al, 7.9wt.% Cr was added. The compressive tests showed that 30%∼40% CSR values of the alloy had been kept in a wide temperature range of 1173K-1373K at strain rates of 10-2sec-1 and 10-2sec-1 in contrast with 15%∼25% CSR values of the alloy without Cr addition.In practical hot rolling process, at initial deformation temperature of 1373K, strain rate of 1.0 sec-1 and by controlling reduction within 10∼15% each rolling pass, Ni3Al ingots were successfully hot-rolled into polycrystals with different deformations, the maximum of which was 55%. The deformed alloys had manifestly enhanced mechanical properties shown by tensile tests.The dislocation configurations of deformed alloys have been investigated by using transmission electron microscope(TEM).

Response of spray-deposited, stirred-cast and conventional cast Pb-Sn alloys to deformation in the semi-solid state

Pb-35 wt% Sn alloys were deformed in the semi-solid state. The effects of the initial microstructures, deformation temperatures and deformation rates on the microstructures and the formability of the alloy were studied. A physical phenomenological model is proposed to explain the different behaviours of the stress-strain curves of semi-solid forming of various materials under various conditions. Three different processes, spray deposition (S/D), semi-solid synthesizing (SSS) and conventional casting (CC) were used to produce the Pb-35 wt% Sn alloys with different initial microstructures. Two strain rates, (0.083 and 0.00083 s−1) and two deformation temperatures, (190 and 200°C) were used in this study. There is no significant variation in particle size and in sphericity during semi-solid forming of Pb-35wt% Sn alloys. The deformation stress increases monotonically as strain increases during semi-solid deformation of S/D materials, which consist of smaller solid particles. However, for SSS and CC materials, which consist of larger solid particles, the deformation stress increases in the beginning to a local maximum, then decreases to a minimum before it starts to increase again as strain increases. This phenomenon is more noticeable at lower deformation temperatures and higher strain rates. The deformation stresses required for deformation at higher deformation rates and at lower deformation temperatures are larger than those at lower deformation rates and at higher deformation temperatures, respectively.