Initial Deformation Temperature Research Articles

Hot deformation behavior and dynamic recrystallization constitutive modeling of Al–Cu–Mg powder compacts processed by extrusion at elevated temperatures

The deformation behavior of Al–Cu–Mg sintered preforms has been investigated by extrusion in the temperature range of 450–550°C and strain rate range of 0.1–0.3 s−1, respectively. The aim of this study is to analyze the effect of initial preform relative density on the hot deformation behavior and to model and predict the flow stress of extruded samples using constitutive equations. The true stress–strain curves exhibit three stages of deformation, which represent work hardening, dynamic recovery, and dynamic recrystallization during deformation at different temperatures, strain rates, and initial preform relative densities of 70%, 80%, and 90%, respectively. The results show that the flow stress values are influenced by initial preform relative density, deformation temperature, and strain rate. Microstructural examination of extruded specimens has been performed by optical microscopy and scanning electron microscopy. Arrhenius-type constitutive equations are developed to predict the flow stress of hot-extruded powder metallurgy processed aluminum alloy (Al–4%Cu–0.5%Mg). Zener–Hollomon parameter is used to explain the relationship between peak flow stress, temperature, and strain rate in an exponential equation containing the deformation activation energy and material constants. Subsequently, the statistical indicators correlation coefficient ( R) and the average absolute relative error are assessed to confirm the validity of constitutive equations. The results indicate the experimental and predicted peak flow stress values are in good agreement, which indicate the accuracy and reliability of the developed model for powder metallurgy processed Al–4%Cu–0.5%Mg preforms.

New insights into biomass combustion ash categorisation: A phylogenetic analysis

Combustion of biomass within power stations is a more sustainable way to generate electricity than the use of fossil fuels provided the feedstock is sustainably grown. The physical and chemical properties of biomass combustion ash from different feedstocks were statistically analysed using 168 published database records. Plant taxonomy of the feedstock has a strong influence on the major element composition of the ash, and biomass feedstocks that are burnt commercially can usefully be categorised as hardwood, softwood, grass crop residues, and non-grass crop residues. The most abundant elements in hardwood ashes are calcium > potassium > phosphorous, whereas in the softwood ashes they are calcium > silicon > potassium. The most abundant elements in eudicot straw ashes are potassium > calcium > chlorine > phosphorous, and in grass straw ashes they are calcium > potassium > calcium > chlorine. Differences in major element chemistry between the feedstock categories are visualised using a ternary plot of the normalised calcium oxide, dipotassium oxide, silicon dioxide contents. Other properties depend principally on whether the feedstock is herbaceous or woody. Herbaceous feedstocks produce significantly more ash (typically 5–9%) than woody feedstocks (typically 1–2%) and their ash has a significantly lower initial deformation (melting) temperature than ash from woody feedstocks, and thus has greater potential to form slag and foul the furnace. These findings allow for the impact on ash characteristics to be include in commercial and operational decisions about power station feedstock.

Effect of heat treatment and thermomechanical processing on microstructure and tensile property of Ti-44Al-8Nb-0.2W-0.2B-0.5Y alloy

High Nb-TiAl (Ti-44Al-8Nb-0.2W-0.2B-0.5Y, at.%) ingot was fabricated by vacuum arc remelting (VAR). The as-cast ingot was hot-isostatic pressed (HIP) and homogenizing annealing processed. The influence of heat treatment temperature and thermomechanical processing on the microstructure and tensile property of the alloy was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and tensile tests. It was found that the high Nb-TiAl alloy after HIP and annealing was mainly composed of coarse α2/γ lamellae, β/B2 phase and γ phase and the solidification path of this alloy was: L→L+β→β→α+β→α→α+β+γ→α2+β+γ. The water quenching results showed that the alloy was in α single phase region at 1,340 °C. After heating at 1,340 °C for 30 min followed by furnace cooling, the alloy showed a full lamellar microstructure and its ultimate tensile strength was about 538 MPa, with an elongation of 0.3% at room temperature. Free-crack forged pancakes with fine-grained fully lamellar structure (FFLS) were obtained with an initial deformation temperature of 1,340 °C and the ultimate tensile strength of forged alloy was about 820 MPa, with an elongation of 0.9% at room temperature, which was much higher than that of alloy after HIP and annealing because of microstructural refinement.

Effect of the ash melting behavior of a corn straw pellet on its heat and mass transfer characteristics and combustion rate

The effect of ash melting behaviors on the characteristics of heat and mass transfer and combustion rate for the corn straw pellet were investigated by experiment and simulation methods. Considering that the fusion temperature range of ash is from 1418 K to 1558 K, four temperatures (1193 K, 1326 K, 1465 K, and 1618 K) were chosen as the operating temperatures. Results show that the molten ash exists as the spherical particles. At operating temperature between the initial deformation temperature and flow temperature, the spherical particles sharply increase, which contributes to the increase in oxygen concentration at the pellet surface, but limits that inside the pellet. Molten ash delays the char reaction. The tendency reaches the maximum at this temperature range. When the operating temperature is higher than flow temperature, the molten ash peels off from the pellet surface, which exposes the part of the pellet covered by molten ash to the environment directly, thereby accelerating the increase in oxygen concentration inside the pellet.

Deformation-induced martensite in austenitic stainless steels: A review

Recent progress in the understanding of the deformation-induced martensitic transformation, the transformation-induced plasticity (TRIP) effect, and the reversion annealing in the metastable austenitic stainless steels are reviewed in the present work. For this purpose, the introduced methods for the measurement of martensite content are summarized. Moreover, the austenite stability as the key factor for controlling the austenite to martensite transformation is critically discussed. This is realized by analyzing the effects of chemical composition, initial grain size, applied strain, deformation temperature, strain rate, and deformation mode (stress state). For instance, the effect of initial grain size is found to be complicated, especially in the ultrafine grained (UFG) regime. Furthermore, it seems that there is a critical grain size for changing the trend of α′-martensite formation. Decreasing the deformation temperature motivates the formation of α′-martensite, but there is a critical temperature for achieving the maximum tensile ductility. Afterwards, the modeling techniques for the transformation kinetics and the contribution of deformation-induced martensitic transformation to the strengthening of material and also strength-ductility trade-off are critically surveyed. The processing of UFG microstructure during reversion annealing, the effects of the recrystallization of the retained austenite, the martensitic shear and diffusional reversion mechanisms, and the annealing-induced martensitic transformation are also summarized. Accordingly, this overview presents the opportunities that the strain-induced martensitic transformation can offer for controlling the microstructure and mechanical properties of metastable austenitic stainless steels.

Low-cost additives to improve the fusion behaviour of hydrochar ash

Hydrochars produced from agro-industrial wastes contain significant amounts of alkali metals and other inorganic elements that lead to different ash-related issues in energy systems. This work aims to modify the composition of hydrochar ash by adding rice hulls and/or mineral additives (i.e., lime, bentonite and kaolin) to improve their fusion behavior. Two series of samples were prepared to analyze the effect that the use of additives before or after the HTC processing of olive mill waste at 225 °C for 2 h had on the hydrochar properties. Hydrochars were then ashed, in agreement with UNE-EN 18122:2016, and the corresponding ashes subsequently characterized through XRF and ash fusion tests to determine their ash composition and ash characteristic fusion temperatures (AFTs), respectively. Among the studied additives, rice hulls led to the best results, as their use increased the initial ash deformation temperature to >1500 °C and resulted in the lowest hydrochar ash content. Using rice hulls before or after the HTC process did not affect the ash behavior, but it did change the hydrochar properties as a fuel. The joint HTC of rice hulls and feedstock led to a less carbonized solid with 13% higher moisture content and 15% lower energy density. Accordingly, the addition of rice hulls to ready-produced hydrochars is recommended to maintain the energy benefits of HTC as possible. The use of rice hulls as a low-cost additive to improve the fusion behavior of hydrochar ash opens new avenues for hydrochars in energy conversion processes with limited ash-related operational problems.

Neural network prediction of parameters of biomass ashes, reused within the circular economy frame

Artificial neural networks were used for the prediction of three biomass ash fusion temperatures: initial deformation temperature IDT, hemispherical temperature HT and flow temperature FT based on chemical composition of the ash. Applicability of 400 neural network configurations (of linear, MLP, RBF and GRNN types) was verified statistically. Multilayer perceptron with 12 inputs representing fractions of the ash compounds, 11 hidden neurons and three outputs (IDT, HT, FT) proved to be the optimal neural model configuration. Statistical analysis suggested also, that considering intrinsic dispersion within the raw experimental data (literature data supplemented with the authors’ own results describing the halloysite addition effect), quality of the resulting 3-output IDT-HT-FT model (IDT prediction with R 2 0.615, HT with R 2 0.756 and FT with R 2 0.729) could be regarded satisfactory for the identification and generalization of the discussed relationships. Analysis of the neural model sensitivity in respect to the input variables demonstrated, that the most important factors affecting all ash transition temperatures in the 3-output IDT-HT-FT model were: K 2 O, SiO 2 , CaO and Al 2 O 3 fractions. Moreover, individual sensitivity in respect to IDT, HT and FT temperatures slightly varied (characteristics provided by independently established 1-output networks – IDT model, HT model and FT model, respectively). Statistically verified neural network working as the 3-output IDT-HT-FT model can be applied in various computational tasks in biofuels energy sector required by Industry 4.0 principles, as well as in the selected Circular Economy problems. • Chemical compositions of the ashes were correlated with their melting temperatures. • Ash melting temperatures can be effectively predicted by neural network model. • Predictions of neural models are more accurate compared to statistical models. • Sensitivity of each melting temperature in respect to ash components is different. • The results can improve the technologies of biomass energy conversion.

Nanoscale Analysis on Spark Plasma Sintered Fly-Ash Bricks and their Comparative Study with SiN-Zr Refractory Bricks

Background: Industries such as thermal power plants use coal as a source of energy and release the combustion products into the environment. The generation of these wastes is inevitable and thus needed to be reused. In India, coals with high ash content usually between 25 to 45% are used. The refractory bricks that were used earlier in steel industries were mainly based on silica, magnesia, chrome, graphite. In modern days, several other materials were introduced for the manufacturing of refractory bricks such as mullite, chrome-magnesite, zircon, fused cast, and corundum. The materials selection for refractory brick manufacturing depends on various factors such as the type of furnace and working conditions. Objectives: The current work aims to focus on the fly-ash subjected to spark plasma sintering process with a maximum temperature of 1500 °C and pressure 60 MPa for 15 minutes and to characterize to observe the properties with respect to their microstructure. Methods: Fly-ash collected from Rourkela Steel Plant was sintered using spark plasma sintering machine at the Indian Institute of Technology, Kharagpur. The powder placed in a die was subjected to a heating rate of 600-630 K/min, up to a maximum temperature of 1500˚C. The process took 15 minutes to complete. During the process, the pressure applied was ranging between 50 to 60 Mpa. 5-10 Volts DC supply was given to the machine with a pulse frequency of 30-40 KHz. The sintered product was then hammered out of the die and the small pieces of the sintered product were polished for better characterization. The bricks collected from Hindalco Industries were also hammered into pieces and polished for characterization and comparison. Results: The particles of fly-ash as observed in SEM analysis were spherical in shape with few irregularly shaped particles. The sintered fly-ash sample revealed grey and white coloured patches distributed around a black background. These were identified to be the intermetallic compounds that were formed due to the dissociation of compounds present in fly-ash. High- temperature microscopy analysis of the sintered sample revealed the initial deformation temperature (IDT) of the fly-ash brick and the refractory brick which were found to be 1298 °C and 1543 °C, respectively. The maximum hardness value observed for the sintered fly-ash sample was 450 Hv (4.413 GPa) which is due to the formation of nano-grains as given in the microstructure. The reason behind such poor hardness value might be the absence of any binder. For the refractory brick, the maximum hardness observed was 3400 Hv (33.34 GPa). Wear depth for the sintered fly-ash was found to be 451 μm whereas for the refractory brick sample it was 18 μm. Conclusion: The fly-ash powder subjected to spark plasma sintering resulted in the breaking up of cenospheres present in the fly ash due to the formation of intermetallic compounds, such as Cristobalite, syn (SiO2), Aluminium Titanium (Al2Ti), Magnesium Silicon (Mg2Si), Maghemite (Fe2O3), Chromium Titanium (Cr2Ti) and Magnesium Titanium (Mg2Ti), which were responsible for the hardness achieved in the sample. A large difference in the maximum hardness values of sintered fly-ash and refractory brick was observed due to the hard nitride phases present in the refractory brick.

Design and optimization of induction heating for tungsten heavy alloy prior to rotary swaging

Induction heating is advantageously used in the industry to (pre)heat workpieces from ferromagnetic metallic materials. However, its application for heating of paramagnetic workpieces is still a challenge. The presented study focuses on design and optimization of induction heating for a pre-sintered WNiCo tungsten heavy alloy billet intended to be subjected to plastic deformation via warm rotary swaging. Firstly, induction heating to the initial deformation temperature of 900 °C is simulated via two different computational software based on the finite element method (FEM) in order to perform the best possible optimization of the heating process. Secondly, experimental induction heating is performed, prior to subsequent warm rotary swaging, to verify the designed process. Comparison of the final billet temperatures and their developments acquired via simulation and experiment exhibited satisfactory correlation. The study is supplemented with structure observations documenting the required heating through the WNiCo billet; the swaged structure exhibited deformed tungsten agglomerates, as well as high quality oxidation-free surface.

Investigation of the microstructure evolution and mechanical properties of a TC6 alloy blade preform produced by cross wedge rolling

Cross wedge rolling (CWR) is one of the most effective plastic deformation methods utilized for the production of shaft parts or non-shaft preforms with refined grains and improved mechanical properties. The main goal of this work was to study the influence of CWR process parameters on the microstructure evolution and mechanical properties of a TC6 alloy and determine the suitable process parameters for a TC6 alloy blade preform fabricated with CWR. The results showed that the volume fraction of the equiaxed α phase ( $$ f_{\alpha \_e} $$ ) decreased from ~ 0.38 to ~ 0.04 by increasing the initial deformation temperature, and the elongation (El) also decreased from ~ 19.6 to ~ 11.8% because dislocation slip first started in the equiaxed grains and then dispersed into the adjacent grains. Thus, additional equiaxed grains contributed to an increased plasticity. Moreover, with an increasing area reduction, the value of $$ f_{\alpha \_e} $$ increased from ~ 0.14 to ~ 0.31, and the grain refinement and microstructure uniformity also increased. In addition, the El was significantly reduced by over 50%, but the ultimate tensile strength (UTS) and yield strength (YS) increased under WC (water cooling) conditions due to the precipitation of the acicular secondary α phase and pinning effect of the small equiaxed α phase. Based on the determined suitable parameters, the TC6 alloy blade preform was successfully manufactured by CWR, the microstructure was evenly distributed, and the UTS, YS and El were 1120.1 MPa, 1020.9 MPa and 15.2%, respectively, which meet the current technical requirements.

Evaluation of ash composition and deposition tendencies of biomasses and torrefied products from woody and shrubby feedstocks: SRC poplar clones and common broom

This work intended to compare ash composition and deposition tendencies biomasses and of torrefied products of SRC poplar clones and common broom. These biomasses were assessed in a previous study as these delivering torrefied products with better fuel quality. Ash analysis for quantification of inorganic major and minor ash elements of biomasses and torrefied products was performed with an inductively coupled plasma- optical emission spectrometer (ICP-OES). The ash melting profiles were experimentally determined. These results allowed the calculation of empirical indexes for evaluation of slagging and fouling tendencies. Independence was established between torrefaction dynamics properties such as mass loss, fixed carbon, volatiles and ash inorganic components for biomasses and torrefied products and with physical–chemical deposition indexes. Results showed that biomasses and torrefied products of common broom and in a lesser extent of AF2 and AF8 poplar clones were prone to a silicate melt induced slagging pattern, whilst the other poplar clones’ feedstocks should exhibit an alkali induced slagging profile. Correlation analysis showed different patterns of interconnectedness of ash elements and physical properties for biomasses and torrefied products. For example, initial deformation, hemispheric and flow temperature and alkali indexes were shown with higher relevance for characterization of slag/foul tendencies in biomasses and ash fusibility index, although fundamental for both feedstocks, were more influenced by oxides in torrefied biomasses. In non-torrefied products the major interaction of temperature indexes was observed with alkali indexes. The two databases generated in this work on ash composition and properties of biomasses and torrefied products can contribute to planning of research actions on biomass torrefaction as a tool for upgrading of solid biofuel qualities.

The effect of co-combustion of waste from flour milling and highly mineralized peat on sintering of the ash residue

The combustion of some types of plant biomass leads to the sintering of their mineral part with the formation of deposits on the heating surfaces. Operational experience shows that the joint combustion of several types of biomass can help to solve this problem. The aim of this work is to study the effect of co-combustion of waste from flour milling and highly mineralized peat on the sintering of the ash residue. Various analysis methods (ISO, EDXRF, TGA, and DSC), as well as a experiment in the constructed experimental combustion unit, were used in the work. Wheat bran with a low initial deformation temperature (tA = 780 °C) and highly mineralized peat from the Tomsk region (Ad = 22.8%) were taken for the investigation. These resources are unpromising when considered individually as fuel. Using a bran-peat fuel mixture with a peat fraction of 5 wt % and more makes it possible to obtain an unsintered powdery ash residue. The optimal amount of peat addition to bran during combustion is 5 wt %. A decrease in the proportion of peat leads to sintering of the ash residue, an increase in the proportion of peat increases the ash content of the mixture.

Modeling flow behavior of sintered Al–4%B4C composite during high–temperature upsetting

The hot deformation behavior of sintered Al–4%B4C composites was studied in this work. The main aim of this work is to estimate the effect of initial relative density (IRD), deformation temperature and strain rate on the hot deformation behavior and development of constitutive equations for predicting the hot deformation behavior. For this purpose, upsetting was performed in a hydraulic press for obtaining true stress–true strain curve data of sintered Al–4%B4C composites. The tests were carried out at different IRDes of 80%, 85% and 90% for various temperatures of 573 K, 673 K and 773 K and strain rates of 0.1 s−1, 0.2 s−1 and 0.3 s−1. The test reveals that the effect of IRD, deformation temperature and strain rate on flow stress curves is significant. The constitutive equations have been developed for predicting the flow stress behavior during the hot upsetting of sintered Al–4%B4C composite and it’s validated with experiments. In addition, the required activation energies (Q) of sintered Al–4%B4C composites during the hot upsetting were calculated for various IRDes of 80%, 85%, and 90% was 161.06, 172.28 and181.05 KJ/mol, respectively, which is higher than the value of pure aluminum (144.3 KJ mol−1).

Microstructure and texture evolution of Mg-RE-Zn alloy prepared by repetitive upsetting-extrusion under different decreasing temperature degrees

The repetitive upsetting-extrusion (RUE) experiments of Mg-RE-Zn alloy were carried out to study the grain refinement and texture evolution under different decreasing temperature degrees during the deformation process. The results showed that during the RUE processing, the samples underwent dynamic recrystallization (DRX) and exhibited the similar bimodal microstructure comprising coarse deformed grains and fine dynamic recrystallized grains around. The continuous dynamic recrystallization (CDRX) process and the discontinuous dynamic recrystallization (DDRX) process occurred simultaneously, promoting grain refinement. The particles and the second phases precipitated, which effectively induced DRX to occur through the particle-stimulated nucleation (PSN). As the degree of decreasing temperature and the initial deformation temperature increased, the average grain size and texture intensity of the alloy decreased because the volume fraction of DRXed grains with small grain size and weak texture increased.

The effects of ultra-fine-grained structure and cryogenic temperature on adiabatic shear localization in titanium

The deformation at low temperatures (173 K and 77 K) in ultrafine-grained (100 and 500 nm) titanium is investigated and its effect on adiabatic shear localization is established. In comparison with coarse-grained titanium, the strength of ultrafine-grained titanium is higher due to the classic Hall-Petch effect while the strain hardening approaches zero. Our results show that shear localization in dynamic deformation is also altered. The width of the shear band of coarse-grained titanium decreases from 30 to 18 μm (by 40%) with decreasing the initial deformation temperature to 77 K. In contrast, for 100 nm titanium, the width of shear band decreases more significantly, from 4 μm at room temperature to 1 μm (a 75% decrease) at 77 K. This difference is attributed to the combined effects of the decrease in the thermal conductivity and specific heat capacity, and the increase in thermal softening rate. These changes in the width are consistent with the predictions of the Grady and Bai-Dodd theories. Ultrafine- and nano- recrystallized grains are observed inside the bands which are dependent on initial grain size and initial deformation temperature. The dislocation evolution is evaluated for the different conditions using a Kocks-Mecking formulation; the rotational dynamic recrystallization mechanism responsible for forming the ultrafine/nanosized grains (40–250 nm) is successfully modeled incorporating the differences in initial temperature and grain size. Our results and analysis are important in enhancing the understanding of the structural evolution processes under high strain-rates and cryogenic temperatures.

Effects of Typical Physical Properties on Tribological Behaviors of Three Kinds of Polymer Materials for Water-Lubricated Bearings

The stretching, shearing, deformation, peeling, and temperature rise phenomena at the micro–nano contact interface have a great influence on its tribological properties and significantly affect the service life of key moving parts made of polymers. The physical properties of the three typical polymer materials used for ship bearing polymer materials (ultra-high-molecular-weight polyethylene, synthetic rubber, and polypropylene) were examined to investigate their effects on the wear behaviors. The results showed that synthetic rubber has good wear resistance because of its excellent shear strength, tensile strength, and high initial thermoplastic deformation temperature. Low initial thermoplastic deformation temperature resulted in great wear to the polypropylene material under dry friction, whereas its good wettability resulted in good wear resistance under water-lubricated condition. The ultra-high-molecular-weight polyethylene had the poorest wear resistance under water-lubricated condition because it had the poorest shear strength and tensile strength. The knowledge gained herein provides a better understanding of the relationships between the physical behaviors of polymer materials and their friction and wear mechanisms, along with guidance for selecting and designing polymer friction pairs for ship bearings.

The impact of ash pellet characteristics and pellet processing parameters on ash fusion behaviour

The Ash Fusion Test (AFT) is considered to be the most popular method of characterising the melt characteristics of solid fuel ash. This study shows how pellet preparation can make significant improvements to repeatability. Pelleting pressure, pellet particle size, pellet shape, and furnace ramp rate were investigated to establish the most repeatable representation of ash melting relevant to pulverised fuel combustion in a furnace in an oxidizing atmosphere up to 1600 °C. A 5 mm machine pressed pellet was found to produce the best results as it identified the earliest initial deformation temperature (IDT), gave the least error, and displayed the greatest visible change in pellet height to enable easy identification. Reducing maximum ash particle size to <72 µm and increasing the pressure of the pelleting process was also shown to produce a 120 °C reduction in the IDT when compared with other methods. Reducing the ashing temperature and retaining volatiles lost during high temperature ashing were shown to have a negligible impact on IDT. The characteristic AFT curve was also used to quantify the extent of shrinkage and swelling during the test.

Investigating the effects of process parameters on the cross wedge rolling of TC6 alloy based on temperature and strain rate sensitivities

In this work, the influences of the initial deformation temperature (T0), area reduction (φ) and rolling speed (n) on the cross wedge rolling (CWR) of TC6 alloy were investigated with a 3D elastic-plastic coupled thermomechanical and microstructural finite element (FE) model based on temperature and strain rate sensitivities. The developed model was suggested to be reliable by comparing the simulated results to those of thermal tests, hot compression tests and CWR experiments. The distribution of the volume fraction of the alpha phase gradually increased from the centre to the outer layer. With increases in the initial deformation temperature (T0), the average volume fraction of the alpha phase (AVF) decreases. Moreover, the standard deviation of the volume fraction of the alpha phase (SDF) was smaller in sections S1 and S2 than that in section S3, which means that the alpha phase is more uniformly distributed in the deformed region. With increases in the area reduction (φ), the AVFs and SDFs decrease, which also indicates the improvement of distribution homogeneity. Additionally, the sensitivity rate of the area reduction (R(φ)AVF) was lowest when the area reduction (φ) was between 51 and 64%. Rolling speed (n) should be controlled to balance the two competitive thermal mechanisms. The max-min permissible rolling speed is related to the initial deformation temperature (T0), and it should be approximately 8 r/min in the present study.

Prediction of coal ash fusion temperatures using computational intelligence based models

In the coal-based combustion and gasification processes, the mineral matter contained in the coal (predominantly oxides), is left as an incombustible residue, termed ash. Commonly, ash deposits are formed on the heat absorbing surfaces of the exposed equipment of the combustion/gasification processes. These deposits lead to the occurrence of slagging or fouling and, consequently, reduced process efficiency. The ash fusion temperatures (AFTs) signify the temperature range over which the ash deposits are formed on the heat absorbing surfaces of the process equipment. Thus, for designing and operating the coal-based processes, it is important to have mathematical models predicting accurately the four types of AFTs namely initial deformation temperature, softening temperature, hemispherical temperature, and flow temperature. Several linear/nonlinear models with varying prediction accuracies and complexities are available for the AFT prediction. Their principal drawback is their applicability to the coals originating from a limited number of geographical regions. Accordingly, this study presents computational intelligence (CI) based nonlinear models to predict the four AFTs using the oxide composition of the coal ash as the model input. The CI methods used in the modeling are genetic programming (GP), artificial neural networks, and support vector regression. The notable features of this study are that the models with a better AFT prediction and generalization performance, a wider application potential, and reduced complexity, have been developed. Among the CI-based models, GP and MLP based models have yielded overall improved performance in predicting all four AFTs.

FUEL PROPERTIES OF UKRAINIAN CORN STOVER

In order to provide reliable and efficient thermal conversion, it is necessary to understand the physical and chemical properties of corn stover. The properties of corn stover depend on species, climatic and weather conditions, soil type, fertilizer input etc. Thus, it is necessary to study the fuel from various locations.&#x0D; The present paper describes analysis results of corn stover from a single location in Kyiv region, Ukraine. The soil was fertilized with anhydrous ammonia 80 kg/ha. Elemental composition (W, A, C, H, S, N, O, Cl), calorific values, ash melting temperatures and ash chemical composition of the samples have been tested.&#x0D; The comparative analysis of the samples with foreign analogues has been carried out. It is shown that the test samples of corn stover from Kyiv region are characterized by ash initial deformation temperatures of 1160 - 1200 °C. These temperatures are higher than the average agricultural biomass values and typical for woody biomass. The relatively high ash melting temperature reduces risks of sintering and deposit formation on the furnace inner surface.