Mathematical Modeling of Particle Stratification in Jigs

Recognizing mathematical modeling as a powerful tool for systematic process analysis and control, this paper attempts to critically'review the theories and mathem-atical models which have been advanced to explain and simulate the behaviour ofjigg ing process. The existing literature on mathematical modeling and quantitative analysis of jigging has been divided into six subheads : (i) classical theory, (ii) potential theory, (iii) dispersion models, (iv) energy dissipation theory, (v) stochastic analysis and (vi) empirical models. A new modeling approach based on Newtonian mechanics is used to describe the stratification behavior of particles in jig. In this approach,the motion of solid material is treated using the discrete element method (DEM) while the corre-sponding motion of the liquid is determined by marker and cell (MAC) technique. For illustration purpose, a jig bed consisting of 100 particles of two different densities is simulated. Preliminary results show that the model predicts the stratification of particles reasonably well

A mathematical model to characterize volatile matter evolution during carbonisation in metallurgical coke ovens

The carbonisation mechanism in the coke oven chamber is quite complex and, although much useful information has been generated by empirical studies on both industrial batteries and pilot ovens, attempts to mathematically model the coke oven phenomena met with only limited success. In this study, a mathematical model to simulate volatile matter evolution during carbonisation process for Indian coals has been developed. This model is a part of the endeavour to develop a rigorous mathematical model to simulate the main physical , chemical changes and transient heat transfer phenomena occurring during thermal decomposition of coals in coke oven carbonisation. To have sufficient generality for the applications to coke oven practices, the mathematical model describes the kinetics of release of main volatile matter constituents , thereby, permitting the changes in the mass and composition of solid residue to be estimated by element balances. The prediction of volatile matter evolution has been made from coal ultimate analysis and heating profile based on the principles of kinetics and rate phenomena. The aim of this mathematical model is to predict the yield and composition of volatile matter as a function of charge temperature and to relate these to the changes in the semi-coke composition for some typical Indian coals used for coke making in the metallurgical coke ovens. The quantity of volatile matter loss from coal during carbonisation was also determined experimentally using a standard thermogravimetric analyser (TGA), in which the weight of the sample undergoing test is monitored continuously while the sample is heated at a constant rate. The computer based mathematical model predictions for volatile matter yield are verified with the experimental results and found to be in good agreement

A Mathematical Model to Characterize Volatile Matter Evolution during Carbonisation in Metallurgical Coke Ovens

The carbonisation mechanism in the coke oven chamber is quite complex and, although much useful information has been generated by empirical studies on both industrial batteries and pilot ovens, attempts to mathematically model the coke oven phenomena met with only limited success. In this study, a mathematical model to simulate volatile matter evolution during carbonisation process for Indian coals has been developed. This model is a part of the endeavour to develop a rigorous mathem- atical model to simulate the main physical, chemical changes and transient heat transfer phenomena occurring during thermal decomposition of coals in coke oven carbonisation. To have sufficient generality for the applications to coke oven practices, the mathematical model describes the kinetics of release of main volatile matter constituents, thereby, permitting the changes in the mass and composition of solid residue to be estimated by element balances. The prediction of volatile matter evolution has been made from coal ultimate analysis and heating profile based on the principles of kinetics and rate phenomena. The aim of this mathematical model is to predict the yield and composition of volatile matter as a function of charge temperature and to relate these to the changes in the semi-coke composition for some typical Indian coals used for coke making in the metall-urgical coke ovens. The quantity of volatile matter loss from coal during carbonisation was also determined experimentally using a standard thermogravimetric analyser (TGA), in which the weight of the sample undergoing test is monitored continuously while the sample is heated at a constant rate. The computer based mathematical model predictions for volatile matter yield are verified with the experimental results and found to be in good agreement

Thin Layer Chromatography of Pesticides and Their Residues

Recent progress in the analysis of organo-phosphorus, organo-chlorine, carbamate, urea, uracil pesticides and their residues by thin layer chromatorgraphic methods employing chemical and enzymatic methods is reviewed

Simulation of industrial gravity separation processes using a general purpose simulator

Gravity separation processes have been used in the mineral industry to separate particles under the action of hydr-odynamic and gravitational forces. Although these equip-ments are extensively used for tonnage processing in coal industry, their use has been now extended to waste trea-tment such as separation of valuable metallic matter from slag. However, these processes never run at their best due to lack of understanding of the process and the under-lying principles of separation. For efficient operation it is desirable that trial runs and pilot tests are conducted but these are often time consuming and expensive. Against this background, this paper attempts to show the capabi-lities of numerical simulation to gain a better under-standing of the process with a view to improve its performance.Data from different coal washeries are colle-cted to simulate the behaviour of the plants. Results of simulation utilizing jigging for coal washing is found to be in good agreement with the plant data. The same coal is also treated in other gravity separation processes in order to decide upon a particular washing circuit

Recovery of Cu, Ni, Co and Mn from sea nodules by direct reduction smelting

Polymetallic nodule contains various metals like copper, nickel, cobalt, manganese, iron, lead, zinc, aluminum, etc. Of these, copper, nickel and cobalt are of much importance and in great demand world over. In fact, due to their extensive technological use these three metals are fast depleting from the earth surface. Hence a world-wide research is progressing on sea nodules as an alternative future source of these metals. India is entirely dependent on imports to meet its requirements of cobalt and nickel both of which are most strategic in nature. In this respect, India has made remarkable progress in recovering these metals from sea nodules. The recovery process so far developed in India is based on either purely hydrometallurgical or pyro-hydrometallurgical routes. The processes generate very dilute leach solution, the downstream processing of which is very difficult. Generation of concentrated leach solution from sea nodule would make the process simpler and economical which may not be possible by direct leaching process. Therefore, it has been planned to explore direct smelting of sea nodules to recover copper, nickel and cobalt along with part of iron in the form of alloy followed by individual metal recovery through matte formation and dissolution. Initial studies on direct reduction smelting of Indian sea nodule were conducted using coke as reductant in lab scale experiments. Various parameters like smelting temperature, reductant concentration, holding time etc. have been optimized to obtain an alloy of suitable composition. At a smelting temperature of 1400 oC, recovery of 90-92% Cu, 92-95% Ni and 80-85% Co is obtained in the form of alloy in a recrystallized alumina crucible which can be further treated to recover these metals in pure form. The iron content in the alloy varies significantly with coke concentration. The slag generated after smelting can be directly treated for production of standard grade Fe-Si-Mn without blending

A stochastic model for prediction of Erosion-oxidation interaction on boiler grade steel Surfaces

Fly ash particles entrained in the flue gas from boiler furnaces in coal-fired power stations can cause serious erosive wear on steel surfaces along the flow path. Such erosion can reduce significantly the operational life of the boiler components. A fundamentally-derived mathematical model embodying the mechanisms of erosion involving cutting wear, plastic deformation wear and effect of temperature on erosion behaviour, has been developed to predict erosion rates on the coal fired boiler components such as boiler tubes, economizer and airpreheater assemblies at room and elevated temperature. Various grades of steels, commonly used in the fabrication of boiler components and published data pertaining boiler fly ash has been used for modelling the process. The model incorporates the tensile properties of the target metal surface at room and elevated temperatures, as well as the characteristics of the ash particle dynamics in the form of impingement angle, impingement velocity and composition of the ash particle in terms of the silica content. The mathematical model has been implemented in an userinteractive in-house computer code, (EROSIM–1 ) to predict the erosion rates at room and elevated temperature for various grades of steel normally used in boiler components. The model predictions have been found to be in good agreement with the published data. The model will be calibrated in future with the plant and experimental data generated from a high temperature air-jet erosion testing facility. It is hoped that the calibrated model will be useful to the power plant industry for erosion analysis of boiler components

Analytical model for erosion behaviour of impacted fly-ash particles on coal-fired boiler components

Fly ash particles entrained in the flue gas from boiler furnaces in coal-fired power stations can cause serious erosive wear on steel surfaces along the flow path. Such erosion can significantly reduce the operational life of the boiler components. A mathematical model embodying the mechanisms of erosion on behaviour, has been developed to predict erosion rates of coal-fired boiler components at different temperatures.Various grades of steels used in fabrication of boiler components and published data pertaining to boiler fly ash have been used for the modelling. The model incorporates high temperature tensile properties of the target metal surface at room and elevated temperatures and has been implemented in an user-interactive in-house computer code (EROSIM–1), to predict the erosion rates of various grades of steel. Predictions have been found to be in good agreement with the published data. The model is calibrated with plant and experimental data generated from a high temperature air-jet erosion-testing facility. It is hoped that the calibrated model will be useful for erosion analysis of boiler components

A mathematical model to characterize effect of silica content in the boiler fly ash on erosion behaviour of boiler grade steel

Fly ash particles entrained in the flue gas of coal-fired boilers can cause serious erosion on the critical components along the flow path. Such erosion can significantly jeopardise operational life of the boiler. A first principle based theoretical model has been developed embodying the mechanisms of erosion involving cuttingwear, plastic deformationwear and effect of temperature on erosion behaviour, to predict erosion rates of pertinent boiler grade steels. Various grades of steels commonly used in the fabrication of boiler components and published data pertaining to boiler fly ash has been used in modelling the phenomena. The model also provides a quantitative predictive framework to study the effect of percentage of silica content in the ash particles on the erosion potential. The erosion sensitivity of particle impact velocity, angle of impingement and variation of surface temperature of the substrate (steel) have also been studied as a function of silica content in the ash. The model has been implemented in a computer code to predict the erosion rates at room and elevated temperature for various grades of steels under different particle impact conditions. The model predictions have been found to be in good agreement with the published data. This investigation illustrated that any minor increase in silica level in the ash can considerably aggravate the erosion rates, signifying the fact that silica content in the ash plays a critical role in characterising erosion potential of fly ash