Department of Chemical and Mining Engineeering

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    Dissolution of Kinetics of alpha-phase in TA6V Titanium Alloy
    (Science Press - Beijing, 2011-06) Demhas, Moukrane; Katemi, Richard J.; Appolaire, Benoit; Aeby-Gautier, Elisabeth; Denand, Benoit
    The complexity and diversity of microstructure involved in titanium alloys make it rather difficult to quantitatively describe microstructural evolution. In the present study we focus on microstructure evolutions during heating and isothermal holding considering the effect of the initial microstructure on the dissolution kinetics of alpha-phase. Quantitative microstructure characterizations have been realized. At first, in situ high energy X-ray synchrotron and electrical resistivity was used to follow the dissolution kinetics of  phase. Then, an algorithm capable of quantifying various microstructural data was developed. The microstructural features include the amount of nodular and lamellar alpha-phase, the mean equivalent diameter and the aspect ratio of nodular alpha- phase. This algorithm was applied to TA6V4 samples submitted to different isothermal temperature. The initial microstructure of the samples was either a duplex microstructure (lamellar and nodular alpha-phase) or a nodular microstructure. The dissolution kinetics of alpha-phase was compared with the equilibrium calculations predicted by ThermoCalc. It appears clearly that a large amount of phase is dissolved on heating in spite of a rapid heating rate.
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    Investigations of Residual Stress Distributions in Retained Austenite and Martensite in Carbonitrided Low Alloy Steel
    (Trans Tech Publications, 2014) Katemi, Richard J.; Epp, Jeremy; Hoffmann, Franz; Steinbacher, Matthias
    Specimens of low alloy steel were carbonitrided under different conditions to attain varying levels of carbon and nitrogen contents. The residual stress depth distribution was evaluated in martensite and retained austenite by X-ray diffraction. Beside standard evaluations, triaxial residual stress states with σ≠0 in both phases were also considered. High values of residual stresses in both phases were observed. The sign, magnitude and location of maximum compressive residual stresses were greatly influenced by the level of carbon and nitrogen contents
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    Influence of Tempering and Cryogenic Treatment on Retained Austenite and Residual Stresses in Carbonitrided 18CrNiMo7-6 Low Alloy Steel
    (Tanzania Journal of Engineering and Technology, 2019-06) Katemi, J. Richard; Epp, Jeremy
    This work investigated the influence of tempering conditions coupled with cryogenic treatment on thermal stabilization of retained austenite and residual stress distributions in carbonitrided 18CrNiMo76 low alloy steel samples. The carbonitriding conditions were set to enable attaining surface carbon and nitrogen content of 0.87 and 0.34 mass.-percent respectively. After carbonitriding, some of the samples were subjected to varying tempering conditions followed by cryogenic treatment at -120 °C using nitrogen gas. Analysis of both retained austenite and residual stresses was conducted using X-ray diffraction. In the as-quenched state, carbonitrided samples contained 52 mass.-percent. Samples that were directly subjected to the cryogenic treatment after quenching retained only about 20 mass.-percent of austenite. Samples subjected to variant tempering conditions coupled with cryogenic treatment retained at least 30 masses.-percent of austenite. A thermal stabilization of retained austenite which increases with increasing temperature was identified. On tempering at 240°C for 14 hours retained austenite becomes unstable and decomposes to bainite leading to the low initial amount of retained austenite before cryogenic treatment. It can be concluded that the tempering process coupled with cryogenic treatment leads to an increasing hardness, to higher compressive residual stresses as well as to a shift of the location of maximum compressive residual stress toward the surface.
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    Financial analysis of the impact of increasing mining rate in underground mining, using simulation and mixed integer programming
    (Journal of the Southern African Institute of Mining and Metallurgy, 2017-04) Salama, Abubakary; Nehring, Micah; Greberg, Jenny
    This paper challenges the traditional notion that mine planners need to plan production so as to incur the lowest mining cost. For a given mine configuration, a mine that increases its mining rate will incur increased mining costs. In an environment in which operations are fixated on cost reduction, a proposal that increases costs will not be readily accepted. Such a proposal requires financial justification-the increase in costs might be recuperated by the additional production. This paper evaluates the net present value (NPV) across a range of copper prices for two underground orebodies located at different depths, using a production rate of 300 kt per quarter and a scenario that introduces additional equipment and costs for 450 kt per quarter. The evaluation was based on the changes of NPV for the orebody located at a shallow depth compared with the orebody at a greater depth. Discrete event simulation combined with mixed integer programming was used for analysis. Unlike traditional sensitivity analysis, this study re-optimizes the mine plan for each commodity price at each production rate. The results show that, for the low mining rate at the final copper price, an NPV of A$1530.64 million is achieved, whereas an NPV of A$1537.59 million is achieved at a higher mining rate. Even though pushing mining rates beyond traditional limits may increase mining costs, this option may be beneficial at certain commodity prices, particularly when prices are elevated
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    The effects of orepass loss on loading, hauling, and dumping operations and production rates in a sublevel caving mine
    (Journal of the Southern African Institute of Mining and Metallurgy, 2018-04) Skawina, Bartlomiej; Greberg, Jenny; Salama, Abubakary; Gustafson, Anna
    Orepass failure is a well-known problem in deep mines, and the risk of losing an orepass is associated with severe production disturbances. In the near future, one possible scenario in the Loussavaara Kiirunavaara Aktiebolag (LKAB) Malmberget mine is to concentrate the mining operation in fewer, but larger, production areas. In this paper we evaluate the effects of orepass loss on loading, hauling, and dumping operations and production rates using discrete event simulation, by simulating part of the Malmberget mine loading and hauling system under different environmental and operational constraints
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    Alternative process flow for underground mining operations: analysis of conceptual transport methods using discrete event simulation
    (MDPI, 2016-09) Greberg, Jenny; Salama, Abubakary; Gustafson, Anna; Skawina, Bartlomiej
    As the near surface deposits are being mined out, underground mines will increasingly operate at greater depths. This will increase the challenges related to transporting materials from deeper levels to the surface. For many years, the ore and waste transportation from most deep underground mines has depended on some or all of the following: truck haulage, conveyor belts, shafts, rails, and ore pass systems. In sub-level caving, and where ore passes are used, trains operating on the main lower level transport the ore from ore passes to a crusher, for subsequent hoisting to the surface through the shaft system. In many mines, the use of the ore pass system has led to several problems related to the ore pass availability, causing production disturbances and incurred cost and time for ore pass rehabilitation. These production disturbances have an impact on the mining activities since they increase the operational costs, and lower the mine throughput. A continued dependency on rock mass transportation using ore passes will generate high capital costs for various supporting structures such as rail tracks, shaft extensions, and crushers for every new main level. This study was conducted at an existing underground mine and analyzed the transport of ore from loading areas at the lower levels up to the existing shaft points using trucks without employing ore passes. The results show that, when the costs of extending ore passes to lower levels become too great or ore passes cannot be used for production, haul trucks can be a feasible alternative method for transport of ore and waste up the ramp to the existing crusher located at the previous main level. The use of trucks will avoid installing infrastructure at the next main level and extending the ore passes to lower levels, hence reducing costs
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    Petrophysical interpretation in shaly sand formation of a gas field in Tanzania
    (Journal of Petroleum Exploration and Production Technology, 2019-12-13) Mkinga, Oras Joseph; Skogen, Erik; Kleppe, Jon
    An onshore gas field (hereafter called the R field—real name not revealed) is in the southeast coast of Tanzania which includes a Tertiary aged shaly sand formation (sand–shale sequences). The formation was penetrated by an exploration well R–X wherein no core was acquired, and there is no layer-wise published data of the petrophysical properties of the R field in the existing literature, which are essential to reserves estimation and production forecast. In this paper, the layer-wise interpretation of petrophysical properties was undertaken by using wireline logs to obtain parameters to build a reservoir simulation model. The properties extracted include shale volume, total and effective porosities, sand fractions and sand porosity, and water saturation. Shale volume was computed using Clavier equation from gamma ray. Density method was used to calculate total and effective porosities. Thomas–Stieber method was used to determine sand porosity and sand fraction, and water saturation was computed using Poupon–Leveaux model. The statistics of the parameters extracted are presented, where shale volume obtained that varies with zones is between 6 and 54% volume fraction, with both shale laminations and dispersed shale were identified. Total porosity obtained is in a range from 12 to 22%. Sand porosity varies between 15 and 25%, and sand fraction varies between 33 and 93% height fraction. Average water saturation obtained is between 32 and 49% volume fraction.
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    EOS Model and Black-Oil PVT Table Generation for a Tanzanian Reservoir
    (International Journal of Applied Science and Technology, 2019) Mkinga, Oras Joseph; Kleppe, Jon; Rwechungura, Richard Wilfred; Raphael, Matheo L.
    Tuning of an EOS model and generation of Black-oil PVT tables for a gas field in Tanzania, here named R reservoir, are presented. The Soave-Redlich-Kwong equation of state was tuned using experimental data and PhazeComp software to obtain the EOS model which represents fluid behavior change in the R reservoir. A contribution is provided in a relationship between specific gravity and molecular weight, which is a modified form of Soreide equation for C7+ characterization. Constants of the equation are determined using linear regression to fit experimental data. A residual oil in the reservoir is recognized using EOS calculation; PVT data generated in this paper can be used to study its potential to condensate blockage and well deliverability. Gas and oil PVT tables are generated for saturated and undersaturated condition, they can be used in reservoir simulation of R reservoir.
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    Non-Isothermal Degradation and Thermodynamic Properties of Pine Sawdust
    (Scientific Research Publishing, 2018-12-28) Said, Mahir; John, Geoffrey; Chaula, Zephania; Samwel, Manyele; Mhilu, Cuthbert
    The study of non-isothermal kinetics analyzed the reactivity of pine sawdust, while the thermodynamic properties analyzed energy consumed and released from the pine sawdust. The kinetic parameters were determined by analyzing mass loss of pine sawdust components by using Thermogravimeric analyzer. The cellulose has the highest conversion rate of 9.5%/min at 610 K compared to hemicellulose and lignin, which are 5%/min at 600 K and 2%/min at 800 K, respectively. The activation Energy for cellulose, hemicellulose and lignin was 457.644 kJ/mol, 259.876 kJ/mol, and 89.950 kJ/mol, respectively. The thermodynamic properties included the change of Gibbs free energy for cellulose and hemicellulose, which were −214.440 and −30.825 kJ/mol respectively, their degradation was spontaneous in forward direction, while change of Gibbs free energy for lignin was 207.507 kJ/mol, which is non-spontaneous reaction. The positive value of change of entropies for the active complex compounds formed from hemicellulose and cellulose is less stable, while the active complex compounds of lignin are characterized by a much higher degree of arrangement since its change of entropy is negative. The kinetic and thermodynamic properties show that pine sawdust is a good candidate for production of char since it is easier to remove hemicellulose through thermal process.
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    Contribution of Liquid Biofuels to Socio-Economic Rural Development
    (Journal of the Geographical Association of Tanzania, 2016) Mlay, Happiness; Katima, Jamidu H.Y; Minja, Rwaichi J.A
    The rural community still lacks access to clean, cost effective and sustainable form of energy that is needed to power their socio-economic activities, particularly for agriculture, water supply and food processing. Understanding that energy has a close link with poverty reduction, economic growth and sustainable development, a study on the process of modifying plant oil (PO) to produce a suitable liquid biofuel that can run diesel engines commonly used in rural areas for various social-economic activities was carried out. The research was part of works by Policy Innovation System for Clean Energy Security (PISCES) research project, which was a five-year initiative project funded by the UK’s Department for International Development (DFID). PISCES, which had partners in Kenya, India, Sri Lanka, United Kingdom and Tanzania, intended to provide policy makers with information and approaches that can unlock the potential of bioenergy to improve energy access and livelihoods in rural communities. The PO used was indigenous non-edible oil from Jatropha (Jatropha Curcas L.) seeds. Modified Plant Oil (MPO) presents a potential clean, cost-effective, sustainable and accessible fuel to meet rural basic energy needs. MPO can also power rural agroprocessing activities by being used in power tillers, millers, water pumps, etc., and become an important key for socio-economic development of rural population relying on agricultural activities. The use of renewable energy from PO will contribute to sustainable energy source and to reduce CO2 emission, contributing to reduce climate change problems.
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    Lactic Acid Production from Sisal Boles Juice by Lactobacillus Delbrueckii Sp. Delbrueckii
    (2018) Msuya, N; Katima, J.H.Y; Masanja, E; Minja, R. J. A; Temu, A.K
    The use of different concentrations of sugar from sisal boles juice for production of Lactic acid (LA) using Lactic Acid Bacteria (LAB) has been studied with the intention of analysing the effect of initial sugar concentration, process temperature and initial medium pH on the produced lactic acid concentration, yield and productivity. All the linear variables (initial sugar conc., pH and temperature), two way and three way interactions were statistically significant for LA yield at p-values of less than 0.05 with correlation coefficient of 0.997. There was no significant effect on LA productivity of three way interactions (Temp.*pH*Initial Conc.). Maximum condition for production of LA occurred at a temperature of 37°C, initial pH of 6 and initial sugar concentration of 120 g/L which corresponded with the highest LA concentration of more than 24 g/Land a yield of 93%. This study shows that sisal boles juice has potential to produce LA.
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    Thermal-Acid Hydrolysis of Sisal Boles Juice for Lactic Acid Production
    (2018) Msuya, N; Katima, J.H.Y; Minja, R. J. A; Masanja, E; Temu, A.K
    The effect of reaction temperature, time and pH on the maximum total sugar concentration during thermal-acid hydrolysis of sisal boles juice was investigated. The Minitab software (V. 17) was used to design a 2n full factorial design for sisal juice hydrolysis and analyse the effects of the variables on the response. Thermal-acid hydrolysis can be carried out at a moderate temperature of 60°C with a concentrated hydrochloric acid at pH of one within a period of 30 minutes to achieve a sugar yield of 39%. The breakdown of complex sugars to simple sugars of sisal bole juice is basically a function of acid concentration in sugar solution. Lowering pH of the juice contributed to increase in hydrolysis rate. The use of ANOVA analyses gave evidence that linear, 2- way interactions and 3-way interactions of all the variables: temperature (60-100°C), time (30-60 min) and pH (1-5) significantly affected the sugar yield. This amount of sugar yield from sisal boles juice is higher than the yield of 26% which has been reported. The hydrolysed juice was also subjected into fermentation for lactic acid and results showed favourable LA yield was obtained with the recommended thermal-acid hydrolysis in this study.
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    Characterization of Sisal Boles for Production of Polylactic Acid (PLA)
    (2018) Msuya, N; Katima, J.H.Y; Minja, R. J. A; Masanja, E; Temu, A.K
    Biobased biodegradable plastics (bioplastics) show a large range of properties which can compete with non-biodegradable thermoplastics in packaging, textile and biomedical applications. Polylactic acid (PLA) is one of the most promising bioplastics, which are synthesized by polymerization of Lactic Acid (LA). Traditionally LA is produced from pure sugars and food crop sources like potatoes, cassava, corn, wheat, rice, sugar beet, sugar cane, and others. However, because of competition with existing uses, alternatives raw materials are being researched. One such alternative is the sisal boles. Sisal bole is part of the 98% of the sisal biomass which is traditionally counted as waste. Sisal boles as raw material for PLA are advantageous since it is not competing with food. This work characterizes sisal boles juice and its potential to produce biodegradable plastics. The sisal boles juice was extracted from chopped autoclaved boles using a hydraulic pressing machine. The juice was hydrolyzed to allow the sugar polymers to break into monomer sugar. The boles have been found to comprise of up to 97.94% (w/v) organic matters and total sugar content in juice of up to 30% (w/v). The produced juice mineral content levels were within the recommended working fermentation range with necessary nutrients for LA producing microorganisms. Sisal boles can therefore be one of the good raw materials for lactic acid production
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    Separation and Purification of Lactic Acid from Sisal Wastes
    (2018) Msuya, N; Minja, R. J. A; Katima, J.H.Y; Masanja, E; Temu, A.K
    The aim of this paper was separation and purification of Lactic acid (LA) produced from Sisal Waste by investigating the influence of modified hybrid short path evaporation (M-HSPE) system on the concentration of LA. A 22 full factorial design was used to study the influence of temperature and time on the concentration of LA and % mass obtained in distillate and residue flask. Minitab V.17 was used in designing the LA concentration experiments and in calculating the effect of each variable and their interactions. Higher LA concentration of 108 g/L occurred at system temperature of 47°C for 25 minutes. This represented a concentration of 4.5 times the initial concentration (24 g/L) with 100% recovery in residues stream/ flask. Therefore, the M-HSPE system was able to concentrate LA to almost twice the original hybrid short path evaporation (HSPE) system. According to ANOVA, LA concentration presented a correlation coefficient of 0.993, which confirm that, linear model correlated well with the experimental data. The system temperature (Temp.), operation time (time) and the interaction between system temperature and time were statistically significant variables for LA concentration at alpha = 0.05.
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    Fluoride occurrence in domestic water supply sources in Tanzania: A Case of Meru District Arusha Region
    (2018) Mbabaye, Godfrey; Minja, Rwaichi; Mtalo, Felix; Legonda, Isaack; Mkongo, Godfrey
    Surface and ground water are the major sources of water supply in Meru district. Most of the people in Meru rural areas depend on surface water in rivers and ground water shallow and deep wells and springs for house hold activities. The presence of fluoride in high concentrations in drinking water or cooking water causes severe health problems to the people. Distribution of fluoride concentrations in Meru district domestic water sources was studied by referencing the location of water sources using Extrex 20 garmin hand held GPS instrument. Fluoride concentrations were measured using Metrohm Ag/AgCl reference electrode connected to a Metrohm potentiometer (826 pH/Ion Meter) in a laboratory. Fluoride concentrations were found to range between 0.76 and 1103 mg/L. Around 69% of 146 samples collected had fluoride concentrations above 1.5 mg/L which is the WHO recommended standard while 47% of the samples had fluoride concentrations exceeding 4.0 mg/L as recommended by the Tanzania Bureau of Standards. The results indicate that, residences in five wards of Meru district namely Kikatiti, King’ori, Leguruki, Maji ya Chai, and Ngarenanyuki are exposed to high levels of fluoride posing risk of dental and skeletal fluorosis. Generally, the study observed that most of the ground and surface water resources in Meru district are contaminated with high fluoride concentration and therefore waters from most sources in the areas (wards) need to be defluoridated to be potable.
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    Standardizing defluoridation of community waters using bone char
    (Journal of Water Supply: Research and Technology—AQUA | 66.2 | 2017, 2017-01) Godfrey K. Mbabaye, Felix Mtalo, Rwaichi J. A. Minja and Isack Legonda
    Different bone char (BC) preparation methods affect the physical chemical properties and therefore the capacity to remove fluoride. Fluoride removal capacities of BC prepared at three controlled temperatures, with particle grain sizes of 250–500 μm, 500–1,000 μm and 1,000–1,800 μm were determined in column experiments with an initial fluoride concentration of 8.55 mg/L. The sorbent was calcined at 400W C, 500W C and 600W C. BC calcined at 400W C had better fluoride removal performance compared to those calcined at 500W C and 600W C due to decreased pore volume and surface area as the calcination temperature was increased. There was a reduced mass transfer effect to the adsorption sites in pores as the BC particle size was increased. The equilibrium adsorptions Langmuir and Freundlich isotherms were tested. For the Langmuir equilibrium adsorption isotherm, maximum monolayer coverage (Q) was determined to be 3.512 mg/g, and the value of the separation factor (r) obtained was 0.1394 indicating favorable adsorption as it lies between 0 and 1. The Freundlich governing equilibrium adsorption isotherm model gave a value of 1/n equal to 0.445. This indicates a favorable adsorption process, since the bond energies increase with surface density of the adsorbent.
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    Bubble Size and Gas-Liquid Interfacial Area Measurements Using Molten Paraffin Waxes in Bubble Columns
    (American Institute of Chemical Engineers, 1987) Bukur, Dragomir B.; Patel, Snehal A.; Daly, James G.; Raphael, Matheo L.
    Experiments were conducted in 0.05 m ID and 0.23 m ID by 3 m tall bubble columns with different types of molten waxes as the liquid medium and nitrogen as the gas, under processing conditions typical or Fischer-Tropsch synthesis over iron catalysts (i.e. gas velocities up to 0.15 m s, and temperatures between 200 and 270/sup 0/C) to estimate gas liquid interfacial area from measured values of average gas hold-up and Sauter mean bubble diameter. The gas hold-up was estimated from visual observations of the expanded and static liquid heights, and the Sauter was estimated from bubble size measurements obtained by photography and dynamic gas disengagement. The paraffin wax (FT-300) used in the authors' studies is non-coalescing and has a tendency to foam. The amount of foam is greater for runs conducted in the order of increasing gas velocities, than in runs with decreasing velocities. Thus, two values of hold-up are possible and the start-up procedure determines which one will be attained. At higher gas velocities (> 0.05 m/s) the foam disappears and a transition to the slug flow, churn-turbulent regime takes place. Reactor waxes are coalescing in nature and do not produce foam. Despite similar hold-ups for the different waxes at higher gas velocities, the Sauters are significantly different and this is reflected in the specific gas-liquid interfacial areas, with larger values obtained with the paraffin wax compared to values with reactor waxes.
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    Recovery and Kinetics Study of Isoelectric Precipitation of Sunflower Protein in a Tubular Precipitator
    (1997) Raphael, Matheo L.
    Oilseed sunflower is one of the major vegetable oil sources. The residue after the extraction of oil (defatted meal, DM) contains a substantial amount of nutritious protein which is recoverable by extraction and precipitation methods. For effective recovery of the solid proteins from the solids-liquid suspension, it is imperative to have large particles with a narrow spread in their size distribution and high solids concentration. In this research, up to 97 % w/w and 65 % w/w of the proteins in the laboratory and industrially defatted sunflower meals, respectively, were extracted using aqueous alkaline solutions at pH 10.0. Up to 84 % of these soluble proteins were recovered as solids when the pH was lowered from 10.0 to 4.0 (isoelecmc pH) using aqueous HCI acid. The amount of proteins recovered as solids decreased with decreasing concentrations of the acid.
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    Protein in a Tubular Precipitator
    (1997) Raphael, Matheo L.
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    Hydrodynamics of Fischer-Tropsch Synthesis in Slurry Bubble Column Reactors
    (1987) Bukur, Dragomir B.; Daly, James G.; Patel, Snehal A.; Raphael, Matheo L.; Tatterson, Garry B.
    An improved photographic technique was employed to obtain pictures, for bubble size analysis, in experiments conducted in the Unit AMk2G (511 cm ID, 305 cm tall glass column)] During these experiments measurements of the average gas hold-up were made at 200 and 265oc using FTk300 paraffin wax as the liquid medium and nitrogen as the gas. Additional experiments were performed adding oxygenates, stearyl alcohol and stearic acid, (5 - 10 % by weight) to the wax at a temperature of 265°C. The addition of oxygenates did not have a significant effect on the average gas hold'up.