Department of Chemical and Mining Engineeering

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The 2005 and 2006 Eruptions Of Ol Doinyo Lengai: Assessing Deep and Shallow Processes At an Active Carbonatite Volcano Using Volatile Chemistry And Fluxes
(2006-11) Fischer, Tobias; Burnard, Pete; Marty, Bernard; Palhol, Fabien; Mangasini, Frank; Shaw, A. M.
960's and the oldest natrocarbonatite tuffs have been dated to 1250 years B.P.. Earlier eruptions produced phonolitic and nephelinitc lavas [1]. Since the 1960's the volcano has erupted frequently producing carbonatite lava flows. Explosive eruptions are much less frequent but have occurred in 1966, 1983 [1] and 1993 [3] producing ash, cones and natrocarbonatite tephra. In July 2005, we launched an expedition to the crater to collect gas and rock samples. On July 4, the volcano began erupting low viscosity, low T (540C) high velocity (2 m/sec) lava flows at a rate of about 0.3 m3/sec. By afternoon, the lava was flowing over the eastern crater rim. During the eruption we sampled gases from nearby hornitos at 120 and 168C, yielding pristine magmatic gases characterized by 75 mol% H2O, 22% CO2, < 1% SO2, H2S, HCl and traces of H2, He, Ar, N2, CH4 and CO. CO2-CH4-CO gas equilibrium temperatures are 580C consistent with lava flow temperatures. N2-He-Ar abundances indicate an upper mantle origin of volatiles, confirmed by isotopes [4]. SO2 flux measured by mini DOAS was low (10 t/day). CO2 fluxes calculated using CO2/SO2 are 3000 to 4000 t/day. Volatiles measured in the carbonatite lavas by SIMS show low H2O (< 0.7 wt%), high S (0.2 to 1 wt%) and Cl (0.6 to 1.4 wt%) and variable F (0.06 to 0.7 wt%). CO2 contents are 30 wt% with major and trace elements typical of natrocarbonatite lavas previously reported in [1]. The release of all CO2 (30 wt% or 20 t/day) from eruption lavas would only produce a small fraction of the measured CO2. In March 2006 eyewitnesses [3] reported the occurrence of an explosive eruption and some of us returned to the volcano on May 12. The morphology of the crater had changed and was now filled with lava 2 m deep. The central cone area had collapsed. We sampled a deposit of carbonatite ash containing accretionary lapilli suggesting water-magma or water-ash interaction. The measured SO2 flux was low (approx. 10 t/day). Our data and observations imply that 1) Ol Doinyo Lengai gases originate from the upper mantle and have equilibrium temperatures consistent with carbonatite magmas, 2) the CO2 flux measured during the eruption cannot be produced by the eruption of carbonatite lavas and additional CO2 is released from the mantle, 3) explosive eruptions (such as in 2006) may be triggered by hydromagmatic processes. Alternatively the fountain material interacted with rain at the surface.
Alternative Process Flow for Underground Mining Operations: Analysis of Conceptual Transport Methods Using Discrete Event Simulation
(MDPI AG, Basel, Switzerland, 2016-06-30) Greberg, Jenny; Salama, Abubakary Juma; Gustafson, Anna; Skawina, Bartłomiej
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.
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
Analysis of Different Techniques for Improving Performance of Flat Plate Solar Collectors for Fruits Drying
(2014-06) Bakari, Ramadhani; Minja, Rwaichi J. A.; Njau, Karoli N.
Analysis of Pyrolysis Kinetics and Energy Content of Agricultural and Forest Waste
(2014-03) Said, Mahir M.; John, Geoffrey R.; Mhilu, Cuthbert F.; Manyele, Samwel
Selected agricultural and forest wastes included rice husk, coconut husk, cashewnut shell, eucalyptus, pine and mangrove were used for thermal characterization. The studied materials have heating value between 13 and 23 kJ/kg, such that the biomass material can be used as a fuel by directly burning, but their energy content is lower as compared to coal and other fossil fuels. The energy content of the biomass material can be improved through pyrolysis process for the mentioned materials, the cashew nut shell had higher energy content than other biomass material due to its high hydrogen to carbon ratio and low oxygen to carbon ratio. Thermochemical characteristic depicted high degradation at a heating rate of 10 K/min. All studied materials except mangrove and pine, maximum degradation occurred at 5 K/min. The reactivity of coconut husk was highest whilst cashew nut shell had the least reactivity. The activation energy for cashew nut shell obtained was 336.41 kJ/mole and the activation energy of the other biomass ranged between 220 and 130 kJ/mol. The coconut husk, pine, eucalyptus and rice husk are more reactive than mangrove and cashewnut shell.
Analyzing energy consumption and gas emissions of loading equipment in underground mining
(Canadian Institute of Mining, Metallurgy and Petroleum., 2015) Salama, Abubakary Juma; Greberg, Jenny; Skawina, Bartlomiej; Gustafson, Anna
In an environment of rising energy prices and mining at greater depths, cost-efficient loading and hauling equipment is essential. Conducted at an underground mining operation, this study analyzes the energy consumption and gas emissions of diesel and electric load-haul-dump machines (LHDs) with similar bucket capacities. Based on energy prices from the first quarter of 2014, results of discrete event simulation show that energy costs for diesel and electric LHDs are US$0.24/t and US$0.07/t, respectively. Also, diesel LHDs emit 2.68 kg CO2 per litre of diesel fuel, whereas using electric machines reduces the need for ventilation to mitigate engine heat and emissions and reduces energy costs.
Applicability of X-ray microtomography for Characterizing the Microstructure of Frozen Apple during Storage
(4th IIR Conference on Sustainability and the Cold Chain location:Auckland, New Zealand date:6-7 April 2016, 2016) Vicent, Victor; Ndoye, Fatou-Toutie; Verboven, Pieter; Nicolaï, Bart; Alvarez, G.
X-ray microtomography (X-ray micro-CT) was applied to visualise the change of 3D microstructure during freezing of ‘Jonagold’ apple at a pixel resolution of 3.83 m. To better understand the microstructure evolution during freezing, pore size distributions were carefully analysed. This work highlighted the applicability of X-ray micro-CT to visualise the microstructure evolution in frozen apple samples subjected to three different freezing protocols (at -6 °C, -12 °C, -20 °C). Freezing process was done directly on cooling stage mounted on micro-CT system that allows one to follow the structure of the materials in frozen state. It was observed that slow rate of heat removal at -6 °C damages cellular tissue of apple considerably as noted on the spatial irregularity of pores. Instead; slightly damaging of apple tissues was observed for the latter two freezing protocols (i.e. at -12 °C and -20 °C). From this study, we manage to show the application of X-ray micro-CT to reveal and quantify the 3D microstructure of frozen apple tissue during freezing.
Arsenic Adsorption Capabilities of Soil-Bentonite Mixtures as Buffer Materials for Landfills
(2002-01) Minja, Rwaichi J. A.; Ebina, Takeo
Removal and fixation of As (III) and As (V) from aqueous solution by soil/bentonite mixtures were studied to develop reliable clay liners for waste landfill sites. One of two soils such as, Masatsuchi. soil (weathered granite) and Murram soil (pumice) was used as a main body of the liner, and Wyoming bentonites were mixed with the soils because of its superior impermeability. As the result of batch experiments, it was shown that large part of As was removed by Masatsuchi soil without pH buffer, andth e result was better than those of Murram soil. Both soils appeared to have best adsorption of As (V) and As (III) within pH ranges of 3-6.5 and 7-9.5 at where the dominant species in the aqueous solution were H2AsO4- and H2AsO3-, respectively. A long-term leak test showed that Masatsuchi soil-Wyoming bentonite combination had the ability to remove all the As (III) from 4 ppm aqueous solution for more than 100 days.
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.
Carbohydrate Analysis of Pulps Using Enzymatic Hydrolysis and High Pressure Liquid Chromato- Graphy
(1999) Syverud, Kristin; Moe, Størker T.; Minja, Rwaichi J. A.
A revised method for analysis of carbohydrates in pulps is presented. The method utilizes commercially available enzyme preparations for enzymatic hydrolysis of the pulp, followed by acid hydrolysis for complete cleavage of oligomers that are still present. Quantification of monosaccharides in the hydrolysate was performed by HPLC using a Pb-sulphonate/polymer column and deionized water as the mobile phase. Integration of the chromatograms was performed using least squares fitting of partially resolved peaks by commercial software. The method requires moderate operator skills and low investment costs for specialized analytical equipment.
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
The Combustion Characteristics of Biomass Syngas from High Temperature Air, Entrained Flow and Circulating Fluidized Bed Gasifiers
(SSRN Electronic Journal, 2014-02-21) Said, Mahir M.; Chaula, Zephania; John, Geoffrey R.; Mhilu, Cuthbert F.
The study has been performed to determine fundamental combustion characteristics of syngas. Three technologies were selected to produce the syngas; High Temperature Agent Gasifier (HTAG), Entrained Flow Gasifier (EFG) and Circulating Fluidized Bed Gasifier (CFBG). Although the material used for production of syngas was the same, wood biomass, the compositions of syngas obtained were different. The adiabatic flame temperatures were determined at different air to fuel ratio. The maximum adiabatic temperature for HTAG, EFG and CFBG syngas at stoichiometric condition were 1846 K, 2250 K and 2234 K respectively. It has been observed that combustion of CFBG syngas produces more nitrogen oxide (NOx) than when using syngas of EFG. The high NOx in CFBG is caused by the high methane content, which increases the adiabatic flame temperature to 2200 K at stoicheometric condition. The lowest NOx emission was observed in HTAG syngas. The adiabatic temperature increased linearly with the preheating temperature, whilst oxygen enrichment increased the adiabatic temperature. It has been concluded that syngas produced from EFG and CFBG are better candidate as gaseous fuel in combustion chamber than HTAG syngas.
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.
Correlation of Hydraulic Conductivity of Clay–Sand Compacted Specimens with Clay Properties
(Elsevier, 2004) Ebina, Takeo; Minja, Rwaichi J. A.; Nagase, Takako; Onodera, Yoshio; Chatterjee, Abhijit
Hydraulic conductivity of compacted specimens consisting of 1 of 16 clay samples and siliceous sand/natural soils was measured using permeameters with flexible wall cells. Clay samples studied were eight natural bentonites, one purified montmorillonite, five standard clay samples, one synthetic hectorite, and two cation-exchanged bentonites. The clay content to whole solid was fixed at 11.5% w/w, and the mixtures were rammed in a mold to form disk compactions. A higher hydraulic conductivity was observed with increase in the Ca/Na ratio of clay. Hydraulic conductivity was also affected by bentonite content of the clays and the mineral content. A relation between the hydraulic conductivity and the characteristic index properties of the clays such as chemical concentration, methylene blue adsorption capacity (MB), and so on were elucidated, and then a polynomial expression was derived to reproduce measured hydraulic conductivity data. This relation was then utilized to estimate hydraulic conductivity of blended bentonites from characteristic properties of the component bentonites.
Description of a New Howardite Meteorite Fall in Southern Tanzania; Proposed Meteorite Name Kilimani
(2009) Kinnunen, Kari A.; Lindqvist, Kristian; Pakkanen, Lassi; Rutaihwa, Augustina; Baruti, Karim R.
This report summarizes laboratory and other data of a new meteorite that fell in southern Tanzania in July, 2003. This data is required by the Meteoritical Society for registration and approval of the proposed name. The rock fragments were originally collected by locals and later identified and studied in Geological Survey of Finland (GTK) during next years. Earlier contacts and previous scientific co-operation between University of Dar Es Salaam, the Geological Survey of Tanzania (GST) and GTK enabled this study. The meteorite was identified as polymict brecciated achondritic howardite. It is proposed that it should be named Kilimani according to the village in which it fell. The meteorite is the 10th known from Tanzania. So far nine meteorites were known from Tanzania (see Grady 2000). Ivuna and Mbozi are the most widely known Tanzanian meteorites. Nine out of these now ten Tanzanian meteorites are witnessed falls.
Development and Testing of a Probe to Monitor Gas-Side Fouling in Cross Flow
(Taylor & Francis, 2002-05) Temu, Abraham K.; Næss, Erling; Sønju, O. K.
A probe to monitor gas-side fouling in cross flow has been developed and tested in laboratory experiments. The probe is suitable for monitoring both the heat flux and the mass accumulated on the front and rear side of a cylinder in cross flow. A procedure for converting the mass accumulation measurements to thermal resistance is developed. Experimental results obtained using the mass accumulation method are compared to data obtained by heat flux measurements, and show good agreement in terms of the thermal fouling factor. It is also shown that the test results are in good agreement with other experimental results found in the literature. The probe is well suited for distinguishing the thermal effect (thermophoresis) from the other forces contributing to fouling. It is also useful for nonfouling heat transfer studies, providing average heat transfer coefficients on the front and rear sides of a cylinder.
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.
Effect of Glass Thickness on Performance of Flat Plate Solar Collectors for Fruits Drying
(Hindawi Publishing Corporation, 2014) Bakari, Ramadhani; Minja, Rwaichi J. A.; Njau, Karoli N.
This study aimed at investigating the effect of thickness of glazing material on the performance of flat plate solar collectors. Performance of solar collector is affected by glaze transmittance, absorptance, and reflectance which results into major heat losses in the system. Four solar collector models with different glass thicknesses were designed, constructed, and experimentally tested for their performances. Collectors were both oriented to northsouth direction and tilted to an angle of 10° with the ground toward north direction. The area of each collector model was 0.72 m2 with a depth of 0.15 m. Low iron (extra clear) glass of thicknesses 3 mm, 4 mm, 5 mm, and 6 mm was used as glazing materials. As a control, all collector performances were analysed and compared using a glass of 5 mm thickness and then with glass of different thickness. The results showed that change in glass thickness results into variation in collector efficiency. Collector with 4 mm glass thick gave the best efficiency of 35.4% compared to 27.8% for 6 mm glass thick. However, the use of glass of 4 mm thick needs precautions in handling and during placement to the collector to avoid extra costs due to breakage.
Effect of H-Mordenite Zeolite as a Component in Co-Mo-Al2O3 Hydroprocessing Catalysts Used for the Conversion of Boscan Heavy Oil
(Elsevier, 1991) Minja, Rwaichi J. A.; Ternan, Marten
The effect of H-mordenite zeolite as a component in Co-Mo-Al2O3 hydroprocessing catalysts has been studied. Catalysts containing up to 20% H-mordenite were used for hydrocracking Boscan heavy oil at 13.9 MPa. Although the acidic sites on the external surface of the zeolite crystals were expected to increase cracking reactions, little effect on conversion was observed. As the H-mordenite content of the catalyst increased, the bulk density and the specific surface area of the catalysts decreased substantially. When the reaction results were expressed on the basis of constant residence time and constant catalyst surface area there was an increase in the reaction parameter with increasing H-mordenite content of the catalyst. It was also found that coke deposition increased with the increasing H-mordenite content of the catalyst. These two observations suggest that H-mordenite caused an increase in the number of acidic sites in the catalyst. The results indicate that catalysts with H-mordenite would produce greater conversions than catalysts without H-mordenite, if the extrudates could be prepared in such a way that the catalyst bulk density does not change when the H-mordenite is added.
Effect of mild hydrothermal pretreatment on biomass pyrolysis characteristics and vapors: A Mass and Energy Balance Perspective
(2015) Cuvila, Carlos Alberto; Said, Mahir M.; Kantarelis, Efthymios; Saffaripour, M.; Yang, Weihong
Mozambique has vast forestry resources and also considerable biomass waste material such as bagasse, rice husks, sawdust, coconut husks and shells, cashew nut shell and lump charcoal waste. The potential of the total residues from the agricultural sector and the forest industry is estimated to be approximately 13 PJ. This amount of energy covers totally the production of charcoal which amounted to approximately 12.7 PJ in 2006. Although biomass is an attractive renewable source of energy, it is generally difficult to handle, transport

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