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Analysis of Waste-Rock Transportation Process Performance in an Open-Pit Mine Based on Statistical Analysis of Cycle Times Data

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Engineering（科研） 2017年第7期9卷 649-679页

作者： samwel victor manyele Department of Chemical and Mining Engineering College of Engineering and Technology University of Dar es Salaam Dar es Salaam Tanzania

In this paper, the performance of a waste rock transportation process in an open pit mine was assessed by using cycle time data. A computerized truck-excavator dispatch system was used to record the cycle times. The process was broken into seven steps (or components of the total cycle), durations of which were recorded for a period of 1 month, leading to N = 60,690 data points or dispatches. The open pit mine studied consisted of 12 waste types loaded by 14 excavators and hauled by 49 trucks (at a trucks-to-excavator ratio of 3.5:1) in 75 changing locations. The string-type data was coded using integers to allow a FORTRAN code to extract process performance parameters using statistical analysis. The study established a wide range of parameters including: the waste material generation rate (about 1.73 million t/month, 81% comprising waste rock), truck fill factor, f, total cycle time (Tct), production capacity, theoretical cycle time, non-productive cycle time Tnp, and cycle time performance ratio (CTPR), denoted as Tpr. The factors affecting the process performance include: truck model, excavator model, location (haul distance and road conditions) and material type. For a fixed material type and tonnage, the PDFs of the cycle time components were logarithmic in nature, capable of differentiating performance variations under different factors. It was concluded that the performance of the waste material transportation system in this mine was determined to be acceptable due to mean value of Tpr = 2.432 being closer to unity. Reduction measures were suggested to minimize the cycle time for the process bottlenecks determined from Pareto analysis (that is, full haul, empty haul and loading processes).

关键词： Potentially Acid-Forming (PAF) Rock Non-Acid Forming (NAF) Rock Truck Utilization Truck Fill-Factor Queuing Time Loading Cycle Time Full and Empty Haul Total Cycle Time Theoretical Cycle Time Non-Productive Cycle Time Cycle Time Performance Ratio

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Analysis of the Effect of Subgroup Size on the X-Bar Control Chart Using Forensic Science Laboratory Sample Influx Data

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Engineering（科研） 2017年第5期9卷 434-456页

作者： samwel victor manyele Department of Forensic Science and DNA Services Government Chemist Laboratory Authority (GCLA) Dar es Salaam Tanzania

This paper analyzes the effect of subgroup size on the x-bar chart characteristics using sample influx (SIF) into forensic science laboratory (FSL). The characteristics studied include changes in out-or-control points (OCP), upper control limit UCLx, and zonal demarcations. Multi-rules were used to identify the number of out-of-control-points, Nocp as violations using five control chart rules applied separately. A sensitivity analysis on the Nocp was applied for subgroup size, k, and number of sigma above the mean value to determine the upper control limit, UCLx. A computer code was implemented using a FORTRAN code to create x-bar control-charts and capture OCP and other control-chart characteristics with increasing k from 2 to 25. For each value of k, a complete series of average values, Q(p), of specific length, Nsg, was created from which statistical analysis was conducted and compared to the original SIF data, S(t). The variation of number of out-of-control points or violations, Nocp, for different control-charts rules with increasing k was determined to follow a decaying exponential function, Nocp = Ae–α, for which, the goodness of fit was established, and the R2 value approached unity for Rule #4 and #5 only. The goodness of fit was established to be the new criteria for rational subgroup-size range, for Rules #5 and #4 only, which involve a count of 6 consecutive points decreasing and 8 consecutive points above the selected control limit (σ/3 above the grand mean), respectively. Using this criterion, the rational subgroup range was established to be 4 ≤ k ≤ 20 for the two x-bar control chart rules.

关键词： Forensic Science Laboratory Sample Influx Statistical Analysis X-bar Control Chart Sub-Group Size Control Chart Rules Multi-Rules for X-Bar Chart Out-of-Control Points

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Optimization of Evidence Analysis Cost Using Arbitrary Re-Sampling Techniques for Sample Influx into Forensic Science Laboratory

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Engineering（科研） 2017年第5期9卷 457-481页

作者： samwel victor manyele Department of Forensic Science and DNA Services Government Chemist Laboratory Authority Dar es Salaam Tanzania

This study analyzes the sample influx (samples per case file) into forensic science laboratory (FSL) and the corresponding analysis costs and uses arbitrary re-sampling plans to establish the minimum cost function. The demand for forensic analysis increased for all disciplines, especially biology/DNA between 2014 and 2015. While the average distribution of case files was about 42.5%, 40.6% and 17% for the three disciplines, the distribution of samples was rather different being 12%, 82.5% and 5.5% for samples requiring forensic biology, chemistry and toxicology analysis, respectively. Results show that most of the analysis workload was on forensic chemistry analysis. The cost of analysis for case files and the corresponding sample influx varied in the ratio of 35:6:1 and 28:12:1 for forensic chemistry, biology/DNA and toxicology for year 2014 for 2015, respectively. In the two consecutive years, the cost for forensic chemistry analysis was comparatively very high, necessitating re-sampling. The time series of sample influx in all disciplines are strongly stochastic, with higher magnitude for chemistry, biology/DNA and toxicology, in this order. The PDFs of sample influx data are highly skewed to the right, especially forensic toxicology and biology/DNA with peaks at 1 and 3 samples per case file. The arbitrary re-sampling plans were best suited to forensic chemistry case files (where re-sampling conditions apply). The locus of arbitrary number of samples to take from the submitted forensic samples was used to establish the minimum and scientifically acceptable samples by applying minimization function developed in this paper. The cost minimization function was also developed based on the average cost per sample and choice of re-sampling plans depending on the range of sample influx, from which the savings were determined and maximized. Thus, the study gives a forensic scientist a business model and scientific decision making tool on minimum number of samples to anal

关键词： Forensic Science Laboratory Sample Influx Arbitrary Sampling Analysis Cost Minimum Number of Samples Minimum Analysis Cost Toxicology Forensic Chemistry DNA Analysis

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Investigation of Excavator Performance Factors in an Open-Pit Mine Using Loading Cycle Time

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Engineering（科研） 2017年第7期9卷 599-624页

作者： samwel victor manyele Department of Chemical and Mining Engineering College of Engineering and Technology University of Dar es Salaam Dar es Salaam Tanzania

This study presents the effect of excavator model, loading operation location, shift availability and truck-shovel combination on loading cycle time and productivity of an open-pit mine. The loading cycle time was used to assess the material loading system performance which is one of the key components of the total cycle time for material transportation in an open-pit mine. Loading is among the components of cycle time during which material is being handled. The data analyzed?was?collected from a computerized dispatch system at GGM from which 62,000 loading dispatches per month involving several shifts, 14 excavators and 49 trucks were loaded. About 4465 dispatches per excavator and 1276 dispatches per truck were assessed using loading cycle time data for each dispatch for a period of four months (between August and December). Under fixed tonnage loaded and waste type (33 t of non-acid forming waste rock),?it was observed that loading cycle time depends on excavator model, location and truck being loaded. Average cycle times, PDFS?and CDFS of loading cycle time series were used to identify differences in performance under different situations. It was concluded that shift availability for excavators, loading location, excavator model and truck-shovel combinations strongly affect the productivity during loading process in an open-pit mine.

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Hydrodynamics of the Pilot Scale Wet Scrubber with Restricted Outlet Absorbent Flow Rate

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Engineering（科研） 2012年第7期4卷 339-348页

作者： samwel victor manyele Department of Chemical and Mining Engineering College of Engineering and Technology University of Dar es Salaam P.O. Box 35131 Dar es Salaam Tanzania

This paper presents the hydrodynamics of the wet scrubber coupled to a pilot CFB incineration facility. The scrubber was operated using tap water as a scrubbing liquid. The outlet liquid flow rate, Qo, and accumulation rate, Qa, strongly depend on the inlet liquid flow rate, Qin, with different profiles. At higher Qin values, Qo stabilizes, leading to higher Qa and finally flooding. The values of Qa were higher than Qo except for Qin ranging between 0.53 and 0.72 L/s (safe operating range) in which Qa ≌ Qo and Qa = Qin/2. The outlet-to-inlet liquid flow rate ratio, Qo/Qin decreased for Qin > 0.53 L/s. The increase in the accumulation-to-inlet liquid flow rate ratio, Qa/Qin, at higher Qin indicates a change in flow regime towards flooding, accompanied by an abrupt increase in the height of accumulating liquid, Ha. The difference between Qa/Qin and Qo/Qin (denoted as, ΔQao/Qin), shows a minimum close to zero in the safe operating range. The gas flow rate towards the wet scrubber had slight effect on Qo and Qa when Qin was maintained constant. The ratio Qo/Qin decreased slightly with Ha/Ht irrespective of gas velocity. Changing the liquid-to-gas ratio, L/G and Qin strongly affects the maximum and minimum values of Qo/Qin and Qa/Qin.

关键词： Wet Scrubber Liquid Accumulation Rate Liquid Accumulation Level Outlet Liquid Flow Rate Liquid-to-Gas Ratio Valve Opening Position Incineration

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Analysis of Medical Waste Incinerator Performance Based on Fuel Consumption and Cycle Times

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Engineering（科研） 2012年第10期4卷 625-635页

作者： samwel victor manyele Ignatio Simon Kagonji Department of Chemical and Mining Engineering Collage of Engineering and Technology University of Dar es Salaam P.O. Box 35131 Dar es Salaam Tanzania

A detailed assessment of an incinerator based on fuel consumption and cycle time data is presented in this paper. The study was conducted at Temeke district hospital for 22 months consecutively covering 654 days of daily data collection on fuel consumption and cycle times. The composition for the medical waste incinerated varied between 15% and 35% for sharps waste and between 65% and 85% for other waste, with mean values of 25% and 75%, respectively. The results revealed poor performance of the incinerator due to higher fuel consumption (above 30 L/cycle). The incineration cycle times were observed to range between 2 and 4 hours, all of which were too high for the loading rates observed (55 - 214 kg). A strong dependency of diesel oil consumption on cycle time was observed due to lack of temperature control leading to continuous fuel flow into the burners. The incineration capacity was very low compared to other incinerators in terms of tons per year. This paper gives an insight on the factors affecting incinerator performance assessed based on diesel oil consumption and cycle times. It can be generalized that the incinerator performance was poor due to several factors ranging from poor incinerator design, operator skills, waste management practices, waste storage practices, etc. The hospital was advised to install a new incinerator with short incineration cycle time (30 - 40 minutes) and lower fuel consumption (10 L/cycle) at a loading rate of 200 kg/cycle.

关键词： Waste Combustion Incinerator Performance Medical Waste Incineration Fuel Consumption Incineration Cycle Time Sharps Waste Incinerator Capacity Fuel Effectiveness

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Performance Improvement for Sisal Waste Anaerobic Biodegradation by Digester Redesign and Feed Size Reduction

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Engineering（科研） 2015年第9期7卷 553-566页

作者： Yusufu Risasi Rajabu samwel victor manyele Department of Mechanical and Industrial Engineering College of Engineering and Technology University of Dar-es-Salaam Dar es Salaam Tanzania

This Anaerobic Digestion of Sisal decortication residue (SDR) from sisal decorication unit at Hale biogas plant in Tanga (Tanzania) is presented. The study was done to address the challenges facing Katani limited at Hale biogas plant. This plant was built as pilot before building other biogas plants. These challenges were like high retention time of substrate which was SDR, low biogas productivity, high investment costs due to large tanks sizes and low plant availability. From the study, it was discovered that, when particle size was reduced biogas production increased, degradation of SDR also increased and no significant change in biogas composition. Increase in biogas yield of 30% and 129% were recorded for reduced SDR compared to raw size SDR digested at atmospheric condition and 40°C respectivelly. SDR degradation measured in TS and VS removal efficiency, showed increase in degradation of about 5% for the reduced particle size compared to raw size particle. The study concluded that SDR was good raw material for biogas production when 90% of the particles reduced to less than 2 mm. To maximize production, digestion must be conducted at high temperature around 40°C with constant monitoring and control of all para-meters. This will increase plant availability by increasing efficiency and life span of the pumps and stirrers.

关键词： Anaerobic Digestion Sisal Decortication Residue Biogas

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Assessment of Incineration Process Performance in a District Hospital Using Statistical Analysis

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Engineering（科研） 2012年第8期4卷 421-434页

作者： samwel victor manyele Ignatio Simon Kagonji University of Dar es Salaam Dar es Salaam Tanzania

The objective of this study was to assess the performance of an old existing medical waste incinerator in a district (Temeke) hospital. The medical waste incinerated was grouped into two categories: sharps waste and other waste. The parameters assessed included amounts of sharps and other waste incinerated, amount of fuel used and the incineration cycle time. One incineration cycle was conducted per day and data was collected for 22 months (N = 653). It was established that the total waste incinerated per day ranged from 70 to 120 kg, completing the process between 2 and 4 hrs and consuming 20 to 40 L of fuel per day. The analysis showed further that sharps waste incinerated were 25% of the total waste while other waste incinerated were about 75% on average. The average diesel oil used was 30 L/day and average cycle time was observed to be 3 hrs, both being excessively high indicating that the performance of the incin-erator was poor. The statistical analysis was used to reveal stronger variations in other waste than sharps waste. The PDF plots, skewness and kurtosis values indicated that there were weak variations in the daily diesel oil consumed and incineration cycle time while stronger variations were observed in the other waste compared to sharps waste data. Normalization of the incinerator performance data allowed comparison between different data types also indicating poor performance of the incinerator. Proper segregation at point of generation and proper storage of medical waste was recommended. It was further recommended for the hospital to install a new and efficient incinerator with short incineration cycle time and less fuel consumption.

关键词： Incinerator Performance Medical Waste Incineration Fuel Consumption Incineration Cycle Time Sharps Waste Statistical Analysis

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A Kinetic Study of Anaerobic Biodegradation of Food and Fruit Residues during Biogas Generation Using Initial Rate Method

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Engineering（科研） 2013年第7期5卷 577-586页

作者： William Wanasolo samwel victor manyele John Makunza Department of Chemical and Mining Engineering College of Engineering and Technology University of Dar es Salaam Dar es Salaam Tanzania

A kinetic study of biogas production from Urban Solid Waste (USW) generated in Dar es Salaam city (Tanzania) is presented. An experimental bioreactor simulating mesophilic conditions of most USW landfills was developed. The goal of the study was to generate the kinetic order of reaction with respect to biodegradable organic waste and use it to model biogas production from food residues mixed with fruit waste. Anaerobic biodegradation was employed under temperature range of 28℃ - 38℃. The main controls were leachate recirculation and pH adjustments to minimize acid inhibitory effects and accelerate waste biodegradation. The experimental setup comprised of three sets of bioreactors. A biodegradation rate law in differential form was proposed and the numerical values of kinetic order and rate constant were determined using initial rate method as 0.994 and 0.3093 mol0.006·day-1, respectively. Results obtained were consistent with that found in literature and model predictions were in reasonable agreement with experimental data.

关键词： Urban and Municipal Solid Waste Biogas Production Anaerobic Biodegradation Mesophilic Conditions Order of Reaction Kinetic Model Initial Rate Method Renewable Energy Bioreactor Landfill Biodegradable Organic Waste

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Analysis of Employee’s Longevity and Academic Development in Forensic Science Laboratory

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Engineering（科研） 2019年第4期11卷 206-230页

作者： Gloria Cuthbert Omari samwel victor manyele George Mwaluko Department of Mechanical and Industrial Engineering College of Engineering and Technology University of Dar es Salaam Dar es Salaam Tanzania Government Chemist Laboratory Authority Dar es Salaam Tanzania

This paper presents the detailed analysis of academic development index and longevity among forensic science laboratory (FSL) employees as the key factors for improving organizational performance based on human capital development. The data were collected from human resource database involving 171 (88%) employees out of 195. New mathematical formulations were developed for academic development index Ad, a measure of the time delay in academic development while working within FSL, simple longevity (Ls) and complex longevity (Lc), based on years served and academic certificates attained. The values of Ad, Ls and Lc were compared for different units and departments including zonal laboratories between Y2014 and Y2016. Both total and average values of Ls, Lc?and Ad indicated an imbalance in the distribution of staff in different laboratories, necessitating re-allocation to improve performance. The employment trend analysis shows that the work force has been diversified from Y2004 to Y2016 leading to improved management of finance, procurement and human resource in the FSL. As a result of a training program, the percent of staff with MSc has been increasing from about 3.5% in Y2004 to 9% in Y2015. The average values of longevity and academic development index were observed to be the better parameters for comparing laboratories or units than the total values. Results show a balanced staff distribution based on Lc and Ad is inevitable for improved performance. It was concluded that the new indices (Ad and Lc) are important tools for describing the development of the workforce and competitiveness of the FSL.

关键词： Forensic Science Laboratory Academic Development Index Simple Longevity Complex Longevity

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