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Item Developing a Surface Water - Groundwater Interaction Model for Letaba River System in South Africa.(University of the Witwatersrand., 2006) Katambara, Z; Ndiritu, J.G.There is a constant increase in water demand and a pressing need to conserve the environment in the Letaba River system. This is leading to a situation where the demand for water may have outstripped the capacity of the existing resources to sustainably meet them. In the past dams were constructed and boreholes drilled as a strategy of reconciling demand and supply and this is evidenced by the numerous dams and boreholes in the Letaba River system. There are five major dams; three of which have a capacity exceeding 60 million cubic meters and also more than 3000 boreholes in the river basin. Currently, all the dams are stressed and the releases from Tzaneen Dam, intended to meet the water requirements of downstream users including Kruger National Park fail to meet these requirements substantially. Although these demands are high and probably exceed the system’s capacity, it is likely that the reliability of supply can be improved significantly if the surface water - groundwater (sw/gw) interactions within the basin are modeled comprehensively and then incorporated into system operation. This paper reports on an ongoing development of a sw/gw model of the Letaba River System. The model development intends to maximize the use of the relevant available information and data and recognizes the existence of an interaction zone which forms a major link of many of the processes that will be included in the model. It has been found that the scale of monitoring processes in the river system is inadequate and is a significant constraint to the development of the model that is expected to impact on the level of confidence in model implementation and application. Incorporation of uncertainties will therefore be an integral part of the modeling.Item An Artificial Neural Network Model of the Crocodile River System for Low Flow Periods.(Wits, 2009-01-21) Sebusang, Nako M.With increasing demands on limited water resources and unavailability of suitable dam sites, it is essential that available storage works be carefully planned and efficiently operated to meet the present and future water needs.This research report presents an attempt to: i) use Artificial Neural Networks (ANN) for the simulation of the Crocodile water resource system located in the Mpumalanga province of South Africa and ii) use the model to assess to what extent Kwena dam, the only major dam in the system could meet the required 0.9m3/s cross border flow to Mozambique. The modelling was confined to the low flow periods when the Kwena dam releases are significant. The form of ANN model developed in this study is the standard error backpropagation run on a daily time scale. It is comprised of 32 inputs being four irrigation abstractions at Montrose, Tenbosch, Riverside and Karino; current and average daily rainfall totals for the previous 4 days at the respective rainfall stations; average daily temperature at Karino and Nelspruit; daily releases from Kwena dam; daily streamflow from the tributaries of Kaap, Elands and Sand rivers and the previous day’s flow at Tenbosch. The single output was the current day’s flow at Tenbosch. To investigate the extent to which the 0.9m3/s flow requirement into Mozambique could be met, data from a representative dry year and four release scenarios were used. The scenarios assumed that Kwena dam was 100%, 75%, 50% and 25% full at the beginning of the year. It was found as expected that increasing Kwena releases improved the cross border flows but the improvement in providing the 0.9m3/s cross border flow was minimal. For the scenario when the dam is initially full, the requirement was met with an improvement of 11% over the observed flows.Item An Investigation for Energy Sustainability in Cement Industries in Tanzania: The Case of Mbeya Cement(Technische Universität Berlin Institut für Energietechnik, 2017) John, John PiusCement production processes are facing crucial sustainability issues such as inefficient en‐ ergy and raw material use, product supply, production cost and environmental pollution. High energy and material use dominated by inefficient characteristics of cement production processes, in turn, lead into depletion of non‐renewable resources, increased production costs as well as environmental degradation due to emissions. The main objective of the study was to investigate performance of cement industry in Tanza‐ nia relative to sustainable energy utilization. Most of past researches have evaluated the per‐ formance of cement production processes using first law of thermodynamics alone (mass and energy balances) with the objective of improving energy efficiency. Although this ap‐ proach sheds light on the question of improvement of energy use in the processes, it has some limitations. The limitations are imposed by the internal irreversibility due to combustion and other physico‐chemical nature of reactions dominating the whole processes. The current emerging approach, which overcomes limitations imposed to the first law approach is ex‐ ergy‐based method, relatively new in evaluation of performance of cement production pro‐ cesses. However, owing to complexity of cement production processes, applying an exergy‐ based method manually is very difficult and complex. The current study proposes combined approach of exergy based method and modeling as well as simulation. The model was successfully developed, validated using real plant data and was used to predict the performance of the cement dry rotary kiln system of Mbeya Cement production processes. Data obtained from modeling and simulation were further used to evaluate the performance of processes, individual components, sub‐systems and overall kiln system at large using exergy based method. The approach not only simplifies the analyses but also gives detailed insight of real processes, source and type of real imperfections, its magnitudes and how imperfections can be minimized. Major findings indicated that the rotary kiln sub‐systems and the overall kiln system have poor exergetic performance, suggesting that potential for improvement exists. The overall exergy efficiency of the kiln system is around 33 %. Also results indicated that the rotary kilns have the lowest exergetic efficiency of about 14 % followed by the clinker cooler with exergetic efficiency of about 41.11 %. The highest source of irreversibility encompassed chemical reactions, especially calcination and clinker burning processes with exergy destruc‐ tion of 2,813.75 kJ⋅kgcl−1 and 1,148.17 kJ⋅kgcl−1. Results from parametric analysis suggested that if measures for improvements of processes, components and sub‐systems are taken, a significant amount of fuel and specific energy could be saved. Furthermore, it was confirmed that if the avoidable exergy destruction is minimized, processes, system components and sub‐systems performance could be improved from exergetic point of view.