No description available.

No description available.

M.Tech. (Chemical Engineering) / Laboratory and pilot plant trials were carried out on a modified carbonatation process to reduce overall refining costs. Sulphur dioxide dosages of less than 250ppm on brix were added to carbonatated liquors. The resultant filtered liquor had an additional 4,6% colour removal and a 10% ash gain relative to factory liquors. Reducing sugars and filterability were not affected. Additional colour removal of 14% was noted in the affinated crystal colour of crystals grown from the resultant brown liquors in the SMRI pilot pan. The failure of the combined carbonatation - sulphitationLaboratory and pilot plant trials were carried out on a modified carbonatation process to reduce overall refining costs. Sulphur dioxide dosages of less than 250ppm on brix were added to carbonatated liquors. The resultant filtered liquor had an additional 4,6% colour removal and a 10% ash gain relative to factory liquors. Reducing sugars and filterability were not affected. Additional colour removal of 14% was noted in the affinated crystal colour of crystals grown from the resultant brown liquors in the SMRI pilot pan. The failure of the combined carbonatation - sulphitation process to remove the ash that the carbonatation process does, negates the cost benefits of the additional colour removals. The reason for the ash "gain" is that the sulphur dioxide partially dissolves the calcium carbonate, releasing the adsorbed ash and colour. The colour is then adsorbed onto the calcium sulphite. process to remove the ash that the carbonatation process does, negates the cost benefits of the additional colour removals.

Submitted in fulfillment of the requirements of the degree of Master of Engineering: Chemical Engineering, Durban University of Technology, Durban, South Africa, 2015. / The implementation of new water regulations from the local government has been a motivation for most industries to treat the effluent before disposal or reuse within the plant, in order to save costs and avoid sanctions. Tongaat-Huletts sugar refinery has therefore invested in this collaborative research with the Durban University of Technology in order to investigate new technologies for wastewater treatment and water recovery using an organic coagulant called chitosan. Chitosan is a natural non-toxic polymer extracted from the exoskeleton of crustaceans. Chitosan has gained extensive attention as a coagulant in the treatment of wastewaters from various industries. However, no attention has been given to the coagulation of effluents from the sugar industry using this polymer. In this work, chitosan coagulant (CCo) was prepared by dissolution of known amounts of chitosan powder in aqueous acid at 50℃. The solution was diluted to desired concentrations using distilled water at room temperature. The removal of impurities using chitosan was investigated for two effluent streams from the sugar refinery, namely the final effluent (FE) and the resin effluent (RE) by applying the one-factor-at-a-time (OFAT) method. The optimum chitosan loading was found to be 138 mg/l for the RE and 7.41 mg/l for the FE, beyond which the efficiency of the coagulant decreased. The coagulation of FE removed 97% of the total suspended solids (TSS), 61% colour and 35% chemical oxygen demand (COD). The treatment of RE resulted in the removal of 68% TSS, 30% colour and 15% COD due to its high content of impurities. Therefore, RE was not considered for statistical studies. The Box-Behnken (BBD) design, which is a statistical response surface methodology (RSM) model was used to study the simultaneous effect of pH, coagulant loading and settling time on the removal of the COD, TSS and colour, with the help of an overlay plot for the FE. The optimum values from the overlay plot were 92% for TSS, 83% for colour and 29% for COD. The model equations generated by the BBD for individual responses involved all the manipulated variables contrary to the OFAT which only considered one manipulated parameter per response. Moreover, the BBD allowed the simultaneous analysis of all the parameters and the identification of interactions which occur when the effect of one factor is dependent on the level of another. The most important interaction for the removal of TSS was the combination of the variation in pH and coagulant dosage. The COD removal was mostly affected by the interaction between the coagulant loading and the settling time. The colour removal increased with the simultaneous increase of the pH and the settling time. A comparative study between the wastewaters from the sugar industry, the brewery industry and milk processing industry revealed that the performance of the chitosan was also affected by the amount of total dissolved solids (TDS) in the wastewater. A model was developed relating the TSS, COD and TDS from all these wastewaters, and was used to predict the TSS removal for the effluent from the olive oil mills and the wastewater from the winery. Chitosan can be considered as a good alternative to inorganic and synthetic coagulants for the pre-treatment of the FE due to its ability to efficiently remove the levels of TSS and colour. Furthermore, the production of chitosan from crustacean shells is a good method of reducing pollution from the fishery industry. Chitosan can be produced locally at low cost due to both the abundance of crustacean shells in the coastal regions of South Africa and the simplicity of its preparation process. It is recommended that a mathematical model be developed to accurately predict the influence of chitosan on all types of effluent. Such a model will provide an indication of the performance of the chitosan and guide experimenters. It is further recommended that the effect of the use of organic coagulants on the destabilization of dissolved solids in wastewater be given greater attention.

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a timeconsuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. The above two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The composite fouling experiments were performed in a novel closed-loop circulation system simulating the effect of feed composition of successive stages of evaporation cycle in a single run. In addition, the fouling-loop system was operated in a constant composition mode to study the effects of thermal hydraulic conditions on composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2. Some of the highlights of the obtained results are as follows: ??? Identification of a complex interactive process in calcium oxalate monohydrate ??? silica (COM-SiO2) systems by investigation of the kinetics and thermodynamics of COM-SiO2 coprecipitation in water and sugar solutions, and an understanding of the mechanisms of these interactions; ??? Development of a novel fouling-loop system, which is simple, efficient and cost effective for the study of the effect of juice composition on scale formation in various stages of juice evaporation; ??? Elucidation of composite fouling mechanisms, e.g., a feed composition dependent fouling mechanism is proposed; ??? Isolation and verification of the existence of certain species in composite deposits, which is known to be thermodynamically unstable. In other words, it is established that calcium oxalate trihydrate is stable under certain conditions; ??? Evaluation of the role of thermal hydraulic operating parameters in determining the characteristics of subcooled flow boiling heat transfer and in determining the strength of the composite deposit; ??? Development and validation of an empirical model to predict the subcooled flow boiling heat transfer coefficients in water and sugar solutions; ??? Development of an analytical model incorporating the effects of operating parameters for COM and SiO2 composite fouling in sugar solutions. This model predicted the experimental data better than available models. Results of this work are significant, not only because they have made a valuable contribution to advance the fundamental understanding of heat exchanger fouling, but also because they may play a key role in the development of scale control and removal strategies to minimize the composite fouling in Australian sugar mill evaporators. For example it was found that, in order to effectively minimize the rate of composite fouling and reduce the scale tenacity, it would be necessary to control thermal hydraulic operating conditions, especially the fluid velocity, and to adjust the initial CaOx/SiO2 supersaturation ratio to the optimum value. To achieve the optimal CaOx/SiO2 ratio, certain device can be developed to sequentially measure oxalic acid and SiO2 concentrations in juice so that the correct proportions of chemicals can be added. Model simulations of the composite fouling rate may also effectively and economically provide comparative and relevant information essential for process optimisation and evaporator design

No description available.

This dissertation is concerned with the application of tomography within the sugar industry; in particular non-accessible locations found in a sugar mill. In this study, the focus of research is that of a vacuum pan, and if better understood through tomographical techniques could significantly improve mill efficiency and throughput. The tomography system comprises unique mechanical interfaces, data acquisition modules and software algorithms in order to generate images which reflect the dynamics in the tomographical sensor zone. The distribution of gas (low conductivity) and liquid (high conductivity) within a tube is of main interest in order to understand the boiling dynamics and ultimately pan design. This is attained by determining the internal cross-sectional spatial distribution of conductivity of a number of tubes within the pan simultaneously. Thermal properties of the contents of the sugar pan (a syrup-like substance known as massecuite) at different boiling stages can be estimated based on the tomographical data. Data acquisition is achieved via an in-house designed electronic state machine. A neighbourhood back-projection reconstruction technique was developed in MATLAB in order to generate tomographical images. Results from the system have identified different boiling dynamics which improve the understanding and design of vacuum sugar pans. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2010.

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a timeconsuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. The above two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The composite fouling experiments were performed in a novel closed-loop circulation system simulating the effect of feed composition of successive stages of evaporation cycle in a single run. In addition, the fouling-loop system was operated in a constant composition mode to study the effects of thermal hydraulic conditions on composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2. Some of the highlights of the obtained results are as follows: ??? Identification of a complex interactive process in calcium oxalate monohydrate ??? silica (COM-SiO2) systems by investigation of the kinetics and thermodynamics of COM-SiO2 coprecipitation in water and sugar solutions, and an understanding of the mechanisms of these interactions; ??? Development of a novel fouling-loop system, which is simple, efficient and cost effective for the study of the effect of juice composition on scale formation in various stages of juice evaporation; ??? Elucidation of composite fouling mechanisms, e.g., a feed composition dependent fouling mechanism is proposed; ??? Isolation and verification of the existence of certain species in composite deposits, which is known to be thermodynamically unstable. In other words, it is established that calcium oxalate trihydrate is stable under certain conditions; ??? Evaluation of the role of thermal hydraulic operating parameters in determining the characteristics of subcooled flow boiling heat transfer and in determining the strength of the composite deposit; ??? Development and validation of an empirical model to predict the subcooled flow boiling heat transfer coefficients in water and sugar solutions; ??? Development of an analytical model incorporating the effects of operating parameters for COM and SiO2 composite fouling in sugar solutions. This model predicted the experimental data better than available models. Results of this work are significant, not only because they have made a valuable contribution to advance the fundamental understanding of heat exchanger fouling, but also because they may play a key role in the development of scale control and removal strategies to minimize the composite fouling in Australian sugar mill evaporators. For example it was found that, in order to effectively minimize the rate of composite fouling and reduce the scale tenacity, it would be necessary to control thermal hydraulic operating conditions, especially the fluid velocity, and to adjust the initial CaOx/SiO2 supersaturation ratio to the optimum value. To achieve the optimal CaOx/SiO2 ratio, certain device can be developed to sequentially measure oxalic acid and SiO2 concentrations in juice so that the correct proportions of chemicals can be added. Model simulations of the composite fouling rate may also effectively and economically provide comparative and relevant information essential for process optimisation and evaporator design

Submitted in fulfilment of the academic requirements for M-Tech in Chemical Engineering, ML Sultan Technikon, 2001. / The purpose of this investigation was to identify and then optimise the factors that affect the decolourisation during the carbonatation process. Batch carbonatation tests, carried out in a pilot plant in the laboratory, were performed to establish the effect of selected factors on the decolourisation of melt. / M

Climbing film evaporators are in widespread use in the South African sugar industry, with the vast majority of the local sugar mills currently utilising these evaporators as first effect vessels in multiple effect evaporator sets. However, it is generally considered that the performance of these evaporators has not been maximised, and that improvements could be achieved by proper optimisation of the operating parameters. Unfortunately, very little comprehensive design information has been published in the literature. owing to the complexity of the heat transfer and hydrodynamic interactions in the evaporator tube. Attempts at performance improvement have been hampered by the lack of any theory to explain fully the effects of the operating parameters and physical properties of the feed liquor on the performance of the evaporator. In this study. a mathematical model of the climbing film evaporator system was developed in order to assess the effects of changing operating conditions on evaporator performance, based on as solid a theoretical foundation as cunendy possible. The model was tested against experimental data from a pilot plant climbing film evaporator and this experimental data was used to enhance the accuracy of the model by means of process identification. Because of the complexity of the model and the extensive computational time required for its solution, a simplified evaporator model was also developed, based on Iinearisation of the system of ordinary differential equations describing the climbing film evaporator system. This simplified model was used to predict trends in evaporator behaviour under various operating conditions. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.