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- Volume 20, Issue 2, 2015
South African Journal of Chemical Engineering - Volume 20, Issue 2, 2015
Volume 20, Issue 2, 2015
Source: South African Journal of Chemical Engineering 20, pp 1 –17 (2015)More Less
Use of a neural network approach to the solution of complex tasks is demonstrated on first, the identification of a food chemical specification ("Chemical Engineering case") and second, the prediction of survival and prognosis for leukaemia patients ("Non-Chemical Engineering case").
In the first case product colour was identified as an important quality feature, which significantly affects marketing of food grade antioxidants used for preservation of edible oils. The product quality is specified in terms of the "Lovibond colour index". Production of phenolic antioxidant in a well-established operation exhibited for an extended period of time a variation of the product colour. Due to the complexity of the technological process it is impossible to pinpoint a simple reason for variations. The product is synthesised in a batch reactor, the crude product is then recovered from post-reaction batch via crystallisation and refined in a complex purification process to get the final product, which meets specification. It is unclear, whether the undesirable colour is formed during the synthesis itself or results from underperformance of the purification process. Data from the manufacturing process were collected over 140 batches, where the impurity profile of crude product was recorded along with some other purification parameters. Impurity profile included an occurrence of 32 different compounds, some of them occurring on a random basis. The neural network model predicts the final product quality on the basis of a crude product impurity profile. Thus the process management decision to premeditate the product can be made well in advance during the process. Should the prediction show that the final product would not meet the required specification, corrective measures can be implemented well in advance to rescue the final product.
In the second case the neural network model attempts to predict survival rate of leukaemia patients over two and three year periods based on 38 medical factors of patients and treatment procedures chosen, which make it possible to apply the right treatment at an early stage.
Source: South African Journal of Chemical Engineering 20, pp 18 –30 (2015)More Less
Emissions of greenhouse gases mostly from fossil fuels are responsible for global warming and climatic changes. This has led to research in bioenergy to reduce greenhouse emissions because bioenergy is part of the carbon cycle, and can only emit greenhouse gases that are part of the carbon cycle. The drawback is its low calorific value when it is in its raw form. Torrefaction improves its energy content to values that are comparable to coal.
In this study, marula seeds and blue gum wood, two of South Africa most abundant biomass, were blended with coal both raw and torrefied to see the impact of the torrefaction process on energy density. Blending was done at different ratios to see the optimum results. Results showed that highest calorific value was obtained at 100% marula seeds and 0 % coal, and it was recommended for further studies. Blue gum wood due to its high moisture had slightly higher heating value than the reference coal but from an economical point of view it was not attractive for further studies. This showed the significance of the torrefaction process in increasing heating value of selected biomass in the hope of reducing effects of greenhouse gas emissions.
Solvent extraction separation of zirconium (IV) and hafnium (IV) as chloride and fluoride feedstock solutions using amine extractantsSource: South African Journal of Chemical Engineering 20, pp 31 –55 (2015)More Less
Due to lanthanide contraction zirconium (Zr(IV)) and hafnium (Hf(IV)), which have very similar chemical properties, occur together in nature. However, for the use in nuclear reactors the Zr must essentially be Hf free ((<5<50ppm). To attain this, the solvent extraction of zirconium and hafnium from fluoride and chloride solutions with tertiary (Alamine 336) and quaternary (Aliquat 336) amines in cyclohexane was investigated. Results obtained show that while, the extraction from fluoride-based compounds (K2Zr(Hf)F6) was unsuccessful for both Zr and Hf species, the extraction from the chloride- based compounds (Zr(Hf)Cl4) was possible. Both higher acid and extractant concentrations resulted in an increased extraction of both Zr and Hf. While for both Alamine 336 and Aliquat 336 the maximum extractions of Zr(IV) was achieved after 30 minutes, Aliquat 336 generally yielded higher Zr extractions, while the use of Alamine 336 mostly resulted in increased selectivities. It was subsequently shown that most of the metal species (99.8%) could be recovered from the loaded organic solution using only deionised water. Finally a numerical method was applied on this particular case study to propose a seven stage solvent extraction process for the production of nuclear grade Zr(IV).
Impact of coal quality on thermal power plant savings : a case study for an Indian thermal power plantSource: South African Journal of Chemical Engineering 20, pp 56 –68 (2015)More Less
Majority of Indian thermal power plants receive coal from different seams or collieries with frequent variations in individual coal quality. This variation in coal quality effect the overall power generation cost which is again related to various cost component in a complex way. These cost components are coal transportation, ash disposal, plant maintenance and operation, reduction in plant peak and rated capacity, and plant availability. In this paper a methodology is presented to quantify different coal utilization cost components, each proportional to the ash content of the coal. The impact of different cost components varies within 5% to 30% or even more than that for some specific situation. This uncertainty in total economic penalties attributable to ash content is quantified by taking a stochastic approach. To illustrate, two coals containing 22% and 32% ash are considered. These coals are pulverized and used for power generation where the incremental utilization costs range from Indian rupees (Rs) 255 to Indian rupees (Rs) 665 per tonne (1,000 kg) of coal. The result leads to a conclusion that coal beneficiation may have broader economic justification than sometimes realized. The model can be used to determine the realistic value of a coal and optimal beneficiation levels.
Source: South African Journal of Chemical Engineering 20, pp 69 –79 (2015)More Less
In this study, the reclamation of end-of-pipe textile effluent originating from a reactive dyeing textile mill was investigated using low energy membrane based processes. Effluent quality, salt recovery and membrane recovery were the main parameters used to evaluate the membrane process. Flat sheets of the SR90 and NF90 Dow FilmTech nanofiltration (NF) membranes were used on a pilot scale membrane system. The UF multipore membrane was used in the pretreatment runs. The quality of reclaimed water was measured against the specified water quality in terms of the internal criteria for effluent recycle (ICFER) provided by the mill. It was required to optimize the SR90 and NF90 membrane performances so as to set operating parameters for pilot study. The average critical flux for the SR90 membrane was found to be ±31 LMH at 5 bar TMP when directly feeding the effluent without any pretreatment. The average critical flux for the NF90 membrane was found to be approximately ±15 LMH at 10 bar TMP when no pretreatment was used. All rejections were found to be >90% for all specified parameters as per Table 1. The quality results from the SR90 and NF90 membranes with pretreatment showed that the permeate could be recycled and reused in the dying processes within the mill. It was however concluded that the NF90 membrane produces high quality effluent as compared to the SR90. It was of importance to determine if the SR90 and NF90 membranes could be recovered and reused after directly feeding un-pretreated feed effluent. The flux recoveries on the SR90 and NF90 membranes were 84.72% and 82.17%, respectively after chemical cleaning. It was further concluded that the salt initially fed in the dying process could be recovered from the waste stream especially when using the SR90 membrane for reuse. However, the colour parameter was found to be slightly out of specification when using the SR90 membrane. To improve the colour of effluent produced when using the SR90, it was recommended that a granular activated carbon filter needs to be employed downstream of the process to polish the effluent.
Source: South African Journal of Chemical Engineering 20, pp 80 –90 (2015)More Less
This paper evaluates the viability of anaerobic digestion technology as a treatment process for organic waste with an intention of solving the landfill crisis as well as mitigation of greenhouse gases. The proposed technology consists of two digesters system using soaking as a pre-treatment method, and with recirculation of the process water and digested sludge. A financial model was developed to evaluate the economic feasibility of this technology as a renewable energy. Instead of the waste decomposing at local landfills, is converted into a source of energy while the by-products of the process are treated and used as fertilizers. This technology will require a capital investment of R2,2773,900 with a capacity to treat 730000 kg of waste annually. The annual production cost of R1, 269,138 was calculated. The proposed model has debt repayments of R2,478,551. The total revenue from year 2 - 5 was R2,360,800, R2,930,158, R3,457,314.6 and R3,988,407.6, respectively. These AD facilities can produce up to 110960 kWh per annum of biogas fuel. The net present value of R3,042,592, internal rate of return (IRR) of 33% and (BCR) of 1.96 shows that the technology is economically feasible.