Browsing by Author "Fraser, Duncan McKenzie"

Now showing 1 - 8 of 8
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    Capital cost targets for the optimum synthesis of mass exchange networks
    (1998) Hallale, Nick; Fraser, Duncan McKenzie
    Pinch Technology is very well developed for heat exchanger network synthesis (HENS). It is possible to predict, on thermodynamic grounds, the minimum energy, capital and total costs for a network. These targets are set before any design and can also be optimised at this stage. Special design techniques exist which allow the targets to be met - or closely approached - in practice. The approach has recently been extended to mass exchange network synthesis (MENS). However, prior to this study, it was not as well developed for this field as it had been for HENS. Only targets for the minimum operating costs could be set and then achieved in design. Capital cost targets for MENS did not exist. The usual approach was to use the minimum number of mass exchange units - which could be targeted - as an attempt to minimise the capital cost of the network. However, this is not sufficient since the exchanger sizes are also important. This meant that there was no guarantee that the capital cost and hence total cost had been truly minimised. This thesis has developed a new method for targeting the minimum capital costs for mass exchange networks. The method is simple and based on insight, rather than relying on a mathematical 'black-box'. New graphical tools, the y-* composite curve plot and the y-y* composite curve plot have been introduced for this purpose and these allow the minimum exchanger sizes to be predicted before design. The new capital cost targets can be traded off against the established operating cost targets in order to optimise the total cost with no design being necessary.
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    Design of consistently near-optimal heat exchanger networks by a two-stage optimisation approach
    (1998) Gcabva, Sibusiso Joshua; Fraser, Duncan McKenzie
    Research in the field of Heat Exchanger Network Synthesis has been active as far back as 1965. Although the problem statement has remained essentially unchanged since then, numerous techniques have been developed to solve the heat exchange problem. Despite significant progress achieved over the years, a number of design issues remain unresolved or vaguely understood. Consequently, consistent generation of near-optimal heat exchanger networks is not guaranteed. This project has therefore been undertaken to develop a flexible design technique that can be used to gain further insight into the nature of a heat exchanger network. The objective of this project was to develop a network design technique that could be used to consistently generate networks that are near optimal. The main feature of the network design technique developed is the application of the optimisation process at two levels. The first level is match optimisation, and the second level is network optimisation. The objective function to be minimised is the total annual cost. The total annual cost is the sum of the annual cost of energy and the annual cost of capital. The annual cost of energy is the sum of the annual costs of hot utilities and cold utilities. The annual cost of capital is the sum of the annual costs of process, hot utility, and cold utility exchangers.
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    Energy management in industry : a case study on the brewing industry
    (1992) De Villiers, Mark Graham; Dutkiewicz, Ryszard Karol; Fraser, Duncan McKenzie
    The industrial sector is the main energy user in South Africa, using about half the national total, and compared to most other industrialised countries South Africa has a high in_dustrial energy intensity, thus necessitating improved industrial energy management. The malt brewing industry was chosen as a case study industry to illustrate the potential for improved energy management in industry. Ohlsson's brewery in Cape Town was analysed in detail and energy management improvements identified for that brewery were ·expanded to include the malt brewing industry in general, by comparing Ohlsson's brewery to other breweries in South Africa. It was found that energy requirements at Ohlsson's Brewery could be reduced by 12-20%, by the implementation of economically feasible energy management schemes. However, mainly because of discrepancies in coal prices between Ohlsson's Brewery and most other breweries in South Africa, energy requirements for the brewing industry in general can be reduced by 7-13%. This translates to be a monetary saving of R242 000-R486 000/month, which is evenly spread between coal, electricity, and maximum demand savings. No single large energy saving scheme was identified, but the potential. savings are due to a number of schemes. The potential energy savings identified in this study exclude the savings as a result of the implementation of process sensitive schemes, which were considered beyond the scope of this study. Nevertheless some process sensitive schemes, associated with boiling in the brewhouse, could result in substantial savings. The energy usage target identified for South African breweries is higher than current energy requiiements for breweries in the Britain and Germany when climatic and operational constraints are taken into account. This is because Britain and Germany have higher energy costs relative to production costs, government incentive schemes for reducing energy usage, and more stringent environmental legislation often necessitating the recovery of brewhouse vapours.
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    Hybrid synthesis method for mass exchange networks
    (2001) Msiza, Andrew Khutso; Fraser, Duncan McKenzie
    Process synthesis can be approached from three techniques: heuristics, physical and thermodynamic insight, and mathematical programming. Hybrid methods where two or all of the synthesis methods are combined are now becoming used, taking advantage of the combined strength of the individual techniques. In this thesis the option of combining pinch analysis (a physical and thermodynamic insight-based approach) and superstructure-based programming is explored.
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    Interval based MINLP superstructure synthesis of heat and mass exchange networks
    (2007) Isafiade, Adeniyi Jide; Fraser, Duncan McKenzie
    This study presents a new technique for synthesizing heat and mass exchange networks. The method involves generating superstructures using the temperature/composition interval concept from the physical insight approach. The superstructures are partitioned into temperature/composition intervals using the supply and target temperatures/compositions of either the hot/rich or cold/lean set of streams. The opposite kind of streams are made to participate (float) in all the intervals defined. Their ability to exchange heat/mass in these intervals is however subject to thermodynamic feasibility. The resulting superstructure is optimised as a mixed integer non linear programming (MINLP) model. The superstructure is hot/rich streams based if hot/rich streams are used to define the intervals otherwise it is cold/lean stream based.
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    Problem solving in chemical engineering : a study of the solution of mass balance problems by second year students
    (2002) Dhliwayo, Evelyn Chengetanai; Fraser, Duncan McKenzie; Ensor, Paula; Case, Jenni
    Bibliography: leaves 106-111
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    A spreadsheet-based tool for synthesis of heat and mass exchange networks
    (2003) Ndwandwe, Khaya; Fraser, Duncan McKenzie
    The objective of this project was to develop a user-friendly program for applying Pinch Technology approach to both Heat Exchanger Networks Synthesis (HENS) and Mass Exchanger Networks Synthesis (MENS) for use by ordinary engineers. Pinch Technology is a structure independent approach.
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    Supply and target-based superstructure synthesis of heat and mass exchange networks
    (2011) Azeez, Oluwatosin Sarafa; Fraser, Duncan McKenzie
    This study presents three new methods for superstructure synthesis of heat exchanger networks (HENs) and mass exchanger networks (MENs) that involve the use of key parameters in HEN and MEN to define superstructure intervals. The key parameters are the stream supply and target temperatures/compositions. The Supply-Based Superstructure (SBS) uses the supply temperatures/compositions of both the hot/rich streams and the cold lean streams. The Supply and Target-Based Superstructure (S&TBS) uses the supply temperatures/compositions of hot/rich streams and the target temperatures/compositions of cold/lean streams for the definition of the superstructure intervals. The Target and Supply-Based Superstructure (T&SBS) uses the target temperatures/compositions of hot/rich streams and the supply temperatures/compositions of cold/lean streams for the definition of the superstructure interval boundaries.