SciELO - Scientific Electronic Library Online

 
vol.103 issue5-6A theory of quantitative trend analysis and its application to South African general electionsLower Triassic postcanine teeth with allotherian-like crowns author indexsubject indexarticles search
Home Pagealphabetic serial listing  

South African Journal of Science

On-line version ISSN 1996-7489

S. Afr. j. sci. vol.103 n.5-6 Pretoria May./Jun. 2007

 

RESEARCH ARTICLES

 

On cooling-water systems design for South African industry: Two recent developments

 

 

Thokozani Majozi; Nongezile Nyathi

Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa

 

 


ABSTRACT

This paper presents two recent developments in the targeting and design of cooling-water systems using process integration. The basis of this work is the observation that true optimization of any cooling-water system, comprising a cooling tower and a network of operations that use cooling water, can be realized only by considering the system as a whole. Traditional approaches have focused separately on either the cooling tower or the operational network. Optimality, in the context of this paper, refers to minimum cooling-water flowrate to the network or maximum return temperature to the source of the cooling water (a cooling tower). Only systems with at least two cooling towers instead a single one are considered here, to highlight the complexity of a typical cooling-water system. The first exercise is based on a graphical technique in which targeting for the minimum cooling water precedes design of the cooling-water network to achieve the target. The second exercise uses mathematical modelling to optimize a superstructure that entails all possible topological arrangements of the cooling-water network. An industrial case study involving a South African explosives manufacturing plant is used to demonstrate the effectiveness of both techniques. Cooling-water savings of more than 20% were realized with modest capital investment.


 

 

“Full text available only in PDF format”

 

 

References

1. Linnhoff B., Mason D.R. and Wardle I. (1979). Understanding heat exchanger networks. Computers and Chemical Engineering 3, 295-302.         [ Links ]

2. El-Halwagi M.M., El-Halwagi A.M. and Manousiouthakis V. (1992). Optimal design of dephenolization networks for petroleum-refinery wastes. Trans. IChemE 70b, 131-139.         [ Links ]

3. Wang Y.P. and Smith R. (1994). Wastewater minimization. Chemical Engineering Science 49, 981-1006.         [ Links ]

4. Wang Y.P. and Smith R. (1995). Time pinchanalysis. Trans. IChem E 73a, 905-914.         [ Links ]

5. Wang Y.P. and Smith R. (1995). Waste minimization with flowrate constraints. Trans. IChemE 73, 889-904.         [ Links ]

6. Olesen S.G. and Polley G.T. (1997). A simple methodology for the design of water networks handling single contaminants. Trans. IChemE 75a, 420-426.         [ Links ]

7. Doyle S.J. and Smith R. (1997). Targeting water reuse with multiple contaminants. Trans. IChemE 75b, 181-189.         [ Links ]

8. Alva-Argáez A., Kokossis A.C. and Smith R. (1998). Wastewater minimization of industrial systems using an integrated approach. Computers and Chemical Engineering 22 (Suppl.), S741-S744.         [ Links ]

9. Savelski M.J. and Bagajewicz M.J. (2000). On the optimality conditions of water utilization systems in process plants with single contaminants. Chem. EngngSci. 55, 5035-5048.         [ Links ]

10. Jödicke G., Fischer U. and Hungerbühler K. (2001). Wastewater reuse: a new approach to screen for designs with minimal total costs. Computers and Chemical Engineering 25, 203-215.         [ Links ]

11. Hallale N. (2002). A new graphical targeting method for water minimization. Adv. Environ. Res. 6, 377-390.         [ Links ]

12. Kasperski M. and Niemann H-J. (1988). On the correlation of dynamic wind loads and structural response of natural-draught cooling towers. J. Wind Engng Ind. Aerodyn. 30(1-3), 67-75.         [ Links ]

13. Bartoli G., Borri C. and Zahlten W (1992). Nonlinear dynamic analysis of cooling towers under stochastic wind loading. J. Wind Engng Ind. Aerodyn. 43(1-3), 2187-2198.         [ Links ]

14. Wittek U. and Meiswinkel R. (1998). Non-linear behaviour of RC cooling towers and its effects on the structural design. Engineering Structures 20(10), 890-898.         [ Links ]

15. Sudret B., Defaux G. and Pendola M. (2005). Time variant finite element reliability analysis - application to the durability of cooling towers. Structural Safety 27, 93-112.         [ Links ]

16. Soylemez M.S. (2001). On the optimum sizing of cooling towers. Energy Conserv. Mngt 42, 783-789.         [ Links ]

17. Knoche K.F. and Bosnjakovic F. (1998). Pinch analysis for cooling towers. Energy Conserv. Mngt 39, 1745-1752.         [ Links ]

18. Martinez S.S., Gallegos A.A. and Martinez E. (2004). Electrolytically generated silver and copper ions to treat cooling water: an environmentally friendly novel alternative. Int. J. Hydrogen Energy 29, 921-932.         [ Links ]

19. Kim J.K. and Smith R. (2001). Cooling water system design. Chem. Engng Sci. 56, 3641-3658.         [ Links ]

20. Bernier M.A. (1994). Cooling tower performance: Theory and experiments. ASHRAE Transactions Res. 100, 114-121.         [ Links ]

 

 

Received 13 January 2005.
Accepted 12 January 2007.

 

 

Author for correspondence. E-mail: thoko.majozi@up.ac.za

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License