South African Journal of Science
On-line version ISSN 1996-7489
Print version ISSN 0038-2353
MAJOZI, Thokozani and NYATHI, Nongezile. On cooling-water systems design for South African industry: Two recent developments. S. Afr. j. sci. [online]. 2007, vol.103, n.5-6, pp.239-244. ISSN 1996-7489.
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.