A TWO STEP APPROACH TO OPTIMIZATION OF RECIRCULATING COOLING TOWER SYSTEM

Cooling tower is one of the unit that is involved with water network system and it can
contribute to higher water savings for a plant if maximum attention is given to it.
Much of the works only concentrate on individual cooling tower unit, especially in
improving the performance of the internals. Nonetheless, work on the total cooling
water system, which addresses the issues of interactions between the cooling tower
and its associated heat exchangers or coolers, has received lesser attention. The
objective of this study is to develop a systematic method for optimization strategy to
improve efficiency of the existing cooling tower system, based on the established
empirical model. A well-known Merkel’s Equation (Perry and Green, 1997) is used to
predict the cooling tower performance. The basic idea in this optimization strategy is
to minimize cooling water circulation in cooling tower through water reuse so as to
maximize cooling tower return temperature. A two-stage approach is adopted in the
optimization procedure. The first stage is to address the cooling tower performance
itself. This effort takes into account the minimum approach temperature, pressure
drop and fouling issues so that any modification of process parameters are within the
acceptable limits of the cooling tower. In the second stage, cooling water composite
curve, which is similar to a conventional water pinch technology, is proposed to
identify water reuse opportunities. Further design of water reuse is carried out by
mathematical approach using General Algebraic Modelling System (GAMS) mainly
when composite curve unable to identify water reuse opportunity. Finally, the
economics of the proposed improvement are then presented to demonstrate its cost
effectiveness. Based on the case studies, application of water reuse enables the total
operating cost of the cooling water systems to be reduced up to 27% for case study 1
and 28% for case study 2. While for case study 3, the additional product capacity
could be obtained up to 15%. These findings show a great promise for industrial
application as the methodology developed in this thesis can be used to improve the
performance of the cooling water system.