This project is a sequel to WRC Report No. 851/1/03 entitled The Application of Pinch Analysis for the Rational Management of Water and Effluent in an Industrial Complex. The earlier report set out the basis and methodology, together with some practical guidelines, for applying water pinch analysis to an industrial system, and presented some case studies as practical examples. This report is mostly concerned with further case studies which had not been completed at the time of the previous report. However these case studies do reflect some development in theoretical understanding which occurred during the intervening period. Thus the two reports are complementary to one another, and should be considered together. In particular, the literature survey and general theoretical background to water pinch
analysis are contained in the previous report, while this report starts to address some issues which were raised in the previous report.
Industrial processes usually require water with a range of qualities, and produce several
effluents with a range of qualities, which allow the possibility of a hierarchical use of water.
Possible strategies for reducing the consumption of fresh water and the production of
wastewater include:
- re-use: wastewater from one process can be directly re-used in others, provided the level of contamination is sufficiently low to meet the requirements of the subsequent processes;
- regenerative re-use: wastewater can be treated to reduce the levels of contaminants before being re-used in other processes. In this option, the water is not recycled to the process from it came;
- regenerative recycling: after regeneration, water can be recycled to the process from which it came. This is generally more difficult than re-use, because recycling tends to build up contaminants.
Pinch analysis is a process integration tool, which was first developed for the design of heat recovery systems during the late 1970s. Using the analogies between heat and mass-transfer, a similar approach was developed for the design of mass-exchange systems. This work formed the basis for the design of water-using systems. It took the design objective to be to minimise water consumption by maximising the reuse of water, using a graphical technique ( which was termed Water Pinch Analysis. However the technique was difficult (although possible) to extend to accommodate the practical constraints and characteristics of water-using systems, such as multiple contaminants, flow rate constraints, piping costs, etc. The added desire to introduce cost optimisation required that the problem be formulated
using mathematical programming techniques.
Water Pinch Analysis thus involves a set of systematic formal techniques to handle the complex problem of hierarchical water allocation to a system consisting of a number of processes, and choosing the best combination of strategies. The theory that appears in the literature is still developing. The practical application of this theory is not as well established in the open literature, and particularly not in a South African context.
Project Objectives
As originally stated, the project objectives were:
- to promote the wide spread application of pinch analysis for the management of water and effluents;
- to develop the technique for the specific problems associated with South African industry;
- to promote better water management by undertaking pinch analysis studies at selected sites;
- to enhance the capacity within South Africa to undertake pinch analysis studies and to promote the wider understanding of the technique within educational institutions, industry and government by training people in the technique.