WaterPinch™: Making a Difference

ChE in Action: Linnhoff March

     Over the last two decades, attitudes to the environment have changed. We no longer accept that pollution is inevitable. Instead, the public is aware that improvements are possible and believes that the expense should be met. The response of governments has been to introduce new legislation and to establish regulatory authorities with increased powers to enforce compliance.

     Today, reducing waste has become one of the greatest challenges facing the process industries. Because water is one of industry’s major waste products, the ability to reclaim wastewater for re-use is an important step toward overall waste reduction.  Identifying and deploying optimal water re-use is a challenge. Modern technologies present a myriad of confusing alternatives that the engineer may consider. The basic message of WaterPinch™ analysis should be the starting point:

Figure 1: Purity Profile

Case Studies

Case Study 1: Chemical Plants

Figure 2: Water Conservation Strategy for Unilever’s Warrington Plant

      Unilever’s Vinamul plant in Warrington, England, produces about 200 different specialty chemicals, principally paints and adhesives, using batch processing. Because of wide variations in processing requirements and tight quality specifications the plant had a strong preference for the use of utilities rather than recovered process water - steam for heating, cooling tower water for cooling and freshwater for washing. Changing environmental perceptions and rising costs for raw water and effluent treatment caused the management to re-evaluate this philosophy. 

      The WaterPinch™ project (using the early UMIST methods) resulted in a simple segregation, collection, and re-use strategy as shown schematically in Figure 2. The design reduced freshwater demand by 50% and wastewater effluent flow by 65%. Together these reductions were estimated to be worth US $100K per year. However, the real savings lie in the future, when on-site treatment will be required prior to discharge. The reduced wastewater flow is expected to save about 50% of the capital cost of any future treatment plant. Furthermore, at the higher concentrations resulting from lower flow, it becomes feasible to introduce new treatment technology for total recovery of product species from the effluent water, thus virtually eliminating all pollution [1]. 

Case Study 2: Polymer Plants

Figure 3: Water Conservation Strategy for Polymer Plant

      A chemicals and fibres plant in the South Eastern US was planning a capacity expansion spanning 5 years. Wastewater flow to the treatment plant was expected to increase by 20%, which was beyond the treatment plant’s hydraulic limit. It was recognised that if wastewater flowrate could be reduced by 20% the capital cost of expanding the wastewater treatment plant, along with the associated permitting requirements, could be avoided.  The engineering staff had looked at a number of options for reducing water consumption, such as two-stage filtration, reducing filtration temperature, etc., but none of them were found to be economically feasible.

      Ultimately, a WaterPinch™ analysis was undertaken. The key projects which emerged are highlighted in Figure 3. Net wastewater flow was reduced by 21% and freshwater intake was reduced by 16%. The capital cost of implementing the conservation measures was less than one-third of the projected cost of expanding the wastewater treatment facility. The permitting procedure was avoided entirely[2].

Case Study 3: Refineries

Figure 4: Water Conservation Strategy for Amoco's Yorktown Refinery

     Amoco’s oil refinery in Yorktown, Virginia, USA negotiated a special arrangement with the E.P.A. (Environmental Protection Agency) to pilot test a co-operative approach to environmental compliance. The concept was to achieve air and water emissions reduction through process integration rather than conventional end-of-pipe treatment [1, 3].

     Data from the project was subsequently analysed using WaterPinch™. The essential results are shown in Figure 4.

     Freshwater consumption was reduced by 14% and wastewater effluent flow was reduced by 24%. The stripper reboiler project was not strictly necessary for water conservation as the stripper bottoms stream was being re-used in the cooling tower anyway. However, it was recommended because it shifts the cooling tower make-up mix towards freshwater which helps to mitigate odour emissions (due to trace amounts of phenolics) from the cooling tower.

**WaterPinch™ is a registered trademark of Linnhoff March Ltd.
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Literature Cited

1.  Hamilton, R. and D. Dowson, "Pinch Cleans Up", The Chemical Engineer, 566, 21, 1994

2.  Buehner, F. W. and J. D. Kumana, "Freshwater and Wastewater Minimisation-Concepts, Software and Results", presented at the Chemputers IV Conference, Houston (March 1996)

3.  Linhoff, B. and R. A. Tainsh,   "Intelligent Networking of Process Wastewater Streams in the Chemical Industry", Paper submitted to the GVC Conference "Verfahrenstechnik der Abwasswer-und-Schlammbehandlung", Wurzburg, 14-16 October 1996

Read More About WaterPinch™

In the market for this type of solution?  Let the people at Linnhoff March know that you found them at www.cheresources.com!

By: Tainsh, R.A. and Rudman, A.R., Linnhoff March
techsupport@linnhoffmarch.com