Beginning with the design below the pinch, if we are to maintain a minimum temperature difference of
20 ºC, then we cannot use cooling water below 30 + 20 = 50 ºC. The lowest utility cost design would therefore use cooling water to cool stream 1 from 55 ºC to 50 ºC (duty 200 kW). A second cooler would then be needed to cool stream 1 from 50 ºC to 40ºC using chilled water (duty 400 kW). The annual utility cost of this design would be 200(18.1) + 400(129.6) = $55,460.