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● Case 5: IPI with centralized/inner-fab RCW
tanks, without the use of cross-fab pipeline

Figure 3 shows the superstructure for a receiving tank,
like a buffer where the wastewater is held before being sent Finally, the objective shown in Eq. (19) is to
to treatment systems. The water balance for each receiving minimize the freshwater consumption. Besides, the
tank is given in Eq. (12). It is worthy of mention that effluent design problem is a mixed-integer nonlinear program
treatment is quite important for environmental concern, but (MINLP) for the binary variables and bilinear terms.
this part is omitted and kept for future work

Equation (13) defines the lower and upper limits to the
connecting flow rates with the use of binary variables. y*=1 Results
denotes the existence of the connection between *.
he example with fifteen water-using units
divided into three individual fabs (each adapted
Tfrom Wang et al., 2003, Example 2; Zheng et al.,
So far, the aforementioned equations constitute a basis 2006, Case study 2; and Gunaratnam et al., 2005, Case
for inter-fab water integration, as a general case of hybid study 1) is provided to illustrate the application of the
design options. For convenience, the equations are grouped proposed formulation. The solution tool is the General
to a set Ω 0 ≡{Equations (1)-(13)}. Five integration schemes Algebraic Modeling System (GAMS, Brooke et al.,
are considered in this work, as described below: (Note: IPI 2003), and the solver for MINLP is BARON.
cen
=inter-fab integration; p=index for fabs; M cen and M are sets In case 1, without any inter-fab integration, the
of centralized and inner-fab mains).
respective freshwater consumptions of individual fabs
● Case 1: No IPI without using RCW tanks: are 111.81 ton/h, 111.83 ton/h and 183.59 ton/h, with a
total amount of 407.24 ton/h. In case 2, inner-fab RCW
tanks are put in each fab to enhance the operability,
but the mixing effect increases the overall freshwater
consumption from 407.24 ton/h to 421.82 ton/h. In case
● Case 2: No IPI with inner-fab RCW tanks
3, direct IPI is carried out and the overall freshwater
consumption is reduced from 407.24 ton/h to 354.46
ton/h in comparison with case 1. However, direct IPI
would be hard to operate for control problems and
the network complexity. Therefore, indirect IPI is
performed in case 4. Although the overall freshwater
consumption is slightly increased to 355.54 ton/h
● Case 3: direct IPI (Chew et al., 2008) because of the mixing effect, the network structure
will be simpler. For some larger scale problems,
centralized RCW tanks would be employed in addition
to inner-fab mains for practical needs so case 5 is to
● Case 4: indirect IPI (Chew et al., 2008)
be examined. The freshwater consumption is slightly
increased to 362.1, but the operability of the whole fab
can be improved when compared to cases 3 and 4. The
resultant network configurations for cases 2 and 5 are
shown in Figs. 4 and 5, respectively.

NEW FAB TECHNOLOGY JOURNAL APRIL 2012 19