Page 18 - Vol.06

Special
Report
特別企劃

set of water-using units where a set of transfer- From To
able contaminants with fixed mass loads are Water-Using Water-Using
Units i Units i
required to remove. A set of freshwater supplies
with known concentrations are available for From Water-Using To
service; a set of inner-plant and/or inter-plant RCW tanks M Unit i S RCW tanks
m m
water mains would be used to increase the
network flexibility. The objective is to determine From To
an optimal operating strategy for the inner-plant Freshwater Receiving
Supplies w Tanks r
and inter-plant water integration scheme, which
targets the minimum freshwater consumption
Figure 1. Superstructure for a water-using unit
and wastewater production.

Mathematical Formulation
Superstructures for processing equipments
are built and shown in Figures 1-3, on which the From To
Water-Using Water-Using
mathematical formulation is based. In addition Units i Units i
to the constraints to ensure design specifications
and feasibility, the problem consists of water and From RCW To
RCW tanks M S RCW tanks
contaminant balance equations. Following this, m’ Tank m m’
a general formulation is presented first, and then
various integration schemes can be represented From To
Freshwater Receiving
by imposing supplementa l constraints Supplies w Tanks r
appropriately.
Figure 1 depicts the superstructure of all Figure 2. Superstructure for a RCW tank
possible flow connections for a water-using
unit i, where the input water would come
from other water-using units i', water mains
m, and freshwater supplies w. Similarly, the
From
output water may be sent to other water-using
Water-Using
units i', water mains m, or receiving tanks r. Units i
According to the superstructure, the water and
contaminant balances for each water-using unit From To
RCW
can be derived as given in Eqs. (1)-(3) and Eqs. RCW tanks M Tank m Treatment
(4)-(7), respectively. Note that c is the index for m Systems
contaminants.
Figure 3. Superstructure for a receiving tank

Figure 2 depicts the superstructure of all possible flow
connections for a RCW tank m, where the input water may come
from water-using units i, other RCW tanks m', and freshwater
supplies w. Meanwhile, the output water may be sent to water-
using units i, other RCW tanks m', or receiving tanks r. RCW tanks
would be distributed to individual fabs (zones), or centralized,
whose purpose is to simplify the overall network complexity. In
accordance with this superstructure, the water and contaminant
balances are derived in Eqs. (8)-(10) and Eq. (11), respectively.

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