Page 143 - Sustainability in the Process Industry Integration and Optimization

120 Cha p te r F i v e

5.6.2 Illustrative Example: A Brewery Plant
This section discusses the case study of a brewery plant (Tokos and
Novak Pintarič, 2009) as a means to illustrate how mathematical
optimization is used to solve water minimization problems. In the
brewery studied, the ratio (by volume) of process water consumed to
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product beer sold was 6.04 : 1; this translated into 653,300 m /y of
water consumed. In terms of the ratio set by BREF (2006), this
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freshwater consumption exceeded the upper limit by 144,900 m . In
light of these figures, the company undertook to improve its process
by retrofitting modifications to its existing water network so that the
plant’s usage of freshwater would be minimized.
Production at the brewery plant involves a mixture of water-
using batch and semicontinuous processes. Water-using operations
in the packaging area are operated mainly in batch mode, with the
exception of rinsers for nonreturnable glass bottles and cans.
Wastewater stream from semicontinuous processes can be reused in
batch processes with a lower purity requirement. Hence, the basic
formulation first proposed is designed to enable the efficient
integration of semicontinuous and batch water-using processes.
The continuous wastewater streams are treated as limited
freshwater sources, and the unused wastewater is discharged. In the
next step, the model is extended by including options for installing
intermediate storage tanks for the collection of unused wastewater
streams for reuse over subsequent time intervals. This particular
design modification is motivated by differences in the operating
schedules of the filling lines. The superstructure representation for
water reuse and regeneration reuse (as defined in Section 5.2.4) is
depicted in Figure 5.5.
Opportunities for regeneration reuse were analyzed in the
brewhouse and in the cellar (see Figure 5.6), since these processes
were characterized by a high concentration of contaminants. Here
the basic model is extended by installing a local (on-site) wastewater
treatment unit that can operate in either batch or continuous mode,
thereby enabling water regeneration reuse and recycling. The
scheduling of batch wastewater treatment units is performed
simultaneously so that the treatment schedule will coincide with the
fixed schedule of the batch process. The design includes the option to
install storage tanks before and after treatment; this enables
wastewater and/or purified water to be stored until required by the
treatment schedule.
As reported in Tokos and Novak Pintarič (2009), the integration
of the water network in the packaging area made it possible for
wastewater from the can rinser to be reused in the pasteurization
processes. In this way, freshwater consumption could be reduced by
23 percent and the common costs of freshwater and wastewater
treatment by 22 percent. These improvements do not require the