Page 57 - Sustainability in the Process Industry Integration and Optimization

34 Cha p te r T h r ee

often leads to changes in the conceptual model; the result is an
iterative feedback loop, as shown in the figure. A similar correction
loop is also present at the output of the implementation block. The
discussion that follows addresses only those activities in Figure 3.1
that involve conceptual and mathematical modeling.

3.10.1 Conceptual Modeling
Conceptual modeling involves collecting and organizing essential
information about the phenomena in the process under consideration.
This step is often referred to as data extraction (Williams, 1999). The
process operating units are described along with the relevant features
of their behavior. The important constraints for the units’ capacities
and other limitations are identified and added to the description, as
is topological information about the process network. The main
purpose of this description is to serve as an interface between the
process operators and the modelers. Therefore, it is important that
the description be concise enough that modelers can efficiently grasp
the workings of the complete system. That being said, the description
must contain sufficient detail to complete the study.
Extracting Data About the Operating Units
When a production process is modeled for the purpose of Process
Integration, the data extraction involves four main steps:
1. Description of the process operating units and their
interconnections; creation of a flowsheet that reflects this
description.
2. Identification of the heating and cooling needs of the process
through use of the flowsheet and related data about the
operating units.
3. Definition of the Heat Integration process streams: identifying
for each stream the values for its heat load, as well as the
supply and target temperatures. Some process streams may
need to be segmented. This is done if the specific heat capacity
of a given process stream varies significantly within the
interval between its supply and its target temperature.
4. Analysis of the collected data.

If the goal is to minimize water use and wastewater discharge,
then the various water-using operations are analyzed and their
relevant properties are recorded in some standard form. The most
popular way to express the water requirements (Wang and Smith,
1994; Kuo and Smith, 1997) of an operation is in terms of the limitations
on (1) inlet and outlet concentrations of different contaminants and
(2) flow rates of the water to be consumed. This topic is discussed in
more detail in Chapter 12.