Page 153 - Sustainability in the Process Industry Integration and Optimization

130 Cha p te r S i x

6.3.3 Emergy-Pinch Analysis
The concept of emergy (embodied energy) was first developed by
Odum in the late 1980s (Odum, 1996). Along with other definitions
referring to life cycle, it may be defined in terms of solar transformity
(Brown and Ulgiati, 2004). Solar emergy is the solar energy directly
or indirectly necessary to obtain a flux of energy in a process. The
unit of emergy is the solar emergy Joule (seJ), an extensive quantity,
which denotes the available energy of a certain type (heat, electrical,
etc.) that undergoes transformations. Transformity, an intensive
quantity, is defined as the emergy input per unit of exergy (available
energy) output: seJ/J.
The first step in the practical process of emergy analysis is
collecting information for the calculation of solar transformities
ST [seJ/unit] of the chain of activities involved in making a resource
available to the process. This is the most difficult part of the
methodology because transformity databases—although rapidly
growing and continuously updated by researchers—are not
comprehensive. The second step is the calculation of solar emergy
SE [seJ/y] followed by calculation of the solar emergy investment
SEI [seJ/g]:

SE [seJ/y]= ST [seJ/unit] · Amount [units/y] (6.1)

SEI [seJ/g]= SE [seJ/y]/Amount [g/y] (6.2)
The combined Pinch–emergy analysis is used in the preliminary,
conceptual design stage. The Emergy Composite Curve (ECC) is
analogous to the Pinch CCs. In the ECC, solar transformity is plotted
against solar emergy; the CC is then matched up with the total
emergy investment (TEI) supply line, which is restricted by the ECC
at the Pinch point. Analyses are based on ECC benefit from using
both emergy and Pinch features.
Each stream in the ECC carries three pieces of information:

1. Transformity: the past emergy investment or “history” of the
stream
2. The “market” potential of the stream in terms of usability:
the heat (temperature) potential of a thermal stream or the
concentration limits of a water stream
3. The stream’s future in terms of further usability (regenerative
reuse)

In the case of Heat Pinch Analysis, the hot and cold streams will have
different signs for this component of final emergy investment. The
sign on the required emergy investment to heat the cold streams will
be the opposite of the one for available emergy. Hence, at this level of