APPLYING THERMOECONOMICS TO THE ANALYSIS OF ... - circe

Every human activity has an environmental impact, with the food system being an important (and mandatory)
human activity. There is a wide variation in environmental impact according to the type of food, and the method of
producing the food. An important feedback principle links the environment and food systems. The environment
influences the quality and capacity of food production, which in turn influences the environment. A degraded
environment may be less healthy for humans and other organisms, and also less able to produce the range and amount
of food that an environment in better condition could achieve (Riley, M., 2005). Each basic process that comprises the
food chain has an efficiency and a resources cost that could be evaluated by means of the thermoeconomic analysis,
allowing the identification of improving options.
2. THE FUEL –PRODUCT MODEL
Symbolic Exergoeconomics (Torres, 2004) provides general relationships between the production demand and the
resources cost with the efficiency and irreversibilities of the individual process of an energy system. It is based on the
productive structure of the system and is represented by the fuel – product table, (fig. 1) which describes how the
production processes are related.
F0 F1 … Fn
P0 E01 … E0n
P1 E10 E11 … E1n
… … … Eij …
Pn En0 E1n … Enn
Figure 1. Generic Fuel-Product Table
In this table, the useful energy carried from the i-th process to the j-th process is represented as E ij . The sum of each
row of the table is the production of each process, and the sum of each column is the resources or fuel required for each
process.
Symbolic exergoeconomic provides two different representations of the productive model:
The FP representation allows relating the production and the cost of each process of the system as a function of:
F ≡ E , … E
• The external resources ( )
e 10 n0
• The efficiency of each process, represented by K D , a diagonal matrix whose elements are the unit
•
consumption of each process: κi ≡ Fi / Pi
.
The distribution ratios, represented by FP , a matrix whose elements are defined as yij ≡ EjiPj. The production of each process is obtained as:
( ) 1
P =〈 P| Fe The total production demand is calculated as:
where 〈 P| = KD− −
FP (1)
t
P T = y0P F e
(2)
y ( , , ) is a vector that contains the distribution ratios related to the environment.
t
where 0 ≡ y01 … y0n
The production cost of each process is given by:
*
CP=〈 P | C0where *
〈 P | = ( UD−
−1
FP )
(3)
the vector C0 ≡ ( c01E01, …, c0nE0n) contains the cost of the external resources and c 0i represents its unitary cost. The
magnitude used to measure the external resources determines the type of cost obtained.
The other representation, called PF representation, allows expressing the resources and their costs as a function of:
• The production demand P s ≡ ( E10, …,
En0)
• The efficiency of each process i i / i F P ≡ ε
• The junction ratios, represented by PF , a matriz which elements are defined as qij ≡ Eij/ Fi
The resources used in each process are obtained as:
( ) 1
F = F Pswhere 〈 F | = HD−
−
PF (4)
−1
and HD ≡ K D is a diagonal matrix (n× n), containing the efficiency ε i of each process.
The cost per production unit can be obtained as:
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