APPLYING THERMOECONOMICS TO THE ANALYSIS OF ... - circe

Table 1. Fuel-Product Table of the food chain (GJ)
0 F 1 F 2 F 3 F 4
F 5
F Total
P0 80 7 15 13.5 0 115.5
P1 0 0 60 0 0 0 60
P2 5 0 0 51.5 3.5 0 60
P3 0 0 0 0 0 1.9 1.9
P4 0 0 0 0 0 3.1 3.1
P5 3.6 0 0 0 0 0 3.6
Total 8.6 80 67 66.5 17 5
Equations (3) and (5) allow computing the production cost. These equations could be also used to decompose the
costs considering the different types of resources. The resource cost vector can be separated into two parts:
fossil biomass
fossil
C0 = C0 + C 0 , where the cost due to fossil fuels in terms of energy resources is C 0 = (0, E02, E03, E04,0)
, and
biomass
the cost due to biomass is C 0 = ( E01,0,0,0,0)
, therefore the production cost due to fossil fuel could be computed as:
fossil
CP= *
P
fossil
C0
(8)
and in the same way the production cost due to biomass is:
biomass
CP= *
P
biomass
C0
(9)
Similar expressions could be used to compute the unitary production cost.
Table 2. Efficiency and production costs of the processes for the base case
Fossil Fuels Biomass Total
Process κ P c (GJ/GJ) P C (GJ) P c (GJ/GJ) P C (GJ) P c (GJ/GJ) C P (GJ)
1 1.33 0.00 0.00 1.33 80.00 1.33 80.00
2 1.12 0.12 7.00 1.33 80.00 1.45 87.00
3 35.00 11.06 21.01 36.14 68.67 47.20 89.68
4 5.48 4.49 13.91 1.51 4.67 5.99 18.58
5 1.39 9.70 34.92 20.37 73.33 30.07 108.25
Total 13.43 35.50 80.00 115.50
In table 2 the efficiency values of each system process are shown. The ratio of the total fossil fuel required per
fossil
calorie consumed is approximately 10:1 ( c P,5
= 9.70 ), a clear indicator of the high inefficiency of the current food
chain. Also note that the production of meat (process 3) requires 2.5 times more fossil energy resources (11.06 vs. 4.49)
than the vegetal production (process 4). By far, the most inefficient process (identified by κ ) is the production of meat.
Starting with the base case we will analyze several scenarios, in order to demonstrate the capabilities of the
thermoeconomic approach for the evaluation of the environmental impact of the food system, and for the identification
of potential improvements.
3.2 Recycling biomass residues
Our aim now is to identify and quantify possible optimization options of the food chain system. In the first scenario,
we are going to analyze the effect of recycling 10% of crop residues (2 GJ) and reusing them as fuel in the next process.
The unit consumption of the first process is reduced to κ 1 = 1.29 and the external resources of the second process to
C 02 = 5. We assume that the distribution ratios and the final demand of the system do not change.
Using Eqn. (3) it is possible to compute the production costs. Since biomass energy and the cost distribution matrix
*
P does not change, the production costs due to biomass do not change either.
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