Environmental Engineering Reference
In-Depth Information
Table 13.4
Operational energy intensity during transportation of food by a consumer
from the grocery store to home assuming 10 kg of grocery per trip and average fuel
efficiencies suggested by the Environmental Protection Agency.
Type of vehicle
City-highway combined fuel
consumption (km/L [mile/gal])
Energy intensity
(MJ/tonne-km)
Sport utility
6.3 (15)
504
Midsize sedan
10.1 (24)
315
Compact sedan
12.6 (30)
252
Following is the calculation of the operating energy intensity (EI) for the SUV:
1 gallon
1 mile
121 MJ
EI
=
×
×
=
504 MJ/tonne-km
0.01 tonne
×
15 mile
1.6 km
gallon
Calculations for the other two vehicles are similar and results are presented in Table 13.4.
If these results are compared with the energy intensity of a plane (the largest of all massive
transport systems), which uses 10 MJ/tonne-km, then an SUV needs 50 times more, a midsize
sedan 31, and a compact sedan 25 times more energy to transport the same weight of goods
and distance than a plane.
Energy intensity in the transportation of food products
Energy intensity works well with high density materials, such as coal, sand, and mineral ore.
The concept also applies to food products with high to intermediate bulk density. For
instance:
Liquid foods transported in bulk, such as milk, juices, and vegetable oils with densities
between 900 and 1,050 kg/m
3
.
●
Grains with a bulk density between 600 and 750 kg/m
3
and granules and powders, which
include sugar, starch, and flours, with densities that range between 700 and 800 kg/m
3
.
●
Roots and tubers that have a relatively high-bulk density that varies between 550 and
700 kg/m
3
.
●
On the other hand, most food products due to fragility, protection, or convenience are
placed in packages that increase the weight associated with the food as well as volume,
which affects energy intensity. Typical examples of products with low weight and high
volume are dried foods including pasta, breakfast cereals, and chips. These products fill the
space available in the vehicle far before reaching its maximum weight limit of cargo.
According to federal regulations, in the United States, the maximum gross weight for a
combination vehicle is 36,364 Kg (80,000 lb). The typical tare (empty weight) of a 5-axle
tractor-semitrailer is 13,636 kg (30,000 lb) thus leaving 22,727 kg (50,000 lb) for cargo.
Considering that a volume of a 5-axle tractor-semitrailer enclosed van is around 108 m
3
(4,000 ft
3
) then the cut-off bulk density of a product that would fill the whole space of the
van (assuming that the whole cargo space can be filled) without exceeding the maximum
weight allowed is 210 kg/m
3
(12.5 lb/ft
3
). So any product with a bulk density (including pack-
aging) of more than 210 kg/m
3
will reach the maximum weight limit before filling completely
the trailer's volume and vice versa.
