Environmental Engineering Reference
In-Depth Information
Table 11.2
Energy consumption for the production of fresh, canned, frozen, and dehydrated selected
fruits and vegetables.
Fresh (MJ/kg)
Canned (MJ/kg)
Frozen (MJ/kg)
Dehydrated (MJ/kg)
Corn
12.2
24.0
29.7
86.3
Carrots
11.0
21.4
29.7
86.3
Apples
13.8
0.9
21.4
54.0
Potatoes
14.5
20.9
34.8
62.1
From Buffington and Zar, 1977.
IMPROVING ENERGY EFFICIENCY OF FOOD-PROCESSING
PLANTS
Energy in food-processing plants
Food-processing plants consume two kinds of energy: electricity and heat. Electricity powers
motors (that produce mechanical energy to run pumps, fans, conveyor belts, mixers, and
grinders), lights, control systems, and air-conditioning equipment. Heat, used for processing,
is produced generally at the facility by burning fossil fuels, especially natural gas, in two
different ways:
Direct-fired heat, such as in fryers, ovens, and dryers.
●
Indirect-fired heat to heat boilers and produce steam that is then distributed around
the plant.
●
In the United States, the most important fuels used in food processing are electricity,
natural gas, and coal. Approximately 91 percent of the electricity is purchased and 9 percent
is generated on site with cogenerating power systems that also produce steam. Among input
costs, energy ranks third after raw materials and labor (EPA, 2007a). In terms of energy
consumption per dollar value, the US food industry utilizes 2.74 MJ for each dollar gener-
ated (2.6 KBtu/$), one of the lowest ratios when compared across different energy sectors
(
see
Table 11.3).
The total consumption of energy by the food-manufacturing industry in the United States
during 2002 was 1.18 EJ (1,116 T (TBtu) ), of which 0.61 EJ (575 TBtu) came from natural
gas, 0.24 EJ (230 TBtu) from electricity, 0.19 EJ (184 TBtu) from coal, 0.03 EJ (32 TBtu)
from fuel oil, and the rest from other sources including 0.01 EJ (5 TBtu) from liquefied natural
gas and 0.001 EJ (1 TBtu) from coke (Table 11.3) (EPA, 2007a).
It is estimated that 75 percent of the energy is used in heating and cooling (e.g., steam
systems, ovens, furnaces, and refrigeration units), 12 percent to drive processing
equipment (e.g., pumps, fans, conveyors, mixers, grinders, and other process equipment),
8 percent for facility functions (e.g., heat, ventilation, and lighting), and the rest for other
uses (EPA, 2007a). As an example, the US fruit and vegetable processing industry alone
consumes over 0.11 EJ (100 TBtu) of energy per year that is purchased as fuel
(77 percent) and electricity (23 percent) (Table 11.4) (Masanet et al., 2008). And this is
not the most energy-intensive food industry. Corn wet milling is by far the most energy
demanding food-processing operation with around 0.23 EJ (220 TBtu) per year (Galitsky
et al., 2003).
