Environmental Engineering Reference
In-Depth Information
trip and continue throughout the waiting time in the parking lot until the truck is unloaded,
which may vary from a few hours to a day or so. A result of decomposition of these raw
materials is emissions of VOCs, which can be mitigated through better management and
scheduling practices.
Emissions during rendering are more difficult to control with the technology currently used
by the industry. Cookers, which are the heart of the rendering facility, are closed vessels, so
VOCs and foul smells can be captured right at the source in a concentrated state. However,
subsequent operations, such as separation of fat and protein, conveying, and grinding, are
generally open to the air and prone to release VOCs and smells that require the handling and
treatment of large amounts of air. A solution to reduce the amount of air sent to the scrubber
is to enclose the equipment, which is technically challenging. This would decrease the amount
of air handled that would translate in savings in indirect emissions through purchased
electricity.
Emissions from the use of electricity
Electricity is the preferred source of energy for illumination, control systems, and mechanical
devices in food-processing plants. Electricity feeds motors that run, pumps, fans, refrigeration
units, compressors, conveyor belts, and mixers. Any approach that reduces energy consumption
will subsequently reduce indirect carbon dioxide emissions. Tactics can be simple, such as
maintaining the equipment in optimal operating conditions (e.g., plugging air and water leaks
and reducing water and operational air pressures) to more expensive ones such as investing in
efficient electric motors or refrigeration equipment.
A more fundamental reduction of carbon dioxide emissions, which requires substantial
capital investment and technical challenges, is on-site generation of renewable electricity. This
may include solar, wind, biogas, biomass, or landfill gas energy, and the use of cogeneration
or trigeneration systems. When on-site production is not possible, off-site renewable energy,
low carbon energy, or “green energy” can be purchased at a premium from the grid where
available. Chapter 11 analyzes different approaches to reduce carbon emissions from
consumption of electricity.
Emissions from refrigeration
Refrigeration is responsible for three types of emissions:
1. Indirect emissions of carbon dioxide from consumption of electricity by compressors and
fans in stationary facilities.
2. Direct emissions of carbon dioxide from the use of fuel to run refrigeration equipment
during transportation.
3.
Direct emission of hydrofluorocarbon and hydrochlorofluorocarbon gases due to acciden-
tal leaks in pipes, joints, and equipment.
In traditional compression refrigeration systems, indirect emissions from electricity can
be cut, besides with proper maintenance, only by increasing the equipment efficiency.
Efficiency can be improved with more efficient compressors and fans, evaporative condens-
ers, automatic air purge valves, liquid pressure amplification systems, and better control
systems.
Another alternative is the replacement of compression equipment with absorption systems
that can take advantage of waste heat. In contrast with compression systems that use electricity
