|dc.description.abstract||The long held belief that hydrocarbon energy sources
are limitless is rapidly being disproven. While non-renewable
resources such as gas, oil, and coal become limiting,
the fear of an energy shortage is becoming very real. This
energy scare is resulting in campaigns to make the public
more concerned with how remaining sources of energy are used.
An examination of the major industrial users of hydrocarbon
fuels reveals that tremendous amounts of energy in
the form of heat are released into the environment every day.
This heat is released in the gaseous state or as a heated
effluent. In many cases, the high quality of this heat
would allow it to be used for beneficial purposes.
The concept of using waste heat is not new. Many
attempts have been made in the past or are presently being
undertaken to put waste energy to work. In many cases,
these attempts have not been successful due to technical,
economic, or political problems. Dwindling energy supplies
and a conservation-minded public mean that greater efforts
must be made to solve these problems.
There are two basic reasons for undertaking projects
which make use of waste heat sources. The first is economic
and the second is ecological. The economic reasons
become obvious when the rapidly rising cost of conventional
energy sources is considered. The ecological reasons are
based on concern for the environment when large quantities
of thermal waste are released into it. Besides these basic
reasons, many would argue there is a social or moral obligation
to make more efficient use of natural resources than
is presently the case.
Often steam-electrical generating stations or other industrial
plants release large quantities of heated water
into lakes or rivers. This can have disastrous effects on
ecological relationships. Thus, projects may have as their
main concern the dissipation of heat in a way that is not
harmful to the environment. Usually the most economic way
of dissipating this heat in an ecologically sound manner"is
to find a practical use for it. Systems must be designed
to utilize the waste heat to economically improve the conversion
efficiency of the fuels burned and at the same time
reduce environmental risks.
The major problem in utilizing waste heat from the
cooling water of steam-electrical generators is to develop
efficient transfer systems that remove the heat. Often the
heat is of low quality so the design of the transfer system
is critical. Some designs use closed-system heat exchangers
and others make use of contact-type heat exchangers.
Although the heat released as part of gaseous exhausts
is one-third of that released as heated water, it still has
great potential as an alternative energy source. Exhaust
gases also present an ecological concern because many of
the by-products of hydrocarbon fuel combustion contain
pollutants that are harmful to the atmosphere. Systems
that utilize the heat of the exhaust, as well as removing
harmful components, would serve a dual purpose.
When the hot exhaust gases of hydrocarbon combustion
are considered, the temperature of the gases released is
often much higher than is the case with heated water, but
the noxious components of the exhaust present problems.
Heat exchangers that are part of a closed system and prevent
the entry of noxious materials must be used or else
the noxious component must be removed from the exhaust to
allow its direct use. If the latter method is possible,
a benefit other than heating could be realized. The exhaust
from hydrocarbon fuels contains large quantities of
carbon dioxide which could be used to enhance the growth
of crops located in protected environments.
In order to test this concept, experiments were conducted
from August 1974 to January 1976 by the Departments
of Horticulture Science and Mechanical Engineering to
study the feasibility of using the exhaust from a natural
gas-fired turbine for greenhouse heating and carbon dioxide
enrichment. The merits of the system were evaluated
using the tomato as a test plant.||en_US