Environmental Engineering Reference
In-Depth Information
verting the sensible heat of gas into radiation energy at a high
rate of conversion efficiency. When burned gases behind the flame pass through the
porous solid wall, the sensible heat is converted into radiation energy and the
unburned mixture is preheated using this radiation energy.
In contrast, the direct (internal) heat recirculation methods are methods of
feeding back heat directly from the side of burned gases to the side of unburned
gases by inserting, for example, a porous metal with high thermal conductivity into
the flame zone, changing the internal structure of the flame and forming an additional
enthalpy flame. Many research activities using several of the above-mentioned meth-
ods have been conducted in the past and some remarkable research results have been
reported.
the function of con
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as used in large-scale industrial furnaces as a waste heat recovery
unit to realize high thermal efficiency and energy conservation. The recovered waste
heat was used to preheat the combustion air, which was then fed to a burner. The
preheated air resulted in energy conservation and good combustion performance.
However, the disadvantages included incorporating a large-scale heat recovery sys-
tem for waste heat. Furthermore, the temperature of the preheated air was only about
600 to 700˚C, at best. To obtain further substantial energy savings, it was found
necessary to recover combustion waste heat thoroughly and feed it back to the
unburned side effectively. An effective means for achieving this is the development
of a regenerative burner having better function for effective waste heat recovery.
This has been the topic of active research and development since the beginning of
the 1980s.
At British Gas and later at Hotwork International (United Kingdom), throughout
the 1970s and the 1980s, substantial efforts were allocated to the development of
both recuperative and regenerative burners.
A recuperator w
ve burners could offer only
modest fuel savings, since the combustion air could be preheated to temperatures
typically not higher than 600˚C. The burners equipped with regenerators (beds
packed with ceramic balls) offered much higher preheating levels typically up to a
1000˚C with a cycle time of 30 to 40 s. Such substantial air preheating was possible
only when the furnace exit gases, entering the regenerator, were at temperatures
typically of 1300 to 1400˚C.
Further progress in the regenerator design was made in Japan, at Nippon Furnace
(NFK), at the beginning of 1990s. New honeycomb-type regenerators were shown
to be more compact and possessed smaller thermal inertia. The honeycomb regen-
erators operated at a very small temperature difference (typically of 50 to 100˚C)
between the furnace exit temperature and the combustion air temperature. They
provided possibilities for achieving combustion air preheating up to 1200˚C, thus
further improving furnace efficiency.
The technology carried through in the
Recuperati
3
Development of High Performance Indus-
trial Furnace Project
is high-cycle alternating regenerative combustion technology.
It employs high temperature air, preheated to temperatures in excess of 1000˚C,
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