Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~1133'~
J a~S~t
It is known from U.S. Patents No.~ 2~9 and 1,966,591 that the
efficiency of combustion of a continuous open flame can be improved by feeding
steam directly into the flame. By "continuous" is meant a flame which usually
burns continuously for at least one minute at a time.
The present invention provides a method of improving the efficiency
of a continuous open flame of a burner of a furnace comprising feeding steam
from the vicinity of the burner into helical flow patterns directly into the
flame at a controlled rate such that the oxygen of the steam exceeds 15% of
the oxygen theoretically required for complete combustion but less than the
rate at which the flame would be extinguished.
It appears that optimum results are attained when the rate is such
that the steam furnishes 60-90% more oxygen (as steam) than the oxygen (as
air) which is theoretically required for complete combustion of the fuel.
When the steam supplies more than 100% additional oxygen, the flame might be
extinguished if the temperature of the steam is near 100C before it is
exposed to the heat of the flame. If its original temperature is higher, the
steam may be fed into the flame at even greater rates without extinguishing
the flame.
When the flame is shut off, the flow of steam should be interrupted ~-~
until after the flame is re-ignited. ~sually a delay of 5-10 seconds after
re-ignition should be sufficient to insure against accidentally extinguishing
the flame.
Where the fuel is a gas, it is desirably mixed with the steam before
being fed into the flame. Where the steam is generated from water, a fuel
such as alcohol may be dissolved in the water. Where the steam is generated
in drying a substance, the volatile matter may be a gaseous fuel.
From another aspect, the invention provides in a furnace, a burner
having a continuous open flame and means for feeding steam from the vicinity
of the burner into helical flow patterns directly into the flame at a control-
led rate such that the oxygen as steam exceeds 15% of the oxygen theoretically
required for complete combustion but less than the rate at which the flame
would be extinguished.
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33'7
The invention also provides apparatus for heating materials to drive
off water and other volatiles comprising: a furnace having a continuous open
flame, a drying chamber, means for applying heat from the furnace to the
drying chamber, means for collecting volatiles emitted from the drying chamber,
and means for feeding said volatiles directly into the open flame.
1 ~
33'7
When the steam ls ~irst fed into a continuous open
flame, any yellow or red color disappears, and the entire
~lame becomes blue and lengthens in a pulsating manner.
The maximum length of the pulsating flame substantially
exceeds that of the unmodified flame. If the flame tends
to grow to a length exceeding that of the combustion chamber,
the flame should be directed into a devious (e.g., helical)
path.
The invention is applicable to a variety of fuels
including methane, petroleum oil, wood, coal and alcohol.
Where the fuel contains significant amounts of water, its
j water content should be taken into account in calculating
the maximum rate of adding water as steam without danger of
accidentally extinguishing the flame.
Under conditions of high ambient humidity, it may
; be desirable to take into account the quantity of water in
the combusti~n air and to reduce the rate of applied steam
accordingly-to insure against extinguishing the flame. Under
conditions of high humidity, the combustion air for natural
gas may contain water in an amount furnishing oxygen tas
water) about equaling 5% of the oxygen (as air) theoretically
required for complete combustlon. -~
Depending upon the choice of fuel, a typical
installation in the prior art may call for about 200% excess
combustion air for maximum fuel efficiency. In the practice
of the present invention, it is generally possible to reduce
the combustion air to the theoretical level or even below.
This by itself produces considerably increased heating
efficiency, especially where the combustion air is supplied
at ambient temperature. In a heating plant which draws
33'7
combustion air from the area belng heated, there is less
danger of suffocation and less waste since the combustion
air normally goes up the chimney.
In the practice of the present invention, the
elimination of excess combustion air is believed to provide
greater assurance against accidentally extinguishing the
flame when steam is being fed into the flame at very
high rates.
For instaliations in which it would be incon-
venient to reduce the flow of combustion air mechanically,part of the steam may be fed into the combustiQn air line
to replace part of the combustion air.
When steam was applied at an optimum rate to the
flame of a conventional alfalfa drier, the fuel consumption
was reduced about 20%. By applying the steam emitted from
the drying alfalfa to the flame, the total reduction in fuel
consumption was about 35%, the additional saving apparently
being due to combustion of gaseous fuel emitted from the
alfalfa. Comparable savings in fuel consumption should be
reaIized in the drying of other materials which evolve
water, e.g., cotton, grain, milk, fish, eggs, wood,
textiles, feces and latex paint.
It is theorized that when the steam strikes the
flame, some of the water disassociates into hydrogen and
oxygen, and combustion of the hydrogen and the avail-
ability of nascent oxygen enhances the heat output.
Whether or not that theory is correct, the degree of
increased efficiency of combustion is startling and of
tremendous significance in this era of fuel shortages.
33`;'
In the drawing:
FIGURE 1 is a schematic elevation, partly cut away
to a central section, of a rotary alfalfa drier incorporat-
ing the present invention; and
FIGURE 2 is an enlarged cross section along line
2-2 of Figure 1.
As seen in Figure 1, a cylindrical hot-air
furnace 10 which is lined with fire brick is connected to
the central flue of a con~entional drum-type alfalfa drier
12. Alfalfa entering a belt-fed hopper 14 is drawn through
the drier 12 in an S-shaped path by a thermostatically
controlled blower 16 and through a duct 18 to a conventional
cyclone separator 19. The dried alfalfa drops through a
chute 20 while water and other volatiles from the alfalfa
in the form of steam rise to a skimmer 22 and are drawn by
the suction of a fan 24 through a conduit 26 and fed
directly into the flame of the furnace 10. A humidistat
(not shown3 in ~he conduit 26 controls an intake 28 o~
additional steam as required to supply the furnace at the
des~red rate.
As seen in Figure 2, the furnace 10 is equipped
with five gun-type burners 30. A series of vanes 32
directs the steam from the conduit 26 into helical flow
patterns and thence directly into the flame of the burners.
The helical flow of the steam redirects the flame into a
helical path, thus insuring good circulation both within
the furnace 10 and within the flue of the drier 12.
~xample
In an experimental operation of apparatus as
illustrated in Figures 1 and 2, the combustion chamber of
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the furnace was 1.~7 m ln diameter and 6 m in length.
Initially, alfalfa was fed into the hopper 14 at a rate of
3000 kg per hour and the blower 16 was operated at about
225 m per minute. The steam produced reached a temperature
of about 130C in the duct 18 and about 115C in the con-
duit 26.
As the steam began to be fed into the flame, the
te~perature of the drier 12 increased. The thermostatic
controls had been pre-ad~usted to respond to such decrease
in temperature by reducing the ratio of combustion air to
natural gas. That ratio was initially 34:1 and was gradually
reduced to the theoretical 17 13 thus dimin~shing the cool-
ing effect of the combustion air. The ability to operate
at the theoretical ratio was deemed to be due in part to the
effect of the steam feedback and in part to better mixing
; by virtue of greater turbulence. Before reaching the 17:1
ratio, two of the five burners had been shut off, and addi-
tional steam was being added through the intake 28. In
steady operation, the total steam being fed into the flame
was 0.74 kg per m3 of combustion air.
Before any steam was generated, the temperature of
the furnace 10 was 2090C. After two burners had been shut
off and additional steam was being added, the furnace tem-
perature was 2070C. The flame slowly pulsated to a maximum
length extending well into the drier 12, thus substantially
increasing the temperature in the drier. The rate at which
the alfalfa was fed into the hopper was gradually increased
to 4500 kg per hour and was drled at that faster rate as
effectively as it was lnitlally without any steam feedback.
The more rapidly dried alfalfa reportedly had substantially
l33'~
higher protein content than was obtained using an unmodified,
but otherwise identical drier. The operator of the equip-
ment reported that the modi~ied drier required only 2.59
~oules/kg of water driven off as compared to 4.05 joules/
5 kg without any feedback. - -'
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