Note: Descriptions are shown in the official language in which they were submitted.
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Radiant Heating Apparatus
Field of the Invention
The present invention relates to an apparatus used to
provide large quantities of radiant heat energy over a
relatively large surface area. The radiant heating apparatus
of the present invention can be used with roadway surface
reconditioning machines such as scarifiers and patchers.
Background of the Invention
The use of a radiant heating apparatus will be discussed
in conjunction with scarifiers and patchers. However, the use
of a radiant heater of the present invention is not limited to
scarifiers and patchers.
The term "scarifier" denotes a machine that travels
slowly along a roadway while heating the existing asphalt to a
relatively high temperature. It then loosens the hot asphalt
and finally smooths down the loosened hot material to form a
reconditioned and resurfaced roadway.
The term "patcher" denotes a machine that heats a small
area of asphalt to a relatively high temperature. The treated
area is hand raked and finally rolled to produce a
reconditioned patch of asphalt.
A critical component of scarifiers and patchers is the
heater assembly for applying heat to the old roadway surface.
It is desirable to apply as much heat as possible to the
asphalt, and to do so as quickly as possible, because the
amount of heat that can be transferred to the asphalt per unit
time will determine how fast the machines can recondition a
roadway surface. The efficiency of heat transfer will also
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determine the depth to which the asphalt can be heated.
The other major component of a radiant heating apparatus
is the fuel-air supply system. This system supplies the
necessary high pressure propane gas into the burner unit. It
is important that the propane gas be supplied at a high
pressure in order to produce a 1000 premix of air and propane
gas.
Prior Art
Prior art heating units used in scarifiers and patchers
utilized a series of porous firebricks as the heater units.
These bricks are designed so that a gaseous fuel consisting of
a mixture of propane and air introduced into a hollow rear
space can flow through the bricks and burn at or adjacent the
surfaces thereof to provide a large area radiant heater. The
entire heater unit is extremely heavy due to the large number
of bricks used; as a result, fire brick systems require the
use of heavy hydraulics to lift the heater units.
The brick heating units are also subject to frequent
breakage when the machines are bumped against a curb etc. The
cost of replacement bricks is substantial, and the labour to
install them requires specialized skill. As a result, heating
units that utilize firebricks are extremely expensive to
operate and maintain.
In the past open flame burners have been used in heater
units, which would overheat certain portions of asphalt. In
addition, the open flames have also been blamed for starting
fires among shrubs and other vegetation along the side of the
road.
Prior art fuel-air supply systems required the use of
high-powered blowers, for use in a porous brick heating unit,
in order to adequately mix air with propane gas. These
systems require many valves and regulators to ensure the
air/gas mixture is adequate for obtaining a 1000 premix.
Summary of the Invention
The present invention relates to a radiant heating
apparatus used to heat large surface areas to a high
temperature. The radiant heating apparatus is comprised of a
novel heater unit and a novel fuel supply system.
The fuel supply system that feeds the heater unit
requires the use of a small pump and a vaporizer, or merely a
vaporizer.
In accordance with one aspect of the invention there is
provided a radiant heating unit comprising: a) supply means
for supplying a quantity of high pressure gaseous fuel at a
predetermined pressure; b) a housing having an open bottom,
an upper chamber communicating with said open bottom, and an
upper aperture communicating with said upper chamber; c)
first mesh retaining means covering said open bottom; d) a
layer of ceramic wool resting on said first mesh retaining
means and substantially covering said open bottom, said layer
of ceramic wool having a bottom outer surface; e) second mesh
retaining means covering said open bottom and resting on said
layer of ceramic wool; f) fuel-air mixture means located
above and connected to said upper aperture and connected to
said supply means for providing a 1000 combustible mixture to
A
said upper chamber, said 1000 combustible mixture passing
through said layer of ceramic wool, and burning at said
bottom outer surface of said layer of ceramic wool, said
fuel-air mixture means comprising: g) venturi means in
communication with outside air; and h) orifice means located
within said venturi means and connected to said supply means,
wherein said gaseous fuel passing through said venturi means
draws sufficient outside air through said venturi means to
mix with said gaseous fuel to provide said 100% combustible
mixture.
In accordance with another aspect of the invention there
is provided a high pressure supply means for supplying and
vaporizing a combustible. gaseous fuel at a predetermined
pressure, said fuel supply means comprising: a) a propane
tank for storing liquid propane having a supply pipe and a
return pipe; b) a pump connected to said supply pipe and
having an outlet pipe; c) a vaporizer having an input
connected to said outlet pipe and an output for gaseous
propane; d) a by-pass valve connected between said outlet
pipe and said return pipe for controlling the pressure of the
liquid propane at a predetermined maximum at the input to
said vaporizer; and e) a control regulator connected to the
output of said vaporizer to control the pressure of the
gaseous propane to said predetermined pressure.
In accordance with yet another aspect of the invention
there is provided a high pressure supply means for supplying
and vaporizing a combustible gaseous fuel at a predetermined
pressure, said fuel supply means comprising: a) a propane
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tank for storing liquid propane having a supply pipe and a
return pipe; b) a vaporizer having an input connected to said
supply pipe and an output for gaseous propane; c) a first
control regulator connected between said output of said
vaporizer and said return pipe of said propane tank, wherein
said first control regulator regulates the return flow of
pressurized propane gas to said propane tank; and d) a second
control regulator connected to the output of said vaporizer
to control the pressure of the gaseous propane to said
predetermined pressure.
Brief Description of the Drawings
The present invention will be described in detail
hereinbelow with the aid of the accompanying drawings, in
which:
Figure 1 illustrates a side view of a heater unit of a
radiant heating apparatus, and
Figure 2 is a schematic diagram of a first embodiment of
a fuel supply system for the radiant heating apparatus of
Figure 1, and
Figure 3 is a schematic diagram of a second embodiment
of a fuel supply system for the radiant heating apparatus of
Figure 1.
Description of the Preferred Embodiments
Figure 1 illustrates a radiant heating unit 30. The
heater unit 30 consists of a steel frame 32 oriented above
and attached to a first layer of steel mesh 34 and a layer of
ceramic fibre material 36, such as Kaowool (TM). A second
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layer of steel mesh 38 is placed on top of ceramic fibre 36.
High pressure propane gas is fed by a supply line 42
through an orifice 43 into a venturi 44. The flow of high
pressure gas, at a specific velocity, through the narrow
portion of venturi 44 causes primary air to mix with the
propane gas to produce a 100 combustible mixture. This
mixture is deflected by a deflector plate 46 in chamber 40,
which distributes the gaseous mixture evenly into ceramic
fibre layer 36. The gaseous mixture is ignited at the bottom
outer surface (at first layer 34) of ceramic fibre 36. The
flow of the gaseous mixture cools the upper outer surface (at
second layer 38) of ceramic fibre 36, which prevents the upper
surface of fibre 36 from becoming excessively hot.
The ceramic fibre material 36 used as the infra-red
combustion surface is very light, has low thermal
conductivities, low heat storage and excellent resistance to
thermal shock. For example, Kaowool (TM) brand of ceramic
fibre has a much lower thermal conductivity than the commonly
use Alumino-Silicate Firebrick. These characteristics ensure
that the ceramic fibre can withstand extremely high
temperatures for prolonged periods of time.
Figure 2 illustrates a first embodiment of a fuel supply
system that is capable of supplying high pressure gaseous fuel
necessary for heating unit 30.
The first fuel supply system consists of a propane tank
50 from which liquid propane is drawn off by a pump 52 through
a supply pipe 5l to a vaporizer 56. The propane gas from the
output of vaporizer 56 passes through a control regulator 58
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where its pressure is reduced from 100 psi to between 30 and
80 psi, as indicated by a gauge 62. The propane gas continues
through supply line 42 into heater unit 30. Liquid propane at
a pressure above 100 psi is returned to propane tank 50
through a liquid return pipe 55 by a by-pass valve 54.
Figure 3 illustrates a second embodiment of the fuel
supply system, which does not require the use of a pump, but
is capable of supplying fuel to heating unit 30.
The second fuel supply system consists of propane tank 50
from which liquid propane is fed, by gravity, through supply
pipe 51 into vaporizer 56. A portion of the vaporized propane
gas at the output of vaporizer 56 passes through a regulator
60, set at 100 psi, and returns into propane tank 50 through a
vapour return pipe 53. The regulator 60 will shut-off
automatically when the pressure of the propane gas has reached
100 psi. Consequently, the liquid propane is forced into pipe
51 by the high pressure gaseous propane at the top of tank 50.
If the pressure of the gaseous propane drops below 100 psi
regulator 60 is opened to force additional liquid propane into
supply pipe 51, which will eventually return the pressure of
the vaporized propane gas to 100 psi.
A majority of gaseous propane from the output of
vaporizer 56 is passed through control regulator 58, which
reduces the pressure of the gaseous propane from 100 psi to
between 30 and 80 psi, as indicated by gauge 62. The propane
gas continues through supply line 42 into heater unit 30.
These high volume suppliers do not require the use of
large blowers since the air is mixed with the high pressure
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propane in venturi 44 and chamber 40. This provides the
necessary 100% premix, of air and gas, to ensure efficient
combustion.
