Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02799648 2013-01-07
Early Filing Date Patent Application
This is a formal request for an Early Filing Date
Natural Draft Combustion Mixer
BACKGROUND OF INVENTION
A natural draft combustion mixer is a device that is utilized in processes
where heat is required
and achieved by means of heat release from the combustion reaction of fuel and
air in a
combustion chamber. The mixer is used to perform the mixing of the fuel and
air to achieve a
mixture above the LEL (lower explosive limit) and below the UEL (upper
explosive limit). The
primary air shutter is used to control the amount of air that is entering the
mixer to attain the
required combustion properties. An orifice, of various sizes depending on
capacity
requirements, is used to calculate the actual volume of fuel per unit time
that passes through
from a point of predetermined pressure to an area of atmospheric pressure. It
is also the point
where the well known physics principle of high velocity creating a low
pressure area is used to
cause atmospheric pressure to push air into the mixer or induce air. The
mixture exits through a
nozzle at which point the ignition actually occurs and the combustion reaction
takes place.
Traditionally, the primary air shutter has been located at a point upstream
from the point of
fuel introduction. Thus, the flow of cold primary air must pass by the orifice
and, as a result,
strips heat away from the orifice. The orifice is prone to freezing due to the
varying
composition/water content of the fuel being used in conjunction with the
pressure drop that
occurs at this point. In order to change the capacity of the mixer, the
orifice needs to change in
CA 02799648 2013-01-07
size and/or the pressure adjusted. This typically involves the dismantlement
of the mixer
assembly to provide access to the orifice.
SUMMARY OF THE INVENTION
The object of this invention is to prevail over the drawbacks relating to
prior art in this field as
stated above.
The primary air intake has been relocated to a position downstream of the fuel
gas point of
introduction. Now the stream of fuel leaving the orifice is at its highest
velocity, and thus,
lowest pressure, at the point of air induction rather than the traditional
upstream location. This
allows for a greater volume of air, if required, vs a traditional style mixer.
A removable orifice holder has been designed to allow for the removal of only
the holder to
access the orifice for maintenance and set-up. This allows the rest of the
assembly to remain
stationary as it is not required to be removed from the combustion chamber.
A port has been positioned adjacent to the orifice location to allow the use
of an orifice preheat
line to be installed. This port provides a point of entrance for the high
temperature, products
of combustion (POC) from the mixing chamber into the mixer housing. These POC
can be
drawn back and directly across the orifice, using the same physics principle
as previously
discussed, to further prevent the freeze off issues traditionally encountered.
BRIEF DESCRIPTION OF DRAWINGS
Fig.1 is an exploded view of the mixer assembly with an optional venturi
barrel
Fig. 2 is a view of all components assembled to form complete mixer
DETAILED DESCRIPTION OF INVENTION
With reference to Figs 1-2 the mixer component orientation and construction
can be explained.
Fig. 2 shows the location of the fuel inlet to the mixer.
As shown in Fig. 1 the mixer is comprised of three mandatory separate
components with an
optional component that will assist in the mixing of the fuel if required. The
main mixer body 3
contains the port for the preheating of the orifice 4 by utilizing the high
temperature POC as
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well as the port for the orifice holder 1. A portion of the main body 3 has a
reduced diameter
and four rectangular holes removed from the stock at 90 degrees in an array
around the
outside diameter. The reduction of diameter allows for the primary air shutter
5 to slide over
top of the mixer body 3. The reduced diameter portion of the mixer body 3 and
the primary air
shutter are of the same length. This is the base for the primary air shutter 5
which also has the
same dimensioned four holes removed at a 45 degree offset from the mixer body
3 holes. This
allows for the primary air to be adjusted within the completely open and
completely closed
positions of the shutter. The mixing shutter 5 has the same outside diameter
as the mixer body
3 and an internal diameter slightly larger than the outer diameter of the
reduced section of the
mixer body 3. This allows for the primary air shutter 5 to rotate freely about
the center line axis
of the mixer. Fig. 2 shows the set screw hole 2 that allows for the primary
air shutter to be
secured in the desired position and also constrains the degrees of rotation
between the
completely open and completely closed position of the primary air shutter (3,
Fig. 1.). The
optional venturi barrel 6 is shown in Fig. 1 and is used to aide in mixing of
the air/fuel before
the nozzle. Fig. 1 shows the orifice 2 threaded into the orifice holder 1 and
is threaded into the
port 7 located at the back of the mixer body 3. It is this configuration that
allows the orifice
holder to be removed from the assembly allowing maintenance or set-up to
easily be
performed on the orifice without the need to remove the entire mixer asSembly
from the
combustion chamber.
With reference to Fig. 1, as the fuel passes through the orifice 2, the high
velocity gas creates a
low pressure area at the primary air shutter 5 thus, inducing air into the
mixer body 3. The
primary air shutter 3 is rotated to adjust the amount of air entering the
mixer, based on the
required amount of air needed to attain the desired combustion reaction.
A line, such as a piece of stainless steel tubing, may be connected between
the orifice preheat
port 4 and the flame front where the POC are produced. As the high velocity
fuel enters the
mixer, the low pressure created draws high temperature POC down and across the
adjacent
orifice, effectively heating the orifice well above the temperature at which
ice will form.
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