Note: Descriptions are shown in the official language in which they were submitted.
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A FUEL PREHEATER FOR A LOW MAINTENANCE FLUID
HEATER
RELATED APPLICATIONS
This is a division of Canadian patent application 2,582,517
filed March 22, 2007 and entitled LOW MAINTENANCE FLUID
HEATER AND METHOD OF FIRING SAME.
FIELD OF THE INVENTION
This invention relates in general to boilers, and, in
particular, to a low maintenance fluid heater with a
removable burner unit to facilitate maintenance of the fluid
heater.
BACKGROUND OF THE INVENTION
Boilers for heating water and other fluids for use in
heating systems, industrial processes and the like are well
known in the art. In general, such boilers employ a ceramic-
lined or enamel-lined firebox where a fossil fuel is
combusted to provide an energy source for heating the fluid
to a desired temperature. The fluid is normally heated by
circulating flue gases through a "water wall" formed of a
plurality of pipes or channels through which the fluid is
circulated.
For certain applications, fluid heaters for rapidly
heating large volumes of water or other fluids are required.
Such applications include the heating of hydrocarbon well
fracturing fluids, which are generally but not exclusively
aqueous fluids that are typically heated to about 15 C-50 C
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before they are injected into a hydrocarbon well. Portable
heaters for this application must be lightweight, rugged,
efficient and capable of high heat output. While fluid
heaters of this type are known, they are expensive to
construct and maintain, and are not necessarily capable of
the heat generation required to rapidly heat large volumes of
well fracturing fluids in the field.
There therefore exists a need for an efficient, low
maintenance fluid heater.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a fluid
preheater for a low maintenance fluid heater.
The invention therefore provides a fuel preheater for
preheating a fluid fuel that is combusted by a plurality of
fluid fuel burners of a removable combustion unit for a fluid
heater having a combustion chamber with walls and floor
through which the fluid to be heated is circulated, the fuel
preheater comprising: a metal box constructed with a front
wall formed by an outer wall of the removable combustion
unit; and a metal plate welded diagonally across the metal
box to divide the metal box into two separate chambers, a
fuel preheating chamber adjacent the outer wall and an
insulation chamber adjacent the combustion chamber, the
insulation chamber being filled with a heat resistant
insulation to inhibit overheating of the fluid fuel.
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The invention further provides a fuel preheater for
preheating a fluid fuel that is to be combusted by fluid fuel
burners of a combustion unit for a fluid heater having a
combustion chamber with walls and floor through which the
fluid to be heated is circulated, and the combustion unit
forms one wall of the combustion chamber, the fuel preheater
comprising: a fuel preheater box having a front wall formed
by an outer wall of the combustion unit; and a metal plate
welded diagonally across the metal box to divide the
preheater box into two separate chambers, comprising a fuel
preheating chamber adjacent the front wall and an insulation
chamber adjacent the combustion chamber, the insulation
chamber being filled with a heat resistant insulation to
inhibit overheating of the fluid fuel.
The invention yet further provides a fuel preheater that
preheats a fluid fuel before it is combusted by fluid fuel
burners supported by a combustion unit of a fluid heater that
comprises a combustion chamber with walls and a floor through
which the fluid to be heated is circulated, the combustion
unit forming one wall of the combustion chamber, and the fuel
preheater comprises: a fuel preheater box having a front
wall formed by an outer wall of the combustion unit; a metal
plate welded diagonally across the preheater box, which
divides the preheater box into two separate chambers,
comprising a fuel preheating chamber adjacent the front wall
and an insulation chamber adjacent the combustion chamber,
the insulation chamber being filled with a heat resistant
insulation to inhibit overheating of the fluid fuel; a first
fitting in a passage through the front wall, the first
fitting being connected to a pressurized fluid fuel supply
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line that delivers the fluid fuel to the fuel preheating
chamber; and a second fitting in another passage though the
front wall, the second fitting being connected to a fuel line
that delivers the preheated fluid fuel to one of the fluid
fuel burners.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the
invention, reference will now be made to the accompanying
drawings, in which:
FIG. 1 is a schematic side elevational view of one
embodiment of the fluid heater in accordance with the
invention showing a facing sidewall partially cut away to
illustrate a burner unit and coil stack of the fluid heater;
FIG. 2 is a schematic top plan view of a part of the
coil stack of the fluid heater taken along lines 2-2 of FIG.
1;
FIG. 3 is a schematic cross-sectional view of the fluid
heater wall construction in accordance with the invention,
taken along lines 3-3 of FIG. 2;
FIG. 4 is a schematic front elevational view of the
fluid heater shown in FIG. 1, with the combustion unit
removed for maintenance;
FIG. 5 is a schematic diagram of a plan view cross-
section of an exemplary floor construction for the fluid
heater in accordance with the invention, showing an exemplary
flow path through the floor for fluid to be heated;
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FIG. 6 is a schematic diagram of an end of a combustion
chamber shown in FIG. 1 adjacent one side of a combustion
unit of the fluid heater, showing the wall partially cut
away to illustrate a fluid flow path through the wall;
FIG. 7 is a schematic diagram of an end of a combustion
chamber shown in FIG. 1 remote from the combustion unit of
the fluid heater, showing the wall partially cut away to
illustrate a fluid flow path through the wall;
FIG. 8 is a schematic diagram an end of a combustion
chamber shown in FIG. 1 adjacent the other side of the
combustion unit, showing the wall partially cut away to
illustrate a fluid flow path through the wall;
FIG. 9 is an isometric diagram of a reverse-flow corner
of a coil stack chamber of the fluid heater shown in FIG. 1;
FIG. 10 is a schematic diagram of an outer side of an
exemplary combustion unit for the fluid heater shown in FIG.
1;
FIG. 11 is a schematic cross-sectional diagram of a fuel
preheater for the fluid heater in accordance with the
invention;
FIG. 12 is a schematic front elevational view of the
fluid heater shown in FIG. 4, with the combustion unit in an
operative position; and
FIG. 13 is a schematic side elevational view of the
fluid heater mounted to a truck bed, with fuel tanks in
accordance with a further aspect of the invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a fluid heater that is light
weight, so it is easily transported; robust, so it has a long
service life; modular, so it is quickly and easily
maintained; adapted to burn a heavy hydrocarbon waste fuel,
so it is economical to operate; and produces high heat
output, so it is capable of quickly heating large volumes of
fluid to a desired temperature. The floor and walls of the
fluid heater are constructed entirely of rectangular metal
tubing through which the fluid to be heated is circulated
before it enters a coil stack positioned directly over a
combustion chamber of the fluid heater. Consequently, all
surfaces of the fluid heater exposed directly to flame are
cooled by the fluid to be heated and efficiently transfer
heat to that fluid. A combustion unit of the fluid heater is
removable to permit maintenance of the combustion unit and
the coil stack to be performed easily and efficiently.
FIG. 1 is a schematic side elevational view of one
embodiment of a fluid heater 20 in accordance with the
invention, showing a facing sidewall 22 partially cut away to
illustrate a burner unit, generally indicated by reference
24, and coil stack, generally indicated by reference 26, of
the fluid heater 20.
In one embodiment outer walls of the fluid heater 20,
which define a combustion chamber 30 in front of the
combustion unit 24 and a coil stack chamber 32 that surrounds
the coil stack 26 are a substantially square structure
constructed entirely of rectangular tubular steel of an
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appropriate gauge and composition dependent on a
corrosiveness of the fluid to be heated. A floor 28 of the
fluid heater 20 is also constructed of the same rectangular
tubular steel material. In one embodiment, the floor 28 and
outer walls 30, 32 of the fluid heater 20 are constructed of
2"x6" (5cm x 15cm) rectangular tubular steel, with an
exception of a coil stack support beam 34, which in one
embodiment is constructed of an 811x8" (20cm x 20cm) square
tubular steel.
Fluid to be heated is pumped in to an inlet pipe 40
welded to a bottom edge of the floor 28 and circulated along
a circuitous path through the floor to an opposite side of
the floor 28, as will be explained below with reference to
FIG. 5. The fluid is then circulated up through a conduit 42
into the sidewall of the combustion chamber 30 adjacent the
combustion unit 24. The fluid again follows a circuitous
path around the outer walls of the combustion chamber 30 and
the coil stack support beam 34, as will be explained below
with reference to FIGs. 6-8, until it enters tubular conduits
74a, 74b interconnected by a removable joint 76, which
conducts the fluid from the coil stack support beam to the
bottom of the coil stack chamber wall 32. The removable joint
76 permits the coil stack chamber 32 to be removed from the
fluid heater 20 to provide access to the coil stack 26, if
required. The fluid to be heated travels in a circuitous path
around the coil stack chamber wall 32, as will be explained
below with reference to FIG. 9, until it enters a conduit 44
welded to a top of the coil stack chamber wall 32. The fluid
then circulates through the coil stack 26, as will be
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explained below with reference to FIG. 2, and exits the fluid
heater 20 via an outlet pipe 46 routed through a side of the
coil stack support beam 34 and connected to, for example, a
storage tank from which the fluid to be heated was pumped.
As it is apparent, a top of the coil stack chamber 32 is
inwardly inclined. In one embodiment, the inward inclination
is at an angle of about 45 . A top edge 48 of the coil stack
chamber 32 defines a rectangular flue gas vent 50 through
which flue gases produced by the burner unit 24 are exhausted
after they rise through the closely spaced and overlapping
coils of the coil stack 26, as will likewise be explained
below in more detail with reference to FIG. 2.
The burner unit 24 includes a plurality of burners. In
this embodiment, the burner unit 24 includes 4 burners 52a-
52d. In one embodiment, each of the burners 52a-52d are
manufactured by the Hauck Manufacturing Company located in
Lebanon, Pennsylvania, USA, and designed to burn a heavy
hydrocarbon waste fuel, such as used engine lubricating oil.
However, the burners 52a-52d may be designed to burn any
carbonaceous fluid fuel, including gaseous fuels, such as
propane or natural gas. Each burner head is located in the
back of a ceramic cone 54a-54d, into which atomized fuel is
ejected by the respective burner heads in a manner well known
in the art. Located between each pair of ceramic cones 54a,
54b and 54c, 54d is a fuel preheating chamber 55a, 55b as
will be explained below in more detail with reference to FIG.
11. For practical reasons, an outer wall of the burner unit
24 is not cooled by the fluid to be heated. Consequently,
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sacrificial steel plates are hung about 1" (2.5cm) in front
of the outer wall of the burner unit 24 by pins (not shown)
connected to the outer wall of the burner unit 24. In this
embodiment, three sacrificial plates are used. A center T-
shaped plate 56 and two L-shaped side plates 57a, 57b. The
sacrificial plates are replaced as required and provide heat
protection required by the burners and other components of
the burner unit 24, which will be described below in more
detail with reference to FIG. 10.
In operation, pressurized combustion air is supplied to
the burner unit 24 by a blower 60, also available from Hauck
Mfg. Co., which delivers the pressurized combustion air to
the burner unit 24 through a combustion air supply pipe 61.
As will be explained below in more detail with reference to
FIG. 10, the combustion air is distributed in equal
proportion to the burners 52a-52d and to a hollow floor 62 of
the combustion unit 24. The combustion air delivered to the
hollow floor 62 is exhausted into the combustion chamber
through a plurality of oblong slots 64, supplying extra
combustion air to the combustion chamber 30. This permits
fuel to be delivered to the burners at twice the
manufacturer's recommended fuel pressure, i.e. 80 psi rather
than 40 psi. In this way, the BTU output of the burner unit
is nearly doubled and the efficiency of the fluid heater 20
is greatly improved in comparison to an efficiency of known
units of the same type.
FIG. 2 is a schematic top plan view of a lower part of
the coil stack 26 of the fluid heater 20, taken along lines
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2-2 of FIG. 1. In one embodiment of the fluid heater 20, the
coil stack 26 has 9 pipes 68 in each layer interconnected by
U-shaped (180 ) elbows 70, and is 11 layers high. The pipes
68 and the elbows 70 are 3" (7.5cm) in diameter and made of
steel. Each layer of coils in the coil stack 26 is separated
by 1" x 0.5" (2.5cm x 1.25cm) flat steel bar stock 72 that is
welded to each end of each pipe 68. As is apparent, the
coils in each layer of the coil stack are staggered with
respect to the layer immediately below and the layer
immediately above, so that flue gas must follow a circuitous
path upward through the 11 layers of the coil stack before it
exits through the flue gas vent 50 (see FIG. 1). This
ensures that heat energy is efficiently extracted from the
flue gas, while facilitating cleaning of the coil stack 26.
Cleaning of the coil stack is accomplished by directing
compressed air and/or high-pressure water through the coil
stack 26 via the flue gas vent 50 (see FIG. 1) after the
burner unit 24 is removed from the combustion chamber, as
will be explained below in more detail with reference to FIG.
4.
As explained above, the coil stack support beam 34 is
connected to the combustion chamber wall 32 by the
interconnected conduit 74a, welded to a circular opening in
an outer side of one end of the combustion chamber support
beam 34 (see FIG. 1), and the conduit 74b welded to a
circular opening in a bottom of the coil stack chamber wall
32 to permit the coil stack chamber to be removed, if
required. A plurality of fasteners 78 connect the coil stack
chamber wall 32 to the coil stack support beam 34, as will be
explained below in more detail with reference to FIG. 3.
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FIG. 3 is a schematic cross-sectional view of the fluid
heater wall construction in accordance with the invention,
taken along line 3-3 of FIG. 2. As explained above, both the
combustion chamber wall 30 and the coil stack chamber wall 32
are constructed of a 2"x6" rectangular steel tubing 80.
Fluid 90 to be heated is circulated through the combustion
chamber wall 30, the coil stack support beam 34 and the coil
stack chamber wall 32, as explained above with reference to
FIG. 1. In one embodiment of the fluid heater 20, a channel
iron 86 is welded along an outer edge of a top of the coil
stack support beam 34 to removably support a bottom edge of
the coil stack chamber wall 32. As will be explained above,
the fasteners 78 retain the bottom of the coil stack chamber
wall in the channel iron 86. In one embodiment, the latches
receive bolts 79 that are removed when the coil stack chamber
wall must be removed from the fluid heater 20.
FIG. 4 is a schematic rear elevational view of the fluid
heater 20 shown in FIG. 1, with the combustion unit 24
removed for maintenance. When the combustion unit 24
requires maintenance or the coil stack 26 requires cleaning,
the combustion air supply pipe 61 (see FIG. 1) is
disconnected from a combustion air inlet 25, which will be
described below with reference to FIG. 10. Fasteners that
connect the combustion unit 24 (not shown) to the fluid
heater 20 are then removed and the combustion unit 24 is
removed from the fluid heater 20. Since the floor 28 and
walls 30 of the combustion chamber are all constructed of
steel continuously cooled by the fluid being heated, and the
combustion chamber is not lined with refractory cement or
other insulation material, the only maintenance required in
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the combustion chamber is occasional ash removal. With
respect to the combustion unit 24, the ceramic cones 54a-54d
occasionally require replacement and nozzles of the burner
heads 52a-52d require the maintenance well known in the art.
However, this maintenance is readily and quickly accomplished
after the burner unit 24 is removed from the fluid heater 20.
FIG. 5 is a schematic diagram of a top plan cross-
section of an exemplary construction for the combustion
chamber floor 28 of the fluid heater 20, showing an exemplary
flow path through the floor 28 for fluid to be heated. As
explained above, the floor 28 is constructed of a plurality
of rectangular steel tubings 80 that are edge-welded together
to construct a flat floor that is about 2" thick. A 6" long
rectangular slot 94 is cut in opposite sides of each end of
the sidewalls of the rectangular tubings 80, to form a flow
path 94 between the adjacent rectangular steel tubings 80
after they are edge welded together. A steel plate 95 is
welded across the respective open ends of the rectangular
steel tubings 80. The inlet pipe 40 is welded to a 3"
(7.5cm) circular hole cut in one side of the bottom of the
floor 28, as explained above with reference to FIG. 1. The
position and orientation of the inlet pipe 40 permits all
fluid to be drained from the fluid heater 20 to prevent
damage due to freezing or corrosion after a fluid heating job
is completed. A rectangular slot is cut in an opposite top
side of the floor 28 and the conduit 42 is welded to a
perimeter of that rectangular slot to provide fluid
communication with the fluid flow path through the combustion
chamber wall 30, as explained above with reference to FIG. 1.
The fluid 90 to be heated is pumped through the inlet pipe 40
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and circulates at a substantially constant flow rate through
the circuitous path shown until it flows through the conduit
42 and enters a bottom of the combustion chamber wall 30 (see
FIG. 1).
FIG. 6 is a schematic diagram of an end of the
combustion chamber wall 30 shown in FIG. 1, adjacent one side
of the combustion unit 24 of the fluid heater 20. The
combustion chamber wall 30 is shown partially cut away to
illustrate the fluid flow path through the wall. As
explained above, fluid leaves the floor 28 via the conduit 42
and enters a bottom of the combustion chamber wall 30. The
rectangular steel tubings 80 are edge-welded together to form
the combustion chamber wall 30. Rectangular slots 96 that
are about 6" (15cm) long are cut in the sidewalls of adjacent
rectangular steel tubings 80 to provide a flow path between
the respective rectangular steel tubings 80. At a top of the
combustion chamber wall 30, the fluid to be heated enters the
coil stack support beam 34 (not shown).
FIG. 7 is a schematic diagram of an end of the
combustion chamber wall 30 shown in FIG. 1 remote from the
combustion unit 24 of the fluid heater 20, showing the
combustion chamber wall 30 partially cut away to illustrate
the fluid flow path around those corners of the wall 30. As
can be seen, the corners are mitered and butt-welded to
provide an uninterrupted flow path around the corner for the
fluid 90 to be heated. This same construction is used for
the corners of the coil stack chamber 32, with the exception
of one corner, which is a reverse-flow corner shown in FIG. 9
and described below.
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FIG. 8 is a schematic diagram an end of the combustion
chamber wall 30 shown in FIG. 1 adjacent the opposite side of
the combustion unit 24 of the fluid heater 20, showing the
wall partially cut away to illustrate a fluid flow path
through the wall 30. This side of the combustion chamber
wall 30 is constructed essentially the same as the opposite
side shown in FIG. 6, except that the slots 96 are cut in
opposite sidewalls of each rectangular steel tubing 80.
FIG. 9 is an isometric diagram of a reverse-flow corner
of the coil stack chamber wall 32 of the fluid heater 20
shown in FIG. 1. In one embodiment of the fluid heater 20,
the reverse flow corner is located above the fluid conduit
42. As explained above, the fluid to be heated enters a
bottom of the coil stack chamber wall through the conduit 74b
(see FIGs. 1 and 2). In the reverse flow corner, the
rectangular steel tubings 80 are mitered as explained above.
However, a steel plate 98 is welded between the mitered ends
to block fluid flow between those ends. Otherwise, the
reverse-flow corner is constructed on one side as shown in
FIG. 6 and on the other side as shown in FIG. B.
As seen in FIGs. 6-9, the fluid to be heated travels a
circuitous path through the walls of the fluid heater 20
around the combustion chamber wall 30 and the coil stack
chamber wall 32 at a substantially constant velocity due to
the consistent cross-sectional area of the flow path.
Although not shown, a rectangular slot 96 is cut in the
bottom side of the coil stack support beam'34 to provide a
fluid flow path from the top rectangular steel tubing 80 in
the combustion chamber wall 30. Alternatively, a conduit (not
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shown) is used to provide a fluid path from the combustion
chamber wall 30 to the coil stack support beam. A partition
(not shown) is butt-welded in the mitered corner of the coil
stack support beam 34 between the two rectangular slots, in a
similar way to that described above with reference to FIG. 9.
FIG. 10 is a schematic diagram of an outer side of an
exemplary combustion unit 24 for the fluid heater 20. As
explained above with reference to FIG. 1, in this embodiment
the combustion unit 24 includes four burners 52a-52d mounted
to an outer wall 101 of the combustion unit 24. Each burner
52a-52d is supplied with pressurized fuel from one of the
fuel preheating chambers 55a, 55b (see FIG. 1) by a fuel line
102a-102d. The fuel is supplied from a fuel tank, as will be
explained below with reference to FIG. 13, by a fuel supply
line 104. A fitting 106 branches to a fitting 108 which is
connected to the fuel preheating chamber 55a. A similar
fitting 108 connects the fuel line 104 to the fuel preheating
chamber 55b. Fittings 110 connect the respective fuel lines
102a-102d to the respective fuel preheating chambers 55a,
55b.
As will be understood by those skilled in the art, a
waste fuel burner requires some way of igniting the burners
52a-52d. Consequently, the burner unit 24 includes a gaseous
fuel ignition system, in one embodiment a propane ignition
system. Propane fuel is supplied via a propane fuel line 112
connected to a propane fuel tank and regulator (not shown).
Fittings 114 branch to propane burner fuel supply lines 116
connected to propane burners 118, which are secured to ports
120a-120d that respectively support the propane burners 118a-
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118d in an orientation so that flame output from the
respective propane burners 118a-118d is directed into the
respective ceramic cones 54a-54d (see FIG. 1). Once the
respective burners 52a-52d are ignited, the propane burners
118a-118d are extinguished.
Combustion air is supplied to the combustion unit 24
through the combustion air input 25 to a combustion air
distribution chamber 125 connected to a combustion air
distribution box 122. In the one embodiment, the combustion
air distribution box 122 is a 3"x8" (7.5cm x 20cm)
rectangular steel tubing. As explained above, the combustion
air supply pipe 61 connects to the combustion air input 25.
Pressurized combustion air is supplied from the combustion
air distribution box 122 to the respective burners 52a-52d by
respective combustion air supply lines 124a-124d. A volume
of compressed combustion air that is substantially equal to
the volume delivered collectively to the burners 52a-52d is
delivered by rectangular combustion air supply channels 126a-
126c (in one embodiment 6"x2" (15cm x 5cm) steel channels
welded to the combustion chamber wall 101) to the hollow
combustion unit floor 62, as explained above with reference
to FIG. 1. The combustion wall 101 and the combustion unit
floor 62 are thus further cooled by the combustion air, while
the combustion air is preheated to improve efficiency of the
waste fuel burn. Steel plates 121 welded to opposite ends of
the combustion air distribution box 122 and the combustion
unit floor 62 provide rigidity required to permit the
combustion unit 24 to be removed from the fluid heater 20,
and handled as required.
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FIG. 11 is a schematic cross-sectional diagram of one
embodiment of the fuel preheater 55a of the combustion unit
24. The fuel preheater 55b is identically constructed. As
described above, fitting 108 connects the pressurized fuel
supply line 104 to the fuel preheater 55a. A fuel delivery
line 132 delivers fuel 130 to a bottom of a fuel preheating
chamber. The fuel rises as it is heated and exits through
fitting 110 to a fuel line 102a-102b. The fuel preheater 55a
is a box constructed of steel plate. The front of the fuel
preheater 55a is formed by the outer wall 101 of the
combustion unit 24. A steel plate 134 is welded diagonally
across the steel box to divide it into two chambers, the fuel
preheating chamber and an insulation chamber that is filled
with ceramic fire cement 136 to prevent the fuel from
overheating. A sight tube 138 pierces the front wall 101,
the steel plate 134 and a rear wall 103 of fuel preheater
55a. The sight tube optionally has a cover 140 pivotally
supported by a pivot pin 142. The sight tube 138 permits an
operator of the combustion unit 24 to observe the combustion
chamber of the fluid heater 20.
FIG. 12 is a schematic front end elevational view of the
fluid heater 20 shown in FIG 4, with the combustion unit 24
in an operative position. In one embodiment, the fluid
heater 20 has a panel 150 hinged to a side of the combustion
chamber floor 28 by one or more hinges 152. When not in use
and during transport, the panel 150 covers the outer side of
the combustion unit 24 to protect the burners 52a-52d, fuel
lines 104, 112, etc. The panel 150 is secured in the closed
position by latches (not shown).
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FIG. 13 is a schematic side elevational view of the
fluid heater 20 mounted to a truck bed 200, equipped with a
fuel tank 202 in accordance with a further aspect of the
invention. Since the fluid heater 20 is designed to burn
used engine oil, and since such fuels have to be preheated in
order to sustain combustion, the fuel tank 202 in accordance
with the invention is designed to heat the fuel above a
required combustion temperature, i.e. 140 F for waste engine
oil. Consequently, an insulated heater line 210 is connected
to hollow sealed tube 212 constructed of a 5" (12.5cm) steel
tube (not shown) welded inside the hollow sealed tube 212,
which is 6" (15cm) in diameter. The hollow sealed tube 212
extends through a bottom of the fuel tank 202. The insulated
heater line 210 is equipped with fittings for connecting it
to the engine cooling system of a truck engine (not shown) of
a truck with the truck bed 200. The insulated heater line
210 is filled with engine coolant fluid that is circulated
through an annular space between the inner tube and the
hollow sealed tube 212 when the truck engine is operating. A
return line (not shown) forms an endless loop with the engine
cooling system. A side port inlet (not shown) at one end of
the hollow sealed tube 212 inside the tank extends through
the annular space between the hollow sealed tube and the
inner tube and delivers fuel from the fuel tank 202 to the
inner tube. The fuel supplied to the burners 52a-52d enters
the inner tube through the side port. The fuel travels
through the inner tube and is preheated to about 140 F before
it enters a fuel supply line (not shown) that is in turn
connected to the fuel supply line 104 of the combustion unit
24. In one embodiment of the invention, the fuel tanks 202
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and 204 are pressurized with compressed air to deliver fuel
to the burners 52a-52d at the desired 80 psi. For clarity of
illustration, none of the auxiliary equipment such as the
blower 60, etc. is shown in FIG. 13.
In summary, as explained above, during use of the fluid
heater 20: fluid to be heated is pumped in through the inlet
pipe 40; follows the circuitous path through the combustion
chamber floor 28; enters the combustion chamber wall 13
through the conduit 42; follows the circuitous path through
the combustion chamber wall and enters the coil stack support
beam 34; circulates through the coil stack support beam 34
and enters the coil stack chamber wall 32 through the
conduits 74a, 74b; follows the circuitous path through the
coil stack chamber wall 32 to the tubular conduit 44 where
the fluid enters the top of the coil stack 26 and circulates
down through the coil stack 26 to the outlet pipe 46 where it
is returned to the storage tank (not shown). Flue gas 220
produced by fuel combusted by the combustion unit 24 is
exhausted through a top of the coil stack cover 160.
Consequently, all surfaces of the fluid heater 20 that are
directly exposed to flame are continuously cooled by the
fluid to be heated. As a result, the only maintenance
required for all components except the combustion unit 24 is
the removal of ash as required. As explained above, this is
readily accomplished using compressed air and/or water after
the combustion unit 24 is removed. If the coil stack 26 ever
requires more thorough maintenance, the coil stack chamber
wall 32 can be removed by disconnecting the fasteners 78 and
the conduit joint 76 and hoisting coil stack chamber wall 32
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CA 02651787 2009-07-31
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off of the fluid heater 20 to provide full access to the coil
stack 26.
Although the invention has been described with reference
to specific embodiments in which specific configurations of
tubing have been used, it will be understood in the art that
a fluid heater in accordance with the invention can also be
constructed using cylindrical, hexagonal or octagonal tubing,
or any combination of square, rectangular, round, pentagonal,
hexagonal or octagonal tubing without departing from a spirit
or scope of the invention.
Furthermore, although the invention has been described
with specific reference to a portable fluid heater, the fluid
heater in accordance with the invention is equally adapted
for use in stationary applications and provides all of the
above-noted advantages of being robust and easily maintained
whether it is used for a stationary or a portable
application.
The embodiments of the invention described above are
therefore intended to be exemplary only. The scope of the
invention is intended to be limited solely by the scope of
the appended claims.
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