U.S. patent application number 15/980047 was filed with the patent office on 2019-11-21 for once-through steam generator for use at oilfield operation site, and method.
The applicant listed for this patent is Propak Systems Ltd.. Invention is credited to Mitchell Galvin, Derek Law, Jonathan J. Wiersma.
Application Number | 20190353344 15/980047 |
Document ID | / |
Family ID | 68532481 |
Filed Date | 2019-11-21 |
View All Diagrams
United States Patent
Application |
20190353344 |
Kind Code |
A1 |
Law; Derek ; et al. |
November 21, 2019 |
ONCE-THROUGH STEAM GENERATOR FOR USE AT OILFIELD OPERATION SITE,
AND METHOD
Abstract
A once-through steam generator for use at an oilfield operation
site includes: a control module having an enclosure including
controls for operating the steam generator, a radiant module
including a radiant chamber, and a convective module including an
economizer heat exchanger. The enclosure is erected prior to
transportation to the operation site.
Inventors: |
Law; Derek; (Airdrie,
CA) ; Galvin; Mitchell; (Airdrie, CA) ;
Wiersma; Jonathan J.; (Airdrie, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Propak Systems Ltd. |
Airdrie |
|
CA |
|
|
Family ID: |
68532481 |
Appl. No.: |
15/980047 |
Filed: |
May 15, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F22B 29/06 20130101;
F22B 37/68 20130101; F22D 1/003 20130101; F22B 35/10 20130101 |
International
Class: |
F22B 29/06 20060101
F22B029/06; F22B 35/10 20060101 F22B035/10; F22D 1/00 20060101
F22D001/00; F22B 37/68 20060101 F22B037/68 |
Claims
1. A once-through steam generator for use at an oilfield operation
site, the steam generator comprising: a control module supported by
a first steel frame and having an enclosure comprising controls for
operating the steam generator, the enclosure being erected prior to
transportation to the operation site; a radiant module supported by
a second steel frame and comprising a radiant chamber having a
burner installed at an end thereof, the burner being configured to
provide a heat transfer of between about 80 million Btu/h and about
200 million Btu/h; a convective module comprising an economizer
heat exchanger, and wherein the radiant module supported by the
second steel frame is transportable separately from the control
module supported by the first steel frame.
2. (canceled)
3. The steam generator of claim 2, wherein the enclosure is
configured to accommodate the burner.
4. (canceled)
5. The steam generator of claim 1, wherein the radiant module
further comprises at least one water conduit and at least one steam
conduit, said conduits being external to the radiant chamber.
6. The steam generator of claim 5, wherein one or more of the
conduits comprise: an electrical heating element disposed thereon,
and a thermal insulation layer covering the conduit and the
electrical heating element.
7. (canceled)
8. The steam generator of claim 1, wherein each steel frame is
configured to be installed on a plurality of steel piles.
9. The steam generator of claim 1, wherein each of the control
module and the radiant module is installed on the respective steel
frame prior to delivery to the operation site.
10. The steam generator of claim 1, wherein the enclosure has an
insulated interior sized to accommodate at least one worker.
11. A method of installing a once-through steam generator at an
oilfield operation site, the method comprising: providing each of:
a control module supported by a first steel frame and having an
enclosure comprising controls for operating the steam generator,
the enclosure being erected prior to transportation to the
operation site, a radiant module supported by a second steel frame
and comprising a radiant chamber having a burner installed at an
end thereof, the burner being configured to provide a heat transfer
of between about 80 million Btu/h and about 200 million Btu/h, a
convective module comprising an economizer heat exchanger, wherein
the radiant module supported by the second steel frame is
transportable separately from the control module supported by the
first frame; and installing the control module, the radiant module
and the convective module at the operation site.
12. The method of claim 11, wherein said providing further
comprises: transporting each of the control module, the radiant
module and the convective module to the operation site.
13. The method of claim 12, further comprising, prior to said
transporting: testing said controls for operating the steam
generator.
14. The method of claim 11, further comprising, prior to said
installing: forming a foundation in ground at the operation
site.
15. The method of claim 14, wherein the foundation comprises an
array of steel piles.
Description
FIELD OF THE INVENTION
[0001] The subject application generally relates to steam
generation for oilfield operations, and in particular to a
once-through steam generator for use at an oilfield operation site,
and a method.
BACKGROUND OF THE INVENTION
[0002] In the field of enhanced oil recovery, steam generators are
used to generate high pressure steam for injection into underground
oil reservoirs for recovery of heavy crude oil. In particular, the
high pressure steam is injected into a first horizontal wellbore
drilled into an oil reservoir to heat the oil and to reduce its
viscosity. The heated oil flows downward by gravity and enters a
second horizontal wellbore situated below the first wellbore, where
it is pumped to the surface. This approach is referred to as
steam-assisted gravity drainage (SAGD).
[0003] A commonly-used type of steam generator in SAGD systems is
the once-through steam generator (OTSG), which comprises a feed
water circuit that follows a continuous, serpentine path through a
radiant chamber into which heat energy is directed. The heat energy
converts the water into high pressure steam as it passes through
the circuit.
[0004] Once-through steam generators have been previously
described. For example, U.S. Patent Application Publication No.
2014/0262257 to Costanzo et al. describes a small supercritical
OTSG that includes a radiant section with a furnace coil, and a
convection section downstream of the radiant section that includes
a superheater which is fluidically connected to the furnace coil.
The OTSG may optionally be devoid of a steam separator. An
economizer can also be included downstream of the superheater.
Supercritical steam can be generated using the OTSG for use, among
other things, in enhanced oil recovery applications.
[0005] U.S. Pat. No. 8,951,392 to James describes a modular
portable evaporator system for use in steam-assisted gravity
drainage (SAGD) systems having an evaporator, with a sump
comprising an oil skimming weir, a short tube vertical heat
exchanger including an outer shell containing short tubes provided
for lower water circulation rate. The system also has, external to
the evaporator, a compressor compressing evaporated steam from the
tube-side of the heat exchanger and routing to the shell side of
the same exchanger, a distillate tank to collect hot distilled
water, a recirculation pump to introduce liquids from the sump into
the heat exchanger and an external demister protecting the
compressor from liquid impurities. The evaporator receives produced
water from the process into the sump and provides cleaned hot water
to the boiler.
[0006] Improvements are generally desired. It is therefore at least
an object to provide a novel once-through steam generator for use
at an oilfield operation site, and a method.
SUMMARY OF THE INVENTION
[0007] It should be appreciated that this summary is provided to
introduce a selection of concepts in a simplified form that are
further described below in the detailed description. This summary
is not intended to be used to limit the scope of the claimed
subject matter.
[0008] Accordingly, in one aspect there is provided a once-through
steam generator for use at an oilfield operation site, the steam
generator comprising: a control module having an enclosure
comprising controls for operating the steam generator, the
enclosure being erected prior to transportation to the operation
site; a radiant module comprising a radiant chamber; and a
convective module comprising an economizer heat exchanger.
[0009] The radiant chamber may have a burner installed at an end
thereof. The enclosure may be configured to accommodate the burner.
The burner may be configured to provide a heat transfer of between
about 80 million Btu/h and about 200 million Btu/h.
[0010] The radiant module may further comprise at least one water
conduit and at least one steam conduit, said conduits being
external to the radiant chamber. One or more of the conduits may
comprise: an electrical heating element disposed thereon, and a
thermal insulation layer covering the conduit and the electrical
heating element.
[0011] The control module and the radiant module may each be
supported by a respective steel frame. Each steel frame may be
configured to be installed on a plurality of steel piles. Each of
the control module and the radiant module may be installed on the
respective steel frame prior to delivery to the operation site.
[0012] The enclosure may have an insulated interior sized to
accommodate at least one worker.
[0013] In another aspect, there is provided a method of installing
a once-through steam generator at an oilfield operation site, the
method comprising: providing each of: a control module having an
enclosure comprising controls for operating the steam generator,
the enclosure being erected prior to transportation to the
operation site, a radiant module comprising a radiant chamber, and
a convective module comprising an economizer heat exchanger; and
installing the control module, the radiant module and the
convective module at the operation site.
[0014] The providing may further comprise: transporting each of the
control module, the radiant module and the convective module to the
operation site. The method may further comprise, prior to said
transporting: testing said controls for operating the steam
generator.
[0015] The method may further comprise, prior to said installing:
forming a foundation in ground at the operation site. The
foundation may comprise an array of steel piles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Embodiments will now be described more fully with reference
to the accompanying drawings in which:
[0017] FIG. 1 is a side view of a steam-assisted gravity drainage
(SAGD) system comprising a once-through steam generator;
[0018] FIGS. 2A to 2D are isometric, elevation, plan and rear
views, respectively, of the steam generator of FIG. 1;
[0019] FIGS. 3A to 3D are isometric, plan and side elevation views
of a radiant module forming part of the steam generator of FIG.
1;
[0020] FIG. 4 is a sectional view of a radiant chamber forming part
of the radiant module of FIGS. 3A to 3D;
[0021] FIGS. 5A and 5B are isometric and plan views, respectively,
of an evaporator coil forming part of the radiant chamber of FIG.
4;
[0022] FIG. 6 is an isometric view of a skid forming part of the
radiant module of FIGS. 3A to 3D;
[0023] FIGS. 7A to 7G are isometric, plan, front, rear, side
elevational and sectional views of a control module forming part of
the steam generator of FIG. 1;
[0024] FIG. 8 is an isometric view of a skid forming part of the
control module of FIGS. 7A to 7G;
[0025] FIGS. 9A and 9B are sectional end and sectional side views,
respectively, of a portion of a steam output line forming part the
radiant module of FIGS. 3A to 3D;
[0026] FIG. 10 is an isometric view of the steam generator of FIG.
1, installed on a foundation at an operation site; and
[0027] FIG. 11 shows a prior art enclosure partially surrounding a
pair of prior art once-through steam generators.
DETAILED DESCRIPTION OF EMBODIMENTS
[0028] The foregoing summary, as well as the following detailed
description of certain examples will be better understood when read
in conjunction with the appended drawings. As used herein, an
element or feature introduced in the singular and preceded by the
word "a" or "an" should be understood as not necessarily excluding
the plural of the elements or features. Further, references to "one
example" or "one embodiment" are not intended to be interpreted as
excluding the existence of additional examples or embodiments that
also incorporate the described elements or features. Moreover,
unless explicitly stated to the contrary, examples or embodiments
"comprising" or "having" or "including" an element or feature or a
plurality of elements or features having a particular property may
include additional elements or features not having that property.
Also, it will be appreciated that the terms "comprises", "has",
"includes" means "including by not limited to" and the terms
"comprising", "having" and "including" have equivalent
meanings.
[0029] As used herein, the term "and/or" can include any and all
combinations of one or more of the associated listed elements or
features.
[0030] It will be understood that when an element or feature is
referred to as being "on", "attached" to, "connected" to, "coupled"
with, "contacting", etc. another element or feature, that element
or feature can be directly on, attached to, connected to, coupled
with or contacting the other element or feature or intervening
elements may also be present. In contrast, when an element or
feature is referred to as being, for example, "directly on",
"directly attached" to, "directly connected" to, "directly coupled"
with or "directly contacting" another element of feature, there are
no intervening elements or features present.
[0031] It will be understood that spatially relative terms, such as
"under", "below", "lower", "over", "above", "upper", "front",
"back" and the like, may be used herein for ease of description to
describe the relationship of an element or feature to another
element or feature as illustrated in the figures. The spatially
relative terms can however, encompass different orientations in use
or operation in addition to the orientation depicted in the
figures.
[0032] Turning now to FIG. 1, a steam-assisted gravity drainage
(SAGD) system is shown, and is generally indicated by reference
numeral 20. SAGD system 20 comprises a once-through steam generator
(OTSG) 22 installed at an operation site 24 on ground surface that
is generally proximate an underground oil reservoir 26. The steam
generator 22 is configured to generate high pressure steam for
injection into the oil reservoir 26 for recovery of heavy crude
oil. The SAGD system 20 has a feed water supply 28, which provides
water to the steam generator 22 for generating a supply 32 of high
pressure steam. The high pressure steam is conveyed to a steam
injection wellhead 34, which pumps the high pressure steam into the
ground via a first horizontal wellbore 36 located in in the
vicinity of the oil reservoir 26. Steam flux 38 exits the first
horizontal wellbore 36 and heats heavy crude oil in the oil
reservoir 26, thereby rendering the heavy crude oil less viscous. A
mixed flux 42 of heavy crude oil and water flows downward by
gravity, and enters a second horizontal wellbore 38 located below
the first horizontal wellbore 44, from which it is pumped to the
surface by a recovery wellhead 46. The recovery wellhead 46
provides an output 48 comprising the mixture of heavy crude oil and
water for subsequent separation and processing.
[0033] The steam generator 22 may be better seen in FIGS. 2 to 10.
The steam generator 22 has a modular design, and comprises a
control module 52, a radiant module 54, and a convective module 56.
Each of the control module 52, the radiant module 54, and the
convective module 56 is fabricated separately at a manufacturing
site (not shown) distant from the operation site 24, and is
transported separately in a prefabricated state from the
manufacturing site for installation at the operation site 24.
[0034] The control module 52 comprises an enclosure 60 in the form
of an insulated building that is supported by a skid 64 in the form
of a steel frame. The steel frame comprises a plurality of steel
beams that are joined by one or more of bolts, rivets and welds to
provide the skid 64. The enclosure 60 is erected prior to
transportation to the operating site 24, and defines an insulated
interior space 66 that is accessible to workers for accessing
controls and instruments associated with operation of the steam
generator 22.
[0035] The control module 52 comprises a main feed water supply
line 68, which conveys water from the feed water supply 28 to the
radiant module 54. The control module 52 also comprises a glycol
supply line 72 and a glycol return line 74, which convey glycol to
and from a heater 76 for heating the interior space 66, a
pressurized air line 78 for supplying pressurized air to activate
the controls and instruments of the enclosure 60, and a cooling
water supply line 82 and a cooling water return line 84, which
convey water to and from a steam testing station 86 for cooling
steam samples for testing. The control module 52 further comprises
a fuel gas supply line 88, which conveys fuel gas from a fuel gas
source (not shown) to a burner 90 for combustion. The control
module 52 also comprises an air preheater 92, a preheated air duct
94 and a preheated air blower 96, which are configured to provide
heated air to the burner 90, where it is combined with the fuel gas
and burned to yield a heated flux including heat energy and
combustion products. In this embodiment, the burner 90 is sized to
provide a heat transfer of between about 80 million Btu/h and about
200 million Btu/h. The air preheater 92, the preheated air duct 94
and the preheated air blower 96 are positioned on an exterior
platform 98 supported by the skid 64, external to the enclosure
60.
[0036] In the embodiment shown, the enclosure 60 has a removable
panel 102 disposed on a wall facing the radiant module 54. The
removable panel 102 is configured to be removed to allow the burner
90 to be accommodated in an area 104 of the interior space 66, upon
installation of the control module 52 and the radiant module 54 at
the operation site 24.
[0037] The radiant module 54 comprises an elongate radiant chamber
106 that is supported by a skid 108 in the form of a steel frame.
The steel frame comprises a plurality of steel beams that are
joined by one or more of bolts, rivets and welds to provide the
skid 108. The burner 90 is mounted at a first end of the radiant
chamber 106, and is configured to direct the heated flux through
the interior of radiant chamber 106 toward the convective module
56. The radiant chamber 106 comprises a cylindrical housing 112
that surrounds an annular evaporator circuit 114 that extends
generally the length of the radiant chamber 106. The annular
evaporator circuit 114 comprises a pair of tubes 116 and 118 that
are arranged in a serpentine manner within an annular volume to
define a longitudinal passage 122, through which the heated flux
flows. The radiant chamber 106 has an exhaust duct 124 at a second
end thereof, which is configured to convey the heated flux to the
convective module 56.
[0038] The radiant module 54 comprises a main feed water supply
line 128 exterior to the radiant chamber 106, which is configured
to be connected to the main feed water supply line 68 of the
control module 52. The main feed water supply line 128 splits into
a first feed water supply line 132 and a second feed water supply
line 134. Each of the first and second feed water supply lines 132
and 134 is configured to be connected to a respective one (1) of
two (2) economizer water circuits (not shown) forming part of an
economizer heat exchanger (not shown) housed in the interior of the
convective module 56. As will be understood, heated flux flowing
from the radiant chamber 106 into the convective module 56 passes
over the economizer water circuits, thereby preheating the water.
As will be understood, splitting the feed water into first and
second feed water supply lines 132 and 134 increases the surface
area exposed to the heated flux, and thereby increases the heat
transfer efficiency of both the radiant module 54 and the
convective module 56.
[0039] The convective module 56 comprises an enclosure 136 that is
in fluid communication with the exhaust duct 124 of the radiant
chamber 54. As noted above, the interior of the enclosure 136
houses the economizer heat exchanger, which is configured to
preheat water flowing through the first and second feed water
supply lines 132 and 134 using the heated flux flowing from the
radiant chamber 106. The enclosure 136 is also in fluid
communication with a stack 138, which is configured to discharge
the heated flux to atmosphere.
[0040] Turning again to the radiant module 54, the radiant module
54 comprises a first preheated water line 142 and a second
preheated water line 144, each of which has a first end that is
configured to be connected to a respective one of the economizer
water circuits arranged in the enclosure 136 of the convective
module 56. Second ends of the first and second preheated water
lines 142 and 144 are connected to inputs 116a and 118a of the
tubes 116 and 118 of the annular evaporator circuit 114, and each
convey preheated water into the radiant chamber 106, in which the
preheated water flowing therethrough is converted to high pressure
steam.
[0041] The radiant module 54 further comprises a first steam output
line 152 and a second steam output line 154, which are connected to
outputs 116b and 118b of the annular evaporator circuit 114 and
which each convey high pressure steam generated in the radiant
chamber 106. The first and second steam output lines 152 and 154
are combined into a single steam output line 156, which is
configured to be connected to a main steam line 158 of the control
module 52.
[0042] At least some of the external water lines and steam lines of
the control module 52 and the radiant module 54 are heated and
insulated, or "winterized", to provide protection against freezing.
For example, FIGS. 9A and 9B show a portion of the steam output
line 156, which comprises a conduit in the form of a pipe 158
through which the high pressure steam is conveyed, electric heat
tracing in the form of one or more electrical heating elements 162
fastened to an outer surface of the pipe by bands 164, and a
thermal insulation layer 166 covering the pipe 158 and the one or
more electrical heating elements 162 and the bands 164. In the
example shown, there are three (3) electrical heating elements 162
fastened to the pipe 158, and the bands 164 are segments of
fiberglass tape; however other suitable fasteners may alternatively
be used. In this embodiment, each of the main feed water supply
line 128, the first and second feed water supply lines 132 and 134,
the first and second preheated water lines 142 and 144, the first
and second steam output lines 152 and 154, the steam output line
156, and the main steam line 158, are "winterized" in the above
described manner. Further, in this embodiment, each of the main
feed water supply line 128, a lower portion of each of the first
and second feed water supply lines 132 and 134, a lower portion of
each of the first and second preheated water lines 142 and 144, the
first and second steam output lines 152 and 154, the steam output
line 156, and the main steam line 158 are "winterized" in the above
described manner at the manufacturing site, prior to transportation
to the operation site 24.
[0043] Returning to the control module 52, the main steam line 158
extends into the interior space 66 of the enclosure 60, and is
connected to one or more controls and instruments for enabling
workers in the enclosure 60 to monitor and control steam output. A
steam output line 168, which is connected to the main steam line
158, conveys steam out of the control module 52 for subsequent use
downstream in the SAGD system 20.
[0044] In use, the control module 52, the radiant module 54, and
the convective module 56 are prefabricated separately. Prior to
transportation, instruments and controls of the steam generator 22
are tested at the manufacturing site. More specifically, the
testing involves testing communication between the instruments and
the control system of the steam generator 22, which are housed in
the enclosure 60, and testing the functionality of one or more of
the instruments. For example, testing of pressure instruments
involves a calibration that comprises an application of pressure
and a resetting of zero and high range readings; testing of
temperature instruments involves checking that ambient temperature
is correctly measured, and confirming failure of each temperature
instrument upon disconnection; testing of control valves involves
auto-calibration of each valve, and stroking of each valve from the
open position to the closed position; and testing of fire detection
systems involves illuminating the interior space 66 with a high
intensity light to simulate a fire. Other testing of instruments
and controls is also carried out at the manufacturing site.
[0045] After testing, the control module 52, the radiant module 54,
and the convective module 56 are each transported separately in a
prefabricated state for installation at the operation site 24.
Prior to installation, an array of steel piles 172, each in the
form of a steel pipe having a square cap plate, is arranged in the
ground at the operation site 24 to collectively provide a
foundation 174. The control module 52 and the radiant module 54 are
then each positioned onto a respective portion of the foundation
174, such that the skid 64 of the control module 52 and the skid
108 of the radiant module 54 each directly contacts ends of the
piles 172. The skids 64 and 94 are then fastened to the piles 172
using one or more of bolts, rivets and welds. The convective module
56 is then installed on the radiant module 54, and the stack 138 is
installed on the enclosure 136. Pipe connections and electrical
connections between any of the control module 52, the radiant
module 54, and the convective module 56 are made, as necessary.
[0046] As will be appreciated, the modular design of the steam
generator 22 allows each of the control module 52, the radiant
module 54 and the convective module 56 to be prefabricated at a
location other than the operation site 24. As will be understood,
this minimizes the amount of field work needed at the operation
site 24, which advantageously reduces the cost associated with
bringing the steam generator 22 to an operational status the
operation site 24, as compared with conventional OTSGs.
Additionally, the modular design of advantageously allows the steam
generator 22 to be rapidly brought to operational status, enabling
the steam generator 22 to be used for production more quickly than
conventional OTSGs.
[0047] As will be appreciated, the prefabricated enclosure 60 of
the control module 52 advantageously eliminates the requirement to
construct a separate enclosure housing instruments and controls at
the operation site, as would otherwise be required for conventional
OTSGs. As will be understood, this feature reduces the cost and
time associated with installation of the steam generator 22 at the
operation site, which allows the steam generator 22 to be used for
production more quickly and at a lower installation cost as
compared to conventional OTSGs.
[0048] Additionally, and as will be appreciated, the prefabricated
nature of the enclosure 60 of the control module 52 allows
instruments and controls of the steam generator 22 to be tested at
the manufacturing site prior to shipping and installation at the
operation site. As will be understood, this ability to pre-test the
instruments and control systems further reduces the cost and time
associated with installation of the steam generator 22 at the
operation site, which allows the steam generator 22 to be used to
generate oilfield production more quickly and at a lower
installation cost as compared to conventional OTSGs.
[0049] As will be appreciated, the "winterization" comprising the
electrical heating elements 162 and thermal insulation layer 166
allow each of the main feed water supply line 128, the first and
second feed water supply lines 132 and 134, the first and second
preheated water lines 142 and 144, first and second steam output
lines 152 and 154, the steam output line 156 and the main steam
line 158 to be located externally of the enclosure 60. As will be
understood, this eliminates the need to provide an enclosure having
what would otherwise be a very large footprint around one or more
of lines 128, 132, 134, 142, 144, 152, 154, 156 and 158 to provide
"winterization" (namely, protection against freezing) of these
external lines.
[0050] Additionally, and as will be appreciated, the steel frame
structure of steam generator 22 allows the skids 64 and 94 to be
supported directly by steel piles 172. As will be understood, the
steel piles 172 may simply be driven to various depths as needed to
compensate for any uneven grade, so as to provide a foundation 174
that is level. This feature advantageously enables the steam
generator 22 to be installed in a quick and facile way on ground
that is not uniformly flat and without requiring excavation.
[0051] Additionally, and as will be understood, the modular design
of the steam generator 22 has a small footprint, which
advantageously eliminates the need for concrete foundations that
are otherwise required to support conventional OTSGs having large,
field-erected enclosures. For example, FIG. 11 shows a conventional
once-through steam generating system 500 that comprises a pair of
conventional OTSGs partially housed in a field-erected enclosure
501 which, owing to the large size and the non-modular design of
the conventional OTSGs, is required to be supported by a
conventional concrete foundation 503. As will be appreciated, such
conventional concrete foundations 503 are costly, and require
additional resources in the field to produce. Additionally, the
field-erected enclosure 501 includes field-erected enclosure
extensions 505 that extend along the sides of radiant chambers 507
of the conventional OTSGs. The field-erected enclosure extensions
505 are otherwise required to provide protection against freezing
to water lines (not shown) and steam lines (not shown) that extend
partially the lengths of and external to the radiant chambers 507,
and which each also require a respective portion 509 of the
conventional concrete foundation 503.
[0052] Although in the embodiment described above, the enclosure 60
has a removable panel 102 disposed on a wall facing the radiant
module for allowing the burner 90 to be accommodated in the
interior space 66, in other embodiments, the enclosure may have
other provisions. For example, in other embodiments, the enclosure
may alternatively be provided with a hinged door, or simply an
opening or other aperture. Still other arrangements may
alternatively be used.
[0053] Although embodiments have been described above with
reference to the accompanying drawings, those of skill in the art
will appreciate that variations and modifications may be made
without departing from the scope thereof as defined by the appended
claims.
* * * * *