Note: Descriptions are shown in the official language in which they were submitted.
CA 02958688 2017-02-22
"INTEGRATED BURNER ASSEMBLY"
FIELD
Embodiments taught herein relate to burner systems for use in
hazardous locations and, more particularly to integrated burner systems having
pre-
assembled components for simplifying installation, certification and supply.
BACKGROUND
Natural draft burners are used in a variety of process apparatus, such
as line heaters, reboilers, heat treaters, free water knockout drums, storage
tanks
and the like, commonly used in the oil and gas industry. One or more natural
draft
burners are supported in a firetube which extends into the vessel for
transferring
heat directly or indirectly thereto for heating fluids therein.
Such equipment is often located on oil and gas sites, or other
industrial sites having the possibility of fugitive hydrocarbons and at which
ignition
sources are carefully controlled.
On-site areas having process apparatus are generally classified as
Class I, Division 2, according to the National Electrical Code (NEC) or NFPA
70, a
regionally adoptable standard for the safe installation of electrical wiring
and
equipment in the United States. A similar code, the Canadian Electrical Code
(CEC)
or CSA C22.1, is a standard published by the Canadian Standards Association
(CSA) pertaining to the installation and maintenance of electrical equipment
in
Canada.
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An area is generally classified in North America as Class l, Division 2
when one of the following conditions exists:
= volatile flammable liquids or flammable gases are handled, processed or
used, but the hazardous liquids, or gases will normally be confined within
closed containers or closed systems from which they can escape only in
event of accidental rupture or breakdown of such containers or systems, or
as a result of abnormal operation of equipment; or
= ignitable concentrations of gases or vapors are normally prevented by
positive mechanical ventilation, and which might become hazardous through
failure or abnormal operations of ventilating equipment; or
= adjacent to a Class l, Division 1 location and to which ignitable
concentrations of gases or vapors might occasionally be communicated
unless such communication is prevented by adequate positive pressure
ventilation from a source of clean air, and effective safeguards against
ventilation failure are provided.
Under the CEC, to operate a fired heater in a Division 2 area, the fired
heater must be totally enclosed, all surfaces exposed to the atmosphere must
operate below the temperature that would ignite a flammable substance present
in
the hazardous area, the combustion air intake and exhaust discharge must be
equipped with a flame arresting device, and electrical components isolated
from the
atmosphere or at an energy level below that required to ignite a specific
hazardous
atmospheric mixture. Otherwise, the fired heater must be located outside the
hazardous area.
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A flame arrestor ensures adequacy of a flow of primary air from the
surrounding atmosphere for burner combustion while preventing propagation of
the
flame from the burner, back along the combustion air source, to the
atmosphere.
The volume within a burner housing to which a flame arrestor has been
installed,
inherently exposed to the burner combustion conditions, is generally
considered a
non-classified area according to the appropriate codes.
It is common practice to utilize burner systems that are connected to
burner management or control systems. Such systems both monitor burner
operation, including the presence of flame, and to ensure safe start-up,
operation
and shutdown of the burners. The burner management system generally comprises
flame-detectors for main burners and pilot burners to ensure the burners are
lit. The
control system is connected to fail-safe mechanisms and solenoid-operated
valves
for shutting off the flow of gas or vapours to the burners should a flame not
be
sensed. The burner control system generally comprises circuitry to re-light
the
burners when safe to do so and may provide communication of data to a data
acquisition system. The control system also acts to modulate the burner flame
intensity based on temperature requirements of the various process apparatus.
In addition to fugitive emissions in the general atmosphere about the
burner system, the burner itself can be a source of combustible vapors. In the
absence of a burner management system, when the flame is not present, gas
could
continue to flow at least to the pilot, irrespective the lack of the flame,
releasing
unburned fuel. Further as the process apparatus begins to demand heat, gas is
also fed to the main burner irrespective of the absence of a flame. Release of
gas,
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from the unlit pilot and main burners, to the atmosphere creates an ignition
or
explosion risk.
Under the various electrical codes, specific wiring requirements are
established for use in hazardous or classified areas such as Class 1, Div 2.
Conventional burner systems, as described above, typically utilize one or more
burners and a control unit. The control unit is wired to the burners for
managing the
burner and for managing the valve train which supplies the gas. The control
unit
and connective wiring generally comprises a complex system of mechanically
protected wiring systems to meet the code. "Mechanically protected" generally
means that, while the electrical equipment is capable of producing sufficient
energy,
such as heat or electrical spark, to ignite an explosive atmosphere, it has
been
mechanically protected or contained so as to prevent the ignition. In the case
of
electrical equipment located in hazardous areas, explosion proof enclosures,
rigid
conduit fittings and hermetic sealing are known methods of mechanical
protection.
In common practice, a burner assembly, flame arrestor, burner
management system or control unit and the valve train are delivered to a site.
Onsite, specialized personnel are employed to electrically connect between the
various components of the system, taking into consideration the necessary
electrical codes, particularly where the combustion unit is to be placed in a
hazardous Class 1, Division 2 area. Once connected, the system must be
inspected onsite to ensure compliance with the various codes. The electrical
connections are many, between various controls, valves and sensors, and each
connection or junction must be in compliance.
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This is a time consuming and expensive system and fraught with re-
work to bring the installation into compliance. Further, if improperly
installed, such
systems present significant hazard to onsite personnel.
Clearly, there is a need for simplified, safe installation procedures for
combustion units and cost effective wiring systems to meet the electrical code
requirements.
SUMMARY
Embodiments of integrated burner assemblies, for use in classified
hazardous areas taught herein, effectively utilize a designated general or non-
classified area classification inside a burner housing to simplify wiring
connections
between various components of a managed burner system. A valve train which
supplies fuel to the burner and a control unit which manages the burner
assembly
and the valve train are mounted external to the burner housing in a classified
area
such as a Class 1 Division 2 hazardous area. Mechanically protected wiring is
used
to connect the valve train and control unit to the non-classified area of the
burner
housing. The wiring connections inside the non-classified area, between the
mechanically protected wiring from the control unit and the burner, and
between the
mechanically protected wiring from the control unit and the mechanically
protected
wiring from the valve train, can be pre-wired, or the final connections wired
in the
field, are open connections free of mechanical protection.
In one broad aspect, an integrated burner system for use in a
classified area comprises a burner housing having a burner assembly, an air
inlet
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end and a combustion end. A flame arrestor is fluidly connected to the air
inlet end
for forming a non-classified area in the burner housing between the burner
assembly and the flame arrestor. A control system is located in the classified
area
external to the burner housing. Mechanically protected wiring extends between
the
control system and the non-classified area of the burner housing. A valve
train, in
the classified area external to the burner housing, supplies fuel to the
burner for
combustion thereat. Mechanically protected wiring extends between the valve
train
and the non-classified area of the burner housing. Electrical connections are
formed
within the non-classified area of the burner housing, between the burner
assembly,
the mechanically protected wiring from the control system and the mechanically
protected wiring of the valve train area.
In another broad aspect, a method for pre-assembly of an integrated
burner system for equipment used in a classified environment comprises
installing a
burner assembly at a combustion end of a burner housing and installing a flame
arrestor at an air intake end of the burner housing forming a non¨classified
area
between the burner assembly and the flame arrester. A control unit, located in
the
classified area, is connected using mechanically protected wiring to the non-
classified area. A valve train, located in the classified area is fluidly
connected to the
burner for supplying fuel thereto. The valve train is connected using
mechanically
protected wiring to the non-classified area. Open electrical connections are
formed
in the non-classified area between the burner assembly, the mechanically
protected
wiring from the control unit and the mechanically protected wiring from the
valve
train.
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In embodiments, the non-classified area forms a first chamber. A
perimeter of the burner housing is extended and a discontinuous barrier is
located
therein for forming a second non-classified chamber. The electrical
connections are
housed in the second non-classified chamber and the barrier acts as a heat
barrier
to minimize damage to the electrical connections in the second chamber.
In embodiments, the second chamber is below the first chamber. A lip
is formed along the discontinuity of the barrier for forming a containment in
the first
chamber for receiving any liquid, such as condensation from the burner,
therein.
The containment prevents the liquid from freely draining into the second
chamber.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1A is a simplified schematic illustrating a burner assembly in a
burner housing and a prior art mechanically protected wiring method for
electrical
connections between a control unit, each of the components of a valve train
supplying fuel to the burner assembly, and the burner assembly itself;
Figure 1B is a schematic illustrating a conventional, prior art
mechanically protected wiring method between a burner housing having a flame
arrestor installed thereto and a valve train, the valve train being installed
in an
explosion proof enclosure separate from the burner housing, and a control unit
external thereto;
Figure 1C is a schematic illustrating a prior art burner system having a
burner housing, and at least portions of the valve train located internal to
an
extension of the burner housing, all connections for each of the valve train
and the
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control unit within the housing being classified as located in a hazardous
area, the
electrical connections therein being mechanically protected connections;
Figure 2A is a schematic illustrating a wiring method according to an
embodiment taught herein, having a control unit pre-wired to a portion of a
non-
classified burner housing and components of a valve train also pre-wired to
the non-
hazardous burner housing, all electrical connections being completed within
the
non-classified burner housing using non-hazardous wiring methods, all pre-
wiring
being mechanically protected wiring methods;
Figure 2B is an overall schematic of the cross-section of the burner
housing and the wiring method of Fig. 2A, the electrical connections being
made
within an perimeter extension of the non-classified area of the burner housing
to
which a flame arrestor has been installed;
Figure 3 is an enlarged side view according to Fig. 2B and illustrative
of example components selected from the valve train and the control unit; and
Figure 4 is an end front view according to Fig. 3, with an end door
supporting the flame arrestor, opened for viewing the electrical connections
housed
in the non-classified area.
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DETAILED DESCRIPTION
PRIOR ART
As shown simplistically in Fig. 1A, all electrical equipment and wiring
located in a Class 1, Division 1 or Division 2 hazardous area is required to
be in
accordance with regulations set forth according to appropriate electrical
codes.
Mechanically protected electrical systems are used. For example, mechanically
protected wiring W between components of the system is run in rigid metal
conduit
or threaded steel intermediate conduit 2. Conduit fittings are suitable for
the
hazardous location. Flexible connections are typically required and, where
crossing
boundaries between classifications, the connections and fittings are sealed S
thereat. Generally, the connections are also liquid tight. Explosion proof
junction
boxes 4 may also be required for effecting electrical connections between
components. Components such as solenoids 6, pressure switches 8 and the like,
used to control and monitor the flow of fuel, are typically hermetically-
sealed units
with electrical leads extending therefrom. Those leads must be terminated in
accordance with the codes.
Others have provided = integrated systems which have a pre-
assembled package including a burner 10 and a flame arrester 12, both of which
are in a housing 14. Further, a burner management system or control unit 16
and a
valve train 18 are included in the package for delivery to the site. Known
systems
however still require mechanically protected wiring methods for use in
hazardous
Class 1, Division 2 locations. On-site, personnel are expected to connect the
valve
train components and control unit, and then certify the system.
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Having reference to Fig. 1B, and in one prior art approach to enable a
level of pre-certification, a model Integral 950 Flame Arrester, from Heating
Solutions International Inc. of Lloydminster, Saskatchewan, Canada, provides
an
explosion-proof, mechanically protected enclosure X provided adjacent the
burner
housing 14 and connected thereto through mechanically protected connections. A
flame arrestor 12 is installed to the burner housing 14. The enclosure X is a
separate enclosure from the burner housing 14. As the enclosure X contains
both
electrical and fuel-handling components of the valve train 18, as well as
wiring W
between the control unit 16 and the burner assembly 10, the environment within
the
enclosure is classified as hazardous under Class 1, Division 2. Therefore, the
system continues to require complex and costly, mechanically protected wiring
methods to be used within the enclosure X, as well as external thereto.
As shown in Fig. 1C, in another series of known pre-assembled
systems available from Kenilworth Combustion of Vermilion, Alberta, Canada,
the
burner housing 14 has the burner 10 and flame arrestor 12 installed thereto.
Components of the valve train 18, including gas/fuel connections, as well as
wiring
connections 20 to the burner 10 and valve train 18 from the control unit 16
are
located within an extension of the burner housing 14 and supported
structurally
therefrom. Again, despite connection of the flame arrestor 12 to the burner
housing
14, the burner housing 14 cannot be considered non-hazardous as it houses both
electrical and fuel-handling components. Thus, the wiring connections 20 both
therein and wiring W external thereto must be in compliance with the complex
electrical requirements of Class 1 Division 2 as described above.
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EMBODIMENTS
As shown in Fig. 2A, embodiments of a burner assembly 22 taught
herein effectively utilize a general or non-classified classification
designated inside
the burner housing 14 to simplify wiring connections 20. The open wiring
connections can be pre-wired, or the final connections wired in the field,
free of
mechanically protected considerations. A control unit 16 is connected to the
burner
housing 14 using mechanically protected methods. Electrical components 24 of
the
valve train 18, for supplying fuel to the burner 10 and the like, located
external to the
burner housing 14, are connected to the burner housing 14 using mechanically
protected methods. Wiring W extends from each of the electrical components 24
and control unit 16, from their respective explosion proof environments, to
the non-
classified area A of the burner housing 14. Further, open electrical
connections 20,
extend from the burner housing 14 to the burner 10, free from mechanically
protected considerations.
The burner housing 14 comprises an air inlet end 26 and a
combustion end 28, the burner 10 being mounted at the combustion end 28 and
the
flame arrestor 12 being mounted to the air inlet end 26. At least the portion
of the
burner housing 14 therebetween is classified as the non-classified area A.
The control unit 16, valve train 18 and electrical components 24
thereof are located external to the burner housing 14, generally in a Class 1,
Division 2 location. Wiring W is supplied from the control unit 16 to the
burner
housing 14 and from the valve train's electrical components 24 to the burner
housing 14, using mechanically protected wiring methods, suitable for Class 1,
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Division 2 locations. The electrical components 24 in the valve train 18 are
typically
hermetically sealed solenoids, pressure switches and the like, already in
compliance with mechanically protected requirements.
The wiring W, received at the non-classified burner housing 14 from
the control unit 16 is readily connected therein, such as at a terminal block
B, to the
burner 10 and an ignition unit 28 and to other wiring W received from the
electrical
components 24 using simplified wiring methods suitable for non-classified or
non-
hazardous areas. Thus, overall, the electrical wiring is simplified compared
to the
prior art systems shown in Figs. 1A to 1C and the resulting costs reduced.
The burner system 22 can be pre-assembled, pre-wired, pre-tested,
and inspected prior to delivery onsite. Once onsite, personnel need only mount
the
system 22 to the onsite equipment, connect the control unit 16 to a source of
power
and connect the valve train 18 to a source of fuel. Wiring at the terminal
blocks B
can remain as pre-wired, or be finalized, or revised, such work being
performed in
the non-classified area of the burner housing 14, without a concern for
disturbance
of any individual mechanically protected connections.
Having reference to Figs. 2B, 3 and 4, in an embodiment, the burner
housing 14 is a first non-classified chamber 30 for housing the burner 10
therein.
An example of the system can include a natural draft burner assembly.
The burner housing 14 is extended to form a second non-classified
chamber 32 connected to the first chamber 30. The second non-classified
chamber
32 is used for housing the wiring connections 20 therein. A door 34 is hinged
to the
burner housing 14 to cover an access opening 36 in the burner housing 14 for
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enclosing both the non-classified first and second chambers 30,32. A flame
arrester 12 is pre-installed in the door 34 of the burner housing 14. A gasket
38,
best seen in Fig. 4, is connected to seal between the door 34 and the burner
housing 14. In embodiments, the gasket 38 is a tadpole gasket riveted to the
burner housing 14 to surround the access opening 36.
A heat barrier 40 is formed between the first and second chambers
30,32 to minimize damage to the wiring connections 20 as a result of heat from
the
burner 10. The heat barrier 40 is discontinuous therebetween, maintaining the
non-
classified designation therebetween. In an embodiment, the heat barrier 40
forms a
gap 42 between the access opening 36 and a front end 44 of the heat barrier
40.
Further, in embodiments having the second chamber 32 located below
the first chamber 30, an upwardly extending lip 46 is formed about the
discontinuity,
forming a containment C in the first chamber 30 to receive and accumulate
liquid
therein. Liquid present therein is generally as a result of condensation from
the
burner 10. The containment C acts to prevent the liquid from freely draining
into the
second chamber 32 and mitigates risk of contact with the wiring connections 20
therein. In an embodiment, the upwardly extending lip 46 is formed along the
heat
barrier's front end 44 to form the containment C.
Combustion air is generally admitted through a plurality of
passageways 48 formed in a flame cell 50 of the flame arrester 12 to provide a
source of primary air for the burner 10. Flame propagation from the burner
housing
14, to the atmosphere without, is prevented by the plurality of passageways 48
of
the flame cell 50. Applicant understands the passageways cause a reduction in
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flame generated heat therein, thereby extinguishing any flame. Once installed,
the
flame arrester 12 is tested using standard API flame testing.
The ignition unit 28 for controlling ignition of the burner 10, including a
pilot burner, is also housed within the second chamber 32. Wiring WI to one or
more
igniters generally passes through the heat barrier 40 using the simplified
wiring
methods for non-classified areas and can be protected using liquid tight
fittings as
the ignition wiring W1 passes through the containment C.
Fuel lines F connecting the valve train 18 to the burner 10 are not
routed through the second chamber 32, thereby maintaining the second chamber
32 as a non-classified area. Further, unlike the prior art, piping, regulators
and the
like which handle the passage of fuel through the valve train 18 are located
external
to the second chamber 32 for maintaining the second chamber 32 as a non-
classified area.
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