Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND DISCUSSION
Increased emphasis in recent years on the energy
efficiency of industrial processes has led to efforts to
partially recover the enormous expenditures of energy
required in paint finishing operations on automotive pro~
duction lines. Such energy recovery efforts are coupled
with increasingly stringent requirements ~o reduce the pol- ~;
lutants produced by such industrial processes.
One aspect of the paint finishing operation which
consumes a particularly heavy share o the total energy re-
quired is the paint curing oven, wherein the painted surfaces
are cured after application of the paint by being passed
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through ovens hav:ing radiator surfaces heated by the use of
gas or other fuel-fired heaters.
Traditionally, the products of combustion in a fuel~
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fired heater would be individually vented or exhausted through
the atmosphere passing upwardly and through the roof of the
factory. Many modern large automotive manufacturing facilities ~ -~
having a large number of paint curing oven heaters space them
along the length of the curing oven. The individual venting
of each heater represents a considerable expense since the
roof must be penetrated for each vent and flashing and other
hardware installed. The resultant installations are also ex~
pensive to maintain. -~
The shop area around the ovens must also be venti-
lated since the radiation of heat from the ovens is consid-
erable, and also some leakage of fumes is inevitable, thus
requiring additional roof vents.
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In addition, if any filtering or other treatment
of the exhaust gas is required, the number of individual
treatment installations would render the treatment of the
exhaust gases impractical or inordinately expensive.
If ~he recovery of the heat energy in the exhaust gases were
attempted by collection of the gases into a common ductwork,
the len~th of such installation, as well as the relatively
high temperature of these exhaust gases, i.e., 300-750F,
would entail considerable capital expense, This is in part due
to the need to provide a costly and complex ducting system,
since such ductwork should be insulated to minimize the
substantial heat loss which would otherwise occur due to the
relatively elevated temperature of the exhaust gas. Also~ the
consid~rable thermal contraction and ex ansion of ~the ducting ~ ~ -
undergoing such wide temperature variations indirectly receiv-
ing such hot gases req~ires the use of elaborate thermal
expansion compensating connections.
Finally, the need to maintain the proper back pres~
sure in each exhaust stack, while compensating for changes
in flow which would occur by shutting off individual hsaters,
creates the need for costly flow balancing dampers in the ;
duct system. ;;
There are many other lower grade heat sources in
industrial installations from which additional heat energy
could be potentially recovered. However, the potential energy
may be insufficient to justify the capital expenditure. For
example~ the air above the paint curing ovens is generally
heated by radiation to relatively modest temperature levelsr
i.e., of 95F. As another example, cascade body coolers are
commonly employed in which air is successively recirculated in
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stages over the vehicle car bodies as they pass through the
cooler. The air is then exhausted to the atmosphere at a
temperature well above ambient levels, but much cooler than
the heater exhaust gases.
Accordingly, it is an object of the present inven-
tion to provide a relatively low cost ducting system for the
recovery of heat contained in relatively high temperature
gases such as e~haust gases from fuel-fired heaters such as
are in paint curing ovens.
It is another object of the present invention to -
provide such a ducting system which also provides for the
simultaneous recovery of heat energy from relatively lower
grade heat sources.
It is a further object of the present invention
to provide such a heat recovery system for a paint curing `
oven which also acts to prevent leakage from the oven interior ~ ~-
and thereby reduces the ventilation requirements~ for instal-
lations within a shop building.
SUMMARY OF THE INVENTION
These and other objects of the present invention,
which will become apparent upon a reading of the following
specification and claims, are achieved by drawing the hot
exhaust gases into a large cross sectional area collector
duct passing over the paint curing ovens, through which is
also drawn a large volume of relatively cooler air or other
gas from secondary heat sources to reduce the temperature of
the mixture of yases sufficiently to enable the use of a
relatively inexpensive, uninsulated collector duct, which
does not require the use of thermal expansion joints nor flow
balancing dampers. The secondary heat sources may comprise
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moderately warmed room air heated by radiation from the paint curing ovens
or from the body coolers.
The warm gas flow is passed through a recovery heat exchanger
unit prior to being exhausted to the atmosphere.
In one alternate version, the collec-tor duct is secured directly
to the roof of the paint curing oven, and in communication with an air
space extending about the oven walls and roof, such that air warmed by the
walls and roof as well as any leakage gases are drawn into the collector
duct.
In another variation, a positive pressure is created in the air
space to preclude such gas leakages.
Stated otherwise, the present invention provides a metho~ of
recovering heat from a plurality of sources of a relatively hot gas, the
method including the'steps of: circulating into the interior of a collec~or
duct a volume of gas at a relatively low temperature; introducing the
relatively hot gas from each of said plurality of sources into the interior
of said collector duct; and recovering heat energy from the mixture of said
low temperature gas and said hot gas.
The present invention also provides a duct system for the collec- ~ ~
tion of hot gases for heat energy recovery, comprising: a collector duct; ' ''
means for inducing flow of a relatively cooler temperature gas through the
interior of said collector duct; means for introducing said hot gas into the
interior of said collector duct into said flow of cooler temperature gas;
means for recovering heat energy from said mixture of said 'hot gas and cooler
temperature gas circulated in said collector duct.
The invention will now be described in greater detail with refer-
ence to the accompanying drawings.
DESCRIPTION OF'THE DRAWINGS
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FIGURE 1 is a diagrammatic representation of an installation
inco~porating a duct system of the present invention.
FIGURE 2 is an enlarged'view of an individual section of the
ducting system showing the details of the joint between the exhaust vent
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stack from each of the fuel-fired heatersand the collector duct.
FIGURE 3 is a sectional view taken along the lines 3-3 of FIGURB 2.
FIGURE 4 is a sectional view of a paint curing oven incorporating -.
one variation of the ducting system depicted in FIGURES 1 through 3. ~
FIGURE 5 is a view of section 5-5 -taken in FIGURE 4. ~ ~.
FIGURE 6 is a fragmentary sectional view of a paint curing oven
incorporating another variation of the ducting system according to the ~ :
present invention.
FIGURE 7 is an enlarged view of the wall section of the paint
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curing oven shown in FIGURE 6.
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FIGURE 8 is a sectional view of a paint curing
oven depicting a ducting system modification of the system
depicted in FIGURE 6.
DETAILED DESCRIP?ION
In the following detailed description, certain
specific terminoloyy will be utilized for the sake of clarity
and a particular embodiment described in accordance with the
requirements of 35 USC 112, but it is to be understood that
the same is not intended to be limiting and should not be so
construed inasmuch as the invention is capable of taking many
forms and variations withln the saope of the appended claims.
Referring to the drawings and particularly to
FIGURE 1~ the system is depicted as applied to an automotive ~ -
palnt finishing installation. In this installation, a paint
lS curing oven 10 is provided with a plurality of fuel-fired
oven heaters 12 disposed spaced~along the length of ~he paint ~
curing oven. Since such ovens may be of considérable length, -
i.e., 300 feet or more, a number of such oven heaters 12 are
normally required. -
~rhe car bodies 14 are caused to pass through the
length o~ the paint curing oven 10 on a conveyor 16 or other
similar equipment. After passing through the interior of
the paint curing oven 10, the car bodies 14 pass into a body
cooler enclosure 18 in which the heated car bodies 14 are
cooled by a cascade flow arrangement of air circulated through
the body cooler enclosure 18 in a manner well known in the ;
art.
According to the concept of the present invention,
the exhaust gases from each of the oven heaters 12 are col-
lected in the ducting system, which includes the vertical
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vent stacks 20, extending from each of the oven heaters 12,
each in turn ~ommunicating with a relatively large cross
sectional area collector duct 22. The collector duct 22 ex- -
tends over the paint curing oven 10, along the length there- ' -
of, so as to be in position to be connected to each of the ~ ~ -
vent stacks 20.
Collector duct 22 is also provided with inlet
registers 24 at spaced points along the length thereof so :
as to allow the induction of the relatively warm shop air
which has been heated by radiation from the paint curing
oven 10.
In addition, warm air or gases from other second- -~
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ary heat sources in which are generated warmed air of a
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relatively moderate temperature may be collected in the col- :
lector duct 22, as for example, ~the discharge air~passing
through an exhaust~duct 26 which receives the air passed -~ :
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over the car bodies 14. -
The inducted flow into the collector duct 22; is
achieved by the use of a circulation blower 28 acting at
the discharge end of the collector duct 22 such as to draw
in the warm air flow and through the inlet reg}sters 24 and
the vent exhaust gas flow from the vent stacks 20. :
The warm mixture is passed through a recovery heat
exchanger unit 30 which may also incorporate the necessary ~ :
filtering or other pollution prior to being discharged through
an exhaust stack 32 passing through the building roof 34.
The heat recovered in the heat exchanger unit 30
is transferred as by a liquid circulation in lines 31 and 33
to suitable utilization equipment as in conjunction with the
air conditioning equipment associated with the paint spray
booth.
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Referring to FIGU.RES 2 and 3, the details o~ the
installation of the vent stacks 20 with the collector duct
22 is dep.icted. Each section of the vent stack 20 is pref-
erably insulated along .its length as by an insulator sleeve
36. Each vent stack 20 is preferably provided with an elbow
positioned in the interior of the collector duct 22.
A terminal elbow fitting 38 serves to introduce ~ ~
the exhaust gases into the air flow within the collector duct :
22 centrally of the collector duct 22 and directing it in a
direction aligned with the direction o flow induced by the
circulation blower 28,
This assures a good mixing of the exhaust gases :
and avoids the development~o~ excessive heating of the col- ; .
lector duct 22 to a relatively elevated level.
The terminal elbow fitting 38 is also provided with
a relatively loose fit as by the clearance 40 between each
elbow 38 and the sidewall of the collector duct 22 and allows
for the clearance required to compensate for contraction and
e~pansion of the ducting~ ; ;
In addition, if an individual oven heater:12 is
not operatea, the absence of the exhaust gases from a given ;~
one of the vent stacks 20 will not imbalance th~ flow or
create an undesirable change in the static pressure within the ; :
collector duct 22 since additional inflow will be inducted . ! '
through.~ha clear~nce.spaae (as well as~being:~.taken in by i -
extra ~low through the inlet registers 24)~
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Accordingly, -the method and duct system provides
for collection of the hot gases by a relatively low cost
ducting system, since the high temperature gases are diluted
with the moderate temperature air flow induced by the drawing
in of shop air and/or air from waste heat sources in which
the air is much more modestly heated. This dilution produces
relatively moderate temperature levels in the air exhaust gas
mixture flowing in the collector duct 22l such that ducting
can be uninsulated and the use of expansion joints, etc., are
not required even forvery long runs of the ducting~
In addition, the arrangement whereby the flow is
drawn in by a circulation blower 28 at the collection end of
the ducting eliminates the need for use of special balancing
damper systems to make certain that the proper back pressure
conditions are contained in each of the oven heaters 12 and
allows a loose flt of the vent stacks 20 and the collector~
duct 22.
This arrangement therefore allows the recovery of
substantial energy from such installations without entailing
~0 the considerable capi~al expense which would be required by
conventional methods.
In addition, the use of the centralized recovery
system eliminates the need ~or numerous exhaust stack instal-
lations, both ~or venting of the shop air and for the ex-
hausting of the gases from the fuel-fired oven heaters such
that there is realized a substantial savings in the cost of
such installations tending to offset the cost of the heat
recovery e~uipment.
While this system and method have special applica-
tion to paint curing ovens, it is to be understood that the
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same could be applied to other systems in which relatively
hot gases are to be collected through ducting which must ex-
tend over considerable distances and also that the secondary
heat sources may come from any number of suitable waste heat
sources as are very typically present in industrial installa-
tions.
Referring to FIGURES 4 and 5, an alternate version
of this ducting system is depicted, which serves to more effi-
ciently recover the heat lost through the paint curing oven
10 roof and walls and to reduce the leakage of gases from the
interior of the paint curing oven into the surrounding shop
air.
This arrangement includes the installation of the
collector duct 22 directly to roof 42 Gf the paint curing
oven 10, rather than being supported spaced abové it, as in
the above-described embodiment. Each of the vent stacks 20
associated with the oven heaters 12 has, as before, a terminal
elbow fitting 38, directing the exhaust gases into the central
region of the collector duct 22, so as ko mix the same with
the relatively cooler air contained within collector duct 22.
Collector duct 22 is placed in communication with
an air space 44 located withln the paint curing oven roof 42
and walls 46 by a series of longitudinal slots 48 disposed in
the outer skin 50 of the paint curing oven roof 42 panels.
The walls and roof of the paint curing oven 10 are
formed of shee~ metal panels, each ha~ing an inner and outer
layer spaced apart to define the air space 44. Air space 44
in turn is in communication with the longitudinal slots 48 ;
such that air is drawn upwardly through the air space 44 and
into the collector duct 22. Collector duct 22 in this case
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takes the form of a -three-sidedl hat-shaped section with
the bottom flanges 52 received in a sliding fit within re-
tainer strips 54 so as to accommodate the thermal e~pansion
and con-traction of collector duct 22. Thus, the interior of
-the paint curing oven 10 heating the air contained within ~- -
air space 44 tends to recover the radiation heat losses from
the paint curing oven 10.
At the same time, any leakage tending to occur from
the paint curing oven 10 is collected by the induction of air
through the collector duct 22 such as to prevent passage of
the same into the outer surrounding air.
Accordingly, it can be seen that a more efficient
heat collection is achieved by this method and also any leak-
age which would otherwise occur is minimized or entirely
eliminated. -
FIGURES 6 through 8 depict a modification of this
version. In this case, the paint curing oven 10 is constructed
of panel sections, each cOnSisting of an inner sheet metal
panel 56, an intermediate insulating layer, as o~ fiber glass
batting 58, faced with a foil layer 60 and with outer metal
panels 62 spaced apart from the foil layer 60 such as to pro-
vide an air space 64. The collector duct 22 is mounted to
the roof 42 of the paint curing oven 10 as in the previous
variation with the vent stacks 20 each emptying into the col-
lector duct 22.
Thus, the air moving through air space 64 also
serves to collect the escaping or leaking gas from the interior
of paint curing oven 10, as well as recovering any ~inal heat
losses passing through the insulating layer 58.
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The movement of air through air space 64 is
~acilitated by the provision of louver openings 66 provided
at the bottom of each wall panel indicated generally at 68 ~: ~
which provide for the induction of air at the lower-most ~.. -
region of each wall panel 68 and the flow of air through the ~.
full height of the wall panel 68.
FIGURE 8 depicts a variation of the version shown ~.
in FIGURE 6, in which a plenum 70 is provided extending along
the bottom of the paint curing oven 10 adjacent the louver
openings 66. A blower 72 is provided which serves to pres-
surize thF interior of the plenum 70 and cause a positive
pressure to be exerted within the ~ir space 64 of each wall ~ ~-
panel 68.
This positive pressure tends to preclude any escape
of gases due to the greater-than-room pressure~e~isting in
the air space 64 such that a sllght: inflow to~the interior
of the paint curing oven 10 wlll occur rather~than outflow,
thereby preventing the escape:of any of the gases from the .
interior of the paint curing oven 13.
Accordingly, it can be seen that not ODly iS the :~
recovery of heat:energy rendered more efficient, but further
the paint curing oven is made to operate in a very clean
fashion, even though the installation is located within a
building structure thus eliminating the need for extensive ~ :
individual ventilation in the region of the paint curing
ovens. All of this has been carried out by relatively low
cost and easily installed ducting panel structures which do
not require the extensive use of thermal compensation connec- .
tors, etc. The outer skins of the paint curing oven are also
rendered much cooler such as to reduce the need for increased
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building air conditioning capacity due to the radiated
heat in the vicinity of the paint curing ovens, and improv-
ing the comfort level in the building.
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