[0001] This invention pertains to flame fired heat exchangers for cooking systems where
atmospheric pollutants are generated from the cooking process and are circulated to
the heat exchanger for treatment.
[0002] The cooking of potato chips, corn chips, chicken, meat balls and the like in a hot
oil bath causes a mist to be generated over the bath. This mist includes hydrocarbons,
particulates, oil droplets, smoke, water released from the food product as well as
fats and other carbonaceous and odor creating elements released during the cooking
process. These will be called "pollutants" below. While at one time it was common
to release such pollutants to the atmosphere, today's clean air requirements prescribe
that a plant operator minimize to a high extent the amount of pollutants released
into the environment.
[0003] To achieve a minimal release of pollutants it has been observed that improvements
are required to heat exchangers used in food cooking systems for remote heating of
either a cooking fluid such as oil or water or the heating of a heat transfer fluid
such as a thermal oil. Such improvements should produce a result that the odors emitted
from the system are greatly reduced, if not undetectable, which is the most desirable
condition indicating that pollutants are at a very low acceptable level. It is believed
that the delivery of a large amount of the pollutants from the cooker to the heat
exchanger combustion chamber often times passes through the combustion chamber and
out the exhaust stack leaving a telltale smell in the vicinity of the plant and this
is objectionable. The flow of gases in the combustion chamber, it is believed, is
in a laminar pattern which tends to minimize mixing of the pollutants with the combustion
gases. Thus, improvements in the combustion chamber design should ideally give a higher
measure of mixing such as generating a greater amount of turbulent flow of the pollutant
vapors and the combustion products so that a very minimum of odor is detectable issuing
from the heat exchanger stack. A known parameter for dwell time or residence time
of gases in a combustion chamber is three-tenths of a second at 760°C (1400°F) and,
when products are held for this time in the combustion chamber, thorough treatment
and odor reduction is achieved provided there is sufficient turbulence to ensure mixing
of the pollutants and combustion gases.
[0004] The invention in summary is directed to a flame fired heat exchanger for a system
for cooking a food product in a cooking fluid thereby generating cooking vapors and
odor pollutants, such vapors and pollutants being released to the combustion chamber
of the heat exchanger for incineration. The heat exchanger comprises a housing enclosing
a tube array for carrying the cooking fluid or heat transfer fluid (thermal oil) to
be heated for cooking the food product and a combustion chamber having burner means
arranged therein for projecting a flame into the combustion chamber. Plenum means
are disposed on the housing for receiving the cooking vapors from the cooking system
and having a discharge opening for releasing vapors and odor pollutants into the combustion
chamber. Baffle means are mounted in the combustion chamber extending thereacross
and spaced from the burner to just beyond the coolest portion of the burner flame
and having a central opening in the baffle serving to pass combustion gases therethrough
along a path toward the tube array and to an exhaust discharge. A frusto-conically
shaped body is mounted in the combustion chamber in a spaced-apart relationship from
the baffle so as to increase the turbulence in the flow and to define an annular slot
along the sidewalls of the body through the opening in the baffle. The body projects
towards the burner flame and has a central flow passageway therethrough.
[0005] In the accompanying drawings:
FIG. 1 is a schematic view of a food cooking system wherein the cooking fluid is heated
in a pollution-controlled heat exchanger;
FIG. 2 is a view taken in the direction of the arrows 2-2 of FIG. 1;
FIG. 3 is a view taken in the direction of the arrows 3-3 of FIG. 2;
FIG. 4 is a sectional view taken in the direction of the arrows 4-4 of FIG. 1; and
FIG. 5 is a view taken in the direction of the arrows 5-5 of FIG. 4.
[0006] As shown in FIG. 1 of the drawings, a flame fired heat exchanger 10 is arranged in
a system 11 for cooking a food product in a cooker 12. The cooker 12 may be equipped
for cooking potato chips, corn chips, chicken parts, meat balls and the like and,
to this end, is provided-with a cooking fluid or heat transfer fluid maintained by
the heat exchanger 10 in the desired cooking range typically from about 82°C (180°F)
to about 204°C (400°F) and in the case of a heat transfer fluid in a range of from
204°C (400°F) to about 315°C (600°F). One or more oil outlets 13 from the cooker 12
deliver oil to a fines removal unit 14 where solids are removed from the cooking oil
before delivery to a main system pump 16 which delivers oil in the direction of the
arrows 15 to a heating tube bundle 17 of the heat exchanger 10 for reheating. The
oil emerges from the tube bundle 17 and is delivered by a conduit 18 through one or
more oil inlets 19 into the cooker 12.
[0007] To prevent vapor emissions from the cooker 12 from polluting the atmosphere surrounding
the plant where the system 11 is installed, the pollutants generated in the cooking
process within the cooker 12 are collected from a cooker exhaust 21. A fann 22 creates
a draft or a negative pressure over the cooking fluid in the cooker 12 so that the
vapors from the cooking products are drawn through the exhaust 21, first encountering
an oil mist eliminator 23 which serves to remove oil droplets from the cooker exhaust
for reuse of the oil in the process. A control 24 is interposed in the cooker exhaust
line 21 ahead of the fan 22 so that the cooker exhaust may be delivered to a plenum
26 downstream of the fan 22, the plenum being equipped to exhaust vapors from the
cooker 12 to a location within the heat exchanger 10 adjacent to a burner 34 for entrainment
into the turbulent flow of the products of combustion. An air dilution stream including
fresh air and exhaust from the heat exchanger is delivered through a conduit 28 into
the cooker exhaust 21 flow and is controlled by regulators 29 and a barometric damper
30 to ensure that the necessary volume mixture and temperature of the mixtures reaches
the plenum 26 and discharges into a combustion chamber 31 of the heat exchanger 10.
[0008] The heat exchanger 10, shown schematically in FIG. 1, is generally L-shaped having
a generally horizontally disposed combustion chamber 31 arranged at a right angle
to a tube bundle compartment 32 which houses the tube bundle 17. The walls of the
heat exchanger 10 are formed from steel and are well-insulated as indicated by the
cross-hatching in FIG. 1 with use of refractories 33 well-known in the industry. The
burner 34 is mounted at one end of the combustion chamber 31 and may burn either liquid
or gaseous fuel as dictated by fuel availability and cost. The burner is arranged
to project a flame 27 axially along the center portion of the combustion chamber 31
towards a baffle 36 having a central orifice 37 through which the combustion gases
must flow from the combustion chamber 31 to a exhaust 38 of heat exchanger 10.
[0009] So as to increase turbulence for mixing and reduce laminar gas flow within the combustion
chamber, there is mounted in a substantially occluding relationshop with respect to
the aperture or orifice 37 a frusto-conically shaped body 41 mounted with the larger
base disposed away from the flame and the narrower base disposed closer to the flame
27, FIGS. 4 and 5. The conical-like member 41 is supported from the baffle plate 36
by one or more gusset plates 42 and is arranged concentric with the orifice 37 so
as to provide, as viewed in FIG. 4, an annular slot 44 through which the combustion
gases flow. In other words, the conical body 41 serves somewhat as a plug or target
within the combustion chamber for increasing the turbulence, uniformity of gas temperature
and uniformity of gaseous mixing between the pollution gases introduced into the combustion
chamber from the plenum 26 and the products of combustion released by the burner 34.
The plug or target 41 has a centrally arranged opening 46 which serves as a gas passageway
into the tube chamber 32. Thus, the flow of heating gases from the combustion chamber
to the tube chamber takes place through the annular slot 44 and through the cylindrical
opening 46. The presence of the opening serves to reduce laminar flow along the conical
surface of the body 41 and to reduce the stagnation zone of gas flow behind or downstream
of the body 41.
[0010] A typical effective relationship between the inside radius "A" of the combustion
chamber 31, the radius "B" of the orifice 37 and the radius "C" of the base of the
plug 41 is as follows: A = 0.91 m (36 in); B = 0.57 m (22.5 in); and C = 0.53 m (21
in). The distance from the baffle plate 36 to the base of the plug 41 can be about
0.41 m (16 in).
[0011] These dimensions were selected so as to create a condition within the combustion
chamber of reduced laminar gaseous flow and increased turbulent flow. At typical firing
rates to maintain a combustion chamber temperature of about 760°C (1400°F), the gas
flow across the target or plug 41 as indicated generally by the arrows in FIG. 5 generates
a
vena contracta which is larger in area than the orifice 37 and which dwells a distance upstram from
the baffle plate 36. Gas flow through the orifice 37 generates a
vena contracta which is smaller in area than the orifice 37 and which dwells a distance downstream
from the baffle plate 36. This serves to create a more turbulent condition and to
hold the gases in the combustion chamber a somewhat longer time than if the foregoing
structures were absent. One important result is a decrease in laminar flow through
the combustion chamber with increased temperature and mixing uniformity of the pollutants
with the combustion gases to achieve a more complete incineration of the pollutants,
reaching the desired low level of pollutant emissions into the atmosphere from the
heat exchanger exhaust 38.
[0012] So that the position of the plug or target body 41 may be optimized with respect
to the most desirable position as to the selected temperature zone of the flame and
its location on the orifice plate 36, one or more of the gusset members 42 and supports
43 are provided with a series of openings and fasteners whereby different positions
may be selected for adjustment of the body 41.
[0013] The baffle 36 is supported from the steel sidewall 35 of the heat exchanger by arcuately-spaced
gussets 48 as shown in FIG. 4. Slots 49 are cut in the baffle plate 36 opening into
the orifice 37 so as to accomodate for expansion and contraction of the baffle plate
in accordance with the heat load imposed upon it.
[0014] Referring more particularly to FIGS. 2 and 3, the plenum 26 is equipped with a drain
51 and discharge valve 52 so that any liquid collected therein may be removed. It
will be seen that the neck 53 of the plenum enshrouds the burner flame 27, thus ensuring
that pollution products delivered by the pollution fan to the plenum will be introduced
into the combustion chamber in pattern concentric with the burner flame 27.
1. A flame fired heat exchanger (10) for coupling to a system (11) for cooking a food
product in a cooking fluid thereby generating cooking vapors and odor pollutants released
during cooking which are retrieved and circulated to the flame burner of the heat
exchanger for incineration serving to reduce the pollutants released to the atmosphere,
and comprising:
housing means (32) enclosing a tube array (17) for a heat transfer or a cooking
fluid to be heated for cooking the food product, and a combustion chamber (31),
burner means (34) arranged on the housing to project a flame (27) into the combustion
chamber (31),
plenum means (26) proximate the burner means (34) and equipped to receive cooking
vapors from the cooking system and having a discharge opening (53) serving to release
such vapors and odor pollutants into the combustion chamber (31),
baffle means (36) mounted in the combustion chamber (31) and extending thereacross
in a plane generally normal to the principal axis of the burner flame (27), the baffle
means (36) having a central opening (37) therein serving to pass combustion gases
therethrough along the path towards the tube array (17) to an exhaust discharge (38)
from the heat exchanger (10), and
a frusto-conically shaped, turbulence increasing body (41) mounted in the combustion
chamber (31) spaced apart from the baffle means (36) so as to define an annular flow
slot (44) along the sidewalls of the body (41) through the opening (37) in the baffle
means (36), the body (41) being arranged to project towards the burner flame (27)
and having a central flow passageway (46) extending therethrough.
2. A heat exchanger as claimed in claim 1, wherein means (42,43) are provided for mounting
the frusto-conically shaped body (41) in a manner for spacing the body at selected
distances from the baffle means (36) for changing the size of and the flow rates through
the annular slot (44).
3. A heat exchanger as claimed in claim 1, wherein the turbulence increasing body (41)
is positioned a distance with respect to the baffle means (36) with the major base
of the body closest to and generally parallel with the baffle means (36), and the
diameter of the major base being selected so that the vena contracta created by gas
flow with respect to the body (41) is larger in diameter than the diameter of the
central opening (37) in the baffle means (36).
4. A heat exchanger as claimed in claim 1, 2 or 3, wherein the minor base of the turbulence
increasing body (41) has an opening (46) for gas flow therethrough serving to improve
mixing of the pollutants and combustion gases.
5. A heat exchanger as claimed in claim 3, wherein the diameter of the major base of
the body (41) is selected so that the said vena contracta is larger in diameter than the vena contracta created by gas flow through the central
opening (37) of the baffle means (36).
6. A combination of a cooking system and a heat exchanger as claimed in any preceding
claim.