Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A HEAT EXCHANGER
FIELD OF THE INVENTION
The present disclosure is related to energy conservation and global
sustainability by recycling
exhaust heat from a manufacturing operation. More particularly, the present
disclosure relates to a
heat exchanger suitable for use in the recycling and reclaiming of exhaust
heat from the drying
section of a papermaking machine and process.
BACKGROUND OF THE INVENTION
0
Disposable paper products such as facial tissue, sanitary tissue, paper
towels, and the like are
typically made from one or more webs of paper.
Processes for the manufacture of disposable
paper products can vary, but generally involve the preparation of aqueous
dispersion of papermaking
fibers. The aqueous dispersion is deposited on a Fourdrinier wire to form an
embryonic web of
papermaking fibers on the wire. The Fourdrinier wire and embryonic web can
then be transferred to
5 a through air drying belt. The resulting web of cellulosic fibers is
then brought into contact with
various drying cylinders including a Yankee drying drum, and preferably
impressed thereagainst.
The tissue is then dried to the desired moisture level on the Yankee drying
drum and removed
therefrom.
One of the drawbacks of the production of such web materials, especially those
web
0 materials suitable for consumer tissue and towel production is that a
considerable amount of water is
required to produce the embryonic web and considerable heat energy is required
to dry the resulting
embryonic web to produce the final consumer product. Until now, most of the
water and heat
energy used in the drying process is wasted by venting to the environment.
This heat is generally in
the form of steam or moist air generated during the aforementioned drying
process. To those
5 familiar with such drying processes, the wasted heat may exceed 80%
of the electrical energy used
in the process
With an increase in the need for disposable paper products and with the
simultaneous
increase in the cost and decreased availability of natural and energy
resources, there is an increased
need to recover and use any wasted heat in order to recover the thermoenergy
produced during the
0 paper drying process for use. Clearly, any energy exhausted to the
atmosphere lowers the
profitability of the process.
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When a typical paper drying process is utilized, the quantity of waste heat
generated can be
as high as 2,000 kWh of energy per one ton of pulp produced and used. It is
therefore appreciated
that a large amount of thermal energy is wasted during the course of the
drying process and such
energy leaves in the form of the steam and/or moist air created during the
process. As a result, there
have been attempts to recover such heat in various types of recovery systems
where the atmospheric
steam generated during this process is utilized to provide heat in various
other situations. For
example, such heat recovery systems utilize the steam as a remote heating
source for housing
developments, for heat ventilation air and/or sanitary water, as well as to
preheat combustion and/or
drying air of a paper manufacturing machine.
0 It has been previously suggested that any waste heat and process
steam produced during the
drying process should be immediately re-injected and used in the drying
section in the paper
manufacturing machine. Current processes can recycle limited quantities of
moist air. However, at a
certain level of moisture saturation, energy savings from these recycle
systems are lost in reduced
drying capability of the hot air stream.
5 As known in the prior art, a principal object of heat recovery
systems is to replace primary
energy in an economical way. In some heat recovery systems, heat exchangers,
such as plate heat
exchangers and tubular heat exchangers can be used. In prior art plate heat
exchangers, a plate
structure forms two systems of ducts perpendicular to one another. A medium
that delivers heat
flows in one set of ducts and a medium that receives heat flows in the other
set of ducts. The heated
0 receiving medium is then further processed for reuse. Tubular heat
exchangers are generally
provided with a supply of steam or water, and the tubes are surrounded by ribs
or equivalent so as to
increase the heat exchange area. In lamellar radiators, the tubes are
typically fitted between a plate
structure, and water flow in the ducts formed by the plate structure, for
example glycol water.
Another form of heat recovery system provides a heat exchanger where an air
flow that is
5 moist, saturated, or near its saturation curve is arranged to be used
as the air flow that delivers heat.
In this system, the air flow that delivers heat is arranged to flow inside
vertically oriented tubes
substantially from a top of each tube toward a bottom of each tube. The air
flow that receives heat is
arranged to flow in a direction substantially horizontally through gaps
between the tubes. In this
manner, any condensate coming from the moist air flow that delivers heat in
the tubes flows
0 downward along the inner walls of the tubes and is collected in a
basin positioned within the duct
work of the heat exchanger below the bottom of the tubes.
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However, such a system is severely flawed. Since, the hot, moisture-laden and
often particle-
laden air goes through the described tubes, the insides of the tubes tends to
foul with particle build-
up. Clearly, fouling and the production of a condensate layer becomes a
significant detriment to
efficient heat transfer. This reduces the overall efficiency of the system and
can even render the
system inoperable. This clearly does not provide any benefit to the user of
the system and increases
system maintenance.
Thus, it would be advantageous to provide the capability to preheat cold, dry
air using warm,
moist air while recovering water from the exhaust air stream simultaneously.
This can provide
significant system energy reduction and significant sustainability benefits in
a typical disposable
0 paper product manufacturing process. If such a system were to provide
heat exchange rates of 20-40
MMBTU/ hr, it may be possible to reduce equivalent amounts of natural gas
usage while recovering
40-80 GPM of water per machine. Further, the vacuum created by the condensing
water vapor may
be expected to deliver 20,000-60,000 CFM of vacuum capacity which may overcome
some of the
resistance losses caused by the energy recovery process. Besides
sustainability efforts, a method for
5 recovering heat and water from moist exhaust air can provide economic
benefits as well. Such a
system should enable air to air heat recovery of a moist, fiber laden hot
exhaust air stream to a clean
and dry inlet air stream. Such a system should also minimize fouling and other
maintenance-driven
issues related to the recovery equipment.
0 SUMMARY OF THE INVENTION
The present disclosure provides for a heat exchanger. The heat exchanger
generally
comprises a duct and a plurality of substantially parallel tubes, each having
an outer wall and
arranged in said duct to define gaps therebetween. The heat exchanger also
comprises first means
for directing an air flow through said duct that delivers heat through the
gaps and over said outer
5 walls of said tubes and second means for directing an air flow that
receives heat through said tubes;.
An inlet disposed at a first region of said duct and an outlet disposed at a
second region of said duct
disposed distal from said first region so that in said duct, the air flow that
delivers heat flows from
said inlet to said outlet and condensate forms on said outer wall of said
tubes and flows toward said
outlet. The air flow that delivers heat generally comprises air that is moist,
saturated, or near its
0 saturation curve. The heat exchanger also comprises collecting means
arranged in the duct for
collecting the condensate flowing along the outer walls of the tubes upon
exiting from the duct at the
outlet.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an exemplary but non-limiting energy recovery
process of the
present disclosure;
FIG. 2 is a plan view of an exemplary but non-limiting heat exchanger suitable
for use with
the energy recovery process of the present disclosure;
FIG. 3A is a cross-sectional view of the exemplary but non-limiting heat
exchanger of FIG. 2
taken at line 3A, 3B ¨ 3A, 3B; and,
FIG. 3B is another cross-sectional view of the exemplary but non-limiting heat
exchanger of
FIG. 2 taken at line 3A, 3B ¨ 3A, 3B showing the spray system in operation.
0
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1, the exemplary and non-limiting energy recovery process 10
shown can
generally receive a waste heat energy stream 12 in the form of steam, hot air
exhaust, moisture laden
heated air, particle and/or fiber laden heat exhaust, and the like. One of
skill in the art will recognize
5 that any manufacturing process that takes an air stream, supplies heat
energy to the stream to
accomplish a task and then vents the exhaust is suitable for use with the
process and apparatus of the
present disclosure. Some exemplary manufacturing process utilizing such
processes are herein
described.
For example, by way of non-limiting example, several known pollution control
systems
0 utilize afterburners to oxidize volatile organic compound process off-
gasses. It is well known that
pre-heating this process off-gas stream results in a better and more efficient
oxidation process.
Similarly, the radiant heat emitted from a circuit board manufacturing process
can be utilized
to provide ambient heating to other locations within the manufacturing
operation during cool
weather seasons.
5 Further still and by way of non-limiting example, a product such as a
continuous web of
textile or paper product is generally dried by passing the web substrate over
a plurality of sequential
heated rotary cylinders. These cylinders are generally heated internally by
means of supplied steam
or externally by large gas-fired burners. Typically, the hot exhaust gasses
and/or waste energy
stream resulting from the drying process are usually dissipated in the
surrounding atmosphere.
0 Significant energy is required to extract the water residing within the
paper product. This is even
more evident when it is understood that these web materials are typically
manufactured to be about
feet wide and are subject to manufacturing speeds of such drying operations
typically ranging
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from 3,000 to 5,000 feet per minute. This requires the webs to be dried very
quickly as the final
drying stages of typical paper manufacturing operations provide a final
product that has about 3%
moisture content.
Returning to FIG. 1, the energy recovery process 10 envisions several process
steps and non-
5 limiting options suitable for use with the described energy recovery
process 10. If the waste heat
energy stream 12 is in the form of hot and dry exhaust gas, a step to
determine if additional moisture
should be added to the waste heat energy stream 12 can be provided. This step
is represented in
FIG. 1 as 14. In a situation where the waste heat energy is not saturated, and
it has been determined
that moisture should be added, one selects "yes" on the decision point.
Alternatively, if the waste
0 heat energy stream 12 is in the form of steam, then additional saturation
may not be required, this
can result in the selection of "no" on the decision point. In a preferred
embodiment of the energy
recovery process 10, one of skill in the art would recognize that it may be
preferred that the waste
heat energy stream 12 to be treated be saturated. Without desiring to be bound
by theory, it would
be readily appreciated by one of skill in the art that saturation of the waste
heat energy stream 12 can
5 enable and enhance latent heat transfer. Naturally, it should be
understood by one of skill in the art
that if a decision is made to not saturate waste heat energy stream 12, the
herein described equipment
and process is still suitable for use. The use or non-use of a saturated waste
heat energy stream 12
should not be considered as limiting the scope of the invention disclosed
herein. Furthermore, the
terms "saturated waste heat energy stream 12" and "waste heat energy stream
12" are used
0 interchangeably herein without effect on the overall disclosure or the
equipment described herein.
In any regard, the now saturated or unsaturated waste heat energy stream 12
can then be
routed to a unique heat exchanger 16. The heat exchanger 16 is shown in detail
in FIGS. 2, 3A, and
3B. The saturated waste heat energy stream 12 is passed in accordance with the
crossflow principle
through the heat exchanger 16. The heat exchanger 16 preferably includes means
for directing the
5 saturated waste heat energy stream 12 into and through the heat exchanger
16 (e.g., fans, make-up
air, etc) as may be required. The heat exchanger 16 also preferably comprises
a number of tubes 32
over which the saturated waste heat energy stream 12 is passed (i.e., external
to tubes 32). Fresh air
34 (e.g., clean and uncontaminated) to be heated by the saturated or
unsaturated waste heat energy
stream 12 can be passed through each of the tubes 32 (i.e., internal to tubes
32). Without desiring to
0 be bound by theory, contact of the saturated waste heat energy stream 12
with the external surface of
each of the tubes 32 imparts heat energy to each of the tubes 32. This heat
energy is then transferred
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to the cool fresh air 34 passing through the tubes which can then be recycled
in to the manufacturing
or other production/use stream.
Additionally, it should be understood that cooling of the saturated waste heat
energy stream
12 with the external surface of the tubes 32 caused by a loss of energy upon
contact with the tubes
32 can cause any moisture contained within the saturated waste heat energy
stream 12 to condense.
This condensate can then be collected and also recycled into the manufacturing
process or any other
production/use stream.
As mentioned supra, heat exchanger 16 preferably consists of a series of tubes
32 containing
the fresh air 34 passed therethrough that are to be heated by the saturated
waste heat energy stream
0 12. The saturated waste heat energy stream 12 flows over the tubes 32
that are to be heated to
provide the heat required to heat the fresh air 34 contained within tubes 32.
In a preferred
embodiment, the tubes 32 can be fabricated into a complete unibody
construction for heat exchanger
16. In an alternate preferred and non-limiting embodiment, a set of tubes 32
comprising only a
portion of the tubes 32 envisioned to provide a complete heat exchanger 16 can
be manufactured as
5 an assembly and provided, for example, as a tube bundle 44. It is
believed that each tube bundle 44
can be fabricated as incremental, individual units containing a plurality of
tubes 32 that are designed
to be a portion of the total architecture of the heat exchanger 16. The
resulting tube bundles 44 can
be arranged and interconnected as may be required by the end user into an
array to form a complete
heat exchanger 16. For ease of construction, the inlets and outlets of the all
the tubes 32 or the
0 respective tube bundles 44, or any portion thereof, comprising heat
exchanger 16 can be in common
fluid communication through a respective inlet plenum or manifold 50 and/or a
respective outlet
plenum or manifold 52. In any regard, it is envisioned that the heat exchanger
16 can comprise
several design features relating to the disposition of the tubes 32 into any
required arrangement
articulated infra in order to provide the design required by the user for the
waste heat energy stream
5 12 to be treated.
For example, to be able to transfer heat well, the tube 32 material selected
should preferably
have good thermal conductivity for the operation and for the waste heat energy
stream 12 to be
treated. Because heat is transferred from a hot (outer) side to a cold (inner)
side through the tubes
32, one of skill in the art will understand that there is a temperature
difference through the width of
0 the tubes 32. Because of the tendency of the tube 32 material to
thermally expand differently at
various temperatures, thermal stresses may occur during operation. This is in
addition to any stress
imparted to the tubes 32 from the pressures exerted upon the tubes 32 from the
fluids (such as waste
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heat energy stream 12) themselves. The tube 32 material also should be
compatible with both the
shell and tube 32 side fluids for long periods under the operating conditions
(temperatures, pressures,
pH, etc.) to minimize deterioration such as corrosion. All of these
requirements call for careful
selection of strong, thermally-conductive, corrosion-resistant, high quality
tube materials, typically
metals, including copper alloy, stainless steel, carbon steel, non-ferrous
copper alloy, Inconel ,
nickel, Hastelloy , titanium, high conductivity coppers, brasses, wrought
Martensitic stainless steel,
aluminum bronzes, 90/10 aluminum bronze, 92/8 aluminum bronze, hard (wrought),
93/7 aluminum
bronze, hard (wrought), 95/5 aluminum bronze, 1/2 hard (wrought), 95/5
aluminum bronze, hard
(wrought), nickel iron aluminum bronze, as extruded (wrought), combinations
thereof, and the like.
0 Further, tubes 32 can be provided in several non-limiting types including
plain, longitudinally
finned, radially finned, extruded, rolled, seamed, and the like.
As would be appreciated by one of skill in the art, there are several thermal
design features
that are to be taken into account when designing the tubes 32 to be placed
into shell and tube heat
exchangers. It was surprisingly found that using a small tube 32 diameter
makes the heat exchanger
5 16 both economical and compact. However, larger tube 32 diameters can be
used. One of skill in the
art should consider the tube 32 diameter, the available space, and cost. One
of skill in the art would
consider the thickness of the wall of the tubes 32 to ensure that any flow-
induced vibration has
resistance, that there is sufficient axial strength in the structure, that
there is sufficient hoop strength
(to withstand internal tube pressure), and that there is sufficient buckling
strength (to withstand
0 overpressure in the shell).
It should also be understood by one of skill in the art that tube 32 length
should be considered
in order to make the heat exchanger 16 as long as physically possible whilst
not exceeding
production capabilities. Additionally, one of skill in the art will appreciate
that it is practical to
ensure that the tube 32 pitch (i.e., the center-center distance of adjoining
tubes 32) is not less than
5 1.25 times the outside diameter of the tube 32. However, one of skill in
the art could use any tube
pitch desired to provide the desired air flow and transfer necessary to
optimize the performance of
heat exchanger 16 for the waste heat energy stream 12 used. Further, it should
be understood that
the use of corrugated tubes 32 can increase the turbulence of the fluids
involved. Without desiring to
be bound by theory, it is believed that turbulence can increase heat transfer
and provide better
0 performance. However, it should be understood that the arrangement of
tubes 32 can be provided in
any orientation, spacing, and the like to suit the waste heat energy stream 12
to be treated.
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Further, one of skill in the art should consider the positioning of tubes 32
within the heat
exchanger 16. There are four main types of tube layout, which are, triangular
(30 ), rotated
triangular (60 ), square (90 ) and rotated square (45 ). It was found, and one
of skill in the art will
no doubt appreciate, that triangular patterns may give greater heat transfer
as they force the fluid to
flow in a more turbulent fashion around the tubes 32. One of skill in the art
will appreciate that
square patterns can be employed where high fouling is experienced and cleaning
is more regular.
In principle, it is believed that the heat exchanger 16 can be thought of as
two fluid streams
that are thermally connected (e.g., saturated waste heat energy stream 12 and
cool fresh air 34). Let
the fluid streams be of equal length, L, with a heat capacity (energy per unit
mass per unit change in
0 temperature) and let the mass flow rate of the fluids through the heat
exchanger 16 be (mass per unit
time), where the subscript i applies to saturated waste heat energy stream 12
and cool fresh air 34.
If one assumes a steady state, so that the temperature profiles are not
functions of time, the
temperature profiles for the fluid streams (in which each can be thought of as
being contained in a
pipe) can be represented as Ti(x) and T2(x) where x is the distance in the
tube. Assume also that the
5 only transfer of heat from a small volume of fluid in one tube is to the
fluid element in the other tube
at the same position. There will be no transfer of heat along a tube due to
temperature differences in
that tube. By Newton's law of cooling the rate of change in energy of a small
volume of fluid is
proportional to the difference in temperatures between it and the
corresponding element in the other
tube. To wit:
dui
_____________________________________ =
dt
71- r
Here, u(x) is the thermal energy per unit length and y is the thermal
connection constant per
unit length between the two tubes. This change in internal energy results in a
change in the
temperature of the fluid element. The time rate of change for the fluid
element being carried along
5 by the flow is:
dZ1
__________________________________________________ and,
cit di
du2 di
________________________________________ =
Lit
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where Ji = Cij is the "thermal mass flow rate". The differential equations
governing the heat
exchanger may now be written as:
;
al
-7-1 _.. = ".(.Th - TO and,
0
."
.01',. ..
'12 = - = -^itT.1 - TZ) =
, .
. al;
Note that, since the system is in a steady state, there are no partial
derivatives of temperature
with respect to time, and since there is no heat transfer along the tube,
there are no second
derivatives in x as is found in the heat equation. These two coupled first-
order differential equations
may be solved to yield:
.,4
k
E. i __
= .i. i -1 --r- C
_.
0 k
where ki = IIIJI, k2 = 7 /J2, k = k I + k2 and A and B are two as yet
undetermined
constants of integration. Let TO and 172.0 be the temperatures at x=0 and let
T.L.Land 112:L be the
temperatures at the end of the tube at x = L. Define the average temperatures
in each tube as:
Ti = I
T 171 (1)dx and,
5 . 0
1 'AL
T2 = -i r T2 (X ) dx
L., .. o
Using the solutions above, these temperatures are:
Bki B k.,),
0 = A + _________________________________________________________
k k
1721, = A 4-
.T1 = A _____________________________ kL A +B k.:,.i= e .
,
k2. L k2 L
Choosing any two of the above temperatures will allow the constants of
integration to be
eliminated, and that will allow the other four temperatures to be found. The
total energy transferred
is found by integrating the expressions for the time rate of change of
internal energy per unit length:
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art rLthii
L TEO -/Lin T1). and,
dt dt
"L¨
_________________________________________________ =J( ) = e Ti
fit 0 dt
5
By the conservation of energy, the sum of the two energies is zero. The
quantity T2 ---- Ti
is known as the "log mean temperature difference" and is a measure of the
effectiveness of the heat
exchanger in transferring heat energy. Without desiring to be bound by theory,
it is believed that the
heat exchanger of the present invention can be made profitable with as low as
40% thermal
efficiency, provided the costs of construction are reasonable. Thus, it should
be understood that the
0 heat exchanger of the present invention would provide an efficiency
of greater than 50%, or greater
than 60%, or greater than 80%, or greater than 90%. However, it should be
appreciated that even
lower thermal efficiency payouts may be possible with longer project life
analysis or even lower cost
construction methods.
In practice, saturated waste heat energy stream 12 is passed through gaps
defined between
5 the tubes 32. Preferably, the saturated waste heat energy stream 12
passes through the heat
exchanger 16 in a direction that is generally orthogonal to the longitudinal
axis of tubes 32 and the
air flow occurring therein.cross flow to the cold, dry air stream,.
Any water condensed in the heat exchanger 16 from waste heat energy stream 12
flows into a
basin 18. From the basin 18, any condensed water removed from the saturated
waste heat energy
0 stream 12 can be recirculated. By way of non-limiting example, this
recirculation can be directed
toward a spraying system 20 used for providing water to enable saturation of
an unsaturated waste
heat energy stream 12 prior to entry of the waste heat energy stream 12 into
the heat exchanger 16.
Additionally, any condensed water removed from the saturated waste heat energy
stream 12 can be
used for re-introduction into various portions of the papermaking process and
systems
5 communicatingly associated thereto 22. By way of non-liming example,
clean water can be
provided for input into the initial stages of the papermaking process, such as
the pulper as well as
other systems associated with the preparation of pulp for the production of
paper products.
Similarly, clean recycled water can be provided for input into a steam
generation system used to
generate the steam necessary for the various drying stages of the papermaking
process.
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Additionally, if the condensed water stream is heated, this heated water can
be filtered and input into
a potable or unpotable water supply stream.
Even still the clean recycled water can be provided for input into the heat
exchanger 16 to
provide a cleaning benefit to the external surfaces of the tubes 32 disposed
within the heat exchanger
16 used in the heat exchanging process described herein. Such a cleaning
benefit can be realized by
the incorporation of spray system 40. An exemplary spray system 40 can
incorporate a pump or an
equivalent actuator for passing the flow of water into the nozzles of spray
system 40. Spray system
40 was surprisingly found to provide excellent cleaning abilities inasmuch as
any particulate matter
residing within the saturated waste heat energy stream 12 will tend to bind
upon the outer surface of
0 tubes 32 comprising heat exchanger 32. It should be realized by one of
skill in the art that the
efficiency of heat exchanger 16 is dependent upon the most efficient transfer
of thermal energy from
the saturated waste heat energy stream 12 disposed upon the outside of tubes
32 to the fresh air 34
disposed within tubes 32. The deposition of particulate matter or any other
contaminant upon the
outer surface of tube 32 can impact the heat transfer and ultimately the
efficiency of the heat
5 exchanger 32. Providing a spray system 40 that effectively washes
particulate matter from the outer
surface of tube 32 can be reasonably assumed to assist in maintaining optimal
heat transfer and
optimal efficiency of heat exchanger 16.
Further, it was surprisingly found that by providing the saturated waste heat
energy stream 12
in contact with the outer surface of tube 32 eliminates the significant draw-
backs associated with the
0 systems found in the prior art. For example, any particulate matter
residing in the saturated waste
heat energy stream 12 does not have the opportunity to become impacted upon
the inner surface of
tube 32 resulting in a difficult, if not nearly impossible, cleaning task.
Such a system would likely
require a complete disassembly of the system in order to effect any cleaning
process. Any
particulate deposition upon the outer surface of tubes 32 is more readily
removable than impacted
5 particulate matter disposed within a tube 32.
The cooled flow of exhaust air from waste heat energy stream 12 may still
contain moisture
droplets even after waste heat energy stream 12 has passed through the heat
exchanger 16. Thus, the
remaining waste heat energy stream 12 can be passed through a drop trap
disposed in a supplied
exhaust duct. As shown in FIG. 2, the saturated waste heat energy stream 12 is
preferably
0 introduced into the top portion of the heat exchanger 16. After this, the
saturated waste heat energy
stream 12 passes through the heat exchanger 16 and any condensate falls mostly
onto the bottom of
the heat exchanger 16. This condensate can be removed through an exhaust duct,
or it can be
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recirculated to be used again in spraying system 20 for further saturation of
the incoming waste heat
energy stream 12 or it can be used in spray system 40 for cleaning the outer
surfaces of the tubes 32
of heat exchanger 16, and the like. In either case, any condensate retrieved
by heat exchanger 16
would likely be passed into appropriate ducting in which there is a pump or an
equivalent actuator
for passing the flow of water into the spray system 20 or spray system 40.
Since a large quantity of
water is employed in the arrangement of the present invention in the heat
exchanger 16, it is easy to
keep the heat exchanger 16 clean, in which case it does not require a large
amount of cleaning,
which also provides the advantage that the exhaust side of heat exchanger 16
is not readily blocked.
The heat exchanger in accordance with the present disclosure is suitable for
use as a heat
0 exchanger to provide clean and heated exhaust air 42. For example, clean
and heated exhaust air 42
can be used to provide pre-heated replacement air for a paper machine or for
any other application of
recovery of heat. A route for the recovered clean and heated exhaust air 42
can be selected by
diverter 24. For example clean and heated exhaust air 42 can be routed by
diverter 24 to provide
pre-heated replacement air for a paper machine as discussed supra.
Alternatively, clean and heated
5 exhaust air 42 can be used for climate control within the manufacturing
facility or other related
operations in the form of heated room air. In the event of a malfunction,
maintenance, any exigent
circumstance, and the like, clean and heated exhaust air 42 can alternatively
be vented to the
atmosphere.
It is believed that the heat exchanger 16 in accordance with the invention can
be used highly
0 advantageously in process outlets at paper, pulp and board machines, in
particular in the process
outlets of a dryer section of such machines. In any event, when the present
invention is applied to
paper mills utilizing several paper machines, a favorable situation can be
obtained whereby
substantial thermal recovery is achieved. The present invention provides both
a technically and
economically feasible solution for recovering and re-utilizing large
quantities of heat and other
5 energy generated during paper production in order to dry paper. It is
based upon the idea that the
pressure of the steam need only be raised as is required. As a result, the
arrangement can be made
even more practical by connecting it together with an additional steam
generating system, such as
the back pressure power station described.
Various other variations and modifications from the embodiments described can
also be
0 included. For example, the heat exchanger 16, diverter 24, and basin 18
may be constructed as an
integral unit or as separate units, as described. Also, several parallel
vaporizers can be utilized to
produce steam at different pressures. Each of them may then be fed into a
surface steam feeding
CA 02872276 2014-10-30
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PCT/US2013/038095
13
group of the papermaking machine dryer section without the need for raising
the pressure and
preferably without lowering the pressure. For example, such a system can be
used to increase dry
hot air temperature for use in through air drying.
The dimensions and values disclosed herein are not to be understood as being
strictly limited
to the exact numerical values recited. Instead, unless otherwise specified,
each such dimension is
intended to mean both the recited value and a functionally equivalent range
surrounding that value.
For example, a dimension disclosed as "40 mm" is intended to mean "about 40
mm."
Every document cited herein, including any cross referenced or related patent
or application,
is hereby incorporated herein by reference in its entirety unless expressly
excluded or otherwise
0 limited. The citation of any document is not an admission that it is
prior art with respect to any
invention disclosed or claimed herein or that it alone, or in any combination
with any other reference
or references, teaches, suggests or discloses any such invention. Further, to
the extent that any
meaning or definition of a term in this document conflicts with any meaning or
definition of the
same term in a document incorporated by reference, the meaning or definition
assigned to that term
5 in this document shall govern.
While particular embodiments of the present invention have been illustrated
and described, it
would be obvious to those skilled in the art that various other changes and
modifications can be
made without departing from the spirit and scope of the invention. It is
therefore intended to cover
in the appended claims all such changes and modifications that are within the
scope of this
0 invention.
