Note: Descriptions are shown in the official language in which they were submitted.
j` WO gl/13205 . ` : : ' 2 0 7 S 9 9 3 PCI`/US91/01 167
STE~;M SHOWER AND VACUUM APPAR~TUS
AND METHOD OF US ING SAME
BACKGROUND OF THE INVENTION
This invention relates to papermaking and more
particularly to an apparatus and a method for controlling
the temperature of a web or sheet of paper as it enters the
press section through the utilization of a stepping motor to
open and close valve pipes in order to control the
application of steam against the sheet surface and the
corresponding withdrawal of the steam by a suction device
through the opposite side of the sheet that contacts the
forming fabric (wire).
In the forming section of a paper making machine, water
is removed from the pulp to form a web. The drainage rate
of the water is proportional to the viscosity and surface
tension of the trapped water. Further water expression
(removal) is accomplished in the press section. Increasing
sheet temperature decreases the water viscosity and surface
tension, hence augmenting the expression of water. As shown
in U.S. Pat. Nos. 3~574~338! 3,945,570, 4,050,630 and
4,163,688, it is common practice to app~y steam to a sheet
; in the forming section and prior to the sheet entering the
press section so that the latent heat of the steam increases
the temperature of the sheet.
It is a common practice to utilize a vacuum source
beneath the web to remove water. The vacuum source can also
serve to draw the steam into the web and increase steam
penetration. This increased steam penetration serves to
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increase the operating efficiency of the steam shower and
the heat transfer to the web. This vacuum source is
typically run at a constant uniform vacuum level in the
t~ansverse or cross direction (CD) without any ~egulation of
volume once the machine has stabilized.
The press section of a paper making machine is located
before the dryer section. Therefore, increasing the water
removal rate through the press section serves to decrease
the moisture content of a sheet entering the dryer section,
thereby either reducing the energy consumption required to
further dry the sheet or increasing production (speed) at
constant dryer section energy consumption.
Typically when steam is applied to a section of the web
or sheet with excess moisture, the steam will migrate to an
alternate section of the web or sheet where there is less
moisture before it penetrates the web. This happens because
where there is less moisture the opposing vacuum system
works "better" and actually more suction gets through the
web to withdraw the steam. This te~ds to exaggerate rather
than solve the moisture problem. This invention sets out to
eliminate this "steam migration" problem by applying vacuum
to the appropriate section effectively preventing the steam
from traveling to a "dry spot" in the web. ~ater expression
is also proportional to the level of vacuum applied. Thus
applying higher vacuum to that portion of the web with
higher moisture increases the water removal rate.
In any steam application, consumed steam should be
maximized for its effective use. To maximize the effective
usage, the percentage of consumed steam that condenses on
and in the sheet for the purpose of raising the sheet
temperature should be maximized, and the percentage of
consumed steam that does not condense but instead exhausts
to the atmosphere as wasted energy should be minimized.
There are certain applications where the steam
~ application does not have to be positionally and
volumetrically controlled. In other applications however,
it is necessary to impart steam to the process in controlled
. amounts at specified positions across the machine for
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profiling certain sheet qualities. This controlled
imparting of steam is commonly performed as part of a
closed-loop control system, where the sheet quality variable
in question is scanned on-line at equally spaced increments
across the machine. The results obtained by the scanning
device,~through the use of computer analysis, are used to
automatically control the steam flow applied to the sheet in
accordance with the desired sheet quality criteria.
The ability of known steam shower apparatus to
repeatedly apply a uniform steam flow is presently limited
to the accuracy and repeatability of pneumatically actuated
control valves.
For the same reasons that it is important to accurately
control the steam flow to the sheet, it is also important to
maintain uniform heat-transfer, over the portion of the
sheet in question.
SUMMARY OF THE INVENTION
According to the present invention, a steam shower
apparatus is provided for use in controlling the temperature
of a sheet by applying steam against the upper surface of
the sheet. Directly beneath this steam application zone is
a corresponding vacuum zone. The vacuum zone's purpose is
to enhance profilability and increase the response of the
steam shower itself. The vacuum zone acts as the bottom
half of a steam-web-vacuum sandwich.
The controlled application of steam across the machine
at equally spaced increments can be employed to control the
initial and hence final moisture profile of the sheet. The
controlled removal of moisture/steam at such equally spaced
increments is accomplished by the use of a measurement
computer system which controls a stepping motor. The
stepping motor in turn controls the appropriate valves in
both the vacuum and steam zones in order to send a certain
amount of both vacuum and steam to the web. This process
varies the amount of steam application and vacuum volume
directly beneath the steam application zone. This can be
accomplished because directly beneath the steam application
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WO91/13205 2 0 7 5 9 9 3 PCT/US91/01167 -~ ~
zone is a vacuum steam removal zone of similar dimensions.
When the output of steam is increased through the steam box
the vacuum beneath this individual zone is increased. This '
combination of steam application and steam removal serves to
enhance the effectiveness of the process as well as enable
the operator's to have better control of the web's profile. '
The marrying of the steam application to the vacuum source
insures that the steam goes where it is intended. The
vacuum could be increased without changing the steam rate to
increase water removal.
Accordingly, the principal object of the apparatus is
to make maximum usage of generated steam and efficiently
utilize the energy required for generating steam when
applying steam to a paper web.
A further object of the present invention is to provide
a steam shower apparatus for a paper making machine which
applies steam in such a way that the entrainment of
non-condensable air into the condensation space, which
sevsrely hampers condensation heat transfer, is limited or
eliminated.
Another object of the present invention is to provide a
steam shower,apparatus for a paper making machine that
allows for improved accuracy and repeatability of steam flow
control, vacuum flow and level control.
Still another object of the,present invention is to
provide a steam shower apparatus for a paper making machine
that applies steam to a sheet in such a way that uniformity
of heat-transfer is,provided in the cross-machine direction
(non-uniformity is necessary for profile correction).
Yet another object of the present invention is to
eliminate the moisture condensation on the outermost
surfaces of the apparatus to prevent dripping on the sheet
traveling through the apparatus.
These and other features and objects of the present
invention will be more fully understood from the following '
detailed description which should be read in conjunction -
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with the several flgures in which corresponding reference
numerals refer to corresponding parts throughout the several
views.
BRIEF DESCRIPTION OF THE DRAWING
Fig. l is a schematic view of a portion of a paper
making machine including the steam shower/vacuum apparatus
of the present invention.
Fig. 2 is a sectional view of a steam shower/vacuum
apparatus of the present invention, positioned adjacent to
the sheet, employing positional steam flow control and
positional vacuum flow control.
FIG. 3 is a sectional view of a further alternate
embodiment of the steam shower/vacuum apparatus shown in FIG
l in which the bottom surface of the apparatus is heated by
a resistance electrical heater.
FIG. 4 is a sectional view of a further alternate
embodiment of the steam shower/vacuum shown in FIG. l in
which the steam supply manifold forms the bottom portion of
the apparatus.
FIG. 5 is a sectional view of an additional embodiment
of the steam shower/vacuum apparatus shown in FIG. 5.
; FIG. 6 is a simplified plan view of another embodiment
of the steam shower/vacuum apparatus shown in FIG. 6 with
only the steam supply manifold of the apparatus being shown.
FIG. 7 is a sectional view of a stepper motor with
valve body positioned within both the steam and vacuum
zones.
FIG. 8 is a schematic view of the computer control
system which controls the amount of both steam and vacuum
applied to the web.
FIG 9 is a schematic view of the logic control panel
shown in FIG 8.
DES~RIPTION OF THE PREFERRED EMBODIMENTS
At the outset the present invention is described in its
broadest overall aspects with a more.detailed description
following.
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In it's broadest overall aspects the present invention
is a steam profiling apparatus which includes steam showers
lO, positioned at strategic locations on the paper making
machine, with a device for creating a vacuum 21, positioned
directly beneath the steam shower. As is shown in FIG. l, a
steam shower vacuum combination is positioned on the forming
section of a paper making machine with one or more
additional steam shower vacuum couples positioned so that
the web flows between them after it leaves the forming
section of the paper making machine and before it enters the
press section. In the preferred embodiment, the steam
- shower extends across the entire width of the paper making
machine producin~ a line of steam in the cross machine
direction. The vacuum positioned directly beneath the steam
shower also has a vacuum chamber which extends beneath the
steam shower so as to produce a zone of lower pressure
directly beneath the zone where the steam is being applied
to the web.
As shown in Fig. l, the steam apparatus lO includes a
steam supply manifold 12 which applies steam thrQugh a feed
pipe 14 to a chamber 16 leading to a combination Coanda
nozzle 18 and impingement nozzle 20. The vacuum apparatus
21 includes a vacuum supply manifold 22 which through a
feed-pipe 24 reduces the pressure in a chamber 26 that is
positioned parallel to an'd directly beneath the steam zone
discussed above. The Coanda nozzle 18 is arranged in the
apparatus so that the steam flowing through the Coanda
nozzle 18 is directed along a surface of the apparatus lO
which is positioned adjacent and parailel to the sheet 28
which is to be heated. The steam flows in a direction
opposite to the direction of travel of the sheet. The
direction of travel of the sheet is shown by arrow 30. The
main purpose of this Coanda nozzle 18 is to remove the
boundary layer of entrained air traveling with the sheet 28.
This layer of air normally acts as an insulator preventing
the steam from penetrating the sheet 28. Additionally, a
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corresponding vacuum chamber 26 is located opposite the
steam nozzle 18 and 20 to maximize the amount of steam drawn
into the web and subsequently increase profilability.
A preferred embodiment of the present invention
includes means for heating the outside bottom surface of the
apparatus to prevent discharge steam condensing thereupon
and dripping moisture on the sheet. For example, the
outside bottom surface could be heated electrically, for
example with an electrical resistance heater. In another
variation, the steam supply manifold is located in the lower
portion of the apparatus so that the bottom wall of the
apparatus is also the bottom wall of the steam supply
manifold. In still another variation, the apparatus is
mounted above the traveling sheet so that a downstream
corner of the apparatus contacts the web so that steam is
back pressured between the sheet and the apparatus.
The key to this invention is the marriage of the two
devices (steam shower and vacuum chamber) with both the
steam and coordinate control system. The control system
will adjust the vacuum section beneath the steam section as
appropriate. Quite simply this system will recognize when
it is necessary for it to increase or decrease steam and/or
vacuum flow and react accordingly. Currently, those methods
available are limited to profilable steam boxes and
DQ~-profilable vacuum boxes. The present invention is a new
device (i.e. profilable vacuum system coupled to a
profilable steam system) that requires the sophistication of
a combined control s~stem to operate effectively. This is
shown in FIGS 8 and 9. This is done by the use of a
measurement computer system 40. The measurement computer
system 40 measures the quality of the paper which is
affected;by the steam shower and vacuum apparatus. The
measurement computer system 40 then electrically sends a
signal to the operators console 42. The operators console
4? interprets the signal and sends a signal to the logic
control panel 44. The logic control panel 44 receives the
computer's signal and outputs instructions 52 for the
stepper motor chamber to control the appropriate valves in
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WO91/13205 ;; 2 0 7 ~ 9 9 3 PCT/US91/01167 ~-
both the vacuum zone and the steam zone 54 which will adjust
the inlet orifices in both the vacuum and steam zone, and
ultimately send a certain amou~t of both vacuum and steam to
the web. In addition, the logic control panel 44 controls
aspects of the steam by analyzing the pressure 46 and
temperature 50 of such steam and sending a si~nal 48 to the
steam supply before the steam enters the apparatus. If, for
instance, the vacuum system was not operated in conjunction
with an opposing steam shower, it's effect on moisture
control or web preheating would be minimal. The vacuum
section serves to enhance the effectiveness of the steam
shower by increasing the percentage of steam brought into
the sheet at the appropriate location and limiting the
migration of steam to adjacent locations.
As is stated above, the purpose of a conventional
profiling steam shower is to correct moisture
inconsistencies in the web. The steam shower does this by
applying steam to those sections that have more moisture
than desired, effectively preheating those particular
sections of the web. As the web is passed through the dryer
the excess moisture which has been preheated will evaporate
sooner, thus actually reducing the moisture level in that
section.
Without simultaneous control of the steam shower and
the vacuum system, too much operator interaction would be
necessary for the system to be effective. This invention's
purpose is to allow the computer to tie into a closed loop
measurement gauge, or to allow an operator to push a single-
control and have the appropriate steam valve open as well as
have the opposing vacuum valve open. The complex
interactions between steam, vacuum and water removal are not
readily reduced by machine operators, therefore the computer
based control system, shown in Fig. 8, is necessary to
obtain the maximum benefit from this actuator pair.
Therefore, it is essential to marry these two devices
together to ensure proper operation.
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The steam shower apparatus for supplying steam to a web
or sheet includes an air-foil type nozzle, utilizing the
Coanda effect, to impart steam in a direction roughly
parallel but opposite in direction to the direction of
travel of the sheet. This Coanda effect steam foil.blocks
the boundary layer of entrained air traveling with the sheet
and subsequently serves to increase efficiency. In the
interest of limiting the entrainment of non-condensible air
into the condensing-space located between the apparatus and
the sheet, the counter parallel-flow nature of the system
insures that the exhausting steam creates a positive
pressure "wall" at the incoming or downstream edge of the
apparatus, thereby decreasing the volume of air which can be
entrained by the moving sheet. At the outgoing or upstream
edge of the apparatus, the velocity of the sheet serves to
limit the volume of air entering the condensing space, close
to the surface of the exiting sheet.
An additional feature of the invention is that the high
velocity counter-flow running parallel to the sheet insures
that even after exhausting at the upstream edge, a
significant percentage of the non-condensed steam continues
to flow roughly parallel to the sheet for a considerable
distance, effectively preheating the sheet before it
actually enters the apparatus. This non-condensed steam
thereby serves to effectively utilize some of the exhaust
steam which would otherwise be wasted.
In addition to the Coanda nozzle, the steam shower
utilizes a unique hole pattern to impart steam into the web
via impingement, thereby insuring uniformity of steam flow
and heat transfer in the cross-machine direction at the
desired positional location. The Coanda nozzle blocks the
boundary layer of entrained air and preheats the web while
` the impingement nozzle applies pressurized steam into the
web. This combination of the two application techniques
maximize the efficiency of the steam shower itself.
Both æteam and vacuum are supplied to the apparatus and
conveyed across the machine width by an oversized
distribution header (typically having a ten inch diameter)
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WO91/13205 i` ~ 2 0 ~ 5 9 9 ~ PCT/US91/01167 -
to insure uniform supply distribution across the machine,
feed-pipes (typically having a two inch diameter) located
normal to the axis of the supply manifold traverse the
diameter of the supply manifold.
Any undesirable condensation in the supply manifold,
being heavier than vapor, collects in the bottom of the
manifold where it is bled to drain at the rear of the
apparatus. The removal of condensation from the manifold
insures that condensation in the nozzle exit-flow is
minimized.
In a preferred embodiment, the impingement chamber 16,
shown in Fig. l, and corresponding nozzle are divided into
several chambers and associated nozzles by positioning
baffles around several feed pipes. Each of the these feed
pipes is connected to a direct-current stepper motor. As
shown in Figure 7, a direct-current stepping motor 110 is
mounted on the outboard end of the feed-pipe 112. A valve
pipe 124 is located within the feed-pipe 112. A lead-screw
type coupling 114 connects the stepping motor shaft 116 to a
valve stem 118 which connects to the translating
valve-poppet 120 located in the body of the feed-pipe in the
region of the inlet orifice 122. As the stepper motor shaft
116 changes its position, it turns the coupling 114, which
causes the valve stem 118 to move longitudinally toward the
valve poppet 120. The valve poppet 120 i5 ~oved to open or
close the orifice 122 in the valve pipe 124. This is done
to either totally close the orifice 122 to prevent steam in
the steam zone, and vacuum in the vacuum zone from entering
the valve pipe 124 at the inlet orifice 122, or to partially
close the orifice 122 to thereby adjust the volume of steam
and vacuum entering the valve-pipe 124. Positioning of the
stepper motor shaft angle translates the valve poppet 120 so
as to increase or decrease the available open-area of the
feed-pipe inlet orifice. As a result, the flow-rate of
steam through the feed-pipe inlet orifice may be controlled,
thereby enabling the controlled application of steam to the
sheet.
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The choice of a stepping-motor llO as the preferred
type of valve actuator is particularly important to the
accuracy and repeatability of the control process. The
small angular increments of shaft position 116 (typically 2
degrees per step), combined with the turn-down ratio of the
lead-screw coupling 114 combine to provide approximately
5000 precise and repeatable available valve-poppet 120
positions over a total valve-poppet travel of one inch. The
specific values cited above may be changed in accordance
with specific design requirements, but this example serves
to indicate the extraordinary control definition, accuracy
and repeatability available with such an actuator.
In addition to the above stated features, an attractive
aspect of the stepping-motor actuator is that it may be
electrically coupled through actuator lines, directly to a
computer control system, as seen in Figures 8 and 9. Such ~ -
coupling eliminates the need for any intermediate signal
conversion (i.e. from electric to pneumatic), with an
attendant presumed improvement in both control, accuracy and
repeatability.
The stepping-motor actuator, of course, may be replaced
by any type of actuator which will operate a poppet-like
; device to provide the desired steam flow control.
The main body of the apparatus is insulated about the
supply-manifold with suitable insulation to minimize the
likelihood of condensation carry-over and to maximize the
usage of the steam latent heat for the purpose intended.
The apparatus includes two separate structural
chambers, the manifold/nozzle chamber 16 (which in the
preferred embodiment is of fixed standardized length) and
the control chamber 12 (which in the preferred embodiment is
of variable length). ~he variable-length may be chosen so
as to provide the apparatus length required to aid in the
attainment of the necessary steam condensing rate for each
specific application. Alternatively, both lengths may be
chosen as fixed values, so as to provide a fixed apparatus
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WO91/13205 ~ PCT/US91/01167 ~-
length deemed to be satisfactory for the attainment of
successful performance over the full range of expected
applications.
In certain applications, it is important that no
moisture other than that resulting from film condensation at
the steam-sheet interface is deposited on a sheet traveling
through the apparatus. Under certain conditions in the
embodiments described above, moisture condenses on the
bottom surface of the apparatus and eventually drips onto
the sheet. It has been found that by maintaining the
temperature of the outside surface above 180 degrees
Fahrenheit, no discharged steam condenses on the outside
bottom surface because the surface is too hot for any
condensation to occur at atmospheric conditions. As a
result there is no dripping of moisture on the sheet.
Maintaining this temperature can be achieved in various
ways. ~he bottom surface of the apparatus can be heated
electrically, by means conventional to the art. For
example, the bottom surface can be heated with a resistance
electrical heater, as shown in FIG. 3. In addition,
modifications can be made in the structure of the apparatus
to achieve the requisite goals.
The embodiment of the steam shower apparatus shown in
FIG. 4 also eliminates this condensation. In FIG. 4, the
steam supply manifold is configured so that the steam supply
manifold constitutes the entire bottom surface of the
apparatus. Steam within the steam supply header is either
at a sufficient pressure (approximately 5-lS psig) or at a
sufficient superheat temperature to insure that the
; temperature of the outside bottom surface 146 is above 180
degrees Fahrenheit.
Steam can also escape from the downstream side of the
apparatus because the sheet may carry steam as it exits the
: apparatus. Steam can also leak out at the upstream side of
the apparatus which is much cooler than bottom surface.
This condensed steam then drips on the sheet and may result
in sheet irregularities. To prevent this dripping, drip
shields are positioned at the downstream and upstream edges
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WO91/13205 ;' PCT/US91/01167
of the apparatus respectively. The shield is an extension
of the bottom surface so that the temperature of this shield
is approximately the same as the bottom surface. As a
result any steam striking this shield will be vaporized by
the shield, and any other steam that passes around the
shield and condenses on the apparatus will fall into the
pocket created between the shield and the apparatus. This
collected water may then be drained away.
The foregoing invention has been described with
reference to its preferred embodiments. Various alterations
and modifications will, however, occur to those skilled in
the art.
The "steam shower" apparatus could be constructed of a
reduced cross-machine length, in any of the embodiments, to
provide an apparatus whose function is to operate over only
a reduced percentage of the actual paper-machine width.
These and other alterations and modifications are
intended to tall wLthin the scope of the .p~ended clai=s.
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