Patent Abstract:
An apparatus for decreasing heat emission and enhancing a vacuum system in a papermaking machine is provided. Such an apparatus includes a drying device having an inlet for receiving heated air for removing moisture from a paper web and an outlet for exhausting the moisture-containing air from the drying device. A vacuum system is configured to produce a suction and receive the moisture-containing air. A web handling device is disposed upstream of the drying device and is configured to interact with the web before the web is directed to the drying device. The web handling device is further configured to receive a portion of the moisture-containing air from the drying device, wherein the portion of the moisture-containing air is directed through the web by the web handling device to facilitate dewatering of the web before the moisture-containing air is received by the vacuum system. The web handling device is also configured to provide the moisture-containing air at a supply pressure with respect to the suction produced by the vacuum system such that the web handling device operates at an above-ambient pressure. Associated apparatuses and methods are also provided.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to papermaking machines and, more particularly, to papermaking machine configured to selectively recirculate exhaust air from a dryer so as to increase dewatering efficiency in processes upstream of the dryer, to reduce emissions from the papermaking machine, and to enhance a vacuum system associated with the papermaking machine. 
     2. Description of Related Art 
     Drying devices such as, for example, through-air dryers and Yankee dryers, are often employed in papermaking machines for drying a paper web after the paper web has been formed. Such drying devices often use a combination of heat and flowing air to dry the paper web and, as such, the exhaust from such drying devices comprises moisture-laden hot air. Generally, the venting of the exhaust from a drying device to atmosphere is undesirable for several reasons. For example, venting of the hot, moisture-laden air releases thermal energy that could be applied to other processes within the papermaking machine. Further, releasing the hot, moisture-laden air may increase undesirable papermaking plant emissions and may be unfavorably received by or may adversely affect neighbors surrounding the papermaking plant. In addition, significant and continuous environmental testing associated with the emissions may also be required. Accordingly, it would be desirable to reduce, minimize, or eliminate the emission of exhaust from such papermaking machine drying devices. 
     In some instances, the papermaking machine may be configured such that the exhaust from the drying device is recirculated through the drying device in order to reduce the heat input necessary to provide the heated air to the drying device, as well as to reduce emissions. In other instances, some of the exhaust from the drying device may be used to reduce process heat demands or to heat buildings. However, the heat from the exhaust of the drying devices often exceeds the amount of heat that can practically be re-used. In addition, a certain amount of the exhaust from the drying device must often be diverted so as to, for instance, remove excess condensates from the exhaust, wherein the exhaust may then be recirculated through the drying device. In such instances, though, the diverted portion may still be vented to atmosphere and thus will continue to undesirably contribute to plant emissions. 
     In order to reduce the amount of moisture to be removed from the web by the drying devices, many papermaking machines employ vacuum devices prior to the drying devices for partially dewatering the web. However, for example, in papermaking machines employing through-air dryers, it often undesirable to press or compact the web, though the web must still be dewatered to, for instance, about 18% to about 32% dryness. The vacuum devices thus employed to provide the necessary vacuum for dewatering the web to such an extent, and without pressing the web, often undesirably consume a significant amount of energy. 
     Thus, there exists a need for a papermaking machine having reduced emissions from the exhaust of the drying device(s). Further, it would be desirable for such a papermaking machine to have an efficient non-compacting (in the case of a machine employing a through-air dryer) dewatering process before the web is directed through the drying device(s). In addition, it would be desirable for the papermaking machine to exhibit reduced energy consumption with respect to the vacuum system and/or other high energy-consumption systems associated with the machine. 
     BRIEF SUMMARY OF THE INVENTION 
     The above and other needs are met by the present invention which, in one embodiment, provides an apparatus for decreasing heat emission and enhancing a vacuum system in a papermaking machine. Such an apparatus includes a drying device configured to dry a paper web, wherein the drying device has an air inlet for receiving heated air for removing moisture from the web and an air outlet for exhausting the moisture-containing air from the drying device. A vacuum system is configured to produce a suction and to receive the moisture-containing air. A web handling device is disposed upstream of the drying device and is configured to interact with the web before the web is directed to the drying device. The web handling device is further configured to receive a portion of the moisture-containing air from the air outlet of the drying device, wherein the portion of the moisture-containing air is directed through the web by the web handling device so as to facilitate dewatering of the web before the moisture-containing air is received by the vacuum system. The web handling device is also configured to provide the moisture-containing air at a supply pressure with respect to the suction produced by the vacuum system such that the web handling device operates at an above-ambient pressure. 
     Another advantageous aspect of the present invention comprises a method of decreasing heat emission and enhancing a vacuum system in a papermaking machine. The papermaking machine includes a drying device configured to dry a paper web, wherein the drying device has an air inlet for receiving heated air for removing moisture from the web and an air outlet for exhausting the moisture-containing air from the drying device, a web handling device disposed upstream of the drying device and configured to interact with the web before the web is directed to the drying device, and a vacuum system for producing a vacuum. A portion of the moisture-containing air from the air outlet of the drying device is directed to the web handling device, and through the web to the vacuum system, at a supply pressure with respect to the suction produced by the vacuum system such that the web handling device operates at an above-ambient pressure, so as to facilitate dewatering of the web. 
     Still another advantageous aspect of the present invention comprises an apparatus for increasing dewatering efficiency of a paper web in a papermaking machine. Such an apparatus includes a drying device configured to dry the web, wherein the drying device has an air inlet for receiving heated air for removing moisture from the web and an air outlet for exhausting the moisture-containing air from the drying device. An air handling device has an air inlet for receiving incoming air to be heated and an air outlet in communication with the air inlet of the drying device for directing the heated air thereto. A web handling device is disposed upstream of the drying device and is configured to interact with the web before the web is directed to the drying device. The web handling device is configured to receive a mixture of a portion of the heated air from the air outlet from the air handling device and a portion of the moisture-containing from the air outlet from the drying device for facilitating dewatering of the web, wherein the web handling device is further configured to interact with the web at an above-ambient pressure. 
     Yet another advantageous aspect of the present invention comprises a method of increasing dewatering efficiency of a paper web in a papermaking machine. The papermaking machine includes a drying device configured to dry a paper web, wherein the drying device has an air inlet for receiving heated air for removing moisture from the web and an air outlet for exhausting the moisture-containing air from the drying device. An air handling device has an air inlet for receiving incoming air to be heated and an air outlet for directing the heated air to the drying device, while a web handling device is disposed upstream of the drying device and is configured to interact with the web before the web is directed to the drying device. Accordingly, a portion of the moisture-containing air is first directed from the air outlet of the drying device, while a portion of the heated air from the air outlet of the air handling device is concurrently directed to be mixed therewith, before the mixture of air is directed to the web handling device. Thereafter, the mixture of air is directed through the web at the web handling device, the web handling device being operated at an above-ambient pressure, so as to facilitate dewatering of the web. 
     Thus, embodiments of the present invention meet the above-identified needs and provide significant advantages as detailed further herein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIGS. 1A-1B  schematically illustrate alternative embodiments of a papermaking machine according to the present invention; 
         FIG. 2  is a schematic illustration of an air circulation system showing waste air from the drying devices being directed to upstream web handling devices, with a vacuum system in communication with a web handling devices, according to one embodiment of the present invention; 
         FIG. 3  is a schematic illustration of an air circulation system having a hot air supply device in association with a vacuum system, according to one embodiment of the present invention; and 
         FIG. 4  is a schematic illustration of a through-air dryer showing a hood associated with the TAD extending over a vacuum box, with a blower extending into the hood opposite to the vacuum box, according to one embodiment of the present invention; and 
         FIG. 5  is a schematic illustration of air circulation system showing a mixture of waste air from the drying devices and fresh hot air from an air handling device being directed to upstream web handling devices, with a vacuum system in communication with a web handling devices, according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
       FIGS. 1A-1B  illustrates an example of a papermaking machine according to one embodiment of the present invention, the papermaking machine being indicated generally by the numeral  10 . Such a machine  10  includes a former  100  for forming a paper web  20  on a forming fabric  50 . Such a machine  10  further comprises one or more drying devices such as, for example, an impingement dryer (not shown), a through-air dryer  400 , and/or a Yankee dryer  500 . The drying devices generally include a drying fabric  600  configured to receive the web  20  from the forming fabric  50  and to transport the web  20  through the through-air dryer(s)  400  to the Yankee dryer  500 . In some embodiments, the drying fabric  600  may also comprise the forming fabric  50  in that the web  20  may be formed directly on the drying fabric  600 , which may eliminate the forming fabric  50 . At the Yankee dryer  500 , the web  20  is separated from the drying fabric  600 , dried by the Yankee dryer  500 , creped from the Yankee dryer  500 , and then directed to a reel-up  700 . Note, however, that some embodiments may not include a Yankee dryer  500 . 
     Generally, the web  20  may be dewatered, transferred between fabrics at various points between the former  100  and the drying devices, and otherwise handled by one or more various web handling devices  75 . For example, after the web  20  is formed on the forming fabric  50  by the former  100 , the web  20  may be directed through a hot air supply device  150  for dewatering the web  20 . In some instances, where the web  20  is transferred from the forming fabric  50  to the drying fabric  600 , a vacuum box  200  may be provided for facilitating transfer of the web  20  to the drying fabric  600 . In still other instances, a molding box  300  may be disposed prior to the drying devices to structure the web  20 , to provide additional dewatering of the web  20 , to pre-heat the web  20  prior to the web  20  entering the drying device, and/or, for example, to provide a seal arrangement for a drying device as discussed, for example, in U.S. Pat. No. 6,199,296, also assigned to the assignee of the present invention and incorporated herein in its entirety by reference. One skilled in the art will appreciate, however, that web handling devices  75  such as the hot air supply device  150 , the vacuum box  200 , and the molding box  300  are only examples of the web handling devices  75  that may be disposed between the former  100  and the drying devices for dewatering the web  20  and that embodiments of the present invention may include any combinations of these devices and/or other dewatering or web handling devices  75 . As will be described further herein, the hot air supply device  150 , the vacuum box  200 , and the molding box  300  are configured to require a suction for operation. Therefore, in some instances, the hot air supply device  150 , the vacuum box  200 , and the molding box  300  are configured to be operably engaged with a common vacuum system  900  (as shown in FIG.  2 ), though, in some cases, a separate vacuum system (not shown) may be provided for each device.  FIG. 1B  also shows the web handling devices  75  in phantom, indicating that embodiments of the present invention may include one or more such web handling devices  75  or any combinations thereof and, as such, it will be understood that embodiments of the present invention are neither restricted by the particular number or type of the web handling devices  75  which may be implemented therein. 
     As shown in  FIGS. 1A ,  1 B, and  2 , one embodiment of a papermaking machine  10  may include, for example, two consecutive through-air dryers (TADS)  400  and a Yankee dryer  500 . Each TAD  400  and the Yankee dryer  500  may be supplied with air by a common air handling device  800 , or in some instances, by separate air handling devices (not shown), wherein the air is typically heated by a heat source  850  and directed to the drying device by a fan  860 . The heat source  850  may comprise, for example a direct gas-fired heater having a fuel inlet  830  and a combustion air fan  840 , though many different types of direct and indirect heaters may be implemented to provide the necessary heat. The air handling device  800  generally takes in incoming air through an air inlet  810  and provides the air through an air outlet  820 , wherein the air outlet  820  is configured to duct or channel the heated air to the drying devices. In the case of the Yankee dryer  500 , the heated air is introduced into an air inlet  510  in the hood  550  of the Yankee dryer  500  and then exhausted through an air outlet  520  from the hood  550 . The TAD  400 , however, may be configured for either an inward flow or an outward flow, and one skilled in the art will appreciate that both configurations may be implemented herein within the spirit and scope of the present invention. For an inward flow TAD  400 , as shown in  FIG. 1 , the heated air is supplied to an air inlet  410  in the hood  450  extending about the perforated drying cylinder  460 , and then exhausted through an air outlet  420  extending from the drying cylinder  460  or, for example, an exhaust plenum extending across the dead zone of a single through-air dryer or between adjacent through-air dryers. Accordingly, for an outward flow TAD, the heated air would be supplied through an air inlet extending into the drying cylinder or an intake plenum extending across the dead zone of a single through-air dryer or between adjacent through-air dryers and then exhausted from an air outlet extending from the hood. 
     Note that, as shown in  FIGS. 2 and 5 , several of the drying devices  400 ,  500  are shown in phantom to reinforce that a papermaking machine  10  according to embodiments of the present invention may generally include one or more drying devices, such as an impingement dryer, a TAD, and a Yankee dryer, and the TAD  400  not shown in phantom is intended to indicate that the papermaking machine  10  may, in some instances, comprise a single drying device which may be, for example, the TAD  400 , a Yankee dryer, an impingement dryer, or any other suitable dryer, or combinations thereof, consistent with the spirit and scope of the present invention. Likewise, several of the web handling devices  75  are shown in phantom to reinforce that a papermaking machine  10  according to embodiments of the present invention may generally include one or more web handling devices  75 , such as hot air supply device  150 , a vacuum box  200 , and a molding box  300 , and the vacuum box  200 /blower  250  type of drying device  75  not shown in phantom is intended to indicate that the papermaking machine  10  may, in some instances, comprise a single web handling device  75  which may be, for example, the vacuum box  200 , a hot air supply device  150 , a molding box  300 , or any other suitable web handling device, or combinations thereof, consistent with the spirit and scope of the present invention. 
     The exhaust air from each of the TAD  400  and the Yankee dryer  500  typically contains moisture extracted from the web  20  during the drying process. In addition, the exhaust air may still include a significant amount of thermal energy, though more so in the case of the exhaust air from the Yankee dryer  500 . As such, in some instances, the exhaust air may be routed back to the air inlet  810  of the air handling device  800  for reheating by the heat source  850  and recirculation through the drying devices by the fan  860 , as shown in  FIG. 2 , wherein the recirculation of the hot exhaust air may lower the power consumption requirements of the heat source  850 . However, one skilled in the art will appreciate that such recirculation is not always implemented and, in other instances, the hot exhaust air may be used for other purposes or released to atmosphere. As such, in instances, where hot exhaust air recirculation is implemented, it would be disadvantageous to recirculate the moisture present in the exhaust air since this could lower the efficiency of the drying devices and, in some instances, may cause rewetting of the web  20 . Accordingly, in either instance, a portion of the exhaust air, otherwise referred to as the waste air (indicated as element  750  in FIG.  2 ), is diverted from the air outlet(s)  420 ,  520  of the drying device(s)  400 ,  500 . Thus, one advantageous aspect of the present invention involves directing the waste air  750  to the web handling devices  75 , such as the hot air supply device  150 , the vacuum box  200  and the molding box  300 , so as to increase the dewatering efficiency thereof. In some situations, all, part, or none of the remainder of the exhaust air may be recirculated through the drying devices  400 ,  500  via the air handling device  800 . Where all of the remainder of the exhaust air is recirculated through the drying devices  400 ,  500 , substantially none of the exhaust air is vented to atmosphere, thereby advantageously reducing plant emissions, though recirculation of some of the remainder of the exhaust air will also advantageously reduce plant emissions as compared to releasing that exhaust air to atmosphere. 
     In one instance where the waste air  750  is directed to a web handling device  75 , the web  20  is first formed by the former  100  on a forming fabric  50 , which may comprise, for example, a Fourdrinier or forming wire, or a through-air drying (TAD) fabric. A hot air supply device  150  is disposed downstream of the former  100  and comprises a hot air supply hood  160  and a vacuum box  170 . As a matter of background, some prior art air presses are configured to direct pressurized ambient temperature air through the web as it is sandwiched between two fabrics, such as shown, for example, in U.S. Pat. Nos. 6,331,230; 6,306,258; 6,306,257; 6,228,220; and 6,080,279. However, a hot air supply device  150  according to one embodiment of the present invention is configured for application with respect to a fabric, in some instances, only a single fabric. That is, in instances, where the web  20  is formed on a single forming fabric  50 , the hot air supply hood  160  is disposed adjacent to the web  20  being transported thereby on the forming fabric  50 , while the vacuum box  170  is disposed adjacent to the forming fabric  50 , opposite the web  20 , as shown in FIG.  3 . Accordingly, only a single fabric is present in a hot air supply device  150  in some embodiments of the present invention. In such instances, the hot air supply hood  160  is configured to supply hot air, more particularly, the waste air  750 , to the web  20 , where the waste air  750  then is pulled through the web  20  and the forming fabric  50  by the suction from the vacuum box  170 , and thus any moisture removed from the web  20  is collected by suction from the vacuum box  170 . The vacuum box  170  is in communication with the vacuum system  900  which supplies the necessary suction. As with the web handling devices  75  discloses herein, the hot air supply device  150  is further configured to operate at close to and slightly above ambient pressure. That is, in instances where no suction is provided at the vacuum box  170 , the supply pressure of the waste air  750  to the hot air supply hood  160  is adjusted such that the pressure in the hot air supply hood  160  is close to and slightly above ambient pressure. Thereafter, during operation of the hot air supply device  150 , as the suction from the vacuum box  170  is increased, the supply pressure of the waste air  750  to the hot air supply hood  160  is also increased so as to maintain the pressure therein at close to and slightly above ambient pressure. As such, the effect is thereby to operate the web handling device  75 , such as the hot air supply device  150 , at a pressure close to and slightly above ambient. 
     The vacuum system  900  may comprise, for example, a liquid ring pump  910  employing a water source  920  such as, for example, a cooling tower, for providing the necessary seal water therefor, and a water spray source  930  disposed in a spray chamber  940  between the pump  910  and the vacuum box  170 , the function of which will become more evident below. Thus, according to one advantageous aspect of the present invention, the waste air  750  from any single drying device or any combination or all of the drying devices may be directed to the hot air supply hood  160  of the hot air supply device  150 , wherein the hot air supply hood  160  is configured to direct the waste air  750  through the web  20  and the forming fabric  50  for collection by the vacuum box  170 . The waste air from a TAD  400  is typically in the range of about 25° C. to about 180° C., while the waste air from a Yankee dryer  500  is typically between about 250° C. to about 340° C. Thus, directing the heated moisture present in the waste air  750  from the drying devices through the web  20  generally decreases the viscosity of the water in the web  20 , making the water more easily removed by the suction from the vacuum box  170 , and thereby facilitating and increasing the efficiency of the dewatering process, while also preheating the web  20  for further downstream processes. This benefit provides a distinct advantage over double fabric air presses using pressurized ambient temperature air. 
     However, the waste air from the hot air supply device  150  collected by the suction from the vacuum box  170  may still contain a significant amount of thermal energy after it has been directed through the web  20 , particularly when the waste air  750  is directed from the Yankee dryer  500  or a combination of both the Yankee dryer  500  and the TAD  400 . According to one purpose of the present invention, this waste air preferably should not be vented to atmosphere. As such, the waste air is directed through the spray chamber  940  where the waste air interacts with a water spray provided by the water spray source  930 . The water spray serves to condense a substantial amount of the moisture in the waste air while removing thermal energy therefrom, thereby cooling and volumetrically contracting or densifying the air. The water to the water spray source  930  may be provided by the cooling tower  920  or another water source, and the condensate collected from the waste air in the spray chamber  940  may be collected and returned to the cooling tower  920  where the thermal energy may be conveniently dissipated. The densified air further produces a pressure drop with respect to the waste air entering the spray chamber  940  and thus also reduces the required capacity of the pump  910  relative to instances in which ambient air is directed through the web handling device. This effect may be more significant where the thermal energy of the waste air  750  is greater, such as in instances where the air directed to the hot air supply device  150  is directed from the Yankee dryer  500 . One skilled in the art, however, will appreciate that condensation of the moisture in the waste air and densification of the air may be accomplished in other manners. For example, in some instances, an increase in the flow of seal water to the pump  910  may provide the necessary condensation of the moisture in the waste air and the densification of the air at the pump  910 . A vacuum system  900  configured in this manner provides, in some instances, an added benefit of removing particulate matter from the waste air, which may then be filtered from the cooling water returning to the cooling tower. 
     According to one embodiment of the present invention, after being transported through the hot air supply device  150 , the web  20  may be transferred from the forming fabric  50  to the drying fabric  600  at a transfer area  650 . Where the web  20  is transferred to the drying fabric  600 , another web handling device  75  comprising, for example, a vacuum box  200 , may be disposed adjacent to the drying fabric  600  for facilitating the transfer of the web  20  to the drying fabric  600 . The vacuum box  200  operates with a suction provided thereto by the vacuum system  900 . In such a configuration, the transfer area may further include a blower  250  disposed adjacent to the forming fabric  50  for directing air through the forming fabric  50  and through the web  20  so as to facilitate the transfer of the web  20  to the drying fabric  600  and to provide additional dewatering of the web  20 . Thus, in another advantageous aspect of the present invention, the waste air  750  from the drying devices may also be directed through the blower  250 , the forming fabric  50 , the web  20 , and the drying fabric  600 , and to the vacuum box  200 , so as to facilitate more efficient dewatering of the web  20  while also preheating the web  20 , or maintaining the earlier preheating of the web  20 , for further downstream processes. As previously discussed, in some embodiments, the vacuum box  200 /blower  250  arrangement is configured to operate at a pressure of close to and slightly above ambient. Further, the waste air  750 , after passing through the web  20 , is collected by suction of the vacuum box  200  and then directed from the vacuum box  200  to the vacuum system  900 . As such, the aforementioned advantage of condensing the moisture within the waste air, while densifying the air, so as to decrease the required capacity of the vacuum system  900 , may also be realized. 
     In some instances, if necessary, embodiments of the papermaking machine  10  may further include a molding box  300  disposed adjacent to the drying fabric  600 , prior to the drying devices, for further structuring and/or dewatering of the web  20 . The molding box  300  may have a corresponding blower  350  disposed adjacent to the web  20 , opposite the drying fabric  600 , for directing air through the web  20  to assist in the dewatering process. Thus, in another advantageous aspect of the present invention, the waste air  750  from the drying devices may also be directed through the blower  350 , the web  20 , and the drying fabric  600 , and to the molding box  300 , so as to facilitate more efficient dewatering of the web  20  while also preheating the web  20 , to structure the web  20 , or to maintain the earlier preheating of the web  20 , as the web  20  enters the drying devices. Also, as previously discussed, in some embodiments, the molding box  300 /blower  350  arrangement is configured to operate at a pressure of close to and slightly above ambient. Further, the waste air  750 , after passing through the web  20 , is collected by the suction from the molding box  300  and then directed from the molding box  300  to the vacuum system  900 . As such, the aforementioned advantage of condensing the moisture within the waste air, while densifying the air, so as to decrease the required capacity of the vacuum system  900 , may also be realized. 
     According to a further advantageous aspect of the present invention, the hood  450  of the first TAD  400  may extend upstream of the drying cylinder  460  thereof so as to at least partially cover and oppose the molding box  300 , as shown in FIG.  4 . In such a configuration, the molding box  300  may comprise, for example, part of a sealing arrangement for a plenum extending across the dead zone of a single TAD or between the dead zones of adjacent TADs as described in commonly assigned U.S. Pat. No. 6,199,296. However, embodiments of the present invention may also have the blower  350  operably engaged with the hood  450  generally opposite to the molding box  300 . The air handling device  800  supplies heated air through the heat source  850  at a temperature, for example, of about 225° C. to the TAD  400 , wherein the through-air drying process is more efficient if the web  20  is at or about the temperature of the heated air upon entering the TAD  400 . Accordingly, in some instances, the waste air  750  from the drying device(s) is directed to the blower  350  for pre-heating the web  20  to a desired temperature, immediately as the web  20  enters the TAD  400 . That is, since the blower  350  is incorporated into the hood  450  and the web  20  passing by and being heated by the blower  350  immediately enters the TAD  400 , the web  20  therefore enters the TAD  400  at the desired temperature. In such instances, the molding box  300 /blower  350  arrangement is also configured to operate at a pressure of close to and slightly above ambient, further taking into account the heated air supplied to the hood  450 . 
       FIG. 5  schematically illustrates another embodiment of a papermaking machine  10  according to the present invention. In some instances, the waste air  750  from the drying devices may not have the desired thermal energy for the upstream processes. Such a situation may occur when, for example, the machine  10  comprises only one or more TADs  400  and does not include a Yankee dryer  500 . In such instances, a portion of the heated air (indicated as element  760  in  FIG. 5 ) being directed from the air outlet  820  of the air handling device  800  to the air inlets of the respective drying devices, may be diverted and mixed with the waste air  750  from the drying devices so as to increase the thermal energy thereof. The flow of the diverted portion of the heated air  760 , as well as the waste air  750  from the drying devices, may be controlled, for example, by appropriate fans  870 ,  880 , dampers (not shown), and/or controllers (not shown). According to one embodiment of the present invention, the exhaust from the drying device(s) may be configured such that about 10% of the exhaust air is diverted as the waste stream  750  to the web-handling device(s). In another embodiment, the air outlet  820  of the air handling device  800  may be configured such that about 10% of the heated air  760  is diverted to the web handling device(s). The condition of the mixture of the waste air  750  from the drying device(s) and the portion of the heated air  760  from the air handling device  800  may, in some instances, be controlled by varying the flow of the respective streams. However, if necessary, the waste air  750  from the drying device(s), or the mixture of the waste air  750  from the drying device(s) and the portion of the heated air  760  from the air handling device  800 , may be directed through a single conditioning device  890  (shown in phantom) for appropriately adjusting the condition of the air entering all of the web handling device(s) or, in some instances, through an individual conditioning device  895  for each web handling device, wherein each conditioning device  895  is configured to provide heated air having the appropriate condition for the respective web handling device  75 . 
     A papermaking machine  10  configured according to embodiments of the present invention as described herein, in some instances, substantially eliminates emissions from the exhaust of drying devices that might normally be undesirably vented to atmosphere. Further, in some instances, an exhaust stack may be eliminated altogether, thereby simplifying construction and reducing the cost of environmental testing. In addition, losses internal to the machine  10  may also be controlled. For example, the supply of the waste air from the drying device(s) or, in some instances, the mixture of the waste air from the drying device(s) and the portion of the heated air from the air handling device  800 , may be controlled so as to match or slightly exceed the capacity of the vacuum system  900 . In this manner, seepage of room air into or excessive hot air leakage out of the web handling device(s)  75  can be avoided. Further, with respect to the drying device(s), pressure sensors (not shown) may, in some instances, be placed within the hood of the respective drying device so as to monitor the pressure therein. As such, the supply of the waste air from the drying device(s) or, in some instances, the mixture of the waste air from the drying device(s) and the portion of the heated air from the air handling device  800 , may be controlled such that the pressure within the hood is maintained at approximately atmospheric pressure, and preferably slightly above ambient. Such a provision also facilitates the avoidance of seepage of room air into or excessive hot air leakage out of the drying device. 
     Thus, embodiments of the present invention may advantageously reduce or eliminate emissions due to the exhaust from the drying devices of a papermaking machine, thereby simplifying construction and reducing the need for environmental testing. Further, the enhancement of the web handling device(s)  75 , for dewatering the web upstream of the drying device(s), with the supply of the waste air from the drying device(s) or, in some instances, the mixture of the waste air from the drying device(s) and the portion of the heated air from the air handling device  800 , increases the heat transfer to the web  20 , thus resulting in a more efficient and less energy-consuming dewatering process. In addition, particularly when high temperature air is directed to the web handling device(s)  75 , a substantial reduction in the required capacity of the vacuum system  900  may also be realized. 
     In order to demonstrate the advantageous aspects of the present invention, a hot air supply device  150 , having a hot air supply hood  160  as previously described, was implemented in a paper making machine  10  and operated at a slightly above-ambient pressure to prevent ingress of room air. The following process parameters were implemented: 
                                                     Product:   20.5   g/m 2  towel base sheet           Wire Speed:   1040   m/min           Vacuum Box Configuration:   2 × 16   mm wide slots           Vacuum Box Suction Level:   60   kPa                        
The following results, consistent with the advantageous aspects of the present invention as described herein,were obtained:
 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Temp. 
                   
                   
                 Vacuum 
                   
                   
               
               
                 Air 
                 in 
                 Web 
                 Web 
                 System 
                 Web 
                 Web 
               
               
                 Supply 
                 Vacuum 
                 Entering 
                 Temp. 
                 Capacity 
                 Entering 
                 Dryness 
               
               
                 Temp. 
                 Box 
                 Temp. 
                 Rise 
                 Reduction 
                 Dryness 
                 Increase 
               
               
                 (° C.) 
                 (° C.) 
                 (° C.) 
                 (° C.) 
                 (%) 
                 (%) 
                 (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 25 
                 17.4 
                 26.5 
                 −2.3 
                 Base 
                 25.5 
                 1.7 
               
               
                 161 
                 24.1 
                 27.0 
                 4.9 
                  7 
                 25.6 
                 1.9 
               
               
                 262 
                 28.5 
                 28.3 
                 9.2 
                 12 
                 26.3 
                 1.9 
               
               
                 330 
                 30.8 
                 29.8 
                 10.5 
                 17 
                 25.7 
                 2.3 
               
               
                   
               
             
          
         
       
     
     Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which these invention pertain having the benefit of the teachings presented in the foregoing description and the associated drawings. For example, in some embodiments of the invention, the former may be configured to form the web on a single through-air drying fabric, wherein the single TAD fabric transports the web through the various web handling devices and the drying devices. Accordingly, in such instances, the forming fabric and the drying fabric are one in the same. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Technology Classification (CPC): 3