Abstract:
A method for providing fresh air fed through a fan to a burner of a dryer, thereby charging the burner, when the dryer is operated with recirculating air. In commercial dryers in which the drying air is heated by a burner, it is customary to reuse the moist air leaving a drum containing the laundry to be dried as recirculating air. The recirculating air component is increased with increasing drying of the laundry. At the end of the drying operation, when the moist air no longer contains as much moisture as at the start, the moist air is used as recirculating air. The burner then no longer gets enough combustion air, which leads to an incomplete combustion. The dryer can be operated with a higher recirculating air component, an optimal combustion being guaranteed through the charging of the burner with fresh air. The invention permits more economical drying.

Description:
STATEMENT OF RELATED APPLICATIONS 
     This patent application is based on and claims the benefit of German Patent Application No. 10 2012 005 199.9 having a filing date of 16 Mar. 2012. 
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The invention relates to a method for drying laundry, wherein air for drying the laundry is heated by a burner and, at least during a part of the drying operation, at least a part of the air used to dry the laundry is fed back to the burner as recirculating air, if need be together with fresh air, and to a dryer for laundry, comprising a drum for receiving the laundry to be dried and comprising at least one burner for heating air which serves for the drying. 
     Prior Art 
     Dryers for commercial laundries possess at least one burner, preferably a gas burner, for heating air which is used for drying. The air heated by the burner is passed through a preferably rotationally drivable drum containing the laundry to be dried. The air here absorbs moisture from the laundry to be dried. The moist air is afterwards led as waste air into the open and/or is fed back as recirculating air to the at least one burner and reheated by this. 
     At the beginning of the drying, the air leaving the drum contains the most humidity. This air cannot, or can only in small part, be reused as recirculating air. It must therefore, at least for the most part, be passed out of the dryer. At the beginning of the drying, only a small amount of recirculating air is therefore being carried. A large amount of fresh air is then fed, at least for the most part, via the burner to the dryer. As a result of this very large fresh air component, the at least one burner gets sufficient combustion air. At the conclusion of the drying operation, air having only a small amount of humidity leaves the drum. A relatively large amount of recirculating air and only a small amount of fresh air are then fed to the burner. The at least one burner then contains only very little fresh air or no fresh air at all, with the result that the burner works uneconomically. In many cases, an incomplete combustion with undesirable soot formation can ensue. 
     The object of the invention is to provide a method and a dryer for drying laundry, which can be operated with a relatively large recirculating air component, or with only recirculating air, economically and without negative impacts on combustion. 
     A method for the achievement of this object is a method for drying laundry, wherein air for drying the laundry is heated by a burner and, at least during a part of the drying operation, at least a part of the air used to dry the laundry is fed back to the burner as recirculating air, if need be together with fresh air, characterized in that the fresh air is transported to the burner at least during a part of the drying process. According to this, the fresh air is transported to the at least one burner at least during a part of the drying process. As a result of the active transport of fresh air to the burner, the fresh air is virtually blown or forced into the burner. A type of charging of the burner with fresh air occurs. As a result, the burner is also then supplied with sufficient fresh air if the recirculating air is returned in full or for the most part to the at least one burner without this adversely affecting the combustion. The drying can hence be realized with more recirculating air than previously. The inventive method thereby provides more economical drying. 
     A further advantageous embodiment of the method provides for, where necessary, feeding fresh air to the recirculating air after the recirculating air has been warmed by the respective burner. This happens before the warmed recirculating air has reached the laundry to be dried. In this way, only that quantity of fresh air which is necessary to the optimal operation of the burner needs to be fed to this same. If required, additional fresh air can be added directly to the warmed recirculating air, which can lead to more economical drying by, for example, increasing the amount of air available for drying the laundry. 
     An advantageous refinement of the method provides for the fresh air to be fed under pressure, preferably through at least one fan or a blower, to the burner. This type of transport of the fresh air to the at least one burner represents the simplest and most effective charging of the burner. Through adjustment of the fan speed, the quantity of fresh air fed to the burner can be adjusted or controlled in accordance with requirements, so that the respective burner receives as much fresh air as it requires, based on the respective recirculating air component. The burner can thus receive that quantity of fresh air which is required for the, in each drying phase, optimal operation, wherein the quantity of fresh air can be increased the greater the recirculating air component becomes which is returned to at least one burner. 
     A further advantageous embodiment of the method provides for, where necessary, fresh air to also be fed behind the respective burner to the recirculating air warmed by this same. This happens before the warmed recirculating air has reached the laundry to be dried. In this way, only that quantity of fresh air which is necessary to the optimal operation of the burner needs to be fed to this same. Fresh air which is required over and above this can be fed directly to the warmed recirculating air. That too leads to more economical drying. 
     A dryer for the achievement of the object stated in the introduction is a dryer for laundry, comprising a drum for receiving the laundry to be dried and comprising at least one burner for heating air which serves for the drying, characterized in that an air flow generator for the transport of fresh air to the burner is assigned to the at least one burner. In this dryer, it is provided to assign to the at least one burner an air flow generator for the transport of fresh air to the burner. The at least one air flow generator ensures a virtually forced supplying of fresh air to the burner, in that the air flow generator virtually pumps and/or forces fresh air into the burner, to be precise particularly when, due to a relatively large recirculating air component, the burner can no longer automatically draw in the fresh air necessary for optimal combustion. 
     Advantageously, the air flow generator is assigned to a supply line for fresh air to the respective burner, or to a common supply line for all burners. The fresh air can be transported by the at least one air flow generator in the at least one supply line directly to the or each burner. 
     A further advantageous embodiment of the dryer provides that the at least one air flow generator is configured to generate a variable stream of fresh air to the burner. As a result, the fresh air can be adjusted or controlled in accordance with requirements. A sufficient quantity of fresh air for optimal operation, in particular for optimal combustion, is thereby fed to the respective burner. 
     In one advantageous embodiment of the dryer, the air flow generator is configured as at least one fan. If a plurality of burners are present, a dedicated fan is preferably assigned to each burner, though one fan can also be jointly assigned to all burners. As a result, each burner can be specifically and, if necessary, individually supplied with fresh air in sufficient quantity. 
     A preferred refinement of the invention provides, behind the at least one burner, a preferably variable and/or closable feed opening for fresh air which can be mixed to the air warmed by the burner. 
     It can preferably be provided that at least one fan or at least one blower for the generation of a recirculating air flow, and/or a closable or variable waste air outlet for at least a part of the recirculating air, are provided. The at least one fan can generate a specific recirculating air flow, in particular a recirculating air flow having a desired flow velocity and/or a desired recirculating air stream. The closable or variable waste air outlet serves to regulate the recirculating air component which is returned to the at least one burner and, having been warmed, is fed from this back to the laundry. That part of the moist air which is not used as recirculating air can be led off into the open for evacuation of the moisture which accrues when the laundry is dried in the dryer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred illustrative embodiment of the invention is explained in greater detail below with reference to the drawing, wherein: 
         FIG. 1  shows a schematic cross section through a dryer, 
         FIG. 2  shows a schematic cross section through the dryer according to  FIG. 1 , with arrows for illustration of the air flows, and 
         FIG. 3  shows a schematic horizontal section III-III through an upper part of the dryer in the region of a burner. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The dryer represented schematically in the figures serves for the highly effective and energy efficient drying of laundry. Such a dryer is used, above all, in commercial laundries. In the dryer which is shown here, air for drying of the laundry is heated by a single burner  10 . The dryer can also, however, have a plurality of burners  10  arranged in parallel or in series. The burner  10  can be constituted both by a gas burner and by an oil burner. 
     The dryer possesses an outer housing  11 , preferably a closed, box-like housing  11 , in which a drum  13 , which can be driven in rotary motion about a horizontal rotational axis  12 , the said burner  10 , a recirculating air fan  14  and, further below, the described air guide ducts are disposed. 
     The rotationally drivable drum  13  serves to receive the laundry to be dried. It possesses a loading and unloading opening (not shown). In particular the casing  15  of the cylindrical drum  13  is of air-permeable configuration to enable air used for the drying to flow through the drum  13  and the initially damp laundry present therein. The drum  13  is rotatably mounted in a lower compartment  16  of the housing  11 . 
     The drum  13  is partially surrounded at a short distance from the cylindrical casing  15  by air-impermeable, arc-shaped walls  17  and  18 . The walls  17  and  18  lie on a circular path running concentrically around the rotational axis  12 , whereby the air-impermeable walls  17  and  18  surround the cylindrical casing  15  of the drum  13  at a short distance apart for the formation of a narrow gap  19  between the casing  15  of the drum  13  and the walls  17  and  18 . Each of the preferably equal-sized walls  17  and  18  extends over about 120° to 150°, preferably about 135°, of the periphery of the drum  13 . In this way, between transverse rims, running parallel to the rotational axis  12 , of different walls  17  and  18  are formed openings which are left free by these same and are diametrically opposing, to be precise an upper air inlet opening  20  and a lower air outlet opening  21 . Mutually facing, spaced-apart transverse rims of the walls  17  and  18  are sealed in the region of the air inlet opening  20 , with respect to a horizontal partition  23  demarcating the lower compartment  16  from an above-situated upper compartment  22 , by transverse walls  24  and  25 . In addition, a lower transverse rim of the (in  FIG. 1 ) right-hand wall  17  is separated by a horizontal wall  26  to the nearest (left-hand) external wall  27  of the housing  11 . 
     In the upper compartment  22  of the housing  11  is located, at a distance from the external wall  27 , the recirculating air fan  14 , though this can also be in the form of a different air flow generator, for example a blower. In addition to the recirculating air fan  14 , there is also arranged in the upper compartment  22 , roughly in the middle, the burner  10 , to be precise such that a schematically indicated elongate flame tube  28  for generating a plurality of adjacent flames runs parallel to the rotational axis  12 . The axes of the flames run horizontally, to be precise transversely to the rotational axis  12 . Alternatively, the burner  10  can also be configured such that it generates just a single horizontal flame, extending transversely to the rotational axis  12 . 
     In the shown illustrative embodiment, the burner  10  is housed in the upper compartment  22 . For this purpose, a rear wall  29  is assigned to the burner  10  on the rear side. Above and beneath the burner  10  are located parallel, horizontal air guide walls  30 ,  31 , which are both connected to the rear wall  29 . Parallel, free edges  32  of the air guide walls  30  and  31  form a preferably elongate, vertical air outlet opening  33  of the housing surrounding the burner  10  and made up of the rear wall  29  and the air guide walls  30  and  31 . The substantially fully open air outlet opening  33  thus forms a wide-slot opening or wide-slot nozzle. The air outlet opening  33  is distanced from an external wall  34  of the housing  11 , which external wall lies opposite the external wall  27  of the housing  11 . Similarly, the upper air guide wall  30  is distanced from an upper top wall  35  of the housing  11  of the dryer. Consequently, the rear wall  29 , which extends only up to the upper air guide wall  30 , ends also at a distance below the top wall  35  of the housing  11 . 
     In a bevelled upper, right-hand corner region between the horizontal top wall  35  and the vertical (right-hand) external wall  34  is located an air vent  36 . Below the air vent  36  is provided, inside the upper compartment  22 , a recirculating air flap  37 . The recirculating air flap  37  is pivotable about a horizontal pivot axis  38 , preferably by a drive (not shown). The recirculating air flap  37  is pivotable to the point where it, on the one hand, in an open setting completely closes off the air vent  36  and, on the other hand, in a closed setting extends the free edge  32  of the air guide wall  30  above the burner  10  to the external wall  34  and thereby forms a seal. Between the said extreme settings, optional intermediate settings of the recirculating air flap  37  are possible. 
     By virtue of the above-described configuration of the housing  11 , in particular of the lower compartment  16  and of the upper compartment  22 , a specific air flow can be induced in the dryer. Thus, the air outlet opening  21  opens out into a backflow chamber  39  closed off by the wall  18 , the transverse wall  25 , the wall  26  and the external wall  27 . By an opening (not shown in the figures) in the partition  23 , the backflow chamber  39  in the lower compartment  16  is connected to a backflow chamber  40  in the upper compartment  22 . This backflow chamber  40  is bounded by the partition  23 , the top wall  35 , an upper part of the external wall  27 , the rear wall  29  behind the burner  10  and the air guide wall  30 , distanced from the top wall  35 , above the burner  10 . 
     Between the upper part of the external wall  34  and the air outlet opening  33  situated at a distance therefrom, the chamber, surrounding the burner  10 , between the air guide walls  30  and  31 , the transverse walls  24 ,  25  and the air inlet opening  20  into the drum  13  is formed an inflow chamber  41 . Via the inflow chamber  41 , the upper compartment  22  and the lower compartment  16  are also connected to each other by an appropriate opening in the partition  23 . When the recirculating air flap  37  is closed, the backflow chamber  40  and the inflow chamber  41  can be separated from each other. By the middle setting (shown in  FIG. 1 ) of the recirculating air flap  37 , a partial connection of the backflow chamber  40  to the inflow chamber  41  and a partial opening-up of the air vent  36  is adjustable. 
     According to the invention, an air flow generator is assigned to the burner  10 . This is represented symbolically in  FIG. 3 . This particular illustrative embodiment relates to an air flow generator configured as a fan  42 . The air flow generator can also be formed by a plurality of fans  42 . Through an intake opening (not shown), the fan  42  draws in fresh air from outside the housing  11  of the dryer and transports this to the burner  10 , preferably into the burner  10 . As a result of the lateral arrangement of the fan  42  next to the housing  11 , supply air or fresh air is transported or blown by the fan into the housing  11  in a direction parallel to the rotational axis of the drum  13 . The fresh air transported by the fan  42  into the housing makes its way inside the burner  10 , for which purpose it flows through the housing surrounding the burner  10 . If need be, it can be provided to transport the fresh air through the elongate flame tube  28 , to be precise preferably together with the gas to be combusted by the burner  10 . It is also conceivable, however, to feed the supply air or fresh air transported by the fan  42  to the inside of the burner  10  past the outside of the flame tube  28  or around the burner  10 . 
     The fan  42  can be driven by, for example, an electric motor  43 . Preferably, the speed of the electric motor  43  is variable or controllable or can be regulated. The throughput of fresh air or supply air through the fan  42  can thereby be altered and thus adapted to requirements. A desired stream of fresh air can thereby be transported to the burner  10 . 
     Opening out into the inflow chamber  41 , behind the air outlet opening  33  between the air guide walls  30  and  31 , viewed in the direction of flow, is a fresh air socket (not represented in the figures) disposed on a wall of the housing  11 . The opening of the fresh air socket is preferably variable in cross section. It is also conceivable for the fresh air socket to be able to be totally shut off. Via the fresh air socket, additional fresh air can be fed to the inflow chamber  41  (in the direction of flow) behind the burner  10  and/or outside this same. The quantity of fresh air is variable by altering the cross section of the fresh air socket. The fresh air supply via the fresh air socket can also be totally cut off. 
     The inventive method is explained in greater detail below with reference to the previously described dryer with reference to, in particular,  FIG. 2 : 
     The drying operation commences with the supply of air  44  heated by the burner  10  through the inflow chamber  41  and the air inlet opening  20  to the rotationally driven drum  13  in which the laundry to be dried is found. As the air  44  flows along the laundry, which initially is still very damp, the air absorbs a large amount of moisture. As a result, relatively moist air  45  leaves the drum  13  through the air outlet opening  21 . The moist air  45  flows through the backflow chamber  39  in the lower part  16  into the backflow chamber  40  in the upper compartment  22 , where it is transported onward by the recirculating air fan  14 . 
     The moist air  45  containing, at the start of the drying operation, a high moisture component is initially, with the recirculating air flap  37  completely or almost completely closed, evacuated fully or for the most part through the air vent  36  from the housing  11  of the dryer, as waste air  46 . As replacement for the evacuated waste air  46 , fresh air is fed to the dryer from outside. This happens mainly through the burner  11 , where the fresh air fed from outside serves as combustion air. This fresh air is initially drawn in automatically by the burner  10 . For the support of the air supply to the burner  10 , it can also already be provided in this drying stage, however, for fresh air to be transported to the burner  10  through the fan  42 . Additionally or alternatively, further fresh air can, where necessary, be fed behind the burner  10  directly to the inflow chamber  41 . 
     As the drying process progresses, the moisture content in the moist air  45  declines. Then a part of the moist air  45  is fed as recirculating air past the burner  10  and/or through the burner  10  to the drum  13  containing the laundry to be dried. For this purpose, the recirculating air flap  37  is partially opened by being pivoted in the clockwise direction (related to the representation in  FIG. 2 ) about the pivot axis  38 . The recirculating air flap  37  is opened sufficiently wide for the desired recirculating air stream to set in, i.e. a specific moist air component  45  is again fed as recirculating air  47  to the drum  13  and a remaining moist air component  45  is passed through the air vent  36  as waste air  46  into the open. That part of the moist air  45  which is passed through the air vent  36  as waste air  46  into the open is replaced by fresh air, which the fan  42  transports to the burner  10  or which can still be drawn in automatically by the burner  10 . This fresh air is passed through the burner  10  and here serves as combustion air. The air leaves the burner  10  as heated air  44 , which in the inflow chamber  41  mixes with the recirculating air  47  and, together with this same, is re-fed as heated air  44  to the drum  13 . 
     In dryers, in particular of the kind for commercial laundries, recirculating air  47  is employed in order to reuse the thermal energy in the moist air  45  and avoid having to reheat so much cold fresh air. The recirculating air component  47  is therefore gradually increased with increasing drying time. To this end, the recirculating air flap  37  is gradually opened further, so that it increasingly closes the air vent  36  and little moist air  45  having still considerable residual heat escapes through the air vent  36  into the open. 
     As the component of moist air  45  which has been reused and returned to the burner  10 , i.e. recirculating air  47 , increases, the burner  10  is itself able to draw in only little fresh air from outside. Sufficient fresh air is then no longer available to the burner  10 . This gives rise to an unfavorable or incomplete combustion, which, inter alia, can lead to harmful soot formation. It is therefore provided according to the invention to transport fresh air through the fan  42  to the burner  10  as the recirculating air component  47  increases. The burner  10  is then boosted or charged virtually with fresh air, which is forced or pumped through the fan  42  to the burner  10 . The burner  10  thereby receives sufficient fresh air for optimal combustion, whereby, in the end phase of the drying, drying can be realized with more recirculating air than has hitherto been normal, or with recirculating air only. 
     If, due to the fresh air transported by the fan  42  to the burner  10 , only recirculating air  47  is employed at the end of the drying operation, so that the whole of the moist air  45  is then reused as recirculating air  47 , then the recirculating air flap  37  lies fully open, in that, as a result of having been pivoted up to the air vent  36 , it closes this off, so that no moist air  45  can any longer flow as waste air  46  through the air vent  36  into the open and the whole of the moist air  45  can be fed back to the burner  10  as recirculating air. The burner reheats the recirculating air, so that the thereby heated recirculating air is fed back to the drum  13  containing the almost dry laundry. 
     The moist air  45  used as recirculating air  47  can be passed, wholly or partially with the fresh air transported by the fan  45  to the burner  10 , through the burner  10 . If the moist air  45  used as recirculating air is led only partially through the burner  10 , a part of the moist air  45  is led past the burner  10 , likewise as recirculating air, to join before the air outlet opening  33  with the air  44  heated by the burner  10  and/or warmed recirculating air, so that the recirculating air  47 , and the air  44  warmed by the burner  10  and likewise formed from recirculating air  47 , can be fed in its entirety through the inflow chamber  41  back to the drum  13  containing the laundry. 
     If the dryer is operated completely or for the most part with recirculating air  47 , behind the air outlet opening  33  a bit more fresh air can, where necessary, be fed from outside directly to the inflow chamber  41 . This is generally unnecessary, however, in the case of complete or almost complete recirculating air operation. 
     The fresh air transported by the fan  42  to the burner  10  and through this same is variable in quantity by appropriate controlling of the speed of the fan  42 . It is thereby possible to alter both the stream of fresh air to and through the burner  10  and the pressure of the fresh air. The burner  10  can thereby be charged or boosted more or less strongly according to the recirculating air component  47 . 
     At the start of the drying operation, when little circulating  47  is employed, the fan  42 , if need be, can be totally switched off, so that the burner  10  then automatically draws in the necessary fresh air. Only once the recirculating air component increases, in particular predominates, or only recirculating air  47  is used, is the fan  42  started up, so that fresh air, preferably under pressure, is then transported to the burner  10  or blown into the burner  10 , the pressure and/or the quantity of fresh air which is transported by the fan  42  to the burner  10  rising continuously with the increase in the recirculating air component  47 . Where the dryer is operated only with recirculating air  47 , the stream of fresh air and/or the pressure of the fresh air, by appropriate operation of the fan  42 , reach a maximum. 
     REFERENCE SYMBOL LIST 
     
         
           10  burner 
           11  housing 
           12  rotational axis 
           13  drum 
           14  recirculating air fan 
           15  casing 
           16  lower compartment 
           17  wall 
           18  wall 
           19  gap 
           20  air inlet opening 
           21  air outlet opening 
           22  upper compartment 
           23  partition 
           24  transverse wall 
           25  transverse wall 
           26  wall 
           27  external wall 
           28  flame tube 
           29  rear wall 
           30  air guide wall 
           31  air guide wall 
           32  edge 
           33  air outlet opening 
           34  external wall 
           35  top wall 
           36  air vent 
           37  recirculating air flap 
           38  pivot axis 
           39  backflow chamber 
           40  backflow chamber 
           41  inflow chamber 
           42  fan 
           43  electric motor 
           44  air 
           45  moist air 
           46  waste air 
           47  recirculating air