Abstract:
The invention relates to a dryer for a textile fabric web, comprising a dryer chamber ( 2 ) and having at least one drum ( 3   a ) which is arranged in the dryer chamber ( 2 ) and around at least part of which the fabric web ( 5 ) is wrapped, wherein heated drying air flows through the fabric web ( 5 ) and is discharged via an interior chamber of the drum ( 3   a ), characterized in that the dryer ( 1 ) has a separate additional compartment ( 10 ) via which fresh air ( 11 ) is supplied and exhaust air ( 13 ) is discharged.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a dryer for a textile fabric web, and to a method of drying a textile fabric web. 
     For drying textile fabric webs, dryers are known in which one or more drums are arranged in a housing. A textile fabric web is supplied to the dryer via an opening in the dryer compartment, the textile fabric web being wrapped around a large part of the periphery of the drum and then being discharged from the dryer compartment again. Usually, fresh air is also supplied via this opening, the fresh air being heated inside the dryer compartment and mixed with the circulating air in order to be able to absorb the greatest possible amount of moisture. While the fabric web is wrapped around the drum, the mixture of circulating air and fresh air flows through the fabric web, absorbs at least some of the moisture of the fibre web and is discharged again via the interior chamber of the drum. A volumetric sub-flow from this volumetric flow is discharged as exhaust air, the moist exhaust air being discharged via channels above the drums, which as a result of the rotating drums requires elaborate and expensive sealing and a high level of maintenance. In order to avoid the suction effect from the environment of the dryer, there have subsequently been added to the dryer compartment supply lines or channels for fresh air which can be coupled, for example, to a heat exchanger for heating the fresh air. 
     A previously described dryer is disclosed in DE 10 2009 016 019 A1. In dryers of this design the circulation of the fresh air takes place at right angles to the withdrawal direction of the moist air, that is to say at right angles to the drum axis, with the result that the air circulation inside the dryer compartment is disrupted. A further disadvantage is that, for reasons of lack of available space, modification is often complicated and it is not possible to couple the fresh air channel to a heat exchanger. Since the dryers are positioned very close together in a row of different processing units that treat the textile fabric web in succession, there is often no room subsequently to install a channel for fresh air between the units. 
     DE 1 729 499 A1 discloses a perforated drum dryer having intermediate compartments arranged at the end faces of the perforated drums. Fresh air is fed to these intermediate compartments and mixed with the drying air. Some of the used exhaust air is discharged via the fan chamber. The intermediate compartment is fixedly integrated in the dryer housing and cannot be retrofitted with a heat exchanger. 
     SUMMARY OF THE INVENTION 
     The problem of the invention is to provide a dryer for a textile fabric web in which guidance of exhaust air and fresh air can be effected in a way that is advantageous in terms of flow behaviour, wherein it is also possible, if required, subsequently to install a heat exchanger. 
     In accordance with the technical teaching of the invention, the dryer for a textile fabric web comprises a dryer chamber having at least one drum which is arranged in the dryer chamber and around at least part of which the fabric web is wrapped, wherein heated drying air flows through the fabric web and is discharged via an interior chamber of the drum, wherein the dryer has a separate additional compartment via which fresh air is supplied and exhaust air is discharged. 
     The features of the invention make it possible for the connections for the fresh air and the exhaust air to be arranged on the dryer in such a way that the air flow for the drying process in the dryer chamber  2  and inside the drum is not disrupted. As a result of the additional compartment, the drying air expands, so that its flow speed on leaving the drum is several times lower. Withdrawal of the exhaust air from the additional compartment has only an extremely small effect on the drying process. Furthermore, as a result of the reduced pressure in the additional compartment the fresh air can be freely drawn in and conducted into the heating and fan chamber. 
     In an advantageous arrangement of the invention, the additional compartment is arranged between an end face of the dryer and a heating and fan chamber. For energy-related reasons, the removal of the exhaust air from the drying air in the additional compartment is at its most optimum, because here the drying air has its lowest energy level. Accordingly, the loss of energy through the exhaust air is at its lowest. This results in a solution which is advantageous to the drying process in terms of flow behaviour and which can be arranged between the units arranged one after the other, irrespective of the available space. In addition, the clearly defined interface allows the use of a heat recovery means under optimum conditions. The energy balance can therewith be further improved. 
     Inside the additional compartment, the fresh air mixes with the drying air. Due to the fact that means for heating the fresh air and drying air are arranged inside the heating and fan chamber, the heated drying air has to travel only a short way to the dryer chamber, during which it does not cool down. 
     An energy-efficient improvement is achieved by constructing the means in the form of heat exchangers, the heat exchangers utilising the exhaust air from the additional compartment to heat the fresh air and drying air. 
     The fresh air and exhaust air flowing in the additional compartment can be separated from one another by means for division into segments. The additional compartment can likewise be divided into segments analogously to the number of drums. The individual segments can be separated from one another by walls in order that there is no exchange of air between the segments. By division into partly permeable segments, for example in the form of perforated plates, the exhaust air or the fresh air can be distributed to a plurality of segments. This can likewise be effected by means of guide plates. 
     The arrangement of the fans at the heating and fan chamber for circulating the drying air has the advantage that the dryer can be of relatively compact construction. 
     Inside the additional compartment there are arranged connections through which the drying air can be extracted from the dryer chamber or from the drums by means of the fans. The connections can in turn be constructed in a way that is advantageous in terms of flow behaviour in order to minimise flow losses. 
     The method according to the invention for drying a textile fabric web is characterised by the steps of heating drying air and conducting it into a dryer chamber in which a fabric web is wrapped around at least part of at least one drum arranged inside the dryer chamber, wherein the heated drying air flows through the fabric web and is discharged via an interior chamber of the drum, wherein fresh air is supplied to a separate additional compartment and exhaust air is discharged via the additional compartment. 
     The additional compartment has no effect on the flow conditions inside the dryer chamber and the drum. On entering the additional compartment the exhaust air undergoes a significant reduction in flow speed, whereas as a result of the reduced pressure in the additional compartment the fresh air can be freely drawn in and conducted into the heating and fan chamber. 
     A circulation system is created in which a mass sub-flow of exhaust air is withdrawn from the drying air and a mass sub-flow of fresh air is supplied thereto, the exhaust air being removed from the drying air at the location at which the drying air has its lowest energy level, namely in the additional compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail below with reference to a possible exemplary embodiment which is shown diagrammatically in the drawings, wherein 
         FIG. 1 : is a diagrammatic front view of a serial dryer; 
         FIG. 2 : is a view corresponding to  FIG. 1  with a heat recovery means; 
         FIG. 3 : is a side view in section of the serial dryer according to the invention; 
         FIG. 4 : is a rear view of the serial dryer with the heating and fan chamber removed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a dryer  1  in the form of a serial dryer. Inside a dryer chamber  2 , three drums  3   a ,  3   b ,  3   c  are arranged one after the other and with their axes  4   a ,  4   b ,  4   c  in a row. A fabric web  5  is guided into the dryer chamber  2  via an inlet  6 . By means of a guide roller  7 , the fabric web  5  is guided first under the first drum  3   a , then above the second drum  3   b  and subsequently under the third drum  3   c . By means of the guide roller  8 , the fabric web  5  is guided out of the dryer chamber  2  through an outlet  9 . Heated drying air flows through the fabric web  5  during its passage through the dryer chamber  2 , the drying air absorbing the moisture of the fabric web  5  and being extracted via the interior of the drums  3   a  to  3   c.    
     According to the invention, there is arranged at the dryer chamber  2  an additional compartment  10  into which the channel  12  for the fresh air  11  and the channel  14  for the exhaust air  13  open. 
     The additional compartment  10  is constructed so as to be fully distinct and separate from the dryer chamber  2 . The heating and fan chamber  22  is arranged at the additional compartment  10 . The dryer chamber  2  is connected to the heating and fan chamber  22  by air channels above and below the drums  3   a - 3   c . The additional compartment  10  is connected to the dryer chamber  2  via the end-face openings of the drums  3   a - 3   c.    
     In  FIG. 2 , the dryer  1  from  FIG. 1  is equipped with an optional heat recovery means. The same parts have been given the same reference numerals. On the housing of the fan  15  adjoining the channel  14  there is positioned a further channel  16  which causes the exhaust air  13  to flow through a further heat exchanger  17  and discharges it via a channel  18 . The heat exchanger  17  is simultaneously connected to the channel  12 , so that before the fresh air  11  flows into the additional compartment  10  it has already undergone an increase in temperature as a result of the heat exchanger  17 . This optional retrofittable solution enables the thermal efficiency of the dryer  1  to be further increased. 
     Unlike the prior art, here the fresh air  11  does not flow directly into the dryer  1 , but first flows into the additional compartment  10  in which further heating takes place as a result of mixing with the drying air after it has flowed through the fabric web  5 . In previous designs, such intermixing of the fresh air with the drying air took place before flowing through the fabric web  5 , thus influencing the temperature of the drying air before the fabric web  5 . Utilising the difference in temperature between exhaust air  13  and fresh air  11  is sufficient to bring about a further increase in the thermal efficiency of the dryer  1 . 
       FIG. 3  shows a lateral section through a dryer  1 . The fans  19   a - 19   c , which extract the moisture-saturated drying air from the drums  3   a - 3   c , are flange-mounted on the heating and fan chamber  22  and are connected to the additional compartment  10  via connections  20   a - 20   c  or adapters. On the opposite side, the drums  3   a - 3   d  are likewise connected to the additional compartment  10  via connections. The drying air flows out of the drums  3   a - 3   c  into the additional compartment  10  and from the additional compartment  10  via the connections  20   a - 20   c  into the extraction cross-section of the respective fans  19   a - 19   c . In the region of the drum  3   a , the exhaust air is removed from the additional compartment  10  via a channel  14  which is arranged at the end face (see  FIGS. 1 and 2 ). At the end of the channel  14 , a fan  15  provides the necessary air flow. The fresh air supply is effected in the region of the drum  3   c  via the additional compartment  10  to which the channel  12  is connected at the end face. 
     As a result of the additional compartment  10 , the drying air expands, so that its flow speed on leaving the drum  3   a ,  3   b ,  3   c  is several times lower. Furthermore, as a result of the reduced pressure in the additional compartment  10 , the fresh air  11  can be freely drawn in and thereby supplied to the heating and fan chamber  22  with drying air. 
     Inside the heating and fan chamber  22  there can be arranged heating elements  21  in the form of heat exchangers, one or more gas heaters or electric heaters, which heat the discharged drying air  11 , including the fresh air, to the drying temperature. 
       FIG. 4  shows a rear view of the dryer  1 , in which the heating and fan chamber  22  have been omitted. Here it is possible to see the openings of the drums  3   a - 3   c  via which the drums  3   a - 3   c  are connected to the additional compartment  10  by means of connections. The fresh air  11  is introduced into the additional compartment  10  via a channel  12 . Inside the additional compartment  10  there are arranged separating plates  23  in the form of perforated plates which divide the additional compartment  10  into segments, so that it is possible to influence the distribution of the fresh air to the individual fans  19   a - 19   c . It is likewise possible, by means of guide plates (not shown), to influence the distribution of the fresh air inside the additional compartment  10 , for example to separate it from the exhaust air. 
     From the additional compartment  10 , by means of the fans  19   a - 19   c  the mixture of fresh air and drying air flows into the heating and fan chamber  22 . This is a circulation system from which a mass sub-flow in the form of exhaust air is withdrawn and to which a mass sub-flow in the form of fresh air is supplied. 
     The heating and fan chamber  22  is arranged as a separate compartment in the region of the rear end face of the dryer  1 , the additional compartment  10  being arranged in between. The drive means of the fans  19   a ,  19   b ,  19   c  are arranged outside the heating and fan chamber  22 , the fan impellers are located inside. Each fan  19   a ,  19   b ,  19   c  is associated with a drum  3   a ,  3   b ,  3   c . The fans  19   a ,  19   b ,  19   c  are connected via connections  20   a - 20   b  or adapters to the additional compartment  10  and the latter is connected, likewise via connections or adapters, to the drums  3   a ,  3   b ,  3   c.    
     REFERENCE NUMERALS 
     
         
           1  dryer 
           2  dryer chamber 
           3   a, b, c  drum 
           4   a, b, c  axis 
           5  fabric web 
           6  inlet 
           7  guide roller 
           8  guide roller 
           9  outlet 
           10  additional compartment 
           11  fresh air 
           12  channel 
           13  exhaust air 
           14  channel 
           15  fan 
           16  channel 
           17  heat exchanger 
           18  channel 
           19   a, b, c  fan 
           20   a, b, c  connection 
           21  heating element 
           22  heating and fan chamber 
           23  separating plate