Abstract:
An apparatus for solvent recovery from a solvent/gas mixture from the exhaust air of systems processing printing, painting or other solvents, wherein the solvent/gas mixture from at least one oil-containing solvent/gas mixture is cooled down to a temperature below the lower condensation temperature of the oil of the solvent mixture using a heat exchanger, wherein a further, second heat exchanger is connected upstream of the heat exchanger, said second heat exchanger cooling the solvent/gas mixture specifically to the condensation temperature of an oil present in the mixture and both heat exchangers produce a recovery unit.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an apparatus for solvent recovery from a solvent-gas mixture, such as exist, for example, in print shops, paint shops, coating installations and the like. The solvent-gas mixture has at least one oil and is cooled down by a heat exchanger to a temperature below the condensation temperature of the at least one oil. 
     An apparatus of this type is known from EP 944423 B1. This apparatus is intended to purify the exhaust air from the drying equipment and machine enclosure of offset machines. In this case, the exhaust air is led through a liquefier to condense out the additives or contaminants contained in the exhaust air and through at least one separator element for the further purification of the exhaust air. By means of clever conditioning of the air parameters of the purified exhaust air provided to be fed back to the dryer and machine enclosures, it is possible to improve the workspace climate and to reduce emissions into the environment. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object of further developing an apparatus for solvent recovery from a solvent-gas mixture from the exhaust air from printing, varnishing or other solvent-processing installations, wherein, from a solvent-gas mixture containing at least one oil, by means of a heat exchanger, the solvent-gas mixture is cooled down to a temperature below the lower condensation temperature of the oil from the solvent mixture, in such a way that such highly efficient recovery of oils from the solvent-gas mixture is possible that oils obtained from the process can be introduced into the ink production circuit once more. This object is achieved by the features as claimed; a particularly advantageous method for solvent recovery is described in the method claims. 
     The invention first begins with the finding that, for environmental and cost reasons, it may be advantageous not to feed in particular expensive synthetic oils which are contained in a solvent-gas mixture from the exhaust air of printing presses or varnishing machines to an environmentally polluting combustion process, as has been usual hitherto, but firstly to purify the exhaust air from such oil residues, in order then to use them further in the process and to recover the oils in order to be able to feed them to an ink production operation again. To this end, at least one further, second heat exchanger is connected upstream of the usual heat exchanger in the apparatus, which cools down the solvent-gas mixture specifically to the condensation temperature of an oil contained in the mixture, the two heat exchangers forming a recovery unit. 
     Advantageously, a third heat exchanger is integrated into the recovery unit, is connected upstream of the second heat exchanger and cools down the solvent-gas mixture specifically to the condensation temperature of the oil having the higher condensation point in the solvent-gas mixture. As a result, in a first separation stage, it is possible for example to separate out mineral oils, which make up the predominant proportion of the oil content of a solvent-gas mixture. In a second stage, far more valuable synthetic oils are separated out, residual oil constituents and water in a third stage (first heat exchanger). The exhaust air extracted from the heat exchanger stages goes into an agglomerator and droplet trap in order to filter out aerosols, in order that the exhaust air can at least to some extent also be discharged into the environment whilst complying with the German air pollution control regulations. By means of the apparatus according to the invention, for the first time with printing presses specific recovery of solvent oils is possible, it being possible both for mineral and for synthetic oils to be separated so cleanly from the start that they can be supplied to an ink production process. 
     The recovery quality is improved further by a recovery unit that comprises an agglomerator and/or a droplet separator, which is arranged downstream of the first heat exchanger, droplet separators being known in principle. 
     The apparatus can be employed particularly well when a dryer unit is connected upstream of the recovery unit and, during the drying process, enriches a gaseous drying medium and a solvent-gas mixture with the at least two oils. 
     At least part of the drying medium used for the drying process can be the exhaust gas from an internal combustion engine, it being possible for the mechanical energy resulting from the internal combustion engine to be used at least partly to operate the recovery unit and/or the dryer unit, so that the result is a largely integrated, self-contained system. Since the dryer unit of the method according to the invention is not, as in the prior art, a widespread integrated dryer (combustion of the diffusing solvent within the dryer in order to utilize the heat produced in the combustion for drying the paper web), here an internal combustion engine can fulfill a plurality of functions within the method. For instance, firstly the mechanical energy can be used to produce power, which in turn can be used for the overall process (pumps), and secondly the exhaust gases from the internal combustion engine can also be used for drying the paper webs. The internal combustion engine can be constructed either as a fluidic machine (gas turbine) or as an internal combustion motor (reciprocating piston motors, rotary piston motors, double-rotary piston motors). The selection of the internal combustion engine can in this case be based on the size of the print shop and in accordance with the associated drying-gas and/or energy consumption. 
     At least part of the exhaust gas from the internal combustion engine can be fed to an absorption refrigerating machine; the refrigeration output resulting from this can advantageously be used for supporting for the operation of the recovery unit, for the cooling of further machines and/or for the air-conditioning of the operating building of a print shop. The fact that part of the exhaust gas from the internal combustion engine can be converted via an absorption refrigerating machine into refrigeration output means that, in the ideal case, “no external energy” is needed for the recovery unit for the specific setting of the temperatures in the heat exchangers. Finally, the exhaust gas led to the absorption refrigerating machine can be controlled and regulated in such a way that this gas is used as a controlled variable for the recovery unit (therefore for the heat exchangers), is used for the machine cooling and/or is used for the building air-conditioning. In particular, the control and regulation of the temperature of the heat exchangers is necessary when the volume flow of gases derived from the dryers and passing through the heat exchangers varies. The control and regulation of the temperature of the heat exchangers indirectly by the exhaust gases led to the absorption refrigerating machine (which supplies the recovery unit with cold) constitutes control and regulation which is simple both in technical and design terms. 
     Several dependent claims deal with the management and treatment of the air streams used within the apparatus; further apparatus claims relate to a particularly advantageous combination of heat exchangers, agglomerators, dryer units and internal combustion engine. 
     In a further development of the invention, the residual gas emerging from the recovery unit is at least to some extent supplied to the dryer unit as process gas and/or used, at least to some extent, with the admixture of fresh air as building room air. For example, the process air supplied to the dryer unit can be used as sealing air. Sealing air is needed in the dryer units in order, as a paper web is led through the dryer unit, to interlock its input and output region in the manner of an airlock, so that as far as possible no gas located within the dryer can escape from the latter. In particular in the case of using exhaust gases from an internal combustion engine, which usually contain a considerable proportion of CO 2 , it is necessary not to allow this CO 2 -containing gas to escape from the dryer unit in an uncontrolled manner. Since, in addition, the residual gas from the recovery unit still has a temperature of 20-80° C., the use of this gas as a sealing gas within the dryer unit is very suitable, since this does not have any detrimental influence on the dryer unit and the drying process taking place therein. Alternatively or additionally, the residual gas emerging from the recovery unit can be used with the addition of an oxygen-containing medium (for example fresh air) for air-conditioning the operating spaces of the print shop. 
     According to an advantageous refinement of the apparatus, at least one of the heat exchangers is constructed with multiple stages, so that the latter, for example, comprises a plurality of plates, at least the first stage (plate) of the second and/or third heat exchanger being wetted with the oil to be condensed out in each case within the respective heat exchanger. As a result of wetting at least the first stage of the heat exchanger with the oil to be condensed out, the effectiveness of the heat exchanger is increased. Such wetting of at least one stage of a heat exchanger can in principle also be applied in the agglomerators. 
     With regard to an overall energy balance for the overall apparatus which is as low as possible, it is advantageous if the at least two parallel-operated recovery unit can be controlled in such a way that the residence time of the solvent-gas mixture in the dryer unit can be influenced. Control of the residence time of the solvent-gas mixture can be achieved firstly by the design and the at least parallel connection of the recovery unit. Additionally or alternatively, a gas reservoir can be connected upstream, which stores the solvent-gas mixture in the event of an increased solvent-gas mixture accumulation and feeds it in a constant manner to the recovery unit. Furthermore, it is advantageous if the parallel-connected dryer units are designed differently in such a way that the exhaust gases arising in the respective dryers in the highest efficiency range can be led to the correspondingly designed recovery unit. 
     In a refinement of the invention, the first heat exchanger can be set in such a way that the medium fed by it to the agglomerators and/or droplet separators has a defined temperature. The first heat exchanger, connected upstream of the agglomerators and/or droplet separators therefore fulfils a dual function, firstly it is intended to separate the water and the residual oil components which could not be separated out from the upstream heat exchangers and, as a second function, it is intended to cool the gas leaving it to a defined temperature. This defined temperature is preferably coordinated with the most efficient operating range of the agglomerators and/or droplet separators. 
     The method, as claimed, provides for the solvent-gas mixture originating from a dryer device to be led to a recovery unit and, as the solvent-gas mixture is led through the series-connected component parts of the recovery unit, at least two oils are condensed out of the solvent-gas mixture and each collected in a collector. The constituent parts of the oil recovery unit comprise a first and a second heat exchanger, the solvent-gas mixture being led to the first through the second heat exchanger and then through the first heat exchanger. As the solvent-gas mixture is led through the second heat exchanger, it is cooled down specifically there to the condensation temperature of an oil. During the subsequent passage of the solvent-gas mixture through the first heat exchanger, the solvent-gas mixture is cooled down below the lowest condensation temperature of the at least two oils of the solvent-gas mixture. 
     In a further development of the method, before the solvent-gas mixture is led through the second heat exchanger, it is led through a third heat exchanger connected upstream of the second. This heat exchanger cools down the solvent-gas mixture specifically to the condensation temperature of the oil having the higher condensation point, so that the oil separated off there can be collected in a container separately from that from the second heat exchanger. 
     In particular, a method in which the gas emerging from the oil recovery unit is used, at least to some extent, as sealing gas for a dryer and/or as room air is advantageous in this case. It is therefore made possible to close a gas management circuit, at least for a proportion of the gas, so that the original drying gas is admixed with solvents within the dryer, is led from the dryer into the oil recovery unit and there is separated from the oil constituents and, following the oil recovery unit, can at least proportionally be “reused” as a supporting gas or sealing gas within the dryer unit. Here, supporting gas means a gas within the dryer unit which is used to support a paper web and is used only in a second function for the drying of the paper web. Since the drying is of secondary importance for the supporting gas, this can also have a lower temperature. 
     In the method according to the invention, the drying gas used for the dryer can be the exhaust gas from an internal combustion engine. As a result of the high temperature of the exhaust gas which emerges from the internal combustion engine, said gas is well-suited for drying a medium (paper web) within the dryer. 
     A further energy circuit can be closed by at least some of the exhaust gas from the internal combustion engine being led to an absorption refrigerating machine which, by using the refrigeration output/refrigeration energy obtained from it, supplies the first, second, third heat exchanger and/or regions of the building with refrigeration energy. 
     The invention is explained in more detail by using the exemplary embodiments in the drawing figures, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a schematic block circuit diagram in which a solvent recovery unit is incorporated within a print shop drying process; 
         FIG. 2  shows a schematic block circuit diagram according to  FIG. 1 , in which the solvent recovery unit and the possible uses of the gases emerging from the latter are illustrated in more detail; 
         FIG. 3  shows a schematic block circuit diagram of a heat exchanger, illustrated in more detail, belonging to the oil recovery unit; 
         FIG. 4  shows a schematic block circuit diagram relating to the possible uses of the gas within the overall apparatus. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     In drawing  FIGS. 1 and 2 , heat exchangers  2 ,  3 ,  4  within a solvent recovery unit  5  are illustrated. The heat exchangers  2 ,  3 ,  4  are connected in series, so that the solvent-gas mixture has to pass firstly through the third heat exchanger  4 , after that through the second heat exchanger  3 , then through the first heat exchanger  2  and lastly through an agglomerator or droplet separator  6 . The third heat exchanger  4  cools down the solvent-gas mixture specifically to the condensation temperature of the oil having the higher condensation point and therefore collects the higher-condensing oil in a first container  7 . The second heat exchanger  3  cools down the solvent-gas mixture emerging from the third heat exchanger  4  specifically to the condensation temperature of the oil still in the solvent-gas mixture, so that a further oil is separated off at the second heat exchanger  3  and is collected in a separate, second container  8 . 
     The apparatus  1  is advantageously equipped with two solvent recovery unit  5 , which are integrated into the gas management process so as to be connected in parallel. As a result, for example, one heat exchanger  2 ,  3 ,  4  of the first solvent recovery unit  5  can be maintained or replaced while the solvent-gas mixture treatment process can be continued unchanged via the second solvent recovery unit  5 ′. 
     The overall apparatus  1  is distinguished in particular by a drying system  9  connected upstream of the solvent recovery unit  5 ,  5 ′, which in turn comprises a plurality of dryer units  10 ,  10 ′,  10 ″. In the dryer units, for example a printed paper web (not illustrated) can be dried. The solvents originating from the printing inks from the drying process of the printed paper web enrich the drying medium (gas) and is fed to the solvent recovery unit  5 ,  5 ′ in order to separate out the individual oil constituents of the solvent-gas mixture. In this case, the drying medium used for the drying system  9  is the exhaust gases  11  from an internal combustion engine  12 . The exhaust gas  11 , the temperature of which is controlled by the combustion process of the internal combustion engine  12 , is suitable as a drying medium for drying the paper web. The mechanical energy resulting from the internal combustion engine  12  can, for example, be used via a generator  13  for the production of electrical energy  14 , and this electrical energy can be used to operate the recovery unit  5 ,  5 ′, the drying system  9  and/or further technical equipment belonging to the apparatus  1 . 
     Some of the exhaust gas  11  from the internal combustion engine  12  can be fed to an absorption refrigerating machine  15  for the further optimization of the overall energy balance. The refrigeration output/refrigeration energy  16  resulting from the absorption refrigerating machine  15  is in this case led to the heat exchangers  2 ,  2 ′,  3 ,  3 ′,  4 ,  4 ′, the oil recovery unit  5 ,  5 ′, for cooling further machines  17  and/or for air-conditioning parts of the building. Furthermore, via a control or regulating element  18 , the distribution of the exhaust gas  11  from the internal combustion engine  12  can be led proportionally to the drying system  9 , the absorption refrigerating machine  15  or exhaust gas purification installation (not illustrated) connected upstream of the environment. By means of such a control or regulating element  18  and/or a further control or regulating element (not illustrated), which is used to distribute the refrigeration output  16  from the absorption refrigerating machine  15  to the heat exchangers  2 ,  2 ′,  3 ,  3 ′,  4 ,  4 ′, partial regulation of the output at least of parts of the overall apparatus  1  can therefore be accomplished. For instance, it is possible to compensate for a varying exhaust-gas/drying demand of the dryer unit  10 ,  10 ′,  10 ″ by means of the two or by means of one of the control or regulating elements  18 . In principle, the supply of drying medium to the drying system  9  can be variable in terms of volume and/or temperature, in particular this can be controlled in a simple way by admixing fresh air. The residual gas  19  emerging from the solvent recovery unit  5 ,  5 ′ is at least partly discharged from the system (the industrial process) into the environment  20 . Furthermore, a control/regulating element  21  connected downstream of the solvent recovery unit  5 ,  5 ′ can supply the residual gas  19  emerging from the recovery unit  5 ,  5 ′ wholly or partly to the drying system  9  again as process air and/or at least partly, with the admixture of fresh air and/or fresh air treated by the refrigeration output  16  from the absorption refrigerating machine  15 , can be supplied to further machines  17  and/or parts  23  of the building (room air-conditioning). 
     The gas  19  emerging from the solvent recovery unit  5 ,  5 ′ is led through a re-cooler  24  and used within the drying system  9 , at least to some extent, as sealing gas  25  and/or as supporting gas  26 . In drawing  FIG. 1 , the gas  19  supplied to the dryer units  10 ,  10 ′,  10 ″ is illustrated as that which is used as sealing gas  25  and/or supporting gas  26 . Here, it can be seen that fresh air  22  can be admixed with the gas  19  for these applications. The sealing gas  25  within the drying process is understood to be the gas which, on the inlet and outlet side of the paper web guidance in the dryer unit  10 ,  10 ′,  10 ″, is used for the purpose of preventing further gas (e.g. drying gas) from the drying system  9  from escaping from the latter. The sealing gas  25  therefore has an airlock function. The supporting gas  26  is used to support the paper web “floating” and to form an opposing support for an application of drying gas acting more intensively on the paper web. 
     In drawing  FIG. 3 , a heat exchanger  2 ,  2 ′,  3 ,  3 ′,  4 ,  4 ′ of the overall apparatus is illustrated in more detail. Here, it can be seen that this comprises three stages  27 ,  28 ,  29 , for example. Stages  27 ,  28 ,  29  of this type can be constructed in the manner of plates, for example, and are used in that the oil to be condensed out is deposited on them and is fed to a collecting container  7 ,  8 . In order to increase the level of efficiency of the heat exchangers  2 ,  2 ′,  3 ,  3 ′,  4 ,  4 ′, it is advantageous if wetting at least of the first stage  27  of the second or third heat exchanger  3 ,  3 ′,  4 ,  4 ′ with the oil to be condensed out in each case is carried out. This oil used for that purpose can be taken either from the collecting container  7 ,  8  and/or a further additional oil reservoir  30 . This method can also be used for the agglomerators and/or droplet separators  6 . The wetting of at least the first stage  27  facilitates the deposition of similar oil from the solvent-gas mixture. 
     The control/regulating element  31  illustrated in drawing  FIG. 2  distributes the solvent-gas mixture emerging from the drying system  9  to the solvent recovery unit  5 ,  5 ′. Here, care should be taken in the distribution that the at least two parallel-operated oil recovery unit  5 ,  5 ′ are driven in such a way that the residence time of the solvent-gas mixture in the solvent recovery unit  5 ,  5 ′ can be influenced. For example, the two parallel-connected solvent recovery unit  5 ,  5 ′ can be dimensioned differently and therefore have a different performance capability in terms of solvent recovery. In particular, depending on the quantity of the solvent-gas mixture to be treated, the solvent recovery unit or both solvent recovery units  5 ,  5 ′ can be used in order to ensure a defined volume flow or a defined residence time of the solvent-gas mixture in the recovery unit  5 ,  5 ′. It has been shown in practice that leading solvent-gas mixture too quickly through the solvent recovery unit  5 ,  5 ′ substantially impairs the effectiveness of the recovery unit  5 ,  5 ′. 
     In particular, the control and regulation of the first heat exchanger  2 ,  2 ′ is important, since this has a substantial formative influence on the discharge temperature of the gas passing through it. The effectiveness of the agglomerator and/or droplet separator  6  in turn depends on the temperature of the gas passing through it. Therefore, the first heat exchanger  2 ,  2 ′ should, if appropriate, be controlled and regulated by the refrigeration output feed line  16  of the absorption refrigerating machine  15  in such a way that the gas leaving the latter has a defined temperature matched to the agglomerator and/or droplet separator  6 . 
     In drawing  FIG. 5 , further possible uses of the gas within the overall installation are once more illustrated schematically; in this case the exhaust gas  11  from the internal combustion engine  12  is supplied to the drying nozzles, supporting gas nozzles (supporting gas  26 ) and/or the sealing gas nozzles (sealing gas  25 ). The gas discharged from these respective nozzles is supplied to the heat exchangers  2 ,  2 ′,  3 ,  3 ′,  4 ,  4 ′ of the solvent recovery unit  5 ,  5 ′ and, after passing through the latter for use as supporting gas  26 , sealing gas  25  is used as exhaust air (the environment  20 ) and/or, by admixing fresh air  22 , as room air for the building  23 . In particular as a result of recycling the exhaust gas  19  to the supporting gas nozzles or the sealing gas nozzles, despite the intensive use of drying gas, supporting gas and sealing gas, as compared with the prior art an overall economical system is achieved. This means that, using gas recycling of this type, “more gas-wasteful” dryer types can be used for the (for example print shop operation) paper drying process. 
     When the gas  19  is used for the supporting gas nozzles or for the sealing gas nozzles, exhaust gas  11  from the internal combustion engine  12  can be admixed with the gas  19 . 
     LIST OF DESIGNATIONS 
     
         
           1  Apparatus 
           2 ,  2 ′ Heat exchanger (first) 
           3 ,  3 ′ Heat exchanger (second) 
           4 ,  4 ′ Heat exchanger (third) 
           5 ,  5 ′ Solvent recovery unit 
           6  Agglomerator/droplet separator 
           7  Container 
           8  Container 
           9  Drying system 
           10 ,  10 ′,  10 ″ Dryer unit 
           11  Exhaust gas from  12   
           12  Internal combustion engine 
           13  Generator 
           14  Electric power 
           15  Absorption refrigerating machine 
           16  Refrigeration output 
           17  Machines 
           18  Control/regulating element 
           19  Gas 
           20  Environment 
           21  Control/regulating element 
           22  Fresh air 
           23  Building 
           24  Re-cooler 
           25  Sealing gas 
           26  Supporting gas 
           27  Stage  1  of  10   
           28  Stage  2  of  10   
           29  Stage  3  of  10   
           30  Oil reservoir 
           31  Control/regulating element