Patent Application
20240059058
This application claims priority to German Patent Application No. 10 2022 120 972.5 filed Aug. 19, 2022, the disclosure of which is hereby incorporated by reference in its entirety.
The invention relates to a device and a corresponding method for cleaning the exhaust air from a drying unit for drying a recording medium printed to in an inkjet printing device.
Inkjet printing devices may be used for printing to recording media, for example paper. For this purpose, one or more nozzles are used in order to fire ink droplets onto the recording medium, and thus to generate a desired print image on the recording medium.
An inkjet printing device can comprise one or more drying units in order to dry the recording medium after application of the print image and thereby fix the applied ink on the recording medium. A drying unit can have a drying route with a plurality of drying modules. The individual drying modules can be configured to blow a warmed gaseous drying medium, in particular air, toward the surface of the recording medium in order to dry said recording medium. The drying modules can thereby be arranged along the drying route such that the recording medium does not come into contact with the drying modules and floats through the drying unit.
In addition to water, other substances, in particular solvent and/or hydrocarbons, are also extracted from a recording medium within the scope of the drying of said recording medium, which substances are conveyed out of the drying unit together with the exhaust air. The exhaust air may be cleaned in a cleaning unit in order to reduce the amount of solvent. The exhaust air cleaning can thereby be effected via condensation of volatile hydrocarbons by means of a heat exchanger.
A fouling of the exhaust air cleaning unit, in particular of the heat exchanger, can occur during the operation of a printing device. The present document deals with the technical object of enabling an efficient and reliable cleaning of the exhaust air cleaning unit, in particular of the heat exchanger, of a printing device. The object is respectively achieved as discussed hereinafter.
According to one aspect, a device is described for cleaning exhaust air from a printing device by means of a heat exchanger. The device is configured to operate the heat exchanger in a standard phase such that the output temperature of the exhaust air at the output of the heat exchanger exhibits a standard value, in order to have the effect that hydrocarbons are condensed out of the exhaust air. The device is also configured to operate the heat exchanger in a regeneration phase such that the output temperature of the exhaust air exhibits a reduced value relative to the standard value, in order to have the effect that water—in particular additional water—is condensed out of the exhaust air.
According to a further aspect, a device is described for cleaning exhaust air from a printing device by means of a heat exchanger. The device is configured to operate the heat exchanger in a standard phase such that the output temperature of the exhaust air at the output of the heat exchanger exhibits a standard value, in order to have the effect that hydrocarbons are condensed out of the exhaust air. The device is also configured to operate the heat exchanger in a regeneration phase such that a cleaning fluid is introduced into the heat exchanger and/or into exhaust air that flows at the heat exchanger, such that condensate generated in the heat exchanger is liquefied and/or diluted by the cleaning fluid.
According to a further aspect, a heat exchanger, a drying unit, and/or a printing device are described that comprise at least one of the devices described in this document.
According to a further aspect, a method is described for cleaning exhaust air from a printing device by means of a heat exchanger. The method comprises the operation of the heat exchanger in a standard phase such that the output temperature of the exhaust air at the output of the heat exchanger exhibits a standard value, via which it is effected that hydrocarbons are condensed out of the exhaust air. The method also comprises the operation of the heat exchanger in a regeneration phase such that the output temperature of the exhaust air exhibits a reduced value relative to the standard value, via which it is effected that water is condensed out of the exhaust air.
According to a further aspect, a method is described for cleaning exhaust air from a printing device by means of a heat exchanger. The method comprises the operation of the heat exchanger in a standard phase such that the output temperature of the exhaust air at the output of the heat exchanger exhibits a standard value, via which it is effected that hydrocarbons are condensed out of the exhaust air. The method also comprises effecting, during a regeneration phase, that a cleaning fluid—water in particular—is introduced into the heat exchanger and/or into exhaust air that flows at the heat exchanger, such that condensate generated in the heat exchanger is liquefied and/or diluted by the cleaning fluid.
The terms Fig., Figs., Figure, and Figures are used interchangeably in the specification to refer to the corresponding figures in the drawings.
In the following, exemplary embodiments of the invention are described in detail using the schematic drawings. Thereby shown are:
The printing device 100 depicted in
In the depicted example, the print group 140 of the printing device 100 comprises two print bars 102, wherein each print bar 102 can be used for printing with ink of a defined color, for example black, cyan, magenta, and/or yellow, and MICR ink if applicable. Different print bars 102 can be used for printing with respective different inks. Furthermore, the printing device 100 comprises at least one fixing or drying unit 150 that is configured to fix a print image printed onto the recording medium 120.
A print bar 102 can comprise one or more print heads 103 that, if applicable, are arranged in a plurality of rows side-by-side in order to print the dots of different columns 31, 32 of a print image onto the recording medium 120. In the example depicted in
In the embodiment illustrated in
The printing device 100 also comprises a control unit or control device 101, for example an activation hardware and/or a controller, that is configured to drive actuators of the individual nozzles 21, 22 of the individual print heads 103 of the print group 140 in order to apply the print image onto the recording medium 120 depending on print data.
The print group 140 of the printing device 100 thus comprises at least one print bar 102 having K nozzles 21, 22 that can be activated with a defined line timing in order to print a line, said line traveling transverse to the transport direction 1 of the recording medium 120, with K pixels or K columns 31, 32 of a print image onto the recording medium 120, for example with K>1000. In the depicted example, the nozzles 21, 22 are installed so as to be immobile or fixed in the printing device 100, and the recording medium 120 is directed past the stationary nozzles 21, 22 with a defined transport velocity.
As presented above, the printing device 100 can comprise a drying unit 150 that is configured to dry the recording medium 120 after application of the ink by the one or more print bars 102, and therewith to fix the applied print image onto the recording medium 120. For this purpose, the drying unit 150 can be controlled by the control unit 101 of the printing device 100. For example, the drying can take place depending on the quantity of the applied ink and/or depending on the type of the recording medium 120. For example, the temperature and/or the volumetric flow of the gaseous drying medium can be adapted depending on the quantity of the applied ink and/or depending on the type of the recording medium 120.
The drying unit 150 depicted in
A contactless float drying by means of a forced convection can thus be used to dry a recording medium 120. As depicted in
During the drying, water vapor and solvent vapors escape from the recording medium 120. A gas mixture of water vapor and solvent vapor thus appears in the housing 155 of the drying unit 150. The gas mixture can be conveyed out of the housing 155 with a ventilator in order to avoid a flammable gas mixture forming inside the housing 155, and in order to remove the moisture from the housing 155 of the drying unit 150. In this document, the gas mixture is also referred to as exhaust gas and/or as exhaust air.
An exhaust air cleaning via condensation of volatile hydrocarbons in the exhaust air 205 of a printing device 100 can thus be implemented by means of an air-water heat exchanger 210. In operation, deposits can occur on the air-side components of the exhaust air cleaning, for example on the fins of the heat exchanger register, in the floor pan of the heat exchanger housing, and/or in the condensate drain lines. Examples of deposits are paper dust from the paper drying, and/or substances that evaporate from the recording medium 120 within the scope of the drying, and/or ink, which are introduced into the exhaust air cleaning with the exhaust air 205 to be cleaned. The deposited substances can be dust-like substances and/or substances that solidify due to the cooling of the exhaust air 205.
The thermal transfer between the exhaust air 205 and the heat exchanger 210 is reduced by deposits on the components—in particular the air-side components—of the heat exchanger 210, whereby the process of the exhaust air cleaning is disrupted. Moreover, blockages may be created in the condensate outflow region of the heat exchanger 210, such that the condensate can drain anywhere in the printer in an uncontrolled manner.
Given fouling, the components of the exhaust air cleaning can be cleaned by maintenance personnel with the aid of a cleaning agent (water, for example). The maintenance activity that is connected with this is lined with a relatively high time and personnel cost, and leads to an unwanted interruption of operation of the printing device 100.
In this document, measures are described that enable an automatic regeneration cleaning of the exhaust air cleaning components, in particular of the heat exchanger 210, during the operation of the printing device 100. The deliberate condensing of water out of the exhaust air 205 can be effected as a measure of the regeneration cleaning, wherein the one or more exhaust air cleaning components can be flushed out of the exhaust air 205 via the water that has condensed out. The condensing out of water can be effected via supercooling of the exhaust air 205 below the dew point of the water contained in the exhaust air 205. As an alternative or additional measure for regeneration cleaning, a cleaning medium, in particular a cleaning fluid, for example water, can be introduced into the exhaust air 205 and/or into the fouled region of the heat exchanger 210.
Via an automated regeneration cleaning occurring during running printing operation, the functionality of the exhaust air cleaning can be ensured without complicated maintenance tasks needing to be performed. The temperature profile of the heat exchanger 210 can also be adapted in an optimized manner to the requirements of the exhaust air cleaning in order to reduce the quantity of VOCs (Volatile Organic Compounds), i.e. the quantity of hydrocarbons, according to the respective requirements, without the consistency of the condensate thereby needing to be considered, since a sufficiently high fluidity of the condensate can be effected via the repeated, in particular cyclical, increase in the quantity of fluid in the heat exchanger 210.
Furthermore, the operation of the exhaust air cleaning can be focused on the efficient condensing out of VOCs, without the continuous fluidity of the generated condensate needing to be considered.
Via the general lowering of the temperature of the exhaust air 205 from the input temperature 221 to the output temperature 223, it can be effected that VOCs, i.e. hydrocarbons, condense on the heat exchanger surface 211, and thus the exhaust air 205 can be cleaned. The condensate 212 appearing in the heat exchanger 210 can be conducted via a drain line into a capture container 213. The quantity 224 of condensate 212 thereby typically depends on the output temperature 223 of the exhaust air 205. The heat exchanger 210 can be configured to vary the output temperature 223 of the exhaust air 205, for example by changing the temperature and/or the volumetric flow of the cooling fluid 204, for example in order to increase the water fraction in the condensate 212 as needed, and in order to thereby achieve a higher fluid quantity. This increased fluid quantity has the effect of a regeneration cleaning of the heat exchanger 210.
Alternatively or additionally, the heat exchanger 210 can comprise an injection unit 230, for instance a pump and/or an injection nozzle, that is configured to introduce a cleaning fluid 230, in particular a cleaning liquid, into the exhaust air flow, for example at the input of the heat exchanger 210. The quantity of fluid in the heat exchanger 210 can thus be increased as needed in order to effect a regeneration cleaning of the heat exchanger 210.
For the temporary supercooling of the exhaust air 205, the cooling power of the heat exchanger 210 can be increased in a regeneration phase, for instance via a control and/or regulation, in order to fall below the dew point of the water contained in the exhaust air 205. An injection unit 230 can be used for the introduction of a cleaning fluid 231. The dedicated introduction of a cleaning fluid 231 has the advantage that the quantity of fluid that is made available for the regeneration cleaning of the heat exchanger 210 can be set independently of the printing process and of the ink quantity that is applied therein. A regeneration cleaning of the heat exchanger 210 via an introduced cleaning fluid 231 can, if applicable, be implemented in a dedicated process step, even if no recording medium 20 is printed to, such that the temperature of the heat exchanger register, of the heat exchanger housing, of the exhaust air 205, and/or of the cleaning fluid 231 can be specifically adjusted for a regeneration cleaning of the heat exchanger 210 that is as optimized as possible.
In the housing of the heat exchanger 210, the exhaust air 205 of the printing device 100 that is charged with VOCs thus flows with a defined input temperature 221, in particular when a recording medium is printed to. In the heat exchanger 210 with the surface temperature 222, the exhaust air 204 is supercooled to the output temperature 223. All substances for which the supercooling of the exhaust air 205 falls below their respective dew point thereby condense out on the surface 211 of the heat exchanger 210, for example on fins or on a tube bundle, and flow as condensate 212 into a capture container 213.
The goal of the exhaust air cleaning is typically to condense out as many VOCs as possible, and thereby as little water as possible, from the exhaust air 205 in the printing operation, in order to limit the quantity 224 of condensate 212 that must be processed.
By lowering the output temperature 223 of the exhaust air 205 from the standard value 310 to the reduced value 311, the quantity 224 of the condensate 212 can thus be increased, as is presented by way of example in
Alternatively, the duration Δt2 and/or the frequency of the regeneration phases 402 can be adapted dynamically, for example depending on the quantity 224 of condensate 212 accumulating in the printing operation.
The quantity of condensate 212 per time unit can be determined on the basis of the measured values 503, 505, 512. In particular, a check can be made as to whether a defined minimum outflow volume of condensate 212 was created in the interval Δt1. If this is so, the temporary decrease in the output temperature 223, i.e. the implementation of a regeneration phase 402, can thus be omitted in order to avoid the accumulating quantity of condensate being unnecessarily increased.
If a volumetric flow rate is no longer measurable within the interval Δt1, the temperature decrease can be activated in order to initiate a regeneration phase 402. The temperature decrease can be deactivated, for example after expiration of the duration Δt2, in order to end the regeneration phase 402. Alternatively or additionally, the temperature decrease can be deactivated as soon as a defined outflow volume 504 is achieved.
The method 600 comprises the operation 601 of the heat exchanger 201 in a standard phase 401 such that the output temperature 223 of the exhaust air 205 at the output of the heat exchanger 210 exhibits a standard value 310 via which it is effected that hydrocarbons are condensed out of the exhaust air 205. The operation of the heat exchanger 210 in the standard phase 401 can thereupon be focused and/or optimized to reduce the quantity and/or the concentration of hydrocarbons in the exhaust air 205. The heat exchanger 210 is preferably to be operated for more than 50%, in particular for more than 80% or for more than 90%, of the operating time in the standard phase 401.
The method 600 also comprises the operation 602 of the heat exchanger 210 in a regeneration phase 402 such that the output temperature 223 of the exhaust air 205 exhibits a reduced value 311 relative to the standard value 310, via which it is effected that water is condensed out of the exhaust air 205. The operation of the heat exchanger 210 in the regeneration phase 402 can thereupon be focused and/or optimized to effect a regeneration cleaning of the heat exchanger 210. The heat exchanger 210 is preferably operated for less than 50%, in particular for less than 20% or for less than 10%, of the operating time in the regeneration phase 402.
Via the insertion of one or more regeneration phases 402 into the standard operation, i.e. between one or more standard phases 401, of the heat exchanger 210, an efficient and reliable regeneration cleaning of the heat exchanger 210 can be enabled, in particular without thereby needing to interrupt the printing operation of the printing device 100.
By decreasing the output temperature 223 from the standard value 310 to the reduced value 311, the quantity of hydrocarbons in the condensate 212 is typically also increased in addition to the quantity of water in the condensate 212. The standard value 310 of the output temperature 223 can be established such that, at the standard value 310, the exhaust air 205 at the output of the heat exchanger 210 exhibits a target concentration of hydrocarbons, for example 50 g/m3, at least averaged over time. In other words, in a standard phase 401 it can be effected that the exhaust air 205 at the output of the heat exchanger 210 exhibits a target concentration of hydrocarbons. On the other hand, in a standard phase 401 an optimally low quantity 224 of condensate 212 is generated in order to keep the expenditure for post-processing of the condensate 212 low.
In a regeneration phase 402, the quantity 224 of condensate 212 can be increased, in a time-limited manner, by reducing the output temperature 223 to the reduced value 311, in order to effect a reliable regeneration cleaning of the heat exchanger 210. The concentration of hydrocarbons in the exhaust air 205 at the output of the heat exchanger 210 is thereby typically also reduced to below the target concentration.
The method 610 comprises the operation 611 of the heat exchanger 210 in a standard phase 401 such that the output temperature 223 of the exhaust air 205 at the output of the heat exchanger 210 exhibits a standard value 310 via which it is effected that hydrocarbons are condensed out of the exhaust air 205.
Furthermore, the method 610 comprises effecting 612, during a regeneration phase 402, that a cleaning fluid 231 (in particular water) is introduced (in particular injected) into the heat exchanger 210 and/or into the exhaust air 205 that flows to the heat exchanger 210, such that condensate 212 generated in the heat exchanger 210 is liquefied and/or diluted by the cleaning fluid 231. Via the (possibly additional) injection of a cleaning fluid 231, an especially reliable regeneration cleaning of the heat exchanger 210 can be enabled, in particular independently of the printing operation of the printing device 100.
A device 101, for instance a control unit and/or a controller for a printing device 100 and/or for a drying unit 150 and/or for a heat exchanger 210, is thus described that is designed for cleaning exhaust air 205 from a printing device 100 by means of a heat exchanger 210. The device 101 can be part of the printing device 100 and/or of the drying unit 150 and/or of the heat exchanger 210.
The device 101 is configured to operate the heat exchanger 210 in a standard phase 401, for instance for a standard operation of the heat exchanger 210, such that the output temperature 223 of the exhaust air 205 at the output of the heat exchanger 210 exhibits a standard value 310, in order to effect that hydrocarbons are condensed out of the exhaust air 205. In the standard phase 401, a cleaning of the exhaust air 205 can thus be at least primarily effected.
The device 101 is also configured to operate the heat exchanger 210 in a regeneration phase 402 such that the output temperature 223 of the exhaust air 205 exhibits a value 311 that is reduced relative to the standard value 310, in order to have the effect that water is condensed out of the exhaust air 205. In addition to the exhaust air cleaning, a regeneration cleaning of the heat exchanger 210 can be effected in the regeneration phase 402.
The device 101 can be configured to operate the heat exchanger 210 alternately in a standard phase 401 and in a regeneration phase 402. Alternatively or additionally, the device 101 can be configured to repeatedly interrupt an operation of the heat exchanger 210 in the standard phase 401 with a regeneration phase 402. In particular, by default an operation in a standard phase 401 can take place that is interrupted by a regeneration phase 402 as needed in order to effect a regeneration cleaning of the heat exchanger 210. A lasting, reliable exhaust air cleaning can thus be efficiently enabled.
The heat exchanger 210 can be designed to transfer thermal energy from the exhaust air 205 to a cooling fluid 204 in order to lower the exhaust air temperature from the input temperature 221 at the input of the heat exchanger 210 to the output temperature 223, and in order to thereby generate a condensate 212 from the exhaust air 205 that comprises hydrocarbons, in particular VOCs.
The device 101 can be configured to reduce the temperature of the cooling fluid 204, and/or to increase the volumetric flow of the cooling fluid 204, in order to reduce the output temperature 223 of the exhaust air 205 from the standard value 310 to the reduced value 311. Generally expressed, the device 101 can be configured to increase the cooling capacity of the heat exchanger 210 in order to reduce the output temperature 223 of the exhaust air 205 at the output of the heat exchanger 210 from the standard value 310 to the reduced value 311.
Alternatively or additionally, the device 101 can be configured to increase the temperature of the cooling fluid 204, and/or to reduce the volumetric flow of the cooling fluid 204, in order to increase the output temperature 223 of the exhaust air 205 from the reduced value 311 to the standard value 310. Generally expressed, the device 101 can be configured to reduce the cooling capacity of the heat exchanger 210 in order to increase the output temperature 223 of the exhaust air 205 from the reduced value 311 to the standard value 310. An efficient and reliable switching between a standard phase 401 and a regeneration phase 402 can thus be effected.
The reduced value and/or the standard value of the output temperature of the exhaust air are preferably such that the fraction of water in the condensate 212 generated from the exhaust air 205 in the heat exchanger 210 is higher at the reduced value 311, in particular is higher by a factor of 5 or more, than at the standard value 310. Alternatively or additionally, the reduced value and/or the standard value of the output temperature of the exhaust air are preferably such that the quantity 224 of condensate 212 generated per time unit is greater at the reduced value 311, in particular is greater by a factor of 5 or more, than at the standard value 310. The reduced value 311 of the output temperature 223 can be below the dew point of water, and/or the standard value 310 of the output temperature 223 can be above the dew point of water. A particularly efficient and reliable exhaust air cleaning and regeneration cleaning can be effected via such a selection of the standard value 310 and/or of the reduced value 311.
In a static operation, the heat exchanger 210 can be periodically operated in a regeneration phase 402 with a defined repetition rate. The duration of the periodically repeated regeneration phases 402 can thereby be consistent. A particularly efficient and reliable exhaust air cleaning and regeneration cleaning are thus enabled.
On the other hand, the device can be configured to determine one or more measured values 503, 505, 512 with regard to the quantity 224 of condensate 212 that is generated from the exhaust air 205 in the heat exchanger 210, for example that is generated per time unit. Whether—starting from a regeneration phase 402—a transition from the regeneration phase 402 into a subsequent standard phase 401, or whether—starting from a standard phase 401—a transition from a standard phase 401 into a subsequent regeneration phase 402, is effected or not can then be determined depending on the one or more measured values 503, 512 in a flexible and customized manner. A dynamically adapted insertion of regeneration phases 401 can thus take place. The efficiency and the reliability of the exhaust air cleaning and regeneration cleaning can thus be further increased.
The device 101 can be configured to determine, while the heat exchanger 210 is being operated in a standard phase 401 and on the basis of the one or more measured values 503, 505, 512, whether a predefined minimum quantity of condensate 212 has been generated from the exhaust air 205 or not in a time interval Δt1. The transition from the standard phase 401 into the subsequent regeneration phase 402 can be effected if, possibly only when, the predefined minimum quantity of condensate 212 has not been generated from the exhaust air 205 in the time interval Δt1. Alternatively or additionally, the heat exchanger 210 can continue to be operated in the standard phase 401 if the predefined minimum quantity of condensate 212 has been generated from the exhaust air 205 in the time interval Δt1. A customized insertion of regeneration phases 402 can thus be reliably effected.
The device 101 can be configured to determine, while the heat exchanger 210 is being operated in a regeneration phase 402 and on the basis of the one or more measured values 503, 505, 512, whether or not a predefined target quantity 504 of condensate 212 has already been generated from the exhaust air 205 since the beginning of the regeneration phase 402. The transition from the regeneration phase 402 into the subsequent standard phase 401 can be effected if the predefined target quantity 504 of condensate 212 has already been generated, or as soon as it is generated, from the exhaust air 205. Alternatively or additionally, the heat exchanger 210 can continue to be operated in the regeneration phase 402 if the predefined target quantity 504 of condensate 212 has not yet been generated from the exhaust air 205. A particularly efficient and reliable regeneration cleaning of the heat exchanger 210 can thus be effected.
The device 101 can be configured to introduce a cleaning fluid 231, in particular water, into the heat exchanger 210 and/or into exhaust air 205 that flows to the heat exchanger 210, for example at the input of the heat exchanger 210, during the regeneration phase 402, such that condensate 212 generated in the heat exchanger 210 from the exhaust air 205 is liquefied and/or diluted by the cleaning fluid 231. The quality of the regeneration cleaning of the heat exchanger 210 can be further increased by the dedicated introduction of a cleaning fluid 231.
A further device 101 for cleaning exhaust air 205 from a printing device 100 by means of a heat exchanger 210 is described. The aspects described in this document are also applicable to this device 101 individually and/or in combination.
The device 101 is configured to operate the heat exchanger 210 in a standard phase 401 such that the output temperature 223 of the exhaust air 205 at the output of the heat exchanger 210 exhibits a standard value 310, in order to effect that hydrocarbons are condensed out of the exhaust air 205. The device 101 is also configured to effect, during a regeneration phase 402, that a cleaning fluid 231, in particular water, is introduced into the heat exchanger 210 and/or into exhaust air that flows to the heat exchanger 210, such that condensate 212 generated in the heat exchanger 210 is liquefied and/or diluted by the cleaning fluid 231. An exhaust air cleaning and a regeneration cleaning of the heat exchanger 210 can thus be efficiently and reliably effected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 120 972.5 | Aug 2022 | DE | national |
