Patent Application
20210293482
The present invention relates to a thermodynamically controlled process for the drying of drying goods.
Furthermore, the present invention relates to a process for the thermodynamic control of a drying plant for the drying of drying goods as well as to the control of the respective drying process.
Additionally, the present invention relates to a thermodynamically controlled drying plant for the drying of drying goods.
A process for the drying of coated drying goods in a dryer is known from the German patent DE 10 2008 034 746 B4, paragraphs [0008] and [0009], during which process the hot clean gas exiting the thermal post-combustion chamber is led through a clean gas pipe through the dryer and a first circulation gas recuperator for the purpose of heating the circulating gas, thereafter, is led in a further the clean gas pipe through the dryer and then is led through at least one second circulating gas recuperator and, at last, is led to a fresh air recuperator for the heating of the fresh air, which is fed into the dryer in the inlet and outlet region of the drying goods. In doing so, the fresh air is led through a ring gap enclosed between the outer shell and the outer housing of the thermal post-combustion chamber before entering the fresh air recuperator.
The piping of the clean gas pipe through the dryer section by section and the thermal radiation resulting therefrom contribute substantially to the heating. With this kind of drying plants for car bodies the clean gas pipe behind the post-combustion chamber has a length of about 100 m. The clean gas has a temperature level of about 400° C. upon the exit out of the post-combustion chamber. This temperature is now lowered by the heat dissipation section by section in the dryer and in the recuperators thus far that the temperature after the fresh air recuperator is about 180° C. At the same time, the clean gas in the usage area of the dryer significantly exceeds the temperature level of the dryer so that it can be used for heating the dryer. In the case that the clean gas pipe sections in the dryer are configured as broad channels and are arranged below the car body conveyor, the quality of the drying of the floor assemblies which requires a lot of thermal energy is improved. Furthermore, in this process, the fresh air is led through the ring gap enclosed between the outer shell and the outer housing of the thermal post-combustion chamber before entering the fresh air recuperator. Thereby, the heated fresh air which is heated therein only requires a small additional heating for which the clean gas temperature present at the end of the clean gas pipe suffices.
The figure of the German patent DE 10 2008 034 746 B4 shows an embodiment of the dryer.
A process for the efficient use of the hot air streams in a car body coating facility is known from the European patent EP 2 295 909 B1, paragraphs [0005] and [0006], wherein the exhaust air from the dryer is led over an exhaust air ventilator unit of a thermal post-combustion chamber and is heated therein and is led by way of the clean gas pipe as clean gas through circulating gas recuperators and at least one fresh air recuperator, wherein the circulating air taken from the dryer and the fresh air are heated. In doing so, the fresh air taken from the fresh air recuperator is mixed with the circulating air taken from the dryer, and the resulting circulating air-fresh air mixture is heated in the circulating air recuperators and is again supplied to the dryer. In doing so, the quantitative air balance in the dryer is adjusted once and then locked.
This way, the fresh air reaches in the circulating air-fresh air mixture directly the heating zone and the stopping zone of the dryer. Therefore, the temperature level of the fresh air needs not be on the same temperature level of the dryer, but can be significantly lower because the circulating air recuperators raise the proportion of the fresh air in the circulating air-fresh air mixture to the temperature level of the dryer. This way, it is achieved that the clean gas temperature upstream of the fresh air recuperator can be far lower than the temperature of the dryer.
The figure of the European patent EP 2 295 909 B1 shows an embodiment of the dryer.
It is essential for the known processes and facilities that temperature of the thermal post-combustion facility is always held constant because the exhaust temperature of the thermal post-combustion facility always shows an unsteady behavior upon the controlling of the volume flow and, therefore, is not deemed controllable.
It is an object of the present invention to provide a process and a facility or plant which has additional technical possibilities for the control of drying plants or dryers and leads to further energy savings.
Accordingly, the object was solved by the drying plant of the invention for drying goods in accordance with the claim 1 and the drying process of the invention according to patent claim 9. The dependent claims referring back directly or indirectly to these claims refer to advantageous embodiments of the drying plant and the process of the invention.
In the context of the present invention, the term “variable” means that the respective temperatures and volume flows are or will be adjusted continuously to the respectively desired necessary process conditions during the performance of the of the drying process of the invention and of the thermodynamic regulatory procedure of the invention.
The drying plant of the invention is essentially built up from corrosion resistant and heat stable materials, preferably from metals, and in particular from stainless steel. In the case of parts of the drying plant which are less thermally stressed or not stressed at all, other materials like plastics, glasses or wood are used. In particular, thermally stable plastics like thermoplastics and thermoset plastics which can be reinforced with glass fibers, steel fibers, basalt fibers, carbon fibers, textile fibers, and mats of steel or glass can be used. Moreover, the plastics can contain fire retardants. Examples of thermally stable thermoplastics are polyamides, polyimides, polyamideimides, polysulfones, polyethersulfones, polyetherketones and polyetheretherketones.
The drying plant of the invention comprises at least one, preferably one, drying tunnel through which the drying goods are conveyed in the conveying direction. Preferably, the drying goods of formed objects which are particularly preferably built up from wood, plastics, glasses, metals, fabrics and composites of at least two of these materials.
The drying goods can be objects of all kind. Examples for drying goods are formed plastic parts, which are partly dissolved and/or melted that their surface, glued composites of all kind, the adhesive layers of which are not yet dried, and coated formed objects of all kind which have been coated by spray coating, powder coating, curtain coating, electrodeposition coating and doctor blade coating, and formed objects which have been printed or painted by sieve printing, intaglio printing, offset printing, relief printing and flexographic printing.
Examples of suitable objects are building parts for architectural purposes like window frames, grids, railings, doors, stairs, rod assemblies, tubes, and mobile buildings, building parts and chassis of means of locomotion such as automobiles, trucks, buses, building machines, motorcycles, mopeds, quads, scooters, pedal-scooters, hoover boards, skateboards, longboards, two-wheel wind runners, locomotives, train wagons, airplane parts, hulls, high-quality household appliances, heating elements, radiators and building parts for sanitary purposes. In particular, the involve building parts and car bodies of automobiles, trucks and buses.
The drying goods are conveyed through the at least one, in particular, one drying tunnel on skids.
Furthermore, the drying plant of the invention comprises at least one, in particular one pipe for volatile organic compounds (VOC) containing exhaust gases from the at least one, in particular one, drying tunnel. The at least one exhaust gas pipe leads to at least one, in particular one blower which is controlled by at least one, in particular one frequency converter and transports in a controlled manner the exhaust gas through another exhaust gas pipe to at least one, in particular one heat exchanger, wherein the exhaust gas is variably heated by the clean gas channeled out of an at least one, in particular, one thermal post-combustion facility with at least one additional, in particular one additional clean gas pipe.
The exhaust gas heated to varying temperatures accepts the at least one, in particular, one heat exchanger in varying amounts through at least one, in particular one additional exhaust pipe and enters into at least one, in particular one burner of the at least one, in particular one thermal post-combustion facility.
Fuel is fed into the at least one, in particular one burner through at least one, in particular one fuel pipe in varying amounts. Gases like hydrogen, methane, propane, butane, or mixtures from at least two of these flammable gases, as well as liquid fuels like heating oil, kerosene, gasoline, diesel oil, as well as mixtures of at least two of these liquid fuels come into consideration as fuel. In particular, natural gas is used.
The resulting gas mixture of varying composition is burned in the at least one, in particular one combustion chamber in at least one flame, preferably, however, in at least at least two or more flames. This way, clean gas of varying composition and varying temperature results in the at least one, in particular one combustion chamber of the at least one, in particular one thermodynamic post-combustion facility subject to the composition of the gas mixture and its temperature, which temperature is mainly determined by the temperature of the heated exhaust gas.
For example, thermal post-combustion facilities as described in the German patent DE 10 2008 034 746 B4, paragraph [0018] can be used. Compact thermal post-combustion facilities, wherein the heat exchangers and the combustion chambers are forming one unit come into question. Compact thermal post-combustion facilities of this type are available from the company Wenker GmbH & Co. KG, Ahaus, Germany.
The drying plant of the invention comprises furthermore at least one, in particular one cold bypass which circumvents the at least one, in particular one heat exchanger by connecting the at least one, in particular one exhaust gas pipe before the at least one, in particular one heat exchanger with an at least one, in particular, one exhaust gas pipe downstream of the at least one, in particular one heat exchanger. The exhaust gas stream through the at least one, in particular one cold bypass is controlled by at least one, in particular one pilot valve. The inlet temperature of the exhaust gas before the entry into the combustion chamber is regulated by the cold bypass. The temperature in the combustion chamber is controlled by the pilot valve for the fuel.
The clean gas originating in the at least one, in particular, one combustion chamber is fed through at least one, in particular one clean gas pipe to the at least one, in particular, one heat exchanger, wherein it heats the exhaust gas and is thereby cooled. After the one, in particular one heat exchanger, the clean gas is fed to at least one, preferably to at least two, and in particular to at least three heat consumers. In the heat consumers, the energy flow ĖWA is extracted from the clean gas. The energy flow E is the first derivation of E for energy. The basic controlling rule of the energy flow Ė must be calculated with the absolute temperatures. The regulating variables are therefore referred to absolute zero (−273° C.). Therefore, the controlling equation to be established for the first measuring station downstream of the heat exchanger is equation I:
Ė
TNV[W]+ĖAG[W]=ĖWA[W]+ĖRGD[W] (I)
with:
ĖRGD=energy flow of the clean air exhaust via the roof and
Ė=TTNV×f({dot over (V)}) with {dot over (V)}=volume streams,
TNV=thermal post-combustion facility,
AG=exhaust gas,
WA=heat consumer,
RGD=clean air exhaust via the roof.
This way, the following is covered:
“Energy generated by the thermal post-combustion facility+energy contained in the exhaust gas=energy used up in the process+energy discharged over the roof”.
Seen from the vantage point of the post-combustion facility, the controlling equation becomes equation II:
Ė
TNV[W]=ĖWA[W]+ĖRGD[W]−ĖAG[W] (II)
Thereby, the control difference Δ before the control unit is obtained as equation III:
Δ={ĖWA[W]+ĖRGD[W]−ĖAG[W]}−ĖTNV[W] (III)
with ĖWA [W]+ĖRGD [W]−ĖAG [W]=target value and ĖTNV [W]=actual value.
The target value can be defined more precisely:
(i) ĖWA [W] as the heat reduction of the dryer T to be compensated,
The regulating variable is the volume stream V at normal conditions (i.N.: Temperature=273,15 K, pressure=1013,25 mbar).
The term ĖRGD [W]−ĖAG [W] also contains the absolute temperature. In order to be able to control energetically optimized, a reference temperature has to be fixed. Customarily, the Celsius scale is used as the reference station. It makes more sense to use as the reference station, the target value over the roof. In this case, term ĖRGD [W] equals zero and disappears. Instead of this, the target value over the roof ĖRGD [W] appears again in the temperature difference. One can also take any temperature as the reference temperature as well as the temperature of the crude gas.
Thereafter, the term ĖAG [W] disappears and the temperature of the crude gas appears again in the term ĖRGD [W] in the temperature difference.
If at least one, in particular one compact, thermal post-combustion facility is used, the at least one, in particular, one combustion chamber and the at least one, in particular, one heat exchanger jointly act as energy supply ĖTNV.
The energy output over the at least one, in particular one heat consumer to the at least one, in particular one, drying tunnel can also be calculated by the volume stream of the circulating air. The chimney temperature, i.e., the temperature of the clean gas in the at least one, in particular one, clean gas pipe downstream of the at least one, in particular one heat consumer also appears as a target value in the controlling equation ĖRGD.
Therefore, one needs as the measured quantities at least:
When the target value is reached during the energy control, namely that the compared amounts of energy are equal and, therefore, the control difference is zero, the target value over the roof is also reached.
In turn, the combustion chamber temperature follows the equation IV:
T
BK
=f({dot over (V)}variabel) (IV),
wherein {dot over (V)}variabel=volume stream of the clean gas RG in the clean gas pipe LRG [m3 per hour under normal standard conditions].
Equation IV defines a setting window, wherein the combustion chamber temperature at a minimum volume stream is between 600° C. and 800° C., preferably, between 650° C. and 720° C. and, in particular, between 680° C. to 690° C., and at a maximum volume stream is between 700° C. and 900° C., preferably, between 700° C. and 750° C. and, in particular, between 720° C. and 730° C., whereby, however, both temperature ranges are chosen such that they do not overlap.
Preferably, the volume streams are in a range of from 3000 m3 per hour and 30,000 m3 per hour and, in particular, 4000 m3 per hour and 20,000 m3 per hour (all values under normal standard conditions).
The heat quantity removed in the heat consumers or the clean gas which transports the removed heat quantity at the respective clean gas temperature and clean gas amount serve for heating the at least one, in particular one drying tunnel of the drying plant of the invention, whereby the complete cycle of the variably controlled volume streams is closed. In this case, the amount of energy, which is transported by the exhaust gas stream can cause an energy recovery in drying plants for the cathodic electrodeposition coating which require high temperatures.
Examples of suitable heat consumers are waste heat boilers, recuperators, heat exchangers and gas pipes. A particularly preferred combination of clean gas pipes, circulating gas pipes, circulating gas recuperators and fresh air recuperators which are downstream from a thermal post-combustion facility and pipes for the exhaust gas from the drying tunnel which are upstream from a thermal post-combustion facility are known from the figure of the German patent DE 10 2008 034 746 B4.
The rest of the clean gas is led through at least one, in particular, one additional clean gas pipe through a waste heat boiler if necessary or at least one fresh air recuperator into at least one, in particular one chimney or stack and, from there, released to the atmosphere. By the regulation of the amount of energy which should be released over the roof, the level of the volume streams, i.e, m3 per hour per drying goods such as car bodies can be regulated. The higher the target value is set, the higher is the amount of air per drying good.
The drying plant of the invention and the drying process of the invention are preferably electronically controlled by the at least one, in particular one thermodynamic control of the invention. For the purposes of the thermodynamically controlled process of the invention, the drying plant of the invention comprises
For the thermodymamic control
The thermodynamically controlled process of the invention controls the drying plant of the invention so that the volume streams in the drying plant of the invention are always within the range of the threshold values determined by the expert opinion relating to explosion, and that no condensation of gases can occur.
Preferably, the process of the invention for drying of coated drying goods in at least one, in particular one drying plant of the invention is carried out whilst the drying goods are conveyed through at least one, in particular one drying tunnel in conveying direction and are dried thereby whilst
(i) the volatile organic compounds containing exhaust gases generated thereby are sucked off through at least one, in particular one exhaust gas pipe from the at least one, in particular one drying tunnel,
(ii) are transported by at least one, in particular, one blower controlled by an actuator to 1, in particular one heat exchanger, whereby the amount of the sucked off exhaust gases is controlled,
(iii) are, at least temporarily, heated in at least one, in particular one heat exchanger by the clean gas from the at least one, in particular, one thermal post-combustion chamber facility in which at least one, in particular, one clean gas pipe is heated to exhaust gas temperatures,
(iv) are transported through at least one, in particular one cold bypass circumventing the at least one, in particular one heat exchanger and connecting the at least one, in particular one exhaust gas pipe upstream and downstream of the at least one, in particular one heat exchanger, the cold bypass being regulated by at least one, in particular one pilot valve controlled by at least one, in particular one control station, which control valve remains temporarily open or closed or remains partially or completely open or closed during the complete drying process, whereby the exhaust gas temperature is kept constant or is varied if necessary,
(v) are transported through at least one, in particular, one additional exhaust gas pipe from the at least one, in particular one heat exchanger to the at least one, in particular one burner and
(vi) are mixed with the fuel which is supplied by at least one, in particular one fuel pipe in varying amounts, and
(vii) are burned in the at least one, in particular, one burner in the at least one, in particular one combustion chamber of the at least one, in particular one thermal post-combustion facility in at least one flame, in particular in at least two or more flames at variable combustion chamber temperatures, whereby
(vii) the resulting clean gas RG having variable temperature is transported out of the at least one, in particular one combustion chamber through at least one, in particular one clean gas pipe to the at least one, in particular one heat exchanger wherein it variably heats the sucked off exhaust gases at least temporarily,
(ix) the clean gas exiting the at least one, in particular one heat exchanger is transported to at least one, preferably, to at least two, and, in particular to at least three heat consumers wherein varying amounts of heat are taken from the clean gas, which amounts are used, to varying heatingly of the at least one, in particular one drying tunnel, whereupon
(x) the clean gas is released over the roof into the atmosphere.
Preferably, the clean gas is released into the atmosphere either directly or through at least one chimney or at least one, in particular one waste heat boiler upstream from the chimney. If necessary, fresh air can be supplied in order to cool the clean gas further to a harmless temperature.
The drying plant of the invention, the drying process of the invention and the thermodynamically controlled regulatory process of the invention shows numerous advantages.
Thus, the complete drying plant of the invention is calculated and controlled with standard volume streams so that at any arbitrary location the varying volume streams and the energy requirements can be determined independent of pressure and temperature.
Reliable and tested measuring systems, as for example, the Venturi measurements and temperature sensors such as PT 100 can be used so that the operational safety is guaranteed and the availability of the complete plant survives.
A substitute control station can be added which ensures the emergency operation of the drying plants of the invention when additional measuring units fail. The values to be set can be gleaned from the ongoing operation.
By the use of the reserve design and/or by the enlargement of the heat exchangers the required process parameters can be maintained at all operating conditions and at all locations of the drying plant of the invention.
By dynamizing the combustion chamber temperature in dependency of the volume stream, the emission values of noxious substances can be kept constant by the drying process of the invention and the regulatory process of the invention and can be set at a low value.
Furthermore, the spreading of the controllable volume streams by the drying process of the invention and the thermodynamic regulatory process of the invention can be widened. This way, the controllable power output of the thermal post-combustion facility can be significantly enhanced.
In the case of the compact thermal post-combustion facilities a higher volume stream is led through the cooling shell by controlling the exhaust gas temperature upstream from the combustion chamber at a minimum volume stream due to which the thermal combustion chamber is at its hottest temperature, whereby the skin of the combustion chamber is cooled exactly when it's necessary.
The dynamization or variation of the combustion chamber temperatures cause an automatic transition into the intermitting operation. The transition into the intermitting operation needs not switched on any longer. This way, no overheating of the drying plant of the invention occurs during the idle mode and the operation of the drying plant is independent of incidences in the coating cabins.
The mode of operation with adjusted optimal volume streams lowers the consumption of the electrical energy of the exhaust gas blowers. Moreover, energy consuming throttle valves or measures increasing the pressure loss are no longer necessary.
The possibility for the simple adjustment of the volume streams per drying good opens up the opportunity of optimizing the consumption of energy on the one hand and the cleaning efforts due to condensate on the other hand.
In total, significant energy savings can be achieved as compared with customary drying plants so that one can react particularly flexibly to rising energy prices.
The drying plant of the invention and the process of the invention are explained in detail by the Examples with reference to the
In the
The drying plant of the invention T was designed for minimum volume streams {dot over (V)}min. of 5,000 m3/hour and for maximum volume streams {dot over (V)}max. of 10,000 m3/hour. The emission setting window ESF was predetermined by corner points of 680° C. and 690° C. as well as 720° C. and 730° C. Plant components which were particularly thermally stressed were built mainly with stainless steel. Plant components which were less thermally stressed were built mainly with shock resistant and thermally stable plastics made flame retardant, if necessary. The drying plant T was electronically controlled by a thermodynamic control. The drying plant T was subject to an expert opinion relating to explosion.
The drying plant T of the invention for drying of coated drying goods LTG, in particular, car bodies, comprised
For the purposes of the electronic control, the drying plant T of the invention contained
As the measuring instruments, customary and known instruments for measurements at high temperatures and hot gas streams are used.
For purposes of the electronic control of the drying plant T, the thermodynamic control unit TDR received
For the purposes of control, the thermodynamic measuring station TDR put out after the calculation
The controlling algorithm was based on the following mathematical correlations:
The controlling equation for the measuring station 8 downstream of the heat exchanger WT was equation I:
Ė
TNV[W]+ĖAG[W]=ĖWA[W]+ĖRGD[W] (I).
Seen from the vantage station of the post-combustion facility, the controlling equation became equation II:
Ė
TNV[W]=ĖWA[W]+ĖRGD[W]−ĖAG[W] (II)
Thereby, the control difference Δ upstream of the control unit was obtained as equation III:
Δ={ĖWA[W]+ĖRGD[W]−ĖAG[W]}−ĖTNV[W] (III)
with ĖWA [W]+ĖRGD [W]−ĖAG [W]=target value and ĖTNV [W]=actual value.
The target value could be defined more precisely:
The regulating variable is the volume stream {dot over (V)} at normal or standard conditions (i.N.: Temperature=273,15 K, pressure=1013,25 mbar).
The combustion chamber temperature TBK followed in turn, the equation IV:
T
BK
=f({dot over (V)}variabel) (IV),
wherein {dot over (V)}variabel=volume stream of the clean gas RG in the clean gas pipe LRG [m3 per hour under normal standard conditions].
For the heater HZTT of the drying zone TT, the thermal power ĖWA [W] was taken from the heat consumers WA.
The drying plant T of the invention could be combined, for example, with the configuration described in detail in the Figure of the German patent DE 10 2008 034 746 B4. The following reference signs in italic refer to the known Figure. In the drying plant, the clean gas exited the thermal post-combustion facility TNV 9 by the clean gas pipe 24, 24a, 24b and 24c. The three last mentioned sections were laid section by section at the floor of the drying tunnel so that the drying goods could be particularly well heated from below. The clean gas pipes exited the floor of the drying tunnel and the clean gas contained therein heated the circulating gas in the circulating gas recuperators 10 and 12, which circulating gas was fed to them by the circulating gas pipes 17 from the drying tunnel and was then led back into the drying tunnel. The clean gas which was cooled down was further cooled in the fresh air recuperator 14 before the discharge into the atmosphere, and the fresh air heated in this way was again led back into the drying facility via the fresh air pipes 15a and 15b.
This way, not only the significant advantages of the drying plant T of the invention could be combined with the advantages of the drying plant according to the German patent DE 10 2008 034 746 B4 thus resulting in new particular advantages, but significant energy savings and a significant reduction of the emissions of NOx, complete carbon, carbon monoxide and formaldehyde could be achieved. When using a combustion with oil, sulfur dioxide was also observed.
With the combination of the drying plant T of the invention with a compact thermal post-combustion facility TNV of Wenker GmbH & Co. KG, Ahaus, Germany, the thermal post-combustion facility TNV could be run with significant more stable emissions, and the controllable performance range of the TNV could be considerably extended when one held the exhaust gas temperature TWT upstream from the combustion chamber BK constant with the help of the control station R of the cold bypass BP and changed the combustion chamber temperature. TBK dependent on the volume stream {dot over (V)}min. to {dot over (V)}max. within the limits “Minimum combustion chamber temperature TBK to maximum combustion chamber temperature TBK”.
The possibility of circumventing the intermission set up moreover enabled the drying plant T of the invention to let drying goods LTG, in particular, car bodies, enter at low combustion chamber temperatures TBK. Therefore, the minimum amount of air could be used maximally in order to dry the car bodies, which was not possible in the prior art drying processes, in particular, during the usage of the intermission set up.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 005 578.8 | Jul 2018 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/000207 | 7/10/2019 | WO | 00 |
