WO2011134630A1

WO2011134630A1 - Heat exchanger for rapidly heating and cooling fluids

Info

Publication number: WO2011134630A1
Application number: PCT/EP2011/002045
Authority: WO
Inventors: Klaus Schubert; Peter Pfeifer; Manfred Kraut; Roland Dittmeyer
Original assignee: Karlsruher Institut für Technologie
Priority date: 2010-04-30
Filing date: 2011-04-21
Publication date: 2011-11-03
Also published as: DE102010018869A8; EP2564143A1; DE102010018869A1

Abstract

The invention relates to a heat exchanger for rapidly heating and cooling a fluid in at least one micro-channel (1), comprising a heating section (2), a residence time section (3) and a cooling section (4). The aim of the invention is to provide an improved heat exchanger system having greater efficiency. The aim is achieved by a heat exchanger in which the heating section and the cooling section are thermally connected to each other and only the residence time section has power supply means (5).

Description

Heat exchanger for rapid heating and cooling of fluids

The invention relates to a heat exchanger system, preferably a microstructured heat exchanger system and a method for rapid heating and cooling of fluids, preferably liquids according to the first and tenth patent claim.

In heat exchanger systems of the type mentioned above, fluid mixtures are rapidly heated to a specific temperature, kept at this temperature for a certain period of time, and then rapidly cooled again in the same system. The fluid or the fluid mixture passes through a plurality of heat exchangers or heat exchanger areas in one or more fluid passages in the heat exchanger system serially, preferably continuously by means of a continuous fluid flow. Such heat exchanger systems serve, for example, the sterilization of fluids, the controlled performance of chemical reactions or catalytic decomposition reactions.

A well-known version of a heat exchanger system comprises a plurality of separate heat exchangers and reaction chambers arranged one behind the other, which are each provided for a partial step (heating, reaction, cooling).

EP 1 162 888 B1 describes, by way of example, a method for killing harmful microorganisms in liquids by briefly heating to above 140 ° C. and subsequent cooling when using two serially connected microstructured crossflow heat exchangers. For optional maintenance of an isothermal hold time between heating and cooling, the use of a third intermediate heat exchanger is suggested.

However, series-connected micro-heat exchangers require additional connection components such as fluid connections and / or connection lines. These not only form dead volumes but also represent system disturbances and sources of error. Consequently, a device for evaporating liquid media is proposed by way of example in DE 101 32 370 B4, in which two heating devices are integrated as a heat exchanger with an intermediate volume arranged therebetween in a microstructure apparatus.

However, the latter embodiment can be limited to a heat exchanger system of the type mentioned transferred. While two heaters are fundamentally similar in their temperature range and can also be arranged functionally next to one another in a microstructure apparatus, the integration of a heating and a cooling device in a common microstructure body inevitably leads to increased heat losses due to the short heat transfer paths without further heat-insulating measures. The efficiency is reduced accordingly with an increase in heat losses.

Based on this, the object of the invention is to propose a further improved heat exchanger system and method for heating and cooling a fluid with an increased efficiency.

The object is achieved by a heat exchanger system and a method having the features of claims 1 and 10, respectively. Subclaims indicate advantageous embodiments.

To achieve the object, a heat exchanger and a method for rapid heating and cooling of a fluid is proposed, in which the fluid is passed through at least one microchannel and heated and cooled therein. Optionally, the fluid in the microchannels is maintained at a temperature level between heating and cooling for a certain time (dwell time). The temperature level is ideally defined by a target temperature, but in practice defined by a temperature interval between a lower and an upper dwell time. The temperature span extends preferably ± 5%, more preferably ± 2% of the target temperature in ° C, preferably around this target temperature.

In each of the microchannels, the fluid passes through a heating section for heating, a cooling section for cooling, and a residence time section therebetween. The residence time zone comprises at least one area in which the fluid is converted from a heating into a cooling, preferably the area in which the fluid assumes the aforementioned temperature level or temperature interval.

The fluid passes through the heat exchanger as a fluid stream, preferably as a continuous fluid stream, more preferably - as designed - as a stationary fluid stream.

The method for rapidly heating and cooling a fluid in at least one microchannel comprises heating the fluid in a heating path (first step). Subsequently, in a second step, a forwarding of the fluid in a residence time with the same temperature or the aforementioned temperature level or temperature interval, followed by an introduction and cooling of the fluid in the cooling section (third step).

What is essential is a thermally conductive connection between heating section and cooling section, which enables a transfer of heat energy from the fluid to be cooled in the cooling section to the fluid to be heated in the heating section. In the third step, the fluid releases heat directly to the fluid in the first step.

The residence time section, preferably only the residence time section, has power supply means, preferably heating means. They not only determine the temperature level in the residence time, but also compensate for the heat losses in the aforementioned process, in particular the heating and cooling. The heating means preferably comprise fluid guides for receiving and / or passing one or more tempering fluids on or around the microchannels in the region of Residence time distance. As tempering fluid serve liquid and gaseous fluids, preferably thermal oils, salt and metal melts or gases. Alternatively, it is proposed to provide the fluid guides inside, in particular in the region of the microchannels of the residence time section, with a catalyst which triggers a chemical catalytic reaction with heat development (exothermic reaction) in the tempering fluid and selectively enables heating of the residence time section or a part thereof. In this case, it is advantageous for a more homogeneous tempering and / or temperature distribution, the fluid guides, in particular the catalyst-coated fluid guide sections as reaction chamber with extended cross section and / or with an enlarged surface for the heat transfer (eg heating or cooling fins ) to design. Optionally, the reaction space can also be designed as a reaction mixing chamber with a merging and again bifurcation of a plurality of fluid guides. Another embodiment provides electric heating cartridges or heating elements as heating means, which are used or integrated near the residence time in the heat exchanger.

One possible embodiment provides for a fluidic connection between the microchannels in the residence time path and the fluid guides. Thus both the tempering fluids as mixing additives or as reactants can be mixed into the fluids in the microchannels as well as any gases or vapors from evaporation or decomposition in the fluid can be diverted from the microchannels into the fluid channels, preferably aspirated. The driving force for the Eimischung or suction is the pressure difference between the fluid in the

Micro channels and the tempering fluids in the fluid guides. A preferred embodiment provides a membrane, preferably a selectively gas-permeable membrane (for the selective removal of gases) between microchannels and fluid channels.

The heating section comprises, if a process is carried out with a heating with a vapor or gas formation, an evaporator section and optionally an overheating section, the cooling section a Condensation section. If the fluid to be heated enters the heating section in a vapor or gaseous state, the heating-up section only consists of an overheating section.

Preferably, a plurality of parallel-connected microchannels are provided, further preferably in the heat exchanger bundle parallel to each other. The parallel-connected microchannels further preferably have the same geometric dimensions.

A further embodiment provides that the microchannels of the heating section and / or the cooling section have at least one intermediate volume into which all or one of the microchannels of the heating section and / or the cooling section terminate and exit again. Several preferably similar intermediate volumes with preferably an equal number of inflowing and outflowing microchannels (microchannel groups) can be arranged parallel to one another and thus form a voluminous group. Mixing of the microchannel groups with each other is in turn realized by a second, the first downstream Voluminagruppe of mutually parallel intermediate volumes, which are arranged offset with respect to the previous intermediate volumes, i. span from these deviating microchannel groups.

The intermediate volume or volumes serve to intermix fluid flow from the microchannels during heating or cooling, particularly to reduce material and thermal inhomogeneities, and thus, e.g. of premature local evaporation. The intermediate volumes may also be provided with inlets or outlets for admixtures of additional fluids and / or selective aspirations, e.g. of gases - as otherwise described in the other context - use.

Likewise, the residence time range can be used and designed as a reaction volume or a plurality of reaction volumes arranged in parallel for a chemical reaction. It is within the scope of further embodiments of the invention to design the power supply means not as a heating means, but as a coolant, wherein the fluid to be treated is first introduced into the cooling section and cooled, then in the residence time a temperature minimum passes, then reheated in the heating to become. As described above, the heating path and the cooling section are thermally connected to each other.

The invention and details of the invention will be explained in more detail with reference to further embodiments with the following figures. Show it

FIG. 1 shows an embodiment of a micro heat exchanger with countercurrent heat exchange element, FIG.

2 shows an embodiment of a micro-heat exchanger with cross-flow heat exchanger element,

3 shows a detailed view in the region of the residence time distance with electric heating cartridges,

1 shows an embodiment of a micro heat exchanger with countercurrent heat exchange element and a power segregation by catalytic reaction,

5 shows a single film of a micro heat exchanger with grooved incorporated fluid guides for a heating line and

6 shows a schematic representation of the process sequence for the production of hydrogen cyanide from formamide.

A heat exchanger of the aforementioned type, as disclosed in FIGS. 1 and 2 in a respective sectional view, comprises at least one microchannel 1 with a heating section 2, a residence section 3 and a cooling section 4, wherein the heating section and the cooling section are thermally connected to each other and the residence time section has power supply means 5. The microchannels are flowed through by a fluid idstrom, wherein the flow direction 9 is indicated by arrows. The fluid flow is in the supply 10, that is, before entry into the heating section 2, a starting temperature _e i _n and leaves the cooling coil _from having an exit temperature T.

Fig.l shows an embodiment in which the heating section 2 and cooling section 4 are flowed through in countercurrent to each other (countercurrent heat exchange element). The extent of the heating and the cooling and thus the countercurrent heat exchange element, but also the residence time 3 in the heat exchanger is represented by dimension arrows and dashed lines. The part of the residence time section facing the aforementioned countercurrent heat exchange element is the power input path 8, which is preferably equipped with larger and / or more strongly dimensioned power supply means 5 compared to the remaining area of the residence time section. These reinforced power supply means serve in addition to the temperature of the power input point and the thermal buffering between heating / cooling and the remaining residence time and also to compensate for heat losses in the heat exchanger, in particular caused by the temperature difference between the starting temperature _e in and the outlet temperature T _out . If appropriate, endothermic or exothermic reactions taking place in the fluid flow or inlets or outlets of partial flows in the fluid flow must be taken into account in the heat exchanger, in particular in the dwelling time zone.

2 shows an embodiment in which the heating sections 2 and cooling sections 4 are flowed through in cross-flow to each other (cross-flow heat exchange element). In this case, the extent of the cooling sections 4 comprises only a partial area 12 of the heating-up section, which in this exemplary embodiment has additional inlet cooling channels 13 and heat-insulating cavities 11. The inlet cooling channels are used for tion of a coolant and thus the regulation of the inlet temperature _e in the fluid flow, while the heat-insulating cavities 11 reduce the action of the coolant in the portion 12.

Fig.l to 6 show examples of embodiments of Mikroärmetausehern. The illustrated variants comprise at least one heat exchanger of the aforementioned type, wherein the microchannels 1 are integrated as groove-shaped incorporated fluid guides and the power supply means 5 in sheets 6 (individual sheets) of a film stack. Breakthroughs 7 serve as fluid guide connections between two microchannels. The thermal connection between the heating and cooling path takes place via the remaining film section between the microchannels.

The two superimposed and one-sided structured films in FIGS. 1 to 4 with the heating section 2 and the cooling section 4 can be replaced by a film structured on both sides, the heating section 2 being incorporated on one side of the film and the cooling section 4 being incorporated on the other side ,

Basically, with the aid of the inlet cooling channels 13 and thermal insulation cavities 11, not only Τ _θ ι _η , but also T _aus in the fluid flow can in principle be set in all designs. The Wärmedämmkavität is also replaced by other thermal insulation. Particularly advantageous for low heat losses and thus high efficiency is a design of all films 6, which are not used for the transfer of heat, eg between heating section 2 and cooling section 4 or between residence section 3 and power supply means 5, from a thermal insulator such as a porous material, Plastic or a non-metallic material (eg glass, ceramics).

3 shows a cut-out detailed view of a residence time section 3 of a heat exchanger as described above, alternatively with electric heating cartridges 15 as power supply means 5. As in the preceding figures, the residence time section comprises a tion insertion 8, which preferably (but not shown) has a higher density of cartridge heaters or more powerful cartridge heaters to compensate for losses in particular from the areas of the heating sections 2 and 4 cooling lines. The heating cartridges are used in at least one film, preferably in separate films in holes 14, alternatively in recesses or in ril- lenförmigen cavities. A slight interference fit with optional thermal paste between the inner wall of the holes and the cartridge heaters used promotes heat input in an advantageous manner.

FIG. 4 exemplarily represents a design with a power input through chemical reactions, preferably catalytic reactions with heat development. As in the aforementioned embodiments, the power supply means are arranged in the region of the residence time section 3, more preferably in the power input section 8. They include fluid guides 16, in which a reactive gas, such as preferably CH ₄ or H _{2, is introduced} into the heat exchanger and from there is sprayed into a gas channel 18, preferably flat, through injection openings 17. The gas channel is traversed by an oxygen-containing gas, preferably air, in particular in the region of the power input path 8 to a reaction in the example for the exothermic reaction of oxygen 0 ₂ with hydrogen H ₂ or hydrocarbon CH ₄ comes. The gas channel is preferably coated with a catalyst for reaction control and / or concentration, more preferably in the region of the power input section 8 or the residence time section 3. The gas flow 19 heated by the reaction preferably transfers heat in countercurrent directly to the fluid flow in the channels 1, Preferably, as shown in the example, first on the residence time section 3 and then also on the heating 2. An effective heat transfer is achieved by a thin membrane 20 between the gas flow 19 and fluid flow (flow direction 9). By contrast, the cooling section 4 is preferably thermally insulated from the gas flow and preferably has an increased heat conductivity selectively acting on the heating section. The heat from the cooling section is preferred on the Heating the fluid flows used in the heating sections and then does not escape into the gas flow. If the membrane has a fluid-tight design, only heat is transferred via it. An alternative embodiment provides a non-fluid-tight or selectively permeable membrane, which allows mass transfer between the fluid and the gas and can be used to generate and control reactions in the fluid flow.

The reactions on the gas side (gas flow 19) are preferably a selective oxidation, for example the partial oxidation of hydrocarbons to synthesis gas, the selective oxidation of CO in the presence of hydrogen, the production of hydrogen peroxide from hydrogen and oxygen in the Oxygen depletion, production of peroxide compounds (propene oxide, epoxybutene) or oxidative dehydrogenation of hydrocarbons such as propene. During these reactions optionally a selective separation of individual reaction products, such as hydrogen over the membrane 20; the resulting free reaction space is the reaction additionally available. Selective removal of gases also allows adjustment of higher reaction pressures, exploiting the shift in thermodynamic equilibrium by removing the hydrogen; This results in higher sales and higher efficiency. Reactions on the fluid side (with liquid fractions esp. In the heating section 2) are preferably hydrogenations in the gas phase, such as nitrobenzene or toluene, or in ionic liquids, if their temperature stability allows a coupling with the oxidation reaction. Endothermic reactions on said fluid side, which do not require a membrane, are preferably surface-catalyzed decomposition reactions (methanol, propane, etc.) or reforming processes. The coupling of a hydrogen-oxygen reaction to hydrogen peroxide on the gas side could also be connected via a non-selective membrane 20 with an epoxidation, wherein the product hydrogen peroxide would be useful as Epoxidierungsreagenz. Heat exchangers in which the fluid is vaporized and preferably also recondensed preferably have correspondingly adapted evaporator sections and possibly cooling sections. 5 shows by way of example in phantom top view of a sheet 6 with groove-shaped incorporated microchannels 1 in the region of the heating section 2 as well as the delay zone 3 with power input path 8. The Aufheizstre ^¬ bridge comprises Besides one Flüssigkeitsaufheizstrecke 23 as schematically shown an evaporation path 21 for the phase transition from liquid to vapor / gaseous and / or an overheating section 22 for further overheating of the steam or gas. The essential design of these subregions, in particular the evaporator section, takes into account the volume increase in the fluid flow when the microchannels flow through. Consequently, the liquid heating section and the superheat section, in which idealized no changes in the physical state of the fluid take place, each have a constant cross section with a large specific surface area for rapid heat transfer. The region in which a phase transition takes place with an increase in volume, preferably the evaporator section, is characterized by a continuous increase in cross section of the microchannels in the flow direction (see FIG. For the synchronization of the evaporation in all microchannels, it is also proposed to provide means for pressure equalization between the microchannels between the microchannels. These means comprise either a fluidic connection such as passages between the

Microchannels or a design of the evaporator section or a part thereof as one or more intermediate volumes 29. The intermediate volumes each bundle and connect a number of microchannels. In the case of a plurality of intermediate volumes, these can be connected in parallel to one another in each case for a bundle, wherein, in the context of a further embodiment, additional volumes cascaded and offset enable a fluidic connection of the bundles to one another. Preferably, a number of, with only one intermediate volume, all the microchannels from the liquid heating section open into the intermediate volumes and into the superheat section. Analogously to the heating section shown in FIG. 5, a cooling section, which is also to be used for a recondensation or a condensation, can in principle be made variable in its flow cross section as a function of the fluid composition in the flow direction. In this case, all the measures mentioned incl. The means mentioned for a pressure equalization in particular for the area around a condensation section in an analogous manner applicable. As in the flowchart of a procedure acc. 6, the cooling section 4 consists of three areas. The residence time line 3 first opens into the gas cooling section 26, which is designed for the cooling of the gas or the vapor to the condensation temperature (boiling temperature). Ideally, but not necessarily in the real state, no condensation takes place here. From the gas cooling section, the microchannels open into the condensation section 25, which is designed for a complete condensation, ie a transfer of gaseous or vaporous constituents into liquid constituents and is designed to be tapered in its flow cross section, preferably adapted to a volume reduction. In the Flüssigkeitsabkühlstrecke 24 downstream of the condensation section follows _from further cooling of the present as a liquid fluid on T.

A volume change in a phase transition and / or a change in cross section of the microchannels can be used as an alternative or additional measure also for a change in the flow rate in the microchannels 1 in the flow direction 9 and thus the locally to be effected heat transfer between cooling and heating.

Fig. 6 schematically shows a continuous chemical process in a heat exchanger (preferably countercurrent circuit) of the aforementioned type again, in the example, the continuous production of isocyanate 28 is shown as the starting liquid liquid carbonate 27 (RN-CO-CH ₃ ) as the input fluid. Carbonate is starting from Τ _θ _. _η heated from 10 to 50 ° C, preferably 15 to 25 ° C, more preferably 20 to 22 ° C in the heating section 2, evaporated and at 250 to 350 ° C, preferably 260 to 340 ° C, more preferably 270 to 330 ° C superheated initiated in the residence time zone 3, there reacts on a solid catalyst, for example MgO, to a gaseous mixture of isocyanate and methanol, which in the subsequent cooling section with release of heat the heating section is condensed and cooled to T _aus in the range between 15 and 60 ° C, preferably 20 to 55 ° C and more preferably 35 to 45 ° C. The residence time section serves as a reaction volume, depending on the desired temperature and reaction control as separate microchannels or as a common intermediate volume for microchannel bundles.

Bezugszeichexiliste

1 microchannel

2 heating section

3 residence time distance

4 cooling section

5 power supply means

6 foil

7 breakthrough

8 power input line

9 flow direction

10 feed area

11 thermal insulation cavity

12 subarea

13 inlet cooling channel

14 holes

15 heating cartridges

16 fluid guides

17 injection opening

18 gas channel

19 gas flow

20 membrane

21 evaporator section

22 overheating section

23 liquid heating section

24 liquid cooling section

25 condensation section

26 gas cooling section

27 carbonate

28 isocyanate

29 intermediate volume

Claims

claims

1. A heat exchanger for rapidly heating and cooling a fluid in at least one microchannel (1) with a heating section (2), a residence time section (3) and a cooling section (4), wherein the heating section and the cooling section are thermally connected to each other and the residence time path power supply means (5).

2. Heat exchanger according to claim 1, wherein the heating section comprises an evaporator section (21) and / or an overheating section (22).

and / or the cooling section comprise a condensation section (25).

3. Heat exchanger according to claim 1 or 2, wherein the microchannels of the heating section and / or the cooling section have at least one intermediate volume (29), in each of which all microchannels (1) of the heating and / or Abkühlstrecke lead and open.

4. Heat exchanger according to one of the preceding claims, wherein the heating section and the cooling section are formed by a countercurrent heat exchange element.

5. Heat exchanger according to one of the preceding claims, wherein the residence time section (3) comprises a reaction volume.

6. Heat exchanger according to one of the preceding claims, wherein the power supply means (5) are heating means.

7. A heat exchanger according to claim 6, wherein the heating means comprise fluid guides for at least one tempering fluid and / or a reaction space for carrying out an exothermic catalytic reaction.

8. Heat exchanger according to claim 7, wherein there is a fluidic connection between residence time distance and fluid guidance.

9. micro heat exchanger, comprising at least one heat exchanger according to one of the preceding claims, comprising a film stack with films (6) with grooved micro channels (1) and openings (7) as fluid guide connections.

A method for rapidly heating and cooling a fluid in at least one microchannel, wherein the fluid is heated in a first step in a heating section, fed in a subsequent second step of a residence time at a constant temperature and cooled in a third step in a cooling section,

characterized in that

the fluid in the third step gives off heat to the fluid in the first step and heat losses in the process are compensated by heating the residence time section.