EP0699289A1 - Water heater - Google Patents

Water heater

Info

Publication number
EP0699289A1
EP0699289A1 EP94918778A EP94918778A EP0699289A1 EP 0699289 A1 EP0699289 A1 EP 0699289A1 EP 94918778 A EP94918778 A EP 94918778A EP 94918778 A EP94918778 A EP 94918778A EP 0699289 A1 EP0699289 A1 EP 0699289A1
Authority
EP
European Patent Office
Prior art keywords
water heater
combustion
fuel
heater according
chamber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP94918778A
Other languages
German (de)
French (fr)
Other versions
EP0699289B1 (en
Inventor
Konstantin Ledjeff
Juergen Gieshoff
Alex Schuler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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Filing date
Publication date
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Publication of EP0699289A1 publication Critical patent/EP0699289A1/en
Application granted granted Critical
Publication of EP0699289B1 publication Critical patent/EP0699289B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C13/00—Apparatus in which combustion takes place in the presence of catalytic material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C13/00—Apparatus in which combustion takes place in the presence of catalytic material
    • F23C13/02—Apparatus in which combustion takes place in the presence of catalytic material characterised by arrangements for starting the operation, e.g. for heating the catalytic material to operating temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
    • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D11/00—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space
    • F23D11/005—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space with combinations of different spraying or vaporising means
    • F23D11/008—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space with combinations of different spraying or vaporising means combination of means covered by sub-groups F23D5/00 and F23D11/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
    • F24H1/0027—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters using fluid fuel
    • F24H1/0045—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters using fluid fuel with catalytic combustion

Definitions

  • the invention relates to a water heater according to the preamble of claim 1, as e.g. is known from DE-OS 3332572. Furthermore, the applicant's patent 4204320.4 also describes a water heater which has, in particular, a first advantageous combustion stage. For the rest, reference is made to this application for further understanding, in particular of the first combustion stage and to the detailed explanations of the second combustion stage. For better clarity, the reference numbers in this application correspond in part. those of patent 4204320.
  • the object of the invention is therefore according to the water heater. to develop the preamble of claim 1 so that liquid fuels can be used without substantial cracking. This object is achieved by the water heater according to claim 1.
  • the invention makes it possible to thermally couple the first stage of the two-stage catalytic burner to the evaporation chamber.
  • the evaporation chamber is designed as a combustion chamber, for which purpose it has an ignition device. If necessary, e.g. a bypass of the feed for the liquid fuel.
  • the water heater has a supply of primary air to the combustion chamber for this purpose.
  • the fuel is supplied in isolation so that the fuel reaches the evaporation space without cracking.
  • the evaporation chamber can be rotationally symmetrical and to let it rotate, since the fuel is then pressed against the wall and comes into better contact with the wall there, which is on the back of the first combustion stage as a result of the Reaction reaction of the fuel gas-air mixture on the catalyst layer is heated.
  • the subject of the application is a two-stage catalytic burner for liquid fuels and their mixtures with internal evaporation or gasification.
  • the fuel In the interior of the burner, the fuel is vaporized or gasified, possibly with the supply of air (primary air).
  • the energy required for this is provided by the heat of combustion.
  • the fuel gas / air mixture (with added secondary air, which can be the sole air supply after the starting phase) flows over a catalytic surface and reacts there to about 80-85%.
  • the reaction temperatures are around 800 - 900 ° C. Radiation, heat conduction and convection give off heat to the cooling medium and to the evaporation zone.
  • the second stage the remaining fuel is converted in a monolith catalyst.
  • the narrow channels ensure good mass transport and thus a high power density. Temperatures of approximately 1000 ° C. are thus reached, which enable complete conversion. Part of the heat for preheating the primary air can be extracted from the monolith, which e.g. is advantageous for intermittent operation.
  • the catalytic burner (Fig. 1) consists of two stages 16, 20.
  • the first stage consists of a metal tube 31 or ceramic tube coated on the outside with catalyst 13. This catalyst tube is surrounded by a ceramic or metal tube and a cooling jacket, so that a gas gap arises between the catalyst tube and the ceramic tube 11.
  • the mixture of vaporized, gaseous fuel and air flows in this gas gap and reacts on the catalyzed surface of the tube 31.
  • the second stage which is arranged above the first, consists of a ceramic honeycomb structure (monolith), which is coated with catalyst.
  • the exhaust gas from the first stage with the remaining fuel flows through this monolith and reacts completely.
  • the feed line for the primary air and the liquid fuel mixture is arranged centrally in the monolith.
  • Two concentrically arranged pipes 8 and 41 which are passed through the monolith from above, form the feed line for the liquid fuel and the primary air.
  • the primary air which is preheated by the adjacent monolith, flows in the outer tube 41.
  • the liquid fuel flows in the inner tube. This is preheated only slightly, since the gas gap between this tube and the monolith has an insulating effect, so that no evaporation or cracking can occur in the feed tube.
  • These concentric tubes end at the top of the first burner stage.
  • the liquid fuel is finely atomized by means of a nozzle 42 and introduced into the interior of the catalyst tube of the first burner stage, which thus forms the evaporation chamber 40 or combustion chamber.
  • the concentrically supplied primary air which has been preheated by the monolith, also flows into the interior of the catalyst tube through bores made in a ring around the fuel feed line.
  • a high proportion of primary air ensures that the liquid fuel can be evaporated far below its boiling temperature.
  • the addition of primary air can be switched off after the start phase.
  • a fine evaporation surface is achieved through the fine atomization of the fuel and good mass transfer numbers are achieved through the flow of the primary air.
  • the evaporation energy is provided by the heat of the preheated air and by the supply of heat (heat conduction, convection and radiation) from the catalytic tube.
  • the fuel gas / air mixture flows downwards in the interior of the evaporation chamber or burner chamber.
  • a cone 45 built up on the bottom of the burner guides the gas at the lower end of the catalyst tube into the annular gap between the ceramic tube and the catalyst tube.
  • the secondary air is added, which flows directly into the ring gas gap from below.
  • the cone has two main functions. Its task is to allow the fuel gas / air mixture to flow evenly into the annular gap. Without this cone, dead space areas could easily form on the bottom of the burner, from which crack products, for example, could collect. Another important point is that the cone is emitted by the radiation from the evaporation space (rear of the catalyst room) is heated. This can prevent parts of the fuel from condensing out again at the bottom of the burner or when deflected into the gas gap.
  • the fuel gas / air mixture with the added secondary air flows upwards in the annular gap between the ceramic and catalyst tubes. Some of the fuel reacts on the catalytic surface. The energy released is distributed as follows:
  • the catalyst tube is heated or kept at the reaction temperature
  • the catalyst tube has a temperature of approx. 700 - 900 ° C. In this first stage, approximately 80% of the fuel is converted.
  • the gas mixture flows upwards from the annular gap of the first stage into the expanded space below the honeycomb coated with catalyst (e.g. Pt).
  • catalyst e.g. Pt
  • the cross-sectional expansion leads to a slowdown in the flow velocity and to thorough thorough mixing again before the second burner stage.
  • the gas now flows through the narrow channels of the catalyst honeycomb, the remaining fuel being completely converted.
  • the good sales in this second stage are due to the following conditions:
  • the honeycomb reaches temperatures of approx. 900-1000 ° C; the reaction rate is so high at this temperature that the fuel can be completely converted with the relatively long residence time (low flow rate).
  • the primary air the supply of which is located in the center of the honeycomb, can be a little be preheated.
  • the preheating temperature of the primary air must not be too high anyway, since otherwise crack reactions could occur when encountering the atomized fuel.
  • the exhaust air from the second combustion stage is then used in a (not shown) heat exchanger to further heat the water or fluid 2 heated in the first combustion stage.
  • the entire burner is started by igniting a flame in the evaporation chamber.
  • the primary air flow is so large that complete combustion is guaranteed.
  • the flame heats the inside of the catalytic converter tube through radiation, heat conduction and convection.
  • the hot exhaust gases flow downwards, are led through the cone at the bottom into the gas gap and flow through this upwards and through the honeycomb.
  • the hot exhaust gas gives off the heat and thus heats the burner with the honeycomb. If the burner has reached a temperature level at which the catalytic reaction can proceed with a correspondingly high reaction rate (approx. 600 ° C), the flame is switched off. This can be done by briefly switching off the primary air and / or the fuel supply.
  • Crack products formed, which are deposited on the hot inside of the catalyst tube, can be eliminated by igniting a flame in the interior of the catalyst tube at certain time intervals. This flame is operated with excess air so that the cracked products can be burned out on the surfaces.
  • openings 44 are made from the gas space between the first and second stage to the interior of the catalyst tube (evaporation space). These openings, which can be designed as nozzles, cause part of the exhaust gas from the first burner stage to recirculate through the evaporation chamber.
  • the hot exhaust gas brings additional heat required for the evaporation into the evaporator space 3.
  • the water vapor from the combustion present in the recirculated exhaust gas causes parts of the fuel to be reformed to carbon monoxide or carbon dioxide and hydrogen, and any cracking reactions that may occur can thus be minimized
  • the primary air can be dispensed with.
  • FIG. 3 shows a burner in which a highly porous structure 43 is attached to the inside of the catalyst tube.
  • This structure means that some of the injected fuel droplets, especially the larger ones, are deposited on the porous body and thus do not come into contact with the hot wall of the catalyst tube. Because the temperatures are kept low there can be no cracking.
  • the porous structure can consist of ceramic or metal and can be configured as a cuboid, cylinder or also as a tube. The structure can also be coated with catalyst material to accelerate the evaporation reaction.
  • the first stage of the two-stage catalytic burner is thermally coupled to the evaporation chamber.
  • the evaporation chamber also serves as a combustion chamber for the preheating.
  • the thermal coupling between the first catalyst stage and the evaporation space enables a heat flow from this space, which is then the combustion space, to the first catalyst stage and, in the case of catalytic burner operation, a heat flow from the first catalyst stage to the evaporation space, in order to achieve the required level Provide enthalpy of vaporization.
  • the basic structure of the burner according to the invention is not limited to the sketched tube geometry, but can also be transferred to rectangular channels or plate-shaped arrangements.
  • the water heater can advantageously also be used for heating warm air or another fluid to be heated.

Abstract

The invention relates to a water heater with an inlet (8) for liquid fuels, several outlets (41, 46) for fresh air, an inlet for a fluid (2) to be heated, at least two combustion stages (16, 20) through which the fuel-air mixture flows, with catalytic combustion chambers which are at least partly surrounded by at least one fluid chamber (4) filled with the fluid (2) and with an exhaust gas heat exchanger for the fluid (2) to be heated, through which the exhaust gas from the combustion chambers flows. The first combustion stage (16) has an evaporation chamber (40) having at least partially the catalyst coating (13) on the outside of its edge (31).

Description

WarmwasserbereiterWater heater
Die Erfindung betrifft einen Warmwasserbereiter gemäß dem Oberbegriff des Anspruchs 1 , wie er z.B. aus der DE-OS 3332572 bekannt ist. Weiterhin wird in dem Patent 4204320.4 der Anmelderin ebenfalls ein Warmwasserbereiter beschrieben, der insbesondere eine erste vorteilhafte Verbrennungsstufe aufweist. Im übrigen wird auf diese Anmeldung Bezug ge¬ nommen zum weiteren Verständnis insbesondere der ersten Verbrennungsstufe sowie auf die ausführlichen Darlegungen zur zweiten Verbrennungsstufe. Zur besseren Übersichtlich¬ keit entsprechen die Bezugszeichen dieser Anmeldung z.T. denen des Patentes 4204320.The invention relates to a water heater according to the preamble of claim 1, as e.g. is known from DE-OS 3332572. Furthermore, the applicant's patent 4204320.4 also describes a water heater which has, in particular, a first advantageous combustion stage. For the rest, reference is made to this application for further understanding, in particular of the first combustion stage and to the detailed explanations of the second combustion stage. For better clarity, the reference numbers in this application correspond in part. those of patent 4204320.
1. Einleitung1 Introduction
Bei der Verbrennung von fossilen Energieträgern entstehen außer dem Treibhausgas Koh¬ lendioxid noch weitere Schadstoffe wie Schwefeldioxid und Stickoxide. Bei herkömmlichen Flammenbrennern sind die Reduzierungsmöglichkeiten, hauptsächlich der Stickoxide, durch die Flammenstabilität und die Bildung von Kohlenmonoxid eingeschränkt. Eine deutliche Reduzierung der Stickoxidemissionen ist bei der flammenlosen Verbrennung an Oxidationskatalysatoren (z.B. Pt) durch die niedrige Reaktionstemperatur zu erreichen. Katalytische Brenner bieten weiterhin den Vorteil, daß Mischungen aus Brennstoffen mit unterschiedlicher Energiedichte in einem weiten Bereich des Mischungsverhältnisses stabil umgesetzt werden können. 2. Stand der TechnikWhen fossil fuels are burned, other pollutants such as sulfur dioxide and nitrogen oxides are formed in addition to the greenhouse gas carbon dioxide. In conventional flame burners, the reduction options, mainly nitrogen oxides, are limited by the flame stability and the formation of carbon monoxide. A significant reduction in nitrogen oxide emissions can be achieved with flameless combustion on oxidation catalysts (eg Pt) due to the low reaction temperature. Catalytic burners also offer the advantage that mixtures of fuels with different energy densities can be stably implemented in a wide range of the mixing ratio. 2. State of the art
Brenner für Benzin, Diesel oder z.B. Methanol sind heute nur als herkömmliche Flammen¬ brenner erhältlich. Aufgrund der hohen Reaktionstemperatur (Flammentemperatur) haben solche Brenner hohe Stickoxidemissionen. Es gibt Möglichkeiten auch bei solchen Brennern die Emissionen zu reduzieren, z.B. Flammenkühlung oder Änderung der Luftzahl, dies führt jedoch dazu, daß die Flammenstabilität abnimmt und die Kohlenmonoxidemissionen zu¬ nehmen.Burners for gasoline, diesel or e.g. Today, methanol is only available as a conventional flame burner. Because of the high reaction temperature (flame temperature), such burners have high nitrogen oxide emissions. There are ways to reduce emissions even with such burners, e.g. Flame cooling or change in the air ratio, but this leads to a decrease in flame stability and an increase in carbon monoxide emissions.
Dieser Stand der Technik hat den Nachteil, daß er nicht besonders für flüssige Treibstoffe geeignet ist. Aufgabe der Erfindung ist es daher, den Warmwasserbereiter gem. dem Ober¬ begriff des Anspruchs 1 so weiterzubilden, daß flüssige Brennstoffe ohne wesentliches Cracken verwendet werden können. Diese Aufgabe wird durch den Warmwasserbereiter nach Anspruch 1 gelöst. Durch die Erfindung ist es möglich, die erste Stufe des zweistufigen katalytischen Brenners thermisch an den Verdampfungsraum anzukoppeln.This prior art has the disadvantage that it is not particularly suitable for liquid fuels. The object of the invention is therefore according to the water heater. to develop the preamble of claim 1 so that liquid fuels can be used without substantial cracking. This object is achieved by the water heater according to claim 1. The invention makes it possible to thermally couple the first stage of the two-stage catalytic burner to the evaporation chamber.
Eine vorteilhafte Weiterbildung für den katalytischen Spaltbrenner ist in Anspruch 2 be¬ schrieben.An advantageous further development for the catalytic cracking burner is described in claim 2.
Gemäß Anspruch 3 ist der Verdampfungsraum als Brennkammer ausgebildet, wozu sie eine Zündeinrichtung aufweist. Als Zündflamme kann ggf. z.B. ein Bypass der Zuführung für den flüssigen Brennstoff dienen. Außerdem weist der Warmwasserbereiter zu diesem Zweck eine Zufuhr von Primärluft zum Verbrennungsraum auf.According to claim 3, the evaporation chamber is designed as a combustion chamber, for which purpose it has an ignition device. If necessary, e.g. a bypass of the feed for the liquid fuel. In addition, the water heater has a supply of primary air to the combustion chamber for this purpose.
Gemäß Anspruch 4 wird der Brennstoff isoliert zugeführt, damit der Brennstoff ohne zu cracken in den Verdampfungsraum gelangt.According to claim 4, the fuel is supplied in isolation so that the fuel reaches the evaporation space without cracking.
Weiterhin ist es vorteilhaft, zur Zerstäubung des Brennstoffs eine Düse oder andere Einrich¬ tungen vorzusehen (Anspruch 5).Furthermore, it is advantageous to provide a nozzle or other devices for atomizing the fuel (claim 5).
Es kann vorteilhaft sein, einen Teil des Abgases aus der ersten Stufe in den Verdampfungs¬ raum zurückzuführen, da dann der flüssige Brennstoff leichter verdampft wird und das beim Verbrennungsvorgang entstehende Wasser bzw. Wasserdampf ebenfalls mögliche Crackreaktionen minimiert. Gemäß Anspruch 8 kann es vorteilhaft sein, Einrichtungen zur Lenkung des Gasstromes im Verdampfungsraum vorzusehen, insbesondere können diese Einrichtungen thermisch iso¬ liert sein, wenn sie nicht von der ersten Verbrennungsstufe beheizt sind.It can be advantageous to return part of the exhaust gas from the first stage to the evaporation chamber, since the liquid fuel is then more easily evaporated and the water or water vapor produced during the combustion process also minimizes possible cracking reactions. According to claim 8, it can be advantageous to provide devices for directing the gas flow in the evaporation space, in particular these devices can be thermally insulated if they are not heated by the first combustion stage.
Weiterhin kann es von Vorteil sein, den Verdampfungsraum rotationssymmetrisch auszubil¬ den und ihn rotieren zu lassen, da dann der Brennstoff an die Wand gedrückt wird und dort im besseren Kontakt mit der Wand kommt, die auf der Rückseite von der ersten Verbren¬ nungsstufe infolge der Umsetzungsreaktion des Brenngas-Luftgemisches an der Katalysa¬ torschicht beheizt wird.Furthermore, it can be advantageous to design the evaporation chamber to be rotationally symmetrical and to let it rotate, since the fuel is then pressed against the wall and comes into better contact with the wall there, which is on the back of the first combustion stage as a result of the Reaction reaction of the fuel gas-air mixture on the catalyst layer is heated.
3. Beschreibung von Ausführungsbeispielen3. Description of exemplary embodiments
Gegenstand der Anmeldung ist ein zweistufiger kataiytischer Brenner für flüssige Brennstoffe und deren Gemische mit interner Verdampfung bzw. Vergasung. Im Innenraum des Bren¬ ners wird der Brennstoff, eventuell unter Luftzufuhr (Primärluft), verdampft bzw. vergast. Die dafür notwendige Energie wird durch die Verbrennungswärme bereitgestellt. Das Brenn¬ gas/Luft-Gemisch (mit zugegebener Sekundärluft, die nach der Startphase die alleinige Luftzufuhr sein kann) überströmt eine katalytische Fläche und reagiert dort zu ca.80 - 85 % ab. Die Reaktionstemperaturen liegen bei ca.800 - 900°C. Über Strahlung, Wärmeleitung und Konvektion wird Wärme an das Kühlmedium und an die Verdampfungszone abgege¬ ben. In der zweiten Stufe wird in einem Monolith-Katalysator der restliche Brennstoff umge¬ setzt. Durch die engen Kanäle wird ein guter Stofftransport und somit eine hohe Leistungs¬ dichte erreicht. Damit werden Temperaturen von ca. 1000°C erreicht, welche einen vollstän¬ digen Umsatz ermöglichen. Aus dem Monolith kann ein Teil der Wärme zur Vorheizung der Primärluft abgezogen werden, was z.B. bei intermittierendem Betrieb von Vorteil ist.The subject of the application is a two-stage catalytic burner for liquid fuels and their mixtures with internal evaporation or gasification. In the interior of the burner, the fuel is vaporized or gasified, possibly with the supply of air (primary air). The energy required for this is provided by the heat of combustion. The fuel gas / air mixture (with added secondary air, which can be the sole air supply after the starting phase) flows over a catalytic surface and reacts there to about 80-85%. The reaction temperatures are around 800 - 900 ° C. Radiation, heat conduction and convection give off heat to the cooling medium and to the evaporation zone. In the second stage, the remaining fuel is converted in a monolith catalyst. The narrow channels ensure good mass transport and thus a high power density. Temperatures of approximately 1000 ° C. are thus reached, which enable complete conversion. Part of the heat for preheating the primary air can be extracted from the monolith, which e.g. is advantageous for intermittent operation.
Beschreibung:Description:
Der katalytische Brenner (Bild 1) besteht aus zwei Stufen 16,20. Die erste Stufe besteht aus einem an der Außenseite mit Katalysator 13 beschichteten Metallrohr 31 oder auch Keramik¬ rohr. Dieses Katalysatorrohr wird von einem Keramik- oder Metallrohr und einem Kühlmantel umgeben, so daß zwischen dem Katalysatorrohr und dem Keramikrohr 11 ein Gasspalt ent¬ steht. In diesem Gasspalt strömt das Gemisch aus verdampftem, gasförmigem Brennstoff und Luft und reagiert an der katalysierten Oberfläche des Rohrs 31. Die zweite Stufe, die oberhalb der ersten angeordnet ist, besteht aus einer keramischen Wabenstruktur (Monolith), die mit Katalysator beschichtet wird. Das Abgas aus der ersten Stufe mit dem verbliebenen Restbrennstoff strömt durch diesen Monolith und reagiert dabei vollständig ab. Zentrisch in dem Monolith ist die Zuleitung der Primärluft und des flüssigen Brennstoffge- mischs angeordnet.The catalytic burner (Fig. 1) consists of two stages 16, 20. The first stage consists of a metal tube 31 or ceramic tube coated on the outside with catalyst 13. This catalyst tube is surrounded by a ceramic or metal tube and a cooling jacket, so that a gas gap arises between the catalyst tube and the ceramic tube 11. The mixture of vaporized, gaseous fuel and air flows in this gas gap and reacts on the catalyzed surface of the tube 31. The second stage, which is arranged above the first, consists of a ceramic honeycomb structure (monolith), which is coated with catalyst. The exhaust gas from the first stage with the remaining fuel flows through this monolith and reacts completely. The feed line for the primary air and the liquid fuel mixture is arranged centrally in the monolith.
Zwei konzentrisch angeordnete Rohre 8 und 41 , die von oben durch den Monolithen durch¬ geführt sind, bilden die Zuleitung des flüssigen Brennstoffs und der Primärluft. Im äußeren Rohr 41 strömt die Primärluft, die durch den angrenzenden Monolithen vorgewärmt wird. Im inneren Rohr fließt der flüssige Brennstoff. Dieses wird nur leicht vorgewärmt, da der Gas¬ spalt zwischen diesem Rohr und dem Monolith isolierend wirkt, so daß im Zuleitungsrohr kein Verdampfen oder Cracken eintreten kann. Diese konzentrischen Rohre enden in Höhe der Oberkante der ersten Brennerstufe. Der flüssige Brennstoff wird mittels einer Düse 42 fein zerstäubt in das Innere des Katalyserohrs der ersten Brennerstufe eingebracht, die so den Verdampfungsraum 40 bzw. Brennkammer bildet. Die konzentrisch zugeführte Primär¬ luft, die durch den Monolithen vorgewärmt wurde, strömt durch ringförmig um die Brenn¬ stoffzuleitung angebrachte Bohrungen ebenfalls in das Innere des Katalyserohrs. Durch einen hohen Anteil an Primärluft wird erreicht, daß der flüssige Brennstoff weit unterhalb sei¬ ner Siedetemperatur verdampft werden kann. Die Zugabe von Primärluft kann im günstigen Fall nach der Startphase abgeschaltet werden. Weiterhin wird durch die feine Zerstäubung des Brennstoffs eine große Verdunstungsoberfläche und durch die Strömung der Primärluft gute Stoffaustauschzahlen erreicht. Die Verdunstungsenergie wird durch die Wärme der vorgeheizten Luft und durch die Wärmezufuhr (Wärmeieitung, Konvektion und Strahlung) von dem Katalyserohr bereitgestellt.Two concentrically arranged pipes 8 and 41, which are passed through the monolith from above, form the feed line for the liquid fuel and the primary air. The primary air, which is preheated by the adjacent monolith, flows in the outer tube 41. The liquid fuel flows in the inner tube. This is preheated only slightly, since the gas gap between this tube and the monolith has an insulating effect, so that no evaporation or cracking can occur in the feed tube. These concentric tubes end at the top of the first burner stage. The liquid fuel is finely atomized by means of a nozzle 42 and introduced into the interior of the catalyst tube of the first burner stage, which thus forms the evaporation chamber 40 or combustion chamber. The concentrically supplied primary air, which has been preheated by the monolith, also flows into the interior of the catalyst tube through bores made in a ring around the fuel feed line. A high proportion of primary air ensures that the liquid fuel can be evaporated far below its boiling temperature. In the favorable case, the addition of primary air can be switched off after the start phase. Furthermore, a fine evaporation surface is achieved through the fine atomization of the fuel and good mass transfer numbers are achieved through the flow of the primary air. The evaporation energy is provided by the heat of the preheated air and by the supply of heat (heat conduction, convection and radiation) from the catalytic tube.
Das Brenngas/Luft-Gemisch strömt im inneren des Verdampfungsraumes bzw. Brenner¬ raumes nach unten. Ein auf dem Boden des Brenners aufgebauter Kegel 45 leitet das Gas am unteren Ende des Katalysatorrohrs in den Ringspalt zwischen Keramik- und Katalysator¬ rohr. An dieser Stelle wird die Sekundärluft zugegeben, die direkt von unten in den Ringgas¬ spalt einströmt. Der Kegel hat im wesentlichen zwei Funktionen. Er hat die Aufgabe, das Brenngas /Luft-Gemisch gleichmäßig in den Ringspalt einströmen zu lassen. Ohne diesen Kegel könnten sich leicht Totraumgebiete am Boden des Brenners bilden, an denen sich z.B. evtl. anfallende Crack-Produkte sammeln könnten. Ein weiterer wesentlicher Punkt ist, daß der Kegel durch die Abstrahlung des Verdampfungsraumes (Rückseite des Katalysator raumes) erwärmt wird. Dadurch kann verhindert werden, daß am Boden des Brenners oder bei der Umlenkung in den Gasspalt Teile des Brennstoffs wieder auskondensieren können.The fuel gas / air mixture flows downwards in the interior of the evaporation chamber or burner chamber. A cone 45 built up on the bottom of the burner guides the gas at the lower end of the catalyst tube into the annular gap between the ceramic tube and the catalyst tube. At this point, the secondary air is added, which flows directly into the ring gas gap from below. The cone has two main functions. Its task is to allow the fuel gas / air mixture to flow evenly into the annular gap. Without this cone, dead space areas could easily form on the bottom of the burner, from which crack products, for example, could collect. Another important point is that the cone is emitted by the radiation from the evaporation space (rear of the catalyst room) is heated. This can prevent parts of the fuel from condensing out again at the bottom of the burner or when deflected into the gas gap.
Das Brenngas/Luft-Gemisch mit der zugegebenen Sekundärluft strömt im Ringspalt zwi¬ schen Keramik- und Katalysatorrohr nach oben. Dabei reagiert ein Teil des Brennstoffs an der katalytischen Oberfläche ab. Die dabei frei werdende Energie verteilt sich wie folgt:The fuel gas / air mixture with the added secondary air flows upwards in the annular gap between the ceramic and catalyst tubes. Some of the fuel reacts on the catalytic surface. The energy released is distributed as follows:
1. das Katalysatorrohr wird aufgeheizt bzw. auf der Reaktionstemperatur gehalten1. the catalyst tube is heated or kept at the reaction temperature
2. das Reaktionsgas wird aufgeheizt2. the reaction gas is heated
3. es wird Wärme an das Innere des Kataiysatorrohrs abgegeben; diese wird zur Verdampfung des flüssigen Brennstoffgemisches benötigt; die Wärme wird durch Konvektion, Wärmeleitung und Strahlung übertragen3. heat is given off to the inside of the catalyst tube; this is required for the vaporization of the liquid fuel mixture; the heat is transferred by convection, heat conduction and radiation
4. vom Katalysatorrohr wird ebenfalls durch Konvektion, Wärmeleitung und Strah¬ lung Wärme an das Keramikrohr abgegeben; von dort wird die Wärme durch Wärmeleitung weiter nach außen an den mit Kühlmedium (Wasser, Luft) durch- flossenen Doppelmantel abgegeben.4. Heat is also given off from the catalyst tube to the ceramic tube by convection, heat conduction and radiation; From there, the heat is dissipated to the outside through the double jacket through which cooling medium (water, air) flows.
Das Katalysatorrohr hat eine Temperatur von ca.700-900°C. In dieser ersten Stufe werden ca.80% des Brennstoffs umgesetzt.The catalyst tube has a temperature of approx. 700 - 900 ° C. In this first stage, approximately 80% of the fuel is converted.
Aus dem Ringspalt der ersten Stufe strömt das Gasgemisch nach oben in den erweiterten Raum unterhalb der mit Katalysator (z.B. Pt) beschichteten Wabe. Die Querschnittserweite¬ rung führt zu einer Verlangsamung der Strömungsgeschwindigkeit und zu einer nochmali¬ gen gründlichen Durchmischung vor der zweiten Brennerstufe. Das Gas strömt nun durch die engen Kanäle der Katalysatorwabe, wobei der verbliebene Brennstoff vollständig umge¬ setzt wird. Der gute Umsatz in dieser zweiten Stufe kommt durch folgende Gegebenheiten zustande:The gas mixture flows upwards from the annular gap of the first stage into the expanded space below the honeycomb coated with catalyst (e.g. Pt). The cross-sectional expansion leads to a slowdown in the flow velocity and to thorough thorough mixing again before the second burner stage. The gas now flows through the narrow channels of the catalyst honeycomb, the remaining fuel being completely converted. The good sales in this second stage are due to the following conditions:
1. der Stofftransport zum Katalysator ist aufgrund der engen Kanäle sehr gut1. The mass transfer to the catalyst is very good due to the narrow channels
2. durch die geringen Wärmeverluste aus der Wabe und die Wärmeproduktion auf¬ grund der Reaktion erreicht die Wabe Temperaturen von ca.900-1000°C; die Reaktionsgeschwindigkeit ist bei dieser Temperatur so hoch, daß bei der relativ großen Verweilzeit (niedrige Strömungsgeschwindigkeit) der Brennstoff vollstän¬ dig umgesetzt werden kann. Obwohl durch die schlechte Wärmeleitfähigkeit des keramischen Monolithen nur sehr wenig Wärme abgeführt wird, kann damit doch die Primärluft, deren Zufuhr im Zentrum der Wabe angebracht ist, ein we nig vorgeheizt werden. All zu hoch darf die Vorheiztemperatur der Primärluft oh¬ nedies nicht sein, da sonst beim Zusammentreffen mit dem verdüsten Brennstoff Crackreaktionen auftreten könnten.2. due to the low heat losses from the honeycomb and the heat production due to the reaction, the honeycomb reaches temperatures of approx. 900-1000 ° C; the reaction rate is so high at this temperature that the fuel can be completely converted with the relatively long residence time (low flow rate). Although very little heat is dissipated due to the poor thermal conductivity of the ceramic monolith, the primary air, the supply of which is located in the center of the honeycomb, can be a little be preheated. The preheating temperature of the primary air must not be too high anyway, since otherwise crack reactions could occur when encountering the atomized fuel.
Die Abluft aus der zweiten Verbrennungsstufe wird dann in einem (nicht darge¬ stellten) Wärmetauscher benutzt, das in der ersten Verbrennungsstufe erwärmte Wasser bzw. Fluid 2 weiter zu erwärmen.The exhaust air from the second combustion stage is then used in a (not shown) heat exchanger to further heat the water or fluid 2 heated in the first combustion stage.
Der Start des gesamten Brenners erfolgt dadurch, daß im Verdampfungsraum eine Flamme entzündet wird. Der Primärluftstrom ist dabei so groß, daß eine vollständige Verbrennung gewährleistet ist. Die Flamme erhitzt durch Strahlung, Wärmeleitung und Konvektion das Katalysatorrohr von Innen. Die heißen Abgase strömen nach unten, werden durch den Kegel am Boden in den Gasspalt geleitet und strömen durch diesen nach oben und durch die Wabe. Dabei gibt das heiße Abgas die Wärme ab und heizt somit den Brenner mit der Wabe auf. Hat der Brenner ein Temperaturniveau erreicht, bei dem die katalytische Reaktion mit entsprechend großer Reaktionsgeschwindigkeit ablaufen kann (ca.600° C), dann wird die Flamme abgeschaltet. Dies kann erfolgen durch ein kurzfristiges Abschalten der Primärluft und/oder der Brennstoffzufuhr.The entire burner is started by igniting a flame in the evaporation chamber. The primary air flow is so large that complete combustion is guaranteed. The flame heats the inside of the catalytic converter tube through radiation, heat conduction and convection. The hot exhaust gases flow downwards, are led through the cone at the bottom into the gas gap and flow through this upwards and through the honeycomb. The hot exhaust gas gives off the heat and thus heats the burner with the honeycomb. If the burner has reached a temperature level at which the catalytic reaction can proceed with a correspondingly high reaction rate (approx. 600 ° C), the flame is switched off. This can be done by briefly switching off the primary air and / or the fuel supply.
Evtl. entstandene Crackprodukte, die sich an der heißen Innenseite des Katalysatorrohrs ab¬ scheiden, können dadurch beseitigt werden, daß in gewissen Zeitabständen im Innenraum des Katalysatorrohrs eine Flamme gezündet wird. Diese Flamme wird mit Luftüberschuß be¬ trieben, so daß die Crackprodukte an den Oberflächen ausgebrannt werden können.Possibly. Crack products formed, which are deposited on the hot inside of the catalyst tube, can be eliminated by igniting a flame in the interior of the catalyst tube at certain time intervals. This flame is operated with excess air so that the cracked products can be burned out on the surfaces.
In Bild 2 ist der gleiche Brenner nochmal dargestellt, jedoch sind hier Öffnungen 44 vom Gasraum zwischen erster und zweiter Stufe zum Inneren des Katalysatorrohrs (Verdampfungsraum) angebracht. Diese Öffnungen, die als Düsen ausgestaltet sein können, bewirken, daß ein Teil des Abgases aus der ersten Brennerstufe durch den Verdampfungs¬ raum rezirkuiieren kann. Dies bringt folgende Vorteile:The same burner is shown again in FIG. 2, but here openings 44 are made from the gas space between the first and second stage to the interior of the catalyst tube (evaporation space). These openings, which can be designed as nozzles, cause part of the exhaust gas from the first burner stage to recirculate through the evaporation chamber. This has the following advantages:
1. durch seitliche Zuströmung bzw. Ansaugung des Abgases aus der ersten Stufe erfolgt eine gute Durchmischung und weitere Verdünnung des Brennstoff/Luft- Gemisches im Inneren des Katalysatorrohrs; dies führt zu einer schnelleren Ver¬ dampfung1. by lateral inflow or suction of the exhaust gas from the first stage, thorough mixing and further dilution of the fuel / air mixture takes place inside the catalyst tube; this leads to faster evaporation
2. das heiße Abgas bringt zusätzliche, für die Verdampfung benötigte Wärme in den Verdampferraum 3. der im rezirkulierten Abgas vorhandene Wasserdampf aus der Verbrennung be¬ wirkt, daß Teile des Brennstoffes zu Kohlenmonoxid bzw. Kohlendioxid und Wasserstoff reformiert werden, und somit evtl. auftretende Crackreaktionen minimiert werden können2. The hot exhaust gas brings additional heat required for the evaporation into the evaporator space 3. The water vapor from the combustion present in the recirculated exhaust gas causes parts of the fuel to be reformed to carbon monoxide or carbon dioxide and hydrogen, and any cracking reactions that may occur can thus be minimized
4. bei ausreichender Rezirkulation des Abgases kann auf die Primärluft verzichtet werden.4. With sufficient recirculation of the exhaust gas, the primary air can be dispensed with.
In Bild 3 ist ein Brenner dargestellt, bei dem im Inneren des Katalysatorrohrs eine hochpo¬ röse Struktur 43 angebracht ist. Diese Struktur bewirkt, daß ein Teil der eingedüsten Brenn¬ stoff-Tropfen, besonders die größeren, auf dem porösen Körper abgeschieden werden und somit nicht mit der heißen Wand des Katalysatorrohrs in Berührung kommen. Dadurch, daß die Temperaturen dort niedrig gehalten werden, kann kein Cracken auftreten. Die poröse Struktur kann aus Keramik oder Metall bestehen und als Quader, Zylinder oder auch als Rohr ausgestaltet sein. Die Struktur kann auch mit Katalysatormaterial beschichtet sein, um die Verdampfungsreaktion zu beschleunigen.Figure 3 shows a burner in which a highly porous structure 43 is attached to the inside of the catalyst tube. This structure means that some of the injected fuel droplets, especially the larger ones, are deposited on the porous body and thus do not come into contact with the hot wall of the catalyst tube. Because the temperatures are kept low there can be no cracking. The porous structure can consist of ceramic or metal and can be configured as a cuboid, cylinder or also as a tube. The structure can also be coated with catalyst material to accelerate the evaporation reaction.
Erfindungsgemäß wird die erste Stufe des zweistufigen katalytischen Brenners thermisch an den Verdampfungsraum angekoppelt. Der Verdampfungsraum dient gleichzeitig als Brenn¬ kammer für die Vorheizung. Die thermische Kopplung zwischen der ersten Katalysatorstufe und Verdampfungsraum ermöglicht während der Startphase einen Wärmestrom aus diesem Raum, der dann Brennraum ist, zu der ersten Katalysatorstufe und bei katalytischem Bren¬ nerbetrieb umgekehrt einen Wärmestrom von der ersten Katalysatorstufe zum Verdamp¬ fungsraum, um dort die erforderliche Verdampfungsenthalpie bereitzustellen.According to the invention, the first stage of the two-stage catalytic burner is thermally coupled to the evaporation chamber. The evaporation chamber also serves as a combustion chamber for the preheating. The thermal coupling between the first catalyst stage and the evaporation space enables a heat flow from this space, which is then the combustion space, to the first catalyst stage and, in the case of catalytic burner operation, a heat flow from the first catalyst stage to the evaporation space, in order to achieve the required level Provide enthalpy of vaporization.
Der prinzipielle Aufbau des erfindungsgemäßen Brenners ist nicht auf die skizzierte Rohr¬ geometrie beschränkt, sondern auch auf rechteckige Kanäle oder plattenförmigen Anord¬ nungen übertragbar.The basic structure of the burner according to the invention is not limited to the sketched tube geometry, but can also be transferred to rectangular channels or plate-shaped arrangements.
Der Warmwasserbereiter kann vorteilhafterweise auch zur Erwärmung von Warmluft oder ei¬ nes anderen zu erheizenden Fluids verwendet werden. The water heater can advantageously also be used for heating warm air or another fluid to be heated.

Claims

Patentansprüche Claims
1. Warmwasserbereiter mit einem Einlaß (8) für flüssige Brennstoffe, mehreren Einlas¬ sen (41, 46) für Frischluft, einem Einlaß für ein aufzuheizendes Fluid (2), mindestens zwei von dem Brennstoff-Luft-Gemisch durchströmten Verbrennungsstufen (16, 20) mit katalytischen Brennkammern, die zumindest teilweise von mindestens einer mit dem Fluid (2) gefüllten Fluidkammer (4) umgeben sind und mit einem Abgaswärme¬ tauscher für das zu erwärmende Fluid (2), der von dem aus den Brennkammern ent¬ weichenden Abgas durchströmt ist,1. Water heater with an inlet (8) for liquid fuels, several inlets (41, 46) for fresh air, an inlet for a fluid to be heated (2), at least two combustion stages (16, 20 ) with catalytic combustion chambers, which are at least partially surrounded by at least one fluid chamber (4) filled with the fluid (2) and with an exhaust gas heat exchanger for the fluid (2) to be heated, through which the exhaust gas escaping from the combustion chambers flows is
d a durch gekennzeichnet,characterized,
daß die erste Verbrennungsstufe (16) einen Verdampfungsraum (40) aufweist, der auf der Außenseite seiner Berandung (31) mindestens teilweise die Katalysatorschicht (13) der katalytischen Brennkammer (11) der ersten Verbrennungsstufe (16) aufweist.that the first combustion stage (16) has an evaporation chamber (40) which on the outside of its boundary (31) at least partially has the catalyst layer (13) of the catalytic combustion chamber (11) of the first combustion stage (16).
2. Warmwasserbereiter nach Anspruch 1 ,2. Water heater according to claim 1,
d adurch gekennzeichnet,characterized,
daß die erste katalytische Brennkammer (11) der ersten Verbrennungsstufe (16) als ein kataiytischer Spaltbrenner (11) ausgebildet ist. that the first catalytic combustion chamber (11) of the first combustion stage (16) is designed as a catalytic split burner (11).
3. Warmwasserbereiter nach den Ansprüchen 1 - 2,3. Water heater according to claims 1-2,
d adurch gekennzeichnet,characterized,
daß der Verdampfungsraum (40) als Brennkammer zum Starten des Warmwasserbe¬ reiters ausgebildet ist und eine Zufuhr (41) für Primärluft und eine Zündeinrichtung mit ggf. eigener Zuleitung für Brenngas bzw. beheizter Zuleitung für den flüssigen Brennstoff aufweist.that the evaporation chamber (40) is designed as a combustion chamber for starting the Warmwasserbe¬ rider and has a supply (41) for primary air and an ignition device with possibly its own supply line for fuel gas or heated supply line for the liquid fuel.
4. Warmwasserbereiter nach den Ansprüchen 1 - 3,4. Water heater according to claims 1-3,
d adurch gekennzeichnet,characterized,
daß die Brennstoffzufuhr in den Verdampfungsraum thermisch isoliert ausgebildet ist.that the fuel supply in the evaporation chamber is thermally insulated.
5. Warmwasserbereiter nach den Ansprüchen 1 - 4,5. Water heater according to claims 1-4,
d adurch gekennzeichnet,characterized,
daß eine Düse (42) z.B. Piezokristalle, poröse Keramik oder Verwirbelungsdüse, und/oder eine poröse Struktur (43) zur Zerstäubung und/oder Verdampfung des Brennstoffes vorgesehen sind.that a nozzle (42) e.g. Piezo crystals, porous ceramics or swirling nozzles, and / or a porous structure (43) for atomizing and / or evaporating the fuel are provided.
6. Warmwasserbereiter nach den Ansprüchen 1 - 5,6. Water heater according to claims 1-5,
d adurch gekennzeichnet,characterized,
daß eine Öffnung (44) zur Abgasrezirkulation aus dem Ausgang der ersten Verbren¬ nungsstufe in den Verdampfungsraum vorgesehen ist. that an opening (44) is provided for exhaust gas recirculation from the exit of the first combustion stage into the evaporation chamber.
7. Warmwasserbereiter nach den Ansprüchen 1 - 6,7. Water heater according to claims 1-6,
d adurch gekennzeichne ,characterized by,
daß im Verbrennungsraum eine Einrichtung (45) zur Lenkung des Gasstroms vorge¬ sehen ist.that a device (45) for directing the gas flow is provided in the combustion chamber.
8. Warmwasserbereiter nach den Ansprüchen 1 - 7,8. Water heater according to claims 1-7,
d adurch gekennzeichnet,characterized,
daß der Verbrennungsraum bewegbar, z.B. rotierbar ausgebildet ist.that the combustion chamber is movable, e.g. is rotatable.
9. Warmwasserbereiter nach den Ansprüchen 1 - 8,9. Water heater according to claims 1-8,
d adurch gekennzeichnet,characterized,
daß die Berandung (31) des Verdampfungsraums (40) ein Zylinder ist, der auf der äußeren Mantelfläche mindestens teilweise die Katalysatorschicht (13) aufweist. that the boundary (31) of the evaporation chamber (40) is a cylinder which at least partially has the catalyst layer (13) on the outer surface.
EP94918778A 1993-05-26 1994-05-24 Water heater Expired - Lifetime EP0699289B1 (en)

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EP0699289B1 (en) 1997-01-22
WO1994028359A1 (en) 1994-12-08

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