DE19601957A1 - Gas-fired heat generator with honeycomb catalyst elements in series - Google Patents

Abstract

A catalytic heat generator has a number of consecutive monolithic honeycomb catalyst elements (6, 7, 8, 9) spaced apart downstream of a burner (4) and with heat transfer coils (10, 11, 12) located between each pair of elements. A fan-assisted air-gas mixt. supply (21, 35) includes a three-way mixing valve (22) whose first outlet (23) is connected to the burner, and whose second outlet (24) is connected to the space between the burner and the first catalyst element. Also claimed is a process for operation of the appts. in which the burner is supplied with air-gas mixt. only during the start-up phase to preheat the catalyst to a critical temp. t1, after which the air-gas mixt. is supplied only to the catalyst. The temp. of the reactor is then kept constant, esp. by regulation of the quantity of fuel supplied.

Description

The invention relates to a catalytic heat generator and a method for operating such a heat generator gers according to the preambles of claims 1 and 2.

A combination of a conventional flame burner with egg nem oxidation honeycomb catalyst has become known from DE-PS 39 05 775. The pollutant reduction is achieved by catalytic afterburning of the exhaust gases of a conventional type of burner. For example, the honeycomb catalyst is additionally installed in a gas heater between the burner and the heat exchanger. The disadvantage is that in any case a Grundverbren voltage with a conventional burner for fossil fuels - combined with high pollutant emissions - must take place. Since the catalytic converter can only be loaded up to a maximum temperature of 900 ° C, the burner must convert the main part of the combustion gas-air mixture in the flame, so that a relatively high flame temperature results and consequently a considerable NO _x emission in Purchase must be made. This NO _x emission can only be reduced by catalytic afterburning in combination with an air ratio limitation of 1.05 and sufficiently high CO emissions.

The invention has for its object a catalytic Heat generator and an associated combustion process give, taking advantage of catalytic combustion, esp in particular, the low levels of pollutants in the exhaust gases can be exploited further zen are.

The task is characterized by the distinctive features of the independent pending claims solved. The claimed heat generator is characterized above all by the layered structure of the Wa Body reactor with heat dissipation between the layers and through the optional or mixed application of fuel gas to the Flame burner and the honeycomb reactor. The intermediate switching of heat exchangers or heat exchanger strings possible effective cooling of the honeycomb reactor, which thanks to the three-way mixing valve also as the sole heat generator ger can act. The flame burner is only used for preheating of the honeycomb reactor to the working temperature of approx. 500 ° C. If all honeycomb layers are at this critical temperature have taken, the conversion of the gas-air mixture takes place through catalytic reaction without additional heat input. The three Directional mixing valve is then switched over so that only the second outlet-side connecting line with the gas / air Ge mixing guide is connected. The flame burner connected first output-side connecting line is blocked, whereby the Flame burner goes out.  

The features of claim 2 make it easy to adapt the amount of fuel to be converted catalytically to that in the exhaust gas current residual amount of fuel reached. Because in everyone Stage, that is, successive honeycomb layers, less unburned fuel mixture is available, the honeycomb must always be narrower or longer or narrower and become longer so that it is almost the same at all levels che turnover rate comes about. The latter is advantageous because thereby maintaining the minimum Ar mentioned above working temperature is not endangered and because Dimensioning of the heat exchanger or heat exchanger shear strands does not depend on the gradation of the honeycomb layers.

In general, as proposed in claim 3, four is sufficient Honeycomb layers to provide a full fuel ensure settlement in the honeycomb body reactor.

The check grid according to claim 4 prevents in the one Switching phase of the heat generator in which the flame burner Operation is an adherence of the flames to the flames against overlying surface of the honeycomb layer closest to the burner. Soon the non-return grill can also be used in the known manner Cooling rods act, causing heat to be removed from the flame rich offers an additional guarantee that the honeycomb body perreactor not heated up to its destruction area becomes.

The intermediate heat exchangers are preferred approximately formed heat exchanger strands according to claim 5.  

The honeycomb layers generate a large proportion of radiation heat from the heat exchangers or heat exchanger shear strands should be recordable. For heat transfer from Radiant heat is primarily copper or aluminum pipes suitable according to claim 6. A slat trim is possible.

When training with the features of claim 7 is a simple and effective hydraulic connection of the heat rope shear or heat exchanger strands reached. The through fin double jacket can alternatively or simultaneously to the intermediate heat exchangers or heat exchanger shear strands with a honeycomb downstream of the burner Layered finned heat exchanger for front rank convective heat transfer. This last one Heat exchanger essentially serves to harness the heat mecapacity of the almost pollutant-free exhaust gas. Especially ergie big is the heat yield when this finned heat exchanger acts as a condensation heat exchanger and thus the heat generator ger is constructed according to claim 8 according to the condensing principle. When the flames are burning upright, the combustion chamber can be cylinder shaped with exhaust deflection over the upper edge his. The exhaust gas then flows on the outer surface of the combustion chamber over and finally gets into one of the lower devices richly separated fireplace. In this area there is also Condensate drain provided. As a heat exchanger medium flow ner double jacket is not the in this embodiment Combustion chamber, but the concentrically surrounding the combustion chamber Exhaust gas routing trained. The branched off from the double jacket Enforce heat exchangers or heat exchanger strands with their  Connection piece this exhaust duct and also the combustion chamber wall.

The embodiment according to claim 9 is particularly advantageous, because of the thermal bridge connection of the check grid to the Double jacket a further improvement of the above Cooling rod function of the check grid is achieved. also the grid heat also comes to the efficiency of the heat generator benefit.

An advantageous embodiment is characterized by the features of Claim 10 characterized, which is special simple unit and reliability of the switching or mixing function of the three-way mixing valve. The honeycomb layer temperature as a reference variable for the adjustment of the The valve can be on all layers of the honeycomb reactor be measured, switching to the second output side connecting line of the mixing valve through the control or Control device is preferably initiated when all Honeycomb layers a temperature above the minimum work have assumed temperature. With optimal dimensioning and Design of the intermediate heat exchanger relation wise heat exchanger strands and the honeycomb layers can, however a very even temperature distribution within the Combustion chamber can be reached, so that only a few temperatures sensors for control or regulation are required. For The three-way mixing valve can be further simplified according to claim 11 also designed as a three-way switch valve his. In the basic position, which is necessary for the commissioning phase of the  Heat generator is provided, a connection of the Gas-air mixture supply with both the first and with the second connecting line exist. That way before given mixture proportions then feed both the flame burner as well as the catalytically coated monolithic honeycomb body perreactor, so that a partial conversion even in the start phase the fuel mixture by catalytic conversion can.

A method of operating such a heat generator is described in claim 12. After that, the three way The mixing valve is activated precisely when it is preheated the minimum working temperature of the honeycomb body reactor is reached. The further regulation takes place in Dependence on the honeycomb layer temperature by dosing the amount of fuel supplied. The target temperature to be observed the range of the reactor temperature is according to the che mix structure of the catalytically coated monolithic wa body reactor, that is, according to its temperature durability, on the order of 500 ° C to 800 ° C.

The invention is illustrated below with the aid of two embodiments games explained.

Show it:

Fig. 1 is a schematic representation of a first execution form of a catalytic heat source,

Fig. 2 shows the time course of the honeycomb layer temperature and the fuel gas throughput and

Fig. 3 is a schematic representation of a second embodiment of a catalytic heat generator.

The heat generator according to Fig. 1 consists essentially of egg ner cylindrical combustion chamber 1 which is surrounded by an annular space 2 concentrically to the exhaust duct and by a heat exchange medium through fin NEN double jacket 3. In the combustion chamber 1 , a conventional flame burner 4 and downstream of its exhaust gases, a catalytically coated monolithic honeycomb body reactor 5 is arranged. The honeycomb body reactor 5 consists of 4 separate honeycomb layers 6 , 7 , 8 and 9 between which 3 heat exchanger strands 10 , 11 and 12 are arranged. The Wärmetau shear strands 10 , 11 and 12 are connected to the double jacket 3 in series or in parallel. A flow 13 and a return 14 are also connected to the double jacket 3 , between which at least one consumer, for example a circulation heater or the primary circuit of a heating water / process water heat exchanger, is connected in a circulation (not shown). The passage cross sections of the catalytically active honeycombs decrease from stage to stage in the flow direction of the exhaust gases. In this way, despite the decrease in the proportion of fuel gas which has not yet been converted upstream, approximately the same conversion performance is achieved on each honeycomb layer 6 to 9 . This implementation is transmitted in the form of radiation and convection to the heat exchanger strands 10 to 12 . In order to clarify the heat transfer by radiation in the drawing, the ge jagged arrows 15 are provided. The heat exchanger strands 10 to 12 consist of bare copper or aluminum tubes with high emission coefficients, which facilitates heat transfer by radiation. These heat exchanger strands 10 to 12 can have fins. Downstream of the comb-distant honeycomb layer 9 , a finned heat exchanger 16 , which is also hydraulically connected to the double jacket 3, can additionally be provided. By means of this finned heat exchanger 16 , a residual utilization of the exhaust gas heat takes place and thus the exhaust gas is cooled down to below the condensation point. The cooled down to below 50 ° C exhaust gases such a trained as a condensing th heat generator are in the lower area of the device in egg NEN connecting piece 17 for a chimney not shown ge conducts. A condensate drain 18 is also arranged at a lowest point of the annular space 2 provided for the exhaust gas routing within the device.

If no finned heat exchanger 16 is provided, the double jacket, through which water flows, can also be equipped with fins on the exhaust side.

The device is further equipped with two non-return grids 19 and 20 which on the one hand prevent the flame from adhering to the honeycomb layer 6 closest to the burner and on the other hand contribute to the required cooling of this honeycomb layer 6 . Both check gratings 19 and 20 are extended via thermal contact bridges through the annular space 2 through to the double jacket 3 . The heat from the flames or exhaust gases from the flame burner 4 can be dissipated very effectively in the double jacket 3 in this way. The two grids 19 and 20 consequently act in the manner of the known cooling rods.

In this embodiment, a three-way mixing valve 22 is seen in front of the fuel gas supply to the flame burner 4 and / or the honeycomb reactor 5 in a gas-air mixture supply 21 . The three-way mixing valve is provided with two connection lines 23 and 24 ausgangsseiti, the first of which is connected to the flame burner 4 and the second between the two non-return grids 19 and 20 in the combustion chamber 1 . The three-way mixing valve 22 is used in normal operation only in two positions, namely with partial release of both connecting lines during a commissioning phase of the heat generator and with the exclusive release of the second connecting line 24 during the stationary burner operation. For these control functions, the three-way mixing valve 22 is connected via a control line 25 to a controller 26 . The controller 26 in turn is acted upon by signal lines 27 , 28 , 29 and 30 , which lead to temperature sensors 31 , 32 , 33 and 34 . The four temperature sensors 31 to 34 are each in contact with the top of the four honeycomb layers 6 to 9 . Depending on the Temperatursigna len a gas solenoid valve 35 is struck by the controller 26 via a further control line 36 in the stationary state.

The mode of operation of the heat generator according to FIG. 1, that is, its control or regulation is explained in more detail below with reference to FIG. 2.

In the starting phase, part of the fuel gas or all of the fuel gas is fed via the three-way mixing valve 22 and the first connection line 23 to part of the fuel gas to the flame burner 4 and ignited there. The resulting exhaust gas - if desired - flows through the honeycomb reactor 5 together with the remaining fuel gas which flows into the combustion chamber 1 through the second connecting line. The honeycomb body reactor 5 is heated and works increasingly in the sense of after-combustion or post-oxidation. At the time t 1, a temperature of 500 ° C. is measured by the temperature sensors 31 to 34 on all the honeycomb layers 6 to 9 . At this time t₁ the gas supply is briefly interrupted, as can be seen from the lower part of the diagram. At the same time, the three-way mixing valve 22 is switched over in such a way that only the second connecting line 24 is connected to the gas-air mixture supply 21 . The fuel gas supply is resumed at time t₂. The time required for the gas supply interruption depends on the grid temperature, which should be below 700 ° C. After switching on the gas supply again, it must be ensured that the grid temperature and the honeycomb temperature is below 900 ° C in order to prevent the non-return grid 19 and 20 from igniting and, ultimately, to prevent overheating and thus destruction of the honeycomb body 6 most grid. From the time t₂, a steady state occurs, in which the entire fuel gas is implemented in four stages on the honeycomb layers 6 to 9 . Since the honeycomb layers 6 to 9 emit radiation (jagged arrows 15 ) both on their top and on their underside, the intermediate heat exchanger strands 10 to 12 must have a sufficiently high emission coefficient of their surface. Furthermore, the honeycomb layers 6 to 9 must be sufficiently thin to avoid "hot spots". It must be ensured that sufficient heat can be extracted from the honeycomb by radiation. The degree of conversion at the respective honeycomb layer 6 to 9 is determined by the thickness of the layer and the flow cross-section of the honeycomb. Within the operating temperature typical for the actuator, which is essentially in the range of 500 ° C to 800 ° C according to the chemical structure, a conventional control by influencing the total fuel gas throughput is also possible by superimposition. In this way, the heat requirement within the limits set by the operating temperature can also be taken into account by modulating the gas solenoid valve 35 in accordance with the control 26 .

The catalytic heat generator shown in FIG. 3 differs from the variant according to FIG. 1 with regard to the hydraulics of the double-jacket heat exchanger. In the return-side entrance area, the water supply is divided up by means of a partition 23 into an inner channel 44 and an outer channel 45 . The water entering the outer channel 45 flows through the double jacket 3 , cools the honeycomb reactor 5 and extracts heat from the exhaust gas flowing past in the annular space 2 . For a better heat transfer from the exhaust gas flow control plates and / or in the annular space 2 protruding fins 40 are provided. The water flowing through the inner channel 44 is distributed over three coils 36 , 37 and 38 , which are arranged between the honeycomb layers 6 , 7 , 8 and 9 . The coils 36 , 37 and 38 open into the double jacket 3 , which is also flowed through by the water from the outer channel 45 in the direction before 13 . Due to the developing under pressure, the water from the coils 36 , 37 and 38 is sucked and also transported to the flow 13 . In this way it is ensured that the coils 36 , 37 and 38 are flowed through, the heat exchange effectiveness can be regulated via the flow rate. The Fließge speed is dependent on the amount of heat demand. Such a control can be implemented, for example, by a valve 41 with motorized adjustment 42 arranged in the return line 14 .

The invention is not limited to the above bene embodiment. Rather, it is a number of variants conceivable, even if fundamentally different Execution make use of the features of the invention.

Claims (12)

1. Catalytic heat generator with a combustion chamber in which a fan-assisted gas-air mixture supply connected ner flame burner is arranged, the gases from which act on at least one heat exchanger, a catalytically coated monolithic honeycomb reactor being provided in the exhaust gas path, characterized in that the honeycomb body reactor ( 5 ) consists of a plurality of honeycomb layers ( 6 , 7 , 8 , 9 ) distanced from one another in the exhaust gas flow direction, between which heat exchangers or strands ( 9 , 10 , 12 ) of a heat exchanger are arranged, so that an effective Radiation heat extraction is possible. In the gas-air mixture supply ( 21 ), a three-way mixing valve ( 22 ) is provided, whose ste output-side connection line ( 23 ) is connected to the flame burner ( 4 ) and the sen second output-side connection line ( 24 ) between the flame burner ( 4 ) and the next honeycomb layer ( 6 ) opens into the combustion chamber ( 1 ). 2. Heat generator according to claim 1, characterized in that the flow cross sections layers downstream of successive honeycomb layers ( 6 , 7 , 8 , 9 ) decrease. 3. Heat generator according to one of the preceding claims, characterized in that four honeycomb layers ( 6 , 7 , 8 and 9 ) are provided. 4. Heat generator according to one of the preceding claims, characterized in that current on the burner next to the honeycomb layer ( 6 ) min least a check grid ( 19 , 20 ) is arranged. 5. Heat generator according to one of the preceding claims, characterized in that between the honeycomb layers ( 6 , 7 , 8 , 9 ) of orderly heat exchangers or heat exchanger strands ( 10 , 11 , 12 ) of a heat exchanger for convective and radiative heat transfer are formed . 6. Heat generator according to claim 5, characterized in that the heat exchanger or heat exchanger strands ( 10 , 11 , 12 ) of a heat exchanger made of copper or aluminum tubes made of stainless steel. 7. Heat generator according to one of the preceding claims, characterized in that the combustion chamber ( 1 ) is surrounded by a double jacket ( 3 ) through which heat is exchanged with heat and which is provided with the heat exchanger strands provided between the honeycomb layers ( 6 , 7 , 8 , 9 ) ( 10 , 11 , 12 ) hydraulically connected and / or a lamella heat exchanger ( 16 ) for convective heat transfer is connected to the downstream of the honeycomb layer ( 9 ) furthest from the burner. 8. Heat generator according to one of the preceding claims, characterized by the training as condensing device, wherein in the lower loading area of the device, an exhaust gas outlet ( 17 ) and a condensate drain ( 18 ) are provided. 9. Heat generator according to claim 7, characterized in that the or the Rückschlaggit ter ( 19 , 20 ) on the double jacket ( 3 ) via a thermal bridge connection is or are. 10. Heat generator according to one of the preceding claims, characterized in that the three-way mixing valve ( 22 ) with a honeycomb layer temperature-controlled control or re gel device ( 26 ) is connected. 11. Heat generator according to one of the preceding claims, characterized in that the three-way mixing valve ( 22 ) is designed as a three-way switching valve. 12. A method of operating a heat generator according to one of the preceding claims, characterized in that the flame burner ( 4 ) only in a start phase for preheating the honeycomb reactor ( 5 ) to a critical temperature t 1 via the first connecting line ( 23 ) of the three-way -Mischven tils ( 22 ) is supplied with a gas-air mixture and that after reaching the critical temperature t₁ only the honeycomb body gate ( 5 ) via the second connecting line ( 24 ) of the three-way mixing valve ( 22 ) with gas-air - Mixture is supplied, with a target temperature range of the reactor temperatures, in particular by regulating the amount of fuel supplied, is observed.