DE102006034479B4 - Process for the evaporation and combustion of liquid fuel - Google Patents

Abstract

Method for vaporizing and burning liquid fuel, in which the liquid fuel is burned as a secondary fuel following a start-up phase operated with a primary fuel,
characterized by the following steps during phases (a) and (b):
(a) during a first phase (start-up phase)
A primary fuel is fed to a combustion chamber (24, 112) and burned, with combustion and exhaust gases flowing through the combustion chamber in a preferential flow direction,
- Is formed as a heat exchanger, within the combustion chamber (24; 112) located in the combustion and exhaust gas flow of the primary burner evaporator (14) of air or oxygen-containing gas flows through as purge gas,
(b) during a second phase (stationary phase)
The air or the purge gas in the evaporator (14) is replaced by secondary fuel after reaching a certain temperature at a predetermined point within the combustion system,
- The secondary fuel through the evaporator (14) within the combustion chamber (24; 112) in countercurrent to the combustion and exhaust gases of the ...

Description

The The invention relates to a process for evaporation and combustion of liquid fuel as Secondary fuel. The invention is particularly suitable for low NOx combustion of vegetable oil.

For as possible complete, d. H. also low in nitrogen, and soot-poor guided Combustion of liquid fuels are often used today so-called Blaubrenner, in which the Combustion with non-luminous blue flame particularly soot-poor done can. The well-known Blaubrenner are generally for the combustion designed for fossil fuels and less for the combustion of vegetable oils suitable. In particular, then problems with deposits through Cracking reactions.

Conventional Blaubrenner are for example from the DE 44 30 888 A1 or the DE 23 06 342 known.

Also, in systems that instead of a nebulization or spraying process involve a vaporization process for liquid fuels, there is the danger of deposits in the evaporator area by cracking reactions and on the other hand, the boiling point of oils depending on the composition above the autoignition temperature. Such a plant is for example from the FR 28 03 905 A1 known. This shows a heater for vegetable oil, in which the fuel, namely the vegetable oil, is guided in the combustion chamber through a conduit system and heated.

From the DE 103 42 763 A1 For example, a gas burner for liquid fuel is known in which the combustion of vegetable oil is started with an external ignition device operated, for example, with kerosene or diesel oil. To start a firing process, the igniter preheats the evaporator coil. The resulting heat is sufficient to start the evaporation process in the evaporator coil and to ignite an escaping gas flow.

From the DE 39 27 159 A1 is a pressure evaporator burner, in particular for field cookers, known in which below a combustion chamber open at the bottom of a Druckzerstäuberdüse liquid fuel for preheating operation is arranged. The design serves the task of modifying a designed for liquid fuels pressure evaporator burner so that with the least design effort optionally even without conversions, operation with gaseous fuel is possible. For this purpose, a further nozzle is provided, which is fed from an independent supply line with gaseous fuel.

From the EP 97315 A2 Another oil burner assembly for field cookers is known. The apparatus has a heated steamer upstream of the burner tube to which a starter mixing nozzle communicating with it at the start of operation and associated with an air supply and a fuel supply is associated. The fuel supply line to the starter mixing nozzle or spray nozzle is designed as a capillary tube.

The The object of the invention is the problems in the prior art to avoid and to provide a method with associated device, the especially for the burning of vegetable oils suitable is.

The Task is solved with a method according to claim 1. Advantageous embodiments of the invention are specified in the subclaims.

• (a) während einer ersten Phase (Anlaufphase)
• – wird ein Primärbrennstoff einer Brennkammer (24; 112) zugeführt und verbrannt, wobei Brenn- und Abgase in einer Vorzugs-Strömungsrichtung durch die Brennkammer strömen,
• – wird ein als Wärmetauscher ausgebildeter, innerhalb der Brennkammer (24; 112) im Brenn- und Abgasstrom des Primärbrenners befindlicher Verdampfer (14) mit Luft oder sauerstoffhaltigem Gas als Spülgas durchströmt,
• (b) während einer zweiten Phase (stationäre Phase)
• – wird die Luft oder das Spülgas im Verdampfer (14) ab Erreichen einer bestimmten Temperatur an einer vorbestimmten Stelle innerhalb des Brennsystems durch Sekundärbrennstoff ersetzt,
• – wird der Sekundärbrennstoff durch den Verdampfer (14) innerhalb der Brennkammer (24; 112) im Gegenstrom zu den Brenn- und Abgasen des Primärbrenners (26) zugeführt und vor oder in die Brennkammer eingebracht,
• – wird die Zufuhr des Primärbrennstoffs verringert.

According to this invention, the process of vaporizing and burning liquid fuel, in which the liquid fuel is burned as a secondary fuel following a run-up phase with a primary fuel, is characterized by the following steps during phases (a) and (b):

• (a) during a first phase (start-up phase)
• - a primary fuel of a combustion chamber ( 24 ; 112 ) and burned, wherein combustion and exhaust gases flow in a preferred flow direction through the combustion chamber,
• - is designed as a heat exchanger, within the combustion chamber ( 24 ; 112 ) located in the combustion and exhaust gas flow of the primary burner evaporator ( 14 ) flows through with air or oxygen-containing gas as purge gas,
• (b) during a second phase (stationary phase)
• - is the air or the purge gas in the evaporator ( 14 ) replaced by secondary fuel after reaching a certain temperature at a predetermined point within the combustion system,
• - is the secondary fuel through the evaporator ( 14 ) within the combustion chamber ( 24 ; 112 ) in countercurrent to the combustion and exhaust gases of the primary burner ( 26 ) and introduced before or into the combustion chamber,
• - The supply of primary fuel is reduced.

According to the device, a spatial separation of evaporator and process zone is realized. For this purpose, in the combustion chamber of a conventionally designed as such burner (hereinafter referred to as a primary burner), an evaporator for the liquid fuel to be burned mainly - the secondary fuel or the oil-integrated, from which the evaporated oil via a fuel supply device (which can preferably be provided with throttle nozzles) can escape into the combustion chamber and is then burned there. The evaporator is designed in the form of a heat exchanger: heat from the combustion and exhaust gas stream of the primary burner is first transferred via a heat transfer surface to the secondary fuel to be evaporated and the fuel is evaporated. The vaporized liquid fuel, which constitutes the secondary fuel according to the invention, is fed into the combustion chamber via fuel supply devices, generally nozzles, in particular throttle nozzles. This should be done close to the primary fuel supply, so that especially in the start-up phase of the secondary fuel can ignite in the primary fuel stream.

Of the Evaporator thus also takes the same function as a secondary burner true.

One Combustion system for the evaporation and combustion of liquid fuel as secondary fuel includes a primary burner for one at least during a start-up phase to be used primary fuel, a combustion chamber and a secondary fuel supply as well a device for the feeder of the secondary fuel with a within the combustion chamber in the combustion and exhaust gas flow of primary burner arranged as a heat exchanger trained evaporator through the purge air and secondary fuel within the evaporator in countercurrent to the combustion and exhaust gas flow direction of the primary burner supplied are.

optional is one for the retrofit Conventional combustion systems designed device as above described.

at the method according to the invention the thermal NOx formation is largely suppressed, the burner itself with small NOx emission by small apparatus Expense is distinguished.

to Preparation of the state of the stationary phase is first awaited until the gas in the evaporator is at a certain temperature heated Has. The secondary fuel is preferably only from reaching a certain temperature supplied at a predetermined location within the combustion system. Preferably finds this temperature measurement output of a substantially isothermal High temperature range in the combustion chamber, d. H. usually in Dwell area of the combustion chamber, more preferably in the evaporator and / or in the exhaust gas discharge.

It should be at least 600 ° C, preferably at least 800 ° C be measured before in phase (b) located in the evaporator Air or the purge gas through the liquid secondary fuel replaced and this is then continuously fed to the combustion.

Preferably can the primary fuel supply in phase (b) depending from the over the secondary burner supplied Liquid fuel quantity be reduced. It is particularly advantageous if the primary fuel supply in phase (b) is shut down to zero and the combustion after the start-up phase (phase (a)) solely by the liquid, within the combustion chamber in countercurrently supplied secondary fuel, so for example the vegetable oil, is fed. The process then works autothermally and the evaporator, at the same time the secondary burner is located in the combustion gas stream, or combustion and Exhaust gas flow, of the secondary fuel supplied by the evaporator itself. In the autothermal state is over the plant set a substantially stationary temperature profile, which may be subject to periodic fluctuations.

In Advantageous development of the invention, the state of the Burner constantly checked using certain parameters and it would re-primary fuel supplied once it was found that the operating state in the secondary fuel combustion not more autothermic. Therefore, as soon as the above-mentioned temperature profile and the autothermal Condition will be left and the temperature at the for the measurement intended point (or more points) falls too sharply the combustion of the secondary fuel supported for a short time or with a low primary fuel quantity, and Although at least until a time when the autothermal State again.

To therefore, the primary burner can preferably shut down in a standby state.

In a further preferred embodiment becomes the primary fuel supply in dependence of the exhaust gas temperature controlled.

It is currently considered to be particularly advantageous when purge air and / or secondary fuel near the primary fuel supply are introduced, preferably exit or more preferably outside of the flame area. This area inside a combustion chamber, outside the Flammbereiches of the associated Brenners becomes common also referred to as dwell area. The material flows from evaporated secondary fuel and burning primary fuel, or combustion and exhaust gases (combustion gases) of the primary fuel should mix well. Therefor can the secondary fuel For example, in the direction of the combustion and exhaust gas flow or in a the turbulence thereby promoting Angle be introduced.

Device-wise this can be realized by the output of the evaporator or on this output or the outputs arranged Sekundärbrennsoff-discharge devices, such as B. controllable valves or throttle nozzles, are aligned, that an exiting flow of material transverse to or obliquely in the direction the preferred direction of the combustion and exhaust gas flow of the primary burner extends or is directed.

The Procedure can also be done that way be that the fuel and exhaust flow within the combustion chamber is recirculated. Device is provided for this purpose, that inside the combustion chamber internals for the recirculation of the combustion and exhaust gas flow are present. This can basically all types of installations be that redirect the combustion and exhaust flow and so at least a part attributed to this stream, z. B. baffles or concentric, possibly perforated pipes. method and devices for the exhaust gas recirculation of burners, especially blue burners, are known in the art and can adapted here.

Preferably however, a recirculation path separated from the combustion chamber becomes educated. This is done in a preferred embodiment with the help of a flame tube, which is integrated into the combustion chamber and the combustion chamber into an inner actual combustion chamber area, the flame area of the primary burner includes, and an outer area, namely the recirculation path, divided. In a particular embodiment are inner combustion chamber, inside the flame tube, and outer circulation path except for possibly adjustable in size openings completely in the fire tube separated from each other.

Especially It may be advantageous to recirculate the secondary fuel Supply combustion and exhaust gas.

According to one further advantageous embodiment can the secondary fuel with the combustion air for the primary burner supplied become.

According to another alternative, it is also possible to supply the combustion system with an oxidatively by post combustion to be cleaned exhaust gas. This can preferably be done by introducing the exhaust gas to be purified into a combustion chamber antechamber used as a mixing space or by supplying it directly with the combustion air for the primary burner. ( 18 For this purpose, for example, at least one line for exhaust gas to be purified by oxidation can open into the combustion chamber or the combustion chamber antechamber.

In the most preferred embodiments is the secondary fuel an oil, preferably a vegetable oil or a vegetable oil containing mixture.

In the associated device, the heat exchanger integrated in the combustion chamber serves as an evaporator for the secondary fuel and as a secondary burner. ( 19 In a particularly preferred embodiment, the heat exchanger is designed as a piping system, preferably as a spiral-guided pipe. In this way, a large heat transfer area can be generated.

At the Outlet of the evaporator, d. H. of the heat exchanger for the preheating of the secondary fuel in the fuel and exhaust stream of the primary burner, is as a secondary fuel dispenser preferably at least one nozzle for the levy of purge air and secondary fuel provided in the combustion chamber or a combustion chamber antechamber. This nozzle or these nozzles can as Orifice (s) be educated.

advantageously, is the exit of the evaporator and there arranged Secondary fuel dispensers within the combustion system in a flame area of the primary burner surrounding area in the combustion chamber or the combustion chamber antechamber. For example, the output of the evaporator can be immediately output the flame area of the primary burner, d. H. at the transition of flame area and dwell within the combustion chamber. Alternatively, the output is either further downstream in the dwell area of the combustion system, or upstream the flame area or in an annular area around the flame area around. When the exit of the evaporator upstream the flame area is arranged, it can in particular in a combustion chamber anteroom lead, that of the combustion chamber frequently by means of a combustion air shutter or by other means is separated.

Of the Combustion chamber can have openings to the combustion chamber, through combustion air fed into the combustion chamber can be. At the openings they can also be nozzles act, often However, this is combustion air supply from a combustion chamber antechamber from realized by a combustion air shutter, as above described.

Of the primary burner is preferably designed as a blue flame burner and can be a usual geometry for blue burners have. Suitable burner forms are known to the person skilled in the art.

In a further embodiment it is provided that the combustion chamber widens in the flow direction.

As can be seen from the foregoing description, which is characterized Invention and. a. characterized in that the firing system, a device for the supply of a secondary fuel in the combustion chamber or a combustion chamber anteroom with an inside the combustion chamber in the combustion and exhaust gas flow of a primary burner arranged as a heat exchanger trained evaporator includes, by the scavenging air and secondary fuel within the evaporator in countercurrent to the combustion and exhaust gas flow direction of the primary burner can be fed. The device can be used for the retrofit Conventional combustion systems provided and in adaptation to known Burner be designed accordingly.

The process according to the invention can be described in its basic form as follows:
During operation, the combustion chamber is constantly supplied with possibly preheated combustion air and the fuel supply is switched between two operating states, of which in a first operating state - the start-up operation from the cold state - fuel through the primary burner to produce at least partially in the combustion chamber with a stable flame combusting fuel / air mixture is introduced into the combustion chamber. During this phase of operation, (purge) air is passed through the evaporator.

There the conventional primary burner only for the starting operation required This can be both solid and liquid or gaseous Be operated fuel ben, the specific ignition behavior account of the individual fuels. Are z. B. pure vegetable oils as fuel for the primary burner Used, this will preheat to temperatures above 70 ° C to ensure a trouble-free Ignite of the primary burner sure.

exceeds the temperature of the introduced into the combustion chamber scavenging the Ignition (about 600 to 800 ° C) for the Mixture of combustion air and the liquid fuel, with Help of the secondary burner is to be burned, is switched to a second operating state - the heating mode.

For this Now the purge air supply switched off and liquid Fuel (eg vegetable oil) passed the evaporator while at the same time the fuel supply for the primary burner in dependence from the over the secondary burner supplied Fuel quantity is reduced. By increasing the fuel supply for the Secondary burner can For this an autothermal operating condition can be set, d. H. for the evaporation fuel and warming the combustion air necessary energy is solely from the combustion by the secondary burner applied fuel applied. A supply of fuel over the primary burner is no longer necessary and the primary burner switches into one Standby.

The Method can be advantageously carried out so that the temperature measured from the combustion chamber exiting exhaust gases and the primary burner supplied Fuel quantity depending controlled by the measured temperature. In a manner according to the invention trained device, the control can also be done automatically, if a temperature measuring device to measure the temperature of the combustion chamber escaping gases and a control device provided are the distribution of the total of the combustion chamber fuel supplied controls.

At the Flow through the evaporator heated the oil and enters as oil vapor via the fuel supply device into the combustion chamber, at a position in the flow direction the combustion and exhaust gases in front of the heat exchanger or in the front area of the heat exchanger. In the operation of the invention the facility is it possible for the secondary fuel to produce an oil vapor preheated to over 800 ° C. The oil pressure is about 15 bar, and may for example be about 25 bar.

The Fuel nozzle assembly (Throttle nozzles) of the evaporator or secondary burner in the form of the heat exchanger, d. H. in particular also its nozzle outlet cross-section, is expediently, but not necessarily, designed and dimensioned such that the leaking fuel at least substantially the same speed as the nozzle outlet (s) around flowing combustion air whereby the mixing between the fuel and the Combustion air is delayed becomes.

Of the name is Fuel oil is fed into the cold combustion air, where immediately the Oxidation of the oil vapor starts. The released heat of reaction of the exothermic reaction leads to warming the combustion air, whereby a temperature increase with the following self-ignition the mixture is counteracted.

A further reduction of the temperature in the combustion chamber via the evaporator itself, in which a further part of the released reaction heat is used for the heating of the secondary fuel.

By both measures, flame combustion is prevented and the reaction of the secondary fuel is carried out according to the principle of nitrogen oxide-poor flameless oxidation (FLOR ^® principle or gas phase oxidation principle).

Very simple structural conditions arise in this burner when the combustion chamber from the air supply device is acted upon with the entire combustion air. Depending on Purpose are also embodiments conceivable in which a (lesser) proportion of the combustion air in the first and / or the second operating state at the combustion chamber is passed in a dwell area.

Should the second operating state is ended, the supply of the secondary fuel finished and it is expediently purge air passed through the evaporator. This will cause the rest in the evaporator located secondary fuel transferred to the combustion chamber and the evaporator is cleaned at the same time.

Further Details and advantages of the invention will become apparent from the following Description in conjunction with the drawings in which

1 a schematic representation of an apparatus for evaporation and subsequent low-NOx combustion of the same shows;

2 the starting operation of the device according to 1 explained, wherein still no liquid (secondary) fuel is supplied to the combustion chamber;

3 the power operation of the device according to 1 schematically illustrated, wherein the added amount of (secondary) fuel is controlled by the exit temperature of the gases from the combustion chamber;

4 a schematic representation of an apparatus for evaporation and subsequent low-NOx combustion of the same in connection with an external recirculation of hot combustion gases shows;

5 the starting operation of the device according to 4 explained, wherein still no liquid (secondary) fuel is supplied to the combustion chamber;

6 the power operation of the device according to 5 schematically illustrated, wherein the added amount of (secondary) fuel is controlled by the exit temperature of the gases from the combustion chamber;

7 shows a schematic representation of an apparatus for oxidative exhaust gas purification, in which the premix of vaporized liquid fuel and exhaust gas takes place in a pre-mixing chamber arranged immediately in front of the burner;

8th the starting operation of the device according to 7 explained, wherein still no exhaust gas of the combustion chamber or the premixing chamber is supplied;

9 the cleaning operation of the device according to 7 schematically illustrated, wherein the amount of liquid fuel added to the exhaust gas in the pre-mixing space is controlled by the exit temperature of the gases from the combustion chamber;

10

contraption for the Evaporation of secondary fuel

12

feed for secondary fuel

14

Evaporator (Heat exchanger)

16

fuel supply means for secondary fuel (Throttle nozzles)

18

Valve in line 12

20

Burning system containing device 10

22

Line for discharging gases 24

24

Combustion chamber of 20

26

Primary burner of 20

28

(Fuel) pipe for 26

30

Valve in line 28 for controlling the amount of fuel

32

Heat exchanger for preheating the fuel in line 28

34

Line for combustion air for 26

36

Passage openings for combustion air for 26 to the combustion chamber 24 (to the combustion chamber)

38

40

Pipe for purging the evaporator 14

42

Valve to line 40

44

Temperature measuring device

50

flame tube

52

Openings) in flame tube for return

54

recirculation

56

inner space of the flame tube

100

contraption for oxidative emission control

110

management for discharging gases

112

combustion chamber

114

Combustor anteroom

116

Temperature measuring device

118

120

Passageways in the basket of the basket burner 124

122

Basket of basket burner 124

124

basket burner

126

Line for the supply of primary fuel to the basket burner 124

128

Valve in line 126

In the 1 to 3 is schematically one in its entirety with 10 designated device for the evaporation of a via a line 12 the device 10 supplied liquid fuel (eg vegetable oil) and subsequent nitrogen oxide combustion of the same in various operating conditions, namely at rest ( 1 ), in start-up mode ( 2 ) and in power operation ( 3 ).

The device 10 consists essentially of the supply line 12 for the liquid (secondary) fuel, the evaporator 14 formed in the form of a heat exchanger and a number of fuel supply means 16 , which are generally designed as nozzles, in particular throttle nozzles. To control the secondary fuel quantity supplied to the burner is the valve 18 into the pipe 12 switched on. With the valve open 18 can allow the evaporator 14 liquid (secondary) fuel are supplied as fuel vapor via the fuel supply 16 is introduced into the combustion chamber.

For cleaning purposes, especially after closing the valve 18 , the evaporator can 14 over the line 40 and the valve switched on in this line 42 with another oxygen-containing gas, eg. B. ambient air to be rinsed.

The device 10 is in a conventionally trained burning system 20 integrated. The burning system 20 consists of the essentially thermally insulated and with a line 22 for discharging gases provided combustion chamber 24 and the primary burner 26 , The primary burner 26 can over a line 28 be supplied with solid, liquid or gaseous fuel, wherein for controlling the amount of fuel supplied to the burner, the valve 30 into the pipe 28 is turned on. In order to preheat the fuel can additionally heat exchanger 32 into the pipe 28 be integrated. The combustion air needed and possibly preheated combustion air is from the burner 26 via wire 34 sucked in and passes over the passages 36 into the combustion chamber.

The device described operates as follows: In start-up mode ( 2 ) is the valve 18 closed, and over the line 12 there is no (secondary) fuel in the combustion chamber 24 initiated. Instead, valve is 42 opened and over wire 40 flows in small quantities of another oxygen-containing gas, eg. B. ambient air into the combustion chamber 24 , The valve 30 is wide open and it forms a far into the combustion chamber 24 reaching flame, resulting in the combustion chamber 24 and in that the combustion chamber 24 over the line 22 leaving gas quickly sets a desired high temperature value (usually in the range between 750 and 900 ° C), the one of the outlet temperature of the gas in the line 22 measuring temperature measuring device 44 determined and via a not shown here, known per se control device for controlling the valves 18 . 30 and 42 is used. In this case, during the starting operation, during which the combustion chamber is heated and no (secondary) fuel is burned, only the valve 30 more or less wide open while the valve 18 remains closed during the entire start-up operation. The dashed line connecting the temperature measuring device 44 and valve 30 symbolizes their control technology coupling.

Finally, when a certain predetermined temperature value is reached ( 3 ), the valve becomes 42 closed and valve 18 open, so that instead of the other oxygen-containing gas now to be burned (secondary) fuel via the line 12 , the evaporator 14 and the fuel supply devices 16 the combustion chamber 24 is supplied. Due to the high temperatures in the combustion chamber 24 , which are usually between 750 and 900 ° C, is the over line 12 supplied liquid (secondary) fuel in evaporator 14 heated above the boiling temperature and evaporated, so he as fuel vapor through the fuel supply 16 into the combustion chamber 24 entry. To maintain the temperatures in the combustion chamber, only a relatively small support flame is now required, so that only small amounts of primary fuel through the valve 30 the primary burner 26 be supplied. The exothermic oxidation reaction takes place predominantly in the combustion chamber, which is preferably constructed of thermally insulating walls 24 instead, with the maintenance of the most constant possible exhaust gas temperature via the control of the supplied amount of liquid (secondary) fuel. Accordingly, the valve 18 depending on the temperature measuring device 44 measured values more or less wide, the dashed line is to illustrate the coupling of these two functional units. Because the oxidation reaction predominantly in the combustion chamber 24 and does not run in the small flame, the so-called "prompt" -NO _x formation, which takes place in the flame front, largely suppressed. In addition, since the so-called "thermal" NO _x formation is negligible in the above-mentioned temperatures between 750 and 900 ° C. which are usual in such a thermal afterburning apparatus, extremely low nitrogen oxide concentrations in the combustion chamber can be achieved with such a device 24 over the line 22 achieve discharged gas. Since the nitrogen oxides are formed mainly in the zone of flame combustion, it is therefore essential to the invention to keep the flame emerging from the burner as small as possible.

In the 4 to 6 show in combustion systems with external recirculation for hot combustion gases schematically the use of the device according to the invention 10 for the evaporation of one over a line 12 the device 10 supplied liquid fuel (eg vegetable oil) and subsequent low-NOx combustion of the same in different operating conditions, namely at rest ( 4 ), in start-up mode ( 5 ) and in power operation ( 6 ).

By an additional in the combustion chamber of device 20 integrated flame tube 50 a recirculation path arises 54 for the hot combustion gases passing through an opening 52 in interior of the flame tube 50 to be led back. The size of the opening 52 can be regulated.

In such firing systems ( 4 ) is the device 10 preferably in the interior of the flame tube 50 installed while the fuel feeders 16 in the recirculation path 54 are arranged so that vaporized (secondary) fuel and hot combustion gases can mix.

In startup mode ( 5 ) is the valve 18 closed, and over the line 12 there is no (secondary) fuel in the combustion chamber 24 initiated. Instead, valve is 42 opened and over wire 42 flows in small quantities of another oxygen-containing gas, eg. B. ambient air in the Rezirkulationsweg 54 , The valve 30 is wide open and it forms a far into the combustion chamber 24 reaching flame as well as the recirculation of the hot combustion gases. This raises in the combustion chamber 24 and in that the combustion chamber 24 over the line 22 leaving gas quickly a desired high temperature value (usually in the range between 750 and 900 ° C), one of the outlet temperature of the gas in the line 22 measuring temperature measuring device 44 determined and via a not shown here, known per se control device for controlling the valves 18 . 30 and 42 is used. In this case, during the starting operation, during which the combustion chamber is heated and no (secondary) fuel is burned, only the valve 30 more or less wide open while the valve 18 remains closed during the entire start-up operation. The dashed Ver connecting line between temperature measuring device 44 and valve 30 symbolizes their control technology coupling.

Finally, when a certain predetermined temperature value is reached ( 6 ), the valve becomes 42 closed and valve 18 open, so that instead of the other oxygen-containing gas now to be burned (secondary) fuel via the line 12 , the evaporator 14 and the exit devices 16 the recirculation path 54 is supplied. Due to the high temperatures in the combustion chamber 24 , which are usually between 750 and 900 ° C, is the over line 12 supplied liquid (secondary) fuel in evaporator 14 heated above the boiling temperature and evaporated, so he called fuel vapor from fuel feeders 16 exits, with the hot combustion gases in the recirculation path 54 mixes and as a mixture over the openings 52 in the interior of the flame tube 56 entry. To maintain the temperatures in the flame tube and combustion chamber, only a relatively small supporting flame is now required, so that only small amounts of primary fuel via the valve 30 the primary burner 26 be supplied. The exothermic oxidation reaction takes place predominantly in the interior of the flame tube 56 instead, with the maintenance of the most constant possible exhaust gas temperature via the control of the supplied amount of liquid (secondary) fuel. Accordingly, the valve 18 depending on the temperature measuring device 44 measured values more or less wide, the dashed line is to illustrate the coupling of these two functional units. Since the oxidation reaction predominantly in the flame tube interior 56 and does not run in the only small flame, the so-called "prompt" -NO _x formation is largely suppressed in this Variente. Also, the so-called "thermal" NO _x formation is negligible due to the above temperatures between 750 and 900 ° C, resulting in extremely low nitrogen oxide concentrations from the combustion chamber 24 over the line 22 discharged gas can be achieved. Since the nitrogen oxides are formed mainly in the zone of flame combustion, it is therefore essential to the invention to keep the flame emerging from the burner as small as possible.

In the 7 to 9 is schematically one in its entirety with 100 designated apparatus for oxidative purification of a via a line 102 the device 100 supplied exhaust gas in various operating states, namely at rest ( 7 ), in start-up mode ( 8th ) and in the cleaning operation ( 9 ). Into the device 100 became the device 10 for the vaporization of a liquid fuel and subsequent low-NOx combustion thereof integrated, wherein the fuel supply means 16 in the combustion chamber anteroom 114 open, so that the evaporated (secondary) fuel itself with an over in the combustion chamber antechamber 114 opening line 12 can mix the supplied exhaust gas. The combustion chamber anteroom 114 serves as premixing room.

The device 100 consists of the im essential thermally insulated and with a pipe 110 for discharging gases provided combustion chamber 112 and the combustion chamber anteroom 114 that have passages 120 of which, for reasons of clarity, only a few have been provided with reference numerals in the basket 122 of the here designed as a basket burner burner 124 connected to each other.

The burner 124 can over a line 126 with fuel gas, z. As natural gas, are supplied, wherein for controlling the fuel gas supplied to the burner of the valve 128 into the pipe 126 is turned on.

The device described operates as follows: In start-up mode ( 8th over the line 12 no exhaust gas is still in the combustion chamber antechamber 114 introduced, but another oxygen-containing gas, eg. B. ambient air. The valve 18 is closed, and over the line 12 there is no (secondary) fuel in the combustion chamber antechamber 114 initiated. Instead, valve is 42 opened and over wire 40 flows in small quantities of another oxygen-containing gas, eg. B. ambient air over the evaporator 14 in the combustion chamber anteroom 114 ,

The valve 128 is wide open and it forms in the burner basket 122 one far into the combustion chamber 112 reaching flame, resulting in the combustion chamber 112 and in that the combustion chamber 112 over the line 110 leaving gas quickly sets a desired high temperature value (usually in the range between 750 and 900 ° C), the one of the outlet temperature of the gas in the line 110 measuring temperature measuring device 116 determined and via a not shown here, known per se control device for controlling the valves 18 . 42 and 128 is used. In this case, during the start-up operation, during which the combustion chamber is heated and no exhaust gas is cleaned, only the valve 128 more or less wide open while the valve 18 remains closed during the entire start-up operation. The dashed line connecting the temperature measuring device 116 and valve 128 symbolizes their control technology coupling.

Finally, when a certain predetermined temperature value is reached ( 9 ), is replaced by the other oxygen-containing gas over the line 102 the oxygen-containing exhaust gas to be cleaned, the combustion chamber antechamber 114 , which now serves as premixing room, fed. At the same time the valve 42 closed and valve 18 open. Due to the high temperatures in the combustion chamber 112 , which are usually between 750 and 900 ° C, is the over line 12 supplied liquid (secondary) fuel in evaporator 14 heated above the boiling temperature and evaporated, so he as fuel vapor through the fuel supply 16 in the premix room 114 entry. Instead of the other oxygen-containing gas can now exhaust and evaporator 14 generated and via the exit devices 16 fed (secondary) fuel vapor in the in 9 for clarity, hatched premix space 114 Mingle before passing through the openings in the burner basket 122 into the combustion chamber 112 transgressed.

To maintain the temperatures in the combustion chamber, only a relatively small support flame is now required, so that only about 5 to 10% of the total fuel flow rate through the valve 128 the burner 124 be supplied. The exothermic oxidation reaction takes place predominantly in the combustion chamber, which is preferably constructed of thermally insulating walls 112 instead of maintaining the most constant possible exhaust gas temperature via the control of the exhaust gas in the premixing chamber 114 admixed, evaporated (secondary) fuel quantity takes place. Accordingly, the valve 18 depending on the temperature measuring device 116 measured values more or less wide, the dashed line is to illustrate the coupling of these two functional units. Since also here the oxidation reaction predominantly in the combustion chamber 112 and not in the small flame in the burner basket 122 expires, the so-called "prompt" -NO _x formation, largely suppressed. In addition, since the so-called "thermal" NO _x formation is negligible in the above-mentioned temperatures between 750 and 900 ° C. which are usual in such a thermal afterburning apparatus, extremely low nitrogen oxide concentrations in the combustion chamber can be achieved with such a device 112 over the line 110 discharged gas, the so-called clean gas, achieve.

Again, it is essential to the invention to keep the emerging from the burner flame as small as possible. In cleaning mode, this is done as follows: The burner 124 over the line 126 supplied fuel gas, ie z. As natural gas is oxidized under "rich" conditions such that oxygen-containing exhaust gas gradually (according to the position of the openings 120 in the burner basket 122 in 7 ) is supplied. The about the fuel supply 16 in the premix room 114 introduced (secondary) fuel mixes there with the over the lines 12 supplied exhaust gas before entering the combustion chamber 112 and is thereby diluted to such an extent that it can be regarded as an "ignition-unwanted" mixture (mixture outside the ignition limit) and therefore not oxidized as a flame but only in the combustion chamber in the gas phase (flameless oxidation). The exhaust gas must not otherwise with egg be blown at a certain pressure in the combustion chamber, only the pressure drop of the burner basket (in the order of 10 to 15 mbar) is overcome.

in the The scope of the inventive concept are numerous modifications and Further education possible, the z. B. refer to the burner. So it is z. B. possible, instead the basket burner shown to use so-called point burner. At least essential to the invention is that the exhaust gas to be cleaned the evaporated (secondary) fuel already admixed before entering the combustion chamber, so that only a relatively small flame forms and the oxidation reaction of fuel vapor and the organic in the exhaust gas Compounds primarily takes place as gas phase oxidation.

Claims (11)

A process for vaporizing and burning liquid fuel in which the liquid fuel is burned as a secondary fuel following a run-up phase with a primary fuel, characterized by the following steps during phases (a) and (b): (a) during a first phase (start-up phase ) - is a primary fuel of a combustion chamber ( 24 ; 112 ) and burned, with combustion and exhaust gases flowing in a preferred flow direction through the combustion chamber, - is formed as a heat exchanger, within the combustion chamber ( 24 ; 112 ) located in the combustion and exhaust gas flow of the primary burner evaporator ( 14 (b) during a second phase (stationary phase) - is the air or the purge gas in the evaporator ( 14 ) is replaced by secondary fuel after reaching a certain temperature at a predetermined point within the combustion system, - the secondary fuel is passed through the evaporator ( 14 ) within the combustion chamber ( 24 ; 112 ) in countercurrent to the combustion and exhaust gases of the primary burner ( 26 ; 124 ) and introduced before or into the combustion chamber, - the supply of the primary fuel is reduced. A method according to claim 1, characterized in that the secondary fuel output of a substantially isothermal high temperature region in the combustion chamber ( 24 ; 112 ), more preferably in the evaporator ( 14 ) and / or in the exhaust gas discharge ( 22 ; 110 ) is supplied. A method according to claim 2, characterized in that at least 600 ° C, preferably at least 800 ° C are measured before in phase (b) that in the evaporator ( 14 ) purge gas is replaced by the liquid secondary fuel. Method according to one of claims 1 to 3, characterized that the primary fuel supply in phase (b) depending from the secondary fuel supply is reduced and preferably shut down to zero. Method according to one of claims 1 to 4, characterized that the primary fuel supply dependent on is controlled by the exhaust gas temperature. Method according to one of claims 1 to 5, characterized in that purge air and / or secondary fuel outside the flame region of the primary burner ( 26 ; 124 ) are introduced. Method according to one of claims 1 to 6, characterized in that the combustion and exhaust gas flow within the combustion chamber ( 24 ; 112 ) is recirculated. Method according to one of claims 1 to 7, characterized that the secondary fuel is supplied with the recirculated fuel and exhaust gas. Method according to one of claims 1 to 8, characterized in that the secondary fuel with the combustion air for the primary burner ( 26 ; 124 ) is supplied. Method according to one of claims 1 to 9, characterized in that with the combustion air for the primary burner ( 26 ; 124 ) is supplied oxidatively by post combustion to be cleaned exhaust gas. Method according to one of claims 1 to 10, characterized that the secondary fuel an oil, preferably a vegetable oil or a vegetable oil containing mixture.