EP0210205B1 - Device for combustion of liquid and gas fuels producing nitrogen oxide-free exhaust gases - Google Patents

Abstract

A method for a four-step nitrogen oxide-free transformation of gas and liquid fuels with air in heat generators comprises the precombustion of a partial fuel gas stream into a cooled ring chamber (40), followed by the catalytic transformation of said partially cooled fuel gas with the remaining gas quantity, by the cooling of the gas thus cracked into a heat exchanger (42), by the precombustion of part of said cracked gas in another cooled ring chamber (41) and by the transformation of said flue gas with the remaining quantity of cracked gas in a second catalyst into a flue gas with minimum air excess. Said flue gas is then cooled into a second heat exchanger (43). The method comprises the combination in a single heat exchanger unit of all the four steps of heat exchange, comprised of the cooling in the annular chambers (66, 68) and the heat exchangers (42, 43) mounted downstream of the catalysts. The device used to implement such method comprises air admission devices (45, 61), the fuel admission device (44), the cracked gas admission devices (49, 58) and two water-cooled ring chambers (66, 68) containing catalyst blocks, as well as two heat exchange stages (42, 43).

Description

The invention relates to a combustion unit for liquid and / or gaseous fuels with air in a heat generator.

Methods and devices for the combustion of liquid and gaseous fuels with nitrogen oxide-free exhaust gases are already known. The aim is to burn fuel gases such as natural gas, LPG or heating oil in such a way that no nitrogen oxides are generated.

In the case of previously known gas and oil combustion plants, it is customary to burn the fuels in a flame which, at least locally, has temperatures well above 1,300 ° C. and thus generates nitrogen oxides. In addition, an excess of air is required for complete combustion, which prevents the relatively complete utilization of the heat release. Efforts to reduce nitrogen oxide formation led to a greater cooling of the flames and thus to a further reduction in the heat utilization of the fuel. In addition, dividing the reaction into a gasification reaction with partial catalytic oxidation and subsequent cooling of the fuel gas produced and subsequent combustion in a second stage did not give the desired result. The intermediate cooling of the fuel gas dissipated only little heat, and in the second stage significantly higher temperatures were generated, which both limited the durability of the catalysts and led to nitrogen oxide formation due to overheating. In addition, ignition problems arose in such a device since, under the given conditions of a reducing atmosphere, larger ignition energies would be required to start the device.

In connection with internal combustion engines, a device for generating fission gas is known (US-A-4131 086), in which fuel from hydrocarbon and air are mixed in a "rich" mixture ratio in a combustion chamber. After their ignition and combustion, the resulting combustion gases leave the combustion chamber, heat a catalytic reaction chamber via a heat exchanger and - before they enter it - are again mixed with fuel of the above type. This prevents the second supply line of fuel from coming into direct contact with the flames in the combustion chamber. This is to achieve an endothermic reaction with little air or little oxygen in the downstream catalytic reaction chamber, so that heat dissipation is avoided. However, the problem of the combustion of fuel gases without nitrogen oxides has not been addressed.

To remedy this, the invention proposes a combustion unit of the type mentioned at the outset, which has the following: a combustion chamber, into which a fuel / air mixture is fed via a first line; an ignition device for the fuel / air mixture to form a hot combustion gas; a cooled outer wall belonging to the combustion chamber for cooling the combustion gas; a mixing space which is formed within the combustion chamber for mixing the cooled combustion gases with additional fuel, the additional fuel being admixed via a second line; a catalytic reaction chamber downstream of the combustion chamber for reaction with the cooled combustion gases which are already mixed with the additional fuel; and a heat exchanger downstream of the catalytic reaction chamber. In a further development from the special point of view of the generation of cracked gas, the combustion unit can be provided with a line leading from the heat exchanger, which line is connected to the first and second line of a downstream combustion unit, preferably of the type according to the invention.

With the above-mentioned development, the reaction of the conversion of the fuel with the air is achieved at all points, so that the heat release by the combustion reactions and subsequent flue gas cooling can take place in a temperature range below 1300 ° C. or under a reducing atmosphere, or nitrogen oxides formed in a reducing atmosphere under catalytic action can be reduced. Only about half of the gaseous fuel, in the range between 30 and 70%, is almost completely burned with the total air of the first stage in a preliminary stage in a cooled ring chamber. The hot flue gases only cool down to temperatures of 1200 to 1600 ° C in the annular chamber, which only has 1-2% of the total heat exchange surface. They are mixed with all the remaining combustion gas at the top of the cylinder and, in the mixed state, are introduced into a catalyst which, while the fuel gas / exhaust gas mixture cools, converts it to a fuel gas containing CO and H2. This conversion is necessary because such a fuel gas burns more easily and soot-forming side reactions after mixing the gas are prevented by the catalytic reactions. After the gas has left the catalyst, it is cooled in a heat exchanger stage to temperatures above the dew point and fed to the second stage in two partial streams.

In the case of a liquid fuel, the conversion in the 1st stage takes place in that a partial stream of the gasification gas formed is returned to the ring chamber of the 1st stage and there completely burns with the partial stream of air. The amount of liquid fuel added is added to the hot combustion gas at the top of the 1st stage. As in the case of gaseous fuel, the mixture converts to a fuel gas in the 1st stage catalyst.

In addition, it is possible to arrange the uppermost ceramic or metal plate of the catalyst unit at the point where the liquid jet hits meets. This plate has a hole that is so small that only about half of the oil reaches the next plate directly. The scarce half of the injected oil is reflected and burned in the flame above the plate.

The resulting flue gases cool down partly with radiation and convection with the surrounding water-cooled surfaces, mix with the unburned oil to form a reactive mixture and are converted into fuel gas in the subsequent catalyst block.

In contrast to the gaseous fuel, not only can the entire amount of gasification gas be supplied to the second stage in the case of the liquid fuel, but a partial stream can be returned to the annular chamber of the first stage.

Small portions of the liquid fuel are added to the ring chamber for the starting process until the gasification gas is formed.

To protect the catalyst of the 2nd stage, approximately half of the gasification gas (30 to 90%) with the total amount of combustion air from the 2nd stage is burned in an annular chamber and partially cooled by the water jacket of this annular chamber. Due to the small surface of the annular chamber there is a cooling down to approx. 1000 ° C (800 to 1100 ° C), so that in the head of the chamber with the addition of the remaining quantity of gasification gas a mixture quantity of approx. 600 ° C is formed, which in the subsequent catalyst is converted to a clean exhaust gas with a small excess of air.

The subsequent heat exchanger ensures that the heat content in the exhaust gas is almost completely given off to the heating medium in the pipes, for example process water or water from the heating circuit. The almost complete heat dissipation is favored by the fact that combustion of the gas in the catalytic converter does not result in a flame volume and no soot-containing by-products which impair the heat transfer to the pipes.

The device according to the invention consists of the mixing heads of the two stages closed off with perforated plates with the gas inlets in the upper part of the head and the gas outlets through the perforated plates, from the cooled annular chambers with the mixture inlets and ignition devices with the catalyst located in the center and the subsequent heat exchangers.

The device contains the gas transfers from the 1st stage with an inlet into the ring chamber of the 2nd stage and an introduction into the mixing head.

• Fig. 1 eine erfindungsgemäße Verbrennungseinheit in zweifacher, hintereinandergeschalteter Ausführung,
• Fig. 2 eine Verbrennungseinheit in einfacher Ausführung,
• Fig. 3 eine Verbrennungseinheit in einfacher Ausführung, die zum Anschluß an die Verbrennungseinheit gemäß Fig. 2 geeignet ist,
• Fig. 4 eine axiale Ansicht sowie eine querschnittliche Ansicht eines Wärmetauschers und
• Fig. 5 ein Wärmezeugersystem mit mehreren erfindungsgemäßen Verbrennungseinheiten.

Further features, details and advantages of the invention emerge from the subclaims and the following description of preferred embodiments of the invention with reference to the drawing. Each shows in a schematic representation:

• 1 shows a combustion unit according to the invention in double, series-connected design,
• 2 a combustion unit in a simple design,
• 3 shows a combustion unit in a simple design, which is suitable for connection to the combustion unit according to FIG. 2,
• Fig. 4 is an axial view and a cross-sectional view of a heat exchanger and
• Fig. 5 shows a heat generator system with several combustion units according to the invention.

With 101 the first line for the entry of the gas-air mixture of the 1st stage is designated, which admits the fuel gas stream mixed with the combustion air of the 1st stage into the annular combustion chamber 103 of the 1st stage. This fuel gas-air flow is ignited by the ignition device, for example a spark plug 102.

The hot burned gas sweeps along the medium-cooled outer wall 125 on the way up through the combustion chamber 103 and is thereby cooled.

The partially cooled exhaust gas reaches the head of the combustion chamber 103, where the remaining amount of fuel gas is mixed with the hot flue gas. The use of a mixing gap 105, which is formed by the perforated plate 106 and the upper boundary of the catalytic reaction chamber 107, is advantageous for this purpose. The hot flue gas sucks in the remaining amount of fuel gas in this gap, which is introduced into the gas chamber 108 from above through the perforated plate 106.

The mixing of the components is improved by the inlet opening 109 and the chamber-like mixing space 110 located in front of the catalyst, so that the hot mixture has a homogeneous concentration distribution when introduced into the catalyst 111 of the catalytic reaction chamber 107. This is necessary because the catalyst 111 can consist of a catalyst honeycomb that prevents the gases from mixing in the catalyst. The catalyst 111 is clamped by an insulation mat 112 in the housing 113 and thermally insulated, so that the active substance of the catalyst 111 remains protected by the higher temperatures in the combustion chamber 103 surrounding the catalyst.

After the catalyst 111, the heat exchanger 114 is arranged, which cools the resulting cracked gas to a temperature above the dew point temperature.

The cracked gas discharged from the heat exchanger 114 into the line 115 passes through the line 116 together with the combustion air of the second stage into the channel-like and annular combustion chamber 117 of the second stage.

The ignition device 118, which ignites the mixture of the combustion chamber 117, is also located there.

The combustion of the amount of cracked gas in the annular chamber is highly stoichiometric, i.e. the amount of air is sufficient to completely burn the gas.

At the upper end of the annular chamber is the gas chamber 119, which catalyzes the perforated plate 120 and the upper cover plate of the other table reaction chamber 121 forms the mixing chamber of the flue gas of the combustion chamber and the remaining amount of fission gas. This subset of the cracked gas is introduced into the gas chamber 119 through the line 122.

The mixture of the flue gas with excess air and the cracked gas enables the gas 123 to be converted into a slightly overstoichiometric flue gas from which the heat can be obtained quite effectively.

This takes place in the subsequent heat exchanger 124, which enables the flue gas to be cooled as completely as possible.

Fig. 2 shows a further structure of the cracked gas generating part according to the invention. The base body, which contains the device for the ignition device 204 and for the injection nozzle 202, which injects the fuel discontinuously and in a controlled manner, is designated by 201. The flame chamber of the combustion chamber 211 is designated by 203, where the flame, which is cooled by the surrounding water-cooled outer walls 205, is formed by the reflection of part of the oil, the mixing with the gasification air, and ignition by the ignition device 204. A part of the gasification air is led directly into the vicinity of the ignition device 204 through a small bore 206 which is provided with an air filter 207. The cooling of the base body 201 takes place in such a way that the required gasification air is sucked through the inlet opening 208 of the cover hood 209, in order to then sweep past the surface of the base body 201 and to pass through the outlet 210 into the foot of the combustion chamber 211 below the flame arrester 212.

The hot flue gases arising in the flame chamber 203 mix with the unburned oil, which was not reflected by the storage plate 213 with the bore 214. The mixture enters the catalyst 215, which consists of one or more catalyst blocks. There the mixture of hot flue gas and oil vapor converts to a cracked gas consisting essentially of CH4, CO, H2 and the exhaust gas components.

The hot cracked gases are cooled in a subsequent heat exchanger (not shown in FIG. 2) and mixed with air in the second stage in accordance with the content of the older national DE application P 35 03 413.0 converted to flue gas.

3 shows the construction of the combustion part according to the invention. 320 with the base plate is designated, through the inlet 321, a portion of the cracked gas can flow into the combustion chamber 322. The combustion air flows through the throttle device 323 to the outlet opening 324 and thereby cools the base plate 320. The air preheated in this way mixes at 325 with the remaining cracked gas. This mixture is ignited with the ignition device 326. The flame cools down on the surrounding water-cooled wall surface 327. In the combustion chamber 322, the exhaust gases mix with the cracked gas from 321. In the catalyst system 328, which can consist of one or more catalyst blocks, the oxidation takes place with the remaining cracked gas products to give exhaust gas.

Fig. 4 shows the structure of a heat exchanger element. The split or exhaust gas flows through the pipes 31 fastened in the base plate 30 and heats the cooling water on the shell side, which enters at 32 and exits again at 33. Due to the round outer cylinder of the heat exchanger 34, increased water pressure with thin walls is possible.

It has been shown in the heat exchangers that it is expedient to use straight tube heat exchangers which, in 3 or 4 blocks in succession, effect the cracked gas cooling, the exhaust gas pre-cooling, the exhaust gas after-cooling and the condensation of the flue gas moisture and thus heat the heating water in countercurrent.

5 shows the structure and flow pattern of the individual material flows. The fission gas generation part is symbolized by 40 and the combustion part by 41. 42 denotes the cracked gas heat exchanger in the form as shown in FIG. 4. 43 denotes the heat exchanger system, consisting of one or more heat exchanger elements of the same type, as they were shown in Fig. 4.

The heating oil for heat and fission gas is injected at 44. The air for the partial combustion enters the cover at 45, leaves it at 46 and is then passed below the flame arrester at 47 into the annular space. At 48, the cracked gas leaves the cracked gas generating part 40 and is cooled in the heat exchanger 42. A part of the cracked gas leaves the idle train 50 at 49 in order to be guided into the head of the combustion part 41 via a control member 51 at 53. At 58 the remaining part of the cracked gas is branched off, at 59 mixed with the air; which enters the cover at 60 via the throttle element 61 and exits again at 62. The hot exhaust gases leave the combustion part 41 at 54, are cooled in the heat exchanger system 43 and leave the device according to the invention at 55. The blower 56 generates the resistance-related negative pressure in the device and thus sucks all gases through the device and sends them into the chimney 57.

The cold water enters the heat exchanger system 43 at 63, passes through the pipe connection 64 into the fission gas heat exchanger 42, which it leaves again at 65. At 66, the water enters the foot of the annular gap of the cracked gas generating part 40 and is conducted at the head thereof via the pipe connection 67 into the annular gap of the combustion part 41. Warmed to its usage temperature, the warm water leaves the device according to the invention at 68 in order to be forwarded to the individual consumers via line 69. Embodiments

The first exemplary embodiment (FIG. 1) describes the temperature and volume flow curve of a nitrogen oxide-free combustion of natural gas with a thermal output of 100 kW.

The volume flow data refer to the standard state (0 ° C, 760 Torr).

Via the first line 101 (Fig. 1) to flow tangentially 0.013267 m ³ / s air and 0.001393 m ^3/2 CH4 in the combustion chamber 103 of the 1st stage gem. Fig. 1 and are ignited there with the spark plug 102. The gas mixture burns in the foot of the brewing chamber 103 at a temperature of approx. 2060 ° C. to 0.01466 m ³ / s flue gas.

A possibly inserted spiral made of heat-resistant material forces the exhaust gas jet to wind around 3 times on the way into the annular chamber head around the catalyst 111.

The exhaust gases sweep along the water-cooled outer wall 125 and cool down to about 1600 ° C.

When entering the mixing gap 105, the exhaust gases accelerate and generate a negative pressure, which causes a gas quantity of 0.001393 m ³ / s to be drawn in from the gas chamber 108 via the perforated plate 106.

The gas, which is now homogeneously mixed, passes through the inlet opening 109 and the mixing space 110 through the catalyst 111, where it reacts to 0.01884 m ³ / s of cracked gas in endothermic processes. Before entering the first stage heat exchanger 114, the gasification gas has a temperature of 886 ° C. and a temperature of approximately 130 ° C. at the outlet.

The cracked gas leaves the 1st combustion stage via line 115.

0.01413 m ³ / s of cracked gas and 0.013267 m ³ / s of air flow tangentially through line 116 into the ring channel of the second stage and are ignited there with the ignition device 118. The gas mixture burns at the foot of the combustion chamber 117 of the second stage at a temperature of 1280 ° C to 0.02531 m '/ s flue gas.

On the way to the head of this combustion chamber 117, the gas circulates with the aid of a heat-resistant spiral about 3 times around the catalyst 123 and cools down to about 1060 ° C. on the water-cooled outer wall 126.

In the mixing zone, the remaining amount of cracked gas of 0.00471 m ³ / s is fed to the flue gas via line 122 of gas chamber 119 and perforated plate 120, mixed homogeneously via the inflow opening and the mixing chamber and fed to the catalyst.

The flue gas / cracked gas mixture is converted into 0.02932 m ³ / s flue gas in exothermic processes.

Before entering heat exchanger 124 of the second combustion stage, the flue gas has a temperature of 1260 ° C. In heat exchanger 124, it is cooled to approx. 45 ° C. and leaves the second combustion stage via line 127 without nitrogen oxide.

Special features of the method according to the invention are explained in more detail in the second exemplary embodiment:

The energy of a fuel oil flow of 0.00046 kg / s, which corresponds to an equivalent energy potential of 20 kW, is to be implemented free of nitrogen oxide and used to heat water to 90 ° C.

20-degree air flows with a volume flow of 9.59 m3iN / h over the cover plate of the cracked gas generating part and heats up by approx. 5 ° C. A pipe connection then leads it into the foot above the flame arrester in the annular gap of the fission gas generation part. Above the flame arrester, the atmospheric oxygen burns with part of the injected oil at an average temperature of 1900 ° C. The resulting exhaust gas of 10.39 m3iN / h combines with the remaining oil in the catalyst system, giving off heat in 12.98 m3iN / h fission gas at an average temperature of 955 ° C. The cracked gas is cooled to 100 ° C in the subsequent heat exchanger.

The 100-degree cracked gas flow (12.98 m3iN / h) is divided in the combustion stage in such a way that 9.73 m3iN / h are conducted into the foot of the annular gap and 3.25 m3iN / h into the head. The air volume of 9.59 m3iN / h required for the combustion flows over the cover plate of the combustion head, warms up by approx. 3 ° C, is mixed with the cracked gas stream, which is led into the foot of the annular gap, and ignited. At approx. 1350 ° C the gas mixture burns to 17.82 m3iN / h exhaust gas. It emits heat into the combustion chamber head and is mixed here with the remaining cracked gas. In the subsequent catalyst system, the free oxygen from the exhaust gas stream oxidizes with the components of the cracked gas to a total of 20.55 m3iN / h exhaust gas. In the following heat exchanger system, the exhaust gas is cooled to approx. 43 ° C with condensation.

The described gasification / nerburning process releases approximately 35% of the energy contained in the heating oil in the gasification stage and approximately 65% in the combustion stage. The water-cooled walls of the gasification and combustion stage play an important role in the heat dissipation, since together they dissipate approx. 20% of the sensible heat into the water.

A third exemplary embodiment of the device is described below with reference to FIG. 1.

The CH4 / air mixture flows tangentially through the first line 101 into an approximately 5-30 mm wide and approximately 150-300 mm high ring channel 103, in which it is ignited in the foot with a spark plug 102. The flue gas then flows into the head of the ring channel 103 while cooling.

In the approx. 4-15 mm wide annular gap 105, the flue gas mixes with the CH4, which is fed in via a perforated plate 106, then passes through the inlet opening 109 into the Mixing space 110 and then flows through the catalyst 111. Both the mixing space 109 and the catalyst 111 have a diameter of 100-150 mm.

The heat exchanger 114 of the 1st combustion stage consists of smooth tubes in the region of the gas temperatures of over 700 ° C., and finned tubes in the temperature range below.

Due to the catalyst honeycomb, the flame length is kept very short, so that an empty flame / blasting space is dispensed with and the first layer of smooth tubes can therefore be installed about 10 mm behind the catalyst.

The installation of several throttle cables ensures that the fission gas is in the speed range of w (o) = 1-2 m / s.

In the second combustion stage, a partial stream of the cracked gas is branched off, mixed with air and conducted and ignited in the base of the 5-30 mm wide and 150-300 mm high ring channel.

The first gas inflow lines 101 (1st stage) and 116 (2nd stage) are each equipped with flame arresters.

The flow and mixing path of the gas in the 2nd combustion stage is identical to that in the 1st combustion stage. The dimensions of the annular or gap-shaped combustion chamber, the admixture of the remaining cracked gas, the mixing device and the catalyst are also kept approximately identical to those of the 1st combustion stage.

The design criteria for the second stage heat exchanger 124 are the same as for the first stage heat exchanger 114, i.e. in the area of gas temperatures over 700 ° C smooth tubes, then finned tubes.

The construction of several throttle cables is also planned in order to maintain an adequate gas speed.

The catalytic combustion and the associated short flame length also allow the 1st smooth tube layer to be installed approx. 10 mm behind the catalytic converter.

Fourth embodiment of the device

The air for the gasification stage flows through the cover hood, which has a diameter of 150 mm, and passes through a pipe, NW 40, into the foot of the annular gap with an outer diameter of 169 mm and an inner diameter of 152 mm. From here, the air passes the flame arrester, which holds about 40% of the free annular space with its holes.

In the flame chamber, part of the oil burns, the rest with the exhaust gas into the catalyst system, which consists of three individual catalyst blocks, each 30 mm deep and 100 mm in diameter. The boundary to the flame space is formed by a storage plate, which reflects 50% of the oil when it hits the flame space, but lets the other 50% through a fine hole of approx. 1 mm. The external dimensions of this storage plate correspond to those of a catalyst block.

According to the catalyst system, the cracked gas flows through a cooler with a diameter of 159 mm and a length of 230 mm, the water to be heated on the jacket side and the gas on the pipe side flowing through 121 pipes, NW 10.

After the heat exchanger, the gas flows from bottom to top through an empty train with the dimensions 200 x 180. At the end of this train, part of the cracked gas, regulated by a butterfly valve, is fed into the head of the combustion cable through a NW 40 pipe. The remaining cracked gas at the end of the empty train is also removed through a pipe NW 40, mixed with the air that is sucked in through the cover, ignited and passed into the annular gap of the combustion part, which has the same dimensions as that of the cracked gas generation part. In the combustion chamber, the mixture with the cracked gas and the conversion to exhaust gas takes place in the catalyst system, which is identical to that of the cracked gas generating part. Only the storage plate is replaced by an additional catalyst block.

The exhaust gas is cooled in a heat exchanger system. This system consists of three individual heat exchangers, each with the same dimensions and the same structure as the heat exchanger for cracked gas cooling. The heat exchange itself takes place in counterflow. The exhaust gases are drawn off via a pipe NW 40 via a blower, which generates a vacuum of 50 mmWS, and fed into the chimney.

Reference symbol list (Fig. 1)

• 101 - (mixture entry) first line
• 102 - Ignition device, spark plug
• 103 - (annular chamber) annular combustion chamber
• 104 - not occupied
• 105 - mixing gap
• 106 - perforated plate
• 107 - (Catalyst chamber) catalytic reaction chamber
• 108 - gas chamber
• 109 - Inlet opening
• 110 - (Mixing chamber) chamber-like mixing room
• 111 - catalyst
• 112 - insulation mat
• 113 - housing
• 114 - heat exchanger
• 115 - Fission gas line
• 116 - line
• 117 - (second stage annulus) combustion chamber
• 118 - Ignition device
• 119 - gas chamber
• 120 - perforated plate
• 121 - mixing zone
• 122 - line
• 123 - catalyst
• 124 - 2nd stage heat exchanger
• 125 - outer wall
• 126 - 2nd stage outer wall
• 127 - line

Reference symbol list (Fig. 2)

• 200 - first line
• 201 - basic body
• 202 - injector
• 203 - Flame room
• 204 - Ignition device
• 205 - wall
• 206 - bore
• 207 - Air filter
• 208 - inlet opening (second line)
• 209 - cover
• 210 - outlet
• 211 - combustion chamber
• 212 - flame arrester
• 213 - storage disk
• 214 - bore
• 215 - catalyst

Reference symbol list (Fig. 3)

• 320 - base plate
• 321 - inlet
• 322 - combustion chamber
• 323 - throttle device
• 324 - outlet opening
• 325 - mixing room
• 326 - Ignition device
• 327 - wall surface
• 328 - catalyst system

Claims (12)

1. Combustion unit for liquid and/or gaseous fuels with air in a heat generator. having a combustion chamber (103, 203, 211), into which a fuel/air mixture is fed via a first duct (101, 200), having an ignition device (102, 204) for the fuel/ air mixture to form a hot combustion gas, having a cooled outer wall (125, 205) of the combustion chamber (103, 203, 211) for cooling the combustion gas, having a mixing chamber (110) inside the combustion chamber (103, 203, 211) for mixing the cooled combustion gases with additional fuel via a second duct (122, 206), having a catalytic reaction chamber (107, 215) connected in series for the reaction with the cooled combustion gases mixed with additional fuel, and having a heat exchanger (114) connected in series to the catalytic reaction chamber (107, 215).

2. Combustion unit according to claim 1, having a duct (115) for cracked gas, which duct is connected to the first and second ducts (116, 122) of a similar combustion unit connected in series (Fig. 1).

3. Combustion unit according to claim 1 or 2, characterised in that the catalytic reaction chamber (107, 215) has a plurality of catalyser blocks connected in series.

4. Combustion unit according to one of claims 1-3 wherein the combustion chamber (103) is formed substantially as the annular chamber surrounding the catalyser blocks (111).

5. Combustion unit according to one of claims 1-4, wherein the first duct (101) is formed for mixing the fuel with air in an over-stoichiometric ratio and the mixing chamber (110) is located immediately in the inlet region (109) to the catalytic reaction chamber (107).

6. Combustion unit according to one of claims 1-5, wherein the mixing chamber (110) is formed for mixing the partly cooled combustion gas with additional fuel by means of a perforated panel (106, 120) and a catalyser cover plate, which are mounted on the upper end in the combustion chamber (103).

7. Combustion unit according to one of claims 1-6, wherein a vortex chamber is interposed between the mixing chamber (110) and the catalytic reaction chamber (107).

8. Combustion unit according to claim 3 and one of claims 1, 2, and 4-7, wherein the catalyser blocks (111, 215) are each composed of an insulated, honeycomb-shaped block, which is mounted inside a cylindrical catalyser chamber (107), in such a manner as to be suitable for detoxifying exhaust fumes from combustion motors.

9. Combustion unit according to one of claims 1-8, wherein an oil injection valve or nozzle (202) is mounted in the combustion chamber (103, 203, 211), opposite which is a porous panel (213), which reflects 20 to 50% of the oil sprayed on to it into the combustion chamber.

10. Combustion unit according to claim 9, wherein the porous panel has a bore (214).

11. Combustion unit according to claim 9 or 10, wherein one or more catalyser panels are connected in series to the porous panel (213).

12. Combustion unit according to one of claims 1-11, wherein the heat exchanger is formed with straight tubes or as a straight tube heat exchanger.

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