DE8717721U1 - Boiler system with external exhaust gas recirculation - Google Patents

Description

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Waiter Dreizler, 7000 Stuttgart 1 Boiler system with external flue gas recirculation

The invention is based on a gas- or oil-fired heating boiler system equipped with a forced draught burner, in which an exhaust gas recirculation (ARF) is used to reduce nitrogen oxides (NO _x ) in the exhaust gas according to the preamble of the main claim.

It is known that the NO _x content in the exhaust gases of boiler systems can be reduced by means of an exhaust gas recirculation system or exhaust gas recirculation. Since the formation of NO _x depends on the flame temperature, the aim of the exhaust gas recirculation system is, among other things, to cool the flame temperature in order to reduce this content from over 100 ppm NO _x in the exhaust gases during normal combustion to under 50 ppm.

In a known boiler system with ARF (FR-PS 10587944) of the generic type, the ARF

A fan is arranged in the line in order to force some of the exhaust gases from the exhaust pipe back to the burner. Such boiler systems operating with an ARF fan have been known for more than 15 years and are used primarily in large-scale power plants and the like. With these known boiler systems, a reduction of NO _x in the exhaust gas is possible to as low as 50 ppm, with up to 25% of the exhaust gases from the smoke pipe being returned to the burner. Although this type of ARF has largely prevailed in practice, it does have considerable disadvantages. One disadvantage is that the ARF fan requires additional purchasing and monitoring expenditure, since such an ARF fan must be exhaust-proof and the power line to the fan motor is also subject to particular stresses.

Another disadvantage is the ongoing operating costs, for example for the electric drive and maintenance of the equipment. Especially with the

\ Application for smaller boiler systems, for example

In the household sector, for example, the operating noises caused by the exhaust fan can be disturbing. : In addition, the required air flow for such ARF fans

I' the necessary safety equipment, which

, must be checked continuously and of course also represent an additional source of interference. Another problem is that, starting from the relatively low

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At low temperatures of around 180°C, the recirculated exhaust gases are further cooled before being introduced into the burner of the boiler system due to the usually long exhaust gas removal line, which can lead to the formation of condensate in the exhaust gas removal line, particularly in the fan.

In another known boiler system with ARF (DE-OS 2365186), the very hot exhaust gas is sucked in in the combustion chamber in the area of the burner head of the forced air burner and led to the burner fan via a jacket pipe that coaxially surrounds the burner, where it is mixed with fresh air and returned to the combustion tube. The suction negative pressure of the burner fan is used to drive the ARF. With this type of exhaust gas recirculation, a certain reduction in the NO _x content in the exhaust gas by 10 - 15% is also achieved - but not the desired ^. 50 ppm, particularly because the exhaust gas temperatures are too high. With this recuperative exhaust gas recirculation, exhaust gas with temperatures of around 850° C is added to the fresh air, resulting in a significant increase in the mixture temperature before combustion, so that the desired cooling of the flame temperature required to reduce the NO _x in the exhaust gas cannot be achieved. The aim of these well-known ARF hot gases is primarily to achieve a blue flame combustion with a correspondingly high level of efficiency and not a low NO _x emission. In doing so, it is accepted that the fan of the oil or gas burner becomes extremely hot.

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with the consequence that thermal protection measures are required for various burner control devices. With this high-temperature ARF, the main effect is the low density of the hot exhaust gases, which corresponds to the temperature, so that when mixed with fresh air, they make up a large proportion of the volume, resulting in poor preparation conditions for the combustion air to be mixed with gas or oil. These processes for achieving a blue-burning flame are also more than 15 years old.

The invention with the characterizing features of the main claim has the advantage that, without an additional exhaust gas fan, exhaust gas values of less than 50 ppm NO _x can be achieved in the boiler system, thus meeting the desired hygiene requirements with little CO, little soot and little excess air. Because the relatively cool exhaust gases with temperatures between 150 and 180° C are mixed directly with the fresh air in the burner fan, any condensates that are still in a vaporous state are carried along and decomposed again in the subsequent combustion process. The amount of heat absorbed in this way causes a relative cooling of the flame temperature with the above-mentioned advantages of an extraordinarily strong reduction in the NO _x content in the exhaust gas, without any noticeable deterioration in efficiency in relation to fuel consumption. The place where the exhaust gases are taken from the boiler system,

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can be located in the exhaust pipe or in a boiler pass downstream of the combustion chamber - the only important thing is that the flue gas temperatures are ^. 200° C. The extraction cell can therefore advantageously be located near the burner fan in such a downstream boiler pass, so that only a short ARF line is required. This makes it possible to operate with extremely low ARF temperatures, especially in gas-fired systems (condensing boilers).

According to an advantageous embodiment of the invention, the combustion air blower works with a blower wheel (tangential blower), whereby the exhaust gas return line is guided through the outer wall of an air intake box or air intake pipe in the direction of the engine axis at least up to the front opening of the blower wheel. This ensures a largely uniform, optimal negative pressure for every position of the air control flap and/or the air throttle disc to convey the partial exhaust gas quantity supplied in the ARF line and a uniform distribution and mixing of the partial exhaust gas quantity with the combustion air in the area of the blower wheel.

According to a further embodiment of the invention, the air throttle disc is mounted on the section of the exhaust gas recirculation line arranged in the intake box so that it can move relative to an air intake opening and its position can be adjusted by means of a

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box, in particular a threaded spindle. Such a fixed adjustable air throttle disc is known per se (DE-OS 2365186), but not in connection with a modulating furnace. The air throttle disc is used to pre-set the air intake opening, while the actual adjustment of the current burner setting is carried out by the air control flap when the modulating fan burner is operating via an electronic burner control.

According to a further advantageous embodiment of the invention, the fan burner has a fuel-air composite control system for generating a modulating burner operation, with a fuel control element (gas control flap), an air control flap and a composite rod, as well as a servomotor for one of these control elements. The air control flap is connected to the fuel control element by the composite rod, so that when the fuel supply is reduced, the supply of combustion air is also throttled.

According to a further embodiment of the invention, the air throttle disc and/or the air control flap are arranged upstream of the fan wheel with a pivot axis running transversely to the direction of air flow, whereby the end piece of the exhaust gas return line runs perpendicular to the pivot axis and next to at least one of these control elements, namely in the quadrant not covered by its pivot area. This arrangement

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design, a space-saving arrangement is achieved.

According to a further advantageous embodiment of the invention, an exhaust gas control flap is arranged in the exhaust gas recirculation line, preferably outside the air intake box or the air intake pipe, which can be adjusted via a servomotor depending on combustion variables. The exhaust gas control flap enables the intake of partial exhaust gases to be adjusted, for example, to the combustion air throughput or the metered fuel quantity.

According to an advantageous development of this feature, the exhaust gas control flap is connected to the air control flap and/or the fuel control element via a linkage. This means that the exhaust gas partial quantity is adapted to the air flow rate assigned to the modulating burner setting. If the burner and thus the air setting is larger, the exhaust gas control flap is also opened further in order to allow a larger exhaust gas partial quantity to flow in with this operating position and to ensure a sufficient exhaust gas proportion in the combustion air for the desired NO _x reduction. On the other hand, the exhaust gas control flap uses its linkage to throttle the exhaust gas partial quantity at low power and lower air requirements in order to counteract the higher suction that occurs when the air control flap is closed more at the open end of the ARP line in the area of the fan wheel. In addition, upstream of the

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A manually adjustable exhaust throttle valve must be provided in the exhaust gas control valve in the ARF line, which enables the partial exhaust gas quantity to be throttled independently of the position of the exhaust gas control valve.

According to a further embodiment of the invention, the exhaust gas return line in the inner boiler area is guided through a water-carrying boiler jacket, so that the inlet of the exhaust gas return line is still located inside the boiler, but outside the combustion chamber. This embodiment achieves even cooler temperatures for the exhaust gas portion and a lower thermal load on the burner parts affected by it.

According to a further embodiment of the invention, the inlet of the exhaust gas recirculation line is directed against the exhaust gas flow. This advantageously increases the delivery pressure in the exhaust gas recirculation line.

According to a further advantageous embodiment of the invention, the exhaust gas recirculation line is designed to be flexible at least in sections and is preferably made of flexible stainless steel corrugated pipe.

According to a further embodiment of the invention, the exhaust gas recirculation line is thermally insulated from the outside. This advantageously keeps the heat losses of the recirculated exhaust gases to the outside low, which prevents the formation of condensates in the exhaust gas recirculation line.

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supply line is reduced.

Further advantages and advantageous embodiments of the invention can be found in the following description, the drawings and the claims.

drawing

Several embodiments of the subject matter of the invention are shown in the drawing and described in more detail below. They show:

Fig. 1 shows the heating boiler system according to the invention in partial section seen from above, according to the line I-I in Fig. 2;

Fig. 2 is a partial side view of the example shown in Fig. 1;

Fig. 3 is a representation corresponding to Fig. 1 of a second embodiment;

Fig. 4 a variant with fixed throttle disc in partial section and seen from above and

Fig. 5 shows another variant in the same representation.

Description of the embodiments

In the embodiments shown in Fig. 1-5, the inventive structure of boiler systems and fan burners with external exhaust gas recirculation

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- hereinafter also abbreviated to ARF - for the purpose of reducing NO _x to values below 50 ppm. Fig. 1 and 3 show a single-pass boiler 1 with "hot" combustion chamber 2, exhaust gas diversion 3, exhaust gas nozzle 4 and exhaust pipe 5.

Any commercially available boiler of a different design, for example with two or three boiler passes, can also be operated with the forced draught burner according to the invention for effective NO _x reduction.

A burner flame 7 of a blower burner 9 burns in a combustion chamber 6, which is formed by a ventilation housing 10 with motor 11 and combustion air blower wheel 12, a burner housing 13 with burner head 14 and fuel supply 15 as well as with solenoid valve 16, gas control flap 17 and other gas safety fittings, as well as a burner flame tube 18 in its main components. An air intake box 19 or alternatively an air intake nozzle 20 (Fig. 3) is tightly attached to the inlet of an intake opening 21 of the valve housing 10. The air intake box 19

- or alternatively the air intake port 20 - has a combustion air cross-section 22a or 22b upstream that is open to the atmosphere.

Fig. 1 and 3 show a liebläse burner according to the invention with continuously modulating operation in a view from above, with the boiler in the burner and exhaust gas nozzle plane in section

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I-I is drawn according to Fig. 2. The fan burner is shown in a partial section through the plane of the air intake opening 21 of the fan housing 10.

Fig. 2 shows a side view of this gas blower burner according to the invention from the outside with a partial view of the boiler 1. As can be seen from Fig. 1, the air intake box 19 is firmly and tightly mounted in front of the intake opening 21 on the ventilation housing 10; it has an end (combustion air cross-section) 22a that is open to the atmosphere at a right angle to the right of the intake opening 21, the air passage cross-section of which can be changed in a known manner by an air control flap 23a depending on the modulating burner setting. According to the invention, an end piece 32a of an exhaust gas recirculation line (ARF line) 35 is guided from the outside through the wall 25 of the air intake box 19 and further through the air throttle disc 24a so far inwards that the open end extends into the plane of the fan wheel 12 by means of an air throttle disc 24a arranged in an adjustable manner between the air control flap 23a and the fan wheel 12 in front of the air intake opening 21. At this point, there is a largely uniform, optimal negative pressure for every position of the air control flap 23a and/or the air throttle disc 24a to convey the partial exhaust gas quantity supplied externally in a manner to be described in the ARF line 35, whereby in the area of the fan wheel 12 there is a uniform

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Distribution and mixing with the combustion air occurs. In this way, mechanical conveying by means of special exhaust gas blowers can be dispensed with, the decisive feature of the present invention. A different arrangement of the end piece 32c of the ARF line 35 is shown in dashed lines in Fig. 1, in which a suitable negative pressure is also ensured.

Fig. 1 shows the further design of the air throttle disc 24a, which is mounted twice on the end piece 32a of the ARF line 35 via a bracket 39 connected to it and is arranged so as to be displaceable via a threaded spindle 26 and an adjustment knob 27 in order to be able to preset the air intake opening 21. The air control flap 23a is used for the actual adjustment of the current burner setting when the modulating fan burner is operating under electronic burner control. The simultaneous control of the fuel supply 15 via a connecting rod does not need to be discussed here. Connected to the air control flap 23a via a further connecting rod 28a is an exhaust gas control flap 29, which is also installed according to the invention in the ARF line 35 upstream outside the intake box 19 and ensures that the exhaust gas partial quantity is adjusted in accordance with the air throughput assigned to the modulating burner setting. If the burner and thus the air setting is larger, the exhaust gas control flap 29 is also opened further in order to allow a larger amount of exhaust gas to flow in in this operating position and to ensure a sufficient proportion of exhaust gas in the combustion air for the desired NO _x reduction.

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afford.

On the other hand, the exhaust gas control flap 29, via its connecting rod 28a, causes a throttling of the exhaust gas partial flow at low power and lower air requirements in order to counteract the higher suction; which occurs when the air control flap 23a is more closed at the open end of the ARF line 32a in the area of the fan wheel 12.

The ARF line 35 is attached to the wall 25 of the air intake box 19 with a flange 33.

A manually adjustable exhaust throttle valve 30 is installed upstream of the exhaust control valve 29 in the external (outer) EGR line 35. It enables the partial exhaust gas quantity to be throttled in advance, independent of the position of the exhaust control valve 29.

The ARF line 35 is routed around the outside of the boiler 1 and opens into the exhaust pipe 5 behind the exhaust nozzle 4 of the boiler 1, whereby it is attached to the exhaust pipe 5 with a flange 38 and opens at an angle or alternatively in an arc shape (Fig. 3) with an open end 37 pointing upstream. This is intended to increase the discharge pressure by an additional exhaust gas backup. The ARF line 35 is preferably partially designed as a flexible pipe.

Alternatively, the ARF line with its open

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End 37 through the water-carrying part of the boiler 1 into a downstream boiler pass (shown in dash-dotted lines in Fig. 1), for which the boiler must be adjusted by the manufacturer. This variant leads to even more cooled temperatures of the boiler part and enables a lower thermal load on the burner parts it affects. Depending on the boiler design and the number of downstream boiler passes, the ARF line is introduced in the front, side or rear part of the boiler.

Fig. 3 shows a view from above with a section through the boiler 1 at the height of the exhaust gas nozzle center and a partial section through the fan burner 9 in the plane of the air intake opening 21, another embodiment with a cylindrical air intake pipe 20 which lies close to the ventilation housing 10 in front of the intake opening 21 and whose cylinder axis is arranged approximately centrally to the motor and fan wheel axis and has a fixed adjustable air throttle disk 24b at its open end 22b. In the direction of the air intake opening 21 - downstream - the air control flap 23b required for the modulating fan burner is mounted, driven by the servomotor 36 (Fig. 2), which in turn adjusts the exhaust gas control flap 29 mounted in the ARF line 35 via the connecting rod 28b - as already described - in the same way. The air throttle disc 24b arranged at the open end 22b serves to preset the

17.07. 1989 Su/Wi - 15 - the • a ·· a· at a· · · G1590 position Air control flap also at open

23b nor sufficient suction for conveying the exhaust gas partial quantity at the end piece 32b of the ARF line 35, which is inserted laterally near the fan housing 10 into the air intake pipe 20 and bent at a right angle to the fan wheel. The place where the ARF line 35 is inserted is selected in the area of the quadrant 34 not covered by the air control flap 23b, which swivels by approximately 90°. The air control flap 23b and the air throttle disc 24b can also be moved closer together in terms of axial distances if the quadrants 34 not covered by the swivel angle for the adjustment range are selected to "overlap".

In further addition to the external EFR line 35 according to Fig. 3, the exhaust throttle valve 30 is installed upstream of the exhaust control valve 29.

The end piece 32b of the ARF line 35 can be introduced into the air intake pipe 20 from different directions (horizontally from the front or back, vertically from above or below) if the air control flap 23b and the air throttle disc 24a are also pivoted. A particularly space-saving arrangement of the components within the air intake pipe 20 is therefore achieved, as already described, by the air throttle disc and the air control flap being in the non-covered quadrant of the pivoting range.

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overlap and the ARF line is also introduced in such a quadrant 34.

Fig. 4 shows a variant of the end piece 32b of the ARF line 35 with a modulating fan burner for the arrangement in the air intake pipe 20b. Instead of the air throttle disc 24b, a fixed throttle disc 31 is used.

Fig. 5 shows another variant with a single-stage fan burner design. Here, the components "air control flap" and "composite rods" for stepless control of the combustion air are omitted. Instead, the combustion air is preset in a shortened air intake pipe 20c using the air throttle disc 24b. In addition, the ARF line only has the exhaust throttle flap 30.

As shown in dash-dotted lines in Fig. 1 and 3, the air control flap 23c can also be arranged downstream of the fan wheel 12. The connecting rod 28c is then modified accordingly.

In the case of external exhaust gas recirculation, whenever the exhaust gas recirculation line 35 has cooled down, for example during combustion breaks, condensate can form in this exhaust gas recirculation line 35, which can be collected in a condensate cup 40 arranged at the lowest point of the exhaust gas recirculation line 35. As soon as the exhaust gas recirculation line 35 is warm

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This condensate is evaporated again and added to the combustion air as steam.

In order to keep the condensate content as low as possible and also to keep other heat losses of the recirculated exhaust gases as low as possible, the exhaust gas recirculation line 35 is thermally insulated from the outside by a jacket 50. Furthermore, the exhaust gas recirculation pipe 35 can consist of a flexible corrugated pipe made of stainless steel, particularly at the curved points 51.

When the invention is used for condensing boilers, ie boilers in which the efficiency is increased by keeping the boiler water temperature as low as possible, close to the water temperature supplied to the radiators, among other means, the exhaust gas temperatures are 50 ^° C, so that a constant condensate is formed, which must also be continuously drained away. A siphon pipe 52 can be used for this, as shown in dashed lines in Fig. 1, which must also be arranged at the lowest point of the exhaust gas return line 35.

All features presented in the description, the following claims and the drawing can be essential to the invention both individually and in any combination with one another.

17.07.1989 Su/Wi boiler G1590 Combustion chamber Reference number list Exhaust gas diversion 1 Exhaust nozzle 2 Exhaust pipe 3 Firebox 4 Burner flame 5 Blower burner 6 Ventilation housing 7
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9 Blower wheel 10 Burner housing 11 Burner head 12 . Fuel supply 13 Solenoid valve1 14 Gas control valve 15 Burner flame tube 16 Air intake box 17 Air intake pipe 18 Air intake pipe 19 Air intake pipe 20 Air intake opening 20b Combustion air cross-section 20c Combustion air cross-section 21 Air control flap 22a Air control flap 22b Air control flap 23a Air throttle disc 23b Air throttle disc 23c Wall of 19 24a Threaded spindle (boiler draft) 24b Adjustment knob 25 Composite rods 26 Composite joints 27 Composite rods 28a Exhaust control flap 28b Exhaust throttle valve 28c permanently mounted throttle disc 29 End piece of the ARF line 30 End piece of the ARF line 31 End piece of the ARF line 32s 32b quadrant 32c ARF management 33 Actuator 34 flange 35 Bracket connection 36 Condensation cup 38 Coat 39 Curvature point 40 Siphon pipe 50 51 52

Claims (11)

17.07.1989 Su/Wi G 1590 Walter Dreizier, 7000 Stuttgart 75 Heating boiler system with external exhaust gas recirculation Protection claims 1. Boiler system - with a gas or oil fired boiler - with a forced air burner for gas or oil, which has a drive motor, a combustion air blower, a ventilation housing, a burner head, a flame tube and an air throttle disc that controls the maximum air quantity, in particular an arbitrarily adjustable air throttle disc, - with an exhaust pipe - and with an external (outside the boiler) exhaust gas return line,
characterized, that the exhaust gas return line (32a,b,c, 35) has its inlet in the exhaust gas pipe (5) or in a boiler flue (4) downstream of the combustion chamber (6). 17.07.1989 Su/Wi
G1590 (37) and opens into the negative pressure area of the combustion air blower (12) 2. Heating boiler system according to claim 1, characterized in that the combustion air blower works with a blower wheel (12) (tangential blower) and that the exhaust gas recirculation line (32a, b, c, 35) is guided through the outer wall (25) of an air intake box (19) or air intake pipe (20) in the direction of the engine axis at least up to the front opening of the blower wheel (12). 3. Heating boiler system according to claim 1 or 2, characterized in that the fan burner (9) has a fuel-air compound control system with a fuel control element (gas control flap) (17), an air control flap (23a, b, c) and a compound rod (28a, b, c) as well as a servomotor (36) for one of these control elements (17, 23a, b, c). 4. Heating boiler system according to claim 2 or 3, characterized in that the air throttle disc (24a) is mounted displaceably relative to an air intake opening (21) on the section (32a) of the exhaust gas recirculation line (35) arranged in the intake box (19) and that its position can be changed via a device (27), in particular a threaded spindle (26), accessible from outside the intake box (19). 17.07.1989 Su/Wi
G1590 5. Heating boiler system according to one of the preceding claims, characterized in that the air throttle disc (24a,b) and/or the air control flap (23a,b) are arranged upstream of the fan wheel (12) with a pivot axis running transversely to the air flow direction and that the end piece (32a,b) of the exhaust gas recirculation line (35) runs perpendicular to the pivot axis and next to at least one of these control elements (23a,b, 24a,b), specifically in the quadrant not covered by its pivot range (34). 6. Heating boiler system according to one of the preceding claims, characterized in that an exhaust gas control flap (29) is arranged in the exhaust gas recirculation line (35), preferably outside the air intake box (19) or the air intake pipe (20), which can be adjusted via a servomotor (36) depending on combustion parameters. 7. Heating boiler system according to claim 6, characterized in that the exhaust gas control flap (29) is connected to the air control flap (23a,b,c) and/or the fuel control element (17) via a connecting rod (28a,b,c). 8. Heating boiler system according to one of the preceding claims, characterized in 17.07.1989 Su/Wi
C1590 -A- e t that the exhaust gas return line (35) branches off from a downstream boiler pass and is led through a water-carrying jacket, whereby the inlet (37) of the exhaust gas return line (35) is still arranged inside the boiler (1), but outside the combustion chamber (6). 9. Heating boiler system according to one of the preceding claims, characterized in that the inlet (37) of the exhaust gas recirculation line (35) is directed against the exhaust gas flow. 10. Heating boiler system according to one of the preceding claims, characterized in that the exhaust gas recirculation line (35) is designed to be flexible at least in sections and preferably consists of flexible stainless steel corrugated pipe. 11. Heating boiler system according to one of the preceding claims, characterized in that the exhaust gas return line (35) is thermally insulated towards the outside.