EP0663563B1 - Method of combustion in combustion apparatuses and combustion apparatus - Google Patents

Abstract

The boiler (1) is fired by a burner (2) for liquid or gas fuels. The escaping flue gases pass from the combustion chamber (5) between the walls of outer and inner water-cooled heat exchangers (6, 12), thence past the outside of the combustion chamber. Before they reach the regions between the heat exchangers, the flue gases first circulate in another heat-exchanging space (15) inside the inner exchanger and then, a portion of the flue gases is returned to the burner flame roots through openings (4) in the flame tube (3). The heat-exchanging spaces have devices to increase turbulence like seams, rings, disks, etc.

Description

The invention relates to a method for operating the combustion of fuels in combustion plants a boiler fired by a burner, in which the thermal energy of the fuel transferred to a heat transfer medium is, as well as on a device for performing a such a method according to the preambles of the claims 1 and 9.

For the transfer of the thermal energy of a fuel to one Heat transfer medium, and thus for the efficiency of one Total combustion plant, is the design of the boiler or the heat generator of great importance. The construction the boiler is essentially influenced by the Geometry of the firebox and through the guidance of the Combustion gases. Boiler constructions are designed so that as much heat as possible, that arises during the chemical conversion of the fuel, completely transferred to the heat transfer medium without loss becomes. In addition to water, low or High pressure steam and organic liquids into consideration.

Depending on the type of heat transfer, the known ones Divide boiler designs into two construction elements: the combustion chamber in which the combustion process takes place and the thermal energy essentially through radiation or transfer heat radiation to the combustion gases becomes; and downstream cooled heat exchange surfaces, via the combustion gases change their enthalpy by convection dispense the heat transfer medium.

According to the state of the art - especially in one medium output range - preferably so-called three-pass boilers used. These are mostly cylindrical Furnace equipped, the "hot" combustion gases at the end of the combustion chamber via a deflection chamber in the secondary heat exchange surfaces, consisting of steel pipes, be performed.

Another well-known boiler design is the boiler with Reverse flame in the firebox. The flame burns in one cylindrical firebox closed at the back and the combustion gases are in the cylindrical firebox redirected again and returned to the boiler entrance. Via a corresponding deflection chamber at the boiler entrance then the combustion gases at the front of the Boiler according to the three-pass principle, the convective secondary heat exchange surfaces fed.

In the known boiler designs is particularly to ensure that the geometry of the firebox and the Exhaustion of the combustion gases exactly on the flame geometry and thus matched to the performance of the burner are. In addition to avoiding convection and radiation losses this applies in particular to avoiding the Cooling of the combustion gases inside the boiler, for example if the firebox is oversized. If the combustion gases come out of the combustion chamber to a temperature below the water or acid dew point cool down, the exhaust gases condense, which permanent formation of corrosion in the boiler and in the exhaust pipes caused. Boiler corrosion is major attributed to the corrosive effect of sulfuric acid. But also a condensate failure, for example ash parts of fuel oil, soot, etc. leads to one over time Attack on the boiler materials and finally on their Destruction.

Examples of known boiler designs show the following publications:

From DE-A-3 612 910 a firing system and a Method for operating the same according to the above Kind known. The known furnace system includes one Boiler surrounded by a water-bearing housing is. The boiler also includes a combustion flame and the combustion gas-absorbing interior, in which a tubular insert is introduced. The interior is closed on its downstream side, so that the combustion gases are redirected there and then into one Heat exchange space between the wall of the tubular insert and the water-bearing housing wall are removed. The problem of corrosion prevention will not, however addressed.

Furthermore, those known from GB-A-2 224 346 Combustion system the combustion gases generated during combustion after exiting the boiler's combustion chamber on downstream water-cooled heat exchanger surfaces passed - until they finally through the "exhaust" exit the furnace. Here takes place a pure convective energy transfer from the combustion gases to the heat exchange medium, usually water, instead; however, there are no heat exchange rooms to avoid provided by corrosion formation.

Corrosion, especially boiler corrosion To be largely avoided in the known boiler designs for different performance areas of Burners also require different boiler sizes to pass through Adaptation of the combustion chamber geometry to the burner output Avoid lowering the exhaust gas temperatures in the boiler.

The invention aims to provide a firing system as well a method of operating the same ask for a large burner output range without Risk of corrosion formation is designed.

This object is achieved by the invention of claims 1 and 9. Further preferred embodiments of the Invention result from the dependent claims.

After that, the combustion gases that are produced during combustion of the fuel in the boiler arise, at least in part between a hot heat radiating surface, i.e. one hot radiant area, which is essentially the thermal energy transferred to the combustion gases by heat radiation, and a convective cooled by the heat transfer medium Heat exchanger surface to which the combustion gases give off their enthalpy by convection from the boiler dissipated. In this way, the combustion gases flow through an intermediate space - furthermore as a heat exchange space designated - between the convective heat exchanger surface an infinitely large heat exchanger or heat bath and the hot radiation surface. As a result, the combustion gases flowing through the heat exchange chamber on the one hand Thermal energy to the convective heat exchanger surface and at the same time take heat from the Radiation area. In doing so, those diverted in the firebox are deflected Combustion gases through a heat exchange space between a burner flame tube protruding into the combustion chamber and an inner heat transfer jacket surrounding the flame tube dissipated. The flame burns in one its downstream end closed firebox, and the combustion gases are shaped accordingly of the firebox floor in the firebox redirected and about the above Heat exchange space between flame tube and internal heat transfer jacket dissipated. By reversing the combustion gases over the flame will first turn on complete, perfect burnout of the fuel guaranteed. Then the combustion gases get into the o.g. Heat exchange room, especially at low burner outputs a cooling of the combustion gases below critical Dew point temperatures prevented.

When the burner output is high, the heat is released by the combustion gases to the heat exchanger surface - and thus to the Heat transfer medium - greater than the heat absorption from the radiation surface, so that finally a cooling of the combustion gases he follows. When the burner output is low, heat is emitted and heat absorption of the combustion gases essentially in equilibrium so that the combustion gas temperature is kept constant in this performance range. Of the The value of the lower limit temperature of the combustion gases depends the temperature and geometry of the thermal contact surfaces from. Depending on the design, especially the Heat radiation surfaces, the limit temperature can be set to one certain value - at least above the critical dew point temperatures - Set so that the danger excluded from corrosion and other condensate failures is. Due to the exhaust gas routing according to the invention Boilers are such firing systems for a large one Burner output range - preferably approx. 30% up to 100% - suitable.

In a preferred embodiment of the invention the combustion gases are in a heat exchange space between the uncooled heat radiating wall of the combustion chamber and an outer one surrounding the combustion chamber wall Heat transfer jacket, in particular water jacket performed (claims 2 and 10). Extend the radiant heat Areas of the glowing combustion chamber wall during operation and the convective heat exchanger surfaces of the outer heat transfer jacket over the entire circumference and the axial height of the Combustion chamber, this is a particularly effective heat transfer from the combustion chamber wall to the combustion gases and further guaranteed to the heat transfer medium.

The combustion gases are preferably also conducted in a region between the outer and the inner heat transfer jacket, in particular water jacket (claims 3 and 11). If both heat transfer jackets extend over the entire axial length of the combustion chamber, this achieves effective cooling of the combustion gases, which release a large part of their thermal energy by convection to the heat transfer medium. If the inner heat transfer jacket on the inside of the combustion chamber wall extends around the flame as a flame cooling cylinder, part of the thermal energy of the combustion gases is also transferred directly from the hot flame zone to the heat transfer medium and, at the same time, a reduction of the NO _x by cooling the combustion chamber Education reached.

Another preferred embodiment of the invention is that the combustion gases redirected in the combustion chamber first through the heat exchange space between the flame tube and flow inside the heat transfer jacket, then again deflected and through the purely convective heat exchanger room performed between the outer and inner heat transfer jacket and finally the heat exchange space between the combustion chamber wall and flow through the outer heat transfer jacket (Claims 4 and 12). Such exhaust gas routing works both on the stabilization of the lower exhaust gas limit temperature at low burner output, as well the most effective possible heat transfer to the heat transfer medium at high burner outputs. The redirected combustion gases first flow through radiation and Convection determined heat exchange space, then a pure one convective heat exchange room and finally another Radiation and convection heat exchange room.

To increase the effective heat contact area, are outer and inner heat transfer jackets with heat exchange fins equipped (claim 13). For the same reason, too the outside of the combustion chamber wall with the corresponding Provide heat exchange fins (claim 14). This will achieved that the combustion gases as high as possible Part of the amount generated in the combustion chamber during combustion transferred to the heat exchange surfaces and alike as much heat as possible from the heat radiating surfaces, especially the combustion chamber and flame tube walls can.

For good heat exchange even at low exhaust gas temperatures to ensure, are in the above Heat exchange rooms Devices promoting turbulence, in particular Beading, rings, disks and twisted metal strips, arranged (Claim 15). This also leads to an enlargement the thermal contact surface and thus to an improved Heat transfer.

According to a further preferred exemplary embodiment, part of the deflected combustion gases is returned to the flame root area via cutouts in the flame tube of the burner, in particular after the combustion gases have passed through the heat exchange space between the flame tube and the inner heat transfer jacket (claims 5 and 16). The internal exhaust gas recirculation - especially when the combustion gases cool down beforehand - enables an effective reduction in flame temperatures, which further leads to a reduction in NO _x formation.

The invention has proven to be particularly advantageous Furnace and the method for operating the furnace in connection with a modulating or controllable burner (claims 7, 17). Such a burner contains a continuously controllable control valve and a appropriately controllable blower for regulating the supplied Amount of combustion air. This can reduce the burner output continuously changed over a larger control range become. In connection with the connection Flue gas routing in the boiler is both at high burner output guaranteed at all times, even with low burner output, that the exhaust gas temperature is the critical dew point not less. The boiler construction according to the invention is therefore controllable for all performance areas Suitable burner.

The burner output is preferably automatically dependent the reduced heat output of the heat transfer medium changed so that between the individual load points - So minimum and maximum combustion heat output - the Burner can adjust automatically at every load point, so that the fuel and combustion air supply of the removed Thermal output of the heat transfer medium corresponds. On the Basis of the exhaust gas management according to the invention is with the help of such a modulating burner the burner output regulated such that the temperature of the heat transfer medium in the boiler, especially the boiler water in the boiler wall constant regardless of the load on the combustion system remains (claim 8).

This also makes the temperature particularly advantageous the heat exchange jackets or the convective heat exchange surfaces in the boiler, which the combustion gases flow past, kept at a constant value. As a consequence, that the temperature of those emerging from the boiler Combustion gases are kept at a defined value, to counteract the condensation of the exhaust gases.

The boiler according to the invention is particularly cost-effective made of simple steel and / or cast iron (claim 18). Due to the guidance of the combustion gases according to the invention can be beneficial on expensive corrosion resistant Boiler materials are dispensed with.

Fig. 1

ein Ausführungsbeispiel der erfindungsgemäßen Kesselkonstruktion im Längsschnitt;

Fig. 2

einen Querschnitt entlang der Linie A-A' in Fig. 1; und

Fig. 3

ein Beispiel für die erfindungsgemäße Feuerungsanlage mit Kessel-, Speicher- und Versorgungskreislauf.

Further advantages and refinements of the invention also result from the following description of preferred exemplary embodiments. Therein, reference is made to the attached schematic drawing. The drawing shows:

Fig. 1

an embodiment of the boiler construction according to the invention in longitudinal section;

Fig. 2

a cross section along the line AA 'in Fig. 1; and

Fig. 3

an example of the furnace system according to the invention with boiler, storage and supply circuit.

1 shows a longitudinal section through a boiler 1, that of a burner 2, preferably a modulating one Burner being fired. The burner 2 opens with his Flame tube 3 in a combustion chamber 5 of the boiler 1. Die Combustion air is sent to burner 2 in the direction of the arrow I fed.

In the flame tube 3 are downstream - not shown in Fig. 1 Burner baffle plate 2 - horizontal slots 4 evenly distributed over the circumference of the flame tube 3 for the internal return of the combustion gases to the root area the flame.

The boiler 1 contains an outer one of a boiler circuit fed water jacket 6, which is essentially extends over the entire axial boiler length and the Fully surrounds combustion chamber wall 8 at a distance. Of the outer water jacket 6 fulfills the function of a heat exchanger or warm bath and is on the inside with Fitted heat exchanger fins 10, the radially inward directed almost over the entire axial length of the water jacket 6 run. There is also an inner water jacket 12 between the outer water jacket 6 and the flame tube 3 arranged such that he the flame tube 3 at a distance completely surrounds. The inner water jacket 12 is with convective heat exchanger fins facing the boiler axis 14 equipped.

The firebox 5 is closed at its rear end, so that the combustion gases are deflected in the combustion chamber 5 and in Direction upstream. Another deflection area forms the inner wall of the boiler at the front end of the boiler 1, so that the inflowing from the combustion chamber 5 Combustion gases redirected again and in the downstream direction between the outer water jacket 6 and the inner one The water jacket 12 and the combustion chamber wall 8 flow up to they finally the boiler 1 through the combustion gas outlet 13 leave.

The result is a combustion gas flow realized, the combustion gases in succession three Flow through annular heat exchange rooms: a first one Heat exchange space 15 between the flame tube 3 and the inner Water jacket 12 in which the combustion gases heat energy pick up from the "glowing" flame tube and at the same time Heat by convection via the heat exchanger fins 14 deliver the inner water jacket 12; a second one convective heat exchange space 16 between the inner 12 and the outer water jacket 6; and finally a third Heat exchange space 17 between the outer water jacket 6 and the uncooled heat radiating combustion chamber wall 8, in which also heat exchange through radiation and convection with the combustion gases.

Due to the inventive design of the outer 6 and inner water jacket 12 around the heat radiating surfaces the combustion chamber wall 8 or the flame tube 3 at high burner output the heat emission of the combustion gas flow to the water coats greater than the heat absorption from the heat radiating surfaces, so that a The combustion gases are cooled. With low burner output stand against heat emission and heat absorption the combustion gases in equilibrium so that the combustion gas temperature in this performance range essentially remains constant. It is particularly due to the absorption of heat from the flame tube 3 or from the combustion chamber wall 8 kept above the critical dew point temperatures. Because of the pronounced heat contact surfaces in the heat exchange rooms 15 and 17 is the limit temperature of the combustion gases clear even with the lowest burner output above a critical value of approx. T = 110 ° C. So there is no risk of corrosion.

In the case of a modulating furnace such as that used in the invention Combustion system is preferably used, depending on the burner's load, the combustion gases cooled in heat exchange rooms 15 and 17 or - ideally - with a low burner output at a constant Value held.

Furthermore, the modulating firing saves depending the burner system load, frequent burner starts, which causes high starting emissions and the formation of corrosion when Start of the burner can be avoided.

The sectional view in Fig. 2 along the line A-A 'of Boiler construction in Fig. 1 illustrates that the outer 6 and the inner water jacket 12 conducting each other in Connected and jointly supplied by the boiler circuit become. 2 shows the radially inward directed heat exchanger fins 10 or 14 of the water jackets 6 or 12.

Finally, Fig. 3 shows a furnace according to the invention with a boiler 1, in the combustion chamber a modulating Burner 2 protrudes. The boiler 1 is via a storage circuit 18 connected to a hot water tank 20, which is fed by boiler 1 with hot water. Parallel to Storage circuit 18, a boiler circuit 22 is arranged, which in turn is connected to a consumer circuit via a heat exchanger 24 26 is coupled.

3 with a thermostat T, the burner output of the modulating burner 2 is controlled as a function of the heat output removed from the supply circuit 26 such that the temperature of the (boiler) water in the boiler circuit is at a constant value, for example to T _K = 60 ° C, remains. In connection with the exhaust gas guide according to the invention in the boiler 1, the temperature of the combustion gases emerging from the boiler 1 is thereby fixed to a certain value independently of the load on the supply circuit 26.

If the flow temperature in the consumer circuit is also kept at a constant value, e.g. at T _V = 30 ° C, then - depending on the load on the consumer 28 - hot water with T _K = 60 ° from the boiler circuit can be supplied in defined quantities in a mixing device 30 the consumer circuit 26 are mixed.

Claims (18)

1. A method for operating the combustion in combustion apparatuses having a boiler (1) heated by a burner (2), whereby

   the combustion gases are conveyed out of the boiler (1) between a hot heat-radiating surface and a cooled, more particularly a water cooled, heat exchanger surface (12),

   characterised in that

   the combustion gases deflected in the combustion chamber (5) are conveyed through a heat exchange chamber (15) between a heating tube (3) extending into the combustion chamber (5) and an inner heat transfer shell (12).
2. A method according to Claim 1,
   characterised in that the combustion gases are conveyed in a heat exchange chamber (17) between an outer heat transfer shell (6), more particularly a water jacket, and a wall (8) of a combustion chamber (5) of the boiler (1).
3. A method according to Claim 1 or 2,
   characterised in that the combustion gases are conveyed in a heat exchange chamber (16) between the outer (6) and inner heat transfer shell (12).
4. A method according to Claim 1, 2 and 3,
   characterised in that the combustion gases deflected in the combustion chamber (5) first of all flow upstream through the heat exchange chamber (15), then are deflected and are conveyed downstream in succession through the heat exchange chambers (12) and (17).
5. A method according to one of the preceding Claims,
   characterised in that a part of the combustion gases are returned via apertures (4) in the heating tube (3) into the flame root of the burner flame.
6. A method according to Claim 6,
   characterised in that before returning into the flame root region the combustion gases are conveyed through the heat exchange chamber (15).
7. A method according to one of the preceding Claims,
   characterised by the use of an adjustable or modulating burner (2).
8. A method according to Claim 8,
   characterised in that the temperature of the heat transfer medium is kept constant in the boiler circulation (22).
9. A combustion apparatus, more particularly for performing a method as specified by one of the preceding Claims, having:

   a boiler (1), which is heated by a burner (2), the heating tube (3) of which opens into a combustion chamber (5) of the boiler (1),

   an inner heat transfer shell (12), more particularly a water cooling jacket, which surrounds the hot heat-radiating heating tube in the boiler (1) at a distance;

   an end at the outlet of the combustion chamber (5) for the deflection of the combustion gases;

   wherein

   the inner heat transfer shell (12) surrounds the heating tube (3) at a distance in such a manner that the deflected combustion gases can be carried away between the inner heat transfer shell (12) and the heating tube (3) (heat exchange chamber 15)).
10. A combustion apparatus according to Claim 9,
    characterised in that a further outer heat transfer shell (6) surrounds the walls (8) of the combustion chamber (5) at a distance (heat exchange chamber (17)).
11. A combustion apparatus according to Claim 9 or 10,
    characterised in that the outer heat transfer shell (6) surrounds the inner heat transfer shell (12) at a distance (heat exchange chamber 16).
12. A combustion apparatus according to Claim 9, 10 and 11,
    characterised in that a deflection region is provided on the inner walls of the boiler, so that after their passage through the heat exchange region (15) the combustion gases (are) deflected on the inner walls of the boiler and flow in succession through the heat exchange chambers (16) and (17).
13. A combustion apparatus according to one of Claims 9 to 12,
    characterised in that the inner (6) and/or outer heat transfer shells (12) is/are equipped with heat exchange ribs (10; 14).
14. A combustion apparatus according to one of Claims 9 to 13,
    characterised in that heat exchange ribs are provided on the outside of the combustion chamber wall (8).
15. A combustion apparatus according to one of Claims 9 to 14,
    characterised in that the turbulence-increasing devices, more particularly beads, rings, disks and twisted strip, are disposed in the heat exchange chamber (15; 16; 17).
16. A combustion apparatus according to one of Claims 1 to 15,
    characterised by one or more apertures (4) in the heating tube (3) for the internal return of exhaust gas into the flame root region, more particularly after the passage of the combustion gases through the heat exchange chamber (15).
17. A combustion apparatus according to one of Claims 9 to 16,
    characterised by a modulating or adjustable burner (2).
18. A combustion apparatus according to one of Claims 9 to 17,
    characterised in that the boiler (1) is produced from steel and/or grey cast iron.

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