Regenerative burner

Abstract

A regenerative burner comprising: a head of a burner (11) containing at least two regenerators (12-15); each regenerator (12-15) comprises a pair of valves (20-23) for connecting each regenerator (12-15) alternately to an incoming combustion air inlet (16) and to an exhaust gas outlet (17); a fuel supply device (30); a combustion air supply device (31); an exhaust gas discharge device (32); said combustion air supply device (31) is in contact with said fuel supply device (30); said exhaust gas discharge device (32) is in contact with said combustion air supply device (31); characterised by comprising regulating means suitable to allow a portion of the total exhaust gases to pass through the outlet of the exhaust gas discharge device (32).

Description

[0001] “REGENERATIVE BURNER” DESCRIPTION

[0002] The present invention relates to a regenerative burner.

[0003] Regenerative burners are used in melting furnaces, forging furnaces, heat treatment furnaces, heating furnaces and glass furnaces.

[0004] These burners use the heat of the exhaust gases to preheat the supporter of combustion. The system is based on pairs of burners that exchange heat through a heat exchanger that stores and transfers heat during alternating cycles of intake and of exhaust gas ejection. Depending on size and on conditions of use, this type of burner ensures a considerable reduction in consumptions relative to conventional burners supplied with air at ambient temperature.

[0005] In regenerative burners, heat exchange between exhaust gases and combustion air takes place by alternating the operation of a pair of burners in a series of cycles with a fixed period: the exhaust gases produced by the first burner are drawn in by the second burner of the pair, preheating a heat exchanger.

[0006] During the subsequent cycle, operation is inverted and the combustion air that is sent to the burner is preheated by the heat stored by the heat exchanger in the previous cycle.

[0007] Due to thermodynam ics, the regenerative burner cannot draw in more than 80% of the exhaust gases produced by the burner. The remaining 20% of exhaust gases must always be evacuated by an auxiliary exhaust gas duct, normally a chimney positioned in the furnace.

[0008] The document EP2184538 describes a regenerative burner characterised by the presence of an exhaust gas outlet channel and where the regenerators are arranged in the exhaust gas outlet channel, so that the flow of the exhaust gases is in contact with the outer surfaces of the regenerators.

[0009] The document EP2184538 states that this considerably helps to reduce pressure loss in the burner, so that the energy consumption of the exhaust gas fan can be considerably reduced, thereby lowering the operating costs of the burner.

[0010] The object of the present invention is to provide a regenerative burner that is more efficient than burners of the prior art.

[0011] In accordance with the present invention, these and other objects are achieved by a regenerative burner comprising: a head of a burner containing at least two regenerators; each regenerator comprises a pair of valves for connecting each regenerator alternately to an incom ing combustion air inlet and to an exhaust gas outlet; a fuel supply device; a combustion air supply device; a exhaust gas discharge device; said combustion air supply device is in contact with said fuel supply device; said exhaust gas discharge device is in contact with said combustion air supply device; characterised by comprising regulating means suitable to make a portion of the total exhaust gases pass through the outlet of the exhaust gas discharge device.

[0012] Further features of the invention are described in the dependent claims.

[0013] The advantages of this solution compared to solutions of the prior art are several.

[0014] The regenerative burner in accordance with the present invention also allows exploitation of the exhaust gases (typically 20%) to be evacuated, extracting them from a central duct.

[0015] These exhaust gases to be evacuated preheat the combustion air in a recuperative manner. Preheating is always active when the burner is on.

[0016] The remaining portion of exhaust gases (typically 80%) is regenerated according to the conventional design of a regenerative burner.

[0017] With this solution the exhaust gases are forced to pass through the central duct. This leads to a greater speed of the exhaust gases (hence a more effective heat exchange), and said 20% of exhaust gases heat precisely 20% of air that passes through the central duct, allowing greater control and uniform ity of the temperatures.

[0018] In the document EP2184538, 80% of the exhaust gases pass through three regenerators, while the remaining 20% of the gases flows over all six regenerators. However, this means that 20% of the exhaust gases has a large passage section for a relatively small flow rate of said exhaust gases. This means low speed, on which the convective heat exchange coefficient is dependent. Moreover, said 20% of the exhaust gases only partly flows over tubes with which heat exchange useful to increase efficiency takes place, namely the three regenerators through which 80% of the combustion air passes. Contact with the three remaining regenerators through which exhaust gases flow does not generate any heat exchange.

[0019] Instead, in the present case, as intake only takes place centrally, there is very precise control of the intake pressure, and regulation is finer tuned, to the great advantage of heat exchange efficiency.

[0020] The features and the advantages of the present invention will be apparent from the following detailed description of a practical embodiment thereof, illustrated by way of non-lim iting example in the accompanying drawings, wherein:

[0021] Fig. 1 schematically shows a regenerative burner in accordance with the present invention in a perspective view;

[0022] Fig. 2 schematically shows a regenerative burner in accordance with the present invention in a partially sectional side view, in a first operating condition;

[0023] Fig. 3 schematically shows a regenerative burner in accordance with the present invention in a partially sectional side view, in a second operating condition;

[0024] Fig. 4 schematically shows a regenerative burner in accordance with the present invention in a partially sectional side view, in operating condition.

[0025] With reference to the accompanying drawings, a regenerative burner in accordance with the present invention comprises a head of the burner 1 1 , preferably of cylindrical shape, although it could have any shape, for example square, which comprises, in the case represented, four regenerative tubes 12-15 inclusive of heat exchanger (not shown).

[0026] The number of regenerative tubes can be any, but in an even number, which operate alternately as combustion air inlet tubes and exhaust gas discharge tubes in predefined time cycles, for example ranging from 30 seconds to 120 seconds.

[0027] The regenerative tubes 12-15 are preferably arranged along a circumference, although they can have other arrangements, such as along a quadrilateral.

[0028] The regenerative tubes 12-15 are typically cylindrical in shape, although they can have other shapes, such as a parallelepiped. They can also contain ceram ic balls of various sizes, typically ranging from 12 to 22 mm in diameter.

[0029] Each regenerative tube 12-15 has an outlet facing the furnace (not shown) and has an inlet that is connected alternately to a combustion air inlet 16 and to an exhaust gas outlet 17.

[0030] In particular, in the case shown with four regenerative tubes 12-15, there are four valves, preferably butterfly valves, which alternately open and close the combustion air inlet 16 and the exhaust gas outlet 17 as a function of the cycle.

[0031] A first valve 20 is connected on one side to the combustion air inlet 16 and on the other side to the inlet of two of the four regenerative tubes, marked with the numbers 12 and 14.

[0032] A second valve 21 is connected on one side to the combustion air inlet 16 and on the other side to the inlet of the other two of the four regenerative tubes, marked with the numbers 13 and 15.

[0033] A third valve 22 is connected on one side to an exhaust gas outlet 17 and on the other side to the inlet of two of the four regenerative tubes, marked with the numbers 12 and 14.

[0034] A fourth valve 23 is connected on one side to an exhaust gas outlet 17 and on the other side to the inlet of the other two of the four regenerative tubes, marked with the numbers 13 and 15.

[0035] Typically 80% of the combustion air, but preferably a portion ranging from 50% to 90% of the combustion air, is made to pass through the inlet 16, for example regulated by means of a regulating valve (not shown).

[0036] Typically, 80% of the exhaust gases, but preferably a portion ranging from 50% to 90%, for example regulated by means of a regulating valve (not shown), or by means of an orifice (not shown) with a suitable diameter calibrated in the factory, is made to pass through the exhaust gas outlet 17.

[0037] The head of the burner 1 1 further comprises a fuel supply device 30, which consists of a suitable tube that supplies the fuel to be burnt in the furnace.

[0038] The fuel supply device 30 is arranged in the centre of the head of the burner 10 and inside a combustion air supply device 31 . The head of the burner 1 1 further com prises a further exhaust gas discharge device 32, which consists of a tube inside which the combustion air supply device 31 , and consequently the fuel supply device 30, are arranged.

[0039] Therefore, the fuel supply device 30, the combustion air supply device 31 and the exhaust gas discharge device 32 are arranged coaxially to one another with the device 32 on the outside, the device 30 in the centre, and the device 31 in intermediate position between them .

[0040] The devices 30-32 are located at the centre of the head of the burner 1 1 . The four regenerative tubes 12-15 are located externally and coaxially thereto.

[0041] The devices 30-32 are physically separated by the four regenerative tubes 12-15 and do not interfere with them . The flows of combustion air and of exhaust gases are also separated from one another.

[0042] The combustion air supply device 31 comprises a tube and the fuel supply device 30 is positioned on its longitudinal axis.

[0043] The exhaust gas discharge device 32 comprises a further tube and the fuel supply device 30 is positioned on its longitudinal axis.

[0044] Typically, 20% of the total combustion air, but preferably a portion ranging from 10% to 50%, for example regulated by means of a regulating valve 25 or a calibrated orifice (not shown), is made to pass through the inlet of the combustion air supply device 31 .

[0045] Typically, 20% of the total exhaust gases, but preferably a portion ranging from 10% to 50%, for example regulated by means of a calibrated orifice 26 or a regulating valve (not shown), is made to pass through the outlet of the exhaust gas discharge device 32.

[0046] Operation of the invention is apparent for the person skilled in the art from the above description, and in particular is as follows.

[0047] The combustion air regulating devices (valves or orifices) are calibrated so that the incom ing combustion air to the regenerative tubes is the predeterm ined quantity, for example 80% of the total incom ing combustion air, and so that the combustion air entering the supply device 31 is the predeterm ined quantity, for example 20% of the total incom ing combustion air.

[0048] The exhaust gas regulating devices (valves or orifices) are also calibrated so that the quantity of exhaust gases flowing from the regenerative tubes is the predeterm ined quantity, for example 80% of the total outgoing exhaust gases, and so that the exhaust gases exiting from the exhaust gas discharge device 32 is the predeterm ined quantity, for example 20% of the total outgoing exhaust gases. During operation of the burner, in a first time, the valves 20 and 23 will be open and the valves 21 and 22 will be closed, with the air and exhaust gas flows as shown in Fig. 2.

[0049] In a second time, the valves 21 and 22 will be open and the valves 20 and 23 will be closed, with the air and exhaust gas flows as shown in Fig. 3.

Claims

CLAIMS1 . A regenerative burner comprising: a head of a burner (1 1 ) containing at least two regenerators (12-15); each regenerator (12-15) comprises a pair of valves (20- 23) for connecting each regenerator (12-15) alternately to an incom ing combustion air inlet (16) and to an exhaust gas outlet (17); a fuel supply device (30); a combustion air supply device (31 ); an exhaust gas discharge device (32); said combustion air supply device (31 ) is in contact with said fuel supply device (30); said exhaust gas discharge device (32) is in contact with said combustion air supply device (31 ); characterised by comprising regulating means suitable to allow a portion of the total exhaust gases to pass through the outlet of the exhaust gas discharge device (32).

2. The burner in accordance with claim 1 , characterised in that said fuel supply device (30) is positioned centrally to said head of the burner (1 1 ).

3. The burner in accordance with one of the preceding claims, characterised by comprising a plurality of regenerators (12-15) arranged on a circumference coaxial and external to said fuel supply device (30).

4. The burner in accordance with claim 3, characterised in that said combustion air supply device (31 ) is coaxial to said fuel supply device (30).

5. The burner in accordance with claim 4, characterised in that said exhaust gas discharge device (32) is coaxial to said combustion air supply device (31 ).

6. The burner in accordance with claim 1 , characterised in that said combustion air supply device(31 ) comprises a tube and the fuel supply device (30) is positioned on its longitudinal axis.

7. The burner in accordance with claim 1 , characterised in that said exhaust gas discharge device(32) comprises a further tube and the fuel supply device (30) is positioned on its longitudinal axis.

8. Burner in accordance with claim 1 , characterised by comprising regulating means suitable to allow 20% of the total combustion air to pass through the inlet of the combustion air supply device (31 ).

9. The burner in accordance with claim 1 , characterised by comprising regulating means suitable to allow 20% of the total exhaust gases to pass through the outlet of the exhaust gas discharge device (32).

10. The burner in accordance with claim 1 , characterised by comprising regulating means suitable to allow 80% of the exhaust gases to pass through the exhaust gas outlet (17).

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