Power supply for hot oxygen burner

Abstract

The present invention relates to the supplying power to burners for oxy-fuel combustion glass melting furnaces, including a fuel injecting means and a hot oxygen power supplying means, the dispensing of oxygen being carried out so as to develop a staged combustion, a fraction of the oxygen being concurrently injected into the fuel, said oxygen being supplied essentially without heating prior to the supplying thereof into the fuel injecting means.

Claims

1. A power supply to burners of at least one glass melting furnace operating by oxy-combustion, the power supply comprising: at least one fuel injection unit; at least one supply unit that supplies a first oxygen fraction of hot oxygen at a temperature of 350° C. to 650° C.; and at least one supply unit that supplies a second oxygen fraction to the fuel injection unit, wherein distribution of the first and second oxygen fractions is carried out in order to develop a staged combustion, the second oxygen fraction is injected concurrently with a fuel, and the second oxygen fraction is introduced essentially without being heated prior to its supply into the fuel injection unit.

2. The power supply according to claim 1, in which the second oxygen fraction represents at most 10% of a total of the first and second oxygen fractions.

3. The power supply according to claim 1, in which the second oxygen fraction represents from 1.5 to 7% of a total of the first and second oxygen fractions.

4. The power supply according to claim 1, wherein the at least one supply unit for hot oxygen is at least two supply units, which are located at a distance from the fuel injection unit and symmetrically in relation to the at least one fuel injection unit.

5. The power supply according to claim 4, comprising at least two series of hot oxygen supply units on either side of the fuel injection unit.

6. The power supply according to claim 5, wherein the proportion of hot oxygen supplied increases as supplying is performed at a point more remote from the fuel injection unit.

7. The power supply according to claim 5, comprising two series of supply units on either side of the fuel injection unit, wherein the distances between the fuel injection unit and a closest supply point for hot oxygen are essentially of the same order as a distance separating a first and a second supply point located on the same side of a fuel injection units.

8. The power supply according to claim 7, wherein the closest supply point for hot oxygen to the fuel injection unit is at most equal to the supply point that is not as close.

9. The power supply according to claim 8, wherein the closest supply point to the fuel injection unit is in a range of between 20 and 40% of that of the supply point that is a furthest distance away.

10. The power supply according to claim 1 comprising at least two identical fuel injection units, the operation of which can be modulated for each of the at least two identical fuel injection units, such that each can operate alone or simultaneously with the other injector.

11. The power supply according to claim 10, comprising two fuel injection units, each of which is independent and can be momentarily interrupted in operation for maintenance.

12. The power supply according to claim 9, comprising at least two different fuel injectors, each being dedicated to a given fuel.

13. The power supply according to claim 12, comprising at least one injector which supplies a gas and at least one injector which supplies at least one liquid fuel.

14. The power supply according to claim 13 that allows a choice of fuel employed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a is a schematic sectional view of a burner used according to the invention;

(2) FIG. 1b is a front view of the burner of FIG. 1a;

(3) FIG. 2a is a view similar to that of FIG. 1a, wherein the burner comprises two fuel supply means;

(4) FIG. 2b is a front view of the burner of FIG. 2a;

(5) FIG. 3 is a view of the burner of Figure is partially showing the supply means of the burner;

(6) FIG. 4 is similar to the previous figure and relates to the burner of FIG. 2a;

(7) FIG. 5 schematically shows a type of supply circuit for hot oxygen on one side of a furnace fitted with burners.

(8) The burner of FIG. 1a comprises a refractory block 1 which forms part of the wall of the furnace. This block is advantageously formed from several parts assembled together by a reinforcement (not shown) located on the outer side in relation to the furnace. The refractory block has several conduits passing through it which open onto the inside face of the furnace and allow the supply of fuel and oxygen.

(9) The arrangement of the various supply conduits is dependent on the combustion operation required and also on the general form of the flame.

(10) In the case of furnaces operating by means of oxy-combustion, a substantial advantage lies in the absence of nitrogen, which at very high temperature leads to the formation of NOx oxides. Nevertheless, large industrial furnaces cannot be perfectly sealed against the outside atmosphere. Some air, and thus nitrogen, will still enter, even if one endeavours to maintain a certain tightness, in particular by dynamic means.

(11) The presence of even residual nitrogen can lead to the presence of NOx in reduced quantity. Since the proportions of these pollutants must be as low as possible, it is advantageous to control the operation of the furnace working with oxy-combustion in order to further minimise formation thereof.

(12) It is known that the formation of nitrogen oxides is promoted by the highest temperatures reached in the flames. Therefore, the use of burners according to the invention aims to limit the higher temperatures present locally in the flames with the same developed power.

(13) A technique for limiting the temperatures lies in ensuring that the fuel is progressively brought into contact with the oxygen carrier. The procedure is usually referred to as “staged combustion”.

(14) To achieve the staged combustion procedure, a low proportion of oxygen is introduced together with the fuel so that the flame is stabilised at the injection point. However, the quantity of oxygen must remain low so as not to concentrate too significant a portion of the combustion energy with low volume and increase the temperature of the flame.

(15) Beyond the injection point the flame is successively supplied with oxygen by the mixture of this primary flame with the jets of oxygen emitted from the injection nozzles located on the wall at some distance from the fuel injection nozzle and the primary oxygen injection nozzle. These secondary supplies are arranged as a function of the characteristics of the gas flows (flow rate, emission rate, temperature), the expansion thereof and the length of flame required.

(16) In the illustration in FIGS. 1a and 1b, the fuel supply is shown schematically by conduit 2. This conduit is concentric to conduit 3 that conveys the primary oxygen. The whole assembly is arranged in the centre of the burner.

(17) On either side of the primary supply means, two “secondary” 4 and “tertiary” 5 supply means complete the oxygen supply necessary to assure complete combustion of the fuel injected at 2.

(18) The usage of this type of burner can advantageously follow the directions outlined in publications WO 02/081967A and WO 2004/094902A, both with respect to the spatial distribution of the injections and with respect to the respective quantities of fuel and oxygen used.

(19) The distribution of oxygen over the conduits is advantageously such that the quantity increases with the distance separating its injection point from that of the fuel. In the configuration shown in FIGS. 1a and 1b, the supplies through conduits 4 are advantageously less significant than those conducted from conduits 5.

(20) As an indication, the ratio of the respective supply for conduits 4 (Q.sub.1) and 5 (Q.sub.2) lies in the range of between 0.2 and 0.6, for example.

(21) To obtain a flame with an overall shape that is substantially plane, the axes of the different conduits are advantageously arranged in the same plane. A plane flame is advantageous in the case of glass melting furnaces. It allows the largest possible surface of the bath to be directly exposed to the radiation emitted by the flame or indirectly to that of the refractory materials exposed to this flame, in particular those of the crown of the furnace.

(22) The arrangement of the injection points can be substantially different when the shape of the flame is not controlled by a heat exchange with a plane surface. In particular, the supplies can be arranged concentrically around the primary injection point.

(23) The burners shown schematically in FIGS. 2a and 2b have the previous general structure. They differ from this through the presence of two supplies for fuel 2 and primary oxygen 3.

(24) The provision of two injection points, which can be as close to one another as space conditions allow, is intended to make maintenance operations easier. The closer the injection points are, the closer the mode of operation resembles that in which a single primary supply is arranged.

(25) Whatever precautions are taken, the operation of the burners can lead to a fouling by the decomposition products of the fuels. To minimise this risk, the ends of the nozzles are advantageously set back slightly in relation to the inside wall of the furnace. The reason for the set back arrangement is also to provide protection for the end of the injection pipe. By proceeding in this manner, the temperature is essentially lower than that prevailing in the furnace, in particular because of the circulation of the fuel itself and that of the “cold” oxygen. It is to be noted that even if the fuel is preheated to increase the energy efficiency, the temperatures reached are limited to avoid the risk of thermal decomposition in the supply conduits.

(26) Maintenance operations must be conducted on the furnace without interrupting operation. It is necessary to assure that these operations hardly change the operating process. The stoppage of a burner in large glass melting furnaces, which usually comprise between 6 and 12 of these, can be momentarily compensated by a corresponding increase in the activity of the adjacent burners. This still results in a change in the general equilibrium of the fire curve and possibly also in the circulation of fumes which are used further along in the heating cycle of the oxygen, as indicated.

(27) An alternative solution for minimising the influences of maintenance operations lies in the use of burners having two fuel injections, for example. Advantageously, the two injections are then used simultaneously. When a maintenance operation needs to be conducted, the operation of one of these injection means is momentarily interrupted. The second injection means possibly takes over a part of or all the supply corresponding to that of the injector out of operation.

(28) This way of proceeding maintains the spatial distribution of the energy in the furnace in an almost identical manner.

(29) When the first injector is replaced, the second can undergo maintenance in turn.

(30) In these maintenance operations, the most usual procedure is to remove the fuel injection lance from the refractory block, through which it penetrates into the furnace. The freed opening is momentarily blocked to prevent the penetration of air.

(31) The fuel supplies do not generally require conduits that have any special corrosion-resistant characteristics. Usual materials such as traditional stainless steels are sufficient and, above all, these conduits can bear connectors, valves and other elements that are able to be disassembled during these maintenance operations.

(32) The removal of these conduits does not cause significant problems. The question no longer arises when the primary oxygen is injected with the fuel at a relatively low temperature, e.g. a temperature not exceeding 100° C.

(33) In order to bring the energy efficiency of the burners to the highest level, it is advantageous to use the oxygen that is preheated to temperatures that can reach or exceed 550° C. In these conditions the oxygen conduits must have very particular resistance qualities and welds or connection elements must be avoided or reduced as far as possible. For this reason, the supply conduits for the hot oxygen all remain in place during maintenance operations.

(34) FIGS. 3 and 4 show the elements of the burners of FIGS. 1 and 2 integrating into them additional elements for the supply of hot oxygen.

(35) Conduits 4 and 5 are connected to a supply tank 6 to supply hot oxygen. The provision of a valve between the supply tank 6 and the burner is avoided. The distance between the supply tank and the burner is as short as the space in the vicinity of the furnace will allow.

(36) The straight conduits shown can have curves. It is preferred that the severity of these curves is as low as possible to minimise the impact of the hot oxygen on their walls, which is likely to cause erosion thereof eventually.

(37) The quantity of oxygen distributed over each conduit is continuously determined by the dimensions of regulating nozzles located either in the conduits or at the junction of conduits 4 and 5 with the supply tank 6.

(38) The supply tank is itself supplied by a conduit 19 connected to a heat exchanger (not shown in these figures), in which the oxygen is heated. Since there is no ability to interpose valves over the course of the hot oxygen, the changes in operation are controlled from the cold oxygen fed into the exchanger. These changes are necessarily limited.

(39) The supplies for fuel and cold oxygen shown in FIGS. 3 and 4 are formed by conduit 3. This conduit 3 envelopes the fuel conduit 2. The respective supply circuit of these two conduits can be separated at the level of the clips 7 and 8. Once these clips are undone, conduits 2 and 3 can be removed from the refractory material to carry out their repair.

(40) FIGS. 2 and 3 schematically show the possible layout in the case where the fuel passing through the central conduit 2 is in gas form. When the fuel is in liquid form, its introduction requires the use of means that allow this liquid to be atomised. In particular when the atomisation is achieved by means of a gas (vapour, air . . . ), the fuel feed conduit must still comprise a feed conduit for this atomisation gas to close to the injection point.

(41) As shown in FIG. 4, the supply of “cold” oxygen through conduits 3 can be regulated separately by means of valves 9 and 10, for example.

(42) As proposed in the unpublished European Patent Application No. 08 102 880, filed on Mar. 25, 2008, still with respect to minimising difficulties associated with the transport of hot oxygen, the thermal exchanger in which the oxygen is heated is preferably disposed as close to the burner as possible. For the same reasons, the number of burners supplied from one exchanger is limited. Preferably, each exchanger does not supply more than two burners, and it is particularly preferred if each exchanger is only connected to one burner. In this way, the oxygen flow rate for each burner can be controlled independently of the other burners and the oxygen can be controlled before it passes into the heat exchanger.

(43) FIG. 5 schematically shows an oxygen supply assembly of a furnace intended, for example, for melting glass materials.

(44) The furnace 11 is shown in partial plan view. Its side refractory wall 12 bears a series of schematically shown burners 13 inserted into the wall. Each burner 13 is supplied with oxygen in two ways. A first series of conduits 14 conveys the cold oxygen to feed the primary combustion, as described above. A second series of conduits 15 supplies the heat exchangers 16. At the outlet of these heat exchangers the hot oxygen is transported up to the burners through conduits 17 that represent overall the different supplies of hot oxygen of each burner.

(45) In the diagram in FIG. 5, the heat exchangers 16 cause a preheated fluid coolant to flow in counterflow to the oxygen. In the shown embodiment, the heating of this fluid coolant is conducted in a recuperator 18, in which the fumes F exiting from the furnace 11 flow.

(46) While it is possible in principle to conduct a heat exchange directly between the fumes and the products to be preheated, the endeavour to operate in the best conditions with respect to efficiency and safety results in more complex exchange assemblies and in particular through the use of the intermediate fluid coolant.

(47) In a first “recuperator” 18 the fumes reheat the intermediate fluid, e.g. air, nitrogen, CO.sub.2, or any appropriate fluid that circulates, for example, in a loop between this recuperator and the exchangers 16, in which the oxygen is reheated. An alternative to the intermediate fluid such as air is to not use the loop and recover the hot air at the outlet of the secondary exchangers through a boiler or other means of energy recovery.