GB2058331A

GB2058331A - Gas burner with air injection adapted to operate within a very wide range of caloric output values

Info

Publication number: GB2058331A
Application number: GB8027821A
Authority: GB
Original assignee: Societe National Elf Aquitaine; Societe Nationale Elf Aquitaine Production SA
Current assignee: Societe National Elf Aquitaine; Societe Nationale Elf Aquitaine Production SA
Priority date: 1979-08-31
Filing date: 1980-08-28
Publication date: 1981-04-08
Also published as: DE3032119A1; FR2464433A1; NL8004846A; ES8105462A1; ES494531A0; DE3032119C2; IT1132602B; FR2464433B1; GB2058331B; CA1143277A; IT8024393A0; GR69945B

Abstract

This invention is related to a gas burner with air injection, adapted to be operated with flow rates which can be varied within a very wide range of flow rate values, especially with very low flow rates, comprising gas inlet means 1, air inlet means 2 and a divergent conduit 3 wherein said air and said gas are mixed to form an air/gas mixture, the end portion of said divergent conduit being provided with at least two air and/or gas inlet stages 30, 31, wherein the minimum inner diameter of the second one of said inlet stage is at least substantially equal to the inner diameter of the end of the first one of said stages. <IMAGE>

Description

SPECIFICATION Gas burner with air injection adapted to operate within a very wide range of caloric output values The present invention is related to a gas burner with air injection which is adapted to be operated with flow rates which can be varied within a very wide range of flow rate values, and which, more particularly, is adapted to operate at very low flow rates.

The construction of gas burners with air injection is extremely important in numerous industrial fields, especially in the field of heavy chemical industry where such burners are an imperative requirement when it is desired to produce on a large scale a great number of substances to be adapted to-be used as raw materials in the field of transformation or conversion industries.

It is known that most of the conventional gas burners with air injection have fixed flow crosssections for the injected gas and air.

Consequently, the injection velocity in such fixed flow cross-sections will decrease as the required caloric output decreases. Now, in the low velocity range, said injection velocity will drop to values which are insufficient for achieving satisfactory mixing of the gas and the air and, consequently, for ensuring complete, fast and stable combustion.

This characteristic of the conventional burners entails certain drawbacks: indeed, it is necessary, on account of the above-described feature, to use, in many operations, furnaces provided with a plurality of burners adapted to be ignited successively as the required caloric output varies.

Consequently, it is necessary, in such installations, to change the burners frequently during operation, which entails a succession of operations and comparatively long off-time periods, as well as re-igniting the burners, whereby the manufacturing cost of the final product is considerably increased.

Furthermore, the heat developed in the furnace results, when such an installation is used, in rapid deterioration of the extinguished burners, when the furnaces in question are provided with refractory brickwork and maintained at elevated temperatures and when pressurized furnaces are used.

With a view to eliminating the abovementioned drawbacks it is necessary, in certain installations, to blow air, fumes or vapor onto the extinguished burners so as to cool the same while carrying out the required operations, which results in considerable waste of thermal energy.

Several constructions have already been designed which allow the air injection crosssection and the gas injection cross-section to be varied with a view to maintaining the velocity of these media at sufficiently high values even when the required caloric output varies.

However, when operating with very low output values, these known constructions fail to yield satisfactory results, since the outlet section of the burner cannot be varied, so that the velocity of the gas/air mixture flow remains very low.

More particularly, the following known burner 'arrangements may be cited, by way of example: British patent specification nO 61 5 822 discloses a burner fed with injected air; however, this known burner is of the type commonly designated as an "induction burner", wherein the atmospheric air is aspired due to a vacuum induced by the flow of the combustible gas in the burner, no blower being used for introducing the air into such burner. While this known burner is designed to improve the quality of the gas/air mixture, no mention is made in the abovereferenced specification of the possibility of operating this burner with gas flow rates which vary within very wide limits. Also, the known device does not allow the air pressure to be equalized, or to be adjusted to a value close to that of the gas pressure.

The burner disclosed in Belgian patent specification nO 421 627 comprises a device for adjusting the inlet rate of the gas, which is located upstream of the mouth of an ejector. This mouth has a constant cross-section, resulting in a considerable increase of the outlet velocity of the gas flow when the flow rate increases, and thus in a risk of separation or destabilisation of the flame.

French patent specification nO 758 974 is related to a burner having at least two combustion air inlet stages. The gas is introduced through a conduit having an outlet portion with a constant cross-section, which does not allow the burner to be operated with widely varying flow rates, since the latter would result in too large variations of the combustible gas outlet flow velocity, as well as inflame destabilising phenomena.

German patent specification nO 2 742 393 too discloses a device comprising at least two inlet stages, and further comprising tiltable blades allowing the cross-sectional area of the combustion air injection flow to be varied. These blades control a secondary air circuit and must never be brought into a completely closed position, since this would result in entirely sealing off the primary air circuit. Furthermore, this known burner arrangement has another drawback, similar to that of other known devices mentioned herein above, which resides in a constant cross-section of the combustible gas outlet conduit, resulting in prohibiting very wide variations of the gas flow rate, since under these conditions such variations would bring about a considerable risk of destabilisation.

The burner of the so-called "induction" type disclosed in French patent specification n 770 478 comprises means for adjusting the gas flow rate, which are located upstream of the outlet opening of a conduit the end portion of which has a constant cross-section. This burner involves the above-described risks of flame destabilisation, when operated with flow rates that vary within wide limits.

French patent specification nO 521 856 discloses an arrangement wherein the air flow rate is controlled as a function of the gas flow rate.

However, this known construction is not very elaborate and does not allow the secondary air flow rate to be controlled independently of the primary airflow rate.

It is a primary object of the present invention to overcome the drawbacks of the known constructions, as mentioned herein above, and to provide a gas burner adapted to operate in a satisfactory manner with very low flow rates, whereby such burner can be mounted as a single burner in furnaces wherein the provision of a plurality of burners has been an imperative requirement up to now.

With these and other objects in view, the present invention provides a gas burner with air injection, adapted to be operated with flow rates which can be varied within a very wide range of flow rate values, especially with very low flow rates, comprising gas inlet means, air inlet means and a divergent conduit wherein said air and said gas are mixed to form an air/gas mixture, the end portion of said divergent conduit being provided with at least two air and/or gas inlet stages, wherein the minimum inner diameter of the second one of the said inlet stages is at least substantially equal to the inner diameter of the end of the first one of said stages.

The provision of one single burner adapted to be operated at flow rates which may vary within very wide limits constitutes a considerable advantage for any type of furnace, and especially for the furnaces used for preparing sulphur by burning hydrogen sulphide (SH2) in accordance with the CLAUS process.

When a furnace of this latter type is used, any fluid medium for cooling an extinguished burner has a deleterious effect on the yield of the process by causing a dilution of the reactant gas. This results in a production loss, rapid corrosion and increased pollution of the atmosphere.

Furthermore, a low flow velocity of the gases at the outlet of the conduit results in poor mixing of said gases and consequently poor yield of the reaction which, in turn, increases the pollution of the atmosphere.

In contradistinction thereto, when a high gas flow velocity is maintained over the entire length of the flow path, even under conditions of low flow rates, the result will be a more satisfactory mixing of the gas and the air and consequently a flame of reduced length, a higher flame temperature and an improved yield of the reaction.

As already stated herein above, according to one particular feature of the invention, the minimum inner diameter of the second inlet stage is at least substantially equal to the inner diameter of the end of the above-mentioned first inlet stage.

Due to this arrangement, a far better continuity of the decrease of the gas/air mixture flow is obtained downstream of the first one of said inlet stages.

According to another feature of the invention, the burner comprises separate adjusting means for adjusting the respective flow path crosssection of the injected gas and the injected air.

According to still another feature of the invention the means for adjusting the flow path section of the injected gas comprise a sealing member slidabiy mounted on the orifice of the gas inlet nozzle and controlled by manual or powerdriven control means.

In a particular embodiment of the invention said control means are actuated in accordance with the pressure prevailing in said conduit.

According to yet another feature of the invention the air flows, in each one of said inlet stages, through an array of tiltable blades adapted to van, the cross-section of the air inlet flow and associated with a control lever.

According to a further feature of the invention the divergent conduit through which flows the air/gas mixture comprises a comparatively narrow or restricted neck portion the dimensions of which are chosen so as to accommodate the minimum flow rate at which the burner is adapted to be operated.

According to one advantageous feature of the invention a servo-device is provided for actuating adjustable closing members adapted to control the air flow rate.

Other objects, features and advantages of the invention will become apparent from the detailed description herein below which refers to the appended drawing, and which is given by way of illustration, but not of limitation.

The single figure of the appended drawing is a schematic sectional view of one embodiment of the burner according to the present invention.

As shown in the figure, the burner according to the invention comprises gas inlet means 1 for introducing gas flowing in the direction indicated by arrow A, and air inlet means 2 for introducing combustion air in the direction indicated by arrow B.

The gas introduced through gas inlet means 1, as well as the air introduced through air inlet means 2 are mixed with each other in a divergent conduit 3 from which the resulting mixture AB issues, and which will be described in more detail herein after.

The pressurized gas inlet means 1 comprise a nozzle 4 opening, at one of its ends 5, into the above-mentioned conduit 3, said nozzle end 5 being associated with a slidably mounted closing member 6 adapted to be moved in a longitudinal direction along the axis I-I of nozzle 4. The longitudinal displacement of closing member 6, which determines the gas injection flow crosssection, is controlled by means of a control system 7 connected to closing member 6 by a rod 8.

Combustion air inlet means 1 comprise a caisson 9 from which the air issues and períietrates divergent conduit 3 through a grid 10 constituted by tiltable blades 11 which allow the crosssectional area of the airflow injected into the divergent conduit to be modified by means of a control lever 12.

In accordance with the present invention, divergent conduit 3 comprises a plurality of combustion air inlet stages (two inlet stages in the embodiment shown), with a view to allowing the burner to be operated at very widely varying caloric output (or flow rate) values, and more especially at very low output (or flow rate) values.

In the embodiment in the figure, divergent conduit 3 comprises two stages 30 and 31, the entire amount of the gas being injected through the first stage 30, while the air may be injected successively through stages 30 and 31.

It should be noted that the divergent conduit may comprise more than two inlet stages, and that the total amount of the gas to be introduced may be injected in the form of partial gas streams through the inlet stages shown, without departing from the spirit of the invention.

With a view to allowing the combustion air B to be introduced through the inlet stages, caisson 9 is divided into two compartments 90 and 91 connected to stages 30 and 31, respectively, of divergent conduit 3.

Each one of compartments 90, 91 is connected to a grid 10 comprising tiltable blades 11 allowing the injection cross-section to be modified by means of levers 12.

Detailed data of a practical embodiment of the invention are given in the following Example.

EXAMPLE A burner according to the invention comprises a nozzle 5 having an inner diameter of 75 mm, and a closing member 6 for adjusting the flow rate of said nozzle.

While the temperature of an acid gas containing about 60% hydrogen sulfide and 40% carbon dioxide was 400C and its pressure 60 millibars above the pressure prevailing in the furnace, the maximum admissible flow rate was adjusted to a value of 1641 Nm3/h.

The acid gas flow rate being about 1 60 to 540 Nm3/hour,an air flow of 240 to 810 Nm3/h proportional to the gas flow was injected from compartment 90 into the first inlet stage 30.

Under these conditions the second inlet stage only received cooling air at a low flow rate, and a preferably stable flame front was established in the first inlet stage.

When the acid gas flow rate exceeded 540 Nm3/h the air flow rate in the first inlet stage 30 was maintained at its maximum value, while the excess air required for satisfactory combustion was injected into the second inlet stage 31 from compartment 91. The flame front then moved and resumed a stable condition in the second inlet stage.

The invention is not limited to the embodiments described and shown herein; many variations and modifications may be envisaged by those skilled in the art, without departing from the spirit and the scope of the invention as defined in the appended

Claims

claims. CLAIMS

1. A gas burner with air injection comprising gas inlet means, air inlet means and a divergent conduit wherein said air and said gas are mixed to form an air/gas mixture, the end portion of said divergent conduit being provided with at least two air and/or gas inlet stages, wherein the minimum inner diameter of the second one of the said inlet stages is at least substantially equal to the inner diameter of the end of the first one of said stages.

2. The gas burner of claim 1, which comprises separate adjusting means for adjusting the respective flow path cross-sections of the injected gas and the injected air.

3. A gas burner according to any one of claims 1 and 2, wherein said means for adjusting the flow path section of the injected gas comprise a sealing member slidably mounted on the orifice of the gas inlet nozzle and controlled by manual or powerdriven control means.

4. A gas burner according to any one of claims 1 to 3, wherein said control means are actuated in accordance with the pressure prevailing in the said conduit.

5. The gas burner of claim 4, wherein the air flows, in each of said inlet stages, through an array of tiltable blades adapted to vary the cross-section of the air inlet flow and associated with a control lever.

6. A gas burner according to any one of claims 1 to 5, wherein the divergent conduit through which flows the air/gas mixture comprises a comparatively narrow or restricted neck portion the dimensions of which are chosen so as to accommodate the minimum flow rate at which the burner is adapted to be operated.

7. A gas burner according to any one of claims 1 to 6, wherein a servo-device is provided for actuating adjustable closing members adapted to control the air flow rate.