FR2745064A1 - Gas supply for flame cutter - Google Patents

Abstract

The gas burner (10) has a mixer (12) with its outlet connected to a feed duct of the burner. The mixer has an inlet connected to a collecting reservoir (14) for combustible gas feed and another inlet connected to a local reservoir (16) for gas. The collecting reservoir can be a reserve of natural gas. The mixer can have multiple gas inlets connected to local sources of different gases.

Description

 The present invention relates to an installation for implementing a flame, of the type comprising a gas burner, in particular a torch.

 Many industrial applications use a flame fueled by a combustible gas, including welding and flame cutting applications. The quality of the flame and the efficiency of the flame depend on the combustible gas with which the torch is fed.

 In flame cutting applications, acetylene provides short preheating times and fast metal cutting. However, this gas is relatively expensive for the applications considered.

 In addition, the acetylene stored in bottles is conditioned with a solvent. The latter may be entrained with the acetylene leaving the bottle if the output flow is high.

 Natural gas, which consists mainly of methane, supplied by the collective distribution network is relatively cheap. However, the yield of this gas is relatively poor.

 Weakly doped gases are known whose results are poor in the case of the supply of a heating flame. These gases are for example hydrocarbons whose added dopant gases are in a proportion much less than 5%.

Furthermore, mixtures of gases, such as the gases called "Crylene" (mixture comprising about 73% ethylene, 22% acetylene and 5% propylene), "Tetrene" (mixture of "MAPP" type comprising about 39% of methylacetylene and propadiene, 44% of propylene and 17% of a mixture of butane, propane and their unsaturated derivatives). These gases are currently marketed by
Air Liquide and allow to obtain a flame with a good performance for an acceptable cost of use.

 These gases are delivered in bulk by truck and stored in liquid form in permanent tanks, for large consumers. Tetena can also be delivered and stored in bottles.

 These distribution modes have disadvantages. Bottle packaging requires the user to manage the stock of bottles and planned supplies. Delivery by truck also requires a regular supply and imposes the presence of large tanks at the place of use, which presents dangers.

 In the case of a gas mixture withdrawn from a liquefied gas storage, whether bottle or tank, the composition of the mixture in the storage varies during racking. In fact, except in the case of sophisticated mixtures such as "Crylene" and "Tétrène", the saturation vapor pressures of each gas of the mixture being different, the composition of the mixture in the vapor phase is different from that of the liquid phase mixture. . This leads to a gradual change in the composition of the mixture at the outlet of the storage.

 The present invention aims to provide a solution to the problem of feeding a burner fuel gas, does not have the disadvantages mentioned above, and which allows operation of the burner with acceptable performance for a moderate cost .

 For this purpose, the subject of the invention is an installation for implementing a flame, of the aforementioned type, characterized in that it comprises, upstream of said burner, a mixer whose output is connected to a duct. supplying said burner with fuel, said mixer comprising an input connected to a collective network supplying fuel gas, and another input connected to a local storage of doping gas.

According to particular embodiments, the installation may have one or more of the following characteristics
- the collective gas supply network is a natural gas supply network
the mixer comprises a plurality of doping gas inlets, connected to local storage of different doping gases
the mixer comprises means for adjusting the composition of the mixture of gas from the network and doping gas
the or a doping gas is a gas conditioned in bottles, in particular acetylene
the or a doping gas is a gas conditioned in liquid form in a reservoir
the mixer is such that the added dopant gas (s) form at the exit at least 10 g of the mixture
or the doping gas is a gas comprising a multi-link carbon chain, in particular ethylene or acetylene
the or a doping gas is hydrogen; and
said doping gas is "Crylene" and / or "Tetrene"
the mixer incorporates a device with a venturi effect making it possible to increase the pressure of the mixture at the outlet of the mixer by using the overpressure of the doping gas
The subject of the invention is also a process for implementing a flame, in particular for flame cutting, characterized in that
- a combustible gas is collected from a collective network
a doping gas is taken from a local storage;
the two gases are mixed "in situ" in a predetermined proportion; and
- the mixture is burned.

 In the case of flame cutting, in one embodiment of this method, the flow rate of the doping gas, with respect to the network gas flow, is reduced at the end of the preheating phase.

The invention will be better understood on reading the description which will follow, given solely by way of example and with reference to the drawings on which
- Figure 1 is a schematic view of an installation according to the invention, implementing a single doping gas; and
- Figure 2 is a schematic view of an installation according to the invention, implementing several different doping gases.

 The installation shown in FIG. 1 essentially comprises a burner 10, for example a torch, and a mixer 12, supplied on the one hand by a bypass of the collective network 14 for supplying natural gas and on the other hand by a storage device. local 16 doping gas.

 The torch 10 is for example an oxycutting torch, whose oxygen supply means are not shown.

 As shown, a first input of the mixer 12 is connected by a pipe 18 to the collective supply network 14. This network provides a supply of natural gas, mainly methane, low cost.

 The second inlet of the mixer 12 is connected to the storage means 16 by a pipe 20. The storage means 16 are constituted for example by a bottle or an acetylene frame, or by a permanent reservoir of liquid fuel gas which is replenished periodically by truck. These storage means are provided on the same site of use of the torch, for example a laboratory, a building site, a workshop or a factory.

 The mixer 12 comprises input means 18A, 20A for controlling the flow rates of the two gases, to which are directly connected the lines 18 and 20, respectively. These flow control means are formed for example by manual or motorized valves. The outputs of the adjustment means 18A, 20A are connected to mixing means 22 provided in the mixer 12. These mixing means can be formed by joining the outlet ducts of the adjustment means 18A, 20A in a single duct, or by any other appropriate means more complex.

 The output of the mixing means 22 is connected by a pipe 24 to the fuel gas supply of the torch 10.

 The mixer 12 ensures the mixing of the methane from the collective network and the acetylene from the local storage means 16. Thus, the torch 10 is fed with a mixture of high efficiency combustible gases prepared directly at the site of use.

 The adjustment means 18A and 20A allow adjustment of the composition of the fuel mixture with which the torch is fed. Thus, the operator can determine the composition of the desired mixture to obtain optimum flame performance.

 For this purpose, the adjustment means 18A, 20A can be controlled directly from the torch 10 by any type of remote control means not shown. The operator can thus vary the composition of the mixture depending on the different phases of the work he is doing. In particular, in the case of oxycutting, the proportion of the doping gas can be increased during the preheating phase and then reduced during the cutting phase.

 It is understood that with such an installation, it is possible to enjoy the benefits of using a gas with high efficiency at a moderate cost and with simplified management.

 In addition, problems of storage of bottles or tanks are partially solved since only the doping gas must be stored. Thus, the dimensions of the gas storage area can be reduced, making it possible to improve the safety of the establishment.

 In Figure 2 is shown an alternative embodiment of an installation according to the invention. As before, this installation comprises a torch 40 and a mixer 42, one of whose inputs is connected to the collective network 44 for supplying natural gas. In this variant embodiment, the mixer 42 comprises, in addition to the natural gas inlet, three separate inputs for different doping gases.

 As shown, three different dopant gas storage containers 46, 48, 50 are provided and are connected by pipes denoted respectively 52, 54 and 56 to three separate inputs of the mixer 42. As previously, flow control means, noted respectively 52A, 54A and 56A, are provided at the input of the mixer 42. Similarly, adjustment means 58 of the natural gas flow from a tapping 60 on the collective supply network 44 are provided for the natural gas.

 The outlets of the flow control means 52A, 54A, 56A, 58 are connected to mixing means 62, the single outlet of which is connected to the torch 40 by a flexible pipe 64.

 It is conceivable that with such an installation, it is possible, depending on the applications of the torch to change the composition of the mixture used for feeding it. In particular, different dopants, or mixtures of these dopants, in combination with the natural gas from the network 44, can be implemented.

 As before, the composition of the fuel mixture can be manually modified before use or during use of the torch.

 In addition, the adjustment means 52A, 54A, 56A and 58 may also be formed by motorized valves controlled by control means, ensuring an automatic adjustment of the composition of the mixture according to a predetermined program, taking into account by example the successive phases of use of the torch 40 in an automated cutting process of a room.

 It is conceivable that such an installation can be extended to the use of several torches, by multiplying the number of mixers, each of which is connected in parallel to the collective natural gas supply network, and on the or each storage of doping gas.

 Furthermore, the doping gas may be any other type of fuel gas than acetylene, for example "Crylene", "Tetrene" or more broadly a mixture of "MAPP" type.

 However, it is interesting, if the gas distributed by the network is methane, to use a doping gas comprising a multi-linked carbon chain such as ethylene or acetylene. In the context of oxycutting, such a mixture makes it possible to obtain a fuel flame which compensates for the local decarburization of the metal bordering the kerf.

 In general, it is appropriate in a plant as described above to mix a gas with a low specific power and / or a low flame temperature, supplied by the network, with one or more gases of high specific power and / or at a temperature of high flame, added as a doping gas.

 Two examples showing the advantage of adding acetylene to methane in cutting applications will now be described.

Example 1
A first test focused on the evolution of the initiation time in full sheet for a cutting torch according to the proportion of acetylene in the feed mixture.

 The tests were conducted with a "Pyrosaf 400C" torch fitted with a "Mach 3S" cutting head of 10/10 caliber. This material is marketed in France by SAF (Soudure Autogène Française).

 The tests focused on cutting pre-sanded sheets 20 mm thick.

 The dimensions of the test pieces were 100 mm x 100 mm. The cutting oxygen pressure was set at 5 bar relative and the purity of the cutting oxygen used was greater than 99.9%.

 The test pieces before testing were at room temperature, between 10 and 15 ° C.

 The measurement concerned the priming time, ie the time required to bring the sheet to the cutting temperature (approximately 1300ex) from the ambient temperature.

 As the cutting temperature is difficult to define, the priming time is defined experimentally as the minimum heating time which has made it possible to obtain a cutting primer of the sheet during the supply of cutting oxygen. In order to determine the initiation time, a series of tests are carried out during which samples are heated with the same gas mixture initially at room temperature for different periods of time. Immediately after the heating, oxygen is provided each time cutting. The priming time is the minimum period of time which has given rise to priming, i.e., beginning of combustion of the specimen in the oxygen jet.

 The results obtained are recorded in Table 1 which follows.

 The quantity A corresponds to the consumption ratio, that is to say the heating oxygen flow rate brought back to the fuel flow rate.

TABLE I

<tb>;<SEP> 2 <SEP><SEP> Flow <SEP> Flow <SEP> Flow <SEP> A <SEP> Height <SEP> Time <SEP> Gain <SEP> of
<tb><SEP> C2H2 <SEP> CH4 <SEP> C2H2 <SEP> O2 <SEP> Nozzle <SEP> Start Time <SEP> Time
<tb><SEP> (l / h) <SEP> (l / h) <SEP> (I / h) <SEP> (mm) <SEP> (sec) <SEP> (%) <SEP>
<tb><SEP> 0 <SEP> 300 <SEP> - <SEP><SEP> 480 <SEP> 1.6 <SEP> 5.5 <SEP> 75 <SEP><SEP> - <SEP>
<tb><SEP> 5 <SEP> 285 <SEP> 15 <SEP> 473 <SEP> 1.58 <SE> 5.3 <SE> 65 <SEP> 13
<tb><SEP> 10 <SEP> 270 <SEP> 30 <SEP> 465 <SEP> 1.55 <SEP> 5 <SEP> 60 <SEP> 20
<tb><SEP> 15 <SEP> 255 <SEP> 45 <SEP> 458 <SEP> 1.53 <SEW> 4.6 <SEP> 55 <SEP> 26
<tb><SEP> 20 <SEP> 240 <SEP> 60 <SEP> 450 <SEP> 1.5 <SEP> 4.3 <SEP> 50 <SEP> 33
<tb><SEP> 25 <SEP> 225 <SEP> 75 <SEP> 443 <SEP> 1.48 <SEP> 4 <SEP> 45 <SEP> 40
<Tb>
It is found that the priming time is inversely proportional to the acetylene content of the mixture.

In particular, a time saving of 40% is observed for a mixture composed of 75 t of methane and 25% of acetylene.

Example 2
A second test examined the evolution of the cutting time of a steel rod with a diameter of 3.2 mm as a function of the proportion of acetylene in the feed mixture.

 The same material as in Example 1 was used. The dart has been moved tangentially to the steel rod. Two series of experiments were carried out with fuel flow rates respectively equal to 40 l / h and 60 l / h.

The corresponding results have been recorded respectively in the following tables II and III
TABLE II

<tb><SEP> Flow <SEP> Flow <SEP> Flow <SEP> A <SEP> Time <SEP> of <SEP> Gain <SEP> of
<tb> C2H2 <SEP> CH4 <SEP> C2H2 <SEP> 0z <SEP> cut <SEP> mean <SEP> time
<tb><SEP> (I / h) <SEP> (l / h) <SEP> (I / h) <SEP> (sec) <SEP> (t) <SEP>
<tb><SEP> O <SEP> 40 <SEP> - <SEP> 64 <SEP> 1.6 <SEP> 12.3 <SEP> - <SEP>
<tb><SEP> 5 <SEP> 38 <SEP> 2 <SEP> 63 <SEP> 1.58 <SEP> 11.2 <SEP> 9
<tb> 10 <SEP> 36 <SEP> 4 <SEP> 62 <SEP> 1.55 <SEP> 10.9 <SEP> 11
<tb> 15 <SEP> 34 <SEP> 6 <SEP> 61 <SEP> 1.53 <SEP> 10.8 <SEP> 12
<tb> 20 <SEP> 32 <SEP> 8 <SEP> 60 <SEP> 1.5 <SEP> 10.2 <SEP> 17
<tb> 25 <SEP> 1 <SEP><SEP> 30 <SEP> 10 <SEP> 59 <SE> 1.48 <SEP> 9.5 <SEP> 23
<Tb>
TABLE III

<SEP> t <SEP> Flow <SEP> Flow <SEP> Flow <SEP> A <SEP> Tempos <SEP> of <SEP> Gain <SEP> of
<tb> CH4 <SEP> CH4 <SEP> C2H2 <SEP> 02 <SEP> cut <SEP> mean <SEP> time
<tb><SEP> (l / h) <SEP> (1 / h) <SEP> (l / h) <SEP> (sec) <SEP> (%) <SEP>
<tb><SEP> o <SEP> 60 <SEP> - <SEP> 96 <SEP> 1.6 <SEP> 9.1 <SEP> - <SEP>
<tb><SEP> 5 <SEP> 57 <SEP> 3 <SEP> 94.5 <SEP> 1.58 <SEP> 8.8 <SEP> 3
<tb><SEP> 10 <SEP> 54 <SEP> 6 <SEP> 93 <SEP> 1.55 <SEP> 8.5 <SEP> 7
<tb><SEP> 15 <SEP> 51 <SEP> 9 <SEP> 91.5 <SEP> 1.53 <SEP> 8.2 <SEP> 10
<tb> 20 <SEP> 48 <SEP> 12 <SEP> 90 <SEP> 1.5 <SEP> 7.3 <SEP> 20
<tb><SEP> 25 <SEP> 45 <SEP> 15 <SEP> 88.5 <SEP> 1.48 <SEP> 7.1 <SEP> 22
<Tb>
In both cases, there is a significant reduction in the cutting time during an acetylene addition.

The reduction observed is of the order of 25% for a mixture consisting of 75% methane and 25% acetylene.

 In addition, the doping gas may also be a gas that does not contain a carbon atom, for example hydrogen. Hydrogen added to methane gives interesting results in polishing and flame glazing applications.

 On the other hand, the mixer that it comprises one or more inputs for doping gases can be controlled automatically by a suitable remote control device controlled by a management system of a gas supply installation, such as "TELEFLO" systems. "and" DATAL "offered by Air Liquide.

 In addition, in the case where the gas pressure from the collective supply network is low, it is possible to increase the pressure of the mixture at the mixer outlet by integrating thereto a device venturi effect. In this case, the overpressure of the doping gas is used to compensate for the low relative pressure of the gas supplied by the network.

 In such a device venturi effect, the main conduit in which the doping gas is conveyed comprises a section of reduced section over a short length. This section is formed by a convergent followed by a divergent one. In the convergent portion of this section of reduced section considering the direction of flow opens an axial conduit for supplying gas from the network.

 The foregoing description refers to a collective distribution network, and in particular to a communal or regional distribution network. Of course, the invention also applies to a local network specific to a company, an industrial site or a workshop. In addition, the gas distributed by the network may be different from methane. It may consist for example of propane, butane, or propylene.

Claims (13)

 1.- Installation for implementing a flame, of the type comprising a gas burner (10; 40), in particular a torch, characterized in that it comprises, upstream of said burner (10; 40), a mixer (12; 42) whose output is connected to a feed pipe of said fuel burner, said mixer having an inlet connected to a collective fuel gas supply network (14; 44) and another input connected to a local storage (16; 46, 48, 50) of doping gas.  2.- Installation according to claim 1, characterized in that the network (14; 44) collective gas supply is a natural gas supply network.  3.- Installation according to claim 1 or 2, characterized in that the mixer (42) comprises a plurality of doping gas inlets, connected to local storage (46, 48, 50) of different doping gases.  4.- Installation according to any one of the preceding claims, characterized in that the mixer (12; 42) comprises means (18A, 20A, 52A, 54A, 56A, 58) for adjusting the composition of the gas mixture from network and doping gas.  5.- Installation according to any one of the preceding claims, characterized in that the or a doping gas is a gas packaged in bottles, especially acetylene.  6.- Installation according to any one of the preceding claims, characterized in that the or a doping gas is a gas conditioned in liquid form in a tank.  7.- Installation according to any one of the preceding claims, characterized in that the mixer (12, 42) is such that the added dopant gas (s) form at the outlet at least 10% of the mixture.  8.- Installation according to any one of the preceding claims, characterized in that the or a doping gas is a gas comprising a carbon chain with multiple bond, especially ethylene or acetylene.  9.- Installation according to any one of claims 1 to 7, characterized in that the or a doping gas is hydrogen.  10.- Installation according to any one of claims 1 to 7, characterized in that the or a doping gas is "Crylène" and / or "Tétrène".  11.- Installation according to any one of the preceding claims, characterized in that the mixer incorporates a venturi effect device for increasing the pressure of the mixture at the outlet of the mixer using the overpressure of the doping gas.  12. A method for implementing a flame, in particular for flame cutting, characterized in that  - a combustible gas is collected from a collective network  a doping gas is withdrawn from a local storage  the two gases are mixed "in situ" in a predetermined proportion; and  - the mixture is burned.  13.- Process according to claim 12, for oxycutting, characterized in that reduces the flow rate of the doping gas, relative to the gas flow of the network, at the end of the preheating phase.