US 3908602 A
A hot water or steam generator in which a water reservoir, always containing liquid, is disposed at the base of a plurality of tubes running through a catalyst-containing chamber for the flameless oxidation of a hydrocarbon fuel to heat the water. The heated water, in liquid or vapor state, is passed in a closed or open circuit to operate a heat-consuming load such as an engine or heat exchanger.
Description (OCR text may contain errors)
United States Patent 1 Brulfert et al.
[ Sept. 30, 1975  Filed: Oct. 1, 1973  Appl. No.: 402,576
 Foreign Application Priority Data Oct. 4. 1972 France 72.35754 Mar. 15. 1973 France 73.09377 Mar. 16. 1973 France 73.09632  US. Cl. 122/4 D; 122/367 PF; 431/329  Int. Cl. F228 1/00; A21D 4/00  Field of Search 122/4 D, 367 R, 367 PF, 122/451; 431/329; 60/108  References Cited UNITED STATES PATENTS 2.082.338 6/1937 Hays 122/367 7--I i l l I i i i ii .2 I i i ii I i i 1 3.070.077 12/1962 Huet 122/451 3.110.300 11/1963 Brown et al. 122/4 X 3,387,590 6/1968 Bishop i 1 122/4 3.704.748 l2/l972 Hapgood 122/367 X Primary E \'aminerl(enneth W. Sprague Attorney. Agent, or Firm-Karl E Ross; Herbert Dubno  ABSTRACT A hot water or steam generator in which a water reservoir. always containing liquid, is disposed at the base of a plurality of tubes running through a catalystcontaining chamber for the flameless oxidation of a hydrocarbon fuel to heat the water. The heated water, in liquid or vapor state. is passed in a closed or Open circuit to operate a heat-consuming load such as an engine or heat exchanger.
6 Claims, 6 Drawing Figures US. Patent Sept. 30,1975 Sheet 1 Of4 3,908,602
US. Patent Sept. 30,1975 Sheet 2 of4 3,908,602
US. Patent Sept. 30,1975 Sheet 3 of4 3,908,602
U.S. Patent Sept. 30,1975 Sheet4 01*4 3,908,602
i: 2 1 I if FIG. 6
STEAM OR HOT WATER GENERATOR USING THE CATALYTIC COMBUSTION OF HYDROCARBONS The present invention relates to a generator for steam or hot water, using the catalytic combustion of gaseous or liquid hydrocarbons.
It is known that the essential characteristic of the chemical phenomenon called catalytic oxidation" is to effect complete combustion of the hydrocarbons at a relatively low temperature, of the order of 120C to 400C, without releasing any toxic products, and without flame, ash or smoke.
It is, therefore, a method of producing heat, and, speaking more generally, of producing energy, which is clean and as such requires no chimney nor any kind of flue pipe. It is also a heat producing process which is particularly economical, with near l% efficiency since there is no wastage of calories, and in which the cost price of the hydrocarbons per thermal unit is found to be the lowest when compared to all other means of heating or heat production, the reduction in the cost being of the order of 25 to 30%, and even 35%.
The aim of the present invention is to provide an apparatus using the catalytic combustion of hydrocarbons in order to produce pressurized steam or hot water whose energy or heat can be collected in various ways according to the intended purpose.
This steam or hot water generator has, according to the invention, at least one catalyst element capable of producing, when it is brought into contact with a hydrocarbon in the presence of air and by the catalytic oxidation of the hydrocarbon, an exothermic reaction giving a maximum temperature of the order of 400C, which is employed to vaporize or heat up a fluid flowing in a closed or open circuit. This fluid can be water or any other suitable liquid.
Preferably, this generator has several catalyst elements arranged vertically in the form ofa battery inside a heat-insulated casing, the space between these elements being filled up by banks of tubes through which the fluid runs, and which tubes are joined to each other in such a way as to form a wall-like screen without any intervening gaps between the elements, the elements being supplied with fuel by a main piping system which serves as many banks of diffusers as there are catalyst elements.
The catalyst elements, which can with advantage be on the basis of platinum sponge, cobalt sponge or ferronickel sponge, are excited by electric-resistance element or by spark equipment in which the spark is produced by electric, electronic or piezoelectric means.
In one construction, the combustible hydrocarbon is a pressurized gas, such as butane 0r propane, and the supply to the catalyst elements is effected from a source of gas, after the gas has passed through a suitable pressure regulator.
According to another embodiment, the combustible hydrocarbon is liquid under normal conditions, and the supply to the catalyst elements is effected by capillarity, injection or atomization.
The steam produced, collected in a reservoir situated above the catalyst elements, can pass through a circuit which can vary according to the intended purpose.
In one system, the steam which is produced feeds at least one receiver such as a steam engine or a turbine, the steam being passed through a closed circuit formed by a reservoir situated at the foot of the catalyst elements and permanently containing a liquid coming from a steam condenser and a cooling radiator, by the steam reservoir situated above the catalyst elements, and by a heat-insulated piping system for conducting the steam to the receiver and for the return of fluid.
The receiver is, for example, a closed circuit steam engine having at least one cylinder which communicates, through two opposite inlet ports and two opposite exhaust ports which are alternately covered and uncovered by a distributing device, with the heatinsulated steam supply and return pipes, the steam acting in each cylinder alternately on one and the other of the faces of a piston whose piston rod is associated with means for transmitting and converting the movement.
The steam generator of the invention, associated with such an engine forms a silently operating unit, is nonpolluting, and is of high efficiency, so that it has great advantages when compared with conventional engines. The high efficicncy is obtained due to the doubleacting pistons, to suitable lagging for heat insulation, and to a high steam pressure between 25 and 50 kg/cm whereas in the best of Diesel engines the pressure scarcely reaches 15 kg/cm In another embodiment of the invention, the steam or hot water produced supplies at least one heatexchanger. Depending on the kind of heat exchanger or exchangers, the generator can be adapted for different purposes:
a. for use in closed-circuit central heating for dwellings or industrial premises, using radiators, hot-air outlets or any suitable means of distributing and diffusing the heat produced;
b, for use in domestic or industrial water heaters; and
c. for use in central heating and water heating in combination.
Furthermore, the generator of the invention can be provided with a number of additional components for regulation and safety, such as pumps, valves, a pressurestat, a thermostat, an atmospheric monitor, by-pass pipes, etc., which are described later,
The invention will be better understood with the aid of the following description and reference to the attached schematic drawing in which:
FIG. 1 is a view in vertical section of a first embodiment, supplied with liquid hydrocarbons and used for running a closed-circuit steam engine;
FIG. 2 is a view of part of this engine showing, in longitudinal section, its motive cylinders;
FIG. 3 is a view of part of this engine, showing in longitudinal section its distributing chambers;
FIG. 4 is a view in transverse section showing a motive cylinder and the two corresponding distributing chambers of this engine;
FIG. 5 is a view in vertical section of a second embodiment of the steam generator of the invention, supplied with gaseous hydrocarbons and used for a heating installation with radiators;
FIG. 6 is a view in vertical section of a third form of construction of this steam generator, supplied with liquid hydrocarbons and used in a heating installation with pulsed air.
The form of construction represented in FIG. 1 is specially adapted to an engine represented in FIGS. 2 to 4. Broadly speaking, this steam generator contains catalyst elements which, when in contact with a liquid or gaseous hydrocarbon fuel, produce an exothermic reaction by catalytic oxidation a reaction which supplies pressurized steam acting on the pistons of the engine which is described later.
The engine, represented by way of example, has two opposing cylinder blocks 1. Obviously, the dimensions vary according to the motive power desired, but they are always relatively small.
Each cylinder block 1, is provided with removable sleeves 2 and 2a. The sleeve 2 defines the chamber of a motive cylinder 3, while the sleeves 2a, of which there are two, each define a distributing chamber, 4 and 5 respectively, situated at the side of the motive cylinder 3.
The distributing chamber 4 communicates with the motive cylinder 3 via two inlet ports 6a and 6!) for the pressurized steam, situated near the two ends of these cylinders 3 and 4.
The distributing chamber 5 communicates with the motive cylinder 3 via two exhaust ports 7a and 7!) for the steam, these also being situated near the two ends of these cylinders 3 and S.
A pipe 8, coming from the steam generator 9, leads into the distributing chamber 4. Another pipe 10 connects the distributing chamber 5 to the generator 9. The introduction of the steam is done through the pipe 8, and it is exhausted through the pipe 10.
In the chamber of each motive cylinder 3 is housed a motive piston 12, made solid with a rod 13. An oil duct 14, which runs through the rod 13, leads into the motive piston 12 and ensures the lubrication of the top of the motive cylinder 3. The sleeve 2 has an intermediate partition 15 through which the rod 13 passes.
The end of this rod 13 outside the chamber of the motive cylinder 3 is rigid with an auxiliary piston 16 which is a sliding fit in the outside part 17 of the sleeve 2.
The seal round the rod 13 is obtained by selflubricating packing rings 18 of the passive type, in which the sealing action increases with the pressure exerted in the chamber of the motive piston 3.
These packing rings 18 are themselves held in position by the rings 19.
In each of the distributing chambers 4 and 5 there is housed a slide valve 20, rigid with a rod 22. Each of the slide valves 20 has a substantially cylindrical shape, and its ends form two heads 20a and 20b, equipped with sealing rings. The distance apart of the heads 20a and 20b is so selected that when one of them is covering one of the ports 60, 6b, 7a or 7b of the distribution chamber, the other port is uncovered. The rod 22 emerges from the chamber through an intermediate partition 23 in the sleeve 2a.
Self-lubricating packing rings 24, which fit against the partitions 23, ensure the seal round the rods 22. These packingrings 24 are of the same type as the ones 18 described above for the chambers of the motive cylinders 3.
The seal at the ends of the motive cylinders 3 and also at the ends of the distributing chambers 4 and 5 is obtained by the common rings 25 and 26.
The cylinder blocks 1 and the inlet and exhaust pipes 8 and 10 for the steam are heat-insulated by suitable lagging 27.
Between the two cylinder blocks 1 is situated a crankcase 28 through which passes a motive shaft 29. The transmission of the movement of the motive pistons 12 to the shaft 29 is carried out, as in an engine or the conventional type, by connecting rods 30 hinged to the auxiliary pistons 16. These connecting rods are attached to a crankshaft (not shown) provided in the motive shaft 29.
A camshaft 32, whose rotation is synchronized with that of the motive shaft 29, enables the alternate movement of the slide valves 20 to be obtained. To this end, the rods 22, which are fixed to the slide valves 20, are each hinged to a push-rod 33 held against a cam 34 by a compression spring 35 fitted around the rod 22.
The arrangement described above and represented in FIGS. 2 to 4 is only a particularly suitable construction. Thus, the cylindrical slide valves 20 can be replaced by slides of a different type, by poppet valves or by any other reciprocating or rotary distribution device which would play the same part. The mechanical transmission of the conventional type can be replaced by a hydraulic transmission, the auxiliary pistons 16 then becoming compressors for the oil. Likewise, the number of cylinder blocks 1 is in no way restrictive, since the engine can just as well be made with a single cylinder as with a plurality of cylinders.
The generator 9, which furnishes the steam at the necessary pressure for supplying the motive cylinders 3 is housed in a casing, insulated by suitable legging 36; the dimensions of this casing depend on the power desired.
ln this casing are arranged, as in a battery, catalyst elements 37, fixed on vertical supports 38. These elements are composed of platinum sponge, cobalt sponge or ferronickel sponge, have a very long life, of the order of ten years.
The supplying of the fuel is effected via a piping system 39 which serves a series of banks of diffusers 40, each of which serves a catalyst element 37.
Between the elements 37 are arranged vertical tubes 42 which terminate at their two ends in reservoirs 43 and 44 respectively. One of the reservoirs 43, situated at the foot of the casing, serves all the tubes 42, while the reservoir 44, situated at the top of the casing, consists here of two chambers 44a and 44b which communicate with each other through one or more linking tubes.
The steam circuit is closed outside the casing, be-
tween the reservoirs 43 and 44. A heat-insulated inlet pipe 8, already mentioned, leaves the upper reservoir 44 to terminate at the distributing chamber 4. An exhaust pipe 10, also already mentioned, leaves the distributing chamber 5 to terminate at a condenser 45, situated at the top of a cooling radiator 46, whose foot communicates via a pipe 47 with the bottom reservoir 43.
An air-inlet pipe 48 is situated on the side of the easing; it is equipped with a filter 49 to retain dust particles, and also with an adjustable inlet butterfly valve 50.
When in contact with the fuel introduced via the diffusers 40, and in the presence of the air admitted via the pipe 48, the catalyst elements 37 release considerable heat, their temperature becoming about 400 450C. Consequently, the liquid which has collected in the lower reservoir 43 is vaporized in the tubes 42, and there is obtained in the upper reservoir 44 a pressure varying between 25 and 50 kglcm The vaporizing tubes 42 arranged between the catalyst elements 37, are joined to each other by vanes or by some other means (not shown) so as to form a walllike screen, without any intervening gaps, between the elements 37; this screen prevents direct radiation from one element to another.
The pressurized steam, brought to the cylinder blocks 1 by the pipe 8 is led alternately to the inlet ports 6a and 6b because of the reciprocating movements of the heads a and 20b of the slide valves 20.
The steam, admitted in this way to the motive cylinders 3, acts alternately on one and the other faces of the motive pistons 12 before it escapes, its pressure spent, through the outlet ports 7a and 7b and the pipe 10. The action of the steam is simultaneously exerted on the inner face of one piston 12 and on the outer face of the other piston 12.
The cycle terminates by the cooling operation and the final expansion of the steam in the condenser 45 and the radiator 46. It should be noted that the pistons 12 continuously produce power, and there is no dead time.
If required, part of the steam furnished by the generator 9 can follow a different cycle, for example for operating a turbine.
Various auxiliary components enable the unit to operate under the best conditions.
A pulsator pump 52, driven by the motive shaft 29, ensures the fuel supply via the piping 39. Here, the fuel is a liquid, but in an alternative form of this engine a pressurized gas can be used, for example butane or propane.
The control of the system is effected by the air-inlet butterfly valve 50 and also by a valve 51 in the pipe 39, equipped with a manual actuator which plays a similar role to that of the accelerator of a conventional engine.
A valve 53 with a variable opening, situated in the inlet pipe 8, gives a supplementary possibility of control, by acting directly on the amount and pressure of the steam is admitted.
The cooling operation is speeded up by a pipe 54 which takes liquid drawn off from the foot of the radiator 46 by means of the pump 55 driven by the motive shaft 29. This liquid is atomized, via an injector 56, inside the condenser 45.
A bypass pipe 57 connects the inlet pipe 8 directly to the condenser 45. It is equipped with a butterfly valve 58 controlled by a calibrated spring, and forming a safety device in case of excess pressure.
The exciting of the catalyst elements 37 is effected by an electrical-resistance element 59 which at the startup is switched on by hand, but which is capable of being automatically stopped and re-started when this is necessary.
Finally, the constant supply of water or any other liquid chosen to be subjected to the calorific radiation of the catalyst elements 37 is taken, preferably, from the foot of the radiator 46 via a pulsator 60 fitted in the pipe 47 and brought into action by the engine according to its steam and pressure requirements.
The rise in temperature and pressure, although rapid, requires a certain period of time. Therefore, means permitting an immediate start-up can be associated with the engine. For example, an auxiliary reservoir can be filled with compressed air at IOkg/cm during the operation of the steam engine. Piping connects this reservoir to the cylinder blocks 1, so that the expansion of the compressed air actuates the engine in the same way as steam. As soon as steam becomes available, this network is automatically cut out of circuit.
FIGS. 5 and 6 represent two other forms of construction of this steam generator, these being intended for producing heat. In the same way as in the form of construction previously described, the catalyst elements 37 are arranged as a battery, in groups of two, some face to face and others back to back, inside a casing which is heat-insulated by suitable lagging 36. The number of catalyst elements 37 is decided upon either according to the number of radiators or hot air outlets to be served, or according to the desired output of hot water, or, as the occasion might arise, according to these two requirements together. The fuel supply to the catalyst elements 37 is effected by piping 39 which serves as many banks of diffusers 40 and starting-up devices 61 as there are elements 37 in the generator 9.
Whhen working with propane or butane gas, corresponding to FIG. 5, this supply to the catalyst elements 37 is effected from a gas source 62 after the gas has passed through a suitable pressure regulator 63. When the generator is fed with a liquid fuel, corresponding to FIG. 6, the supply to the catalyst elements 37 is effected preferably by capillarity, injection or atomization. The fuel contained in a tank 64 flows either by gravity, in which case the tank is arranged to give a head, as shown in dotted lines in FIG. 6, or is pumped by a pulsator pump 52 driven by an electric motor or by an auxiliary steam turbine 65.
A primary valve 51, manually operated, allows the fuel to reach the main piping system 39 and the banks of diffusers 40. The igniting of the catalyst elements 37 is simultaneously performed at the foot of each of them by a single contact actuating a device 66 in which the spark is produced either by an electric battery or any other source of electricity, by an electronic device, or by a method of self-ignition of the piezoelectric type.
The quantity of gaseous or liquid fuel admitted to the diffusers 40 of the catalyst elements 37, and also the reignition of the latter when necessary by the device 66, are automatically controlled by a pressure-stat 67 coupled into the piping system 39 via small-bore pipes from one of the chamber 44a. This pressure-stat is preset for this purpose, in the case of a closed circuit steam system, according to the calorific diffusion requirement of the radiators 68 (FIG. 5) or of the hot-air outlets served by piping 69 from a blower 70 (FIG. 6) or, again, according to the desired temperature and output of hot water in the case of the generator being used solely for heating water, or combining water-heating with central heating. In the latter case it is obvious that the generator cannot operate as a closed circuit, and requires piping 71, indicated in dotted lines in FIGS. 5, connected to a general water supply circuit. The pressure-stat 67 can be replaced by a thermostat.
In the main piping system 39 for introducing the fuel, and inside the casing, there is arranged, for reasons of safety and in compliance with legal regulations, an atmospheric monitor 72 so that the fuel is cut off in the event of any defect in the operation of the generator or of any alteration of the atmosphere inside the casing (leakage of gas or other fuel).
Naturally, one and the same monitor can exercise control, should the occasion arise, at the actual source of the fuel.
Between the catalyst elements 37 and directly subjected to their calorific radiation there are arranged banks of tubes 42 in which water or any suitable liquid circulates when it is a question of a boiler operating in closed circuit solely for central heating, or with the addition of water from outside in the case of water heating alone or water-heating in conjunction with central heating, it being understood that one or other of these two functions can be stopped at any moment merely by operating cocks fitted for this purpose in the corresponding circuits.
The tubes 42 can be of steel, duraluminum, cast iron or any other metal or alloy. They are joined to each other by vanes or by any other means so as to form a wall-like screen, without intervening gaps, between the catalyst elements 37 thus preventing direct radiation from one element to another. Their section varies according to the temperature and the output likely to be demanded of them.
The tops of the tubes 42 are joined to steam chambers 44a and 44b which communicate with each other via one or more linking tubes 73 and which also communicate with distribution pipes 74 through non-return valves 75.
In the heating installation with radiators represented in FIG. 5, the pipes 74 communicate with a steamcondensing flask 76, the capacity of which is determined by the number of radiators 68 to be served, and- /or in the case of operation a water heater, whether or not combined with the heating system, by the temperature and the output of hot water desired.
In the heating installation with pulsed air represented in FIG. 6, a tubular or honeycomb type radiator 77 is supplied with steam or hot water via the pipes 74. The blower 70 projects a current of air through the radiator 77 and this air is collected by the pipe 69 so that it can be directed towards the hot air distribution outlets.
A pump of the same type as the pump 52 can be fitted in one of the pipes 74 between the steam chambers 44a and 44b and the flask 76, this pump acting as a circulator.
The banks of the tubes 42 are joined at their foot to a main tube 47 which, in the case ofa generator operating in closed circuit, is supplied from a reservoir 78 into which all the water-return tubes 79 lead after the water has been used in the radiators 68 (FIG. or in the tubular or honeycomb radiator 77 associated with the pulsed air blower 70 (FIG. 6).
When operating with hot water, without producing steam, the water supply to the tube 47 and to the radiators including those of the pulsed air system, can be likewise obtained by fitting a circulator in the circuit, according to the needs and requirements of the latter.
When operating with steam, the water-return tubes 79 terminate in a reception vessel 80 whose role it is to ensure, by means of a float 81, that the reservoir 78 is always maintained at a constant level which corresponds by the simple principle of communicating vessels, to the most desirable level in the tubes 42 for the optimum efficiency of the boiler.
The part played by the float 81 is, therefore to regulate the admission of the water to the reservoir 78 from the balancing vessel 80.
In the case of a pump 52 driven by a steam turbine 65 (shown in FIG. 6), the turbine is supplied with steam through a small-bore pipe 82 from one of the steam chambers 44a situated at the top of the banks of tubes 42. The return of the steam takes place via a tube 83. In this case, and during the short period of time, to seconds at the most, preceding the first production of steam by the catalyst elements for bringing the turbine 65 into action, the starting up of the turbine is effected either by a clockwork timing device or by a small electric motor working from batteries or from the mains; in any case the two devices are automatically removed from the circuit by a cutout operated by the steam when it starts operating the turbine.
As is obvious, and as can already be seen from the foregoing, the invention is not restricted only to the forms of construction of this steam generator which have been described above by way of nonrestrictive examples; on the contrary, the invention covers all the alternative ways in which it can be constructed and applied, within the scope of the appended claims.
What we claim is:
l. A steam or hot water generator using the catalytic combustion of hydrocarbons as the sole heating-energy source, comprising a heat-insulated casing forming a housing; a plurality of vertically arranged elongated catalyst elements spaced apart in said housing and capable of producing, when brought into contact with a hydrocarbon in the presence of air and by the catalytic oxidation of the hydrocarbon, an exothermic reaction at a maximum temperature of the order of 400C, the catalyst elements comprising a substance selected from the group which consists of platinum sponge, cobalt sponge and ferronickel sponge; means for feeding said hydrocarbon and air into contact with said catalyst element; means including banks of tubes in said housing between said elements heated by said reaction for passing watter through said housing and to a heatconsuming load, said water being heated in said tubes, saidtubes being laterally joined together to form gapfree wall-like screens around each element; respective diffusers at each of said elements for admitting the hydrocarbon as a fuel thereto; and a main piping system for delivering the hydrocarbon to the diffusers and which serves as many banks of diffusers as there are catalyst elements.
2. The generator defined in claim 1, further compris ing electrical resistances in said casing for the heating of the catalyst element necessary to start up the generator.
3. The generator defined in claim 1, further comprising a single contact situated at 'the foot of said catalyst element, and a device actuated by said contact whereby a spark is produced by electrical, electronic or piezoelectric methods.
4. The generator defined in claim 1 wherein said hydrocarbon is a liquid and said main piping system includes said feeding means with a pulsator pump driven by steam supplied via small-bore piping from said tubes.
5. A steam or hot water generator using the catalytic combustion of hydrocarbons as the sole heating-energy source; comprising a heat-insulated casing forming a housing; a plurality. of vertically arranged elongated catalyst elements spaced apart in said housing and capable of producing, when brought into contact with a hydrocarbon in the presence of air and by the catalytic oxidation of the hydrocarbon, an exothermic reaction at a maximum temperature of the order of 400C the catalyst elements comprising a substance selected from the group which consists of platinum sponge, cobalt sponge and ferronickel sponge; means for feeding said hydrocarbon and air intocontact with said catalyst element; means including banks of tubes in said housing between said elements by said reaction for passing water through said housing and to a heat-consuming load, said water being heated in said tubes, said tubes being laterally joined together to form gap-free walllike screens around each element; respective diffusers at each of said elements for admitting the hydrocarbon as a fuel thereto; and a main piping system for delivering the hydrocarbon to the diffusers and which serves as many banks of diffusers as there are catalyst ele ments, the amount of fuel admitted to the diffusers of the catalyst elements, and also the reignition of these elements being automatically controlled by a pressurestat or thermostat acting on the main fuel supply pipe and connected via small-bore piping to one of the chambers into which the banks of tubes lead, the said pressure-stat or thermostat being pre-set according to the calorific requirements.
6. A steam or hot water generator using the catalytic combustion of hydrocarbons as the sole heating-energy source; comprising a heat-insulated casing forming a housing; a plurality of vertically arranged elongated catalyst elements spaced apart in said housing and capable of producing, when brought into contact with a hydrocarbon in the presence of air and by the catalytic oxidation of the hydrocarbon, an exothermic reaction at a maximum temperature of the order of 400C, the catalyst elements comprising a substance selected from the group which consists of platinum sponge, cobalt sponge and ferronickel sponge, means for feeding said hydrocarbon and air into contact with said catalyst element; means including banks of tubes in said housing between said elements heated by said reaction for passing water through said housing and to a heatconsuming load, said water being heated in said tubes, said tubes being laterally joined together to form a gap free wall-like screens around each element; respective diffusers at each of said elements for admitting the hydrocarbon as a fuel thereto; and a main piping system for delivering the hydrocarbon to the diffusers and which serves as many banks of diffusers as there are catalyst elements, said generator further comprising an atmospheric monitor, intended to cut off the hydrocarbon supply in the event of defective operation.