EP2577165B1

EP2577165B1 - Infrared rays device for environmental heating

Info

Publication number: EP2577165B1
Application number: EP11739170.6A
Authority: EP
Inventors: Pier Luigi Tenci
Original assignee: La Rude Srl
Current assignee: La Rude Srl
Priority date: 2010-05-25
Filing date: 2011-05-19
Publication date: 2015-07-15
Anticipated expiration: 2031-05-19
Also published as: SI2577165T1; ES2549040T3; HUE026412T2; PL2577165T3; IT1400045B1; EP2577165A1; WO2011148402A1; DK2577165T3; ITBS20100098A1

Description

Field of the Invention

The present invention relates to a device for heating the ambient by means of infrared rays, in particular for heating the ambient by means of an infrared radiation with a wavelength of between 3 and 5 micrometers.

State of the Art

In the field of heat generators, the use of the electrical energy or potential chemical energy of a fuel as a primary energy is known.
Electrical heat generators have considerable energy costs due to their low final efficiency compared with the electrical energy available to the user, which efficiency does not usually exceed 30% of the energy of the primary fuel used in a thermoelectric power plant. In practice, in most common work environments, the electrical energy requirement, even for infrared heating, would then have an unsustainable impact, not least due to the amount of electrical power required.
Alternatively to electric heat generators, gas heat generators are available which emit infrared radiations obtained by converting the heat generated by the combustion of gaseous fuels such as, for example, natural gas, methane, liquefied gas, LPG, urban gas of various compositions, gas of any type, normally used to feed boiler burners, stoves and industrial kitchens, for public and/or domestic use. Such devices usually emit infrared radiations at human height, i.e. within a height from the ground normally occupied by the users.
The heat generated by combustion is usually converted into an infrared radiation by means of a mineral fibre of amorphous silica, characterised by a degree of purity of over 99%, associated with the radiating means.
In their turn, gas heat generators can be fixed or moveable.
In gas heat generators of the fixed type, infrared radiation is usually achieved by a direct combustion of gas in an appropriate pipe. These generators are generally positioned at a height of at least four metres, in order to enable a certain distribution of the heat downwards by means of reflecting parabolas, without damaging the people most exposed to them. However, this requirement of a fixed location results in considerable losses of energy: the reflecting parabolas radiate heat not only downwards but also towards the ceiling of the environment.
Furthermore, the final efficiency of infrared heat generators fed by gas fuel is also penalised because the exhaust gases are expelled into the atmosphere at a relatively high temperature of about 250°C: this means that a high proportion of the sensible and latent heat is lost.
Furthermore, there are gas heat generators provided with ceramic plates in which the gas is combusted directly on the surface of the plates at a high temperature of about 700°C. These generators are poorly suited to work environments because, for safety reasons, they must be positioned high up, beyond the reach of any accidental contact by the users. The ceramic plates, heated to a high temperature, emit radiations with a wavelength of about 3 micrometres, this value being unfavourable for absorption by the irradiated human body, which more easily absorbs wavelengths of about 4-5 micrometres. Therefore, their thermal contribution as a whole and also the feeling of thermal well-being on the irradiated surfaces of the body are small.
Moveable heat generators are also available, fed by a bottle of fuel and provided with flame surfaces and radiating metal panels held in a raised position and facing downwards. These types of generators are often used in public places to heat areas that are in the open-air or exposed to draughts. These types of generators have a low efficiency too. Indeed, the need to limit the temperature of the hot surfaces that can be accessed by individuals, and therefore potentially dangerous because of accidental contacts, has a negative impact on efficiency.
Some known generators are described in the German Utility Model DE 29915469U1 , which describes the characteristics of the preamble of claim 1, as well as in FR-A-1375471 and FR-A-1450282 .

Object and Summary of the Invention

The object of the present invention is to overcome the above-mentioned operational limitations and hence to propose a device for heating the ambient by means of infrared rays, with high thermal efficiency, that can be safely used also at human height.
This object is achieved, according to the invention, with a device according to claim 1.
In particular, the device according to the present invention comprises:

a substantially vertical hollow casing, delimiting a central chamber with an entry in its base, a radial outlet and closed by a top cover,
a burner for the combustion of a gas, placed on the base of said hollow casing for the discharge of exhaust gas in said chamber,
a bore on a level with the entry of said chamber to provide an entrance for combustion air and for mixing with the exhaust gas coming from said burner and directed towards the radial outlet of said casing, and
radiating means placed between the entry and the outlet of said chamber, wherein said radiating means include a mattress of fibre of amorphous silica for infrared radiation which define the outlet for the waste gas, and in which said fibre of amorphous silica has a silica (SiO₂) content greater or equivalent to 99%, and a density, per unit of the surface, from between 90 and 120 g/m².

Advantageously, the hot waste combustion gases pass through a multilayer mattress of fibre of amorphous silica adapted for converting the heat of the combusted gas passing through it into an infrared radiation directed towards the ambient. Using amorphous silica maximises the efficiency of the heat exchange and the amount of irradiation of the infrared radiation diffused into the heated ambient, and minimises fuel consumptions and carbon monoxide emissions.
Preferably, the hollow casing is substantially cylindrical and comprises an internal reticular wall and an external reticular wall concentrically distanced; the mattress of fibre of amorphous silica, is placed and held between said walls.
According to a preferred embodiment of the invention, said fibre of amorphous silica has a silica (SiO2) content of about 99.99%. The high silica content prevents the devitrification of the fibres of the mattress, which is most advantageous to the device's useful life. In fact, the devitrification of the silica fibres substantially reduces heat-exchange efficiency and makes the device uneconomical.
Furthermore, the OH-ion content in the mattress is inversely proportional to the degree of purity of the silica fibre. In the case wherein the amorphous silica content is 99% or more, the OH-ions are almost completely absent; this characteristic makes it possible to maintain the efficiency of the infrared transmission of the mattress over time, thus minimising the device fuel consumptions.
Preferably, the mattress of fibre of amorphous silica contains long fibres with a diameter of between 2 and 13 micrometers, more preferably with an average diameter of about 9 micrometers.
Preferably, the fibre of amorphous silica forming the mattress has a density, per unit of surface area, of 110 g/m² .
The above values of diameter and/or density for the fibre of silica enable pressure losses encountered by the flow of fuel and comburent in the burner to be minimised, to the benefit of complete combustion and compliance with the limits set for carbon monoxide emissions. Preferably, the emissions of carbon monoxide are less than 210 ppm.
Preferably, the surface of the mattress of fibre of amorphous silica is exposed towards the radial exit of the casing of the device, and it is enclosed by a tissue also made of fibre of amorphous silica with a silica (SiO₂) content of at least 99% by mass. Such a tissue is in contact with the external wall of the hollow casing.
Preferably, the above-mentioned tissue has a density of 80 - 180 grams/m², preferably about 140 ±40 grams/m².
Preferably, the internal and external reticular walls enclosing the mattress of fibre of amorphous silica have an empty to full ratio from between 80% to 90%, more preferably of about 88%.
Preferably, the mattress of fibre of amorphous silica has an internal portion facing towards the internal reticular wall, covered by noble metals, preferably belonging to the platinum group.
More preferably, the internal portion of the mattress covered with noble metals has a depth of between 5-30 mm, for example between 20 mm and 30 mm. This value of the depth allows carbon monoxide (CO) emissions to be kept well below the limit of 1000 ppm set by Standard UNI EN 301-1 for burners of type 6, with the advantage of being able to use the device according to the invention in work environments.
The device according to the invention is fed by any combustible gas, preferably liquefied gas (LPG) and/or natural gas such as methane.

Brief Description of the Drawings

However, further details of the device according to the invention will emerge from the following description of a preferred embodiment, provided by way of a non-limiting example only and shown in the accompanying drawings, in which:

Fig. 1 is a front sectional view of a first embodiment of the invention;
Fig. 2 is a section taken along the arrows A-A in Fig. 3;
Fig. 3 is a partially cutaway top view of the device 1; and
Figs. 4a, 4b, 4c and 4d show details of four different components.

Detailed Description of the Invention

With reference to Figs. 1 and 2, the device according to the invention is generally denoted by 1 and, as stated above, it is provided for achieving an infrared radiation by direct conversion of the heat from the combustion at a burner 6 using gas fuels. The device 1 substantially comprises a vertical hollow casing 2 having in its base an entry 3 and a radial outlet 4 in the direction of the arrows F in Fig. 1.
The entry 3 is arranged so as to channel a flow of air to be mixed with the gases resulting from said combustion, themselves mixed with air passing from the outside towards the inside of the hollow casing 2, through a perforated member 26 which is typically cylindrical and made of sheet metal.
The radial outlet 4 enables the waste gases to be vented to the atmosphere. Interposed between the inside of the hollow casing 2 and the outlet 4 are converter and radiating means, denoted generally by 5, which are composed of fibre of amorphous silica.
The hollow casing 2 has a substantially cylindrical structure with an annular lower end 24 connected, in use, to a supporting structure 27 which supports the burner 6 and the afore said perforated member 26 enabling the combustion air and for mixing with the exhaust gases to pass from the outside to the inside.
The perforated member 26 also encloses means for conveying, adjusting and igniting the fuel, as well as a portion 28, however not essential, serving as a control panel for igniting the fuel and adjusting the flow by means of a tap 10. At its lower end 29, the perforated member 26 is connected, in use, to an open metal frame 16, preferably cylindrically-shaped, that supports the heating device 1 and, through an arm 13, a reflecting parabola 30 directing the infrared radiation towards a preferred user.
At the top of the hollow casing 2 there is provided a metal cover 25 containing an insulating material 25a, such as ceramic fibre, held inside a base plate 39 and adapted for limiting upward heat dispersion.
The base plate 39 is anchored to the cover 25 by means of at least one metal pawl 40 which is welded to the base plate itself. Positioned above the cover 25, at a certain distance, is a mesh member 31 - Figs. 3, 4a - so as to delimit between them a space 41 in which is held, by radial pressure, a welded mesh 7 - Figs. 3, 4b - surrounding the casing 2 in order to protect against manual contacts.
In particular, the hollow casing 2 has an internal wall 35 and an external wall 36 concentrically spaced, both composed of a stretched metal mesh - Fig. 4 - with an empty to full ratio of at least 85%, to enable the maximum throughput of combusted products without loss of load.
The internal wall 35 is anchored at the top to the outer edge of the base plate 39 of the cover 25; the external wall 36 is anchored at the top to a peripheral rim of said cover 25; both the internal and external walls are mechanically secured at the bottom by a metal ring forming part of the structure 24 at the base of the hollow casing 2.
The converter and radiating means 5 referred to above are arranged and held between the internal reticular wall 35 and the external reticular wall 36. They consist in a mattress of mineral fibres, particularly amorphous silica fibre having advantageously a density, per unit of surface area, of 110 g/m² and an average diameter of the fibre of about 9 micrometres.
In particular, a layer 38 of the mattress of fibre of silica of converter-radiating means 5 which is in contact with the internal reticular wall 35 of the cylindrical casing 2 is treated with noble metals capable of catalysing any unburned residues emitted by the burner. These noble metals are preferably of the Platinum group., Instead, the mattress of fibre of silica of the converter and radiating means 5 is externally lined with a tissue 37 placed adjacent to the external reticular wall 36 of the hollow casing 2 - Figs. 3, 4d. This tissue preferably comprises amorphous and/or washed silica with at least 96 % SiO₂ to aid maximum transparency for infrared radiation.
In the above-described assembly, the panel 28 supports the gas adjuster tap 10, and a flap 11 enables access to a battery-holder 32 for the ignition device 34, connected to the battery 32 by means of the wire 9. Furthermore, a double connection 33 connects the battery 32 in one direction to a microswitch forming an integral part of the tap 10, and connects in the opposite direction the microswitch to the igniter in order to close the battery - microswitch - igniter circuit.
Inside the intermediate member 26, upstream of the tap, there is a pipe 18 to convey the gas from a bottle 15 to the burner 6, whereas downstream of the tap 10 there are the pipes 41 feeding the burner 6. Exiting the burner 6 are wires 42, connecting to the igniter 34, and 43, coming from a thermocouple of the burner and connected to the safety device built into the tap 10.
At the end of the pipe 18, anchored at 8 to the panel 28, there is a rubber - holder element 19 to attach a hose 20 coming from the pressure adjuster 17 connected to the bottle 15.
The gas bottle 15 is located inside a bell 16 whose base 21 is provided with pivoting and/or self-braking wheels 22 to enable the device 1 to be moved within its place of use.
The bell covering the bottle is preferably formed of two half-shells. The reflecting parabola 30 is anchored to one 16 of these by means of the respective arm 13; the other half-shell 14 is provided with a handle 12 and can be opened by means of the hinges 44 in order to insert and/or remove the bottle on a supporting level surface 21.
At the base of the bell 16 there is a hole 23 intended for passing a hose to feed the device 1 with gas if the area to be heated has a gas distribution network. In this case, the bottle 15 can be used as a back-up in those places of the area not served by the gas (LPG) distribution network or the internal distribution network, or it can be totally omitted if methane gas is available.
When the heating device 1 is operating, the waste combusted gas flow, mixed with the air from the opening 3 of the cylindrical body 2, passes through the radiating converter means 5.
The SiO₂ content in the fibre characterising the mattress comprising the radiating means 5 is 99% or more, with an optical refraction index of about 1.46 and a dispersion of about 67, having an absolute transparency band of 0.2-4 micrometres, capable of producing a transmitted thermal power of 17-30kW/m² at a temperature inside the casing 2 of 450°-590°C.
On the whole, whereas the average temperature of the radiating means 5 is about 330°C, the temperature of the peripheral portion of the radiating means 5 in contact with the reticular wall 36 is about 105°=190°C, whose mostly-emitted wavelength can be easily absorbed by the users, is in the range from 4 to 5 micrometres, and enables 80-100 % absorption by the user.
The cylindrical casing 2 made as described above and having an empty to full ratio of more than 80% does not cause a loss of load for the combustion waste gas. The theoretical loss of load value, which can be calculated as 9x10^-4 - 12x10^-4 Pascal, is absolutely negligible for the purposes of complete combustion at the burner, without altering the emission values of any unburned products.
Purely by way of a non-limiting example, the thermal power that can be delivered by the device 1 can be adjusted from 1 kW up to 7.5 kW. The limit range of thermal enjoyment is within about 5 metres from the radiating means 5. When the reflecting parabola 30 is fitted, the maximum distance of thermal enjoyment can be as far as 6 metres.
Advantageously, the heating device can be arranged with its radiating means 5 at human height, so that the user can enjoy its effects directly over a large surface area of the body.
Moreover, the metal mesh 7 provides protection against accidental contact with the emitting surface 4 from outside, and the reflecting parabola enables the infrared thermal radiation emitted by the surface 4 of the casing 2 to be oriented and directed, if necessary. Another important aspect of the infrared radiation heating provided by the device 1 is the uniformity of thermal diffusion in the surrounding area, preventing concentrations of localised heat which are undesirable for the user.
The operation of the device 1 originates at the burner 6, which uses gas fuels to generate the heat required for the subsequent conversion into infrared radiation through the fibre of amorphous silica contained in the radiating means 5.
In order to achieve a high efficiency based on the thermal power transmitted, and therefore an energy saving, still having sufficient energy to heat the users in the desired place, the device 1 has an average radiant temperature of about 330°C and, at the same time, uses the sensible and latent heat of the gas flow combusted in the burner 6 and emitted into the surrounding ambient. These requirements are satisfied also thanks to the virtually negligible values of any residual emissions of unburned products such as: carbon monoxide (CO), coming from the combustion in the burner 6.
The burner 6 releases the unburned products well within the legal limits for use in environments such as hangars, for example. The unburned products released into the hollow casing 2 by the burner 6 are within 150-700 ppm, depending on the operating power, expressed in amount of carbon monoxide (CO).
Then, the amorphous silica fibre incorporated into the converter-radiating means 5 performs a further reduction of carbon monoxide emissions which reach values of 45-210 ppm on exiting the surface 4, such values being considerably below the legal limits for burners of type 6 as used in the device 1.
Achievement of both this environmental advantage and the improved thermal enjoyment by the user is favoured by the catalyzing metal coating 28 on the internal surface of the radiating converter 5, i.e. on the amorphous silica fibre exposed to the flow of gas coming directly from the flame of the burner 6, said radiating converter 5 thus having a high capacity for converting the unburned products into water vapour and CO₂.
In fact, the radiating converter 5, made as described above, allows any unburned residue to be reduced by over 70%, leaving mainly water vapour and CO₂ as the components of combustion.
In other words, the device of the invention enables high thermal efficiency to be achieved in that it allows the use of both the sensible heat of the combusted gas and the latent heat of the water vapour contained in the waste combusted gas, which is expelled directly into the ambient to be heated and which is added to that mostly irradiated as infrared radiations.

Claims

A device for heating the ambient by means of infrared rays, comprising
- a substantially vertical hollow casing (2), delimiting a central chamber with an entry (3) in its base, a radial outlet (4) and closed by a top cover,

- a burner (6) for the combustion of a gas, placed on the base of said hollow casing for the discharge of exhaust gas in said chamber,

- a bore on a level with the entry of said chamber to provide an entrance for combustion air and for mixing with the exhaust gas coming from said burner and directed towards the radial outlet of said casing, and

- radiating means (5) placed between the entry (3) and the outlet (4) of said chamber,
characterized in that said radiating means (5) include a mattress of fibre of amorphous silica for infrared radiation which define the outlet for the exhaust gas, said fibre of amorphous silica having a silica (SiO₂ content greater or equivalent to 99%, and a density, per unit of the surface, from between 90 and 120 g/m².
A device according to claim 1, wherein said hollow casing (2) is substantially cylindrical and comprises an internal reticular wall (35) and an external reticular wall (36) concentrically distanced and wherein the mattress of fibre of amorphous silica is placed and held between said walls.
A device according to claim 1 o 2, wherein the mattress of fibre of amorphous silica (5) contains long fibres with a diameter of between 2 and 13 micrometers, preferably with an average diameter of 9 micrometers.
A device according to any of the claims from 1 to 3, wherein the fibre of amorphous silica forming the mattress has a density, per unit of the surface, of about 110 g/m².
A device according to any of the claims from 1 to 4, wherein the mattress of fibre of amorphous silica has the surface exposed towards the radial outlet (4) enclosed in a tissue (37), made of a fibre of amorphous silica with a silica content (SiO₂) of at least 99%, said tissue being in contact with the external wall of the hollow casing (2).
A device according to claim 5, wherein said tissue (37) has a density of between 80 -180 grams/m², preferably 140 ±40 grams/m².
A device according to claim 2, wherein the internal reticular wall (35) and the external reticular wall (36) enclosing the mattress of fibre of amorphous silica (5) have an empty to full ratio from between 80% to 90%, preferably 88%.
A device according to claim 2, wherein the mattress of fibre of amorphous silica (5) has an internal portion (38) facing towards the internal reticular wall (35), covered by noble metals, preferably belonging to the platinum group.
A device according to claim 8, wherein the portion (38) of the mattress of fibre of amorphous silica (5) treated with a noble metal has a width of between 5-30 mm, preferably of between 20 mm and 30 mm.
A device according to any of the previous claims, wherein the burner (6) is fed with any type of combustible gas, preferably liquefied petroleum gas (LPG) and/ or natural gas, methane.