MC986A1 - Installation for heating or vaporizing liquids or gases - Google Patents

Description

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The present invention relates to an installation for heating or vaporizing liquids or gases, and in particular water, for example for heating, for recovering industrial heat, for use in energy technologies, etc.

The installation preferably takes the form of a boiler which receives, by radiation, the heat released by combustion on heat exchange surfaces, the fraction of heat transmitted by convection being negligible.

Modern boilers in which radiation constitutes the principal and practically the sole means of heat transfer, according to the theory to which the invention belongs, are still in the early stages of their development. Therefore, such boilers cannot be compared directly or indirectly with conventional boilers, because in the latter, both the combustion process and the design ensure that the largest fraction of the heat is transferred solely through convection heat exchange surfaces. However, even with these conventional boilers, tests have been carried out to operate them with flameless heating, with a view to achieving, through improved radiation, more advantageous specific power outputs of the heat exchange surfaces. The desired increase in power output for these boilers was limited to

reduced values, because, on the one hand, the temperatures reached on the surface of the ceramics remain low, because it is impossible to release significant amounts of heat, and, on the other hand, the choice of flameless burner types and their mounting 30 in relation to the heat exchange surfaces proved to be inappropriate.

Publications exist that deal with the first trials of new types of boilers operating solely by radiation. These boilers have heat exchange surfaces embedded in a layer of fireclay. Such an installation exhibits characteristics of both flame-tube and water-tube boilers. Since the approach was based solely on general principles relating to the transfer of heat released by surface combustion, it was not possible to increase the efficiency as technically feasible as might have been hoped by introducing radiant heat transfer elements.

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"The boiler technology" This is why radiant boilers corresponding to this type of design have not received the expected reception in practice.

It is only recently that the principle of the structure of radiant boilers has been modified by utilizing, for the first time, the efficient properties of certain ceramic or other materials at high temperature potentials. This was made possible by intensively guiding the combustion onto the active surface of these materials. In this way, the heat exchange fraction by radiation has become predominant over other types of heat transfer. This has allowed for considerably higher thermal loads on the heat exchange surfaces.

15 However, these types of boilers pre

they feel certain drawbacks from a construction point of view,

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which do not allow for the full use of the processes of this fluid heating principle"

We know of single-chamber boilers 20 forming the smallest functional unit. These boilers have either smooth walls or walls formed by ribs which are directed only in the direction of passage of the combustion gases. Such a boiler is close, from the point of view of its characteristics, to a flame-tube boiler, 25 even if this boiler is formed by cast iron elements joined in a way known to form more powerful units, or even if it is a steel reactor unit; assembled in a battery, and in which the liquid to be heated is accumulated. The flat and smooth surfaces of the shallow or longitudinal ribs, and in particular of the reaction chambers, in the shape of elongated rectangles, have heat exchange surfaces that are not advantageously distributed for radiation and at the same time allow unburned gases to escape to pass into the upper areas of the reaction chamber, along the heat exchange surfaces. There is, therefore, a reduction in radiation. A large part of the hollow heat exchange surfaces surrounding the fluid to be heated are only weakly affected by radiation. All these disadvantages mean that the volume and weight of the boiler cannot be reduced further, and the realization of such a

Boilers require a lot of work and complex machinery.

The present invention aims to create an installation of the type indicated above, receiving a lining of a gas-permeable radiating material, such as zirconium silicate, which is brought to a hot state in which it radiates practically all the thermal energy released on its surface. The radiating material is in direct contact with the heat exchange surfaces and is enclosed by them.

To this end, the invention relates to an installation of the type indicated above, characterized in that the heat exchange surfaces are made in the form of hollow envelopes of cylindrical or prismatic shape, through which the fluid to be heated passes and which are grouped around the same axis, intermediate volumes, continuously filled with radiant material, located between the envelopes, and the lower part of the envelopes comprising a common housing for homogenizing and distributing the fuel-air mixture.

In such a boiler, the material that fills the gaps between the heat exchange surfaces can cause combustion known as "symmetrical contact combustion," which is the only way to create a thermal regime for i

which this material delivers, by radiation, practically, thanks to its properties, all the thermal energy released at its surface. The radiation occurs in wavelength ranges between 0.5 and 6 microns. The term "surface" refers to the surface of all the particles of the filling material, including pores, channels, etc. The term "surface" is not limited to surfaces in contact with the heat exchange surfaces.

According to another characteristic of the .inf^nt-ion, the various coaxial heat exchange envelopes are equipped with radial hollow ribs, of semi-circular, triangular or prismatic shape. These ribs are preferably obtained by winding metal pipes having the corresponding profile, to form spirals with one or more threads with a constant radius of curvature.

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These spirals are traversed by the heated liquid, and the spirals are preferably closely adjacent.

According to a variant of the embodiment, the coaxial envelopes have a horizontal axis of symmetry, such that instead of a continuous spiral, each envelope is formed by a greater number of distinct threads that are directly adjacent and whose intervals are joined.

At the lowest point, to a common liquid supply. At the highest point, the pipes are connected to a common fluid outlet.

The boiler according to the invention consists of one, two, or more hollow shells, preferably of the same height, which have a shape corresponding to what has been described and whose heat exchange surfaces may be perfectly smooth, but which nevertheless preferably have ribs corresponding to the desired profiles,

"along their entire height" These ribs are located in parallel planes, perpendicular to the axis of symmetry of the envelope, that is to say transverse to the direction of passage of the combustion gases"

In the case of envelopes formed by circular tubes and constituting a spiral with one or more threads, the threads being connected in series or in series-parallel, the surfaces of the tubes naturally form 25 ribs. Tubes having a profile other than a circular profile must be wound so as to form corrugated heat exchange surfaces for the envelope.

According to one variant, the envelopes can be made by press profiling the walls, 30 from sheets9 or by casting as an assembly, or by joining elements having an external surface of suitable shape and which together form the surface ribs.

According to another feature of the invention, a common housing is provided in the lower part of the envelopes to homogenize and distribute the fuel-air mixture in the various intervals between the envelopes. This common housing is very advantageous because it ensures a single, regular thermal regime in all the intervals filled with radiant material.

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which allows for maximum heating. This assembly represents an improvement over known assemblies in which each chamber is equipped with a separate homogenization and distribution device. As in the installation according to the invention, the hollow casings are grouped according to the power required to form a larger boiler, that is to say, they are fitted one inside the other. It is necessary that the various heat exchange casings be dimensioned in such a way that the casing closest to the axis of symmetry has the smallest distance between

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its periphery and its axis and constitutes the smallest basic unit, each other envelope being further away with its periphery from the axis of symmetry. This radial gap is chosen 15 in such a way that between two adjacent envelopes there remains a constant interval over the entire periphery, the width of this interval corresponding to the inner diameter of the smallest basic unit.

The reaction chamber of the boiler, 20 that is to say the chamber where combustion takes place as well as the emission of radiation of the released heat, is formed in such a way that the intervals between the various envelopes containing the fluid to be heated, and which are obtained by an appropriate staggering of the radii of the various envelopes, are 25 filled with a radiation material permeable to gases. This material allows for extremely intense kinetic contact combustion of a homogeneous mixture of fuel and an oxidizing agent at its surface, under extreme combustion conditions. That is to say, for such a high flow velocity of the fuel mixture, the order of magnitude of which exceeds the frontal velocity of flame ignition, the temperature of the mixture in the main veins that pass through the radiating material layer remains below the ignition point. Surface combustion obtained in this way allows such a temperature regime in a narrowly limited layer of the radiating material and, as a result of the other properties of this material, in practice all the available heat released by combustion is transmitted by radiation to the metallic walls of the

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"Heat exchange capacity in radiation with wavelengths between 0.5 and 6 microns." In a temperature regime that is at lower potentials and commonly obtained in a known surface, flameless combustion process, the fraction of heat flux transmitted by radiation decreases and the fraction of heat transmitted by convection increases. For this reason, such a combustion process is not suitable for a radiant boiler.

Because the gas-permeable radiation material, which specifically touches the heat exchange surfaces, arrives directly on the areas formed by the transverse ribs, two advantages are obtained.

On the one hand, advantageous angular conditions are achieved for the radiation of the heat exchange surfaces, resulting in an increase in the heat flux over the exchange surface. On the other hand, the transverse ribs constitute an obstacle preventing the unintended free passage of a portion of the fuel mixture along the heat exchange surfaces into the volume above the main combustion zone, which would unintentionally increase this zone. In this way, combustion is concentrated in a small volume below a pyrometric temperature that advantageously influences the intensity of the heat flux in the effective wavelength range.

Due to the grouping of the concentric jackets of the boiler, the heat exchange surfaces of all the inner jackets receive radiation from both sides. Only the outer jacket is an exception to this rule, as it receives radiation from only one side. As a result, the greater the number of concentric jackets, the better the use of the boiler surfaces for heat transfer, which allows for progressive miniaturization of the installation, better utilization, a reduction in self-weight, as well as a reduction in manufacturing work and costs.

The installation allows for a unit

of a very small base which consists of a single hollow casing closed by winding a metal pipe with closely adjacent turns and whose free diameter allows the use of a boiler of this type even if the power required is reduced, the own power of such a basic unit being in itself very high

Thanks to the overall assembly of the heat exchange casing as described above, the heating unit according to the invention saves approximately 30 grams in weight compared to conventional radiant boilers with longitudinal ribs. Above all, a boiler according to the invention allows for higher power outputs. If we compare the power output of a boiler according to the invention, comprising only a single heat exchange casing formed by a pipe wound to constitute a circular cylinder, with a known boiler whose peripheral casing is in the form of a smooth circular cylinder of the same free diameter, or with a boiler whose smooth casing has a prismatic shape with a square profile and whose length on one side corresponds to the diameter of the cylindrical casing according to the invention, we find that the power output of the boiler according to the invention is 84% higher than that of the boiler with a smooth circular cylinder and 10% higher than that of the boiler in the shape of a square prism. In this comparative example, the heights of the various boilers are assumed to be equal. The same advantages as those indicated also apply to a boiler according to the invention composed of several casings.

The present invention is described in more detail with the aid of an exemplary embodiment shown schematically in the accompanying drawings, the installation being in the form of a boiler for heating water. In the drawings §

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- Figure 1 is a vertical cross-sectional view of the boiler;

- Figure 2 is a plan view of the boiler9 with the gas collector cap removed.

The boiler according to the invention shown in Figures 1 and 2 consists of three cylindrical assemblies 1p 2, 3? of circular cross-section which are made by

The winding of three metal tubes, themselves having a circular cross-section, to form three independent spirals with a single pitch, all having the same height. The free diameter of envelope 1 corresponds to the width of the interval formed by a ring between envelopes 1 and 2, as well as between envelopes 2 and 3. The axis of symmetry 4, which is the axis of envelopes 1, 2, 3, is in this case a vertical axis.

The lower ends of the spiral tubes forming the jackets 1, 2, and 3 are connected to a common supply line 5. The upper ends of these tubes are connected to a common discharge line 6 for the heated water. The lower part of the jackets 1, 2, and 3 is closed by a common distribution grid 7 in which a set of orifices 8 in the form of circles or slots is provided. Below the grid 7 is a circular housing 9 having a spiral bottom 10 and a tangential supply line 11, for a homogeneous mixture of hot gases with water. The upper part of the peripheral jackets 1, 2, and 3 is fitted with a collector cap 12 and a chimney 13 for the evacuation of fumes. All the intervals 1.5 between the jackets 1, 2, and 3—intervals whose width is constant—as well as the intermediate volume of jacket 1, whose internal diameter is equal to this width, are filled of a radiating material 14 permeable to gases, for example a zirconium silicate.

The water in the closed boiler is heated in the following way:

For a stabilized thermal regime, a homogeneous fuel-air mixture, in particular in a stoichiometric ratio, is sent from a mixing and homogenizing device (not shown) via a supply line 11. This mixture is sent into the cylindrical casing 9, whose spiral base 10 directs the flow of fuel gas towards the distribution grid 7. The openings 8 in the grid 7 allow the mixture to pass into the radiation-filled chamber 14 above the grid 9.

The dimensions, shape and properties of material 14 are chosen according to the layer thickness, the size of the boiler and the type of fuel

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i used. If, for any power, the dynamic equilibrium between the flow velocities of the fuel mixture in the channels remaining between the grains of the radiation material 14 and the combustion rate 5 directly at the upper surface of the material is stabilized, under extreme conditions, a combustion zone is located at a distance of approximately 10 mm above the grid 7. This combustion zone occupies approximately one-third of the height of the radiation material layer 14. 10 The combustion proceeds with an intensity

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from 60 to 110 million kcal/h in a 1 m³ volume filled with radiating material. For such a concentration of heat released and for a pyrometric temperature exceeding 1600°C, if necessary using a selectively radiating material, it is possible to radiate heat energy precisely in a wavelength spectrum between 0.5 and 6 microns. This radiated energy reaches the semi-circular ribs formed by the pipes constituting the envelopes 1, 2, 3 through which water flows. The water 20 passes through a common supply pipe 5 and exits through a common discharge pipe 6.

The natural ribs formed as described above result in the heat radiation falling on the heat exchange surfaces in a large spherical area, at angles that correspond approximately to an angle of incidence of 90°, thus increasing the heat flux per unit area of the exchanger. The greatest amount of heat is therefore released in the combustion zone.

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A smaller fraction of heat is released in the larger 30 wavelengths, in the remaining two-thirds of the height of the radiation mass 14 material and, in these areas, the material is heated by the combustion gases which are at a lower temperature.

The entire heat exchange is intensified to such an extent that the temperature of the combustion gases, when they leave the radiant material layer (14), which has a total height of 200 to 300 mm, is only 180-250°C, making it unnecessary to include additional heat exchange surfaces in the boiler to recover heat by convection. Despite this, the boiler efficiency is practically on the order of 90%.

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participates in less than 5% of the total heat transferred to the envelopes. 1 <> 2S 3 in the enclosure filled with radiating material 14„

The combustion products that have already cooled in the layer of radiant material 149 accumulate below the collecting cap 12 and are evacuated through the chimney 13. In the boiler, a combustion process can be expected that takes place either under overpressure

either in depression, obtaining a high degree of radiation requires that the combustion zone be as narrow as possible and remain localized in the lower part of the boiler. The transverse ribs of the peripheral jackets 1, 2, 3 act as a resistance, particularly with regard to the passage of the unburned gas mixture along the heat exchange surfaces, so that the combustion zone is not extended in the upper positions and the combustion intensity is not reduced.

Operational tests of a boiler composed of three jackets yielded the following experimental results: g heat output

Average 274,700 kcal/h; average load of the exchange surfaces

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Thermal output 203,000 kcal/m³, efficiency 90.8%. The weight of the boiler itself, without fan or control equipment, was 42 kg. The weight of the zirconium silicate charge was 48 kg. This gives a specific weight of the boiler, without packing, equal to 0.53 kg/1000 kcal/day of installed power. More advantageous figures are obtained if the boiler is adapted to produce saturated steam.

Progressive miniaturization is particularly important for the installation of radiant boilers in residential or industrial buildings, as well as for use as a motive unit or as a source of compressed steam for motor traction. In all cases, the boilers according to the invention contribute to environmental protection because they pollute the atmosphere less than known boilers. From a manufacturing standpoint, the work required to produce a boiler according to the invention is less significant. At least 90% of the weight is saved compared to conventional boilers.

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The machines needed for this manufacturing process are less complex.

The installation has been described above in relation to the heating or vaporization of liquid. However, this device can also be adapted to allow the heating of gas and in particular the heating of air.

Of course the invention is not limited to the example of embodiment described and represented above, from which other embodiment variants can be envisaged, without going out of the scope of the invention.

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Claims (1)

CLAIMS 1°) An installation for heating and vaporizing liquids or gases, filled with a gas-permeable radiating material, in particular zirconium silicate, 5 which can be brought to a hot state in which it radiates practically all of the heat energy released on its upper surface, the radiating material directly touching heat exchange surfaces surrounding it, an installation characterized in that the heat exchange surfaces 10 are made in the form of hollow envelopes (1, 2, 3), cylindrical or prismatic in shape, through which the fluid to be heated passes and which are grouped around the same axis, intermediate volumes (15), continuously filled with radiating material (14), located between the envelopes (1, 2, 3), and 15 the lower part of the envelopes (1, 2, 3) comprising a common casing (9) for homogenizing and distributing the fuel-air mixture. 2°) Installation according to claim 1 characterized in that the envelopes (1, 2, 3) have the shape of hollow ribs on their wall touching the radiation material (l4), these ribs being arranged in radial planes perpendicular to the direction of gas flow. 3°) Installation according to any one of claims 1 and 2, characterized in that the enclosures (1, 2, 3) are formed by wound metal pipes, the turns of which are directly adjacent, the enclosures being connected in series, in parallel or in series-parallel. 4°) Installation according to claim 1, 30 characterized in that the width of the intervals (15) receiving the radiating material (l4) is constant between two adjacent heat exchange surfaces for the various envelopes (1, 2, 3) 5°) Installation according to claim 1, characterized in that the diameter, or the shortest external dimension of the interval (15) used to receive the radiation material (14), is equal, in the smallest central envelope (1), to the width of the interval (15) between the two other envelopes (2, 3) 6°) Installation according to claim 3, 40 characterized in that it consists of a single enclosure (1) which is formed by coiled metal pipes, the coils being directly adjacent"