Patent Description:
The boiler according to the invention is especially suitable for use in a coolant vapor generator for thermal absorption machines, and will be described with particular reference being made to this application, without however intending to thereby limit the possible areas of use thereof for other applications.

As is known, absorption machines, typically chillers or heat pumps, are thermal machines that exploit the ability of a substance, whether liquid or solid, to "absorb" a second chemical species in a gaseous state; for example, an unsaturated solution of water and ammonia can absorb ammonia vapor.

This property makes it possible to produce a refrigeration cycle with a thermochemical compressor: the low pressure coolant vapor is not compressed with an electrically powered mechanical compressor, but absorbed by the absorbent solution, which is then pumped at high pressure, with a reduced level of power consumption, and sent to a generator.

In the generator, the solution is heated up to the point of boiling, resulting in the production of high pressure coolant vapor necessary to produce the refrigeration cycle.

The high pressure vapor, that is rich of coolant, is sent into a condenser and then returns through an evaporator to an absorber.

The hot solution, depleted of coolant, which leaves the generator flows into a solution heat exchanger (or SHX), which serves the purpose of recovering the heat from the depleted solution by pre-heating the solution rich of coolant pumped towards the generator, and then, passing through a lamination valve, this solution also returns to the absorber, where it absorbs the coolant vapor.

In particular, in the generator, the generation of coolant vapor takes place in the boiler, commonly referred to in the practice also as desorber. In the case of direct-flame boilers, the solution rich of coolant is kept boiling by the heat supplied by a burner, hence by exposure to the flame and via the heat exchange with the hot flue gases (fumes) produced therefrom.

During operation, the generator of an absorption thermal machine, in particular of an absorption heat pump, must manage significant variations in the input power to the burner, significant variations in flow rate and level of the solution in the various sections, and significant variations in internal pressure and temperature. All of the foregoing are to occur while ensuring complete safety against leaks to the exterior, especially if ammonia is used, with total absence of maintenance for tens of thousands of hours of work, and without negative impact on the efficiency of heat and mass exchanges in the various components. These drawbacks are even more problematic with respect to the application of thermal machines to the residential sector where the reduction in overall dimensions and the industrialization of the product play a fundamental role.

Clearly, the boiler has an important role to play in obtaining satisfactory results, in particular when used in generators of heat absorption machines.

In the current state of the art, the direct flame boilers used in a generator are made according to two different types of construction:.

These solutions, while making it possible to obtain relatively satisfactory results, still have some drawbacks and can thus be further improved.

In particular, in the case of direct combustion generators with external burner, the heat dispersion losses due to the extremely high temperatures of the burner are difficult to manage with thermal insulation.

In case of installation within the interior of a building, this heat dispersion while participating in the heating of the environment does not contribute to feeding the thermodynamic cycle, consequently leading to a decrease in efficiency of the heat pump.

In the case of external installation, that is to say, in an unheated environment, the negative weight of these dispersions on the overall efficiency becomes critical.

If the burner is positioned under the boiler, the major part of the radiative heat is supplied directly to the bottom of the same, and if the burner is installed alongside the boiler the heat transfer is not symmetrical in relation to the axis of the insulating jacket of the boiler.

The external burner therefore includes respectively concentrated or asymmetrical heat flows, which generate local tensions and related stresses in the walls of the boiler, and which can induce localized corrosion during the normal on/ off cycles of the machine.

With regard to the generators with internal burner and internally finned fire-tube, for example the correct positioning and durability of the fin attachment system are crucial and closely correlated aspects: the direct welding of the internal fins is extremely difficult, while the brazing thereof results in a lower resistance to temperature peaks, due to the limited melting temperature of the brazing material, even though the so-called hard brazing reaches high operating temperatures (> <NUM>).

In addition, systems with fumes circulating within the interior of pipe bundles, while they allow for flexibility in sizing and enable advanced recovery systems, prove to be complex, heavy and expensive, and thus not at all suitable for mass production.

The relevant prior art documents are <CIT>, <CIT> and <CIT>.

The main scope of the present invention is to provide a direct flame boiler, in particular for a coolant vapor generator for absorption thermal machines, as well as a related generator, which allows mitigating, at least partially, one or more of the aforementioned drawbacks.

In particular, within this scope, one object of the present invention is to provide a direct flame boiler, as well as a related generator, that are highly efficient from the thermal standpoint, and in particular in which the heat dispersion losses are reduced or almost completely eliminated as compared to known solutions.

Another object of the present invention is to provide a direct flame boiler, as well as a related generator, in which the local tensions and related stresses in particular in the walls of the boiler, are at least reduced as compared to known solutions, thus decreasing the possibility of inducing localized corrosion, for example during normal ignition cycles.

Not the last object of the present invention is that of realizing a direct flame boiler, as well as a related generator, that present a structure which is simple and can be realized at relatively modest costs.

Further characteristics and advantages of the invention will become apparent from the detailed description that follows, provided purely by way of non-limiting example, with reference to the attached drawings, in which:.

It should be noted that in the detailed description that follows, components that are identical or similar, from a structural and/or functional standpoint, may have the same or different reference numerals, regardless of whether they are shown in different embodiments of the present invention or in distinct parts.

It should also be noted that in order to clearly and concisely describe the present invention, the drawings may not necessarily be to scale and some characteristic features of the description may be shown in a form that is schematic in some way.

In addition, when the term "adapted" or "arranged or organized" or "configured" or "shaped" or a similar term is used in the present document, with reference to any component as a whole, or to any part of a component, or to a combination of components, it is to be understood that it refers to and correspondingly includes the structure and/or configuration and/or shape-form and/or positioning.

In addition, when the term "substantial" or "substantially" is used herein, it is to be understood as including an actual variation by plus or minus <NUM>% relative to that which is indicated as a value, position, or axis of reference.

Furthermore, when the terms "transversal" or "transversally" are used herein they are to be understood as including a direction that is not parallel to the reference part or parts or direction(s)/axis to which they refer; and perpendicularity is to be considered one specific case of transversal direction.

Finally, in the description and in the following claims, the ordinal numerals first, second, et cetera, are used purely for reasons of illustrative clarity and therefore should in no way be construed to be limiting for any reason whatsoever; in particular, the indication, for example, of "a third cavity" does not necessarily imply the presence or the stringent requirement that there be "a first and a second cavity", or vice versa, unless such presence is clearly evident for the correct operation of the embodiments described, nor that the order is to be exactly as in the sequence described with reference to the exemplary embodiments illustrated. <FIG> and <FIG> illustrate two possible embodiments of a direct flame boiler according to claim <NUM>, indicated as a whole by the reference number <NUM>, which is adapted to be used in particular in a generator <NUM> of coolant vapor for thermal absorption machines, of which a possible exemplary embodiment, suitable for working fluids in which the absorbent is relatively volatile, is illustrated in <FIG>.

As schematically illustrated in <FIG>, the generator <NUM> comprises a casing <NUM>, that can be fabricated as one single metal piece or in multiple metal pieces connected to each other, for example in a cylindrical shaped form, which extends as a whole vertically along a substantially vertical reference axis Y.

As illustrated in <FIG>, when installed in the generator <NUM>, the boiler <NUM> according to claim <NUM> substantially constitutes the base thereof and, as will become apparent in greater detail from the following description, is suitable to ensure that an initial solution containing a coolant substance is kept boiling so as to generate streams or flows of vapor containing this coolant.

For example, a solution comprising water and ammonia can be introduced into the boiler <NUM> through the duct <NUM> and/or the duct <NUM>.

The generated vapor streams that contain the coolant, indicated in <FIG> by the letter V, rise towards the top of the generator <NUM>, which depending on the working fluids can act as a distillation column, as in the example of <FIG>. In this case, the vapor streams first pass through, for example a stripping or analyzer section, schematically represented by the reference number <NUM> and then subsequently a dephlegmator, schematically represented by reference number <NUM>.

Taken together as a whole, the stripping section <NUM> and the dephlegmator <NUM> are capable of altering the concentration of coolant in the vapors produced, in the event that a portion of these is constituted by the absorbent substance. This, in particular, can be obtained by cooling at least the vapor streams V coming from the boiler <NUM> according to claim <NUM> so as to obtain a partial condensation of the absorbent, for example water, and thus increase the mass fraction of coolant, that is to say ammonia.

In practice, this alteration occurs through the exchange of matter and/or heat between the vapors and the cooling fluids and/or materials used in the stripper and in the dephlegmator. The embodiments and modes of operation of both the stripping section <NUM> and the dephlegmator <NUM> may be of any type that is known in the art and/or easy to realize for a person skilled in the art; however, these embodiments and modalities are not relevant for the purposes of the description of the boiler <NUM> according to claim <NUM> and for these reasons they are not described herein in greater detail.

As illustrated in the exemplary embodiments in the attached figures, the boiler <NUM> according to claim <NUM> comprises at least:.

In the second cavity <NUM> there is placed a burner <NUM> capable of generating the heat necessary to ensure that the liquid solution present in the first internal cavity <NUM> and in the second internal cavity <NUM> is kept boiling, as will become apparent in greater detail from the following description.

The fourth body <NUM> is interposed between the first body <NUM> and the second body <NUM>, and is integrally connected to them, for example by means of welding.

In the embodiment of <FIG>, the fourth body <NUM> is also integrally connected to the top part of the third body 10B.

Conveniently, the fourth body <NUM> is a cross-flow distributor, and in particular it is configured in a manner such that at least hot fumes produced by the burner <NUM>, indicated in <FIG>, <FIG> and <FIG> by the letters Fc, flow through it flowing from the second internal cavity <NUM> towards the outer surfaces <NUM> of the first body <NUM>, while streams of the boiling liquid solution, indicated in <FIG>, <FIG> and <FIG> by the letter L, flow through it by flowing from the first internal cavity <NUM> of the body <NUM> down into the third internal cavity <NUM>.

When the boiler <NUM> is installed in the generator <NUM>, its vertical reference axis X preferably coincides substantially with the axis Y along which the generator <NUM> as a whole is extended vertically.

As illustrated graphically only in <FIG> for simplicity of description, the first internal cavity <NUM> has an internal extension D1 measured in a transversal direction, and in particular perpendicular, to the vertical reference axis X, which is smaller than the maximum internal extension D2 of the second internal cavity <NUM>, also measured in a transversal direction, and in particular perpendicular, to the vertical reference axis X.

In one possible embodiment of the boiler <NUM> according to claim <NUM>, the streams L flow out from the boiler <NUM> through at least one duct <NUM> (illustrated for simplicity only in <FIG> and <FIG>) provided at the base of the third internal cavity <NUM> and which connects this cavity <NUM> to the exterior.

In their turn, the exiting hot fumes FC flow out for example from an exhaust duct <NUM>, illustrated for simplicity only in <FIG>.

In the embodiments illustrated in <FIG> and <FIG>, the second body <NUM> comprises a first internal cylindrical body which laterally delimits said second internal cavity <NUM> and develops vertically around the substantially vertical reference axis X; this first internal cylindrical body <NUM> therefore has an internal diameter equal to D2.

In turn, the third body 10B comprises a second external cylindrical body which is arranged externally to and substantially concentric with the first internal cylindrical body <NUM> relative to said substantially vertical axis X.

In practice, the two cylindrical bodies <NUM> and 10B are arranged coaxially to each other around the vertical reference axis X which therefore actually constitutes the axis of structural symmetry, and they delimit there-between an interspace which forms the third internal cavity <NUM>.

In the embodiment of <FIG>, the external cylindrical body 10B extends along the axis X, only for a short part beyond the first internal cylindrical body <NUM>, and the third cavity <NUM> is closed at the bottom, for example by means of a metal plate <NUM> of the second body <NUM> welded to the two coaxial cylindrical bodies <NUM> and 10B, and at the top by means of the structure of the fourth body <NUM> welded to the same coaxial cylindrical bodies <NUM> and 10B.

As illustrated in the exemplary embodiments shown in <FIG> and <FIG>, the burner <NUM> preferably has a substantially cylindrical shape and is arranged in the second cavity <NUM> in a central position extending along said vertical reference axis X which in fact also constitutes the axis of structural symmetry thereof.

In its turn, as illustrated in the exemplary embodiments shown in <FIG> and <FIG>, the first body <NUM> also comprises a substantially cylindrical body which develops vertically around the vertical reference axis X which in fact also constitutes the axis of structural symmetry thereof.

In this case, the cylinder of the first body <NUM> has an internal diameter D1 smaller than the internal diameter D2 of the first cylindrical body <NUM>.

For illustrative clarity, in <FIG> the internal extensions D1 and D2, and in particular the diameters, are graphically represented forward in relation to the axis of symmetry X since in <FIG> the boiler is shown cut in a plane not passing through this axis X.

According to one possible embodiment, for example as shown schematically only in <FIG> for simplicity of illustration, the first body <NUM> comprises at least a plurality of metal plates <NUM> which are suitably arranged in sequence with each other along the substantially vertical axis X inside the first cavity <NUM>.

As illustrated, the metal plates <NUM> are positioned mutually among them, in particular staggered, in a manner so as to form a passage pathway for the descending liquid solution (arrows L) or for the ascending vapors (arrows V) produced by boiling, and promote exchanges of mass and/or heat between the flows of liquid streams L and vapor streams V.

Conveniently, the boiler <NUM> according to claim <NUM> further comprises a plurality of fins <NUM> which are fixed on the outer surface <NUM> of the first hollow body <NUM>.

In particular according to one possible embodiment illustrated in <FIG>, there is a helical fin, constituted of a segmented or notched metal strip <NUM> which is fixed on the outer surface <NUM> of the first hollow body <NUM> along substantially all or a predominant portion of the vertical extension thereof.

Clearly, it is possible to use one single continuous strip or a plurality of metal strips <NUM> fixed individually to the outer surface <NUM>.

In practice, the or each strip <NUM> protrudes from the outer surface <NUM> in a transversal direction, in particular perpendicular, relative to the vertical reference axis X, with its teeth that form the fins <NUM>; advantageously, with respect to a direction parallel to the vertical reference axis X, the fins <NUM> are for example staggered between adjacent turns of the fins, in order to facilitate the through- passage of fumes.

For example, each metal strip <NUM> is high frequency resistance welded to the outer surface <NUM> of the first body <NUM>, before the latter is welded to the fourth body or cross-flow distributor <NUM>. In one possible embodiment, the fins <NUM> may have a shorter length in the lower part of the body <NUM> where the temperatures, and therefore the heat exchanges, are greater.

In practice, according to this embodiment, the length of the fins <NUM>, measured along a transversal direction relative to the vertical reference axis X, increases in the ascending direction along the first body <NUM>, that is to say in the direction moving away from the fourth body <NUM>.

In one other possible embodiment, as schematically illustrated in <FIG>, each fin <NUM> comprises, seen in a plane perpendicular to the reference axis X, a shaped body having a U- shaped or C- shaped section; the U- or C-shaped body is fixed on the external surface <NUM> of the first body <NUM> and extends longitudinally along a direction parallel to the vertical reference axis X with the concavity facing outwards relative to the first body <NUM>, that is to say in the direction opposite to the first internal cavity <NUM>.

As well in this case, the fins <NUM> are welded to the external wall <NUM> of the first hollow body <NUM> before the latter is welded to the fourth body <NUM>.

In the embodiment illustrated in <FIG>, the boiler <NUM> according to claim <NUM> comprises moreover, an insulating jacket <NUM> comprising at least one layer of thermal insulating material, for example glass wool, which is arranged laterally around the first body <NUM>, and contained for example in a rigid cylindrical casing, for example made of metal.

In the illustrated embodiment, the insulating jacket <NUM> as a whole preferably has also a cylindrical shape that develops around the vertical axis X, which therefore constitutes the axis of symmetry thereof.

As illustrated, the insulating jacket <NUM> extends above and upwards from the fourth body <NUM> along the vertical reference axis X, and is arranged laterally around the outer surface <NUM> of the first hollow body <NUM> and is spaced apart there-from so as to form with the first hollow body <NUM> an interspace <NUM> within which the fins <NUM> are housed and within which the hot fumes Fc flow.

The rigid casing of the insulating jacket <NUM> is for example fixed below the cross- flow diffuser <NUM>.

In one possible embodiment, illustrated in <FIG>, the boiler <NUM> according to claim <NUM> comprises a further metallic hollow cylindrical body <NUM> which is fixed at its bottom/lower part to the fourth body <NUM> and extends above and upwards along the substantially vertical reference axis X.

In particular, said further metallic cylindrical body <NUM> is arranged laterally around and spaced apart from the first body <NUM> in a manner so as to delimit with it, at least in part, an interspace <NUM>.

In this embodiment, the third external cylindrical body 10B is disposed externally to and extends further along the substantially vertical axis X also around the fourth body <NUM> and up to the further metallic hollow cylindrical body <NUM>.

In this manner, the external cylindrical body 10B delimits with the first cylindrical body <NUM>, the fourth body <NUM>, and the further hollow insulating body <NUM>, a further interspace or cavity <NUM> which, in the lower part, includes in fact also the second internal cavity <NUM>.

Conveniently, a heat exchanger <NUM> is housed within the interspace <NUM>, for example a coil which extends for instance over the entire vertical length of the boiler <NUM> according to claim <NUM>.

Such a coil <NUM> for example makes it possible to drain the solution poor of coolant from the bottom of the boiler <NUM> and to release heat to the solution rich of coolant which instead travels in a countercurrent flow in the downward direction.

Furthermore, there is conveniently an exchange of heat between the cavity <NUM> (containing hot flue gases/fumes) and the interspace or cavity <NUM> (containing the boiling solution).

In this embodiment, on the exterior of the third body 10B an appropriate insulation may be used.

In its turn, as illustrated in greater detail in the exemplary embodiments shown in <FIG>, the fourth hollow body <NUM> comprises one or more first through holes <NUM> which extend in a transversal direction, in particular perpendicular to the substantially vertical reference axis X.

These first through holes <NUM> are configured to cause streams of solution L to flow out from the first internal cavity <NUM> conveying them towards the second body <NUM>, and introducing them into the third cavity <NUM>.

Furthermore, the fourth body <NUM> conveniently comprises one or more second through holes <NUM> which extend in a direction substantially parallel to the vertical reference axis X.

These second through holes <NUM> are configured in a manner such as to cause hot fumes Fc to flow out from the second internal cavity <NUM> making them rise upwards and directing them towards the exterior of the external lateral walls <NUM> of the first body <NUM>.

Furthermore, by flowing through the first holes <NUM>, the streams of vapor, which form in the third internal cavity <NUM>, are also able to rise upwards.

In the boiler <NUM> according to claim <NUM>, the fourth body <NUM> also preferably presents a substantially symmetrical structure in relation to the reference axis X, and is for example made of steel.

In particular, as illustrated in the exemplary embodiments shown in <FIG>, the fourth body <NUM> has a hollowed or flared central portion <NUM>, shaped for example like a cup or glass, having the cavity facing towards the first body <NUM>; along the lateral surface of the hollowed portion <NUM> is defined the inlet of said one or more first through holes <NUM> which then lead into the third internal cavity <NUM>.

Furthermore, the fourth body <NUM> comprises a lateral portion <NUM> which is arranged around the central portion <NUM> along which said one or more second through holes <NUM> are defined. In the embodiment illustrated in <FIG>, the lateral portion <NUM> of the fourth body <NUM> has, for example, a ring shape in which the bottom part <NUM>, for instance is welded to the first cylindrical body <NUM>, and the top part has a laterally protruding flange <NUM> which is welded below the second cylinder body 10B and above the first body <NUM> and the metal cylinder which forms the insulating jacket <NUM>.

Clearly, these connections may be implemented differently; for example, the protruding flange <NUM> may be welded laterally to the second cylinder body 10B.

In the embodiment illustrated in <FIG>, the lateral portion <NUM> has at the top a raised inner edge <NUM> arranged around the hollowed central portion <NUM> that is adapted so as to be fixed, in particular welded, to the first body <NUM>, and an outer edge <NUM> raised at the top and adapted so as to be fixed, for example welded, to the further body <NUM>.

Furthermore, the lateral portion <NUM> has at the bottom a further lower edge <NUM> adapted so as to be fixed, for example welded, to the first cylindrical body <NUM>.

Clearly, with respect to the previously described configuration, which represents a preferred form of realization, the fourth body <NUM> in accordance with claim <NUM> can be differently configured and have any shape suitable for performing the tasks assigned to it, namely configured so that hot fumes Fc produced by the burner <NUM> flows through it flowing from said second internal cavity <NUM> towards the outer surface <NUM> of the first body <NUM>, and flows of said liquid solution flow through it flowing from said first internal cavity <NUM> into said third internal cavity <NUM>.

As previously indicated, once assembled, the boiler <NUM> according to claim <NUM> may be conveniently installed for example at the base of a generator <NUM> for a thermal absorption machine.

During the operation of the generator <NUM>, and with reference to <FIG>, the vapor generated by the boiler <NUM> according to claim <NUM> by boiling the starting solution, for example water and ammonia, indicated by the arrows V, rises from the internal cavity <NUM>, passes through the distributor <NUM>, rises from the internal cavity <NUM> passing among the metal plates <NUM>, then rising through the stripping section <NUM>, and subsequently the dephlegmator <NUM>. Over the course of this route, the mass and/or heat exchanges serve to enable at least partial condensation of the water contained in the vapor, thus going to increase the percentage of coolant obtained.

The rectified coolant vapor (indicated in <FIG> by the arrow VR) is released from the generator head to be used, for example, in the refrigeration cycle of the thermal machine of which the generator <NUM> forms a part.

The condensed vapor V flows downwards travelling along the pathway in the opposite direction and mixes with the liquid solution L entering into the generator.

In practice, it has been found that the boiler <NUM> according to claim <NUM> and the generator <NUM> according to the invention fulfil the intended scope and objects in that they allow realizing a very efficient solution from the thermal standpoint, and in particular wherein the heat dispersion or losses are reduced as compared to known solutions, the local tensions and related stresses in particular in the walls of the boiler, are at least reduced thanks also to the structure being substantially symmetrical, and the heat exchanges are optimized. For example, in particular in the configuration of <FIG>, the fins <NUM> serve to maximize heat transfer from the hot fumes Fc which rise and flow parallel to the axis X of the first hollow body <NUM> rather than perpendicularly thereto; therefore these fumes are forced to constantly change direction in order to pass through the interstices of the fins, consequently providing substantial improvement in respect of the turbulence and heat transfer coefficient.

All of the foregoing is obtained with a simple structure that can be implemented at relatively low costs, and is mechanically robust; for example, the positioning of the fins located externally to the first hollow body <NUM> provides the ability to effectively execute the welds with the consequent benefit thereof in terms of resistance to mechanical stresses and thermal stresses.

Furthermore, both the boiler <NUM> according to claim <NUM> and the generator <NUM> may be advantageously used for the fabrication of a thermal absorption machine, and in particular a heat pump or a chiller;.

Claim 1:
Direct flame boiler (<NUM>), wherein it comprises at least:
- a first body (<NUM>) which extends along a substantially vertical reference axis (X) and at least partially encloses a first internal cavity (<NUM>) suitable for receiving a liquid solution;
- a second body (<NUM>) which, with reference to said substantially vertical axis (X), is arranged below said first body (<NUM>) and at least partially encloses a second internal cavity (<NUM>) in which there is placed a burner (<NUM>) capable of generating heat to keep the liquid solution in the first internal cavity (<NUM>) boiling;
- a third body (10B) which is arranged for at least a part thereof around the second body (<NUM>), said second and third bodies (<NUM>, 10B) delimiting between them a third internal cavity (<NUM>) which is arranged, for at least a part thereof, laterally around said second cavity (<NUM>); and
- a fourth body (<NUM>) which is interposed between said first body (<NUM>) and said second body (<NUM>) and is at least integrally connected to them, said fourth body (<NUM>) being configured so that hot fumes (Fc) produced by the burner (<NUM>) flows through it flowing from said second internal cavity (<NUM>) towards the outer surface (<NUM>) of the first body (<NUM>) and characterized in that the fourth body (<NUM>) is configured so that flows of said liquid solution flow through it flowing from said first internal cavity (<NUM>) into said third internal cavity (<NUM>), wherein said fourth body (<NUM>) comprises one or more first through holes (<NUM>) which extend in a direction transverse to said substantially vertical reference axis (X) and are configured to put said first internal cavity (<NUM>) in communication with said third internal cavity (<NUM>).