Patent Description:
A typical cyclonic combustion chamber comprises a generally cylindrical internal shell, oriented along the horizontal longitudinal axis thereof, which defines a furnace which is provided with nozzles for supplying oxidising gas thereto, with the particularity that these nozzles are distributed and oriented in a convenient manner on the wall of the furnace to induce a cyclonic field therein that sustains the combustible particles that are introduced therein through a feed inlet, guaranteeing a long residence time for these particles inside the furnace and preventing them from leaving it prematurely, through an outlet provided for the combustion gases, favouring the complete combustion thereof.

An example of a cyclonic combustion chamber is described in patent document <CIT>, belonging to the same applicant. Further related combustion units comprising cyclonic combustion chambers are known from patent documents <CIT> and <CIT>. Patent literature documents <CIT> and <CIT> disclose different combustion chambers, provided with vibration mechanisms for ash conveying.

Cyclonic combustion chambers have been shown to be especially useful for biomass combustion, the volatility of which does not prevent burning with an excellent mix between the oxygen in the oxidising gas, usually air, and the combustible material, even allowing the air required to be minimised.

However, biomass fuels have the disadvantage of containing a high proportion of ashes that have a low melting point and a high adherence ability that are deposited on the internal surfaces of the furnace, agglomerating and being detrimental to the combustion process.

Combustion chambers of this type have a discharge opening for the ashes that opens into an ashtray or an ash conveyor and towards which the ashes are intended to be led while combustion is taking place. However, effectively moving the ashes to this point is still a problem without a satisfactory solution.

Even when the ashes are finally led to the outlet opening, the slow advance, and the possible accumulation thereof throughout the furnace, significantly affects the heat exchange through the surface of the internal shell, conventionally with pipes through the inside of which a fluid, usually water, circulates to which the heat released in combustion is transferred.

The presence of these pipes, which entails the cooling of the surface of the shell, has proven to be useful in favouring the solid state of the ashes, which facilitates the extraction thereof from inside the furnace.

Moreover, however, its presence has proven to be detrimental with regard to the flow and evacuation of the ashes resulting from the combustion, favouring the accumulation and agglomeration thereof in the membraned spaces between tubes, preventing the advance of the ashes themselves in the direction of the opening for the discharge thereof, negatively affecting the combustion process.

To remove the ashes that have not been evacuated, which do not reach the discharge opening, stopping the operation of the unit with certain frequency and accessing the inside of the furnace to proceed to the cleaning and unclogging thereof is usually required, reducing the efficiency and productivity of the units as well as hindering the operation and maintenance thereof. With the aim of maximising the time between interventions, some units incorporate steam blowers, although this technique is not effective as the percentage of ash in the combustible material increases, this steam injection in turn having a strong negative impact on the combustion and therefore on particulate and carbon monoxide emissions into the environment.

From document <CIT>, design solutions for cyclonic combustion chambers are known, which include the arrangement of the shell inclined with respect to the horizontal and the modulation of the combustible material and air injection in the combustion chambers to favour the evacuation of the ashes due to the strict control of the temperature and viscosity thereof.

Cyclonic combustion chambers such as the one described in <CIT> have integrated mechanical elements that scrape the internal surface thereof. However, the integration of these elements in the demanding thermal conditions of the combustion chamber increase the cost of manufacturing and maintaining the unit.

Also known are furnaces that have blowers such as the one described in document <CIT>, which use pressurised gas blowers to sweep the inside of the furnace and move the ashes towards the discharge opening that opens into an ash drawer. However, this blowing is not effective for ashes of a particularly adherent nature.

An objective of the present invention is to disclose a combustion unit with a cyclonic combustion chamber that is especially suitable for working with combustible materials which, due to the high content of minerals that they have (particularly potassium and sodium), generate ashes with a low melting point, which are especially adherent. An example of such combustible materials are biomass fuels such as, by way of non-limiting example, sunflower husks, wheat straw, wheat husks, olive pomace, cotton hulls, etc..

A further objective of the present invention is a combustion unit with a cyclonic combustion chamber that solves the problems of evacuating these ashes that have a low melting point and are adherent, affecting the internal combustion medium and the operability of the chamber as little as possible.

Another objective of the present invention is to provide a solution that avoids the presence of moving elements or parts inside the furnace, such as scrapers, which increase unit costs and maintenance costs.

It is also desirable to avoid providing the cyclonic combustion chamber with blowers or the like, which may interfere with the design of the furnace and the cooling thereof, as well as with the combustion process.

To achieve the aforementioned objectives, a combustion unit is proposed comprising a cyclonic combustion chamber, the chamber having, in a known manner, a cylindrical internal shell about an essentially horizontal longitudinal axis, which defines a furnace, in the internal shell of which a front end is differentiated with a feed inlet for the combustible material, and a rear end with a gravity discharge outlet for the ashes generated during combustion and a combustion gas outlet.

In essence, this unit is characterised in that it is provided with a vibration mechanism of the chamber that cyclically impresses to the ashes accumulated on the bottom of the internal shell an upward thrust with an horizontal component in the direction of the rear end of the internal shell in which the discharge outlet for the ashes is located.

On the one hand, the vibration of the chamber produces a repetitive movement on the internal shell that makes it difficult for ash particles with a low melting point to adhere thereto. On the other hand, the same vibration of the chamber that prevents the adhesion of the ashes produces a conveyor effect of the ashes, in this case similar to that produced by a vibrating conveyor belt.

The invention lies in making the entire cyclonic combustion chamber vibrate, and not just the conveyor surface or the surface on which the ashes produced are deposited. This is a measure that differs from others applied to, for example, grates in horizontal boilers or vertical combustion chambers.

Advantageously, the combustion unit described does not have internal elements that interfere with the normal combustion expected from a cyclonic combustion chamber, being able to remove the ashes without stopping the operation of the cyclonic combustion chamber nor reducing the efficiency thereof.

Likewise, due to the control acquired over the conveying speed of the ashes, by means of the possible modulation of the frequency of the vibrations (according to the quantity and quality of the combustible material that is being used), the insulating effect that they produce on the internal shell of the chamber is reduced, consequently improving heat exchange through the wall of said internal shell.

With regard to the definition of the invention, it should be understood that the indefinite articles "a" and "an", as used in this document and in the claims, unless clearly indicated otherwise, mean "at least one". The expression "and/or", as used in the specification and in the claims, should be understood to mean "either or both" of the connected elements, i.e., elements that in some cases are present together and in other cases are present separately. Also, in this document, all transitional expressions such as "with", "comprises", "includes", "having", "contains", "supports", "made up of", and the like should be understood as being open, i.e., meaning including, but not limited to. Only transition expressions such as "consists of" and "essentially consists of" will be closed or semi-closed transition expressions, respectively.

The term "essentially horizontal" used in the definition of the invention is used to explain that the internal shell is in a stretched or folded position, to distinguish it from vertical combustion chambers. As will become clear later, the cylindrical internal shell can be a shell about a horizontal longitudinal axis or with a slight inclination with respect to the horizontal. In preferred variants of the invention, this inclination is less than <NUM>°, preferably less than <NUM>° and more preferably it is approximately <NUM>°.

Embodiments of the invention are described in the dependent claims.

Thus, in a variant of the invention, the chamber is supported on a frame comprising a bed-frame, to which the chamber is fastened, duly contemplating the existing thermal expansions, said bed-frame being movably linked to a fixed chassis, intended to rest steady on the floor of an installation.

In one embodiment, the bed-frame rests on a plurality of straps with first and second opposite ends connected to the bed-frame and to the chassis, respectively, these straps acting by way of a spring, the straps deforming depending on the amplitude of the vibration transmitted to the chamber.

According to a constructive solution, the bed-frame has two upper stringers between which a series of upper crossbars extend; the chassis has two lower stringers between which a series of lower crossbars extend; and the straps are evenly distributed under the chamber, each strap extending between a lower crossbar and an upper crossbar, which are slightly offset from each other, so that the straps are slightly inclined forward.

Preferably, the vibration mechanism transmits a vibration of a sinusoidal nature to the bed-frame, and therefore to the chamber.

Preferably, the amplitude of the vibratory movement is comprised between <NUM> and <NUM>.

The sinusoidal nature of the vibration can be achieved with the intervention of the rotation of an eccentric shaft.

According to a constructive solution of interest, the vibration mechanism comprises a set of connecting rod and crank, the crank being a driving crank rotatably mounted about an axis of rotation that is fixed with respect to the chassis and the distal end of the connecting rod being connected in an articulated manner to the bed-frame.

The invention contemplates that the unit has means for modulating the speed of rotation of the driving crank. For example, using a frequency variator to govern the rotation of a motor that drives said crank.

In this constructive solution, the distal end of the connecting rod can be connected to the bed-frame at a midpoint or at a point moved towards the front end thereof. Preferably, the distal end of the connecting rod is connected to the bed-frame at a point below the chamber and ahead of the midpoint of the internal shell thereof.

In a variant of the invention, the internal face of the internal shell is smooth, without projections or recesses being exhibited.

Preferably for this variant, the chamber has an intermediate shell and an external shell, coaxial with the internal shell.

The internal shell defines with the intermediate shell an annular pressure chamber intended to contain a pressurised working fluid, such as water, this annular pressure chamber having hydraulic connections with the external inlet, called downpipes, and with the external outlet, called riser pipes, that enable the circulation of the working fluid.

The intermediate shell defines with the external shell an annular impulsion chamber with a pneumatic connection with the external inlet of an oxidising gas, said annular impulsion chamber being connected with the furnace by means of a series of nozzles.

This variant of the invention is of interest when the pressures of the working fluid are below an approximate threshold value of <NUM> bars.

In cases where a working fluid is operated at pressures above this threshold value, an alternative variant of the invention is of interest wherein the internal shell comprises, more conventionally, membraned pipes through which the pressurised working fluid, usually water, circulates. These tubes are connected to each other by means of lower manifolds, similar hydraulic connections being provided with the external inlet, called downpipes, and hydraulic connections with the external outlet, called riser pipes.

In this alternative variant, the chamber has an external shell, which defines with the membraned tubes an annular impulsion chamber with a pneumatic connection with the external inlet of an oxidising gas, the aforementioned impulsion chamber being connected with the furnace by means of a series of nozzles.

Preferably, in any of the scenarios described above, the nozzles are distributed along the length of the furnace and flow into the furnace concentrated in the lower quadrants of the circular section of the internal shell, in a direction essentially tangential to the internal face of said internal shell.

Also preferably, the hydraulic connections with the external inlet and outlet of the working fluid are several, and may be pairs, and are distributed along the length of the chamber, and may be diametrically opposed, the inlet connections being located in the lowest area of the annular pressure chamber and the outlet connections being located in the upper area of said annular pressure chamber.

Also preferably, the feed inlet for the combustible material is located at a level above the longitudinal axis, with an inclination with respect to the radial direction. More preferably, following a direction close to a direction tangential to the internal shell.

Preferably, the longitudinal axis of the internal shell is inclined with respect to the horizontal such that the internal shell descends towards the rear end thereof.

According to another aspect of the invention, and in accordance with the foregoing, a method is proposed for removing combustion ashes from inside a cyclonic combustion chamber comprising subjecting a cyclonic combustion chamber to a vibratory movement while the combustion is taking place, movement which in each cycle thrusts the ashes accumulated on the bottom of the furnace of the chamber upwards and with a horizontal component towards one end of the chamber where a gravity discharge outlet for ashes is located.

<FIG> illustrate a combustion unit <NUM> exemplifying the invention.

This combustion unit <NUM> comprises a cyclonic combustion chamber <NUM> and a frame <NUM>, which supports the chamber <NUM>.

The unique feature of this unit <NUM> is that the frame <NUM> has two portions: a lower, fixed chassis <NUM> intended to be placed steady on the floor of an installation; and an upper bed-frame <NUM>, which is linked to the fixed chassis <NUM> able to move with respect thereto, and which carries the chamber <NUM>.

In the example, the bed-frame <NUM> rests, in floating mode, on a plurality of straps <NUM> with opposite first and second ends 33a, 33b connected to the bed-frame <NUM> and to the chassis <NUM>, respectively. The advantages of this mechanical link will be explained later, with the help of <FIG>.

In the example, the chamber <NUM> is firmly fastened to the bed-frame <NUM>, these being two originally separate portions, joined by supports welded to the body of the chamber <NUM> and bolted to the bed-frame <NUM>, sliders being placed in one of these to contemplate the thermal expansions resulting from the heating of said chamber <NUM>. However, the invention contemplates that the bed-frame <NUM> may be an integral part of the chamber <NUM>.

The unit <NUM> of <FIG> is completed with a vibration mechanism <NUM> suitable for transmitting to the bed-frame <NUM>, and thus to the chamber <NUM>, a cyclic forward and backward movement, which will contribute to a desired movement of the ashes inside the chamber <NUM> in a target direction.

More in detail, in the example of <FIG>, the chamber <NUM> is configured such that it has a cylindrical internal shell <NUM> about a respective longitudinal axis <NUM>, which defines a furnace <NUM>, wherein a front end <NUM>, a central portion <NUM>, and a rear end <NUM> can be differentiated.

In the vicinity of the front end <NUM> a feed inlet <NUM> is provided for the combustible material, which in the example is perpendicular to the longitudinal axis <NUM> and is located above the same. Through this configuration, a tangential entry of the combustible material towards the cyclonic chamber is achieved.

At the rear end <NUM>, there is an axial outlet <NUM> for combustion gas, able to be connected to, for example, the body of a boiler; and in the vicinity of said base, at the bottom of the shell <NUM>, there is a gravity discharge outlet <NUM> for the ashes.

Characteristically, the internal face 11a of the internal shell <NUM>, i.e., the wall of the furnace <NUM>, is smooth, which contributes to the fact that, in combination with the vibratory movement that is impressed on the chamber <NUM>, the ashes deposited on the bottom of the shell <NUM> advance towards the discharge outlet <NUM> for the ashes.

<FIG> and <FIG> show that the chamber <NUM> is configured such that the furnace <NUM> is surrounded by two concentric annular chambers. Specifically, the chamber <NUM> has an intermediate shell <NUM> and an external shell <NUM>, coaxial with the internal shell <NUM>.

The internal shell <NUM> defines with the intermediate shell <NUM> an annular pressure chamber <NUM>, which during operation of the unit contains the pressurised working fluid (normally water) to which the energy released during the combustion process is to be transmitted, for generating steam. As occurs in boilers or in a typical cyclonic chamber, this fluid to be evaporated keeps the internal shell <NUM> cool. Said annular pressure chamber <NUM> has hydraulic connections with the external inlet <NUM>, for example, in communication with the pressure body of a boiler, called downpipes <NUM>; and with the external outlet <NUM>, through which a mixture of water with the generated steam circulates, called riser pipes.

The intermediate shell <NUM> defines with the external shell <NUM> an annular impulsion chamber <NUM> with a pneumatic connection with the external inlet <NUM> of an oxidising gas, such as air, said annular impulsion chamber <NUM> being connected with the furnace <NUM> by means of a series of nozzles <NUM> in this case following a tangential direction to the internal shell <NUM>.

In a manner known per se, the nozzles <NUM> are distributed along the length of the furnace <NUM> and flow into the furnace <NUM>, passing through the annular pressure chamber <NUM>, in a suitable way to keep the combustible particles in aerodynamic lift within the combustion area, generating a rotation therein, favouring the mixture of the combustible material with the oxidising gas.

However, as shown in <FIG>, in the present exemplary embodiment, the nozzles <NUM> that flow into one same circular section of the internal shell <NUM> are concentrated in the lower half thereof, i.e., in the lower quadrants thereof, pointing in a direction essentially tangential to the internal face 11a of said internal shell <NUM>.

As regards the hydraulic connections with the outside, downpipes <NUM> and riser pipes <NUM> through which the working fluid <NUM> circulates, several of them are provided and are distributed in pairs along the length of the chamber <NUM> and are located diametrically opposed, the downpipes <NUM> being arranged in the lowest area of the annular pressure chamber <NUM> and the riser pipe connections <NUM> in the upper area of said annular pressure chamber <NUM>.

To cause the forward movement of the ashes generated by combustion inside the furnace <NUM> and deposited on the internal face 11a of the internal shell <NUM>, which is smooth, the vibration mechanism <NUM> transmits a vibratory movement to the chamber <NUM> via the bed-frame <NUM>.

The operating principle consists of impressing a sinusoidal thrust force on the ashes to be moved, generating an upward impulse but also with a horizontal component and towards the discharge outlet <NUM> for the ashes.

This thrust force is impressed on the ashes, causing the internal shell <NUM> to vibrate, causing the ashes to be propelled upwards and forwards during an advance stroke of the vibratory movement, and when the reverse stroke of the vibratory movement suddenly begins, the ashes detach from the internal shell <NUM> due to the thrust received, and are propelled towards the discharge outlet <NUM> for the ashes in a kind of parabolic shot.

In the example, the vibratory movement is generated from the rotation of an eccentric shaft.

To this end, in the example of <FIG>, the vibration mechanism <NUM> used to achieve this purpose comprises a set of connecting rod <NUM> and crank <NUM>, the crank <NUM> being a driving crank rotatably mounted about an axis of rotation <NUM> that is fixed with respect to the chassis <NUM> and the distal end 62b of the connecting rod <NUM> being connected in an articulated manner to the bed-frame <NUM>. In this example, the rotation to the crank <NUM> is transmitted from an outlet shaft of a motor <NUM> by means of a belt-type transmission <NUM>.

The effective dimension of the crank <NUM>, i.e., the location of the connection of the proximal end of the connecting rod <NUM> with respect to the axis of rotation <NUM> of the crank <NUM>, and the inclination of the connecting rod <NUM> may be selected to impress a thrust on the ashes with an optimum modulus and direction. This thrust will be conditioned by other factors, an important one being the inclination that the longitudinal axis <NUM> of the internal shell <NUM> has with respect to the horizontal.

However, a cyclic movement is transmitted to the chamber <NUM> that describes an elliptical path, which results in sinusoidal oscillations, the amplitude of these oscillations being determined from the eccentricity of the articulation between the connecting rod and the crank with respect to the axis of rotation <NUM>, while the frequency is regulated by the speed of rotation of the motor <NUM>, which operates coupled to a frequency variator.

Amplitude values comprised between <NUM> and <NUM> have turned out to be optimal.

In the exemplary unit <NUM> of <FIG>, the longitudinal axis <NUM> of the internal shell <NUM> of the chamber <NUM> has an essentially horizontal orientation. In this case, the bed-frame <NUM> is kept parallel to the floor and the chamber <NUM> rests on the bed-frame without any special inclination.

<FIG> shows a support frame <NUM> for a cyclonic chamber <NUM> that can be used to implement a unit <NUM> according to the invention.

In the frame <NUM>, the bed-frame <NUM> has two upper stringers <NUM> between which a series of upper crossbars <NUM> extend and the chassis <NUM> has two analogue lower stringers <NUM> between which a series of lower crossbars <NUM> extend.

The bed-frame <NUM> is linked to the chassis by means of straps <NUM>, in the form of metal plates, which are regularly distributed, each strap <NUM> extending between a lower crossbar <NUM> and an upper crossbar <NUM>, which are slightly offset from each other, so that the straps <NUM> are slightly inclined forward, i.e., with the second end 33b thereof connected to a lower crossbar <NUM> moved towards what will be the rear end of the internal shell <NUM> (not shown in <FIG>).

In the example, two straps <NUM> are used to join one same pair of upper <NUM> and lower <NUM> crossbars.

Note that the orientation in which the metal plates making up the straps <NUM> remain prevents the transversal movement of the bed-frame <NUM> with respect to the chassis <NUM> but gives the first some freedom of movement up and down and forward and backward, enough so that the vibration can be transmitted thereto by means of the vibration mechanism <NUM>. These strap assemblies <NUM> thus serve as springs, deforming according to the amplitude of the movement impressed by the vibration mechanism.

The unit <NUM> will be completed with means for collecting the ashes evacuated through the discharge outlet <NUM>, not shown in <FIG>, collection means that can be cumulative or for conveying to a separate container. It is envisaged, for example, to arrange an ash drawer placed below the chamber <NUM> in the space defined between the bed-frame <NUM> and the chassis <NUM>, into which the discharge outlet <NUM> for the ashes opens.

The unit <NUM> according to the invention can be implemented in other ways.

<FIG> shows an alternative for a unit <NUM> that is very similar to that represented in <FIG>. For the description of this alternative unit, the same numerical references are used in <FIG> to designate the same, or equivalent, elements or technical features that have been used for the description of the unit according to <FIG>.

The unit in <FIG> corresponds to a model built by way of a "pilot", with a diameter of the furnace <NUM> of <NUM>, a diameter of the annular pressure chamber <NUM> of approximately <NUM>, the assembly having a total length of around <NUM>. The unit was used with satisfactory results during the tests carried out, using meat meal as combustible material and ambient air as oxidising gas, for generating saturated steam at a maximum pressure of <NUM> bar, working with an amplitude of oscillations of <NUM>. and an operating frequency of <NUM>.

One of the main differences with respect to the unit described with reference to <FIG> is that in this case the longitudinal axis <NUM> of the internal shell <NUM> is slightly inclined at an angle α with respect to the horizontal, in the direction that provides a downward path for the ashes towards the discharge outlet <NUM>. In the example of <FIG>, this angle α is approximately <NUM>°. However, other possibilities are envisaged.

Claim 1:
A combustion unit (<NUM>) comprising a cyclonic combustion chamber (<NUM>), the chamber (<NUM>) having a cylindrical internal shell (<NUM>) about an essentially horizontal longitudinal axis (<NUM>), which defines a furnace (<NUM>), in the internal shell (<NUM>) of which a front end (<NUM>) is differentiated with a feed inlet (<NUM>) for the combustible material, and a rear end (<NUM>) with a gravity discharge outlet (<NUM>) for the ashes generated during combustion and a combustion gas outlet (<NUM>), the combustion unit (<NUM>) being characterised in that it is provided with a vibration mechanism (<NUM>) of the chamber (<NUM>) that cyclically impresses to the ashes accumulated on the bottom of the internal shell (<NUM>) an upward thrust with an horizontal component in the direction of the rear end (<NUM>) of the internal shell (<NUM>) in which the discharge outlet (<NUM>) for the ashes is located.