FR3052539A1 - COMBUSTION PROCESS - Google Patents

Abstract

The present invention relates to a method of burning organic material (22), characterized in that it comprises a step of mixing a transfer medium (23) composed of independent solid particles, with organic material (22) and with circulating said mixture in an enclosure (10) and in that said mixture is subjected to combustion using an oxidant introduced inside said enclosure (10).

Description

Field of the invention

The present invention relates to the field of production of heat or cogeneration (heat and electricity) by combustion of organic material used in a solid or liquid form, this material may consist of biomass of predominantly plant or animal origin or fossil as by example of plastics or other products composed of hydrocarbons. The invention particularly relates to a combustion process and the combustion plant from organic material using said process, particularly suitable for the combined production of heat and electricity, in other words cogeneration, using a cycle of Rankine or equivalent, notably using a steam turbine and an alternator. But heat production alone can also be provided by the invention, for use by a hot water or steam heat network, or any other conversion of heat into mechanical energy or cold for example by a group by absorption.

State of the art

The combustion of organic matter is one of the possible routes for its energy recovery, the other main routes being gasification and methanation.

The organic matter is always composed mainly of molecules composed of Carbon C, Hydrogen H and Oxygen 0, often combined with H2O water and mineral elements.

The combustion reaction is ensured by a highly exothermic oxidation of the material, the oxidant being traditionally air in excess of the stoichiometric equilibrium, so as to prevent incomplete combustion.

Ideally the products of the process should be only carbon dioxide, nitrogen and water. In reality, depending on the origin of the raw material entering the process (later called "incoming" in the description of the invention), its purity and the reaction conditions (pressure, temperature, speed, etc. .), elements obtained by chemical recombination with certain elements, and in particular elements such as chlorine, sulfur, etc., appear and are undesirable elements for their effects of corrosion, abrasion and fouling of equipment. In addition, other elements such as nitrogen oxides (NOx), dioxins and furans can be produced during the reactions, posing a high risk to the health of surrounding populations.

According to the current state of the art of organic matter combustion processes, the production of heat and / or electricity is, in a conventional manner, based on three main firing technologies to ensure combustion: in a process of grid boiler, which includes in particular the step grids, the spreader stockers, the rotary grids, the entrants are introduced over a moving grid, in the lower part of an enclosure, in which it undergoes a combustion in same time that it moves under the effect of the movements of the grid. Oxidizer, such as air or oxygen, is introduced into the chamber to allow the combustion of the organic material and thus generate very hot fumes (generally more than 800 ° C). The fumes produced are usually extracted in the upper part, after having passed through a furnace lined with sheets of pressurized tubes, called membranes, in which water to be vaporized, or steam to be heated. Then, the fumes usually pass through a series of exchangers called superheaters intended to overheat the steam. Finally, the fumes, still quite hot, circulate in complementary circuits, called sprays and economisers, and trarismets still heat to the circuit of water or vapor, using exchangers working at various temperatures, until at temperatures in general between 180 and 130 ° C. - In a fluidized bed boiler process, the inputs are previously ground and calibrated and then introduced into a reactor where a mass of particles at more than 500 ° C such as, for example, sand, the divine, dolomite or highfourneau slag. The entrants, attacked by a rapid combustion front, then undergo an oxidation in fractions of seconds. For large-scale installations called circulating fluidized bed, with a power generally greater than 25 MW, a centrifugal separation of the gases produced from the flying particles is carried out. These are then recirculated in the lower part to the reactor for reuse in the home, bringing with it most unburned organic matter particles. The gases produced are collected in a single main outlet placed in the upper position, and the circuit taken by the flue gas is then similar to that of a grate fireplace as described above.

In a so-called spraying furnace, pulverulent material is injected at high speed, which allows an almost instantaneous combustion approaching the combustion of a gaseous fuel, without being able to bring the same homogeneity of the thermal gradients.

These traditional solutions have the following defects in particular: The combustion reactions, which take place in the same chamber, do not make it possible to precisely control the temperatures and the chemical compositions of the reactants present in the different zones of the reactor. In particular, hot spots (usually above 1200 ° C) and localized spots can occur, which can lead to the production of combustion NOx (nitrogen oxides), one of the most harmful air pollutants for health.

In the case of combustion by circulating fluidized bed, which proceeds instantly to the combustion operation, the fumes produced are of better quality. However, the installation is complex, requires sensitive process adjustment variables and is energy-intensive in electrical auxiliaries, because it must ensure the fluidization of heavy sandy elements. The moving particles, usually sand, are themselves very sensitive to physicochemical interactions with certain alkaline elements contained in the ashes, which causes with some inputs, in particular those loaded with potassium, sintering phenomena of the bed, which compromises the fluidity of the particles until triggering the shutdown of the installation.

Description of the invention

The present invention aims to overcome the disadvantages of the state of the art by providing an economical process capable of producing heat and / or electricity and emitting fumes less harmful to the environment. In addition, this process improves the overall energy efficiency and the life of equipment, including heat exchangers.

Thus, the present invention relates to a method of burning organic material, characterized in that it comprises a step of mixing a transfer media composed of independent solid particles, with organic material and circulating said mixture in a chamber and in that said mixture is subjected to combustion using an oxidant introduced inside said enclosure.

According to a preferred embodiment of the invention, said mixture circulates vertically up and down under the effect of its own weight.

By the term "under the effect of its own weight" is meant to indicate that said mixture moves in whole or in part under the effect of gravity and preferentially only under the effect of gravity.

Advantageously, said mixture fills the entire horizontal section of the enclosure over all or part of the height of said enclosure. Preferably, said mixture fills the entire horizontal section of the enclosure over the entire height of said enclosure.

According to a preferred embodiment of the invention, said mixture is subjected to successive combustion steps in different areas of said enclosure.

According to a preferred embodiment of the invention, the combustion fumes produced are totally or partially reinjected inside said enclosure.

According to a preferred embodiment of the invention, said transfer medium passes through said chamber, several successive fluid action zones.

According to a preferred embodiment of the invention, the method comprises an additional step of separating said transfer medium from the mineral material obtained after combustion and that said transfer medium thus obtained is then reused in a process, according to the invention. 'invention.

The present invention also relates to a device for the combustion of an organic material according to a method according to the invention, comprising a combustion chamber comprising an inlet of said organic material, at least one oxidant inlet connected to an oxidizer source, a residual mineral material outlet and a combustion smoke outlet, characterized in that independent solid particles forming a heaped movable transfer media are placed in said enclosure, and in that a transfer media inlet is placed at a end of said enclosure and that a transfer media output is placed at the other end of said enclosure and that a transfer medium transfer means is interposed between the transfer media output and the transfer media input for looping the transfer media.

In the context of the present invention, the term "heaped" means that said mobile transfer media fills the entire horizontal section of the enclosure over all or part of the height of said enclosure. Preferably, said mixture fills the entire horizontal section of the enclosure over the entire height of said enclosure.

According to a preferred embodiment of the invention, said combustion chamber comprises several oxidizer inlets staggered with respect to each other, each being connected to a common or separate source of oxidant.

According to a preferred embodiment of the invention, the axis passing between said input and said transfer media output has an inclination of at least 45 "relative to the horizontal.

According to a preferred embodiment of the invention, the transfer medium has a void ratio of at least 20%.

According to a preferred embodiment of the invention, the independent solid particles constituting said transfer medium each have a developed surface of between 1 and 10 cm 2.

According to a preferred embodiment of the invention, said device further comprises means for regulating the transfer rate of the particles of the transfer medium.

According to a preferred embodiment of the invention, a means for mixing and regulating the flow of organic matter and transfer media particles is associated with the enclosure.

According to a preferred embodiment of the invention, a means of controlling the oxidant flow rate is associated with at least one of the oxidizer inputs.

According to a preferred embodiment of the invention, said device further comprises a means for cleaning the particles of the transfer medium.

According to a preferred embodiment of the invention, said device further comprises means for screening the particles of the media, ensuring among other things the elimination of broken or agglomerated elements, and the separation of ashes.

According to a preferred embodiment of the invention, said device further comprises at least one sealed heat exchanger placed inside said enclosure, in contact with said transfer medium, and connected to an input and an output of fluid, ensuring the increase of the enthalpy of said fluid.

According to a preferred embodiment of the invention, said device comprises at least one sealed heat exchanger placed inside said flue gas outlet, and connected to an inlet and a fluid outlet, ensuring the increase of the enthalpy of said fluid.

In the context of the present invention, the term "zone" or "zone of action" is intended to designate a part of the interior volume of the enclosure in which will flow a stack of individual solid heat transfer particles, called transfer medium and in which said transfer media performs a specific function in interaction with one or more fluids, such as air, combustion fumes, steam, ....

These zones can be defined structurally in the case where a fluid will flow between its inlet and its outlet, in a sealed heat exchanger placed inside the enclosure. Alternatively, an area can be defined by the position of the fluid inlet and outlet. For example, an inlet and a fluid outlet placed on either side of the enclosure will define an area that corresponds to the portion of the enclosure disposed between said inlet and said outlet. In order to prevent two zones of action from being superimposed, the person skilled in the art is able to determine the ideal position of each inlet and outlet, particularly as a function of the physico-chemical nature of the fluid, its speed circulation and loss of loads.

Advantages of the invention

One of the advantages of the invention is that the high thermal inertia of the mobile transfer media, associated with its high conductivity and thermal diffusivity, make it possible to limit temperature fluctuations in the combustion zone. The temperature gradient is much more stable, despite unavoidable variations in dryness or heat capacity of the organic material to be oxidized.

Another advantage is that the thermal capacity of the mobile transfer media can be defined in such a way that the enthalpy transfer takes place at the temperatures required to perfectly control the transformation of the organic matter. In addition, this inertia allows a low thermal pinch and improves the performance of the heat exchange between the fluids and the materials involved.

The process according to the invention has the following characteristics and or advantages:

The heat transfer medium, which is contained in the enclosure, is mobile and non-fixed, unlike fixed packings which certainly provide a large heat exchange surface but which can not easily extracted from the enclosure in order to clean them . This mobility makes it possible to transport energy picked up by the media from one zone of the enclosure to another zone of the enclosure, or even to another enclosure. - The function of the media is to capture the available enthalpy in the enclosure and then restore it. Some solutions known to those skilled in the art have an external oven (gas, electric, ...) in which the media, for example in the form of balls, circulates, so that it is heated by the combustion taking place in the outdoor oven. Then, the media is introduced into a chamber in which the enthalpy brought by the heat transfer medium is enhanced. The enthalpy exchanged therefore comes from a fuel and an external device, such as a gas boiler. According to the invention, the function of the medium is to recover the energy usually lost by the downstream part of the process, and not to consume fuel to provide external energy that can only degrade the energy balance of the process, while fuel could be valorized outside the invention. - The function of heat exchange, especially between the media and a gas (air, syngas or steam) is preponderant.

The media is displaced substantially vertically which allows a maximum and homogeneous filling of the reactor enclosure, unlike rotating horizontal drums or systems with horizontal transfer screw. This thus avoids the recurrent problems of stratification and inhomogeneous mixing of materials with significant differences in density. This also ensures a smooth flow of fluids in the media, because it turns out that in a non-essentially vertical media media particles are peeled off the top wall of the enclosure and thus release a space in which a preferential flow of fluid appears, to the detriment of the performance of the invention. In addition, this vertical arrangement facilitates the setting in motion of the particles by the simple gravity, in particular at high temperatures which disturb the use of mechanical parts such as for example an Archimedean screw. The invention utilizes media that has calibrated porosity spaces, unlike sands found, for example, in fluidized bed boiler or gasification systems that require the use of a fluidizing gas. injected at high pressure, a source of early wear and energy consumption. Thus, according to the invention, the media weighs all its weight on the organic particles that are mixed thereon, so that a compressive effect, crushing, erosion occurs. as well as a mechanical contact promoting the rapidity of thermal exchanges.

Preferably, the method according to the invention implements a controlled flow of a fluid through the medium, minimizing the risk of occurrence of a preferential flow circuit that co-circuits part of the enclosure and greatly reduces interest of the invention. Thus, an enclosure in which the media is disposed in a vertical layer between two perforated guide plates and which would be traversed horizontally horizontally by a gas flowing from one of the guide plates to the other, would not achieve the yield of the process according to the invention. Indeed, if the vertical media bed flowing between the two guide plates is not perfectly homogeneous in porosity, a preferential flow of the fluid could appear in a local part of the media and all the rest of the media would not be active to exchange enthalpy with the fluid circulating in the enclosure. In the method according to the invention, this risk is limited by ensuring a circulation of the coolant along the longest dimension of the medium, that is, preferably along the height in the case of a medium placed by crowding in a vertical enclosure. This vertical flow can in particular be ensured by the use of a solid sheet metal enclosure filled with media and having an inlet and a fluid outlet placed in the high and low position, or conversely, the useful area of the media .

Another advantage is that the transfer speed of the transfer medium can be adjusted in real time according to the required combustion power, thus making it possible to adjust, for example, the parameters of the peripheral methods making it possible to recover the energy emitted during combustion such as, for example, the recirculation of fumes that stabilize the temperature of the hearth, the supply of primary or secondary air as oxidant or the circulation of fluids in the various exchangers ensuring the production of steam.

Another advantage is that the mobile heat transfer medium can be set in motion slowly, for example at a particle displacement speed of less than 0.1 m / s, which is much less energy consuming than a sand fluidization movement in a combustion chamber with a fluidized bed. Indeed, the only significant energy consumed for the movement of said mobile heat transfer medium is the energy of its transfer from the bottom to the top by a lifting means such as a bucket elevator.

Another advantage is that the exchange of enthalpy takes place in the same enclosure, thus avoiding the use of an auxiliary heating furnace that would ensure the temperature rise of balls or any other mass in motion and to avoid constraints related to transfers at very high temperatures.

Another advantage is that it is possible to choose a mobile heat transfer medium made of a material insensitive to chemical attack, acid or oxidation such as, for example, alumina balls (AL203).

Another advantage is that the mobile media does not have to be cleaned in situ, unlike traditional fixed-fill condensation plants which, by their nature, can not easily be removed from the reactor for cleaning.

Another advantage is that the fact that the ashes eventually have a melting point below the ideal combustion temperature of about 850 ° C. does not imply any accumulation of slag in the hearth, or sintering such as those found in fluidized beds, allowing to consider a wider variety of inputs, including agricultural substrates with high potassium levels.

Another advantage is that the control of the temperature gradients and the combustion air introduction zones, divided into several stages, make it possible to greatly limit the production of thermal NOx, but also NOx called fuel.

Another advantage is that it is possible to define two distinct media zones, allowing extremely rapid cooling of the fumes to limit the formation of dioxins in the temperature range 250-450 ° C.

Another advantage is that the absence of direct contact between the flue gases and the steam tubes under pressure makes it possible to envisage raising the superheating temperature of the steam, advantageously above 500 ° C., especially in the case of use of entrants heavily loaded with chlorine and sulfur.

Another advantage is that the performance of the heat exchanges makes it possible to reduce the exchange surfaces and the length of the superheaters, while allowing less sinuous circuits than the conventional boiler superheaters, thus limiting the pressure drops in the boiler. This advantage makes it possible to envisage one or more stages of reheating of the steam and the use of multi-body steam turbines, thus making it possible to restore the steam of the energy exploitable by a steam turbine. This allows to greatly improve the electrical yields. Such an arrangement was previously reserved for very large installations, typically more than 100 MW electric. The invention makes it possible to exploit the reheating of steam for installations with an electrical power of less than 10 MW electric.

Another advantage is that the mass of particles in motion involves a crushing action and dispersion of the incandescent particles, and any particles depolymerized and weakened by the combustion front, which allows a direct contact between the fixed carbon and the oxidant and limits the presence of hot spots confined within incandescent embers, said hot spots being the source of thermal NOx emission by a temperature punctually greater than 1200 ° C. Other advantages and characteristics of the invention are described below according to the possible embodiments of the invention.

The descriptions refer to the following figures in the appendix:

FIG. 1 diagrammatically represents an embodiment of the device according to the invention according to a first combustion version with a valuation of fumes in countercurrent.

FIG. 2 diagrammatically represents a variant of the invention according to a second combustion version with prior drying and flue gas flow while cocurrently

FIG. 3 diagrammatically represents a variant of the invention according to a third version integrating prior drying, combustion and recovery of fumes in co-current

Description of an embodiment

The method according to the invention implements a device for the combustion of an organic material. The objective is to burn the incoming in the presence of oxidant such as, for example, oxygen delivered by air, to channel the heat released and to enhance this heat by heating a heat transfer fluid, for example the water or steam.

According to the invention, the organic material to be treated is introduced into the chamber in the middle of independent solid particles forming a mobile transfer medium. The mixture obtained has several advantageous characteristics described below, especially in terms of thermal inertia, porosity and mass.

The mixture is mobile, that is to say that a slow flow is set up so as to make it pass through different zones of action, the flow rate being preferably less than 6 m / min, and more preferably less than 1 m / min and even more preferably less than 0.1 m / min.

The embodiment described here considers that the flow is vertical downward; however any other direction or direction of flow is possible, even if the implementation is more complex. The flow is slow, that is to say the speed of the particles forming the media is adapted, both to the need of combustion, which must be supplied with fuel (the entrants) present in the mixture, and at the need of thermal inertia provided by the media in the combustion chamber. It is therefore necessary to have a means of regulating the formation of the mixture, so that the flow rate of the entrants and the transfer media flow rate are regulated independently.

Thus, the mixture leaves the feed zone and descends into the combustion zone, supplied · with combustion air. The air flow is regulated so as to allow a controlled power combustion of the inputs brought by the mixture.

Advantageously, the oxidizer feeds are separated so as to create separate combustion zones. but the fumes created by each combustion are combined and evacuated in a single output of the enclosure. According to another variant of the invention, there are several outlets, but at least one ensures the evacuation of a mixture of fumes from the separate combustions.

If necessary, especially in the start-up phase, an auxiliary combustion means or burner, for example comprising a fuel supply and a start-up means (spark), is put in place in the combustion zone.

Advantageously, the combustion zone is divided into three sub-zones, each being fed by a specific air inlet, the flow rate of which is regulated separately in relation to the measurement of the temperature prevailing in the zone. Thus, the temperature gradient in these three sub-areas is precisely controlled. The three air inlets are called primary air, secondary air and tertiary air. This controlled and separate management makes it possible both to maintain an increasing temperature gradient from the first zone, normally stabilized between 250 ° C. and 350 ° C., preferably 300 ° C., and then the second zone, normally stabilized between 450 ° C. and 550 ° C. ° C, preferentially at 500 ° C, up to the third zone, normally stabilized between 750 ° C and 950 ° C, preferably at 850 ° C; and also to ensure the conversion of so-called combustion NOx into elements that are harmless for human health.

Thus, the fumes generated contain a minimum amount of NOX, because no combustion zone reaches more than 1200 * C, as is generally the case with traditional technologies.

Advantageously, a solution for regulating the oxygen content can be obtained by injecting recirculated fumes in a mixture with the air. In a broader way. any kind of regulation of oxygen levels evident to those skilled in the art and preserving the efficiency of the process or the quality of the gases produced is possible. At the end of this combustion, the duration of which can be adjusted by modifying the flow velocity of the media extracted from the bottom of the combustion chamber, the burned mixture then contains only particles of transfer media, advantageously incombustible, mineral ash and unburned organic matter if the power and residence time of combustion have been insufficient. This mixture comprising burnt entrants has a high temperature (typically over 800 ° C) and represents a large energy store, mainly contained in the hot particles of the transfer media.

This hot mass can be used to subject the fumes to a high temperature for a minimal time, for example at more than 800 ° C for more than 2 seconds, so that the dioxins created during combustion are destroyed, and thus respond regulatory constraints in many countries to ensure the destruction of such dioxins.

This energy stock can also be valued by various enthalpy recovery areas.

Thus, the hot mixture may, for example, pass through a vaporization zone of pressurized water or superheating of steam circulating in a sealed exchanger in front of or around which the mixture circulates. The heat exchanges are then by radiation, convection and conduction between the media particles and the walls of the exchanger. These exchanges are advantageously improved if a fluid, such as for example combustion fumes, circulates simultaneously through the mixture. The flow of this fluid around the particles of the transfer medium amplifies the convection phenomena and improves the power of the heat exchanges, and the homogeneity of the temperatures.

In another example, the hot mixture can pass through a preheating zone of the air which will then be used as combustion air during combustion. Thus, the overall efficiency of the process is improved.

Then, the burnt mixture is subjected to a separation step during which the transfer medium is separated from the mineral ash and is reinjected into the process, possibly after one or more specific treatments (cleaning, repair, cooling, reheating, etc.). . The ashes are evacuated for setting in storage center or subsequent valorization, as by spreading, .... The unburnt can be reinjected into the process in association with the recovered media, or separately.

The technical means required to carry out the separation may comprise a perforated screen, a magnetic effect screen (advantageously of the "overband" type, a ballistic screen, an eddy current screen, a vibrating screen, a rotary drum or any other technique known to those skilled in the art according to the nature of the elements to be separated, it is also necessary to separate, in a continuous or periodic manner, the particles of transfer media in good condition from those which are worn, broken and which can no longer fulfill their function.

In addition, the technical means required to carry out the specific treatments may include a cleaning which may be carried out in a pure water bath or with added cleaning agents such as surfactants, or in a bath of solvent, or in a shower of water. water or solvent, or under a jet of cleaning gas or steam, such as steam, or by blowing compressed air. A cleaning variant may use a vibration cleaning device, in particular to separate dust adhering to the media particles by moving them on a vibrating screen, or any other vibration cleaning device, or any other high frequency device, such as ultrasound, with the possible supplement of a bath of cleaning liquid.

The fumes generated during the combustion are obviously hot and can be valorized in two ways: either the configuration of the device according to the invention is said to be "countercurrent", that is to say that if the transfer medium descends by slow flow, the fumes rise. So, the configuration looks like a vertical boiler with conventional water tubes. The fumes rise and pass through a zone of vaporization of pressurized water or superheating of steam circulating in a sealed exchanger in front of which the mixture circulates. The heat exchanges are then by radiation and convection between the smoke and the walls of the exchanger.

Either the configuration is called "co-current", that is to say that the fumes go down with the transfer media, which allows them to stay for a controlled time at a high temperature, as already described.

In all cases, the fumes can be extracted from the enclosure and undergo separate recovery steps such as enthalpy recovery, smoke condensation, ....

According to a variant of the countercurrent configuration, a transfer media bed may be added in the vaporization zone, above the combustion zone. Thus, the media plays an additional role in helping heat transfer in this area.

Organic matter can have any aspect; it can be liquid, for example animal slurry or sewage sludge; it can be solid, such as, for example, silo refusals from agricultural grains or wood chips; it can also be in an intermediate pasty state or in a heterogeneous mixture. Any organic material of size preferably less than 30 cm is suitable.

The mass of the transfer media consists of a set of individual solid particles which are used without cohesion between them. This gives a mass of particles whose size and shape allows a natural flow by the effect of gravity.

This natural flow also allows the entrainment of incoming mixed in said transfer media.

The mass plays a media role which will constantly heat up and cool under the influence of the energy and the fluids involved, so that enthalpy exchanges take place in the different zones of the device according to the invention. .

The storage of heat or thermal inertia is one of the characteristics of the invention. Indeed, the transfer media has a mass that allows to accumulate enthalpy under the effect of its rise in temperature and according to its specific thermal capacity expressed in the unit J / (kg.K). Thus, it is necessary to have a mass transfer medium and / or large heat capacity mass that has a high thermal inertia. Concretely, to guarantee a good stability of the thermal exchanges, it is preferable that the total enthalpy contained in the media. represents at least the enthalpy generated by the combustion of the entrants for 5 min. In addition, it is advantageous to have particles whose density is greater than 2500 kg / m 2 and whose thermal capacity is greater than 300 J / (kg.K).

According to a variant of the invention, the transfer medium may contain a material which changes phase during its use so as to also benefit from the latent heat of phase change of this material, which also makes it possible to have a more great thermal inertia.

For example, a hollow refractory molybdenum steel ball whose melting temperature exceeds 2600 ° C., filled with an aluminum alloy whose melting temperature is 600 ° C., can store, during the solid phase change. - Aluminum liquid at this fixed temperature of 600 ° C, more than 370 kJ / kg of aluminum is the equivalent of the sensible heat of a kg of aluminum heating up to 400 ° C. The thermal inertia of the media is sought because it ensures a storage of the enthalpy that stabilizes the combustion of inputs and heat exchange in the different work areas. Thus, it avoids overheating entrants or fumes, which limits the risk of occurrence of nitrogen oxides. Thanks to the inertia of the media, the distribution of temperatures in the combustion medium is also distributed.

Another advantage of the invention is that the transfer medium provides a high-power heat exchange, both during the combustion of the inputs, but also in the other steps when the transfer medium restores the energy captured to other elements, such as water or water vapor. This result is advantageously obtained by the use of a medium having numerous cavities easily traversed by the fluid. Thus, a transfer medium consisting of balls perforated on 25% of their volume guarantees a porosity (ratio of the void volume to the total solid + empty volume) of more than 50% and therefore a good circulation of the oxidant and / or fumes throughout the enthalpy exchange area.

In addition, in a space of large volume is the focus of combustion of an industrial boiler (several m ^), the oxidizer flow rates are not evenly distributed which creates pockets of combustion more intense than the optimum and others less intense. Thanks to the invention and the more uniform porosity of the media, the oxidant distribution and the combustion powers are more homogeneous.

According to a variant of the invention, it is possible to use simple spheres, the packing of which in a given volume makes it possible to preserve porosities between the spheres, leaving a free passage for the through fluids.

In addition, the exchange power is improved if the media has a good diffusivity, that is to say if the material has a strong ability to transfer heat. The diffusivity coefficient defined by D = lambda / ro / C (where lambda = = thermal conductivity, ro = density and C = specific heat capacity) is preferably greater than 0.2 × 10 -4 m 2 / s.

In addition, the geometry and dimension of the media elements are preferably defined to ensure the presence of a large developed surface swept by the fluids in the presence, said surface being the seat of the heat exchange. Thus, it is advantageous that the media elements have a large developed surface and a low material thickness in order to facilitate the enthalpy exchanges. The preferred compactness parameter, defined as the ratio of the developed surface to the solid volume, is greater than 3 m 2 / m 3, which corresponds, for example, to ball-shaped particles with a diameter of 30 mm and pierced with two orthogonal holes with a diameter of 10 mm.

Finally, the exchange power is improved if the flows of the fluids through the transfer media are made according to a hydraulic or aeraulic regime at high speed or turbulent, such a regime accentuating the performance of convective heat exchange at the surface of the media. transfer. For example, according to a preferred solution, the dimensioning of the device will ensure a fluid flow rate greater than 1 m / s for liquid and greater than 3 m / s for gas.

Advantageously, the transfer medium must withstand the operating constraints during combustion.

Thus, if the combustion takes place at a temperature greater than 900 ° C., it is necessary for the transfer medium to withstand such a temperature. A recommended solution is to use molded spheres composed of alumina ceramic, whose temperature resistance thus reaches limits greater than 1100 ° C or 1800 ° C depending on the purity of the alumina.

Similarly, the use of a molybdenum alloy refractory metal makes it possible to have a material whose melting point is greater than 2200 ° C. and whose mechanical strength is greater than that of an alumina ceramic. .

As the present invention makes it possible to maintain temperatures below 900 ° C. in all points of the device, non-refractory austenitic steel may also be used.

In addition, if the combustion generates fumes containing sulfur or chlorine and moisture, in case of condensation of water vapor during the heat exchange and the cooling of these fumes, sulfuric acid or hydrochloric acid can form and quickly corrode the transfer media. In this case, the material constituting it must be chosen so as to withstand a pH generally less than 3.

Furthermore, the fumes may contain suspended elements may be deposited on the transfer media and thus lead to fouling, with the potential to gradually reduce the porosity of the latter. The circulation of fluids and the efficiency of thermal exchanges would then be degraded. To solve this problem, the device according to the invention advantageously comprises a washing means of the transfer media, regular or continuous.

The choice of the material composing the transfer medium also involves taking into consideration the catalysis phenomena generated by the contact of certain flue gas components with the surface of said transfer medium.

Finally, according to the invention, the transfer medium is set in circulation movement inside the enclosure of the exchanger which assumes that the transfer medium is composed of individual particles that can be moved without bonding between they and without mechanical blocking, which would create a single block impossible to move. It is also advantageous that the elements constituting the transfer medium have sufficient mechanical strength to support the weight of the stacking, especially in the lower part. It is also preferable that the eventual movement of these elements does not break them or abrase them too quickly, so as not to have to replace them too often, due to unavoidable wear.

Thus, the heat transfer transfer medium is composed of individual particles which may be balls or individual elements of the ring type.

Raschig, saddle of Perl, ... which are placed in pile in the combustion chamber.

Advantageously, the elements are of globally spherical shape. The spherical shape facilitates the circulation of the elements in the enclosure without a particle blocking effect between them can occur. Other forms are obviously also possible, as long as they comply with the specifications described above.

Thus, the stack of the transfer medium is preferably mechanically resistant, porous for the circulation of the fluid, massive to improve the thermal inertia, having a large surface developed to ensure a high-power heat exchange and thermal conductivity. to accelerate heat transfer.

According to a variant of the invention shown in FIG. 1 and making it possible to ensure combustion with a flue gas recovery from above and in a counter-current mode, the device 1 comprises an enclosure 10 in which there are two zones of action: a combustion zone 11 and a vaporization zone 12.

The combustion zone 11 is fed from the top with a mixture 21 of inputs 22 and transfer media 23, previously mixed with a mixing means 20. Said mixture 21 is introduced into the chamber through an inlet 26 and distributed uniformly in said enclosure 10 by means of a dispensing means 25. Preferably, this dispensing means 25 comprises one or more Archimedean screws placed horizontally and whose rotation allows the distribution of the mixture 21 of homogeneously over the entire horizontal section of the enclosure 10. The dispensing means 25 may also include a hydraulic or mechanical pusher, which makes the equipment more compact but which however has the disadvantage of a less accurate dosage.

The mixture, 21 is packed in said enclosure 10 and flows by gravity, assisted in this by means of elevation 80, which maintains the circulation of the transfer medium 23 from an outlet 103 placed at the bottom of the enclosure until 'at the entrance 26.

In order to ensure combustion, an oxidizer supply means 30 is placed at the combustion zone 11. This means comprises in particular one or more feed lines 31, 32, 33 which channel and distribute the oxidant homogeneous over the entire horizontal section of the enclosure 10. Advantageously, each supply line 31, 32, 33 has its oxidizer flow rate regulated, for example, using a flow control valve respectively 34, 35, 36 .

For certain applications, particularly certain inputs with very high levels of nitrogen, sometimes more than 1% of the dry matter, the number of oxidizer feed lines 31 32 33 can be increased to better control the curve temperature rise of the inputs, which makes it possible to limit the NOx production of fuels.

The oxidant is typically outside air 41 which, in the case of this example, is preheated using a heating means 40, which uses the heat from the recirculating medium 43 to obtain a heated oxidant 42 and a cooled media 44. The cooled media 44 is then used by the mixing means 20.

In order to enable the device 1 to be started, an auxiliary combustion means 60 or burner is advantageously placed in the combustion zone 11, comprising, for example, a fuel supply 104 and a firing means, not shown.

During this combustion, fumes are generated and are evacuated from the top of the enclosure through the outlet 102.

During this evacuation, the fumes pass through the vaporization zone 12 which comprises a sealed heat exchanger 123. This exchanger 123 is supplied with a fluid to be evaporated or superheated, typically water or steam under pressure, from an inlet 121 to an outlet 122. Thus, the fumes transmit their enthalpy to this exchanger 123. After leaving the enclosure 102, the fumes are still quite hot and this energy can be recovered by any means of recovery of heat adapted to fumes.

At the bottom of the combustion zone 11, a return of smoke coming from the downstream of the process, can be set up by the inlet 101, at a controlled flow rate so as to bring a cold gas into the chamber and thus reduce the power of burning in progress. This smoke recirculation means, in addition to the air supply means 30 therefore participates in the regulation of the power of the combustion.

Finally, at the end of combustion in zone 11, the initial mixture 21 comprises only the initial media 23 and mineral ash brought by the entrants, as well as possibly some unburnt. This final mixture 51 thus constituted is discharged at the outlet 103, and advantageously undergoes separation by means of a separating means 50, which makes it possible to obtain on one side the mineral ashes 53 and on the other hand the media transfer 52.

According to the embodiment of the invention shown in FIG. 2 and making it possible to ensure combustion with prior drying and in a cocurrent mode, a pre-drying zone 13 is located above the combustion zone 11. This zone prior drying 13 is supplied with mixture 21, comprising entrants 22 and particles of transfer media 23. These particles are hotter than incoming, for example 200 ° C, so that during the stay of the mixture 21 in the drying zone 13, the enthalpy of the transfer medium 23 will be transmitted to the input elements to allow the vaporization of the moisture contained in the wet entrants and the drying, at least partially, said entrants.

However, instead of being above the combustion zone, the drying zone can also be located upstream of the combustion zone, in particular for the high power units, a transfer of the mobile heat-transfer medium then being required.

A means 70 for collecting and evacuating the steam produced is implanted in the drying zone 13.

Then, the mixture is introduced into the combustion zone 11 which operates in the same way as in FIG. 1, with the difference that the fumes produced are discharged through an outlet 102 present in the lower part of the enclosure 10, and the media transfer 23 is discharged through an outlet 103, also placed in the lower part of the enclosure, hence the concept of co-current.

After leaving 102, the fumes are very hot and this heat can be enhanced by any means obvious to those skilled in the art.

After the outlet 103, the media is very hot and this heat can be recovered using a heat exchange means 40, possibly after said separation step 50.

Referring to Figure 3, there is shown an embodiment of the invention to ensure combustion in a cocurrent mode with prior drying and vaporization.

The arrangement of the different zones of action is then as follows: a feed mixture 20 - a drying zone 13 - a combustion zone 30 - a stabilization zone 14 - a vaporization zone 15 - a preheating zone The advantage of the device according to FIG. 3 lies notably in the stabilization zone 14, whose function is to maintain the fumes at a temperature of more than 850 ° C. for at least 2 seconds. Thus, the dioxins that eventually formed during combustion are destroyed, the residual carbon monoxide is oxidized to carbon dioxide, the aromatic polycyclic hydrocarbons are degraded and the fixed carbon is oxidized.

In addition, the vaporization zone 15 and the preheating zone 16 comprise a heat exchanger similar to that of zone 12, allowing the heating, vaporization and / or overheating of a fluid introduced through the inlet 161 and discharged. by the exit 152.

Finally, the separation between the zones 15 and 16 makes it possible to evacuate the fumes via the outlet 102 placed between the two zones, and to supply the zone 16 with combustion air, from an inlet 41 to an outlet 42, so that the hot medium can heat this air before its introduction into the combustion zone by the supply means 30. The enclosure 10 is preferably of a stretched and vertical shape, that is to say that among its three characteristic dimensions ( height length Width),. one of the dimensions is large relative to the others, to promote the establishment of a fluid flow from their entry to their exit, so that all the fluid portions that arrive in the enclosure stay there for a equivalent duration and circulate in the media along the same path. A more compact form of enclosure (the three dimensions having about the same value) would be less efficient because the flue gas flow would not be so homogeneous.

Advantageously, the enclosure 10 is insulated so as to minimize heat leakage that could affect the performance of the heat exchange.

When the transfer medium 23 has left the chamber 10, it must be moved from the withdrawal orifice 103 to the reintroduction port 26. For this purpose, when the movement of the transfer medium 23 is high, low in the enclosure, vertical elevation conveying is required. This can be done by Archimedean screw, treadmill, bucket elevator, lift cylinder or any other mechanical means for vertical conveying.

According to a variant of the invention, it is advantageous to have a special zone for condensing the fumes, by cooling them below their dew point, which is generally between 38 and 65 ° C. humidity of the entrants. For example, the burning of dry wood with an excess of air of 20% generates more than 70 grams of water vapor per Nm 2 of smoke, which represents nearly 400 grams of steam per kg. most of the water vapor is produced by the combustion itself. For this purpose, a condensing media device can be put in place.

One of the advantages of such a device is that it can recover latent heat, an energy that can represent up to 30% of the primary energy, while optimizing the recovery of a significant part of sensible heat.

Another advantage is that the condensation action, combined with the permanent slowing down of the rain formed by the condensation, makes it possible to promote the capture of all elements contained in the fumes and water-soluble, or having hydrophilic properties. This concerns most dust, NHS, NOx in the form of NO2, HCl (hydrochloric acid), SO2 (sulfur dioxide).

Another advantage is that the condensates resulting from a Ranline cycle equipped in particular with a condensing steam turbine, can be preheated by the latent heat recovered, as well as all or part of the combustion air, thus making it possible to enhance in electrical energy a part of the latent heat. This last advantage makes it possible to bring a strong improvement of electrical efficiency compared to conventional technologies.

Claims (10)

1- A method of burning organic material (22), characterized in that it comprises a step of mixing a transfer medium (23) composed of independent solid particles, with organic material (22) and to circulate said mixing (21) in an enclosure (10) and in that said mixture is subjected to combustion using an oxidant introduced inside said enclosure (10). 2- combustion process according to the preceding claim, characterized in that said mixture (21) flows vertically up and down under the effect of its own weight. 3- combustion process according to one of the preceding claims, characterized in that said mixture (21) is subjected to successive combustion steps in different areas of said enclosure (10). 4- A combustion process according to one of the preceding claims, characterized in that the combustion fumes produced are totally or partially reinjected inside said enclosure (10). 5. Combustion method according to one of the preceding claims, characterized in that said transfer medium (23) passes through, within said chamber (10), several successive fluid action zones (11, 12, 13, 14, 15, 16, 111, 112, 113). 6. Combustion method according to one of the preceding claims, characterized in that it comprises a further step of separating said transfer medium (23) from said mineral material obtained after combustion and in that said transfer medium (52) ) thus obtained is then reused in a method according to one of the preceding claims. 7- Device (1) for the combustion of an organic material (22) according to a method according to one of claims 1 to 6, comprising a combustion chamber (10) comprising an inlet (26) of said organic material (22). ), at least one oxidant inlet (34, 35, 36) connected to an oxidant source, a residual mineral material outlet (103) and a combustion smoke outlet (102), characterized in that independent solid particles (23) forming a heaped mobile transfer media are placed in said enclosure (10), and in that a transfer media input (26) is placed at one end of said enclosure (10) and that a transfer media output (103) is placed at the other end of said enclosure (10) and transfer media transfer means (80) is interposed between the transfer media output (103) and the transfer media input (26bis) for looping the tranfer media sfert (23). 8- Device (1) according to the preceding claim, characterized in that said combustion chamber (10) comprises a plurality of oxidant inlet (34, 35, 36) staggered relative to each other, each connected to a source of common or separate oxidant. 9- Device (1) according to one of claims 7 to 8, characterized in that a means of regulating the oxidant flow is associated with at least one of the oxidizer inputs (34, 35, 36). 10- Device (1) according to one of claims 7 to 9, characterized in that it comprises at least one sealed heat exchanger (123) placed inside said enclosure, in contact with said transfer medium (23). ), and connected to an inlet (161) and an outlet (162) of fluid, ensuring the increase of the enthalpy of said fluid.