EP3472517B1 - Combustion process - Google Patents

Description

Field of the invention

The present invention relates to the field of the production of heat or cogeneration (heat and electricity) by combustion of organic material used in a solid or liquid form, this material being able to consist of biomass of mainly vegetable or animal or fossil origin such as example of plastics or other products composed of hydrocarbons.

The invention relates in particular to a combustion process and the combustion installation 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. However, heat production alone can also be ensured by the invention, with a view to its use by a hot water or steam heat network, or any other conversion of heat into mechanical energy or into 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 anaerobic digestion.

Organic matter is still mainly made up 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 an oxidation of the material, which is strongly exothermic, the oxidizer being traditionally air in excess relative to 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 (subsequently 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, representing a high risk to the health of surrounding populations.

• Dans un procédé de chaudière à grille, qui comprend notamment les grilles à gradin, les spreader stockers, les grilles rotatives, les entrants sont introduits au-dessus d'une grille en mouvement, dans la partie basse d'une enceinte, dans laquelle elle subit une combustion en même temps qu'elle se déplace sous l'effet des mouvements de la grille. Du comburant, tel que de l'air ou de l'oxygène, est introduit dans l'enceinte afin de permettre la combustion de la matière organique et ainsi générer des fumées très chaudes (en général plus de 800°C). Les fumées produites sont habituellement extraites en partie haute, après avoir traversé un foyer tapissé de nappes de tubes sous pression, dites membranes, dans lesquelles circulent de l'eau à vaporiser, ou de la vapeur à surchauffer. Ensuite, les fumées traversent en général une série d'échangeurs dénommés surchauffeurs destinés à surchauffer la vapeur. En dernier lieu, les fumées, encore assez chaudes, circulent dans des circuits complémentaires, dénommés vaporisateurs et économiseurs, et transmettent encore de la chaleur au circuit d'eau ou vapeur, à l'aide d'échangeurs travaillant à diverses températures, jusqu'à des températures en général comprises entre 180 et 130°C.
• Dans un procédé de chaudière à lit fluidisé, les entrants sont préalablement broyés et calibrés puis introduits dans un réacteur où s'agite une masse de particules à plus de 500°C telles que, par exemple, du sable, de l'olivine, de la dolomite ou du laitier de haut-fourneau. Les entrants, attaqués par un front de combustion rapide, subissent alors une oxydation en quelques fractions de secondes. Pour les installations de grande dimension dites à lit fluidisé circulant, d'une puissance généralement supérieure à 25 MW, une séparation centrifuge des gaz produits d'avec les particules volantes est réalisée. Ces dernières sont alors recirculées en partie basse vers le réacteur afin d'être réutilisées dans le foyer, entraînant avec lui la plupart des particules de matière organique non brûlées. Les gaz produits sont collectés en une seule sortie principale placée en position haute, et le circuit emprunté par les fumées est alors similaire à celui d'un foyer à grilles tel que décrit supra.

According to the current state of the art of organic matter combustion processes, the production of heat and / or electricity conventionally uses three main technologies of stoves enabling combustion to be ensured:

• In a grid boiler process, which notably includes step grids, spreader stockers, rotary grates, the entrants are introduced above a moving grid, in the lower part of an enclosure, in which it undergoes combustion at the same time as it moves under the effect of the movements of the grate. Oxidizer, such as air or oxygen, is introduced into the enclosure in order to allow the combustion of the organic matter and thus generate very hot fumes (generally more than 800 ° C). The fumes produced are usually extracted at the top, after passing through a hearth lined with sheets of pressurized tubes, called membranes, in which water circulates. vaporize, or steam to overheat. Then, the flue gases generally pass through a series of exchangers called superheaters intended to superheat the steam. Finally, the fumes, still quite hot, circulate in complementary circuits, called vaporizers and economizers, and still transmit heat to the water or vapor circuit, using exchangers working at various temperatures, up to at temperatures generally between 180 and 130 ° C.
• In a fluidized bed boiler process, the inputs are crushed and calibrated beforehand and then introduced into a reactor which is agitated by a mass of particles at more than 500 ° C. such as, for example, sand, olivine, dolomite or blast furnace slag. Entrants, attacked by a rapid combustion front, then undergo oxidation in a few fractions of seconds. For large-scale installations called a 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. The latter are then recirculated in the lower part to the reactor in order to be reused in the hearth, carrying with it most of the unburnt organic matter particles. The gases produced are collected in a single main outlet placed in the high position, and the circuit taken by the fumes is then similar to that of a grate hearth as described above.

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

• Les réactions de combustion, qui ont lieu dans une même enceinte, ne permettent pas de maîtriser précisément les températures et les compositions chimiques des réactifs en présence dans les différentes zones du réacteur. Il apparait notamment des points chauds (généralement à plus de 1200°C) et localisés, ce qui peut provoquer la production de NOx de combustion (oxydes d'azote), un des polluants atmosphériques les plus nocifs pour la santé.
• Dans le cas de la combustion par lit fluidisé circulant, qui procède instantanément à l'opération de combustion, les fumées produites sont de meilleure qualité. Toutefois, l'installation est complexe, exige des variables d'ajustement de procédé sensibles et se révèle énergivore en auxiliaires électriques, car il faut assurer la fluidisation d'éléments sableux lourds. Les particules en mouvement, généralement du sable, sont elles-mêmes très sensibles à des interactions physico-chimiques avec certains éléments alcalins contenus dans les cendres, ce qui provoque avec certains entrants, notamment ceux chargés en potassium, des phénomènes de frittage du lit, ce qui compromet la fluidité des particules jusqu'à déclencher l'arrêt de l'installation.

These traditional solutions have the following shortcomings in particular:

• The combustion reactions, which take place in the same enclosure, do not allow precise control of the temperatures and the chemical compositions of the reactants present in the various zones of the reactor. It appears in particular hot spots (generally above 1200 ° C) and localized, which can cause the production of combustion NOx (nitrogen oxides), one of the air pollutants most harmful to 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-consuming in electrical auxiliaries, since it is necessary to ensure the fluidization of heavy sandy elements. The moving particles, generally sand, are themselves very sensitive to physicochemical interactions with certain alkaline elements contained in the ashes, which causes with certain entrants, in particular those charged with potassium, phenomena of sintering of the bed, which compromises the fluidity of the particles until triggering the shutdown of the installation.

EP0381195 discloses a combustion process according to the preamble of claim 1.

Description of the invention

The present invention aims to overcome the drawbacks of the state of the art by proposing an economical process capable of producing heat and / or electricity and emitting fumes that are less harmful to the environment. In addition, this process improves the overall energy efficiency as well as the life of the equipment, in particular the heat exchangers.

Thus, the present invention relates to a method of combustion of organic matter, remarkable in that it comprises a step consisting in mixing a transfer medium composed of independent solid particles, with organic matter and in circulating said mixture in an enclosure and in that said mixture is subjected to combustion using an oxidizer introduced inside said enclosure and in that 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 flows vertically from top to bottom under the effect of its own weight.

This also makes it possible to promote the interaction of the gases and of the mixture of the transfer medium with the organic matter.

By the term "under the effect of its own weight" means that said mixture moves in whole or in part under the effect of gravity and preferably only under the effect of gravity.

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

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

In the context of the present invention, the term "Upstream" and "downstream" are used with reference to the direction of circulation of said mixture.

According to a preferred embodiment of the invention, said transfer medium passes, inside said enclosure, several zones of action of successive fluids.

According to a preferred embodiment of the invention, the method comprises an additional step consisting in separating said transfer medium from the mineral material obtained after combustion and in that said transfer medium thus obtained is then reused in a method, according to '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 matter, at least one inlet of oxidant connected to a source of oxidant, a residual mineral outlet and combustion smoke outlet, remarkable in that independent solid particles forming a stacked mobile transfer medium are placed in said enclosure and in that said transfer medium fills the entire horizontal section of the enclosure over all or part of the height of said enclosure and in that a transfer media outlet is placed at one end of said enclosure and in that a transfer media outlet is placed at the other end of said enclosure and in that a transfer medium transfer means is interposed between the transfer media outlet and the transfer media inlet ensuring the ci looping of the transfer media.

In the context of the present invention, the term “piled up” means that said mobile transfer medium fills the entire horizontal section of the enclosure over all or part of the height of said pregnant. 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 stepped relative to each other, each being connected to a common or separate source of oxidant.

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

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 a fluid inlet and outlet , ensuring the increase in the enthalpy of said fluid.

In the context of the present invention, the term “zone” or “action zone” is intended to designate a part of the interior volume of the enclosure in which a heap of individual heat-transferable solid particles will circulate, called transfer media and in which said transfer medium fulfills a specific function in interaction with one or more fluids, such as air, combustion fumes, steam, etc.

These zones can be delimited structurally in the case where a fluid will circulate 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, a fluid inlet and outlet placed on either side of the enclosure will define a zone which corresponds to the part of the enclosure disposed between said inlet and said outlet. In order to prevent two action zones from overlapping, the person skilled in the art is able to determine the ideal position of each inlet and of each outlet, in particular as a function of the physico-chemical nature of the fluid, of its speed. traffic and pressure losses.

Advantages of the invention

One of the advantages of the invention is that the high thermal inertia of the mobile transfer medium, 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 the inevitable variations in dryness or calorific capacity of the organic matter to be oxidized.

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

• Le média caloporteur, qui est contenu dans l'enceinte, est mobile et non fixe, à la différence des garnissages fixes qui apportent certes une grande surface d'échange thermique mais qui ne peuvent aisément extraits de l'enceinte afin de procéder à leur nettoyage.
• Cette mobilité permet de transporter de l'énergie captée par le média depuis une zone de l'enceinte vers une autre zone de l'enceinte, voire vers une autre enceinte.
• Le média a pour fonction de capter l'enthalpie disponible dans l'enceinte pour la restituer ensuite. Certaines solutions connues de l'homme de l'art disposent d'un four extérieur (à gaz, électrique, ...) dans lequel le média, par exemple sous forme de boulets, circule, de sorte qu'il est chauffé par la combustion ayant lieu dans le four extérieur. Ensuite, le média est introduit dans une enceinte dans laquelle l'enthalpie apportée par le média caloporteur est valorisée. L'enthalpie échangée provient donc d'un carburant et d'un dispositif extérieur, tel une chaudière à gaz. Selon l'invention, la fonction du média est de récupérer de l'énergie habituellement perdue par la partie aval du procédé, et non de consommer du carburant pour apporter une énergie extérieure qui ne peut que dégrader le bilan énergétique du procédé, alors que ce carburant pourrait être valorisé à l'extérieur de l'invention.

• La fonction d'échanges thermiques, notamment entre le média et un gaz (air, syngaz ou vapeur) est prépondérante.
• Le média est déplacé de façon essentiellement verticale ce qui autorise un remplissage maximal et homogène de l'enceinte du réacteur, à la différence des tambours horizontaux tournants ou des systèmes avec vis de transfert horizontale. Cela permet ainsi d'éviter les problèmes récurrents de stratification et de mélange peu homogène des matières présentant des différences de densité importantes. Cela permet aussi de garantir un écoulement des fluides homogène dans le média, car il s'avère que dans un média disposé de façon non essentiellement verticale, les particules de média se décollent de la paroi supérieure de l'enceinte et libèrent ainsi un espace dans lequel un écoulement préférentiel de fluide apparait, au détriment de la performance de l'invention.
• De plus, cette disposition verticale facilite la mise en mouvement des particules par la simple gravité, notamment à des températures élevées qui perturbent l'utilisation de pièces mécaniques comme par exemple une vis d'Archimède.
• L'invention utilise un média qui comporte des espaces de porosité calibrée, à la différence des sables que l'on trouve, par exemple, dans les systèmes de chaudière ou de gazéification à lit fluidisé qui exigent l'emploi d'un gaz de fluidisation injecté à haute pression, source d'usure précoce et de consommation d'énergie. Ainsi, selon l'invention, le média pèse de tout son poids sur les particules organiques qui y sont mélangées, de sorte qu'un effet de compression, de broyage, d'effritement s'effectue, ainsi qu'un contact mécanique favorisant la rapidité des échanges thermiques.
• Préférentiellement, le procédé selon l'invention met en œuvre un écoulement contrôlé d'un fluide à travers le média, en minimisant le risque d'apparition de circuit préférentiel d'écoulement qui court-circuiterait une partie de l'enceinte et réduirait grandement l'intérêt de l'invention. Ainsi, une enceinte dans laquelle le média serait disposé selon une couche verticale prise entre deux tôles de guidage perforées et qui serait traversé de façon globalement horizontale par un gaz circulant depuis une des tôles de guidage vers l'autre, ne permettrait pas de parvenir au rendement du procédé selon l'invention. En effet, si le lit de média vertical qui s'écoule entre les deux tôles de guidage n'est pas parfaitement homogène en porosité, un écoulement préférentiel du fluide pourrait apparaître dans une partie locale du média et tout le reste du média ne serait plus actif pour échanger de l'enthalpie avec le fluide circulant dans l'enceinte. Dans le procédé selon l'invention, ce risque est limité en assurant une circulation du fluide caloporteur le long de la dimension la plus longue du média, soit, de façon préférée, le long de la hauteur dans le cas d'un média placé par entassement dans une enceinte verticale. Cet écoulement vertical peut notamment être assuré par l'utilisation d'une enceinte à tôle pleine remplie de média et disposant d'une entrée et d'une sortie de fluide placées en position haute et basse, ou inversement, de la zone utile du média. Comme le média se déplace de façon essentiellement verticale, les gaz qui le traversent (par ex le gaz comburant ou les fumées produites par la combustion) circulent aussi de façon essentiellement verticale et afin d'éviter les court-circuit il faut une perte de charge égale sur le chemin des gaz, donc une porosité homogène assurée par un remplissage complet d'au moins une partie de l'enceinte sur toute la section transversale à l'écoulement des gaz, dite section horizontale.

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

• The heat transfer medium, which is contained in the enclosure, is mobile and not fixed, unlike fixed linings which certainly provide a large heat exchange surface but which cannot easily be extracted from the enclosure in order to clean them .
• This mobility makes it possible to transport the energy captured by the media from one area of the enclosure to another area of the enclosure, or even to another enclosure.
• The function of the media is to capture the enthalpy available in the enclosure and then restore it. Certain solutions known to those skilled in the art have an external oven (gas, electric, etc.) 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 an enclosure in which the enthalpy provided by the heat transfer medium is valued. The heat exchanged therefore comes from a fuel and an external device, such as a gas boiler. According to the invention, the function of the media is to recover energy usually lost by the downstream part of the process, and not to consume fuel to provide external energy which can only degrade the energy balance of the process, whereas this fuel could be valued outside of the invention.

• The function of heat exchanges, in particular between the media and a gas (air, syngas or steam) is predominant.
• The media is moved essentially vertically which allows maximum and homogeneous filling of the reactor enclosure, unlike rotating horizontal drums or systems with horizontal transfer screw. This thus makes it possible to avoid the recurring problems of stratification and inhomogeneous mixing of the materials having significant differences in density. This also makes it possible to guarantee a uniform flow of fluids in the media, since it turns out that in a media arranged in a non-essentially vertical manner, the particles of media detach from the upper wall of the enclosure and thus free up 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 simple gravity, in particular at high temperatures which disturb the use of mechanical parts such as for example an Archimedes screw.
• The invention uses a medium which has spaces of calibrated porosity, unlike the sands which are found, for example, in boiler or gasification systems with a fluidized bed which require the use of a gas. fluidization injected at high pressure, source of early wear and energy consumption. Thus, according to the invention, the media weighs with all its weight on the organic particles which are mixed therein, so that a compression, grinding, crumbling effect takes place, as well as a mechanical contact promoting the rapid heat exchange.
• Preferably, the method according to the invention implements a controlled flow of a fluid through the media, minimizing the risk of the appearance of a preferential flow circuit which would short-circuit part of the enclosure and greatly reduce the interest of the invention. Thus, an enclosure in which the media would be arranged in a vertical layer taken between two perforated guide plates and which would be traversed generally horizontally by a gas flowing from one of the guide plates towards the other, would not make it possible to reach the yield of the process according to the invention. Indeed, if the vertical media bed which flows between the two guide sheets 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 no longer be active to exchange enthalpy with the fluid circulating in the enclosure. In the process according to the invention, this risk is limited by ensuring a circulation of the heat-transfer fluid 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 full-sheet enclosure filled with media and having a fluid inlet and outlet placed in the high and low position, or vice versa, of the useful area of the media. . As the media essentially moves vertical, the gases which pass through it (for example the oxidizing gas or the fumes produced by combustion) also circulate essentially vertically and in order to avoid short-circuits an equal pressure drop is required on the gas path, therefore a homogeneous porosity ensured by complete filling of at least a part of the enclosure over the entire cross section of the gas flow, known as the horizontal section.

Another advantage is that the speed of movement of the transfer medium can be adjusted in real time as a function of the required combustion power, thus making it possible to adjust, for example, the parameters of the peripheral processes making it possible to recover the energy emitted during combustion such as, for example, the recirculation of fumes which 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 fluidized bed combustion furnace. 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 oven which would ensure the temperature rise of balls or any other moving mass and making it possible to avoid the constraints linked 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, acid or oxidation attacks such as, for example, alumina beads (AL203).

Another advantage is that the mobile media does not have to be cleaned in situ, unlike traditional condensing installations by fixed lining which, by nature, cannot be easily removed from the reactor for cleaning.

Another advantage is that the fact that the ash may have a melting temperature below the ideal combustion temperature, located around 850 ° C., does not imply any accumulation of clinkers in the hearth, or indeed phenomena sintering agents such as those found in fluidized beds, thus making it possible to envisage a greater variety of inputs, and in particular agricultural substrates with high potassium levels.

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

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

Another advantage is that the absence of direct contact between the fumes and the pressurized steam tubes makes it possible to envisage an increase in the superheating temperature of the steam, advantageously above 500 ° C., in particular in the event of use of inputs 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 circuits that are less sinuous than the superheaters in conventional boilers, thereby limiting the pressure drops in the boiler. This advantage makes it possible to envisage one or more stages of steam reheating and the use of multi-body steam turbines, thereby making it possible to restore the steam to energy usable by a steam turbine. This greatly improves the electrical yields. Until now, such an arrangement was reserved for very large power installations, typically of more than 100 MW electric. The invention makes it possible to make the reheating of steam exploitable for installations with an electrical power of less than 10 MW electrical.

Another advantage is that the mass of particles in motion involves an action of crushing and dispersion of the incandescent particles, and of all particles depolymerized and embrittled by the combustion front, which allows direct contact between the fixed carbon and the oxidizer. and limits the presence of hot spots confined within glowing embers, said hot spots being the source of emission of thermal NOx by a temperature punctually higher than 1200 ° C.

Other advantages and characteristics of the invention are described below according to the possible embodiments of the invention.

• La figure 1 représente schématiquement un mode de réalisation du dispositif selon l'invention selon une première version de combustion avec une valorisation des fumées en contre-courant
• La figure 2 représente schématiquement une variante de l'invention selon une seconde version de combustion avec un séchage préalable et un écoulement des fumées en co-courant
• La figure 3 représente schématiquement une variante de l'invention selon une troisième version intégrant un séchage préalable, une combustion et une valorisation des fumées en co-courant

The descriptions refer to the following figures in the appendix:

• The figure 1 schematically represents an embodiment of the device according to the invention according to a first version of combustion with a valuation of counter-current smoke
• The figure 2 schematically represents a variant of the invention according to a second version of combustion with a preliminary drying and a flow of smoke in co-current
• The figure 3 schematically represents a variant of the invention according to a third version integrating a prior drying, a combustion and a recovery of the fumes in co-current

Description of an embodiment

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

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

The mixture is mobile, that is to say that a slow flow is put in place so as to make it pass through different action zones, the flow speed preferably being 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 assumes that the flow is vertical downwards; 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 that the speed of the particles forming the media is adapted both to the need for combustion, which must be supplied with fuel (the inputs) present in the mixture, and to the need for thermal inertia provided by the media in the combustion chamber. It is therefore necessary to have a means for regulating the formation of the mixture, so that the flow rate of the inflows and the flow rate of transfer medium are regulated independently.

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

Advantageously, the oxidizer inlets are separated so as to create separate combustion zones, but the fumes created by each combustion are grouped together and discharged in a single outlet from 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, in particular during the start-up phase, an auxiliary combustion means or burner, for example comprising a fuel supply and a starting means (spark), is put in place in the combustion zone.

Advantageously, the combustion zone is divided into three sub-zones, each being supplied by a specific air inlet, the flow 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-zones is precisely controlled. The three air inlets are called primary air, secondary air and tertiary air. This separate and controlled management allows both to maintain an increasing temperature gradient from the first zone, normally stabilized between 250 ° C and 350 ° C, preferably 300 ° C, then the second zone, normally stabilized between 450 ° C and 550 ° C, preferably at 500 ° C, up to in 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 which are harmless to human health.

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

Advantageously, a solution for regulating the oxygen level can be obtained by injecting recirculated fumes in admixture with air. More broadly, any sort of regulation of oxygen level obvious to a person skilled in the art and preserving the yield of the process or the quality of the gases produced is conceivable.

At the end of this combustion, the duration of which can be adjusted by modifying the speed of flow of the media extracted from the bottom of the combustion chamber, the burned mixture then contains only particles of transfer media, advantageously non-combustible, mineral ash and unburnt organic matter if the power and the residence time of the combustion were insufficient. This mixture comprising the burned inputs at a high temperature (typically more than 800 ° C) and represents a large energy stock, mainly contained in the hot particles of the transfer medium.

This hot mass can be used to subject the fumes to a high temperature for a minimum time, for example above 800 ° C for more than 2 seconds, so that the dioxins created during the combustion are destroyed, and thus meet the regulatory constraints of many countries aimed at guaranteeing the destruction of said dioxins.

This energy stock can also be exploited by various enthalpy recovery zones.

Thus, the hot mixture can, for example, pass through a zone of vaporization of pressurized water or superheating of steam circulating in a sealed exchanger in front of which or around which the mixture circulates. The heat exchanges are then made 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 the combustion fumes, circulates simultaneously through the mixture. The flow of this fluid around the particles of the transfer medium amplifies the phenomena of convection and improves the power of heat exchanges, and the uniformity of temperatures.

According to another example, the hot mixture can pass through an air preheating zone which will then be used as combustion air during combustion. Thus, the overall yield 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, ...) . The ashes are evacuated for storage or subsequent recovery, such as by spreading, etc. The unburnt materials can be reinjected into the process in association with the recovered media, or separately.

The technical means required to carry out the separation may include a screen with holes, a screen with magnetic effect, (advantageously of the “overband” type, a ballistic screen, an eddy current screen, a vibrating screen, a rotating drum or any other technique known to those skilled in the art depending on the nature of the elements to be separated. It is also advisable 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 cleaning which can be carried out in a bath of pure water or with the addition of cleaning agents such as surfactants, or in a bath of solvent, or under a shower of water or solvent, or under a jet of cleaning gas or steam, such as steam, or by blowing compressed air. A cleaning variant can use a vibration cleaning device, in particular in order to separate dust adhering to the media particles by circulating them on a vibrating screen, or any other vibration cleaning device, or any other high frequency device, such as ultrasound, with the possible addition of a bath of cleaning liquid.

• soit la configuration du dispositif selon l'invention est dite à "contre-courant", c'est-à-dire que si le média de transfert descend par écoulement lent, les fumées montent. Alors, la configuration ressemble à une chaudière verticale à tubes d'eau classique. Les fumées montent et traversent une zone de vaporisation d'eau pressurisée ou de surchauffe de vapeur circulant dans un échangeur étanche devant lequel circule le mélange. Les échanges de chaleur se font alors par rayonnement et convection entre les fumées et les parois de l'échangeur.
• Soit la configuration est dite à "co-courant", c'est-à-dire que les fumées descendent avec le média de transfert, ce qui permet de les faire séjourner pendant un temps contrôlé à une haute température, comme déjà décrit.

The fumes generated during combustion are obviously hot and can be valued in two ways

• or the configuration of the device according to the invention is said to be "against the current", that is to say that if the transfer medium descends by slow flow, the fumes rise. So the configuration looks like a vertical water tube boiler. 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 made by radiation and convection between the fumes and the walls of the exchanger.
• Either the configuration is called "co-current", that is to say that the fumes descend with the transfer medium, 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 stages such as enthalpy recovery, smoke condensation, etc.

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

The organic matter can have any appearance; it can be liquid such as, for example, animal manure or sewage sludge; it can be solid such as, for example, refusals to store agricultural grain or forest chips; it can also be in a pasty intermediate state or in a heterogeneous mixture. Any organic material preferably less than 30 cm in size is suitable.

The mass of the transfer medium consists of a set of individual solid particles which are used without cohesion between them. A mass of particles is thus obtained, the size and shape of which allows natural flow by the effect of gravity.

This natural flow also allows the entrainment of the inputs introduced as a mixture within said transfer medium.

The mass plays a role of media which will constantly warm and cool under the influence of the energy and fluids involved, so that exchanges of enthalpy operate in the various 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 which 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 transfer medium of large mass and / or of large mass thermal capacity which has high thermal inertia. Concretely, to guarantee a good stability of the heat 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 ³ and whose thermal capacity is greater than 300 J / (kg.K).

According to a variant of the invention, the transfer medium can contain a material which changes phase during its use so as to also take advantage of the latent heat of phase change of this material, which also makes it possible to have more high 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 -liquid of aluminum at this fixed temperature of 600 ° C, more than 370 kJ / kg of aluminum, ie 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 storage of the enthalpy which stabilizes the combustion of the incoming and the heat exchanges in the different work zones. This avoids overheating the incoming or fumes, which limits the risk of the appearance of nitrogen oxides. Thanks to the inertia of the medium, 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 stages when the transfer medium restores the energy captured at other elements, such as water or steam. 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 beads perforated over 25% of their volume guarantees a porosity (ratio of the vacuum volume to the total solid + vacuum volume) of more than 50% and therefore good circulation of the oxidant and / or the fumes throughout the enthalpy exchange zone.

In addition, in a large volume space that is the combustion hearth of an industrial boiler (several m ³ ), the oxidant flows are not uniformly distributed, which creates pockets of more intense combustion than the optimum and others less intense. Thanks to the invention and the more uniform porosity provided by the medium, the distribution of the oxidant and the combustion powers are more homogeneous.

According to a variant of the invention, it is possible to use simple spheres, the crowding 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 medium has good diffusivity, that is to say if the material has a high capacity to transfer heat. The diffusivity coefficient defined by D = lambda / ro / C (where lambda = thermal conductivity, ro = density and C = thermal mass capacity) is preferably greater than 0.2 10 ^-6 m ² / s.

In addition, the geometry and the dimension of the media elements are preferably defined in order to ensure the presence of a large developed surface swept by the fluids in presence, said surface being the seat of the heat exchange. Thus, it is advantageous for the media elements to have a large developed surface and a low material thickness in order to facilitate the exchanges of enthalpy. The preferred compactness parameter, defined as the ratio of the developed surface area 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 10 mm diameter orthogonal holes.

Finally, the exchange power is improved if the flows of the fluids through the transfer medium take place according to a hydraulic or aeraulic regime at high speed or turbulent, such a regime accentuating the performance of the heat exchanges by convection on the surface of the medium of transfer. For example, according to a preferred solution, the dimensioning of the device will take care to guarantee a fluid flow speed 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 above 900 ° C., the transfer medium must 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 even 1800 ° C depending on the purity of alumina.

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

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

In addition, if combustion generates fumes containing sulfur or chlorine and moisture, in the event of condensation of water vapor during the heat exchange and cooling of these fumes, sulfuric or hydrochloric acid can form and corrode the transfer media quickly. 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 elements in suspension capable of depositing on the transfer medium and thus leading to its fouling, with the potential consequence of gradually reducing the porosity of the latter. The circulation of fluids and the efficiency of heat exchanges would then be degraded. To solve this problem, an exemplary device advantageously comprises a means for washing the transfer medium, regular or continuous.

The choice of the material composing the transfer medium also implies taking into consideration the catalysis phenomena generated by the contact of certain smoke 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 made up of individual particles which can be moved without bonding between them and without mechanical blocking, which would create a single block that cannot be moved. It is also advantageous that the elements constituting the transfer medium have sufficient mechanical strength to support the weight of the stacking carried out, especially at the bottom. It is also preferable that the possible setting in motion of these elements does not break or abrase them too quickly, so as not to have to replace them too often, following an inevitable wear.

Thus, the heat exchanger transfer medium is composed of individual particles which can be balls or individual elements of the Raschig ring type, Perl saddle, etc. which are placed in a heap in the combustion chamber.

Advantageously, the elements are of generally spherical shape. The spherical shape facilitates the circulation of the elements in the enclosure without a blocking effect of particles between them being able to occur.

Other forms are obviously also possible, as long as they meet the specifications described above.

Thus, the stacking 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 guarantee a high power heat exchange and a thermal conductivity. allowing to accelerate heat transfers.

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

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

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

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

For certain applications, in particular certain entrants having very high nitrogen rates, sometimes beyond 1% of the dry matter, the number of feed lines oxidizer 31 32 33 may be increased so as to better control the temperature rise curve of the inputs, which makes it possible to limit the production of NOx from fuels.

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

In order to allow the device 1 to start up, an auxiliary combustion means 60 or burner is advantageously installed 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 by 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 by a fluid to evaporate or to overheat, 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 their outlet from enclosure 102, the fumes are still quite hot and this energy can be recovered by any heat recovery means suitable for the fumes.

At the bottom of the combustion zone 11, a smoke return coming from the downstream of the process, can be implemented by the inlet 101, at a regulated flow rate so as to bring a cold gas into the enclosure and thus reduce the power of the combustion in progress. This smoke recirculation means, in addition to the air supply means 30 therefore participates in the regulation of the combustion power. Finally, after combustion in zone 11, the mixture 21 initial only includes the initial media 23 and mineral ash brought in by the entrants, as well as possibly some unburnt items. This final mixture 51 thus formed is evacuated at outlet 103, and advantageously undergoes separation using a separation means 50, which makes it possible to obtain on one side the mineral ash 53 and on the other side the media transfer 52.

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

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

A means of collecting 70 and evacuating the steam produced is installed in the drying zone 13.

Then, the mixture is introduced into the combustion zone 11 which functions in the same way as according to the figure 1 , with the difference that the fumes produced are evacuated by an outlet 102 present in the lower part of the enclosure 10, and the transfer medium 23 is evacuated by an outlet 103, which is also placed in the lower part of the enclosure, hence the concept of co-current.

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

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

With reference to the figure 3 , there is shown an embodiment of the invention for ensuring combustion in a co-current mode with prior drying and vaporization.

• une alimentation en mélange 20
• une zone de séchage 13
• une zone de combustion 30
• une zone de stabilisation 14
• une zone de vaporisation 15
• une zone de préchauffage d'air 16

The layout of the different action areas is then as follows:

• a mixed feed 20
• a drying area 13
• a combustion zone 30
• a stabilization zone 14
• a spray zone 15
• an air preheating zone 16

The interest of the device according to the figure 3 resides in particular in the stabilization zone 14, which has the function of maintaining the fumes at a temperature of more than 850 ° C. for at least 2 seconds. Thus, the dioxins that may have formed during combustion are destroyed, the residual carbon monoxide is oxidized to carbon dioxide, the polycyclic aromatic hydrocarbons are degraded and the fixed carbon is oxidized.

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

Finally, the separation between zones 15 and 16 makes it possible to evacuate the fumes by the outlet 102 placed between the two areas, and to supply the area 16 with combustion air, from an inlet 41 to an outlet 42, so that the hot media can heat this air before it is introduced 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 compared to the others, in order to favor the setting in place of a flow of fluids from their entry to their exit, so that all the portions of fluid which arrive in the enclosure remain there for an equivalent duration and circulate in the media according to the same path. A more compact enclosure shape (the three dimensions having roughly the same value) would be less efficient because the smoke flow would not be as homogeneous.

Advantageously, the enclosure 10 is insulated so as to minimize thermal leaks which could affect the performance of heat exchanges.

When the transfer medium 23 has left the enclosure 10, it should be moved from the withdrawal orifice 103 towards the reintroduction orifice 26. To this end, when the movement of the transfer medium 23 is upwards low in the enclosure, vertical elevation conveying is required. This can be done by Archimedes screw, conveyor belt, bucket elevator, lift cylinder or any other mechanical means allowing vertical conveying.

According to one example, 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. depending the humidity of the entrants. For example, the combustion of dry wood with an excess of air of 20% generates more than 70 grams of water vapor per Nm ³ of smoke, which represents nearly 400 grams of water vapor per kg of fuel, most of the water vapor being produced by the combustion itself. For this purpose, a condensing media device can be implemented.

One of the advantages of such a device is to be able to recover the latent heat, an energy which 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 action of condensation, combined with the permanent slowing down of the rain formed by the condensation, makes it possible to favor the capture of all elements contained in the fumes and water-soluble, or else having hydrophilic properties. This concerns most of the dust, NH3, NOx in the form of NO2, HCL (hydrochloric acid), SO2 (sulfur dioxide).

Another advantage is that the condensates from a Rankine 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 recover in electrical energy, part of the latent heat. This last advantage makes it possible to bring a strong improvement in electrical efficiency compared to conventional technologies.

Claims (10)

1. Method for the combustion of organic matter (22), comprising a step of mixing a transfer medium (23) made up of independent solid particles, with organic matter (22) and circulating said mixture (21) in an enclosure (10) and in that said mixture undergoes combustion with the aid of an oxidant introduced into said enclosure (10), characterised in that said mixture fills the entire horizontal section of the enclosure along all or part of the height of said enclosure.
2. Combustion method according to the preceding claim, characterised in that said mixture (21) circulates vertically from top to bottom under the effect of its own weight.
3. Combustion method according to one of the preceding claims, characterised in that said mixture (21) undergoes successive combustion steps in different zones of said enclosure (10).
4. Combustion method according to one of the preceding claims, characterised in that the combustion fumes produced are entirely or partly reinjected inside said enclosure (10).
5. Combustion method according to one of the preceding claims, characterised in that said transfer medium (23) traverses, inside said enclosure (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, characterised in that it comprises an additional step of separating said transfer medium (23) from said mineral manner obtained after combustion and in that said transfer medium obtained is subsequently reused in a method according to one of the preceding claims.
7. Device (1) for the combustion of organic matter (22) according to a method according to one of claims 1 to 6, comprising a combustion enclosure (10) comprising an inlet (26) of said organic matter (22), at least one oxidant inlet (34, 35, 36) connected to an oxidant source, a residual mineral matter outlet (103) and a combustion fume outlet (102), in said device, independent solid particles (23) forming a piled movable transfer medium are placed in said enclosure (10), said transfer medium fills the entire horizontal section of the enclosure along all or part of the height of said enclosure, a transfer medium inlet (26) is placed at one end of said enclosure (10) and a transfer medium outlet (103) is placed at the other end of said enclosure (10) and a transfer medium transfer means (80) is inserted between the transfer medium outlet (103) and the transfer medium inlet (26) circulating the transfer medium (23) in a loop.
8. Device (1) according to the preceding claim, characterised in that said combustion enclosure (10), comprises several oxidant inlets (34, 35, 36) staged in relation to one another, each connected to a common or separate oxidant source.
9. Device (1) according to one of claims 7 to 8, characterised in that a means for regulating the oxidant flow rate is associated with at least one of the oxidant inlets (34, 35, 36).
10. Device (1) according to one of claims 7 to 9, characterised in that it comprises at least one impervious heat exchanger placed inside said enclosure, in contact with said transfer medium (23), and connected to a fluid (161) and outlet (152), increasing the enthalpy of said fluid.

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