FR3144645A1 - COMBUSTION SYSTEM CAPABLE OF OPERATING WITH RECYCLING OF COMBUSTION FUMES - Google Patents

Abstract

The combustion system comprises a combustion device (1) allowing the combustion of a fuel by means of at least one oxidizing gas (GC) and comprising an outlet (1a) through which it rejects combustion fumes (FC), an oxidant gas (GC) supply unit (3) comprising a mixer (31) and a source (30) of gaseous dioxygen which supplies a gas rich in dioxygen and which is connected to a first inlet of the mixer (31), a main evacuation circuit (5) connected to the outlet (1a) of the combustion device (1) and opening into the open air, recycling means (4) which comprise a recycling loop (40) between the circuit main exhaust (5) and a second inlet of the mixer (31), at least one recycling fan or compressor (VR) mounted on the recycling loop (40), a bypass (6) which is connected to the recycling loop recycling (40) downstream of the recycling fan or compressor (VR) and which opens into the open air, and a control unit (7) adapted to control at least the recycling fan or compressor (VR). Fig.1

Description

COMBUSTION SYSTEM CAPABLE OF OPERATING WITH RECYCLING OF COMBUSTION FUMES

The present invention relates to the field of combustion with recycling of at least part of the combustion fumes.

Prior art

A so-called " classic " combustion consists of mixing air (oxidant) with a fuel in a combustion installation (furnace, boiler, etc.) under high temperature conditions to create oxidation. The reaction is exothermic and is naturally maintained. The air contains 21% dioxygen (O ₂ ) and the volume of air used is controlled so that the quantity of dioxygen is sufficient for combustion.

In conventional combustion, combustion fumes contain water vapor ( _H2O ) and combustion products in the gas phase, mainly nitrogen ( _N2 ) in the gas phase, and carbon dioxide ( _CO2 ) in the gas phase.

In this text, the term "combustion gas" refers to the gaseous phase combustion products which are released after combustion.

If we want to capture CO₂of these fumes, it is easy to eliminate the water vapor by condensing these combustion fumes and collecting the water in liquid form. On the other hand, the main difficulty lies in the separation of nitrogen and carbon dioxide. In addition, in conventional combustion, and depending on the type of fuel used, the combustion gas can also contain other polluting combustion products in the gaseous phase, in more or less significant quantities, such as for example SOx (sulfur oxides), NOx (nitrogen oxides), HCl (hydrogen chloride), HF (hydrogen fluoride), etc. Consequently, if we want to capture the CO₂From these fumes, it is also necessary to separate the CO₂ of these other pollutants.

Several solutions have been considered to capture _CO2 in fumes from conventional combustion, but their cost remains very high.

To reduce the emission of pollutants in combustion fumes, it is known to replace the above-mentioned conventional combustion with a combustion called "oxycombustion", in which the air (oxidant) is replaced by dioxygen in stoichiometric proportions, the number of oxygen atoms being equal to that necessary to oxidize all the atoms of the fuel.

The production of dioxygen to implement oxycombustion can, for example, be obtained in a known manner by cryogenics or by electrolysis of water.

In the case of oxycombustion of methane (CH ₄ ), for example, combustion fumes are produced consisting of 1/3 CO ₂ in the gas phase and 2/3 water vapor by volume. In the case of other fuels, there will also be pollutants from combustion, such as HCl, SOx, etc. If the fuel is not nitrogenous, advantageously the fumes will naturally not contain NOx.

The equation for the chemical reaction of oxycombustion of methane (CH ₄ ) is:

CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O -891 kJ/mole of CH ₄

This means that each mole of _CH4 will produce 891 kJ of power outwards.

For other fuels, the reactions are similar, with the appearance of other compounds if the fuel contains atoms other than carbon and hydrogen.

In the case of oxycombustion of methane, for example, it is easier to capture _CO2 . All that is needed is to condense the water in the combustion fumes using a cooling or drying process to obtain _CO2 in a gaseous state.

It is therefore known to date that a condenser can be used to condense oxycombustion fumes in order to facilitate the capture of _CO2 .

A major difficulty with oxycombustion, however, lies in the difficulty of controlling combustion, because unlike conventional combustion, the oxycombustion temperature can quickly and uncontrollably become very high in the combustion chamber, so that conventional combustion installations cannot withstand it.

To overcome this difficulty, installations have already been proposed which make it possible to improve oxycombustion by recycling at least part of the _CO2 -rich combustion fumes in the gas phase, preferably by condensing them, so as to mix them with the dioxygen and obtain an oxidizing gas ( _O2 - _CO2 ) which advantageously makes it possible to lower the combustion temperature.

This improvement allows for oxycombustion based on dioxygen with recycling of combustion fumes that is more easily controlled, compared to oxycombustion using only dioxygen as the oxidant, while reducing the emission of pollutants compared to conventional combustion and facilitating the capture of _CO2 where appropriate.

These installations are designed to operate only in oxycombustion with recycling of combustion fumes, which leads to several drawbacks.

The start-up and shutdown procedures of these installations are critical and risky operating phases and can detrimentally lead to oxycombustion temperatures, with recycling of combustion fumes, which are uncontrolled and excessively high in the combustion chamber.

During oxycombustion, with recycling of combustion fumes, a drop in the concentration of dioxygen in the combustion gas that is too significant can lead to an untimely shutdown of combustion in the combustion chamber of the installation, which can have serious consequences, for example in an industrial production line using the thermal energy produced.

Presentation of the invention

The main objective of the invention is to propose a combustion system which can operate with recycling of at least part of the combustion fumes, but which makes it possible to overcome all or part of the aforementioned drawbacks inherent in oxycombustion installations of the prior art which implement such recycling of combustion fumes.

The invention thus relates to a combustion system comprising a combustion device enabling the combustion of a fuel by means of at least one oxidizing gas and comprising an outlet through which it discharges combustion fumes, a unit for supplying oxidizing gas which is connected to the combustion device and enables the combustion device to be supplied with oxidizing gas, said unit for supplying oxidizing gas comprising a mixer and a source of gaseous dioxygen which supplies a gas rich in dioxygen and which is connected to a first inlet of the mixer, a main evacuation circuit connected to the outlet of the combustion device and opening into the open air, recycling means which comprise a recycling loop between the main evacuation circuit and a second inlet of the mixer, at least one recycling fan or compressor mounted on the recycling loop and adapted to circulate a gaseous fluid in the recycling loop towards the second inlet of the mixer from a connection of the recycling loop with the main evacuation circuit, a bypass which is connected to the recycling loop downstream of the recycling fan or compressor (i.e. between the recycling fan or compressor and the second mixer inlet) and which opens into the open air, and a control unit suitable for controlling at least the recycling fan or compressor.

The term " oxygen-rich gas " means that the gas contains at least 40% (volume percentage) oxygen.

More particularly, the control unit is adapted to control the recycling fan or compressor so as to be able to configure the combustion system in an operating mode chosen from at least two different operating modes (M1; M2) and to be able to switch from one operating mode to the other: a first operating mode (M1) in which the recycling fan or compressor is stopped and the mixer is not supplied with oxygen-rich gas from the gaseous oxygen source and is supplied by air entering the bypass, and a second operating mode (M2), in which the recycling fan or compressor is operating, and the mixer is supplied at least with oxygen-rich gas supplied by the gaseous oxygen source and with at least a portion of the combustion fumes discharged by the combustion device.

In said first operating mode (M1), the mixer is supplied at least with air drawn in via the bypass and all of the combustion fumes emitted by the combustion device are discharged into the open air, possibly after having been treated, without being recycled.

As a result, the combustion gas contains at least air and does not contain any oxygen from the gaseous oxygen source. The combustion in the combustion device is thus a conventional combustion.

In this first mode of operation and in a particular variant embodiment, the oxidizing gas preferably consists solely of air.

In said second operating mode (M2), the combustion gas contains at least oxygen-rich gas from the gaseous oxygen source and at least part of the combustion fumes which has been recycled and which has preferably been treated (before recycling or in the recycling loop), in particular by preferably being at least dehumidified.

This means that the combustion in the combustion device is of the oxycombustion type with recycling of at least part of the combustion fumes.

More particularly, in said second operating mode (M2), in a particular operating phase, subsequently designated " degraded oxycombustion ", the oxidizing gas may comprise air, which has been drawn into the ambient air via the bypass. In said second operating mode and in another particular operating phase subsequently designated " enhanced oxycombustion ", the oxidizing gas does not contain air drawn into the ambient air via the bypass .

The combustion device may be a standard combustion device on the market or a particular combustion device that has been specifically developed. This combustion device may have air inlets at different injection points depending on the combustion requirement. Advantageously, the invention can more particularly be implemented without it being necessary to make any modification to this combustion device.

• Le système de combustion comporte en outre au moins un capteur qui est adapté pour au moins mesurer le débit ou la pression de fluide gazeux sortant dans la partie aval du circuit d’évacuation principal située en aval du raccordement de la boucle de recyclage avec le circuit principal d’évacuation et qui délivre un signal de mesure de pression ou débit traité par l’unité de commande.
• Le système de combustion comporte en outre au moins un capteur 60 qui est adapté pour au moins mesurer le débit ou la pression de fluide gazeux sortant dans la dérivation 6, et qui délivre un signal de mesure de pression ou débit traité par l’unité de commande.
• L’unité de commande est adaptée pour commander le ventilateur ou compresseur de recyclage en fonction au moins du débit ou de la pression mesurée par ledit capteur pendant au moins un mode de fonctionnement avec recyclage d’au moins une partie des fumées de combustion.
• L’unité de commande est adaptée pour commander le dispositif (32) de contrôle du débit du gaz riche en dioxygène et le ventilateur ou compresseur de recyclage, de manière à pouvoir passer d’un mode de fonctionnement (M1 ou M2) à l’autre (M2 ou M1) sans arrêter la combustion dans le dispositif de combustion.
• La source de dioxygène gazeux est raccordée à ladite première entrée du mélangeur via un dispositif de contrôle du débit du gaz riche en dioxygène qui est commandé par l’unité de commande, et de préférence qui comporte une vanne de contrôle de débit qui est commandée par l’unité de commande.
• La vanne de contrôle de débit est une vanne à ouverture et fermeture progressives.
• Le système de combustion comporte au moins un capteur adapté pour mesurer la concentration en dioxygène dans le gaz comburant et l’unité de commande est adaptée pour commander le dispositif de contrôle du débit du gaz riche en dioxygène en fonction de la concentration en dioxygène mesurée par ce capteur (au moins pendant un mode de fonctionnement (M2) avec recyclage d’au moins une partie des fumées de combustion.
• Le dispositif de combustion comporte un ventilateur ou compresseur adapté pour alimenter le dispositif de combustion en gaz comburant avec un débit (ϕ _GC) donné, qui est de préférence variable.
• Le débit d’alimentation du dispositif de combustion en combustible est variable et le dispositif de combustion comporte un ventilateur ou compresseur adapté pour alimenter le dispositif de combustion en gaz comburant avec un débit (ϕ _GC) qui varie en fonction du débit d’alimentation du dispositif de combustion en combustible.
• Le système de combustion comporte un dispositif de traitement des fumées de combustion qui est monté sur le circuit d’évacuation principal.
• Le système de combustion comporte un dispositif de traitement des fumées de combustion recyclées qui est monté sur la boucle de recyclage de préférence entre le ventilateur ou compresseur de recyclage et le raccordement de la boucle de recyclage avec le circuit principal d’évacuation.
• Le dispositif de traitement est adapté pour déshumidifier les fumées de combustion.
• Le dispositif de traitement comporte un condenseur.
• Le condenseur comporte au moins un échangeur comportant un liquide refroidissant.
• L’échangeur comporte un bain de liquide refroidissant, et des moyens d’injection permettant de faire passer le fluide gazeux (à déshumidifier à travers ce bain de liquide refroidissant (L), et de préférence les moyens d’injection permettent d’injecter le fluide gazeux à déshumidifier au-dessous de la surface de ce bain de liquide de refroidissant.
• Le dispositif de traitement est adapté pour dépolluer les fumées de combustion et plus particulièrement pour capter un ou plusieurs polluants choisis parmi la liste suivante : particules fines, SOx, NOx, acides, métaux lourds, ammoniac, COV.
• Le système de combustion comporte au moins un capteur adapté pour mesurer la concentration en dioxygène dans le gaz comburant et l’unité de commande est adaptée pour commander le dispositif de contrôle du débit du gaz riche en dioxygène et le ventilateur ou compresseur de recyclage, en fonction de la concentration mesurée en dioxygène dans le gaz comburant, et de préférence de manière à passer d’un mode de fonctionnement (M2) avec recyclage d’au moins une partie des fumées de combustion à un mode de fonctionnent (M1) sans recyclage des fumées de combustion.
• Le système de combustion comporte un dispositif de captage du dioxyde de carbone (CO₂), qui est raccordé à la dérivation et qui est adapté pour capter le dioxyde de carbone (CO₂) dans au moins une partie des fumées de combustion recyclées sortantes évacuées via ladite dérivation et/ou comportant un dispositif de captage du dioxyde de carbone (CO₂), qui est raccordé à la partie aval du circuit d’évacuation principal située en aval du raccordement de la boucle de recyclage avec le circuit principal d’évacuation et qui est adapté pour capter le dioxyde de carbone (CO₂) dans au moins une partie des fumées de combustion non recyclées sortantes évacuées via ladite partie aval du circuit d’évacuation principal.
• Le gaz riche en dioxygène fourni par la source de dioxygène gazeux comporte au moins 50% de dioxygène, de préférence au moins 80% de dioxygène, et plus préférentiellement encore au moins 90% de dioxygène.
• Le gaz riche en dioxygène fourni par la source de dioxygène gazeux est du dioxygène pur ou quasi pur.
• Le système de combustion comporte un dispositif d’injection de dioxyde de carbone raccordé à une entrée du mélangeur et adaptée pour d’injecter du dioxyde de carbone (CO₂) gazeux dans le mélangeur pendant une phase particulière (« oxycombustion dégradée ») du mode de fonctionnement (M2) avec recyclage des fumées de combustion.

More particularly, the combustion system of the invention may comprise the following additional and optional features, taken individually, or in combination with each other:

• The combustion system further comprises at least one sensor which is adapted to at least measure the flow rate or pressure of gaseous fluid exiting in the downstream part of the main evacuation circuit located downstream of the connection of the recycling loop with the main evacuation circuit and which delivers a pressure or flow measurement signal processed by the control unit.
• The combustion system further comprises at least one sensor 60 which is adapted to at least measure the flow rate or pressure of gaseous fluid exiting in the bypass 6, and which delivers a pressure or flow measurement signal processed by the control unit.
• The control unit is adapted to control the recycling fan or compressor as a function of at least the flow rate or pressure measured by said sensor during at least one operating mode with recycling of at least part of the combustion fumes.
• The control unit is adapted to control the device (32) for controlling the flow rate of the gas rich in dioxygen and the recycling fan or compressor, so as to be able to switch from one operating mode (M1 or M2) to the other (M2 or M1) without stopping combustion in the combustion device.
• The source of gaseous dioxygen is connected to said first inlet of the mixer via a device for controlling the flow rate of the dioxygen-rich gas which is controlled by the control unit, and preferably which comprises a flow control valve which is controlled by the control unit.
• The flow control valve is a valve with progressive opening and closing.
• The combustion system comprises at least one sensor adapted to measure the oxygen concentration in the combustion gas and the control unit is adapted to control the device for controlling the flow rate of the oxygen-rich gas as a function of the oxygen concentration measured by this sensor (at least during an operating mode (M2) with recycling of at least part of the combustion fumes.
• The combustion device comprises a fan or compressor adapted to supply the combustion device with combustion gas at a flow rate (ϕ _GC) given, which is preferably variable.
• The flow rate of fuel supply to the combustion device is variable and the combustion device comprises a fan or compressor adapted to supply the combustion device with combustion gas at a flow rate (ϕ _GC) which varies depending on the fuel feed rate of the combustion device.
• The combustion system includes a combustion fumes treatment device which is mounted on the main exhaust circuit.
• The combustion system includes a device for treating recycled combustion fumes which is mounted on the recycling loop preferably between the recycling fan or compressor and the connection of the recycling loop with the main exhaust circuit.
• The treatment device is suitable for dehumidifying combustion fumes.
• The treatment device includes a condenser.
• The condenser comprises at least one exchanger comprising a cooling liquid.
• The exchanger comprises a cooling liquid bath, and injection means for passing the gaseous fluid (to be dehumidified) through this cooling liquid bath (L), and preferably the injection means make it possible to inject the gaseous fluid to be dehumidified below the surface of this cooling liquid bath.
• The treatment device is suitable for depolluting combustion fumes and more particularly for capturing one or more pollutants chosen from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs.
• The combustion system comprises at least one sensor adapted to measure the concentration of dioxygen in the combustion gas and the control unit is adapted to control the device for controlling the flow rate of the gas rich in dioxygen and the recycling fan or compressor, as a function of the measured concentration of dioxygen in the combustion gas, and preferably so as to switch from an operating mode (M2) with recycling of at least part of the combustion fumes to an operating mode (M1) without recycling of the combustion fumes.
• The combustion system comprises a carbon dioxide (CO ₂ ) capture device, which is connected to the bypass and which is adapted to capture carbon dioxide (CO ₂ ) in at least a portion of the outgoing recycled combustion fumes discharged via said bypass and/or comprising a carbon dioxide (CO ₂ ) capture device, which is connected to the downstream part of the main exhaust circuit located downstream of the connection of the recycling loop with the main exhaust circuit and which is adapted to capture carbon dioxide (CO ₂ ) in at least a portion of the outgoing non-recycled combustion fumes discharged via said downstream part of the main exhaust circuit.
• The oxygen-rich gas supplied by the gaseous oxygen source comprises at least 50% oxygen, preferably at least 80% oxygen, and more preferably still at least 90% oxygen.
• The oxygen-rich gas supplied by the gaseous oxygen source is pure or near-pure oxygen.
• The combustion system comprises a carbon dioxide injection device connected to an inlet of the mixer and adapted to inject gaseous carbon dioxide ( _CO2 ) into the mixer during a particular phase (“degraded oxycombustion”) of the operating mode (M2) with recycling of combustion fumes.

Brief description of the figures

• La est une représentation schématique d’une première variante particulière de réalisation d’un système de combustion de l’invention.
• La représente le système de combustion de la dans le premier en mode de fonctionnement M1 (« combustion classique ») ;
• La représente le système de combustion de la dans le deuxième en mode de fonctionnement M2 (« oxycombustion avec recyclage ») et dans une phase de fonctionnement particulière (« oxycombustion dégradée »).
• La représente le système de combustion de la dans le deuxième en mode de fonctionnement M2 (« oxycombustion avec recyclage ») et dans une autre phase de fonctionnement particulière (« oxycombustion améliorée »).
• La est une représentation schématique d’une deuxième variante particulière de réalisation d’un système de combustion de l’invention.
• La représente le système de combustion de la dans le premier en mode de fonctionnement M1 (« combustion classique ») ;
• La représente le système de combustion de la dans le deuxième en mode de fonctionnement M2 (« oxycombustion avec recyclage ») et dans une phase de fonctionnement particulière (« oxycombustion dégradée »).
• La représente le système de combustion de la dans le deuxième en mode de fonctionnement M2 (« oxycombustion avec recyclage ») et dans une autre phase de fonctionnement particulière (« oxycombustion améliorée »).
• Les figures 9 à 13 sont des représentations schématiques de cinq autres variantes particulières de réalisation d’un système de combustion de l’invention.
• La représente un exemple particulier de condenseur pouvant être mis en œuvre dans un système de combustion de l’invention.

The characteristics and advantages of the invention will appear more clearly on reading the detailed description below of several particular variant embodiments of the invention, which particular variant embodiments are described as non-limiting and non-exhaustive examples of the invention, and with reference to the appended drawings in which:

• There is a schematic representation of a first particular variant embodiment of a combustion system of the invention.
• There represents the combustion system of the in the first in operating mode M1 (“classic combustion”);
• There represents the combustion system of the in the second in operating mode M2 (“oxycombustion with recycling”) and in a particular operating phase (“degraded oxycombustion”).
• There represents the combustion system of the in the second in operating mode M2 (“oxycombustion with recycling”) and in another particular operating phase (“enhanced oxycombustion”).
• There is a schematic representation of a second particular variant embodiment of a combustion system of the invention.
• There represents the combustion system of the in the first in operating mode M1 (“classic combustion”);
• There represents the combustion system of the in the second in operating mode M2 (“oxycombustion with recycling”) and in a particular operating phase (“degraded oxycombustion”).
• There represents the combustion system of the in the second in operating mode M2 (“oxycombustion with recycling”) and in another particular operating phase (“enhanced oxycombustion”).
• Figures 9 to 13 are schematic representations of five other particular embodiments of a combustion system of the invention.
• There represents a particular example of a condenser that can be implemented in a combustion system of the invention.

Detailed description Combustion system of Figure 1

• un dispositif de combustion 1, qui est alimenté avec un gaz comburant GC provenant d’une unité 3 d’alimentation en gaz comburant et avec un combustible C provenant d’une source de combustible 2 et qui, en fonctionnement, rejette par une sortie 1a des fumées de combustion FC;
• un circuit principal 5 d’évacuation d’au moins une partie des fumées de combustion émises par le dispositif de combustion 1, lequel circuit principal d’évacuation 5 est raccordé à une extrémité à la sortie 1a du dispositif de combustion 1 et débouche à son extrémité opposée à l’air libre (à la pression atmosphérique) dans l’air ambiant ; ce circuit principal d’évacuation 5 comporte plus particulièrement une cheminée d’évacuation 50 débouchant à l’air libre ;

• des moyens de recyclage 4, qui comportent une boucle de recyclage 40 raccordant le circuit principal d’évacuation 5 à une entrée de l’unité 3 d’alimentation en gaz comburant GC et un ventilateur de recyclage VR, qui est monté sur la boucle de recyclage 40 ; le ventilateur de recyclage VR permet en fonctionnement de faire circuler de manière forcée un fluide gazeux dans la boucle de recyclage 40 depuis le raccordement 40a de la boucle de recyclage 40 avec le circuit principal d’évacuation 5 et en direction de l’unité 3 d’alimentation en gaz comburant GC ;
• une dérivation 6, qui est raccordée (raccordement 40b) à la boucle de recyclage 40 en aval du ventilateur de recyclage VR et qui débouche à l’air libre à la pression atmosphérique dans l’air ambiant ;
• au moins un capteur 51 adapté pour au moins mesurer la pression ou le débit du fluide gazeux sortant qui est évacué à l’air libre via la partie aval 5b du circuit principal d’évacuation 5 située en aval du raccordement 40a de la boucle de recyclage 40 avec le circuit principal d’évacuation 5.

We have schematically represented on the a first variant embodiment of a combustion system of the invention comprising:

• a combustion device 1, which is supplied with an oxidizing gas GC from an oxidizing gas supply unit 3 and with a fuel C from a fuel source 2 and which, in operation, discharges combustion fumes FC through an outlet 1a;
• a main circuit 5 for evacuating at least part of the combustion fumes emitted by the combustion device 1, which main evacuation circuit 5 is connected at one end to the outlet 1a of the combustion device 1 and opens at its opposite end to the open air (at atmospheric pressure) in the ambient air; this main evacuation circuit 5 more particularly comprises an evacuation chimney 50 opening into the open air;

• recycling means 4, which comprise a recycling loop 40 connecting the main exhaust circuit 5 to an inlet of the combustion gas supply unit 3 GC and a recycling fan VR, which is mounted on the recycling loop 40; the recycling fan VR allows in operation to forcibly circulate a gaseous fluid in the recycling loop 40 from the connection 40a of the recycling loop 40 with the main exhaust circuit 5 and in the direction of the combustion gas supply unit 3 GC;
• a branch 6, which is connected (connection 40b) to the recycling loop 40 downstream of the recycling fan VR and which opens into the open air at atmospheric pressure in the ambient air;
• at least one sensor 51 adapted to at least measure the pressure or the flow rate of the outgoing gaseous fluid which is discharged into the open air via the downstream part 5b of the main discharge circuit 5 located downstream of the connection 40a of the recycling loop 40 with the main discharge circuit 5.

The sensor 51 can for example be mounted in a pipe between the connection 40a of the recycling loop 40 with the main evacuation circuit 5 and the evacuation chimney 50, as illustrated in the , or can be mounted directly in the exhaust chimney 50.

In this variant of the embodiment of the , the control unit 7 is adapted to control at least the recycling fan VR as a function of at least the flow rate or the pressure measured by said sensor 51 (detection signal S_{5 1} delivered by the sensor), as will be detailed later.

The control unit 7 can be implemented in various forms, and can for example be produced by means of a programmable electronic control unit, for example of the programmable automaton type or a programmable electronic circuit comprising a microprocessor, a microcontroller or programmable logic circuits of the FPGA type, or can also be produced by means of a specific integrated electronic circuit of the ASIC type.

The bypass 6 may consist of a simple pipe connected at one end to the recycling loop 40 and opening directly into the open air (at atmospheric pressure) at its other end. In its simplest version, this second bypass 6 may also be a simple opening allowing the recycling loop 40 to communicate with the ambient air.

Alternatively, the VR recycling fan can be replaced with an air compressor.

The combustion device 1 generally makes it possible to carry out combustion of the fuel C by means of said oxidizing gas GC, the thermal energy resulting from this combustion being able indifferently according to the invention to be used in any type of application requiring a thermal input, and for example and in a non-limiting manner to heat a fluid in a heating installation or to supply an industrial production line with energy, in particular thermal, mechanical or electrical. This combustion device 1 can indifferently according to the invention comprise a conventional boiler, an oven, or a combustion chamber in which a combustion method is implemented.

The combustion device 1 usually comprises a fan (or compressor) 10 which makes it possible to draw or push the combustion gas GC into the combustion installation 1, with automatic adjustment or regulation of the flow rate ϕ _GC of combustion gas GC entering the combustion device 1 to adapt to the flow rate of the fuel C and satisfy the thermal energy requirements.

The combustion device 1 may be a common combustion device on the market or a particular combustion device that has been specifically developed.

The combustion reaction of fuel C using the oxidizing gas GC produces combustion fumes FC whose composition depends on the fuel C and the oxidizing gas GC.

In the context of the invention, fuel C can be very different from one application to another and can, depending on the case, be in solid, liquid or gaseous form.

The GC combustion gas supply unit 3 comprises a source 30 of gaseous dioxygen (O ₂ ) which supplies an inlet of a mixer 31, via a flow control device 32 controlled by the control unit 7. The other inlet of the mixer 31 is connected to the recycling loop 40.

The source 30 of gaseous dioxygen makes it possible to supply a gas rich in dioxygen, that is to say a gas containing at least 40% (volume percentage) of dioxygen.

Preferably, as will be discussed later, the dioxygen-rich gas may advantageously, but not necessarily, consist of pure or near-pure dioxygen (volume concentration greater than 90%).

The source 30 of gaseous dioxygen may be of any known type and may for example comprise a unit for producing gaseous dioxygen by cryogenics and/or a unit for producing gaseous dioxygen by water electrolysis. The source 30 of gaseous dioxygen may also be a unit for producing a gas rich in dioxygen containing at least 40% of dioxygen obtained by suitable filtration of air using zeolites or equivalent. The source 30 of gaseous dioxygen may also not be designed to produce the gas rich in dioxygen in situ, but may simply comprise a means for storing the gas rich in dioxygen which will have been previously produced on another site.

In a variant, the flow control device 32 can simply make it possible to stop or allow the oxygen-rich gas coming from the source 30 to pass. Preferably, however, this flow control device 32 makes it possible to stop the oxygen-rich gas coming from the source 30 or to allow the oxygen-rich gas coming from the source 30 to pass by allowing adjustment, by the control unit 7, of the gas flow rate at the inlet of the mixer 31.

In the particular embodiment variant of the , the source 30 of gaseous dioxygen supplies for example the mixer 31 with a constant pressure and the flow control device 32 at the inlet of the mixer 31 comprises a valve V1, preferably a solenoid valve, which is controlled by the control unit 7.

Preferably, this valve V1 is a valve with progressive opening and closing.

In another variant, the flow control device 32 at the inlet of the mixer 31 may also include a system for controlling the pressure of the gas at the outlet of the source 30, possibly associated with a valve which may be an on/off valve or a valve with progressive opening and closing, the pressure control system and said valve being controlled by the control unit 7.

Preferably, the GC combustion gas supply unit 3 also comprises at least one sensor 33, which measures the oxygen concentration in the GC combustion gas entering the combustion device 1 and which delivers to the control unit 7 a signal S for measuring this concentration.

Preferably, in the variant of the , the combustion system comprises a device 8 for treating combustion fumes FC, which is mounted on the upstream part 5a of the main evacuation circuit 5 followed upstream of the connection 40a of the recycling loop 40 with the main evacuation circuit 5

In this particular embodiment, this device 8 for treating combustion fumes FC preferably comprises a condenser, which is adapted to condense the combustion fumes FC emitted by the combustion installation 1 by cooling them. More particularly, the condenser of the treatment device 8 can generally comprise any type of exchanger allowing, by any means, to cool the combustion fumes FC so as to condense at least part of the water vapor contained in the combustion fumes F. At the outlet of the treatment device 8, dehumidified combustion fumes FC' (rich in CO ₂ ) are obtained in this case, mainly containing the combustion products in the gas phase produced by the combustion in the combustion device 1, and having an absolute humidity lower than that of the combustion fumes FC at the inlet of the treatment device 8.

This combustion fumes treatment device 8 can also be adapted to depollute the combustion fumes and preferably to capture one or more pollutants chosen from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs. In this case, dehumidified and depolluted combustion fumes FC' (rich in _CO2 ) are obtained at the outlet of the treatment device 8.

In an alternative embodiment, the installation may be devoid of a treatment device 8 or the treatment device 8 may be devoid of means for dehumidifying the combustion fumes and comprise only means for decontaminating the combustion fumes. In this case, the installation preferably comprises a treatment device, which is mounted on the recycling loop 40 downstream or preferably upstream of the recycling fan or compressor VR, and which is adapted to treat the combustion fumes recycled in the recycling loop 40 in order to at least dehumidify them.

The control unit 7 makes it possible to automatically control the recycling fan or compressor VR and the combustion gas supply unit 3 GC, and more particularly in this variant the flow control device 32, by means of the control signals C2 and C1 respectively, generally so as to control the composition of the combustion gas GC.

More particularly, the control unit 7 makes it possible to automatically control the recycling fan or compressor VR and the combustion gas supply unit 3 GC so as to advantageously make it possible to operate the installation in an operating mode chosen from at least two different operating modes (M1 and M2) detailed below and to allow the transition from one operating mode (M1 or M2) to the other (M2 or M1).

Operating modes of the combustion system

The combustion system of the can be configured by the control unit 7 to operate in at least two different main operating modes:

M1 ( ): an operating mode called “classic combustion” in which the recycling fan or compressor VR is stopped and the valve V1 of the flow control device 32 is closed (F).

M2 (Figures 3 and 4): an operating mode called “oxycombustion with recycling” in which the recycling fan or compressor VR operates and is controlled by the control unit 7 and the valve V1 of the flow control device 32 is open (O).

The transition from one operating mode (M1 or M2) to the other (M2 or M1) can be controlled by the control unit 7 simply by appropriately controlling the recycling fan or compressor VR, and the flow control device 32 (more particularly the valve V1). The transition from one operating mode (M1 or M2) to the other (M2 or M1) can advantageously be carried out without stopping the combustion, and in particular without altering the combustion in the combustion device 1, and without stopping the combustion device 1.

Mode of operation M1- “classical combustion” -

In this operating mode, the valve V1 supplying oxygen from source 30 has been closed (F) by the control unit 7 and the recycling fan or compressor VR is stopped.

The fan 10 (or compressor) of the combustion device 1 operates by imposing on the inlet of the combustion device 1 a flow rate ϕ _GC of oxidizing gas GC, which can vary.

The mixer 31 is not supplied with oxygen from the source 30. The mixer 31 is supplied only with incoming air which is sucked in via the bypass 6 and which is conveyed to the inlet of the mixer 31. A conventional combustion is thus carried out in the combustion installation 1 by means of this incoming air used as an oxidizing gas.

The combustion fumes FC, after having been treated (FC’) by passing through the treatment device 8, do not recirculate to the mixer 31 but are evacuated into the open air into the atmosphere by being pushed by the fan (or compressor) 10 in the downstream part 5b of the main evacuation circuit 5.

In an alternative embodiment and optionally, the recycling loop 40 can also be equipped with smoke stop dampers, which are controlled by the control unit 7 in operating mode M1 and which are opened by the control unit 7 in operating mode M2 (recycling of at least part of the combustion fumes). These dampers can also be operated manually.

Operating mode M 2 – " oxycombustion with recycling » – Figure s 3 and 4

In this operating mode, the fan 10 (or compressor) of the combustion installation operates by imposing on the inlet of the installation 1 a given flow rate ( ϕ _GC ) of combustion gas GC which can vary.

The control unit 7 automatically controls the combustion gas supply unit 3 GC, and in particular the flow control device 32, as a function of the oxygen concentration measured in the combustion gas GC by means of the sensor 33 (signal S), so as to produce a gas having an appropriate oxygen level (for example set by a parameterizable preference setpoint) which is required or requested by the combustion.

The control unit 7 also automatically controls the start-up of the recycling fan or compressor VR and automatically controls this recycling fan or compressor VR, depending on the pressure or flow rate measured by the sensor 51.

In particular, the control unit 7 automatically controls the recycling fan or compressor VR, until the flow rate or pressure measured by this sensor 51 reaches at least one predefined and preferably configurable operating setpoint, and automatically regulates the flow rate of this recycling fan or compressor VR so as to maintain said pressure or said flow rate measured by the sensor 51 at this operating setpoint or in the vicinity of this operating setpoint.

This operating instruction is set such that the flow rate of the recycling fan or compressor VR is lower than the flow rate of the combustion fumes FC at the outlet of the treatment device 8 or, in the absence of a treatment device 8, at the outlet of the combustion device 1, so as to recycle at least part FC to the mixer 31.₂combustion fumes, the other part FC₁being discharged into the open air into the atmosphere via the downstream part 5b of the main evacuation circuit 5.

The lower the pressure or flow rate measured by the sensor 51, the greater the flow rate of combustion fumes FC ₂ recycled towards the mixer 31.

In the operating mode M2 of this variant embodiment, if the flow rate of the recycling fan or compressor VR becomes, for example accidentally, greater than the flow rate of the combustion fumes (FC or FC') upstream of the connection 40a of the recycling loop, in this case automatically and safely, all of the combustion fumes are recycled (FC ₂ = FC') to the mixer 31, and no combustion fumes FC ₁ are discharged into the atmosphere, but on the contrary incoming air, coming from the ambient air, is automatically sucked in addition into the downstream part 5b of the main exhaust circuit 5 and is conveyed into the recycling loop 40 to the inlet of the mixer 31. The combustion in the combustion device 1 advantageously does not undergo any disturbance because the pressure in the downstream part 5b (opening into the open air) of the main exhaust circuit 5 is not modified.

• une première phase de fonctionnement dite « oxycombustion dégradée », qui est illustrée sur la .
• une deuxième phase de fonctionnement dite « oxycombustion améliorée » illustrée sur la

This M2 operating mode in practice comprises two operating phases:

• a first phase of operation called “degraded oxycombustion”, which is illustrated in the .
• a second phase of operation called “enhanced oxycombustion” illustrated in the

P operating basis of the - “degraded oxycombustion”

As long as the recycling flow rate of the recycling fan or compressor VR is sufficiently low, a portion FC ₁ of the treated combustion fumes FC' (after passing through the treatment device 8) is discharged into the ambient air via the downstream portion 5b of the main evacuation circuit 5 and another portion FC ₂ of the treated combustion fumes FC' (after passing through the treatment device 8) is recycled in the recycling loop 40 up to the inlet of the mixer 31.

The mixer 31 is supplied with gas rich in dioxygen coming from the source 30 (valve V1 open) with a flow rate ( ϕ O ₂ ) and is supplied with the treated combustion fumes FC ₂ with a flow rate ϕ .

The mixer 31 is also supplied with air which is sucked in from the ambient air, via the bypass 6, with an incoming air flow rate ϕ _AIR and which is conveyed to the mixer 31, via the portion of the recycling loop 40 downstream of the connection 40a of the bypass 6 with the recycling loop 40, at the same time as the combustion fumes FC ₂ .

In operation:ϕ _{GC =} ϕO_{2 +} ϕ ₊ ϕ _AIR

This operating phase continues as long as the flow rate of the VR recycling fan or compressor is below a critical threshold.

In this operating phase, the combustion gas GC contains dioxygen from the dioxygen-rich gas supplied by source 30, the treated and recycled combustion fumes FC ₂ (rich in CO ₂ ) and air.

In this phase of operation,when the flowϕO₂of oxygen-rich gas at the inlet of the mixer 31 increases and/or when the flow rateϕ recycled treated combustion fumes FC₂at the inlet of the mixer 31 increases, the air flowϕ _AIRsucked into the second branch 6 automatically decreases. Conversely, when the flowϕO₂of oxygen-rich gas at the inlet of the mixer 31 decreases and/or when the flow rateϕ treated and recycled combustion fumes FC₂at the mixer inlet 31 decreases the air flowϕ _AIRsucked into the second branch 6 increases automatically.

Operating phase of the – “improved oxycombustion”

We automatically switch to this operating phase when the flow rate of the recycling fan or compressor VR passes above a critical threshold resulting in a reversal of gas flow in the bypass 6, air no longer being sucked into this bypass 6, but a portion FC _{2 2} of the treated and recycled combustion fumes FC ₂ being automatically evacuated into the bypass 6 and the remaining portion FC _{2 1} of the treated and recycled combustion fumes FC ₂ being conveyed to the inlet of the mixer 31.

In this operating phase, the mixer 31 is supplied with dioxygen coming from the dioxygen-rich gas of the source 30 (valve V1 open) with a given flow rate ( ϕ O ₂ ) and is supplied with a flow rate ϕ 1 with the part FC _{2 1} of the treated and recycled combustion fumes FC ₂ ; the other part FC _{2 2} of the treated and recycled combustion fumes FC ₂ is evacuated into the bypass 6 with a flow rate ϕ 2.

In operation:

ϕ ₌ ϕ1+ ϕ2

ϕ _{GC =} ϕ O _{2 +} ϕ ₁

When the flowϕO₂of oxygen-rich gas at the inlet of the mixer 31 is increased, the flow rateϕ ₁from the recycled part FC_{2 1}combustion fumes FC₂automatically decreases and when the flow rateϕO₂of oxygen-rich gas at the inlet of the mixer 31 is reduced, the flow rateϕ ₁from the recycled part FC_{2 1} combustion fumes FC₂increases automatically.

The GC combustion gas thus contains dioxygen from the dioxygen-rich gas from source 30 and the FC _{2 1} part of the combustion fumes FC ₂ .

The transition from one operating phase to the other can be easily and safely controlled by the control unit 7 by automatically adjusting the flow rate of the recycling fan or compressor VR and advantageously without having to switch off the combustion device 1 and without having to stop the combustion in the combustion device 1.

Preferably, in the operating mode M2, the control unit 7 automatically regulates the flow rate ϕ O ₂ of gas rich in dioxygen (for example by closing the valve V1 more or less) such that the concentration of dioxygen measured by the sensor 33 in the oxidizing gas GC is equal to or greater than a given operating setpoint or is within a given operating range. This allows the system to automatically adapt to variations in the flow rate ϕ _GC of oxidizing gas GC (imposed by the combustion device 1), by maintaining an appropriate concentration of dioxygen O ₂ in the oxidizing gas GC.

The combustion system of the may in particular, but not exclusively, operate with a C fuel producing in the “improved oxycombustion” operating phase combustion fumes FC which mainly contain carbon dioxide (CO ₂ ) and water vapour (H ₂ O), and to a lesser extent dioxygen (O ₂ ) and carbon monoxide (CO).

Thus, in a non-limiting and non-exhaustive manner, fuel C used in the combustion system of the may advantageously be a hydrocarbon of any type, and for example a conventional hydrocarbon from oil or natural gas or an unconventional hydrocarbon from shale gas or oil, shale or oil sands, coal methane, biogas, singaz, etc.

For example, when the fuel C is a saturated hydrocarbon of the alkane type (C _n H _2n+2 ), the oxycombustion reaction in the installation is known as:

C _n H _2n+2 + (3n+1)/2 O ₂ → nCO ₂ + (n+1)H ₂ O - Energy (kJ/mole of C _n H _2n+2 )

The fuel can also be a solid or liquid fuel resulting from extraction (coal, wood, etc.) or can contain waste (plastics, recovered materials, etc.)

The recycling at the inlet of the mixer 31 of the combustion gas containing _CO2 makes it possible, in a manner known per se, to better control the oxycombustion reaction in the combustion device 1 and to significantly lower the combustion temperature in this combustion device 1, compared to an oxycombustion reaction which would be carried out using only or essentially pure dioxygen as oxidant.

The combustion system can advantageously operate without time limit in the operating mode M2 (“oxycombustion with recycling”) and in said “degraded oxycombustion” phase with a partial air inlet at least via the bypass 6 (and possibly via another secondary air inlet or a secondary combustion gas inlet connected directly to the combustion device 1), and a partial discharge into the atmosphere of a portion FC ₁ of the combustion fumes FC (in the absence of a treatment device 8) or FC' (with a treatment device), via the downstream portion 5b of the main evacuation circuit 5.

Preferably, when the combustion system has switched to operating mode M2 (“oxycombustion with recycling”), the control unit 7 automatically regulates the flow rate ϕ O ₂ of dioxygen (for example in this particular case by closing the progressive valve V1 more or less) using the measurement signal S of the dioxygen concentration in the oxidant gas G.

The transition from operating mode M1 (“conventional combustion”) to operating mode M2 (“oxycombustion with recycling”) is simple and safe, the risks of untimely and uncontrolled temperature rise of the combustion device 1 being avoided. The transition from operating mode M1 (“conventional combustion”) to operating mode M2 (“oxycombustion with recycling”) advantageously does not require any user intervention on the combustion device 1 and above all does not require stopping combustion.

The change from operating mode M1 to operating mode M2 (“oxycombustion with recycling), in the “degraded oxycombustion” phase or in the “improved oxycombustion” operating phase, can be requested from the control unit 7, at the initiative of the user of the combustion system, for example by means of a manual operating mode change command.

The transition from operating mode M1 to operating mode M2 can also be implemented when starting the combustion system in order to operate it in “oxycombustion with recycling” (M2).

Combustion System Start-up Procedure

When a user wishes to start the combustion system in order to operate it in “oxycombustion with recycling” (M2), he asks the control unit 7, by means of an appropriate command, to carry out a start-up procedure.

The control unit 7 performs this start-up procedure by first configuring the combustion system in operating mode M1 (“conventional combustion”).

Then the combustion device 1 is started, in particular by operating at least the fan (or compressor 10) of the combustion device 1, either manually by the user or automatically for example by the control unit 7, which initially allows the system to operate in conventional combustion (M1).

Then, in a second step, the control unit 7 controls the combustion system, so as to automatically switch to “oxycombustion with recycling” (M2), as previously described, by choosing the operating phase called “degraded oxycombustion” or the operating phase called “improved oxycombustion”.

Such a start-up phase is advantageously simple and secure. In particular, compared to a combustion system of the prior art which is adapted to operate only in improved oxycombustion mode with recycling of combustion fumes, the risks of untimely and uncontrolled temperature rise, which are inherent in this type of installation of the prior art due to a high initial concentration of dioxygen in the combustion gas and a low initial concentration of CO _{2 ,} are avoided during the start-up phase.

Example of piloting of the combustion system to switch from operating mode M 2 ( " oxycombustion with recycling » ) in operating mode M 1 ( " classic combustion » )

It is assumed that the combustion system is configured in operating mode M2 (“oxycombustion with recycling”).

The combustion device 1 operates, the recycling fan or compressor VR operates and the fan 10 (or compressor) of the combustion installation 1 operates by imposing a given flow rate ( ϕ _GC ) of combustion gas GC consisting of air at the inlet of the installation 1.

To switch from this operating mode M2 (“oxycombustion with recycling”) to operating mode M1 (“conventional combustion”), the control unit 7 simply has to command the slowdown until the recycling fan or compressor VR stops, then command the closing of the valve V1.

The transition from operating mode M2 (“oxycombustion with recycling”) to operating mode M1 (“conventional combustion”) is simple, fast and safe, the risks of untimely and uncontrolled temperature rise of the combustion installation 1 being avoided. The transition from operating mode M2 (“oxycombustion with recycling”) to operating mode M1 (“conventional combustion”) advantageously does not require any user intervention on the combustion device 1 and above all does not require stopping combustion.

The change from operating mode M2 to operating mode M1 can be requested from the control unit 7, at the initiative of the user of the combustion system, for example by means of a manual operating mode change command.

The transition from operating mode M2 to operating mode M1 can also be implemented during a combustion system operation shutdown procedure.

Combustion system shutdown procedure

When a user wishes to stop the combustion system while it is operating in “oxycombustion with recycling” (M2), he asks the control unit 7, by means of an appropriate command, to execute a shutdown procedure.

The control unit 7 executes this shutdown procedure by controlling the slowing down until the recycling fan or compressor VR stops, as previously described, then by controlling the closing of the valve V1 of the device 32 for controlling the flow rate of gas rich in dioxygen in order to switch from operating mode M2 to operating mode M1.

Once the combustion system is configured in this operating mode M1 (“conventional oxycombustion”), the combustion device 1 can be shut down in the usual and known manner without incurring any risk.

Such a shutdown phase is advantageously simple and secure. In particular, compared to a combustion system of the prior art which is adapted to operate only in oxycombustion with recycling of combustion fumes, the risks of untimely and uncontrolled temperature rise, which are inherent in this type of installation of the prior art, are avoided during the shutdown phase.

The transition from operating mode M2 to operating mode M1 can also be implemented when the concentration of dioxygen (provided by source 30) in the GC combustion gas becomes insufficient and no longer allows improved oxycombustion with recycling of the combustion gas.

This insufficiency may have several causes, possibly cumulative.

It may happen, for example, that during operation of the combustion system in operating mode M2 (“oxycombustion with recycling”), and in particular in the “enhanced oxycombustion” operating phase, an accidental interruption of the supply of oxygen occurs, for example due to an untimely shutdown of the in situ production of gas rich in oxygen by the source 30 or a source 30 of gas rich in oxygen which is empty.

It may happen, for example, that during operation of the combustion system in operating mode M2 (“oxycombustion with recycling”), and in particular in the “enhanced oxycombustion” operating phase, the supply of dioxygen decreases too significantly, for example due to an untimely slowdown in the in situ production of gas rich in dioxygen by the source 30 or too low a pressure in the source 30.

It may happen, for example, that during operation of the combustion system in operating mode M2 (“oxycombustion with recycling”) and in particular in the “enhanced oxycombustion” operating phase, the combustion device 1 is requested to provide more thermal energy and to respond increases the flow rate ϕ _GC (increase in the flow rate of the fan or compressor 10) in oxidizing gas GC. In this case the additional oxidizing gas is automatically injected through the bypass 6.

If the combustion device 1 reduces the supply of thermal energy, which results in a reduction in the need for the combustion gas GC, the excess combustion gas is discharged via the bypass 6 and the control system 7 adjusts the valve V1 if necessary to reduce the injection of dioxygen into the mixer 31.

In a traditional installation capable of operating only in oxycombustion with recycling of combustion fumes, too significant a drop in the concentration of dioxygen in the GC combustion gas can cause an untimely shutdown of the oxycombustion.

Such an untimely shutdown can advantageously be avoided by means of the combustion system of the invention.

For this purpose, the control unit 7 is preferably designed to monitor, by means of the sensor 33, the oxygen concentration in the combustion gas GC and when the oxygen concentration decreases, to automatically detect whether this oxygen concentration reaches a predefined and preferably configurable critical minimum threshold, and if so to automatically control the combustion system, so as to switch it (as previously described) safely to operating mode M1 (“conventional combustion”), without stopping the combustion in the combustion device 1.

Combustion system of the / CO2 capture

In the particular variant of the , but optionally, the combustion system advantageously comprises a device 11 for capturing carbon dioxide (CO ₂ ) connected to the branch 6 and adapted to capture carbon dioxide (CO ₂ ) in at least part of the outgoing recycled combustion fumes (FC ₂₂ / ) circulating in said derivation 6.

More particularly, this capture device 11 comprises a fan or compressor 110 which makes it possible to suck up a portion of the outgoing recycled combustion fumes (FC ₂₂ / ) circulating in bypass 6 and supplying a _CO2 capture unit 111 (known per se).

Preferably, this capture device 11 and in particular the fan or compressor 110, is controlled automatically (by the control unit 7 by means of the control signal C3) or by another control unit) as a function of the pressure or flow rate of the outgoing combustion fumes circulating in the bypass 6, this pressure or flow rate being measured by a sensor 60 delivering a measurement signal S ₆₀ .

Other non-exhaustive examples of combustion systems in accordance with the invention and capable of operating in operating modes M1 (“conventional combustion”) and M2 (“combustion with recycling”) will now be described.

Combustion system of figures 5 to 8

The combustion system of the differs from that of the in that the connection 40a of the recycling loop 40 with the main evacuation circuit 5 is located upstream of the treatment device 8, between the outlet 1a of the combustion device 1 and the inlet of this treatment device 8, and in that an additional treatment device 8' is mounted on the recycling loop 40, preferably upstream of the recycling fan or compressor VR, that is to say between the recycling fan or compressor VR and the connection 40a of the recycling loop 40 with the main evacuation circuit 5.

Alternatively, the additional treatment device 8’ can be mounted on the recycling loop 40 downstream of the recycling fan or compressor VR.

The treatment device 8 may be adapted to depollute the non-recycled combustion fumes, before their evacuation into the ambient air and preferably to capture one or more pollutants chosen from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs. The treatment device 8’ is preferably adapted to at least dehumidify the combustion fumes recycled in the recycling loop 40 and more particularly comprises at least one condenser or several condensers in cascade.

The explanations given previously on the operating modes M1 and M2 and on the control by the control unit 7 of the recycling fan or compressor VR and of the combustion gas supply unit 3 GC are transposable to this variant of the .

In reference to the and as for the variant of the , in operating mode M1 (“classic combustion), the combustion gas GC consists of the air drawn in by the bypass 6 (the valve V1 being closed and the recycling fan or compressor VR being stopped) and the combustion fumes FC are treated in their entirety by passing through the treatment device 8 and are evacuated (FC') into the ambient air.

In reference to the and in a comparable manner to the variant of the , in operating mode M2 (“ oxycombustion with recycling ” ) and in the “ degraded oxycombustion ” operating phase, the recycling fan or compressor VR operates and the valve V1 is open; a portion FC ₁ of the combustion fumes FC is discharged into the ambient air after having been treated (treatment device 8) and the other portion FC ₂ of the combustion fumes FC is recycled in the recycling loop 40 to the inlet of the mixer 31 having been previously treated in the treatment device 8'. Air is also sucked into the bypass 6 and also supplies the mixer 31. The other inlet of the mixer 31 is supplied with dioxygen coming from the dioxygen-rich gas from the source 30 (valve V1 open) with a given flow rate ( ϕ O ₂ ).

In reference to the and in a comparable manner to the variant of the , in operating mode M2 (“oxycombustion with recycling ») and in the operating phase "oxycombustion improved", the VR recycling fan or compressor is operating and the V1 valve is open. A FC part₁combustion fumes FC is discharged into the ambient air after being treated (treatment device 8) and the other part FC₂combustion fumes FC is recycled in the recycling loop 40 and is treated in the treatment device 8’. An inlet of the mixer 31 is supplied with a flow rateϕ1 with FC part_{2 1}recycled combustion fumes FC₂ and processed, the other party FC_{2 2}recycled combustion fumes FC₂ and treated being evacuated in bypass 6 with a flow rateϕ2.

The other inlet of the mixer 31 is supplied with dioxygen coming from the dioxygen-rich gas of the source 30 (valve V1 open) with a given flow rate ( ϕ O ₂ ).

Combustion system of the – condenser 34 downstream of mixer 31

The combustion system of the differs from that of the in that a condenser 34 has been added. This condenser 34 is supplied at the input by the mixer 31 and is connected at the output to the combustion device 1 and supplies the combustion device 1 with the oxidizing gas GC.

In this variant, when the combustion system is in operating mode M2 (“oxycombustion with recycling”), the combustion fumes FC are recycled to the mixer 31 without necessarily having been dehumidified in the treatment device 8, dehumidification being carried out at least by the condenser 34.

In another variant, the condenser 34 could be mounted in bypass like the treatment device 8 of the .

Combustion system of figure 10

The combustion system of the differs from that of the mainly in that the control unit 7 is adapted to control the recycling fan or compressor VR) as a function of at least the flow rate or pressure measured at least by said sensor 60 (and no longer by the sensor 51 as in the variant of the ) during at least operating mode M2 with recycling of at least part of the combustion fumes.

The higher the pressure or flow rate measured by the sensor 60, the higher the flow rate of recycled combustion fumes FC ₂ in the recycling loop 40.

In particular, the control unit 7 automatically controls the recycling fan or compressor VR, until the flow rate or pressure measured by this sensor 60 reaches at least one predefined and preferably configurable operating setpoint, and automatically regulates the flow rate of the recycling fan or compressor VR so as to maintain said pressure or said measured flow rate at this operating setpoint or in the vicinity of this operating setpoint.

This operating instruction is set such that the flow rate of the recycling fan or compressor VR is lower than the flow rate of the combustion fumes FC at the outlet of the treatment device 8 or, in the absence of a treatment device 8, at the outlet of the combustion device 1, so as to recycle at least part FC to the mixer 31.₂combustion fumes, the other part FC₁being discharged into the open air into the atmosphere via the downstream part 5b of the main evacuation circuit 5.

The explanations that have been given previously on the operation of the combustion system of the are transposable to the combustion system of the .

In the particular variant of the , but optionally, the combustion system advantageously comprises a device 11' for capturing carbon dioxide (CO ₂ ) connected to the downstream part 5b of the main evacuation circuit 5 and adapted to capture carbon dioxide (CO ₂ ) in at least part of the outgoing combustion fumes FC ₁ .

More particularly, this capture device comprises a fan or compressor 110 which makes it possible to suck up a portion of combustion fumes FC circulating in the downstream part 5b of the main evacuation circuit 5 and to supply a _CO2 capture unit 111 (known per se).

Preferably, this capture device 11’, and in particular the fan or compressor 110, is controlled automatically (by the control unit 7 or by another control unit) as a function of the pressure or flow rate of the combustion fumes circulating in the downstream part 5b of the main evacuation circuit 5, said pressure or said flow rate being measured by the sensor 51.

Combustion system of figure 11

The combustion system of the differs from that of the in that in a manner comparable to the , the connection 40a of the recycling loop 40 with the main evacuation circuit 5 is located upstream of the treatment device 8, between the outlet 1a of the combustion device 1 and the inlet of this treatment device 8, and in that an additional treatment device 8' is mounted on the recycling loop 40, preferably upstream of the recycling fan or compressor VR, that is to say between the recycling fan or compressor VR and the connection 40a of the recycling loop 40 with the main supply circuit 5.

Combustion system of the – 8-way “bypass” treatment device

The combustion system of the differs from that of the in that the processing device 8 is connected as a bypass to the main evaluation circuit.

This type of assembly is known to be suitable for treatment devices 8, which have their own fan or compressor, such as for example that described later with reference to the . The explanations that have been given previously on the operation of the combustion system of the also apply to this combustion system of the .

In the variants of figures 5, 9, 10, 11, 13, the treatment device 8 or 8’ can also be mounted in bypass.

Combustion system of the - CO2 injection at start-up

The combustion system of the differs from that of the in that it comprises an additional device 12 connected to an inlet of the mixer 31 and making it possible to inject gaseous carbon dioxide (CO ₂ ) into the mixer 31 during the “degraded oxycombustion” transient phase when switching from the second operating mode M2 in the “degraded oxycombustion” phase to the second operating mode M2 in the “improved oxycombustion” phase, in order to shorten the duration of this transient phase.

This _CO2 injection device 12 comprises, for example, a source 120 of pressurized gaseous _CO2 associated with a valve or solenoid valve 121 controlled by the control unit 7 by means of a control signal C4.

This _CO2 injection device 12 can also be added into the combustion system of figures 5, 9, 10, 11, 12.

Particular example of a condenser – Figure 14

It was represented on the , as a non-limiting example of the invention, a preferred example of a condenser that can be used as a condenser in the treatment device 8 or 8' of a combustion system of the invention.

This condenser comprises an exchanger 12, which comprises an enclosure 120 containing a bath 121 of cooling liquid L and injection means 123, which are adapted to introduce the gaseous fluid F to be dehumidified (i.e. combustion fumes) below the surface of the bath of cooling liquid L.

The coolant L can be simply water or an aqueous solution.

These injection means 123 may more particularly comprise a fan or compressor 123f and an injection duct 123a comprising an intake opening 123b, for example in its upper part 123c. The lower part 123d of the injection duct 123a is immersed in the bath 121 of cooling liquid L and comprises an evacuation opening 123e immersed in the bath 121 of cooling liquid L.

In operation, the fan or compressor 123f makes it possible to suck in the gaseous fluid F to be dehumidified and to introduce it into the injection duct 123 through the inlet opening 123b. This gaseous fluid F escapes from the injection duct 123 through the discharge opening 123e, and is thereby forcibly introduced into the bath 121 of cooling liquid L, below the surface of the bath 121 of cooling liquid L, rises towards the surface of the liquid bath, escapes from the enclosure 120 through the discharge opening 120a of the enclosure 120 after having been dehumidified in the form of a dehumidified gas F'.

The temperature T_Lof the coolant L is always lower than the temperature T_F of the gaseous fluid F at the inlet of the exchanger 12 and is preferably lower than the dew point temperature of the gaseous fluid F.

It should be remembered that the absolute humidity (g _water / kg _{dry air} ) of a gas represents the number of grams of water vapor present in a given volume of gas, relative to the mass of dry gas in this volume expressed in kilograms. Its value remains constant even if the temperature of the gas varies, while remaining above the dew point of the gas.

When passing through the bath 121 of cooling liquid L, the gaseous fluid F undergoes condensation on contact with the cooling liquid L, so that the absolute humidity of the gas F', at the outlet of the exchanger 12 is lower than the absolute humidity of the gaseous fluid F at the inlet of the exchanger 12.

The difference between the absolute humidity of the dehumidified gas F' and the absolute humidity of the incoming gaseous fluid F depends in particular on the difference between the temperature T_F of the incoming gaseous fluid F and the temperature T_Llower the coolant L. The greater the temperature difference ΔT (ΔT = T_F– T_L) between the temperature T_{F of}incoming gaseous fluid F and temperature T_Lof the cooling liquid L is important, and the lower the absolute humidity of the dehumidified gas F' will be compared to the absolute humidity of the incoming gaseous fluid F.

In another variant, the fan or compressor 123f can be connected to the injection conduit 123 and used so as to introduce the gaseous fluid F into this injection conduit 123 by blowing them through the inlet opening 123b of this injection conduit 123.

The exchanger 12 can more particularly be coupled to a heat pump (not shown) which makes it possible to renew the liquid L in the bath by taking calories from it so as to maintain the temperature of this liquid at a sufficiently low level.

In another embodiment, the condenser may comprise several exchangers 12 mounted in cascade.

The invention is not limited to the implementation of an exchanger 12 of the type of that of the . In other embodiments, the exchanger 12 for the condensation of the gaseous fluid F may for example be of the type described in the international patent application WO2016/071648 or in the international patent application WO2020/030419 or may be an exchanger operating by spraying the cooling liquid L in contact with the gaseous fluid F.

The invention is not limited to an exchanger operating with a cooling liquid but can be implemented with any other known type of exchanger allowing dehumidification of a gaseous fluid.

Advantage of implementing gas rich in oxygen combined with a loopback of at least one part combustion fumes

In the case of conventional combustion, for a quantity Qd of fuel C to be burned per hour, a flow rate D of combustion air is used at the inlet of the combustion device. After combustion, combustion fumes are discharged with a flow rate X which must be treated in compliance with the standards for discharge of dust and chemicals. The greater X, the higher the cost of treating the combustion fumes.

In conventional combustion, the air flow D (D<X) at the inlet of the combustion device is defined according to the oxygen requirement for combustion and the management of the combustion device (for example management of the flame in the combustion hearth).

In conventional combustion, combustion fumes contain:

- nitrogen dioxide ( _N2 ) with almost the same mass flow rate as the combustion air,

- carbon dioxide ( _CO2 ) from combustion,

- water from combustion and, where applicable, from the evaporation of water that may be contained in the fuel (for example when the fuel consists of waste or coal) and water from the combustion air,

- dioxygen ( _O2 ) which did not participate in the combustion

- pollutants which depend on the fuel used and which may, for example, include fine particles, acids, Nox, SOx, heavy metals, dioxin, etc.

When the combustion system of the invention operates in “ oxycombustion ” as previously described [addition of the gas rich in dioxygen containing at least 40% of O ₂ with re-looping of a portion of the combustion fumes], the flow rate of the combustion fumes at the outlet of the combustion device which are not recycled and which are discharged directly into the atmosphere and/or which are treated (for example for the capture of CO ₂ ) before discharge into the atmosphere is advantageously lower than the flow rate X mentioned above.

Plus the fraction in O₂ in the gas rich in dioxygen supplied by source 30 is important, and the lower the flow rate of combustion fumes which are not recycled and are discharged

For example, when the gas rich in dioxygen is pure dioxygen, it is possible in practice to recycle the combustion fumes with a high recycling flow rate of up to 10/11 of X and to discharge the rest of the combustion fumes, with a flow rate which is advantageously lower and which can be of the order of 1/11 of X, either directly into the atmosphere, or by treating them beforehand, for example in order to capture the CO _{2 ,} before discharge into the atmosphere and/or by depolluting them.

In another variant embodiment of the invention, the mixer 31 may comprise an additional air inlet and/or the combustion device may comprise an additional air inlet for injecting additional air into the combustion in addition to the recycled combustion fumes and in addition to the gas rich in dioxygen. This will have an effect simply on the aforementioned coefficient of 11 which will in this case be between 1 and 11 depending on the additional air flow injected into the combustion via said additional air inlet.

When the gas rich in dioxygen contains 90% dioxygen, it is possible in practice to recycle the combustion fumes with a high recycling flow rate of up to 9/10 of X and to discharge the rest of the combustion fumes, with a flow rate which is advantageously lower and which can be of the order of 1/10 of X, either directly into the atmosphere, or by treating them beforehand, for example in order to capture the CO _{2 ,} before discharge into the atmosphere and/or by depolluting them, etc.

It should be noted that the constraints on the pollution of the combustion gas at the inlet of the combustion device are less significant than the environmental constraints linked to the pollution of non-recycled combustion fumes, which are increasingly drastic. Depending on the case, it is therefore possible not to treat the recycled combustion fumes or possibly to carry out a treatment of the recycled combustion fumes before they enter the mixer, which is "light" and significantly less expensive than treatment of non-recycled fumes. The total cost of treating combustion fumes can therefore advantageously be significantly reduced.

In return for this significant reduction in the cost of treating combustion fumes, the production of the gas rich in dioxygen induces an additional operating cost, which in practice increases with the fraction of _O2 in the gas rich in dioxygen, but which remains in practice significantly less significant than the cost of treating the combustion fumes. It is therefore up to the person skilled in the art to adapt and find a compromise on a case-by-case basis between the cost of producing the gas more or less rich in dioxygen and the cost of treating the combustion fumes.

In the context of the invention, the dioxygen-rich gas contains at least 40% dioxygen (below this threshold, the reduction in the flow rate of non-recycled fumes is in practice too low). Preferably, the fraction of gaseous dioxygen in the dioxygen-rich gas is at least 80%, more preferably at least 90%. More particularly, the gaseous dioxygen is advantageously pure or quasi-pure gaseous dioxygen (at least 99% O ₂ ).

Claims (23)

Combustion system comprising a combustion device (1) allowing the combustion of a fuel (C) by means of at least one oxidizing gas (GC) and comprising an outlet (1a) through which it discharges combustion fumes (FC), a supply unit (3) for oxidizing gas (GC) which is connected to the combustion device (1) and makes it possible to supply the combustion device (1) with oxidizing gas (GC), said supply unit (3) for oxidizing gas (GC) comprising a mixer (31) and a source (30) of gaseous dioxygen which supplies a gas rich in dioxygen and which is connected to a first inlet of the mixer (31), a main evacuation circuit (5) connected to the outlet (1a) of the combustion device (1) and opening into the open air, recycling means (4) which comprise a recycling loop (40) between the main evacuation circuit (5) and a second inlet of the mixer (31), at least one recycling fan or compressor (VR) mounted on the recycling loop (40) and adapted to circulate a gaseous fluid in the recycling loop (40), towards the second inlet of the mixer (31), from a connection (40a) of the recycling loop (40) with the main evacuation circuit (5), a bypass (6) which is connected to the recycling loop (40) downstream of the recycling fan or compressor (VR) and which opens into the open air, and a control unit (7) adapted to control at least the recycling fan or compressor (VR). Combustion system according to claim 1, further comprising at least one sensor (51) which is adapted to at least measure the flow rate or pressure of gaseous fluid exiting in the downstream part (5b) of the main evacuation circuit (5) located downstream of the connection (40a) of the recycling loop (40) with the main evacuation circuit (5) and which delivers a pressure or flow measurement signal (S ₅₁ ) processed by the control unit (7). Combustion system according to claim 1 or 2, further comprising at least one sensor (60) which is adapted to at least measure the flow rate or pressure of gaseous fluid exiting in the bypass (6), and which delivers a pressure or flow measurement signal (S ₆₀ ) processed by the control unit (7). Combustion system according to claim 2 or 3, wherein the control unit (7) is adapted to control the recycling fan or compressor (VR) as a function at least of the flow rate or pressure measured by said sensor (51 or 60) during at least one operating mode (M2) with recycling of at least part of the combustion fumes. Combustion system according to any one of claims 1 to 4, wherein the control unit (7) is adapted to control the recycling fan or compressor (VR) so as to be able to configure the combustion system in an operating mode chosen from at least two different operating modes (M1; M2) and to be able to switch from one operating mode to the other: a first operating mode (M1) in which the recycling fan or compressor (VR) is stopped and the mixer (31) is not supplied with oxygen-rich gas from the gaseous oxygen source (3) and is supplied by air entering the bypass (6), and a second operating mode (M2), in which the recycling fan or compressor (VR) is operating, and the mixer (31) is supplied at least with oxygen-rich gas provided by the gaseous oxygen source (3) and with at least a portion (FC ₂ or FC ₂₁ ) of the combustion fumes discharged by the combustion device (1). Combustion system according to claim 5, in which the control unit (7) is adapted to control the device (32) for controlling the flow rate of the gas rich in dioxygen and the recycling fan or compressor (VR), so as to be able to switch from one operating mode (M1 or M2) to the other (M2 or M1) without stopping the combustion in the combustion device (1). Combustion system according to any one of claims 1 to 6, wherein the source (30) of gaseous dioxygen is connected to said first inlet of the mixer (31) via a device (32) for controlling the flow rate of the gas rich in dioxygen which is controlled by the control unit (7), and preferably which comprises a flow control valve (V1) which is controlled by the control unit (7). Combustion system according to claim 7, in which the flow control valve (V1) is a valve with progressive opening and closing. Combustion system according to any one of claims 1 to 8, comprising at least one sensor (33) adapted to measure the concentration of dioxygen in the combustion gas (GC) and in which the control unit (7) is adapted to control the device (32) for controlling the flow rate of the gas rich in dioxygen as a function of the concentration of dioxygen measured by this sensor (33) at least during an operating mode (M2) with recycling of at least part of the combustion fumes. Combustion system according to any one of claims 1 to 9, in which the combustion device (1) comprises a fan or compressor (10) adapted to supply the combustion device (1) with combustion gas (GC) at a flow rate (ϕ _GC) given, which is preferably variable. Combustion system according to any one of claims 1 to 10, in which the flow rate of supply of fuel (C) to the combustion device (1) is variable and the combustion device (1) comprises a fan or compressor (10) adapted to supply the combustion device (1) with oxidizing gas (GC) at a flow rate (ϕ _GC) which varies according to the flow rate of fuel (C) supplied to the combustion device (1). Combustion system according to any one of claims 1 to 11, comprising a device (8) for treating combustion fumes (FC) which is mounted on the main evacuation circuit (5). Combustion system according to any one of claims 1 to 12, comprising a device (8') for treating recycled combustion fumes (FC ₂ ) which is mounted on the recycling loop (40) preferably between the recycling fan or compressor (VR) and the connection (40a) of the recycling loop (40) with the main evacuation circuit (5). Combustion system according to claim 12 or 13, wherein the treatment device (8 or 8') is adapted to dehumidify the combustion fumes (FC or FC ₂ ). Combustion system according to claim 14, wherein the treatment device (8 or 8') comprises a condenser (34). Combustion system according to claim 15, in which the condenser comprises at least one exchanger (120) comprising a cooling liquid (L). Combustion system according to claim 16, in which the exchanger (120) comprises a bath (121) of cooling liquid (L), and injection means (123) making it possible to pass the gaseous fluid (FC or FC2) to be dehumidified through this bath of cooling liquid (L), and preferably in which the injection means (123) make it possible to inject the gaseous fluid (FC or _FC2 ) to be dehumidified below the surface of this bath (121) of cooling liquid (L). Combustion system according to any one of claims 12 to 17, in which the treatment device (8 or 8') is adapted to depollute the combustion fumes (FC or FC ₂ ) and more particularly to capture one or more pollutants chosen from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs. Combustion system according to any one of claims 1 to 18, comprising at least one sensor (33) adapted to measure the concentration of dioxygen in the combustion gas (GC) and in which the control unit (7) is adapted to control the device (32) for controlling the flow rate of the gas rich in dioxygen and the recycling fan or compressor (VR), as a function of the measured concentration of dioxygen in the combustion gas (GC), and preferably so as to switch from an operating mode (M2) with recycling of at least a portion (FC ₂ or FC ₂₁ ) of the combustion fumes to an operating mode (M1) without recycling of the combustion fumes. Combustion system according to any one of claims 1 to 19, comprising a device (11) for capturing carbon dioxide (CO ₂ ), which is connected to the bypass (6) and which is adapted to capture carbon dioxide (CO ₂ ) in at least a portion of the outgoing recycled combustion fumes (FC ₂₁ ) evacuated via said bypass (6) and/or comprising a device (11') for capturing carbon dioxide (CO ₂ ), which is connected to the downstream part (5b) of the main evacuation circuit (5) located downstream of the connection (40a) of the recycling loop (40) with the main evacuation circuit (5) and which is adapted to capture carbon dioxide (CO ₂ ) in at least a portion (FC ₁ ) of the outgoing non-recycled combustion fumes evacuated via said downstream part (5b) of the main evacuation circuit (5). Combustion system according to any one of claims 1 to 20, in which the gas rich in dioxygen supplied by the source (30) of gaseous dioxygen comprises at least 50% dioxygen, preferably at least 80% dioxygen, and more preferably still at least 90% dioxygen. A combustion system according to any one of claims 1 to 20, wherein the oxygen-rich gas provided by the gaseous oxygen source (30) is pure or near-pure oxygen. Combustion system according to any one of claims 1 to 22, comprising a device (12) for injecting carbon dioxide connected to an inlet of the mixer (31) and adapted to inject gaseous carbon dioxide ( _CO2 ) into the mixer (31) during a particular phase ("degraded oxycombustion") of the operating mode (M2) with recycling of combustion fumes.