Combustion system capable of operating with a recycling of combustion fumes

Abstract

A combustion system includes: a combustion device for combusting fuel by using an oxidizing gas and which includes an outlet for discharging combustion fumes; a supply unit for supplying oxidizing gas, which is connected to the combustion device for supplying the combustion device, the supply unit having a mixer and a gaseous dioxygen source which supplies a dioxygen-rich gas and is connected to a first inlet of the mixer; a main discharge circuit connected to the outlet of the combustion device and opening to open air; a recycler which includes a recycling loop between the main discharge circuit and a second inlet of the mixer, a recycling fan or compressor mounted on the recycling loop; a bypass connected to the recycling loop downstream of the recycling fan or compressor and which opens to the open air; and a control unit to control at least the recycling fan or compressor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Section 371 National Stage Application of International Application No. PCT / EP2023 / 087505, filed Dec. 21, 2023, and published as WO 2024 / 141436 on Jul. 4, 2024, not in English, which claims priority to French Patent Application No. FR2214633, filed Dec. 29, 2022, the contents of which are incorporated herein by reference in their entireties.TECHNICAL FIELD

[0002] The present invention relates to the field of combustion with recycling of at least part of the combustion fumes.PRIOR ART

[0003] So called “conventional” combustion comprises mixing in a combustion plant (furnace, boiler, etc.) air (an oxidizer) with a fuel under high temperature conditions to create the oxidation. The reaction is exothermic and is naturally sustained. Air contains 21% of dioxygen (O2) and the volume of air used is controlled so that the amount of dioxygen is sufficient for combustion.

[0004] In conventional combustion, the combustion fumes include water vapor (H2O) and gas-phase combustion products, mainly including gas-phase dinitrogen (N2), and gas-phase carbon dioxide (CO2).

[0005] In the present text, the terms “combustion gas” refers to gas-phase combustion products that are discharged after combustion.

[0006] If it is desired to capture the CO2 from these fumes, it is easy to remove 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.

[0007] Furthermore, in conventional combustion, and depending on the type of fuel used, the combustion gas can also comprise other gaseous-phase polluting combustion products, in a more or less substantial amount, such as for example SOx (sulfur oxides), NOx (nitrogen oxides), HCl (hydrogen chloride), HF (hydrogen fluoride), etc. Consequently, if it is desired to capture CO2 from these fumes, it is also necessary to separate the CO2 from these other pollutants.

[0008] Several solutions have been envisaged for capturing CO2 in fumes from conventional combustion, but their cost remains very high.

[0009] In order to reduce the emission of pollutants in combustion fumes, it is known to replace the above-mentioned conventional combustion, by combustion, referred to as “oxy-combustion”, in which the air (the oxidizer) is replaced by dioxygen in stoichiometric proportions, the number of oxygen atoms being equal to what is necessary to oxidize all the atoms of the fuel.

[0010] The production of dioxygen for implementing oxy-combustion may for example be obtained in a known manner by cryogenics or by electrolysis of water.

[0011] In the case, for example, of a methane oxycombustion (CH4), combustion fumes are produced consisting of ⅓ of CO2 in the gas phase and ⅔ of water vapor by volume. In the case of other fuels, there will be in addition the pollutants resulting from the combustion, such as with HCl, SOx, etc. If the fuel is not nitrogen-containing, advantageously the fumes will naturally not contain NOx.

[0012] The equation of the chemical reaction of methane oxycombustion (CH4) is as follows:

[0013] This means that each mole of CH4 will outwardly produce an energy of 891 kJ.

[0014] For other fuels, the reactions are analogous, with the appearance of other compounds if the fuel contains atoms other than carbon and hydrogen.

[0015] In the case for example, of the oxy-combustion of methane, it is notably easier to capture the CO2. To that end it suffices to condense the water of the combustion fumes via a cooling or dewatering process to obtain CO2 in the gaseous phase.

[0016] It is therefore known to date to implement a condenser for condensing the oxy-combustion fumes in order to facilitate the capture of CO2.

[0017] A significant difficulty in oxy-combustion however lies in the difficulty of controlling combustion, because unlike conventional combustion, the oxy-combustion temperature can quickly and uncontrollably become very high in the combustion chamber, to such a degree that conventional combustion apparatuses cannot withstand.

[0018] To overcome this difficulty, apparatuses have already been proposed for improving oxy-combustion, by recycling at least part of the combustion fumes rich in CO2 in the gas phase, preferably also by condensing said combustion fumes them, so as to mix said at least part of the combustion fumes with the dioxygen and to obtain an oxidizing gas (O2—CO2) which advantageously reduces the combustion temperature.

[0019] This improvement allows dioxygen-based oxy-combustion with more easily controlled recycling of the combustion fumes, compared to oxy-combustion using only dioxygen as oxidizer, while reducing the emission of pollutants with respect to conventional combustion and facilitating the capture of the CO2 if necessary.

[0020] These apparatuses are intended to operate only in oxy-combustion with recycling of the combustion fumes, which induces several drawbacks.

[0021] The start-up and shut-down procedures of these apparatuses are critical and risky operating phases and can lead in a detrimental manner to uncontrolled, excessively high temperatures of oxy-combustion, with recycling of the combustion gas, in the combustion chamber.

[0022] During oxy-combustion, with recycling of the combustion gas, an excessive drop in the concentration of molecular oxygen in the oxidizing gas can lead detrimentally to an untimely halting of the combustion in the combustion chamber of the apparatus, which can have serious consequences, for example in an industrial production chain using the thermal energy produced.SUMMARY OF THE INVENTION

[0023] The invention thus relates to combustion system comprising a combustion device for the combustion of a fuel by means of at least one oxidizing gas which comprises an outlet through which combustion fumes can be discharged, a supply unit for supplying oxidizing gas which is connected to the combustion device for supplying the combustion device with oxidizing gas, said oxidizing gas supply unit comprising a mixer and a gaseous dioxygen source which supplies a dioxygen-rich gas and which is connected to a first inlet of the mixer, a main discharge circuit connected to the outlet of the combustion device and opening to the open air, recycling means which comprise a recycling loop between the main discharge 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 discharge circuit, a bypass which is connected to the recycling loop downstream of the recycling fan or compressor and which opens to the open air so as to at least be able to supply the mixer with air entering the bypass, and a control unit adapted to control at least the recycling fan or compressor.

[0024] Said bypass enables at least to supply the mixer with air from the open air entering in the bypass.

[0025] The terms “oxygen-rich gas” mean that the gas contains at least 40% (percentage by volume) of dioxygen.

[0026] More particularly, the control unit is adapted to control the recycling fan or compressor so as to enable to configure the combustion system in an operating mode selected 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 dioxygen-rich gas from the gaseous dioxygen source and is supplied with air entering the bypass, and a second operating mode (M2), in which the recycling fan or compressor operates, and the mixer is supplied at least with dioxygen-rich gas supplied from the gaseous dioxygen source and with at least a portion of the combustion fumes discharged from the combustion device.

[0027] In said first operating mode (M1), the mixer is supplied at least with air sucked in via the bypass and all of the combustion fumes emitted by the combustion device is discharged to the open air, optionally after being treated, and without being recycled.

[0028] As a result, the oxidizing gas contains at least air and does not contain dioxygen from the gaseous dioxygen source. Combustion in the combustion device is thus conventional combustion.

[0029] In this first operating mode and in a particular alternative embodiment, the oxidizing gas preferably consists solely of air.

[0030] In said second operating mode (M2), the oxidizing gas contains at least dioxygen-rich gas from the gaseous dioxygen 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 preferably being at least dehumidified.

[0031] The result is that the combustion in the combustion device is of the oxy-combustion type with recycling of at least part of the combustion fumes.

[0032] More particularly, in said second operating mode (M2), in a particular operating phase, subsequently referred to as “degraded oxy-combustion”, the oxidizing gas can comprise air, which has been sucked in the open air via the bypass. In said second operating mode and in another particular operating phase subsequently referred to as “enhanced oxy-combustion”, the oxidizing gas does not contain air sucked in the open air via the bypass.

[0033] The combustion device can be a standard commercial combustion device or a special combustion device that has been specifically developed. This combustion device can have air inlets at different injection points depending according to combustion requirements. Advantageously, the invention can more particularly be implemented without the need to modify this combustion device.

[0034] More particularly, the combustion system of the invention can comprise the following additional and optional features, taken in isolation, or in combination with one another:

[0035] The combustion system further comprises at least one sensor which is adapted to at least measure the flow rate or pressure of outgoing gaseous fluid in the downstream portion of the main discharge circuit located downstream of the connection of the recycling loop with the main discharge circuit and which outputs a pressure or flow measurement signal processed by the control unit.

[0036] The combustion system further comprises at least one sensor that is adapted to at least measure the flow rate or pressure of outgoing gaseous fluid in the bypass, and that outputs a pressure or flow measurement signal (S60) processed by the control unit.

[0037] 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 (M2) wherein at least part of the combustion fumes is recycled.

[0038] The control unit is adapted to control at least the recycling fan or compressor, and optionally the device for controlling the flow rate of the dioxygen-rich gas, 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.

[0039] The gaseous dioxygen source 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 which preferably comprises a flow-control valve which is controlled by the control unit.

[0040] The flow-control valve is a progressive opening valve and a progressive closing valve.

[0041] The combustion system comprises at least one sensor adapted to measure the dioxygen concentration in the oxidizing gas and wherein the control unit is adapted to control the device for controlling the flow rate of the dioxygen-rich gas as a function of the dioxygen concentration measured by said sensor at least during an operating mode (M2) wherein at least part of the combustion fumes is recycled.

[0042] The combustion device comprises a fan or compressor adapted to supply the combustion device with oxidizing gas at a given flow rate (φGC), which is preferably variable.

[0043] The rate of supply of fuel to the combustion device is variable and the combustion device comprises a fan or compressor adapted to supply the combustion device with oxidizing gas at a rate (φGC), which varies according to the rate of supply of fuel to the combustion device.

[0044] The combustion system comprises a device for treating combustion fumes which is mounted on the main discharge circuit.

[0045] The combustion system comprises a treatment device for treating the 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 discharge circuit.

[0046] The treatment device is adapted to dehumidify the combustion fumes.

[0047] The treatment device comprises a condenser.

[0048] The condenser comprises at least one exchanger comprising a coolant liquid.

[0049] The exchanger comprises a bath of coolant liquid, and injection means for passing the gaseous fluid to be dehumidified through this coolant liquid bath (L), and preferably the injection means make it possible to inject the gaseous fluid to be dehumidified below the surface of this bath of coolant liquid.

[0050] The treatment device is adapted to depollute the combustion fumes and more particularly to capture one or more pollutants selected from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs.

[0051] The combustion system comprises at least one sensor adapted to measure the concentration of dioxygen in the oxidizing gas and the control unit is adapted to control the device for controlling the flow rate of the dioxygen-rich gas and the recycling fan or compressor, according to the measured concentration of dioxygen in the oxidizing gas, and preferably so as to switch from an operating mode (M2) wherein at least a portion of the combustion fumes is recycled to an operating mode (M1) wherein the combustion fumes are not recycled.

[0052] The combustion system comprises a device for capturing carbon dioxide (CO2), which is connected to the bypass and which is adapted to capture carbon dioxide (CO2) in at least part of the outgoing recycled combustion fumes discharged via said bypass and / or comprises a device for capturing carbon dioxide, which is connected to the downstream part of the main discharge circuit located downstream of the connection of the recycling loop with the main discharge circuit and which is adapted to capture carbon dioxide in at least part of the outgoing non-recycled combustion fumes discharged via said downstream part of the main discharge circuit.

[0053] The dioxygen-rich gas supplied by the gaseous dioxygen source comprises at least 50% dioxygen, preferably at least 80% dioxygen, and more preferably at least 90% dioxygen.

[0054] The dioxygen-rich gas supplied from the gaseous dioxygen source is pure dioxygen or near-pure dioxygen.

[0055] The combustion system comprises a carbon dioxide injection device connected to an inlet of the mixer and adapted to inject carbon dioxide (CO2) gas into the mixer during a particular phase (“degraded oxy-combustion”) of the operating mode (M2) wherein the combustion fumes are recycled.BRIEF DESCRIPTION OF THE FIGURES

[0056] The features and advantages of the invention will become more clearly apparent upon reading the following detailed description of several particular alternative embodiments of the invention, which particular embodiments are described by way of non-limiting and non-exhaustive examples of the invention, and with reference to the appended drawings in which:

[0057] FIG. 1 is a schematic representation of a first particular embodiment of a combustion system of the invention.

[0058] FIG. 2 shows the combustion system of FIG. 1 in the first operating mode M1 (“conventional combustion”).

[0059] FIG. 3 shows the combustion system of FIG. 1 in the second operating mode M2 (“oxy-combustion with recycling”) and in a particular operating phase (“degraded oxy-combustion”).

[0060] FIG. 4 shows the combustion system of FIG. 1 in the second operating mode M2 (“oxy-combustion with recycling”) and in another particular operating phase (“Enhanced oxy-combustion”).

[0061] FIG. 5 is a schematic representation of a second particular embodiment of a combustion system of the invention.

[0062] FIG. 6 shows the combustion system of FIG. 5 in the first operating mode M1 (“conventional combustion”).

[0063] FIG. 7 shows the combustion system of FIG. 5 in the second operating mode M2 (“oxy-combustion with recycling”) and in a particular operating phase (“degraded oxy-combustion”).

[0064] FIG. 8 shows the combustion system of FIG. 5 in the second operating mode M2 (“oxy-combustion with recycling”) and in another particular operating phase (“Enhanced oxy-combustion”).

[0065] FIGS. 9 to 13 are schematic representations of five other particular embodiments of a combustion system of the invention.

[0066] FIG. 14 shows a particular example of a condenser that can be implemented in a combustion system of the invention.DETAILED DESCRIPTIONCombustion System of FIG. 1

[0067] FIG. 1 schematically depicts a first particular embodiment of a combustion system of the invention comprising:

[0068] 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, emits combustion fumes FC through an outlet 1a;

[0069] a main discharge circuit 5 for discharging at least part of the combustion fumes emitted by the combustion device 1, which main discharge circuit 5 is connected at one end to the outlet 1a of the combustion device 1 and leads out at its opposite end to the open air (at atmospheric pressure) in the ambient air; this main discharge circuit 5 more particularly comprises a discharge chimney 50 opening to the open air;

[0070] recycling means 4, which include a recycling loop 40 connecting the main discharge circuit 5 to an inlet of the oxidizing gas GC supply unit 3 and a recycling fan VR, which is mounted on the recycling loop 40; the recycling fan VR operates to forcibly circulate a gaseous fluid in the recycling loop 40 from the connection 40a of the recycling loop 40 with the discharge main circuit 5 and toward the oxidizing gas GC supply unit 3;

[0071] a bypass 6, which is connected (connection 40b) to the recycling loop 40 downstream of the recycling fan VR and which leads out to the open air at atmospheric pressure in the ambient air;

[0072] at least one sensor 51 adapted to at least measure the pressure or flow rate of the outgoing gaseous fluid which is discharged to the open air via the downstream portion 5b of the main discharge circuit 5 located downstream of the connecting 40a of the recycling loop 40 with main discharge circuit 5.

[0073] The sensor 51 can for example be mounted in a conduit between the connection 40a of the recycling loop 40 with the main discharge circuit 5 and the discharge chimney 50, as illustrated in FIG. 1, or can be mounted directly in the discharge chimney 50.

[0074] In this particular embodiment of FIG. 1, the control unit 7 is adapted to control at least the recycling fan VR depending at least on the flow rate or the pressure measured by said sensor 51 (detection signal S51 output by the sensor), as will be detailed later.

[0075] The control unit 7 can be implemented in various forms, and can for example be realized by means of a programmable electronic control unit, for example of the programmable logic controller type or of a programmable electronic circuit comprising a microprocessor, a microcontroller or programmable logic circuits of FPGA type, or can also be made of a specific integrated electronic circuit of ASIC type.

[0076] The bypass 6 may consist of a simple pipe connected at one end to the recycling loop 40 and opening directly to the open air (at atmospheric pressure) at its other end. In its simplest version, this bypass 6 can also be a simple opening for communicating the recycling loop 40 with open air.

[0077] Alternatively, the VR recycling fan may be replaced by an air compressor.

[0078] The combustion device 1 generally allows combustion of the fuel C by means of said oxidizing gas GC, and the thermal energy resulting from this combustion can be used indifferently according to the invention in any type of application requiring a heat supply, and for example and in a non-limiting manner can be used to heat a fluid in a heating installation or to supply an industrial production line with energy, in particular thermal, mechanical or electrical energy. The combustion device 1 may also comprise a conventional boiler, an oven, or a combustion chamber in which a combustion process is carried out.

[0079] The combustion device 1 usually comprises a fan (or compressor) 10 which allows the combustion gas GC to be pulled or pushed into the combustion facility 1, with automatic adjustment or regulation of the flow rate φGC of oxidizing gas GC entering the combustion device 1 to adapt to the flow rate of the fuel C and meet the heat energy requirements.

[0080] The combustion device 1 can be a standard commercial combustion device or a particular combustion device that has been developed specifically.

[0081] The combustion reaction of the fuel C by means of the oxidizing gas GC produces combustion fumes FC whose composition depends on the fuel C and the oxidizing gas GC.

[0082] In the context of the invention, the fuel C may be very different from one application to another and may, depending on the case, be in solid, liquid or gaseous form.

[0083] The oxidant gas GC supply unit 3 has a gaseous dioxygen source 30 (O2) which supplies an input of a mixer 31, via a flow control device 32 controlled by the control unit 7. The other input of the mixer 31 is connected to the recycling loop 40.

[0084] The gaseous dioxygen source 30 is operable to provide a dioxygen-rich gas, i.e. a gas containing at least 40% (percentage by volume) of dioxygen.

[0085] Preferably, as will be discussed subsequently, the dioxygen-rich gas can advantageously, but not necessarily, consist of pure dioxygen or quasi-pure dioxygen (volume concentration greater than 90%).

[0086] The gaseous dioxygen source 30 can be of any known type and may for example comprise a cryogenically gaseous dioxygen production unit and / or a gaseous dioxygen production unit by electrolysis of water. The gaseous dioxygen source 30 can also be a dioxygen-rich gas production unit containing at least 40% dioxygen obtained by suitable air filtration using zeolites or the like. The gaseous dioxygen source 30 can also not be configured to produce the dioxygen-rich gas in situ, but may simply include a means for storing the dioxygen-rich gas that will have been previously produced on another site.

[0087] Alternatively, the flow control device 32 can simply stop or pass the dioxygen-rich gas from the source 30. Preferably, however, the flow control device 32 is operable to stop the dioxygen-rich gas from the source 30 or to pass the dioxygen-rich gas from the source 30 by allowing adjustment, by the control unit 7, of the gas flow rate at the input of the mixer 31.

[0088] In the particular embodiment of FIG. 1, the gaseous dioxygen source 30 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.

[0089] Preferably, this valve V1 is a progressive opening valve and progressive closing valve.

[0090] In another variant, the flow control device 32 at the inlet of the mixer 31 can also comprise a system for controlling the pressure of the gas leaving the source 30 optionally associated with a valve which can be an on / off valve or a progressive opening and progressing closing valve, the pressure control system and said valve being controlled by the control unit 7.

[0091] Preferably, the oxidizing gas GC supply unit 3 also comprise at least one sensor 33, which measures the concentration of dioxygen in the oxidizing gas GC entering the combustion device 1 and which delivers to the control unit 7 a signal S measuring this concentration.

[0092] Preferably, in the variant of FIG. 1, the combustion system comprises a combustion fume treatment device 8, which is mounted on the upstream portion 5a of the main discharge circuit 5 positioned upstream of the connection 40a of the recycling loop 40 with the main discharge circuit 5

[0093] In this particular alternative embodiment, this device 8 for treating the 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 making it possible, by any means, to cool the combustion fumes FC so as to carry out a condensation of at least a fraction of the water vapor contained in the combustion fumes F at the outlet of the treatment device 8. in this case, dehumidified combustion fumes FC′ (rich in CO2) containing mainly the combustion products in the gas phase produced by the combustion in the combustion device 1 are obtained. Said dehumidified combustion fumes FC′ (rich in CO2) have an absolute humidity lower than that of the combustion fumes FC at the inlet of the treatment device 8.

[0094] The combustion fume treatment device 8 can also be adapted to depollute the combustion fumes and preferably to capture one or more pollutants selected from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs. In this case, the dehumidified and depolluted combustion fumes FC′ (rich in CO2) are obtained at the outlet of the treatment device 8.

[0095] In a particular embodiment, the installation may be devoid of any treatment device 8 or the treatment device 8 may be devoid of means for dehumidifying the combustion fumes and comprise only means for depolluting the combustion fumes. In this case, the installation preferably comprises a treating 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 recycled combustion fumes in the recycling loop 40 in order at least to dehumidify recycled combustion fumes.

[0096] The control unit 7 automatically controls the recycling fan or compressor VR and the oxidizing gas supply unit 3, and more particularly in this variant automatically controls the flow control device 32, by means of the control signals C2 and C1, respectively, in a general manner so as to control the composition of the oxidizing gas GC.

[0097] More particularly, the control unit 7 automatically controls the recycling fan or compressor VR and the oxidizing gas supply unit 3 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 allow the transition from one operating mode (M1 or M2) to the other (M2 or M1).Operating Modes of the Combustion System

[0098] The combustion system of FIG. 1 can be configured by the control unit 7 to operate in at least two different main operating modes:

[0099] M1 (FIG. 2): an operating mode referred to as “conventional combustion” wherein the recycling fan or compressor VR is stopped and the valve V1 of the flow control device 32 is closed (F).

[0100] M2 (FIGS. 3 and 4): an operating mode referred to as “oxy-combustion with recycling” wherein the fan or recycling compressor VR operates and is controlled by the control unit 7 and the valve V1 of the flow control device 32 is opened (O).

[0101] The switching 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 switching from one operating mode (M1 or M2) to the other (M2 or M1) can advantageously be performed without stopping the combustion, and in particular without altering the combustion in the combustion device 1, and without stopping the combustion device 1.Operating Mode M1—“Conventional Combustion”—FIG. 2

[0102] In this operating mode, the dioxygen supply valve V1 has been closed (F) by the control unit 7 and the recycling fan or compressor VR is stopped.

[0103] The fan 10 (or compressor) of the combustion device 1 operates by imposing on the inlet of the combustion device 1 a flow rate Pec of oxidizing gas GC, which can vary.

[0104] The mixer 31 is not supplied with dioxygen from the source 30. The mixer 31 is supplied with only incoming air which is sucked in the bypass 6 from the open air and which is fed to the inlet of the mixer 31. Conventional combustion is thus carried out in the combustion system 1 by means of this incoming air used as oxidizing gas.

[0105] The combustion fumes FC, after being treated (FC′) through the treatment device 8, do not recirculate to the mixer 31 but are discharged to the open air in the atmosphere by being pushed by the fan (or compressor) 10 into the downstream portion 5b of the main discharge circuit 5.

[0106] 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 the operating mode M1 and which are opened by the control unit 7 in the operating mode M2 (recycling at least a part of combustion fumes). These dampers can also be manually operated.Operating Mode M2—Oxy-Combustion with Recycling—FIGS. 3 and 4

[0107] In this operating mode, the fan 10 (or compressor) of the combustion system operates by imposing on the input of the combustion device 1 a given flow rate (ØGc) of oxidizing gas GC which can vary.

[0108] The control unit 7 automatically controls the oxidizing gas supply unit 3, and in particular automatically controls the flow rate control device 32, depending on the dioxygen concentration measured in the oxidizing gas GC by the sensor 33 (signal S), so as to produce a gas having a suitable dioxygen level (e.g. set by a setpoint which is preferably configurable) as required or requested by the combustion.

[0109] 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, according to the pressure or the flow rate measured by the sensor 51.

[0110] In particular, the control unit 7 automatically controls the fan or recycling compressor VR, until the flow rate or the pressure measured by this sensor 51 reaches at least one predefined and preferably parameterizable operating setpoint, and automatically regulates the flow rate of this recycling fan or compressor VR in such a way 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.

[0111] This operating set point is set such that the flow rate of the recycle fan or compressor VR is smaller 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 to the mixer 31 at least a part FC2 of the combustion fumes, the other part FC1 being discharged to the open air in the atmosphere in the atmosphere via the downstream portion 5b of the main discharge circuit 5.

[0112] The lower the pressure or the flow rate measured by the sensor 51, and the higher the flow rate of the recycled combustion fumes FC2 towards the mixer 31.

[0113] In the operating mode M2 of this particular embodiment, if the flow rate of the recycling fan or compressor VR becomes, for example accidentally, higher than the flow rate of the combustion fumes (FC or FC′) upstream of the connection 40a of the recycling loop, in this case all of the combustion fumes are automatically and safely recycled (FC2=FC′) to the mixer 31, and no combustion smoke FC1 is discharged into the atmosphere, but on the contrary incoming air, from the ambient air, is automatically sucked in addition in the downstream part 5b of the main discharge circuit 5 and is fed 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 to the open air) of the main discharge circuit 5 is not changed.

[0114] In practice, this operating mode M2 comprises two operating phases:

[0115] a first operating phase referred to as “degraded oxy-combustion”, which is illustrated in FIG. 3.

[0116] a second operating phase referred to as “enhanced oxy-combustion” which is illustrated in FIG. 4Operation Phase of FIG. 3—“Degraded Oxy-Combustion”

[0117] As long as the recycling flow rate of the recycling fan or compressor VR is low enough, a part FC1 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 discharge circuit 5 and another part FC2 of the treated combustion fumes FC′ (after passing through the treatment device 8) is recycled in the recycle loop 40 to the inlet of the mixer 31.

[0118] The mixer 31 is supplied with dioxygen-rich gas from the source 30 (valve V1 opened) with a flow rate (φO2) and is supplied with the treated combustion fumes FC2 with a flow rate φ.

[0119] The mixer 31 is also supplied with air which is sucked into the ambient air, via the bypass 6, with a flow rate of air entering φAIR and which is fed 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, together with the combustion fumes FC2.In operation: φGC=φO<sub2>2< / sub2>+φ+φAIR

[0120] This operating phase lasts as long as the flow rate of the recycling fan or compressor VR is below a critical threshold.

[0121] In this operating phase, the oxidizing gas GC contains dioxygen from the dioxygen-rich gas supplied from the source 30, the treated and recycled combustion fumes FC2 (rich in CO2) and air.

[0122] In this operating phase, when the flow rate φO2 of dioxygen-rich gas at the inlet of the mixer 31 increases and / or when the flow rate φ of the treated and recycled combustion fumes FC2 at the inlet of the mixer 31 increases, the air flow rate φAIR sucked into the bypass 6 automatically decreases. Conversely, when the flow rate O2 of dioxygen-rich gas at the inlet of the mixer 31 decreases and / or when the flow rate φO2 of the treated and recycled fumes FC2 at the inlet of the mixer 31 decreases, the air flow rate φAIR sucked into the bypass 6 automatically increases.Operating Phase of FIG. 4—“Enhanced Oxy-Combustion”

[0123] The switching to this operating phase is automatically performed when the flow rate of the recycling fan or compressor VR passes above a critical threshold resulting in an inversion of gas flow in the bypass 6, air no longer being drawn into this bypass 6, but a part FC22 of the treated and recycled combustion fumes FC2 being automatically discharged into the bypass 6 and the remaining part FC21 of the treated and recycled combustion fumes FC2 being routed to the input of the mixer 31.

[0124] In this operation phase, the mixer 31 is supplied with dioxygen from the dioxygen-rich gas of source 30 (valve V1 opened) with a given flow rate (φO2) and is supplied with a flow rate φ1 with the part FC21 of the treated and recycled combustion fumes FC2; the other part FC22 of the treated and recycled combustion fumes FC2 is discharged into the bypass 6 with a flow rate φ2.In Operation:ϕ=ϕ1+ϕ2⁢ϕGC=ϕO2+ϕ⁢1

[0125] When the flow rate φO2 of dioxygen-rich gas at the inlet of the mixer 31 is increased, the flow rate φ1 of the recycled part FC21 of the combustion fumes FC2 automatically decreases and when the flow rate φO2 of dioxygen-rich gas at the inlet of the mixer 31 is decreased, the flow rate φ1 of the recycled part FC21 of the combustion fumes FC2 automatically increases.

[0126] The oxidizing gas GC thus contains dioxygen from the dioxygen-rich gas of the source 30 and the part FC21 of the combustion fumes FC2.

[0127] Transition from one operating phase to the other can easily and safely be controlled by the control unit 7 by automatically adjusting the flow rate of the recycling fan or compressor VR and advantageously without having to put the combustion device 1 off and without having to stop the combustion in the combustion device 1.

[0128] Preferably, in the operation mode M2, the control unit 7 automatically regulates the flow rate of dioxygen-rich gas (e.g. by closing more or less the valve V1) such that the concentration of dioxygen measured by the sensor 33 in the oxidizing gas GC is equal to or higher than a given operating setpoint or is within a given operating range. This allows the system to automatically adapt to flow rate φGC variations of oxidizing gas GC (imposed by the combusting device 1), and to automatically maintaining an appropriate concentration of dioxygen O2 in the oxidizing gas GC.

[0129] Especially, but by no means exclusively, the combustion system of FIG. 1 can be operated with a fuel C which, in the “enhanced oxy-combustion” operating phase, produces combustion fumes FC containing mainly carbon dioxide (CO2) and water vapor (H2O), and to a lesser extent molecular oxygen (O2) and carbon monoxide (CO).

[0130] Thus, in a non-limiting and non-exhaustive manner, the fuel C used in the combustion system of FIG. 1 may advantageously be a hydrocarbon of any type, and for example a conventional hydrocarbon derived from oil or natural gas, or an unconventional hydrocarbon derived from shale gas or oil, bituminous shales or sands, coal gas, biogas, syngas, etc.

[0131] For example, when the fuel C is a saturated hydrocarbon of the alkane type (CnH2n+2), the oxy-combustion reaction in the apparatus is, in a known manner:

[0132] The fuel can also especially be a solid or liquid fuel obtained through extraction (coal, wood, etc.) or can include waste (plastics, salvage materials, etc.)

[0133] Recycling the combustion gas containing CO2 to the inlet of the mixer 31 makes it possible, in a manner known per se, to better control the oxy-combustion reaction in the combustion device 1 and to significantly lower the combustion temperature in this combustion device 1, compared to an oxy-combustion reaction carried out solely or substantially using pure molecular oxygen as an oxidizer

[0134] The combustion system can advantageously operate without a limit of time in the operating mode M2 (oxy-combustion with recycling) and in said degraded oxy-combustion phase with a partial air input at least through the bypass 6 (and optionally through another secondary air inlet or a secondary oxidizing gas inlet directly connected to the combustion device 1), and a partial discharge in the atmosphere of a part FC1 of the combustion fumes FC (in the absence of a treatment device 8) or FC′ (with a treatment device), via the downstream part 5b of the main discharge circuit 5.

[0135] Preferably, when the combustion system has switched to the operating mode M2 (oxy-combustion with recycling), the control unit 7 automatically regulates the flow rate φO2 of dioxygen (e.g. in this particular case by closing more or less the progressive valve V1) using the measurement signal S of the dioxygen concentration in the oxidizing gas GC.

[0136] The transition from the operating mode M1 (conventional combustion) to the operating mode M2 (oxy-combustion with recycling) is simple and secure, the risks of untimely and uncontrolled rise in temperature of the combustion device 1 being avoided. The transition from the operating mode M1 (conventional combustion) to the operating mode M2 (oxy-combustion with recycling) advantageously does not require any intervention by the user on the combustion device 1 and above all does not require the combustion to be stopped.

[0137] The transition from the operating mode M1 to the operating mode M2 (oxy-combustion with recycling), in the degraded oxy-combustion phase or in the enhanced oxy-combustion operating phase, can be requested to the control unit 7, at the initiative of the user of the combustion system, by means for example of a manual control for changing operating mode.

[0138] The transition from the operating mode M1 to the operating mode M2 can also be implemented when starting the combustion system for the purpose of operating the combustion system in the oxy-combustion with recycling mode (M2).Procedure for Starting Up the Combustion System

[0139] When a user seeks to start up the combustion system in order to operate it in “oxy-combustion with recycling” mode (M2), the user requests the control unit 7, by means of an appropriate command, to execute a start-up procedure.

[0140] The control unit 7 executes this start-up procedure by initially configuring the combustion system in operating mode M1 (“conventional combustion”).

[0141] The combustion device 1 is then started, especially by activating 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 makes it possible initially to operate the system in conventional combustion mode (M1)

[0142] Subsequently, in a second step, the control unit 7 controls the combustion system, so as to automatically switch to “oxy-combustion with recycling” mode (M2), as previously described, by choosing the operating phase referred to as “degraded oxy-combustion” or the operating phase referred to as “enhanced oxy-combustion”.

[0143] Such a start-up phase is advantageously simple and safe. In particular, compared with a combustion system of the prior art that is adapted to operate solely in enhanced oxy-combustion mode, with recycling of the combustion fumes, the risks of uncontrolled and untimely temperature rise, which are inherent in this type of apparatus of the prior art due to a high initial concentration of molecular oxygen in the oxidizing gas and a low initial concentration of CO2, are avoided during the start-up phase.Example of Control of the Combustion System to Switch from the Operating Mode M2 (“Oxy-Combustion with Recycling”) to the Operating Mode M1 (“Conventional Combustion”)

[0144] It is assumed that the combustion system is configured in the operating mode M2 (“oxy-combustion with recycling”).

[0145] The combustion device 1 is in operation, the recycle fan or compressor VR operates and the fan 10 (or compressor) of the combustion device 1 operates and imposes a given flow rate (φGC) of oxidizing gas GC consisting of air at the inlet of the combustion device 1.

[0146] To switch from this operating mode M2 (“oxy-combustion with recycling”) to the operating mode M1 (“conventional combustion”), it is sufficient for the control unit 7 to control the slowing down of the fan or the recycling compressor VR until the fan or the recycling compressor VR has stopped, and then to control the closing of the valve V1.

[0147] The transition from the operating mode M2 (“oxy-combustion with recycling”) to the operating mode M1 (“conventional combustion”) is simple, fast and secure, avoiding the risks of an uncontrolled and untimely temperature rise in the combustion device 1. The transition from the operating mode M2 (“oxy-combustion with recycling”) to the operating mode M1 (“conventional combustion”) advantageously does not require any intervention by the user on the combustion device 1 and above all does not require the combustion to be stopped.

[0148] The switch from the operating mode M2 to the operating mode M1 can be requested from the control unit 7, at the initiative of the user of the combustion system, by means of a manual command to switch operating mode, for example.

[0149] The switch from the operating mode M2 to the operating mode M1 can also be implemented during a procedure for shutting down the operation of the combustion systemProcedure for Shutting Down the Combustion System

[0150] When a user wishes to stop the combustion system while the combustion system is operating in “oxy-combustion with recycling” (M2), the user requests the control unit 7, by means of appropriate command, to execute a stop procedure.

[0151] The control unit 7 executes this shutting down procedure by controlling the deceleration of the recycling fan or compressor VR until it is stopped, as previously described, and then by controlling the closing of the valve V1 of the dioxygen-rich gas flow rate control device 32 to switch from the operating mode M2 to the operating mode M1.

[0152] Once the combustion system is configured in this operating mode M1 (“conventional oxy-combustion”), the combustion device 1 can be shut down conventionally without incurring any risk.

[0153] Such a shut-down phase is advantageously simple and safe. In particular, compared with a combustion system of the prior art that is adapted to operate solely in oxy-combustion with recycling of the combustion gas, the risks of uncontrolled and untimely temperature rise, which are inherent in this type of apparatus of the prior art, are avoided during the shut-down phase

[0154] The switch from the operating mode M2 to the operating mode M1 can also be implemented when the concentration of molecular oxygen (supplied by the source 30) in the oxidizing gas GC becomes insufficient and no longer allows enhanced oxy-combustion with recycling of the combustion gas.

[0155] This insufficiency may have several, possibly cumulative, causes.

[0156] It may happen, for example, that during operation of the combustion system in the operating mode M2 (“oxy-combustion with recycling”), and especially in the “enhanced oxy-combustion” operating phase, an accidental interruption of the dioxygen supply occurs, for example due to an untimely halting of the in-situ production of dioxygen-rich gas by the source 30 or a source 30 of dioxygen-rich gas that is empty.

[0157] It may happen, for example, that during operation of the combustion system in the operating mode M2 (“oxy-combustion with recycling”), and especially in the “enhanced oxy-combustion” operating phase, the dioxygen supply decreases too significantly, for example as a result of an untimely slowdown of the in-situ production of dioxygen-rich gas by the source 30 or an excessively low pressure in the source 30.

[0158] It may happen, for example, that during operation of the combustion system in the operating mode M2 (“oxy-combustion with recycling”), and especially in the “enhanced oxy-combustion” operating phase, the combustion device 1 is called upon to supply more thermal energy, and in response increases the flow rate φGC (increasing the flow rate of the fan or compressor 10) of oxidizing gas GC. In this case, the remaining oxidizing gas is automatically injected through the bypass 6.

[0159] If the combustion device 1 reduces the supply of thermal energy, which results in a reduction in the need for the oxidizing gas GC, the surplus oxidizing gas is discharged via the bypass 6, and the control system 7 adjusts the valve V1, if necessary, in order to reduce the injection of dioxygen into the mixer 31.

[0160] In a conventional apparatus able to operate only in oxy-combustion, with recycling of the combustion gas, an excessive drop in the concentration of dioxygen in the oxidizing gas GC can lead to an untimely halting of the oxy-combustion.

[0161] Such an untimely halting can advantageously be avoided by means of the combustion system of the invention.

[0162] To this end, the control unit 7 is preferably designed to monitor, by means of the sensor 33, the concentration of molecular oxygen in the oxidizing gas GC, and when the concentration of dioxygen decreases, to automatically detect whether this concentration of dioxygen reaches a predefined and preferably parameterizable critical minimum threshold, and if so, to automatically control the combustion system, so as to switch it (as previously described) safely to the operating mode M1 (“conventional combustion”), without halting combustion in the combustion device 1.Combustion System of FIG. 1 / CO2 Capture

[0163] In the particular variant of FIG. 1, but optionally, the combustion system advantageously comprises a carbon dioxide (CO2) capture device 11 connected to the bypass 6 and adapted to capture carbon dioxide (CO2) in at least part of the outgoing recycled combustion fumes (FC22 / FIG. 4) circulating in said bypass 6.

[0164] More particularly, this capture device 11 comprises a fan or compressor 110 which can be used to suck a part of outgoing recycled combustion fumes (FC22 / FIG. 4) circulating in the bypass 6 and to supply a CO2 capture unit 111 (known per se).

[0165] Preferably, this capture device 11 and in particular the fan or compressor 110, is automatically controlled (by the control unit 7 by means of the control signal C3) or by another control unit) according to the pressure or the flow rate of the outgoing combustion fumes circulating in the bypass 6, this pressure or this flow rate being measured by a sensor 60 delivering a measurement signal S60.

[0166] Other non-exhaustive examples of combustion system in accordance with the invention and operable in the operating modes M1 (conventional combustion) and M2 (“oxy-combustion with recycling”) will now be described.Combustion System of FIG. 5 to FIG. 8

[0167] The combustion system of FIG. 5 differs from that of FIG. 1 in that the connection 40a of the recycling loop 40 with the main discharge 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, i.e. between the recycling fan or compressor VR and the connection 40a of the recycling loop 40 with the main discharge circuit 5.

[0168] Alternatively, the additional treating device 8′ may be mounted on the recycling loop 40 downstream of the VR recycling fan or compressor.

[0169] The treatment device 8 can be adapted to depollute the non-recycled combustion fumes, before being discharged into the ambient air and preferably to capture one or more pollutants selected from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOC. The treatment device 8′ is preferably adapted to at least dehumidify the recycled combustion fumes in the recycling loop 40 and more particularly comprises at least one condenser or several cascade condensers.

[0170] The explanations given above on the operating modes M1 and M2 and on the control by the control unit 7 of the recycling fan or compressor VR and the oxidizing gas supply unit 3 are repeatable for this variant of FIG. 5.

[0171] With reference to FIG. 6 and as for the variant of FIG. 2, in the operating mode M1 (“conventional combustion”), the oxidizing gas GC is constituted by the air drawn in by the bypass 6 (the valve V1 being closed and the fan or recycle compressor VR being stopped) and all the combustion fumes FC are treated by passing into the treating device 8 and are discharged (FC′) into the ambient air.

[0172] With reference to FIG. 7 and in a manner comparable to the variant of FIG. 3, in operating mode M2 (“oxy-combustion with recycling”) and in the “degraded oxy-combustion” operating phase, the recycling fan or compressor VR operates and the valve V1 is opened; a part FC1 of the combustion fumes FC is discharged into the ambient air after being treated (treatment device 8) and the other part FC2 of the combustion fumes FC is recycled in the recycling loop 40 to the input of the mixer 31 by having been previously treated in the treatment device 8′. Air is also drawn into the bypass 6 and also supplies the mixer 31. The other inlet of the mixer 31 is supplied with dioxygen from the dioxygen-rich gas of the source 30 (valve V1 opened) with a given flow rate (Ø02).

[0173] With reference to FIG. 8 and in a manner comparable to the variant of FIG. 4, in operating mode M2 (“oxy-combustion with recycling”) and in the enhanced oxy-combustion operating phase, the recycling fan or compressor VR operates and the valve V1 is opened. A part FC1 of the combustion fumes FC is discharged into the ambient air after being treated (treatment device 8) and the other part FC2 of the combustion fumes FC is recycled to the recycling loop 40 and is treated in the treatment device 8′. An inlet of the mixer 31 is fed with a flow rate φ1 with a part FC21 of the recycled and treated fumes FC2, the other part FC22 of the recycled and treated fumes FC2 being discharged into the bypass 6 with a flow rate ¢2.

[0174] The other inlet of the mixer 31 is supplied with dioxygen from the dioxygen-rich gas of the source 30 (valve V1 opened) with a given flow rate (φO2).Combustion System of FIG. 9—Condenser 34 Downstream of Mixer 31

[0175] The combustion system of FIG. 9 differs from that of FIG. 1 in that a condenser 34 has been added. This condenser 34 is supplied 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.

[0176] In this variant, when the combustion system is in operation mode M2 (“oxy-combustion with recycling”), the combustion fumes FC are recycled to the mixer 31 without necessarily having been dehumidified in the treatment device 8, a dehumidification being performed at least by the condenser 34.

[0177] In another variant, the condenser 34 could mounted as a bypass-like the treatment device 8 of FIG. 12.Combustion System of FIG. 10

[0178] The combustion system of FIG. 10 differs from that of FIG. 1 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 the pressure measured at least by said sensor 60 (and no longer by the sensor 51 as in the variant of FIG. 1) during at least the operating mode M2 with recycling of at least part of the combustion fumes.

[0179] The higher the pressure or the flow rate measured by the sensor 60, and the higher the flow rate of the recycled combustion fumes FC2 in the recycling loop 40

[0180] 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 parameterizable operating setpoint, and automatically regulates the flow rate of the recycling fan or compressor VR so as to maintain said measured pressure or flow rate at this operating setpoint or in the vicinity of this operating setpoint.

[0181] This operation set point is set such that the flow rate of the recycling fan or compressor VR is smaller 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 to the mixer 31 at least a part FC2 of the combustion fumes, the other part FC1 being discharged to the open air in the atmosphere via the downstream part 5b of the main discharge circuit 5.

[0182] The explanations that have been previously given on the operation of the combustion system of FIG. 1 are transposable to the combustion system of FIG. 7.

[0183] In the particular variant of FIG. 10, but optionally, the combustion system advantageously comprises a carbon dioxide (CO2) capture device 11′ connected to the downstream portion 5b of the main discharge circuit 5 and adapted to capture carbon dioxide (CO2) in at least part of the outgoing combustion fumes FC1.

[0184] More particularly, this capture device comprises a fan or compressor 110 which can be used to suck a part of combustion fumes FC circulating in the downstream part 5b of the main discharge 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 automatically controlled (by the control unit 7 or by another control unit) depending on the pressure or flow rate of the combustion fumes circulating in the downstream portion 5b of the main discharge circuit 5, said pressure or said flow rate being measured by the sensor 51.Combustion System of FIG. 11

[0185] The combustion system of FIG. 11 differs from that of FIG. 10 in that, in a manner comparable to FIG. 5, the connection 40a of the recycling loop 40 with the main discharge 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, i.e. between the recycling fan or compressor VR and the connection 40a of the recycling loop 40 with the main discharge circuit 5.Combustion System of FIG. 12—Treatment Device 8 in Bypass Mode

[0186] The combustion system of FIG. 12 differs from that of FIG. 1 in that the treatment device 8 is mounted as bypass on the main discharge circuit.

[0187] This type of mounting is suitable in a known manner for the treatment devices 8, which have their own fan or compressor, such as for example the one described later with reference to FIG. 14. The explanations that were previously given on the operation of the combustion system of FIG. 1 also apply to this combustion system of FIG. 12.

[0188] In the variants of FIGS. 5, 9, 10, 11, 13, the treatment device 8 or 8′ can also be mounted as a bypass (“bypass”)Combustion System of FIG. 13—CO2 Injection on Start-Up

[0189] The combustion system of FIG. 13 differs from that of FIG. 1 in that it comprises an additional device 12 connected to an inlet of the mixer 31 for injecting carbon dioxide gas (CO2) into the mixer 31 during the “degraded oxy-combustion” transitional phase when switching from the second operating mode M2 in the “degraded oxy-combustion” phase to the second operating mode M2 in the “enhanced oxy-combustion” phase, in order to shorten the duration of this transitional phase.

[0190] This CO2 injection device 12 comprises, for example, a source 120 of pressurized CO2 gas associated with a valve 121 controlled by the control unit 7 by means of a control signal C4.

[0191] This CO2 injection device 12 can also be added to the combustion system of FIGS. 5, 9, 10, 11, 12.Specific Example of a Condenser—FIG. 14

[0192] As a non-limiting example of the invention, FIG. 14 depicts a preferred example of a condenser that can be used as a condenser in treatment device 8 or 8′ of a combustion system of the invention.

[0193] This condenser comprises an exchanger 12, which includes an enclosure 120 containing a bath 121 of coolant 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 coolant liquid L.

[0194] The coolant liquid L may simply be water or an aqueous solution.

[0195] 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 coolant liquid L and comprises a discharge opening 123e immersed in the bath 121 of coolant liquid L.

[0196] In operation, the fan or compressor 123f makes it possible to draw in the gaseous fluid F to be dehumidified and to introduce it into the injection duct 123 via the inlet opening 123b. This gaseous fluid F escapes from the injection duct 123 via the discharge opening 123e, and is thereby introduced forcibly into the bath 121 of coolant liquid L, below the surface of the bath 121 of coolant liquid L, rises to the surface of the bath of liquid, and escapes from the enclosure 120 via the discharge opening 120a of the enclosure 120 after having been dehumidified in the form of a dehumidified gas F′.

[0197] The temperature TL of the coolant liquid L is always less than the temperature TF of the gaseous fluid F at the inlet of the exchanger 12 and is preferably less than the dew temperature (dew point) of the gaseous fluid F.

[0198] It is noted that the absolute humidity (gwater / kgdry 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 that volume expressed in kilograms. Its value remains constant even if the temperature of the gas varies, though while remaining greater than the dew point of the gas.

[0199] While passing through the bath 121 of coolant liquid L, the gaseous fluid F undergoes condensation when in contact with the coolant liquid L, so that the absolute humidity of the gas F′, at the outlet of the exchanger 12, is less than the absolute humidity of the gaseous fluid F at the inlet of the exchanger 12.

[0200] The difference between the absolute humidity of the dehumidified gas F′ and the absolute humidity of the incoming gaseous fluid F depends especially on the difference between the temperature TF of the incoming gaseous fluid F and the lower temperature TL of the coolant liquid L. The greater the temperature difference ΔT (ΔT=TF−TL) between the temperature TF of the incoming gaseous fluid F and the temperature TL of the coolant liquid L, the lower the absolute humidity of the dehumidified gas F′ is compared to the absolute humidity of the incoming gaseous fluid F.

[0201] In another alternative, the fan or compressor 123f can be connected to the injection duct 123 and used to introduce the gaseous fluid F into this injection duct 123 by blowing it through the intake opening 123b of this injection duct 123.

[0202] In particular, the exchanger 12 can be coupled to a heat pump (not shown), which makes it possible to renew the liquid L in the bath by extracting heat energy from it so as to maintain the temperature of this liquid at a sufficiently low level.

[0203] In another alternative embodiment, the condenser may comprise a plurality of exchangers 12 mounted one after another.

[0204] The invention is not limited to the use of an exchanger 12 of the type of FIG. 14. In other alternative embodiments, the exchanger 12 for the condensation of the gaseous fluid F may for example be of the type described in international patent application WO 2016 / 071648 or in international patent application WO 2020 / 030419 or may be an exchanger operating by spraying the coolant liquid L so that it comes into contact with the gaseous fluid F.

[0205] The invention is not limited to an exchanger operating with a coolant liquid, but can be implemented with any other known type of exchanger enabling dehumidification of a gaseous fluid.Advantage of Using Dioxygen-Rich Gas Combined with Recirculation of at Least One Fraction of the Combustion Fumes

[0206] In the case of conventional combustion, for an amount Qd of fuel C to be burned per hour, a flow rate D of oxidizing air is used at the inlet to the combustion device. After combustion, combustion fumes are discharged at a flow rate of X. These fumes must be treated to comply with discharge standards for dust and chemicals. The larger X, the higher the cost of treating the combustion fumes.

[0207] In conventional combustion, the flow rate of air D (D<X) at the inlet to the combustion device is defined according to the oxygen needs for combustion and the management of the combustion device (e.g. flame management in the combustion chamber).

[0208] In conventional combustion, the combustion fumes contain:

[0209] nitrogen dioxide (N2) with almost the same content by mass as the oxidizing air,

[0210] carbon dioxide (CO2) resulting from combustion,

[0211] water from the combustion and, where applicable, from the evaporation of water that may be contained in the fuel (e.g. when the fuel consists of waste or coal) and water resulting from the oxidizing air,

[0212] molecular oxygen (O2) that did not participate in the combustion

[0213] pollutants, depending on the fuel used, which may include fine particles, acids, NOx, SOx, heavy metals, dioxins, etc.

[0214] When the combustion system of the invention operates in “oxy-combustion” mode as previously described (addition of dioxygen-rich gas containing at least 40% O2 with recirculation of a fraction of the combustion fumes), the flow rate of combustion fumes exiting the combustion device which are not recycled and which are discharged directly into the atmosphere and / or which are treated (e.g. for CO2 capture) before discharge into the atmosphere is advantageously lower than the above-mentioned flow rate X.

[0215] The greater the fraction of O2 in the molecular-oxygen-rich gas supplied by the source 30, the lower the flow rate of the combustion fumes that are not recycled and are discharged.

[0216] For example, when the dioxygen-rich gas is pure molecular oxygen, 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 that is advantageously lower and may be of the order of 1 / 11 of X, either directly into the atmosphere, or by previously treating them, for example in order to capture the CO2, before discharging them into the atmosphere and / or by removing pollution from them.

[0217] In another alternative 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 dioxygen-rich gas. This will simply have an effect on the above-mentioned coefficient of 11, which in this case will be between 1 and 11 depending on the additional air flow injected into the combustion via said additional air inlet.

[0218] When the dioxygen-rich gas contains 90% molecular oxygen, it is possible in practice to recycle the combustion fumes with a high recycling rate of up to 9 / 10 of X and to discharge the rest of the combustion fumes, with a flow rate that is advantageously lower and may be of the order of 1 / 10 of X, either directly into the atmosphere, or by previously treating them, for example in order to capture the CO2, before discharging them into the atmosphere and / or by removing the pollution from them, etc.

[0219] It should be emphasized that the constraints on the pollution of the oxidizing gas entering the combustion device are less than the environmental constraints linked to the pollution of non-recycled combustion fumes, which are increasingly stringent. According to the case, the recycled combustion fumes may therefore be left untreated, or the recycled combustion fumes may be treated before entering the mixer, which is “light” and much less costly than treating the non-recycled fumes. The total cost of treating the combustion fumes can therefore advantageously be significantly reduced.

[0220] In return for this significant reduction in the cost of treating the combustion fumes, the production of dioxygen-rich gas incurs an additional operating cost, which in practice increases with the fraction of O2 in the dioxygen-rich gas, but which in practice remains significantly lower than the cost of treating the combustion fumes. It is therefore up to the skilled person to adapt and find a compromise on a case-by-case basis between the cost of producing gas that is more or less dioxygen-rich and the cost of treating the combustion fumes.

[0221] In the context of the invention, the dioxygen-rich gas contains at least 40% molecular oxygen (below this threshold, the reduction in the flow rate of non-recycled combustion fumes is too small in practice). Preferably, the fraction of molecular oxygen gas in the dioxygen-rich gas is at least 80%, more preferably at least 90%. More particularly, the dioxygen-rich gas is advantageously pure molecular oxygen gas or near-pure molecular oxygen gas (at least 99% O2).

[0222] An exemplary aspect of the present disclosure proposes 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 drawbacks inherent in the oxy-combustion apparatuses of the prior art that implement such a recycling of the combustion fumes.

[0223] Although the present disclosure has been described with reference to one or more examples, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure and / or the appended claims.

Claims

1. A combustion system comprising:a combustion device for combusting a fuel by using at least one oxidizing gas and which comprises an outlet through which combustion fumes can be discharged;a supply unit for supplying oxidizing gas and which is connected to the combustion device for supplying the combustion device with oxidizing gas, said oxidizing gas supply unit comprising a mixer and a gaseous dioxygen source which supplies a dioxygen-rich gas and which is connected to a first inlet of the mixer;a main discharge circuit connected to the outlet of the combustion device and opening to open air;a recycler which comprise a recycling loop between the main discharge 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 discharge circuit;a bypass which is connected to the recycling loop downstream of the recycling fan or compressor and which opens to the open air so as to at least be able to supply the mixer with air entering the bypass; anda control unit adapted to control at least the recycling fan or compressor.

2. The combustion system according to claim 1, further comprising at least one sensor which is adapted to at least measure a flow rate or pressure of outgoing gaseous fluid in a downstream portion of the main discharge circuit located downstream of the connection of the recycling loop with the main discharge circuit and which outputs a pressure or flow measurement signal processed by the control unit.

3. The combustion system according to claim 1, further comprising at least one sensor that is adapted to at least measure a flow rate or pressure of outgoing gaseous fluid in the bypass, and that outputs a pressure or flow measurement signal processed by the control unit.

4. The combustion system according to claim 2, wherein 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 wherein at least part of the combustion fumes is recycled.

5. The combustion system according to claim 1, wherein the control unit is adapted to control the recycling fan or compressor so as to enable to configure the combustion system in an operating mode selected from at least two different operating modes and to be able to switch from one operating mode to the other, the at least two different operating modes comprising: a first operating mode in which the recycling fan or compressor is stopped and the mixer is not supplied with dioxygen-rich gas from the gaseous dioxygen source and is supplied with air entering the bypass, and a second operating mode, in which the recycling fan or compressor operates, and the mixer is supplied at least with dioxygen-rich gas supplied from the gaseous dioxygen source and with at least a portion of the combustion fumes discharged from the combustion device.

6. The combustion system of claim 1, wherein the gaseous dioxygen source is connected to said first inlet of the mixer via a flow control device for controlling the flow rate of the dioxygen-rich gas, which is controlled by the control unit.

7. The combustion system according to claim 6, wherein the flow control device comprises a flow-control valve which is controlled by the control unit and the flow-control valve is a progressive opening valve and a progressive closing valve.

8. The combustion system according to claim 6, wherein the control unit is adapted to control at least the recycling fan or compressor, and the flow control device for controlling the flow rate of the dioxygen-rich gas, so as to be able to switch from one operating mode to another without stopping the combustion in the combustion device.

9. The combustion system according to claim 1, comprising at least one sensor adapted to measure the dioxygen concentration in the oxidizing gas and wherein:wherein the gaseous dioxygen source is connected to said first inlet of the mixer via a flow control device for controlling a flow rate of the dioxygen-rich gas; andthe control unit is adapted to control the flow control device for controlling flow rate of the dioxygen-rich gas as a function of a dioxygen concentration measured by said sensor at least during an operating mode wherein at least part of the combustion fumes is recycled.

10. The combustion system according to claim 1, wherein the combustion device comprises a fan or compressor adapted to supply the combustion device with oxidizing gas at a given flow rate.

11. The combustion system according to claim 1, wherein a rate of supply of fuel to the combustion device is variable and the combustion device comprises a fan or compressor adapted to supply the combustion device with oxidizing gas at a rate (φGC), which varies according to the rate of supply of fuel to the combustion device.

12. The combustion system according to claim 1, comprising a device for treating combustion fumes which is mounted on the main discharge circuit.

13. The combustion system according to claim 1, comprising a treatment device for treating the recycled combustion fumes which is mounted on the recycling loop between the recycling fan or compressor and the connection of the recycling loop with the main discharge circuit.

14. The combustion system according to claim 12, wherein the treatment device is adapted to dehumidify the combustion fumes.

15. The combustion system of claim 14, wherein the treatment device comprises a condenser.

16. The combustion system of claim 15, wherein the condenser comprises at least one exchanger comprising a coolant liquid.

17. The combustion system according to claim 16, wherein the exchanger comprises a bath of coolant liquid, and an injector for passing the gaseous fluid to be dehumidified through the coolant liquid bath.

18. The combustion system according to claim 12, wherein the treatment device is adapted to depollute the combustion fumes and more particularly to capture one or more pollutants selected from the following list: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs.

19. The combustion system according to claim 1, comprising at least one sensor adapted to measure a concentration of dioxygen in the oxidizing gas and wherein:wherein the gaseous dioxygen source is connected to said first inlet of the mixer via a flow control device for controlling a flow rate of the dioxygen-rich gas; andthe control unit is adapted to control the flow control device for controlling the flow rate of the dioxygen-rich gas and the recycling fan or compressor, according to the measured concentration of dioxygen in the oxidizing gas, and so as to switch from an operating mode wherein at least a portion of the combustion fumes is recycled to an operating mode wherein the combustion fumes are not recycled.

20. The combustion system according to claim 1, comprising a device for capturing carbon dioxide, which is connected to the bypass and which is adapted to capture carbon dioxide in at least part of the outgoing recycled combustion fumes discharged via said bypass and / or comprising a device for capturing carbon dioxide, which is connected to a downstream part of the main discharge circuit located downstream of the connection of the recycling loop with the main discharge circuit and which is adapted to capture carbon dioxide in at least part of the outgoing non-recycled combustion fumes discharged via said downstream part of the main discharge circuit.

21. The combustion system of claim 1, wherein the dioxygen-rich gas supplied by the gaseous dioxygen source comprises at least 50% dioxygen.

22. The combustion system according to claim 1, wherein the dioxygen-rich gas supplied from the gaseous dioxygen source is pure dioxygen or near-pure dioxygen.

23. The combustion system according to claim 1, comprising a carbon dioxide injection device connected to an inlet of the mixer and adapted to inject carbon dioxide gas into the mixer during a particular phase of the operating mode wherein the combustion fumes are recycled.

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