A combustion system capable of operating with recycle of combustion gas

Abstract

The combustion system includes a bypass (6) that opens to ambient air during two different operating modes (M1 “conventional combustion”; M2 “oxy-fuel combustion”), the bypass (6) having the function of introducing air into the recycle loop (40) when the discharge valve (V3) is at least partially open and the recycle valve (V2) is open or closed, and discharging an excess (G2) of the combustion gas (G) generated by the combustion device (1) from the recycle loop (40) and supplying another fraction (G1) of the combustion gas (G) generated by the combustion device (1) to the mixer (31) when the discharge valve (V3) is closed and the recycle valve (V2) is open.

Description

Technical Field

[0001] The present invention relates to the field of combustion having at least partial recycle of combustion gas.

Background Art

[0002] So-called "conventional" combustion consists of mixing fuel with air (oxidant) in a combustion device (furnace, boiler, etc.) under high temperature conditions to create oxidation. The reaction is exothermic and self-sustaining. Air contains 21% molecular oxygen (O2), and the volume of air used is controlled so that the amount of molecular oxygen is sufficient for combustion.

[0003] In conventional combustion, combustion flue gas contains water vapor (H2O) and combustion products (mainly molecular nitrogen (N2) and carbon dioxide (CO2)) in the gas phase.

[0004] As used herein, the term "combustion gas" refers to the gas-phase combustion products released after combustion.

[0005] If it is desired to capture CO2 from these combustion flue gases, it is easy to remove water vapor by condensing these combustion flue gases and collecting liquid water. On the other hand, the main difficulty lies in separating nitrogen and carbon dioxide. Furthermore, in conventional combustion, depending on the type of fuel used, the combustion gas also contains more or less other polluting combustion products in the gas phase, such as SOx (sulfur oxides), NOx (nitrogen oxides), HCl (hydrogen chloride), HF (hydrogen fluoride), etc. As a result, if it is desired to capture CO2 from these combustion flue gases, it is necessary to separate these other pollutants.

[0006] Several solutions can be considered for capturing CO2 from the flue gas from conventional combustion, but their costs remain extremely high.

[0007] In order to reduce the release of pollutants in combustion flue gas, it is known to replace the above-described conventional combustion with a combustion called "oxy-fuel combustion", in which air (oxidant) is replaced with molecular oxygen in stoichiometric proportion, and the number of oxygen atoms is equal to that required to oxidize all the atoms of the fuel.

[0008] The production of molecular oxygen for carrying out oxy-fuel combustion can be obtained by known methods such as, for example, by cyclo-generation or by electrolysis of water.

[0009] For example, in the case of oxy-fuel combustion of methane (CH4), combustion flue gas consisting of a volume ratio of 1 / 3 CO2 and 2 / 3 water vapor in the gas phase is produced. In the case of other fuels, there will also be pollutants generated from combustion such as HCl, SOx, etc. If the fuel does not contain nitrogen, advantageously, the flue gas will, of course, not contain NOx.

[0010] The chemical reaction formula for the oxy-fuel combustion of methane (CH4) is as follows: JPEG2025519550000002.jpg12166

[0011] This means that each mole of CH4 generates 891 kJ of energy externally.

[0012] For other fuels, the reaction is similar, and if the fuel contains atoms other than carbon and hydrogen, other compounds will appear.

[0013] For example, in the case of oxy-fuel combustion of methane, it is extremely easy to capture CO2. For this purpose, in order to obtain CO2 in the gas phase, it is sufficient to condense the water in the combustion flue gas by a cooling or drying process.

[0014] Therefore, it is currently known to install a condensing device for condensing oxy-fuel combustion flue gas in order to facilitate the capture of CO2.

[0015] However, a significant difficulty in oxygen combustion lies in the difficulty of combustion control. This is because, unlike conventional combustion, the oxygen combustion temperature can rapidly and uncontrollably bring the combustion chamber to an extremely high level that conventional combustion devices cannot withstand.

[0016] To overcome this difficulty, devices have already been proposed that can improve oxygen combustion by condensing and recycling at least a part of the combustion gas essentially containing CO2 in the gas phase, mixing them with molecular oxygen to obtain an oxidizing gas (O2-CO2), and advantageously reducing the combustion temperature.

[0017] This improvement enables molecular oxygen-based oxygen combustion with a more easily controlled recycling of the combustion gas compared to oxygen combustion using only molecular oxygen as an oxidant, while reducing pollutant emissions compared to conventional combustion and facilitating CO2 capture.

[0018] These devices are intended to operate only in oxygen combustion with combustion gas recycling, which has a number of drawbacks.

[0019] The start-up and shutdown procedures for these devices are important and dangerous operating steps that can lead in a harmful way to an uncontrollably high temperature in the combustion chamber during oxygen combustion with combustion gas recycling.

[0020] During oxygen combustion with combustion gas recycling, an excessive decrease in the concentration of molecular oxygen in the oxidizing gas can lead in a harmful way to a sudden stop of combustion in the combustion chamber of the device, which can have serious consequences, for example, in an industrial manufacturing chain that uses the generated thermal energy.

[0021] International Patent Application WO2011 / 148298 also proposed a combustion system that recycles combustion gas by a fan mounted on the recycle loop. This combustion system can operate either in conventional combustion with air supply or in oxygen combustion with molecular oxygen supply and without air supply, and in both cases the fan mounted on the recycle loop operates. This publication further describes the installation of a control unit, which is programmed to control the air supply ratio and the molecular oxygen supply ratio during the transition period so that it can switch from conventional combustion with air supply to oxygen combustion with molecular oxygen supply and without air supply without interrupting the combustion process.

[0022] When the combustion system described in this publication operates in the oxygen combustion mode, a malfunction of the molecular oxygen source can cause, for example, a sudden uncontrolled decrease in the concentration of molecular oxygen in the oxidizing gas supplied to the combustion chamber. This defect in molecular oxygen can have multiple possible cumulative causes (an unexpected interruption of the supply of molecular oxygen due to a sudden stop of on-site molecular oxygen generation or depletion of the source of molecular oxygen; or a sudden decrease in the flow rate or pressure of the molecular oxygen supply). However, an excessive decrease in the concentration of molecular oxygen in the oxidizing gas can lead in a harmful way to a sudden stop of oxygen combustion.

[0023] The technical solution described in International Patent Application WO2011 / 148298 has the drawback that it cannot automatically adapt its operation in case of a sudden defect in molecular oxygen.

[0024] Furthermore, in the above-described combustion system, when trying to apply pressure to the combustion chamber to provide more thermal energy during oxygen combustion, there is a problem that an uncontrollably high temperature is reached in the combustion chamber, posing a risk of explosion. Conversely, when trying to reduce the amount of thermal energy from the combustion chamber during oxygen combustion, there is a risk of causing a sudden stop of combustion. Summary of the Invention Problems to be Solved by the Invention

[0025] The main object of the present invention is to propose a combustion system that can operate with at least partial recycling of combustion gas and can overcome all or some of the above-mentioned drawbacks inherent in prior art oxy-fuel combustion devices that implement recycling of combustion gas.

Means for Solving the Problem

[0026] That is, the present invention relates to a combustion device for the combustion of fuel with at least one oxidizing gas, an oxidizing gas supply unit connected to the combustion device, the oxidizing gas supply unit including a mixer and a source of molecular oxygen-rich gas connected to a first inlet of the mixer via a device for supplying and controlling the flow rate of the molecular oxygen-rich gas, a recycling means including a recycling loop between the combustion device and a second inlet of the mixer and a recycling valve mounted on the recycling loop, a first bypass of the recycling loop including a discharge valve, a second bypass of the recycling loop downstream of the first bypass and the recycling valve, and a control unit. The control unit can set the combustion system to an operating mode selected from at least two different operating modes (M1; M2) and can switch from one operating mode to another, and can control the device for controlling the flow rate of the molecular oxygen-rich gas, the recycling valve, and the discharge valve. In the first operating mode (M1), the recycling valve is closed, the discharge valve is open, the mixer is not supplied with molecular oxygen-rich gas from the source of molecular oxygen gas (the device for controlling the flow rate is closed), and in the second operating mode, the recycling valve is open, the discharge valve is at least partially open or closed, and the mixer is supplied with at least the molecular oxygen-rich gas supplied by the source of molecular oxygen gas and at least a part of the combustion gas generated by the combustion device (the device for controlling the flow rate is open).

[0027] The second bypass is open to ambient air during both operating modes (M1; M2), and on the one hand, in the two operating modes (M1; M2), the second bypass allows air to enter the recycle loop and at least incoming air to be supplied to the second inlet of the mixer when the discharge valve is at least partially open and the recycle valve is closed or open. On the other hand, in the second operating mode, the second bypass has the function of allowing an excess of the combustion gas generated by the combustion device to be discharged from the recycle loop and another fraction of the combustion gas generated by the combustion device to be supplied to the second inlet of the mixer when the discharge valve is closed and the recycle valve is open.

[0028] The term "molecular oxygen-rich gas" means that the gas contains at least 40% (by volume) of molecular oxygen.

[0029] In the first operating mode (M1), the mixer is supplied with at least air led in from the ambient air via the second bypass, and the combustion smoke discharged by the combustion device is discharged via the first bypass without being recycled.

[0030] As a result, the oxidizing gas contains at least air and does not contain molecular oxygen from a source of molecular oxygen gas. Therefore, the combustion in the combustion device is conventional combustion.

[0031] In this first operating mode and one particular alternative embodiment, it is preferred that the oxidizing gas consists only of air.

[0032] In the second operating mode (M2), the oxidizing gas contains at least a molecular oxygen-rich gas from a source of molecular oxygen gas and at least a part of the recycled combustion gas.

[0033] As a result, the combustion in the combustion device is oxygen combustion with recycle of the combustion gas.

[0034] In particular, in the second operating mode (M2), in one particular operating stage (hereinafter referred to as "degraded oxygen combustion"), the oxidizing gas can include air, and the air is introduced from the ambient air via the second bypass. In the second operating mode, in another particular operating stage (hereinafter referred to as "enhanced oxygen combustion"), the oxidizing gas does not include any air introduced from the ambient air via the second bypass.

[0035] In the present invention, the second bypass is a two-way bypass and thus acts as a passive safety device.

[0036] When the combustion system is in the first operating mode, the flow of incoming air introduced into the recycle loop via the second bypass automatically adapts without any intervention in the combustion system. In particular, the flow rate of the incoming air introduced into the recycle loop automatically adapts to the flow rate of the combustion gas generated by the combustion device and, if necessary, automatically compensates for changes in this flow rate of the combustion gas. In the second operating mode (a particular operating stage referred to as "degraded oxygen combustion") having a discharge valve that is at least partially open, the flow rate of the incoming air introduced into the recycle loop via the second bypass automatically adapts to the flow rate of the combustion gas generated by the combustion device and to the flow rate of the molecular oxygen-rich gas, and, if necessary, automatically compensates for changes in this flow rate of the combustion gas and / or changes in the flow rate of the molecular oxygen-rich gas.

[0037] When the combustion system is in the second operating mode with the discharge valve closed (the operating stage referred to as "enhanced oxygen combustion"), any excess combustion gas generated by the combustion device is discharged from the recycle loop via the second bypass at a flow rate that automatically adapts without any intervention in the combustion system. In particular, the flow rate of the excess combustion gas discharged from the recycle loop via the second bypass automatically adapts to the flow rate of the combustion gas generated by the combustion device and to the flow rate of the molecular oxygen-rich gas, and, if necessary, automatically compensates for changes in this flow rate of the combustion gas and / or changes in the flow rate of the molecular oxygen-rich gas.

[0038] In particular, in contrast to the solution described in international patent application WO2011 / 148298, between the second bypass and the second inlet of the mixer (i.e., downstream of the second bypass), the recycle loop of the combustion system of the present invention lacks forced air circulation means such as a fan or a compressor, and such forced air circulation means would prevent the release of the excess of the combustion gases generated by the combustion device from the recycle loop through the second bypass by introducing air into the recycle loop through the second bypass.

[0039] The combustion device can be a standard commercially available combustion device or a specially developed dedicated combustion device. This combustion device can have air inlets at different injection points according to the combustion conditions. Advantageously, the present invention can be implemented without any need to modify this combustion device.

[0040] In particular, the combustion system of the present invention can include any of the following additional features, either alone or in combination with each other: - A device for controlling the flow rate of the molecular oxygen-rich gas includes a flow control valve controlled by a control unit. - The flow control valve is a valve that opens and closes stepwise. - The recycle valve is a valve that opens and closes stepwise and / or the discharge valve is a valve that opens and closes stepwise. - The combustion system includes at least one sensor adapted to measure the concentration of molecular oxygen in the oxidizing gas, and the control unit can control the device for controlling the flow rate of the molecular oxygen-rich gas according to the concentration of molecular oxygen measured by the sensor, at least during the second operating mode (M2). - The combustion device includes a fan or a compressor adapted to supply the oxidizing gas to the combustion device at a predetermined flow rate, and the flow rate is preferably variable. - The rate of fuel supply to the combustion device is variable, and the combustion device includes a fan or compressor capable of supplying oxidizing gas to the combustion device at a rate that varies according to the rate of fuel supply to the combustion device. - The combustion system includes a carbon dioxide injection device connected to the inlet of the mixer and adapted to inject carbon dioxide gas into the mixer during a specific operating stage of the second operating mode (M2) ("degraded oxygen combustion"). - The combustion system includes a condenser in the recycle loop, and the condenser can dehumidify the combustion flue gas, discharge the combustion gas at the outlet, and recycle at least a part of it to the inlet of the mixer. - The combustion system includes a condenser adapted to dehumidify the oxidizing gas before introducing the oxidizing gas into the combustion device. - The condenser includes at least one heat exchanger containing a coolant. - The heat exchanger includes a bath of coolant and injection means capable of moving the gaseous fluid through the bath of coolant for dehumidification, and preferably the injection means can dehumidify the gaseous fluid below the surface of the bath of coolant. - The combustion system includes at least one sensor adapted to measure the concentration of molecular oxygen in the oxidizing gas, and the control unit is adapted to control the flow rate of the molecular oxygen-rich gas, the recycle valve, and the discharge valve in order to switch from the second operating mode to the first operating mode according to the measured concentration of molecular oxygen in the oxidizing gas. - The control unit is adapted to control the flow rate of the molecular oxygen-rich gas, the recycle valve, and the discharge valve in order to be able to switch from one operating mode (M1 or M2) to another operating mode (M2 or M1) without stopping the combustion in the combustion device. - The control unit is adapted to continuously control the opening of the device for controlling the flow rate of the molecular oxygen-rich gas, the opening of the recycle valve, and preferably the total or partial closing of the discharge valve in order to switch from the first operating mode (M1) to the second operating mode (M2). - The control unit is adapted to continuously control the opening of the discharge valve, the closing of the recycle valve, and the closing of the device for controlling the flow rate of the molecular oxygen-rich gas in order to switch from the second operating mode (M2) to the first operating mode (M1). - The combustion system includes a carbon dioxide (CO2) capture device adapted to capture carbon dioxide (CO2) in at least a portion of the combustion gas when the combustion system is operating in the second operating mode (M2). - The molecular oxygen-rich gas supplied by the source of molecular oxygen gas contains at least 50% molecular oxygen, preferably at least 80% molecular oxygen, more preferably at least 90% molecular oxygen. - The molecular oxygen-rich gas supplied by the source of molecular oxygen gas is pure or nearly pure molecular oxygen (at least 99% O2). - The combustion system includes a pollutant removal device mounted on the recycle loop and adapted to capture one or more pollutants selected from particulate matter, SOx, NOx, acids, heavy metals, ammonia, and VOCs.

Brief Description of the Drawings

[0041] The features and advantages of the present invention will become apparent upon reading the following detailed description of some specific alternative embodiments of the present invention with reference to the accompanying drawings. The specific alternative embodiments are described by way of non-limiting and non-exhaustive examples of the present invention.

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0042] Combustion system of FIG. 1 Figure 1 schematically shows a first alternative embodiment of the combustion system of the present invention, including the following: - A combustion device 1 that is supplied with an oxidizing gas GC from a unit 3 for supplying the oxidizing gas GC and with a fuel C from a fuel source 2, and that emits combustion fumes FC during operation; - Recycling means 4 including a recycling loop 40 between the outlet of the combustion device 1 and the inlet of the unit 3 for supplying the oxidizing gas GC, and including a recycling valve V2 mounted on the recycling loop 40; - A first bypass 5 connected to the recycling loop 40 and including a discharge valve V3; - A second bypass 6 connected to the recycling loop 40 downstream of the first bypass 5 and the recycling valve V2 and open to the open air; - A control unit 7.

[0043] The combustion device 1 generally enables the oxygen combustion of fuel by the oxidizing gas GC, and the thermal energy generated from this combustion can be used in accordance with the present invention in an exchangeable manner in any type of application that requires heat supply, for example, heating a fluid in heating equipment or supplying energy to industrial manufacturing equipment in a non-limiting way, particularly thermally, mechanically, or electrically. According to the present invention, this combustion device 1 can include a conventional boiler, furnace, or combustion chamber in which a combustion process is carried out.

[0044] The combustion device 1 usually includes a fan (or compressor) 10 that guides or pushes the oxidizing gas GC into the combustion device 1, and the flow rate θ of the oxidizing gas GC entering the combustion device 1 is adapted to the flow rate of the fuel C and satisfies the need for thermal energy. GC It has an automatic adjustment or setting.

[0045] The combustion device 1 can be a standard commercially available combustion device or a special combustion device developed specifically.

[0046] The combustion reaction of the fuel C by the oxidizing gas GC generates combustion flue gas FC, and its composition depends on the fuel C and the oxidizing gas GC.

[0047] In the context of the present invention, the fuel C can vary extremely between one application and another and can be in solid, liquid, or gaseous form as the case may be.

[0048] The unit 3 for supplying the oxidizing gas GC includes a source 30 of molecular oxygen gas (O2) that supplies the mixer 31 at the inlet via a flow control device 32 controlled by the control unit 7. The other inlet of the mixer 31 is connected to the recycle loop 40.

[0049] The source 30 of molecular oxygen gas supplies a molecular oxygen-rich gas (i.e., a gas containing at least 40% (by volume) of molecular oxygen).

[0050] Preferably, as described below, the molecular oxygen-rich gas advantageously consists of pure or almost pure molecular oxygen (volume concentration greater than 90%), but this is not essential.

[0051] The source 30 of molecular oxygen gas can be of any known type and may include, for example, a unit for generating molecular oxygen gas by low temperature and / or a unit for generating molecular oxygen gas by electrolysis of water. The source 30 of molecular oxygen gas can also be a unit for generating a molecular oxygen-rich gas containing at least 40% molecular oxygen obtained by suitable filtration of air using zeolite or the like. The source 30 of molecular oxygen does not have to be designed to generate the molecular oxygen-rich gas in situ and may only include means for storing the molecular oxygen-rich gas generated in advance at another location.

[0052] In one alternative, the flow control device 32 can only stop or enable the flow of the molecular oxygen-rich gas from the source 30. However, preferably, this flow control device 32 can stop or enable the flow of the molecular oxygen-rich gas from the source 30 by making the gas flow rate at the inlet of the mixer 31 adjustable by the control unit 7.

[0053] In a specific alternative embodiment of FIG. 1, the source 30 of molecular oxygen gas supplies the mixer 31 at a constant pressure, for example, and the flow control device 32 at the inlet of the mixer 31 includes a valve V1, preferably a solenoid valve, which is controlled by the control unit 7.

[0054] Preferably, this valve V1 is a valve that opens and closes stepwise.

[0055] In another alternative example, the flow control device 32 at the inlet of the mixer 31 can also include a system for controlling the pressure of the gas at the outlet of the source 30. It can be associated with a valve, which can probably be an on / off valve or a valve that opens and closes stepwise, and the pressure control system and the said valve are controlled by the control unit 7.

[0056] Preferably, the unit 3 for supplying the oxidizing gas GC also includes at least one sensor 33, which measures the concentration of molecular oxygen in the oxidizing gas GC entering the combustion device 1 and sends a signal S indicating this concentration to the control unit 7.

[0057] In a specific alternative embodiment of FIG. 1, the first bypass 5 is connected to the recycle loop 40 upstream of the valve V2. In the simplest case, the first bypass 5 can consist of a simple pipe adapted with a discharge valve V3, and the discharge valve V3 enables controlling the flow of the fluid circulating in the said pipe.

[0058] The second bypass 6 is connected to the recycle loop 40 downstream of the valve V2.

[0059] In a specific alternative embodiment of FIG. 1, this second bypass 6 is directly open to the open air.

[0060] The second bypass 6 can consist of a simple pipe with one end connected to the recycle loop 40 and the other end directly open to the open air. In its simplest form, this second bypass 6 can also be a simple opening that enables the recycle loop 40 to communicate with the ambient air.

[0061] In another alternative embodiment, the second bypass 6 can also supply one or more cascade treatment devices for the combustion fumes FC escaping through this second bypass 6, for example, one or more pollutant removal devices arranged in parallel.

[0062] In the context of the present invention, the recycle valve V2 can be an on / off valve, more preferably a valve that opens and closes in steps. Similarly, the discharge valve V3 can be an on / off valve, more preferably a valve that opens and closes in steps.

[0063] The valves V2 and V3 are preferably solenoid valves or pneumatic valves or hydraulic valves.

[0064] Preferably, in the alternative of FIG. 1, the combustion system includes a condenser 8 which is mounted on the recycle loop 40 downstream of the first bypass 5 and upstream of the second bypass 6, which is adapted to condense the combustion flue gas FC discharged by the combustion device 1 by cooling when the recycle valve V2 is open.

[0065] In the context of the present invention, this condenser 8 can generally include any type of heat exchanger capable of cooling the combustion flue gas FC by any means so as to condense at least a part of the water vapor contained in the combustion flue gas F.

[0066] In a particular alternative of FIG. 1, the recycle valve V2 is mounted on the recycle loop 40 upstream of the condenser 8. In another alternative, the recycle valve V2 can be mounted on the recycle loop 40 after the condenser 8 (i.e., downstream of the condenser) and before the second bypass 6 (i.e., upstream of the second bypass 6).

[0067] The control unit 7 adapts the composition of the oxidizing gas GC and advantageously operates the device in an operating mode selected from at least two different operating modes (M1 and M2) detailed below, and is able to automatically control the combustion system, in this particular case the three valves V1, V2 and V3 respectively by control signals C1, C2 and C3 so as to switch from one operating mode (M1 or M2) to the other operating mode (M2 or M1).

[0068] This control unit 7 can be implemented in various ways, for example, by a programmable electronic control circuit such as a programmable logic controller, or a programmable electronic circuit including a microprocessor, a microcontroller, or an FPGA type programmable logic circuit, or by an application-specific integrated electronic circuit.

[0069] Combustion system operation mode The combustion system of FIG. 1 can be configured by the control unit 7 to operate in at least two different main operating modes: M1 (FIG. 2): An operating mode referred to as "conventional combustion", in which the valve V1 of the flow control device 32 and the recycle valve V2 are closed (F), and the discharge valve V3 is open (O). M2 (FIGS. 3 and 4): An operating mode referred to as "oxy-fuel combustion with recycle", in which the valve V1 of the flow control device 32 and the recycle valve V2 are open (O), and the discharge valve V3 is either open (wholly or partially) or closed (F).

[0070] The transition from one operating mode (M1 or M2) to another operating mode (M2 or M1) can be driven by the control unit 7 by simply appropriately controlling the flow control device 32 (especially the valve V1), the recycle valve V2, and the discharge valve V3, and can be advantageously achieved without stopping the combustion in the combustion device 1 and without closing the combustion device 1.

[0071] Operation mode M1 - "Conventional combustion" - FIG. 2 In this operating mode, the valve V1 for supplying molecular oxygen from the source 30 and the recycle valve V2 are closed (F) by the control unit 7. Only the discharge valve V3 is open.

[0072] The fan 10 (or compressor) of the combustion device 1 imposes a variable flow rate θ GC of the oxidizing gas GC at the inlet of the combustion device 1.

[0073] The mixer 31 is not supplied with molecular oxygen from the source 30. The mixer 31 is supplied only with air that is drawn from the ambient air via the second bypass 6 and conveyed to the inlet of the mixer 31 in a portion 40a of the recycle loop 40 downstream of the second bypass 6.

[0074] The combustion flue gas FC is not recycled to the mixer 31 (the recycle valve V2 is closed), but is discharged into the ambient air by being pushed by a fan (or compressor) 10 in the first bypass 5 (the discharge valve V3 is open).

[0075] Operation mode M2 - "Oxygen combustion with recycle" - FIGS. 3 and 4 In this operating mode, the valve V1 for supplying molecular oxygen from the source 30 and the recycle valve V2 are open (O) by the control unit 7. The discharge valve V3 is open (O) (entirely or partially - Figure 3), or closed (F) (Figure 4).

[0076] The fan 10 (or compressor) of the combustion device operates by imposing a variable flow rate (θ GC ) of the oxidizing gas GC at the inlet of the combustion device 1.

[0077] The operating mode M2 includes two operating stages; - The so-called "degraded oxygen combustion" operating stage (which is shown in Figure 3), - The so-called "promoted oxygen combustion" operating stage (which is shown in Figure 4).

[0078] Operation stage of FIG. 3 - "Degraded oxygen combustion" A fraction of the combustion flue gas FC exiting the combustion device 1 is discharged into the ambient air (the discharge valve V3 is at least partially open), and another fraction exiting the combustion device 1 is recycled in the recycle loop 40 to the inlet of the condenser 8 (the recycle valve V2 is open).

[0079] By passing through the condensation device 8, the recycled combustion flue gas FC is cooled and dehumidified by the condensation of water vapor present in the combustion flue gas FC.

[0080] At the outlet of the condensation device 8, a dehumidified combustion gas G is obtained. The combustion gas G contains combustion products in the gas phase generated by combustion in the combustion device 1 and has an absolute humidity lower than that of the combustion flue gas FC at the inlet of the condensation device 8.

[0081] The mixer 31 is supplied with a molecular oxygen-rich gas from the source 30 (the valve V1 is open) at a flow rate (θO2) and with the dehumidified combustion gas G at a flow rate θ.

[0082] The mixer 31 is also supplied with air, and the air is AIR introduced from the ambient air through the second bypass 6 at an incoming air flow rate θ and carried to the mixer 31 together with the dehumidified combustion gas G through a portion 40a of the recycle loop 40 downstream of the bypass 6.

[0083] In operation, θ GC = θO2 + θ + θ AIR

[0084] This operating stage continues as long as the discharge valve V3 is not fully closed.

[0085] In this operating stage, the oxidizing gas GC contains molecular oxygen from the molecular oxygen-rich gas supplied by the source 30, the recycled combustion gas G, and air.

[0086] In this operating stage, when the flow rate θO2 of the molecular oxygen-rich gas at the inlet of the mixer 31 increases and / or when the flow rate θ of the recycled combustion gas G at the inlet of the mixer 31 increases, the flow rate θ AIR of the air introduced into the second bypass 6 automatically decreases. Conversely, when the flow rate θO2 of the molecular oxygen-rich gas at the inlet of the mixer 31 decreases and / or when the flow rate θ of the recycled combustion gas at the inlet of the mixer 31 decreases, the flow rate θ of the air introduced into the second bypass 6AIR automatically increases.

[0087] Operation stage of FIG. 4 - "Enhanced oxygen combustion" In this operating stage, the valve V1 and the recycle valve V2 for supplying molecular oxygen from the source 30 are opened (O), and the discharge valve V3 is closed (F).

[0088] The combustion flue gas FC exiting the combustion device 1 is not discharged into the ambient air through the closed discharge valve V3, but is recycled in the recycle loop 40 (the recycle valve V2 is open) at the inlet of the condenser 8 and is dehumidified by passing through the condenser 8.

[0089] In this operating stage, the mixer 31 is supplied with molecular oxygen from the molecular oxygen-rich gas of the source 30 (the valve V1 is open) at a predetermined flow rate (θO2), a fraction G1 of the combustion gas G exiting the condenser 8 is supplied at a flow rate θ1, and the other surplus fraction G2 of the combustion gas G exiting the condenser 8 is discharged into the open air at a flow rate θ2 by passing through the second bypass 6.

[0090] During operation, JPEG2025519550000003.jpg18166

[0091] When the flow rate θO2 of the molecular oxygen-rich gas at the inlet of the mixer 31 increases, the flow rate θ1 of the recycled fraction G1 of the combustion gas G automatically decreases, and when the flow rate θO2 of the molecular oxygen-rich gas at the inlet of the mixer 31 decreases, the flow rate θ1 of the recycled fraction G1 of the combustion gas G automatically increases.

[0092] Therefore, the oxidizing gas GC contains molecular oxygen from the molecular oxygen-rich gas of the source 30 and the recycled fraction G1 of the combustion gas G.

[0093] Advantageously, the transition from the "degraded oxygen combustion" operating stage (valve V3 is at least partially open) to the "accelerated oxygen combustion" operating stage (valve V3 is closed), or vice versa, can be achieved without the need to close combustion device 1 and without the need to stop combustion in combustion device 1.

[0094] Preferably, in operating mode M2, control unit 7 automatically adjusts the flow rate θO2 of the molecular oxygen-rich gas such that the concentration of molecular oxygen measured by sensor 33 in oxidizing gas GC is equal to or greater than a predetermined operating set point, or within a predetermined operating range (for example, by closing valve V1 somewhat). This makes it possible to maintain an appropriate concentration of molecular oxygen O2 in oxidizing gas GC and to automatically adapt the system to variations in the flow rate θ GC of oxidizing gas GC (imposed by combustion device 1).

[0095] In particular, but not exclusively, the combustion system of FIG. 1 can be operated with fuel C, which produces combustion flue gas FC containing mainly carbon dioxide (CO2) and water vapor (H2O), and to a lesser extent molecular oxygen (O2) and carbon monoxide (CO) in the "accelerated oxygen combustion" operating stage.

[0096] Thus, in a non-limiting and non-exhaustive manner, fuel C used in the combustion system of FIG. 1 can advantageously be any type of hydrocarbon, for example conventional hydrocarbons derived from oil or natural gas, or special hydrocarbons derived from shale gas or oil, bituminous shale or sand, coal gas, biogas, synthesis gas, etc.

[0097] For example, when fuel C is an alkane type of saturated hydrocarbon (C n H 2n+2 ), the oxygen combustion reaction in the device is known as follows: JPEG2025519550000004.jpg11166

[0098] The fuel can also be a solid or liquid fuel (such as coal, wood) obtained especially through extraction, or can contain waste (such as plastics, salvage materials).

[0099] By recycling the combustion gas containing CO2 to the inlet of the mixer 31, in a method known per se, the oxy-fuel combustion reaction in the combustion device 1 can be well controlled, and the combustion temperature in this combustion device 1 can be significantly reduced compared to an oxy-fuel combustion reaction carried out using only pure molecular oxygen as the oxidant or using substantially pure molecular oxygen as the oxidant.

[0100] Various operating cases of the combustion system in FIG. 1 are described in detail.

[0101] Example of control of the combustion system for switching from operation mode M1 ("Conventional combustion") to operation mode M2 ("Oxygen combustion with recycle") The combustion system is configured in the operating mode M1 (“conventional combustion”-FIG. 2), It is assumed that the molecular oxygen supply valve V1 and the recycle valve V2 are closed (F) by the control unit 7, and only the discharge valve V3 is open (O).

[0102] The combustion device 1 is in operation, and the fan 10 (or compressor) of the combustion device 1 imposes a predetermined flow rate (θ GC ) of the oxidizing gas GC consisting of air at the inlet to the device 1.

[0103] To switch from this operating mode M1 (“conventional combustion”) to the operating mode M2 (“oxy-fuel combustion with recycle”), the control unit 7 preferably controls the opening of the molecular oxygen supply valve V1 stepwise, preferably controls the opening of the recycle valve V2 stepwise, and preferably controls the full or partial opening of the discharge valve V3 stepwise, preferably continuously.

[0104] Accordingly, the combustion system switches to the operating mode M2 (“oxy-fuel combustion with recycle”).

[0105] Unless the discharge valve V3 is completely closed, the combustion system is in the operating stage referred to as the aforementioned "degraded oxygen combustion" (Figure 3). The concentration of molecular oxygen in the oxidizing gas GC increases over time, while at the same time the concentration of air in the oxidizing gas decreases, and the air is replaced by molecular oxygen. The combustion system can advantageously be operated without time limit in the operating mode M2 ("oxygen combustion with recycling"), and in the "degraded oxygen combustion" stage, there is partial air intake at least through the opening 6 and possibly through another second air inlet, and partial discharge of the flue gas FC through the bypass 5 or another partial outlet for the flue gas FC.

[0106] When the discharge valve V3 is completely closed and the sum of the flow rate θO2 of molecular oxygen and the flow rate θ of the combustion gas G (θO2 + θ) is greater than the flow rate θ of the oxidizing gas imposed by the combustion device 1 GC the combustion system automatically switches to the "accelerated oxygen combustion" operating stage (Figure 4).

[0107] Preferably, when the combustion system switches to the operating mode M2 ("oxygen combustion with recycling"), the control unit 7 uses the measurement signal S of the concentration of molecular oxygen in the oxidizing gas GC to automatically adjust the flow rate θO2 of molecular oxygen (for example, in this particular case, by gradually closing the valve V1 somewhat).

[0108] The switch from the operating mode M1 ("conventional combustion") to the operating mode M2 ("oxygen combustion with recycling") is simple and safe because it can avoid the risk of a sudden uncontrolled temperature rise in the combustion device 1. The switch from the operating mode M1 ("conventional combustion") to the operating mode M2 ("oxygen combustion with recycling") advantageously requires no intervention from the user for the combustion device 1, and in particular does not require the combustion to be stopped.

[0109] The switch from the operating mode M1 to the operating mode M2 (''oxygen combustion with recycling'') in the ''deteriorated oxygen combustion'' operating stage or the ''accelerated oxygen combustion'' operating stage can be requested by the user of the combustion system from the control unit 7, for example, by a manual command to switch the operating mode.

[0110] The switch from the operating mode M1 to the operating mode M2 can also be carried out when the combustion system is started to operate it in the ''oxygen combustion with recycling'' mode (M2).

[0111] Procedure for starting the combustion system When the user attempts to start the combustion system to operate it in the ''oxygen combustion with recycling'' mode (M2), they request the control unit 7 to perform the start-up procedure by an appropriate command.

[0112] The control unit 7 performs the start-up procedure by initially configuring the combustion system in the operating mode M1 (''conventional combustion'').

[0113] The combustion device 1 is started manually by the user or automatically, for example, by the control unit 7, in particular by starting at least the fan (or compressor 10) of the combustion device 1, which enables the system to be initially started in the conventional combustion mode (M1).

[0114] Then, in a second step, the control unit 7 controls the combustion system to automatically switch to the ''oxygen combustion with recycling'' mode (M2) as described above, by selecting the operating stage referred to as ''deteriorated oxygen combustion'' or by closing the discharge valve V3 completely and increasing the flow rate θO2 of the molecular oxygen-rich gas supplied by the source 30 until the operating stage referred to as ''accelerated oxygen combustion'' is reached.

[0115] Such a starting phase is advantageously simple and safe. In particular, compared to prior art combustion systems adapted to operate only in the boosted oxy-fuel combustion mode with recycle of combustion gases, the risk of an uncontrolled sudden temperature increase inherent in this type of prior art device due to the high initial concentration of molecular oxygen and the low initial concentration of CO2 in the oxidizing gas is avoided during the starting phase.

[0116] Example of control of the combustion system for switching from operation mode M2 ("Oxygen combustion with recycle") to operation mode M1 ("Conventional combustion") The combustion system is configured in the operating mode M2 (“oxy-fuel combustion with recycle”), and it is assumed that the molecular oxygen supply valve V1 and the recycle valve V2 are opened (O) by the control unit 7, and the discharge valve V3 is at least partially open or closed (F).

[0117] The combustion device 1 is in operation, and the fan 10 (or compressor) of the combustion device 1 imposes a predetermined flow rate (θ GC ) of the oxidizing gas GC consisting of air at the inlet to the device 1.

[0118] To switch from the operating mode M2 (“oxy-fuel combustion with recycle”) to the operating mode M1 (“conventional combustion”), the control unit 7 maintains the control of the oxygen level in the oxidizing gas GC by means of the valve V1, and thus maintains combustion, and first controls the overall opening of the discharge valve V3, preferably in steps, while discharging the excess combustion gases to the outside. The bypass 6 makes it possible to supply external air or to discharge the excess combustion gases required by the combustion device 1. Then, in a second step, once the opening of the valve V3 is complete, the control unit 7 controls the closing of the recycle valve V2, preferably in steps, which makes it possible to prevent the recycle of the combustion gases to the inlet of the mixer 31. Once the closing of the valve V2 is complete, the control unit 7 controls the closing of the molecular oxygen supply valve V1, preferably in steps, which prevents the injection of the molecular oxygen-rich gas (supplied by the source 30) into the oxidizing gas GC and makes it possible to switch the combustion system to “conventional combustion” (M1).

[0119] Alternatively, the closing of the molecular oxygen supply valve V1 and the closing of the recycle valve V2 can be controlled simultaneously by the control unit 7.

[0120] Alternatively, the opening of the discharge valve V3, the closing of the molecular oxygen supply valve V1, and the closing of the recycle valve V2 need not be continuous but can be controlled simultaneously by the control unit 7.

[0121] The switch from the operating mode M2 ("oxygen combustion with recycling") to the operating mode M1 ("conventional combustion") is simple and safe because it avoids the risk of an uncontrolled sudden temperature increase in the combustion device 1. The switch from the operating mode M2 ("oxygen combustion with recycling") to the operating mode M1 ("conventional combustion") advantageously does not require intervention from the user for the combustion device 1, and particularly advantageously does not require the combustion to be stopped.

[0122] 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, for example by a manual command for switching the operating mode.

[0123] The switch from the operating mode M2 to the operating mode M1 can also be carried out during the procedure for stopping the operation of the combustion system.

[0124] Procedure for stopping the combustion system When the user attempts to stop the combustion system while operating in the "oxygen combustion with recycling" mode (M2), they request the control unit 7 to carry out the stop procedure by an appropriate command.

[0125] The control unit 7 carries out the stop procedure by controlling the flow control valve 32 of the molecular oxygen-rich gas, the valve V3, and the valve V2 (switching from the operating mode M2 to the operating mode M1) as described above.

[0126] Once the combustion system is configured in this operating mode M1 (“conventional oxy-fuel combustion”), the combustion device 1 can be stopped as usual without any risk.

[0127] Such a stop phase is advantageously simple and safe. In particular, compared to prior art combustion systems adapted to operate only in oxy-fuel combustion with combustion gas recycling, the uncontrolled sudden temperature rise inherent to this type of prior art device is avoided during the stop procedure.

[0128] The switch from operating mode M2 to operating mode M1 can also be carried out when the concentration of molecular oxygen (supplied by source 30) in the oxidizing gas GC becomes insufficient and oxy-fuel combustion with combustion gas recycling is no longer possible.

[0129] This insufficiency may have multiple, possibly cumulative causes.

[0130] For example, during operation of the combustion system in operating mode M2 (“oxy-fuel combustion with recycling”), particularly in the “accelerated oxy-fuel combustion” operating phase, an accidental interruption of the molecular oxygen supply occurs, for example, due to a sudden stop in the on-site production of molecular oxygen-rich gas by source 30, or by source 30 of an emptied molecular oxygen-rich gas source.

[0131] For example, during operation of the combustion system in operating mode M2 (“oxy-fuel combustion with recycling”), particularly in the “accelerated oxy-fuel combustion” operating phase, the molecular oxygen supply significantly decreases, for example, as a result of a sudden decrease in the on-site production of molecular oxygen-rich gas by source 30, or an overly low pressure in source 30.

[0132] For example, during operation of the combustion system in operating mode M2 (“oxy-fuel combustion with recycling”), particularly in the “accelerated oxy-fuel combustion” operating phase, the combustion device 1 is required to supply more thermal energy, and in response to this requirement, the flow rate θ of the oxidizing gas GC GCIncrease (increase the flow rate of the fan or compressor 10). In this case, the remaining oxidizing gas is automatically injected through the second bypass 6.

[0133] If the combustion device 1 reduces the supply of thermal energy, which results in a reduced need for the oxidizing gas GC, the excess oxidizing gas is released through the bypass 6, and the control system 7 adjusts the valve V1 to reduce the injection of molecular oxygen into the mixer 31 if necessary.

[0134] In a conventional device that can only operate with oxygen combustion having a recycle of combustion gas, an excessive decrease in the concentration of molecular oxygen in the oxidizing gas GC can lead to a sudden stop of oxygen combustion.

[0135] Such a sudden stop can be advantageously avoided by the combustion system of the present invention.

[0136] For this purpose, the control unit 7 monitors, by means of the sensor 33, the concentration of molecular oxygen in the oxidizing gas GC and automatically detects whether, when the concentration of molecular oxygen decreases, it has reached a predefined, preferably parameterizable, critical minimum threshold value, and if so, is designed to automatically control the combustion system to switch it (as described above) to the safe operating mode M1 ("conventional combustion") without stopping the combustion in the combustion device 1.

[0137] Furthermore, further non-exhaustive examples of the combustion system according to the present invention that can operate in the operating modes M1 ("conventional combustion") and M2 ("oxygen combustion with recycle") will be described.

[0138] Combustion system of FIG. 5 - Condenser 8 in bypass mode The combustion system of FIG. 5 differs from that of FIG. 1 in that the condenser 8 is mounted as a bypass in the recycle loop 40.

[0139] This type of mounting is suitable in a known manner for a condensing device 8 having its own fan or compressor as described below with reference to FIG. 11. The description previously given of the operation of the combustion system of FIG. 1 also applies to the combustion system of FIG. 5.

[0140] Combustion system of FIG. 6 - Condenser 34 downstream of mixer 31 The combustion system of FIG. 6 differs from that of FIG. 1 in that the condensing device 8 is replaced by a condensing device 34, the condensing device 34 is supplied at the inlet by a mixer 31, and is connected at the outlet to the combustion device 1, and the oxidizing gas GC is supplied to the combustion device 1.

[0141] In this alternative, when the valve V2 is open and the combustion system is in the operating mode M2 (“oxy-fuel combustion with recycling”), the combustion flue gas FC is recycled to the mixer 31 without being dehumidified by the condensing device 34.

[0142] In another alternative, the condensing device 34 can be mounted as a bypass, like the condensing device 8 of FIG. 5.

[0143] In another alternative, the combustion system can include a condensing device 8 upstream of the mixer 31 and a condensing device 34 downstream of the mixer 31.

[0144] Combustion system of FIG. 7 - Positions of valves V2 and V3 after condenser 8 The combustion system of FIG. 7 differs from that of FIG. 1 in that a first bypass 5 including a recycle valve V2 and a discharge valve V3 is connected to a recycle loop 40 downstream of the condensing device 8. In this configuration, the condensing device 8 is used in two operating modes M1 and M2.

[0145] Combustion system of FIG. 8 - CO 2 Capture The combustion system of FIG. 8 differs from that of FIG. 1 in that it includes an additional CO2 capture device 10 adapted to operate when the combustion system is operating in the operating mode M2 (“oxy-fuel combustion with recycling”) and the “accelerated oxy-fuel combustion” phase.

[0146] This device 10 includes, for example, a CO2 capture unit 101, a bypass 100 connecting the CO2 capture unit 101 to a second bypass 6, a valve V4 mounted on the bypass 100 and controlled by a control unit 7 according to a control signal C4, and a sensor 102 that detects the direction of circulation of the gaseous fluid in the second bypass 6 and sends a detection signal S 103 to the control unit 7. The device 10 may also include a fan or a compressor capable of sucking in the combustion gas circulating in the second bypass 6.

[0147] The second bypass 6 is provided with an adjustable check valve CA. The check valve CA can be adjusted so that the gaseous fluid (in this case, air) can freely pass through the second bypass 6 in one direction from the outside (ambient air) to the inside of the second bypass 6, and restricts the flow of the gaseous fluid in the opposite direction, or is controlled by the control unit 7, or is adjustable to block the reverse flow of the gaseous fluid when the return pressure in the second bypass 6 is greater than a predefined pressure, or is controlled by the control unit 7.

[0148] When the combustion system is in the first operating mode M1 and the second operating mode M2 stage ("deteriorated oxygen combustion"), the valve V4 is closed, and the check valve CA allows air to enter the second bypass 6 from the outside and reach the mixer 31 in the recycle loop 40.

[0149] When the combustion system switches to the operating mode M2 ("oxygen combustion with recycle") and the "promoted oxygen combustion" stage, the sensor 102 detects a change in the direction of circulation of the gaseous fluid due to the escape of the combustion gas G2 into the second bypass 6, and the control unit 7 automatically controls the opening of the valve V4, thereby supplying all or part of the combustion gas G2 escaping from the recycle loop 40 into the second bypass 6 to the CO2 capture unit 101. During this stage, the check valve CA blocks or restricts the flow of the combustion gas to the open air outlet of the second bypass 6.

[0150] When the combustion system exits the "promoted oxygen combustion" stage and enters the transition stage ("deteriorated oxygen combustion"), the sensor 102 detects a change in the direction of circulation of the gaseous fluid by the air drawn into the second bypass 6, and the control unit 7 automatically controls the closing of the valve V4.

[0151] This CO2 capture device 10 can also be added to the combustion systems of FIGS. 5-7, 9 and 10.

[0152] In another alternative, the CO2 capture device can be mounted on the recycle loop 40 between the first bypass 5 and the second bypass 6 and is activated by the control unit 7 when the direction of circulation of the gaseous fluid in the bypass 6 is outward.

[0153] Combustion system of FIG. 9 - CO injection at startup 2 Injection The combustion system of FIG. 9 differs from that of FIG. 1 in that it includes an additional device 11 connected to the inlet of the mixer 31 for injecting carbon dioxide gas (CO2) into the mixer 31 when it switches from the second operating mode M2 of the "deteriorated oxygen combustion" stage to the second operating mode M2 of the "promoted oxygen combustion" stage in order to shorten the period of this transition stage during the "deteriorated oxygen combustion" transition stage.

[0154] This CO2 injection device 11 includes a source 110 of pressurized CO2 gas associated with a valve V5 controlled by the control unit 7, for example by a control signal C5.

[0155] This CO2 injection device 11 can also be added to the combustion systems of FIGS. 5-8 and 10.

[0156] Combustion system of FIG. 10 - Pollutant removal device 12 The combustion system of FIG. 10 differs from that of FIG. 1 in that it is equipped with at least one pollutant removal device 12 (known per se) mounted on the recycle loop 40 and adapted to capture one or more pollutants selected from particulate matter, SOx, NOx, acids, heavy metals, ammonia, and VOCs in the combustion gas circulating through the recycle loop 40.

[0157] As shown in FIG. 10, this pollutant removal device 12 is preferably mounted upstream of the second bypass 6. However, it can also be mounted between the bypass 6 and the mixer 31.

[0158] This pollutant removal device 12 can also be added to the combustion systems of FIGS. 5 - 9.

[0159] Special example of a condenser - FIG. 11 As a non - limiting example of the present invention, FIG. 11 depicts a preferred example of a condenser that can be used as the condenser 8 or 34 mounted particularly as a bypass in the combustion system of the present invention.

[0160] This condenser includes a heat exchanger 12, and the heat exchanger 12 includes a container 120 containing a bath 121 of a coolant L and injection means 123, which are adapted to direct a gaseous fluid F (i.e., the combustion flue gas FC of the alternative examples of FIGS. 1 - 5 and 7 - 10, or the combustion gas exiting the mixer 31 of the alternative example of FIG. 6) to be dehumidified under the surface of the bath of the coolant L.

[0161] The coolant L may simply be water or an aqueous solution.

[0162] These injection means 123 can particularly include a fan or compressor 123f and an injection duct 123a including an intake opening 123b, for example, at its upper part 123c. The lower part 123d of the injection duct 123a is immersed in the bath 121 of the coolant L and includes a discharge opening 123e immersed in the bath 121 of the coolant L.

[0163] In operation, the fan or compressor 123f is capable of sucking in the gaseous fluid F to be dehumidified (i.e., the combustion flue gas FC of the alternative examples of FIGS. 1 to 5 and 7 to 10, or the combustion gas exiting the mixer 31 of the alternative example of FIG. 6) and introducing them into the injection duct 123 through the suction opening 123b. This gaseous fluid F escapes from the injection duct 123 through the discharge opening 123e, thereby being forcibly introduced under the surface of the coolant L bath 121 into the coolant L bath 121, rising to the surface of the liquid bath, and escaping from the container 120 through the discharge opening 120a of the container 120 after being dehumidified in the form of the dehumidified gas F'.

[0164] The temperature T of the coolant L L is always lower than the temperature T of the gas fluid F at the inlet of the heat exchanger 12 F and preferably lower than the dew point temperature (dew point) of the gaseous fluid F.

[0165] The absolute humidity of the gas (g water / kg dry air ) represents the number of grams of water vapor present in a given volume of the gas relative to the mass of dry gas in the volume expressed in kilograms. It should be noted that that value remains constant even if the temperature of the gas remains above the dew point of the gas but varies.

[0166] When passing through the coolant L bath 121, the gaseous fluid F undergoes condensation when contacting the coolant L such that the absolute humidity of the gas F' at the outlet of the heat exchanger 12 is lower than the absolute humidity of the gaseous fluid F at the inlet of the heat exchanger 12.

[0167] The difference between the absolute humidity of the dehumidified gas F' and the absolute humidity of the incoming gaseous fluid F depends particularly on the difference between the temperature T F of the incoming gaseous fluid F and the lower temperature T L of the coolant L. The greater the temperature difference ΔT (ΔT = T F - T L ) between the temperature T F of the incoming gaseous fluid F and the temperature T L of the coolant L, the lower the absolute humidity of the dehumidified gas F' compared to the absolute humidity of the incoming gaseous fluid F.

[0168] In another alternative example, 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 the gaseous fluid F through the suction opening 123b of this injection duct 123.

[0169] In particular, the heat exchanger 12 can be coupled to a heat pump (not shown), and the heat pump can update the liquid L by extracting heat energy therefrom so as to maintain the temperature of the liquid L in the bath at a sufficiently low level.

[0170] In another alternative embodiment, the condensing device preferably includes a plurality of heat exchangers 12 mounted one behind the other.

[0171] The present invention is not limited to the use of the heat exchanger 12 of the type shown in FIG. 11. In other alternative embodiments, the heat exchanger 12 for condensing the gaseous fluid F can be of the type described, for example, in international patent application WO2016 / 071648 or international patent application WO2020 / 030419, or can be a heat exchanger that operates by injecting the coolant L so that the coolant L comes into contact with the gaseous fluid F.

[0172] The present invention is not limited to heat exchangers that operate with a coolant, and can be implemented with any other known type of heat exchanger that enables dehumidification of the gaseous fluid.

[0173] Advantages of using a molecular oxygen-rich gas in combination with the recirculation of at least one fraction of the combustion flue gas In the case of conventional combustion, for the amount Qd of fuel C burned per hour, the flow rate D of the oxidizing air is used at the inlet to the combustion device. After combustion, the combustion flue gas is discharged at a flow rate of X. These flue gases must be treated to comply with the emission standards for dust and chemicals. The larger X is, the higher the cost of treating the combustion flue gas.

[0174] In conventional combustion, the air flow velocity D (D < X) at the inlet to the combustion device is defined according to the oxygen conditions for combustion and the management of the combustion device (for example, the management of the flame in the combustion chamber).

[0175] In conventional combustion, the combustion flue gas contains the following: - Nitrogen dioxide (N2) having a mass content almost the same as that of oxidizing air, - Carbon dioxide (CO2) generated from combustion, - Water from the evaporation of water that may be contained in the combustion and, if applicable, in the fuel (for example, when the fuel consists of waste or coal), and water generated from oxidizing air, - Molecular oxygen (O2) that did not contribute to the combustion, - Pollutants that may include particulate matter, acids, NOx, SOx, heavy metals, dioxins, etc., depending on the fuel used.

[0176] When the combustion system of the present invention operates in the "oxy-combustion" mode as described above (addition of a molecular oxygen-rich gas containing at least 40% O2 with a partial recycle of the combustion flue gas), it is advantageous that the flow velocity of the combustion flue gas exiting the combustion device that is not recycled and is directly released into the atmosphere and / or treated (for example, for CO2 capture) before being released into the atmosphere is lower than the above-mentioned flow velocity X.

[0177] The higher the fraction of O2 in the molecular oxygen-rich gas supplied by source 30, the lower the flow velocity of the combustion flue gas released without recycling.

[0178] For example, when the molecular oxygen-rich gas is pure molecular oxygen, in practice, the combustion flue gas is recycled at a high recycle flow rate up to 10 / 11 of X, and the remainder of the combustion flue gas is directly released into the atmosphere at an order of 1 / 11 of X or, preferably, at a lower flow rate than that, and / or they are released by treating them in advance (for example, for CO2 capture) and / or removing pollutants from them before releasing them into the atmosphere.

[0179] In another alternative embodiment of the present invention, the mixer 31 can include an additional air inlet, and / or the combustion device can include an additional air inlet for injecting additional air into the combustion in addition to the recycled combustion flue gas and in addition to the molecular oxygen-rich gas. This will simply have an effect on the 11 coefficients described above. It will be between 1 and 11 depending on the additional air flow injected into the combustion through the additional air inlet in this case.

[0180] When the molecular oxygen-rich gas contains 90% molecular oxygen, in practice, recycle the combustion flue gas at a high recycle flow rate up to 9 / 10 of X and the remainder of the combustion flue gas at a flow rate on the order of 1 / 10 of X or preferably lower, and release them directly into the atmosphere or, for example, treat them beforehand to capture CO2 or remove pollutants from them before releasing them into the atmosphere.

[0181] It should be emphasized that the restrictions on pollutants in the oxidizing gas entering the combustion device are less than the environmental restrictions linked to the pollutants in the non-recycled combustion flue gas, which are becoming increasingly stringent. Therefore, in this case, the recycled combustion flue gas may remain untreated, or the recycled combustion flue gas may be treated before entering the mixer, which is "lighter" and much less costly than the treatment of non-recycled flue gas. Therefore, the total cost for the treatment of the combustion flue gas can be advantageously significantly reduced.

[0182] Returning to this significant reduction in the treatment cost of the combustion flue gas, the production of the molecular oxygen-rich gas incurs additional operating costs, which actually increase the fraction of O2 in the molecular oxygen-rich gas but remain significantly lower than the treatment cost of the combustion flue gas. Therefore, it is up to those skilled in the art to find and adapt a case-by-case compromise between the production cost of the gas that is more or less rich in molecular oxygen and the treatment cost of the combustion flue gas.

[0183] In the context of the present invention, the molecular oxygen-rich gas contains at least 40% molecular oxygen (below this threshold, the decrease in the flow rate of the non-recycled combustion flue gas is actually too small). Preferably, the fraction of molecular oxygen gas in the molecular oxygen-rich gas is at least 80%, more preferably at least 90%. In particular, it is advantageous for the molecular oxygen-rich gas to be pure or almost pure molecular oxygen gas (at least 99% O2).

Claims

1. A combustion device (1) for the combustion of a fuel (C) by at least one oxidizing gas (GC), an oxidizing gas (GC) supply unit (3) connected to the combustion device (1), the mixer (31), and a source (30) of molecular oxygen gas connected to a first inlet of the mixer (31) via a device (32) for supplying a molecular oxygen-rich gas and controlling the flow rate of the molecular oxygen-rich gas, an oxidizing gas (GC) supply unit (3) including a source (30) of molecular oxygen gas; a recycle means (4) including a recycle loop (40) between the combustion device (1) and a second inlet of the mixer (31), and a recycle valve (V2) mounted on the recycle loop (40); a first bypass (5) of the recycle loop (40) including a discharge valve (V3); a second bypass (6) of the recycle loop (40) downstream of the first bypass (5) and the recycle valve (V2); and a control unit (7) adapted to control a device (32) for controlling the flow rate of the molecular oxygen-rich gas, the recycle valve (V2), and the discharge valve (V3) so that the combustion system can be set to an operating mode selected from at least two different operating modes (M1; M2) and switched from one operating mode to another operating mode. In a first operating mode (M1), the recycle valve (V2) is closed, the discharge valve (V3) is open, the mixer (31) is not supplied with molecular oxygen-rich gas from the source (3) of molecular oxygen gas, and in a second operating mode (M2), the recycle valve (V2) is open, the discharge valve (V3) is at least partially open or closed, the mixer (31) is supplied with at least the molecular oxygen-rich gas supplied by the source (3) of molecular oxygen gas and at least a part of the combustion gas generated by the combustion device (1), and the second bypass (6) is open to the open air during both operating modes (M1; M2), and on the one hand, the two operating modes (M1;In the second operating mode (M2), the second bypass (6) has the function of allowing air to enter the recycle loop (40) and supply at least incoming air to the second inlet of the mixer (31) when the discharge valve (V3) is at least partially open and the recycle valve (V2) is closed or open. On the other hand, in the second operating mode (M2), the second bypass (6) allows an excess (G2) of the combustion gas (G) generated by the combustion device (1) to be discharged from the recycle loop (40) and another fraction (G1) of the combustion gas (G) generated by the combustion device (1) to be supplied to the second inlet of the mixer (31) when the discharge valve (V3) is closed and the recycle valve (V2) is open. A combustion system characterized by having such a function.;

2. The combustion system according to claim 1, wherein an apparatus (32) for controlling the flow rate of the molecular oxygen-rich gas includes a flow rate control valve (V1) controlled by a control unit (7).

3. The combustion system according to claim 2, wherein the flow rate control valve (V1) is a valve that opens and closes stepwise.

4. The combustion system according to any one of claims 1 to 3, wherein the recycle valve (V2) is a valve that opens and closes stepwise and / or the discharge valve (V3) is a valve that opens and closes stepwise.

5. The combustion system according to any one of claims 1 to 4, wherein the combustion system includes at least one sensor (33) adapted to measure the concentration of molecular oxygen in the oxidizing gas (GC), and the control unit (7) is adapted to control an apparatus (32) for controlling the flow rate of the molecular oxygen-rich gas according to the concentration of molecular oxygen measured by the sensor (33) at least during a second operating mode (M2).

6. The combustion device (1) includes a fan or compressor (10) adapted to supply an oxidizing gas (GC) to the combustion device (1) at a predetermined flow rate (θ ＧＣ ), and the flow rate (θ ＧＣ ) is preferably variable. The combustion system according to any one of claims 1 to 5.

7. The rate of supply of fuel (C) to the combustion device (1) is variable, and the combustion device (1) has a rate (θ ＧＣ ) that varies according to the rate of supply of fuel (C) to the combustion device (1). A fan or compressor (10) adapted to supply the oxidizing gas (GC) to the combustion device (1). The combustion system according to any one of claims 1 to 6.

8. The combustion system according to any one of claims 1 to 7, comprising a carbon dioxide injection device (11) connected to the inlet of the mixer (31) and adapted to inject carbon dioxide gas (CO ２ ) into the mixer (31) during a specific stage ("degraded oxygen combustion") of the second operating mode (M2).

9. The combustion system according to any one of claims 1 to 8, wherein the combustion system includes a condenser (8) in a recycle loop (40), the condenser (8) being adapted to dehumidify the combustion fumes (FC) and discharge the combustion gas (G) at an outlet and recycle at least a part thereof to the inlet of the mixer (31).

10. The combustion system according to any one of claims 1 to 9, wherein the combustion system includes a condenser (34) adapted to dehumidify the oxidizing gas (GC) before introducing the oxidizing gas (GC) into the combustion apparatus (1).

11. The combustion system according to claim 9 or 10, wherein the condenser (8 or 34) includes at least one heat exchanger (120) containing a coolant (L).

12. The combustion system according to claim 10, wherein the heat exchanger (120) includes a bath (121) of the coolant (L) and injection means (123) for moving the gaseous fluid (FC or GC) through the bath (121) of the coolant (L) to dehumidify it, and preferably the injection means (123) can dehumidify the gaseous fluid (FC or GC) below the surface of the bath (121) of the coolant (L).

13. The combustion system includes at least one sensor (33) adapted to measure the concentration of molecular oxygen in the oxidizing gas (GC), and the control unit (7) controls the flow rate of the molecular oxygen-rich gas, the recycle valve (V2) and the discharge valve (V3) to switch from the second operating mode (M2) to the first operating mode (M1) according to the measured concentration of molecular oxygen in the oxidizing gas (GC). The combustion system according to any one of claims 1 to 12, which is adapted to do so.

14. The control unit (7) is adapted to control the flow rate of the molecular oxygen-rich gas, the recycle valve (V2) and the discharge valve (V3) so that it can switch from one operating mode (M1 or M2) to another operating mode (M2 or M1) without stopping the combustion in the combustion device (1). The combustion system according to any one of claims 1 to 13, which is adapted to do so.

15. The control unit (7) is adapted to continuously control the opening of the device (32) for controlling the flow rate of the molecular oxygen-rich gas, the opening of the recycle valve (V2), and preferably the total or partial closing of the discharge valve (V3) to switch from the first operating mode (M1) to the second operating mode (M2). The combustion system according to any one of claims 1 to 14, which is adapted to do so.

16. The control unit (7) is adapted to continuously control the opening of the discharge valve (V3), the closing of the recycle valve (V2), and the closing of the device (32) for controlling the flow rate of the molecular oxygen-rich gas to switch from the second operating mode (M2) to the first operating mode (M1). The combustion system according to any one of claims 1 to 15, which is adapted to do so.

17. When the combustion system is operating in the second operating mode (M2), carbon dioxide (CO ２ ) is captured in at least a portion of the combustion gas (G). The carbon dioxide (CO ２ ) capture device (10) adapted to capture is included in the combustion system according to any one of claims 1 to 16.

18. The combustion system includes at least one pollutant removal device (12) mounted on the recycle loop (40) and adapted to capture one or more pollutants selected from particulate matter, SOx, NOx, acids, heavy metals, ammonia, and VOCs. The combustion system according to any one of claims 1 to 17, which is adapted to do so.

19. The molecular oxygen-rich gas supplied by the source (30) of molecular oxygen gas contains at least 50% molecular oxygen, preferably at least 80% molecular oxygen, and more preferably at least 90% molecular oxygen. The combustion system according to any one of claims 1 to 17, which is adapted to do so.

20. The combustion system according to any one of claims 1 to 17, wherein the molecular oxygen-rich gas supplied by the source (30) of molecular oxygen gas is pure or almost pure molecular oxygen.

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