Combustion system capable of operating with recirculation of combustion gases

Abstract

A combustion system capable of operating with recirculation of combustion gas. The combustion system comprises a bypass (6) in two different operating modes (M1 / "normal combustion"; the exhaust valve (V3) leads to the open air during the exhaust valve (V3, M2 / "oxygen combustion"), and on the one hand, in two operating modes (M1, M2), when the exhaust valve (V3) is at least partially open and the recirculation valve (V2) is closed or open, has a function of allowing air to enter the recirculation circuit (40), and on the other hand, in a second operating mode (M2), when the exhaust valve (V3) is closed and the recirculation valve (V2) is open, has a function of allowing air to enter the recirculation circuit (40). And a mixer (31) having a function of allowing an excess portion (G2) of the combustion gas (G) generated by the combustion device (1) to be discharged from the recirculation loop (40), the other portion (G1) of the combustion gas (G) generated by the combustion device (1) being supplied to the mixer (31).

Description

Technical Field

[0001] The invention relates to the field of combustion with recirculation of at least a portion of the fuel gas. Background Art

[0002] The so-called "conventional" combustion consists in mixing air (oxidant) with fuel to produce oxidation under high temperature conditions in a combustion device (furnace, boiler, etc.). The reaction is exothermic and naturally sustained. 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, the combustion flue gas contains water vapor (H2O) and gaseous combustion products, mainly gaseous molecular nitrogen (N2), and gaseous carbon dioxide (CO2).

[0004] As used herein, the term "combustion gases" refers to gaseous combustion products released following combustion.

[0005] If it is desired to capture CO2 from these flue gases, the water vapor can be easily removed by condensing these combustion flue gases and collecting the water in liquid form. On the other hand, the main difficulty lies in the separation of nitrogen and carbon dioxide. In addition, in conventional combustion, depending on the type of fuel used, the combustion gases may also contain other gaseous polluting combustion products in more or less significant amounts, such as SOx (sulfur oxides), NOx (nitrogen oxides), HCl (hydrogen chloride), HF (hydrogen fluoride), etc. .... Therefore, if it is desired to capture CO2 from these flue gases, it is also necessary to separate CO2 from these other pollutants.

[0006] Various solutions for capturing CO2 from flue gases from conventional combustion have been considered, but their costs remain very high.

[0007] In order to reduce the emission of pollutants in the combustion fumes, it is known to replace the above-mentioned conventional combustion with a combustion called "oxycombustion", in which the air (oxidant) is replaced by molecular oxygen in a stoichiometric proportion, the number of oxygen atoms being equal to the number required to oxidize all the atoms of the fuel.

[0008] The production of molecular oxygen for carrying out the oxycombustion can be obtained, for example, in a known manner by cryogenic means or by water electrolysis.

[0009] In the case of oxygen combustion of, for example, methane (CH4), the resulting combustion flue gas consists of 1 / 3 gaseous CO2 and 2 / 3 water vapor by volume. In the case of other fuels, there will also be pollutants from the combustion, such as HCl, SOx, etc. If the fuel does not contain nitrogen, the flue gas will advantageously be naturally free of NOx.

[0010] The chemical reaction equation for the oxygen combustion of methane (CH4) is shown below:

[0011] CH4+2O2→CO2+2H2O-891kJ / mole CH4

[0012] This means that each mole of CH4 will generate 891 kJ of energy externally.

[0013] For other fuels, the reactions are similar, and if the fuel contains atoms other than carbon and hydrogen, other compounds will appear.

[0014] In the case of oxygen combustion of methane, for example, it can be seen that capturing CO2 is easier. For this purpose, it is sufficient to condense the water from the combustion flue gases by a cooling or drying process to obtain gaseous CO2.

[0015] Therefore, it has hitherto been known to use a condenser to condense the oxycombustion flue gases in order to capture CO2.

[0016] However, a significant difficulty with oxy-combustion is that it is difficult to control the combustion because, unlike conventional combustion, the temperature of oxy-combustion can quickly and uncontrollably become very high in the combustion chamber, making it unbearable for conventional combustion equipment.

[0017] To overcome this difficulty, devices have been proposed that enable oxycombustion to be improved by condensing and recycling at least a portion of the combustion gas substantially containing CO2 in gaseous phase to mix it with molecular oxygen and obtain a combustion-supporting gas (O2-CO2) that advantageously reduces the combustion temperature.

[0018] This improvement enables molecular oxygen-based oxycombustion with more controllable recirculation of combustion gases compared to oxycombustion using only molecular oxygen as an oxidant, while reducing pollutant emissions and facilitating CO2 capture compared to conventional combustion.

[0019] These plants are designed to operate solely with oxycombustion with recirculation of combustion gases, which leads to several disadvantages.

[0020] The start-up and shut-down processes of these plants are critical and risky operating phases and can adversely lead to uncontrolled and excessive temperatures in the combustion chamber for oxy-combustion with recirculation of combustion gases.

[0021] During oxycombustion, with recirculation of the combustion gases, an excessively significant reduction in the molecular oxygen concentration in the combustion-supporting gases can adversely lead to an untimely stoppage of the combustion in the combustion chamber of the device, which can have serious consequences, for example in industrial production chains using the generated thermal energy.

[0022] International patent application WO 2011 / 148298 also proposes a combustion system in which combustion gases are recirculated by means of a ventilator installed on a recirculation loop. The combustion system can be operated either in conventional combustion with air supply or in oxycombustion with oxygen supply and without air supply, the ventilator installed on the recirculation loop being in operation in both cases. The publication further describes the use of a control unit programmed to control the air supply flow rate and the molecular oxygen supply flow rate during a transition period, thereby being able to switch from conventional combustion with air supply to oxycombustion with molecular oxygen supply and without air supply without interrupting the combustion process.

[0023] When the combustion system described in the publication is operated in an oxy-combustion mode, a failure of the molecular oxygen source may occur, for example resulting in an untimely and uncontrolled drop in the oxygen concentration in the combustion-supporting gas supplied to the combustion chamber. This lack of molecular oxygen may have several possible cumulative causes: an unexpected interruption of the molecular oxygen supply due to an untimely stoppage of the in-situ production of molecular oxygen or an empty molecular oxygen source; an untimely slowdown of the in-situ production of molecular oxygen; or an untimely drop in the flow rate or pressure of the molecular oxygen supply. An excessive drop in the molecular oxygen concentration in the combustion-supporting gas may detrimentally result in an untimely stoppage of oxy-combustion.

[0024] The technical solution described in international patent application WO 2011 / 148298 has the disadvantage of not being able to automatically adapt its operation in the event of an untimely lack of molecular oxygen.

[0025] Furthermore, in the above combustion system, when it is desired to require more heat energy from the combustion chamber during oxy-combustion, there is a risk of reaching uncontrolled and excessively high temperatures in the combustion chamber and causing an explosion. Conversely, when it is desired to reduce the heat energy supply from the combustion chamber during oxy-combustion, there is a risk of causing an untimely stoppage of combustion. Summary of the invention

[0026] Purpose of the invention

[0027] The main purpose of the present invention is to propose a combustion system which can operate with recirculation of at least part of the combustion gases, but which also makes it possible to overcome all or part of the above-mentioned disadvantages inherent in prior art oxy-combustion plants implementing such a combustion gas recirculation.

[0028] Summary of the Invention

[0029] The present invention therefore relates to a combustion system, which comprises a combustion device for burning fuel with the aid of at least one combustion-supporting gas; a combustion-supporting gas supply unit, which is connected to the combustion device and comprises a mixer and a gaseous molecular oxygen source, which provides a gas rich in molecular oxygen and is connected to a first inlet of the mixer via a flow control device for the molecular oxygen-rich gas; a recirculation device, which comprises a recirculation loop between the combustion device and the second inlet of the mixer, and a recirculation valve installed on the recirculation loop; a first bypass, which is implemented on the recirculation loop and comprises a discharge valve; a second bypass, which is implemented on the recirculation loop downstream of the first bypass and the recirculation valve; and a control unit. The control unit is suitable for controlling a flow control device for the molecular oxygen-rich gas, a recirculation valve and a discharge valve so as to be able to configure the combustion system into an operating mode selected from at least two different operating modes (M1; M2) and to be able to switch from one operating mode to another: a first operating mode (M1), in which the recirculation valve is closed, the discharge valve is open, and no molecular oxygen-rich gas from a gaseous molecular oxygen source is supplied to the mixer (the flow control device is closed); and a second operating mode (M2), in which the recirculation valve is open and the discharge valve is at least partially opened or closed, and the mixer is supplied with at least molecular oxygen-rich gas provided by the gaseous molecular oxygen source (the flow control device is open) and at least a part of the combustion gas generated by the combustion device.

[0030] The second bypass is connected to the open air during both operating modes (M1; M2) and, on the one hand, in both operating modes (M1; M2), when the discharge valve is at least partially open and the recirculation valve is closed or open, has the function of allowing air to enter the recirculation loop to supply at least the incoming air to the second inlet of the mixer, and on the other hand, in the second operating mode (M2), when the discharge valve is closed and the recirculation valve is open, has the function of allowing a surplus portion of the combustion gas generated by the combustion device to be discharged from the recirculation loop, another portion of the combustion gas generated by the combustion device supplies the second inlet of the mixer.

[0031] The term "gas rich in molecular oxygen" means that the gas contains at least 40% (volume percentage) of molecular oxygen.

[0032] In said first operating mode (M1), the mixer is supplied with at least air sucked in from the ambient air via the second bypass, and the combustion fumes exhausted by the combustion plant are discharged via the first bypass without being recirculated.

[0033] As a result, the combustion-supporting gas contains at least air and no molecular oxygen from the gaseous molecular oxygen source. The combustion in the combustion device is therefore conventional combustion.

[0034] In this first operating mode and in a particular embodiment variant, the combustion-supporting gas preferably consists exclusively of air.

[0035] In the second operating mode (M2), the combustion-supporting gas comprises at least a gas rich in molecular oxygen from a gaseous molecular oxygen source and at least a portion of the combustion gas which has been recycled.

[0036] As a result, the combustion in the combustion device is of the oxy-combustion type with recirculation of the combustion gases.

[0037] More specifically, in said second operating mode (M2), in a particular operating phase subsequently referred to as "degraded oxycombustion", the combustion-supporting gas may contain air sucked in from the ambient air via the second bypass. In said second operating mode and in another particular operating phase subsequently referred to as "intensive oxycombustion", the combustion-supporting gas does not contain air sucked in from the ambient air via the second bypass.

[0038] In the present invention, the second bypass is bidirectionally circulated, thus playing a role of passive safety.

[0039] When the combustion system is in a first operating mode, the flow rate of the intake air drawn into the recirculation loop via the second bypass is automatically adapted without intervening in the combustion system. In particular, the flow rate of the intake air drawn into the recirculation loop is automatically adapted to the flow rate of the combustion gas produced by the combustion device and, if necessary, automatically compensates for changes in the flow rate of this combustion gas. In a second operating mode in which the discharge valve is at least partially open (a particular operating phase of so-called "degraded oxy-combustion"), the flow rate of the intake air drawn into the recirculation loop via the second bypass is automatically adapted to the flow rate of the combustion gas produced by the combustion device and the flow rate of the gas enriched with molecular oxygen and, if necessary, automatically compensates for changes in the flow rate of this combustion gas and / or changes in the flow rate of the gas enriched with molecular oxygen.

[0040] When the combustion system is in the second operating mode with the exhaust valve closed (the so-called "enhanced oxygen combustion" operating phase), any excess portion of the combustion gas produced by the combustion device is discharged from the recirculation loop via the second bypass, and its flow rate is automatically adapted without intervening in the combustion system. In particular, the flow rate of the excess portion of the combustion gas discharged from the recirculation loop via the second bypass automatically adapts to the flow rate of the combustion gas produced by the combustion device and the flow rate of the gas rich in molecular oxygen, and automatically compensates for changes in the flow rate of this combustion gas and / or changes in the flow rate of the gas rich in molecular oxygen when necessary.

[0041] More particularly, and in particular unlike the solution described in international patent application WO 2011 / 148298, the recirculation circuit of the combustion system of the invention does not have a device for forced air circulation of the ventilator or compressor type between the second bypass and the second inlet of the mixer (i.e. downstream of the second bypass), which prevents said excess portion of the combustion gases generated by the combustion device from being discharged from the recirculation circuit via the second bypass by sucking air into the recirculation circuit via the second bypass.

[0042] The combustion device can be a common combustion device on the market or a specific combustion device developed in a specific way. Such a combustion device can have air inlets at different injection points according to the needs of the combustion. Advantageously, the present invention can be implemented more particularly without any changes to the combustion device.

[0043] More particularly, the combustion system of the present invention may include the following additional and optional features, alone or in combination with each other:

[0044] - The flow control device of the molecular oxygen-rich gas comprises a flow control valve controlled by a control unit.

[0045] - The flow control valve is a progressive opening and closing valve.

[0046] - The recirculation valve is a progressive opening and closing valve and / or the discharge valve is a progressive opening and closing valve.

[0047] - The combustion system comprises at least one sensor adapted to measure the molecular oxygen concentration in the combustion-supporting gas, and wherein the control unit is adapted to control the flow control device of the molecular oxygen-rich gas according to the molecular oxygen concentration measured by the sensor at least during the second operating mode (M2).

[0048] The combustion device comprises a ventilator or a compressor which is suitable for supplying combustion-supporting gas to the combustion device at a given flow rate which is preferably variable.

[0049] The flow rate of the fuel supplied to the combustion device is variable, and the combustion device comprises a ventilator or a compressor adapted to supply combustion-supporting gas to the combustion device at a flow rate that varies according to the flow rate of the fuel supplied to the combustion device.

[0050] The combustion system comprises a carbon dioxide injection device connected to the inlet of the mixer and suitable for injecting gaseous carbon dioxide into the mixer during a specific operating phase of the second operating mode (M2), the so-called "degraded oxycombustion".

[0051] The combustion system comprises a condenser on a recirculation loop suitable for dehumidifying the combustion fumes and discharging combustion gases at an outlet, at least part of which is recirculated to the inlet of the mixer.

[0052] - The combustion system comprises a condenser adapted to dehumidify the combustion-supporting gas before it is introduced into the combustion device.

[0053] - The condenser comprises at least one exchanger containing a cooling liquid.

[0054] The exchanger comprises a bath of cooling liquid, and injection means capable of passing the gaseous fluid to be dehumidified through this bath of cooling liquid, and preferably capable of injecting the gaseous fluid to be dehumidified below the surface of this bath of cooling liquid.

[0055] -The combustion system comprises at least one sensor adapted to measure the molecular oxygen concentration in the combustion-supporting gas, and a control unit adapted to control the flow control device of the molecular oxygen-rich gas, the recirculation valve and the discharge valve so as to switch from the second operating mode to the first operating mode depending on the measured molecular oxygen concentration in the combustion-supporting gas.

[0056] The control unit is adapted to control the flow control device of the molecular oxygen-rich gas, the recirculation 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 combustion in the combustion device.

[0057] The control unit is adapted to sequentially control the opening of the flow control device of the molecular oxygen-rich gas, the opening of the recirculation valve and preferably the full or partial closing of the discharge valve in order to switch from the first operating mode (M1) to the second operating mode (M2).

[0058] The control unit is adapted to sequentially control the opening of the discharge valve, the closing of the recirculation valve and the closing of the flow control device of the molecular oxygen-rich gas in order to switch from the second operating mode (M2) to the first operating mode (M1).

[0059] - the combustion system comprises a carbon dioxide (CO2) capture device adapted to capture carbon dioxide (CO2) in at least a part of the combustion gases when the combustion system is operated in a second operating mode (M2).

[0060] The molecular oxygen-enriched gas provided by the gaseous molecular oxygen source comprises at least 50% molecular oxygen, preferably at least 80% molecular oxygen, even more preferably at least 90% molecular oxygen.

[0061] - The molecular oxygen-enriched gas provided by the gaseous molecular oxygen source is pure or nearly pure (at least 99% O2) molecular oxygen.

[0062] The combustion system comprises at least one depollution device installed on the recirculation loop and suitable for capturing one or more pollutants chosen from: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The characteristics and advantages of the invention will emerge more clearly on reading the following detailed description of several particular embodiment variants of the invention, described by way of non-limiting and non-exhaustive examples of the invention and with reference to the accompanying drawings, in which:

[0064] - Figure 1 is a schematic diagram of a first specific embodiment variant of a combustion system according to the invention.

[0065] - Figure 2 In the first operating mode M1 (“normal combustion”) Figure 1 Combustion system;

[0066] - Figure 3 In the second operating mode M2 ​​(“combustion with recirculated oxygen”) and in a specific operating phase (“degraded oxygen combustion”) Figure 1 combustion system.

[0067] - Figure 4 In the second operating mode M2 ​​(“combustion with recirculated oxygen”) and in another specific operating phase (“enhanced oxygen combustion”) Figure 1 combustion system.

[0068] - Figure 5-10 are schematic diagrams of five other specific embodiment variations of the combustion system of the present invention.

[0069] - Fig.11 Specific examples of condensers that may be implemented in the combustion system of the present invention are shown. DETAILED DESCRIPTION

[0070] Detailed instructions

[0071] Figure 1 Combustion system

[0072] Figure 1 A first embodiment variant of the combustion system according to the invention is schematically shown, comprising:

[0073] - a combustion device 1 which is supplied with combustion-supporting gas GC from a combustion-supporting gas GC supply unit 3 and with fuel C from a fuel source 2 and which during operation emits combustion fumes FC at an outlet;

[0074] - a recirculation device 4, which comprises a recirculation loop 40 between the outlet of the combustion device 1 and the inlet of the combustion-supporting gas GC supply unit 3 and a recirculation valve V2 installed on the recirculation loop 40;

[0075] a first bypass 5 , which is connected to the recirculation circuit 40 and which comprises a discharge valve V3 ,

[0076] a second bypass 6 which is connected to the recirculation circuit 40 downstream of the first bypass 5 and the recirculation valve V2 and which opens into the open air;

[0077] - Control unit 7.

[0078] The combustion device 1 generally enables the combustion of a fuel C by means of said combustion-supporting gas GC, the heat energy generated by this combustion being indiscriminately used according to the invention in any type of application requiring heat supply and, for example and without limitation, for heating a fluid in a heating device or for supplying energy, in particular thermal, mechanical or electrical energy, to an industrial production chain. Such a combustion device 1 may indiscriminately comprise according to the invention a conventional boiler, a furnace or a combustion chamber in which the combustion process is carried out.

[0079] The combustion device 1 generally comprises a ventilator (or compressor) 10, which enables the combustion-supporting gas GC to be drawn out of or pushed into the combustion device 1, wherein the flow rate of the combustion-supporting gas GC entering the combustion device 1 is automatically adjusted or regulated. GC To adapt to the flow of fuel C and meet the thermal energy requirements.

[0080] The combustion device 1 may be a common combustion device on the market or a specific combustion device developed in a specific manner.

[0081] The combustion reaction of the fuel C with the aid of the combustion-supporting gas GC produces a combustion flue gas FC whose composition depends on the fuel C and the combustion-supporting gas GC.

[0082] In the context of the present invention, the fuel C can be very different depending on the application and can be in solid, liquid or gaseous form as the case may be.

[0083] The combustion-supporting gas GC supply unit 3 includes a gaseous molecular oxygen (O2) source 30, which is supplied to an inlet of a mixer 31 via a flow control device 32 controlled by a control unit 7. The other inlet of the mixer 31 is connected to a recirculation loop 40.

[0084] The gaseous molecular oxygen source 30 makes it possible to provide a gas rich in molecular oxygen, ie a gas comprising at least 40% (volume percentage) of molecular oxygen.

[0085] Preferably, as will be discussed later, the molecular oxygen-rich gas may advantageously but not necessarily consist of pure molecular oxygen or nearly pure molecular oxygen (concentration greater than 90% by volume).

[0086] The gaseous molecular oxygen source 30 may be of any known type and may, for example, include a unit for producing gaseous molecular oxygen by cryogenics and / or a unit for producing gaseous molecular oxygen by water electrolysis. The gaseous molecular oxygen source 30 may also be a unit for producing a molecular oxygen-enriched gas containing at least 40% molecular oxygen obtained by suitable filtration with the aid of zeolite or equivalent. The gaseous molecular oxygen source 30 may also not be designed to produce a molecular oxygen-enriched gas in situ, but may simply include a device for storing a molecular oxygen-enriched gas previously produced at another location.

[0087] In a variant, the flow control device 32 may simply stop or allow the passage of the molecular oxygen-rich gas from the source 30. However, preferably, this flow control device 32 enables the stopping of the molecular oxygen-rich gas from the source 30 or the passage of the molecular oxygen-rich gas from the source 30, so that the gas flow at the inlet of the mixer 31 can be adjusted by the control unit 7.

[0088] exist Figure 1 In a particular embodiment variant, the gaseous molecular oxygen source 30 is supplied to the mixer 31 , for example at 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 and closing valve.

[0090] In another variant, the flow control device 32 at the inlet of the mixer 31 can also include a pressure control system for the gas at the outlet of the source 30, which is optionally associated with a valve that can be a switching valve or a progressive opening and closing valve, and the pressure control system and the valve are controlled by the control unit 7.

[0091] Preferably, the combustion-supporting gas GC supply unit 3 further comprises at least one sensor 33 which measures the concentration of molecular oxygen in the combustion-supporting gas GC entering the combustion device 1 and transmits a measurement signal S of this concentration to the control unit 7 .

[0092] exist Figure 1 In a particular embodiment variant, the first bypass 5 is connected upstream of the valve V2 to the recirculation loop 40. In the simplest case, the first bypass 5 can consist of a simple pipe equipped with a discharge valve V3 making it possible to control the flow rate of the fluid circulating in said pipe.

[0093] The second bypass 6 is connected to the recirculation loop 40 downstream of the valve V2 .

[0094] exist Figure 1 In a particular embodiment variant, this second bypass 6 opens directly into the open air.

[0095] This second bypass 6 can be constituted by a simple pipe, one end of which is connected to the recirculation loop 40 and the other end leads directly to the open air. In its simplest form, this second bypass 6 can also be a simple opening allowing the recirculation loop 40 to communicate with the ambient air.

[0096] In another embodiment variant, the second bypass 6 can also supply a treatment device or a plurality of cascade treatment devices, for example a depollution device or a plurality of cascade depollution devices, of the combustion flue gases FC escaping via this second bypass 6 .

[0097] In the context of the present invention, the recirculation valve V2 can be an on-off valve or, more preferably, a proportional on-off valve. Likewise, the discharge valve V3 can be an on-off valve or, more preferably, a proportional on-off valve.

[0098] Valves V2 and V3 are preferably solenoid valves or pneumatic or hydraulic valves.

[0099] Preferably, Figure 1 In a variant, the combustion system includes a condenser 8, which is installed on the recirculation loop 40, downstream of the first bypass 5 and upstream of the second bypass 6, and when the recirculation valve V2 is opened, the condenser 8 is suitable for condensing the combustion flue gas FC discharged by the combustion equipment 1 by cooling it.

[0100] In the context of the present invention, this condenser 8 may generally comprise any type of exchanger allowing the combustion flue gases FC to be cooled by any means so as to achieve the condensation of at least part of the water vapor contained in the combustion flue gases F.

[0101] exist Figure 1 In a specific variant, the recirculation valve V2 is installed on the recirculation loop 40 upstream of the condenser 8. In another variant, the recirculation valve V2 may be installed on the recirculation 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).

[0102] The control unit 7 enables automatic control of the combustion system and, in this particular case, of the three valves V1, V2 and V3, respectively, by means of control signals C1, C2 and C3, so as to adapt the composition of the combustion-supporting gas GC and advantageously allow the device to operate in an operating mode selected from at least two different operating modes (M1 and M2) described in detail below, and to switch from one operating mode (M1 or M2) to another operating mode (M2 or M1).

[0103] This control unit 7 can be implemented in various forms and, for example, can be implemented with the aid of a programmable electronic control unit, such as a programmable automa- te type, or a programmable electronic circuit including a microprocessor, a microcontroller or a programmable logic circuit of the FPGA type; or it can also be implemented with the aid of a specific integrated electronic circuit of the ASIC type.

[0104] Operation mode of combustion system

[0105] Figure 1 The combustion system can be configured by the control unit 7 to operate in at least two different main operating modes:

[0106] M1( Figure 2 ): An operating mode referred to as "normal combustion" in which the valve V1 and the recirculation valve V2 of the flow control device 32 are closed (F) and the exhaust valve V3 is open (O).

[0107] M2( Figure 3 and 4 ): operating mode known as “oxygen combustion with recirculation”, in which valve V1 of flow control device 32 and recirculation valve V2 are open (O) and exhaust valve V3 is open (O) (completely or partially) or closed (F).

[0108] The switch from one operating mode (M1 or M2) to another operating mode (M2 or M1) can be controlled by the control unit 7 simply by appropriately controlling the flow control device 32 (more particularly the valve V1), the recirculation valve V2 and the discharge valve V3, and can advantageously be achieved without stopping the combustion in the combustion device 1 and without shutting down the combustion device 1.

[0109] Operating mode M1 - "Normal combustion" - Figure 2

[0110] In this operating mode, the supply valve V1 and the recirculation valve V2 of molecular oxygen from the source 30 have been closed (F) by the control unit 7. Only the discharge valve V3 is open (O).

[0111] The fan 10 (or compressor) of the combustion device 1 applies a variable flow rate θ of the combustion-supporting gas GC at the inlet of the combustion device 1.GC to run.

[0112] The mixer 31 is not supplied with molecular oxygen from the source 30. In the portion 40a downstream of the second bypass 6 of the recirculation loop 40, the mixer 31 is only supplied with air, which is sucked in from the ambient air via the second bypass 6 and delivered to the inlet of the mixer 31. Conventional combustion is thus achieved in the combustion device 1 with the aid of this air as combustion-supporting gas.

[0113] The combustion flue gas FC is not recirculated to the mixer 31 (the recirculation valve V2 is closed), but is pushed by the ventilator (or compressor) 10 in the first bypass 5 and discharged into the ambient air (the discharge valve V3 is open).

[0114] Operating mode M2 ​​- "Combustion with recirculated oxygen" - Figure 3 and 4

[0115] In this operating mode, the supply valve V1 and the recirculation valve V2 of molecular oxygen from the source 30 have been opened (O) by the control unit 7. The discharge valve V3 is open (O) (full or partial - Figure 3 ) or Close (F)( Figure 4 ).

[0116] The ventilator 10 (or compressor) of the combustion device applies a variable given flow rate (θ) of the combustion-supporting gas GC at the inlet of the device 1. GC ) to run.

[0117] This operation mode M2 ​​includes two operation phases:

[0118] - a phase of operation called "degraded oxy-combustion" Figure 3 Shown in.

[0119] - an operating phase called "enhanced oxy-combustion" Figure 4 Shown in.

[0120] Figure 3 Operational phase - "degraded oxy-combustion"

[0121] Part of the combustion flue gases FC leaving the combustion device 1 is discharged into the ambient air (discharge valve V3 is at least partially open), and another part of the combustion flue gases leaving the combustion device 1 is recirculated in the recirculation loop 40 (recirculation valve V2 is open) to the inlet of the condenser 8.

[0122] By passing through the condenser 8 , the recirculated combustion flue gases FC are cooled and dehumidified by condensation of the water vapor present in these combustion flue gases FC.

[0123] At the outlet of the condenser 8 , a dehumidified combustion gas G is obtained which contains gaseous combustion products produced by the 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 condenser 8 .

[0124] The mixer 31 is supplied with a gas rich in molecular oxygen from the source 30 (valve V1 open) at a flow rate (θO2) and with dehumidified combustion gas G at a flow rate θ.

[0125] The mixer 31 is also supplied with air at an inlet air flow rate θ 空气 The portion 40 a which is sucked in from the ambient air via the second bypass 6 and which is conveyed to the mixer 31 together with the dehumidified combustion gases G via the portion 40 a downstream of the bypass 6 in the recirculation loop 40 .

[0126] In operation: θ GC =θO2+θ+θ 空气

[0127] This operating phase continues as long as the discharge valve V3 is not completely closed.

[0128] In this operating phase, the combustion-supporting gas GC comprises molecular oxygen from the molecular oxygen-rich gas supplied from the source 30, the recirculated combustion gas G and air.

[0129] In this operation phase, 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 recirculated combustion gas G at the inlet of the mixer 31 increases, the air flow rate θ sucked into the second bypass 6 increases. 空气 On the contrary, 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 recirculated combustion gas G at the inlet of the mixer 31 decreases, the air flow rate θ sucked into the second bypass 6 空气 Automatically increase.

[0130] Figure 4 Operation phase - "Enhanced oxy-combustion"

[0131] In this operating phase, the supply valve V1 and the recirculation valve V2 of molecular oxygen from the source 30 are open (O), and the exhaust valve V3 is closed (F).

[0132] The combustion flue gases FC leaving the combustion device 1 are not discharged into the ambient air via the closed discharge valve V3 , but are recirculated in the recirculation loop 40 (recirculation valve V2 open) to the inlet of the condenser 8 and are dehumidified by passing through the condenser 8 .

[0133] In this operating phase, the mixer 31 is supplied with molecular oxygen of molecular oxygen-rich gas from the source 30 (valve V1 is open) at a given flow rate (θO2) and with a portion G1 of the combustion gas G leaving the condenser 8 at a flow rate θ1; another excess portion G2 of the combustion gas G leaving the condenser 8 is discharged to the open air through the second bypass 6 at a flow rate θ2.

[0134] In operation:

[0135] θ=θ1+θ2

[0136] θ GC =θO2+θ1

[0137] 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 recirculated portion 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 recirculated portion G1 of the combustion gas G automatically increases.

[0138] The combustion-supporting gas GC thus contains molecular oxygen from the molecular oxygen-rich gas from the source 30 and also a recirculated portion G1 of the combustion gas G.

[0139] Advantageously, the transition from the "degraded oxygen combustion" operating phase (valve V3 at least partially open) to the "enhanced oxygen combustion" operating phase (valve V3 closed) or vice versa can be achieved without having to shut down the combustion device 1 and without having to stop the combustion in the combustion device 1.

[0140] Preferably, in the operating mode M2, the control unit 7 automatically adjusts the flow rate θO2 of the molecular oxygen-rich gas (for example by closing the valve V1 more or less) so that the concentration of molecular oxygen in the combustion-supporting gas GC measured by the sensor 33 is equal to or greater than a given operating set point or within a given operating range. This allows the system to automatically adapt the flow rate θO2 of the combustion-supporting gas GC. GC changes (applied by the combustion device 1) to maintain an appropriate concentration of molecular oxygen O2 in the combustion-supporting gas GC.

[0141] Figure 1 The combustion system can be operated in particular, but not exclusively, with a fuel C which, in an "enhanced oxy-combustion" operating phase, produces a combustion flue gas FC which mainly comprises carbon dioxide (CO2) and water vapor (H2O), as well as smaller amounts of molecular oxygen (O2) and carbon monoxide (CO).

[0142] Therefore, without limitation and without exhaustion, Figure 1The fuel C used in the combustion system may advantageously be any type of hydrocarbon and for example conventional hydrocarbons derived from petroleum or natural gas or unconventional hydrocarbons derived from shale gas or oil, bituminous shale or sand, coal gas, biogas, synthesis gas, etc.

[0143] For example, when the fuel C is an alkane type saturated hydrocarbon (C n H 2n+2 ), the oxygen combustion reaction in the device is as follows:

[0144] C n H 2n+2 +(3n+1) / 2O2→nCO2+(n+1)H2O-energy (kJ / mol C n H 2n+2 )

[0145] The fuel may also be a solid or liquid fuel obtained in particular from mining (coal, wood, etc.), or may include waste materials (plastics, recycled materials, etc.).

[0146] The recirculation of the combustion gas containing CO2 to the inlet of the mixer 31 makes it possible to better control the oxygen combustion reaction in the combustion device 1 in a manner known per se and to significantly reduce the combustion temperature in this combustion device 1 compared to an oxygen combustion reaction carried out using only or essentially pure molecular oxygen as an oxidant.

[0147] We will now describe in detail Figure 1 Various operating conditions of the combustion system.

[0148] Controls the combustion system to switch from operating mode M1 ("conventional combustion") to operating mode M2 ​​("using recirculated oxygen"). Examples of "combustion")

[0149] Assume that the combustion system is configured to operate in mode M1 (“conventional combustion” - Figure 2 ), the molecular oxygen supply valve V1 and the recirculation valve V2 have been closed (F) by the control unit 7, and only the exhaust valve V3 is opened (O).

[0150] When the combustion device 1 is in operation, the fan 10 (or compressor) of the combustion device 1 applies a given flow rate (θ) of the combustion-supporting gas GC composed of air at the inlet of the device 1. GC ).

[0151] In order to switch from this operating mode M1 (conventional combustion) to the operating mode M2 ​​("combustion with recirculated oxygen"), the control unit 7 preferably sequentially controls the opening of the molecular oxygen supply valve V1 (preferably gradually), the opening of the recirculation valve V2 (preferably gradually), and the full or partial closing of the exhaust valve V3 (preferably gradually fully or partially closing).

[0152] The combustion system thus switches to operating mode M2 ​​(“combustion with recirculated oxygen”).

[0153] As long as the exhaust valve V3 is not completely closed, the combustion system is in the previously described operating phase known as "degraded oxygen combustion" ( Figure 3 ). The concentration of molecular oxygen in the combustion-supporting gas GC increases over time, while at the same time the concentration of air in the combustion-supporting gas decreases, the air being replaced by molecular oxygen. The combustion system can advantageously be operated indefinitely in operating mode M2 ​​("combustion with recirculated oxygen") and in the "degraded oxygen combustion" phase, wherein air is introduced at least via the opening 6 and optionally via a further second air inlet section, and the flue gases FC are discharged via the bypass 5 or a further flue gas FC partial outlet section.

[0154] When the discharge valve V3 is completely closed and when the sum of the flow rate θO2 of the molecular oxygen and the flow rate θ of the combustion gas G (θO2+θ) becomes greater than the flow rate θ of the combustion-supporting gas applied by the combustion device 1 GC The combustion system automatically switches to the so-called "enhanced oxygen combustion" operating phase ( Figure 4 ).

[0155] Preferably, when the combustion system has switched to operating mode M2 ​​("combustion with recirculated oxygen"), the control unit 7 automatically regulates the flow rate θO2 of molecular oxygen by using the measurement signal S of the molecular oxygen concentration in the combustion-supporting gas G (for example, in this particular case by more or less closing the progressive valve V1).

[0156] The switch from operating mode M1 (“conventional combustion”) to operating mode M2 ​​(“combustion with recirculated oxygen”) is simple and safe, avoiding the risk of an untimely and uncontrolled increase in the temperature of the combustion device 1. The switch from operating mode M1 (“conventional combustion”) to operating mode M2 ​​(“combustion with recirculated oxygen”) advantageously does not require any intervention of the user on the combustion device 1 and, most importantly, does not require stopping the combustion.

[0157] The “degraded oxycombustion” phase or the “enhanced oxycombustion” phase of the transition from operating mode M1 to operating mode M2 ​​(“combustion with recirculated oxycombustion”) can be initiated by the user of the combustion system, for example by means of a manual command to change the operating mode, the request being issued by the control unit 7 .

[0158] The switch from the operating mode M1 to the operating mode M2 ​​can also be carried out when starting up the combustion system so that it is operated in the “combustion with recirculated oxygen” mode ( M2 ).

[0159] Combustion System Startup Procedure

[0160] When the user wants to start the combustion system so that it operates in “combustion with recirculated oxygen” mode ( M2 ), he requests the control unit 7 to carry out a start-up procedure by means of appropriate commands.

[0161] The control unit 7 carries out the start-up procedure by initially configuring the combustion system to the operating mode M1 (“normal combustion”).

[0162] The combustion device 1 is then started, in particular by putting at least the fan (or compressor 10) of the combustion device 1 into operation, either manually by a user or automatically, for example, by the control unit 7, which makes it possible to initially operate the system in a conventional combustion mode (M1).

[0163] Then, in a second step, the control unit 7 controls the combustion system so as to automatically switch to the "combustion with recirculated oxygen" mode (M2), which is achieved, as described above, by selecting the operating stage known as "degraded oxygen combustion" or by completely closing the exhaust valve V3 and increasing the flow rate θO2 of the molecular oxygen-rich gas supplied by the source 30 until the operating stage known as "enhanced oxygen combustion" is reached.

[0164] Such a start-up phase is advantageously simple and safe. In particular, the risk of untimely and uncontrolled temperature rise inherent in prior art devices of this type due to the high initial concentration of molecular oxygen and the low initial concentration of CO2 in the combustion-supporting gas is avoided during this start-up phase, compared to prior art combustion systems adapted to operate only in an intensive oxy-combustion mode with recirculation of combustion gases.

[0165] Controls the combustion system to switch from operating mode M2 ​​("combustion with recirculated oxygen") to operating mode M1 ("conventional Examples of "combustion")

[0166] Assuming that the combustion system is configured in operating mode M2 ​​("combustion with recirculated oxygen"), the molecular oxygen supply valve V1 and the recirculation valve V2 have been opened (O) by the control unit 7, and the exhaust valve V3 is at least partially opened or closed (F).

[0167] When the combustion device 1 is in operation, the fan 10 (or compressor) of the combustion device 1 applies a given flow rate (θ) of the combustion-supporting gas GC composed of air at the inlet of the device 1. GC ).

[0168] In order to switch from this operating mode M2 ​​("combustion with recirculated oxygen") to the operating mode M1 ("conventional combustion"), the control unit 7 initially controls the full opening (preferably gradual opening) of the discharge valve V3, while maintaining control of the oxygen level in the combustion-supporting gas GC by means of the valve V1, which makes it possible to maintain combustion and allows the excess combustion gas to be discharged to the outside. The bypass 6 allows the supply of external air or the discharge of excess combustion gas according to the needs of the combustion device 1. Then, in a second step, once the opening of the valve V3 is completed, the control unit 7 controls the closing (preferably gradual closing) of the recirculation valve V2, which makes it possible to prevent the combustion gas from being recirculated to the inlet of the mixer 31. Once the closing of the valve V2 is completed, the control unit 7 controls the closing (preferably gradual closing) of the molecular oxygen supply valve V1, which makes it possible to prevent the gas rich in molecular oxygen (supplied by the source 30) from being injected into the combustion-supporting gas GC and switches the combustion system to "conventional combustion" (M1).

[0169] As a variant, the closing of the molecular oxygen supply valve V1 and the closing of the recirculation valve V2 may be controlled simultaneously by the control unit 7 .

[0170] As a variant, the opening of the discharge valve V3 , the closing of the molecular oxygen supply valve V1 and the closing of the recirculation valve V2 are not necessarily sequential but may be controlled simultaneously by the control unit 7 .

[0171] The switch from operating mode M2 ​​("combustion with recirculated oxygen") to operating mode M1 ("conventional combustion") is simple and safe, avoiding the risk of an untimely and uncontrolled increase in temperature in the combustion device 1. The switch from operating mode M2 ​​("combustion with recirculated oxygen") to operating mode M1 ("conventional combustion") advantageously does not require any intervention of the user on the combustion device 1 and, most importantly, does not require stopping the combustion.

[0172] The switch from the operating mode M2 ​​to the operating mode M1 can be initiated by a user of the combustion system, for example by means of a manual command to change the operating mode, the request being issued by the control unit 7 .

[0173] The switch from the operating mode M2 ​​to the operating mode M1 can also be carried out during a shutdown procedure of the operation of the combustion system.

[0174] Shutdown Procedures for Combustion Systems

[0175] When the user wants to shut down the combustion system which is operating in the “combustion with recirculated oxygen” mode ( M2 ), he requests the control unit 7 to execute a shut-down procedure by means of a suitable command.

[0176] The control unit 7 carries out this closing procedure by controlling the flow control device 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 previously described.

[0177] Once the combustion system has been configured in this operating mode M1 (“conventional oxycombustion”), the combustion plant 1 can be shut down in a conventional manner without any risk.

[0178] Such a shut-down phase is advantageously simple and safe. In particular, the risk of untimely and uncontrolled temperature increases inherent to prior art devices of this type is avoided during this shut-down phase, compared to prior art combustion systems adapted to operate only in oxy-combustion mode with recirculation of combustion gases.

[0179] The transition from operating mode M2 ​​to operating mode M1 may also be implemented when the concentration of molecular oxygen in the combustion-supporting gas GC (supplied by the source 30 ) becomes insufficient and no longer allows an enhanced oxycombustion with recirculation of combustion gases.

[0180] This deficiency may have several possible cumulative causes.

[0181] For example, it may happen that during operation of the combustion system in operating mode M2 ​​(“combustion with recirculated oxygen”), and in particular in the “enhanced oxygen combustion” operating phase, an unexpected interruption of the molecular oxygen supply occurs, for example due to an untimely stoppage of the in-situ generation of molecular oxygen-rich gas from the source 30 or an empty molecular oxygen-rich gas source 30.

[0182] For example, it may happen that during operation of the combustion system in operating mode M2 ​​(“combustion with recirculated oxygen”), and in particular in the “enhanced oxygen combustion” operating phase, the molecular oxygen supply is reduced too significantly, for example due to an untimely slowdown in the in-situ generation of molecular oxygen-rich gas from source 30 or to a pressure in source 30 that is too low.

[0183] For example, it may happen that during operation of the combustion system in operating mode M2 ​​(“combustion with recirculated oxygen”), and in particular in the “enhanced oxygen combustion” operating phase, the combustion device 1 is required to provide more thermal energy and responds thereto by increasing the flow rate θ of the combustion-supporting gas GC. GC (The flow rate of the ventilator or compressor 10 increases). In this case, additional combustion-supporting gas is automatically injected through the second bypass 6.

[0184] If the combustion device 1 reduces the supply of thermal energy (which results in a reduced demand for combustion-supporting gas GC), excess combustion-supporting gas is exhausted via the bypass 6 and the control system 7 adjusts the valve V1 to reduce the injection of molecular oxygen into the mixer 31 as necessary.

[0185] In a conventional apparatus capable of operating only in oxycombustion with recirculation of the combustion gas, an excessive decrease in the molecular oxygen concentration in the combustion-supporting gas GC may disadvantageously lead to an untimely stop of the oxycombustion.

[0186] Such untimely stops can advantageously be avoided by the combustion system of the present invention.

[0187] For this purpose, the control unit 7 is preferably designed to monitor the molecular oxygen concentration in the combustion-supporting gas GC with the aid of a sensor 33 and, when the molecular oxygen concentration decreases, automatically detects whether the molecular oxygen concentration reaches a predetermined (and preferably parameterizable) critical minimum threshold value and, if so, automatically controls the combustion system so as to safely switch it (as described above) to operating mode M1 ("conventional combustion") without stopping the combustion in the combustion device 1.

[0188] Further non-exhaustive examples of combustion systems that are in accordance with the invention and that can be operated in operating modes M1 (“conventional combustion”) and M2 (“combustion with recirculation”) will now be described.

[0189] Figure 5 Combustion system - condenser in "bypass" 8

[0190] Figure 5 Combustion system and Figure 1 The combustion system of FIG. 4 differs in that the condenser 8 is installed as a bypass on the recirculation loop 40 .

[0191] This type of installation is suitable in a known manner for a condenser 8 which has its own ventilator or compressor, for example as described below. Fig.11 Those described. Figure 1 The explanation of the operation of the combustion system also applies to Figure 5 of this combustion system.

[0192] Figure 6 Combustion system - condenser 34 downstream of mixer 31

[0193] Figure 6 Combustion system and Figure 1 The combustion system of is different in that the condenser 8 has been replaced by a condenser 34 which is supplied at the inlet by the mixer 31 and at the outlet is connected to the combustion device 1 and supplies the combustion device 1 with combustion-supporting gas GC.

[0194] In this variant, when the valve V2 is open and the combustion system is in operating mode M2 ​​(“combustion with recirculated oxygen”), the combustion flue gases FC are recirculated to the mixer 31 without being dehumidified, the dehumidification being carried out by the condenser 34 .

[0195] In another variation, the condenser 34 may be Figure 5The condenser 8 in the embodiment is installed in a "bypass" manner.

[0196] In another variant, the combustion system may include a condenser 8 upstream of the mixer 31 and a condenser 34 downstream of the mixer 31 .

[0197] Figure 7 Combustion system - Position of valves V2 and V3 after condenser 8

[0198] Figure 7 Combustion system and Figure 1 The combustion system of is different in that a recirculation valve V2 and a first bypass 5 comprising a discharge valve V3 are connected to the recirculation loop 40 downstream of the condenser 8. In this configuration, the condenser 8 is used in two operating modes M1 and M2.

[0199] Figure 8 Combustion System - CO2 Capture

[0200] Figure 8 Combustion system and Figure 1 The combustion system of EMI15.1 differs in that it comprises an additional CO2 capture device 10 adapted to operate when the combustion system operates in mode M2 ​​(“combustion with recirculated oxygen”) and in the “enhanced oxygen combustion” phase.

[0201] This device 10 comprises, for example, a CO2 capture unit 101, a bypass 100 connecting the CO2 capture unit 101 to the second bypass 6, a valve V4 mounted on the bypass 100 and controlled by the control unit 7 by means of a control signal C4, and a sensor 102, which detects the circulation direction of the gaseous fluid in the second bypass 6 and transmits the detection signal S 103 is delivered to the control unit 7 . The device 10 may also include a ventilator or a compressor which enables the combustion gases circulating in the second bypass 6 to be sucked in.

[0202] The second bypass 6 is equipped with an adjustable check valve CA, which allows a gaseous fluid (in this case, air) to pass freely through the second bypass 6 in one direction from the outside (ambient air) to the inside of the bypass 6, and can be adjusted or controlled by the control unit 7 to restrict the flow of the gaseous fluid in the opposite direction, or can be adjusted or controlled by the control unit 7 to prevent the flow of the gaseous fluid in the opposite direction when the return pressure in the second bypass 6 is greater than a predetermined pressure.

[0203] When the combustion system is in the first operating mode M1 and in the phase in the second operating mode M2 ​​(“degraded oxycombustion”), the valve V4 is closed and the non-return valve CA lets air from the outside into the second bypass 6 and the recirculation loop 40 as far as the mixer 31 .

[0204] When the combustion system switches to mode M2 ​​("combustion with recirculated oxygen") and the "enhanced oxygen combustion" phase, the sensor 102 detects the 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 recirculation loop 40 into the second bypass 6 to the CO2 capture unit 101. During this phase, the check valve CA blocks or restricts the flow of the combustion gas to the open-air outlet of the second bypass 6.

[0205] When the combustion system leaves the "enhanced oxycombustion" phase and enters the transition phase ("degraded oxycombustion"), the sensor 102 detects the change in circulation direction of the gaseous fluid due to air being sucked into the second bypass 6, and the control unit 7 automatically controls the closing of the valve V4.

[0206] This CO2 capture device 10 can also be added to Figures 5 to 7 , Fig. 9 and Fig.10 in the combustion system.

[0207] In another variant, the CO 2 capture device may be installed on the recirculation loop 40 between the first bypass 5 and the second bypass 6 and activated by the control unit 7 when the circulation direction of the gaseous fluid in the bypass 6 is outwards.

[0208] Fig. 9 Combustion system - CO2 injection at start-up

[0209] Fig. 9 Combustion system and Figure 1 The combustion system of the embodiment of the present invention is different in that it comprises an additional device 11 connected to the inlet of the mixer 31, which is used to inject gaseous carbon dioxide (CO2) into the mixer 31 during the "degraded oxygen combustion" transition phase when switching from the "degraded oxygen combustion" phase of the second operating mode M2 ​​to the "enhanced oxygen combustion" phase of the second operating mode M2, so as to shorten the duration of this transition phase.

[0210] This CO 2 injection device 11 comprises, for example, a source 110 of pressurized gaseous CO 2 associated with a valve V5 controlled by the control unit 7 by means of a control signal C5 .

[0211] This CO2 injection device 11 can also be added to Figures 5 to 8 and Fig.10 in the combustion system.

[0212] Fig.10 Combustion system - decontamination equipment 12

[0213] Fig.10 Combustion system and Figure 1The combustion system differs in that it comprises at least one depollution device 12 (known per se) installed on the recirculation loop 40 and suitable for capturing one or more pollutants chosen from the following: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs in the combustion gases circulating in the recirculation loop 40.

[0214] like Fig.10 As shown, the decontamination device 12 is preferably installed upstream of the second bypass 6. However, it can also be installed between the bypass 6 and the mixer 31.

[0215] The decontamination device 12 may also be added to Figures 5 to 9 in the combustion system.

[0216] Specific example of condenser - Fig.11

[0217] As a non-limiting example of the present invention, Fig.11 A preferred example of a condenser is shown which may be used as the condenser in the combustion system of the present invention, in particular as a condenser 8 or 34 in a "bypass" installation.

[0218] This condenser comprises an exchanger 12 comprising a housing 120 containing a bath 121 of a cooling liquid L and injection means 123 suitable for injecting the gaseous fluid F to be dehumidified (i.e. Figure 1-5 and Figure 7-10 The combustion flue gas FC of the variant or for Figure 6 The combustion gases leaving the mixer 31) are introduced below the surface of a bath of cooling liquid L.

[0219] The cooling liquid L may simply be water or an aqueous solution.

[0220] These injection means 123 may more particularly comprise a ventilator or compressor 123f and an injection duct 123a comprising, for example, an inlet opening 123b in its upper portion 123c. The lower portion 123d of the injection duct 123a is immersed in the bath 121 of the cooling liquid L and comprises a discharge opening 123e immersed in the bath 121 of the cooling liquid L.

[0221] In operation, the ventilator or compressor 123f enables the gaseous fluid F to be dehumidified (i.e., for Figure 1-5 and Figure 7-10 The combustion flue gas FC of the variant or for Figure 6The combustion gases leaving the mixer 31 of the embodiment of the present invention are introduced into the injection pipe 123 via the inlet opening 123b. This gaseous fluid F escapes from the injection pipe 123 via the discharge opening 123e and is thus forcibly introduced into the bath 121 of the cooling liquid L, below the surface of the bath 121 of the cooling liquid L, rises towards the surface of the liquid bath and escapes from the housing 120 via the discharge opening 120a of the housing 120 after having been dehumidified in the form of a dehumidified gas F'.

[0222] The temperature of the coolant L is T L is always lower than the temperature T of the gaseous fluid F at the inlet of the exchanger 12 F And preferably below the dew point temperature (dew point) of the gaseous fluid F.

[0223] It should be noted that the absolute humidity of the gas (g 水 / kg 干燥空气 ) expresses 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 when the temperature of the gas changes but remains above the dew point of the gas.

[0224] While passing in the bath 121 of cooling liquid L, the gaseous fluid F undergoes condensation in contact with the cooling liquid L, so that the absolute humidity of the gas F′ at the outlet of the exchanger 12 is less than that of the gaseous fluid F at the inlet of the exchanger 12 .

[0225] The difference between the absolute humidity of the dehumidified gas F' and the absolute humidity of the incoming gaseous fluid F depends in particular on the temperature T of the incoming gaseous fluid F. F The lower temperature T of the coolant L L The difference between the temperature T of the incoming gaseous fluid F F The temperature T of the coolant L L The temperature difference between F -T L ), the larger the absolute humidity of the dehumidified gas F' is compared to the absolute humidity of the incoming gaseous fluid F.

[0226] In another variant, a ventilator or compressor 123 f may be connected to the injection duct 123 and used to introduce the gaseous fluid F into the injection duct 123 by blowing it through the inlet opening 123 b of the injection duct 123 .

[0227] The exchanger 12 may more particularly be coupled to a heat pump (not shown) which makes it possible to renew the liquid L in the bath by extracting thermal energy therefrom, thus maintaining the temperature of this liquid at a sufficiently low level.

[0228] In another embodiment variant, the condenser may comprise a plurality of exchangers 12 mounted in cascade.

[0229] The present invention is not limited to using Fig.11 the exchanger 12 of the type shown in. In other implementation variants, the exchanger 12 for condensing the gaseous fluid F can be, for example, of the type described in international patent application WO2016 / 071648 or international patent application WO2020 / 030419, or can be an exchanger that operates by spraying a coolant L that comes into contact with the gaseous fluid F.

[0230] The present invention is not limited to exchangers that operate using a coolant, but can be implemented using any other known type of exchanger that allows the dehumidification of the gaseous fluid.

[0231] Advantages of using a gas rich in molecular oxygen in combination with recycling of at least part of the combustion flue gases

[0232] In the case of conventional combustion, for the amount Qd of fuel C to be burned per hour, the flow rate D of the combustion-supporting air is used at the inlet of the combustion device. After combustion, the combustion flue gas is discharged at a flow rate 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.

[0233] In conventional combustion, the air flow rate D (D < X) at the inlet of the combustion device is defined according to the oxygen required for combustion and the management of the combustion device (such as the flame management in the combustion chamber).

[0234] In conventional combustion, the combustion flue gas contains:

[0235] - Nitrogen dioxide (N2), which has a mass flow rate almost the same as that of the combustion-supporting air,

[0236] - Carbon dioxide (CO2) generated by combustion,

[0237] - Water generated by combustion, and in appropriate cases, water generated by the evaporation of water that may be contained in the fuel (for example, when the fuel consists of waste or coal), as well as water generated by the combustion-supporting air,

[0238] - Molecular oxygen (O2) that did not participate in combustion

[0239] - Pollutants, which depend on the fuel used and can include, for example, fine particles, acids, NOx, SOx, heavy metals, dioxins, etc. etc.

[0240] When the combustion system of the present invention is operated in the "oxygen combustion" mode as previously described [addition of a molecular oxygen-rich gas containing at least 40% O2) using recirculation of a portion of the combustion flue gases], the flow rate of the combustion flue gases leaving the combustion device that is not recirculated and is discharged directly into the atmosphere and / or is treated before being discharged into the atmosphere (for example for CO2 capture) is advantageously lower than the above-mentioned flow rate X.

[0241] The greater the O2 fraction in the molecular oxygen-rich gas supplied by the source 30, the lower the flow rate of combustion fumes that are not recycled and discharged.

[0242] For example, when the molecular oxygen-rich gas is pure molecular oxygen, it is practical to recirculate the combustion flue gases at a high recirculation rate of up to 10 / 11 of X, and to discharge the remaining combustion flue gases at an advantageously lower rate (which may be approximately 1 / 11 of X), either directly into the atmosphere or after pre-treatment (e.g., to capture CO2) and / or decontamination prior to discharge into the atmosphere.

[0243] In another embodiment variant of the invention, the mixer 31 may comprise an additional air inlet and / or the combustion device may comprise an additional air inlet, making it possible to inject additional air into the combustion in addition to the recirculated combustion fumes and in addition to the gas enriched with molecular oxygen. This will simply have an effect on the above-mentioned coefficient value 11, which in this case is between 1 and 11 depending on the additional air flow rate injected into the combustion via the additional air inlet.

[0244] When the molecular oxygen-rich gas contains 90% molecular oxygen, it is practical to recirculate the combustion flue gases at a high recirculation rate of up to 9 / 10 of X, and to discharge the remaining combustion flue gases at an advantageously lower rate (which may be about 1 / 10 of X), either directly into the atmosphere or after pre-treatment (e.g. to capture CO2) and / or decontamination, etc., before discharge into the atmosphere.

[0245] It should be emphasized that the limits on the pollution of the combustion-supporting gases entering the combustion equipment are less than the environmental limits related to the pollution of the non-recirculated combustion flue gases, which are becoming increasingly stringent. Therefore, depending on the situation, the recirculated combustion flue gases can be left untreated, or the recirculated combustion flue gases can be "lightly" treated before entering the mixer and at a much lower cost than treating the non-recirculated flue gases. Therefore, the overall costs of treating the combustion flue gases can be advantageously significantly reduced.

[0246] In exchange for this significant reduction in the costs of treating the combustion flue gases, the production of gas enriched with molecular oxygen causes additional operating costs, which in practice increase with the fractional proportion of O2 in the gas enriched with molecular oxygen, but which in practice remain significantly lower than the costs of treating the combustion flue gases. Therefore, it is possible for a person skilled in the art to adjust and find a compromise between the costs of producing gas enriched with more or less molecular oxygen and the costs of treating the combustion flue gases, depending on the specific circumstances.

[0247] In the context of the present invention, the gas enriched in molecular oxygen contains at least 40% molecular oxygen (below this threshold, the reduction in the flow of non-recirculated flue gas is too small in practice). Preferably, the fraction of gaseous molecular oxygen in the gas enriched in molecular oxygen is at least 80%, more preferably at least 90%. More particularly, the gas enriched in molecular oxygen is advantageously pure or almost pure gaseous molecular oxygen (at least 99% O2).

Claims

1. A combustion system, comprising a combustion device (1) for burning a fuel (C) by means of at least one combustion-supporting gas (GC); a combustion-supporting gas (GC) supply unit (3), which is connected to the combustion device (1) and comprises a mixer (31) and a gaseous molecular oxygen source (30), the gaseous molecular oxygen source (30) providing a molecular oxygen-rich gas and being connected to a first inlet of the mixer (31) via a molecular oxygen-rich gas flow control device (32); a recirculation device (4), which comprises a recirculation loop (40) between the combustion device (1) and a second inlet of the mixer (31), and a recirculation device (41) installed in the recirculation loop (41). 0); a first bypass (5), which is implemented on the recirculation loop (40) and which includes a discharge valve (V3); a second bypass (6), which is implemented on the recirculation loop (40) downstream of the first bypass (5) and the recirculation valve (V2); and a control unit (7), which is suitable for controlling the flow control device (32) of the molecular oxygen-rich gas, the recirculation valve (V2) and the discharge valve (V3), so that the combustion system can be configured to an operating mode selected from at least two different operating modes (M1; M2) and can be switched from one operating mode to another operating mode: a first operating mode (M1; M2) 1), in which the recirculation valve (V2) is closed, the discharge valve (V3) is open, and no molecular oxygen-enriched gas from the gaseous molecular oxygen source (3) is supplied to the mixer (31); and a second operating mode (M2), in which the recirculation valve (V2) is open and the discharge valve (V3) is at least partially open or closed, and the mixer (31) is supplied with at least molecular oxygen-enriched gas provided by the gaseous molecular oxygen source (3) and at least a portion of the combustion gas produced by the combustion device (1), wherein the second bypass (6) is connected to the open air during both operating modes (M1; M2) and on the one hand in both operating modes (M1, M2) 2), when the discharge valve (V3) is at least partially opened and the recirculation valve (V2) is closed or opened, it has the function of allowing air to enter the recirculation loop (40) to supply at least the incoming air to the second inlet of the mixer (31), and on the other hand, in the second operating mode (M2), when the discharge valve (V3) is closed and the recirculation valve (V2) is opened, it has the function of allowing the excess part (G2) of the combustion gas (G) generated by the combustion device (1) to be discharged from the recirculation loop (40), and the other part (G1) of the combustion gas (G) generated by the combustion device (1) is supplied to the second inlet of the mixer (31).

2. The combustion system according to claim 1, wherein the flow control device (32) of the molecular oxygen-rich gas comprises a flow control valve (V1) controlled by the control unit (7).

3. The combustion system according to claim 2, wherein the flow control valve (V1) is a progressive opening and closing valve.

4. The combustion system according to any one of claims 1 to 3, wherein the recirculation valve (V2) is a progressive opening and closing valve and / or the exhaust valve (V3) is a progressive opening and closing valve.

5. A combustion system according to any one of claims 1 to 4, comprising at least one sensor (33) suitable for measuring the molecular oxygen concentration in the combustion-supporting gas (GC), and wherein the control unit (7) is suitable for controlling the flow control device (32) of the molecular oxygen-rich gas according to the molecular oxygen concentration measured by the sensor (33) at least during the second operating mode (M2).

6. A combustion system according to any one of claims 1 to 5, wherein the combustion device (1) comprises a ventilator or compressor (10) adapted to generate a preferably variable given flow rate (θ GC ) supplies combustion-supporting gas (GC) to the combustion device (1).

7. A combustion system according to any one of claims 1 to 6, wherein the flow rate of the fuel (C) supplied to the combustion device (1) is variable, and the combustion device (1) comprises a ventilator or a compressor (10) which is adapted to supply the fuel (C) at a flow rate (θ GC ) supplies combustion-supporting gas (GC) to the combustion device (1), the flow rate (θ GC ) varies according to the flow rate of fuel (C) supplied to the combustion device (1).

8. A 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 suitable for injecting gaseous carbon dioxide (CO2) into the mixer (31) during a specific phase ("degraded oxycombustion") of the second operating mode (M2).

9. A combustion system according to any one of claims 1 to 8, comprising a condenser (8) on a recirculation loop (40), which is suitable for dehumidifying the combustion flue gases (FC) and discharging combustion gases (G) at an outlet, at least part of which is recirculated to the inlet of the mixer (31).

10. A combustion system according to any one of claims 1 to 9, comprising a condenser (34) adapted to dehumidify the combustion-supporting gas (GC) before it is introduced into the combustion device (1).

11. Combustion system according to any one of claims 9 or 10, wherein the condenser (8 or 34) comprises at least one exchanger (120) containing a cooling liquid (L).

12. A combustion system according to claim 10, wherein the exchanger (120) comprises a bath (121) of cooling liquid (L), and an injection device (123) capable of passing the gaseous fluid (FC or GC) to be dehumidified through this bath of cooling liquid (L), and preferably, wherein the injection device (123) enables the gaseous fluid (FC or GC) to be dehumidified to be injected below the surface of the bath (121) of cooling liquid (L).

13. A combustion system according to any one of claims 1 to 12, comprising at least one sensor (33) suitable for measuring the molecular oxygen concentration in the combustion-supporting gas (GC), and wherein a control unit (7) is suitable for controlling a flow control device (32) of a gas rich in molecular oxygen, a recirculation valve (V2) and a discharge valve (V3) so as to switch from a second operating mode (M2) to a first operating mode (M1) according to the measured molecular oxygen concentration in the combustion-supporting gas (GC).

14. A combustion system according to any one of claims 1 to 13, wherein the control unit (7) is suitable for controlling the flow control device (32) of the molecular oxygen-rich gas, the recirculation valve (V2) and the discharge valve (V3) so as 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 (1).

15. A combustion system according to any one of claims 1 to 14, wherein the control unit (7) is adapted to sequentially control the opening of the flow control device (32) of the molecular oxygen-rich gas, the opening of the recirculation valve (V2) and preferably the full or partial closing of the discharge valve (V3) in order to switch from the first operating mode (M1) to the second operating mode (M2).

16. A combustion system according to any one of claims 1 to 15, wherein the control unit (7) is adapted to sequentially control the opening of the exhaust valve (V3), the closing of the recirculation valve (V2) and the closing of the flow control device (32) of the molecular oxygen-rich gas in order to switch from the second operating mode (M2) to the first operating mode (M1).

17. The combustion system according to any one of claims 1 to 16, comprising a carbon dioxide (CO2) capture device (10), which is suitable for capturing carbon dioxide (CO2) in at least a part of the combustion gas (G) when the combustion system is operated in the second operating mode (M2).

18. A combustion system according to any one of claims 1 to 17, comprising at least one depollution device (12) installed on the recirculation loop (40) and suitable for capturing one or more pollutants selected from the following: fine particles, SOx, NOx, acids, heavy metals, ammonia, VOCs.

19. The combustion system according to any one of claims 1 to 17, wherein the molecular oxygen-rich gas provided by the gaseous molecular oxygen source (30) comprises at least 50% molecular oxygen, preferably at least 80% molecular oxygen, even more preferably at least 90% molecular oxygen.

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

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