Combustion system capable of operating with combustion flue gas recirculation

Abstract

The combustion system comprises: a combustion device (1) capable of combusting a fuel with at least one combustion-supporting gas (GC), comprising an outlet (1a) through which combustion fumes (FC) are discharged; a combustion-supporting gas (GC) supply unit (3) comprising a mixer (31) and a gaseous oxygen source (30) which provides oxygen-enriched gas and is connected to a first inlet of the mixer (31); a main discharge circuit (5) connected to the outlet (1a) of the combustion device (1) and leading to the atmosphere; a recirculation device (4) comprising a recirculation loop (40) between the main discharge loop (5) and the second inlet of the mixer (31), at least one recirculation fan or compressor (VR) mounted on the recirculation loop (40); a bypass (6) connected downstream of the recirculation fan or compressor (VR) to the recirculation circuit (40) and leading to the atmosphere; and a control unit (7) adapted to control at least the recirculation fan or the compressor (VR).

Description

Technical Field

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

[0002] So-called "conventional" combustion involves mixing air (an oxidant) with fuel at high temperatures in a combustion device (furnace, boiler, etc.) to produce oxidation. This reaction is exothermic and naturally continuous. Air contains 21% oxygen (O2), and the amount of air used is controlled to ensure that the oxygen content is sufficient for combustion.

[0003] In conventional combustion, the combustion flue gas includes water vapor (H2O) and gaseous combustion products mainly including gaseous nitrogen (N2) and gaseous carbon dioxide (CO2).

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

[0005] If one wishes to capture CO₂ from these flue gases, it is easy to remove the water vapor by condensing the combustion flue gases and collecting the water in liquid form. Conversely, the main difficulty lies in separating nitrogen and carbon dioxide. Furthermore, in conventional combustion, depending on the type of fuel used, the combustion gases may also contain other gaseous pollutants such as SO₂ (sulfur oxides), NO₂ (nitrogen oxides), HCl (hydrogen chloride), and HF (hydrogen fluoride). Therefore, if one wishes to capture CO₂ from these flue gases, it is also necessary to separate the CO₂ from these other pollutants.

[0006] Several solutions have been envisioned to capture CO2 from flue gases of conventional combustion, but their costs remain high.

[0007] In order to reduce the emission of pollutants in the combustion flue gases, it is known to replace the above-mentioned traditional combustion with a combustion called "oxygen combustion", in which the air (oxidant) is replaced by 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 oxygen for carrying out the oxycombustion can be achieved, for example, in a known manner by cryogenic techniques or by electrolysis of water.

[0009] For example, in the case of oxycombustion of methane (CH4), the resulting combustion flue gas is composed by volume of 1 / 3 gaseous CO2 and 2 / 3 water vapor. In the case of other fuels, combustion also produces pollutants such as hydrogen chloride (HCl) and sulfur oxides (SOx). If the fuel does not contain nitrogen, the flue gas will advantageously also be free of nitrogen oxides (NOx).

[0010] The chemical reaction equation for the combustion of methane (CH4) with oxygen is as follows:

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

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

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

[0014] For example, in the case of methane oxycombustion, it can be seen that CO2 is more easily captured. To do this, it is only necessary to condense the water in the combustion flue gas through cooling or dehydration processes to obtain gaseous CO2.

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

[0016] However, a major difficulty with oxy-combustion is the difficulty in controlling combustion because, unlike conventional combustion, the temperature of oxy-combustion in the combustion chamber quickly and uncontrollably becomes very high, which is beyond the capability of conventional combustion equipment.

[0017] To overcome this difficulty, some devices have been proposed that allow improving oxycombustion by recycling at least part of the CO2-rich gaseous phase combustion flue gases, preferably also by condensing said combustion flue gases in order to mix them with oxygen and obtain a combustion-supporting gas (O2-CO2) that advantageously reduces the combustion temperature.

[0018] This improvement allows easier control of oxygen-based oxycombustion with combustion flue gas recirculation compared to oxycombustion using only oxygen as an oxidant, while reducing pollutant emissions relative to conventional combustion and facilitating CO2 capture when necessary.

[0019] These plants are designed to operate exclusively with oxy-combustion with combustion flue gas recirculation, which leads to several disadvantages.

[0020] The start-up and shutdown procedures of these plants are critical and dangerous operating phases that can lead to uncontrolled and excessive temperatures in the combustion chamber for oxy-combustion with recirculation of combustion flue gases in a harmful way.

[0021] In oxycombustion processes with combustion flue gas recirculation, an excessive drop in the oxygen concentration in the combustion-supporting gas can lead to an untimely cessation of combustion in the combustion chamber of the system in a harmful manner, which can have serious consequences, for example, in industrial production chains that use the generated heat energy. Summary of the Invention

[0022] Purpose of the Invention

[0023] The main object of the present invention is to provide a combustion system which can be operated with at least a portion of the combustion flue gas recirculated and which can overcome all or part of the above-mentioned disadvantages inherent in the prior art oxy-combustion plants using such combustion flue gas recirculation. SUMMARY OF THE INVENTION

[0025] Therefore, the present invention is directed to a combustion system comprising: a combustion device capable of burning fuel using at least one combustion-supporting gas, comprising an outlet through which the combustion device discharges combustion flue gases; a combustion-supporting gas supply unit connected to the combustion device, allowing combustion-supporting gas to be supplied to the combustion device, the combustion-supporting gas supply unit comprising a mixer and a gaseous oxygen source, the gaseous oxygen source providing oxygen-rich gas and connected to a first inlet of the mixer; a main exhaust loop connected to the outlet of the combustion device and leading to the atmosphere; a recirculation device comprising a recirculation loop between the main exhaust loop and the second inlet of the mixer, at least one recirculation fan or compressor installed on the recirculation loop, the recirculation fan or compressor being suitable for causing the gaseous fluid to flow in the recirculation loop from the connection between the recirculation loop and the main exhaust loop toward the second inlet of the mixer; a bypass connected to the recirculation loop downstream of the recirculation fan or compressor (that is, between the recirculation fan or compressor and the second inlet of the mixer) and leading to the atmosphere; and a control unit suitable for controlling at least the recirculation fan or compressor.

[0026] The bypass allows at least the mixer to be fed with air entering into the bypass.

[0027] The term "oxygen-rich gas" refers to a gas containing at least 40% (volume percentage) oxygen.

[0028] More specifically, the control unit is suitable for controlling the recirculation fan or compressor so as to be able to configure the combustion system in one operating mode selected from at least two different operating modes (M1; M2) and to be able to switch from one operating mode to the other: a first operating mode (M1), in which the recirculation fan or compressor is stopped and the mixer is not supplied with oxygen-enriched gas from the gaseous oxygen source, but with air entering in the bypass; and a second operating mode (M2), in which the recirculation fan or compressor is operated and the mixer is supplied with at least oxygen-enriched gas provided by the gaseous oxygen source and at least a portion of the combustion flue gases discharged by the combustion device.

[0029] In the first operating mode (M1), the mixer is fed at least with air drawn in via the bypass, and all combustion flue gases emitted by the combustion device are discharged to the atmosphere, after treatment if necessary, without recirculation.

[0030] The combustion-supporting gas thus comprises at least air and no oxygen from the gaseous oxygen source. The combustion in the combustion device is therefore conventional combustion.

[0031] In this first operating mode and in a particular variant embodiment, the combustion-supporting gas preferably consists only of air.

[0032] In the second operating mode (M2), the combustion-supporting gas comprises at least oxygen-rich gas from a gaseous oxygen source and at least a portion of the combustion flue gases which is recycled, preferably treated (before recycling or in a recycling loop), and in particular preferably at least dehumidified.

[0033] The combustion in the combustion device is thus of the oxycombustion type with at least a portion of the combustion fumes being recirculated.

[0034] More specifically, in the second operating mode (M2), in a specific operating phase hereinafter referred to as "degraded oxy-combustion", the combustion-supporting gas may contain air drawn in from the atmosphere via a bypass. In another specific operating phase of the second operating mode, hereinafter referred to as "enhanced oxy-combustion", the combustion-supporting gas does not contain air drawn in from the atmosphere via a bypass.

[0035] The combustion device can be a common combustion device on the market or a specially developed special combustion device. The combustion device can have air inlets at different injection points according to the combustion requirements. Advantageously, more particularly, the present invention can be applied without any modification of the combustion device.

[0036] More specifically, the combustion system of the present invention may include the following additional and optional features, taken alone or in combination with each other:

[0037] - the combustion system further comprises at least one sensor adapted to measure the flow rate or pressure of the outgoing gaseous fluid in at least a downstream portion of the main exhaust circuit situated downstream of the connection of the recirculation circuit to the main exhaust circuit, and to transmit a flow rate or pressure measurement signal processed by the control unit.

[0038] The combustion system further comprises at least one sensor 60 adapted to measure at least the flow rate or pressure of the outgoing gaseous fluid in said bypass 6 and to send a flow rate or pressure measurement signal processed by a control unit.

[0039] The control unit is adapted to control said recirculation fan or compressor at least during an operating mode with recirculation of at least a portion of the combustion fumes, at least as a function of the flow or pressure measured by the sensor.

[0040] - the control unit is adapted to control at least the recirculation fan or compressor and, if necessary, the oxygen-enriched gas flow control device, so as 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.

[0041] - A gaseous oxygen source is connected to the first inlet of the mixer via an oxygen-rich gas flow control device controlled by a control unit, preferably comprising a flow control valve controlled by the control unit.

[0042] -The flow control valve is a progressive opening and closing valve.

[0043] - the combustion system comprises at least one sensor adapted to measure the oxygen concentration in the combustion-supporting gas, and the control unit is adapted to control the oxygen-enriched gas flow control device according to the oxygen concentration measured by the sensor, at least during the operating mode (M2) with recirculation of at least a portion of the combustion flue gases.

[0044] - The combustion device comprises a device suitable for a given flow rate (φ GC ) A fan or compressor that supplies combustion-supporting gas to the combustion device, wherein the given flow rate is preferably variable.

[0045] The supply flow rate of the fuel to the combustion device is variable, and the combustion device includes a flow rate (φ) adapted to be varied according to the supply flow rate of the fuel to the combustion device. GC ) A fan or compressor that supplies combustion-supporting gas to the combustion device.

[0046] The combustion system comprises treatment devices installed on the main exhaust circuit for treating the combustion fumes.

[0047] The combustion system comprises treatment means for treating the recirculated combustion fumes, which are installed on the recirculation circuit, preferably between the recirculation fan or compressor and the connection of the recirculation circuit to the main exhaust circuit.

[0048] - The treatment device is suitable for dehumidifying the combustion flue gases.

[0049] - The treatment device comprises a condenser.

[0050] The condenser comprises at least one exchanger containing a cooling fluid.

[0051] The exchanger comprises a cooling liquid bath and injection means allowing the gaseous fluid to be dehumidified to pass through said cooling liquid (L) bath, preferably said injection means allowing the gaseous fluid to be dehumidified to be injected below the surface of the cooling liquid bath.

[0052] The treatment device is suitable for cleaning combustion flue gases, more particularly for capturing one or more pollutants selected from the following list: fine particles, sulphur oxides SOx, nitrogen oxides NOx, acids, heavy metals, ammonia, volatile organic compounds.

[0053] -The combustion system comprises at least one sensor suitable for measuring the oxygen concentration in the combustion-supporting gas, and the control unit is suitable for controlling the oxygen-enriched gas flow control device and the recirculation fan or compressor according to the measured oxygen concentration in the combustion-supporting gas, preferably in order to switch from an operating mode (M2) with recirculation of at least a portion of the combustion flue gases to an operating mode (M1) without recirculation of the combustion flue gases.

[0054] - the combustion system comprises a carbon dioxide (CO2) capture device connected to the bypass and suitable for capturing carbon dioxide (CO2) from at least a portion of the recirculated combustion flue gases discharged through said bypass, and / or the combustion system comprises a carbon dioxide (CO2) capture device connected to a downstream part of the main emission circuit located downstream of the connection between the recirculation circuit and the main emission circuit and suitable for capturing carbon dioxide (CO2) from at least a portion of the non-recirculated combustion flue gases discharged through the downstream part of the main emission circuit.

[0055] The oxygen-rich gas provided by the gaseous oxygen source comprises at least 50% oxygen, preferably at least 80% oxygen, yet more preferably at least 90% oxygen.

[0056] - The oxygen-enriched gas provided by the gaseous oxygen source is pure oxygen or nearly pure oxygen.

[0057] - The combustion system comprises a carbon dioxide injection device connected to the inlet of the mixer and suitable for injecting gaseous carbon dioxide (CO2) into the mixer during a specific phase of the operating mode (M2) with recirculation of combustion flue gases ("degraded oxy-combustion") . BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The features and advantages of the present invention will become more apparent upon reading the following detailed description of several specific variant embodiments of the present invention, which are described by way of non-limiting and non-exhaustive examples of the present invention with reference to the accompanying drawings, in which:

[0059] - Figure 1 is a schematic diagram of a first specific variant embodiment of the combustion system of the present invention.

[0060] - Figure 2 The first operating mode M1 (“conventional combustion”) is shown. Figure 1 Combustion system.

[0061] - Figure 3The diagram shows the second operating mode M2 ​​("recirculating oxygen combustion") and a specific operating phase ("degraded oxygen combustion"). Figure 1 Combustion system.

[0062] - Figure 4 The diagram shows the second operating mode M2 ​​("recirculating oxygen combustion") and another specific operating phase ("enhanced oxygen combustion"). Figure 1 Combustion system.

[0063] - Figure 5 FIG. 1 is a schematic diagram of a second specific variant embodiment of the combustion system of the present invention.

[0064] - Figure 6 The first operating mode M1 (“conventional combustion”) is shown. Figure 5 Combustion system.

[0065] - Figure 7 The diagram shows the second operating mode M2 ​​("recirculating oxygen combustion") and a specific operating phase ("degraded oxygen combustion"). Figure 5 Combustion system.

[0066] - Figure 8 The diagram shows the second operating mode M2 ​​("recirculating oxygen combustion") and another specific operating phase ("enhanced oxygen combustion"). Figure 5 Combustion system.

[0067] - Figures 9 to 13 Schematic diagrams of five other specific variant embodiments of the combustion system of the present invention.

[0068] - Figure 14 A specific example of a condenser that may be employed in the combustion system of the present invention is shown. DETAILED DESCRIPTION

[0069] Figure 1 Combustion system

[0070] Figure 1 A first variant embodiment of the combustion system of the present invention is schematically shown in FIG. , the combustion system comprising:

[0071] - Combustion device 1, supplied with combustion-supporting gas GC from combustion-supporting gas supply unit 3 and fuel C from fuel source 2, discharges combustion flue gas FC through outlet 1a during operation;

[0072] a primary exhaust circuit 5 for exhausting at least part of the combustion fumes emitted by the combustion device 1, said primary exhaust circuit 5 being connected at one end to the outlet 1a of the combustion device 1 and opening out at the opposite end into the open air (at atmospheric pressure); said primary exhaust circuit 5 more particularly comprising an exhaust chimney 50 opening out into the atmosphere;

[0073] - a recirculation device 4, comprising a recirculation loop 40 connecting the main exhaust loop 5 to an inlet of the combustion-supporting gas GC supply unit 3, and a recirculation blower VR mounted on the recirculation loop 40; the recirculation blower VR, when in operation, is capable of forcibly causing the gaseous fluid to flow in the recirculation loop 40 from the connection 40a between the recirculation loop 40 and the main exhaust loop 5 toward the combustion-supporting gas GC supply unit 3;

[0074] a bypass 6 connected (connection 40 b ) to the recirculation circuit 40 downstream of the recirculation blower VR and opening into the open air at atmospheric pressure;

[0075] at least one sensor 51 adapted to measure at least the pressure or the flow of the outgoing gaseous fluid discharged to the atmosphere through the downstream portion 5b of the primary exhaust circuit 5 downstream of the connection 40a of the recirculation circuit 40 with the primary exhaust circuit 5 .

[0076] The sensor 51 may be installed, for example, in a pipe between the exhaust chimney 50 and the connection 40a of the recirculation loop 40 to the main exhaust loop 5, as shown in FIG. Figure 1 As shown, or it can be installed directly in the exhaust chimney 50.

[0077] exist Figure 1 In this variant embodiment, the control unit 7 is adapted to control the flow rate or pressure measured by the sensor 51 (the detection signal S transmitted by the sensor). 51 ) to control at least the recirculation fan VR, as will be described in detail later.

[0078] The control unit 7 can be implemented in various forms, for example by means of a programmable electronic control unit, for example of the programmable logic controller type, or by means of a programmable electronic circuit comprising a microprocessor, a microcontroller or a programmable logic circuit of the FPGA type, or also by means of a specific integrated electronic circuit of the ASIC type.

[0079] The bypass 6 may consist of a simple pipe connected at one end to the recirculation loop 40 and opening directly to the open air (at atmospheric pressure) at its other end. In its simplest version, this second bypass 6 may also be a simple opening allowing the recirculation loop 40 to communicate with the ambient air.

[0080] As a variant, the recirculation blower VR can be replaced by an air compressor.

[0081] The combustion device 1 generally allows the combustion of the fuel C using a combustion-supporting gas GC. According to the invention, the heat energy generated by this combustion can be used without distinction in any type of application requiring a thermal energy input, for example, in a non-limiting manner, for heating a fluid in a heating system or for providing energy, in particular thermal, mechanical or electrical energy, to an industrial production chain. According to the invention, the combustion device 1 can also without distinction comprise a conventional boiler, a furnace, or a combustion chamber in which the combustion process is carried out.

[0082] The combustion device 1 generally includes a blower (or compressor) 10, which allows the combustion-supporting gas GC to be sucked or pressed into the combustion device 1 and automatically adjusts or regulates the flow rate φ of the combustion-supporting gas GC entering the combustion device 1. GC , to adapt to the flow rate of fuel C and meet the thermal energy requirements.

[0083] The combustion device 1 can be a common combustion device on the market or a specially developed special combustion device.

[0084] The fuel C utilizes the combustion reaction of the combustion-supporting gas GC to generate combustion flue gas FC, and the components of the combustion flue gas depend on the fuel C and the combustion-supporting gas GC.

[0085] Within the scope of the present invention, the fuel C may be very different depending on the application and may be in solid, liquid or gaseous form, as the case may be.

[0086] The combustion-supporting gas GC supply unit 3 comprises a gaseous oxygen (O 2 ) source 30 which is supplied to one 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 .

[0087] The gaseous oxygen source 30 allows for the provision of an oxygen-rich gas, ie a gas comprising at least 40% by volume of oxygen.

[0088] Preferably, as will be discussed later, the oxygen-rich gas may advantageously, but not necessarily, consist of pure oxygen or quasi-pure oxygen (volume concentration greater than 90%).

[0089] The gaseous oxygen source 30 may be of any known type and may, for example, include a unit for cryogenically producing gaseous oxygen and / or a unit for producing gaseous oxygen by electrolysis of water. The gaseous oxygen source 30 may also be a unit for producing an oxygen-enriched gas containing at least 40% oxygen, obtained by properly treating air with zeolites or the like. The gaseous oxygen source 30 may not be designed to produce the oxygen-enriched gas on-site, but may simply include a device for storing oxygen-enriched gas that has been previously produced at another location.

[0090] In a variant, the flow control device 32 may allow simply stopping the flow of oxygen-enriched gas from the source 30 or letting it pass. However, preferably, the flow control device 32 allows stopping the flow of oxygen-enriched gas from the source 30 or letting it pass by allowing the control unit 7 to adjust the gas flow at the inlet of the mixer 31.

[0091] exist Figure 1 In a specific variant embodiment, the gaseous oxygen source 30 supplies gas to the mixer 31 at a constant pressure, for example. The flow control device 32 for controlling the flow at the inlet of the mixer 31 includes a valve V1 controlled by the control unit 7, preferably a solenoid valve.

[0092] Preferably, the valve V1 is a progressive opening and closing valve.

[0093] In another variant, the flow control device 32 for flow control at the inlet of the mixer 31 may also include a pressure control system for controlling the pressure of the gas leaving the source 30, which is associated with a valve if necessary, which can be a fully open or fully closed valve or a progressive opening and closing valve, and the pressure control system and the valve are controlled by the control unit 7.

[0094] Preferably, the combustion-supporting gas GC supply unit 3 further includes at least one sensor 33 , which measures the oxygen concentration in the combustion-supporting gas GC entering the combustion device 1 and transmits a measurement signal S of the concentration to the control unit 7 .

[0095] Preferably, Figure 1 In a variant embodiment, the combustion system comprises a treatment device 8 for treating combustion flue gases, which is installed on the upstream portion 5a of the main exhaust circuit 5, which is located upstream of the connection 40a of the recirculation circuit 40 with the main exhaust circuit 5.

[0096] In this particular variant embodiment, the treatment device 8 for treating the combustion flue gases FC preferably comprises a condenser suitable for condensing the combustion flue gases FC discharged by the combustion device 1 by cooling these gases. More specifically, the condenser of the treatment device 8 can generally comprise any type of exchanger that allows cooling the combustion flue gases FC by any means so as to condense at least a portion of the water vapor contained in the combustion flue gases F. At the outlet of the treatment device 8, in this case, dehumidified combustion flue gases FC' (enriched in CO2) are obtained, which mainly contain gaseous combustion products resulting from the combustion in the combustion device 1, and the dehumidified combustion flue gases FC' (enriched in CO2) have an absolute humidity lower than the absolute humidity of the combustion flue gases FC at the inlet of the treatment device 8.

[0097] The treatment device 8 for treating the combustion flue gases may also be adapted to purify the combustion flue gases, preferably by capturing one or more pollutants selected from the following list: fine particulate matter, SOx, NOx, acids, heavy metals, ammonia, volatile organic compounds. In this case, dehumidified and purified combustion flue gases FC' (enriched in CO2) are obtained at the outlet of the treatment device 8.

[0098] In a variant embodiment, the apparatus may not be provided with the treatment device 8, or the treatment device 8 may not be provided with a device for dehumidifying the combustion flue gas, but may only include a device for purifying the combustion flue gas. In this case, the apparatus preferably includes a treatment device installed on the recirculation loop 40 downstream or preferably upstream of the recirculation fan or compressor VR, and adapted to treat the recirculated combustion flue gas in the recirculation loop 40 so as to at least dehumidify the recirculated combustion flue gas.

[0099] The control unit 7 allows automatically manipulating the recirculation fan or compressor VR and the combustion gas GC supply unit 3 (more particularly in this variant the flow control device 32 ) to control the composition of the combustion gas GC, typically through control signals C2 and C1 respectively.

[0100] More specifically, the control unit 7 allows automatic control of the recirculation fan or compressor VR and the combustion gas GC supply unit 3, so as to advantageously allow the device to operate in one operating mode selected from at least two different operating modes (M1 and M2) detailed below, and allows switching from one operating mode (M1 or M2) to another operating mode (M2 or M1).

[0101] Operating modes of the combustion system

[0102] Figure 1 The combustion system can be configured by the control unit 7 to operate in at least two different main operating modes:

[0103] M1( Figure 2 ): An operating mode called "conventional combustion" in which the recirculation fan or compressor VR is stopped and the valve V1 of the flow control device 32 is closed (F).

[0104] M2( Figure 3 and Figure 4 ): An operating mode known as “oxy-combustion with recirculation”, in which the recirculation blower or compressor VR is running and controlled by the control unit 7, and the valve V1 of the flow control device 32 is open (O).

[0105] Switching from one operating mode (M1 or M2) to another (M2 or M1) can be controlled by the control unit 7 simply by appropriately controlling the recirculation fan or compressor VR and the flow control device 32 (more specifically, the valve V1). Switching from one operating mode (M1 or M2) to another (M2 or M1) can advantageously be done without stopping combustion, in particular without changing the combustion in the combustion device 1, and without stopping the combustion device 1.

[0106] Operating mode M1 - "Conventional combustion" - Figure 2

[0107] In this operating mode, the control unit 7 has closed (F) the valve V1 supplying oxygen from the source 30 and the recirculation blower or compressor VR is stopped.

[0108] The fan 10 (or compressor) of the combustion device 1 applies a possibly variable combustion-supporting gas GC flow rate φ at the inlet of the combustion device 1. GC to run.

[0109] The mixer 31 is not supplied with oxygen from the source 30. The mixer 31 is only supplied with intake air drawn in via the bypass 6 and delivered to the inlet of the mixer 31. Thus, in the combustion system 1, conventional combustion is performed with this intake air acting as combustion-supporting gas.

[0110] After being treated (FC′) in the treatment device 8 , the combustion flue gas FC is not recycled to the mixer 31 but is pushed by the fan (or compressor) 10 into the downstream portion 5 b of the main exhaust circuit 5 and discharged into the open air.

[0111] In a variant embodiment, the recirculation circuit 40 can optionally also be equipped with flue gas shutoff valves which are controlled by the control unit 7 in the operating mode M1 and opened by the control unit 7 in the operating mode M2 ​​(recirculation of at least part of the combustion flue gases). These shutoff valves can also be operated manually.

[0112] Operating mode M2 ​​- "Oxygen combustion with recirculation" - Figure 3 and Figure 4

[0113] In this operating mode, the fan 10 (or compressor) of the combustion device applies a given flow rate (φ) of the combustion-supporting gas GC at the inlet of the combustion device 1, which may vary. GC ) to run.

[0114] The control unit 7 automatically controls the combustion-supporting gas GC supply unit 3, especially the flow control device 32, based on the oxygen concentration (signal S) in the combustion-supporting gas GC measured by the sensor 33, so as to produce a gas having a suitable oxygen rate needed or required for combustion (for example, set by a preferably parameterizable set value).

[0115] According to the pressure or flow measured by the sensor 51 , the control unit 7 also automatically starts and controls the recirculation fan or compressor VR.

[0116] In particular, the control unit 7 automatically controls the recirculation fan or compressor VR until the flow or pressure measured by the sensor 51 reaches at least a predetermined, preferably parameterizable, operating setpoint, and automatically adjusts the flow of the recirculation fan or compressor VR so as to keep the pressure or the flow measured by the sensor 51 at or near the operating setpoint.

[0117] The operating set value is set so that the flow rate of the recirculation fan or compressor VR is less than the flow rate of the combustion flue gas FC at the outlet of the treatment device 8, or in the absence of the treatment device 8, less than the flow rate of the combustion flue gas FC at the outlet of the combustion device 1, so as to recirculate at least a portion FC2 of the combustion flue gas to the mixer 31, and the other portion FC1 is discharged into the open atmosphere through the downstream portion 5b of the main exhaust circuit 5.

[0118] The lower the pressure or flow rate measured by the sensor 51 , the higher the flow rate of the combustion flue gas FC2 recirculated in the direction of the mixer 31 .

[0119] In operating mode M2 ​​of this variant embodiment, if the flow rate of the recirculation fan or compressor VR, for example, unexpectedly becomes higher than the flow rate of the combustion fumes (FC or FC') upstream of the connection 40a of the recirculation circuit, in this case all the combustion fumes are automatically and safely recirculated (FC2 = FC') to the mixer 31, no combustion fumes FC1 are discharged to the atmosphere, but instead, intake air from the ambient air is automatically sucked into the downstream portion 5b of the main exhaust circuit 5 as a supplement and conveyed into the recirculation circuit 40 as far as the inlet of the mixer 31. The combustion in the combustion device 1 is advantageously not disturbed in any way, since the pressure in the downstream portion 5b of the main exhaust circuit 5 (opening to the atmosphere) does not change.

[0120] The operating mode M2 ​​actually includes the following two operating stages:

[0121] -The first operating stage, called "degraded oxygen combustion", is shown in Figure 3 middle.

[0122] - The second operating stage, called "enhanced oxygen combustion", is shown in Figure 4 middle.

[0123] Figure 3 Operational phase - "degraded oxygen combustion"

[0124] As long as the recirculation flow of the recirculation fan or compressor VR is low enough, a part FC1 of the treated combustion flue gas FC' (after passing through the treatment device 8) is discharged into the ambient air through the downstream part 5b of the main discharge circuit 5, while another part FC2 of the treated combustion flue gas FC' (after passing through the treatment device 8) is recirculated in the recirculation circuit 40 to the inlet of the mixer 31.

[0125] Oxygen-rich gas from source 30 (valve V1 open) is supplied to the mixer 31 at a flow rate (φO2), and treated combustion flue gas FC2 is supplied to the mixer at a flow rate φ.

[0126] The mixer 31 is also supplied with air at an inlet air flow rate φ 空气 It is sucked in from the ambient air via the bypass 6 and conveyed to the mixer 31 simultaneously with the combustion flue gases FC2 via the portion of the recirculation circuit 40 downstream of the connection 40 a of the bypass 6 with the recirculation circuit 40 .

[0127] Running: φ GC =φO2+φ+φ 空气

[0128] This operating phase lasts as long as the flow rate of the recirculation fan or compressor VR is below the critical threshold.

[0129] In this operating phase, the combustion-supporting gas GC comprises oxygen from the oxygen-rich gas supplied by the source 30, recycled treated combustion flue gas FC2 (rich in CO2) and air.

[0130] In this operation phase, when the flow rate φO2 of the oxygen-rich gas at the inlet of the mixer 31 increases and / or when the flow rate φ of the recycled treated combustion flue gas FC2 at the inlet of the mixer 31 increases, the flow rate φ of the air sucked into the second bypass 6 increases. 空气 On the contrary, when the flow rate φO2 of the oxygen-rich gas at the inlet of the mixer 31 decreases and / or when the flow rate φ of the recycled treated combustion flue gas FC2 at the inlet of the mixer 31 decreases, the flow rate φO2 of the air sucked into the second bypass 6 will automatically increase.

[0131] Figure 4 Operational stage - "Efficient oxygen combustion"

[0132] When the flow rate of the recirculation fan or compressor VR exceeds a critical threshold, it automatically switches to this operating phase, which is manifested by the gaseous flow in the bypass 6 being reversed, air is no longer drawn into the bypass 6, and a portion of the treated combustion flue gas FC2 is recycled. 22 The remaining part of the treated combustion flue gas FC2 will be automatically discharged into the bypass 6 and recycled. 21 It will be delivered to the inlet of the mixer 31.

[0133] In this operating phase, the mixer 31 is supplied with oxygen from the oxygen-rich gas from the source 30 at a given flow rate (φO2) (valve V1 is open) and with a portion of the recycled treated combustion flue gas FC2 at a flow rate φ1. 21 ; Another part of the recycled treated combustion flue gas FC2 FC 22 It is discharged into the bypass 6 at a flow rate φ2.

[0134] Runtime:

[0135] φ=φ1+φ2

[0136] φ GC =φO2+φ1

[0137] When the flow rate φO2 of the oxygen-rich gas at the inlet of the mixer 31 increases, the recirculation portion FC2 of the combustion flue gas FC 21 The flow rate φ1 of the oxygen-rich gas at the inlet of the mixer 31 is automatically reduced. When the flow rate φO2 of the oxygen-rich gas at the inlet of the mixer 31 is reduced, the recirculation part FC 21 The flow rate φ1 will automatically increase.

[0138] Therefore, the combustion-supporting gas GC contains oxygen from the oxygen-rich gas of the source 30 and part of the FC 21 .

[0139] The control unit 7 can easily and safely control the switch from one operating phase to another by automatically regulating the flow of the recirculation fan or compressor VR, advantageously without stopping the combustion device 1 and without stopping the combustion in the combustion device 1 .

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

[0141] Figure 1The combustion system can be operated in particular, but not exclusively, with a fuel C, which generates, in an "oxygen-combustion" operating phase, a combustion flue gas FC which comprises mainly carbon dioxide (CO2) and water vapor (H2O), and also to a lesser extent oxygen (O2) and carbon monoxide (CO).

[0142] Therefore, in a non-limiting and non-exhaustive manner, Figure 1 The fuel C used in the combustion system can advantageously be any type of hydrocarbon, such as conventional hydrocarbons from petroleum or natural gas, or unconventional hydrocarbons from shale gas or shale oil, oil shale or asphalt sandstone, coal gas, biogas, synthesis gas, etc.

[0143] For example, when the fuel C is an alkane (C n H 2n+2 ) type saturated hydrocarbons, the oxygen combustion reaction in the device is in a known manner:

[0144] C n H 2n+2 (3n+1) / 2O2→nCO2+(n+1)H2O-Energie(kJ / mole de C n H 2n+2 )

[0145] (Energie(kJ / molede C n H 2n+2 ) means: Energy (kJ per mole C n H 2n+2 ), that is, per mole of C n H 2n+2 The energy produced is expressed in kilojoules)

[0146] The fuel may also be a fuel obtained by mining, in particular solid or liquid (coal, wood, etc.), or may consist of waste (plastics, recycled materials, etc.)

[0147] Recirculating the CO2-containing combustion gas to the inlet of the mixer 31 is known per se to allow better control of the oxygen combustion reaction in the burner 1 and a significant reduction in the combustion temperature of the burner 1 compared to an oxygen combustion reaction using only or essentially pure oxygen as an oxidant.

[0148] The combustion system can advantageously be operated in operating mode M2 ​​("oxygen combustion with recirculation") and indefinitely in a "degraded oxygen combustion" phase, wherein at least part of the air is introduced via the bypass 6 (if necessary via another secondary air inlet or a secondary combustion gas inlet directly connected to the combustion device 1) and a part FC1 of the combustion flue gases FC (in the absence of a treatment device 8) or FC' (in the presence of a treatment device) is discharged to the atmosphere via the downstream part 5b of the main emission circuit 5.

[0149] Preferably, when the combustion system has switched to operating mode M2 ​​("oxygen combustion with recirculation"), the control unit 7 automatically regulates the oxygen flow rate φO2 by using the measurement signal S of the oxygen concentration in the combustion gas GC (for example, in this particular case, by more or less closing the progressive valve V1).

[0150] Switching from operating mode M1 ("conventional combustion") to operating mode M2 ​​("oxygen combustion with recirculation") is simple and safe, avoiding the risk of an untimely and uncontrolled increase in the temperature of the combustion device 1. Switching from operating mode M1 ("conventional combustion") to operating mode M2 ​​("oxygen combustion with recirculation") advantageously does not require any user intervention in the combustion device 1, in particular, without requiring the combustion to be stopped.

[0151] At the initiative of the user of the combustion system, for example by means of a manual control for changing the operating mode, a request can be made to the control unit 7 to switch from the operating mode M1 to the operating mode M2 ​​("oxygen combustion with recirculation") in the "degraded combustion" phase or in the "enhanced combustion" operating phase.

[0152] When starting up the combustion system, a switch from the operating mode M1 to the operating mode M2 ​​can also be effected in order to operate the combustion system in “oxygen combustion with recirculation” ( M2 ).

[0153] Combustion System Startup Procedure

[0154] When the user wishes to start the combustion system so that it operates in “oxygen combustion with recirculation” ( M2 ), he requests the control unit 7 to carry out the start-up procedure by means of appropriate commands.

[0155] The control unit 7 performs the start-up procedure by initially configuring the combustion system to operating mode M1 (“conventional combustion”).

[0156] The combustion device 1 is then started, either manually by the user or automatically by the control unit 7 , for example, and in particular at least the fan (or compressor 10 ) of the combustion device 1 is operated, which initially allows the system to be operated with conventional combustion ( M1 ).

[0157] Then, secondly, the control unit 7 controls the combustion system so as to automatically switch to "oxy-combustion with recirculation" (M2) by selecting the operating phase called "degraded oxy-combustion" or the operating phase called "enhanced oxy-combustion", as previously described.

[0158] Advantageously, this startup phase is simple and safe. In particular, compared to prior art combustion systems adapted to operate solely in an oxyfuel combustion mode with combustion flue gas recirculation, the risk of uncontrolled and untimely temperature increases, inherent in such prior art systems due to the high initial oxygen concentration and the low initial CO2 concentration in the combustion gas, is avoided during the startup phase.

[0159] Example of controlling a combustion system to switch from operating mode M2 ​​("oxygen combustion with recirculation") to operating mode M1 ("conventional combustion")

[0160] It is assumed that the combustion system is configured in operating mode M2 ​​(“oxygen combustion with recirculation”).

[0161] The combustion device 1 is running, the recirculation fan or compressor VR is running, the fan 10 (or compressor) of the combustion device 1 is running, and a given flow rate (φ) of the combustion-supporting gas GC composed of air is applied at the inlet of the combustion device 1. GC ).

[0162] To switch from this operating mode M2 ​​("oxygen combustion with recirculation") to operating mode M1 ("conventional combustion"), the control unit 7 only needs to control the recirculation fan or compressor VR to slow down until the recirculation fan or compressor VR stops, and then control the valve V1 to close.

[0163] Switching from operating mode M2 ​​("oxygen combustion with recirculation") to operating mode M1 ("conventional combustion") is simple, fast, and safe, avoiding the risk of an uncontrolled and untimely temperature increase in the combustion device 1. Switching from operating mode M2 ​​("oxygen combustion with recirculation") to operating mode M1 ("conventional combustion") advantageously does not require any user intervention in the combustion device 1, in particular without requiring the combustion to be stopped.

[0164] 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 to switch the operating mode.

[0165] The switch from the operating mode M2 ​​to the operating mode M1 can also be performed when the combustion system is running a shutdown procedure.

[0166] Combustion System Shutdown Procedure

[0167] When the user wishes to stop the combustion system while it is operating in “oxygen combustion with recirculation” mode ( M2 ), he requests the control unit 7 to execute a stop procedure by means of an appropriate command.

[0168] The control unit 7 executes the stop procedure by controlling the recirculation fan or compressor VR to decelerate until it stops as described above, and then controls the valve V1 of the oxygen-rich gas flow control device 32 to close to switch from the operation mode M2 ​​to the operation mode M1.

[0169] Once the combustion system has been configured in this operating mode M1 (“conventional oxy-combustion”), the combustion device 1 can be shut down in a conventional manner known per se without any risk.

[0170] This shutdown phase is advantageously simple and safe. In particular, compared to prior art combustion systems adapted to operate solely with oxy-combustion with combustion flue gas recirculation, the risk of uncontrolled and untimely temperature increases inherent in such prior art devices is avoided during the shutdown phase.

[0171] Switching from operating mode M2 ​​to operating mode M1 can also be achieved when the concentration of oxygen in the combustion gas GC (supplied by source 30 ) becomes insufficient and no longer allows efficient oxycombustion with combustion gas recirculation.

[0172] This deficiency may have several overlapping reasons.

[0173] For example, it may happen that during operation of the combustion system in operating mode M2 ​​("oxygen combustion with recirculation"), in particular during the "enhanced oxycombustion" operating phase, the oxygen supply is unexpectedly interrupted, for example due to an untimely cessation of the on-site production of oxygen-rich gas by the source 30 or exhaustion of the oxygen-rich gas source 30.

[0174] For example, it may happen that during operation of the combustion system in operating mode M2 ​​("oxygen combustion with recirculation"), in particular during the "enhanced oxygen combustion" operating phase, the oxygen supply is excessively reduced, for example due to an untimely slowdown in the production of oxygen-rich gas on site in source 30 or due to too low a pressure in source 30.

[0175] For example, it may happen that during the operation of the combustion system in operating mode M2 ​​("oxygen combustion with recirculation"), especially in the "enhanced oxygen combustion" operating phase, the combustion device 1 needs to provide more thermal energy, and the flow rate φ of the combustion-supporting gas GC is increased accordingly to meet this requirement. GC (Increase the flow rate of the blower or compressor 10). In this case, the additional part of the combustion-supporting gas is automatically injected through the bypass 6.

[0176] If the combustion device 1 reduces the heat energy supply, which is manifested as a reduced demand for combustion-supporting gas GC, the excess combustion-supporting gas is discharged through the bypass 6 and the control system 7 adjusts the valve V1 to reduce the injection of oxygen into the mixer 31 when necessary.

[0177] In conventional plants which can be operated solely with oxycombustion with combustion gas recirculation, an excessive drop in the oxygen concentration in the combustion-supporting gas GC can disadvantageously lead to an unintended shutdown of the oxycombustion.

[0178] Such unplanned stops can advantageously be avoided using the combustion system of the present invention.

[0179] To this end, the control unit 7 is preferably designed to monitor the oxygen concentration in the combustion-supporting gas GC using the sensor 33, and when the oxygen concentration decreases, automatically detect whether the oxygen concentration reaches a predetermined, preferably parameterizable minimum critical threshold value, and if so, automatically control 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.

[0180] Figure 1 Combustion system / CO2 capture

[0181] exist Figure 1 In a particular variant, but optionally, the combustion system advantageously comprises a carbon dioxide (CO2) capture device 11 connected to the bypass 6, suitable for capturing the recycled combustion flue gases (FC) from at least a portion of the gases circulating in said bypass 6. 22 / Figure 4 ) to capture carbon dioxide (CO2).

[0182] More specifically, the capture device 11 comprises a fan or compressor 110 which can suck in a portion of the recirculated combustion flue gas (FC) flowing in the bypass 6. 22 / Figure 4 ) and fed to a CO2 capture unit 111 (known per se).

[0183] Preferably, the capture device 11, in particular the fan or compressor 110, is automatically controlled (by the control unit 7 using the control signal C3 or by another control unit) according to the pressure or flow of the outflowing combustion fumes circulating in the bypass 6, which pressure or flow is determined by the transmitted measurement signal S 60 The sensor 60 measures.

[0184] Further non-exhaustive examples of combustion systems according to the invention and operable in operating modes M1 (“conventional combustion”) and M2 (“oxy-combustion with recirculation”) will now be described.

[0185] Figures 5 to 8 Combustion system

[0186] Figure 5 The combustion system is different from Figure 1 The combustion system is characterized in that the connection 40a of the recirculation loop 40 with the main emission loop 5 is located upstream of the treatment device 8, between the outlet 1a of the combustion device 1 and the inlet of the treatment device 8; and in that the additional treatment device 8' is installed on the recirculation loop 40, preferably upstream of the recirculation fan or compressor VR, that is, between the recirculation fan or compressor VR and the connection 40a of the recirculation loop 40 with the main emission loop 5.

[0187] As a variant, an additional treatment device 8 ′ could be installed on the recirculation loop 40 downstream of the recirculation blower or compressor VR.

[0188] The treatment device 8 may be adapted to purify the non-recirculated combustion flue gases before they are discharged into the ambient air, preferably by capturing one or more pollutants selected from the following list: fine particulate matter, SOx, NOx, acids, heavy metals, ammonia, volatile organic compounds. The treatment device 8' is preferably adapted to at least dehumidify the recirculated combustion flue gases in the recirculation loop 40, and more particularly comprises at least one condenser or a plurality of condensers in cascade.

[0189] The above description of the operating modes M1 and M2 and of the control of the recirculation blower or compressor VR and the combustion gas GC supply unit 3 by the control unit 7 is applicable to Figure 5 This variant of .

[0190] refer to Figure 6 , as for Figure 2 In a variation of the above, in operating mode M1 ("conventional combustion"), the combustion-supporting gas GC is composed of the air sucked in through the bypass 6 (the valve V1 is closed and the recirculation fan or compressor VR is stopped), and the combustion flue gas FC is all processed by entering the treatment device 8 and discharged (FC') into the ambient air.

[0191] refer to Figure 7 , with Figure 3 In a similar manner to the variant, in operating mode M2 ​​("oxycombustion with recirculation") and in the "degraded oxycombustion" operating phase, the recirculation fan or compressor VR is in operation and valve V1 is open; a portion FC1 of the combustion flue gases FC is discharged into the ambient air after being treated (by treatment device 8), while another portion FC2 of the combustion flue gases FC is recirculated to one inlet of mixer 31 in recirculation loop 40 after being previously treated in treatment device 8'. Air is also drawn into bypass 6 and is likewise supplied to mixer 31. The other inlet of mixer 31 is supplied with oxygen at a given flow rate (φO2) in the form of oxygen-enriched gas from source 30 (valve V1 open).

[0192] refer to Figure 8 , with Figure 4 In a similar manner to the variant, in operating mode M2 ​​("oxygen combustion with recirculation") and in the "enhanced oxygen combustion" operating phase, the recirculation fan or compressor VR is in operation and the valve V1 is open. A portion FC1 of the combustion flue gas FC is discharged to the ambient air after being treated (by the treatment device 8), and another portion FC2 of the combustion flue gas FC is recirculated to the recirculation loop 40 and treated in the treatment device 8'. One inlet of the mixer 31 is supplied with a portion FC2 of the recirculated treated combustion flue gas FC at a flow rate φ1. 21 , another part of the recycled treated combustion flue gas FC2 22 It is discharged into the bypass 6 at a flow rate of φ2.

[0193] The other inlet of the mixer 31 is supplied with oxygen at a given flow rate (φO2) in the form of oxygen-enriched gas from the source 30 (valve V1 is open).

[0194] Figure 9 Combustion system - condenser 34 downstream of mixer 31

[0195] Figure 9 The combustion system is different from Figure 1 The combustion system is improved by adding a condenser 34. The condenser 34 is supplied by the mixer 31 at the inlet and is connected to the combustion device 1 at the outlet, and supplies the combustion-supporting gas GC to the combustion device 1.

[0196] In this variant, when the combustion system is in operating mode M2 ​​(“oxycombustion with recirculation”), the combustion flue gases FC are recirculated to the mixer 31 without necessarily being dehumidified in the treatment device 8 , the dehumidification being performed at least by the condenser 34 .

[0197] In another variation, the condenser 34 may be Figure 12 The processing device 8 in the embodiment is installed in a bypass mode ("by-pass").

[0198] Figure 10 Combustion system

[0199] Figure 10 The combustion system is different from Figure 1 The combustion system is characterized in that the control unit 7 is adapted to control at least during the operating mode M2 ​​with at least partial combustion flue gas recirculation at least according to at least the sensor 60 (no longer by Figure 1 The flow or pressure measured by the sensor 51) in the variant embodiment is used to control the recirculation fan or compressor VR.

[0200] The greater the pressure or flow rate measured by the sensor 60 , the greater the flow rate of the recirculated combustion flue gas FC2 in the recirculation loop 40 .

[0201] In particular, the control unit 7 automatically controls the recirculation fan or compressor VR until the flow or pressure measured by the sensor 60 reaches at least a predetermined, preferably parameterizable, operating setpoint, and automatically adjusts the flow of the recirculation fan or compressor VR in order to keep said measured pressure or flow close to this operating setpoint or this operational setpoint.

[0202] The operating set value is set so that the flow rate of the recirculation fan or compressor VR is less than the flow rate of the combustion flue gas FC at the outlet of the treatment device 8, or in the absence of the treatment device 8, less than the flow rate of the exhaust flue gas FC at the outlet of the combustion device 1, so as to recirculate at least a portion FC2 of the combustion flue gas to the mixer 31, while the other portion FC1 is discharged into the open atmosphere via the downstream portion 5b of the main exhaust circuit 5.

[0203] Front Figure 1 The instructions for combustion system operation also apply to Figure 7 combustion system.

[0204] exist Figure 10 In a particular variant embodiment, but optionally, the combustion system advantageously comprises a carbon dioxide (CO2) capture device 11 ' connected to the downstream portion 5b of the main exhaust circuit 5 and suitable for capturing carbon dioxide (CO2) from at least a portion of the outgoing combustion flue gases FC1.

[0205] More specifically, the capture device comprises a fan or compressor 110 which can draw in a portion of the combustion flue gases FC circulating in the downstream portion 5b of the main exhaust circuit 5 and feed it to a CO2 capture unit 111 (known per se).

[0206] Preferably, the capture device 11 ′, in particular the fan or compressor 110 , is automatically controlled (by the control unit 7 or another control unit) as a function of the pressure or flow of the combustion gases circulating in the downstream portion 5 b of the main exhaust circuit 5 , said pressure or flow being measured by the sensor 51 .

[0207] Figure 11 Combustion system

[0208] Figure 11 The combustion system is different from Figure 10 The combustion system is: Figure 5In a similar manner, the connection 40a of the recirculation loop 40 with the main exhaust loop 5 is located upstream of the treatment device 8, between the outlet 1a of the combustion device 1 and the inlet of the treatment device 8; and in that: the additional treatment device 8' is installed on the recirculation loop 40, preferably upstream of the recirculation fan or compressor VR, that is, between the recirculation fan or compressor VR and the connection 40a of the recirculation loop 40 with the main exhaust loop 5.

[0209] Figure 12 Combustion system-bypass treatment device 8

[0210] Figure 12 The combustion system is different from Figure 1 The combustion system is characterized in that the treatment device 8 is installed in a bypass manner ("by-pass") on the main exhaust circuit.

[0211] This type of installation is known for treatment devices 8 having their own fans or compressors, for example as described below. Figure 14 As mentioned above. Figure 1 The instructions for combustion system operation also apply to Figure 12 combustion system.

[0212] exist Figure 5 、 9 In the variants of , 10, 11, 13, the treatment device 8 or 8' can also be installed in a bypass manner ("by-pass").

[0213] Figure 13 Combustion system - CO2 injection at start-up

[0214] Figure 13 The combustion system is different from Figure 1 The combustion system is characterized in that it includes an additional device 12 connected to an inlet of the mixer 31, which can inject gaseous carbon dioxide (CO2) into the mixer 31 during the "degraded oxygen combustion" transition phase when switching from the second operating mode M2 ​​of the "degraded oxygen combustion" phase to the second operating mode M2 ​​of the "enhanced oxygen combustion" phase, so as to shorten the duration of this transition phase.

[0215] The CO 2 injection device 12 comprises, for example, a source 120 of pressurized gaseous CO 2 associated with a valve or solenoid valve 121 controlled by the control unit 7 using a control signal C4 .

[0216] The CO2 injection device 12 can also be increased to Figure 5 、 9 , 10, 11, 12 combustion systems.

[0217] Specific example of condenser- Figure 14

[0218] As a non-limiting example only, Figure 14 1 shows an example of a preferred condenser, which can be used as a condenser in the processing device 8 or 8' of the combustion system of the present invention.

[0219] This condenser comprises an exchanger 12 comprising a housing 120 containing a bath 121 of cooling liquid L and injection means 123 suitable for introducing the gaseous fluid F to be dehumidified (ie the combustion fumes) below the surface of the cooling liquid L bath.

[0220] The cooling liquid L may simply be water or an aqueous solution.

[0221] The injection device 123 may more specifically include a fan or compressor 123f and an injection pipe 123a, which includes an air inlet 123b in its upper portion 123c. The lower portion 123d of the injection pipe 123a is immersed in the cooling liquid L bath 121 and includes a discharge port 123e immersed in the cooling liquid L bath 121.

[0222] During operation, the fan or compressor 123f allows the gaseous fluid F to be dehumidified to be sucked in and introduced into the injection pipe 123 through the air inlet 123b. The gaseous fluid F escapes from the injection pipe 123 through the discharge port 123e, thereby being forced into the cooling liquid L bath 121 and below the surface of the cooling liquid L bath 121. It rises toward the surface of the cooling liquid bath and escapes from the housing 120 through the discharge port 120a of the housing 120 in the form of dehumidified gas F' after being dehumidified.

[0223] The temperature T of the coolant L L Always lower than the temperature T of the gaseous fluid F at the inlet of the exchanger 12 F , preferably below the dew point temperature (dew point) of the gaseous fluid F.

[0224] It is worth noting that the absolute humidity of the gas (g 水 / kg 干空气 ) expresses the number of grams of water vapor present in a given volume of gas, related to the mass of dry gas in that volume expressed in kilograms. Its value remains constant even if the gas temperature changes, but remains above the gas's dew point.

[0225] When passing through the cooling liquid L bath 121 , the gaseous fluid F comes into contact with the cooling liquid L and condenses, so that the absolute humidity of the gas F′ coming out of the exchanger 12 is lower than the absolute humidity of the gaseous fluid F entering the exchanger 12 .

[0226] The difference between the absolute humidity of the dehumidified gas F' and the absolute humidity of the incoming gaseous fluid F depends inter alia on the temperature T of the incoming gaseous fluid F. FThe lower temperature T of the coolant L L The difference between the temperature T of the incoming gaseous gas F F The temperature T of the coolant L L The temperature difference ΔT (ΔT = T F -T L ), the greater the absolute humidity of the dehumidified gas F' is, the lower the absolute humidity of the incoming gaseous fluid F is.

[0227] In another variation, a blower or compressor 123 f may be connected to the injection duct 123 and used to introduce the gaseous fluid F into the injection duct by blowing it through the air inlet 123 b of the injection duct 123 .

[0228] More particularly, the exchanger 12 may be connected to a heat pump (not shown) which allows the cooling liquid L in the cooling liquid bath to be renewed by extracting heat therefrom, in order to keep the temperature of this cooling liquid at a sufficiently low level.

[0229] In another variant embodiment, the condenser may comprise a plurality of exchangers 12 mounted in cascade.

[0230] The present invention is not limited to the use Figure 14 Exchanger type exchanger 12. In other variant embodiments, the exchanger 12 for condensing the gaseous fluid F may be of the type described in international patent application WO2016 / 071648 or international patent application WO2020 / 030419, or may be an exchanger that operates by spraying a cooling liquid L into contact with the gaseous fluid F.

[0231] The invention is not limited to exchangers operating with cooling liquids, but can also be implemented with any other known type of exchanger capable of dehumidifying a gaseous fluid.

[0232] Advantages of using oxygen-enriched gas in combination with recirculation of at least part of the combustion flue gases

[0233] In conventional combustion, a combustion air flow rate D is used at the burner inlet for the hourly fuel quantity Qd burned. After combustion, flue gases are discharged at a flow rate X. These flue gases must be treated in accordance with emission standards for dust and chemicals. The greater the value of X, the higher the flue gas treatment costs.

[0234] In conventional combustion, the air flow rate D (D <X)。

[0235] In conventional combustion, the combustion flue gas contains:

[0236] - nitrogen dioxide (N2), with a mass flow rate that is almost identical to that of the combustion air,

[0237] - Carbon dioxide (CO2) produced by combustion,

[0238] - water from the combustion, possibly from the evaporation of water possibly contained in the fuel (for example when the fuel consists of waste or coal), and water from the combustion air,

[0239] -Oxygen that does not participate in combustion (O2)

[0240] - Pollutants, which depend on the fuel used and may include, for example, fine particulate matter, acids, nitrogen oxides, sulfur oxides, heavy metals, dioxins, etc.

[0241] When the combustion system of the present invention is operated in "oxygen combustion" as described above (oxygen-rich gas containing at least 40% O2 is added and a part of the combustion flue gas is recycled), the flow rate of the combustion flue gas leaving the combustion device without being recycled and being discharged directly into the atmosphere and / or being treated before being discharged into the atmosphere (for example for CO2 capture) is advantageously lower than the above-mentioned flow rate X.

[0242] The greater the proportion of O2 in the oxygen-rich gas supplied by source 30, the lower the flow rate of combustion flue gases that are not recirculated and exhausted.

[0243] For example, when the oxygen-rich gas is pure oxygen, it is practical to recirculate the combustion flue gas at a high recirculation flow rate of up to 10 / 11 of X, and to discharge the remaining combustion flue gas at an advantageously lower flow rate either directly into the atmosphere or to pre-treat it, for example, to capture CO2 and / or purify it, before discharging it into the atmosphere, wherein the lower flow rate may be about 1 / 11 of X.

[0244] In another variant embodiment of the invention, the mixer 31 and / or the combustion device may include an additional air inlet, thereby allowing the injection of additional air into the combustion, in addition to the recirculated combustion flue gases and in addition to the oxygen enrichment. This simply affects the coefficient of 11 mentioned above, which in this case will be between 1 and 11, depending on the flow rate of additional air injected into the combustion through the additional air inlet.

[0245] When the oxygen-rich gas contains 90% oxygen, it is actually possible to recirculate the combustion flue gas at a high recirculation rate of up to 9 / 10 of X, and to discharge the remaining combustion flue gas directly into the atmosphere at an advantageously lower flow rate, or to pre-treat it before discharge into the atmosphere, for example to capture CO2 and / or purify it, etc., wherein the lower flow rate can be about 1 / 10 of X.

[0246] It should be emphasized that restrictions on the pollution of combustion-supporting gases entering the combustion device are less important than the increasingly stringent environmental regulations regarding pollution from non-recirculated combustion flue gases. Consequently, the recirculated combustion flue gases can be left untreated, or, if necessary, subjected to "light" treatment before entering the mixer. This treatment is significantly less expensive than treating non-recirculated flue gases. This advantageously allows for a significant reduction in the overall cost of treating combustion flue gases.

[0247] The significant reduction in flue gas treatment costs comes at the expense of producing oxygen-enriched gas. While this cost increases with the proportion of O₂ in the oxygen-enriched gas, it remains significantly lower than the flue gas treatment cost. Therefore, those skilled in the art should find a compromise between the cost of producing gases with varying degrees of oxygen enrichment and the cost of flue gas treatment, depending on the specific circumstances.

[0248] In the context of the present invention, the oxygen-rich gas contains at least 40% oxygen (below this threshold, the reduction in the flow rate of non-recirculated combustion flue gases is practically too small). Preferably, the proportion of gaseous oxygen in the oxygen-rich gas is at least 80%, more preferably at least 90%. More specifically, the oxygen-rich gas is advantageously gaseous pure oxygen or nearly gaseous pure oxygen (at least 99% O2).

Claims

1. A combustion system comprising: A combustion device (1) capable of burning fuel (C) using at least one combustion-supporting gas (GC), comprising an outlet (1a) through which the combustion device discharges combustion flue gas (FC); a combustion-supporting gas (GC) supply unit (3) connected to the combustion device (1) and allowing the combustion-supporting gas (GC) to be supplied to the combustion device (1), the combustion-supporting gas (GC) supply unit (3) comprising a mixer (31) and a gaseous oxygen source (30), the gaseous oxygen source providing oxygen-rich gas and connected to a first inlet of the mixer (31); a main exhaust circuit (5) connected to the outlet (1a) of the combustion device (1) and leading to the atmosphere; and a recirculation device (4). The invention comprises a recirculation circuit (40) between the main discharge circuit (5) and the second inlet of the mixer (31), at least one recirculation fan or compressor (VR) installed on the recirculation circuit (40), the recirculation fan or compressor being suitable for circulating the gaseous fluid in the recirculation circuit (40) from the connection (40a) of the recirculation circuit (40) and the main discharge circuit (5) in the direction of the second inlet of the mixer (31); a bypass (6) connected to the recirculation circuit (40) downstream of the recirculation fan or compressor (VR) and leading to the atmosphere so as to be able to supply at least the mixer (31) with air entering the bypass (6); and a control unit (7) adapted to control at least the recirculation fan or compressor (VR).

2. The combustion system according to claim 1, wherein: The combustion system further comprises at least one sensor (51) adapted to measure at least the flow rate or pressure of the outflowing gaseous fluid in a downstream portion (5b) of the main discharge circuit (5) located downstream of the connection (40a) of the recirculation circuit (40) with the main discharge circuit (5), and to send a flow rate or pressure measurement signal (S) which is processed by a control unit (7). 51 ).

3. The combustion system according to claim 1 or 2, wherein: The combustion system further comprises a flow meter adapted to measure at least the flow rate or pressure of the outflowing gaseous fluid in the bypass (6) and to send a flow rate or pressure measurement signal (S) which is processed by a control unit (7). 60 ) of at least one sensor (60).

4. The combustion system according to claim 2 or 3, wherein: The control unit (7) is adapted to control the recirculation fan or compressor (VR) at least during an operating mode (M2) with recirculation of at least a portion of the combustion flue gases, at least according to the flow or pressure measured by the sensor (51 or 60).

5. The combustion system according to any one of claims 1 to 4, wherein: The control unit (7) is adapted to control the recirculation fan or compressor (VR) so as to be able to configure the combustion system in one operating mode selected from at least two different operating modes (M1; M2) and to be able to switch from one operating mode to the other: a first operating mode (M1) in which the recirculation fan or compressor (VR) is stopped and the mixer (31) is not fed with oxygen-enriched gas from the gaseous oxygen source (3) but with air entering the bypass (6); and a second operating mode (M2) in which the recirculation fan or compressor (VR) is operated and the mixer (31) is fed with at least oxygen-enriched gas provided by the gaseous oxygen source (3) and at least a portion of the combustion flue gas (FC2 or FC 21 ).

6. The combustion system according to any one of claims 1 to 5, wherein: The gaseous oxygen source (30) is connected to the first inlet of the mixer (31) through an oxygen-enriched gas flow control device (32), which is controlled by a control unit (7) and preferably includes a flow control valve (V1) controlled by the control unit (7).

7. The combustion system according to claim 6, wherein: The flow control valve (V1) is a progressive on-off valve.

8. The combustion system according to claim 6 or 7, wherein: The control unit (7) is adapted to control at least the recirculation fan or compressor (VR) and, if necessary, the oxygen-enriched gas flow control device (32) so as 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 (1).

9. The combustion system according to any one of claims 1 to 8, wherein: The combustion system comprises at least one sensor (33) adapted to measure the oxygen concentration in the combustion-supporting gas (GC); and the control unit (7) is adapted to control the oxygen-enriched gas flow control device (32) according to the oxygen concentration measured by the sensor (33) for measuring the oxygen concentration, at least during an operating mode (M2) in which at least a portion of the combustion flue gas is recirculated.

10. The combustion system according to any one of claims 1 to 9, wherein: The combustion device (1) comprises a device adapted to burn the fuel at a given flow rate (φ GC ) A blower or compressor (10) supplies combustion-supporting gas (GC) to the combustion device (1), wherein the given flow rate is preferably variable.

11. The combustion system according to any one of claims 1 to 10, wherein: The supply flow rate of the fuel (C) to the combustion device (1) is variable, and the combustion device (1) includes a flow rate (φ) adapted to be varied according to the supply flow rate of the fuel (C) to the combustion device (1). GC ) A fan or compressor (10) supplies combustion-supporting gas (GC) to the combustion device (1).

12. The combustion system according to any one of claims 1 to 11, wherein: The combustion system comprises a treatment device (8) installed on the main exhaust circuit (5) for treating combustion flue gases (FC).

13. The combustion system according to any one of claims 1 to 12, wherein: The combustion system comprises a treatment device (8') for treating recirculated combustion flue gases (FC2), which is installed on the recirculation circuit (40), preferably between the recirculation fan or compressor (VR) and the connection (40a) of the recirculation circuit (4) to the main exhaust circuit (5).

14. The combustion system according to claim 12 or 13, wherein: The treatment device (8 or 8') is suitable for dehumidifying the combustion flue gases (FC or FC2).

15. The combustion system according to claim 14, wherein: The treatment device (8 or 8') comprises a condenser (34).

16. The combustion system according to claim 15, wherein: The condenser comprises at least one exchanger (120) containing a cooling liquid (L).

17. The combustion system according to claim 16, wherein: The exchanger (120) comprises a cooling liquid (L) bath (121) and an injection device (123) allowing the gaseous fluid (FC or FC2) to be dehumidified to pass through the cooling liquid (L) bath, preferably, the injection device (123) allows the gaseous fluid (FC or FC2) to be dehumidified to be injected below the surface of the cooling liquid (L) bath (120).

18. The combustion system according to any one of claims 12 to 17, wherein: The treatment device (8 or 8') is suitable for purifying the combustion flue gases (FC or FC2), more particularly for capturing one or more pollutants selected from the following list: fine particles, sulfur oxides SOx, nitrogen oxides NOx, acids, heavy metals, ammonia, volatile organic compounds.

19. The combustion system according to any one of claims 1 to 18, wherein: The combustion system comprises at least one sensor (33) adapted to measure the oxygen concentration in the combustion-supporting gas (GC); and the control unit (7) is adapted to control the oxygen-enriched gas flow control device (32) and the recirculation fan or compressor (VR) according to the measured oxygen concentration in the combustion-supporting gas (GC), preferably so as to remove at least a portion of the combustion flue gas (FC2 or FC 21 ) is switched from the operating mode without recirculation of combustion flue gases (M2) to the operating mode without recirculation of combustion flue gases (M1).

20. The combustion system according to any one of claims 1 to 19, wherein: The combustion system comprises a carbon dioxide (CO2) capture device (11) connected to a bypass (6) adapted to capture at least a portion of the recirculated combustion flue gases (FC) discharged through said bypass (6) 21 ) capture carbon dioxide (CO2); and / or the combustion system comprises a carbon dioxide (CO2) capture device (11') which is connected to the downstream part (5b) of the main emission circuit (5) located downstream of the connection (40a) between the recirculation circuit (40) and the main emission circuit (5) and is suitable for capturing carbon dioxide (CO2) from the non-recirculated combustion flue gases flowing out of at least a part (FC1) discharged through the downstream part (5b) of the main emission circuit (5).

21. The combustion system according to any one of claims 1 to 20, wherein: The oxygen-rich gas provided by the gaseous oxygen source (30) comprises at least 50% oxygen, preferably at least 80% oxygen, and even more preferably at least 90% oxygen.

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

23. The combustion system according to any one of claims 1 to 22, wherein: The combustion system comprises a carbon dioxide injection device (12) connected to the inlet of the mixer (31) and suitable for injecting gaseous carbon dioxide (CO2) into the mixer (31) during a specific phase of the operating mode (M2) with recirculation of combustion flue gases ("degraded oxy-combustion")

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