Method for cold starting a thermodynamic system having a gas turbine cycle with cooled compression, regeneration and reheating during the expansion

Abstract

The present invention relates to a method for cold starting a thermodynamic system comprising two turbochargers (TC1, TC2), two catalytic combustion chambers (CCC1, CCC2), the second catalytic combustion chamber (CCC2) being equipped with electric heating means (RE), two electric machines (MEL1, MEL2) each connected to one of the turbochargers (TC1, TC2), fuel injection means (FI1, FI2), and a heat recovery device (REC), characterised in that it successively comprises a step (10) of activating the electric heater (RE) until a first determined temperature of the second catalytic combustion chamber (CCC2) is reached, a step of rotating the two turbochargers (TC1, TC2) by their electric machine (MEL1, MEL2) at minimum rotation speeds, a step (20) of starting the injection of fuel into the second catalytic combustion chamber (CCC2), and a step (30) of starting the injection of fuel into the first combustion chamber (CCC1) when it reaches a second determined temperature.

Description

[0001] Description

[0002] Title: Cold start process of a gas turbine type cycle thermodynamic system with cooled compression, regeneration and reheating during expansion.

[0003] The present invention claims priority from French application No. 2404373 filed on 26.04.2024, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004] The present invention relates to the field of gas turbines. More particularly, the invention relates to a method for cold starting a thermodynamic system with a gas turbine cycle, featuring cooled compression, regeneration, and reheating during expansion.

[0005] Gas turbine-type energy converters are well-known in electricity generation. These machines consist of a compressor that compresses air and increases its pressure, a combustion chamber that uses fuel to produce thermal energy, and a turbine that recovers the work done by the gases. Part of the power produced by the turbine drives the compressor, and another part drives an electric generator to produce electrical power. In an automotive application, this electricity can be used to recharge the traction battery of an electric or hybrid vehicle.

[0006] In particular, the gas turbine cycle thermodynamic system with cooled compression, regeneration, and reheating during expansion (a device known in English as an "Intercooled Reheat Gas Turbine," or IRReGT) is a device with strong potential for automotive applications. This cycle allows for very high efficiency as well as very high power density (i.e., high net specific work).

[0007] Such a thermodynamic system is described, for example, in document FR3124847A1. The thermodynamic system described in document FR3124847A1 comprises two combustion chambers and proposes a method for controlling this system during startup by combining the operation of the electric generator in engine mode with fuel injection into the second combustion chamber. Indeed, startup is a polluting phase because the system components are cold. However, injecting this fuel into the second combustion chamber during the startup phase reduces pollutant emissions.

[0008] Therefore, there is a need to improve the start-up of such thermodynamic systems, which is the most polluting phase, in order to reduce polluting emissions.

[0009] The invention aims to solve this problem. To achieve this objective, the invention provides a cold start method for a thermodynamic system comprising:

[0010] - a first turbocharger comprising:

[0011] - a first compressor and a first turbine

[0012] - a second turbocharger comprising:

[0013] - a second compressor and a second turbine

[0014] - two catalytic combustion chambers, the second catalytic combustion chamber being equipped with electrical heating means for this second combustion chamber,

[0015] - a first electric machine connected in rotation to the first turbocharger and a second electric machine connected in rotation to the second turbocharger,

[0016] - fuel injection means for each combustion chamber,

[0017] - a heat recovery unit connected to the second compressor and the first combustion chamber, this first combustion chamber being connected to the second turbine, this second turbine being connected to the second combustion chamber, this second combustion chamber being connected to the first turbine, characterized in that it successively comprises:

[0018] - an activation stage of the electric heater until a first predetermined temperature is reached in the second catalytic combustion chamber,

[0019] - a stage of rotating the two turbochargers using their electric motor at minimum rotational speeds,

[0020] - a fuel injection start-up stage in the second catalytic combustion chamber,

[0021] - a fuel injection start-up step in the first combustion chamber when it reaches a second predetermined temperature. The technical effect is to allow for the rapid activation of the catalytic combustion chambers, the first combustion chamber being heated by air preheated by the recuperator.

[0022] Various additional features can be provided, alone or in combination.

[0023] In one embodiment, the first determined temperature corresponds to a so-called initiation temperature of the second catalytic combustion chamber.

[0024] In one embodiment, the second determined temperature corresponds to a so-called initiation temperature of the first catalytic combustion chamber.

[0025] In one embodiment, the thermodynamic system includes a step of increasing the rotational speed of the turbochargers to intermediate rotational speeds when the second combustion chamber reaches its nominal operating temperature.

[0026] In one embodiment, the thermodynamic system includes a step of increasing the fuel injection flow rate in both combustion chambers to intermediate fuel flow rates when the second combustion chamber reaches its nominal operating temperature.

[0027] In one embodiment, the thermodynamic system includes a step of increasing the fuel injection flow rate in the first combustion chamber to an intermediate fuel flow rate when the second combustion chamber reaches its nominal operating temperature, the increase in the fuel injection flow rate in the second combustion chamber taking place for an intermediate temperature of the second combustion chamber between the ignition temperature and the nominal operating temperature.

[0028] In one embodiment, the thermodynamic system includes a step of increasing the fuel flow rates injected into the two combustion chambers to nominal fuel flow rates, once both combustion chambers have reached their nominal operating temperature. The invention also relates to a thermodynamic system comprising:

[0029] - a first turbocharger comprising:

[0030] - a first compressor and a first turbine

[0031] - a second turbocharger comprising:

[0032] - a second compressor and a second turbine

[0033] - a first electric machine connected in rotation to the first turbocharger and a second electric machine connected in rotation to the second turbocharger,

[0034] - two combustion chambers,

[0035] - fuel injection means for each combustion chamber,

[0036] - a heat recovery unit connected to the second compressor and to a first combustion chamber, this first combustion chamber being connected to the second turbine, this second turbine being connected to the second combustion chamber, this second combustion chamber being connected to the first turbine, characterized in that the two combustion chambers are catalytic combustion chambers, the second catalytic combustion chamber only being equipped with means for electrically heating this second combustion chamber, and in that the system further comprises control means configured to implement a starting method according to one of the variants previously described.

[0037] In one embodiment, the electrical machines are electric motor-generators.

[0038] The invention also relates to a motor vehicle comprising a thermodynamic system according to one of the variants described above, the electric machines powering a traction battery of the vehicle.

[0039] Other features and advantages will become apparent upon reading the following description of a particular, non-limiting embodiment of the invention, made with reference to the figures in which:

[0040] [Fig 1]: This figure schematically represents a motor vehicle conforming to the invention.

[0041] [Fig. 2]: This figure schematically represents an embodiment of the thermodynamic system according to the invention. [Fig. 3]: This figure schematically represents an example of an embodiment of a catalytic combustion chamber.

[0042] [Fig.4] This figure schematically represents the steps of a cold start phase of the thermodynamic system of figure 2.

[0043] Figure 1 shows a motor vehicle comprising, within the dotted outline, a thermodynamic system 1 of the invention. As illustrated in Figure 2, the thermodynamic system 1 comprises electrical machines MEL1 and MEL2 so as to convert the mechanical energy produced by this thermodynamic system 1 into electrical current.

[0044] The electric machines MEL1 and MEL2 are connected to an electrical network comprising a battery B and an electric motor MEL used for vehicle traction. AC / DC converters can be used to manage the electrical flow within the network. Thus, the electric machines MEL1 and MEL2 can recharge battery B. Battery B is used to power the traction electric motor MEL. Thermodynamic system 1 is therefore mechanically decoupled from the traction system and can operate at its maximum efficiency.

[0045] As illustrated in Figure 2, the thermodynamic system comprises a first turbocharger TC1 and a second turbocharger TC2.

[0046] The first turbocharger TC1 comprises a first compressor C1 and a first turbine TU2. The second turbocharger TC2 comprises a second compressor C2 and a second turbine TU1. More specifically, the first turbocharger TC1 forms a "low pressure" stage, and the second turbocharger TC2 forms a "high pressure" stage.

[0047] The turbochargers TC1 and TC2 are electrified here, meaning that each one includes an electric machine, MEL1 and MEL2, respectively. Each turbocharger TC1 and TC2 is rotationally connected to its corresponding electric machine, MEL1 and MEL2. The electric machines MEL1 and MEL2 can operate in both motor and generator modes: as a motor to drive the system when needed, and as a generator to recover the energy produced by combustion through the rotation of the turbocharger.

[0048] The thermodynamic system includes an IC cooler for the air exiting the first compressor, C1. This IC cooler can be an air-to-air or air-to-water heat exchanger. The inlet of the IC cooler is connected between the compressed air outlet of the first compressor, C1, and the air inlet of the second compressor, C2.

[0049] The thermodynamic system also includes two catalytic combustion chambers CCC1 and CCC2.

[0050] The thermodynamic system also includes a REC recuperator. This recuperator is a heat exchanger connected between the compressed air outlet from the second compressor C2 and the inlet of this compressed air into the first combustion chamber CCC1. The outlet of the first combustion chamber CCC1 is then connected to the inlet of the second turbine TU1.

[0051] The output of the second turbine TU1 is connected to the inlet of the second catalytic combustion chamber CCC2 and the output of the second catalytic combustion chamber CCC2 is connected to the inlet of the first turbine TU2.

[0052] The thermodynamic system further includes a recovery branch BR connecting the outlet of the first turbine TU2 to an inlet of the heat recovery unit REC and passing through it. The side of the REC through which the recovery branch BR passes is called the hot side of the recuperator, since the gas flow comes directly from the first turbine TU2 after undergoing a second catalytic combustion in the catalytic combustion chamber CCC2. Conversely, the side of the REC receiving compressed air from the second compressor C2, and from which the air is directed to the first catalytic combustion chamber CCC1, is called the cold side of the recuperator.

[0053] The thermodynamic system is configured to be traversed by a gaseous flow FG, described later, between the different elements composing it.

[0054] The use of a second CCC2 catalytic combustion chamber for reheating between the turbines increases power density, which reduces the required airflow at the same power output and reduces the size of the device.

[0055] The thermodynamic system can be equipped with an air filter FA positioned upstream of the first compressor to filter the air admitted into this first compressor C1. The system is also equipped with a first fuel injection system FI1 in the first catalytic combustion chamber CCC1 and a second fuel injection system FI2 in the second catalytic combustion chamber CCC2.

[0056] The two combustion chambers CCC1 and CCC2 are catalytic combustion chambers. Having two catalytic combustion chambers allows for greater flexibility in the system's operation. These catalytic combustion chambers oxidize the injected fuel through catalysis, generating heat.

[0057] With catalytic combustion chambers, exhaust gas temperatures of around 950°C are obtained. In the case of lean mixture operation, in other words with an excess of oxygen, since the temperature is below 1200°C (according to the Pischinger diagram), the formation of nitrogen oxides at the source is avoided.

[0058] The CCC1 and CCC2 catalytic combustion chambers each comprise a catalytic substrate or core, which can be ceramic or metallic, through which the fuel-air mixture can pass. The catalytic core has a catalytic coating adapted to the oxidation of the fuel. This catalytic coating may include materials with catalytic properties such as platinum, rhodium, or palladium.

[0059] The gas flow FG in the system is now described. Generally, the gas flow FG follows the arrows shown in Figure 2, which connect the various components, and passes through these components. Ambient air is first drawn into the air filter FA by the first compressor C1. This air then passes through the filter. The air is compressed in this first compressor C1 before entering the cooler IC, where it is cooled. The air exiting the cooler IC then enters the second compressor C2, where it is compressed a second time before entering the recuperator REC, specifically the cold side of the recuperator. In the recuperator REC, the air is heated by the hot gases from the recovery branch BR, which originates from the turbine outlet TU2. The air exiting the recuperator REC thus enters the first catalytic combustion chamber CCC1.At the outlet of the first catalytic combustion chamber CCC1, a first expansion occurs in the high-pressure turbine TU1 followed by a heating phase in the second catalytic combustion chamber CCC2 before entering the low-pressure turbine TU2 to undergo a second expansion. At the outlet of the first turbine TU2, the hot gases enter the hot side of the recuperator REC to heat the air coming from the second compressor C2, i.e. the cold side of the recuperator REC.

[0060] These catalytic combustion chambers become active when the temperature of the catalytic block exceeds a certain ignition temperature. This ignition temperature can be, for example, between 300°C and 350°C. This temperature varies depending on the type and quantity of catalytic materials used in the catalytic block. If the catalyst has not yet reached at least its ignition temperature, it is not active and its efficiency is reduced.

[0061] To facilitate the ignition of the catalytic combustion chamber, an electric heater RE is planned, as illustrated in Figure 3, to be placed upstream of the catalytic block PC in the second catalytic combustion chamber CCC2. Upstream and downstream are defined here relative to the direction of gas flow FG.

[0062] In a preferred embodiment, an electric heater RE is used only for the second catalytic combustion chamber CCC2. The REC heat recovery unit of the thermodynamic system preheats the air entering the first catalytic combustion chamber using the hot gases from the TU2 turbine. Thus, during the start-up phase, the REC heat recovery unit recovers some of the heat energy from the TU2 turbine to preheat the air entering the first catalytic combustion chamber CCC1. Consequently, an electric heating element is not required for the first catalytic combustion chamber CCC1. The REC heat recovery unit acts as the electric heating element. This reduces mass and cost, facilitates integration, and improves durability.

[0063] The thermodynamic system 1 also includes control means UC, arranged to control the fuel injection means, FI1, FI2, the electric heater RE, the electric machines MEL1, MEL2, as well as to implement the cold start process of the thermodynamic system 1 which is now described.

[0064] To monitor the operation of thermodynamic system 1, temperature sensors can be used to determine the temperatures used in the process. Thermocouples are preferably used as temperature sensors. Referring to Figure 4, the cold start procedure for thermodynamic system 1 comprises the following steps:

[0065] In step 10, the electric heater RE is activated until a predetermined initial temperature T1 is reached in the second catalytic combustion chamber CCC2. This initial temperature T1 preferably corresponds to the ignition temperature of the second catalytic combustion chamber CCC2. At this stage, the electric motors are not activated, and the rotational speed of the turbochargers TC1 and TC2 is zero. Fuel injection is also not activated at this stage.

[0066] Once the initial temperature T1 is reached, in step 20 the two electric machines MEL1 and MEL2 are activated in motor mode to rotate the two turbochargers TC1 and TC2 at a minimum speed Rmintd and Rmintc2. This generates a gas flow in thermodynamic system 1. These minimum rotation speeds can be identical. For example, the minimum speed can be between 5000 and 10000 rpm. Also at this stage, fuel injection into the second combustion chamber CCC2 begins. This fuel injection is performed at an initial minimum fuel flow rate Qminccc2. At this stage, no injection is carried out in the first combustion chamber CCC1. The electric heater RE remains active at this stage.

[0067] Fuel injection into the second combustion chamber CCC2 further increases its temperature and increases the temperature of the first combustion chamber CCC1, via the recuperator REC.

[0068] When the temperature of the first combustion chamber CCC1 reaches a predetermined second temperature T2, fuel injection into the first combustion chamber CCC1 begins in step 30. This second temperature T2 preferably corresponds to the activation temperature of the first catalytic combustion chamber CCC1. This fuel injection is performed according to a second minimum fuel flow rate Qminccd. At this stage, the operating speed of both turbochargers TC1 and TC2 can be maintained at their minimum operating speeds Rmintd and Rmintc2. The electrical resistance RE can be deactivated during this stage.

[0069] When the second combustion chamber CCC2 reaches its nominal operating temperature (for example, approximately 950°C), in step 40 the rotational speed of the turbochargers TC1 and TC2 is increased to intermediate speeds Rinttd and Rinttc2. These intermediate speeds can be the same as, or higher than, the minimum speed Rminl and Rmin2. For example, the intermediate speed can be between 10,000 and 100,000 rpm. Also in step 40, the fuel injection rate in both combustion chambers is increased to intermediate fuel flow rates Qintccd and Qintccc2, which are higher than the minimum fuel flow rates. The intermediate fuel flow rates injected into combustion chambers CCC1 and CCC2 can be the same.

[0070] Alternatively, the fuel injection flow rate in the second combustion chamber CCC2 can be increased to the intermediate fuel flow rate Qintccc2 before it has reached its nominal operating temperature, i.e. when the second combustion chamber CCC2 has reached an intermediate temperature between its ignition temperature and its operating temperature, for example between 650 and 750°C.

[0071] When both combustion chambers CCC1 and CCC2 have reached their nominal operating temperature, at step 50 the fuel flow rate injected into both combustion chambers CCC1 and CCC2 is increased to nominal fuel flow rates, Qnomccd and Qnomccc2, which are higher than the intermediate fuel flow rates. The turbochargers C1 and C2 also reach their nominal rotational speeds, Rnomd and Rnomc2, which are higher than the intermediate rotational speeds. For example, the nominal speed may exceed 100,000 rpm.

[0072] During this process, the MEL1 and MEL2 electric machines switch from motor mode to generator mode when the turbine to which they are connected produces more power than the associated compressor consumes.

[0073] The invention is not limited to the embodiments described. Alternatively, a glow plug can be added upstream of each combustion chamber and downstream of each fuel injection device, the activation of which ensures the complete evaporation of the injected fuel before it enters its combustion chamber.

[0074] The invention reduces start-up time and emissions at the source. It also reduces the electrical energy required during the start-up phase.

Claims

Demands 1. Cold start method for a thermodynamic system comprising: - a first turbocharger (TC1) comprising: - a first compressor (C1) and a first turbine (TU2) - a second turbocharger (TC2) comprising: - a second compressor (C2) and a second turbine (TU1) - two catalytic combustion chambers (CCC1, CCC2), the second catalytic combustion chamber (CCC2) being equipped with electrical heating means (RE) for this second combustion chamber (CCC2), - a first electric machine (MEL1) connected in rotation to the first turbocharger (TC1) and a second electric machine (MEL2) connected in rotation to the second turbocharger (TC2), - fuel injection means (FI1, FI2) for each combustion chamber (CCC1, CCC2), - a heat recovery unit (HRU) connected to the second compressor (C2) and the first combustion chamber (CCC1), this first combustion chamber (CCC1) being connected to the second turbine (TU1), this second turbine (TU1) being connected to the second combustion chamber (CCC2), this second combustion chamber (CCC2) being connected to the first turbine (TU2), characterized in that it successively comprises: - a step (10) of activating the electric heater (RE) until a first determined temperature (T1) of the second catalytic combustion chamber (CCC2) is reached, - a step of rotating the two turbochargers (TC1, TC2) by their electric machine (MEL1, MEL2) at minimum rotation speeds (Rmintd, Rmintc2), - a step (20) of starting fuel injection into the second catalytic combustion chamber (CCC2), - a step (30) of starting fuel injection into the first combustion chamber (CCC1) when it reaches a second determined temperature (T2).

2. Method according to claim 1, characterized in that the first temperature (T 1 ) determined corresponds to a so-called initiation temperature of the second catalytic combustion chamber (CCC2).

3. A method according to claim 1 or claim 2, characterized in that the second temperature (T2) determined corresponds to a so-called initiation temperature of the first catalytic combustion chamber (CCC1).

4. A method according to any one of claims 1 to 3, characterized in that it comprises a step (40) of increasing the rotational speed of the turbochargers (TC1, TC2) to intermediate rotational speeds (RinttCCCI, Rinttc2) when the second combustion chamber (CCC2) reaches its nominal operating temperature.

5. A method according to any one of claims 1 to 4, characterized in that it comprises a step (40) of increasing the fuel injection flow rate in the two combustion chambers (CCC1, CCC2) to intermediate fuel flow rates (QintCCCI, QintCCC2) when the second combustion chamber (CCC2) reaches its nominal operating temperature.

6. A method according to any one of claims 1 to 4, characterized in that it comprises a step (40) of increasing the fuel injection flow rate in the first combustion chamber (CCC1) to an intermediate fuel flow rate (QintCCCI) when the second combustion chamber (CCC2) reaches its nominal operating temperature, the increase in the fuel injection flow rate in the second combustion chamber (CCC2) taking place for an intermediate temperature of the second combustion chamber (CCC2) between the ignition temperature and the nominal operating temperature.

7. A method according to any one of claims 4 to 6, characterized in that it comprises a step (50) of increasing the fuel flow rates injected into the two combustion chambers (CCC1, CCC2) to nominal fuel flow rates (QnomCCCI, QnomCCC2), when both combustion chambers (CCC1, CCC2) have reached their nominal operating temperature.

8. Thermodynamic system (1) comprising: - a first turbocharger (TC1) comprising: - a first compressor (C1) and a first turbine (TU2) - a second turbocharger (TC2) comprising: - a second compressor (C2) and a second turbine (TU1) - a first electric machine (MEL1) connected in rotation to the first turbocharger (TC1) and a second electric machine (MEL2) connected in rotation to the second turbocharger (TC2), - two combustion chambers (CCC1, CCC2), - fuel injection means (FI1, F2) for each combustion chamber (CCC1, CCC2), - a heat recovery unit (HRU) connected to the second compressor (C2) and to a first combustion chamber (CCC1), this first combustion chamber (CCC1) being connected to the second turbine (TU1), this second turbine (TU1) being connected to the second combustion chamber (CCC2), this second combustion chamber (CCC2) being connected to the first turbine (TU2), characterized in that the two combustion chambers (CCC1, CCC2) are catalytic combustion chambers, the second catalytic combustion chamber (CCC2) only being equipped with means for electric heating (RE) of this second combustion chamber (CCC2), and in that the system further comprises control means (UC) configured to implement a starting method according to one of the preceding claims.

9. System (1) according to the preceding claim, characterized in that the electric machines (MEL1, MEL2) are electric motor-generators.

10. Motor vehicle comprising a thermodynamic system (1) according to one of claims 8 or 9, the electric machines (MEL1, MEL2) supplying a traction battery (B) of the vehicle.

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